Crystal Growth of Ultrafine Iron-Nickel Alloy Particles by Gas-Evaporation Technique

本研究的目的是研究气体蒸发技术制备超细铁镍合金颗粒的晶体生长机理。气体蒸发技术是一种在低压惰性气体气氛中蒸发材料制备超细颗粒的方法。已知在较宽的组成范围内，在高温下存在α （bcc结构）和γ （fcc结构）两相共存。通过对三种起始材料的蒸镀，研究了制备条件对起始材料生长机理的影响。对于混合粉末材料生长的颗粒，由于粉末中含有氧分子，颗粒表面被氧化。不管起始材料线的成分如何，从铁和镍缠绕的线中生长出来的粒子都是由α或γ的单相组成的。在% Ni箔中，Fe-36生长出的大多数颗粒由α或γ的单相组成，它们形成交替的长链。这可能部分源于时空波动。α和γ粒子成核阶段的铁和镍蒸气密度。另一种可能是淬火效应。在本例中，高温下的单γ相通过冷却过程被淬火。事实上，在极少数情况下，在单相粒子中观察到由两相组成的粒子。对于两相粒子，α相由α相析出。

The aim of this study is to investigate a crystak growth mechanism of ultrafine iron-nickel alloy particles prepared by a gas-evaporation technique, that is, a method preparing ultrafine particles by evaporation ot material in an atomosphere of inert gas at a low pressure. It is known that there coexist two phases of alpha (bcc structure) and gamma (fcc structure) in the wide composition range at a high temperature. Three kinds of starting materials were evaporeted from a tungsten boat, in order to study the difference of growth mechanizm due to the preparation conditions. For the particles grown from mixed powder material, the particle surfaces were oxidized, because of the oxygen molecules contained in the powder. The particles grown from wound wires of iron and nickel consisted of a single phase of either alpha or gamma, inspite of the composition of starting material wires. Most of the particles grown from Fe-36 at% Ni foil consisted of a single phase of either alpha or gamma, and they formed alternating long chains. This may originate partly because of the spatiotemporal fluctuation. of iron and nickel vapor densities at the nucleation stages of the alpha and gamma particles. The other possibility is the quenching effect. In the present case, the single gamma phase at elevated temperature is quenched through the cooling process. In fact, on rare occasions, particles consisting of two phases were observed among the single-phase ones. For the two-phase particles, the alpha phase precipitated from the gamma phase.