以Cr~(2+)为生核剂制得的镍粉做晶种,对镍氨溶液的高压氢还原过程进行了研究。各种因素对还原速度的影响表明,反应似在化学动力学区内进行,反应速度与加入的晶种量、氢分压平方根成正比,而在大部分镍还原完成前与镍离子浓度无关。初步认为镍离子的还原反应在晶种表面进行,晶种的作用是活化氢分子和生成金属镍的相变中心。反应可设想以下面步骤进行: 1.H_2(g)(?)H_2(l) (快) 2.H_2(l)(?)2H~* (快) 3.Ni~(2+)(?)(Ni~(?))~* (快) 4.2H~*+(Ni~(2+))~*(?)Ni°+2H~+ (慢) 5.2H~++2NH_3→2NH_4~+ (快) 方程式4为速度的控制步骤。
Studies were made on high pressure hydrogen reduction of Ni ammoniacal solution to metallic Ni with fine Ni powder, which was also prepared by hydrogen reduction with Cr~(2+) as nucleating agent, added as solid seed. Results indicate that the reduction was carried out under chemical reaction rate control region. The rate of reduction is proportional to the amount of Ni powder as solid seed added,and to the square root of partial pressure of hydrogen and is not influenced by the concentration of Ni ion in solution up to most of Ni reduced. Both activation of hydrogen molecules and phase transformation of Ni are believed to proceed on the surface of Ni powder added. Reaction can be considered to proceed according to the following scheme with reaction 4 as the rate controlling step:(5) 2H~++2NH_3=2NH_4~+ fast
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