US3457107A - Method and composition for chemically polishing metals - Google Patents

Description

3,457,107 METHOD AND COMPOSITHQN FOR CHEMICALLY POLEHING METALS Floyd Louis Michelson, Chicago, and Eugene Frank Maisel, Palatine, Ill., assignors to The Diversey Corporation, Chicago, llll., a corporation of Illinois No Drawing. Filed July 20, 1965, Ser. No. 473,504 Int. Cl. BOSb 3/08, 3/04 US. Cl. 1343 Claims ABSTRACT OF THE DISCLOSURE Compositions and processes for chemically polishing stainless steel. The stainless steel is first treated with an aqueous alkaline oxidizing solution, such as a sodium hydroxide-sodium permanganate solution, to condition the metal surface. The stainless steel is then treated with an acid bright dip solution containing hydrochloric, nitric and phosphoric acids and a small amount of specific surfactants.

This invention relates to a method and a composition for chemically polishing metals. More particularly, the invention relates to a method of chemically polishing a stainless steel surface having an oxide coating thereon and to a composition useful in performing the method.

Methods for polishing and brightening stainless steel surfaces include mechanical polishing and bufling, electro-polishing, and chemical polishing. Mechanical polishing involves extensive handling of the Work, resulting in high labor costs, and often cannot be performed because of the intricate form and nature of the work. Electropolishing often produces satisfactory results, but expensive equipment and large quantities of electrical energy are required. Prior chemical polishing methods in some cases produce a grainy or satiny surface as contrasted to a polished surface and in other cases are relatively sensitive to changes in the concentration of the materials employed,

so that they are diflicult to work with. In addition, the I materials are employed in relatively high concentrations, resulting in high drag out losses, i.e., losses due to material remaining on the articles removed from the polishing bath, which is lost or becomes a contaminant in subsequent treating operations. Prior chemical polishing methods also have a tendency to remove unduly large quantities of metal from the articles, thus excessively altering their dimensions.

During the fabrication of articles made of stainless steel, they frequently are welded, brazed or subjected to other heat treatment which produces a heat scale. This scale is unsightly and tends to aggravate corrosion of the article, and consequently it must be removed.

US. Patent No. 3,072,515 discloses a method and composition for descaling and chemically polishing metals, particularly stainless steel. The metal surface is contacted with an aqueous solution of hydrochloric acid, nitric acid, and an additive having a polyoxyethylene chain in its molecule, as more particularly described in the patent. The solution may also contain phosphoric acid to enhance the action of the reactants. The metal surface is polished to a smooth, near-mirror finish while dissolution of the base metal and drag out losses are minimized.

It has now been discovered in accordance with the present invention that chemical polishing employing the solution of the foregoing patent may be improved and chemical polishing also may be effected with other solutions by subjecting a metal surface to a pretreatment which conditions or activates the surface. In particular, the metal surface is contacted with an aqueous alkaline oxidizing solution to condition the surface and prepare it for oxide removal and subsequent chemical polishing of the surface. The polishing action according to the abovernentioned patent is improved, and other polishing solutions may be employed which previously failed to produce an acceptable polished surface.

The pretreated metal surface is then contacted with an aqueous solution containing hydrochloric acid, nitric acid, and a surfactant. The surfactant may constitute a compound having a polyoxyethylene chain in its molecule, as defined in the patent, or it may constitute one of an additional class of compounds as described hereinafter. The solution also may contain phosphoric acid, which enhances the action of the solution, apparently stabilizing the solution and inhibiting pitting of the metal surface.

In this manner, metal surfaces, especially stainless steel surfaces, are chemically polished to remove scale and oxides and give a surface having a smooth, near-mirror finish. Reference to stainless steel herein refers to the alloys of principally iron, chromium, and nickel, or of iron and chromium, together with minor constituents.

In addition to producing bright polished surfaces on metals such as stainless steel, the invention is advantageous in that the solutions require only relatively low cost materials which are employed in relatively low concentrations, thereby minimizing drag out losses. Only a relatively small amount of base metal is removed in the process of the invention, so that changes in the dimensions of the finished articles are minimized.

