The current work contains experimental and theoretical work about the formation of martensite from the austenitic state of the steel Hardox 450. Simulation of rolling and subsequent quenching of martensitic steel plates requires a model that can account for previous deformation, current stresses and the temperature history, therefore dilatometry experiments were performed, with and without deformation. Two austenitization schedules were used and in the standard dilatometry the cooling rates varied between 5-100 °C/s, in order to find the minimum cooling rate that gives a fully martensitic microstructure. Cooling rates larger than 40°C/s gave a fully martensitic microstructure. The cooling rate of 100 °C/s was used in the deformation dilatometry tests where the uniaxial deformation varied from 5-50 %. The theoretical work involved modelling of the martensite formation and the thermal/transformation strains they cause in the steel. Characterizations were done using light optical microscopy, hardness tests and electron backscatter diffraction technique. The parent austenite grains of the martensitic structure were reconstructed using the orientation relationship between the parent austenite and the martensite. Kurdjumov-Sachs orientation relationships have previously been proven to work well for low-carbon steels and was therefore selected. The standard implementation of the Koistinen-Marburger equation for martensite formation and a more convenient approach were compared. The latter approach does not require the storage of initial austenite fraction at start of martensite formation. The comparison shows that the latter model works equally well for the martensite formation. The results showed that the use of martensite start and finish temperatures calibrated versus experiments for Hardox 450 works better when computing thermal expansion than use of general relations based on the chemistry of the steel. The results from deformation dilatometry showed that deformation by compressive uniaxial stresses impedes the martensite transformation. The simplified incremental model works well for deformation with 5 % and 10 %. However, the waviness in the experimental curve for deformation 50 % does not fit the model due vi to large barrelling effect and the large relative expansion for the material that the sample holders are made of. Crystallographic reconstruction of parent austenite grains were performed on a hot-rolled as-received reference sample and dilatometry samples cooled with 60 °C/s and 100 °C/s. The misorientation results showed that the samples match with the Kurdjumov-Sachs orientation relationship in both hot rolled product and dilatometry samples. When misorientation between adjacent pixels are between 15° and 48°, then the boundary between them was considered as a parent austenite grain. The austenitic grain boundaries of the sample cooled at 100 °C/s is in general identical with the hot rolled sample when considering high angle boundaries (15°-48°). The results from the hardness tests showed that the rolled product exhibits higher hardness as compared to samples cooled by 100 °C/s and 60 °C/s. This can be attributed to the formation of transition-iron-carbides in the hot rolled product due to longer exposure of coiling temperature.

An in-depth study of Al2W3O12 negative thermal expansion (NTE) ceramic was performed, focused on synthesis, phase mappings, and the underlying mechanisms shown to be responsible for NTE. Review of the literature has shown inconsistencies in reported values of the dilatometry measured coefficients of thermal expansion, and the temperature for the known monoclinic to orthorhombic phase transition. Two synthesis techniques are introduced: an ionic-liquid non-hydrolytic sol-gel synthesis route; and a low temperature solid state reaction synthesis for Al2W3O12. X-ray diffraction, Raman spectroscopy, and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) were used to verify the techniques. Two differential scanning calorimetry (DSC) experiments (high and low temperature) were performed on the material showing the transition between -5 and -20 °C and no other phase changes until a reported degradation above 1100 °C. Extensive dilatometry on the material led to the discovery of elastic transitions occurring in the polycrystalline sample capable of explaining the inconsistencies in reported dilatometry results. This is further developed into a proposed model defining the regions between these transitions. Each region has a different thermal expansion as well as a direct effect on the reaction of the material upon cooling. This proposed model may allow more consistent reporting of dilatometry results for NTE materials. Raman spectroscopy was performed from 25-725 °C on the material showing both a joining in the tungsten-oxygen bending modes as well as a broadening in the tungsten-oxygen stretching modes. This is consistent with Al-O-W angle changes along the same temperature range reported in literature as well as the transverse vibrational modes responsible for NTE.

Sintering is a one of the key step in a processing of bulk ceramic materials. New sintering methods were invented in the last years. These new sintering methods, according to their authors, can be used for obtaining finer final microstructure of ceramics only by modifying the heating schedule. This work is focused on an influence of the Two Step Sintering method on the final microstructure for oxide ceramics. Obtained experimental results have shown that the effectivity of the Two Step Sintering method is rising with crystallographic symmetry of used material. Thesis is also focused on a high-temperature dilatometry and concept of the Master Sintering Curve. This concept was used for calculation of the activation energy of sintering and finding different sintering mechanisms acting in the intermediate and final stage of sintering. Activation energy of sintering was compared with activation energy of grain growth with target to find the kinetic window. Kinetic window can allow a sintering without a grain growth. Master Sintering Curve method was also used in a pressure assisted unconventional sintering technique Spark Plasma Sintering. Master Sintering Curve applied to a Spark Plasma Sintering technique reveals and quantified different sintering mechanisms acting in Spark Plasma Sintering. These findings led to preparation of transparent tetragonal ZrO2.

