Dissertations / Theses on the topic 'Fibre de carbonate de calcium'
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1
Longkaew, Khansinee. "Preparation of calcium carbonate particles for application in natural rubber composites." Electronic Thesis or Diss., Le Mans, 2024. https://cyberdoc-int.univ-lemans.fr/Theses/2024/2024LEMA1003.pdf.
Abstract:
Cette recherche vise à synthétiser différents types et formes de particules de carbonate de calcium (CaCO3) à l'échelle submicrométrique et nanométrique, et à étudier leurs applications en tant que charges renforçantes pour les composites de caoutchouc naturel (NR). L'étude a donc été divisée en deux parties. Premièrement, la procédure de préparation des particules de CaCO3 était basée sur la méthode de précipitation en solution entre les ions carbonate (CO32-) et les ions calcium (Ca2+). La deuxième partie concerne l'étude des propriétés mécaniques des composites NR/CaCO3. La première partie a commencé par la précipitation de (NH4)2CO3 et de CaCl2 dissous dans 50 % en poids de saccharose comme milieu aqueux. Cette condition a entraîné la formation de CaCO3 sphérique, ce qui a été mis en évidence au microscope électronique à balayage (MEB). L'analyse au microscope électronique à transmission (TEM) a révélé une taille de particule de 0,42 ± 0,14 µm avec un rapport d'aspect d'environ un. Lorsque la réaction de précipitation s'est produite en présence d’huile d'olive saponifiée, la propriété de surface du CaCO3 est passée d'hydrophile (angle de contact avec l'eau de 28 ± 2°) à superhydrophobe (angle de contact avec l'eau de 163 ± 2°). Les phases polymorphes typiques de CaCO3 ont été caractérisées par diffraction des rayons X (DRX), infrarouge à transformée de Fourier par réflexion totale atténuée (ATR-FTIR) et spectroscopie Raman. Ces techniques ont révélé que le CaCO3 sphérique non traité et traité représentait environ 99 % du polymorphe de la vatérite. Dans le processus de précipitation utilisant des solutions aqueuses 1 M de Na2CO3 et 1 M de CaCl2 réalisé à 80 ± 1 °C, du CaCO3 sous forme de fibres agglomérées a été obtenu avec un rapport d'aspect compris entre 8 et 9. Le CaCO3 superhydrophobe sous cette forme a également été synthétisé avec succès. L'angle de contact avec l'eau des fibres traitées et non traitées est respectivement de 29 ± 2° et 167 ± 2°. De plus, le CaCO3 sphérique dispersé dans l'eau à 80°C a donné naissance à des nanoparticules de CaCO3 en forme de fibre qui ont été obtenues via la transformation de la vatérite sphérique en aragonite nanofilaire longue avec le rapport d'aspect le plus élevé de 156,9 par rapport aux autres formes de CaCO3. La fibre CaCO3 non traitée était hydrophile avec un angle de contact avec l'eau de 31 ± 1°, tandis que la fibre CaCO3 traitée avec du savon donnait un angle de contact avec l'eau de 165 ± 5° ; elle était donc superhydrophobe similaire aux autres polymorphes de CaCO3 synthétisés. La DRX a révélé que le CaCO3 en forme de fibres, non traitées et traitées, contenait en majorité de l'aragonite et en moindre mesure de la vatérite et de la calcite. La stabilité thermique de différents types de CaCO3 a également été évaluée par analyse thermogravimétrique (TGA). Les résultats ont montré la calcination des cristaux de CaCO3, du saccharose et du savon. La deuxième partie a consisté à incorporer le CaCO3 préparé (0, 5, 10, 20, 40, à 60 pce) dans du latex naturel (NR). Il a été constaté que la vatérite CaCO3 non traitée et traitée était stable dans le milieu latex NR. De plus, les polymorphes du CaCO3 non traité et traité en forme de fibres étaient également stables dans leurs formes lorsqu'ils étaient ajoutés au latex NR. Les propriétés mécaniques du NR/CaCO3 comprenaient la résistance à la traction, l'allongement à la rupture, la résistance à la déchirure et la dureté Shore A. Il a été constaté que la résistance à la traction des composites NR/CaCO3 augmentait lorsque la charge de CaCO3 augmentait. La résistance à la traction du NR s'est améliorée de 22,68 ± 2,22 MPa de NR pur jusqu'à 23,94 ± 0,97 MPa lorsque des poudres de CaCO3 sphériques non traitées (20 phr) ont été ajoutées, et à 25,28 ± 0,80 MPa de CaCO3 sphérique traité (20 phr) de NR rempli. (...)This research aims to synthesize different types and shapes of calcium carbonate (CaCO3) particles at a submicrometric and nanoscale, and investigate their applications as reinforcing fillers for natural rubber (NR) composites. The study was therefore divided into two parts. Firstly, the preparation procedure of CaCO3 particles was based on the solution precipitation method between carbonate ions and calcium ions. The second part focused on investigating the mechanical properties of NR/CaCO3 composites. The first part started with the precipitation of (NH4)2CO3 and CaCl2 dissolved in 50% by weight of sucrose as the aqueous medium. This condition resulted in spherical CaCO3 with particle size of 0.42±0.14 µm with an aspect ratio of about one. When the precipitation reaction occurred in the presence of olive soap, the surface property of the CaCO3 was changed from hydrophilic (water contact angle of 28±2o) to superhydrophobic powders (water contact angle of 163±2o). The typical polymorphic phases of CaCO3 were characterized. The results revealed that both untreated and treated spherical CaCO3 were about 99% of the vaterite polymorph. In the precipitation process using Na2CO3 and CaCl2 aqueous solutions performed at 80±1C, bundle-liked CaCO3 was obtained with an aspect ratio in the range of 8–9. The superhydrophobic bundle-liked CaCO3 was also successfully synthesized by soap treatment. The water contact angle of untreated and treated bundle-liked are 29±2o, and 167±2o, respectively. Furthermore, the spherical CaCO3 dispersed in water at 80C resulted in the fiber-shaped CaCO3 nanoparticles which were achieved via the polymorph transformation from spherical vaterite to long nano-wired aragonite with the highest aspect ratio of 156.9. The untreated fiber CaCO3 was hydrophilic with a water contact angle of 31±1o, while the treated fiber CaCO3 with soap resulted in 165±5o of water contact angle, hence it was superhydrophobic similar to other synthesized CaCO3 polymorphs. The XRD revealed that the untreated and treated bundle-liked and fiber-shaped CaCO3 contained the majority of aragonite followed by vaterite and calcite polymorphs. The second part was carried out to incorporate the prepared CaCO3 (0,5,10,20,40,60 phr) in NR latex. It was found that the CaCO3 polymorphs were stable in the NR latex medium. The mechanical properties of NR/CaCO3 included tensile strength, elongation at break, tear strength, and hardness Shore A. It was found that the tensile strength of NR/CaCO3 composites increased when CaCO3 loading was increased. The tensile strength of NR improved from 22.68±2.22 MPa of neat NR up to 23.94±0.97 MPa when untreated spherical CaCO3 powders (20 phr) were added, and to 25.28±0.80 MPa of treated spherical CaCO3 (20 phr) filled NR. The maximum tensile strength of NR/untreated bundle-liked CaCO3 was 30.59±3.50 MPa at 40 phr of loading while 31.51±1.02 MPa of NR/treated bundle-liked CaCO3 at filler loading 20 phr was obtained. The treated CaCO3-filled NR vulcanizates gave higher tensile strength than the untreated ones. This was caused by better compatibility of filler dispersion between the hydrophobicity of treated CaCO3 and hydrophobic property of NR. As a result, it was found that the NR filled with untreated fiber CaCO3 particle provided the highest tensile strength of 31.66±1.80 MPa at 10 phr of filler loading, over other types of CaCO3. The nanoparticle, large surface area, and high aspect ratio of fiber/ long nano wired of CaCO3 enhanced the interfacial adhesion between CaCO3 and NR matrix which could transfer stress from rubber to filler effectively during stretching. This resulted in the reinforcing efficacy of the fiber CaCO3. In summaroze, the prepared CaCO3 powders have the potential to broaden their application not only as diluents or additives but also as reinforcing agents
2
Reygrobellet, Jean-Noël. "Recyclage de composites fibres de verre-polyester insaturé-carbonate de calcium par réincorporation dans des matrices thermoplastiques." Montpellier 2, 2000. http://www.theses.fr/2000MON20038.
