Les processus de dégradation chimique des céramiques réfractaires sont des phénomènes complexes. Atravers des exemples concrets issus de la littérature et de travaux de recherche, les notions et les propriétésfondamentales permettant d’expliquer les différents modes de dégradation des matériaux réfractaires sontprésentées. A l’issu de cet état de l’art, une méthodologie adaptée à l’étude de la corrosion des réfractaires,prenant en compte une approche multi-échelle allant du macroscopique au microscopique, est proposée.Cette méthodologie, permettant de déterminer les mécanismes responsables de la corrosion en fonction del’environnement des matériaux, a été appliquée à la corrosion des réfractaires à base de SiC utilisés dans lesunités de valorisation énergétique (UVED). L’analyse post-mortem des échantillons a permis de constater laformation de para-wollastonite, dans la porosité et autour des grains de SiC, en face chaude. D’autresphases telles que la cristobalite et la microline ont également été observées jusqu’à mi-épaisseur desréfractaires. A travers une modélisation thermochimique, la nature des agents d’agression a été déterminéeet correspond essentiellement à une condensation d’espèces sulfatées (CaSO4, K2SO4 et Na2SO4) en facechaude et dans la porosité des matériaux. Les essais de corrosion en laboratoire par les sulfates, ont permisde mettre en évidence une dégradation similaire à celle rencontrée dans les UVED.L’ensemble des résultats permet d’envisager deux voies d’amélioration qui sont :- la voie matériaux par une modification de la matrice et notamment une diminution de la porosité et/ou l’ajoutd’une couche protectrice en face chaude imperméable aux gaz ;- une voie procédé en modifiant les isothermes de condensation des matériaux (réduire la température enface chaude afin d’éviter la condensation des espèces dans la porosité des matériaux). / The chemical wear processes of ceramic refractories are complex phenomena. Relying on real applicationsand research works, notions and fundamental properties, which describe different wear mechanisms ofrefractory materials, are introduced. Then, a methodology adapted to the study of refractory corrosion,including a multi-scale approach (macroscopic and microscopic), is offered.This methodology, which makes it possible to define main mechanisms of corrosion according to theenvironment of refractories, was applied to the corrosion of silicon carbide refractories used in municipal solidwaste-to-energy facilities (WtE). The post-mortem analyses showed the formation of para-wollastonite, in theporosity and around the SiC grains, on the hot face of materials. Other phases such as cristobalite andmicroline were also formed down to the core of the refractories. From thermo-chemical modelling, the natureof the corrosive agents was calculated and corresponds to the condensation of sulphates (CaSO4, K2SO4 andNa2SO4) on the hot face and into the porosity of materials. The in-lab corrosion tests by sulphates, inconditions close to those met in WtE, are in accordance with the autopsy of corroded samples taken fromincinerator plants.All results suggest two axes of improvement:- a material way by a modification of the matrix and particularly the reduction of the porosity and/or theaddition of protective layer on the hot face ;- a technical way by a modification of condensation isotherms of refractories (reducing the temperature on thehot face to avoid the condensation of sulphate species in the porosity of materials).