The influence of silane treated amorphous fumed silica fillers on properties of the cured epoxy was examined in the first part of the study. Silica particles were treated with 3- aminopropyldiethoxymethylsilane (APDS) and 3-aminopropyltriethoxysilane (APTS) coupling agents. The filler and coupling agents decreased the mobility of the polymer chains in the vicinity of the filler leading to an increase in the activation energy for the glass transition and an increase in cooperativity. Fumed silica did not significantly affect moisture diffusion properties. Next, a linear dilatometer was used to investigate the effects of cure conditions, mold types, and the presence of filler in the model epoxy. These studies revealed that there was substantial shrinkage in the cured epoxy on heating it through its glass transition region. The shrinkage was determined to be the result of stress in the epoxy generated during cure and could be minimized by curing at lower temperatures, followed by a postcuring heat treatment. Additional free volume in the sample increased the magnitude of the shrinkage by allowing increased stress release through increased network mobility. Decreasing the polymer mobility by adding fillers decreased the observed shrinkage. The influence of the model epoxy crosslink density was examined by varying the content of 1,4-butanediol in the model system. Addition of 1,4-butanediol led to a decrease in the modulus and glass transition temperature, which resulted in a reduction in residual stress and subsequent shrinkage. Moisture uptake increased with the addition of 1,4-butanediol due to an increase in the free volume of the epoxy. However, even with greater moisture uptake, the addition of 1,4-butanediol to the epoxy increased its adhesion to quartz by promoting lower residual stress and increased energy dissipation. These results indicate that bulk diffusion of water is not the controlling factor in adhesive degradation in this system. / Ph. D.

Alkali compounds were added to a South African coal with a high swelling propensity and the behaviour of the blends were investigated. A vitrinite-rich bituminous coal from the Tshikondeni coal mine in the Limpopo province of South Africa was used. To reduce the influence of the minerals in the coal, the coal was partially demineralized by leaching with HCl and HF. The ash content of the coal sample was successfully reduced from 17.7% to 0.6%. KOH, KCl, K2CO3 and KCH3CO2 were then added to the demineralized coal in mass percentages of 1%, 4%, 5% and 10%. The free swelling indices (FSI) of the blends were determined and the samples were subjected to acquisition of TMA and TG-MS data. Addition of these potassium compounds to the demineralized coal reduced the swelling of the vitrinite-rich coal. From the free swelling indices of the various mixtures, it was concluded that the potassium compounds reduce the swelling of the coal in the following order of decreasing impact: KCH3CO2 > KOH > K2CO3 > KCl. From dilatometry experiments done on the blends with the 10% addition of potassium compounds, it was seen that with the addition of potassium compounds to the demineralized coal, a reduction in dilatation volume was obtained. The influence of the potassium compound in decreasing order: K2CO3> KOH> KCH3CO2> KCl. An increase in the softening temperature was observed for the demineralized coal-alkali blends. Thermogravimetric analyses were performed on the demineralized coal-potassium blended samples (<75 μm). These samples were pyrolyzed under a nitrogen atmosphere to a maximum temperature of 1200 °C using a heating rate of 10 °C/min. The relative reactivity for each of the blends with the different wt% addition was determined. From these results it was seen that KCH3CO2 increased the relative reactivity, whereas the KOH, KCl and K2CO3 showed an inhibiting influence. The attached mass spectrometer provided information on the low molecular mass gaseous products formed in the various temperature ranges as the thermal treatment proceeded. From the mass spectroscopy results, it was found that the potassium compounds decreased the temperature at which maximum evolution of H2 takes place. Thermomechanical analyses were performed on the 10 wt% addition of the potassium compounds to the demineralized coal. During TMA analyses, the sample was heated to 1000 °C using a heating rate of 10 °C/min. From the TMA result obtained it was clear that the addition of KCl did not have an influence on the swelling of the demineralized coal. All results are discussed. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Os aços maraging são aços de baixo teor de carbono com estrutura martensítica (CCC), que são endurecidos pela precipitação de fases intermetálicas. O objetivo deste trabalho é estudar as transformações de fases desses aços: precipitação, reversão da martensita para a austenita e transformação martensítica. Nesse trabalho, foram caracterizadas uma corrida de aço maraging da série 300 e três corridas da série 350, usando diversas técnicas complementares: microscopia ótica, microscopia eletrônica de varredura com análise dispersiva de energia, microdurômetro, difração de raios-X, ferritoscópio e dilatometria. Os resultados obtidos mostraram que as corridas com maiores teores de cobalto e titânio apresentaram maiores valores de microdureza nos estados solubilizado e envelhecido. Por outro lado, medidas dilatométricas mostraram que há uma influência significativa tanto da composição química, quanto da taxa de aquecimento nas reações de precipitação e reversão da martensita para a austenita. No entanto, a transformação martensítica mostrou-se dependente apenas da taxa de aquecimento. / Maraging steels are steels with a low carbon martensitic structure (BCC), which are hardened by precipitation of intermetallic phases. The aim of this work is to study the phase transformations of these steels: precipitation, martensite to austenite reversion and martensitic transformation. In this study, one cast of 300 grade and three casts of 350 grade were characterized using several complementary techniques: optical microscopy, scanning el ectron microscopy with energy dispersive analysis, microhardness, X-ray diffraction, ferritoscope and dilatometry. The results showed that the casts with higher concentrations of cobalt and titanium showed higher microhardness in the solution annealed and aged states. On the other hand, dilatometry measurements showed that there is a significant influence of both the chemical composition and the heating rate on the reactions of precipitation and reversion of martensite to austenite. However, the martensitic transformation was dependent solely on the heating rate.

