硫酸盐溶液体系三价铬电镀阻氢剂的研究

Study on hydrogen evolution inhibitor for trivalent chromium electroplating in sulfate bath

在由40 g/L Cr2（SO4）3、60 g/L HCOONa、100 g/L Al2（SO4）3、30 g/L尿素、60 g/L Na2SO4和30 g/L H3BO3组成的三价铬镀液中,通过测量阴极极化曲线,研究了四甲基硝酸铵、四乙基硝酸铵和四丙基硝酸铵这3种季铵盐对电沉积过程中阴极表面析氢的影响。其中,四丙基硝酸铵对硫酸盐体系电镀铬析氢的抑制效果最好。通过正交试验研究了四丙基硝酸铵的添加量、温度、pH和电流密度对镀铬电流效率的影响,得到最佳工艺条件为：四丙基硝酸铵1.5 mg/L,温度40℃,p H 2.5,电流密度20 A/dm^2。上述4个因素中,四丙基硝酸铵添加量对电流效率的影响最显著。在最佳工艺条件下电镀1 h,电流效率为32%,镀层厚度为57.67μm,耐蚀性较优。

The effects of three kinds of quaternary ammonium salt including tetramethylammonium nitrate, tetraethylammonium nitrate and tetrapropylammonium nitrate on the hydrogen evolution at cathode surface during the electrodeposition of chromium in a bath containing 40 g/L Cr2（SO4）3, 60 g/L HCOONa, 100 g/L Al2（SO4）3, 30 g/L urea, 60 g/L Na2SO4 and 30 g/L H3BO3 were studied by measuring cathodic polarization curves. It is shown that tetrapropylammonium nitrate has the best inhibition efficiency of hydrogen evolution for chromium electroplating in sulfate bath. The effects of dosage of tetrapropylammonium nitrate, temperature, p H and current density on the current efficiency of chromium deposition was studied by orthogonal test. The optimal process conditions were obtained as follows： tetrapropylammonium nitrate 1.5 mg/L, temperature 40 ℃ p H 2.5 and current density 20 A/dm^2. The dosage of tetrapropylammonium nitrate has the most significant effect on the current efficiency among the said four factors. The current efficiency is 32% when the plating under the optimal conditions lasts for 1 h, and the chromium coating obtained features a thickness of 57.67 μm and a good corrosion resistance.