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H_2S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Ag_2O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S~(2-)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 Ag_2S和黑色Cu_2S的形成.
The purpose of this paper is to investigate the corrosion and the tarnish behaviour of 925Ag75Cu and 925Ag40Cu35Zn alloys in synthetic sweat at 37℃ and H_2S 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 Ag_2O 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 H_2S atmosphere at room temperature of these two 925Ag alloys are induced by S~(2-) 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 H_2S to form white ZnS, which significantly retards the reaction between Ag or/and Cu and H_2S to form grayish black Ag_2S and black Cu_2S.
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