Preparation And Properties Of New Ceramics Matrix Gry Control Rod Neutron Absorber Material

In this thesis,YAG and Tm:YAG ceramics were fabricated by solid-state reaction and pressureless sintering method with high-purity commercial powders ofα-Al₂O₃,Y₂O₃ and Tm₂O₃ as raw materials.Properties and morphology of powders and ceramics were studied by characterization methods such as XRD,SEM and EDS.The influence of sintering temperature,dwell time,the kinds and amount of sintered aids,doping concentration of Tm³⁺on the sintering densification and properties of ceramics was researched.The mechanical properities,elongation ratio and thermal expansion diffusivity at room temperature to 800℃,and corrosion resistance in subcritical water of YAG and Tm:YAG ceramics were tested,and neutron absorption rate of Tm:YAG ceramics versus differint doping amount were simulated by MNCP softwar.The main results of the work are as follow:（1）When YAG ceramic with 0.5wt%TEOS doped was sintered at 1650℃for 9h,the relative density was closed to 99.5%,and no second phase can be observed.With the temperature increased,the grain grew to bigger,and porosity got increased.Mechanical properties test shows that the hardness,fracture toughness and bending strength were all higher than that of the reported YAG ceramics which fabricated by vacuum sintered or hot pressing sintering,and elongation ratio and thermal expasion diffusivity were in agreement with the obtained values reported by literatures.When the amount of TEOS was less than0.5wt%,the relative density of YAG ceramics was only 96.5%,when the amount exceeded0.5wt%,second phase on the grain boundary began to appeared.（2）MgO has a better effect on promoting YAG sintering densification and reducing sintering temperature.When YAG ceramic doped with 0.05wt%MgO was sintered at1650℃,the relative density reach about 99.5%.Compared with the YAG ceramics doped with TEOS aids,the the mechanical properties of samples with MgO single doped were obvious lower.As to the ceramic samples using TEOS+MgO as sinering aids,the relative density got lower with the increased of MgO concentration when the ceramics were sintered at 1650℃.（3）The doping of Tm³⁺can improve sintering rate,reduce sintering temperature and promote grain growth,but the porosity would get increased.Compared with YAG ceramics,the elongation ratio of Tm:YAG was lower,and thermal expasion diffusivity was higher.When 0.5wt%TEOS was accepted as sintering aids,as the doping concentration of Tm³⁺increased,the hardness and bending strength decreased,and fracture toughness improved.When 0.05wt%MgO was doped,with the doping concentration of Tm³⁺increased,the hardness decreased,but bending strength and fracture toughness improved.（4）Corrosion test of YAG and Y_2.1Tm_0.9Al₅O₁₂ ceramics was taken in subcritical water（T=360℃,P=18MPa）.The result shows that the quality didn’t change after corrosion,and XRD analysis showd no new substance formed,it illustrated that all the ceramics showed excellent corrosion resistance in subcritical water.The The SEM surface morphology showed obvious corrosion pit on YAG ceramics surface,and corrosion resistance of YAG ceramics doped with TEOS were better than that of specimens with MgO doped.For Y_2.1Tm_0.9Al₅O₁₂ ceramics,hardly corrosion phenomenon can be observed on surface.