NaOH和NiSO4添加剂浓度对短碳纤维化学镀银结构和导电率的影响

目的制备镀层均匀、结合力好的短碳纤维镀银层。方法以葡萄糖为还原剂,在短碳纤维表面进行化学镀银,研究了NaOH浓度、NiSO_4添加剂浓度对短碳纤维化学镀银层结构和性能的影响。采用X射线衍射仪、扫描电子显微镜对镀银碳纤维的结构、形貌和成分进行分析,测试了镀银后纤维的密度、导电率。采用冷热循环法评估镀层与碳纤维的结合强度。结果增大NaOH浓度可提高银氨络合物离子浓度,加快了反应速率。合适的NaOH浓度有助于获得高质量的镀银层,低浓度和高浓度NaOH条件下均会产生漏镀和镀层不均匀现象,导致镀银碳纤维性能的降低。NiSO_4添加剂加入到溶液中后,Ni~(2+)将优先吸附在碳纤维表面,这不仅增大了碳纤维表面银单质的形核率,同时也降低了反应速率。合适的NiSO_4浓度有助于改善银镀层的质量,低浓度和高浓度NiSO_4条件下得到的镀层性能均不足。结论 NaOH质量浓度为7g/L时获得的镀银层分布均匀,结晶度良好,密度较大,导电率也较好。NiSO_4浓度为5×10~(-5) mol/L时能获得光滑、均匀、平整的镀层,密度最大,导电率最优。

Effects of Concentration of NaOH and NiSO4 Additives on Structure and Electrical Conductivity of Silver-coated Short Carbon Fibers by Electroless Plating

The work aims to prepare the short carbon fiber silver layer with good uniformity and binding force. The sil-ver-coated short carbon fibers were prepared by plating methods with glucose as reducing agent. The effects of NaOH and NiSO4 concentrations on the microstructure and properties of the silver-plated layers were studied. X-ray diffraction method and scanning electron microscopy were used to analyze the microstructure, morphology and composition of the electroless plated silver layers. The density and conductivity of silver-plated fibers were tested. The hot and cold cycling test method was employed to evaluate the bonding strength between the silver-plated layers and the short carbon fibers. Increasing NaOH concentrations led to the increase of the silver-ammonium complex ions, and thus accelerated the reaction rate. Proper NaOH concentration was beneficial to obtaining high-quality silver-plated layer. However, the leakage plating phenomena and coating unevenness occurred under both low and high concentrations of NaOH, which reduced the performance of silver-plated carbon fiber. The Ni2+ ions in NiSO4 additives could be adsorbed on the surface of the carbon fibers prior to other particles. This could improve the nucleation rates during silver depositions. However, the high concentrations of NiSO4 additives depressed the reaction rate of silver depositions. When NaOH concentration is 7 g/L, uniform silver-plated layer with good crystallinity, large density and better conductivity can be obtained. When 5×10-5 mol/L NiSO4 is selected, the smooth, uniform and flat silver-plated layer with the highest density and the best conductivity can be produced.