三价铬电镀研究进展

Progress of Research on Chromium Plating with Trivalent Chromium Compound

介绍了三价铬电镀的工艺特点,重点介绍了三价铬电镀中杂质的去除和镀硬(厚)铬工艺。三价铬电镀对杂质非常敏感,极少量的杂质就会大大恶化镀层质量。常采用沉淀法、离子交换树脂、螯合剂等方法来除去杂质;另外,三价铬不能镀厚铬也是目前面临的一大难题,原因之一是因为阴极上有大量的氢气析出,pH升高,从而Cr3+形成氢氧化物,附着在镀件表面,致使镀层不致密,易脱落而无法增厚;此外,Cr3+氧化产物Cr6+还会毒化镀液。因此,要镀上厚铬,就必须对镀液进行调整,如降低pH,或选择更好的缓冲剂等方法。

The removal of impurities in the bath and the hard chromium plating process were discussed. Trivalent chromium plating is highly sensitive to impurities. A trace of impurity would exacerbate the coatings quality down. Usually sedimentation, ion exchange resin and chelater are adopted to remove impurities. The difficulty to get hard chromium coating is another obstacle need to be solved in production. There are two reasons responsible to this difficulty. One is the hydrogen evolution at cathode that leads to the rise of pH value at the cathode, and in turn makes the Cr^(3+) change into a hydroxides, adsorption of which on the substrate results in the trivalent chromium coating non-compact and loose, and prevents the plating from conduction. Then a thick coating cannot be obtained and only soft chromium coating could be expected. Another one of the reasons is related to Cr^(6+), the products of Cr^(3+) oxidation which poisons the plating solution. It is necessary for getting a hard coating to control the pH value of the plating solution or to use a better pH adjustor in the plating bath.