3
Safa, Ali Ibrahim 1953. "Catalytic Calcination of Calcium Carbonate." Thesis, North Texas State University, 1985. https://digital.library.unt.edu/ark:/67531/metadc330965/.
Abstract:
The calcination of calcium carbonate in a cement or a lime kiln uses approximately two to four times the theoretical quantity of energy predicted from thermodynamic calculation depending upon the type of the kiln used (1.4 x 10^6 Btu/ton theoretical to 6 x 10^6 Btu/ton actual). The objective of this research was to attempt to reduce the energy required for the calcination by 1. decreasing the calcination temperature of calcium carbonate, and/or 2. increasing the rate of calcination at a specific temperature. Assuming a catalytic enhancement of 20 percent in the industrial applications, an energy savings of 300 million dollars annually in the United States could be reached in the cement and lime industries. Three classes of compounds to date have shown a positive catalytic effect on the calcination of calcium carbonate. These include alkali halides, phospho- and silico-molybdate complexes, and the fused carbonates system.
4
Xu, Yaling Pelton Robert H. "Calcium carbonate adhesion in paper /." *McMaster only, 2005.
5
Loste, Madoz Eva. "Morphological control of calcium carbonate." Thesis, Queen Mary, University of London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398861.
6
Daly, P. J. "Dissolution kinetics of calcium carbonate." Thesis, University of Liverpool, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372693.
7
Picard, Quentin. "Biomatériaux hybrides : tissu de fibres de carbone / phosphates de calcium : synthèse, caractérisation et biocompatibilité." Thesis, Orléans, 2015. http://www.theses.fr/2015ORLE2073/document.
Abstract:
Ce travail a consisté à élaborer un biomatériau hybride constitué d’un tissu de fibres de carbone (TFC) revêtu de phosphates de calcium (CaP) déposés par un procédé de sono-électrodéposition et à étudier l’influence des paramètres expérimentaux sur la composition chimique, la microtexture et la structure des revêtements phosphocalciques, ainsi que la biocompatibilité in vitro du biomatériau hybride. La densité de courant s’est avérée être un paramètre important. Pour de fortes densités de courant (≥ 100 mA/g), un régime d’électrolyse rapide de l’eau entraîne la formation d’un dépôt aciculaire d’hydroxyapatite déficitaire en calcium (CaD-HAP) carbonatée avec la présence éventuelle d’une phase de calcite. Pour de faibles densités de courant (≤ 50 mA/g), un régime d’électrolyse lent de l’eau entraîne la formation d’un dépôt plaquettaire de CaD-HAP carbonatée issu de l’hydrolyse in situ du phosphate octocalcique plaquettaire préalablement précipité. Pour l’ensemble des dépôts, les particules sont constituées d’un coeur de CaD-HAP carbonatée de structure ordonnée et d’une surface hydratée de CaD-HAP carbonatée de structure désordonnée qui résulte de l’existence d’une zone de sursaturation lors de la précipitation des CaP. La sono-électrodéposition se révèle être un procédé versatile capable d’orienter la synthèse des phases de CaP, avec pour une faible densité de courant appliquée l’obtention d’un dépôt biomimétique comparable à la partie minérale du tissu osseux obtenue par le processus d’ostéogénèse naturelle. Des tests de viabilité in vitro réalisés avec des ostéoblastes humains primaires ont montré que la nanoporosité et le caractère hydrophile des TFC n’impactent pas la biocompatibilité et que les paramètres tels que le précurseur des fibres, l’ensimage et/ou la forme lobée des fibres semblent favoriser l’adhésion et la prolifération des cellulesThis work is focused on the synthesis of a novel hybrid biomaterial made of carbon fibers cloth (CFC)/ calcium phosphates (CaP) using the sono-electrochemical technique and the study of the influence of experimental parameters on the chemical composition, microtexture and structure of CaP deposits and on in vitro biocompatibility. Current density is shown to be a crucial parameter. Specifically, at high current densities ((≥ 100 mA/g), the fast water electrolysis rate leads to a needle-like deposit consisting in a major phase of carbonated calcium deficient hydroxyapatite (CaD-HAP) mixed with a calcium carbonate phase. At low current densities (≤ 50 mA/g), the slow water electrolysis rate generates a plate-like carbonated CaD-HAP phase, coming from the in situ hydrolysis of a former octacalcium phosphate phase. Whatever the experimental conditions, particles of the deposits consists in a carbonated CaD-HAP core showing an ordered structure, surrounded by a hydrated and disordered carbonated CaD-HAP surface layer which results of the formation of oversaturated domains during CaP precipitation. Sono-electrodeposition is shown to be a versatile process able to control the nature of CaP phases. Especially, at low current density a biomimetic CaP deposit is obtained, similar to the mineral part of bones produced during natural osteogenesis. In vitro biologic tests using primary human osteoblasts showed that the nano-porosity and hydrophilicity of the carbon fibers do not affect the biocompatibility and that fiber precursor, sizing and lobe shaped fibers seems to favor adhesion and proliferation of human cells
8
Lam, Siu Kai Raymond. "Calcium carbonate deposition in synthetic systems." Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492548.
Abstract:
The work presented in this thesis is concerned with the nucleation and growth of calcium carbonate (CaCO3). CaCO3 deposition on fabrics during the washing process is a major problem, causing fabric damage and harshness. It is important to understand the mechanism of CaCO3 nucleation in order to control its precipitation. The extent of crystallisation on different model fabrics was first investigated in order to understand the principal factors governing the crystal deposition. Surface topography of the fabrics such as the presence of steps and kinks was found to be the dominating factor for the nucleation of CaC03 crystals under the experimental conditions.
9
D'Souza, Sharon Marie. "Molecular imprinting of calcium carbonate crystals." Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428182.
10
Wang, Q. "A computational study of calcium carbonate." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1333995/.
Abstract:
This thesis presents the results of computer simulation studies of impurity incorporation in calcite and the aggregation of calcite particles, using a combination of classical computational techniques based on interatomic potentials, namely molecular mechanics and molecular dynamics simulations. Firstly, the atomistic simulation techniques have been employed to investigate the thermodynamics of mixing in calcite with seven divalent cationic impurities (Mg2+, Ni2+, Co2+, Zn2+, Fe2+, Mn2+ and Cd2+), based on the calculation of all inequivalent site occupancy configurations in 2 × 2 × 1 and 3 × 3 × 1 supercells of the calcite structure. In addition to the enthalpy of mixing, the configurational entropy and mixing free energy have also been calculated, providing an insight into the mixing behaviour as a function of the temperature for a series of carbonate solid solutions. The calculations have revealed that the solubility of the cationic impurities in calcite is largely related to the cationic coordination distance with oxygen. Secondly, the aggregation process has been investigated implementing classical computational techniques, and especially the interaction of a calcite nanoparticle with the major calcite surfaces, where the adhesion energy and optimised geometries of a typical calcite nanoparticle on different surfaces in vacuum and aqueous environment have been calculated. The results show the orientation of a nanoparticle is a key factor that effects the interactions, besides the size and structure of the nanoparticle. The most stable aggregated configuration occurs when the lattices of the nanoparticle and the surface are perfectly aligned. Finally, a number of symmetric calcite tilt grain boundaries have been constructed to act as models of two calcite nanoparticles, after collision has occurred but before growth has a chance to commence. Molecular dynamics simulations were then employed to study the stability of these tilt grain boundaries and the growth of a series of calcium carbonate units at the contact points in the pure and hydrated calcite tilt grain boundaries. The calculation have proved that the initial incorporation of a CaCO3 unit is preferential at the obtuse step in a grain boundary, and the growth velocity of the acute step is 1.3 to 2.1 times higher than that of the obtuse step, once the initial growth unit has been deposited on the steps. This study has evaluated the conditions required for the growth of new calcium carbonate materials in the calcite tilt grain boundaries.
