Sintering of Si3N4 Ceramics with Additives Containing Yttrium and Ytterbium Oxides with Microwave and Traditional Heating

Abstract

Compaction processes, phase transformation, and porous structure evolution are compared for materials based on silicon nitride containing yttrium and ytterbium oxides under microwave and traditional heating conditions. Experiments by microwave heating are performed in a special gyrotron device operating at a frequency of 30 GHz in a nitrogen atmosphere at normal pressure with a constant heating rate of 30, 60, and 90 deg/min. Traditional sintering is carried out in a tubular continuous furnace with a tungsten muffle in a nitrogen atmosphere at normal pressure with a heating rate of 60 deg/min. It is established that under microwave heating conditions compaction of the test materials and the start of the α →β phase transformation occur at temperatures 100-150 deg lower than those typical for traditional heating. In material with a reduced amount of oxide additives compaction is accompanied by an increase in the proportion of large pores which is the reason for a slow-down in compaction both with traditional heating and with microwave one. It is suggested that the reason for acceleration of mass transfer with microwave heating is the specific nature of the interaction of the microwave field with the liquid phase formed, promoting development of non-diffusion transfer of solid-phase elements dissolved within it and the mechanical effect on its particles.