US3897287A - Method of sealing and desmudging of anodized aluminum - Google Patents

Abstract

Addition of sulfate to hydrolyzable metal salt sealing solution to promote subsequent mineral acid removal of smudge from the surface of anodized aluminum.

Description

United States Patent 1191 Meyer et al.

1451 July 29, 1975 1 METHOD OF SEALING AND DESMUDGING OF ANODIZED ALUMINUM [75] lnventors: Raymond J. Meyer, Apollo; Ford Simpson, Jr., Lower Burrell; Michael P. Boland, North Washington Twp., Westmoreland County, all of Pa.

[73] Assignee: Aluminum Company of America, Pittsburgh, Pa.

[22] Filed: Aug. 11, 1972 [211 Appl. No.: 279,821

[52] U.S. CI. 156/22; 148/624; 148/627;

252/792; 204/35 N [51] Int. Cl. C23c 3/00; C23f 13/00 [58] Field of Search 148/614, 6.24, 6.1, 6.27;

2,836,526 5/1958 Marosi 148/624 3,374,155 3/1968 Weber 148/614 3,615,892 10/1971 Heinzeuman et al.... 148/624 3,615,897 10/1971 Banush 148/624 3,652,429 3/1972 Deltombe 148/6.1

3,689,379 9/1972 Treiber 148/6.1

3,709,742 1/1973 Jacobs 148/6.1 3,749,596 7/1973 Yoshimura.... 148/627 3,767,474 10/1973 Cohn 148/627 3,767,474 10/1973 Cohn 148/6.1 3,791,940 2/1974 Alexander 204/35 Primary ExaminerDouglas J. Drummond Assistant ExaminerJerome W. Massie Attorney, Agent, or Firm-J0hn P. Taylor; Abram W. Hatcher [57] 1 ABSTRACT Addition of sulfate to hydrolyzable metal salt sealing solution to promote subsequent mineral acid removal of smudge from the surface of anodized aluminum.

8 Claims, 2 Drawing Figures [56] References Cited UNITED STATES PATENTS 2,008,733 7/1935 Tostcrud 148/614 A/VOD/ZED ALUMINUM M/NL'RAL 4 0/0 DESMUDGl/VG WA TER RlNS/NG PATUHEE M29 1975 SHEET PRIOR ART b "a" After Treatment W a Smudge Formed by Non- Hydrolyzable Me ith Surface 41% Sulfate HNO ickel ic Salt (N tall Acetate) By Itself THIS INVENTION d "c" After Treatment With c y Non-Sulfate drolyzable Metall Acetate) Plus Soluble Sulfa Surface 41% HNO Smudge Formed b y ic Salt (Nickel Fig /0 A/VOD/ZED ALUM/IVUM SEAL/N6 WITH HOT AQUEOUS NON-SULFATE HYDROLYZABLE METALLIC .SALT

CONTA lNl/VG 30-2000 M/LL/GRAMS PER L/TER SOLUBLE SULFATE /4- MINERAL ACID DESMUDGl/VG I6- WATER R/NS/NG FIG. 2.

METHOD OF SEALING AND DESMUDGING OF ANODIZED ALUMINUM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to treatment of anodized aluminum. The anodized aluminum of this specification is an aluminum or aluminum base alloy which has an anodic oxide coating thereon such as conventionally formed, for example, by electrolytic treatment with sulfuric acid or sulfuric acid/sulfophthalic acid. More particularly, it relates to improved sealing and desmudging of anodized aluminum.

2. Description of the Prior Art Removal of unattractive multicolored smudge formed during sealing of anodized aluminum, both dyed and undyed, with a hydrolyzable metallic salt such as those employed by Tosterud in U.S. Pat. No. 2,008,733, has for some time presented a constant problem to the aluminum industry, particularly in architectural applications. Limited success in solving this problem has been achieved by treating the smudgecontaining surface with mineral acids. Another approach has been to add wetting agents to the Sealing bath to minimize the amount of smudge formed. This is sometimes successful. However, in many instances use of either of these procedures results in some permanent smudge. Furthermore, with the development of the acid dissolution test, which involves, after acid desmudging, checking the weight loss (mg/in upon treatment with chromic/phosphoric acid, it has been found that known desmudging procedures have often been detrimental to the seal, this being shown when weight loss by the acid dissolution test exceeds 2 mglin With the benefit of the acid dissolution test, we have now found that use ofa sulfate as the hydrolyzable metallic salt in the aqueous sealing bath, while provid ing a surface which is readily desmudged with mineral acids, is unsatisfactory because it sometimes has a tendency to cause an inferior seal.

