- 2,964,434 United States Patent Office Patented Dec. 13, 1960

2 to provide an acidic bath having a pH of not more than 1, preferably not more than 0.5. M - 2,964,434 Boron, in a soluble form, may be added to the bath as borophosphoric acid (HPO'HBO), boric acid, PCKLNG AND RUSTNHBTING BATH FOR borax, boron phosphate, boric acid and phosphoric acid, FERROUs METALS, AND USE OF SAME borax and phosphoric acid, and the like. In the event William B. Coleman, Crete, Ill., assignor to Victor Chem that sufficient phosphoric acid is present in the bath, as ical Works, Chicago Heights, Ill., a corporation of the pickling acid, to maintain the pH of the bath at 1 Illinois or below, preferably 0.5 and below, the soluble boron 10 compound need not be added to the bath in conjunction No Drawing. Filed June 17, 1957, Ser. No. 666,249 with phosphoric acid or as a phosphate. Regardless of 8 Claims. (C. 148-6.17) how my pickling-phosphatizing bath is prepared, it is es sential to my invention that boron-phosphate be present in the acidic bath and that the bath contains a sufficient This invention relates to a pickling-phosphatizing bath 5 concentration of free acid from the group consisting of which effects the efficient pickling of ferrous metal and phosphoric acid, sulfuric acid, and admixtures thereof, at the same time phosphatizes the surface of said metal, to enable the bath to have a pH of not more than 1, and the use of said bath in treating ferrous metal. preferably not more than 0.5. The term "boron-phosphate' herein refers to the pres When sulfuric acid is used as a pickling acid, the pro ence of phosphate ions and soluble boron in a pickling 20 portion of boron-phosphate that should be present in the phosphatizing bath which has a sufficient concentration bath may be determined by trial so as to produce a bath of a pickling acid from the group consisting of sulfuric that effects the desired degree of rust-resistance or phos acid, phosphoric acid, and admixtures thereof, to enable phatization on the pickled ferrous metal surfaces. It the bath to have a pH of not more than 1, preferably has been found that at least about 0.4% by weight bor not more than 0.5. The exact chemical nature or com 25 on-phosphorus compound or boron-phosphate, based on position of the boron-phosphate present in the bath can all the constituents of the bath, should be added to or not be defined with precision; however, boron and phos present in an acidic pickling solution containing, as the phate constituents are present in the acid bath in the pickling acid, a concentration of about 7% by volume form of ions, complexes, compounds, or moieties. The Sulfuric acid wherein the sulfuric acid has a specific boron-phosphate may be separately formed and added 30 gravity of 1.84. Substantially complete rust protection to the acid bath as such, or may be formed in situ in the is obtained when the boron-phosphate or boron-phos acid pickling bath. phorus compound added to or present in a 7% by vol The pickling of ferrous metal surfaces to remove rust ume Sulfuric acid bath is increased to about 1 to 2% by and mill scale has been practiced for many years, par weight of all the contents of the pickling-phosphatizing ticularly in steel mills which utilize hot rolling and stamp 35 bath. Although larger amounts of boron-phosphorus ing procedures. The most commonly used pickling pro compound or boron-phosphate may be added to or pres cedure involves dipping ferrous metal articles, such as ent in the sulfuric acid pickling bath, no apparent ad steel, in a hot, aqueous sulfuric acid bath comprising vantage is obtained when more than 2% by weight bor about 7% by volume sulfuric acid for a sufficient period on-phosphate or boron-phosphorus compound is added to to dissolve and remove the oxide scale from the surface 40 or present in the bath. of the article. In addition to the use of sulfuric acid Also, my pickling-phosphatizing bath may be prepared in pickling baths, hydrochloric acid and phosphoric acid by the addition of boron, in a soluble form, to a bath are Sometimes used for the same purpose. The metal containing phosphoric acid as the pickling acid. For surface resulting from such pickling operation is some example, with a 20% by volume pickling solution of what roughened and is usually satisfactory for subse 45 75% by weight phosphoric acid, the addition of 2% quent coating operations, such as painting, bonderizing, by Weight of borophosphoric acid to the bath will give etc., but is not entirely satisfactory from the standpoint Substantially complete rust-resistance to pickled steel sur of resisting the formation of rust during storage and han faces. dling prior to such coating operations. The use of sulfuric acid and/or phosphoric acid, as The use of a phosphoric acid pickling bath does not, 50 the pickling acid, is superior to hydrochloric acid; how as might be expected, produce any appreciable phos ever, when employing a 7% by weight hydrochloric acid phatizing effect on the surface of ferrous metal because pickling bath, 2% by weight of borophosphoric acid, of the high free acid content required for pickling oper based on all the constituents of the bath, will give par ations. Similarly, phosphatizing or rust-proofing pro tial rust protection. The addition of at least 5% by cedures which utilize phosphoric acid baths are not suit 55 Weight borophosphoric acid will be required to give sat able for pickling operations because of the low free acid isfactory rust protection for the pickled steel surface in content present in the baths used in such coating pro a 7% by Weight hydrochloric acid pickling bath. cedures. For practical purposes it is preferred to use sulfuric My invention relates to a pickling bath which may be acid as the pickling acid. used to pickle ferrous metal surfaces, and, at the same 60 In carrying out my pickling-phosphatizing procedure, time, produce a phosphatized surface on the metal which rusted or scaled steel panels were cleaned with a deter offers improved resistance to subsequent rusting in nor gent solution to remove the grease and oil from the mally corrosive atmospheres. I have now discovered surface, although such cleaning is not necessary, and that such a pickling-phosphatizing bath may be prepared the panels were dipped in various acid pickling baths by providing an aqueous acidic pickling bath having bor 65 which had previously been heated to a temperature of on-phosphate therein and which has a sufficient concen about 180 F. The panels were allowed to remain in tration of a pickling acid from the group consisting of the pickling bath for a three-minute period or until Sulfuric acid, phosphoric acid, and admixtures thereof, the scale and rust were removed. The panels were then 2,964,484 3 4. dried at the preferred temperature of about 180-210 compound does not inhibit the pickling action of the F.; however, in cases wherein the treated steel pieces large proportion of free phosphoric acid in the bath. have sufficient thickness to retain high levels of heat, It is believed that the phosphatizing action of my new, artificial heating is not necessary to dry the coating. The highly acidic pickling solution is due to the formation of test panels were then placed in a chamber in the corrosive a complex boron-phosphate or iron-boron-phosphate atmosphere formed above a saturated solution of cal coating on the freshly pickled surface of the ferrous metal cium hypochlorite. The panels were allowed to remain article. However, I do not wish to be held to this theory in the corrosive atmosphere for 4 to 24 hours, or until since I have been unable to detect any visible coating on the surface of the control panel was completely covered such surfaces. with rust. The panels which had been pickled-phos O The illustrated examples show aqueous pickling baths phatized in an acid bath which contained boron-phosphate to which boron, in a soluble form, is added, wherein the were checked to determine the percentage of the surface concentration of sulfuric acid (specific gravity of 1.84) area which had become rusted. is about 7% by volume of the bath, and the concentra The following table shows results of these tests where tion of phosphoric acid in the bath is about 20% by in the baths had different compositions. 5 volume of 75% by weight phosphoric acid. These con centrations of pickling acid may be varied over a wide Table range without causing the baths to lose their effective Approx. pickling action. For example, pickling solutions having Percent of as low as 5% by volume of sulfuric acid (specific gravity Example Composition of the Baths Surface 20 Nos. Rusted in of 1.84) and 15% by volume of 75% by weight phos Corrosion phoric acid may be used in the bath. The preferred Tests concentrations shown above were simply selected as rep sentative of the concentrations most commonly used in Sulfuric acid (7% by vol. of 1.84 sp.g.)------75-100 - Borophosphoric acid (2% by wt. of Soln)---- 75 the industry. 3-- Sulfuric acid (7% by vol. of 1.84 sp.g.):-0.4% 50 25 The use of various acid inhibitors and wetting agents by wt. borophosphoric acid. in sulfuric acid pickling baths which contained boron

4------0.8% by wt. borophosphoric acid------5 1.2% by wt. borophosphoric acid. phosphate did not affect the rust-resistant qualities of 2.0% by wt. borophosphoric-acid 2.0% by Wt. borax.------100 pickled steel surfaces, although such additives may be 2.0 by vol. phosphoric acid (75% H3PO)-- 5 employed in some applications wherein their own char 2.0% by wt. borophosphoric acid. 30 9------1.0% by vol. phosphoric acid (75%. HaPO)-- 50 acteristics serve a useful purpose. 0.4% by wt.borax. The foregoing detailed description has been given for 10------1.0% by vol. phosphoric acid (75% H3PO)-- 8 0.8% by wt. borax. clearness of understanding only, and no unnecessary Il------.0% by vol. phosphoric acid (75%. HaPO)-- limitations should be understood therefrom, as modifi 1.2% by wt. borax. 12------2.0% by vol. phosphoric acid (75%. HaPO)- 50 cations will be obvious to those skilled in the art. 0.4% by wit, borax. 35 I claim: 18------2.0% by vol, phosphoric acid (75% HaPO)-- 20 0.8% by wit...borax. 1. A method of pickling and inhibiting the rusting of 14------2.0% by vol. phosphoric acid (75% H3PO)- l the surface of a ferrous metal article in a single bath 1.6% by wt...borax. 15------Phosphoric acid (20% by vol. of 75% HPO)-- 95 comprising: immersing said article in a heated pickling 16------Phosphoric acid (20% by vol. of 75%, HaBO)-- and rust-inhibiting bath having a pH not greater than 2.0% by wit, borophosphoric acid. 40 1 and which contains a minor proportion of a pickling acid equivalent to not more than about 20% concen Although baths which produced panels which had trated acid, said acid being from the group consisting of about 50% of their surface free of rust may be con sulfuric acid, phosphoric acid, and admixtures thereof, sidered as satisfactory pickling-phosphatizing solution, and which contains at least about 0.4% by weight of panels that had less than 25% rust are considered to a boron-phosphate rust inhibitor having a mole ratio have been treated in a distinctly superior pickling of phosphorus to boron of at least about 1 to 1 and not phosphatizing bath. more than about 17.3 to 1; and removing the pickled From the results shown in the table, it can be seen and rust-inhibited article from the bath. from Examples 1, 2, and 15 that substantially no ruste 2. The method of claim 1 wherein the article is im proofing effect is obtained with steel surfaces pickled in mersed in a bath having a pH not greater than 0.5. baths wherein sulfuric acid, borophosphoric acid or 3. The method of claim 1 wherein the boron-phosphate phosphoric acid alone are used as the pickling acid. Ex rust inhibitor comprises a member of the group consist ample 7 shows that sulfuric acid and borax do not phos ing of (a) borophosphoric acid, (b) phosphoric acid phatize ferrous metals because of the absence of a phos plus borax, and (c) phosphoric acid plus boric acid, phate or phosphate ions in the bath. Other examples 5 5 4. The method of claim 1 wherein said bath contains show the outstanding combination effect in the improve not more than about 2% by weight of said boron-phos ment in rust-resistance on the surfaces of the steel panels phate rust inhibitor. which were pickled and phosphatized in sulfuric acid 5. An acidic pickling and rust-inhibiting bath having baths which contained at least 0.4% by Weight of a a pH not greater than 1 and which consists essentially boronphosphorus compound. 60 of water, a minor proportion of a pickling acid equiva Examples 3-6, 8-14, and 16 in the above table show lent to not more than about 20% concentrated acid, said that these boron-phosphate baths contained a phosphate acid being from the group consisting of Sulfuric acid, or phosphorus to boron mole or atom ratio of 1:1 (i.e., phosphoric acid, and admixtures thereof, and which con a mole ratio of 1), or a ratio exceeding this value. tains at least about 0.4% by weight of a boron-phosphate In the use of phosphoric acid pickling baths, effective phosphatizing action is obtained simply by the inclusion rust inhibitor having a mole ratio of phosphorus to boron of a soluble boron compound dissolved in the phosphoric of at least about 1 to 1 and not more than about 17.3 acid solution. If desired, boron-phosphate may be to 1. formed in situ in the acidic pickling bath as long as there 6. The bath of claim 5 having a pH not greater is sufficient free phosphoric acid to maintain the bath 70 than 0.5. at a pH of not more than 1, preferably not more than 7. The bath of claim 5 wherein the boron-phosphate 0.5. Example 16 illustrates the use of borophosphoric rust inhibitor comprises a member of the group con acid which is substantially equivalent to the addition of sisting of (a) borophosphoric acid, (b) phosphoric acid about 0.8% by weight boric acid to the phosphoric acid plus borax, and (c) phosphoric acid plus boric acid. pickling bath; such a low concentration of the boron 75 8. The bath of claim 5 wherein the bath contains 2,964,434 5 6 not more than about 2% by weight of said boron-phos- 2,479,564 Gilbert ------Aug. 23, 1949 phate rust inhibitor. 2,500,673 Gibson ------Mar. 14, 1950 2,559,445 Lotz ------July 3, 1951 References Cited in the file of this patent 2,674,552 Callahan et al. ------Apr. 6, 1954 UNITED STATES PATENTS 5 FOREIGN PATENTS 2,310,381 Zimmer ------Feb. 9, 1943 675,444 Great Britain ------July 9, 1952 2,477,841. Ward ------Aug. 2, 1949 730,897 Great Britain ------June 1, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,964,434 December 13, 1960 William B. Coleman It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below. Column 3 in the table second column there of opposite Example No. 8, for "2.0 by vol. phosphoric acid" read -- 2.0% by vol. phosphoric acid --. Signed and sealed this 3rd day of October 196l.

(SEAL) Attest: ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents USCOMM-DC