11
MacAdam, Jitka. "Calcium carbonate scale formation and control." Thesis, Cranfield University, 2005. http://dspace.lib.cranfield.ac.uk/handle/1826/10544.
Abstract:
Scale formation in domestic
appliances is a widespread problem in the UK. This project
has focussed on calcium carbonate scale formation in electric showers. A literature
survey identified that CaCO; deposition on heated surfaces could be controlled by
chemical or non chemical methods, each with various degrees of effectiveness. One of
the most effective control methods was the addition of chemicals, although this may not
be the most suitable
option for the domestic environment. So here the chemical
inhibitors tested were used for a benchmark for all the other studies. Two
laboratory
tests were involved t allow u to
study CaCO; precipitation and scale formation. The
effect of chemical additives on CaCO; precipitation was investigated using a jar tester.
The
longest delay to precipitation was obtained by polyacrylic acid dosing, closely
followed
by zinc. To study CaCO; formation on a heated surface, a rapid scaling test
was
developed. This test was conducted at 42°C and 70°C to examine and compare a
range of treatment options, including chemical dosing, electrolytic, magnetic and
electronic water
conditioning and low fouling surfaces. From the options examined, the
most successful was
electrolytic dosing of zinc/copper media with over 95% reduction
in
scaling at both temperatures. Further, the use of low fouling surfaces, such as
Diamond - like carbon
coating could also potentially be used in electric showers.
Reduction in
scaling achieved on this surface was on average 68%. Surface properties
of the materials were
analysed using an atomic force microscope and their relationship
with the
scaling behaviour of the surfaces examined. The scaling rates at both
temperatures typically increased with increasing adhesion force but no clear relationship
was found between the
roughness of the surfaces and their scaling behaviour. The
relationship between CaCO3 precipitation and scale formation in synthetic solution and
natural hard water was also
explored here. The induction period in natural hard water
was 55 minutes
longer and the scaling rate 40% lower than i synthetic hard solution of
similar
composition. In addition, two shower test rigs, one based at Cranfield University
and the other in
Attleborough were used in this study. These were used primarily to
enable the
compilation of background data on scale formation in electric showers,
where it was found that the
design of the unit has a significant influence on the scale
formation. The test
rig was also used t test the strategies identified during the
laboratory phase of the work. It was found that electrolytic zinc dosing reduced scaling
by up to 54%, depending on the shower unit design.
12
Finney, Aaron R. "Nucleation and dehydration of calcium carbonate." Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/66884/.
Abstract:
Great challenges remain in our understanding of biomineralisation which impede the design and production of a new class of materials. Recent studies have suggested that calcium carbonate clusters are stable in solution before nucleation, and that these participate in the formation of amorphous calcium carbonate (ACC). The structure and stability of these clusters has not been fully determined. Furthermore, the dehydration of stable ACC before crystallisation remains ambiguous. Exhaustive computational searches have been carried out to provide a sample of clusters up to the sizes suggested for particles persisting before nucleation. A large sample of clusters were simulated at high concentration in water using molecular dynamics (MD). The results suggest that cluster stability is a balance between ionic coordination and ion hydration. At high concentration clusters are generally dynamic in the lower limit of stability, forming chains to which ions frequently aggregate and dissolve. Free energy calculations showed a transition in the favoured coordination levels with cluster size. One dimensional Umbrella Sampling calculations showed that at small sizes a collection of clusters with low average cation–anion coordination were thermodynamically stable. For systems containing sixty ions and above, more compact clusters with internal water, close to the stoichiometries identified for stable hydrated ACC in vivo, were lower in free energy. From MD simulations at experimental concentrations and pH, while dynamic ordering was found, ion pairs dominated in solution and the largest clusters observed contained no more than four ions. These findings, combined with the data at high concentration, allow for a re-evaluation of the proposed nucleation mechanisms for calcium carbonate from solution. ACC simulations identified water–filled channels within the ionic framework. Percolating clusters were found when H2O/CaCO3 was greater than 0.75–0.8. The ACC system fitted well with the percolation theory on a simple cubic site lattice for water, and critical exponents showed a good fit to the theoretical values. Non–standard diffusion was found for water, with a “jump” mechanism of diffusion observed and a cascade of molecule displacements within channels. This original result allows new light to be shed on the dehydration mechanism of ACC.
13
Mitchell, Colin Raymond. "Numerical Simulation of Calcium Carbonate Formation." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1294360826.
14
Olivier, Florian. "Elaboration, caractérisation, dopages et évaluations in vitro et in vivo de matériaux hybrides : Tissus de fibres de carbone / Phosphates de calcium." Thesis, Orléans, 2018. http://www.theses.fr/2018ORLE2052/document.
Abstract:
Ce travail a consisté à optimiser la synthèse de phosphates de calcium (CaP) déposés sur tissus de fibres de carbone (TFC) par procédé de sono-électrodéposition afin d’obtenir des revêtements uniformes. Les paramètres électrochimiques clés optimisés sont le type et la durée de polarisation cathodique ainsi que la température de l’électrolyte. Pour un potentiel constant de -1 V à 70 °C, un régime d’électrolyse contrôlé de l’eau conduit à la formation d’un revêtement plaquettaire d’hydroxyapatite déficitaire en calcium (CDA) carbonatée. Les plaquettes sont composées de particules lamellaires (de quelques dizaines à centaines de nm) constituées de CDA carbonatée de structure ordonnée au coeur et de structure désordonnée car hydratée en surface des particules, organisation typique des apatites biomimétiques. Le matériau hybride a été dopé en strontium, engendrant la formation de revêtements où les ions Ca²+ sont substitués par des ions Sr²+ de manière contrôlée, conférant au biomatériau de nouvelles propriétés en vue d’une application en régénération osseuse. Ce travail a aussi démontré la possibilité d’adsorber de façon sélective des principes actifs ciblés (tétracycline, naproxène, aspirine) dans chaque constituant du matériau hybride. Les courbes de désorption ont mis en évidence deux modes de libération selon le principe actif.Une évaluation biologique des différentes matériaux hybrides a été réalisée. L’étude in vitro a porté sur la viabilité et la prolifération d’ostéoblastes humains en surface des biomatériaux hybrides, démontrant leur biocompatibilité. L’intérêt d’un dopage (Sr²+, aspirine et naproxène) sur l’activité des ostéoblastes a été démontré. Une expérience pilote in vivo a été menée, consistant à créer un défaut osseux dans des fémurs de rats et à étudier l’influence du type de biomatériaux TFC/CaP sur les évolutions quantitative et qualitative de la régénération osseuseOptimization of the synthesis of calcium phosphates (CaP) on carbon fiber cloths (TFC) was performed in using sono-electrodeposition process in order to obtain uniform coatings. The electrochemical potential applied and the electrolyte temperature during the synthesis were determined as being key parameters. For a constant potential of -1 V at 70 ° C, a controlled water electrolysis regime results in the deposit of plate-like calcium-deficient apatite (CDA). This plate-like particles (from a few tens to hundreds of nm in length) consist in an ordered structure of carbonated CDA in their core and in a disordered structure in the hydrated surface, a typical organization of biomimetic apatites. The hybrid material was doped with strontium, resulting in a carbonated CDA coating where the Ca²+ ions are controllably substituted by Sr²+ ions, leading to new properties for a bone regeneration application. This work has also shown the possibility of selectively adsorb targeted active molecules (tetracycline, naproxen, aspirin) in each component of the hybrid material. The desorption curves revealed two modes of release depending on the active molecule.A biological evaluation of the different hybrid materials was carried out. The in vitro study investigated the viability and proliferation of human osteoblasts at the surface of hybrid materials, demonstrating their biocompatibility. The interest of a doping (Sr²+, aspirin and naproxen) on osteoblast activity was demonstrated. An in vivo pilot experiment was conducted, through the creation of a bone defect in rat thighbones to study the influence of TFC/CaP biomaterials on the quantitative and qualitative evolutions of bone regeneration
15
Ahsan, T. "Surface characterization of the precipitated calcium carbonate." Thesis, Brunel University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.374851.
