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1
Ghasemi, Yahya. "Aggregates in Concrete Mix Design." Licentiate thesis, Luleå tekniska universitet, Byggkonstruktion och -produktion, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-61659.
Повний текст джерелаАнотація:
The importance of studying the behaviour and properties of concrete can be highlighted by considering the fact that concrete is the most used man-made material in the world. The very first step in making concrete is its mix design and deciding the type and amount of constitutes used in the production of concrete which should fulfil the requirements of the final product. Mix design models are commonly used for the purpose of proportioning concrete ingredients while anticipating the properties of the final product. The current document deals with the commonly used principals in mix design models namely particle packing theory and excess water/paste layer theories. The conducted studies includes an investigation on accuracy of particle packing models (Toufar, 4C, CPM) and also tries to address the issue with measurement of specific surface area of particles as an essential input to water/paste layer theories. It has been observed that the particle packing models can predict the packing density with acceptable margin. However, it should be mentioned that the particle packing models by themselves are not mix design models but should be rather used as a part of a mix design. In addition, it was found that the accuracy of calculating the specific surface area of particles based on their size distribution curve can be further improved by assuming angular platonic solids as uniform shape of aggregate instead of traditional approach of assuming spheres for aggregates’ shape.
2
Бабенко, Володимир Миколайович. "Закономірності гідродинаміки і масообміну в процесах ректифікації суміші розчинників на новому контактному пристрої". Thesis, НТУ "ХПІ", 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/22718.
Повний текст джерелаАнотація:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.17.08 – процеси та обладнання хімічної технології. – Національний технічний університет "Харківський політехнічний інститут" Міністерства освіти і науки України, м. Харків, 2016.
Дисертацію присвячено дослідженню процесу поділу рідинних гетерогенних сумішей на регулярних контактних пристроях з різними геометричними параметрами насадочних елементів. Досліджено механізм процесу утворення рідинної плівки для колонних апаратів, що застосовуються в ректифікації у відповідності з гідродинамічними характеристиками процесу. Показано, що основним фактором інтенсифікації масообмінного процесу для регулярних контактних елементів, є швидкість відновлення рідинної плівки. Доведено що, основними факторами, які визначають ефективність процесу поділу суміші розчинників, є низький питомий опір апарату по газу і конструктивні особливості контактних елементів ректифікаційній колони. Отримано графічні та емпіричні залежності для розрахунку висоти насадочного шару, питомої поверхні насадки в залежності від лінійної швидкості газу в колонному апараті і геометричних параметрів насадочних пристроїв. Розроблено практичні рекомендації для проектування колонних установок з високими енергетичними показниками. Запропоновано новий регулярний контактний елемент, який поєднує в собі велику питому поверхню з малим гідродинамічним опором. Запропоновано принципову апаратурно-технологічну схему процесу поділу суміші розчинників, яка розроблена й впроваджена на виробництві ПАТ "ФАРМСТАНДАРТ-БІОЛІК" (м. Харків).Dissertation for the degree of candidate of engineering sciences on specialty 05.17.08 – processes and equipment of chemical technology. – National technical university "Kharkiv Polytechnic Institute" of the Ministry of Education and Science of Ukraine, Kharkiv, 2016. The dissertation is dedicated to the study of the separation process of liquid heterogeneous mixtures on the regular contact devices with different geometric parameters of the packing elements. The mechanism of the liquid film formation for the column apparatuses utilized in rectification is investigated according to the hydrodynamic characteristics of the process. It is shown that the main factor in the intensification of mass transfer processes for regular contact devices is velocity recovery of the liquid film. It is proved that the main factors of the solvent mixture separation efficiency are low specific resistance of an apparatus for a gas and constructional characteristics of the contact devices of a rectification column. Graphical and empirical relationships are obtained to calculate height of the packed bed, specific surface of a nozzle, depending on the linear gas velocity in a column apparatus and geometric parameters of the packing devices. Practical recommendations for the design of column units with high energy performance are developed. A new regular contact element that combines large surface area with low hydrodynamic resistance is suggested. A process flow diagram of the solvent mixtures separation is given, which was developed and implemented in the production line of PJSC "PHARMSTANDARD-BIOLIK" (Kharkiv city).
3
Бабенко, Володимир Миколайович. "Закономірності гідродинаміки і масообміну в процесах ректифікації суміші розчинників на новому контактному пристрої". Thesis, НТУ "ХПІ", 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/22717.
Повний текст джерелаАнотація:
Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.17.08 – процеси та обладнання хімічної технології. – Національний технічний університет "Харківський політехнічний інститут" Міністерства освіти і науки України, м. Харків, 2016.
Дисертацію присвячено дослідженню процесу поділу рідинних гетерогенних сумішей на регулярних контактних пристроях з різними геометричними параметрами насадочних елементів. Досліджено механізм процесу утворення рідинної плівки для колонних апаратів, що застосовуються в ректифікації у відповідності з гідродинамічними характеристиками процесу. Показано, що основним фактором інтенсифікації масообмінного процесу для регулярних контактних елементів, є швидкість відновлення рідинної плівки. Доведено що, основними факторами, які визначають ефективність процесу поділу суміші розчинників, є низький питомий опір апарату по газу і конструктивні особливості контактних елементів ректифікаційній колони. Отримано графічні та емпіричні залежності для розрахунку висоти насадочного шару, питомої поверхні насадки в залежності від лінійної швидкості газу в колонному апараті і геометричних параметрів насадочних пристроїв. Розроблено практичні рекомендації для проектування колонних установок з високими енергетичними показниками. Запропоновано новий регулярний контактний елемент, який поєднує в собі велику питому поверхню з малим гідродинамічним опором. Запропоновано принципову апаратурно-технологічну схему процесу поділу суміші розчинників, яка розроблена й впроваджена на виробництві ПАТ "ФАРМСТАНДАРТ-БІОЛІК" (м. Харків).Dissertation for the degree of candidate of engineering sciences on specialty 05.17.08 – processes and equipment of chemical technology. – National technical university "Kharkiv Polytechnic Institute" of the Ministry of Education and Science of Ukraine, Kharkiv, 2016. The dissertation is dedicated to the study of the separation process of liquid heterogeneous mixtures on the regular contact devices with different geometric parameters of the packing elements. The mechanism of the liquid film formation for the column apparatuses utilized in rectification is investigated according to the hydrodynamic characteristics of the process. It is shown that the main factor in the intensification of mass transfer processes for regular contact devices is velocity recovery of the liquid film. It is proved that the main factors of the solvent mixture separation efficiency are low specific resistance of an apparatus for a gas and constructional characteristics of the contact devices of a rectification column. Graphical and empirical relationships are obtained to calculate height of the packed bed, specific surface of a nozzle, depending on the linear gas velocity in a column apparatus and geometric parameters of the packing devices. Practical recommendations for the design of column units with high energy performance are developed. A new regular contact element that combines large surface area with low hydrodynamic resistance is suggested. A process flow diagram of the solvent mixtures separation is given, which was developed and implemented in the production line of PJSC "PHARMSTANDARD-BIOLIK" (Kharkiv city).
4
Elfmarková, Veronika. "Vliv jemnozrnných příměsí na charakter pórového systému betonu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-225906.
Повний текст джерелаАнотація:
Literature does not provide a satisfactory answer to maximum and minimum particle size or the particle size of the mortar phase especially for optimal porosity of concrete. To overcome the shortcomings of the design methods were thought to design a new method for design of concrete mix. This idea is based on a complex analysis of powder materials (determination of granular properties, shape factor of fillers, porosity, packing of powder materials, surface area, etc.) and subsequently to assess the influence to pore system of concrete and physical and mechanical properties in hardened state of concrete. In this work are presented and analyzed two types of fillers – fly ash and limestone dust.
5
Wong, Hin-cheong Henry. "Effects of water content, packing density and solid surface area on cement paste rheology." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/hkuto/record/B39326032.
Повний текст джерела
6
Wong, Hin-cheong Henry, and 黃憲昌. "Effects of water content, packing density and solid surface area on cement paste rheology." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39326032.
Повний текст джерела
7
Dubois, Isabelle E. "Specific surface area of some minerals commonly found in granite." Licentiate thesis, KTH, Industriell ekologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-41259.
Повний текст джерелаАнотація:
The specific surface area, determined by the BET method, is a parameter often used to scale results of mineral studies of surface reactions in terms of rate and capacity to the field scale. Such extrapolations of results from small-scale laboratory experiments to the field-scale are important within many environmental applications. An example of this is for the prediction of radionuclide retention in the bedrock surrounding a deep repository for radioactive waste, following failure of the engineered barriers, where radionuclides may sorb onto minerals constituting the geological environment. As a first step, the approach used in this work is to study the relationship between specific surface area and the particle size (0.075-8 mm) and to approach the field scale via measurements on large, centimetre-sized pieces, for seven natural minerals commonly found in granite: apatite, biotite, chlorite, K-feldspar, hornblende, labradorite and magnetite. The underlying assumption is that sorption of radionuclides can be related to specific surface area of a particular mineral in a continuation of this project.The results show that the phyllosilicates biotite and chlorite have a specific surface area that is about 10 times larger than the other minerals. Over the range of particle size fractions studied, the specific surface area varies between 0.1 and 1.2 m2g-1 for biotite and chlorite. The other studied minerals have specific surface areas varying between 0.01 m2g-1 for the largest fraction and up to 0.06 - 0.12 m2g-1 for the smallest. Results show linear relationships between the specific surface area and the inverse of the particle size for all studied minerals for small particle sizes, as expected. For some minerals, however, the data seemingly can be divided in two linear trends, where a change in internal surface area, surface roughness and/or particle geometry as the particle size decreases may explain this behaviour. Interestingly, for larger particles, there is a deviation from the linearity observed for small particles. Tentatively, this behaviour is attributed to a disturbed zone, created by the mechanical treatment of the material during particle size reduction, extending throughout small particles, but not altering an undisturbed core of the larger particles. In agreement with this, measurements on large pieces show a surface area 5 to 150 times lower than expected from the linear trends observed for the crushed material, implying an overestimation of the surface area and possibly also of the sorption capacities of the rock material from simple extrapolations of experimental results employing finely crushed material to the field situation.QC 20110929
Äspö Radionuclide sorption
8
Sharif, Shasad, Lynn DiMemmo, Martha Davidovich, and Beth Sarsfield. "Applicability of specific surface area determination on pharmaceuticals by inverse gas chromatography." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-185429.
Повний текст джерела
9
Sharif, Shasad, Lynn DiMemmo, Martha Davidovich, and Beth Sarsfield. "Applicability of specific surface area determination on pharmaceuticals by inverse gas chromatography." Diffusion fundamentals 16 (2011) 56, S. 1, 2011. https://ul.qucosa.de/id/qucosa%3A13798.
