925Ag75Cu和925Ag40Cu35Zn合金在人造汗液和H2S气氛中的腐蚀与变色行为

Corrosion and Tarnish Behaviour of 925Ag75Cu and 925Ag40Cu35Zn Alloys in Synthetic Sweat and H2S Atmosphere

摘要:

采用静态腐蚀、XRD、SEM、EDS和XPS，研究了250 ℃时效4 h和70%冷变形+200 ℃时效4 h两种硬化状态下的925Ag75Cu与925Ag40Cu35Zn合金在37 ℃人造汗液和室温H2S气氛中的腐蚀与变色行为。结果表明，这两种925银合金在37 ℃人造汗液中的腐蚀变色是由Cl-和OH-离子引起的，但925Ag40Cu35Zn合金的变色过程明显比925Ag75Cu合金缓慢，腐蚀过程中产生的白色AgCl和灰黑色Ag2O难以在其表面沉积而形成灰黑色腐蚀膜。这两种925银合金在室温H2S气氛中的腐蚀变色是由S2-引起的，但925Ag40Cu35Zn合金的腐蚀变色过程明显比925Ag75Cu合金缓慢，这是由于腐蚀过程中白色ZnS最先形成，从而延缓了灰黑色 Ag2S和黑色Cu2S的形成

Abstract:

The purpose of this paper is to investigate the corrosion and the tarnish behaviour of 925Ag75Cu and 925Ag40Cu35Zn alloys in synthetic sweat at 37 oC and H2S atmosphere at room temperature. The alloys were in two hardening states, viz., aging at 250 ℃ for 4 h and 70 % cold rolling + aging at 200 ℃ for 4 h, and tested by means of static corrosion, examined by XRD, SEM, EDS and XPS. The results show the corrosion and the tarnish in synthetic sweat at 37 ℃ of these two 925Ag alloys are induced by Cl- and OH- anions. The tarnish of 925Ag40Cu35Zn alloy is much slower than that of 925Ag75Cu alloy, and the white AgCl and the grayish black Ag2O produced by corrosion are difficult to deposit on the surface of 925Ag40Cu35Zn alloy resulting in grayish black corrosion film. The corrosion and the tarnish in H2S atmosphere at room temperature of these two 925Ag alloys are induced by S2- anion. The corrosion and the tarnish of 925Ag40Cu35Zn alloy are much slower than 925Ag75Cu alloy. This is because Zn in 925Ag40Cu35Zn alloy reacts earliest with H2S to form white ZnS, which significantly retards the reaction between Ag or/and Cu and H2S to form grayish black Ag2S and black Cu2S