SUMMARY OF THE INVENTION After extended investigation we have further found that this situation can be remedied by addition of 30-2,000 ppm, preferably 200-1 ,000 ppm, of a soluble sulfate to a hydrolyzable metallic salt, preferably nickel acetate or cobalt acetate, sealing bath which contains substantially no sulfate and which we will refer to hereinafter as a nonsulfate hydrolyzable metallic salt. More precisely, our invention involves sealing anodized aluminum with an aqueous non-sulfate hydrolyzable metallic salt bath to which 302,000 ppm of a soluble sulfate have been added and thereafter desmudging the surface with a mineral acid. It is important, in other words, that the aqueous sealing bath contain both a non-sulfate hydrolyzable metallic salt and between 30 and 2,000 ppm of the added soluble sulfate. Surprisingly, this results not only in a substantially smudgefree surface but one which has a satisfactory seal. For some reason, which we are unable to explain, addition of this amount of sulfate results in formation of a smoother smudge which is both less in quantity and easier to remove in the subsequent mineral acid treatment step. Also surprisingly, sulfuric acid now becomes more efficient in smudge removal when used as the mineral acid with which the smudge-containing sealed anodized aluminum surface is treated.

While any compound which supplies the required soluble sulfate is useful according to the invention, among sulfates which we have found most suitable are sulfuric acid, nickel sulfate, sodium sulfate and aluminum sulfate.

Conventional amounts, preferably at least about 1 g/l, of the non-sulfate hydrolyzable metallic salt may be used in the sealing step of the invention.

For most efficient results the mineral acid employed in the desmudging step should be of a concentration of at least about 15% by weight, preferably at least about 20% by weight. Application of the acid may be by spraying, dipping or the like.

The sealing bath used in the sealing step of the invention should be maintained hot, preferably at a temperature of l952l2F. Proper sealing usually requires at least about 15 minutes.

Representative mineral acids useful in the desmudging step of the invention include nitric, hydrochloric, sulfuric, phosphoric, chromic and the like.

Representative non-sulfate hydrolyzable metallic salts useful in the sealing step of the invention include nickel acetate, cobalt acetate and the same and like or similar non-sulfate salts of aluminum, zinc, copper, lead and the alkali metals and the like.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of our invention, reference will now be made to the drawings, which form a part hereof.

In the drawings,

FIG. I is a photomicrographic comparison of anodized aluminum sealed and desmudged according to the present invention with the same anodized aluminum sealed and desmudged according to the prior art.

FIG. 2 is a schematic diagram in flow-sheet form illustrating the sealing and desmudging steps of the invention.

In FIG. 1, which comprises photomicrographic reproductions at 5,000X, the heavy smudge formed (a) by prior art hydrolyzable metallic salt sealing (here 4 g/l nickel acetate) and that left(b) after desmudging with mineral acid (here 5 minutes with 1:1 by volume HNO is contrasted with the light smudge (c) formed by non-sulfate hydrolyzable metallic salt (here nickel acetate) plus added soluble sulfate (here 375 ppm sealing and the almost smudge-free surface ((1) after desmudging with the same mineral acid (5 minutes with 1:1 HNO In FIG. 2, a specimen of anodized aluminum 10 is sealed in a hydrolyzable metal salt sealing solution containing 302,000 mg/l soluble sulfate at 12 and thereafter desmudged at 14 by treatment with a mineral acid. Substantially complete smudge removal is insured by subsequent rinsing with water at 16, followed by spraying with water (not shown), if desired.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples are further illustrative of the invention.

EXAMPLE 1 This example illustrates prior art.

Two specimens of aluminum base alloy sheet containing 0.5 Cu, 0.18 Fe, 0.10 Si, 0.01 Mn, 0.04 Mg, 0.18 Cr and 0.02 Ti were simultaneously anodized in a sulfuric acid/sulfophthalic acid electrolyte at 70F and 24 asf to a plateau voltage of 75 volts. Total anodizing time was 35 minutes. Each specimen was treated as follows:

1. sealed in 4 g/l nickel acetate at 5.6 pH and 212F 2. desmudged for minutes by immersion in 41% by weight I-INO 3. rinsed by immersion in water, followed by spray- After drying, the specimens did not retain on their surface a white chalky smudge or residue that was formed by the sealing step but exhibited a yellowish hue and had a relatively textured appearance.

EXAMPLE 2 The procedure of Example 1 was followed on the same alloy except for use of 0.1 g/l H SO (approximately 100 ppm soluble sulfate) in the nickel acetate sealing solution. After drying, the single specimen was free of surface residue and did not exhibit the yellowish hue or relatively textured appearance of the desmudged specimen of Example 1.