The metal surfaces to be polished preferably are subjected to a conventional preliminary cleaning to remove oil, grease, drawing compounds and the like. The clean surfaces then are contacted with an aqueous alkaline oxidizing solution which preferably contains an alkali metal permanganate such as potassium or sodium permanganate. The solution preferably contains about 24% by weight of the permanganate. It is also preferred that the solution be highly caustic. The desired causticity preferably is provided by a strong base, more preferably an alkali metal hydroxide such as sodium or potassium hydroxide. The base may be employed in a concentration of about 510% by weight. A water softener also may be included, such as an alkali metal carbonate, preferably sodium or potassium carbonate. The softener is employed in a minor effective amount, it being preferred to employ a carbonate in a proportion of about (LS-1% by weight of the solution.

The metal is contacted with the oxidizing solution at an elevated temperature and for a period of time suflicient to condition the metal surface to prepare it for subsequent chemical polishing. It is preferred that the temperature of the solution be in the range of about F. to the boiling point. The metal is maintained in contact with the solution for a period of time in the range of about A to 1 /2 hours, the time varying inversely with the temperature. The resulting pretreated metal preferably is Washed with an acid solution to neutralize caustic remaining on the metal and then rinsed, following which the metal is chemically polished.

The metal is contacted with an aqueous polishing solution preferably containing about 1-10% by weight of hydrochloric acid, about 1-8% by weight of nitric acid, and about 0-60% by Weight of phosphoric acid, and advisably also containing about ODS-20% by weight of a surfactant. It is further preferred that the solution contain about 28% of hydrochloric acid, about 2-6% of nitric acid, about 1535% of phosphoric acid, and about 0.215% of surfactant.

The surfactant may be one of the compounds described in the above identified Patent No. 3,072,515. These surfactants are (l) condensation products of 1 mole of phenol with about -30 moles of ethylene oxide, (2) condensation products of 1 mole of an alkyl phenol having up to about 15 carbon atoms in the alkyl group with about 5-30 moles of ethylene oxide, (3) condensation products of 1 mole of an alkyl amine having about -20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (4) condensation products of 1 mole of an aliphatic alcohol having about 10-20 carbon atoms in the alkyl group with about 5-50 moles of ethylene oxide, (5) condensation products of 1 mole of a polypropylene glycol containing about 10-50 propylene oxide units with about 4-150 moles of ethylene oxide, and (6) mixtures thereof.

Alternatively, other surfactants can be employed which contain an aliphatic chain of 6 to 20 carbon atoms. A preferred group of surfactants includes the cationic aliphatic, araliphatic and heterocyclic amines, non-ionic and anionic aliphatic acid amides, non-ionic aliphatic acid partial esters of polyhydric alcohols and their polyoxyethylene ethers, anionic aliphatic sulfates, anionic aliphatic esters of sulfonated aliphatic acids, anionic aliphatic aryl polyether sulfonates, and anionic aliphatic phosphates.

The cationic aliphatic, araliphatic and heterocyclic amines are primary, secondary, tertiary and quaternary amines containing at least one aliphatic chain of 6 to 20 carbon atoms, which may be a straight or branched chain. Representative compounds include the mono-, diand trin-alkyl fatty amines. Exemplary compounds include the primary, secondary and tertiary fatty amines identified by the trade name Armeen.

Other compounds include the alkyl and the aralkyl quaternary ammonium salts. Preferred compounds of this type contain one alkyl group having from 8 to 16 carbon atoms, two alkyl groups having from 1 to 6 carbon atoms, and an aralkyl group having from 7 to 10 carbon atoms, such as alkyl dimethyl ethylbenzyl ammonium chloride identified by the trade name Onyx BTC 471.

The heterocyclic amines include the substituted glyoxalidines and the substituted oxazolines, employed as their acid addition salts. Representative compounds include l-hydroxyethyl-2-heptadecenyl glyoxalidine identified by the trade name Alro Amine O, and a substituted oxazoline identified by the trade name Alkaterge C.

The non-ionic aliphatic acid amides include the amides of preferably lower aliphatic amines such as amino-ethyl ethanolamine and diethanolamine and fatty acids having a straight or branched aliphatic chain of 6 to 20 carbon atoms. Representative compounds include aminoethyl ethanolamine fatty acid amides identified by the trade name Nopcogen RP and diethanolamine fatty acid amide identified by the trade name Ninol, 1001.