Повний текст джерела
10
Remmen, Krystle D. "A REACTIVE TRACER METHOD FOR THE MEASUREMENT OF SPECIFIC SURFACE AREA IN EGS RESERVOIRS." Thesis, California State University, Long Beach, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=1527408.
Повний текст джерелаАнотація:
Early thermal breakthrough is an issue of concern in the geothermal industry, especially with regard to engineered geothermal systems (EGS). Determination of the specific surface area (SSA) of the fluid/rock interface in an EGS is vital to predicting early thermal breakthrough. An approach to this problem involving the application of tracers with different sorption properties (lithium, bromide, and deuterium) is presented. Upon injection into a reservoir, these tracers react along the fluid/rock interface to varying degrees. The resulting breakthrough separation at the extraction well can be used to derive SSA by applying a modified form of the advection-dispersion equation. For proof of concept, field tests were conducted in a sandstone bedding-plane fracture near Chazy, New York. Results showed minimal breakthrough separation, indicating insufficient sweep of the fracture area, and that lithium was not an ideal tracer in this medium. However, a relative measure of SSA can still be derived.
11
Lazaro, A., J. W. Geus, and H. J. H. Brouwers. "Influence of the Production Process Conditions on the Specific Surface Area of Olivine Nano-Silicas." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/34893.
Повний текст джерелаАнотація:
The production of nano-silica by the olivine route is a cheaper and greener method than the commercial methods (neutralization of sodium silicate solutions and the flame hydrolysis) because of the low cost
of raw materials and the low energy requirements. The produced olivine nano-silica has a specific surface
area between 100-400 m2/g and primary particles between 10 to 25 nm (agglomerated in clusters). The process conditions and the ripening process influence the properties of nano-silica in the following ways i) the
cleaner the nano-silica is the higher the specific surface area is; ii) the higher the filtration pressure is the
higher the surface area is (unless the pressure is so high that the voids of the material collapse reducing
drastically the SSA); iii) the ripening process diminishes the specific surface of nano-silica by two thirds
and could be even further reduced. Thus, modifying the process conditions and/or adding an Ostwald ripening process, nano-silicas with different specific surface areas can be synthesized.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34893
12
ALBANEZ, NELMA E. F. K. "Obtencao de oxido de cerio com alta area superficial especifica." reponame:Repositório Institucional do IPEN, 1996. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10474.
Повний текст джерелаАнотація:
Made available in DSpace on 2014-10-09T12:40:52Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:04:30Z (GMT). No. of bitstreams: 1 02944.pdf: 4594113 bytes, checksum: a3a3f6866bfb45e2b9c9b02b0a6f7796 (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
13
Furuhashi, Toyohisa. "STUDY OF PROPANE ADSORPTION ISOTHERM ON PURIFIED HIPCO SINGLE-WALLED CARBON NANOTUBES." Available to subscribers only, 2009. http://proquest.umi.com/pqdweb?did=1967978731&sid=2&Fmt=2&clientId=1509&RQT=309&VName=PQD.
Повний текст джерела
14
Khadka, Suraj. "A Numerical Study of the Coupled Geomechanical Processes in Sinkholes." University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1532970968316002.
Повний текст джерела
15
Griend, M. C. van de, A. Lazaro, and H. J. H. Brouwers. "The Effect of Hydrothermal Treatment on Olivine Nano-Silica." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/34915.
Повний текст джерелаАнотація:
This paper provides an overview of the effects of ripening the olivine nano-silica to form particles with a
lower specific surface area for optimal use in high performance concrete. The nano-silica was ripened using a
hydrothermal treatment in a mixed batch reactor at 90 °C, pH ranging from 8 to 10 and a silica weight percentage of three and six percent. The specific surface area of the olivine nano-silica can be reduced by
62 percent by Ostwald ripening in 22 hours. This reduction corresponds to a 80 percent drop of the micropore
surface area and a 57 percent drop of the external surface area. The different hydrothermal conditions did not
affect the final specific surface area at the equilibrium. However, the use of a high energy mixer reduced the
specific surface area by 52 percent in only five minutes. Despite the reduction in specific surface area, the aggregates of the original olivine nano-silica are not dissolved during the ripening process.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/34915
16
Giberti, Sara. "Surface Area enhancement of biochar and forestry biomass through activation by means of chemical impregnation with ZnCl2 and H3PO4." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Знайти повний текст джерелаАнотація:
This dissertation is dedicated to the research of methods for the production of activated carbon by means of chemical impregnation from renewable resources such as waste biochar and forestry biomass.
The goal of the research is to find a method that generates high performances activated carbon which can be scaled up and added to the supply chain of an already existing gasification concept located in Innsbruck, Austria.
Biochar has been impregnated with ZnCl2 in ratios of 1:1 and 5:1 and activated in a mixed bed reactor in presence of H2O steam in a temperatures range of 500 and 700 °C for 30 and 60 minutes.
Forestry biomass and biochar have been impregnated with ZnCl2 and H33PO4 in ratios of 1:1, 3:1, 5:1 then pyrolyzed at 500 °C for 1 hour.
The activated carbon has been characterized through N2 adsorption at 77 K, total carbon content and scanning electron microscopy. The best results were obtained with the ZnCl2 5:1 impregnated biomass pyrolyzed at 500 °C for 1 hour, with a specific surface area of 1626 m2/g, a total pore volume of 0,79 cm3/g with a microporous percentage of the 75%, and a total carbon content of 84%.
17
Barančíková, Miriama. "Vysoce porézní keramické materiály připravené metodou Spark Plasma Sintering." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-442603.
Повний текст джерелаАнотація:
Porous ceramic materials are an interesting group of materials due to a wide range of physical properties, low density, and good permeability. Production of a monolith with a shape stability that would also have a high specific surface area and high porosity is a common problem with porous ceramics. The goal of this work was to maintain the high specific surface area and to produce a monolith with a shape stability. Two forms of porous silica nanofibers (as prepared and milled) were used and partially sintered using the Spark Plasma Sintering method (SPS). Different sintering times and temperatures for SPS were tested. The findings revealed that the best SPS conditions were as follows: temperature: 600 °C, sintering time: 5 minutes, pressure: 3 MPa, and the heating rate: 144 °C/min. These sintering conditions resulted in a stable silica based machinable monolith made from fibers or milled fibers. The monoliths have the specific surface area of up to 470 m^2/g and porosity of 72 %, or the specific surface area of up to 422 m^2/g and porosity of 69 % for as prepared fibers and milled fibers, respectively.
18
Jackson, Gavin John. "Local adsorption structure determination of chemically-specific species using normal incidence X-ray standing wavefields." Thesis, University of Warwick, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343835.
Повний текст джерела
19
ZAMPIERON, JOAO V. "Caracterizacao fisica de particulas e reologica de um sistema heterogeneo utilizado em moldalgem de pos por injecao a baixa pressao." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10979.
Повний текст джерелаАнотація:
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
20
Libois, Quentin. "Evolution des propriétés physiques de neige de surface sur le plateau Antarctique. Observations et modélisation du transfert radiatif et du métamorphisme." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU026/document.
Повний текст джерелаАнотація:
Le bilan d'énergie de surface du Plateau Antarctique est essentiellement contrôlé par les propriétés physiques des premiers centimètres du manteau neigeux. Or l'évolution de cette neige de surface est complexe car elle dépend de processus fondamentalement imbriqués: vitesse de métamorphisme, profils de température, pénétration du rayonnement solaire, précipitations, transport de neige par le vent, etc. L'objectif de ces travaux de thèse est d'étudier ces diverses composantes et leur couplage afin de simuler l'évolution de la densité de la neige et de la taille de grain (surface spécifique) sur le Plateau Antarctique. Pour représenter de manière physique l'absorption de l'énergie solaire à l'intérieur du manteau, un modèle de transfert radiatif à fine résolution spectrale (TARTES) a été implémenté dans le modèle de manteau neigeux détaillé Crocus. TARTES permet de calculer le profil vertical d'absorption d'énergie dans un manteau stratifié dont les caractéristiques sont connues. Parmi elles, la forme des grains, explicitement prise en compte dans TARTES, a été peu étudiée jusqu'à présent. C'est pourquoi une méthode de détermination expérimentale de la forme optique des grains est proposée et appliquée à un grand nombre d'échantillons de neige. Cette méthode, basée sur des mesures optiques, des simulations TARTES, et l'inférence bayésienne, a permis de déterminer la forme la plus adéquate pour simuler les propriétés optiques de la neige, et a mis en évidence le fait que représenter la neige par un ensemble de particules sphériques conduisait à surestimer la profondeur de pénétration du rayonnement d'environ 30%. L'impact de l'absorption en profondeur du rayonnement sur les profils de température dans le manteau et son métamorphisme est ensuite étudié par des approches analytique et numérique, mettant en valeur la sensibilité des profils aux propriétés de la neige proche de la surface. En particulier, la densité de la neige sur les premiers centimètres est cruciale pour le bilan d'énergie du manteau car elle impacte à la fois la profondeur de pénétration du rayonnement et la conductivité thermique du manteau. Puisque le modèle Crocus tient compte de ce couplage entre propriétés optiques et physiques du manteau, il est utilisé pour estimer l'influence des conditions météorologiques sur la variabilité temporelle des propriétés physiques de la neige de surface à Dôme C. Ces simulations sont évaluées au regard d'un jeu de données collectées lors de missions de terrain et de mesures automatiques de l'albédo spectral et de la pénétration du rayonnement dans la neige. Ces observations mettent en évidence le rôle primordial des précipitations dans les variations rapides de taille de grain en surface et l'existence d'un cycle saisonnier de cette taille de grain. Ces variations sont bien simulées par Crocus lorsque le forçage atmosphérique qui lui est imposé est adéquat. En particulier, l'impact du vent sur l'évolution du manteau est fondamental car il contrôle la densité de surface par le biais du transport de neige. Ce transport est aussi à l'origine de la variabilité spatiale des propriétés de la neige observée à Dôme C. C'est pourquoi une modélisation stochastique de l'érosion et du transport de neige dans Crocus est proposée. En plus d'expliquer la variabilité spatiale de la densité et de la taille de grain, elle permet de reproduire celle de l'accumulation annuelle ainsi que les variations rapides de hauteur de neige liées à des épisodes de vent. Ces travaux ont permis une meilleure représentation des processus physiques qui contrôlent les variations des propriétés de la neige de surface à Dôme C, tout en soulignant le rôle primordial du vent, dont l'impact sur le manteau est particulièrement complexe à simulerThe surface energy balance of the Antarctic Plateau is mainly governed by the physical properties of the snowpack in the topmost centimeters, whose evolution is driven by intricated processes such as: snow metamorphism, temperature profiles variations, solar radiation penetration, precipitation, snow drift, etc. This thesis focuses on the interactions between all these components and aims at simulating the evolution of snow density and snow grain size (specific surface area) on the Antarctic Plateau. To physically model the absorption of solar radiation within the snowpack, a radiative transfer model with high spectral resolution (TARTES) is implemented in the detailed snowpack model Crocus. TARTES calculates the vertical profile of absorbed radiation in a layered snowpack whose characteristics are given. These characteristics include snow grain shape, a parameter that has been seldom studied. For this reason, an experimental method to estimate the optical grain shape is proposed and applied to a large number of snow samples. This method, which combines optical measurements, TARTES simulations and Bayesian inference, is used to estimate the optimal shape to be used in snow optical models. In addition, it highlights that representing snow as a collection of spherical particles results in overestimation of the penetration depth of solar radiation. The influence of the penetration of solar radiation on the snow temperature profiles is then investigated with analytical and numerical tools. The results point out the high sensitivity of the temperature profiles to surface snow physical properties. In particular, the density of the topmost centimeters of the snowpack is critical for the energy budget of the snowpack because it impacts both the effective thermal conductivity and the penetration depth of light. To simulate the evolution of snow physical properties at Dome C by taking into account their interdependence with snow optical properties, the model Crocus is used, driven by meteorological data. These simulations are evaluated against a set of data collected during field missions as well as automatic measurements of snow spectral albedo and penetration depth. These observations highlight the influence of weather conditions on the temporal variability of surface snow properties. They show the existence of a slow decrease of snow grain size at the surface during summer. Rapid changes are also observed, essentially due to precipitation. These variations are well simulated by Crocus when forced by an appropriate atmospheric forcing. In particular, the impact of wind on the evolution of the snowpack is crucial because it controls the surface density through snow transport. This transport is also responsible for the spatial variability of snow properties observed at Dome C. That is why a stochastic representation of snow erosion and transport in Crocus is proposed. It explains well the observations of the spatial variability of density and grain size, and reproduces the variability of the annual accumulation as well as rapid changes in snow height resulting from drift events. This study improves our understanding of the physical processes which drive the properties of snow close to the surface on the Antarctic Plateau, and also points out the critical role of wind, the impact of which is very difficult to account for in models yet
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Banjara, Shree Ram. "STUDY OF ADSORPTION OF CARBON DIOXIDE ON CARBON BASED NANO-MATERIALS AND EVALUATION OF ISOSTERIC HEAT, SPECIFIC EFFECTIVE SURFACE AREA AVAILABLE FOR ADSORPTION AND ADSORPTION KINETICS." OpenSIUC, 2012. https://opensiuc.lib.siu.edu/theses/915.