EXAMPLE 3 A specimen anodized as in Example 1 was immersed in an aqueous sealing solution containing 4 g/l nickel acetate and 700 mg/l (700 ppm) soluble sulfate (as sulfuric acid) for 20 minutes with air agitation. The treatment temperature was 212F and the pH of the bath 5.7. The specimen was then rinsed by immersion in water before immersion in a static aqueous solution of 41% by weight nitric acid for 5 minutes at 75F. It was then rinsed by immersion in water prior to spraying with water and drying in air. There was an absence of sealing residue or smudge on the specimen after the drying. Excellent seal quality was indicated by an acid dissolution value of less than 2 mg/in as measured by the acid dissolution test.

EXAMPLE 4 Equally good results were obtained by following the procedure of Example 3 except for substituting use of 20% by weight HNO in the desmudging step for the 41% HNO EXAMPLE 5 by weight H- SO was employed in the desmudging step in place of the 41% HNO of Example 3 with successful desmudging.

EXAMPLE 6 EXAMPLE 7 The procedure of Example 3 was followed except that the final water-spraying step was not used. There was substantially complete removal of the smudge formed by the sealing step as a result of the mineral acid (HNO here) treatment step which followed.

EXAMPLE 8 Table I Acid Dissolution (mg/in) Sample Temp. lst n No. (F) pH Interval Interval EXAMPLE 9 Sulfuric acid, sodium sulfate and nickelous sulfate were used in separate instances to supply the soluble sulfate in a 302,000 ppm non-sulfate (here nickel acetate) hydrolyzable metallic salt sealing step according to the invention. In all cases subsequent acid desmudging produced sealed anodized aluminum surfaces meeting commercial architectural requirements.

EXAMPLE 10 The following table records visual observation desmudging results and acid dissolution values for a series of anodized aluminum samples sealed and desmudged according to the invention. Results are compared with those obtained by use of a non-sulfate hydrolyzable metal salt bath to which soluble sulfate was not added. Various concentrations of nitric and sulfuric acids were employed in the desmudging step as indicated in the table. Sealing prior to desmudging was accomplished by using an aqueous bath containing 4 g/l nickel acetate and 721 mg/l soluble sulfate coming from sulfuric acid except for, for comparison of prior art, the samples shown as being sealed in a bath containing nickel acetate only, upon which no acid dissolution tests were run. Sealing was at 208F and at a pH of 5.8 for 20 minutes. Where run, acid dissolution was in two successive steps of 15 minutes each.

Table III Desmudging Desmudging Time Acid Dissolution Concentration 5 1st 15 2nd 15 Specimen Acid (71- by weight) min. min. Visual Appearance min. Min.

mg/in mg/in 1 l-INO 41 X Clean 0.48 0.98 2 H 15 X Clean 0.48 1.01 3 25 X Clean 0.51 0.87 4 35 X Residue 0.56 1.01 5 50 X Residue 0.59 1.23 6 HNO 41 X Clean 0.56 1.02 7 H 80 15 X Clean 0.46 0.91 8 25 X Clean 0.56 0.97 9 35 X Residue 0.69 1.29

Table III Continued Desmudging Desmudging Time Acid Dissolution Concentration 2 5 1st 15 2nd l5 Specimen Acid (7: by weight) min. min. Visual Appearance min. Min.

mg/in mg/in 10 50 X Residue 1.03 1.17 1 1 HNO 41 X Clean 0.41 0.79 12 H 80 X Clean 0.39 0.68 13 25 X Clean 0.35 0.80 14 35 X Clean 0.37 0.68 15 H 80 50 X Clean 0.39 0.65 16 HNO; 4] X Clean 0.40 0.68 17 H 80 15 X Clean 0.33 0.53 18 25 X Clean 0.38 0.63 19 35 X Residue 0.52 0.79 20 50 X Residue 0.56 0.78 21 HNO 41 X Clean 0.22 0.21 22 H SO 15 X Clean 0.19 0.23 23 X Clean 0.22 0.20 24 35 X Clean 0.22 0.23 25 50 X Clean 0.26 0.22 26 HNO; 4] X Clean 0.27 0.22 27 H 80. 15 X Clean 0.25 0.22 28 25 X Clean 0.28 0.21 29 H 50 35 X Residue 0.43 0.24 30 50 X Residue 0.39 0.25 3] HNO; 41 X Clean 0.24 0.20 32 H 50 15 X Clean 0.23 0.19 33 25 X Clean 0.23 0.19 34 35 X Clean 0.25 0.17 35 50 X Clean 0.24 0.19 36 l-lNO 41 X Clean 0.25 0.21 37 H 80 15 X Clean 0.25 0.21 38 25 X Clean 0.27 0.21 39 35 X Clean 0.33 0.32' 40 50 X Clean 0.36 0.35 41" HNO 41 X Iridescence & Residue 42" H SO 15 X lridescence & Residue 43 H 80 25 X lridescence & Residue 44" 35 X Residue 45 X Residue 46 HNO '41 X lridescence & Residue 47" H 50 15 X Iridescence & Residue 48" 25 X lridescence & Residue 49" 35 X Residue 11) II 50 X Residue 51 l-lNO 41 X Clean 0.96 1.32 52 H SO 15 X Clean 0.89 1.81 53 25 X Clean 0.96 1.89 54 35 X Clean 1.06 2.02 55 50 X Clean 1.31 2.67 56 l-lNO 41 X Clean 1.00 2.02 57 H 80 15 X Clean 1.01 2.27 58 25 X Clean 1.04 2.10 59 35 X Clean 1.64 2.55 60 50 X Clean 1.99 2.69

