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Effects of Impurity Oxygen Content in Raw Si Powder on Thermal and Mechanical Properties of Sintered Reaction‐Bonded Silicon Nitrides
Author(s) -
Kusano Dai,
Adachi Shigeru,
Tanabe Gen,
Hyuga Hideki,
Zhou You,
Hirao Kiyoshi
Publication year - 2011
Publication title -
international journal of applied ceramic technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.4
H-Index - 57
eISSN - 1744-7402
pISSN - 1546-542X
DOI - 10.1111/j.1744-7402.2011.02618.x
Subject(s) - materials science , impurity , sintering , silicon nitride , thermal conductivity , silicon , flexural strength , oxygen , fracture toughness , metallurgy , composite material , analytical chemistry (journal) , chromatography , organic chemistry , chemistry
Sintered reaction‐bonded silicon nitrides (SRBSNs) were fabricated from commercially available low‐grade Si powder containing 1.6 mass% of impurity oxygen and 500 ppm of metallic impurities. Powder compacts of the raw Si powder doped with Y 2 O 3 and MgO/MgSiN 2 as sintering additives were nitrided at 1400°C for 8 h under a N 2 pressure of 0.1 MPa, followed by postsintering at 1900°C for 6 h under a N 2 pressure of 0.9 MPa. The SRBSN with Y 2 O 3 and MgO as sintering additives had a four‐point bending strength of about 700 MPa, but lower thermal conductivity of about 89 W/m/K. Thermal conductivity could be improved to over 100 W/m/K without degrading the bending strength by replacing MgO with MgSiN 2 . It is thought that MgSiN 2 decreased the amount of oxygen in the liquid phase formed during sintering, which resulted in reduced lattice oxygen content in the developed β‐Si 3 N 4 grains. In addition, the SRBSN with Y 2 O 3 and MgSiN 2 additive exhibited high fracture toughness of about 9 MPa m 1/2 . These good properties were equivalent to those of the SRBSN fabricated by using a reagent‐grade high‐purity Si powder containing only 0.3 mass% of impurity oxygen.