镍包覆微颗粒材料镀层均匀性研究
文献类型：学位论文
| 作者 | 陈烨 |
| 学位类别 | 硕士 |
| 答辩日期 | 2009-05-22 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 过程工程研究所 |
| 导师 | 张伟刚 |
| 关键词 | Ni/C复合材料 颗粒包覆 镀层均匀性 |
| 其他题名 | Study on Coating Uniformity of Nickel Coated Micro-Particles |
| 学位专业 | 化学工程 |
| 中文摘要 | 在利用湿式加压氢还原法制备镍包覆微颗粒材料的工艺中，金属镍镀层的均匀性对复合颗粒的性能有重要影响。本文对湿式加压氢还原制备球形Ni/C过程中，石墨颗粒表面金属镍镀层的形成规律进行研究，为材料制备及性能提高提供参考依据。 对不同粒径的球形石墨颗粒包覆时，当石墨颗粒粒径从30 μm增加到60 μm左右时，对应的镍镀层厚度从4.5 μm增加至6.0 μm左右。即不同粒径的球形石墨颗粒其单位面积上金属镍的沉积速率不同，且沉积速率随石墨颗粒粒径的增加而增加。降低核心颗粒的粒度分散性，可以减小颗粒的镀层厚度差别。 核心颗粒表面活性的研究表明：石墨表面具有反应活性，金属镍可直接在其表面沉积并形成完整的镍镀层；二氧化硅颗粒表面无反应活性，活化后再包覆才能形成镀覆完整的复合颗粒。金属镍在这两类颗粒表面的镀覆过程存在较大差异。 金属镍的沉积速率受氢气还原镍离子速率的控制，其中氢气在气-液-固三相反应体系中的传质速率对总沉积速率有重要影响。搅拌速率在500~1000 r/min范围内，单叶轮搅拌时氢气传质速率低，镀层的镀覆效果不理想。采用双叶轮联合搅拌，可以有效提高氢气的传质速率及镀层的均匀性。 石墨颗粒表面镍镀层的均匀性与晶体的生长过程密切相关。金属镍的液相形核可能导致游离镍粉和表面吸附颗粒的生成。镍晶体的各向异性生长也使镀层的均匀性降低。金属镍的非均相表面形核过程对均匀致密镀层的形成有决定性影响。 |
| 英文摘要 | In the process of high pressure hydrogen reduction for producing nickel coated micro-particles, performances of obtained composite particles were greatly influenced by the uniformity of nickel coating. The formation mechanism of nickel coating on spherical graphite particle in the process of high pressure hydrogen reduction was studied to provide references for material preparation and its performance enhancement. Graphite particles with different particle sizes were involved in the coating process. The thickness of nickel coating varied form 4.5 μm to 6.0 μm, while the diameter of graphite particle varied from 30 μm to 60 μm. There were discrepancies in nickel deposition rates of per area when graphite particles with different diameters were simultaneously coated. The deposition rate of per area increased with the increase of graphite particle size. Decreasing the size distribution of graphite particles could decrease the variation of coating thickness. The influence of surface reactivity of core particle was studied. Graphite particles belonged to core particles with coating-active surfaces. Nickel could directly deposit and finally form complete coatings on their surfaces. Silicone dioxide particles, which belonged to core particles with coating-inert surfaces, must be activated before coating. There were great discrepancies in the nickel coating process of these two kinds of core particles. Nickel deposit was controlled by the reduction rate of nickel ion. And one of important factors influencing deposition rate was the mass transfer rate of hydrogen in gas-liquid-solid reaction system. Using one impeller to agitate, the mass transfer rate of hydrogen was low and the coating uniformity wasn’t good in the range of 500~1000 r/min stirring speeds. Using two impellers to agitate at the same time, the mass transfer rate of hydrogen was effectively enhanced and the coating uniformity of obtained Ni/C composite was obviously improved. The uniform degree of nickel coating on graphite particle was closely related to the crystallization process of nickel. The homogeneous nucleation process would result to the formation of free nickel powder and the adsorption of nickel grains on particle surface. The anisotropic growth of nickel crystal also made coating uniformity worse. The heterogeneous nucleation process of nickel on surfaces of core particles had decisive influence on the formation of uniform and compact coating. |
| 语种 | 中文 |
| 公开日期 | 2013-09-16 |
| 页码 | 91 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1271]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 陈烨. 镍包覆微颗粒材料镀层均匀性研究[D]. 过程工程研究所. 中国科学院过程工程研究所. 2009. |
入库方式： OAI收割
来源：过程工程研究所
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