Rozprawy doktorskie: „Liquid iron”

1

Parvin, Nader. "Interaction of liquid copper with sintered iron compacts". Thesis, Aston University, 1989. http://publications.aston.ac.uk/11880/.

Pełny tekst źródła

Streszczenie:

Interaction of liquid copper with sintered iron is important in brazing, liquid phase sintering and infiltration. In brazing, the penetration of liquid copper into the pores is to be `avoided', whereas in infiltration processes it is `encouraged', and in liquid phase sintering it should be `controlled' so that optimum mechanical properties are achieved. The main objective of the research is to model the interaction by studying the effect of the process variables on the mechanisms of copper interaction in Fe-Cu and Fe-Cu-C systems. This involves both theoretical and experimental considerations. Dilatometric investigations at 950, 1125 and 1200oC, together with metallographic analyses were carried out to clarify the copper growth phenomenon. It is shown that penetration of liquid copper into the iron grain boundaries is the major cause of dimensional changes. Infiltration profiles revealed that copper penetration between the iron interparticle contact points and along iron grain boundaries is a rapid process. The extent of copper penetration depends on the dihedral angle. Large dihedral angles hinder, and small angles promote copper penetration into the grain boundaries. Dihedral angle analysis shows that the addition of 0.6wt.% graphite reduces the number of zero dihedral angle from 27 to 3o and increases the mean dihedral angle from 9.8 to 41.5o. The dihedral angle was lowest at 1125oC and then increased to higher values as the system approached its equilibrium condition. Elementally mixed (E.M.) Fe-Cu compacts showed a rapid expansion at the copper melting point. However, graphite additions reduced compact growth by increasing the mean dihedral angle. In order to reduce the copper growth phenomenon, iron powder was coated with a thin layer of copper by an immersion coating (I.C.) technique. The dilatometric curves revealed an overall shrinkage in the I.C. compacts compared to their corresponding E.M. compacts. Multiple regression models showed that temperature had the most effect on dimensional changes and density had the most contributing effect upon the copper penetration area in the infiltrated powder metallurgy compacts.

Style APA, Harvard, Vancouver, ISO itp.

2

Sidhu, Mandeep Singh. "Liquid Aluminium Corrosion Characteristics of Cast Iron and Steel". Thesis, University of Canterbury. Mechanical Engineering, 2012. http://hdl.handle.net/10092/7013.

Pełny tekst źródła

Streszczenie:

Cast iron and steel alloys are commonly used for tooling and structural components in Al production, Al die-casting and the aluminizing industry due to their favourable properties including high strength, good formability and low cost. However, the iquid Al corrosion of these materials is one of the crucial concerns in maintaining the efficient production. Al is produced by the electrolytic smelting of alumina. Cast iron and/or cast steel pipes - commonly known as „tapping pipes‟ - are used to extract the liquid Al produced by smelting. Tapping pipes mainly degrade by material loss because liquid Al reacts with nearly all metals. Failure of tapping pipes is a significant contributor to the maintenance expenses; therefore, the primary aim of this research is to develop a material to enhance the life time of tapping pipes. Various test methods were developed in order to examine the effect of molten Al environment on cast iron and steel alloys. The corrosion resistance of these alloys was determined under different conditions of Al flow and temperature. The intermetallic compounds formed by exposing the ferrous to liquid Al were characterized using the Energy Dispersive X-ray Spectroscopy (EDS) and Electron Back Scatter Diffraction (EBSD) techniques. The formation, growth and nature of reaction products were revealed to establish a link to the liquid Al corrosion resistance. A relationship between the chemical composition and liquid Al corrosion resistance of cast irons could not established in the past. In the present work, the corrosion rate was found to depend upon the graphite morphology and fraction of each Fe-C phase of cast iron matrix, which can be controlled by selecting the chemical composition. Moreover, present research suggested the guidelines for producing a cast iron with enhanced liquid Al corrosion resistance. The presence of C-rich phases, graphite flakes and cementite was found to be effective in enhancing the liquid Al corrosion resistance of gray cast irons. Conversely, a higher Si content was found to enhance the susceptibility of cast irons to liquid Al corrosion. The corrosion mechanisms for ferrous alloys in liquid Al are not fully understood. Thus the subsequent analysis of the dissolution data was supported by investigating the reaction products formed between Al and substrate materials. In addition to commonly existent ε-Fe2Al5 and ζ-FeAl3 phases, the formation of Al4C3 and κ-Fe3AlC compounds was confirmed for the first time in the intermetallic layers of ferrous alloys. The Fe3Si phase in the intermetallic layers of high Si cast irons was found, which was believed to facilitate the high corrosion rates of high Si cast irons. Moreover, the mechanism by which C in Fe-substrates affects the liquid Al corrosion resistance can be better understood given the present work. Furthermore, the analysis presented here gives an understanding of the nature, growth and dissolution of intermetallic compounds in several cast iron alloys. Higher Si additions to cast irons played an important role in molten metal corrosion by accelerating the material loss and changing the nature of intermetallic layers. The results of this study clearly indicated that the dissolution and the growth of intermetallic compounds are interrelated and the dissolution and/or spallation of the intermetallic layers may be the primary mode of liquid Al corrosion of ferrous alloys.

Style APA, Harvard, Vancouver, ISO itp.

3

Monaghan, Brian Joseph. "The kinetics of liquid iron dephosphorization using lime based slags". Thesis, University of Strathclyde, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.626859.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

4

Kapilasharmi, Era. "Investigation of Interactions between Liquid Iron Containing Oxygen and Aluminosilicate Refractories". Doctoral thesis, KTH, Materials Science and Engineering, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3625.

Pełny tekst źródła

Streszczenie:

The present work was initiated to investigate runnerrefractory corrosion by molten steel. The aim was to understandthe mechanism of inclusion formation during ingot casting. Thework is also of interest to other unit processes in steelmaking, where refractory corrosion and erosion are seriousproblems. The oxides investigated in the present work werealumina, silica and mullite, which are the main components inrunner refractory. In addition, industrial refractory materialwas investigated.

Two types of experiments were conducted. The first, "rodexperiments", involved dipping a rod of the oxide into an ironbath containing varying amounts of oxygen. After quenching, therods were examined through SEM/EDS analysis. In the second setsof experiments, the wetting behaviour of molten iron onrefractory oxides was investigated by means of the sessile-dropmethod. The reactions were followed in static as well asdynamic modes through contact angle measurements. Temperatureand oxygen partial pressure were, besides time the parametersthat were investigated in the present study. Oxygen partialpressure was defined by introducing a gas mixture of CO-CO₂-Ar into the furnace.

The experimental studies were preceded by a thermodynamicinvestigation of the refractory systems, in order to get afundamental understanding of the reactions that occurred. Phasestability diagrams for the systems were constructed based onthe data available in literature. The diagrams showed that thereaction between alumina and oxygen containing iron would leadto the formation of hercynite at a critical oxygen level in themetal. With silica, the reaction would lead to the formation offayalite. In the mullite case, the reaction products would behercynite at moderate oxygen levels in the melt and hercynitetogether with fayalite at slightly higher oxygenpotentials.

For all substrates, the contact angles started decreasing asthe surface-active oxygen came into contact with the iron drop.At a critical level of oxygen in the metal, a reaction productstarted forming at the drop/substrate interface. The reactionproducts were identified through SEM/EDS analysis and werefound to be in agreement with thermodynamic predictions. In thecase of SiO₂substrate, there were also deep erosion tracksalong the periphery of the drops, probably due to Marangoniflow.

Alumina-graphite refractory reactions with molten iron werealso investigated through Monte Carlo simulations. The resultsshowed that, with increased alumina content in the refractory,the carbon dissolution into the melt decreased. Further, thewetting behaviour at the interface was found to be an importantfactor to considerably reduce the carbon dissolution fromalumina-graphite refractories.

The experimentation was extended to the commercialrefractories used in the ingot casting process at UddeholmTooling AB, Sweden. The analysis of the plant trial samplesindicates that there is less likelihood of a strong corrosionof the refractories that could lead to a significant populationof inclusions in the end product. The impact of the presentexperimental results on refractory erosion is discussed. Theimportance of the results to clean steel processing anddevelopment of new generation refractories are alsopresented.

Style APA, Harvard, Vancouver, ISO itp.

5

Jones, Karen Lorraine. "Analysis of ferredoxin and flavodoxin in Anabaena and Trichodesmium using fast protein liquid chromatography". PDXScholar, 1988. https://pdxscholar.library.pdx.edu/open_access_etds/3812.

Pełny tekst źródła

Streszczenie:

Iron is an essential nutrient for growth of photosynthetic microorganisms such as cyanobacteria and algae. Iron is required for proteins involved in the important processes of carbon and nitrogen assimilation. Low concentrations of iron in cultures or natural waters can lead to iron limitation which affects many aspects of algal metabolism. In natural waters, iron limitation can have effects on the patterns and rates of primary productivity. The cellular content of certain proteins can be affected by media iron concentrations. Methods have been used that assay components of the cell as an indirect measure of iron nutritional status. For example, spectroscopy can be performed to determine the cellular concentration of iron-containing proteins involved in photosynthesis. Organisms grown in media that imitate natural conditions, or organisms collected from their natural habitat are usually dilute. Methods that assay iron nutritional status such as spectroscopy and column chromatography require large sample sizes which are difficult to obtain from natural samples. In addition, methods that utilize techniques such as immunology or radioactive labelling are complex and time-consuming. These considerations led to the necessity of developing a technique that would be simple, rapid and effective on dilute samples. The method developed here utilized fast protein liquid chromatography (FPLC), which fulfilled these requirements. A complete analysis could be done within two to three hours with minimal sample treatment. The FPLC was simple to operate and was effective on a sample containing less than 100 μg of protein. Some photosynthetic organisms, when iron-depleted, can produce the flavin-containing protein flavodoxin (Flv). This protein substitutes for the iron-containing protein ferredoxin (Fd) in Fd-dependent reactions such as the light-induced reduction of NADP. The FPLC technique identified and quantified, in relative terms, Fd and Flv in the cell. Optical spectroscopy was used to verify FPLC retention time assignments. The results illustrated how the FPLC could be used to observe the changes in relative Fd and Flv content as a function of media iron concentration in cultures of the cyanobacterium Anabaena grown in the laboratory. It was found that Fd content decreased and Flv content increased with decreasing media iron concentration. In addition, samples of the cyanobacterium Trichodesmium collected from the ocean near Barbados were analyzed using FPLC to assay relative Fd and Flv content. By analogy with Anabaena, Fd and Flv retention times were identified. Using this technique conclusions could be drawn regarding the changing iron nutritional status of Trichodesmium in its natural habitat .

Style APA, Harvard, Vancouver, ISO itp.

6

Lartigue, Lénaïc. "Synthesis, Characterization, and Theranostic Application of Iron Based Magnetic Nanoparticles". Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20092/document.

Pełny tekst źródła

Streszczenie:

La synthèse de nano-object connait un essor grandissant depuis ces 20 dernières années. Les études fondamentales de système a permis (et permet encore) de trouver de nombreux domaines d'application aux nanotechnologies, que ces soit en catalyse, en électronique, dans le domaine biomédical...La thèse se déroule autour de deux axes de recherches: la synthèse et la description des propriétés magnétique de nanoparticules de fer stabilisé par des liquides ioniques, et la synthèse, l'étude magnétique, et leur évaluation en tant qu'agent de contraste et médiateur d'hyperthermie de nanoparticules de de ferrite fonctionnalisé par des dérivées carbohydrates
The synthesis of nano-object is growing in the last 20 years. Basic research system has (and still allows) to find many areas of application for nanotechnology that is in catalysis, electronics, biomedical ...The thesis proceeds along two lines of research: the synthesis and the description of magnetic properties of iron nanoparticles stabilized by ionic liquids, and the synthesis, magnetic study, and their evaluation as a contrast agent and hyperthermia mediator of functionalized carbohydrate derivatives ferrite nanoparticles

Style APA, Harvard, Vancouver, ISO itp.

7

Chapman, Michael Wallace. "Insoluble oxide product formation and its effect on coke dissolution in liquid iron". School of Mechanical, Materials and Mechatronic Engineering - Faculty of Engineering, 2009. http://ro.uow.edu.au/theses/3039.