16
Hetherington, Nicola B. J. "Synthetic Routes to Multiscale Calcium Carbonate Architectures." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520669.
17
Babou, Kammoe Romuald Brice. "Synthèse de nanoparticules de carbonate de calcium." Thesis, Université Laval, 2010. http://www.theses.ulaval.ca/2010/27760/27760.pdf.
18
Brown, Christopher A. "Aspects of the calcium carbonate-water interface." Thesis, University of Oxford, 1992. http://ora.ox.ac.uk/objects/uuid:0d9222b6-2d2a-4f3d-a0f9-61f91433dd02.
Abstract:
The channel flow method has established the net dissolution kinetics of calcite single crystals at high pH (7.7-9.7) and varying bulk Ca2+ concentrations (0-10 mM), using wide ranges of solution flow rates (10-3-0.3 cm3 s-1). Literature rate equations were in poor agreement with experiment. Modelling with the following mechanism, where Ca2+ and CO32- undergo Langmuirian adsorption: Ca2+(aq) ⇄ Ca2+(ads) CO2-3 (aq) ⇄ CO2-3 (ads) Ca(sup>2+(ads) + CO2-3 (ads) ⇄ CaCO3 (ads) CaCo3 (ads) → CaCo3 (lattice) and the consequent rate law Jnet/mol cm-2s-1 = kpKCaKCO3 {Ksp - [Ca2+]o[CO2-3]o (1 + KCa[Ca2+]o)(1 + KCO3[CO2-3]o) gave excellent agreement with experiment under all conditions studied. This mechanism is shown to explain all literature streaming potential, electrophoresis and kinetic salt effect data. Dissolution of calcite under the above conditions was strongly inhibited by Mg2+ and fully deprotonated forms of succinic acid, 2-sulphobutanedioic acid, phthalic acid and maleic acid. Mechanisms were established; for the maleate dianion, the inhibition was due to the blocking of the dissolution sites at which CaCO3 units are incorporated into the crystal lattice. For the other ions, inhibition arose from competitive Langmuirian adsorption either between CO32- and the anions, or between Ca2+ and Mg2+. A new method to quantify the inhibited dissolution of particulate CaCO3 (=10 μm) via enhanced mass transport of solution to the rotating disc electrode, due to the rotation of the particles in the diffusion layer, has been established. Good agreement was found with that measured independently using the channel flow cell. A.c. impedance spectroscopy has been used to characterise scaled (CaCO3) steel tubes. Results provide scope for (i) monitoring scale growth, and (ii) use in safety control devices for alerting to the scaling of pipe-work.
19
Dobson, Phillip Stephen. "Calcium carbonate crystallisation at the microscopic level." Thesis, University of Warwick, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252524.
20
Pownall, P. G. "The surface electrical properties of calcium carbonate." Thesis, University of Bristol, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379592.
21
Hooper, Rebecca Louise. "Calcium carbonate fillers in rosin-sized papers." Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/32797.
Abstract:
Calcium carbonate is one of the preferred fillers for the paper industry. This research compared the physical and chemical properties of calcium carbonates produced by different methods and their use with a novel rosin sizing system. The effectiveness of a polymeric retention agent, which flocculates particles during paper production, has also been examined.
22
Ondo, Ndjimbi Lilian Urlain. "Production of calcium carbonate from phosphogypsum wastes." Diss., University of Pretoria, 2014. http://hdl.handle.net/2263/79298.
Abstract:
Phosphogypsum is a waste generated during the production of wet phosphoric acid from phosphate rocks. Numerous studies have attempted to find applications for phosphogypsum, but its composition is generally limiting its reuse. For instance, depending on the origin of the phosphaterocks it originates from, phosphogypsum can contain environmentally-problematic elements suchas radionuclides or fluoride.
In this study, the potential of using a South African phosphogypsum waste for the production of calcium carbonate was investigated. The sample was collected from the Rustenburg plant of Omnia and was characterised by a number of analytical techniques. Two different processes of mineral carbonation were studied.
The first method, which can be described as an indirect mineral carbonation route, involved the reaction between phosphogypsum and an aqueous NaOH solution to form Ca(OH)2 where after the Ca(OH)2was converted into CaCO3 using CO2. During the first step of this process, the impurities contained in the phosphogypsum sample was transferred to the Ca(OH)2 precipitate. Upon carbonation, a low grade CaCO3 product, containing more than 10% impurities (such as unreacted gypsum and portlandite) was obtained.
Using the optimised reaction conditions, the effect varying the solid to liquid ratio and merging of the two steps applied during the indirect mineral carbonation route was studied.XRD analysis indicated that most of the carbonated products contained mainly two polymorphs of CaCO3, calcite and vaterite, in varying quantities. Only one set of reaction conditions was effective in both inducing a complete conversion of phosphogypsum into carbonate, and producing a single polymorph of CaCO3 (calcite). The obtained calcite was defined as high-grade, containing close to 100% CaCO3. Its particles were spherical and contained the rare earth elements originally contained in the untreated phosphogypsum.
The second process used in this study, defined as the Merseburg process, involved the reaction between phosphogypsum and an (NH4)2CO3 solution. The effect of varying the reaction time and temperature was studied on the conversion of phosphogypsum into calcium carbonate. The reactions were studied at 3 different temperatures (25°C, 40°C and 65°C) for 1 to 4 hours. It was found that a temperature of 65°C was required to yield the complete conversion of phosphogypsum into high-grade (CaCO3> 99%) calcite. The time had no effect on the conversion rate at this temperature (65°C). The calcite particles formed had cube-like and plate-like structures and contained significant amounts of the rare earth elements contained in the untreated phosphogypsum as impurities.
This study shows that both these processes are able to produce calcite particles which contain most of the rare earth elements (REE) originally present in the untreated phosphogypsum sample. The process involving the use of NaOH may not be suitable for large-scale industrial applications due to cost implications, whereas the Merseburg process may prove to be more favourable.Dissertation (MSc)--University of Pretoria, 2014.
Chemistry
MSc
Unrestricted
23
Venturini, Chiara. "On-surface coupling reactions on calcium carbonate." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30158/document.