The anionic aliphatic acid amides includes the amides of 6-20 carbon atom straight or branched chain aliphatic acids with preferably lower aliphatic aminosulfonic and amino-carboxylic acids. The amino group preferably is also substituted with a 1-6 carbon atom alkyl group. Representative compounds include sodium N-cyclohexyl- N-palmitoyl-taurate identified by the trade name Igepon (IN-42, sodium N-methyl-N-oleoyl-taurate identified by the trade name Igepon T-33, and N-meth.yl-Noleoyl glycine identified by the trade name Sarkosyl O.

The non-ionic aliphatic acid partial esters of polyhydric alcohols and their polyoxyethylene ethers include the 6-20 carbon atom straight or branched chain aliphatic acid partial esters of sorbitol, propylene glycol, and glycerol, and their polyoxyethylene ethers. Representative compounds are sorbitan monooleate identified by the trade name Span 80 and polyoxyethylene sorbitan monooleate, called Tween 80.

The anionic aliphatic sulfates includes the 6-20 carbon atom straight or branched chain alkyl sulfates or sulfate esters. A representative compound is sodium lauryl sulfate identified by the trade name Duponol C.

The anionic aliphatic esters and amides of sulfonated dicarboxylic acids include the 6-20 carbon atom straight or branched alkyl esters of sulfonated lower dicarboxylic acids. A representative compound is sodium sulfosuccinic acid dioctyl ester identified by the trade name Aerosol OT and disodium N-octadecylsulfosuccinamate identified by the trade name Aerosol 18.

The anionic aliphatic aryl polyether sulfonates include the 6-20 carbon atoms straight or branched chain alkyl substituted aryl polyether sulfonates. A representative compound is sodium octyl phenoxy polyethoxy sulfonate identified by the trade name Triton X-200.

The anionic aliphatic phosphates includes the 6-20 carbon atom straight or branched chain alkyl monoand polyphosphates containing up to 8 phosphate radicals. Representative compounds include (Z-ethylhexyl) -Na (P O identified by the trade name Victawet 35B and (capryl) Na (P O identified by the trade name Victawet 58B and monophosphates such as lauryl ester of ortho phosphoric acid.

Additional surfactants which may be employed include the anionic fluorinated aliphatic compounds such as Howchemical FC- and the amphoteric surfactants such as the ethoxylated sodium salt Triton QS-lS.

In the preferred practice of the invention, a concentrate is provided for handling and storage purposes, and the polishing solution may be made up from the concentrate. A preferred concentrate contains about 6-9% by weight of hydrochloric acid, about 25-65% by weight of phosphoric acid, about 1-3% by weight of a surfactant, and the remainder water. The above Patent No. 3,072,515 discloses concentrates of this type containing a compound having a polyoxyethylene chain in its molecule. The present invention provides concentrates useful in practicing the invention which include a surfactant containing an aliphatic chain of 6-20 carbon atoms, as described above. A preferred specific concentrate contains about 8% by weight of hydrochloric acid, about 60% by weight of phosphoric acid, about 2.6% of the surfactant, and the remainder water. A polishing solution is compounded by adding nitric acid and water to a concentrate to provide a solution containing hydrochloric acid, nitric acid, phosphoric acid, and a surfactant in the proportions described above.

The metal to be polished is contacted with the polishing solution in a hath made up of the solution, at an elevated temperature and for a period of time sufficient to produce a bright polished surface. The bath is maintained at a temperature preferably in the range of about -200 F., more preferably l60-190 F. The time required to produce a bright polished surface varies depending upon the temperature of the bath, the composition of the solution, the type of metal, and the condition of the metal surface. Ordinarily, the time required is about 5 to 20 minutes at a temperature in the range of about 190 F., with the time decreasing at increasing temperatures, and increasing at decreasing temperatures. Following the polishing treatment, the metal is rinsed, at which time it is found to have the desired polished surface.

The following examples are illustrative of the invention. The invention is not limited to the examples or to the materials, proportions, conditions and procedures set forth therein. The acid proportions are based on 100% acid except Where otherwise indicated.