Pełny tekst źródła

Streszczenie:

A significant body of work exists around coke dissolution into liquid iron, however there are key aspects of this important reaction that are not well described. This study was focused on gaining the answers to the questions “How does the coke mineral matter behave during coke dissolution?” and “Can the effects of sulphur and oxide layer formation on the dissolution rate be separated and quantified?”. Issues that must be addressed if the understanding of the kinetics of this reaction is to be advanced and coke's use in the blast furnace further optimised.To this end, a detailed investigation was conducted examining the influence of coke mineral matter on coke (carbon) dissolution into liquid iron. This project was focused on the mineral matter layer that forms at the coke/iron interface and how the presence of this layer affects the kinetics of carbon dissolution from the coke into the liquid iron. A range of experimental techniques were used to identify and characterise the mineral layer as it formed at the coke/iron interface and to assess the layers influence on the carbon dissolution kinetics.Carbon dissolution experiments, utilising a carburiser cover technique, were carried out where carbon and sulphur transfer to an iron-carbon melt was measured over time at temperatures of 1450°C, 1500°C and 1550°C. This technique allowed fundamental data on the dissolution rate constant to be calculated, and the effects of temperature, melt sulphur and different carbonaceous materials to be explored.Development of the mineral layer at the coke/iron interface as a function of both time and temperature was studied utilising a quenched carbon dissolution technique that was developed during the project. This technique had the additional benefit of allowing the composition of the melt to be determined for a larger range of elements than the dissolution experiments. The quenched carbon dissolution experiments complemented the carbon dissolution experiments and allowed direct comparisons between the dissolution behaviour measured in the dissolution experiments and the composition and morphology of the mineral layer observed in the quenched samples.The dissolution studies were further complemented by sessile drop measurements of the wetting behaviour of iron on the mineral phases that were identified in the mineral layer present at the coke/iron interface, thermodynamic modelling utilising the MTDATA software package and a conceptual model of the interfacial mineral layer.A mineral layer was observed to have formed at the coke/iron interface during coke dissolution into liquid iron at experimental temperatures ranging from 1450°C to 1550°C. The mineral layer was solid at these temperatures and persistent at the interface. The amount of mineral matter present in the mineral layer was observed to be increasing with increased reaction time. The composition and structure of the mineral layer changed with both experimental time and temperature. The composition of the mineral layer was principally composed of oxides of aluminium and calcium, present as various calcium aluminates and calcium sulphides. Initially the mineral layer was a loose agglomeration of particles of which a majority were alumina particles. As the dissolution reaction proceeded, the loose agglomeration of particles was replaced by an open acicular layer that was predominantly the calcium aluminate CaO.6Al2O3 (CA6). As the dissolution reaction continued further, the calcium aluminates became increasingly richer in calcium oxide, with the predominate phase present in the mineral layer progressing through the calcium aluminates phases CA6 to CaO.2Al2O3 (CA2) and onto CaO.Al2O3 (CA). The apparent calcium enrichment of the mineral layer was observed to occur more rapidly as the experimental temperature increased. Accompanying the compositional changes in the mineral layer, the morphology of the mineral layer was also observed to change. The mineral layer was formed as an initial loose agglomeration of alumina particles, changing to an open acicular structure consisting of CA6/CA2 before being converted to a dense layer as the dissolution reaction proceeded and the composition of the mineral layer changed to CA and calcium sulphide (CaS) appeared at the interface.It was found that the formation of the calcium sulphide layer was preceded by the formation of the calcium aluminate layer. Only after the calcium aluminate layer had experienced progressive calcium enrichment and the CA and CA2 phases had formed did the CaS phase appear at the iron interface. Thermodynamic analysis of the experimental results confirmed that the formation of the calcium enriched calcium aluminates, CA2 and CA, were a necessary requirement to stabilise the calcium sulphide layer for the coke composition studied.The kinetics of carbon dissolution from the coke to the liquid iron were observed to be dependent on the structure of the interfacial mineral layer. This dependence was manifest as two stage behaviour in the first order mass transfer plots. The initial stage, characterised by rapid carbon dissolution, was observed while the mineral layer was developing or had the open acicular structure of the CA6/CA2 layer. The second stage was characterised by a significant reduction in the rate of carbon dissolution. The onset of the second stage was coincident with the change in the composition of the mineral layer from CA6/CA2 to CA2/CA and the associated densification of the mineral layer. In stating that the nature of the mineral layer affects the dissolution kinetics, a change in the reaction control mechanism is implied. This represents a change in the coke dissolution kinetics from simple mass transfer control to a mixed control regime where both mass transfer and the mineral (product) layer are active.In an attempt to overcome the problems associated with the heterogeneity of coke a coke analogue was developed. In the coke analogue the composition and dispersion of the carbonaceous and mineral matter (oxides) are controlled and the porosity is fixed. When single phase calcium aluminates were introduced into the coke analogues, calcium enrichment of the resulting calcium aluminate mineral layer was observed. The observed carbon dissolution kinetics were dependant on the structure of the interfacial calcium aluminate layer. Consistent with the coke dissolution studies, the calcium aluminate layer formed at the coke analogue iron interface during carbon dissolution was at least in part rate controlling the carbon dissolution reaction for the coke analogues studied.Utilising the sessile drop experimental technique the wettability with liquid ironcarbon-sulphur alloys of the predominate phases that were observed in the mineral layer were measured. It was observed that the contact angle decreased as the proportion of lime (CaO) in the calcium aluminate increased. Further it was observed that while the presence of sulphur in the melt increased the contact angle for the alumina and CA6 substrates, on the CA2 and CA substrates the contact angle was decreased. The improvement in the wetting of the CA2 and CA substrates with sulphur was attributed to the formation of CaS at the substrate/droplet interface.This study has produced new fundamental data on the growth and development of the mineral layer and the wettability of the predominate calcium aluminates observed in the mineral layer. These detailed studies have illuminated the changing nature of the layer in terms of both composition and morphology and found that the kinetics of carbon dissolution from the coke to the liquid iron were dependant on the structure of the interfacial mineral layer.

Style APA, Harvard, Vancouver, ISO itp.

8

McPhee, William A. G. "Liquid pool formation and the influence of iron on the sintering of Al-cu alloys /". St. Lucia, Qld, 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16473.pdf.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

9

Antonsson, Tomas. "On the interaction between liquid/ solid during sintering and solidification". Doctoral thesis, KTH, Casting of Metals, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3464.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

10

MEINERO, MARTINA. "Transport properties at the boundaries of Fermi liquid: iron-based and high-Tc superconductors". Doctoral thesis, Università degli studi di Genova, 2019. http://hdl.handle.net/11567/941936.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

11

Palumbo, Enzo A. "The study of a magnesium wire feeding technique for the desulphurization of molten iron and liquid steel /". Thesis, McGill University, 1985. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65333.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

12

Liang, Yu [Verfasser]. "Ultrafast Dynamics of Metalloporphyrins, DNA and Iron-Lanthanide Clusters in the Liquid Phase / Yu Liang". Karlsruhe : KIT Scientific Publishing, 2013. http://www.ksp.kit.edu.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

13

Wiencke, Jan-Christian. "Analysis of the electrochemical processes during the production of liquid iron by Molten Oxide Electrolysis". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0329.

Pełny tekst źródła

Streszczenie:

L'électrolyse en milieu oxydes fondus (MOE) peut être envisagée comme une nouvelle technologie de l’industrie sidérurgique pour la production de fer liquide sans émission de CO2. Dans ce concept, l'électrolyse est utilisée pour produire de l’oxygène gazeux et du fer liquide à des températures supérieures à 1810 K. Dans cette étude sont présentées les principales réactions électrochimiques lors de l’électrolyse en milieu fondu (MgO-Al2O3-SiO2). Une quantité importante de fer liquide a été produite lors d'électrolyses conduites pendant plusieurs heures. L'analyse MEB-EDS du dépôt a révélé un alliage de fer métallique quasi pur, uniquement contaminé par le matériau cathodique. Ce résultat traduit une sélectivité élevée du procédé électrolytique. L'étude de la réponse de l'électrolyte en fonction de la tension électrique et de la concentration de fer a révélé une limitation par la diffusion lors de l’électrolyse de bains de faibles concentrations en oxyde de fer, et à des potentiels inférieurs à 1,5 V. La demi-réaction de la cathode a été identifiée comme la réduction du fer ferreux en fer métallique. L’extrapolation des droites de Tafel sur les courbes courant-tension corrigées de la chute ohmique a conduit à des coefficients de transfert (de la réaction cathodique) proches à 0,6. L’ordre de réaction de réduction de FeII en Fe0 a été évalué autour de 1. L'analyse de la demi-réaction anodique dans les oxydes fondus à faible teneur en fer a montré que les premières espèces éctroactives sont les anions oxydes libres. Pour des tensions électriques croissantes, le transport des anions O2- libres devient limité et le transfert de charge est partiellement attribué à l’oxydation du fer ferreux. Au contraire, dans des mélanges d’oxydes fondus à concentrations élevées en fer, le transfert de charge est réalisé dans toute la gamme de tension par l'oxydation du fer ferreux. C’est seulement à haute tension, que l’oxydation des anions oxyde contribue au transfert des charges. Dans l'ensemble des compositions testées, aucune limitation du courant n’a été observée sur la réaction anodique
Molten oxide electrolysis (MOE) is an ambitious technique for the production of liquid iron by the use of renewable energies and thus lower CO2 emissions in the steel industry. In this concept, electrolysis is used to produce gaseous O2 and liquid iron metal at temperatures above 1810 K. In the experimental study presented here the key-parameters of the electrochemical reactions in a magnesio-aluminosilicate electrolyte and at the electrodes during MOE are investigated. A significant amount of liquid iron metal was produced during experiments of several hours. SEM-EDS analysis of the deposit revealed an alloy of iron metal and of the cathode material, which thereby indicates high process selectivity. Investigation of the electrolyte’s response in dependence of cell voltage and iron concentration inferred a diffusional limitation at low iron oxide concentrations at potentials below 1.5 V. The cathode half-reaction was identified as the reduction of ferrous iron to liquid iron metal. Using Tafel interpretation reaction-transfer coefficients close to 0.6 and an order of reaction around 1 were determined. The analysis of the anode half-reaction showed that in low iron bearing molten oxides, oxide anions were firstly oxidized into O2 gas. At high iron concentrations the charge transfer is conducted in the entire cell voltage range by the oxidation of ferrous iron. The participation of oxide anions in the charge transfer was only witnessed at high cell voltages. In the entire compositional range a limitation of the measured current due to the anode half reaction was not observed

Style APA, Harvard, Vancouver, ISO itp.

14

McCarthy, Fiona Materials Science &amp Engineering Faculty of Science UNSW. "Interfacial phenomena and dissolution of carbon from chars into liquid iron during pulverised coal injection in a blast furnace". Awarded by:University of New South Wales. School of Materials Science and Engineering, 2005. http://handle.unsw.edu.au/1959.4/20797.

Pełny tekst źródła

Streszczenie:

As carbon dissolution rates have been determined for a few chars only, a systematic and comprehensive study was undertaken in this project on the dissolution behaviour of carbon from non-graphitic materials into liquid iron. In addition to measuring the kinetics of carbon dissolution from a number of coal chars into liquid iron as a function of parent coal and coal ash composition, the influence of chemical reactions between solute/solid carbon and ash oxides was also investigated. These studies were supplemented with investigations on one metallurgical coke for the sake of comparison. The wettability of coal chars and coke with liquid iron at 1550 degrees C was measured as a function of time. Being essentially non-wetting, only a marginal improvement in contact angles was observed with time. The accumulation of alumina at the interface was detected for all materials and was seen to increase with time in all cases. Calcium and sulphur also appeared to preferentially accumulate at the interface, concentrating at levels in excess of those expected from the ash composition alone. Despite the high levels of silica in the ash initially, very little silica was detected in the interfacial region, implying ongoing silica reduction reactions. A small amount of silicon was however detected in the iron droplets, indicating silica reduction with solute carbon. It was identified that the reduction reactions can also consume solute carbon in the liquid iron. As this is occurring simultaneously with carbon dissolution into liquid iron, the interdependency of silica reduction and carbon dissolution could potentially limit the observed carbon dissolution rate. A theoretical model was developed for estimating the interfacial contact area between chars and liquid iron. Wettability was found to have a very significant effect on the area of contact. A two-step behaviour was observed in the carbon dissolution of two chars and coke. Slow rates of carbon dissolution in stage II were attributed to very high levels of interfacial blockage by reaction products leading to much reduced areas of contact between carbonaceous material and liquid iron. The first order dissolution rate constants for four chars/coke and the observed trend in first order dissolution rate constants were calculated. These dissolution results compare well with the previously measured dissolution rate constants. The trends in dissolution can be adequately explained on the basis of carbon structure, silica reduction, sulphur concentration in the metal and ash impurities.

Style APA, Harvard, Vancouver, ISO itp.