Mémoire (M.Sc.T.)--Université du Québec à Chicoutimi, 1997. / Document électronique également accessible en format PDF. CaQCU

Thèse (M.Sc.T.) -- Université du Québec à Chicoutimi, 1996. / Bibliogr.: f. 135-139. Document électronique également accessible en format PDF. CaQCU

Ce travail vise à étudier l’hydratation et les propriétés des ciments brushitiques à base de wollastonite dans la perspective d’une application au traitement et au conditionnement de déchets radioactifs de faible ou moyenne activité acides et/ou contaminés en strontium. Une étude des processus conduisant à la prise et au durcissement d’un ciment commercial est d’abord menée. L’influence de la composition de la solution de gâchage sur les réactions mises en jeu est ensuite précisée. Enfin, une première évaluation du potentiel de ce matériau pour la décontamination ou l’immobilisation d’effluents aqueux contaminés en strontium est réalisée.Les pâtes de ciment brushitique à base de wollastonite sont préparées à partir de wollastonite broyée et d’une solution d’acide phosphorique concentrée contenant des cations métalliques (Zn2+ et Al3+) ainsi que du borax. La wollastonite réagit selon un processus de dissolution/précipitation qui conduit à la formation de brushite, de silice amorphe et d’un aluminophosphate de calcium et de zinc amorphe dont la structure a été caractérisée par RMN-MAS du 31P et 27Al. La précipitation de brushite est précédée par la formation transitoire de phosphate monocalcique monohydraté. La simulation thermodynamique à l’aide d’un code de spéciation géochimique de la réaction de la wollastonite avec une solution d’acide phosphorique reproduit bien la séquence de précipitation des phases cristallines observée expérimentalement.Il apparaît que la concentration optimale de l’acide phosphorique dans la solution de gâchage est comprise entre 9 et 10 mol.L-1. Le bore retarde la prise du ciment tandis que le zinc l’accélère. L’ajout d’aluminium, qui permet la précipitation massive d’aluminophosphate de calcium amorphe, s’avère nécessaire pour obtenir un matériau avec de bonnes performances mécaniques. Une étude de surfaces de réponses par plan d’expériences, suivie d’une optimisation multicritères, a permis d’identifier un domaine de compositions de solutions de gâchage conduisant à un matériau possédant les propriétés recherchées (en terme de temps de prise, auto-échauffement et résistance mécanique) pour une matrice de conditionnement de déchets.Une étude cristallographique montre par ailleurs que la brushite peut incorporer au moins 30 % (mol/mol) de strontium en substitution du calcium dans sa structure. Des essais de piégeage du strontium par une pâte de ciment broyée, menés en suspension diluée, conduisent à une isotherme de sorption de type S, témoignant de l’existence de plusieurs mécanismes de rétention. Enfin, un essai de lixiviation sur un monolithe contenant du strontium révèle le bon confinement de ce dernier, avec un coefficient de rétention Rd plus de 100 fois supérieur à celui obtenu avec une pâte de ciment Portland. / This work aims at studying the hydration process and the properties of wollastonite-based brushite cements. These binders may indeed offer new prospects for the treatment or conditioning of low- or intermediate- level radioactive wastes characterized by a strong acidity and/or a contamination by strontium. First, a study of the hydration process is carried out with a commercial cement. Then, the influence of the mixing solution composition on the setting and hardening process is determined. Finally, a first assessment of the potential of this material for the decontamination and immobilization of strontium-containing aqueous effluents is performed.Wollastonite-based brushite cement pastes are prepared by mixing ground wollastonite and a phosphoric acid solution containing metallic cations (Al3+ and Zn2+) and borax. Wollastonite reacts through a dissolution/precipitation process, which leads to the formation of brushite, amorphous silica and amorphous zinc and calcium aluminophosphate whose structure has been investigated by 31P and 27Al MAS-NMR. The brushite precipitation is preceded by the transient formation of monophosphate calcium monohydrate. The thermodynamic simulation of the wollastonite reaction with a phosphoric acid solution, using a geochemical speciation code, fairly well reproduces the precipitation sequence of crystalline phases observed experimentally.It appears that the optimum phosphoric acid concentration in the mixing solution is comprised between 9 and 10 mol.L-1. Boron retards the cement setting whereas zinc accelerates it. The addition of aluminium, which leads to the massive precipitation of amorphous calcium aluminophosphate, is proved to be necessary to obtain a material with high mechanical strength. Thanks to response surface methodology and multi-criteria optimization, a composition domain of the mixing solution is pointed out, leading to a material with good properties (in terms of setting time, self-heating and mechanical strength) for waste conditioning.A crystallographic study also shows that brushite is able to incorporate at least 30 % (mol/mol) of strontium in substitution for calcium in its structure. Strontium retention tests by a ground cement paste in diluted suspension lead to a type S sorption isotherm, meaning that several retention mechanisms are involved. Finally, a leaching experiment performed on a cement monolith containing strontium shows that this species is well confined within the cement matrix, with a retention coefficient at least two orders of magnitude higher than that of a Portland cement paste.

abstract: The main objective of this study is to investigate drying properties and plastic shrinkage cracking resistance of fresh cement-based pastes reinforced with fibers and textiles. Naturally occurring mineral wollastonite has been studied independently as well as in combination with AR-glass textile. A series of blended mixes with Portland cement and wollastonite nano-fibers were developed and tested under low vacuum conditions to simulate severe evaporation conditions and expedite the drying process causing plastic shrinkage cracks. Cumulative moisture loss, evaporation rates, and diffusivity were analyzed by means of a 2-stage diffusion simulation approach, developed previously in Arizona State University. Effect of fiber-matrix interaction on the transport properties of the composite were evaluated using the existing approach. Morphology of the cracked surface was investigated by the means of image analysis wherein length, width, area and density of the cracks were computed to help characterize the contribution of fiber and textile in the cracking phenomenon. Additionally, correlation between cumulative moisture loss and crack propagation was attempted. The testing procedures and associated analytical methods were applied to evaluate effectiveness of four wollastonite fiber sizes and also a hybrid reinforcement system with alkali-resistant glass (ARG) textile in improving shrinkage cracking related parameters. Furthermore, the experimental and analytical approach was extended to magnified version of the existing shrinkage testing set-up to study the size effect of these composites when subjected to matching drying conditions. Different restraining mechanisms were used to study the simulation of the cracking phenomena on a larger specimen. Paste and mortar formulations were developed to investigate size effect on shrinkage resistance of cementitious composites. / Dissertation/Thesis / Masters Thesis Civil Engineering 2014

Orientador: José Angelo Camilli / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-25T17:14:45Z (GMT). No. of bitstreams: 1 Souza_AnaClaudia_M.pdf: 9721509 bytes, checksum: 9b9dc58e5f77704091ed8b7c4b95dfc4 (MD5) Previous issue date: 2014 / Resumo: Os biomateriais podem ser utilizados em diversas áreas da bioengenharia regenerativa, sendo uma opção viável no reparo de lesões ósseas. Atualmente diferentes tipos de biomateriais têm sido estudados, dentre eles as cerâmicas que podem ser classificadas em três tipos: vidros bioativos, vitrocerâmicas e cerâmicas de fosfato de cálcio. As Cerâmicas de Fosfato de Cálcio podem ser subdivididas em Hidroxiapatita e em Cimentos Fosfatos de Cálcio (CFC). Os CFC tem se destacado pela sua fácil manipulação, capacidade de reabsorção e estimulação da osteogênese. No entanto, o CFC tem seu uso restrito como implante, pois possui baixa tenacidade a fratura comparada ao osso natural. Para reforçar o CFC algumas fibras como as de carbono, aramida e carbeto têm sido utilizadas. Outro tipo de reforço são os "whiskers" que compreendem fibras muito curtas. Neste estudo foi utilizado um CFC a base de ?-TCP reforçado com "whiskers" de Wollastonita, uma vitrocerâmica do complexo (CaSiO3), que assim como os vidros bioativos forma uma camada de hidroxiapatita se ligando firmemente aos ossos e tecidos adjacentes. O objetivo deste estudo foi avaliar a biocompatibilidade e o comportamento do CFC acrescido de "whiskers" de Wollastonita in vivo. Para obtenção dos cimentos os pós de ? -TCP com ou sem 10% de "whiskers" de Wollastonita foram adicionados a uma solução aquosa contendo 2,5% em massa de Na2HPO4 (fosfato de sódio bibásico anidro). O biomaterial então se transformou em uma pasta a qual foi moldada no defeito crítico de 5 mm realizado no osso parietal de ratos Wistar. Foram utilizados 30 ratos divididos em dois grupos. O primeiro grupo recebeu o implante de ?-TCP (grupo TCP) e o segundo recebeu implante de ?-TCP acrescido de 10 % de "whiskers" de Wollastonita (grupo TCPW). Cinco animais de cada grupo foram eutanasiados no prazo de 30, 90 e 120 dias. As calvárias foram retiradas e submetidas a processamento histológico com Eosina e Hematoxilina e Tricrômio de Masson. A análise morfométrica foi realizada com auxílio do software NIS-Elements: Advanced Research 3.0 no qual foi possível mensurar a área de osso neoformada nos diferentes períodos de tempo. Os resultados expressaram uma média de área de osso neoformado no grupo TCP de (2, 25%), (2,80%) e (2,93%) após 30, 90 e 120 dias após a implantação respectivamente. No grupo TCPW a área de osso neoformado foi de 4,53% aos 30 dias, 5, 08% aos 90 dias e 3,76% aos 120 dias. Para avaliação macroscópica da resposta do tecido á presença do biomaterial as calvárias de 120 dias foram submetidas ao processo de maceração com Peróxido de Hidrogênio. Concluí se que o ?-TCP acrescido de 10% de "whiskers" de Wollastonita é uma alternativa viável para engenharia tecidual óssea, pois se mostrou biocompatível e capaz de estimular a neoformação óssea / Abstract: Biomaterials can be used in various areas of regenerative bioengineering, being a viable option in the repair of bone lesions. Currently different kinds of biomaterials have been studied, including ceramics that can be classified into three types: bioactive glasses, glass ceramics and ceramics of calcium phosphate. The calcium phosphate ceramics can be subdivided into Hydroxyapatite and Calcium Phosphate Cement (CFC). The CFC has been highlighted for its easy handling capacity of resorption and stimulation of osteogenesis. However, CFCs have restricted its use as an implant because it has low fracture toughness compared to natural bone. To reinforce CFCs carbon fibers, aramid and carbide have been used. Another type of reinforcement are the "whiskers" that comprise very short fibers. In this study we used a CFC-based ?-TCP reinforced with "whiskers" of Wollastonite, a ceramic complex (CaSiO3), so as bioactive glasses form a layer of hydroxyapatite firmly linking the bones and surrounding tissues. The aim of this study was to evaluate the biocompatibility and the behavior of CFC doped "whiskers" of Wollastonite in vivo. To obtain the cement powder of ?-TCP with or without 10% "whiskers" of Wollastonite was added to an aqueous solution containing 2.5 wt% Na2HPO4 (bibasic sodium phosphate anhydrous). The biomaterial is then transformed into a paste which was shaped in the critical defect of 5 mm held in Wistar rat parietal bone. Were used 30 rats divided into two groups. The first group received implantation of ?-TCP (TCP group) and the second received implantation of ?-TCP doped 10% of "whiskers" of Wollastonite (TCPW group). Five animals from each group were euthanised within 30, 90 and 120 days. The calvaria were removed and sent for histological analysis with hematoxylin and eosin and Masson Trichrome. The morphometric analysis was performed using NIS-Elements software: Advanced Research 3.0 in which it was possible to measure the area of newly formed bone in the different periods of time. The results expressed an average area of newly formed bone in the TCP group (2.25%), (2.80%) and (2.93%) after 30, 90 and 120 days after implantation, respectively. TCPW group in the area of new bone formation was 4.53% at day 30, 5.08% at 90 days and 3.76% at 120 days. For macroscopic evaluation of the tissue response to the presence of the biomaterial calvarial 120 days were subjected to maceration process with Hydrogen Peroxide. Concluded that the ?TCP doped 10% of "whiskers" of Wollastonite is a viable alternative for bone tissue engineering because it showed biocompatible and capable of stimulating bone formation / Mestrado / Anatomia / Mestra em Biologia Celular e Estrutural

Orientador: José Angelo Camilli / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-23T08:42:16Z (GMT). No. of bitstreams: 1 Domingues_JulianaAlmeida_M.pdf: 6712230 bytes, checksum: abfef192b69eeb8cc178a08e435692fd (MD5) Previous issue date: 2013 / Resumo: Cimentos de fosfato de cálcio (CFC) a base de ?-TCP, que originam como processo final de cura uma hidroxiapatita deficiente em cálcio (CDHA) são muito utilizados como biomateriais para osso, por possuírem similaridade estrutural e química à porção inorgânica do tecido ósseo. Porém o uso dos CFC se restringe a pequenos defeitos bucomaxilofaciais e recobrimento de próteses metálicas, em função do déficit considerável de suas propriedades mecânicas. Visando melhorar as propriedades mecânicas dos CFCs estudos têm sido direcionados à aplicação de fibras de vários materiais, como as fibras de carbono, as fibras de vidro, as de carboneto, entre outras. No entanto, muitas dessas fibras introduzidas se mostraram tóxicas às células, impedindo sua aplicação clínica. Recentemente, os "whiskers" (fibras curtas de monocristal) de biocerâmicas vêm sendo estudados como outro tipo de reforço, cujos resultados têm se mostrado promissores por melhorarem as propriedades mecânicas e biológicas dos materiais. Nesse trabalho, a resposta biológica das CDHA pura e contendo 5 e 10% de "whiskers" de wollastonita, foram estudadas através de um sistema de cultivo celular com células osteoblásticas, o qual tem sido muito utilizado para elucidar a resposta celular em biomateriais. Porém cultivar células em CDHAs não é uma tarefa fácil, pois o processo de hidrólise sofrido por esses materiais promove a liberação de íons para o meio de cultura, o que acarreta na mudança de pH e concentração iônica do meio. Essas mudanças promoveram a morte das células após 48h de cultivo. Foi possível manter as células viáveis ao longo do tempo realizando a lavagem dos discos de CDHA com DMEM (Dulbecco's Modified Eagle Medium) antes da semeadura e também com a troca diária do meio de cultura. Nossos resultados demonstraram que as CDHA contendo "whiskers" foram capazes de estimular a proliferação celular quando comparadas com a placa de poliestireno e a CDHA pura. No ensaio de MEV foi possível observar uma densa camada celular na superfície da CDHA contendo 10% de "whiskers". A atividade da fosfatase alcalina (FAC) foi significativamente maior nas CDHAs contendo "whiskers", sendo proporcional a concentração de "whiskers" wollastonita nas amostras, o ensaio de mineralização corroborou com o ensaio de FAC, no qual a CDHA contendo 10% de "whiskers" apresentou maior produção de matriz mineralizada. Tendo-se em vista os presentes resultados pode-se dizer que as CDHA contendo "whiskers" de wollastonita são biomateriais promissores para engenharia tecidual óssea, pois foram capazes de estimular a proliferação e diferenciação celular, além da resistência mecânica melhorada pela adição dos "whiskers" / Abstract: Calcium phosphate cements (CFCs) are widely used as biomaterials for bone because they have chemical and structural similarity to the inorganic portion of bone tissue. But the use of CFCs is restricted to maxillofacial small defects and coating metallic prostheses, due to the considerable deficit of its mechanical properties. In order to improve the mechanical properties of CFCs studies have focused on the application of fibers of many materials such as carbon fibers, glass fibers, carbide fibers among others. However, many of these fibers are shown toxic to the cells, preventing their clinical application. Recently, the "whiskers" (short crystal fibers) of bioceramics have been studied as another type of reinforcement and the results have shown promise for improving the mechanical and biological properties of materials. In this work the biological response of hydroxyapatites deficient in calcium (CDHA) pure and containing 5 and 10% "whiskers" of wollastonite, were studied using a cell culture system with osteoblastic cells, which has long been used to elucidate the cell behavior in biomaterials. However cultivating cells in CDHAs is not an easy task because the hydrolysis process undergone by such materials promotes the release of ions to the culture medium, which results in the change of pH and ionic concentration of the medium. These changes promoted cell death after 48 h of cultivation. Cell viability was maintained for 14 days by a simple washing of CDHA discs with DMEM before cell culture and also with daily changes of culture medium. Our results demonstrate that CDHA containing "whiskers" were able to stimulate cell proliferation when compared to the polystyrene plate and CDHA pure. In the assay by SEM was possible to see a dense cell layer on the surface of the CDHA containing 10% "whisker." The alkaline phosphatase activity (ALP) was significantly higher in CDHAs containing "whiskers" being proportional to the concentration of "whiskers" wollastonite samples. The mineralization assay corroborated with ALP assay in which the CDHA containing 10% " whisker "showed higher production of mineralized matrix. In summary the CDHAs containing "whiskers" of wollastonite are excellent biomaterials for bone tissue engineering, because they were able to stimulate cell proliferation and differentiation, as well as mechanical strength improved by the addition of "whiskers" / Mestrado / Biologia Celular / Mestra em Biologia Celular e Estrutural

<p>This thesis focused on testing the suitability of reactive filter media used for phosphorus (P) removal from wastewater as fertilizers, thus recycling P to agriculture. The work compared the P sorption capacity of several materials in order to assess their suitability as a source of P for plants. The selected materials (Filtra P, Polonite and wollastonite) were saturated with P and used as soil amendments in a pot experiment. The amendments tended to improve the yield of barley and ryegrass compared with no P addition. The amendments also increased soil pH, P availability and cation exchange capacity in the studied soils. The substrates studied here can be of particular interest for acid soils. Of the materials studied, Polonite appears to be the most suitable substrate for the recycling of P from wastewater to agriculture</p>

Apatite containing bioceramic materials are considered to be potentially useful for replacement or repair of natural bone. In the present study, the aim was to produce a new composite bioceramic containing crystalline apatite and wollastonite phases with a bimodal grain size distribution. The manufacturing scheme was based on the liquid phase sintering process in which the compacts pressed from powders of apatite (HAP or Si&shy / HAP) and pseudowollastonite was sintered in the presence of a liquid phase. Three distinct fluxing agents, magnesium flux (MCAS), sodium feldspar and sodium frit (NCAS), were prepared to act as additives for generating the liquid phase during sintering. Among those, the use of sodium frit resulted in the expected bimodal microstructural assembly. During the sintering studies, it was discovered that the apatite component of the ceramic was prone to compositional modifications by reaction with the liquid phase. This interaction resulted in a formation of siliconized HAP which crystallized in the form of rod-like grains. Meanwhile wollastonite grains tended to exhibit faceted equiaxed morphology and bonded to rod-like apatite grains with the help of a glassy phase. The results showed significant enhancement in the mechanical properties of apatite-wollastonite composites compared to phase pure hydroxyapatite. For example, the sample with 47.5 wt% Si-HAP2 + 47.5 wt% W + 5 wt% NCASfrit had the highest value of flexural strength, 83.6 MPa, which was almost twice that of hydroxyapatite, 46.3 MPa. The results for other properties such as compressive strength, hardness and fracture toughness also demonstrated the benefit of apatite-wollastonite composite approach.

Mica based glass - ceramics have been produced by subjecting the glasses in the SiO2 , Al2O3 , CaO , MgO, K2O , and F system to a controlled heat treatment called crystallization. TiO2 was added into the batch in the amount of 1 wt% of the glass as nucleating agent. B2O3 additions in the amounts of 1, 2, 4 and 8 wt% of the glass have been made in the batch to see and evaluate the effects of B2O3 additions on the texture of the mica glass ceramics. Crystallization was accomplished in two steps, nucleation and crystal growth. Nucleation temperature was 650 &amp / #61616 / C. Crystal growth temperatures were 850 and 1000 &amp / #61616 / C. The time for holding the specimens at the temperatures was 8 hours. The X-Ray diffraction analysis revealed that resultant glass ceramics possessed not only synthetic fluormica crystals called phlogopite which provide machinability, but also wollastonite crystals which provide biocompatibility. The scanning electron microscopy examinations have indicated that the amount and distribution of the crystalline phases varied as a function of B2O3 content and heat treatment schedule applied.