银纪念币的腐蚀变色研究

银纪念币在大气环境中表面发生变色，失去原有的金属光泽。采用OM，SEM，EMPA，XPS，XRD等现代物理测试技术对变色的银纪念币进行分析。结果表明，银纪念币的变色部位呈均匀的浅褐色，并随机分布着深褐色的斑点。变色银纪念币表面沿着划痕密集分布着蚀孔。表面分析显示，除Ag外，还有S和O元素。XPS，XRD分析发现，变色银纪念币表面存在Ag2S，Ag2SO3和Ag2O。实验室加速变色试验毒明，在含S气体环境中，Ag被氧化生成A82S，导致银纪念币表面变色,从而验证银纪念币的变色是由电化学腐蚀引起的，S和O元素参与了腐蚀历程。     

氧化对铜基件镀银产品电气性能的影响及其预防和解决方法

从镀银工艺和环境两方面探讨了铜基镀银产品氧化的原因,分析了氧化后镀银产品的电气性能,提出了镀银层防变色的措施、氧化后处理方式和镀银层替代方案。     

添加微量硅对925银合金抗硫化变色性能的影响

微量硅在925银铸造过程中可促进合金脱氧，提高合金熔体的洁净度和流动性，但过量硅会劣化合金性能。采用光学显微镜和电子显微镜研究添加微量硅(0.09%~0.15%)对925银微观组织变化的影响。结果表明，随着硅含量升高，925银合金中一次枝晶组织粗大，二次枝晶臂间距增大，当二次枝晶臂间距大于10 μm，合金断裂趋势显著增加。硅元素在925银合金中形成黑色低熔铜基共晶相，并由1~10 μm的点状相转变为8~20 μm的断续条状相，显微硬度变化与共晶二次析出相比例呈对应关系。在925银中梯度添加微量硅使合金硫化腐蚀后色差缩小，提高合金的抗硫化腐蚀变色能力。     

化学镀锡在印刷线路板制备中的应用

从化学镀锡液的基本组成、工艺特点、反应过程及应用等几方面简述了近年来化学镀锡在印刷线路板制备中的研究进展.概括了目前化学镀锡工艺存在的问题,对镀锡过程中出现沉积速率低、锡面易变色、锡须和渗镀等现象进行了详细的讨论,总结了问题出现的原因及解决的方法.同时对化学镀锡的研究方向和发展趋势进行展望.     

铝件镀银出现“黑斑”的原因及其消除

某批次铝零件在镀银后喷漆加工过程中出现了黑斑.从原材料、电镀和喷漆加工工艺等方面对黑斑产生的原因进行了讨论,通过表面和截面形貌观察、电镜分析、能谱分析等方法对黑斑与正常镀银层进行了对比,确定了黑斑为镀银层被硫元素污染所致,并找出了镀银层变色的原因,排除了故障.     

Anti‐tarnish treatment of brass for coinage

The anti‐tarnish film was formed on brass for coinage by 1‐phenyl‐5‐mercaptotetrazole (PMTA), which was studied by accelerated corrosion test (metallic coatings‐thioacetamide corrosion test), polarization curves and electrochemical impedance spectroscopy (EIS) in synthetic sweat solution. The accelerated corrosion test showed that PMTA exhibited better anti‐tarnish performance on brass than that of traditional anti‐tarnish agent benzotriazole (BTA). The polarization measurements showed that PMTA could be classified as a mixed inhibitor for it could restrain both anodic and cathodic reactions. EIS measurements indicated that the inhibition efficiency of PMTA on brass was over 98.4% in synthetic sweat solution. All these results showed that PMTA was an excellent anti‐tarnish agent of the brass for coinage, the optimum treating conditions of which were 0.5 gL^?1, pH = 3, 55°C–85°C, 7 min.     

印制线路板中化学镀锡研究现状与发展

综述了PC B化学镀锡的发展现状及历史。介绍了现阶段化学镀锡工艺的优点及硫酸盐体系与烷基磺酸盐体系2种化学镀锡液的组成。分别介绍了主盐、硫脲、络合剂、还原剂及其它添加剂的作用。对化学镀锡的机理做了探讨。提出了比较合理的改进化学镀锡液的方案,尤其是在提高镀速和改善镀厚性等方面。同时提出了防止镀锡层表面变色和锡须生成的一些有效方法。     

黄铜抗变色表面处理工艺

研究了多种添加剂对人体汗液中黄铜的缓蚀作用,发现含硫有机物ＢＪＬ对黄铜有一定缓蚀作用,与ＢＴＡ有协同效应,虎有以抑制阳极过程为主的特征。研究了一组由ＢＴＡ、ＢＪＬ、含氧有机成膜物ＪＹＱ和辅剂所组成的钝化－涂溶液及工艺,实施此工艺后的黄铜,耐醋酸盐雾腐蚀达８４６ｈ以上。     

Trace Elements in Superalloys

Abstract

In this study, effects of superheated steam on cyclic crack propagation behavior of a heat resistant steel were investigated. Crack propagation experiments were carried out on NF616 (9Cr-0.5Mo-2WVNb) in pressurized superheated steam (600°C/10MPa) under cyclic loading either with or without holding time at constant load. Superheated steam environment has two opposing effects on cyclic crack growth, acceleration and retardation. A modified tarnish rupture (TR) model has been proposed to explain the crack propagation behavior. The crack propagation rate estimated based on the TR-type model well agreed with the experimental data.     

Corrosion process of silver in environments containing 0.1 ppm H2S and 1.2 ppm NO2

The effects of sub‐ppm levels of nitrogen dioxide and hydrogen sulfide, and the adsorbed water on the corrosion of silver were studied in order to get a better understanding of the atmospheric corrosion process. An in situ mass balance was taken to monitor the kinetic behavior and the surface and the corrosion film were analyzed by X‐ray photoelectron spectroscopy (XPS). In H₂S environments, the tarnish film consisted of silver sulfide, and the corrosion rate depended upon oxygen as well as relative humidity. Silver was oxidized by only oxygen and the corrosion behavior conformed to a type of a parabolic law. In NO₂ environments, the corrosion film consisted of nitrate and oxide, and the corrosion rate depended upon oxygen as well as relative humidity. Compared to hydrogen sulfide, the formation of silver nitrate being strong hydroscopic reduced the effect of humidity on corrosion rate. In H₂S + NO₂ environment, the corrosion process was independent of both oxygen and humidity, and the kinetic behavior conformed to a linear law. The difference of corrosion process between H₂S or NO₂ environments and H₂S + NO₂ environments is thought to be due to the role of nitrogen dioxide as an ionic conductor and the presence of strong oxidizing species such as elemental sulfur which can be produced from the following reaction: H₂S + 2NO₂ → S + 2HNO₂. In addition, the role of adsorbed water affecting atmospheric corrosion process was mentioned based on the amount of adsorbed water from the three types of exposure environments.