A low-cost titanium production process, the CSIR-Ti powder process, which aims to produce titanium powder directly by metallothermic reduction of titanium tetrachloride with lithium, has been under development at the Council for Industrial and Scientific Research (CSIR). Crude titanium powder produced using the CSIR-Ti process is inevitably contaminated with by-products such as lithium chloride, lithium and titanium dichloride. These by-products tend to become sources of impurities in titanium powder, specifically oxygen and chloride impurities. The presence of oxygen and chloride impurities has marked effects on the mechanical properties of titanium finished products. Consequently, for the crude titanium powder to be rendered useful downstream, it must be purified and the by-products reduced to concentrations specified in the commercial standards. The present study was undertaken to examine whether acid leaching could be used to selectively dissolve and prevent hydrolysis of the by-products—specifically excess lithium and unreacted titanium dichloride in the crude titanium powder produced by the CSIR-Ti process. A further objective was to determine whether a purified product that meets both oxygen and total residual chloride content as specified by the standards can be achieved. The effects of key leaching variables and their interaction were also investigated to gain fundamental understanding of these effects on the by-products leaching behaviour. A literature study to select a suitable lixiviant and to establish the aqueous chemistry of the byproducts and their effect on the leaching conditions was undertaken. It showed that of the various acids suggested in the literature, hydrochloric acid was the cheapest and that it was more suited for the CSIR-Ti leaching process than nitric acid, due to the common ion chloride. This simplifies the leachate purification process downstream. The literature study established that Ti(II) has no aqueous chemistry but instead is oxidised to Ti(III) in solution. It was found that Ti(III) is easily oxidised to TiO2+ by dissolved oxygen and water. However, the oxidation rate was slow in hydrochloric acid solutions with the advantage that hydrolysis of the ions could be minimised and the precipitation of the oxides or oxychlorides prevented. It was further revealed that the lithium neutralisation reaction is highly exothermic, with the possibility of raising the leachate temperature to 60°C, resulting in the contamination of the titanium powder particles by the oxide layer and precipitated hydrolysis products. Batch leaching tests were carried out using factorial design of experiments to investigate the effect of initial hydrochloric acid concentration, which was estimated by varying the concentration between 0.032 M and 1 M; particle size, which was varied between −10 mm and +10 mm; and the initial temperature, varied between 14°C and 30°C. The resulting data were modelled and analysed using the analysis of variance statistical method. The solid residues were analysed for oxygen and total residual chloride content. The solid residue was also characterised by scanning electron microscopy (SEM) to examine the morphology of the leached particles. Leaching kinetics model fitting was also conducted. The statistical analysis showed that of the three factors investigated, temperature was the factor with the most statistical significance on both the oxygen and chloride concentration in the purified product, followed by particle size. The effect of acid concentration proved to be minimal, a phenomenon attributed to low concentrations of acid-consuming impurities, specifically excess lithium in the crude product. Thus, the two concentrations of hydrochloric acid investigated were found to be efficient to prevent hydrolysis product formation. Scanning electron micrographs revealed that crushing the crude product with a jaw crusher occluded crude titanium pores, thus locking in some by-products in addition to the pores locked by sintering during the metallothermic reduction. The observation showed that residual chloride impurities in the purified product are not just a consequence of hydrolysis products but also byproducts locked deeper in the pores of the product. Based on the parameter ranges evaluated in the study, a product that satisfied both oxygen and chloride standard specifications was achieved when the crude product was leached in both 1 M and 0.032 M initial HCl concentrations, temperature of 30°C and particle size of +10 mm. The combination of (−10 mm and 14°C) at all concentrations also yielded acceptable oxygen and chloride content levels. Overall, it was concluded from the present work that purification of crude CSIR-Ti product by leaching in dilute HCl is technically feasible. / Dissertation (MSc Applied Sciences (Metallurgy))--University of Pretoria, 2014. / Materials Science and Metallurgical Engineering / MSc (Applied Sciences (Metallurgy)) / Unrestricted

