Abstract
When heat and electric field are applied to the sample, sintering takes place within a short time of a few seconds by the flash phenomenon that occurs. In what condition flash does occur is a main issue for the flash sintering technique. In this study, the effect of processing conditions such as sintering atmosphere, sample size, density and grain size on the flash onset of hydroxyapatite was investigated. In a vacuum atmosphere, a flash occurred at a lower temperature by 50–100 °C than in air. The smaller the thickness of the sample, the higher the flash onset temperature due to the larger specific surface area. Flash was also observed in samples which were presintered, having a density of 86–100% and a grain size of 0.2–0.9 μm. When the density and grain size of the sample were higher and larger, the flash onset temperature was higher. It was because the diffusion and conduction path through the grain boundary and the inner surface of the pores with high defect concentration are blocked with an increase of density or grain size. When an electric field was applied during flash sintering, a color change of the sample was observed and the reason was discussed.
Highlights
Flash sintering is a process of consolidating loose powders using thermal energy with an application of electric field
Biesuz et al [16] reported that the electrical conductivity increased when argon gas was sprayed on 8 mol% yttria-stabilized zirconia (8YSZ) sample during flash onset
Francis et al [17] reported that the larger the particle size of 3 mol% yttria-stabilized zirconia (3YSZ) raw material powders, the higher the flash onset temperature and the lower the densification rate
Summary
Flash sintering is a process of consolidating loose powders using thermal energy with an application of electric field. Biesuz et al [16] reported that the electrical conductivity increased when argon gas was sprayed on 8 mol% yttria-stabilized zirconia (8YSZ) sample during flash onset. Francis et al [17] reported that the larger the particle size of 3 mol% yttria-stabilized zirconia (3YSZ) raw material powders, the higher the flash onset temperature and the lower the densification rate. Avila et al [18] reported that the thinner the thickness of the 3YSZ sample, the lower the densification rate during flash sintering, which was due to the specific surface area of the sample
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