調控三價鉻電鍍液pH值對鍍層品質之影響

The Effect of pH Adjustment of Trivalent Chromium Electrolyte on Coating Quality

pH值在三價鉻電鍍中扮演著極為重要的角色，本實驗藉由固定pH值，在甲酸根與尿素錯合的三價鉻鍍液中，探討調整不同pH值方法對鍍液穩定性與鍍層形貌的影響。結果顯示僅以添加KOH調整的鍍液無法達到穩定的狀態，pH隨放置時間緩慢下降，且電鍍時鍍液pH值下降加劇，使鍍層表面留下許多氫氣孔。加入KOH後再加熱，pH值並不會隨時間下降，且電鍍時依然不會有劇烈變化，微結構觀察也發現鍍層表面的氫氣孔數量減少。根據哈氏槽的結果顯示，加熱時間增長會使電流密度實用範圍變窄，在使用同樣具有甲酸根的甲酸銨作為錯合劑時，不需要另外添加KOH也有調整pH值的效果，且pH值穩定，鍍層較霧，鍍層氫氣孔數量減少且呈現粗糙的表面形貌。

pH value plays an important role in trivalent chromium electroplating. The research is devoted to the investigation of different ways to adjust pH value in the electrolyte. The results indicate that pH value in the electrolyte decreases with time and decreases aggressively during electroplating by adding KOH without any other operation. In microstructure observation, there are many hydrogen pinholes in the coating surface. By reheat the solution after adding KOH, the pH value in electrolyte remains unchanged and changes slightly during electroplating. Number of hydrogen pinholes decreases at the same time. According to Hull cell test, quality range would decrease as reheating time prolonged. The purpose of adjust pH value could be achieve without adding KOH by change the complexing agent from formic acid into ammonium formate. When using ammonium formate, pH value remains unchanged and changes slightly during electroplating, too. The coating appears brightless, with no hydrogen pinhole and rough surface microstructure.