HfN Formation and Phase Relationships in the Hf-Si-La-O-N System

In this study,the synthesis is feasibility and formulation design of HfN composite lanthanum silicate ceramics were explored.The feasibility of HfN synthesis by ternary reaction of HfO2-Si3N4-La2O3 system was verified by experiments,and the relationship between reaction pathway of HfO2-Si3N4 binary system and Hf-Si-La-O-N was studied.Considering that the lanthanum silicate salt in the reaction of HfO2-SiO2-La2O3 ternary system was contained in the Si3N4-SiO2-La2O3 system,lanthanum silicate was extended to the HfO2-Si3N4-La2O3-SiO2-HfN(Hf-Si-La-O-N)system,which clarified the coexistence of HfN and the lanthanum salt phases in the system.Experimental phase diagrams of HfO2-SiO2-La2O3 ternary system and Hf-Si-La-O-N system at 1500℃ were proposed.The results show that intermediate product Hf7O8N4 formed in the synthesis of HfN at high temperature in HfO2-Si3N4 binary system.Introduction of La)2O)3 promoted the system to generate HfN which was beneficial to reduce the burning loss rate of ceramics.There existed HfN and La4.67Si3O13,La5Si3NO12,LaSiNO2,La4Si2N2O7,La2Hf2O7 five lanthanum salt phases in the Hf-Si-La-O-N system.