| 摘要 |
Aluminium or its alloys are cleaned by immersion in an aqueous alkaline solution with a pH of at least 11 and containing a water-soluble nitrite and an emulsifying agent and/or a wetting agent. The solution contains 0.1-10% by weight alkali (as NaOH) and a weight ratio of alkali to nitrite (as NaNO2) of from 1:2 to 1:5. The emulsifying or wetting agents specified are alkyl-, alkylaryl- and arylpolyglycol ethers and condensation products of polypropylene oxide and polyethylene oxide and also alkyl-, alkylaryl- and aryl sulphonates and sulphonated polyglycol ethers in a concentration of 0.01-0.2%. A polyhydroxycarboxylic acid or salt, e.g. tartaric acid, gluconic acid, in a concentration of 0.001-0.5% by weight is also present. The aluminium is immersed in the solution and treated at 60 DEG C. Specification 731,035 is referred to. |
