Study On The New Chromate-free Passivation Technique Of Copper By AMT And Its Complex Reagents

Chromate passivation of copper has been prohibited gradually because of appeal from environment protection, but there has been a lack of a kind of equal substitute technique all the while. So this work applies AMT (2-amino-5-mercapta-1,3,4-thiadiazole) to chromate-free passivation of copper, after analyzing why it can inhibit corrosion of copper and why it can passivate bronze. Based on the studies on the inhibition of AMT, AMT and its compound are applied to surface treatment of copper. The treatment effect, the corresponding technological process and the stability of passivation solution are studied by experiments. In addition, the inhibition of AMT, BTA and TTA, the speed of forming film on copper surface and the effect of passivation treatment are studied by electrochemical AC impedance. The inhibition of AMT is studied by weight-losing experiment and compared with BTA and TTA. The result shows that AMT can effectively inhibit the corrosion of copper in acidic, alkaline and neutral solutions. In acidic medium, the inhibition of AMT to copper is superior to BTA and TTA. However, Cl-decreases its inhibition performance. The technique is investigated, based on optimizing the traditional process. Each step of the process is studied. The oxid on the surface of copper can be completely cleaned out in a few seconds by selecting acid cleaning solution. By studying the composition of passivation solution, temperature and time and by orthogonal design, the optimum surface treatment technique is proposed. And the process can be practically simplified according to different conditions. When the optimum technology is applied for brass treatment, it also exhibits perfect effect. By electrochemical AC impedance measurements, the speed of forming film, the effect of passivation treatment and the effect mechanisms of passivation are analyzed. At the same time, we find that AMT is stable. Even organic compound A or B is added into solution, the reaction products during the passivation treatment do not influence its stability. Thus, the passivation solution can be used time and time. Copper and brass treated by the optimum technique can anti-discolour in 48h in hot steam or in a year at atmosphere. The technological process is so simple that the unfamiliar operators can manipulate it. Furthermore, the consumption of reagent is small during passivation process. The passivation solution is stable and does not decompound in some days, and process can become simpler based on the fact. Accordingly, it is a kind of perfect chromate-free passivation technique and can solve the difficulty which chromate passivation is prohibited gradually but no equal substitute technique. It has promising prospect in industrial applications.