Sinterability of monodisperse TiO2 powders

Abstract

Sintering of monodisperse titania powders with a relatively large grain size (0.84 -+ 0.24 l.tm) is investigated. It is established that the use of nonagglomerated monodisperse powders makes it possible to fabricate ceramics with a density of 99.5% of the theoretical value and a narrow distribution of pore sizes without preliminary milling and by relatively simple technological means, namely, cold pressing and casting into gypsum molds followed by sintering at a relatively low temperature. In combination with a high density such a structure makes the developed ceramic material applicable for the production of porous membranes for microbiology and medicine.The wide use of ultradisperse powders in modem ceramic technology is explainable by the desire to intensify the sintering process, decrease the sintering temperature, and improve the properties of the materials produced. However, the advantages of ultradisperse powders are often achieved incompletely in actual practice due to a tendency to form cluster agglomerates. The presence of the latter causes formation of inhomogeneous particle packings in the powder compacts. Such compacts contain coarse interagglomerate pores between dense intraagglomerate regions. In sintering, the compaction rates differ in microvolumes with different densities and cause the growth of interagglomerate pores [1] and the formation ofmicrocracks [2] and other defects. These defects worsen considerably the properties of the sintered material [3]. In order to eliminate the effects caused by the presence of agglomerates the sintering temperature is often increased, causing grain growth in the material and decreasing its mechanical characteristics.The structure of a powder compact can be optimized, the sintering kinetics improved, and the defects removed by using nonagglomerated powders with a narrow size distribution of the particles or monodisperse powders. An analysis of packing in monodisperse powders [4] showed, that they give compacts with a high density and uniform packing of the particles. They exhibit a tendency toward improvement of the factors that promote more rapid and better sintering compared to the packing in powders with a wide size distribution of the particles and powders from agglomerated particles [5].