銀の変色, 腐食に対するベンゾトリアゾールの抑制効果

抄録

The inhibition effects and mechanism of benzotriazole (B.T.A.) on tarnishing and corrosion of silver were studied by means of potentiostatic polarization curves, differential capacity-electrode potential curves, and accelerated testings in H₂S and SO₂ atmospheres. It was recognized that B.T.A. had little inhibition effects in acidic solutions (pH 2.5), but had great effects in almost neutral solutions; because, B.T.A.-Ag complex was formed on the surface in anodic potential region, and B.T.A. was adsorbed on the surface with lone electron-pairs of N-atoms in cathodic potential region. Silver treated with B.T.A. had an enhanced resistance to tarnishing in H₂S atmosphere. It was considered that the prevention would be due to the formation of stable B.T.A.-Ag film on the surface. The galvanic corrosion of silver-plated panels occurred in SO₂ atmosphere, leading to the copper base owing to the presence of pores, was much more markedly inhibited by electrolytic treatment than immersion treatment in B.T.A. solution. It was found that the change in the surface coverage (θ) of B.T.A. treated copper conformed to Langmuir's adsorption formula expressed as follows: θ=Km/(1+Km), where K: adsorption constant and m: concentration of B.T.A. Then, the changes of K by immersion treatment and by electrolytic treatment were measured. As the results, a larger value of K was obtained by electrolytic treatment. Therefore, it was considered that the adsorption of B.T.A. on copper through pores became easier by electrolytic treatment.