ProduÃÃo e estudo da microestrutura e propriedade mecÃnica da cerÃmica Ba2HoZrO5,5 a base de zircÃnia para fabricaÃÃo de cadinhos de alta temperatura

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

In view of the need of use of crucibles for sintering and crystal growth of advanced ceramics in high temperature furnaces, a study has been realized on a new complex cubic perovskite oxide ceramic Ba2HoZrO5,5 based on zirconium in the Ba-H-Zr-O system. Complex perovskites, which have generally A2BBâO6 or A3B2BâO9 type composition, result by ordering of B and Bâ on the octahedral site of the primitive cubic perovskite unit cell. Due to increase in complexity of the unit cell these materials exhibit, a large variety of properties are possible in these materials and hence a more continuous progression of lattice parameter could be produced. Of all these stoichiometric formulations, we produced 2(A (B0,5Bâ0,5)O3) or A2BBÂO6 type Ba2HoZrO5,5 composition which represent a ordered complex cubic perovskite, where cation A is Barium (Ba), cations B and Bâ are Holmium (Ho) and Zirconium (Zr) and anion O is Oxygen (O). A2BBâO6 type complex cubic perovskites exhibit great flexibility in their lattice parameter. We can manipulate the cations B and Bâ on alternate lattice positions in the crystal structure, when their ionic radius are very similar, thus forming an ordered complex cubic perovskite. In a general manner perovskites have a large variety of applications in fundamental areas of science and engineering of materials, such as inert crucibles, which support high temperatures for metallurgical applications, crucibles for crystal growth of high temperature superconductors and substrates for production of thin films . Of all these variety of applications, we concentrated on fabrication of inert crucibles due to scarcity of these products in the market. Ba2HoZrO5,5 ceramics were produced by solid state reaction process and sintered by solid state sintering and liquid phase sintering processes. For sintering, we used two types of processes: direct and indirect sintering. In the direct process, we compacted the ceramic powder and sintered directly at temperatures 1250, 1400 and 1500oC respectively. In the indirect process, ceramic powders were compacted and sintered at 1250oC. After this sinterization samples were powdered, compacted and sintered at 1400oC. After sintering at 1400oC, samples were again powdered, compacted and sintered at 1600oC. For the liquid phase sintering process, Ba2HoZrO5,5 ceramics were added with 0, 1 e 2wt% copper oxide (CuO) and we studied its influence on sintering, microstructure and mechanical properties. Ba2HoZrO5,5 ceramics were subjected to: x-ray diffraction for the study of phases and crys tal structure; Vickers hardness tests for mechanical strength evaluation; scanning electron microscopy along with EDS for the study of microstructural characteristics and elemental analysis. These studies showed that liquid phase sintering using CuO as sintering aid is important for Ba2HoZrO5. ceramics, as CuO additives facilitate the sintering process and improve the mechanical properties without structural characteristics of the matrix

ASSUNTO(S)

sinterizaÃÃo ba2hozro5,5 Ãxido de cobre perovskita engenharia mecanica

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