(AW/A)2=K·t AW-weight increase during oxidation (kg); 1-oxidation duration (s); A-surface area of specimen (m2); K一oxidation rate constant(kg2·m-4·s-l)y K(ZAN)=3.5×10-11(kg2·m-4·s1),is two orders lower than K(MA0)=1.15×10-9(kg2·m4·s-1). 07、 3o0 e 2!4」 .'h Fig.1 Dependence of weight increase on oxidation time Fig.2 SEM micrographs of oxidized surfaces of (a)ZAN and (b)MAO SEM micrographs of oxidized specimens (Fig.2)show that many protrusions appear on the porous oxidation films on specimens MAO,while rather smooth oxidation films adhere on specimens ZAN,indicating better oxidation resistance, Passive oxidation of SisN4 procceds according to the reaction: SigN4+302=3Si02+2N2 It is controlled by diffusion of oxygen through surface SiO2.Greskovich et al.estimated that the oxidation rate constant of CVD-Sia Na at 1400C should be less than 5x 10-13 kg?,m-4.s-1 c). The oxidation resistance of MAO is significantly reduced because of the 37八牙 ， 二 · 甲一 、 一 月 一 一 · 一 。 一 “ · 一 ‘ · 一 ‘ ， 一 ’ · 一 ‘ ’ · 一 ‘ 。 一 ‘ 后 刻〕 口 今 洲 、 ‘ 卜 口门 洲〕 土川 ， ， ， 。 。 一 飞 一 一 一 〔 〕