15

Aluru, Sreenivasa Charan Rajeev Gale W. F. "Microstructure - mechanical property relationships in transient liquid phase bonded nickel-based superalloys and iron-based ODS alloys". Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/doctoral/ALURU_SREENIVASA_32.pdf.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

16

Posner, Esther [Verfasser], i David [Akademischer Betreuer] Rubie. "Mass transport and structural properties of liquid iron alloys at high pressure / Esther Posner ; Betreuer: David Rubie". Bayreuth : Universität Bayreuth, 2017. http://d-nb.info/1135260621/34.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

17

FRONZO, A. DI. "BIOMASS TO LIQUID PROCESS: NEW KIND OF COBALT AND IRON BASED CATALYSTS FOR THE FISCHER-TROPSCH SYNTHESIS". Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/229549.

Pełny tekst źródła

Streszczenie:

Nowadays it is imperative to develop economical and energy-efficient processes for the sustainable production of fuels and chemicals alternative to the ones deriving from petroleum. Climate change and air quality are major environmental concerns because they directly affect the way we live and breathe. In order to meet the present and future threats generated by emissions to the atmosphere, environmental agencies around the world have issued more stringent regulations. One of them is the control of residual sulfur in diesel fuel and emission standards for particulates from diesel vehicles. All these facts have recently aroused renewed interest in the Fischer–Tropsch Synthesis (FTS) because it can produce super clean diesel oil fraction with high cetane number (typically above 70) without any sulfur and aromatic compounds, using syngas - (mixture of H2, CO, CO2) - from natural gas, CH4, coal or, as a new tendency, from biomass. The essential target of FTS is to produce paraffins and olefins with different molecular weight and to limit the maximum formation of methane and CO2. FTS usually requires catalysts based on iron or cobalt. Iron catalysts are often preferred over cobalt–based ones especially when converting syngas with molar H2/CO ratio lower than 2 (corresponding to the stoichiometry required by the FTS reaction). This is also the typical H2/CO ratio of syngas produced from biomass or coal. In fact, iron-based catalysts are active towards the Water Gas Shift reaction (WGS: CO + H2O-> CO2 + H2), increasing the H2/CO ratio. On the other hand when feeding a syngas mixture with a H2/CO ratio close to 2, cobalt catalysts are preferred due to their high selectivity towards heavy hydrocarbons and their low activity in WGS reaction limiting the CO2 formation. Moreover Co-based catalysts exhibit longer life-time and higher CO conversion compared with Fe based catalyst. In this wide and well-known situation it is nowadays imperative to develop new innovative kind of catalysts in order to make possible the conversion of syngas and biosyngas (i.e. syngas produced from biomass) to useful hydrocarbon by FTS process. Considering very recent research results the aim of the PhD’s research was addressed toward the development of three particular kind of catalysts: The first group of catalysts tested were the Co-based hydrotalcites (HTlc) with different amount of Co in two different pilot plants. HTlc-based materials have been recently reported as good catalysts for several processes in the energy field. Up to now the only study reported in literature on the use of synthetic HTlc as FTS catalysts concerns their use as inert supports for the catalytically active metal. According to this study, hydrotalcite-supported catalysts result in higher activity than Co/Al2O3, even in absence of reduction promoters. The second group of catalysts tested were the Co-based catalysts and bimetallic Co-Ru based catalyst synthesized with the help of ultrasound, because the ultrasound are presented in literature as an innovative way to synthesize new kind of materials. Finally, were synthesized and tested samples of Fe-based catalysts supported on silica with the variation of the H2/CO ratio (with the aim to evaluate the performance of biomass) and with the results propose a kinetic model. Concerning the results obtained in this PhD’s research work, it is clear that all the samples tested have given good results. The Co-based catalysts, synthesized using the traditional impregnation method, with an additional step of ultrasound have given good results in comparison with the results in the current literature. The hydrotalcites have given lower results, if compared with the Co-based catalysts synthesized with the help of ultrasound, but they have opened an alternative and innovative way, that has never been tried before. Iron based catalysts allow a direct conversion of the biosyngas, and the results have shown how our catalysts are active with an H2/CO ratio ≤2. Furthermore, trends have been modeled with success. In conclusion, the PhD’s research work, has given a serious contribution to the current state of the art on catalysis in the Fischer-Tropsch synthesis either with cobalt and iron based catalysts. With cobalt has been optimized a traditional synthesis procedure with the introduction of ultrasound, furthermore has been created a completely new kind of catalyst. With iron has continued an optimization’s work of iron supported with high loading metals, so to develop a suitable kinetic model able to work not only with syngas, but also with biosyngas.

Style APA, Harvard, Vancouver, ISO itp.

18

Lebeau, Timothy Charles. "Brake drum production by centrifugal casting". Birmingham, Ala. : University of Alabama at Birmingham, 2008. https://www.mhsl.uab.edu/dt/2009r/lebeau.pdf.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

19

Wang, Huifeng [Verfasser]. "Surface science approach to catalyst preparation : Palladium deposition onto iron oxide films from the liquid phase / Huifeng Wang". Berlin : Freie Universität Berlin, 2012. http://d-nb.info/1029955042/34.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

20

Wang, Hui-Feng [Verfasser]. "Surface science approach to catalyst preparation : Palladium deposition onto iron oxide films from the liquid phase / Huifeng Wang". Berlin : Freie Universität Berlin, 2012. http://nbn-resolving.de/urn:nbn:de:kobv:188-fudissthesis000000039466-3.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

21

Rhamdhani, Muhammad Akbar Brooks Geoffrey. "Reaction kinetics and dynamic interfacial phenomena in liquid metal-slag systems". *McMaster only, 2005.

Znajdź pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

22

Min, Zhenhua. "Catalytic steam reforming of biomass tar using iron catalysts". Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/184.

Pełny tekst źródła

Streszczenie:

Biomass has become an increasingly important renewable source of energy forenhanced energy security and reduced CO[subscript]2 emissions. Gasification is at the core of many biomass utilisation technologies for such purposes as the generation of electricity and the production of hydrogen, liquid fuels and chemicals. However, gasification faces a number of technical challenges to become a commercially feasible renewable energy technology. The most important one is the presence of tar in the gasification product gas. The ultimate purpose of this thesis was to investigate the catalytic reforming of tar using cheap catalysts as an effective means of tar destruction.In this thesis, natural ilmenite ore and novel char-supported catalysts were studied as catalysts for the steam reforming of biomass tar derived from the pyrolysis of mallee biomass in situ in two-stage fluidised-bed/fixed-bed quartz reactors. In addition to the quantification of tar conversion, the residual tar samples were also characterised with UV-fluorescence spectroscopy. Both fresh and spent catalysts were characterised with X-ray diffraction spectroscopy, FT-Raman spectroscopy and thermogravimetric analysis.The results indicate that ilmenite has activity for the reforming of tar due to its highly dispersed iron-containing species. Both the externally added steam and low concentration oxygen affect the tar reforming on ilmenite significantly. The properties of biomass affect the chemical composition of its volatiles and therefore their reforming with the ilmenite catalyst. Compared with sintering, coke deposited on ilmenite is the predominant factor for its deactivation.During the steam reforming process, the char-supported iron/nickel catalysts exhibit very high activity for the reforming of tar. In addition, NO[subscript]x precursors could be decomposed effectively on the char-supported iron catalyst during the steam reforming process. The hydrolysis of HCN and the decomposition of NH[subscript]3 on the catalyst are the key reactions for the catalytic destruction of NO[subscript]x precursors.The kinetic compensation effects demonstrate that the reaction pathways on the char-supported catalysts are similar but different from those on ilmenite. The proprieties of catalyst support could play important roles for the activities of the catalysts and the reaction pathways on the catalysts. The char support as part of the char-supported catalysts can undergo significant structural changes during the catalytic reforming of biomass volatiles.

Style APA, Harvard, Vancouver, ISO itp.

23

Wang, Yu. "Mechanical properties and microstructure of laser sintered and starch consolidated iron-based powders". Doctoral thesis, Karlstad : Faculty of Technology and Science, Materials Engineering, Karlstads universitet, 2008. http://www.diva-portal.org/kau/abstract.xsql?dbid=1593.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

24

Rubasinghege, Gayan Randika S. "Chemical and photochemical reactions on mineral oxide surfaces in gaseous and liquid phases: environmental implications of fate, transport and climatic impacts of mineral dust aerosol". Diss., University of Iowa, 2011. https://ir.uiowa.edu/etd/1173.

Pełny tekst źródła

Streszczenie:

Mineral dust aerosols emitted from the Earth crust during various natural and anthropogenic processes continuously alter the chemical balance of the atmosphere via heterogeneous processes and thus, impact on the global climate. Understanding of heterogeneous chemistry and photochemistry on mineral dust has become vital to accurately predict the effect of mineral dust loading on the Earth's atmosphere. Here, laboratory measurements are coupled with model studies to understand heterogeneous chemistry and photochemistry in the atmosphere with the specific focus on reactions on mineral oxide surfaces. Heterogeneous uptake of gas phase HNO3 on well characterized metal oxides, oxyhydroxides and carbonates emphasized binding of nitric acid to these surfaces in different modes including monodentate, bidentate and bridging under dry conditions. It is becoming increasingly clear that the heterogeneous chemistry, including uptake of HNO3, is a function of relative humidity (RH) as water on the surface of these particles can enhance or inhibit its reactivity depending on the reaction. All the studied model systems showed a significant uptake of water with the highest uptake by CaCO3. Quantitative analysis of water uptake indicated formation of multilayers of water over these reactive surfaces. Under humid conditions, two water solvated nitrate coordination modes were observed that is inner-sphere and outer-sphere, which differ by nitrate proximity to the surface. Photochemical conversion of nitric acid to gas phase nitrous oxide, nitric oxide and nitrogen dioxide through an adsorbed nitrate intermediate under different atmospherically relevant conditions is shown using transmittance FTIR and XPS analysis. The relative ratio and product yields of these gas phase products change with relative humidity. Photochemistry of adsorbed nitrate on mineral aerosol dust may be influenced by the presence of other distinct gases in the atmosphere making it complicated to understand. This thesis converses formation of active nitrogen, NOx and N2O, and chlorine, ClOx, species in the presence of co-adsorbed trace gases, that could potentially regulate the peak concentration and geographical distribution of atmospheric ozone. Here we report formation of atmospheric N2O, from the photodecomposition of adsorbed nitrate in the presence of co-adsorbed NH3 via an abiotic mechanism that is favorable in the presence of light, relative humidity and a surface. Estimated annual production of N2O over the continental United States is 9.3+0.7/-5.3 Gg N2O, ~5% of total U.S. anthropogenic N2O emissions. Not only NH2 but also gaseous HCl react with adsorbed nitrate to activate "inert" N and Cl reservoir species, yielding NOCl, NOx, Cl and Cl2, through adsorbed nitrate under different atmospherically relevant conditions. Mineral dust aerosol is a major source of bioavailable iron to the ocean with an annual deposition of ~ 450 Tg of dust into the open ocean waters. In this study, we report enhanced Fe dissolution from nano scale Fe-containing minerals, i.e.alpha-FeOOH, beyond the surface area effects that can be attributed to the presence of more reactive sites on specific crystal planes exposed. We further report with clear evidence that aggregation impacts on dissolution. Proton-promoted dissolution of nanorods is nearly or completely quenched in the aggregated state. Acid type, presence of oxyanions and light are several other key factors responsible for regulating for iron dissolution. The work reported in this thesis provides insight into the heterogeneous chemistry and photochemistry of mineral dust aerosol under different atmospherically relevant conditions.

Style APA, Harvard, Vancouver, ISO itp.

25

Simelane, Lusanda Susan. "Effect of a multiple micronutrient enriched maize-based liquid meal supplement on iron status of grade 3 and 4 learners attending Sunnyside primary school, Pretoria". Diss., University of Pretoria, 2015. http://hdl.handle.net/2263/46108.

