Red mud is a specific term applied for a residue generated during the processing of aluminum ores, mainly bauxite in the Bayer process, to produce alumina (Al2O3). In several countries where bauxite is mined and processed, distinct red muds are generated in ever growing amounts and becoming an environmental problem. This problem is also affecting the large bauxite processing plants in Brazil and a possible solution for the red mud is its addition to clay ceramics. Before an industrial scale addition is implanted, the specific red mud needs to be characterized for compatible behavior with the ceramic clay matrix. Therefore, the objective of the present work was to characterize a red mud generated in Brazil for an eventual addition to clay ceramic. This was conducted through the determination of density, chemical and mineralogical composition as well as size distribution and microscopic observation of particles. The results indicated that the specific red mud investigated is compatible with clays and has a potential for addition in common red ceramics.
The high pressure and temperature, synthesis of diamond from carbonaceous materials, is a complex process highly dependent on variables such as the catalyst/solvent, the crystalline structure of the precursor material, the processing conditions and the type of compressive chamber. The optimum susceptible precursors to be transformed into diamond are those possessing the perfect hexagonal graphite structure, which is the thermodynamically most stable form of carbon at atmospheric pressure and ambient temperature. However, the majority of both industrial and natural graphites, presents a mixture of different atomic structural arrangements that greatly influence the process of diamond synthesis. In this works the influence of rhombohedral and hexagonal phases existing in the graphite was performed by means of a software refinement of the crystal structures using the Rietveld method. The thermobaric treatment, which determine the structural parameters, was conducted in a high pressure anvil type device with a central concavity. All experiments were carried out at 1200°C and pressures varying from 4.3 to 5.0 GPa. It was determined that the degree of graphite to diamond transformation is directly associated with the content of rhombohedral phase.
LAMAV-CCT-UENF. Campos dos Goytacazes -R J -CEP:28013-602 -Brasil. paranhos@uenf
ResumoEste trabalho apresenta a avaliação de Key words: one-side welding, ceramic backing. 1.IntroduçãoA soldagem unilateral é utilizada tipicamente em aplicações que envolvem acesso apenas por um lado da peça, ou em situações em que a peça não pode ser virada. Obtém penetração total do primeiro passe de solda, evitando-se a subseqüente operação de goivagem para a soldagem no lado oposto da peça [1]. Outras vantagens atribuídas à soldagem unilateral são: redução dos ensaios não destrutivos (END) e dos reparos; diminuição significativa de defeitos como falta de fusão e redução na distorção dos equipamentos após soldagem [2].Entre os diversos tipos de suporte de solda usados na soldagem unilateral, é dedicada atenção neste trabalho ao suporte cerâmico, que tem a capacidade de tolerar a elevada temperatura da poça de solda quando no estado líquido, evitar a formação de gases durante a soldagem e proporcionar um acabamento adequado do cordão de solda, isento de defeitos [3].O uso do suporte cerâmico em operações de soldagem apresenta um forte impacto tecnológico, pois reduz o número de passes de solda, reduz o volume do metal depositado, elevando a produtividade e reduzindo os custos da operação de soldagem [4].O objetivo deste trabalho é avaliar as características
ResumoEste trabalho teve como objetivo observar o percentual de transformação das fases (romboédrica e hexagonal), após tratamento termobárico do hidrocarboneto aromático Antraceno. As amostras foram tratadas sob pressão fixada em 4,5GPa e temperatura variando entre 900 e 1300°C, com o intuito de obter estruturas grafíticas. O percentual de fases foi obtido a partir de dados de difração de Raios X e através de refinamento pelo método de Rietveld, sendo que na temperatura de 1300°C foi possível observar um aumento na fase romboédrica e melhores parâmetros de refinamento. Pode-se concluir que o Antraceno ao ser submetido a altas temperaturas e alta pressão torna possível o aumento da fase romboédrica do material grafítico, o que resulta em melhores condições de síntese do diamante. Palavras-clave: Antraceno; Hidrocarboneto aromático; Grafitização; Método de Rietveld. RIETVELD METHOD OF APPLICATION FOR DETERMINATION OF HEXAGONAL RHOMBOHEDRAL PHASES IN THE DIAMOND SYNTHESIS PROCESS FROM ANTHRACENE AbstractThis study aimed to observe the percentage of transformation phase (rhombohedral and hexagonal) after thermobaric treatment of aromatic hydrocarbon anthracene. The samples were treated under pressure and fixed to 4,5GPa temperature ranging between 900 and 1300°C in order to obtain graphitic structures. The percentage of phases was obtained from data and Xray diffraction using the Rietveld refinement, and at a temperature of 1300°C was possible to observe an increase in the rhombohedral phase and the best refinement parameters. It can be concluded that the anthracene to be subjected to high temperature and high pressure makes it possible to increase the phase of the rhombohedral graphite material, which results in better conditions for diamond synthesis.
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