Thermal Conductivity of in situ Reinforced Silicon Nitride

摘要

Thermal conductivity of in-situ reinforced siliconnitride was improved by promoting grain growth and selecting asuitable additive system in terms of composition and amount.#beta#-Si_3N_4 doped with Y_2O_3-Nd_2O_3 (YN) orY_2O_3-Al_2O_3 (YA) was sintered at 1700 deg C to 2200 degC and the effects of the additive composition, additive amount,and sintering conditions on the thermal conductivity wereinvestigated in relation to the grain growth and microstructure.Higher sintering temperature promoted grain growth; thematerials sintered at temperatures higher than 1900 deg C had amicrostructure of "in-situ composite" with small #beta#-Si_3N_4 matrix grains surrounding much larger, but fewer,elongated #beta#-Si_3N_4 grains. Thermal conductivityincreased with higher sintering temperatures. The effect of theadditive amount on thermal conductivity with YN was rathersmall because the additional additive segregated at multi-grainjunctions. On the other hand, with YA, thermal conductivityconsiderably decreased with a larger additive amount becausethe Al and O in the YA system dissolved into #beta#-Si_3N_4grains to form a #beta#-sialon solid solution, which acted as apoint defect for phonon scattering. The key processingparameters for high thermal conductivity of Si_3N_4 werefound to be the sintering temperature and additive composition.Thermal conductivity of 122 W / (m?K) was produced by theaddition of 1 mol percent YN and by sintering at 2200 deg C.This value was about twice as high as previously reported values.