Pełny tekst źródła

Streszczenie:

Background: About one half of school-age children in developing countries are estimated to be affected by iron deficiency. Failure to treat micronutrient deficiencies can negatively affect health and economic development. Objective: To determine the effect of multiple micronutrient maize-based liquid meal supplement on the iron status and the nutritional status of primary school children. Design: A randomized double-blind placebo controlled trial was conducted. Setting and subjects: The study took place at Sunnyside Primary School in Sunnyside, Pretoria, in the urban area of Tshwane (Gauteng Province, South Africa). Grades 3 and 4 male and female learners aged 8-12 years, enrolled in the 2010 academic year were recruited for the study. Methods: Participants were dewormed, to eliminate parasitic infestaion at the beginning of the study. The experimental product was a maize-based liquid meal supplement enriched with macronutrients and micronutrients including chelated ferrous bisglycinate, while the control had the same macronutrient profile but no added micronutrients. The learners took the meal supplement every morning on school days for 14 weeks. Iron status was measured by Haemoglobin (Hb) levels and the nutritional status was measured by anthropometric measures at baseline and end. Groups were compared with respect to change in Hb and change in anthropometry using an analysis of covariance (ANCOVA) with baseline Hb values as covariate. Testing was done at the 0.05 level of significance. Results: There was no significant difference in the Hb levels at baseline (12.6 ± 1.1 g/dL and 12.8 ± 1.1 g/dL) (P = 0.250) between the experimental and control groups respectively. The prevalence of mild anemia (Hb< 11g/dL) was low in both the experimental and control groups. Over the 14 weeks study period, consumption of experimental products was similar and there was no significant effect on Hb levels of the participants observed (P = 0.806) in the experimental and control groups. There was also no significant change observed in the anthropometry of the participants. Conclusion: The maize-based liquid meal supplement enriched with multiple micronutrients did not have a significant effect on the iron status of the participants in this study, possibly owing to low prevalence of anemia, a low rate of consumption and therefore iron absorption.
Dissertation (MSc)--University of Pretoria, 2015.
tm2015
Animal and Wildlife Sciences
MSc
Unrestricted

Style APA, Harvard, Vancouver, ISO itp.

26

Orsine, Noeber Maciel. "Definição de tecnologias para desaguamento de ultrafinos ricos de minério de ferro : uma aplicação na Vale Carajás - Pará - Brasil". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/140518.

Pełny tekst źródła

Streszczenie:

O minério de ferro produzido no complexo de Carajás traz consigo características mineralógicas que conferem um elevadíssimo teor de Fe em todas as suas frações granulométricas. Dessa forma, ao final da cadeia produtiva, tanto os produtos comerciais mais grosseiros quanto os finos contem cerca de 62% de Fe contido na sua composição. Importante destacar que em Carajás as fases no processamento desse minério são apenas para cominuição e classificação por tamanho. Não existem etapas de concentração e os produtos são diferenciados por suas respectivas curvas granulométricas: o “granulado” - mais grosseiro (> 13 mm), o “Sinter-Feed” (< 13 mm e > 0,5 mm) e o “pellet feed” (< 0,15 mm). Garantir a correta distribuição granulométrica da matéria prima é uma premissa de mercado. A ultima etapa da classificação é feita através de hidrociclones e gera um overflow ultrafino de altíssima superfície específica maior que 6.500 Blaine e com 45% até 95 % < 7 μm. E ainda possui um elevado teor de Fe - cerca de 62 %. Dessa forma os objetivos gerais dessa pesquisa buscaram a solução para essa oportunidade de recuperar e vender esses rejeitos. O estudo sugeriu através de ensaios com tecnologias capazes de desaguar os ultrafinos gerados para 9,00 % de umidade, que é o valor que permite a movimentação e o manuseio desses rejeitos, além de permitir sua incorporação na blendagem de produtos mais grossos. Desse modo, foram realizados experimentos em diversos laboratórios externos e em escala piloto na Usina de Carajás com amostras dos dois rejeitos ultrafinos das duas fases de hidrociclonagem: o natural e o moído. Ficou evidente que o equipamento tem de combinar necessariamente e de forma eficiente dois fatores essências ao desaguamento: elevadíssimas pressões e altas temperatura na operação desses ultrafinos. A produtividade atingida foi da ordem de 50 t/h x m² para o rejeito da hidrociclonagem do Sinter Feed e 40 t/h x m² para o rejeito dos hidrociclones da Moagem.
The Iron ore that is produced in Carajás mining complex brings mineralogical characteristics that give a very high Fe content in all its size fractions. Thus, at the end of the production chain both coarser and fine contains about 62% Fe contained in its composition. Importantly, in Carajás stages in the processing of this ore are for reduction and classification by size. There is thus no concentration steps and products are differentiated by their respective size distribution curves: the "grain" - coarser (> 13 mm), the "Sinter-Feed" (<13 mm and > 0.5 mm) and the "pellet feed" (<0.15 mm). Ensure proper particle size distribution of the raw material is a market premise. The last step of classification is made using hydrocyclones and generates an overflow ultrafine high specific surface area greater than 6.500 Blaine and with 45% to 95% <7 μm. And has a high Fe content - about 62%. The overall objectives of this research sought the solution to this opportunity to recover and sell these “tailings”. The study suggested by testing with technologies capable of flowing into the ultrathin generated to 9.00% of moisture, which is the value that allows movement and handling these wastes, and allows their incorporation into the blending of thicker products. Thus, experiments were carried out in several external laboratories and pilot-scale plant in the Carajás with samples of both ultrafine “tailings” of the two phases of hydrocycloning: the natural and the ground. It was evident that the equipment must necessarily match and two efficiently factors essences to dewatering: very high pressure and high temperature operation of these “tailings”. The productivity achieved was around 50 t/h x m² in reject of the Sinter Feed hydrocycloning and 40 t/h x m² to reject of the grinding hydrocyclones.

Style APA, Harvard, Vancouver, ISO itp.

27

Ward, Nicholas Rhys. "The rate-limiting mechanism for the heterogeneous burning of iron in normal gravity and reduced gravity". Queensland University of Technology, 2007. http://eprints.qut.edu.au/16673/.

Pełny tekst źródła

Streszczenie:

This thesis presents a research project in the field of oxygen system fire safety relating to the heterogeneous burning of iron in normal gravity and reduced gravity. Fires involving metallic components in oxygen systems often occur, with devastating and costly results, motivating continued research to improve the safety of these devices through a better understanding of the burning phenomena. Metallic materials typically burn in the liquid phase, referred to as heterogeneous burning. A review of the literature indicates that there is a need to improve the overall understanding of heterogeneous burning and better understand the factors that influence metal flammability in normal gravity and reduced gravity. Melting rates for metals burning in reduced gravity have been shown to be higher than those observed under similar conditions in normal gravity, indicating that there is a need for further insight into heterogeneous burning, especially in regard to the rate-limiting mechanism. The objective of the current research is to determine the cause of the higher melting rates observed for metals burning in reduced gravity to (a) identify the rate-limiting mechanism during heterogeneous burning and thus contribute to an improved fundamental understanding of the system, and (b) contribute to improved oxygen system fire safety for both ground-based and space-based applications. In support of the work, a 2-s duration ground-based drop tower reduced-gravity facility was commissioned and a reduced-gravity metals combustion test system was designed, constructed, commissioned and utilised. These experimental systems were used to conduct tests involving burning 3.2-mm diameter cylindrical iron rods in high-pressure oxygen in normal gravity and reduced gravity. Experimental results demonstrate that at the onset of reduced gravity, the burning liquid droplet rapidly attains a spherical shape and engulfs the solid rod, and that this is associated with a rapid increase in the observed melting rate. This link between the geometry of the solid/liquid interface and melting rate during heterogeneous burning is of particular interest in the current research. Heat transfer analysis was performed and shows that a proportional relationship exists between the surface area of the solid/liquid interface and the observed melting rate. This is confirmed through detailed microanalysis of quenched samples that shows excellent agreement between the proportional change in interfacial surface area and the observed melting rate. Thus, it is concluded that the increased melting rates observed for metals burning in reduced gravity are due to altered interfacial geometry, which increases the contact area for heat transfer between the liquid and solid phases. This leads to the conclusion that heat transfer across the solid/liquid interface is the rate-limiting mechanism for melting and burning, limited by the interfacial surface area. This is a fundamental result that applies in normal gravity and reduced gravity and clarifies that oxygen availability, as postulated in the literature, is not rate limiting. It is also established that, except for geometric changes at the solid/liquid interface, the heterogeneous burning phenomenon is the same at each gravity level. A conceptual framework for understanding and discussing the many factors that influence heterogeneous burning is proposed, which is relevant to the study of burning metals and to oxygen system fire safety in both normal-gravity and reduced-gravity applications.

Style APA, Harvard, Vancouver, ISO itp.

28

Ward, Nicholas Rhys. "The rate-limiting mechanism for the heterogeneous burning of iron in normal gravity and reduced gravity". Thesis, Queensland University of Technology, 2007. https://eprints.qut.edu.au/16673/1/Nicholas_Ward_Thesis.pdf.

Pełny tekst źródła

Streszczenie:

This thesis presents a research project in the field of oxygen system fire safety relating to the heterogeneous burning of iron in normal gravity and reduced gravity. Fires involving metallic components in oxygen systems often occur, with devastating and costly results, motivating continued research to improve the safety of these devices through a better understanding of the burning phenomena. Metallic materials typically burn in the liquid phase, referred to as heterogeneous burning. A review of the literature indicates that there is a need to improve the overall understanding of heterogeneous burning and better understand the factors that influence metal flammability in normal gravity and reduced gravity. Melting rates for metals burning in reduced gravity have been shown to be higher than those observed under similar conditions in normal gravity, indicating that there is a need for further insight into heterogeneous burning, especially in regard to the rate-limiting mechanism. The objective of the current research is to determine the cause of the higher melting rates observed for metals burning in reduced gravity to (a) identify the rate-limiting mechanism during heterogeneous burning and thus contribute to an improved fundamental understanding of the system, and (b) contribute to improved oxygen system fire safety for both ground-based and space-based applications. In support of the work, a 2-s duration ground-based drop tower reduced-gravity facility was commissioned and a reduced-gravity metals combustion test system was designed, constructed, commissioned and utilised. These experimental systems were used to conduct tests involving burning 3.2-mm diameter cylindrical iron rods in high-pressure oxygen in normal gravity and reduced gravity. Experimental results demonstrate that at the onset of reduced gravity, the burning liquid droplet rapidly attains a spherical shape and engulfs the solid rod, and that this is associated with a rapid increase in the observed melting rate. This link between the geometry of the solid/liquid interface and melting rate during heterogeneous burning is of particular interest in the current research. Heat transfer analysis was performed and shows that a proportional relationship exists between the surface area of the solid/liquid interface and the observed melting rate. This is confirmed through detailed microanalysis of quenched samples that shows excellent agreement between the proportional change in interfacial surface area and the observed melting rate. Thus, it is concluded that the increased melting rates observed for metals burning in reduced gravity are due to altered interfacial geometry, which increases the contact area for heat transfer between the liquid and solid phases. This leads to the conclusion that heat transfer across the solid/liquid interface is the rate-limiting mechanism for melting and burning, limited by the interfacial surface area. This is a fundamental result that applies in normal gravity and reduced gravity and clarifies that oxygen availability, as postulated in the literature, is not rate limiting. It is also established that, except for geometric changes at the solid/liquid interface, the heterogeneous burning phenomenon is the same at each gravity level. A conceptual framework for understanding and discussing the many factors that influence heterogeneous burning is proposed, which is relevant to the study of burning metals and to oxygen system fire safety in both normal-gravity and reduced-gravity applications.

Style APA, Harvard, Vancouver, ISO itp.

29

Chen, Chih-Yao. "A study on positive electrode materials for sodium secondary batteries utilizing ionic liquids as electrolytes". Kyoto University, 2014. http://hdl.handle.net/2433/192207.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

30

Roberts, Melissa Delane. "Assessment of arsenate bioavailability in iron-rich environments: development of a high-pressure liquid chromatography method of quanitification for arsenate sorbed by Fe3+-substituted chelating resins in arsenic-bearing ferrihydrite suspensions". Texas A&M University, 2005. http://hdl.handle.net/1969.1/2450.

Pełny tekst źródła

Streszczenie:

Given that the mobility, bioavailability, and toxicity of arsenate in natural systems is often controlled by the strong binding capacity of iron oxyhydroxides, the objective of this study was to document the interactions of Dowex M4195 Fe3+-substituted chelating resins (a potential fieldbased tool for the quantification of potential arsenate bioavailability) and arsenic-bearing ferrihydrite (AFH) as a function of suspension pH, suspension concentration, and background electrolyte concentration. In 0.5 g AFH/L (0.001 M NaNO3) suspensions, arsenate sorption to the resins was proportional to the degree of acidification of the AFH suspensions by the resins. H+-enhanced dissolution of ferrihydrite artificially increased the arsenate in solution, causing a consistent overestimation of potential arsenate bioavailability. Resin-induced acidification was decreased with increasing suspension concentration. Arsenate sorption to the resins in 0.5 g/L suspensions at pH 8 decreased with increasing NaNO3 concentrations, reflecting the decreasing activity of arsenate under these conditions. The results of this study indicate that the high buffer capacity of natural soils would prevent acidification as a result of resin introduction. Thus, Dowex M4195 Fe3+-substituted chelating resins should provide a reasonable assessment of potential arsenate bioavailability from poorly-crystalline iron oxide minerals. Possibly more importantly, Dowex M4195 Fe3+-substituted chelating resins appear to be a new choice of passive equilibrium sampling device that should work well for the determination of bioavailable arsenate concentrations in the field.

