C - Chemistry – Metallurgy – 04 – B
Patent
C - Chemistry, Metallurgy
04
B
C04B 35/58 (2006.01) B28B 3/00 (2006.01) C04B 35/56 (2006.01) C04B 35/593 (2006.01) C04B 35/64 (2006.01) C04B 35/645 (2006.01) C04B 35/80 (2006.01)
Patent
CA 2036864
ABSTRACT A process for preparing a self-reinforced silicon nitride ceramic body of high fracture toughness comprising hot-pressing a powder mixture containing silicon nitride, a densification aid such as sodium oxide, a conversion aid such as lanthanum oxide and a compound, such as gallium oxide, which enhances growth of .beta.-silicon nitride whiskers-under conditions such that densification and the in situ formation of .beta.-silicon nitride whiskers having a high aspect ratio occur. A novel silicon nitride ceramic of high fracture toughness and high fracture strength is disclosed comprising a silicon nitride crystalline phase wherein at least 20 volume percent of the phase is in the form of whiskers having an average aspect ratio of at least 2.5; a glassy second phase containing the densification aid, the conversion aid, the compound which enhances growth of .beta.-silicon nitride whiskers, and an amount of silica; and not greater than 10 weight percent of the total weight 36,172D-F as other phases. The glassy phase may also include a minor amount, e.g., up to 5.0 weight percent, based upon total weight of the ceramic, of aluminum nitride or boron nitride. The glassy phase optionally includes an amount of a secondary reinforcing material such as silicon carbide whiskers. 36,172D-F
Beaman Donald R.
Dubensky William J.
Pyzik Aleksander J.
Pyzik Barbara M.
Rossow Harold W.
Smart & Biggar
The Dow Chemical Company
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