The cost of an aluminium extrusion die accounts for 35-50% of the total extrusion cost, hence it is important to understand the kinetics of extrusion die heat treatment. The main objective of die heat treatment is to increase the surface hardness so the surface wear property can be enhanced, which extends the die service life. Before the die material is case hardened by processes such as nitriding, the material is first heat treated to certain hardness. Thus the aim of this investigation is to understand the kinetics of carbon diffusion during steel austenitzation because it is significant to steel hardness property.H13 hot work tool steel, a well known material used as a die material for its superior mechanical and hardening properties, was used for the analysis of carbon diffusion during austenization. Samples made of H13 steel were subjected to four different atmospheric conditions: heat treatment without atmospheric control, heat treatment with stainless steel foil wrapping, pack carburization heat treatment and vacuum heat treatment. Three treatment time ranges were also applied for the carbon diffusion modelling. Some samples were further treated by gas nitriding to establish the effect of carbon content on the gas nitriding performance.It was found that decarburization occurred when atmospheric control did not take place during the heat treatment process. Through the carbon diffusion analysis, at austenitizing temperature of 1020ºC, the equilibrium surface carbon content at 1020ºC was 0.157wt%, with activation energy of carbon in H13 steel of 20,200cal/mol, and carbon diffusivity at 1020ºC was 1.97x10-8cm2/s.This study also proved that proper stainless steel foil wrapping on the heat treating material could restrict decarburization process, resulting in a constant hardness profile as vacuum heat treatment does. However the tempering characteristic between this two heat treatment methods are different to each other.For the pack carburization heat treatment, it was noted that the samples suffered from decarburization at early stage of heat treatment as carbon monoxide level was not adequate for carburization process.Results from the gas nitrided samples showed that the thickness and the hardness of the nitrided layer was independent to the carbon content in H13 steel. After 2 rounds of gas nitriding process, further nitriding seemed to have no significant effect on the hardness and thickness of the nitrided layer. Furthermore, the white layer was not observed in the nitrided samples which were heat treated without atmospheric control.

The cost of an aluminium extrusion die accounts for 35-50% of the total extrusion cost, hence it is important to understand the kinetics of extrusion die heat treatment. The main objective of die heat treatment is to increase the surface hardness so the surface wear property can be enhanced, which extends the die service life. Before the die material is case hardened by processes such as nitriding, the material is first heat treated to certain hardness. Thus the aim of this investigation is to understand the kinetics of carbon diffusion during steel austenitzation because it is significant to steel hardness property.H13 hot work tool steel, a well known material used as a die material for its superior mechanical and hardening properties, was used for the analysis of carbon diffusion during austenization. Samples made of H13 steel were subjected to four different atmospheric conditions: heat treatment without atmospheric control, heat treatment with stainless steel foil wrapping, pack carburization heat treatment and vacuum heat treatment. Three treatment time ranges were also applied for the carbon diffusion modelling. Some samples were further treated by gas nitriding to establish the effect of carbon content on the gas nitriding performance.It was found that decarburization occurred when atmospheric control did not take place during the heat treatment process. Through the carbon diffusion analysis, at austenitizing temperature of 1020ºC, the equilibrium surface carbon content at 1020ºC was 0.157wt%, with activation energy of carbon in H13 steel of 20,200cal/mol, and carbon diffusivity at 1020ºC was 1.97x10-8cm2/s.This study also proved that proper stainless steel foil wrapping on the heat treating material could restrict decarburization process, resulting in a constant hardness profile as vacuum heat treatment does. However the tempering characteristic between this two heat treatment methods are different to each other.For the pack carburization heat treatment, it was noted that the samples suffered from decarburization at early stage of heat treatment as carbon monoxide level was not adequate for carburization process.Results from the gas nitrided samples showed that the thickness and the hardness of the nitrided layer was independent to the carbon content in H13 steel. After 2 rounds of gas nitriding process, further nitriding seemed to have no significant effect on the hardness and thickness of the nitrided layer. Furthermore, the white layer was not observed in the nitrided samples which were heat treated without atmospheric control.

