气流氮化制备Al-N粉末的工艺及机理研究

INVESTIGAION OF TECHONOLOGY AND MECHANISM OF MANUFACTURING Al-N POWDER BY NITRIZING

本文采用金属Al粉在高纯氮气中反应的方法制备Al-N粉末,并研究了Al粉的恒温氮化工艺与台阶氮化工艺及研磨与未研磨状态对Al粉氮化效果的影响。结果表明:由台阶氮化工艺所得的Al-N粉末的含氮量高,氮化效果好;由研磨的Al粉制得的Al-N粉末团聚现象较严重,氮含量降低,不如未研磨Al粉的氮化效果好。这是由于台阶氮化工艺可以避免在恒定温度下长时间保温而导致的瞬间放热,以及由此引起的粉末团聚,因而能获得更好的氮化效果;同时,由于在Al粉氮化初期形成的氮化膜与内部粉末的热膨胀率不匹配,导致在粉末表面出现环应力,应力大小与Al粉颗粒的尺寸有直接联系,Al粉颗粒越小,环应力越大,越容易导致膜层破裂而使得膜内Al熔体流出,烧结长大,故研磨不利于提高Al粉的氮化效果。

Al-N powder was prepared by heating Al powder in high purity nitrogen. The influences of initial condition of Al powder and nitrizing technology on properties of Al-N powder were investigated. It was shown that the higher N content the better nitrizing effect is obtained by step-heating. Al-N powder produced from milled Al powder has greater tendency to aggregate and lower nitrogen content. Step-heating can avoid sudden heat release during heating Al powder for a long time, and then the aggregation of Al powder. Grinding is an unfavorable factor to nitrizing due to ring stress of Al powder. The stress is caused by the mismatch of expansion ratio of nitrated film on Al particles formed at the early stage of nitrizing and the powder body, and the smaller the size of Al powder, the greater the ring stressis. The surface of Al-N powder will be brokeh if the stress is great enough,then Al powder will melt and aggregate.