Orientadores: Rubens Caram Junior, Conrado Ramos Moreira Afonso / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-06T17:14:04Z (GMT). No. of bitstreams: 1 Aleixo_GiorgiaTaiacol_M.pdf: 13698827 bytes, checksum: 10117398b384c5a1eda6c62fbfc74507 (MD5) Previous issue date: 2006 / Resumo: Ligas de titânio formam a classe mais versátil de materiais metálicos utilizados para aplicações biomédicas. As ligas de Ti tipo ß usadas em dispositivos ortopédicos envolve, além de excelentes propriedades como baixa densidade, elevada resistência mecânica e excepcional resistência à corrosão, a biocompatibilidade com elementos de liga, tais como Nb, Ta, Zr e Mo. O objetivo deste trabalho foi analisar a estabilidade e metaestabilidade de fases em ligas tipo ß no sistema Ti-Nb através da verificação da influência do teor de nióbio sob diversas condições de tratamento térmico. Para tanto variou-se a adição de Nb de 5% a 30% em peso na liga, obtendo amostras que foram submetidas a condições distintas de resfriamento a partir do campo ß. Amostras obtidas foram caracterizadas no tocante à microestrutura via microscopia ótica, eletrônica de varredura e de transmissão, difração de raios-X, enquanto o comportamento mecânico foi preliminarmente avaliado através de ensaios de dureza Vickers e de medidas de módulo de elasticidade através de técnicas acústicas. Os resultados obtidos indicam que baixas taxas de resfriamento conduzem à microestrutura de equilíbrio (a+ß) enquanto que altas taxas de resfriamento levaram à formação de estruturas metaestáveis. À medida que o teor de Nb foi incrementado e sob altas taxas de resfriamento, obteve-se, respectivamente, martensita a¿ (hexagonal compacta), martensita a¿ (ortorrômbica), fase ? (trigonal) e finalmente, fase ß metaestável. Em relação ao módulo de elasticidade, observou-se que esse parâmetro decresce entre 0 e 15% de Nb e após este último valor, tal constante elástica se eleva como resultado da precipitação de fase ? bem como da possível alteração de dimensões da estrutura cristalina. As ligas Ti-Nb apresentaram uma variabilidade de microestruturas e propriedades que dependem fortemente da composição e condição de resfriamento / Abstract: Titanium alloys form one of the most versatile classes of metallic materials used for biomedical applications. ß Ti alloys for orthopaedic devices involves, besides excellent properties like low density, high mechanical strength and good corrosion resistance, great biocompatibility with alloying elements, such as Nb, Ta, Zr and Mo. The objective of this work was to analyze the stability and metastability of phases in ß Ti-Nb alloys through the evaluation of the influence of percentage of Nb obtained in different heat treatment conditions. In this way, Nb addition was varied from 5 to 30wt% in Ti-Nb system. Samples were obtained and microstructural characterization was made through optical microscopy, scanning and transmission electron microscopy and X-ray diffraction, while mechanical behavior was primarily evaluated by Vickers hardness and elasticity modulus through acoustic techniques. The results obtained indicate that lower cooling rates resulted in the equilibrium microstructures (a+ß), otherwise higher cooling rates led to formation of metastable structures. As the Nb content was increased and under greater cooling rates, it was obtained, respectively, martensite a¿ (hexagonal closed packed), martensite a¿ (orthorhombic), ? phase (trigonal) and finally, metastable ß phase. Regarding modulus of elasticity it was observed that it decreases as the %Nb increases up to 15% and beyond this percentage the modulus increases due the precipitation of ? phase as well as possible variation of crystalline structure dimensions. Ti-Nb alloys presented a great variety of combinations between microstructures and properties that strongly depends on composition and cooling conditions / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