Abstract:
Le couplage covalent sur surface métallique en UHV (Ultra High Vacuum) est une technique émergente permettant de synthétiser des structures moléculaires impossibles à obtenir par la chimie en solution (nanorubans de graphène, polymères 2D par exemple). Aujourd'hui, le plus grand défi reste le développement de ces réactions sur des surfaces isolantes pour différentes applications comme, par exemple, l'électronique moléculaire. En particulier, le couplage de dérivés d'acides benzoïques, greffés sur les surfaces de carbonate de calcium en UHV par des groupes carboxyliques, a été démontré récemment pour la première fois. Lors de ces travaux, nous avons dans un premier temps synthétisé des molécules précurseurs de réactions de couplage (homo-couplage d'éthyne, photopolymérisation, polycondensation et réaction d'Ullmann) sur des surfaces de carbonate de calcium en UHV. Par la suite, nous avons mené cette étude à l'échelle macroscopique (semi-préparatoire), par greffage de molécules sur des microparticules de carbonate de calcium, puis activation de la réaction, et enfin dissolution du substrat afin d'extraire le produit final. Les microparticules ont été obtenues par broyage de produit commercial ainsi que par spray pyrolyse et complètement caractérisées par FTIR, ATG/DTG, DRX, MEB et BET. Les réactions de couplage ont été activées par deux méthodes sans solvant: par broyage dans une broyeuse planétaire ou par traitement thermique sous vide. Alors qu'en UHV le couplage de l'acide 4-iodobenzoïque donne l'acide biphenyldicarboxylique, en mécanochimie nous avons obtenu l'acide benzoïque et par activation thermique l'éther dibenzoïqueCovalent coupling on metallic surfaces in UHV (Ultra High Vacuum) conditions is a new method for preparing molecular structures otherwise impossible to achieve in solution (graphene nanoribbons, 2D polymers for instance). The major challenge is now to extend these reactions from metallic to insulating surfaces, for future applications as, for instance, in molecular electronics. In particular, the coupling reaction of benzoic acid derivatives, grafted on calcite via carboxylic groups, has been demonstrated for the first time in UHV conditions. In the first part of this work, we synthesized precursor molecules for specific reactions (homocoupling of ethynes, photopolymerization, polycondensation and Ullmann reaction) on calcium carbonate in UHV conditions. In the second part of this work we extended this investigation up to the macroscale level (semi-preparative) by grafting molecules on calcium carbonate microparticles, followed by reaction activation and finally by dissolution of the substrate in order to recover the coupling products. The calcium carbonate microparticles were prepared by grinding commercial product or by spray pyrolysis and were fully characterized by FTIR, TG/DTG, XRD, SEM and BET techniques. Then, after grafting of organic reactant, the reactions were activated with two different solvent-free methods: by grinding in a planetary milling machine or by heating the samples in a furnace under vacuum. Whereas in UHV conditions, 4-iodobenzoic acid affords biphenyldicarboxylic acid, mechanochemical condition gives benzoic acid and thermal activation the dibenzoic acid ether
24
Lin, Yong. "Toughening mechanism of polypropylene/calcium carbonate nanocomposites /." View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?CBME%202009%20LIN.
25
Harris, Derek Daniel. "A Kinetic Study of Aqueous Calcium Carbonate." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3845.
Abstract:
Amorphous calcium carbonate (ACC) precipitation is modeled using particle nucleation, growth, and aggregation. The particles are tracked in terms of their radial size and particle density using direct quadrature method of moments (DQMOM). Four separate nucleation models are implemented and are compared to experimental data. In discord with a recent study, it is shown that classical nucleation, coupled with equilibrium chemistry, is in good agreement with experimental data. Novel nucleation mechanisms are presented which fit the experimental data with slightly greater accuracy. Using equilibrium chemistry it is shown that the equilibrium value of ACC is pKeq = 7.74 at 24C, which is a factor of two smaller than the originally published equilibrium constant. Additionally, legacy equilibrium chemistry expressions are shown to accurately capture the fraction of calcium carbonate ions formed into ACC nano-clusters. The density, solubility, and water content of ACC are discussed in a brief review, finding that a wide variety of properties are reported in the literature. Based on literature findings, it is proposed that the broad variety of reported properties may be due to ACC having several unique thermodynamic states. Compelling evidence is presented exposing errors made by experimentalists studying the calcium carbonate system. The errors correct for mistakes of experimental kinetic data of the chemical-potential cascade of calcium carbonate due to the formation of meta-stable phases. Correlations are presented which correct for these mistakes. A time-scale analysis shows the overlapping of kinetic scales and mixing scales within the calcium carbonate system. The kinetic scales are based on classical nucleation theory, coupled with diffusion limited growth. The mixing scales were computed using one-dimensional turbulence (ODT).
26
Jafari, Abbas. "The Effect of Citric Acid on Amorphous Calcium Carbonate, Mesoporous Magnesium Carbonate and Calcium Magnesium Composite : A brief study." Thesis, Uppsala universitet, Nanoteknologi och funktionella material, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-435989.
Abstract:
During the past decades, emission of greenhouse gases has accelerated to unsustainable levels. This is a serious issue that can have a devastating impact on everything from global economy to the terrestrial or marine ecosystem. A method for reducing the emission is named carbon capture and storage, which this project is based on. In this study, different concentrations of citric acid (CA) is used (as an additive) for the enhancement and optimization of carbon dioxid sorption properties of amorphous calcium carbonate (ACC), mesoporous magnesium carbonate (MMC) and calcium magnesium carbonate composite (CMC). These materials were heat treated in a calcination and an alternating carbonation process in order to study the carbon dioxid sorption performance. During the calcination process, CA undergoes a pyrolysis reaction in order to increase the specific surface area of the individual nanoparticles, which is an important factor for the sorption capacity. In the case of CMC, different molar ratios of magnesium oxide and calcium oxide were used in order to alter the concentration of the resulting magnesium oxide prior to heating. All three materials consisted of aggregations of nanometer-sized particles. Thermogravimetric analysis, scanning electron microscopy, surface area and porosimetry and infrared spectroscopy analysis suggest that the carbon dioxid sorption properties and the sintering stability of ACC and MMC do not improve since CA evaporates due to pyrolysis. Sintering was a greater problem for the evaluated CA treated ACC sample. However, in the case of CMC, the sorption and sintering properties were enhanced due to the higher Tamman-temperature of magnesium oxide, specifically for the lower concentration of magnesium oxide. After 19 carbonation cycles, CMC-1:1-25% CA showed signs of improved sintering stability and sorption capacity, compared to ACC-75% CA.Presentationen genomfördes på distans.
27
Gagnon, Gerard R. "The Colloidal Properties and Rheological Behavior of Precipitated Calcium Carbonate Suspensions Dispersed with Sodium Polyacrylate." Fogler Library, University of Maine, 2008. http://www.library.umaine.edu/theses/pdf/GagnonG2008.pdf.
28
England, Jennifer Katherine. "Calcium carbonate biomineralisation in disparate systems : common mechanisms?" Thesis, University of Glasgow, 2005. http://theses.gla.ac.uk/4024/.
Abstract:
This study considers the extent to which four calcium carbonate biomineral systems share common characteristics. Within the sample set, there is a range of ultrastructures and two types of calcium carbonate polymorph (calcite and aragonite). The mini survey includes three invertebrate systems: two members of the Phylum Brachiopoda; the articulated brachiopod Terebratulina retusa (Subphylum Rhynchoenlliformea) and the inarticulated brachiopod Novocrania anomala (Subphylum Craniiformea), and a member of the Mollusca, the bivalve Mytilus edulis. The fourth, outlying vertebrate system, is the eggshell of the domestic fowl, Gallus gallus. The minor element composition of each of the four systems is considered in the context of mineral ultrastructure. The shell of T. retusa comprises two layers; a primary layer of acicular calcite and an underlying secondary layer composed of calcite fibres. In thin section, a variation between the upper and lower portions of the secondary layer is evident. The concentrations of magnesium, sulphur and strontium are significantly greater in the primary layer of the shell. Magnesium concentration also differs between the upper and lower regions of the secondary layer with higher concentration in the upper portion of the secondary layer. The shell of N. anomala consists of two layers; a primary layer of acicular calcite and a secondary layer of calcite semi-nacre. N. anomala has a high magnesium calcite shell. The concentration of minor elements does not differ significantly between the primary and secondary layers. Two calcium carbonate polymorphs occur in the M. edulis shell with an outer calcite layer and an inner aragonite layer. Magnesium concentration is higher in the calcite layer while strontium concentrations are greater in the aragonite layer. Sodium concentration gradually decreases across the calcite layer from the outer surface to the calcite/aragonite boundary and increases in the aragonite layer.
29
Bindley, Lucy Ann. "Calcium carbonate growth and dissolution to the nanoscale." Thesis, University of Warwick, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425538.
30
Rajam, S. "Controlled crystallization of calcium carbonate under Langmuir monolayers." Thesis, University of Bath, 1990. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760610.
31
Al, Qabany Ahmed Abdul Aziz. "Microbial carbonate precipitation in soils." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609845.
32
Bennani-Ziatni, Mounia. "Etude du système phosphate de calcium, carbonate de calcium en milieu eau-éthanol." Toulouse, INPT, 1986. http://www.theses.fr/1986INPT004G.
Abstract:
Composition des phases coprecipitees pour differents rapports carbonate-phosphate. Il existe des domaines monophases, amorphes et polyphases. Stabilite thermique des apatites carbonatees et des calcites phosphatees
33
Bennani-Ziatni, Mounia. "Etude du système phosphate de calcium carbonate de calcium en milieu eau-éthanol." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb375959373.
34
Berry, Jeffrey Nicholas. "Sulfate in foraminiferal calcium carbonate : investigating a potential proxy for sea water carbonate ion concentration." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/53536.
Abstract:
Thesis (M.S.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1988.Includes bibliographical references (leaves 82-85).
The sulfur content of planktonic and benthic foraminifera was measured in specimens recovered from deep-sea sediment cores and individuals grown in culture. A new method for measuring sulfur in foraminiferal calcium carbonate was developed, employing a high-resolution inductively coupled plasma-mass spectrometer. The sulfur measurements, expressed as sulfur-to-calcium (S/Ca) ratios in the foraminiferal shells, ranged from 0.26 to 6.0 mmol/mol. Most analyses fell in the range of 0.7 to 2.5 mmol/mol. Culturing experiments were conducted in the planktonic foraminifer G. sacculifer to test the hypothesis that S/Ca ratios in the foraminifer are inversely proportional to the carbonate ion concentration in the seawater in which they grow, and hence proportional to the pH of the seawater. The slope of the relationship between cultured G. sacculifer S/Ca and the pH of the seawater medium was -1.92 mmol mol-1/pH unit with a least squares linear correlation coefficient, r2=0.927. The S/Ca ratios of planktonic and benthic foraminifera from Holocene and last glacial period sediments were measured in an effort to use the established relationship of S/Ca and pH to calculate the ocean pH gradient between Holocene and glacial time. The results indicate the pH of global ocean deepwater was 0.10 to 0.15 pH units higher during glacial time than today. Smaller pH gradients were seen for some cores which may have been caused by circulation-induced water mass changes. Surface ocean changes in pH over the Holocene-glacial interval seem to vary from region to region, with up to an 0.2 pH unit increase at the Sierra Leone Rise in glacial time. Benthic foraminifera from coretops in the thermocline of the Little Bahama Bank were analyzed for S/Ca to examine the effects of hydrographic variables on S/Ca. The relationship of S/Ca to pH and [CO3=] has a positive slope, at odds with the expected negative slope from the previous results. The S/Ca results do correlate well with salinity, suggesting that salinity or other hydrographic parameters may also influence foraminiferal S/Ca ratios.
by Jeffrey Nicholas Berry.
M.S.
35
Stephens, Christopher James. "On the transformation of amorphous calcium carbonate into calcite." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534898.
36
Bello, Omoregbe. "Calcium carbonate scale deposition kinetics on stainless steel surfaces." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/17647/.
Abstract:
Calcium carbonate scale is one of the most common inorganic scales which deposits on the surface of oil and gas production facilities. This causes significant loss of production and ultimately leads to shut down of production lines if not properly managed. There has been a great amount of research on calcium carbonate deposition studies, but most of these studies have been on understanding calcium carbonate bulk precipitation process. However, little attention have been made on calcium carbonate surface deposition mechanism, which is the main challenge in mitigating scaling in oil and gas and desalination industries. Understanding the mechanism of its formation at different environmental conditions and using a methodology that would reflect the field scenario will gives information required for a reliable predictive model. This study investigated calcium carbonate surface build-up under flow conditions, across a wide range of saturation ratio (SR) at 25oC and 70oC respectively. Both bulk induction time (tind) and surface induction time, which is referred to as scaling time (ts) were determined from capillary flow rig experiments. Mineral scale surface fouling was monitored by a sensitive differential pressure technique with respect to build up of scale on the wall of the capillary cell resulting to change of pressure across the test capillary cell. It was found that, two scaling regimes occur within the brine composition investigated. At SR < 80, surface fouling is controlled by nucleation and growth, while at SR > 80, is controlled by the adhesion of pre-precipitated crystals. This result was supported by the turbidity measurement and inductively coupled plasma mass spectrometry (ICP-MS) analysis. The calcium carbonate growth rate determined by measuring the amount of scale deposited at the surface of the capillary cell by Inductively coupled plasma mass spectrometry analysis (ICP-MS) was smaller compared to the amount of scale predicted from Hagen Poiseuille (HP) equation, where the growth rate is estimated from the pressure drop across the capillary cell as scale build up on the wall of the capillary cell. This was attributed to non-uniformity of the scale layer along the capillary cell which is omitted in the HP equation. A semi empirical model has been developed from the experimental work, which can predict scale deposition growth rate over a period of time and as a function of deposition flux at a given temperature.
37
Doyat, Sylvie. "Mélanges polypropylène-carbonate de calcium : extrusion réactive et rhéologie." Lyon 1, 1998. http://www.theses.fr/1998LYO19009.
Abstract:
L'étude porte sur l'amélioration des propriétés mécaniques du polypropylène par addition de carbonate de calcium. Cet objectif passe par une bonne dispersion de la charge dans la matrice et une adhésion entre les deux phases. Aussi, il convient d'ajouter un agent de liaison pouvant d'une part se fixer sur la charge et d'autre part se greffer sur le PP. Deux voies ont été développées : une chimie radicalaire mettant en jeu un acide carboxylique insature et une réactivité fonctionnelle faisant intervenir un PP greffe anhydride maléique et un aminoacide. Le couplage entre la charge et la matrice devait être réalisé in-situ selon un procédé d'extrusion réactive. Une étude préliminaire dans le squalane a montré qu'il est possible de greffer un alcane en C30 sur le CaCO3 via l'acide vinyle acétique par voie radicalaire. L'acide vinyle acétique améliore la dispersion du CaCO3 dans le PP avec une concentration en acide optimale égale à 3% en poids par rapport à la charge. Les mélanges PP/CaCO3/acide vinyle acétique ont un module d'young supérieur a celui du PP non chargé mais une résistance aux chocs inférieure. Par contre, le greffage radicalaire du monomère à l'état fondu s'est avéré impossible. Dans la partie réactivité fonctionnelle, le tiers-corps est l'acide aminohexanoique. La caractérisation rhéologique dynamique à l'état fondu a mis en evidence que des chaînes de PP-g-AM peuvent être greffées sur le CaCO3 grâce à l'aminoacide. Des mélanges PP/CaCO3 compatibilisés par du PP-g-AM et de l'aminoacide ont été réalisés en une seule étape d'extrusion. Ces mélanges présentent une très bonne dispersion de la charge dans la matrice et une adhésion entre les deux phases. La dispersion et la compatibilisation ont permis d'augmenter le module d'young de 30% par rapport au PP non chargé ainsi que la résistance aux chocs charpy entaillé
38
LEVREL, LE METAYER GAELE. "Microbiogeologie du carbonate de calcium : applications industrielles, implications geologiques." Nantes, 1996. http://www.theses.fr/1996NANT2115.
