Effect of Aluminum Content on Mechanical Properties and Thermal Conductivities of Sintered Reaction-Bonded Silicon Nitride

A systematic study was conducted of the effect of Al impurities on the mechanical and thermal properties of sintered reaction‐bonded silicon nitrides (SRBSNs). 2 mol.% Y2O3 and 5 mol.% MgSiN2 were added as sintering aids to high‐purity raw Si powder, followed by respective additions of 0, 0.01, 0.1,...

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Bibliographic Details
Published in:International journal of applied ceramic technology 2014-05, Vol.11 (3), p.534-542
Main Authors: Kusano, Dai, Hyuga, Hideki, Zhou, You, Hirao, Kiyoshi
Format: Article
Language:English
Subjects:
Additives
Aluminum
Atmospheres
Reduction
Silicon nitride
Sintering
Solid solutions
Thermal conductivity
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Summary:A systematic study was conducted of the effect of Al impurities on the mechanical and thermal properties of sintered reaction‐bonded silicon nitrides (SRBSNs). 2 mol.% Y2O3 and 5 mol.% MgSiN2 were added as sintering aids to high‐purity raw Si powder, followed by respective additions of 0, 0.01, 0.1, 0.2, and 0.4 mass% of Al relative to Si. The prepared powder mixes were press formed and nitrided in a 0.1 MPa nitrogen atmosphere at 1400°C for 8 h. Postsintering of the nitrides was conducted under a pressurized nitrogen atmosphere of 0.9 MPa at 1900°C for 6 h. The SRBSN specimens exhibited hardly any difference in their four‐point bending strength, which ranged from 800 to 850 MPa. However, their fracture toughness clearly decreased with increasing additive Al content. This is thought to be due to a reduction in the proportion of coarse prismatic grains improving the toughness with increasing additive Al content. A significant reduction in the thermal conductivity was also observed with increasing additive Al content. This is conjectured to be due to the formation of SiAlON through a substituted solid solution of aluminum (Al) and oxygen (O) in β‐Si3N4 crystals. An inductively coupled plasma and hot gas extraction method were employed to directly analyze Al and O in β‐Si3N4 particles. Approximately half of the additive Al was confirmed to be in solid solution in β‐Si3N4 particles along with the solid solution of O in a chemical formula that nearly corresponds to β‐Si6–zAlzOzN8–z. The chemical analysis results give a Z value range of 0.0006–0.024.
ISSN:1546-542X
1744-7402
DOI:10.1111/ijac.12035