Example 1 Panels of 24 gauge stainless steel, Type 302 having a 2B (matte) finish that had acquired a thin oxide coating were cleaned to remove oil, grease and the like by immersing them for 10 minutes at F. in a solution of the following composition in water, the composition being employed in a concentration of 6 ounces per gallon of total solution:

Proportion, per- Material: cent by weight Sodium hydroxide 50 Sodium carbonate 47 Sodium oleate 3 The panels were removed from the solution and rinsed with tap water.

The panels were immersed for 30 minutes in the following alkaline oxidizing solution at 200 F., to remove the surface oxides:

Proportion, per- Material: cent by weight Sodium hydroxide 7.9 Potassium permanganate 3.2 Sodium carbonate, anhydrous 0.7 Water 88.2

The panels were removed from the oxidizing solution and rinsed with tap water.

The panels were immersed for 5 minutes in a solution of the following composition diluted with 3 parts by volume of water and maintained at 80 F., to neutralize any caustic remaining on the panels:

Proportion, per- Material: cent by weight Phosphoric acid, 75% conc. Xylene sulfonic acid 5 Octyl phenoxy polyethoxy ethanol containing about 11-13 mols of ethylene oxide 5 Sodium dodecyl diphenyl ether disulfonate 2 Water 83 The panels were removed from the oxidizing solution and rinsed with tap water.

The panels then were immersed for minutes in the following polishing solution maintained at 17 6-180 F.:

Proportion, per- Material: cent by weight Hydrochloric acid 3 Nitric acid 3 Phosphoric acid 24 Aminoethyl ethanolarnine fatty acid amide 1 1 Water Balance 1 Nopcogen RP.

The panels were withdrawn from the bath and rinsed with tap water. They were found to have a bright, smooth near-mirror finish. Without the pretreatment using the oxidizing permanganate solution the panels are substantially less bright and lack the mirror finish.

When the foregoing procedure was repeated with the omission of the aminoethyl ethanolamine fatty acid amide from the polishing bath, no brightening or polishing of the panels was obtained. In addition, non-uniform etching of the panels was observed.

Example 2 The procedure of Example 1 was repeated, with the difference that 5% instead of 3% of hydrochloric acid was employed in the polishing solution. Equivalent results were obtained.

Example 3 The procedure of Example 1 was repeated, with the difference that 5% instead of 3% nitric acid was employed in the polishing solution. Equivalent results were obtained.

Example 4 Example 1 was repeated, employing 15% instead of 24% of phosphoric acid in the polishing solution, and employing 1% of a monoalkyl amine having 68 carbons in the alkyl group (Armeen-8) in place of the aminoethyl ethanolamine fatty acid amide in the polishing solution. The panels were immersed in the polishing solution for minutes. Equivalent results were obtained.

Example 5 The procedure of Example 1 was repeated, employing different surfactants in the polishing solution. A bright, smooth, near-mirror finish was obtained in each case with respective polishing solutions containing 1% by weight of the following surfactants singly or in combination when compatible:

l-hydroxyethyl-2-heptadecenyl glyoxalidine salt (Alro Amine O).

Substituted oxazoline tertiary amine salt (Alkaterge C).

Polyoxyethylene sorbitol oleate (Atlas G-1186).

Diethanolamine fatty acid amide (Ninol 1001).

Sodium lauryl sulfate (Duponol C).

Sodium sulfosuccinic acid dioctyl ester (Aerosol OT).

N-methyl-N-oleyl glycine (Sarkosyl O).

(Capryl) -Na (P O (Victawet 58B).

Fluorinated anionic surfactant (Florochemical FC-95).

Sodium salt of an ethoxylated amphoteric surfactant (Triton QS-15 In the absence of pretreatment with oxidizing solution the finish of the panels is substantially less bright.

Example 6 The procedure of Example 1 was repeated with panels of 24 gauge stainless steel, Type 316 that had acquired a thin oxide coating. The following surfactants can be employed singly or in combination when compatible in respective polishing solutions at a concentration of 1% by weight in each solution, and a bright, smooth nearmirror finish is produced in each case.

Tri-n-alkyl tertairy amines such as Armeen DMCD which is a trialkylamine in which one alkyl group contains 818 carbons and the others are methyl groups and Armeen MZHT which is methyl dehydrogenated tallowamine.

