| 摘要 |
Phosphate coatings are formed on ferrous surfaces by dipping or flooding the surfaces with an acidic zinc phosphate solution containing a high zinc content, nitrate or other oxidising agent incapable of oxidising ferrous to ferric and a low controlled amount of chlorate or other oxidising agent capable of oxidising ferrous to ferric such that the solution contains 0.05 to 1% dissolved iron. This process can be achieved but using novel replenishment and make up solutions. The initial make up solution may be free of chlorate but the replenishment solution will contain a low amount of chlorate or other suitable oxidising agent. The phosphating solution preferably has a zinc/phosphate ratio in the range 0.8-4, a Zn/Ca ratio of 1-4 and a total acid/free acid ratio of 5-9. Use of the solution gives rise to reduced sludge production. The solution may contain conventional additives such as Cu, Co, Ni, fluorides, urea. The surfaces to be treated may first be pickled, degreased then preactivated with either hot water or a titanium ortho- phosphate dispersion. |