Style APA, Harvard, Vancouver, ISO itp.

31

Chen, Shu. "FePt magnetic nanoparticles : syntheses, functionalisation and characterisation for biomedical applications". Thesis, University of St Andrews, 2011. http://hdl.handle.net/10023/2151.

Pełny tekst źródła

Streszczenie:

Iron platinum (FePt) has attracted growing interest because of its high Curie temperature, magneto-crystalline anisotropy and chemical stability. Nanoparticles (NPs) made of this alloy are promising candidates for a wide range of biomedical applications including magnetic separation, magnetic targeted drug delivery, hyperthermia for cancer therapy and also as magnetic resonance imaging (MRI) contrast agents. This thesis presents the synthesis, functionalization and characterization of FePt NPs along with a toxicity study and an investigation into their application as MRI contrast agents. Regarding their synthesis, different approaches have been explored including the co-reduction of Fe and Pt precursors in an aqueous media, the thermal decomposition in a conventional high-boiling solvent such as benzyl ether, and in low-melting organic salts (ionic liquids). The data revealed an inhomogeneous composition distribution of Fe and Pt between particles obtained in aqueous media, due to the iron salts hydrolysis, and a mismatch in the co-reduction kinetic of the two metal precursors. While the iron content in the NPs could be increased by using more hydrolytically stable iron precursors or stronger reducing agents, there are remaining limiting parameters which prevent further Fe content increase in NPs. In contrast, by excluding the water from the reaction system and using a Fe²⁻ iron precursor, homogenous 1:1 Fe to Pt ratio NPs can be obtained through a modified thermal decomposition pathway in benzyl ether. Based on the study of synthesis in this conventional chemical, the potential of ionic liquids (ILs) to be used as novel solvents for FePt NPs synthesis was further explored. It was then demonstrated that ionic liquids (ILs) can not only be used as a solvent for synthesis of FePt NPs, but also can provide an exciting alternative pathway to direct synthesis fct-FePt NPs. In the context of the bioapplication of FePt NPs, a family of FePt NPs was specifically designed to enhance their MRI contrast agents properties. In contrast with previous reports, this thesis demonstrates that FePt NPs can be made non-toxic and provides the first data on their cellular uptake mechanisms. A six times increase in the FePt based T₂ contrast properties compared to clinical iron oxide NPs is reported. The relationship between the MRI contrast properties and the NPs architecture is explored and rationalised as the basis for the design of NPs as enhanced MRI contrast agents. Finally, the first observations of cellular and in vivo MR imaging with FePt NPs is also reported. This study opens the way for several applications of FePt NPs such as regenerative medicine and stem cell therapy, thus providing a bio-platform to develop novel diagnostic and therapeutic agents.

Style APA, Harvard, Vancouver, ISO itp.

32

Hrabovský, Jan. "Biodegradabilní kostní implantáty na bázi železa". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442443.

Pełny tekst źródła

Streszczenie:

This work deals with a current topic, which are biodegradable bone implants. These implants seem to be a suitable candidate for temporary fixations, with their gradual decomposition. An important parameter is not only the mechanical properties so that the material can withstand the load, but above all the corrosion properties and the degradation process. This work introduces the physiology of bone, trace elements and also describes current trends in the field of implants. The last part is a theoretical introduction to cross-stage processes. The practical part is focused on the preparation of iron-based samples with various dopants, subsequent annealing and analysis.

Style APA, Harvard, Vancouver, ISO itp.

33

Buckley, Ragan. "The purine world: experimental investigations into the prebiotic synthesis of purine nucleobases and intercalation of homopurine DNA duplexes". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/48971.

Pełny tekst źródła

Streszczenie:

Formamide is a solvent of great interest to prebiotic chemists because it is liquid over a wide range, it is less volatile than either water or HCN, and it possesses a versatile reactivity. When formamide is heated in the presence of minerals or inorganic catalysts, a variety of products including purine nucleobases are generated. Irradiation of formamide reaction solutions with ultraviolet light increases the yield and diversity of products, and eliminates the need for a mineral catalyst. We have also performed formamide reactions in the presence of pyrite, a mineral which is likely to have been available on the primordial Earth, under a variety of atmospheric conditions. Our results indicate the greatest yield and diversity of products result from the combination of a pyrite mineral catalyst, heat, UV irradiation, and a carbon dioxide atmosphere. Purine nucleobases are simple to synthesize in model reactions and they stack well in aqueous solution; it has been hypothesized that the first nucleic acids were composed of only purine bases, and that water-soluble, cationic, aromatic molecules with large stacking surfaces (“”molecular midwives””) may have aided the assembly of the earliest nucleic acid analogs. We have characterized the interactions of various intercalators with a standard DNA duplex as well as with an antiparallel homopurine DNA duplex and have determined that molecules which possess four or more rings and a curved shape interact selectively with all-purine DNA; such molecules can serve as models for putative prebiotic midwives.

Style APA, Harvard, Vancouver, ISO itp.

34

Farias, Francisco Edson Mesquita. "ProduÃÃo de Hidrocarbonetos atravÃs da SÃntese de Fischer-Tropsch utilizando Catalisadores de Fe/K". Universidade Federal do CearÃ, 2007. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=1273.

Pełny tekst źródła

Streszczenie:

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
A reaÃÃo de sÃntese de Fischer-Tropsch tem merecido grande atenÃÃo pelo seu interesse tecnolÃgico e cientÃfico. Este interesse estÃ associado a conversÃo do gÃs natural em produtos lÃquidos de alta qualidade (gasolina e diesel) e elevado valor agregado. No presente trabalho Ã descrito a metodologia empregada na sÃntese e caracterizaÃÃo de catalisadores de ferro usados na sÃntese de Fischer-Tropsch, com Ãnfase nos catalisadores suportados em sÃlica e catalisadores industriais (utilizados na sÃntese de amÃnia) promovidos com potÃssio e cobre. Pretende-se com esta discussÃo, identificar possÃveis vias para o desenvolvimento de catalisadores mais ativos e seletivos, variando a composiÃÃo do promotor estrutural para fins de otimizar a distribuiÃÃo dos produtos em fraÃÃes de hidrocarbonetos especÃficos (gasolina, diesel e graxa). A reaÃÃo foi conduzida em um reator de leito de lama. O estudo seguiu um planejamento experimental do tipo fatorial quadrado com ponto central e os resultados foram analisados baseados na metodologia dos grÃficos de superfÃcie de respostas. Os efeitos das diferentes condiÃÃes operacionais (temperatura e pressÃo) e dos diferentes teores de potÃssio na distribuiÃÃo dos produtos lÃquidos foram comparados baseados nos cromatogramas, nÃmero mÃdio de carbono (Nn) e no grau de dispersÃo dos produtos. Para todos os catalisadores de ferro empregados neste trabalho, observou-se um aumento no Ãndice que representa o comprimento da cadeia de hidrocarboneto (Nn) com o aumento do teor de potÃssio. Indicando um maior grau de polimerizaÃÃo para os catalisadores de ferro suportados com 18K em ralaÃÃo aos outros (12K, 6K e industrial). Os resultados mostram que, para catalisadores suportados, em pressÃes elevadas (25 e 30atm) favorecem a produÃÃo de graxa, enquanto a seletividade para hidrocarbonetos lÃquidos Ã favorecida a baixa pressÃo (20atm) e baixa temperatura (240ÂC). Para os catalisadores industriais, observou-se um aumento na fraÃÃo graxa em baixas temperaturas (240-255ÂC) e elevadas pressÃes (30atm). Contudo, os resultados de todas as corridas para o catalisador suportado e o industrial promovido e nÃo-promovido apresentaram quantidades significativas de n-parafinas com no mÃximo 35 Ãtomos de carbono que pode ser causados atravÃs das limitaÃÃes geomÃtricas e espaciais dentro dos poros do catalisador que tambÃm podem explicar o motivo pelo qual o Ãndice de dispersÃo da distribuiÃÃo de hidrocarbonetos serem mais baixos para um maior nÃmero de carbonos mÃdio.
The Fischer-Tropsch synthesis has been focus of attention of the scientific and industrial community. This interest is related to the conversion of natural gas into high quality liquid products, such as gasoline and diesel, which have high commercial value. In this work the methodology applied to synthesize and characterize iron-based catalyst used in the Fischer-Tropsch synthesis was described. Emphasis was given to catalysts supported in silica and to industrial catalysts (used in the synthesis of ammonia) impregnated with potassium and copper. The catalysts were tested to identify more active and selective catalysts, changing the amount of structural promoter in order to optimize the product distribution of specific hydrocarbons (gasoline, diesel, wax). The reaction was carried out in a slurry phase reactor. The experiments followed a 22 factorial experimental planning with central point and the results were analyzed based on the surface response methodology. The effects of the operating conditions (temperature and pressure) and of the amount of potassium in the catalyst on the liquid product distribution were compared based on the chromatographs, number average number of carbons (Nn) and distribution dispersion. In all iron based catalyst used in the research, the number average number of carbons (Nn) increased with increasing amount of potassium in the catalyst formulation. This result indicates that the catalyst with 18 K supported in silica showed the highest degree of polymerization in comparison with all other catalysts produced in this research. The results showed that for the catalyst supported in silica high pressures (25 to 30 atm) favor the production of wax, while higher selectivity towards liquid fuels was favored by low pressure (20 atm) and low temperature (240ÂC). For the industrial catalyst, an increase in the wax cat was observed at low temperatures (240-255ÂC) and high pressures (30 atm). The experiments carried out with the both catalysts (silica-supported and alumina-supported) have presented significant amounts of n-paraffins with a maximum of 35 carbons and low dispersion of the product distribution which can be caused by space limitations within the catalyst pores.

Style APA, Harvard, Vancouver, ISO itp.

35

Silva, Jorge Ayrton da. "Analise termica na solidificação de ferros fundidos cinzentos hipoeuteticos". [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264734.

Pełny tekst źródła

Streszczenie:

Orientador: Amauri Garcia
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-08-08T17:48:12Z (GMT). No. of bitstreams: 1 Silva_JorgeAyrtonda_M.pdf: 5941604 bytes, checksum: 9ec8b76ce4cbb57c06994f1a8307f767 (MD5) Previous issue date: 2007
A análise térmica é amplamente utilizada como método de controle de processos metalúrgicos e na investigação da composição química de ferros fundidos na prática de fundição. Um meio confiável de avaliação da composição de ferros fundidos é disponibilizado pela técnica do Carbono Equivalente, que é baseada na mudança de inclinação da curva de resfriamento na temperatura liquidus durante o resfriamento de uma amostra de ferro fundido a partir do estado líquido. O presente trabalho é focado no desenvolvimento de um novo sensor para análise térmica, um sensor de imersão, que objetiva contribuir com determinações mais confiáveis de composição durante as operações de fundição. Foram desenvolvidos experimentos em diferentes empresas de fundição, utilizando-se tanto o sensor de imersão quanto o tradicional sensor tipo cápsula, normalmente utilizado na prática de fundição. As comparações de composições químicas, medidas por essas duas técnicas e medidas fornecidas por análise de espectrometria de emissão óptica, demonstram que geralmente o sensor de imersão fornece resultados mais confiáveis. Uma análise térmica realizada durante o resfriamento de ferro fundido em um dispositivo unidirecional com uma coquilha, e utilizando um conjunto de termopares, permitiu também a determinação quantitativa de variáveis térmicas de solidificação, tais como: coeficientes transitórios de transferência de calor metal/molde e molde/ambiente e taxa de resfriamento à frente da isoterma liquidus
Abstract: Thermal analysis is a widely used method for metallurgical process control and investigation of alloy composition of cast irons in foundry practice. A reliable means of rapidly evaluating the composition of cast irons is available by the Carbon-Equivalent technique, which is based on the change in thermal arrest temperature of the liquidus as the sample of molten cast iron freezes. The present work focuses on the development of a new sensor for thermal analysis, a dip-sensor, wich aims to contribute to more reliable determination of alloy composition during casting operation. Experiments were carried-out in different foundries by using both the dipsensor and the traditional capsule-sensor, which is normally used in foundry practice. The comparison of alloy compositions measured by these two techniques with analysis performed by Arc/Spark spectrometry has shown that generally the dip-sensor provides more reliable results. Thermal analysis conducted during cooling of molten cast iron in a unidirectional chill apparatus, by using a set of thermocouples, has also permitted the quantitative determination of solidification thermal variables, such as: transient metal/mold and mold/ambient heat transfer coefficients and tip cooling rates
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica

Style APA, Harvard, Vancouver, ISO itp.

