The Effects Of Quick Heating On Material Sintering Densification And Synthesis

Comparing with traditional high-temperature treating methods, newly fast sintering methods(SPS and Flash-sintering etc.) show some interesting characters, such as lower sintering temperature, shorter dwelling time and improvement performance of the products. There are increasing doubts about the inner nature of these characters. Though plus-electrimagnetic field, the quick heating processing, the possible plasma and so on were introduced to explain it; however, none was widely accepted. For this, we focused on the heating rate, studied its effects on densification, grain growth, insitu chemical reaction and thermodynamics of several typical materials. Interesting results are list as the following.Firstly, we sintered alumina to study the effects of heating rate on densification and grain growth dynamics. Results show: in pressureless sintering, fast heating could inhibit neck growth during initial stage sintering(mainly control by surface diffusion). So, in intermediate stage sintering, high driving force and densification rate would attained, and finially resulting significant grain growth. However, when pressure was applied, the particle arrangement and plastic flow would greatly suppress densification and grain growth rate. In addition, higher sintering temperature and heating rate could enhance densification and grain growth rate. And fully dense alumina ceramic could be fabricated within 3min when maxium temperature was 1750?.Secondly, we sintered BaTiO3 and synthesized mullite to investigate the effect of heating rate on phase transition and chemical reaction dynamics. Results shows fast heating rate would effectively retain the reconstructive phase transition(cubic-hexagonal) of barium titantate. Morerover, when heating rate was fast enough, the shape of mullite would change greatly. The main differences could be explained in terms of the high heating rate, which would change the nucleation-growth dynamic of mullite.