Effects of Y2O3-MgO extra addition on properties of silicon nitride by Isobam gel tape-casting
To address the problem of dense sintering difficulty of covalent bonded silicon nitride materials,Si tape-casting slices were prepared by gel tape-casting using the Isobam(Isobutylene-anhydride maleic)gel system and Si powder as raw materials,extra adding different amounts of sintering aid Y2O3-MgO(Y2O3 to MgO mole ratio of 4∶3,4％,6％,8％and 10％,by mass).Then they were treated by the two-step firing method,firing at 1 400 ℃ for 2 h and 1 750 ℃ for 2 h in the nitrogen atmosphere to prepare Si3N4 ce-ramic substrate specimens.The effect of the Y2O3-MgO addition on the properties of the Si3N4 ceramic substrates was investigated.The results show that adding Y2O3-MgO can promote the phase transition from α-Si3N4 to β-Si3N4 in the sintered specimens.With the increasing Y2O3-MgO addition from 4％to 8％,more liquid phases are generated during sintering,which promotes the liquid phase mass transfer and leads to the increased number and growth of long columnar β-Si3N4 grains,and the densification,hard-ness,fracture toughness,flexural strength,and thermal conductivity of the specimens increase.However,when the Y2O3-MgO addition is 10％,due to the abnormal growth of β-Si3N4 grains,all the properties of the specimens decrease.The silicon nitride specimen with 8％Y2O3-MgO performs the best comprehensive performance.
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