Alkali compounds were added to a South African coal with a high swelling propensity and the behaviour of the blends were investigated. A vitrinite-rich bituminous coal from the Tshikondeni coal mine in the Limpopo province of South Africa was used. To reduce the influence of the minerals in the coal, the coal was partially demineralized by leaching with HCl and HF. The ash content of the coal sample was successfully reduced from 17.7% to 0.6%. KOH, KCl, K2CO3 and KCH3CO2 were then added to the demineralized coal in mass percentages of 1%, 4%, 5% and 10%. The free swelling indices (FSI) of the blends were determined and the samples were subjected to acquisition of TMA and TG-MS data. Addition of these potassium compounds to the demineralized coal reduced the swelling of the vitrinite-rich coal. From the free swelling indices of the various mixtures, it was concluded that the potassium compounds reduce the swelling of the coal in the following order of decreasing impact: KCH3CO2 > KOH > K2CO3 > KCl. From dilatometry experiments done on the blends with the 10% addition of potassium compounds, it was seen that with the addition of potassium compounds to the demineralized coal, a reduction in dilatation volume was obtained. The influence of the potassium compound in decreasing order: K2CO3> KOH> KCH3CO2> KCl. An increase in the softening temperature was observed for the demineralized coal-alkali blends. Thermogravimetric analyses were performed on the demineralized coal-potassium blended samples (<75 μm). These samples were pyrolyzed under a nitrogen atmosphere to a maximum temperature of 1200 °C using a heating rate of 10 °C/min. The relative reactivity for each of the blends with the different wt% addition was determined. From these results it was seen that KCH3CO2 increased the relative reactivity, whereas the KOH, KCl and K2CO3 showed an inhibiting influence. The attached mass spectrometer provided information on the low molecular mass gaseous products formed in the various temperature ranges as the thermal treatment proceeded. From the mass spectroscopy results, it was found that the potassium compounds decreased the temperature at which maximum evolution of H2 takes place. Thermomechanical analyses were performed on the 10 wt% addition of the potassium compounds to the demineralized coal. During TMA analyses, the sample was heated to 1000 °C using a heating rate of 10 °C/min. From the TMA result obtained it was clear that the addition of KCl did not have an influence on the swelling of the demineralized coal. All results are discussed. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-03-17T11:04:02Z No. of bitstreams: 0 / Made available in DSpace on 2015-03-17T11:04:02Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Resumo: O objetivo deste trabalho foi caracterizar química e metalograficamente o Ti.c.p. antes e após a fundição por Plasma-Skull, e estudar as interfaces entre esse metal e as porcelanas Vitatitankeramik, Triceram e Noritake TI22, empregando-se M.E.V., EDS, Mapeamento Elementar e Dilatometria. Trinta e cinco placas nas dimensões de 25mm x 3mm x 1mm foram fundidas pela máquina nacional Discovery - Plasma, EDG Equipamentos, sendo 5 amostras empregadas para a análise química e metalográfica e as 30 restantes, utilizadas para aplicação das porcelanas, sendo divididas em 3 grupos de 10 placas cada. O tratamento da superfície do metal, bem como a aplicação e as cocções das porcelanas foram realizadas segundo as recomendações de cada fabricante. Posteriormente, as amostras tiveram uma de suas faces laterais lixadas, até a exposição da interface e preparadas para análise por M.E.V. Para os ensaios de Dilatometria, 2 amostras de Ti c.p. e 2 para cada sistema de porcelanas foram confeccionadas na forma de cilindro com 12 mm de comprimento x 2 mm de diâmetro, e em cada amostra foi soldado um termopar de cromel-alumel, para medida de temperatura dos ensaios. As curvas de expansão térmica do Ti c.p. e das três porcelanas, foram levantadas para estudar a compatibilidade entre os conjuntos metalocerâmicos. Os resultados da análise química e das imagens obtidas por Microscopia Óptica, demonstram que o Ti c.p. após a fundição apresenta condições físico-químicas adequadas para receber a aplicação da porcelana. Dos resultados de M.E.V., observa-se