Severe steric effects at the reactive carbon would impede the substitution . 大的立体效应阻止在碳上的取代。
2.
The analysis of oxidation mechanism indicates that the principal causes of thermal oxidation resistance are as follows : rare earth elements have a function to discontinue autooxidation chain reaction and the formed complex structure can hinder the oxidation resistance 经过氧化机制分析，认为抗热氧化效应的原因主要是稀土元素具有中止自动氧化链式反应的作用以及形成的络合结构有阻碍氧化的立体效应。
