钕铁硼磁性材料磷化过程电位影响因素研究

Factors Affecting the Potential in Phosphating of NdFeB Magnetic Material

为了研究钕铁硼磁性材料的磷化机理,并研制钕铁硼磁性材料的磷化剂,应用电化学方法研究了游离酸度、温度、促进剂、表面活性剂对钕铁硼磁性材料磷化动力学行为的影响。结果表明,钕铁硼磁性材料磷化动力学的过程分为:金属阳极溶解→钝化→金属阳极溶解→磷化成膜 4步;所形成的化学转化膜并非单一的磷化膜,而是磷化和钝化的混合膜;游离酸度、温度以及促进剂对钕铁硼磷化影响较大,过高的游离酸度(高于 4. 8)和温度 (高于 40℃)将改变其磷化动力学的过程,使磷化难以成膜或膜层粗糙;促进剂能加速磷化的进行,但氧化性过强的促进剂(氯酸钠)只能增强钕铁硼磁性材料表面的钝化,而不能形成磷化膜。通过正交试验法,确定了钕铁硼常温磷化液的最佳配方和工艺条件:磷酸二氢钠 50g/L,磷酸 12mL/L,钼酸钠 0. 5g/L,促进剂 N0. 2g/L,阴离子表面活性剂 1. 5mL/L, FA1. 5点,TA51点,温度 30℃,时间 5min。所得磷化钝化膜薄而致密,耐腐蚀性能优异。

The influences of acidity, temperature, accelerator, and surfactant on the phosphating dynamic behavior of NdFeB were investigated making use of electrochemical method so as to investigate the phosphating mechanism of and develop phosphating agent for NdFeB magnetic material. The results showed that the dynamic process of NdFeB phosphating included four steps, i.e., the dissolving of anodic metal, the passivating, the re dissolving of the anodic metal, and the phosphated film forming. The resulting chemical conversion film was not a single phosphated film but a mixture of the phosphated passivated coating. The free acidity, temperature, and accelerator had obvious effects on the phosphating process of NdFeB. Overhigh acidity (more than 4.8) and temperature (more than 40 ℃) would cause change of the phosphating dynamic process, which made it difficulty to perform the phosphating or led to an increase in the surface roughness of the coating. Proper accelerators could speed up the phosphating, however, the strong oxidizing agent such as sodium chlorate as the accelerator could only strengthen the surface passivation of the NdFeB and retarded the formation of the phosphated coating. The optimal formula of the phosphating solution and process conditions were determined by orthogonal test as following: 50 g/L sodium dihydrogen phosphate, 12 mL/L phosphoric acid, 0.5 g/L sodium molybdate, 0.2 g/L accelerator N, 1.5 mL/L anion surfactant, free acidity 1.5, total acidity 51, 30 ℃, and 5 min. The final target phosphated passivated coating was thin and dense and had excellent corrosion resistance.