Orientadores: Rubens Caram Junior, Conrado Ramos Moreira Afonso / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-15T14:37:29Z (GMT). No. of bitstreams: 1 Aleixo_GiorgiaTaiacol_D.pdf: 25669452 bytes, checksum: 43f10d141f1b3e5a6d696930ee2f86ec (MD5) Previous issue date: 2009 / Resumo: Este trabalho trata da preparação, processamento e caracterização microestrutral e mecânica de ligas Ti-Nb-Sn tipo ß visando a fabricação de dispositivos ortopédicos para implante. Amostras contendo Ti com teores de 25, 30 e 35% em peso de Nb e 2, 4 e 8% em peso de Sn foram preparadas por fusão a arco, homogeneizadas a 1000ºC/8 h e deformadas plasticamente por forjamento rotativo. Tais amostras foram submetidas a ensaios de resfriamento contínuo objetivando avaliar condições de obtenção de fases metaestáveis. Em seguida, amostras aquecidas a 1000ºC foram resfriadas rapidamente e submetidas a ensaios de calorimetria diferencial de varredura e de raios-X com aquecimento até médias temperaturas, o que permitiu avaliar a decomposição martensítica. Em seguida, amostras aquecidas no campo ß foram resfriadas ao ar, o que resultou em microestruturas com a fase a precipitada na matriz ß. Tais amostras foram caracterizadas no tocante à microestrutura via microscopia ótica, eletrônica de varredura e de transmissão e difração de raios X, enquanto que o comportamento mecânico foi avaliado por meio de testes de dureza Vickers, de medidas de módulo de elasticidade usando técnicas acústicas, ensaios de tração e ensaios de fadiga. Os resultados obtidos indicam que a decomposição da martensita resulta nas fases ß, ? e finalmente, a e também, que a fase ? atua como substrato na nucleação da fase a. O comportamento mecânico das amostras depende diretamente das fases presentes na microestrutura, bem como de suas frações volumétricas. Constatou-se também que o módulo de elasticidade, a dureza e o limite de resistência à tração de amostras resfriadas ao ar exibem valores superiores aos valores obtidos com as amostras resfriadas rapidamente, enquanto que a ductilidade se reduz. Finalmente, observou-se que o limite de fadiga de amostras resfriadas ao ar é máximo para baixos teores de Nb e se reduz com a adição de Sn / Abstract: This work deals with preparation, processing and microstructural and mechanical characterization of ß type Ti-Nb-Sn alloys aiming the manufacturing of orthopedic devices for implants. Ti samples containing Nb at levels of 25, 30 and 35 wt % and Sn at levels of 2, 4 and 8 wt % were prepared by arc melting, homogenized at 1000ºC/8 h and plastically deformed by swaging. These samples were submitted to continuous cooling experiments to evaluate conditions for obtaining metastable phase. Then, samples heated to 1000ºC were rapidly cooled and analyzed by using differential scanning calorimetry and X-ray diffraction at medium temperatures, which allowed the evaluation of martensite decomposition. Next, samples in the ß field were air-cooled, which resulted in microstructures with a phase precipitated into ß matrix. These samples were characterized concerning the microstructure by applying optical, scanning electron and transmission electron microscopies and X-ray diffraction, while the mechanical behavior was evaluated by Vickers hardness test, elastic modulus measurement using acoustic techniques, tensile and fatigue tests. The results obtained indicate that martensite decomposition results in ß, ? and finally a phases. It was also found that ? phase acts as substrate for a phase nucleation. The sample mechanical behavior directly depends on the phases present in the microstructure, as well as their volumetric fraction. It was also observed that elastic modulus, hardness and tensile strength of air cooled samples show higher values than those of rapidly quenched samples, while ductility decreases. Finally, it was observed that fatigue resistance of air cooled samples is higher for low Nb content alloys, however, it decreases with Sn addition / Doutorado / Materiais e Processos de Fabricação / Doutor em Engenharia Mecânica