36

Almeida, Sheila Kênia de. "Detecção de bactérias redutoras de sulfato em efluente e sedimento de mina de urânio". CNEN - Centro de Desenvolvimento da Tecnologia Nuclear, Belo Horizonte, 2005. http://www.bdtd.cdtn.br//tde_busca/arquivo.php?codArquivo=44.

Pełny tekst źródła

Streszczenie:

Um dos graves problemas ambientais oriundos da indústria de mineração é a drenagem ácida de mina que ocorre quando a pirita e outros minerais sulfetados são oxidados devido à presença de oxigênio e água, produzindo ácido sulfúrico que solubiliza metais presentes no solo/rocha. Em uma planta das Indústrias Nucleares do Brasil INB, na Unidade de Tratamento de Minérios (UTM) este problema tem se pronunciado de forma preocupante levando a dissolução de espécies radioativas e metálicas presentes. O tratamento da água ácida usando bactérias redutoras de sulfato, proporciona decréscimo da acidez que é decorrente da redução do sulfato a sulfito e precipitação dos metais como sulfetos. Nesse contexto, o presente estudo foi realizado visando a caracterizar sazonalmente e espacialmente populações de bactérias redutoras de sulfato (BRS) nos efluentes líquidos e amostras de sedimento da cava da mina (CM) e nos bota-foras 4 e 8 (BF4 e BF8) coletadas na UTM. Tais informações poderão permitir posteriormente, estudar mecanismos de biomanipulação a fim de remediar situações impactantes. Menores valores de pH , abaixo de 3,5, foram medidos no período de março a abril em amostras de água da cava da mina e a maior população de BRS (2,8 NMP. mL-1) foi observada em fevereiro em amostras do BF8. Os valores encontrados para matéria orgânica na água foram menores do que aqueles encontrados no sedimento. A concentração de oxigênio dissolvido na água variou de 0,65 g/L a 13,3 g/L. As amostras de sedimento apresentaram maiores valores de BRS (10,2 NMP/mL), quando comparadas com amostras de água (0,63 NMP/mL). Tais resultados eram esperados uma vez que, nas amostras de água coletadas próximas ao sedimento foram observadas menores concentrações de oxigênio dissolvido (7,10g/L) e maiores concentrações de matéria orgânica disponível (17,0 mg/L) quando os resultados foram comparados com aqueles obtidos para amostras de água coletadas na superfície (0,004mg/L). Os resultados mostram, portanto, que o efluente ácido gerado apresenta altos teores de metais estáveis e radioativos, sulfato, baixo pH e presença de bactérias redutoras de sulfato.
One of the most serious environmental problems created by the mining industry is acid mine drainage. In one plant of Nuclear Industries of Brazil - INB, this problem is a matter of concern. The presence of iron sulfites, such as pyrite, generates water with acidity above the levels allowed by the legislation and therefore, inappropriate for releasing straight into the environment. The industry maintain a high cost treatment in acid water from mines and waste disposal which consists in neutralizing and precipitating heavy metals. The treatment of acid water using SRB (sulfate-reducing bacteria) has been used in other countries with quite good technical results as well as economical advantages and thus, the object of this research. The use Sulfate Reducing Bacteria takes to a decreasing of the acidity by reducing sulfate to sulfite and precipitating the stable metals as sulfides. A seasonal study was carried out on the sulfate-reducing bacteria present in the liquid effluent discharged from two wastes disposal of the uranium mine, in phase of decommission, in Caldas/MG. This study shows the presence of SRB in the analyzed environmental, as well as some factors that are related with the amount of SRB presents, such as: dissolved oxygen, pH and organic matter. SRB was presented in water samples with high concentrations of heavy metals and low pH values, as well as in samples with high oxygen levels. The sediment samples were the preferential place for SRB occurrence and site BF8 presented the highest values of SRB.

Style APA, Harvard, Vancouver, ISO itp.

37

Pinkert, Katja. "Mesoporöse Kohlenstoffmaterialien und Nanokomposite für die Anwendung in Superkondensatoren". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-154422.

Pełny tekst źródła

Streszczenie:

Die effiziente Speicherung von elektrischer Energie im elektrochemischen System des Superkondensators wird realisiert durch die Ausrichtung von Elektrolytionen im elektrischen Feld polarisierter, poröser Kohlenstoffelektroden. Der Energieinhalt und die Leistungscharakteristika der elektrostatischen Zwischenspeicherung von Energie bei Lade- und Entladezeiten von wenigen Sekunden bis zu einigen Minuten wird entscheidend durch die Eigenschaften der zur Ladungsspeicherung genutzten Grenzfläche zwischen dem Elektrodenmaterial und dem Elektrolyten bestimmt. Für die Optimierung des Energieinhaltes und der Leistungscharakteristika von Superkondensatoren durch die rationale Modifizierung dieser Grenzfläche konnten entscheidende Trends herausgearbeitet werden. Durch Einbindung eines pseudokapazitiven Eisenoxids in die spezifische Oberfläche des mesoporösen CMK-3 im Redoxverfahren ist die Darstellung einer neuartigen Nanokompositstruktur möglich. Diese weißt eine dreifach höhere spezifische Kapazität im Vergleich zur nicht-modifizierten Kohlenstoffoberfläche unter Beibehaltung der Strombelastbarkeit der Kohlenstoffmatrix auf. Entscheidend für die Weiterentwicklung von Synthesestrategien und die anwendungsorientierte Optimierung für Nanokompositstrukturen ist deren ausführliche Charakterisierung mittels angepasster Verfahren. Die in dieser Arbeit erstmals zur Analyse von porösen CMK-3 basierten Nanokompositstrukturen verwendeten Methoden der Aufnahme eines Tiefenprofils mittels Auger Elektronen Spektroskopie (DP-AES) und der energiegefilterten Transmissionselektronenmikroskopie (EF-TEM) lieferten die Grundlage zur Weiterentwicklung der rationalen, nanoskaligen Grenzflächenfunktionalisierung. In einem weiteren, stark vereinfachten und effektiveren Verfahren der Schmelzimprägnierung der porösen Matrix mit Nitrathydraten, sowie deren anschließendes Kalzinieren zum Übergangsmetall, respektive pseudokapazitiven Übergangsmetalloxid, konnte eine nochmals optimierte Nanokompositstruktur dargestellt werden. Das entwickelte Verfahren wurde für die Einbettung von Nickel/Nickeloxid und Eisen/Eisenoxid in die Oberfläche des mesoporösen CMK-3 eingesetzt. Ein gesteigerter Energieinhalt, wie auch eine deutlich gesteigerte Stabilität der Kapazität bei hohen Strombelastungen für die resultierenden Elektrodenmaterialien konnte eindeutig nachgewiesen werden. Die signifikante Erhöhung der Leistungscharakteristika ist dabei auf die optimale Kontaktierung des Übergangsmetalloxids durch das Übergangsmetall als Leitfähigkeitsadditiv im Sinne einer Kern-Schale Struktur realisiert. Der für das Nanokomposit C-FeO10 berechnete Kapazitätsverlust von < 11 % bei Erhöhung der spezifischen Stromstärke von 1 A/g auf 10 A/g verdeutlicht die beeindruckende Strombelastbarkeit des Materials. In einem weiteren in dieser Arbeit diskutierten Ansatz zur Steigerung des Energieinhaltes eines Superkondensators wurde auf die Verwendung von Ionischen Flüssigkeiten (IL) als Elektrolyt eingegangen. Die gezielte Darstellung eines oberflächenmodifizierten aus Cabiden gewonnen Kohlenstoffmaterials (CDC) unter Beibehaltung der Textur des porösen Systems ermöglichte die Untersuchung des Einflusses der Oberflächencharakteristika des Elektrodenmaterials auf die Strombelastbarkeit des Energiespeichers. Es konnte klar herausgestellt werden, dass für den vielversprechenden IL-Elektrolyten EMIBF4 eine verminderte Polarität, sowie die Abwesenheit azider Protonen an der Oberfläche des Kohlenstoffs deutlich zur Steigerung der Strombelastbarkeit des Speichers beiträgt. Realisiert wurde die Modifizierung der Oberfläche durch deren Chlorierung. Die Einordnung der vielversprechenden Kombinationen aus maßgeschneiderten Elektrodenmaterialien und Elektrolytsystemen wurde anhand der Kenngrößen im Ragone-Diagramm vorgenommen. Die Ergebnisse der Arbeit reihen sich in die derzeit schnell voranschreitende Technologieentwicklung bei Superkondensatoren ein.

Style APA, Harvard, Vancouver, ISO itp.

38

Leclerc, Olivier. "Etude analytique de l'action des dithiocarbonates sur la pyrite : application a la flottation". Paris 6, 1987. http://www.theses.fr/1987PA066474.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

39

Nguyen, Nhung Phuong. "Axial Ligand Mutant: H229A". Digital Archive @ GSU, 2008. http://digitalarchive.gsu.edu/honors_theses/1.

Pełny tekst źródła

Streszczenie:

Many pathogenic bacteria use their iron acquisition mechanisms to live inside hosts. Streptococcus pyogenes is a pathogenic bacterium that uses streptococcal iron acquisition ABC transporter to obtain heme. SiaA (HtsA, spy1795), a lipoprotein located on the cell surface, serves as a heme binding protein. To understand the iron-uptake mechanism, histidine 229, one of the two proposed axial ligands in SiaA, was mutated to alanine. SiaA H229A was expressed in E. coli, lysed by French Press, and purified by fast protein liquid chromatography (FPLC). SDS-PAGE indicated that pure protein was isolated. Nickel affinity FPLC gave purer H229A when 0.5 M imidazole was added to the binding buffer. Overall, histidine 229 is likely to be an axial ligand in wild type SiaA, as shown by the fact the mutant readily lost heme as evidenced by UV-vis spectra.

Style APA, Harvard, Vancouver, ISO itp.

40

Komora, Mojmír. "Závislost povrchové struktury Fe2O3(012) na prostředí". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-382255.

Pełny tekst źródła

Streszczenie:

Táto diplomová práca sa zaoberá štúdiom alfa-Fe2O3(012) vystaveného vodnému prostrediu. Súčasný stav poznania ohľadom oxidov železa s pozornosťou vkladanou do popisu alfa-Fe2O3 a jeho (012) povrchu je stručne zhrnutá. Experimentálná časť tejto práce začína s popisom unikátného zariadenia na depozíciu kvapalnej vody na povrchy monokryštalických vzoriek compatibilného s podmienkami ultra vysokého vákuua. Jednotlivé konštrukčné časti a detaily sú diskutované. Navrhnutý systém bol testovaný na vzorkách striebornej fólie a monokryštálu Fe3O4 s povrchovom v rovine [100]. Chemické zloženie a morfológia povrchu po experimente s kvapalnou vodou je diskutovaná. Navrhnuté zariadenie bolo použité na štúdium interakcie vody so známymi (1x1) a (2x1) povrchovými alfa-Fe2O3(012). Experimentálne dáta ukazujú, že voda sa viaže na obe reconštrukcie disociatívne s určitým množstvom molekulárnej vody naviazanej na adsorbované hydroxydi. (1x1) sa zdá javý stabilná po expozícii rôznym tlakom vodnej pary, zatial čo (2x1) vykazuje zmenu na (1x1) pri expozíciach vyšším tlakom vodnej pary alebo po niekolo minútovej expozíci electrónovému zväzku. Ďalej sú v tejto práci prezentované prvé výsledky z štúdie prechodu (1x1) rekonštrukcie na (2x1) pomocou mikroskpie nízkoenergiových elektrónov. Výsledky ukazujú, že táto premena na nižších teplotách je inciovaná na hranách atomárnych vrstiev a defektov na povrchu, ktorá potom postupuje smerom k stredu atomárnych terás. Meranie na vyšších teplotách vykazuje postupnú premenu povrchu naznačúju viaceru nukleačných centrech z ktorých sa (2x1) povrch širi ďalej.

Style APA, Harvard, Vancouver, ISO itp.

41

Semeniuk, Konstantin. "Correlated low temperature states of YFe2Ge2 and pressure metallised NiS2". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/274346.