Di-n-alkyl secondary amines such as Armeen 20 which has alkyls having 618 carbon atoms.

n-Alkyl primaryamines such as Armeen 8 which has an alkyl having 6-10 carbons.

Quaternary ammonium chloride having two methyl groups, one ethylbenzyl group and one alkyl group having 6 to 20 carbons such as Onyx BTC 471 which has 12-18 carbon atoms in the long chain alkyl group.

1-hydroxyethyl-2-h:ptadecenyl glyoxalidine salt (Alro Amine O).

Substituted oxazoline tertiary amine salts such as Alkaterge C which is 2 heptadecyl 5 methyl 5 hydroxymethyl oxazoline.

Polyoxyethylene sorbitol oleate (Atlas G-l186).

Polyoxyethylene sorbitan oleate (Tween Diethanolamine capric acid amide (Ninol 1001).

Sodium lauryl sulfate (Duponol C).

Sodium N-methyl-N-oleyl-taurate (Igepon T33).

Sodium sulfosuccinic acid dioctyl ester (Aerosol OT).

N-methyl-N-oleyl glycine (Sarkosyl O).

(Capryl) -Na (P O (Victawet 58B).

Fluorinated anionic surfactant (Florochemical FC-).

Sodium salt of an ethoxylated amphoteric surfactant (Triton QS-lS).

Sorbitan monooleate (Span80).

Sodium alkyl aryl polyether sulfonate (Triton X-200).

1 (2 sodium acetato) 1 (2 sodium ethylato) 2- undecyl 4,5-dihydroimidazolium hydroxide (Miranol M).

When the pretreatment with oxidizing solution is omitted the panels are substantially less bright and the finish is not near-mirror like.

Example 7 Pipe couplings of forged stainless steel, Type 304 and Type 316 having a black surface coating of heat scale from prior heat treatment were treated according to the method of Example 1. The couplings were immersed in the polishing solution for about 10 to 20 minutes at a temperature of about 190 F. The couplings came out bright and free of scale.

.7 Example 8 An article was prepared which consisted of a piece of stainless steel, Type 302 and pieces of mild steel copper, and brass attached to the stainless steel by silver solder. The soldering produced a heavy, blue-black heat scale on the stainless steel. The article was treated by the method of Example 1, immersing it in the polishing solution for minutes at about 190 F. A clean and bright surface was produced on the stainless steel, The copper and brass were clean. The mild steel had evidence of a light attack. There was practically no attack. on the silver solder.

Example 9 Welded stainless steel, Type 302 was cleaned in an aqueous solution containing 6 oz./gal. of the composi tion:

Proportion, percent Material: by weight Sodium hydroxide 50 Sodium carbonate 47 Sodium oleate 3 For the cleaning, the solution was used at 160 F. for 10 minutes. Then the stainless steel was rinsed with water and pretreated with an aqueous oxidizing solution containing 0.5 or 1.0 lb./ gal. of a mixture of the following:

Proportion, percent Material: by weight Sodium hydroxide 65 Potassium permanganate 27 Sodium carbonate 8 Material: by weight Phosphoric acid 24 Hydrochloric acid 3 Nitric acid 3 Alkyl aryl polyether alcohol (Triton X-100) 1 Water 69 The solution was used at 170 F. for 10 minutes followed by a water rinse and drying.

The stainless steel samples pretreated with the oxidizing solutions containing 0.5 lb./gal. and 1.0 lb./gal. of the materials specified above gave uniform polished surfaces after the full process was completed as described. The same result was obtained using an oxidizing solution containing 1.0 lb./ gal. of the specified materials for a 60 minute pretreatment followed by the further specified treatments. However, a control which was not pretreated with an oxidized solution but which was treated as otherwise described in this example had the weld seam still scaled, and a very matte band 4 inch thick and /2 inch from the weld seam developed over the polished surface.

The process was repeated except that the Triton X100 in the polishing solution was increased to with a corresponding reduction in the percentage of water. Readings of 24% and 53% absolute specular reflectance respectively were obtained before and after polishing using the cycle of this example. (The significance of specular reflectance values is explained in Example 10.)