Uranoxid (UOx) är ett energitätt material som ofta används i kärnbränsle. UOx-pulver pressas och sintras för att tillverka urandioxidkutsar som förs in i bränslestavar. Stavarna monteras slutligen ihop till ett bränsleknippe. Tillverkningsprocessens stabilitet och förutsägbarhet är viktiga. För att åstadkomma önskvärda egenskaper hos UO2-kutsarna är karaktärisering av UOx-pulvret centralt. Sintringsaktivitet är den viktigaste egenskapen när det kommer till att beskriva hur UOx-pulvret beter sig vid reduktion i högtemperatursintring. Återcyklat UO2 oxideras till U3O8 och kan användas till att styra sintringsaktiviteten tack vare dess porbildande egenskaper. Denna rapport beskriver karaktäriseringen av UOx-pulver och kuts med avseende på fysiokemiska egenskaper relaterade till sintringsaktivitet. Statistiska analyser av historiska data utfördes även och visade på en komplex relation mellan pulveregenskaper och sintringsaktivitet. Effekten av U3O8-pulver i blandningar av UO2-pulver med hög och låg sintringsaktivitet undersöktes. Att variera U3O8-batch hade ingen inverkan på diameterkrympning efter sintring utom i ett fall. Blandningar av UO2-pulver visade på avvikande egenskaper jämfört med det jungfruliga pulvret. UO2-pulvrets kemiska aktivitet undersöktes via oxidering med H2O2. Förbrukningshastigheten av H2O2 var densamma för hög- och lågaktiva UO2-pulver vid samma förhållande mellan specifik yta och lösningsvolym. / Uranium oxide (UOx) is an energy dense material commonly used in nuclear fuel. UOx powder is pressed and sintered to produce uranium dioxide (UO2) pellets which are loaded into fuel rods. The rods are then mounted together in a final nuclear fuel assembly. Stability and predictability of the manufacturing processes during UO2 pellet production is of high importance. To achieve desired properties and quality of the UO2 pellets, the ability to assess the characteristics of the UOx powder is crucial. Sinterability is the most important characteristic which describes the behavior of the UOx powder during reduction in high temperatures. Recycled uranium dioxide is oxidized into U3O8 powder which can be used to modify the sinterability due to its pore forming ability. This study describes the characterization of uranium oxide powders and pellets regarding physicochemical properties relating to sintering behavior. Statistical analyses of historical data were also performed and showed a complexity of the relation between powder properties and  sinterability. The effect of U3O8 powder in different blends of UO2 powders of high and low sinterability were analyzed. Varying U3O8 powder batch did not influence the diameter shrinkage after sintering except for one case. UO2 powder blends showed deviating behavior from their virgin powder constituents. Chemical activity of UO2 was analyzed by oxidation with H2O2. The consumption rate of H2O2 was shown to be equal for active and incative UO2 powders under equal specific surface area/solution volume ratio.

[pt] Esta tese tem como objetivo estudar a viabilidade termodinâmica da reação de acetona a partir de etanol e água realizando cálculos utilizando o programa Thermo-Calc e a base de dados SSUB3 para equilíbrios de gases metaestáveis. Para a validação do método utilizado inicialmente foi calculado o equilíbrio para a reação da metanação de CO2 com H2, esse cálculo ocorreu sem grandes problemas e ainda foi adicionado o estudo da atividade química do carbono para evitar deposição de carbono sólido nos catalisadores. Para os cálculos da acetona foi considerado um equilíbrio metaestável pois ele não foi calculado utilizando todas as espécies químicas possíveis, isso foi feito para simular o efeito de catalisadores, que inibem a formação de algumas dessas espécies, já que se o cálculo fosse feito sem levar isso em conta se notou que a reação que ocorre é a de reforma do etanol pela água. A conversão de etanol e a seletividade das espécies químicas presentes em maior quantidade foram determinadas em função da temperatura e da razão de etanol e água, e os resultados obtidos foram comparados com dados experimentais obtidos com catalisadores diversos. / [en] The mean goal of this thesis is to study the thermodynamic viability of the acetone formation reaction from ethanol and water by performing calculations using the program Thermo-Calc and the SSUB3 database for metastable gas equilibrium. As a validation of the method used the equilibrium was calculated for the methanation reaction of CO2 with H2. This calculation occurred without problems so the study of the chemical activity of the carbon was also added to avoid the deposition of solid carbon on the catalysts. For the acetone calculation, it was considered a metastable equilibrium because it was not possible to calculate using all possible chemical species. This was done to simulate the effects of catalysts, which inhibit the formation of some of these species. If the calculation was made with all chemical species, it was noted that the net reaction is the reform of ethanol by water.The conversion of ethanol and the selectivity of the chemical species present in greater quantities were determined as a function of temperature and ethanol and water ratio, and the results obtained were compared with experimental data obtained with different catalysts.