Повний текст джерелаАнотація:
Single-walled dahlia-like carbon nanohorns treated with H2O2 for 3hrs at 150 ℃ were used as sorbent in a study of CO2 adsorption. This treatment ensures that the nanohorns are open and they have their interior space available for adsorption. Volumetric adsorption measurements on open spherical aggregates of dahlia-like single walled carbon nanohorns were performed at seven different temperatures between 158.66 K and 208.68 K. The waiting time for reaching the equilibrium pressure after adding a dose increased with sorbent loading. Unlike Ne and CF4 adsorption isotherms measured on similar substrate which have two distinct substeps present in the isotherms, the adsorption data for CO2 has a single very broad step present between the lowest coverage and saturation. Results for the loading dependence of the isosteric heat indicate that this quantity depends non-monotonically on the amount of CO2 adsorbed. The effective specific surface area of the open single walled carbon nanohorns sample obtained in this study are compared with the ones obtained with other carbon nanohorn samples; the results clearly indicate that nanohorns are open.
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Carmagnola, Carlo Maria. "Mesure, analyse et modélisation des processus physiques du manteau neigeux sec Implementation and evaluation of prognostic representations of the optical diameter of snow in the SURFEX/ISBA-Crocus detailed snowpack model Snow spectral albedo at Summit, Greenland: measurements and numerical simulations based on physical and chemical properties of the snowpack." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU014.
Повний текст джерелаАнотація:
La neige est un matériau poreux dont la microstructure change en permanence. L'ensemble de ces transformations, qui prend le nom de ``métamorphisme", est susceptible d'affecter les propriétés thermiques, mécaniques et électromagnétiques de la neige au niveau macroscopique. En particulier, les échanges d'énergie et de matière à l'intérieur du manteau neigeux et entre la neige et l'atmosphère sont fortement influencés par l'évolution au cours du temps de la microstructure de la neige. Une représentation adéquate du métamorphisme dans les modèles de manteau neigeux s'avère donc cruciale. La microstructure d'un matériau poreux peut être raisonnablement décrite en se servant d'un nombre réduit de variables. En effet, la masse volumique, la surface spécifique (SSA) et la distribution de courbure permettent de caractériser la microstructure d'un matériau. Cependant, dans le cas de la neige cette approche n'en est qu'à ses débuts et n'a pas encore été appliquée de façon systématique. Des variables semi-empiriques, difficiles à mesurer et dépourvues de lien direct avec d'autres propriétés physiques, sont encore largement utilisées dans les modèles détaillés de manteau neigeux. Ce travail de thèse s'inscrit dans cette tentative de représenter la microstructure de la neige au cours du temps à l'aide de variables bien définies et mesurables sur le terrain. Parmi ces variables, nous nous sommes attachés notamment à la SSA, qui constitue une grandeur essentielle pour l'étude du manteau neigeux et de son évolution temporelle. Différentes lois d'évolution de la SSA ont été étudiées, à partir de relations empiriques basées sur des ajustements de données expérimentales jusqu'aux modèles physiques qui représentent le flux de la vapeur d'eau entre les grains de neige. Ces lois ont été dans un premier temps testées à l'aide d'un modèle simplifié de manteau neigeux et puis introduites directement dans le modèle SURFEX/ISBA-Crocus. Pour ce faire, la SSA dans Crocus a été transformée en variable prognostique, en remplaçant d'autres variables semi-empiriques préexistantes. Les différentes formulations de l'évolution temporelle de la SSA ont été comparées à des mesures de terrain, acquises lors de deux campagnes à Summit (Groenland) et au Col de Porte (France). Ces mesures ont été effectuées en utilisant de nouvelles techniques optiques et ont permis d'obtenir un riche jeu de données avec une grande résolution verticale. Les résultats montrent que les différentes formulations sont comparables et reproduisent bien les mesures, avec un écart quadratique moyen entre les valeurs de SSA simulées et observées inférieur à 10 m^2/kg. Enfin, nous avons contribué à faire le pont entre la microstructure de la neige et ses propriétés macroscopiques. En particulier, nous nous sommes intéressés au lien entre, d'une part, la SSA et, d'autre part, les propriétés mécaniques et optiques. Dans le premier cas, nous avons investigué la corrélation entre la SSA et la résistance à l'enfoncement mesurée avec un Snow Micro Pen (SMP). Les résultats encore préliminaires semblent indiquer que la SSA peut être dérivée de la masse volumique et de grandeurs micro-mécaniques estimées à partir du signal du SMP avec un modèle statistique. Dans le deuxième cas, nous avons simulé l'albédo de surface à Summit à partir des profils mesurés de masse volumique et de SSA et du contenu en impuretés. Les résultats de cette étude ont démontré que l'albédo spectral peut être correctement simulé à l'aide d'un modèle de transfert radiatif et l'énergie absorbée par le manteau neigeux peut être estimée avec une précision d'environ 1%Snow is a porous medium whose microstructure is constantly subjected to morphological transformations. These transformations, which take the name of ``metamorphism", are likely to affect the thermal, mechanical and electromagnetic properties of snow at the macroscopic level. Specifically, the exchange of energy and matter within the snowpack and between the snow and the atmosphere above are strongly impacted by the evolution over time of the snow microstructure. Therefore, an adequate representation of metamorphism in snowpack models is crucial. The microstructure of a porous medium can be reasonably described using a reduced number of variables. Indeed, the density, the specific surface area (SSA) and the curvature distribution are able to characterize the microstructure of such a material. However, in the case of snow this approach is still in its infancy and has not yet been systematically applied. Semi-empirical variables, difficult to measure and not directly linked to other relevant physical properties, are still widely used in so-called detailed snowpack models. This work contributes to the attempt to represent the state of the snow using well-defined and easily measurable microstructural variables. Among these variables, we focused particularly on the SSA, which is a key quantity for the study of snow and its temporal evolution. Different evolution laws of SSA were studied, starting from empirical relationships based on experimental data adjustments to physical models that represent the flow of water vapor between snow grains. These laws were initially tested using a simplified snowpack model and then introduced directly into the SURFEX/ISBA-Crocus snowpack model. To this end, the SSA in Crocus was turned into a prognostic variable, replacing other preexisting semi-empirical variables. The different formulations of the temporal evolution of the SSA were compared with field measurements, acquired during two campaigns at Summit (Greenland) and the Col de Porte (France). These measurements were carried out using new optical techniques and yielded a rich dataset with high vertical resolution. The results show that the different formulations are comparable and reproduce well the observations, with an average root-mean-square deviation value between simulated and measured SSA lower than 10 m^/kg. Finally, we contributed to bridge the gap between snow microstructure and macroscopic properties. In particular, we investigated the link between the SSA on the one hand and the mechanical and optical properties on the other hand. In the first case, we investigated the correlation between the SSA and the penetration resistance measured with a Snow Micro Pen (SMP). The preliminary results suggest that the SSA can be retrieved from the snow density and the micro-mechanical parameters estimated from the SMP signal using a statistical model. In the second case, we simulated the surface albedo at Summit from the measured profiles of density, SSA and impurities within the snowpack. The results of this study showed that the spectral albedo can be simulated successfully using a radiative transfer model and the energy absorbed by the snowpack can be estimated with a good accuracy (about 1%)
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Delibas, Tughan. "Effects Of Granulated Blast Furnace Slag Trass And Limestone Fineness On The Properties Of Blended Cements." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614072/index.pdf.
