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首页> 外文会议>Mechanical properties and performance of engineering ceramics and composites VII >KINETICS OF PASSIVE OXIDATION OF HI-NICALON-S SiC FIBERS IN WET AIR: RELATIONSHIPS BETWEEN SiO_2 SCALE THICKNESS, CRYSTALLIZATION, AND FIBER STRENGTH
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KINETICS OF PASSIVE OXIDATION OF HI-NICALON-S SiC FIBERS IN WET AIR: RELATIONSHIPS BETWEEN SiO_2 SCALE THICKNESS, CRYSTALLIZATION, AND FIBER STRENGTH

机译：HI-Nicalon-S SiC纤维在湿空气中的被动氧化动力学：SiO_2氧化层厚度，结晶度和纤维强度之间的关系

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The strengths of Hi-Nicalon™-S SiC fibers were measured after oxidation in wet air between 700° and 1300℃. The oxidation and scale crystallization kinetics were also measured. Thicknesses of amorphous and crystalline scale were measured by TEM. Oxidation initially produces an amorphous scale that starts to crystallize to cristobalite and tridymite in 100 hours at 1000℃ or in one hour at 1300℃. Crystallization kinetics for oxidation in wet air were slightly slower than those for dry air. The activation energy of 249 kJ /mol for parabolic oxidation to uncrystallized SiO_2 scale in wet air was indistinguishable from that for dry air oxidation, but the pre-exponential factor was ~2x higher. SiC fiber strength changes with oxidation in dry and wet air were very similar. The fiber strength increased by approximately 10% for SiO_2 scale thickness up to -100 nm, and decreased for thicker scales. No significant strength degradation was observed for amorphous scales. All fibers with significantly degraded strength had crystallized or partially crystallized scales.
机译：Hi-Nicalon™-S SiC纤维的强度是在700°至1300℃的湿空气中氧化后测量的。还测量了氧化和结垢结晶动力学。通过TEM测量无定形和结晶鳞的厚度。氧化最初会产生无定形的水垢，在1000℃的100小时或1300℃的1小时内开始结晶为方石英和鳞石英。在湿空气中氧化的结晶动力学略慢于干空气。在湿空气中，抛物线氧化为未结晶的SiO_2垢的活化能为249 kJ / mol，与干空气氧化的活化能没有区别，但前指数因子高约2倍。 SiC纤维强度在干燥和潮湿空气中的氧化变化非常相似。对于高达-100 nm的SiO_2氧化皮，纤维强度增加了约10％，对于较厚的氧化皮，纤维强度降低了。对于无定形氧化皮，没有观察到明显的强度降低。所有强度显着降低的纤维均具有结晶或部分结晶的鳞片。

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