Chromium-free Passivation Study On Surface Of Nickel Metal

In metal surface treatment,electroplated nickel can impart unique physical and chemical properties to metal surfaces,and is widely used in aerospace,automotive,plastic processing,food processing and other fields.There are many fine pores on the metal surface after electroplating nickel,which results in poor corrosion resistance of the nickel-plated film layer and a large negative impact on the formation of the steel shell.Therefore,the nickel-plated metal still needs a passivation process to improve the film layer.Corrosion resistance and overall product performance.Traditionally,chromate passivation has been widely used for the treatment of metal surfaces,but the process involves chromium contamination with serious environmental pollution,and the method has been severely restricted.In this thesis,the steel shell electroplated nickel electronic material is taken as the research object,the chromate passivation is used as the reference,the nitric acid resistance change time,the neutral salt spray test and the salt water immersion test result are the surface passivation treatment corrosion resistance index,and the research is not A new method of chromium passivation.The main research contents and results are as follows:1.Optimize the passivation conditions of chromate solution(potassium dichromate 13.6 g/L,ammonium fluorosilicate 1.36 g/L).Experiments show that the passivation solution has a pH of 2.0,a passivation temperature of 55 ? and a time of 4 min.Under the passivation,the optimum time for nitric acid discoloration of the test piece after passivation is 110 s,and there is no visible discoloration.Neutral salt spray time showed no corrosion spots at 12 h,and the passivation film had the best corrosion resistance.2.Choose the mixture solution of amino sulfonic acid(9 g/L),ammonium fluosilicate(0.9 g/L)and citric acid(11 g/L)as the chrome-free passivation base solution(amino sulfonic acid base solution or base solution for short)to conduct passivation for nickel plating specimens,and optimize the conditions.The results showed that passivation solution pH 2.0,passivation temperature 65 ?,time of 4 min,nitrate discoloration resistance time of 95 s,no apparent change color phenomenon.The passivation film has the best corrosion resistance.Compared with the experimental results of chromate solution passivation,the chromate resistance time was shortened by 15 s,and the neutral salt fog time was shortened by 4 h.3.Research and screening additives for the improvement of chromium-free passivation base liquid(7 kinds of inorganic substances and 4 kinds of organic substances),the passivation experimental conditions are the same as those of chromium-free base liquid.The results showed that the optimum time for the selected inorganic additives and the corresponding nitric acid resistance tests were: ammonium molybdate(14~18 g/L),168 s;cerium oxide(4~8 mg/L),105 s;cerium nitrate 6~10 mg/L,100 s;the optimum time for screening organic additives and corresponding nitric acid resistance are: phytic acid 10~20 ml/L,120 s;ethanolamine 10~20 ml/L,107 s;acrylic resin 10~20 ml/L,98 s.Compared with the passivation effect of sulfamic acid base liquid,the test time of nitric acid-resistant discoloration of ammonium molybdate was extended by 73 s.Among the inorganic and organic additives screened,the improvement effect of base fluid passivation was obvious.4.Orthogonal compounding experiments were carried out on the selected inorganic and organic additives-base fluids to optimize the amount of additives.The results show that the optimal combination of inorganic additives is ammonium molybdate and cerium oxide.The optimal combination of organic additives is phytic acid and ethanolamine.The orthogonal optimization of inorganic-organic-based liquid is optimized.The best combination of additives is ammonium molybdate 18 g/L,strontium oxide 4 mg / L,phytic acid 20 ml / L,ethanolamine 15 ml / L,nitric acid resistance test 305 s,compared with the chromate solution passivation effect,the best compound base solution passivation test piece The nitric acid resistance test time is extended by 180 s.5.Comprehensive detection and comparison of the passivation effects of each sample of the test piece.The formula includes: chromate solution,sulfamic acid base liquid,inorganic-base liquid,organic-based liquid,inorganic-organic-based liquid,comprehensive testing including neutral salt spray test and salt water immersion test,the results show that inorganic-The salt-to-solation time of the organic-base liquid passivation was 24 h,which was longer than the salt spray time passivated by the chromate solution for 12 h.Neutral salt spray test of passivation film The order of corrosion resistance is: inorganic-organic-base liquid passivation > inorganic-base liquid passivation > organic-base liquid passivation > chromate passivation > base liquid passivation;The salt water immersion test verifies the corrosion resistance sequence: inorganic-organic-based liquid passivation > chromate passivation > chromium-free passivation > unpassivated.