Study On The Pressureless Sintering Of γ-AlON Transparent Ceramic Influenced By Sintering Additives

Spinel-structure aluminium oxynitride (γ-AlON) is one of the most important potential materials with combined properties of structural and functional cemmics because of its outstanding optical and mechanical properties.γ-AlON transparent ceramics can be widely used in lighting, optical and medical instruments, laser, armor, infrareddetection, etc.Firstly, single-phaseγ-AlON transparent ceramic powders were used as materials with different mol AlN (32mol%,36mol%,40mol%,44mol%) in this thesis. we study the influence of the powder purity and particle size distribution with the time of ball mill. And we get the uniform dispersion of small particles and purity ofγ-AlON powders through choosing appropriate milling time.Secondly,γ-AlON transparent ceramics were prepared by pressureless sintering usingγ-AlON powders as raw material and Y2O3-La2O3 (m(Y2O3):m(La2O3)= 4:1) as combined sintering additives. The effect of process of preparation and sintering additives onγ-AlON transparent ceramics by pressureless sintering has been systematicly investigated. The results show that the condition for sinteringγ-AlON transparent ceramics is 1900γfor 24h.When the content of 0.1wt% La2O3-Y2O3 combined sintering additives, we can get the sample of 1mm thickness, the maximum rate more than 60% of theγ-AlON transparent ceramics, It's increased by 50% than without adding additives sintering. Meanwhile, The crystalline phase and microstructure ofγ-AlON transparent ceramics were investigated by XRD, SEM, TEM. The effect of combined sintering additives on microstructure optical and mechanical properties ofγ-AlON transparent ceramics was studied. The result shows that appropriate amount of combined sintering additives were dissolved intoγ-AlON grains, which can improve the density and optical property of materials. However, excessive amount combined sintering additives formed liquid phase and were remained in the grain boundary, which degrade the density and optical performance ofγ-AlON ceramics. In this paper, the effect of different sintering additives such as MgO,MgF2 on the pressureless sintering ofγ-AION has also been investigated. We usedγ-AlON power with a nominal content of 44mol%AlN as raw material and 0.5wt% MgO as sintering additive.γ-AlON transparent ceramics with transmmitance around 40% was well synthesized through presureless sintering at 1900℃for 24 hours in a N2 atmosphere.However, AlON ceramics obtained by adding MgF2 as sintering additive under the same condition showed little transparency. The research indicates that effect of introducing Mg ion through different compounds on the transmmitance ofγ-AION transparent ceramics varies a lot.