| 摘要 |
Iron containing scale is removed from a metallic substrate by contacting the scale with a composition which is an aqueous solution consisting essentially of at least 0.5 weight percent of a polyphosphonic acid, or an alkali metal or amine salt of such acid, with the acid being selected from the group of acids having the formulae: <IMAGE> (1) where R1 is selected from the class consisting of C1-C12 alkyl groups, and the group <IMAGE> and <IMAGE> (2) where R2 is selected from the class consisting of -H, -PO3H2, C1-C12 alkyl groups, and the group <IMAGE> The scale is removed from the metallic substrate by contacting THE DESCRIBED SCALE-BEARING SUBSTRATE WITH THE DESCRIBED COMPOSITION AT SELECTED TEMPERATURE AND PH conditions, and over a controlled time period and iron concentration in the composition so that the formation of an undesirable polymeric precipitate in the cleaning solution is avoided. Formation of the precipitate is also avoided by adding ammonium bifluoride to the composition.
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