| 摘要 |
Disclosed is an improved method for coating a zinc surface comprising treating said surface with an aqueous, acidic solution containing: (a) about 0.5 to about 4 percent phosphate ion; (b) an ion selected from the group consisting of zinc ions, manganese ions, and mixtures thereof, said ions being present at a level sufficient to form dihydrogen phosphate with substantially all of said phosphate ions; and (c) about 0.01 to about 1 percent complex fluoride ions; wherein the weight:weight ratio of complex fluoride ions:chloride ions in said solution is at a value of about 8:1 or greater. It is preferred that the ratio complex of fluoride ion to chloride ion (F-:Cl-) in said solution to be maintained at a value of greater than about 8:1, preferably greater than about 10:1, and more preferably greater than about 14:1. The select weight:weight complex fluoride:chloride ratio substantially eliminates the abnormal crystal growth frequently found in treated surfaces while at the same time reduces the need for excess fluoride.
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