Pełny tekst źródła

Streszczenie:

While the free electron model can often be surprisingly successful in describing properties of solids, there are plenty of materials in which interactions between electrons are too significant to be neglected. These strongly correlated systems sometimes exhibit rather unexpected, unusual and useful phenomena, understanding of which is one of the aims of condensed matter physics. Heat capacity measurements of paramagnetic YFe$_{2}$Ge$_{2}$ give a Sommerfeld coefficient of about 100 mJ mol$^{−1}$ K$^{−2}$, which is about an order of magnitude higher than the value predicted by band structure calculations. This suggests the existence of strong electronic correlations in the compound, potentially due to proximity to an antiferromagnetic quantum critical point (QCP). Existence of the latter is also indicated by the non-Fermi liquid T$^{3/2}$ behaviour of the low temperature resistivity. Below 1.8 K a superconducting phase develops in the material, making it a rare case of a non-pnictide and non-chalcogenide iron based superconductor with the 1-2-2 structure. This thesis describes growth and study of a new generation of high quality YFe$_{2}$Ge$_{2}$ samples with residual resistance ratios reaching 200. Measurements of resistivity, heat capacity and magnetic susceptibility confirm the intrinsic and bulk character of the superconductivity, which is also argued to be of an unconventional nature. In order to test the hypothesis of the nearby QCP, resistance measurements under high pressure of up to 35 kbar have been conducted. Pressure dependence of the critical temperature of the superconductivity has been found to be rather weak. μSR measurements have been performed, but provided limited information due to sample inhomogeneity resulting in a broad distribution of the critical temperature. While the superconductivity is the result of an effective attraction between electrons, under different circumstances the electronic properties of a system can instead be dictated by the Coulomb repulsion. This is the case for another transition metal based compound NiS$_{2}$, which is a Mott insulator. Applying hydrostatic pressure of about 30 kbar brings the material across the Mott metal-insulator transition (MIT) into the metallic phase. We have used the tunnel diode oscillator (TDO) technique to measure quantum oscillations in the metallised state of NiS$_{2}$, making it possible to track the evolution of the principal Fermi surface and the associated effective mass as a function of pressure. New results are presented which access a wider pressure range than previous studies and provide strong evidence that the effective carrier mass diverges close to the Mott MIT, as expected within the Brinkman-Rice scenario and predicted in dynamical mean field theory calculations. Quantum oscillations have been measured at pressures as close to the insulating phase as 33 kbar and as high as 97 kbar. In addition to providing a valuable insight into the mechanism of the Mott MIT, this study has also demonstrated the potential of the TDO technique for studying materials at high pressures.

Style APA, Harvard, Vancouver, ISO itp.

42

Achour, Mickaël. "Mécanisme de corrosion du fer par UF₆ liquide à 80°C". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS064.

Pełny tekst źródła

Streszczenie:

Le combustible nucléaire utilisé dans les réacteurs actuels doit répondre à une spécification de composition en ²³⁵U différente de celle de l’uranium naturel. Il est alors nécessaire de procéder à un enrichissement en part fissile avant de fabriquer le combustible utilisé en réacteur. Cet enrichissement est réalisé par centrifugation en phase gaz en utilisant l’uranium sous forme d’hexafluorure d’uranium UF₆. Ce composé clé est fabriqué par l’usine COMHUREX à partir de UF₄, et doit répondre à des exigences de pureté, et sa manipulation, à des exigences de sécurité. Cette molécule est très réactive sous forme gazeuse ou liquide et une corrosion du dispositif industriel métallique est constatée. Cette corrosion doit être étudiée afin d’envisager la pollution causée par les produits de corrosion ou encore la durée de vie de l’installation. L’enjeu de cette thèse est de combler les insuffisances de la littérature sur la question de la corrosion par UF₆ liquide à 80°C, qui n’a jusqu’alors pas fait l’objet de recherches publiées. Des équipements adaptés à la réalisation d’essais de corrosion en milieu nucléaire, à 80°C et 3 bars de pression, et des procédures anoxiques d’analyses de ces essais ont dû être mis en place. La réalisation d’essais de corrosion du fer, matériau modèle, par UF₆ liquide à 80°C a ensuite pu être entreprise afin de déterminer la nature des produits de corrosion, la structure de la couche de corrosion et la cinétique de la réaction entre le fer et UF₆ liquide à 80°C. Ces informations ont pu permettre une réflexion sur le mécanisme de corrosion. Ce manuscrit présente le dispositif et la procédure d’essai mise en place permettant la réalisation d’essais de corrosion puis les résultats obtenus. La nature et la structure de la couche de corrosion ont été obtenues grâce aux précautions anoxiques utilisées tout au long des essais réalisés. Deux comportements distincts sont observés. L’origine expérimentale de cette divergence est discutée. La réflexion sur les observations expérimentales, telles que la nature ou les rapports d’épaisseurs des différentes couches, permet de proposer différentes hypothèses sur le mécanisme de corrosion. Un mécanisme de corrosion du fer par UF₆ liquide à 80°C est donc proposé
The nuclear fuel used in today’s power plants requires a precise uranium isotope composition which is different from natural uranium. Thus, an enrichment process is required, for which gaseous centrifugation is employed using uranium hexafluoride (UF₆). This compound is obtained by fluorination of UF₄ and its handling is submitted to security issues. This compound is highly reactive, in gaseous or liquid state, and the metallic industrial production setup is corroded, leading to solid residues at process temperatures. This corrosion has to be considered in order to predict both the process efficiency (purity, output) and the resulting industrial issues (setup lifetime, corking). This study aims at understanding liquid uranium hexafluoride corrosion at 80°C, which remains unstudied to this day. A dedicated novel test setup along with adapted analysis precautions have been developed in order to perform reliable experiments and corrosion products identification, since those products and UF₆ are moisture sensitive. This study mostly focused on the corrosion of iron as a model material in liquid UF₆. The experimental results obtained, allowed us to follow the evolution of the structure and the nature of the corrosion layer. Two different kinds of layer have been observed and the experimental origin of this divergence is discussed. With those experimental results, a corrosion mechanism is suggested for the corrosion of iron in liquid uranium hexafluoride at 80°C

Style APA, Harvard, Vancouver, ISO itp.

43

Grosselin, Nadège. "Mise au point d'une technique voltampérométrique pour la caractérisation de particules individuelles conductrices de quelques dizaines de microns : application à l'étude de l'adsorption des ions argent et mercure ainsi que du thymol sur la pyrite". Nancy 1, 1998. http://www.theses.fr/1998NAN10142.

Pełny tekst źródła

Streszczenie:

Au cours de ce travail, une nouvelle technique ultramicroélectrochimique pour la caractérisation des grains individuels conducteurs de quelques dizaines de microns à été mise au point. Elle permet, en particulier, la détection d'espèces solubles formées à l'électrode sans devoir imposer des vitesses de balayage extrémement élevées comme c'est le cas avec les ultramicroélectrodes conventionnelles (10 MV/S suffisent). Les études sans ajout d'électrolyte support sont aussi possibles. La comparaison des voltampérogrammes de AG#2SE avec ceux obtenus par les méthodes classiques a mis en évidence qu'il est possible de caractériser des grains du minéral sans interférence contrairement aux pates de carbone. La technique a ensuite été utilisée parallélement à des méthodes spectroscopiques pour l'étude de l'adsorption de AG#+ et de HG#2#+ sur la pyrite FES#2 (pulpes à 0,5% en poids). Il s'avère que les spéciations de l'argent et du mercure à la surface de FES#2 dépendent fortement de la concentration des ions métalliques en solution. Dans le cas où l'argent est à faible concentration, seul AG#2S se forme. Quand la concentration est plus forte, de l'argent métallique est aussi présent. De même, selon la concentration en mercure, une ou deux espèces de stabilité différente se fixent à la surface de la pyrite. La quantité maximale de mercure s'adsorbant sur le minéral (3,5 10#-#5 MOL/G) est vingt fois moins importante que celle d'argent (6,6 10#-#4 MOL/G). Quand de la pyrite est conditionnée simultanément avec les ions AG#+ et HG#2#+, seul le mercure est adsorbé à sa surface. Il libère en solution l'argent si ce dernier était préalablement fixe sur le minéral. La quantité de mercure alors adsorbée atteint 3,2 10#-#4 MOL/G. Enfin, l'action du thymol sur la pyrite a été envisagée dans le but d'inhiber l'oxydation chimique du minéral. Les mesures électrochimiques ont montré que c'est le produit d'oxydation du thymol, et non lui-même, qui s'adsorbe sur la pyrite et limite son oxydation

Style APA, Harvard, Vancouver, ISO itp.

44

PIATTI, ERIK. "Electrochemical gating for superconductivity engineering in materials towards the 2D limit". Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2669688.

Pełny tekst źródła

Streszczenie:

In this thesis work we explored the capability of electrochemical gating to reliably control the ground state of several chosen materials, with a specific focus on the engineering of the superconducting state. We also experimented with different electrolyte compositions in order to best match the electrochemical requirements of the various materials under study (e.g., chemical stability). In the presentation of the results, we will move from the thicker, bulk-like materials down to the truly two-dimensional properties of thin exfoliated single crystals. Chapter 1 presents a general analysis of the field-effect technique based on an electrolytic gate. We discuss the basic principle that allows for the existence of ultrahigh electric fields at the device surface, together with the several pratical limitations and criticalities the technique entails. In particular, we consider the critical distinction between purely electrostatic gating and the regimes where various types of electrochemical interactions are activated between the sample and the electrolyte. We also discuss in detail a purely electrochemical measurement that can be performed on the complete devices in order to determine the amount of charge accumulated in the electric double layer. Chapter 2 shows a selection of our results on superconducting thin films. We analyze extensively the response of conventional BCS superconductor niobium nitride to EDL gating as a function of film thickness (∼ 40−10 nm), and we interpret our data in the framework of a bulk control of the superconducting transition mediated by proximity effect. We then extend our analysis to more complex materials. We show preliminary results on state-of-the-art thin films (∼ 20 nm) of two-gap superconductor magnesium diboride. Finally, we consider thin films of iron-based superconductor barium iron arsenide and show how its Tc can be modulated by the electric field only in the smallest thicknesses available by state-of-the-art growth techniques (∼ 10 nm). Chapter 3 presents our results on thin flakes (∼ 5−10 nm) of transition metal dichalcogenides. We explore via EDL gating the valley occupation in the conduction and of semiconducting molybdenum and tungsten disulphides at high carrier densities. We show preliminary evidence linking the emergence of EDL-induced superconductivity with the population of secondary minima in the bandstructure for molybdenum disulphide. We also exploit electrochemical gating beyond the electrostatic regime to perform field-assisted intercalation of molybdenum disulphide with alkali ions, in an effort to demonstrate both surface and bulk gate-controlled superconductivity in the same device architecture. We find preliminary evidence for the onset of a possible Charge-Density-Wave phase at very high ion doping. Chapter 4 is entirely devoted to our results on few-layer graphene. While we did not observe any gate-induced superconductivity (down to T= 3.5 K) even at the highest induced carrier densities ∼ 6 · 1014 cm-2, we were able to extensively study the dominant scattering mechanisms both in the high and low temperature regimes; in particular, we showed that inelastic scattering for T . 90 K is dominated by electron-electron collisions, in contrast with what was found in the literature for single-layer graphene. Moreover, we observed the emergence of quantum coherence phenomena (weak localization) for T . 20 K in these previously unreached conditions of ultrahigh carrier doping. Finally, in the Conclusions we summarize the most significant results obtained during this thesis work together with the questions that are still left open. Furthermore, we consider some perspectives and future lines of research that could be pursued in the framework of electrolyte gating.

Style APA, Harvard, Vancouver, ISO itp.

45

Darcheville, Marie. "Synthesis of iron oxide nanoparticles and development of magnetic coatings by fluid processing". Thesis, université Paris-Saclay, 2021. http://www.theses.fr/2021UPASP005.