Повний текст джерелаАнотація:
The aim of this research was to determine the effects of the fineness of different mineral additives on loss on ignition, heat of hydration, physical, mechanical and chemical properties of blended cements. For that purpose, portland cement clinker was replaced with granulated blast furnace slag (GBFS), natural pozzolan (NP) and limestone (L) at 6%, 20% and 35% replacement levels. Blended cements containing GBFS and NP were ground to a fineness of 3000, 5000 and 6000 cm2/g. Cements containing L were ground to 3000 cm2/g, 4000 cm2/g and 4500 cm2/g. All of the blended cement types mentioned above were both interground and separately ground to the specified fineness levels. Therefore, a total of 57 different cements were produced. Loss on ignition, heat of hydration, chemical, mechanical and physical analyses were performed on the produced cements. Moreover, the chemical analyses of the cements were obtained for cement particles finer (-45&mum) and coarser (+45&mu
m) than 45 &mu
m in order to determine the ingredients of -45 &mu
m, which is known to be more reactive. As a result it was shown that the grindability differences of the cement ingredients affect the properties of blended cements. An increase in the specific surface area increases both the compressive strength and heat of hydration values and adversely affects the loss on ignition values. The results also showed that if the cement particles were ground finer, it was more prone to moisture which resulted in higher loss on ignition values after longer periods.
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Brňák, Matúš. "Heterogenní radikálová modifikace polypropylenu." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2018. http://www.nusl.cz/ntk/nusl-376886.
Повний текст джерелаАнотація:
The diploma thesis deals with the heterogeneous technique of preparation of grafted polypropylene g maleic anhydride (PP-g-MAH). The knowledge of the course of the reaction and its impact on the PP grafting process are summarized in the theoretical part. The preparation of the grafted PP was carried out in a fluidized polymerization reactor at 115 °C, speed of mixing 210 rpm, reaction time 60 min and pressure 6 bar. The amount of grafted MAH was monitored by using a MAH concentration 3 and 5 wt% and an initiator concentration 0.25; 0.5; 1; and 1.5 wt%. Modification efficiency was compared by using 3 types of PP with different particle morphology and specific surface area. By creating the theoretical model, the maximum surface concentration of MAH was calculated and compared with experimental data. Characterization of PP materials was performed by Electron Scanning Microscopy (SEM), Differential Scanning Calorimetry (DSC) and particle surface analysis by BET. Quantitative analysis of grafted MAH was determined by FTIR spectroscopy and acid-base titration.
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Pronk, Geertje Johanna [Verfasser], Ingrid [Akademischer Betreuer] Kögel-Knabner, and Kai Uwe [Akademischer Betreuer] Totsche. "Biogeochemical interfaces in natural and artificial soil systems: specific surface area, phenanthrene sorptive properties and formation of organo-mineral associations / Geertje Johanna Pronk. Gutachter: Kai Uwe Totsche. Betreuer: Ingrid Kögel-Knabner." München : Universitätsbibliothek der TU München, 2011. http://d-nb.info/1019587717/34.
Повний текст джерела
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Xia, Changlei. "Biomass-Derived Activated Carbon Through Self-Activation Process." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849716/.
Повний текст джерелаАнотація:
Self-activation is a process that takes advantage of the gases emitted from the pyrolysis process of biomass to activate the converted carbon. The pyrolytic gases from the biomass contain CO2 and H2O, which can be used as activating agents. As two common methods, both of physical activation using CO2 and chemical activation using ZnCl2 introduce additional gas (CO2) or chemical (ZnCl2), in which the CO2 emission from the activation process or the zinc compound removal by acid from the follow-up process will cause environmental concerns. In comparison with these conventional activation processes, the self-activation process could avoid the cost of activating agents and is more environmentally friendly, since the exhaust gases (CO and H2) can be used as fuel or feedstock for the further synthesis in methanol production. In this research, many types of biomass were successfully converted into activated carbon through the self-activation process. An activation model was developed to describe the changes of specific surface area and pore volume during the activation. The relationships between the activating temperature, dwelling time, yield, specific surface area, and specific pore volume were detailed investigated. The highest specific surface area and pore volume of the biomass-derived activated carbon through the self-activation process were up to 2738 m2 g-1 and 2.209 cm3 g-1, respectively. Moreover, the applications of the activated carbons from the self-activation process have been studied, including lithium-ion battery (LIB) manufacturing, water cleaning, oil absorption, and electromagnetic interference (EMI) shielding.
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André, Bérangère. "Structure et réactivité de poudres d’aluminium nanostructurées." Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4301.
Повний текст джерелаАнотація:
Les poudres d'aluminium sont depuis longtemps utilisées comme additifs dans de nombreuses formulations pour la pyrotechnie ou les propergols. Introduites en quantité relativement faible dans les propergols des fusées, elles permettent d'accroître significativement les vitesses de combustion. Cependant, les mécanismes à l'origine de cette meilleure réactivité restent encore mal compris et vont bien au-delà d'une simple explication en terme d'augmentation de l'état de division. Au cours de cette thèse nous avons élaboré des poudres d'aluminium par broyage à haute énergie, technique mécanique peu couteuse qui pourrait être une alternative aux procédés de fabrication actuels. Nous montrons que cette méthode permet l'obtention de particules micrométriques ou nanométriques suivant les conditions de broyage. Les particules sont polycristallines et présentent une morphologie en plaquette. Les poudres nanométriques obtenues présentent une réactivité comparable voire même supérieure aux nanopoudres sphériques actuellement élaborées par électro-explosion de fil ou voie plasma. Nous montrons que cette bonne réactivité est lié à la morphologie des particules ainsi qu'à la microstructure de la couche d'alumine native qui passive l'aluminiumAluminium nanopowders have been using for a long time as additives in many formulations for propergol or in pyrotechnics. Introduced in small quantity in rocket propergol they allow to increase the combustion rate. However, the reactivity of aluminium particles is not really understood and not just linked to the size reduction effect. All along this study, we have elaborated aluminium powders using high energy mechanical milling, a mechanical technique with a low cost which could be an alternative process of powders fabrication. We prove that this method allows elaboration of micro and nano-particles as a function of the mechanical parameters. The particles are polycristallines with flake morphology. The obtained nanopowders have a similar reactivity, or better than spherical nanopowders obtained by wire electrical explosion or plasma. We proove that this good reactivity is linked to the particles morphology, as well as also to the microstructure of the native alumina core shell
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Alhawat, Musab M. "Bond Performance between Corroded Steel and Recycled Aggregate Concrete Incorporating Nano Silica." Thesis, University of Bradford, 2020. http://hdl.handle.net/10454/18430.
Повний текст джерелаАнотація:
The current research project mainly aims to investigate the corrosion resistance and bond
performance of steel reinforced recycled aggregate concrete incorporating nano-silica under
both normal and corrosive environmental conditions. The experimental part includes testing
of 180 pull-out specimens prepared from 12 different mixtures. The main parameters studied
were the amount of recycled aggregate (RCA) (i.e. 0%, 25%, 50% and 100%), nano silica
(1.5% and 3%), steel embedment length as well as steel bar diameter (12 and 20mm).
Different levels of corrosion were electrochemically induced by applying impressed voltage
technique for 2, 5, 10 and 15 days. The experimental observations mainly focused on the
corrosion level in addition to the ultimate bond, failure modes and slips occurred.
Experimental results showed that the bond performance between un-corroded steel and
recycled aggregate concrete slightly reduced, while a significant degradation was observed
after being exposed to corrosive conditions, in comparison to normal concrete. On the other
hand, the use of nano silica (NS) showed a reasonable bond enhancement with both normal
and RCA concretes under normal conditions. However, much better influence in terms of bond
and corrosion resistance was observed under advancing levels of corrosion exposure,
reflecting the improvement in corrosion resistance. Therefore, NS was superbly effective in
recovering the poor performance in bond for RCA concretes. More efficiency was reported
with RCA concretes compared to the conventional concrete. The bond resistance slightly with
a small amount of corrosion (almost 2% weight loss), then a significant bond degradation
occurs with further corrosion.
The influence of specific surface area and amount of nano silica on the performance of concrete
with different water/binder (w/b) ratios has been also studied, using 63 different mixtures produced
with three different types of colloidal NS having various surface areas and particle sizes. The
results showed that the performance of concrete is heavily influenced by changing the surface area
of nano silica. Amongst the three used types of nano silica, NS with SSA of 250 m2
/g achieved the highest enhancement rate in terms of compressive strength, water absorption and
microstructure analysis, followed by NS with SSA of 500 m2/g, whilst NS with SSA of 51.4
m2
/g was less advantageous for all mixtures. The optimum nano silica ratio in concrete is
affected by its particle size as well as water to binder ratio.
The feasibility of the impact-echo method for identifying the corrosion was evaluated and
compared to the corrosion obtained by mass loss method. The results showed that the impact-echo testing can be effectively used to qualitatively detect the damage caused by corrosion in
reinforced concrete structures. A significant difference in the dominant frequencies response
was observed after exposure to the high and moderate levels of corrosion, whilst no clear
trend was observed at the initial stage of corrosion.
Artificial neural network models were also developed to predict bond strength for corroded/uncorroded steel bars in concrete using the main influencing parameters (i.e., concrete strength, concrete cover, bar diameter, embedment length and corrosion rate). The developed models
were able to predict the bond strength with a high level of accuracy, which was confirmed by
conducting a parametric study.Higher Education Institute in the Libyan Government MONE BROS Company in Leeds (UK) for providing recycled aggregates BASF and Akzonobel Companies for providing nano silica NS, Hanson Ltd, UK, for suppling cement
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Théodet, Manuel. "Nouvelle génération de précurseurs "bulk" de catalyseur d'hydrodésulfuration synthétisés en milieu fluides supercritique." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2010. http://tel.archives-ouvertes.fr/tel-00559113.
Повний текст джерелаАнотація:
L'objet de ce travail de thèse porte sur la synthèse originale en milieu fluide supercritique (FSC) de précurseurs « bulk » de catalyseurs d'hydrodésulfuration (HDS) à haute surface spécifique (SBET), destinés à l'HDS de composés soufrés réfractaires tels que le 4,6 diméthyldibenzothiophène (4,6¬ DMDBT). Ce projet a été réalisé en collaboration entre l'Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB-CNRS) et l'Instituto de Tecnología Química de Valencia (ITQ-CSIC) dans le cadre du réseau européen d'excellence Functional Advanced Materials and Engineering of Hybrids and Ceramics (FAMEnoe). Les études à l'ICMCB se sont portées sur l'optimisation des paramètres de synthèse en milieu FSC de NixCo1-xMoO4 (0 ≤ x ≤ 1) (précurseurs métalliques, solvant, température, pression). Des poudres de précurseurs « bulk » majoritairement composées de la phase hydratée (NiMoO4.0,75H2O) - phase la plus active en HDS - de composition contrôlée et pouvant atteindre près de 200 m2.g-1 ont été obtenues et caractérisées. Les propriétés catalytiques de ces précurseurs « bulk » après sulfuration ont ensuite été testées à l'ITQ sur la réaction de Deep-HDS d'un mélange modèle et d'une fraction pétrolière réelle. L'étude souligne plus particulièrement leurs meilleures capacités d'hydrogénation et de catalyse de l'HDS du 4,6 DMDBT que le catalyseur commercial utilisé comme référence dans ces travaux.