Example 10 The procedure of Example 9 was followed in polishing heat-treat scaled stainless steel panels using oxidizing solution concentrations and treatment times as indicated in the following Table A:

1 Ingredients as in Example 9. 2 Control stainless steel panel before treatment read 4% absolute specular reflect-once.

Specular reflectance is measured with an apparatus that operates on the same principle as the well-known light meter used in photography, i.e., reflected light is recorded on a scale in the instrument. The instrument is first calibrated by adjusting the indicator to record a maximum of 100% for a given amount of reflected light from a highly polished surface such as a mirror. It is also adjusted to record 5.6% reflectance from a panel of black glass. Table A shows that much higher specular reflectance is obtained when the permanganate oxidizing solution is used than when it is omitted from the polishing process, it being understood that the treatments with the polishing solution are of equal length.

Example 11 A Type 302 stainless steel lot found to be diflicult to polish because of heavy scale was treated as in Example 9, except that the Triton X-100 in the polish solution was replaced by an equal amount of Aliquat 4 (N-fatty trimethyl quaternary ammonium chloride) or FC- (fluorinated anionic surfactant). The results are found in Table B and show that superior results are obtained when the permanganate oxidizing pretreatment solution is used.

TABLE B Percent absolute specular reflectance 2 oxidizing solution concentration 1 Time (min) Aliquat 4 IFS-95 Control 32 37 1 lb./gal 30 38 42 1 Ingredients as in Example 9.

2 Control stainless steel panel before treatment read 24% absoluet Specular reflectance.

Example 12 Type 304 stainless steel was scaled by placing panels on an 800 F. plate temperature hot plate for 1 .and 2 hours, then polished as in Example 9. The results obtained are found in Table C and show the effect the permanganate oxidizing pretreatment solution has when used on difiicult heat scales.

TABLE 0 Percent absolute specular reflectance After After Before polishing polishing no polishing oxidizer in oxidizer in with scale cycle cycle 1 hr. heat scale 21 57% 4 2 hr. heat scale 16 59 1 Example 13 Operating at the acid ratio and the cycle as in Example 9, the high molecular weight surfactant in the polishing solution was replaced with an unsaturated alcohol of the propynol and butynediol types. The results obtained are given in Table D, and show the effect the preferred acid ratio has on polishing.

TABLE D Percent absolute specular reflectance Before polishing After polishing 2 propyn-l-ol 23 54 2 butyne-L4 diol 22% 5 The processed panel surface had a grey cast. However, the unsaturated alcohols such as propynol and butynediol may be used to obtain brightening using the preferred acid ratio.

It will be apparent that various changes and modificatiors may be made in the method and composition of the invention within its spirit and scope. It is intended that such changes and modifications be included within the scope of the appended claims.

What is claimed is:

1. A method of chemically polishing a stainless steel surface having an oxide coating thereon which comprises contacting said surface with an aqueous alkaline oxidizing solution at an elevated temperature and for a period of time sufiicient to condition the surface of the stainless steel for subsequent chemical polishing of said surface, and thereafter contacting said surface with a chemical polishing aqueous solution containing about 1l0% by weight of hydrochloric acid, about 18% by weight of nitric acid, about 0-60% by weight of phosphoric acid, and about 0.05% by weight of a surfactant selected from the group consisting of cationic aliphatic, araliphatic and heterocyclic amines, non-ionic and anionic aliphatic acid amides, non-ionic aliphatic acid partial esters of polyhydric alcohols and their polyoxyethylene ethers, anionic aliphatic sulfates, anionic aliphatic esters of sulfonated aliphatic acids, anionic aliphatic aryl polyether sulfonates, and anionic aliphatic phosphates, at an elevated temperature and for a period of time sufficient to produce a bright polished surface.

2. The method according to claim 1 in which the alkaline oxidizing solution contains an alkali metal permanganate.

3. A method of chemically polishing a stainless steel surface having an oxide coating thereon which comprises contacting said surface with an aqueous alkaline oxidizing solution at an elevated temperature and for a period of time suflicient to condition thesurface of the stainless steel for subsequent chemical polishing of said surface, and thereafter contacting said surface with a chemical polishing aqueous solution containing about 28% by weight of hydrochloric acid, about 26% by weight of nitric acid, about 060% by Weight of phosphoric acid, and about 02-15% by weight of an aminoethyl ethanolamine amide of a fatty acid having an aliphatic chain of 6-20 carbon atoms, at an elevated temperature and for a period of time sufficient to produce a bright polished surface.

