Patented Aug. 23, 1949 2,479,564

UNITED STATES PATENT OFFICE 2,479,564 PHOSPHATE COATING 0F METALLIC ARTICLES Lloyd 0. Gilbert, Davenport, Iowa No Drawing. Application September 14, 1945, Serial No. 616,435 1 Claim. (Cl. 148-615) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 1 . The invention described herein may be manu a typical and satisfactory phosphate coating factured and used by or for the Government for bath: ' governmental purposes, without the payment to Free acidity ______.._points__ 4.0 me of any royalty thereon. ' Total acidity ______do....__ 25 This invention relates to phosphate coating of Proportion of total to free acid ______- 1-6.25 metallic articles and more particularly to a Iron ______-_percent__ 0.40 method of producing greatly improved phosphate Zinc ______do-.._._ 0.35 coatings. This invention has application in the Nitrate ______' ______do____ 2.5 ?eld in which rustproof coatings of metallic phosphates are formed upon articles having a 10 The free acidity is measured in conventional surface of iron, zinc, cadmium, magnesium. manner by titrating 10 cc. sample of the bath aluminum, and alloys thereof by immersing the with 0.1 N sodium hydroxide to the methyl article in an acidic aqueous solution comprising orange end point; the number of cos. of sodium metallic phosphates, such as ferrous phosphates hydroxide ‘required is the point value of the free 15 acidity. The total acidity is determined by and metallic phosphates selected from the titrating a 10 cc. sample of the bath with 0.1 N group consisting of zinc phosphates, manganese sodium hydroxide using phenolphthalein indica and copper phosphates. I have found that improved coatings are pro tor; the number of cos. of sodium hydroxide re quired is the point value of g the total acidity. duced as a result of adding to the phosphate coating bath a compound of boron, which will 20 Iron, zinc and nitrate are determined by con liberate boric acid in the bath at a relatively slow ventional quantitative analytical methods. rate. I prefer to use a metallic ?uoborate, boron The bath described immediately above when operated at a temperature of from 205° F. to 210° phosphate or ?uoboric acid. , It is a characteristic of the boron compounds F. produced a satisfactory coating on a steel which I desire to use that they hydrolyze rela 25 article immersed in the solution for a period oi.’ tively slowly in phosphate coating baths to yield one-half hour. boric acid. As distinguished from this, the bo To the bath described above. which had a rates hydrolyze Very rapidly to give boric acid, volume of 270 gallons, was added one pint of an and hence are undesirable for employment in ac aqueous-solution of zinc ?uoborate having the cordance with the invention. '. .30 following analysis: It‘ is known that additions of boric acid to - . ‘Percent phosphate coating baths result in improvement Zn(BF4)2 ______.4. ______;.._ 47.55 in the ?nishes produced upon metallic articles Free HBF4 ~ 1 ' 0.52 treated in the bath. However, the addition of Free H3303 4.11 35 boric acid is accompanied by many undesirable After the addition of the solution of zinc ?uo results. .The. baths‘ are‘ operated at elevated borate to the bath, a steel article was treated temperatures slightly below the boiling point, therein for a period of one-half hour. 'The ar and, at these temperatures, the boric acid is ticle was found to be coated with a much darker rapidly lost from the bath by volatilization or 40 almost black ?lm exhibiting a. uniformly ?ne ' steam distillation; hence its bene?cial effects are ‘crystalline structure. Such article showed im short lived. Because of the rapid loss of boric proved corrosion resistance as compared to the acid, frequent replenishment is necessary. article similarly prepared in a bath containing The invention will be more particularly de scribed in reference to the coating of ferrous no zinc ?uoborate. 45 It has been found that quantities of ?uoborate metals utilizing a bath containing ferrous greater than one pint of zinc ?uoborate in 2'70 phosphates, zinc phosphates and a-nitrate. It gallons of phosphating solution do not materially Will be understood, however, that this is by way improve the quality of the coating produced. of example only and is'not to be construed as However, the e?ect of the addition extends over a limiting the invention. ‘ The following table gives the characteristics of longer period of time. For example, the effects of 4 one pint of ?uoborate may last for three to four It is believed that boron phosphate hydrolyles days and the ei’iects oi the addition of two pints to yield boric acid and phosphoric acid in accord may last from six to eight days. Even very large ance with the following: additions oi’ zinc ?uorborate up to as much as tour or ?ve gallons per 2'10 gallons 0! phosphate bath do not have any deleterious action. Buch ' Because the addition of boron phosphate to large additions will result in improved coatins the coating bath has a tendency to raise the tree action for a relatively extended period oi’ time. acid value or the bath, boron phosphate can be It is believed that the zinc ?uorborate hydro used- to advantage as‘an addition agent where lyzes in the acid bath to yield boric acid. zinc 10 the tree acidity is lower than desired. ?uoride and hydro?uoric acid in accordance with the iollowing equation: Iclaimr ' ~ The process for rormins a rustproo?ng coating or a metallic phosphate upon a ferrous metal sur iace which comprises subjecting said suriace to The formation of the zinc- ?uoride and the ll the action of an aqueous solution the solutes of hydro?uoric acid is believed to add to the ‘effec which consist essentially of free phosphoric acid, tiveness of the bath by reducing the temperature a phosphate of a metal selected from the group at which the bath may be operated for the pro consisting 0t zinc, manganese and copper, and duction of a superior coating. boron phosphate in the proportion of about one ' Other metallic ?uoborates may be employed in 20 half pound to about three pounds per about 240 a manner siinilar to that described for the em gallons oi said solution. ‘ ployment of zinc ?uoborate. Manganese ?uo borate [Mn(BF4)sl may be advantageously used LLOYD o. GILBERT. in phosphating baths containing a mixture oi’ ferrous and manganese phosphates. Where cop 25 REFERENCES crrEn per is used in the coating bath, additions of cop The following references~'are. of record in the per ?uoborate have been found to produce better ?ie of this patent: coatings. Fluoborio acid may be employed it de sired. Boron phosphate [BPOd also may be used UNITED STATES PATENTS to advantage in any of the phosphating baths. It .30 Number Name Date has been found that additions of from one-hali' 1,610,362 Coslett ______Dec, 14, 1926 pound to three pounds of boron phosphate to 240 1,946,647 Taylor et al ______Feb. 13, 1934 gallons 01' a zinc-ferrous phosphating bath as 2,310,381 Zimmer et a1 ______Feb. 9, 1943 set forth above will condition the bath with,a production of superior coatings for a period of 8 2,312,855 Thompson ______Mar. 2, 1943 from four days to three weeks.