GB522954A - Improvements in or relating to the treatment of iron or zinc, or of alloys of either iron or zinc, for the production thereon of phosphate coatings - Google Patents

Abstract

522,954. Cleaning and coating metals. AMERICAN CHEMICAL PAINT CO. Dec. 20, 1938, No. 37069. Convention date, May 27. [Class 82 (ii)] [Also in Group XXXVI] To produce a phosphate coating on a surface of iron, zinc, or alloys thereof the surface is treated with an acid aqueous solution containing oxalic acid and then, without any intermediate mechanical treatment such as wiping or brushing, is subjected to the action of a phosphate coating solution. Before treatment with the oxalic acid solution the surface may be, cleaned, e.g. by ' pickling, vapour degreasing, alkali cleaning &c. The oxalic acid solution may contain other substances, e.g., sulphuric, nitric, hydrochloric, acetic, or pnosphoric acids, salts such as sodium or potassium nitrate, phosphate, sulphate, chloride, or acetate, organic substances such as alcohols, ethers, acetone &c. wetting agents such as isopropyl naphthalene sulphonic acid, and corrosion inhibitors such as coal ' tar bases, thioureas, sulphite pulp waste liquor, or aldehyde-amine condensation products. If the surface has been subjected to a strong alkakli cleaning, mineral acids are preferably added to the oxalic acid solution. The action of the solution may be accelerated by the presence of copper or silver in solution, e.g., by-addition of copper sulphate, chloride, carbonate, or oxide.'The duration of treatment in the oxalic acid solution is preferably sufficient to etch the surface but not sufficient to produce an oxalate coating, the duration depending on the concentration, the temperature, and the rate of relative, motion between the surface and the solution. The treated surface may be rinsed, and, if desired, dried before it is subjected to the action of the phosphate solution. The, phosphate coating solution is preferably one comprising mainly zinc or manganese phophates used at a temperature below boiling, e.g. 100 - 200‹F.; its action may be accelerated by addition of oxidizing agents or metals such as copper, cobalt or nickel, by violent impingement on the surface to be coated, or by making the piece to be coated an electrode and passing alternating current through the solution. Pretreating solutions -specifically described are solutions of oxalic acid alone, of oxalic acid and copper sulphate, and of oxalic acid, phosphoric acid, butyl alcohol, and denatured alcohol, the last solution being used both for cleaning and etching. Specified phosphatizing baths are made by dissolving (1) zinc oxide and phosphoric acid, (2) manganese carbonate, phosphoric acid, sodium nitrate, and cupric nitrate, and (3) zinc oxide, nickel carbonate, phosphoric acid, and nitric acid. The phosphatized surface may be coated with paint, varnish, lacquer, japan &c.