α-Al2O3 兩階段燒結緻密化之製程研究

Abstract

Abstract In this research, sintering behavior of two α-Al2O3 powders with average particle size 0.1μm (Slurry B) and 0.2 μm (Slurry A) were investigated. Several heating processes were tried. One followed a two-step sintering method given by Chen and Wang [1], The effects of temperature, holding time, initial grain size and porosity were controlled. Various thermal treatments were also done comparing to the conventional (one-step) process. Secondly, TMA was used to analyze the sintering behaviors of the α-Al2O3 at various heating rates, from 2 to 90 oC/min. Finally, an infra-red fast sintering furnace was designed and used to study the heating effect on the fine α- Al2O3. A high density (>99% T.D.) and small average grain size (0.86 μm) were achieved by the two-step sintering of Al2O3 and better than the results by the conventional sintering (1500 oC for 1 h). The other case, sintered Al2O3 – B samples, in a smaller grain size (0.57μm) and a good density (>98% T.D.) were achieved by heating to 1450 oC, then holding at 1350 oC for 20 h. Lower first-step temperature and second-step temperature than the temperatures of sample – A were noted. Different sintering rates indeed influence the sintered densities, e.g. the results of Al2O3 – B, but no influence on the average grain size. The results showed, while the sintering rate increased from 2 oC /min to 90 oC /min, the sintered density decreased from full density to 97%TD if heating to 1500oC then holding for 1 h. For both cases, the initial sintering temperature increased with the heating rate, due to the limitation of heat transfer in Al2O3 samples. Maximum shrinkage rate and the corresponding temperature increased with the heating rate, too. The sintering mechanism of rapid-heating rate has been determined by Young and Cutler [36]. The mechanism of initial sintering belongs to a lattice diffusion, and the activation energy is 688 kJ/mole, which is interpreted as a volume diffusion of Al3+ ions in polycrystalline matrix.