Preparation and Properties of Fine Particles of Noble Metals by Spray-pyrolysis Technique

以金属硝酸盐为原料，在火焰(H_2-O_2-N_2)中喷雾热解法制备了金属微粒(Ag、Pd和Ag-Pd合金)。根据火焰温度的不同，金属颗粒的形成有三种途径。当火焰温度低于金属熔点时，金属颗粒呈非球形和中空(路径1)。当火焰温度高于熔点但不是很高时，金属颗粒通过熔体形成，并成为表面上的球形(路线2)。当火焰温度过高，大部分金属颗粒发生蒸发时，金属蒸气生成超细金属颗粒(路线3)。在路线1和路线2中，颗粒大小主要由金属硝酸盐溶液的浓度决定。在路径3中，粒子的大小主要由金属硝酸盐的进料速度决定，路径2和路径3所制得的银粉制备的导电膜的性能受银粒子的粒度和分散性的影响很大。由高度分散的细小颗粒组成的银粉可制得低阻薄膜(厚度2.0~2.5m，方块电阻率11.6~18.1m/m2，比电阻率2.3~4.7 cm)。

Fine metal particles (Ag, Pd and Ag-Pd alloy) were prepared by spray-pyrolysis technique from metal nitrate, by spraying the aqueous solutions into the flame (H_2-O_2-N_2). There were three routes for the formation of metal particles depending on the flame temperature. When the flame temperature was lower than the melting point of the metal, the metal particles were nonspherical and hollow (route 1). When the flame temperature was above the melting point but not so high, the metal particles were formed via the melt and became perfactly spherical (route 2). When the flame temperature was so high that the evaporation of metal particles took place in large part, ultrafine metal particles were produced from the metal vapor (route 3). In routes 1 and 2, the particle sizes were determined mainly by the concentration of the metal nitrate solution. In route 3, the particle sizes were determined mainly by the feed rate of the metal nitrate.The properties of the electric conduction films prepared from the Ag powders produced by routes 2 or 3 were affected markedly by the particle size and dispersiveness of the Ag particles. Ag powders consisting of fine and highly dispersive particles could give thin films having low electrical resistances (thickness: 2.0-2.5 m, sheet resistivity: 11.6-18.1m /square, specific resistivity: 2.3-4.7 .cm).