Abstract:
La premiere partie du present travail est essentiellement microbiologique et experimentale en laboratoire. Il s'agit d'optimiser un procede de biomineralisation destine a proteger les pierres de taille calcaires. Le procede consiste a appliquer, sur le support a traiter, une suspension d'une souche de bacteries carbonatogenes issues des environnements naturels et de nourrir celles-ci afin qu'elle forment un calcin protecteur. Les recherches portent sur le choix des souches, la composition du milieu nutritif notamment quant a ses activateurs bacteriens, sa composition ionique et l'ajout de produits antifongiques. En outre, ont fait l'objet de recherches en vue de leur optimisation pour le passage au stade industriel, la duree de traitement, la composition du milieu destine a produire industriellement la biomasse bacterienne et les contraintes imposees par la lyophilisation de cette biomasse. La deuxieme partie traite des applications du procede a un essai en vrai grandeur sur une eglise (thouars), puis sur des statues placees ensuite dans differents environnements climatiques (au sens large). Ces chantiers font l'objet d'un suivi quant aux qualites physiques de la protection biominerale. En outre sont proposes de nouveaux produits du concept initial. Ainsi ont ete fabriques et testes des patines biominerales colorees et des ciments biologiques pour la restauration des oeuvres d'art en calcaire. Ainsi, les monuments calcaires peuvent beneficier aujourd'hui d'un lifting bacterien qui, en quelque sorte recree les modalites de formation de la pierre. La troisieme partie est tournee vers la science fondamentale et se nourrit des concepts et des images obtenues au laboratoire. Le premier chapitre fait le point sur les connaissances actuelles en ce qui concerne la carbonatogenese bacterienne et remet en cause les idees recues sur la sedimentation et la diagenese des series carbonatees. Le deuxieme chapitre est consacre a l'etude d'une concretion excentrique recoltee pour l'edification de la souchotheque du laboratoire. Les micro-organismes semblent bien etre responsables de la croissance et de l'excentricite de cet objet. La conclusion reprend les grandes lignes de l'ouvrage mais surtout propose quelques questions qu'auront a resoudre bientot ceux que passionnent et qui pratiquent la microbiogeologie.
39
Alipour, A. "Nanoclay as Substitute of Calcium Carbonate in NBR Compounds." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35036.
Abstract:
The use of organo-modified montmorillonite as substitute of calcium carbonate in NBR compounds
were studied. Rubber containing (3,5,7 phr) of nanoclay (Closite 30 B) were compared with those of reinforced by 10, 20 and 30 phr calcium carbonate as filler. The modified silicate is analysed by X-ray which
suggested intercalation of elastomer chains into silicate layers. Rheological measurement as well as mechanical properties showed both nanoclay and calcium carbonate give rise to a marked increase in elastic
modulus and viscosity which could be attributed to the good interaction between polymer/filler. It was noticed that nanoclay can reinforce the NBR much more noticeably than calcium carbonate.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35036
40
Huang, Jin-Mo. "Model Development for the Catalytic Calcination of Calcium Carbonate." Thesis, North Texas State University, 1987. https://digital.library.unt.edu/ark:/67531/metadc331193/.
Abstract:
Lime is one of the largest manufactured chemicals in the United States. The conversion of calcium carbonate into calcium oxide is an endothermic reaction and requires approximately two to four times the theoretical quantity of energy predicted from thermodynamic analysis. With the skyrocketing costs of fossil fuels, how to decrease the energy consumption in the calcination process has become a very important problem in the lime industry.
In the present study, many chemicals including lithium carbonate, sodium carbonate, potassium carbonate, lithium chloride, magnesium chloride, and calcium chloride have been proved to be the catalysts to enhance the calcination rate of calcium carbonate. By mixing these chemicals with pure calcium carbonate, these additives can increase the calcination rate of calcium carbonate at constant temperatures; also, they can complete the calcination of calcium carbonate at relatively low temperatures. As a result, the energy required for the calcination of calcium carbonate can be decreased.
The present study has aimed at developing a physical model, which is called the extended shell model, to explain the results of the catalytic calcination. In this model, heat transfer and mass transfer are two main factors used to predict the calcination rate of calcium carbonate. By using the extended shell model, not only the catalytic calcination but also the inhibitive calcination of calcium carbonate have been explained.
41
Kawano, Jun. "Molecular Dynamics Simulation on the Polymorphism of Calcium Carbonate." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/149085.
42
Porter, Hannah Elizabeth. "Stabilisation of Geomaterials using Microbially Induced Calcium Carbonate Precipitation." Thesis, Curtin University, 2018. http://hdl.handle.net/20.500.11937/75981.
Abstract:
The Australian landscape has a large number of naturally cemented structures, which provide inspiration for a sustainable cementing material which does not produce carbon dioxide during the manufacturing phase. Structures such as corals, beach rocks and stromatolites are cemented through the process of Microbially Induced Calcium Carbonate Precipitation, (MICP). This thesis reports on the potential for MICP as a replacement or augmentation to chemical binders in geomaterials and evaluates the sustainability of MICP using Life Cycle Analysis.
43
Schnebelen, Mathilde. "Étude de l'agglomération lors de la précipitation de carbonate de calcium par un procédé de carbonatation d'une suspension d'hydroxyde de calcium." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0131/document.
Abstract:
Le carbonate de calcium précipité (CCP) est un additif multi-fonctionnel que l'on trouve dans de nombreuses applications telles que les peintures, la pharmacie, la cosmétique etc. Il peut être synthétisé industriellement par différents procédés mais la voie la plus commune est la carbonatation. Ce procédé consiste à faire barboter du dioxyde de carbone dans une suspension d'hydroxyde de calcium afin de produire des particules de CCP. Toutefois, la problématique inhérente à la synthèse et à l'utilisation de ce précipité est la maîtrise de l'agglomération des monoparticules. En effet, ces dernières sont de taille nanométrique et s'agglomèrent en structures "ouvertes" de taille micrométrique. Cette agglomération a des conséquences directes sur la conduite du procédé ainsi que sur les propriétés d'usage du produit final. Ainsi, le but de ce travail est d'appréhender les mécanismes de ce phénomène, de déterminer sa cinétique et d'étudier l'impact de différents paramètres opératoires dans des conditions industrielles complexes. Sous réserve que les cinétiques de nucléation et croissance cristalline soient connues, le noyau d'agglomération peut être obtenu grâce à un traitement mathématique des distributions de tailles expérimentales. En faisant varier différents paramètres du procédé, il apparait que la constante d'agglomération augmente avec la température alors qu'il existe un optimum par rapport au taux de cisaillement. En se basant sur cette conclusion, une expression de la constante d'agglomération est proposée en fonction du taux de cisaillement, qui pourra être utilisée pour contrôler l'agglomération dans le réacteur industrielPrecipitated calcium carbonate (PCC) is a mineral additive of various applications in paints, pharmacy, cosmetics, etc. It can be industrially synthesized through several ways but the most common one is the carbonation route. It consists in bubbling carbon dioxide in a suspension of calcium hydroxide to get particles of PCC. However, the challenge related to the synthesis and the use of this precipitate is the control of the agglomeration of the monoparticles. Indeed, they are agglomerated in micrometric "loose" structures. This agglomeration has consequences on the run of the process and the end use properties of the final product. Thus, the aim of this work is to understand the mechanisms of this phenomenon, to determine its kinetics and to study the impact of different process parameters under complex industrial conditions. The method to determine the agglomeration kernel is based on the resolution of a population balance using the moment approach. Provided that the kinetic rates of nucleation and growth are known, the agglomeration kernel can be obtained from a mathematical treatment of the experimental particle size distributions. Thanks to an agglomeration kernel model including the crystal growth, it is possible to determine the value of the agglomeration constant. Finally, by varying different process parameters, it also appears that the agglomeration constant increases with temperature whereas an optimum is observed for the shear rate. Regarding to this fact, we can also propose an expression of the agglomeration constant as a function of the shear rate, which can be used to control the agglomeration in the industrial reactor
44
Farrell, Vanessa A. "Calcium: A Simple Guide." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2011. http://hdl.handle.net/10150/146446.