Pełny tekst źródła

Streszczenie:

Ce projet porte sur la réalisation de nouveaux matériaux aux propriétés magnétiques parfaitement contrôlées pour des applications électromagnétiques de types antennes RFID, transmission de puissance sans fil, absorbants radars… Le principe repose sur l’élaboration d’une structure organisée en motifs ou domaines magnétiques définie par des caractéristiques géométriques (taille des motifs, épaisseur, distance entre motifs). La réponse magnétique en perméabilité de tels matériaux est liée aux contributions des domaines et des parois formés, donnant naissance à un matériau dit « multi-bandes » au regard des pics distincts et séparés observés sur son spectre de perméabilité. L’élaboration d’un tel matériau est étudiée par dépôt en voie liquide de nanoparticules d’oxyde de fer. La composition du matériau est fixée à Zn₀.₄Fe₂.₆O₄ afin de combiner une aimantation à saturation forte, et une permittivité diélectrique faible pour une bonne pénétration de l’onde électromagnétique dans le dépôt. Les nanoparticules sont synthétisées par décomposition thermique en voie micro-ondes. Deux gammes de tailles de nanoparticules sont visées : des nanoparticules superparamagnétiques (diamètre inférieur à 20 nm) et ferrimagnétiques. Deux techniques de réalisation de dépôts structurés à partir de suspensions stables de nanoparticules sont discutées : l’aérographie suivie d’une gravure laser, et l’impression jet d’encre. De nombreuses caractérisations physico-chimiques, locales ou globales, ont été effectuées. Un traitement thermique est requis pour la densification du matériau, mais ne permet pas d’obtenir une densité suffisante pour l’application envisagée. Une étude approfondie des propriétés magnétiques statiques et dynamiques des particules et des dépôts est réalisée, et corrélée à leurs caractéristiques structurales par le biais de modèles de champ moléculaire. Des pistes sont ouvertes pour l’élaboration d’un matériau magnétique multi-bandes
The aim of the study is to develop novel materials with well-controlled magnetic properties for electromagnetic applications like RFID antennas, wireless power transmission, radar absorption… The principle is based on the development of an organized framework in patterns or magnetic domains, defined by their geometry (pattern size, thickness, spacing). The permeability response of such materials is linked to the contributions of created domains and walls, giving rise to a “multi-band” material with separate and distinct peaks on its permeability spectrum. The development of such material is studied through fluid processing from iron oxide nanoparticles. A Zn₀.₄Fe₂.₆O₄ material composition is selected in order to provide a high saturation magnetization and a low dielectric permittivity to ensure the penetration of the electromagnetic wave in the coating.The nanoparticles are synthesized by microwave-assisted thermal decomposition. Two ranges of sizes are chosen: superparamagnetic particles (diameter below 20 nm) and ferrimagnetic ones. Two processing methods from stable particle dispersions are discussed: airbrushing followed by a laser etching, and inkjet printing. Several physico-chemical characterizations, at local and global scales, have been performed. An annealing is required to densify the material, but does not provide a suitable density for the desired application. An in-depth study of the static and dynamic magnetic properties of nanoparticles and coatings is done, and correlated to their microstructure through modeling from the molecular field theory. Many guidelines are suggested for the development of a multiband magnetic material

Style APA, Harvard, Vancouver, ISO itp.

46

Elias, Elede Martins. "Ácido fólico e ferro em alimentos". [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/322510.

Pełny tekst źródła

Streszczenie:

Orientador: Helena Teixeira Godoy
Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos
Made available in DSpace on 2018-08-16T14:08:37Z (GMT). No. of bitstreams: 1 Elias_EledeMartins_D.pdf: 34567537 bytes, checksum: a43c23fe63f955db89437e120fcc7705 (MD5) Previous issue date: 2010
Doutorado
Nutrição Experimental e Aplicada à Tecnologia de Alimentos
Doutor em Alimentos e Nutrição

Style APA, Harvard, Vancouver, ISO itp.

47

Pierron, Olivier. "Interactions eau-fer-argilite : rôle des paramètres liquide/roche, fer/argilite, température sur la nature des phases minérales". Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10146/document.

Pełny tekst źródła

Streszczenie:

Les interactions entre le fer métal et l'argilite du Callovo-Oxfordien choisie comme roche hôte pour le stockage des déchets radioactifs, a été étudiée expérimentalement. Le rôle des paramètres clés des transformations (rapports fer/argile, et liquide/roche) ont été étudiés à 90°C, et afin d'accélérer la cinétique des réactions à 150°C et 300°C. Les interstratifiés illite-smectite et les illites sont dissous et remplacés par de nouvelles phases argileuses. Les analyses au MET ont permis de déterminer des Fe-serpentines (phases à 7 Å, groupe de la berthiérine) à 90°C, des phases gonflantes de type smectite tri-octaédrique à 150°C, et des chlorites et des interstratifiés chlorite/smectite à 300°C. Quelle que soit la température, la transformation des feuillets illitiques (I et I/S) n'est pas complète et il reste toujours des feuillets à garniture interfoliaire sodi-calcique, interprétés comme des smectites résiduelles ou néoformées. En comparaison avec le système fer-smectite (bentonite), les différences portent sur la cinétique de réaction, beaucoup plus rapide dans le cas de l'argilite, et l'instabilité du quartz qui comme l'illite contribue à libérer le silicium nécessaire à la formation des silicates de fer. Les transformations observées trouvent des analogies avec les altérations hydrothermales et métasomatoses Fe-Mg des systèmes naturels
The interactions between the iron metal and the argillite from the Callovo-Oxfordian formation chosen as host for the disposal of the radioactive wastes, was experimentally studied. The role of the key parameters of the transformations (iron / clay, and liquid / rock ratios) was studied at 90°C, and, to accelerate reaction kinetics, at 150°C and 300°C. Mixed layered illite-smectite and illites are dissolved and replaced by new clay phases. TEM analyses show that Fe-serpentines (7 Å phases, group of the berthierine) predominates in run products at 90°C, tri-octaedral Fe-rich smectites at 150°C, and chlorites and probably smectite chlorite mixed layered at 300°C. Whatever the temperature, the illite and I/S replacement is not complete and trun products are always accompanied by sodi-calcic residual and/ or newly formed smectites. In comparison with the iron-smectite (bentonite) system, the differences concern the reaction kinetics which are much faster in the case of the argillite, and the instability of the quartz which, as the illite, contributes to release the silicium necessary for the formation of iron silicates. The observed process find analogies with the hydrothermal changes described in natural hydrothermal alterations and Fe-Mg metasomatism

Style APA, Harvard, Vancouver, ISO itp.

48

Heyd, Marie. "Les représentations de la mort dans la création artistique actuelle : histoire, contextualisation, comparaisons". Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAC002.

Pełny tekst źródła

Streszczenie:

Alors que les individus dans la société contemporaine sont unis non par une propriété mais par un devoir et par une dette, par un manque, par une limite prenant la forme d’une charge pour celui qui en est affecté, la postmodernité rend à la mort et à l’absence toute sa densité. À travers la répétition, entre jubilation et désespérance, les artistes figurent la temporalité de l’épreuve par une écriture qui travaille l’instant. Ils racontent ces évènements infimes qui sont les plus fragiles, les plus précaires, ayant pourtant une forte efficacité. Il s’agira ici d’étudier les nouvelles postures devant l’événement historique, quand l’artiste se tient au plus singulier
While individuals in contemporary society are united not by property but by a duty and a debt, a lack, by a limit taking the shape of a responsibility for the one who is affected, postmodernism returns to death and absence all its density. Through repetition, between jubilation and despair, the artist represents the temporality of the event. His writing works the moment. He tells these tiny events that are the most fragile, the most precarious, having nevertheless a strong efficiency. This thesis will try to study the new postures in front of the historic event, when the artist stands in the most singular

Style APA, Harvard, Vancouver, ISO itp.

49

Desplanques, Elsa. "L'usage des textiles dans les pratiques funéraires : le cas des incinération en urne métallique en Europe au Ier millénaire av. J.-C". Thesis, Sorbonne université, 2020. http://www.theses.fr/2020SORUL134.

Pełny tekst źródła

Streszczenie:

L’incinération en urne métallique est une pratique funéraire aristocratique mise en œuvre entre le XIVᵉ et le IIIᵉ siècle av. J.-C. dans certains groupes de population européens. Les urnes employées appartiennent au service utilisé lors du symposion et du banquet. Un grand nombre d’entre elles présente des fragments de textiles, sur les parois intérieures ou extérieures, qui signalent l’usage très répandu de ce matériau. La confrontation des occurrences archéologiques et des sources littéraires, iconographiques et anthropologiques prouve l'importance des tissus au sein des pratiques funéraires et invite à interroger leur rôle matériel, social et symbolique. Au-delà d’une synthèse descriptive de la position des fragments sur les urnes, les investigations autour de l’usage des tissus dans la pratique du dépôt, de la couverture ou de l’emballage textile en contexte funéraire offrent de nouvelles perspectives quant aux pratiques funéraires des groupes de population protohistoriques européens. La remarquable régularité de certaines dispositions des tissus souligne l’importance culturelle et symbolique de ces usages funéraires. L’étude de la disposition des tissus dans les tombes conduit à restituer une situation de l’Homme face à la mort, une manière de concevoir, d’exprimer et de surmonter, par le langage visuel et matériel, un processus naturel inévitable et redouté
The cremation in metallic urns is an aristocratic funerary practice implemented between the XIVth and IIIrd centuries b.c. in some European population groups. The urns employed belong to the service used during the symposium and the banquet. Many of them have textile fragments fixed to their interior or exterior metallic surfaces, which indicates the widespread use of this material. The confrontation of archaeological sources with literary, iconographic and anthropological sources proves the importance of textiles within funeral practices and invites us to question their material, social and symbolic functions. Beyond a descriptive synthesis of the position of the fragments on the urns, investigations about the use of fabrics in the practice of deposit, covering or textile wrapping in the funeral context offer new perspectives on funeral practices of European protohistoric population groups. The remarkable regularity of some layouts of fabrics underlines the cultural and symbolic importance of these funerary uses. The study of the layout of fabrics in tombs leads to the reconstruction of the situation of Man when confronted with death, a way of conceiving, expressing and overcoming, through visual and material language, an inevitable and dreaded natural process

Style APA, Harvard, Vancouver, ISO itp.

50

Rabin, Ségolène. "Etude des mécanismes de distribution des isotopes du fer et du silicium entre les minéraux et les liquides silicatés lors de la différentiation magmatique". Thesis, Toulouse 3, 2021. http://www.theses.fr/2021TOU30206.

Pełny tekst źródła

Streszczenie:

Les compositions isotopiques du fer et du silicium au sein des différents réservoirs géologiques de haute température montrent des variations isotopiques significatives. Cependant, les mécanismes à l'origine de ces fractionnements ne sont pas clairement identifiés. La connaissance de ces mécanismes et des coefficients de fractionnement à l'équilibre est essentielle à l'interprétation des mesures faites sur les roches magmatiques naturelles. Cette étude multidimensionnelle est basée sur le calcul théorique des propriétés isotopiques du fer et du silicium dans les minéraux et les liquides silicatés, l'analyse des isotopes du fer dans les laves des Iles Kerguelen ainsi que le développement d'une méthode d'analyse in situ des isotopes du fer dans les verres silicatés et les olivines grâce à un laser femtoseconde couplé à un spectromètre de masse MC-ICP-MS. Nous présentons les propriétés isotopiques du fer et du silicium d'une variété de minéraux présents dans la croûte et le manteau, ainsi que pour la première fois, de liquides silicatés de diverses compositions. Nos résultats montrent que le fractionnement du fer et du silicium entre les minéraux contenant du Fe2+ est significatif même à haute température. Nous suggérons ici qu'après la température et le redox, les seconds voisins du silicium et du fer influent grandement le fractionnement isotopique. A partir des coefficients de fractionnement entre minéraux et liquides silicatés, nous proposons que la cristallisation fractionnée puisse être le processus majeur impliqué dans l'évolution isotopique du fer et du silicium lors de la différentiation magmatique. L'étude de la composition isotopique en fer des laves de Kerguelen souligne la complexité de l'évolution du point chaud au cours du temps, impliquant potentiellement une hétérogénéité du manteau. Enfin, le développement d'une méthode d'analyse couplant un MC-ICP-MS à un laser femtoseconde, a permis d'effectuer des mesures isotopiques du fer in situ d'olivines et de verres silicatés avec des incertitudes inférieures à 0.2 ‰
Iron and silicon isotope measurements in high-temperature geological reservoirs display significant isotopic fractionations, especially within the Earth's crust. However, the mechanisms involved in these fractionations are not fully understood. Their knowledge and that of the fractionation factors in equilibrium conditions is central to interpret the measurements carried on natural rocks. To address this issue, this work is a multidimensional approach based on first principles calculation of Fe and Si isotope fractionations in minerals and silicate melts, on Fe isotope measurements of lavas from Kerguelen Archipelago and on analytical developments of in situ Fe isotope measurements of glasses and olivines using a femtosecond laser coupled to MC-ICP-MS. We provide the theoretical Fe and Si isotope properties of various minerals relevant to Earth crust formation and, for the first time, of silicate melts. Results suggest that significant Fe and Si isotope fractionations are expected between Fe2+-bearing minerals at high temperature. We also show that, besides temperature and redox changes, iron and silicon second neighbors have a major impact on isotopic fractionations. From our set of equilibrium fractionation factors between minerals and melts, we suggest that fractional crystallization could be the main process involved in Fe and Si isotope evolution during magmatic differentiation. In addition, iron isotope composition of Kerguelen oceanic basalts underlines the complexity of the hotspot evolution, with potential source heterogeneity. Finally, the analytical developments performed on MC-ICP-MS with femtosecond laser, allow in situ Fe isotope measurements of silicate glasses and minerals with an uncertainty better than 0.2‰

Style APA, Harvard, Vancouver, ISO itp.

Rozprawy doktorskie na temat „Liquid iron”

Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych