Une étude de l’oxydation d’une poudre de nanoparticules de cuivre a été menée à 120 - 145°C sous des pressions partielles d’oxygène allant de 1 à 40 kPa. La réaction a été suivie par thermogravimétrie afin d’obtenir les données cinétiques. Des caractérisations chimiques, texturales et morphologiques de la poudre ont été réalisées à différents moments de la transformation. La cuprite (Cu2O) (produit unique) de la réaction croît d’une manière anisotrope et par développement externe autour de la particule initiale qui devient creuse. Une diminution de la surface spécifique et de la porosité de la poudre au cours de la transformation a été mise en évidence.Des tests cinétiques ont montré l’existence d’une étape limitante de croissance jusqu’à un taux de conversion de 0,7 à 140°C. Il a également été montré que pour P(O2) ≤ 4 kPa, les processus de germination et de croissance de l’oxyde interviennent simultanément pendant la réaction et que l’adsorption de l’oxygène est l’étape limitante. Pour P(O2) ≥ 20 kPa, la germination se fait instantanément au début de la transformation dont la vitesse est contrôlée par le processus de croissance, la diffusion du cuivre étant alors l’étape limitante. Deux modèles ont été construits et testés avec succès pour décrire la cinétique dans les deux gammes de P(O2) jusqu’à un taux de conversion donné. Pour expliquer le ralentissement observé au-delà de ce taux de conversion et pour P(O2) ≤ 4 kPa, le modèle a été couplé aux phénomènes de transfert de chaleur et de matière au sein des agglomérats. Ce couplage permet d’évaluer l’hypothèse d’un ralentissement de la réaction par la diffusion des molécules d’oxygène dans les pores de l’agglomérat. / The oxidation of copper nanoparticles at 120 – 145°C was investigated using TGA, DSC, XRD, SEM, TEM and nitrogen adsorption techniques (BET, BJH,..). Isothermal and isobaric studies of the oxidation reaction were carried out under various oxygen partial pressures 1 kPa – 40 kPa. The cuprous oxide (Cu2O) (the unique product of the reaction) grows in an anisotropic manner by outward diffusion of the copper. A considerable decrease of the specific surface area and the porosity of the powder during the transformation was highlighted.It was found that working under P(O2) ≤ 4 kPa leads to reaction where nucleation of Cu2O is in competition with its growth. The study of the dependency of the growth rate on the oxygen partial pressure has shown the adsorption of oxygen to be the rate-determining step. However, when the reaction is conducted under P(O2) ≥ 20 kPa, the nucleation occurs instantaneously in the early beginning of the reaction which will be governed by the growth process. Under these latter conditions of oxygen partial pressure the diffusion of copper ionized vacancies becomes the rate determining step. Hence, two kinetic models have been established to interpret the experimental curves in the two different oxygen partial pressure ranges. The expression of the extent of conversion was successfully confronted to the kinetic data up to an extent of conversion corresponding to the slowdown of the reaction. The kinetic model for P(O2) ≤ 4 kPa was coupled with mass and heat transfer within the porous agglomerate to verify if the diffusion of oxygen molecules in pores is in the origin of the reaction slowdown, this latter hypothesis was found not satisfactory.

Les cermets, nommés M(p)-CMC(s), « Ceramic Matrix Composite dispersed with Metallic Particles », sont prometteurs dans les applications à haute température. Un cermet modèle (304L-YSZ) constitué de 40 % vol. de particules d'acier inoxydable 304L dispersées dans une matrice de zircone partiellement stabilisée à l’yttrium a été préparé par métallurgie des poudres. Les cermets sont homogènes et possèdent une densité voisine de 97 % par rapport à la densité théorique. Une étude cinétique basée sur l’hypothèse de l’étape limitante, a été réalisée afin de proposer un mécanisme et un modèle d’oxydation du cermet. Dans un premier temps, l’oxydation de la poudre d’acier inoxydable a été étudiée sous oxygène à 800 °C. Les expériences d'oxydation sous He (80 %)-O2 (20 %) ont été conduites par thermogravimétrie. Conformément à la littérature, la cinétique d’oxydation de la poudre suit un régime de diffusion. Une couche d’oxyde à base de chrome à croissance externe est observée.En revanche, la cinétique d’oxydation du cermet modèle est différente de celle de la poudre de 304L. Un fort gain de masse est observé dès l’introduction de l’oxygène au début du palier isotherme. Pendant le palier isobare, la prise de masse est lente et n’est pas régie par la diffusion. La caractérisation des cermets oxydés montre que des nodules riches en chrome apparaissent tout d’abord à l’intérieur du métal. Puis une couche d’oxyde à base de chrome et de fer se forme par croissance externe. La matrice de zircone ne limite pas la diffusion de l’oxygène vers le métal. Elle se fissure sous l’action des contraintes mécaniques induites par le changement de volume des particules de 304L pendant l’oxydation. / Ceramic matrix composite dispersed with metallic particles, called M(p)-CMC(s), are being developed for optimizing several functions of industrial components in severe atmospheres at high temperature.The corrosion of a model M(p)-CMC(s), based on 304L stainless steel and yttrium doped zirconia (304L(p)-ZrO2(s); 40%/60% in volume) is studied and compared with the oxidation behaviour of the stainless steel powders. The oxidation behaviour of the model 304L(p)-ZrO2(s) composite produced by powder metallurgy, studied by means of the thermogravimetry under 20 % O2 in helium at 800 °C, is presented. Oxidation curves show a fast increase in mass gain followed by slow one for the composite material. SEM observations and Auger spectroscopy measurements of the oxidized composite indicate an outward complex Cr and Fe rich oxide layer whereas Cr2O3 nodules are observed to nucleate and develop inward. For 304L stainless steel powder, the shape of the mass gain curve is parabolic, in agreement with a diffusion controlled oxidation. SEM observations of oxidised powder and in situ XRD measurements at 800 °C under oxygen show an external growth of Cr2O3 oxide layer.The low resistance to oxidation of the composite (compared to the powder) in the initial period seems to be due to the properties of the zirconia/metallic particles interface obtained after the sintering process. Under reducing conditions, the initial Cr2O3 layer reacts with zirconia matrix. TEM observation of the “as sintered” interface between the metallic particles and the ceramic shows no chromia layer. Sudden changes in oxygen partial pressure during experiments reveal an accelerating effect of the oxygen pressure.

La corrosion à haute température d'alliages métalliques représente un processus d’endommagement critique dans de nombreux domaines industriels. Le suivi en service de la dégradation des équipements opérant sous une atmosphère agressive à haute température devient un objectif majeur pour les industriels. Grâce à sa sensibilité et à son caractère non destructif, l'émission acoustique constitue une méthode intéressante pour suivre l’évolution de la détérioration des matériaux soumis à des formes sévères de corrosion comme le metal dusting pour les alliages de fer ou de nickel en pétrochimie. Notre étude a montré que les transformations irréversibles des matériaux telles que la fissuration peuvent être détectées grâce aux signaux acoustiques émis pendant la corrosion. Un couplage innovant a été développé associant l'émission acoustique in situ avec la thermogravimétrie. Dans un premier temps, ce couplage nous a permis d’étudier et d’approfondir nos connaissances de la corrosion à 900 °C sous atmosphère oxydante d’un alliage de zirconium. Les phénomènes comme la diffusion de l’oxygène dans la zircone ne sont pas émissifs ; par contre les mécanismes de dégradation irréversibles, comme l'initiation et la propagation des fissures dans la couche de zircone, sont décelables dès leur apparition. Dans un second temps, lors de l’étude de la carburation du fer pur ou du fer pré-Oxydé, nous avons démontré que la corrosion par metal dusting qui comporte une étape d’insertion des atomes de carbone dans la matrice de fer est détectable grâce à l’émission acoustique. Il est donc envisageable de suivre ce type de dégradation au moyen de l’émission acoustique lorsqu’il affecte les équipements industriels. / High temperature corrosion of metallic alloys can cause damage to chemical and petrochemical industrial equipment. On line monitoring of the behaviour of components, which operate under corrosive atmosphere at high temperature, has become an important challenge. In order to quantify the level of damage of materials affected by corrosion, acoustic emission seems to be an interesting method due to its sensitivity and its non-Destructive aspect. Based on bibliographic supports, we have developed an experimental device combining thermogravimetric analysis with acoustic emission in order to simultaneously record the sample mass variations and the acoustic signals mainly due to the degradation of materials such as cracks formation during oxidation of metal at high temperature for example.First of all, we have studied Zircaloy-4 corrosion behavior at 900 °C under oxidant gas by means of this innovative equipment. We have demonstrated the feasibility of such a coupling method; mass measurements are not disrupted by acoustic emission chain connected to the thermobalance. Irreversible mechanisms, as cracks initiation and propagation, generate acoustic emission bursts. Analysis of the burst waveforms and of the oxidized sample cross sections allows us to attribute the acoustic events to corrosion or cooling processes. Secondary, metal dusting of pure iron at 650 °C under highly carburising gases (i-C4H10 + H2) was studied. Iron bulk degradation caused by graphite deposition and insertion has been detected using acoustic emission. This result lets us think that this technique can be adapted to monitoring of industrial equipment.

This master thesis deals with the optimization of the procedure of modification of hyaluronic acid structure for the use in the artificial synovial liquids. Based on the literature research, the amino acid alanine was used for the modification of carboxylic group in the glucuronic acid. The main subject of study is the improvement of the stability and mechanical properties of synovial liquid. DLS microrheology, macrorheology, thermogravimetric analysis (TGA), multi-angle light scattering with flow-field flow fractionation (AF4-MALS) and infrared spectroscopy (FTIR) were used for characterization. The theoretical part of this theses submits review of the musculoskeletal system, role of hyaluronic acid in metabolism and summary of synovial liquid. The experimental part focuses on the measurement of the stability and mechanical properties of three artificial samples (first with no modification, second with modified hyaluronic acid and third with modified hyaluronic acid and chondroitin sulphate). These samples were compared with real horse synovial fluid and artificial viscosupplement Orthovisc®.

Orientador: Ivonete Ávila / Resumo: A biomassa apresenta-se como uma promissora alternativa aos combustíveis fósseis por ser renovável, de baixo custo e amplamente disponível. Esta pode ser obtida a partir de resíduos agroindustriais mostrando-se como um importante modelo de energia sustentável. Os principais componentes da biomassa são hemicelulose, celulose e lignina e, por possuírem diferentes propriedades químicas, influenciam diretamente na eficiência de um processo de conversão termoquímica. Metodologias convencionais atualmente aceitas na determinação dos principais componentes da biomassa requerem maior tempo e possuem alto custo. A análise termogravimétrica (TG) é uma técnica rápida e de baixo custo, resultando em curvas TG/DTG que fornecem uma indicação do percentual de cada um dos componentes da biomassa. Entretanto, não há uma metodologia aceita no sentido de substituir o método convencional por via úmida na determinação dos constituintes de materiais lignocelulósicos. Portanto, o objetivo deste estudo é avaliar o efeito da interação entre os componentes do bagaço e da palha de cana-de-açúcar (hemicelulose, celulose e lignina), isolados por diferentes tratamentos químicos, por meio da análise de sinergismo em ensaios termogravimétricos. Este estudo contribuirá para a elaboração de uma metodologia para determinação dos teores desses componentes por meio da análise termogravimétrica, com precisão similar aos métodos convencionais. Os resultados da caracterização química e a caracterização físico-quími... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Biomass presents itself as a promising alternative energy source to replace or reduce the use of fossil fuels because it is renewable, low cost and widely available. This can be obtained from agro-industrial waste, showing itself as an important model of sustainable energy. The main components of biomass are hemicellulose, cellulose and lignin and, due to their different chemical properties, they directly influence the efficiency of a thermochemical conversion process. Currently, the accepted methodologies for determining the main components of biomass require time and are expensive. Thermogravimetric analysis (TGA) is a fast and low-cost technique, resulting in TGA/DTG curves that provide an indication of the percentage of each biomass components. However, there is no accepted methodology in the sense to replace the conventional wet method use to determining the lignocellulosic materials components. Therefore, the objective of this study is to evaluate the effect of the interaction between the components of sugarcane bagasse and straw (hemicellulose, cellulose and lignin), isolated by different chemical treatments, through the analysis of synergism in thermogravimetric tests. This study will contribute to the development of a methodology for determining the content of these components through thermogravimetric analysis, with precision similar to conventional methods. The results of chemical characterization and physico-chemical characterization by FTIR and DRX technique of t... (Complete abstract click electronic access below) / Mestre

M.Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology / This study reports the synthesis and characterization of cobalt oxide nanoparticles using a microwave technique and chemical precipitation with oxidation method. Cobalt complexes were prepared using carboxylic acids (acetic acid, heptanoic acid, and stearic acid) as ligands. The complexes were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and Elemental analyses (EA). Cobalt oxide nanoparticles were synthesized from the complexes via a microwave-assisted technique. A precipitation oxidation preparation reaction was used varying different parameters like pH, time, oxidising agent, heating method and cobalt precursor. The use of the cobalt nitrate and cobalt acetate as cobalt precursors resulted in spherical and cubic nanoparticles respectively. Cobalt precursors containing a longer hydrocarbon chain length, for instance cobalt heptanoate, did not yield cobalt oxide nanoparticles with the precipitation oxidation reaction due non- solubility of the complex. Using cobalt acetate as precursor, an increase in the pH from 7.91 to 10.18 caused the cobalt oxide nanoparticles shape to become well defined cubes with a narrower size range and CoOOH needles formed when the pH was further increased to 12.26. The optimum pH of 10.18 yielded cubic cobalt oxide particles having an average size of 25.45 nm with a standard deviation of 6.12. The nanoparticle size decreased from 35.70 nm to 4.45 nm when the oxygen oxidant was replaced with hydrogen peroxide. Conventional heating with a hotplate yielded nanoparticles with a more homogenous shape and size than microwave heating. The size of the nanoparticles increased from 22.81 nm to 25.45 nm when reaction time changed from 16 hours to72 hours.

The knowledge of kinetics of pyrolysis is important. It is also challenging to find parameters for kinetic which can be applied at different sizes of biomass. Many researchers have been investigating the pyrolysis behavior of wood powders due to heat and mass transfer limitations. They have also been focusing on determining the effects of feedstock characterization, residence time, gas environment, heating rate and the final temperature as well as the arrangement of the pyrolysis reactor and modeling of the kinetics. This project presents a qualitative understanding of the pyrolysis process based on data from slow heating rates. Samples of spruce chips at different masses, namely 4 mg, 200 mg, 500 mg and 800 mg and also 4 mg powder have been used in experiments with thermogravimetric analysis to understand the mass loss behavior. Furthermore, kinetic parameters for biomass are taken from literature and have been used in modeling to understand to which extent these parameters are different for different particle sizes. The kinetic model that is chosen to investigate in this project is where each component of biomass shows different characteristics during the thermal decomposition. The experimental results on wood chips at different sample masses show same behavior for all of them and there is no heat and mass transfer limitations. The results from experiments on powders shows different behavior than for chips at the end of the mass loss curve only. This means less char is produced for powders than it is for the chips. The results from modeling show that kinetic parameters such as activation energy and the prefactor are the same for both powders and chips. The only parameter that is different is the pre-determined char yield for hemicellulose second reaction. The kinetic model and the kinetic parameters used in this report are in good agreement to the experimental results. The model used, where each component show different behavior during its thermal decomposition and the final products are volatiles and char is a reliable model to describe the mass loss behavior of biomass. The difference in the experimental results between powders and chips can be explained by the modeling. It can be stated that the difference is in the char yield from thermal decomposition of hemicellulose. / Kunskap om kinetiken för pyrolysprocessen är viktig. Det är även en utmaning att finna parametrar för kinetiken som kan tillämpas till olika massor och storlekar av biomassa. Många forskare har undersökt pyrolys beteenden på bara träpulver på grund av värme- och massöverföring begränsningar. De har också fokuserat på att undersöka effekterna av råvara karakterisering, uppehållstid, gasmiljö, uppvärmningshastighet och den slutliga temperaturen samt arrangemanget av pyrolysreaktorn och modellering av kinetiken. I detta projekt presenteras en kvalitativ förståelse av pyrolysprocessen baserad på data från långsamma uppvärmningshastigheter. Prover av granflis vid olika massor; 4 mg, 200 mg, 500 mg och 800 mg och även 4 mg pulver har använts i experimenten med thermogravimetric analys för att förstå massförlust uppträdandet. Dessutom har kinetiska parametrar för biomassa tagits från litteratur och har använts i modelleringen för att förstå i vilken utsträckning dessa parametrar skiljer sig åt för pulver och flis. Den kinetiska modellen som har valts att undersökas i detta projekt är den där varje komponent av biomassa visar separata och olika egenskaper under termisk nedbrytning. De experimentella resultat på flis vid olika provmassorna uppvisar samma beteende för dem alla och det finns ingen värme- och massöverföringsbegränsningar. Resultaten från experiment på pulver visar annorluna beteende än för träflis endast i slutet av massförlust kurvan. Detta innebär att mindre kol produceras för pulver än vad det gör för flis. Resultaten från modelleringen visar att kinetiska parametrar såsom aktiveringsenergin och prefactor är densamma för båda pulver och flis. Den enda parameter som skiljer sig är den förutbestämda utbytet av kol för hemicellulosa’s andra reaktion. Den kinetiska modellen och kinetiska parametrar som används i denna rapport är i god överensstämmelse med de experimentella resultaten. Denna modell som används, där varje komponent visar enskilt beteende under dess termisk nedbrytning och slutprodukterna är bara gaser och kol, är en pålitlig modell för att beskriva beteendet för massförlust av biomassa. Skillnaden i de experimentella resultaten mellan pulver och flis kan förklaras av modelleringen. Det kan konstateras att skillnaden är i kol utbytet från sönderdelningen av hemicellulosa.

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[pt] A demanda energética mundial está em constante crescimento e tal cenário faz aumentar a preocupação com os impactos ambientais, muitos deles decorrentes da exploração de combustíveis fósseis e sua utilização desmedida. Neste contexto, o estudo da pirólise da biomassa apresenta uma alternativa para a produção direta de calor que pode vir a ser utilizado em usinas termoelétricas sustentáveis. Uma investigação foi realizada abordando o tema da reciclagem de madeira sobre a possibilidade de aproveitá-la a biomassa principal deste processo. Este trabalho apresenta a caracterização da madeira reciclada bem como da madeira de eucalipto para poder averiguar a similaridade química entre as duas biomassas. Para tanto foram realizadas análises de espectroscopia de infravermelhos (FTIR) e difração de raios-X (DRX), além de análises de microscopia eletrônica de varredura com espectroscopia por dispersão de energia (MEV/EDS). Com o auxílio da técnica de termogravimetria (TG) foram realizados experimentos de pirólise lenta da madeira reciclada, a partir dos quais foram identificados eventos térmicos, caracterizados por perdas de massa. Para verificar um possível efeito oxidante dos óxidos Fe2CoO4 e Co3O4, realizou-se também pirólise lenta da mistura da madeira reciclada com cada um dos óxidos, tendo sido identificados eventos térmicos que não estavam presentes nos experimentos com a madeira pura. Os principais eventos foram avaliados cineticamente por métodos model-free que permitem a determinação da energia de ativação sem a necessidade de assumir uma ordem de reação. Foram utilizados os métodos de Kissinger (KS) e Kissinger-Akahira-Sunose (KAS), empregando os dados de experimentos realizados no TG com cinco taxas de aquecimento diferentes até 1100 graus Celsius. Para o evento térmico de maior importância, entre 200 e 390 graus Celsius tanto na madeira pura quanto na mistura, o ajuste de ambos o métodos foi satisfatório e está de acordo com a literatura. / [en] World s energy demand is constantly growing, and this scenario raises the concern about environmental impacts, many of them resulting from the constant manipulation of fossil fuels and their excessive use. In this context, the study of biomass pyrolysis presents an alternative for the direct production of heat that can be used in sustainable thermoeletric plants. To this end, a research has been carried out on the possibility of taking advantage of recycled wood as the main biomass of this process, an investigation that has been carried out along with a company in the field of wood recycling. This work presents the characterization of a recylced and a typical Brazilian eucalyptus wood with the purpose of proving their chemical similarity. Therefore, analysis of Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) was performed. Thermogravimetric (TG) experiments were carried out with slow pyrolysis of recycled wood and eucalyptus wood, from wich were identified thermal events, characterized by mass losses. To verify a possible oxidative effect of the compounds Fe2CoO4 and Co3O4, slow pyrolysis of a mixture of the recycled wood with each of the oxides was also performed, and thermal events that were not present in the experiments with the pure wood were identified. The main thermal events were kinetic investigated with model-free methods wich allows the determination of the activation energy without the need of a reaction order pre-stipulated. In this workk were tested the Kissinger (KS) and Kissinger-Akahira-Sunose (KAS) model-free methods and the TG data of five different heating rate were collected until 1100 Celsius degrees. For the most relevant thermal event, wich occurs from 200 to 390 Celsius degrees (for recycled wood and its mixture with the oxides) the adjustment of both methods was fine and accordance with literature.

Concrete is the most widely used man-made material in the world. Its versatility, strength, and relative ease of construction allow it to be used in the majority of civil infrastructure. However, concrete production plays a significant role in greenhouse gas emissions, accounting for around 8% of CO2 emissions worldwide. This thesis aims to reduce the demand for cement in concrete construction, thus reducing the carbon footprint of the concrete, by focusing on classifying and determining the effectiveness of seven different quarry by-products as partial replacements of cement. Several methods were utilized in this study to characterize the quarry by-products: particle size distribution, helium pycnometry, X-Ray diffraction, X-Ray fluorescence, scanning electron microscopy, and a modified ASTM C1897 Method A that utilizes isothermal calorimetry and thermogravimetric analysis. These various methods allowed for the determination of the physical properties (e.g., gradation, specific gravity, and morphology) and the chemical properties (e.g., mineralogy and reactivity in a cementitious system). The quarry by-products were classified as four granites, two limestones, and one greenstone. These quarry by-products were found to be non-pozzolanic and non-hydraulic. However, there are indications that there may be reactions with the various clays and feldspars in the quarry by-products with calcium hydroxide, which suggests a degree of reactivity that is not necessarily pozzolanic or hydraulic. / Master of Science / Concrete is the most widely used man-made material in the world. Its versatility, strength, and relative ease of construction allow it to be used in the majority of civil infrastructure. However, concrete production plays a significant role in greenhouse gas emissions, accounting for around 8% of CO2 emissions worldwide. This thesis aims to reduce the demand for cement in concrete construction, thus reducing the carbon footprint of the concrete, by focusing on classifying and determining the effectiveness of seven different quarry by-products as partial replacements of cement. Several methods were utilized in this study to determine the physical properties (e.g., gradation, specific gravity, and morphology) and the chemical properties (e.g., mineralogy and reactivity in a cementitious solution) of the materials. The quarry by-products were classified as four granites, two limestones, and one greenstone. In general, these quarry by-products were not found to be reactive as a supplementary cementitious material, although the data may suggest some degree of reactivity between calcium hydroxide and the clays and/or feldspars in the quarry by-products.