The effectiveness of passivation respectively using a chromate system and a molybdate system was compared.The effects of rare earth compounds i.e.yttrium oxide and cerium nitrate on molybdate passivation were studied.The optimal composition ofmolybdate passivation bath was obtained by orthogonal test as follows:ammonium molybdate 16 g/L,cerous nitrate 8 mg/L,yttrium oxide 8 mg/L,ammonium fluorosilicate 0.5 g/L,and 50vo1％ phosphoric acid as required (adjusting pH to 2.00 ± 0.02).The passivation film obtained on Ni-P alloy coating from the optimal bath at (70 ± 2) ℃ for 8 min is smooth and dark gray,and can endure up to 458 s in nitric acid without discoloration,which is comparable to that of the traditional chromate passivation film (461 s).%先对比了铬酸盐体系与钼酸盐体系对化学镀镍层的钝化效果,然后研究了氧化钇和硝酸铈对钼酸盐钝化的影响,并通过正交试验得到最优钝化液配方为:钼酸铵16g/L,硝酸铈8 mg/L,氧化钇8 mg/L,氟硅酸铵0.5 g/L,1+1磷酸适量(使pH为2.00±0.02).采用最优钝化液在(70±2)℃的温度下对Ni-P合金镀层钝化8 min时,钝化膜表面平整,呈深灰色,耐硝酸变色时间可达458 s,与传统铬酸盐钝化膜的耐硝酸变色时间(461 s)相当.
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