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Darpentigny, Clémentine. "Fonctionnalisation de structures de nanocellulose en fluide supercritique pour des applications de pansements antimicrobiens Ice-templated freeze-dried cryogels from tunicate cellulose nanocrystals with high specific surface area and anisotropic morphological and mechanical properties Highly Absorbent Cellulose Nanofibrils Aerogels Prepared by Supercritical Drying." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAV052.
Повний текст джерелаАнотація:
Dans un contexte où la demande en matériaux médicaux innovants augmente et où la question environnementale devient une préoccupation majeure, l’objectif du projet a été de préparer des pansements antimicrobiens par la voie la plus verte possible. Pour cela, les nanocelluloses ont été retenues comme briques de base biosourcées et biocompatibles pour le design d’architectures poreuses et leur fonctionnalisation par des agents antimicrobiens a été ensuite entreprise en milieu CO2 supercritique (CO2sc) utilisé comme alternative aux solvants organiques en tirant profit de ses spécificités telles qu’une diffusivité élevée, une élimination aisée du solvant et des réactifs résiduels et une compatibilité avec les matériaux fragiles. Ainsi, des structures 2D et 3D, nanopapiers, cryogels et aérogels, ont été préparées à partir de nanofibrilles (NFC) et de nanocristaux (NCC) de cellulose et présentent des propriétés variées en termes de porosité, morphologie et surface spécifique. Dans le but d’introduire une fonction antibactérienne, les cryogels préparés à partir de nanocelluloses de chimie de surface variées ont été dans un premier temps imprégnés en CO2sc d’un antibiotique synthétique, la ciprofloxacine. Les cryogels imprégnés présentent une activité antibactérienne contre les bactéries Gram-positive et Gram-négative. Ensuite, quatre matériaux de surface spécifique croissante tous préparés à partir de NFC ont été imprégnés avec une molécule issue d’huiles essentielles, le thymol. Les résultats montrent un contrôle direct de la quantité imprégnée avec la surface spécifique qui conduit dans le cas des cryo- et aérogels à de bonnes propriétés antimicrobiennes contre deux types de bactéries et une levure. La seconde stratégie de fonctionnalisation a porté sur le greffage covalent d’un silane aminé antimicrobien en CO2sc. Des méthodes d’analyse de surface (spectrométrie photoélectronique X, angle de contact et potentiel zêta de surface) ont permis de confirmer le succès du greffage sur les nanopapiers. Les propriétés antibactériennes par contact des nanopapiers et cryogels greffés ont été confirmées. Ces résultats sont prometteurs pour l’élaboration en conditions supercritiques de dispositifs médicaux antimicrobiens bio-sourcés et biocompatiblesIn a context where the need for innovative medical devices is increasing and the environmental issue is becoming a major concern, the objective of the project the aim of the project was to prepare antimicrobial wound dressings using the greenest possible way. For this purpose, nanocelluloses have been chosen as bio-based and biocompatible building blocks for the design of porous architectures and their functionalization with antimicrobial agents was then undertaken in supercritical CO2 medium (CO2sc) used as an alternative to organic solvents and by taking advantage of its specificities such as high diffusivity, easy removal of solvent and residual reagents and compatibility with fragile materials. Thus, 2D and 3D structures, nanopapers, cryogels and aerogels, were prepared from cellulose nanofibrils (CNFs) and nanocrystals (CNCs), and exhibited various properties in terms of morphology, porosity and specific surface area. In order to introduce antibacterial functionality, cryogels prepared from nanocellulose with varied surface chemistries were impregnated in scCO2 with a synthetic antibiotic, ciprofloxacin. Impregnated cryogels exhibited antibacterial activity against both gram-negative and gram-positive bacterial strains. Then, four materials of increasing specific surface area, all prepared from CNFs, were impregnated with an essential oil molecule, thymol. Results show a direct relationship between of the amount of impregnated molecules and the specific surface that leads in the case of cryo- and aerogels to good antimicrobial properties against two types of bacteria and yeast. In a second strategy, covalent grafting of CNFs structures in supercritical CO2 was investigated with a novel antibacterial aminosilane. Surface analysis characterizations methods (X-ray photoelectron spectroscopy, contact angle and surface zeta potential analysis) confirmed the successful grafting on nanopapers. The contact active properties of grafted nanopapers and cryogels were assessed. These results are very promising for the design of antimicrobial bio-based and biocompatible medical devices using supercritical conditions
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Carmagnola, Carlo Maria. "Mesure, analyse et modélisation des processus physiques du manteau neigeux sec." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-01070005.
Повний текст джерелаАнотація:
La neige est un matériau poreux dont la microstructure change en permanence. L'ensemble de ces transformations, qui prend le nom de ''métamorphisme", est susceptible d'affecter les propriétés thermiques, mécaniques et électromagnétiques de la neige au niveau macroscopique. En particulier, les échanges d'énergie et de matière à l'intérieur du manteau neigeux et entre la neige et l'atmosphère sont fortement influencés par l'évolution au cours du temps de la microstructure de la neige. Une représentation adéquate du métamorphisme dans les modèles de manteau neigeux s'avère donc cruciale. La microstructure d'un matériau poreux peut être raisonnablement décrite en se servant d'un nombre réduit de variables. En effet, la masse volumique, la surface spécifique (SSA) et la distribution de courbure permettent de caractériser la microstructure d'un matériau. Cependant, dans le cas de la neige cette approche n'en est qu'à ses débuts et n'a pas encore été appliquée de façon systématique. Des variables semi-empiriques, difficiles à mesurer et dépourvues de lien direct avec d'autres propriétés physiques, sont encore largement utilisées dans les modèles détaillés de manteau neigeux. Ce travail de thèse s'inscrit dans cette tentative de représenter la microstructure de la neige au cours du temps à l'aide de variables bien définies et mesurables sur le terrain. Parmi ces variables, nous nous sommes attachés notamment à la SSA, qui constitue une grandeur essentielle pour l'étude du manteau neigeux et de son évolution temporelle. Différentes lois d'évolution de la SSA ont été étudiées, à partir de relations empiriques basées sur des ajustements de données expérimentales jusqu'aux modèles physiques qui représentent le flux de la vapeur d'eau entre les grains de neige. Ces lois ont été dans un premier temps testées à l'aide d'un modèle simplifié de manteau neigeux et puis introduites directement dans le modèle SURFEX/ISBA-Crocus. Pour ce faire, la SSA dans Crocus a été transformée en variable prognostique, en remplaçant d'autres variables semi-empiriques préexistantes. Les différentes formulations de l'évolution temporelle de la SSA ont été comparées à des mesures de terrain, acquises lors de deux campagnes à Summit (Groenland) et au Col de Porte (France). Ces mesures ont été effectuées en utilisant de nouvelles techniques optiques et ont permis d'obtenir un riche jeu de données avec une grande résolution verticale. Les résultats montrent que les différentes formulations sont comparables et reproduisent bien les mesures, avec un écart quadratique moyen entre les valeurs de SSA simulées et observées inférieur à 10 m^2/kg. Enfin, nous avons contribué à faire le pont entre la microstructure de la neige et ses propriétés macroscopiques. En particulier, nous nous sommes intéressés au lien entre, d'une part, la SSA et, d'autre part, les propriétés mécaniques et optiques. Dans le premier cas, nous avons investigué la corrélation entre la SSA et la résistance à l'enfoncement mesurée avec un Snow Micro Pen (SMP). Les résultats encore préliminaires semblent indiquer que la SSA peut être dérivée de la masse volumique et de grandeurs micro-mécaniques estimées à partir du signal du SMP avec un modèle statistique. Dans le deuxième cas, nous avons simulé l'albédo de surface à Summit à partir des profils mesurés de masse volumique et de SSA et du contenu en impuretés. Les résultats de cette étude ont démontré que l'albédo spectral peut être correctement simulé à l'aide d'un modèle de transfert radiatif et l'énergie absorbée par le manteau neigeux peut être estimée avec une précision d'environ 1%.
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Islam, G. "Evaluating reactivity and sorptivity of fly ash for use in concrete construction." Thesis, University of Dundee, 2012. https://discovery.dundee.ac.uk/en/studentTheses/94122abd-aa82-4c91-85ea-079505e14489.
Повний текст джерелаАнотація:
This thesis describes research carried out to investigate techniques for (i) rapidly assessing the reactivity of fly ash; and (ii) evaluating its interaction with air-entraining admixtures (AEAs), both with regard to use in concrete. The materials considered for the project included, 54 fly ashes from 8 UK sources, and an additional three materials from Bangladesh, covering a range of fineness, loss-on-ignition (LOI) and production conditions (run-of-station, carbon removed, air-classified, co-combustion, oxy-fuel technology); Portland Cements (PCs) from five UK sources with various properties (strength classes 32.5 R, 42.5 N and 52.5 N); laboratory grade hydrated and quick limes; and three commercial AEAs and a standard laboratory grade reagent (surfactant). The research examining fly ash reactivity considered activity index tests to BS EN 450 (BSI, 2005c) as the reference and investigated tests covering fly ash properties/providing measures of fly ash behaviour to rapidly assess this. These included (i) fly ash fineness (45 µm sieve residue, or LASER particle size distribution (PSD) parameters), LOI and flow properties; (ii) accelerated curing of PC and lime-based mortars (iii) lime consumption by fly ash when combined with PC in paste or suspension (Frattini) or from a saturated lime solution; (iv) various measures of fly ash chemical composition (based on oxide/mineralogical analysis); and (v) a quicklime slaking test. The test results were validated by strength tests with 100 mm concrete cube. Results of the above indicated good correlations between fly ash fineness, mortar flow/water requirement and (pozzolanic) activity index (standard or accelerated curing). However, fly ash reactivity and fresh properties appeared to be influenced by the properties of the test PC (e.g. chemical composition and fineness) and there is a need to take this into account during assessment. Generally, finer fly ashes gave better flow; however, there is an optimum fineness (d90 ~40 µm) for best performance, and which is similar to the fineness of the test PC. Strong correlations between the accelerated and standard cured PC-based mortar indicate the latter can be used to estimate the former taking account of the fly ash properties. In view of eliminating the effect of PC properties on reactivity, mortar tests with laboratory grade hydrated lime suggested potential for this. However, for better assessment, this approach requires further work to address issues relating to slower rates of strength gain and increased time requirements, although high temperature conditions were used for curing. Measuring Ca(OH)2 consumption from fly ash/PC paste or suspension agreed with the behaviour in mortar, but needs special instruments (e.g. TGA or XRF). A similar approach with saturated lime did not work well, despite several measures being taken to try and improve this. The oxide and mineralogical analysis results of fly ash did not give good correlations with activity index, but improved when a factor combining them with fineness was considered. The test results were validated in concrete and with air-classified fly ashes from single sources which gave clear trend/behaviour. The lime slaking test was found to be ineffective for identifying fly ash reactivity. The reactivity assessment results were validated by carrying out concrete strength tests. In general, more consistent trends were obtained for fly ash from single source as noted with mortar earlier. Methods adopted/developed to assess the interaction of fly ash with AEA included (i) the foam index test; (ii) acid blue 80 (AB80) dye adsorption test (spectroscopic method); and (iii) methylene blue test. High variability in foam index test results between different operators were noted, which reflected differences in the degree of shaking applied and difficulties in identification of the test end point. Adoption of an automatic shaker and determination of suitable test conditions reduced this by more than 50%. Reliable test procedures were also established for the AB80 dye adsorption method. The results obtained from these tests gave very good correlations with fly ash specific surface area and the AEA dose required (both with commercial AEAs and standard reagent) for achieving target air contents in mortar and concrete. The methylene blue dye test also gave good correlations with these parameters, but was less effective for low LOI fly ashes. Between laboratory tests were carried out at three UKQAA members and considered, LOI, fineness (45 µm sieve and LASER PSD), and activity index. The results gave good agreement with those obtained at the Concrete Technology Unit for this work and again emphasized the role of fly ash fineness on its reactivity. Overall, fly ash fineness was found to be the best means of rapidly assessing its reactivity. Some of the other methods considered gave promising behaviour but require further refinements. Therefore, it is suggested that in addition to 45 µm sieve residue, other types of fineness measurement (e.g. sub 10 µm quantities, d50 and d90) can be considered suitable alternatives to activity index. Similarly, foam index tests with the automatic shaker or the AB80 test method could both be used as fly ash physical requirement tests, or in production control for air-entrained concrete.
