【作者】 吴青龙；

【导师】 安茂忠；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2007， 硕士

【摘要】 银在常温下具有最高的导电性和导热性,化学稳定性、焊接性能、反光性能也很好。因此,镀银层在工程领域和装饰领域有着广泛的应用。氰化物镀银液具有剧毒性,严重污染环境,危害生产者的健康,废液处理成本较高,所以人们希望用其他电镀工艺来取代氰化物电镀银工艺。本文根据不同无氰镀银体系存在的问题,通过优化筛选的方式确定了以5,5-二甲基乙内酰脲为配位剂的的镀液体系。针对该体系存在的缺点,确定了适合本体系的导电盐、添加剂。通过正交实验方法,结合单因素实验分析,优化了镀液组成及工艺条件,并研究了镀液组成及工艺条件对镀层、镀液性能的影响。研究结果表明在电解液组成及工艺条件为:硝酸银30g/L,5,5-二甲基乙内酰脲100g/L,碳酸钾80g/L,焦磷酸钾40g/L,温度40℃,pH11,电流密度0.4A/dm2条件下能得到合格的银镀层。为了进一步改进银镀层质量,研究了脉冲电流对无氰电镀银的影响。采用正交实验优化的适于脉冲电沉积的镀液,系统分析了导通时间、关断时间、脉冲电流密度等对镀层质量的作用和影响,最终确定了脉冲电沉积银的最佳工艺参数为:占空比40%,周期3ms,平均电流密度0.6A/dm2。在此工艺条件下,镀液的分散能力、覆盖能力、稳定性,镀层的微观表面形貌、结合力、抗变色性能、可焊性等均达到或优于氰化镀银体系,说明此工艺具有工业推广应用价值。通过循环伏安曲线、阴极极化曲线、Tafel曲线及计时电流法等电化学测试手段,研究了DMH体系中银的电沉积过程,并初步探讨了添加剂的作用机理。测试结果表明,DMH在测试范围内稳定,无其它副反应发生。循环伏安曲线表明,银的电沉积是受扩散控制的准可逆电极过程,并有典型的成核环存在,添加剂对阴极电流有明显的抑制作用。Tafel曲线表明,添加剂降低了银电沉积过程的交换电流密度和电化学反应速度常数。计时电流法表明,银在玻碳电极上的电结晶过程属于三维连续成核的生长机理,添加剂不改变成核方式,但会抑制晶体的外延生长。更多还原

【Abstract】 Silver has good chemical stability, electric conductivity and solderability. In view of their excellent properties, silver is a metal electroplated for a wide variety of applications both decorative and functional. Industrial electroplating of silver is conventionally carried out from cyanide solutions containing silver as its cyanide complex metal. However, cyanide compounds have strong toxicity and a large amount of cost is required for securing safe working conditions and waste treatment. Thus, an extensive search has been made for satisfactory alternative electrolytes.In the present work, 5,5-dimethyl hydantoin non-cyanide silver electrodeposition bath was choosed as the research bath. To improve the disadvantage of the process, conductive salt and additive of the bath were studied. Based on the single factors study, the optimal composition formula was obtained by an orthogonal method. And with the optimal formula, the influence of bath composition and operating conditions on the properties of solution and coatings was studied. And the result showed the optimal electrolyte composition and operating conditions were : silver nitrate 30g/L , 5,5-dimethyl hydantoin 100g/L , potassium carbonate 80g/L , potassium pyrophosphate 40g/L ,Temperature 40℃,pH value11,current density 0.4A/dm2.To improve silver coatings, pulse plating process was investigated. Based on the optimal composition and technique conditions by the orthogonal test, the effect of pulse on time, pulse off time and pulse current density on silver coatings was studied particularly and the preferred pulse plating parameters is:the pulse frequency 40%,the duty cycle 3ms,the average current density 0.6A/dm2。It has been found by examinations on dispersing power, throwing power of bath and surface morphology , tarnish resistance power and binding energy of silver films that this technics has the same or better effects than cyanide techics, and fitted for industry。The electrodeposition process from DMH non-cyanide silver electrodeposition bath was investigated by CV, Cathodic polarization curves, Tafel curves and chronoamperometric methods, and the influence of additive on the silver deposition mechanism was also discussed preliminary. The results indicated that the DMH is stabile in the range of measurement region. The results of CV curves indicated that the deposition of metallic silver in DMH electrolyte is a diffusion-controlled and reversiable growth process. It also can be observed from CV curves that a typical hysteresis loop existed and the additives have obvious inhibiting effect on the silver discharge process. The results of Tafel curves showed the additive decrease the exchange current density values and electrode reaction rate constant. Chronoamperometric results indicated that the electrodeposition process of silver at GC electrode belongs to a three-dimensional progressive nucleation mechanism and the additives didn’t change the nucleation mechanism, but inhibits the crystal epitaxial growth.更多还原