considerable amount of intergranular glassy phase,which is formed through reac -tion of the oxide additive with SiOz on the surface of SiaN powder particles. While the oxidation resistance of ZAN is much better than MAO through the use of non-oxide AZ-type additives instead of oxide additives,due to much less amount of intergranular glassy phase with much higher N content and viscosity. 2.2 Bending Strength and Strength Retention at HT The RT and HT bending strength with the strength retention at 1250C and 1400C of specimens are listed in Table 1.It is evident that the bending strength at RT,1250C and 1400C for ZAN are much higher than MAO.The more important fact is that the strength retentions at 1250C and 1400C of ZAN reach 90.2%and 71.0%,while those of MAO are only 61%and 41,5%. Table1 The bending strength and strength retention at1250℃，1400℃. ORT 01250 01400 01250 01400 Specimen % % MPa MPa MPa GRT ORTi ZAN 686 619 484 90,2 71.0 MAO 544 332 226 61,0 41.5 SEM fractographs of specimens after bending strength tests at 1400C shown in Fig.3,it further proved the different characteristics of ZAN and MAO.Many small“spheres”appeared on the fraeture,surface of MAO at 140o'℃，which formed as liquid phase at 1400C under the action of surface tension. (a)ZAN, (b),(c)MAO Fig.3 SEM fractographs after bending strength test at 1400C Cracks between "spheres"and matrix developed after a certain amount of plastic deformation through sliding along the surfaces of these "spheres". While the fracture surface of the bending strength specimen ZAN at 1400C kelpt the brittle characteristics like that of specimen broken at room tempe- 38几 ’ 了 ， ， 。 一 弓 义 一 一 文 ， 直 。 ℃ ℃ 。 ， ℃ ℃ ℃ 。 。 ， 写 ℃ ， ℃ 恤 九 口 盛 口 口 】 仃 口 遵 。 。 。 ℃ ， 卜 ” ℃ ， ℃ ， 蘸馨翼缨蒸鬓蟾蜘黔 ， ， 亡卫 亡 ，， 一 “ ，，， 。 ℃ 一 ， 务参