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Publication numberUS2902394 A
Publication typeGrant
Publication dateSep 1, 1959
Filing dateJul 19, 1956
Priority dateJul 19, 1956
Publication numberUS 2902394 A, US 2902394A, US-A-2902394, US2902394 A, US2902394A
InventorsJeremias Bruno R
Original AssigneePoor & Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Protective metal coating compositions and method of coating
US 2902394 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United States Patent PROTECTIVE METAL COATING COMPOSITIONS AND METHOD OF COATING Bruno R. Jeremias, Detroit, Mich., assignor to Poor & Company, Chicago, 11]., a corporation of Delaware No Drawing. Application July 19, 19.56

Serial NO. 598,762 g 8 Claims. (Cl. 1486.21)

and improved corrosion protecting metal finishing com- 1 position which produces a beautiful bronze color on zinc surfaces, for example, die cast zinc articles.

Another object of the invention is to provide a composition of the type described which produces enhanced corrosion protection on Zinc surfaces.

Another object of the invention is to provide a new and improved method of producing excellent bronze corrosion resistant finishes on zinc surfaced articles. Other objects will appear hereinafter.

In accordance with the invention new and improved metal finishing coating compositions are prepared by intimately mixing chromic acid, a reducing agent capable of reducing a minor proportion of the chromic acid to a state in which the chromium is present as trivalent chromium, acetic acid, sulfuric acid and nitric acid. This composition is initially prepared as a concentrate, preferably by mixing together chromic anhydride, sodium sul fite, acetic acid, sulfuric acid, nitric acid and water. The concentrate is then diluted in actual practice With a relatively large quantity of water so that the final bath which is employed as a finishing composition for metal surfaces only contains around 1.5% to 4% by volume of the original concentrate.

The best mode contemplated for the practice of the invention is illustrated by the following composition which constitutes the concentrate:

Ingredients: Grams per liter Chromic anhydride (CrO 401.0 Sodium sulfite (Na SO- 7.5 Acetic acid 22.5 Sulfuric acid 45.0 Nitric acid 228.0

the remainder being water.

When this composition is diluted with water so that the resultant bath contains 1.5% to 4% by volume of the initial concentrate the said bath is an excellent corrosion protecting composition and provides a beautiful bronze finish on Zinc surfaced articles. The general procedure in providing such a finish on such articles is to immerse the articles in the bath at ordinary temperatures (70 F. to 90 F.) for a period of 5 to 15 seconds, then rinse the article with Water and dry.

In the practice of the invention the amount of chromium present in the concentrate preferably varies from a minimum of about 200 grams per liter to the saturation solubility in the concentrate at a temperature around 20 C.

In the previously described concentrate it is desirable that not more than A: of the chromium initially present in the hexavalent state be reduced to the trivalent state.

Thus if sodium sulfite is used as the reducing agent the maximum amount of sodium sulfite in the concentrate previously described should not exceed about 50 grams per liter. The ratio of reducing agent to chromic acid in the concentrate should provide preferably at least 1 gram per liter and not more than 11 grams'per liter of trivalent chromium. l i

The ratio of sulfuric acid to acetic' acid is rather critical and should be approximately 2:1 on a weight basis. In the concentrate the minimum amount of acetic acid is about 20 grams per liter and the maximum amount of acetic acid preferably does not exceed about 40 grams; per liter, the minimum amount of sulfuric acid is about scribed preferably should not be less than 150 grams per liter nor more than 300 grams per liter- In the final metal finishing bath prepared by dilution.

of the concentrate the amountof chromium should be within the range of 3 grams to grams per liter, preferably 15 to 90 grams per liter. The ratio of S0; :CrO; should be Within the range of about 1:4 to about 1:16 with optimum results being obtained at about 55:20. The treating hath made by diluting the concentrate in the manner previously described Will contain about 0.3 gram per liter to about 0.6 gram per liter of acetic acid and about 0.6 gram per liter to about 1.2 grams per liter of sulfuric acid. The nitric acid in the treating bath will be about 2.25 grams per liter to about 4.5 grams per liter. The weight ratio of sulfuric acid to acetic acid in the metal finishing bath will be the same as the weight ratio in the concentrate, namely, approximately 2:1. The trivalent chromium in the treating bath should preferably be at least 0.015 gram per liter and not more than about 4.4 grams per liter.

Instead of the sodium sulfite other reducing agents can .be used which are capable of reducing hexavalent chro mium compounds to trivalent chromium compounds in' acidic solutions, but it is desirable to employ reducing agents which do not form insoluble by-products with the acid of the acidic aqueous solution. Other examples of preferred reducing agents are sodium thiosulfate, sodium hydrosulfite, potassium sulfite, postassium thiosulfate, potassium hydrosulfite, ammonium sulfite, ammonium thiosulfate, and ammonium hydrosulfite. The hydrosulfites are also commonly referred to as hyposulfites. Other reducing agents which reduce chromic acid in acid solution can be used. Reducing agents such as calcium sullite are undesirable because of the formation of insoluble calcium sulfate.

The reduction reaction between the chromate radical of the chromic acid and the sulfite radical which occurs when a sulfite such as sodium sulfite is mixed with the chromic acid in the presence of water can be expressed by the following equation:

The invention is especially useful in providing a beautiful bronze color and enhanced corrosion resistance to Zinc die castings and to other zinc surfaced articles. An important advantage of the invention is that the metal to be treated can be immersed in the treating solution as previously described and requires no further treatment other than rinsing with Water. In many types of chromic acid treatments heretofore proposed a secondary treatment is required. By the practice of the invention it is possible to produce zinc surfaced articles which show a high resistance to the formation of white corrosion products.

ThGf-BXPI'GSSiOHJ zincsurfaced article is employed herein to cover any article having an exterior surface of'zinoregardlss ofwli'ether the article itselfis made of zinc, a ferrous metal or some other metal capable of being coated-with zinc. "Ihe expression. zinc platedai ti'cleffis employedfhe'rein to describe a zincncoatedr articleinfwhich' the zinc coatinghas' been applid' by, an. electroplatingfprocess;

The invention is. hereby, claimed'as follows ll Alpr'ocessofffinishing'zincsurfaced articles wliicli compri'Sestreatin'gtlie surfaces of such articles with an? aqeuous solution of chromic :acid containing? 1090" grarn's'pe'r liter of"'cliromiiiiriof which at least OLOlS gram per liter but not more than about'4i4 grams per literis'chl'oiniuni in a tiiyalent-"state, the remainder being chromiumyin a hexayalnt'st'ate,, Ol'3fto' T6 gram per Iiter'of acetic acid} 0161a 1.2"grams per liter of sulfuric acid,lcand.about2l Sgrianis per liter to 4.5 grams perli'te'r"of'ni't'ric;acid,' the weight ratio of sulfuric acid to acetic acid being approximately 231 and'the weight ratio of S0 :CrO; beingywithin the range of about l:4 to 131'6.

2f A'p'roce's'sas claimed in claim l'in which the article tobe'treatedis'fimmersed in said aqueous solution atIa,

state',.th'e"remainder being chromium in a liexavalent; 35

grams per liter of sulfuric acid and about 2.5 to 4.5

state, 0.3to 016' gram per liter'of acetioacir 016'to 1.2

grams p'er liter of nitric acid," the weight ratio of sulfuricacid" to acetic acidbeing approximately 23 1 and 1' the weight'ratio ofS'OL; ":CrOt beingv within the rangeoflz4to 1116.

5i An acidic aqueous 'metal'treating solution consisting essentially of an aqueous solutionof'chromic acid containing about 15m 90 'grams per liter of chromium ofwhich at least about (LOIS-gram per liter but 'not more than about 4.4 grams per liter is chromium in a trivalent.

, 4? grams" per" liter of sulfuric acid" and" about 215% 4:5 grams per liter of nitric acid, the weight ratio of sulfuric, acid to acetic acid being approximately 2:1 and the weight ratio of SO; !CIO4 being within the range of 1:4 to 1:16.

6. A concentrate adapted to be added to water to produce an aqueous metal? treating solution, said concentrate consisting essentially of an aqueous solution of chromic aeid containing-- chromium in" an? amount- 1 from about 200 grams per'litertothesaturatiorr solubility in the solution -at2v0-? l 0f: which at least 1' grampent liter and not more-: than 1:1- gratn'sper' litristrivalnt chromium, the remainder being, chromium" in. a hertavalent state;'20"to lflvgramsperr'liter of'acetic acid, 41) to grams per liter ofsulfiiridacid and to 300 grams per liter of nitricfiacidithe weightiratio of sulfuric acid to acetic acid being approximately 2:1 and the weight ratio of S0 ":CrO being within the range of-1 :4to 1:16.

7- A concentrate; as claimed: in claim- 6 in which--= sodium sulfite is :present. in an amount sufiicient; to, pro duce trivalent i chromium within the proportions stated-.2.

8. An acidic aqueous metal treating: concentrate; adap ted tube-diluted with. waterto form a metaliprotecting material,= said concentratehaving the following, approximate compositionr Ingredients? Grams per liter" Chro'm'ic'anhydrideI(CrO)T 401:0 Sodium sulfi'te (Na @80 7:5 Acetic-acid 22(5 Sulfuric acid?" t 45:0. Nitric-acid 228.0

the remainder being water.

. References"Gited-in-tlie 'file of this patent UNITEDSTATES-PATENTS 2,035,380 Wilhelm' Mar. 24, 1936" 2523,9251 Ostran der' Feb; 17, 1953 2,796,372 Chester'feflall June 18; T V EOREI-GNPATENTS 586,517 Great'Britair'r Mar; 21; 1947" 489,887 Great'Bfitain': July 2, 1947 852,634 Germany, Oct, 16,, 19 52:

UNITED STATES PATENT @FFICE CERTIFICATE OF EGRRECTIGN Patent Noa 2,902,394 September 1, 1959 Bruno Re Jeremias It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 35, for "acetic acir" read acetic acid,-- line 4'7, after "state" insert a comma; column 4., line 46, list of references cited, under "FOREIGN PATENTS" for "489,887" read 589,887

Signed and sealed this 23rd day of February 1969 (SEAL) Attest:

KARL Ha AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2035380 *May 13, 1933Mar 24, 1936New Jersey Zinc CoMethod of coating zinc or cadmium base metals
US2628925 *Jun 24, 1947Feb 17, 1953Rheem Mfg CoBright corrosion resistant coating of metals
US2796372 *May 7, 1953Jun 18, 1957Poor & CoCorrosion protecting metal finishing composition
DE852634C *Jan 1, 1949Oct 16, 1952United ChromiumTauchverfahren zur Bildung transparenter Oberflaechenschutzueberzuege auf Zink
GB489887A * Title not available
GB586517A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3090710 *May 25, 1960May 21, 1963Hooker Chemical CorpMethod and solution for producing chromate coatings on zinc and zinc alloys
US3147153 *Dec 9, 1960Sep 1, 1964M & T Chemicals IncProcess for providing a chromate coating on zinc and cadmium surface
US3210220 *Jul 30, 1962Oct 5, 1965Norman E CleggProcess for coating stainless steel
US4161409 *Mar 6, 1978Jul 17, 1979Louis SchiffmanCorrosion inhibitive pigment
US6537678Sep 20, 2000Mar 25, 2003United Technologies CorporationNon-carcinogenic corrosion inhibiting additive
US7341677Jun 30, 2003Mar 11, 2008United Technologies CorporationNon-carcinogenic corrosion inhibiting additive
US7972533Apr 4, 2006Jul 5, 2011United Technologies CorporationChromate free waterborne corrosion resistant primer with non-carcinogenic corrosion inhibiting additive
US20070228332 *Apr 4, 2006Oct 4, 2007United Technologies CorporationChromate free waterborne corrosion resistant primer with non-carcinogenic corrosion inhibiting additive
US20090004486 *Jun 27, 2007Jan 1, 2009Sarah ArsenaultCorrosion inhibiting additive
DE102004001945A1 *Jan 14, 2004Aug 11, 2005Ina-Schaeffler KgSchwarzpassivierung von Zink- oder Zinklegierungsoberflächen
EP1493846A1Jun 30, 2004Jan 5, 2005United Technologies CorporationCorrosion inhibiting additive and corrosion inhibiting coating
U.S. Classification148/266
International ClassificationC23C22/05, C23C22/30
Cooperative ClassificationC23C22/30
European ClassificationC23C22/30
Legal Events
Apr 20, 1981ASAssignment
Effective date: 19810202