High-density micro- and nanogranular ceramics. Transition of open pores to closed ones. Part 1. Preparation of powder, molding material, molding

Abstract

An explanation of the processes that occur when producing high-density micro- and nanogranular ceramics without the use of external pressure is proposed on the basis of data accumulated in the literature. It is known that pore growth begins after the beginning of the transition of open pores to closed ones, which begins at about 30 % open porosity. It is necessary to maintain open pores to the maximum possible total density of sintered ceramics. This can be achieved by slowing down the formation of areas of local compaction (unequal density of samples) by various methods. Preservation of open pores is facilitated by such a decrease in the rate of shrinkage at which a self-consistent compaction of the local seals and the less dense zones surrounding them is realized. Such a regime can be implemented in different ways: by reducing the activity of powder particles (preliminary heat treatment of the powder, preliminary low-temperature sintering ― presintering), the use of additives that slow down shrinkage (obtaining transparent ceramics without external pressure), at the stages of preparing the molding material, molding blanks, removing the binder by adjusting the heating rate of the sample (sintering with an adjustable rate of shrinkage), prolonged sintering at a relatively low temperature in 2-stage sintering. This is part 1 of a series of 3 articles. Ref. 61.