Abstract:
3 pp.Originally published: 2002
It is important to know how much calcium you need to consume each day as more than 2500 mg of calcium each day can be harmful. Calcium should be obtained from foods and beverages first, then from supplements if necessary. Taking more than 500 mg of calcium at one time should be avoided. If you choose to take a calcium supplement, calcium citrate or calcium carbonate should be chosen.
45
Wang, Yuan School of Chemical Engineering & Industrial Chemistry UNSW. "Composite fouling of calcium sulfate and calcium carbonate in a dynamic seawater reverse osmosis unit." Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 2005. http://handle.unsw.edu.au/1959.4/26007.
Abstract:
Deposition of calcium carbonate (CaCO3) and calcium sulfate (CaSO4) causes serious processing problems and limits the productivity of seawater reverse osmosis (RO) desalination. The interactions between CaSO4 and CaCO3 in the dynamic seawater RO systems have been neglected previously because conventional studies mainly focused on individual compounds or mixed compounds in batch systems. The present work evaluates composite fouling behavior of CaSO4 and CaCO3 in a dynamic RO unit. The fouling experiments were performed at constant pressure and velocity by a partial recycling mode which permeate was withdrawn from the system during the recirculation of retentate to simulate the increasing of water recovery level. The fouling phenomena were monitored by the decline of flux. Scanning electron microscopy (SEM) with a combination of elemental dispersive x-ray microanalysis (EDS), and x-ray powder diffraction (XRD) was used to identify the morphological features, chemical compositions and crystalline phases of foulants. The interactions of CaSO4 and CaCO3 were investigated by the comparison between individual CaSO4 or CaCO3 fouling and composite fouling, and by varying SO42-/HCO3- molar ratio of the feed. A recently developed approach, Scaling Potential Index (SPI) incorporated with measured concentration polarization modulus (CP), for assessing the fouling tendency of inorganic salts on the membrane surface was validated in the dynamic tests. In addition, the effectiveness of two generic scale inhibitors, polyacrylic acid (molecular weight =2100, PA) and sodium hexametaphosphate (SHMP) were evaluated. Some of the highlights of the obtained results are as follows: ??????The precipitation kinetics, morphology and adhesive strength of composite scales were different from pure precipitates ??????CaSO4 precipitated as gypsum while CaCO3 precipitated as two crystalline phases: calcite and aragonite ??????The crystalline phases as well as precipitation kinetics were affected by SO42-/HCO3- ratio ??????Scaling Potential Index was able to predict the fouling tendency of CaSO4 and CaCO3 accurately ??????The dosage of PA and SHMP was effective to mitigate fouling Results of this work are significant, not only because they have made contribution to the fundamental understanding of composite inorganic fouling in RO membrane systems which was ignored previously, but also because they may play a key role in the development of scale control.
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Cantaert, Bram. "Controlled crystallisation of calcium phosphate and calcium carbonate via bio-inspired approaches : additives and confinement." Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/4683/.
Abstract:
This thesis describes the investigation of the two bio-inspired approaches, confinement and additives, to manipulate the crystallization of calcium carbonate and calcium phosphate. The first experimental chapter deals with the investigation of calcium phosphate rods grown in confined environments in the absence and presence of polyaspartic acid. Although similar results were obtained in the absence and presence of the additive, growing calcium phosphate in confinement allowed formation of polycrystalline rods with an orientation comparable to bone. This demonstrated that confinement may play a more significant role in bone formation than previously anticipated. The second chapter deals with the effect of positively charged additives on the crystallisation of CaCO3. Although neglected before in literature, this chapter demonstrates that positively charged additives have a profound effect on the crystallisation of CaCO3 changing the morphology to films and fibers. This morphology change was linked to a phase separation process, forming hydrated amorphous droplets of calcium carbonate by a carbonate-polymer interaction, which had the tendency to coalesce and form films. Fiber formation was attributed to oriented attachment of anisotropic particles due to unequal distribution of charge. In the third chapter, based on bone, the mineralisation of collagen by CaCO3 was investigated. By formation of a highly hydrated liquid-like amorphous phase of CaCO3, it was possible to infiltrate the nanoscale gaps of collagen. After crystallisation, nanocrystals of calcite and vaterite were formed, 5 nm thick, but randomly oriented, demonstrating collagen templates the shape but not the orientation of the crystals. In a final chapter hollow rods of CaCO3 were formed by templating them inside membrane pores. The influence of time, pore size, additives and surface chemistry was investigated. Most hollow rods were formed at early timescales which filled up at later times. By changing the surface chemistry, the amount of hollow rods increased significantly in the 200 nm pores
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Madrick, Tracy L. "The availability of calcium from various commercial sources of calcium carbonate and fortified food products." Thesis, Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/53228.
Abstract:
Although the therapeutic benefits of calcium supplementation have yet to be fully determined, popular literature has promoted this practice to combat osteoporosis. This study examined the potential bioavailability of calcium from various supplement and antacid forms. Four dosage levels were studied for each of five sources, including leading supplements Caltrate and Os-Cal, two "calcium rich" antacids, Tums and Rolaids, and a calcium carbonate control. These samples were subjected to four gastric treatments in an in vitro digestion procedure designed to observe the influence of acid secretion on calcium solubility. Depending on the degree of acidity of these solutions, solubility behavior of CaCO3 was highly variable. Normal and reduced acid treatments adequately solubilized between 85 and 88% of the total calcium, whereas negligible quantities were dissolved in deionized water or the achlorhydric solution. Relative availability of calcium from the various sources differed according to gastric treatment. Tums, Caltrate and Os-Cal had dissolution rates that were similar to reagent grade CaCO3. Rolaids provided a significantly lower amount of soluble calcium under all of the experimental conditions (P < 0.001). Amounts of available calcium increased with increasing dosages. The effectiveness of fortification techniques used to increase the calcium content of various food systems was also examined. Fortified orange juice and yogurt samples were found to contain a quantity of available calcium comparable to that found in milk. It was concluded that both of these approaches are reasonable for increasing calcium intakes in individuals with normal gastric secretion.Master of Science
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Patel, Vishal M. "Synthesis of calcium carbonate coated emulsion droplets for drug detoxification." [Gainesville, Fla.] : University of Florida, 2002. http://purl.fcla.edu/fcla/etd/UFE1001175.
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Becker, Alexander. "Structural characterisation of biominerals and biomimetic crytallisation of calcium carbonate." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=97572861X.
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Gupta, Ritika. "Synthesis of Precipitated Calcium Carbonate Nanoparticles Using Modified Emulsion Membranes." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5158.
Abstract:
The synthesis of precipitated calcium carbonate nanoparticles with the use of double water in oil emulsion has been developed. Restricting the mass of calcium ions present in the system makes it possible to predict particle size precipitated. A model was developed to calculate the concentration required to synthesize a desired particle size. This model took into account a coalescence factor. The coalescence factor is described at the probability of two emulsion droplets, with separate nucleation processes within them, colliding and forming one nucleation process. The Ca2+ ions diffused through the oil membrane into the emulsion droplets with (CaCO3)2- ions by concentration gradients and facilitated transport. The size and shape of precipitated calcium carbonate synthesized was confirmed using scanning electron microscope and light scattering. Particles ranging from 100 nm to 1200 nm have been synthesized using mass restriction. The effect of temperature on the crystalline structure of precipitated calcium carbonate was studied. This was done by x-ray diffraction, where it was found that calcite was the dominating crystalline structure.