Papers by Keyword: Air Atmosphere

Abstract: In this paper, a mixture of commercial Al₂O₃ and Y₂O₃ nanopowders was prepared according to the stoichiometric ratios of YAG (Y₃Al₅O₁₂) with 0.5 wt% tetraethyl orthosilicate (TEOS) as a sintering aid. The effects of air and vacuum sintering atmosphere were examined on the phase transformation, densification, in-line transmission, microstructure evolution, grain size distribution, sintering trajectories, and grain growth map of the YAG ceramics. The results showed that all samples were pure YAG phase. Nearly pore-free microstructure (99.8%) and narrow grain size distribution (4-10 μm) with an average grain size of 7 μm was obtained for the sample sintered in the vacuum atmosphere, while both inner and inter pores with abnormal grain growth, wider grain size distribution (9-27 μm) with the average grain size of 12 μm were detected in air atmosphere. Also, the results showed that the specimens sintered in vacuum atmosphere had higher relative densities and smaller grain sizes at all sintering temperatures for 6 h. The maximum transmittance at 1064 nm of the YAG ceramics sintered at air and vacuum atmosphere was 26% and 68%, respectively.

Abstract: MgAl₂O₄-SiC composites were prepared by using MgAl₂O₄ and SiC powder as main starting materials, being pressed to cylindrical specimens of Φ30mm×30mm at 200 MPa and heated respectively at 1400°C and 1500°C for 3 hours in air atmosphere. The room temperature physical properties of sintered samples were tested according to related national standards. The phase compositions were analyzed by XRD. The microstructure of the fracture of the samples was observed by SEM. The results showed that MgAl₂O₄-SiC materials could sintered well in air atmosphere. The mechanism is that SiC was oxidized to form active SiO₂, which reacted with MgAl₂O₄ to produce liquid cordierite promoting the sintering of the materials. The sinterability of MgAl₂O₄-SiC materials was overall improved with increasing the sintering temperature. When the content of SiC of MgAl₂O₄-SiC materials was 10%, the cold crushing strength and bulk density of the samples reached maximums and apparent porosity reached a minimum; the content of SiC was more than 10%, the sinterability of samples deteriorated.