Role of nanopowder agglomerates in forming the structure and properties of ceramic materials

Abstract

A comparative analysis of agglomerates obtained by spray drying and granulation methods and consolidated materials based on them was carried out. The paper provides the results obtained when studying zirconia nanopowders granulated in water medium with an agar agar additive obtained by chemical precipitation with zirconia partially stabilized by yttrium oxide (2.5 mol.%), and TZ-3Y-E powder manufactured by Tosoh Corp. (Japan) that was prepared by spray drying. Agglomerates as well as microsections and fractures of samples were studied by scanning electron, optical, atomic force microscopy, and Raman spectroscopy. The crack resistance coefficient (K1с) of samples was determined by indenting the polished surface of microsections with a Vickers pyramid. The specific surface of the powders measured by nitrogen thermal desorption during granulation remains unchanged indicating a significant open porosity of agglomerates obtained. With increasing compacting pressure under conditions of semi-dry compaction with an aqueous solution of PVA as a binder, agglomerates and even aggregates of granulated powders are destroyed, K1с increases with increasing compaction pressure and the accompanying material microstructure grinding. Powders agglomerated using spray drying break up much less intensively, K1с does not change with increasing pressure. The studies conducted allow us to agree with the authors pointing to the fractal nature of agglomerates obtained from chemically precipitated nanopowders without the use of spray drying. The use of granulated nanopowders in semi-dry compaction with the application of high pressures makes it possible to destroy not only agglomerates, but also aggregates, and to obtain nanostructured ceramics with grain sizes close to the size of initial particles.

Mathematical Description of Nano Indentation Unloading Curve of Ceramic Materials and Test Method of Film Thickness

“…After passing through the polarizer, the light generated by the laser becomes linearly polarized light, and then passes through the quarter wave plate to convert the light incident on the sample surface into elliptically polarized light. When this elliptically polarized light is reflected on the surface of the film to be detected, the change of the polarization state (phase and amplitude) of the light wave can be obtained by the following calculation formula [21][22]. Where, p r and s r are the complex amplitudes of P component and s component respectively.…”