que todos os sistemas apresentaram integridade nas interfaces Ti/Bonder, livre de fendas ou poros, com um bom contato entre a porcelana e o metal, confirmado pelas imagens do Mapeamento Elementar, sugerindo uma adequada interação entre esses materiais. Da análise das imagens do EDS... (Resumo completo, clicar acesso eletrônico abaixo). / Abstract: The aim of this work was to perform a chemical na metalographical characterization of the commercially pure titanium before and after melting by the Plasma-Skull method, and to study the interfaces between this metal and the porcelains Vitatitankeramik, Triceram e Noritake TI22, using SEM, EDS, elementary mapping and dilatometry. Thirty five samples with dimensions 25mm x 3mm x 1mm were melted in a national Discovery-Plasma, EDG Equipaments, five of which were used for chemical analysis and metalography and the remaining thirty, divided in three groups, were used for applications of the porcelains. The metal surface treatment, as well as the applications and firing of the porcelains, were performed according to the recommendations of each manufacturer. Subsequently, one of the lateral surfaces of the samples was polished until the interfaces was exposed and then was prepared for the SEM analysis. Two samples of commercially pure titanium and other two for each system of porcelains were cylindrically shaped with lengths of 12mm and 2mm of diameter, and in each sample Chromel-Alumel thermocouple was welded to measure the temperature of the tests. The thermal expansion curves of the commercially pure titanium and porcelains were measured to study the compatibility of the metal-ceramic systems. The chemical analysis and optical microscopy results show that the commercially pure titanium after the melting exhibits appropriate physical and chemical conditions for the application of the porcelain. The SEM results indicate that all the systems exhibits integrity of the Ti/bonder interface, free of gap and porous, with good contact between metal and porcelain, which was confirmed by the elementary mapping images, suggesting and adequate interaction between these materials. From the analysis of the EDS images... (Complete abstract, click electronic address below). / Orientador: José Roberto Cury Saad / Coorientador: Antônio Carlos Guastaldi / Banca: Marcelo Ferrarezi de Andrade / Banca: Silvio José Mauro / Mestre

Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2015-03-17T11:04:02Z No. of bitstreams: 0 / Made available in DSpace on 2015-03-17T11:04:02Z (GMT). No. of bitstreams: 0 / Cerâmicas à base de alumina pertencem à classe de materiais denominados estruturais, muito utilizados em ferramentas de corte. A alumina possui boas propriedades para uso como cerâmica estrutural e com o objetivo de melhorar suas tenacidade à fratura e resistência mecânica, são produzidos compósitos com diferentes aditivos. Novos estudos apontam para os micro-nanocompósitos, onde a adição de partículas micrométricas deve auxiliar no aumento da resistência mecânica, e de partículas nanométricas, no aumento da tenacidade à fratura. Neste trabalho foram obtidos micro-nanocompósitos à base de Al2O3 com inclusão de partículas nanométricas de NbC e micrométricas de WC com proporções de 2:1, 6:4, 10:5 e 15:10 e micro-nanocompósitos à base de Al2O3 com inclusão de partículas nanométricas de NbC e micrométricas de TaC com proporção de 2:1 em relação à alumina. Para o estudo de densificação, os micro-nanocompósitos foram sinterizados em dilatômetro com taxa de aquecimento de 20 °C / min até a temperatura de 1800 °C, em atmosfera de argônio. Com base nos resultados de dilatometria, corpos de prova foram sinterizados entre 1500°C e 1700°C, com patamar de 30 minutos, em forno resistivo de grafite e atmosfera de argônio. Foram determinadas as densidades, fases cristalinas formadas, durezas e tenacidades, e analisadas as microestruturas dos micro-nanocompósitos. As amostras Al2O3:NbC:TaC sinterizadas a 1700°C atingiram as maiores densidades aparentes (~95%DT) e a amostra sinterizada a 1600°C apresentou microestrutura homogênea e valor de dureza (15,8 GPa) em comparação à alumina pura. As composições com 3% de inclusões são as mais promissoras para aplicações futuras como ferramentas de corte. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP