Compositions – Etching or brightening compositions
Patent
1996-09-24
1998-06-09
Breneman, R. Bruce
Compositions
Etching or brightening compositions
252 792, 252 794, C23F 304, C09K 1306
Patent
active
057628190
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the composition of baths for chemical polishing of stainless steel surfaces.
TECHNOLOGY REVIEW
Chemical polishing of metal surfaces is a technique which is well known chemical polishing of metals!--W. J. Mc G. Tegart--Dunod--1960 --p.122 et seq.); it consists in treating the metal surfaces to be polished with oxidizing baths. Baths including a mixture, in aqueous solution, of hydrochloric, phosphoric and nitric acids are generally employed for chemical polishing of stainless steels. To improve the quality of the polish it is usual to incorporate suitable additives in these baths, such as surface-active agents, viscosity regulators and brighteners. Thus, U.S. Pat. No. 3,709,824 describes a composition of a bath for chemical polishing of stainless steel surfaces, including, in aqueous solution, a mixture of hydrochloric acid, of nitric acid and of phosphoric acid, a surfactant and sulphosalicylic acid as brightener.
Besides the well-known problems relating to the pollution due to phosphates, when spent baths are destroyed by a conventional physicochemical treatment, the precipitatation of phosphoric acid (in the form of calcium phosphates) gives rise to a large volume of sludge. This sludge is toxic and its removal is costly. Japanese patent application JP-A-52/72989 proposes to solve the pollution problem by employing polishing baths which are free from phosphoric acid and include, in aqueous solution, hydrochloric acid, nitric acid, at least one derivative chosen from sulphosalicylic acid, salicylic acid and thiourea, and a cationic surfactant. However, these phosphoric acid-free baths have the disadvantage of being effective only at a temperature which is higher than 80.degree. C., with the result that their rate of polishing is very high; they do not permit slow and efficacious polishing of stainless surfaces.
The invention aims to provide polishing baths without phosphoric acid which are designed for carrying out slow and efficacious chemical polishing of stainless steel surfaces.
SUMMARY OF THE INVENTION
Consequently, the invention relates to phosphoric acid-free baths for chemical polishing of stainless steel surfaces, including, in aqueous solution, a mixture of hydrochloric acid and of nitric acid, an optionally substituted hydroxybenzoic acid and a cationic surfactant, these baths being characterized in that they include, in aqueous solution, ferricyanide complex ions.
In the baths according to the invention the hydroxybenzoic acid acts as a brightener. The hydroxybenzoic acid may be unsubstituted, such as salicylic acid, or substituted, such as 5-sulphosalicylic acid or aminosalicylic acid. Salicylic acid and 5-sulphosalicylic acid are preferred.
DETAILED DESCRIPTION OF THE INVENTION
In the baths according to the invention the cationic surfactant advantageously includes a quaternary ammonium salt. The quaternary ammonium salt is preferably selected from those which include at least one linear or branched, long-chain alkyl radical. Where appropriate it is preferred to select the quaternary ammonium salt from those in which the long-chain alkyl group contains at least 8 carbon atoms, preferably at least 10 carbon atoms, such as, for example, the lauryl, cetyl and stearyl groups. In addition to the long-chain alkyl radical defined above, at least one other linear or branched alkyl radical or a substituted or unsubstituted benzyl radical may be present. Examples are cetyldimethylbenzylammonium, distearyldimethylammonium, lauryldimethylbenzylammonium and lauryltrimethylammonium salts. Quaternary ammonium salts which are especially recommended belong to the class formed by the water-soluble alkylpyridinium, especially cetylpyridinium and laurylpyridinium, salts. The quaternary ammonium salts including a long-chain alkyl radical as defined above are preferably selected from the halides, in particular the chlorides. Alkylpyridinium chlorides are particularly preferred, especially laurylpyridinium chloride. Quaternary ammonium salts that can
REFERENCES:
patent: 2662814 (1953-12-01), Swihart
patent: 3709824 (1973-01-01), Oda et al.
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patent: 4678541 (1987-07-01), Tytgat et al.
English translation of the original Japanese patent application JP 52-072,989 of Oda et al.
Sharpe, A.G., "The Chemistry of Cyano Complexes of the Transition Metals", University Chemical Laboratory, Cambridge, England, Academic Press, pp. vii-xi and 109-115 (1976).
"Fiche Toxicologique No. 195: Hexacyanoferrate (3-) et Hexacyanoferrate (4-) de potassium" established by I.N.R.S., Paris (1984).
Tegart et al.: "Polissage electrolytique et chimique des metaux" 122-129. w/ translation.
Michael B. Bever: "Encyclopedia of Materials Science and Engineering". vol. 6, 1986, Pergamon Press, pp. 4806-4808.
ASTM Designation: D 523-85; "Standard Test Method for Specular Gloss". pp. 121-125.
Franck Christian
Oreins Jean-Marie
Breneman R. Bruce
Goudreau George
Solvay ( Societe Anonyme)
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