【作者】 徐亮；

【导师】 左禹；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2010， 硕士

【摘要】 本文主要开发了一种新型Cr-Pd膜合金电镀工艺,通过正交试验等方法确定了镀液配方中的主盐的络合剂、缓冲剂、阳极去极化剂、润湿剂等的选择和用量,利用电镀过程中的电流效率的变化来确定最佳的温度和pH值。最终利用方波脉冲电镀的方法获得组织均一,结构致密的电镀Cr-Pd合金膜。用Cr-Pd膜合金电镀工艺在不锈钢基体上施镀,。通过电子扫描显微镜(SEM)、能谱(EDS)、X射线光电子能谱(XPS)、X射线衍射(XRD)等方法表征了316L不锈钢表面电镀Cr-Pd合金膜的表面形貌以及膜层的组成与结构。并对电镀Cr-Pd合金膜后的316L不锈钢试样在沸腾的20%H2SO4溶液以及甲乙混合酸中的耐蚀性进行了系统的测试；最后对电镀Cr-Pd合金膜提高耐蚀性的原因进行了探讨。通过电镜照片可以看出,当镀液中Pd2+浓度较低时,膜层的晶粒较大,同时表面存在细微的裂纹,随着Pd2+浓度的增大,膜层的晶粒逐渐变小,同时裂纹也逐渐消失,说明膜层中Pd元素的增加可以细化晶粒。XRD分析结果可知：Cr和Pd元素是以相互夹杂的形式成膜的,Cr元素在Cr(211)面上存在着定向生长的现象,随着膜层中Pd元素含量的增加,Cr(211)面所对应的衍射角逐渐变小,峰位逐渐向左偏移。原因是氢原子在成膜过程中渗入Cr和Pd的晶格之中,从而使二者的晶格常数变大,晶粒度减小。XPS分析结果可知：在Cr-Pd合金膜中,Cr元素的存在形式为Cr(OH)3、Cr单质和Cr2O3, Pd元素的存在形式为单质Pd,其中含有少量的PdO。采用热震法,百格法和划痕法对膜层的附着力进行了检测,结果表明膜层的附着力优良,通过显微硬度测量表征了膜层的物理性能,结果表明：Cr-Pd合金膜的硬度大约是空白不锈钢和镀钯试样的1.5倍,而且随着膜层中Pd含量的增多,显微硬度逐渐减小。用失重法、极化曲线及EIS测试研究了其在沸腾的20%H2SO4溶液以及甲乙混合酸中的腐蚀行为。结果表明,Cr-Pd合金镀膜能够显著提高316L不锈钢在非氧化性强腐蚀介质中的耐蚀性,电镀后316L不锈钢在沸腾的20%H2SO4中的腐蚀速率降低了4个数量级以上,基本上与电镀Pd相同。铬-钯合金膜具有高耐蚀性的原因是Pd有着较高的阴极氢交换电流密度和较高的热力学电势,可以促使Cr膜在非氧化性强腐蚀介质中的电位提高,从而形成稳定的钝化膜。更多还原

【Abstract】 Cr-Pd alloy films with good corrosion resistance, high hardness has been recently developed as a kind of new and protective membrane, To optimize the electroplating 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.An uniform chromium-palladium film on 316 stainless steel was obtained by electroless plating. Scanning electronic microscopy, x-ray photoelectron spectroscopy, weight loss tests and electrochemical measurements were used to character the properties of the film. Corrosion behaviors of the chromium-palladium plated samples in acetic and formic acid mixtures at boiling temperature and the 20% sulfuric acid were studied. Finally, the reasons of the chromium Palladium alloy films enhance the corrosion resistance of 316L stainless steelwere discussed. The electroplated films were mainly composed of chromium and palladium. In the Cr-Pd films both Cr and Pd presented mainly in metallic state, with the grain sizes less than 100 nm. The Cr-Pd plated sample showed higher microhardness than Pd plated sample and 316L stainless steel. On the surface, Cr(OH)3 and Cr2O3 were present. The crystallite size decreased with the increase of Pd content in the Cr-Pd alloy films. The adhesive strength was examined by cross-cut tape test, thermal shock test and Cross-cut tape test, and the adhesion of the film to stainless steel was quite good.In boiling 20% H2SO4 solution, corrosion rates of the Cr-Pd plated samples were about four orders of magnitude lower than that of the original 316L stainless steel samples. With the increase of chromium content in the Cr-Pd films, corrosion potential of the Cr-Pd plated stainless steel samples decreased, but the impedance of the film increased.更多还原