4. The method according to claim 3 in which the alkaline oxidizing solution contains an alkali metal permanganate.

5. A method of chemically polishing a stainless steel surface having an oxide coating thereon which comprises contacting said surface with an aqueous alkaline oxidizing solution at an elevated temperature and for a period of time suflicient to condition the surface of the stainless steel for subsequent chemical polishing of said surface, and thereafter contacting said surface with a chemical polishing aqueous solution containing about 28% by Weight of hydrochloric acid, about 2-6% by weight of nitric acid, about 060% by weight of phosphoric acid, and about 02-15% by weight of a salt of an aliphatic amine having at least one aliphatic chain of 6-20 carbon atoms, at an elevated temperature and for a period of time sufficient to produce a bright polished surface.

6. The method according to claim 5 in which the alkaline oxidizing solution contains an alkali metal permanganate.

7. A method of chemically polishing a stainless steel surface having an oxide coating thereon which comprises cleaning the surface with a caustic solution to remove oil, grease and the like from the surface, rinsing the surface with water, contacting said surface with an alkaline oxidizing solution containing an alkali metal permanganate and maintaining said solution in contact with said surface at a temperature of about 150 F. to the boiling point for a period of time sufficient to condition the surface of the stainless steel for subsequent chemical polishing of the surface, rinsing the surface with water, neutralizing the surface with an aqueous acidic solution, rinsing the surface with water, contacting said surface with a chemical polishing aqueous solution containing about 110% by weight of hydrochloric acid, about 18% by weight of nitric acid, about 0-60% by weight of phosphoric acid and about ODS-20% by weight of a surfactant selected from the group consisting of cationic aliphatic, araliphatic and heterocyclic amines, non-ionic and anionic aliphatic acid amides, non-ionic aliphatic acid partial esters of polyhydric alcohols and their polyoxyethylene ethers, anionic aliphatic sulfates, anionic aliphatic esters of sulfonated aliphatic acids, anionic aliphatic aryl polyether sulfonates, and anionic aliphatic phosphates, at an elevated temperature and for a period of time sufficient to produce a bright polished surface, rinsing the surface with water and drying the surface.

8. A bath which consists essentially of an aqueous solu- I tion containing about l10% by weight of hydrochloric acid, about l8% by weight of nitric acid, about O60% by weight of phosphoric acid, about 0.0520% by weight of a surfactant containing an aliphatic chain of 620 carbon atoms and selected from the group consisting of cationic aliphatic, araliphatic and heterocyclic amines, non-ionic and anionic aliphatic acid amides, non-ionic aliphatic acid partial esters of polyhydric alcohols and their polyoxyethylene ethers, anionic aliphatic sulfates, anionic aliphatic esters of sulfonated aliphatic acids, anionic aliphatic aryl polyether sulfonates, and anionic aliphatic phosphates, and the remainder water.

9. A concentrated mixture which consists essentially of about 69% by weight of hydrochloric acid, about 2565% by Weight of phosphoric acid, about l3% by weight of a surfactant containing an aliphatic chain of 6 to 20 carbon atoms and selected from the group consisting of cationic aliphatic, araliphatic and heterocyclic amines, non-ionic and anionic aliphatic acid amides, nonionic aliphatic acid partial esters of polyhydric alcohols and their polyoxyethylene ethers, anionic aliphatic sulfates, anionic aliphatic esters of sulfonated aliphatic acids, anionic aryl polyether sulfonates, and anionic aliphatic phosphates, and the remainder water.

10. A concentrated mixture which consists essentially of about 8% by weight of hydrochloric acid, about 60% by weight of phosphoric acid, about 2.6% by weight of aminoethyl ethanolamine amide of a fatty acid having 11 12 an aliphatic chain of 6 to 20 carbon atoms, and the 3,125,475 3/1964 Livingston et a1. 25279.1 X remainder Water. 3,220,899 11/1965 Leonard 25279.5

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