Synthesis Of YAG Powders Based On The Crystallization Method And YAG Sintering Character

Yttrium aluminum garnet(YAG) is an important laser host material. YAG ceramic is lower-cost, more stable and more suitable for heavy doping than YAG single crystal. So it has attracted much attention of researchers, as well as it has taken place of YAG single crystal in some places.High quality transparent YAG ceramic is key to the highly transparent YAG laser ceramic. And the sintering character of YAG powders is one of the important factors for the transparent YAG ceramic. So the purpose of the study is to synthesize YAG powders with pure phase, good dispersion and appropriate particle size through an easy and highly effective method, so as to lay a good foundation for the preparation of YAG transparent ceramics.Firstly, nitrate system was chosen to synthesize YAG powders through the crystallization method. And the experiment was made up of three parts.(1) Nitrate process. Y(NO3)3 and Al(NO3)3 were the raw materials for the synthesis of YAG powders. Under heating and stirring, they were crystallized in their solution. And Y3+ and Al3+ were well-distributed in the crystallized precursor due to the large solubility of Y(NO3)3 and Al(NO3)3. Then YAG powders were synthesized by calcining the crystallized precursor at 950 oC. After sintering at 1550 oC, the grains were gathered together to make up a lot of ―grain groups‖. The grains in the ―grain group‖ were close to each other with little gaps among them. However, big gaps were among the ―grain groups‖.(2) Y2O3 process. 2 wt.% Y2O3 nanopowders were added to the raw materials based on nitrate process. YAG powders were synthesized at 850 oC. And the agglomeration and the sintering character of the powers were similar to those of the powders synthesized through nitrate process.(3) Y-PAA process. 50 wt.% Polyacrylic acid([C3H4O2]n, PAA) was added to the raw materials based on Y2O3 process. And YAG powders were synthesized at 700 oC with good dispersion. After sintering, no ―grain group‖ occurred, but the grain sizes were not uniform.Secondly, to improve sintering character of the powders, nitrate+sulfate system was chosen to synthesize YAG powders. The salt precursor of three-layer core-hell structure was made up by ion recombination in the solution of Y(NO3)3, Al(NO3)3 and Al2(SO4)3under heating. And YAG powders were synthesized through calcining the crystallized precursor. Increasing SO2-4content of the raw materials was beneficial for the dispersion of YAG powders, while it was against the synthesis of the pure phase YAG. The powder calcined at 1050 oC was with good dispersion when n(SO2-4)/n(Y3+) of the raw materials was 1.5. After sintering at 1550 oC, the grain size distribution was narrow with grain size of 1.02 um, and the number of the big gaps was very small.By analyzing the dispersion of the powders and their sintering character, it could be found that the factors that affected sintering were as follows:(1) Dispersion. The powders with good dispersion were more suitable for sintering. As the grains grew simultaneously, the grains were with the same size.(2) Primary particle size. The sintering activity of the powders was reduced with the growing primary particle size. However, abnormal grain growth happened when the particles were too small, which resulted in wide grain size distribution.