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Shin, Hyeon Ung. "Catalytic property of fiber media supported palladium containing alloy nanoparticles and electrospun ceramic fibers biodurability study." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1458404276.
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Dazon, Claire. "Expositions professionnelles aux nanomatériaux lors de la manipulation de poudres : relations entre les propriétés des poudres et les caractéristiques des aérosols émis." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0022.
Повний текст джерелаАнотація:
Ce travail s’inscrit dans le cadre de l’évaluation des risques professionnels aux nanomatériaux lors de la manipulation de poudres. Cette démarche est encore contrariée à la fois par l’absence d’une méthodologie de repérage des nanopoudres sur les lieux de travail, opérationnelle et accessible notamment aux hygiénistes, mais également de stratégies robustes de mesurage des expositions. La démarche de recherche a mis en œuvre une campagne expérimentale de caractérisation de poudres industrielles choisies pour leurs larges gammes de propriétés et représentatives des matériaux les plus rencontrés en France. La comparaison des méthodes de caractérisation de la taille des particules constituantes des poudres par microscopie électronique et de la mesure de la surface spécifique en volume (VSSA) a montré que cette dernière est un critère fiable pour repérer des nanopoudres. De fait, une proposition de stratégie expérimentale opérationnelle et prudente de caractérisation reposant en partie sur la détermination de la VSSA a été proposée. Les aérosols des poudres caractérisées dans la première partie de ce travail ont été générés avec les méthodes de dustiness (pulvérulence) du vortex shaker et du petit tambour rotatif, reconnues comme de plus en plus pertinentes pour l’évaluation qualitative des risques. Il ressort de ces expériences que les indices de dustiness selon la métrique surface sont intéressants pour comparer les poudres . L’humidité des matériaux influence significativement la pulvérulence dès lors que l’énergie mise en jeu dans les systèmes est réduite. Enfin, la pulvérulence des poudres est d’autant plus importante que la surface spécifique est élevéeThis work integrates a workplace exposure assessment context to nanomaterials related to powder handling. This step is still suffering a lack of a powder characterization strategy, operational and accessible to risk prevention professionals for nanopowder identification, but also recommendations for exposure measurements are required. However, nanomaterial powders are increasingly harnessed in numerous areas. The research carried out lead to an important powder characterization campaign. The studied materials covered a large set of properties and were representative of the most encountered powders in France. The comparison between the constituent particle sizes of powders by electron microscopy method and the volume specific surface area (VSSA) approach demonstrated this latter criterion is reliable for nanopowder identification according to the recommended european commission definition. So, an original, operational, cautious and accessible powder characterization strategy, putting a stress on the VSSA determination was proposed. Aerosols of the previous characterized powder were generated through the vortex shaker and small rotating drum dustiness methods, more and more recognized as relevant for qualitative workplace exposure assessments. The surface-based dustiness index is highlighted as an interesting metric to classify powders according to their dustiness. The powder moisture content has an impact on the dustiness when the energy involved is reduced. Finally, the more the surface area is, the dustier the powders are. Further research in line with the perspectives addressed should be conducted to deepen the whole results of this study
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Lima, Rita Karolinny Chaves de. "Perovskitas contendo lantânio, ferro e cobalto - melhoramento de propriedades texturais via síntese por nanomoldagem e avaliação como catalisadores na redução de NO com CO." Universidade Federal de São Carlos, 2008. https://repositorio.ufscar.br/handle/ufscar/3872.
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Mixed oxides with perovskite structure have high potential as catalysts in gas depollution processes and particularly in the abatement of nitrogen oxides (NOx). Such solids could be considered as a promising alternative for the replacement of noble metals based catalysts, whose use is predominant. Great flexibility of composition, easy synthesis, low cost and high thermal stability justify the special interest in these materials. However, the low specific surface areas (<10 m2/g) of these solids, when prepared by conventional methods, limit your use in catalytic processes. Some efforts have been made in order to overcome that disadvantage. Nevertheless, the preparation of high surface area ternary or multinary oxides is not easy once their synthesis is associated with solid state reactions carried out at high temperatures. Considering the discussed context, perovskites were obtained in this work by means of a conventional method or via sequencial nanocasting. In the first case, perovskites with LaFe1-xCoxO3 (x = 0, 0.2, 0.3, 0.4, 0.5 and 1) nominal compositions were prepared using the citrate method and nitrate salts as inorganic precursors. In the second case, LaFeO3 and LaFe0.6Co0.4O3 perovskites were obtained by nanocasting using Fluka 05120 activated carbon, Black Pearls 2000 black carbon (Cabot Corporation), and porous carbons nanocasted in Aerosil 200 pyrogenic silica and sílica-SBA-15 mesoporous molecular sieve. X-ray diffraction (XRD), N2 sorption measurements, X-ray fluorescence (XRF), hydrogen temperature programmed reduction (H2-TPR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry (TG) were used to characterize the studied solids. The catalytic activity of the prepared perovskites was evaluated in the reduction of NO to N2 with CO and in the oxidation of the latter compound to CO2. According to the obtained results, it was evident that in comparison with the conventional route, the nanocasting technique using carbons as hard template was efficient to obtain the pure perovskite phase with specific surface areas substantially higher (25 a 49 m2/g). The prepared perovskites were highly active and selective in the reduction of NO to N2 with CO, as well as in the oxidation of the latter compound to CO2. The most active samples were those whose B sites contain up to about 30 % Co. However, the activity of these catalysts decreases strongly with the presence of O2 or water steam. The La-Fe nanocasted binary perovskites showed, in the studied reactions, remarkable higher catalytic activity than the perovskite with the same composition prepared using the conventional method. The higher activity of these materials was related with the increase of their specific surface area. The nanocasted ternary perovskites with LaFe0.6Co0.4O3 composition, despite of the significant increase in their specific surface area, did not show a considerable increase in their activity. This result is in agreement with the behaviour of La-Fe-Co ternary perovskites, in which Co occupies a proportion of B sites greater than 30 %.
Óxidos mistos com estrutura perovskita apresentam alto potencial como catalisadores em processos de despoluição de gases e particularmente no abatimento de óxidos de nitrogênio (NOx). Tais sólidos são uma alternativa promissora para substituição de catalisadores à base de metais nobres, cujo uso é predominante. Vantagens como grande flexibilidade de composição, fácil síntese, baixo custo e elevada estabilidade térmica justificam o especial interesse por esses materiais. Contudo, as baixas áreas superficiais específicas desses sólidos (< 10 m2/g), quando sintetizados por métodos convencionais, limitam o seu uso em processos catalíticos. Algumas tentativas têm sido feitas no sentido de contornar essa desvantagem. No entanto, a obtenção de óxidos ternários ou multinários de alta área superficial específica é especialmente difícil, uma vez que sua síntese está associada a reações no estado sólido realizadas em temperaturas elevadas. Considerando o contexto discutido, neste trabalho foram obtidas perovskitas através de método convencional ou via nanomoldagem seqüencial. No primeiro caso, perovskitas com composição nominal LaFe1-xCoxO3 (x = 0; 0,2; 0,3; 0,4; 0,5 e 1) foram preparadas utilizando o método do citrato e sais de nitratos como precursores inorgânicos. No segundo caso, perovskitas LaFeO3 e LaFe0,6Co0,4O3 foram obtidas por nanomoldagem utilizando carbono ativado Fluka 05120, negro de fumo Black Pearls 2000 (Cabot Corporation), e carbonos porosos nanomoldados em sílica pirogênica Aerosil 200 e peneira molecular mesoporosa sílica-SBA-15. Difração de raios X (DRX), medidas de adsorção/dessorção de N2, fluorescência de raios X (FRX), redução com hidrogênio a temperatura programada (RTP-H2), microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), espectroscopia no infravermelho por transformada de Fourier (IV) e termogravimetria (TG) foram utilizadas para caracterizar os sólidos estudados. A atividade catalítica das perovskitas preparadas foi avaliada na redução de NO a N2 com CO e na oxidação desse último composto a CO2. De acordo com os resultados obtidos, ficou evidente que em comparação com a rota convencional, a técnica de nanomoldagem utilizando moldes de carbono foi eficiente na obtenção da fase perovskita pura com área superficial específica substancialmente maior (25 a 49 m2/g). As perovskitas preparadas foram altamente ativas e seletivas na redução de NO a N2 com CO, bem como na oxidação desse último composto a CO2, sendo mais ativas aquelas cujos sítios B contêm até cerca de 30 % de Co. A presença de O2 ou vapor de água, entretanto, reduz fortemente a atividade desses catalisadores. As perovskitas binárias La-Fe nanomoldadas apresentaram, nas reações estudadas, atividade catalítica consideravelmente superior a da perovskita com a mesma composição preparada pelo método convencional. A maior atividade desses materiais foi relacionada com o aumento da sua área superficial específica. As perovskitas nanomoldadas ternárias com composição LaFe0,6Co0,4O3, apesar do significativo aumento na sua área superficial específica, não apresentaram um aumento considerável na atividade, fato esse condizente com o comportamento de perovskitas ternárias La-Fe-Co, nas quais o Co ocupa uma proporção de sítios B superior a 30 %.
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Elsner, Antje. "Computergestützte Simulation und Analyse zufälliger dichter Kugelpackungen." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2010. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-61829.
Повний текст джерелаАнотація:
In dieser interdisziplinär geprägten Arbeit wird zunächst eine Übersicht über kugelbasierte Modelle und die algorithmischen Ansätze zur Generierung zufälliger Kugelpackungen gegeben. Ein Algorithmus aus der Gruppe der Kollektiven-Umordnungs-Algorithmen -- der Force-Biased-Algorithmus -- wird ausführlich erläutert und untersucht. Dabei werden die für den Force-Biased-Algorithmus als essenziell geltenden Verschiebungsfunktionen bezüglich ihres Einflusses auf den erreichbaren Volumenanteil der Packungen untersucht. Nicht nur aus der Literatur bekannte, sondern auch neu entwickelte Verschiebungsfunktionen werden hierbei betrachtet. Daran anschließend werden Empfehlungen zur Auswahl geeigneter
Verschiebungsfunktionen gegeben.
Einige mit dem Force-Biased-Algorithmus generierte Kugelpackungen, zum Beispiel hochdichte monodisperse Packungen, lassen den Schluss zu, dass insbesondere strukturelle Umbildungsvorgänge an solchen Packungen sehr gut zu untersuchen sind. Aus diesem Grund besitzt das Modell der mit dem Force-Biased-Algorithmus dicht gepackten harten Kugeln große Bedeutung in der Materialwissenschaft, insbesondere in der Strukturforschung.
In einem weiteren Kapitel werden wichtige Kenngrößen kugelbasierter Modelle erläutert, wie z. B. spezifische Oberfläche, Volumenanteil und die Kontaktverteilungsfunktionen. Für einige besonders anwendungsrelevante Kenngrößen (z. B. die spezifische Oberfläche) werden Näherungsformeln entwickelt, an Modellsystemen untersucht und mit bekannten Näherungen aus der Literatur verglichen.
Zur Generierung und Analyse der Kugelpackungen wurde im Rahmen dieser Arbeit die Simulationssoftware „SpherePack“ entwickelt, deren Aufbau unter dem Aspekt des Softwareengineerings betrachtet wird. Die Anforderungen an dieses Simulationssystem sowie dessen Architektur werden hier beschrieben, einschließlich der Erläuterung einzelner Berechnungsmodule.
An ausgewählten praxisnahen Beispielen aus der Materialwissenschaft kann die Vielfalt der Einsatzmöglichkeiten eines Simulationssystems zur Generierung und Analyse von zufälligen dicht gepackten Kugelsystemen gezeigt werden. Vor allem die hohe Aussagekraft der Untersuchungen in Bezug auf Materialeigenschaften unterstreicht die Bedeutung des Modells zufällig dicht gepackter harter Kugeln in der Materialforschung und verwandten Forschungsgebieten.
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Prehl, Janett, and Constantin Huster. "Morphology on Reaction Mechanism Dependency for Twin Polymerization." MDPI, 2019. https://monarch.qucosa.de/id/qucosa%3A34346.
Повний текст джерелаАнотація:
An in-depth knowledge of the structure formation process and the resulting dependency of the morphology on the reaction mechanism is a key requirement in order to design application-oriented materials. For twin polymerization, the basic idea of the reaction process is established, and important structural properties of the final nanoporous hybrid materials are known. However, the effects of changing the reaction mechanism parameters on the final morphology is still an open issue. In this work, the dependence of the morphology on the reaction mechanism is investigated based on a previously introduced lattice-based Monte Carlo method, the reactive bond fluctuation model. We analyze the effects of the model parameters, such as movability, attraction, or reaction probabilities on structural properties, like the specific surface area, the radial distribution function, the local porosity distribution, or the total fraction of percolating elements. From these examinations, we can identify key factors to adapt structural properties to fulfill desired requirements for possible applications. Hereby, we point out which implications theses parameter changes have on the underlying chemical structure.
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Diab, Walaa. "Étude des propriétés physico-chimiques et colloïdales du bassin de la rivière Litani, Liban." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0063/document.
Повний текст джерелаАнотація:
Cette thèse s’inscrit dans l’une des thématiques du «Laboratoire MCEMA», ayant pour projet l’étude physico-chimique des eaux de rivière et l’évaluation de l’influence des activités humaines sur la qualité de l’eau de la rivière LITANI. Ce travail est divisé en trois grandes parties. La 1ère partie a consisté d’étudier les paramètres physico-chimiques (T°, pH, EC, TSS, TDS, ion, etc.) au niveau de l’eau. La 2ème partie s’est concentrée autour de l’analyse des sédiments. Nous avons étudié les sédiments de la rivière de Litani, leurs natures, leurs granulométries, leurs propriétés physico-chimiques (charge et surface spécifique), leurs compositions ainsi que leurs contaminations métalliques. Alors que la troisième a été consacrée à l’étude de l’adsorption de certains polluants présents dans l'eau sur du charbon actif afin d’anticiper sur une étude d’avenir servant à traiter les eaux de cette rivière. Les résultats obtenus entrent dans un projet plus général visant l’étude de méthodes développées pour le traitement des eauxThis thesis is part of one of the focus of research at “MCEMA Laboratory” that concerns the physicochemical study of river water and the evaluation of the possible influence of human activities on the water quality of the Litani River. This work is divided into three principal parts. In the first one, we studied the physicochemical parameters (T, pH, EC, TSS, TDS, ions, etc.) of the water. The second part focuses on the sediment analysis. We studied the sediments of Litani River, their nature, size, composition, physicochemical properties (charge and specific surface area) with the metallic contamination. The third par is devoted the adsorption study of certain pollutants present in water on activated coal in order to anticipate on a future study on the treatment of the water river. The obtained results fall within a broader project on the study of developed methods on the treatment of wastewater
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Mikhailova, Olesia. "Studium možností efektivního využívání a aktivace aktivních příměsí do betonu." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226737.
Повний текст джерелаАнотація:
The theoretical part describes the admixtures that are used in cement replacement. Here also summarizes the findings on the influence of granulomentry, grain shape and fineness of admixtures on the density of the cement matrix. The practical part is experimentally verified the influence of fineness admixtures and grain size on the mechanical properties of concrete. Also, the rheological properties of cement are compared with admixtures depending on the type and dosage and time.
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Lédl, Matěj. "Návrh koncepce využívání mikropříměsí pro betony vysokých užitných vlastností." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226739.
Повний текст джерелаАнотація:
The modern, contemporarily used cement composite types make use of various additives. This diploma thesis is focused on designs of mortars that have been enriched with micro and nano additives, which lead to higher mechanical strength through optimized grading of mortar mixes. This thesis also evaluates the influence of material properties on resulting properties of mortars in fresh and hardened state.
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Augustine, Robin. "Electromagnetic modelling of human tissues and its application on the interaction between antenna and human body in the BAN context." Phd thesis, Université Paris-Est, 2009. http://tel.archives-ouvertes.fr/tel-00499255.
Повний текст джерелаАнотація:
Les réseaux BAN (Body Area Network) révolutionnent le concept de la surveillance et de la prise en charge à distance de la santé du patient. Le BAN fournit des informations sur l'état de santé du patient en temps réel quelque soit l'endroit où il se trouve. Dans le « télé monitoring », des capteurs de mouvement, de respiration ou du rythme cardiaque placés à l'intérieur ou sur le corps humain transmettent des données via le réseau sans fil constituant le BAN, une antenne étant associée à chaque nœud du réseau. La communication peut être in/on, on/on ou on/off selon que les antennes sont placées à l'intérieur, sur ou à l'extérieur du corps. Le développement des BAN nécessite la réalisation de modèles (ou fantômes) simulant au mieux les propriétés électromagnétiques du corps humain. Des antennes portables, miniaturisées doivent être réalisées avec des contraintes d'intégration d'une part (aux vêtements, à des objets type montre ou badge), des contraintes de résistance ou de prise en compte de l'influence du corps d'autre part. La réduction de l'impact des antennes sur les tissus en terme de SAR (Specific Absorption Rate) doit également être considérée. Dans ce travail, l'objectif est de développer des fantômes valables pour les communications dans et sur le corps. Les matériaux de base sélectionnés sont d'origine biologique (biocéramiques et biopolymères) avec des propriétés proches de celles des tissus humains. Ces fantômes étant biocompatibles, ils sont essentiellement non toxiques alors que les fantômes usuels le sont en général. D'autre part, différents types d'antennes conformables, fonctionnant dans la bande ISM 2.4 GHz ont été développées et étudiées dans la perspective du BAN. Les antennes voient leur adaptation et leur efficacité chuter au contact ou à proximité du corps, ce qui constitue un écueil majeur pour établir une bonne communication. Différentes méthodes permettant de réduire l'influence du corps (plan de masse à l'arrière, surface haute impédance, feuille de ferrite polymère) sont testés et leurs avantages et inconvénients développés. Des mesures de SAR permettent aussi de démontrer l'efficacité de ces méthodes sur la réduction de la puissance absorbée par les tissus. Au final, ce travail apporte une contribution à l'étude théorique et expérimentale de l'interaction entre corps humain et antenne dans le cadre des réseaux BAN appliqués à la télésurveillance de la santé
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Tunková, Martina. "Městské lázně." Master's thesis, Vysoké učení technické v Brně. Fakulta architektury, 2010. http://www.nusl.cz/ntk/nusl-215713.
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Tsai, Robert Edison. "Mass transfer area of structured packing." Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-05-1412.
Повний текст джерелаАнотація:
The mass transfer area of nine structured packings was measured as a function of liquid load, surface tension, liquid viscosity, and gas rate in a 0.427 m (16.8 in) ID column via absorption of CO₂ from air into 0.1 mol/L NaOH. Surface tension was decreased from 72 to 30 mN/m via the addition of a surfactant (TERGITOL[trademark] NP-7). Viscosity was varied from 1 to 15 mPa·s using poly(ethylene oxide) (POLYOX[trademark] WSR N750). A wetted-wall column was used to verify the kinetics of these systems. Literature model predictions matched the wetted-wall column data within 10%. These models were applied in the interpretation of the packing results. The packing mass transfer area was most strongly dictated by geometric area (125 to 500 m²/m³) and liquid load (2.5 to 75 m³/m²·h or 1 to 30 gpm/ft²). A reduction in surface tension enhanced the effective area. The difference was more pronounced for the finer (higher surface area) packings (15 to 20%) than for the coarser ones (10%). Gas velocity (0.6 to 2.3 m/s), liquid viscosity, and channel configuration (45° vs. 60° or smoothed element interfaces) had no appreciable impact on the area. Surface texture (embossing) increased the area by 10% at most. The ratio of effective area to specific area (a[subscript e]/a[subscript p]) was correlated within limits of ±13% for the experimental database: [mathematical formula]. This area model is believed to offer better predictive accuracy than the alternatives in the literature, particularly under aqueous conditions. Supplementary hydraulic measurements were obtained. The channel configuration significantly impacted the pressure drop. For a 45°-to-60° inclination change, pressure drop decreased by more than a factor of two and capacity expanded by 20%. Upwards of a two-fold increase in hold-up was observed from 1 to 15 mPa·s. Liquid load strongly affected both pressure drop and hold-up, increasing them by several-fold over the operational range. An economic analysis of an absorber in a CO₂ capture process was performed. Mellapak[trademark] 250X yielded the most favorable economics of the investigated packings. The minimum cost for a 7 m MEA system was around $5-7/tonne CO₂ removed for capacities in the 100 to 800 MW range.text
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Teixeira, Sandra Maria da Silva. "Bioactive ceramics with high specific surface area for osteoconduction." Tese, 2008. http://hdl.handle.net/10216/12336.
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Teixeira, Sandra Maria da Silva. "Bioactive ceramics with high specific surface area for osteoconduction." Doctoral thesis, 2008. http://hdl.handle.net/10216/12336.
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Wang, Cheng-Hua, and 王誠華. "A study on the preparation hausmannite powder with high specific area surface." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/jecxf2.
Повний текст джерелаАнотація:
碩士國立臺北科技大學
材料科學與工程研究所
97
This research focuses mainly on the preparation of haussmannite (Mn3O4) powders with high specific surface area. The whole process comprised of chemical precipitation and oxidation in solution. At first, MnCl2 was recovered by CBM catalyst and reacted with alkaline solution like NH4OH or NaOH. One intermediate product, Mn(OH)2,was formed. If H2O2 was subsequently added into the solution, Mn3O4 powders were obtained from the oxidation of Mn(OH)2. Based on Taguchi method, one L9 orthogonal array was designed and implemented accordingly. A set of relatively practicable experimental conditions was decided and served as a basis for further adjustment of parameters. The prepared samples were compared with four commercial products by means of 3.4.1 XRD分析 39 3.4.2 掃描式電子顯微鏡分析 39 3.4.3 雷射粒徑分析儀 (Mastersizer 2000) 39 3.4.4 發射光譜分析(ICP- Optima 2000) 40 3.4.5 離子層析儀(IC- DIONEX 2008 ) 40 3.4.5 BET比表面積測定儀(ASAP 2020) 41 第四章 結果與討論 42 4.1 使用不同鹼液合成Mn3O4粉末比較 42 4.1.1 實驗步驟差異 42 4.1.2 雷射粒徑分析 43 4.1.3 成份分析 46 4.1.4 XRD結構分析 46 4.1.5 SEM 粉體形貌觀察 48 4.1.6 綜合評估 49 4.2 田口實驗設計-L9直交試驗分析 50 4.2.1 L9直交表實驗統計分析 50 4.2.1.1 L9直交表實驗統計分析----比表面積 51 4.2.1.2 L9直交表實驗統計分析----Ｍn差值 55 4.2.2 反應後之溶液pHXRD, SEM, and ICP. The chemical composition was titrated by EDTA. Furthermore, the specific surface area and the distribution of particle size were also analyzed. . It was found that the specific surface area of Mn3O4 powders reaches its maximum (26 m2/g) when the concentrations of MnCl2 and NaOH were 1M and 2.4M, respectively.
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Wang, Yu-Xuan, and 王于瑄. "High specific surface area TiO2 microspheres as anodes for Na+ ion battery applications." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/64478216263434784730.
Повний текст джерелаАнотація:
碩士國立交通大學
應用化學系碩博士班
104
Among the various battery technologies, lithium ion battery (LIB) is quite mature but there were questions regarding increasing prices of Li mineral reserves and disadvantage in a few specific locations. However, sodium is substantially less expensive, more abundant than lithium which let sodium ion batteries have been considered as a desirable alternative to LIB. Among the known materials, TiO2 is regarded as powerful candidates due to the non-toxic, low cost, and small volume change during Na+ ion insertion. In this study, facile route was established to synthesize high specific surface area TiO2 microspheres by using amino acids (arginine and monosodium glutamate) as the assistances. The solvothermal method was carried out in a heated Teflon stainless-steel autoclave. The as-synthesized TiO2 were further processed at 400 °C under air to generate the nanosheet spheres (NS) and solid spheres with nanosheets (SS). They were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and nitrogen adsorption-desorption analysis. The isotherms revealed specific surface areas were 116 and 91 m2/g, respectively. The products were used as anodes for Na ion battery. The cells of NS showed a reversible capacity 145 mAh/g after 100 discharge/charge cycles at a current density of 0.1 C (1 C = 335 mA/g). The anode reached 85 mAh/g and 62 mAh/g under high rates, 2 C and 5 C respectively. The results showed that high specific surface area TiO2 exhibited good reversible capacity and cyclic stability as promising candidates as anodes for sodium ion batteries.
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Chang, Yi-Chun, and 張亦諄. "Bio-ingredients assisted formation of high specific surface area TiO2 for Li ion battery applications." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/18541547689444420511.
Повний текст джерелаАнотація:
博士國立交通大學
應用化學系碩博士班
103
In this study, microspheres (MS), nanosheet spheres (NS), solid spheres with nanosheets (S-NS), channel-like (CT) and spongy-like porous TiO2 (PT) were synthesized with the assistance of the bio-ingredients as templates. We have proposed reaction pathways and the battery performance were also investigated. First, facile route was established to synthesize high specific surface area TiO2 microspheres using basic amino acid (arginine or monosodium glutamate) as the templates. Titanium tetrabutoxide Ti(OBu)4 was used as the TiO2 precursor and absolute ethanol as the solvent. The solvothermal synthesis was carried out in a heated Teflon stainless-steel autoclave. The as-formed TiO2 precursor solid was further processed at 400 °C under air to generate the TiO2 microspheres (MS), nanosheet spheres (NS) and solid spheres with nanosheets (S-NS). They were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption-desorption analysis. The nitrogen adsorption-desorption isotherms revealed specific surface areas ranging from 30 to 122 m2/g. The products were used as an anode material for Li ion battery. The cells showed remarkable performance that the capacity of the the anode reached 167 mAh/g and 132 mAh/g under high charge/discharge rates, 5 C and 10 C respectively. They also demonstrated good cycling stability at varied charge/discharge rates. Second, we employed a simple sol−gel process to fabricate TiO2 precursors by reacting titanium tetraisopropoxide (TTIP, Ti(OiPr)4), instant yeast, and glucose/starch molecules in an aqueous solution. Remarkably, the yeast cells maintained their physiological activities and occurred respirations in the aerobic reaction. Their respirations produced CO2 and H2O as the metabolites. The evolution of CO2 produces numerous channels in the inorganic matrix. After further processing, porous channel-like TiO2 (CT) was prepared. (macropore size: 1 – 3 µm) The BET/BJH results revealed specific surface areas ranging from 34 to 125 m2/g, and mesoporous size distributions (4 – 100 nm). In addition, potential applications of the as-prepared TiO2 in Li ion batteries were explored. Finally, spongy-like porous TiO2 (PT) was synthesized by using yeast and glucose as the pore forming templates. TiCl4 in C2H5OH(l) containing NH4OH(aq.) was polymerized in the presence of instant yeast and glucose. The organic–inorganic hybrid precursor was further processed to generate macroporous anatase TiO2 (pore size: 2 – 3 µm) with mesopores (4 – 70 nm). The porous TiO2 was coated with a thin layer of carbon by chemical vapour deposition to generate the hierarchical C/TiO2 composite material. The porous products were investigated as anode materials for Li-ion batteries. The capacities of the hierarchical C/TiO2 electrode material remained 180 mAh/g and 142 mAh/g under high charge/discharge rates of 5 C and 10 C, respectively. It demonstrated good cycling stability of 318 mAh/g at 0.1 C at various discharge–charge rates. The excellent performance is attributed to the high specific surface areas and open spaces of the C/TiO2 allowing effortless intercalation/de-intercalation of Li ions.
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HSU, WEI-HSIN, and 徐偉心. "Preparation and application of high specific surface area activated carbon using phenolic resin as precursor." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/bx2pvp.
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Chang, Chih-Wei, and 張智偉. "Process Development and Reaction Mechanism of High Specific Surface Area and High Alpha-Phase Content Si3N4 Powder." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/87483477121447703692.
Повний текст джерелаАнотація:
博士國立成功大學
化學工程學系碩博士班
97
A combustion synthesis method for the synthesis of α- Si3N4 from a reactant compact composed of Si, NaN3 and NH4X and wrapped up with an igniting agent was investigated. Wrapping the reactant compact with the igniting agent (i.e., a mixture of Ti and C powders) was found necessary for the synthesis of Si3N4. In addition to NH4Cl, other ammonium halides (i.e., NH4F, NH4Br and NH4I) were found to be capable of catalyzing the synthesis reaction and NaN3 was considered to exert an essential effect on the combustion synthesis reaction other than functioning as a solid state nitrogen source. It was proposed that Na vapor produced by decomposition of NaN3 reduces SiXX (formed by reaction of Si and NH4X), promoting the nitridation reaction to form Si3N4. Carbothermal reduction and nitridation synthesis of Si3N4 was also investigated by using precursor powders prepared by a solution combustion synthesis method. Glycine or urea (fuel), ammonium nitrate (oxidizer), silicic acid (Si source) and sucrose (major carbon source) were dissolved completely in water. This solution was dried and then heated to undergo the solution combustion synthesis reaction, resulting in a homogeneous mixture of nano sized carbon and SiO2 particles, which possessed with high specific surface areas and could be used as the precursor powder for the carbothermal reduction and nitridation synthesis of Si3N4. When the carbothermal reduction and nitridation reaction was carried out at 1425-1450℃ for 4hr, formation of Si3N4 can be detected only when the C/SiO2 weight ratio is greater than ~ 2.0. The Si3N4 yield increases rapidly as the C/SiO2 weight ratio is increased from ~ 2.0 to 2.8 and decreases with further increase in the C/SiO2 ratio. The α phase content increases with increasing C/SiO2 weight ratio and decreases with increasing temperature. Depending on the C/SiO2 ratio, a Si3N4 yield of ~ 80 % and an α phase content of ~ 90 wt% could be obtained.