" Sealed in sulfate-free nickel acetate solution 45 EXAMPLE 1 l substantially finer structure than the deposit formed 111 This example illustrates the range of soluble sulfate concentration in the sealing step that can be tolerated 50 according to the invention without adversely affecting the quality of the seal. A microscopic study of samples sealed and desmudged under varying conditions was made. An anodized aluminum alloy containing 0.5 Cu,

0.18 Fe, 0.10 Si, 0.01 Mn, 0.04 Mg, 0.18 Cr and 0.02 55 Ti was sealed in boiling water containing 4 g/l nickel acetate plus 0, 75, 375, 750, 1,500 and 2,000 ppm soluble sulfate supplied by H SO The amount of smudge formed decreased in proportion to the concentration of sulfate in the sealing bath. The surface of the sample 60 sealed at a level of 200 ppm sulfate resembled that of an imperfectly sealed film. Transmission electron micrographs taken of a magnification of 50,000X .revealed that this surface was basically the sameas that produced without sulfate or with less sulfate, respectively. The smudge formed by the baths employing s01- uble sulfate was considerably more compact and of a pure nickel acetate solution.

Desmudging was accomplished in 1:1 (by volume) or 41% by weight HNO; for from 3 to 60 minutes. A nitric acid treatment of 5 minutes left considerable surface roughness on the sample sealed in an aqueous solution containing 4 g/l nickel acetate and no sulfate. The samples sealed in baths with 375 ppm and 750 ppm sulfate showed a smooth surface after immersion in nitric acid. Holes in the surface resulted from dissolved intermetallic constituents.

According to the transmission micrographs the acid removed an outer layer of smudge which resembled crinkled tissue paper. It then partially dissolved the intermediate, optically structureless layer that covered the pore mouths. Rather severe attack occurred on lay ers formed in baths containing and 0 ppm sulfate, respectively. The surface roughness of the 2,000 ppm sulfate sample wason the order of only a few hundred angstroms. Since the pattern was very uniform, this surface would probably appear substantially smooth in visible light.

Sealing in solutions containing sulfate not only affected the morphological structure of the surface layer, but also improved its resistance to acid. After 60 minutes of immersion in nitric acid, the sample sealed in pure nickel acetate solution showed severe attack on pores and cell boundaries of the coating. Incipient attack of this nature was visible on the sample sealed with 100 ppm sulfate. The 2,000 ppm specimen, however, showed less surface dissolution than the 100 ppm sample after minutes immersion in acid.

The results of microscopic investigation indicated addition of up to 2,000 ppm soluble sulfate to non-sulfate hydrolyzable metallic salt sealing solutions reduced the volume of the outer smudge layer. The more compact layers were smoother and, therefore, scattered visible light to a lesser extent. In addition, the reduced surface area resulted in a slower rate of reaction during the acid treatment, thus increasing the chemical stability of the sealing layer.

EXAMPLE 12 In this example use of nickel sulfate as the hydrolyzable metallic salt for both sealing and supplying of a soluble sulfate was tried to demonstrate how such use does not work according to the invention but instead results in a detrimental effect on the quality of the seal, as evidenced by a greater than 2 mg/in acid dissolution value except for one sample treated with a sealing bath having a 5.9 pH. For each sample of the following table, however, satisfactory desmudging was obtained by use of 41% by weight nitric acid.

This example, in Table V below, compares desmudging of anodized aluminum after sealing with nickel sulfate as the sole hydrolyzable metallic salt (Samples la, [11, Ic, Ila, Ilb and He) with desmudging after sealing with only a non-sulfate hydrolyzable metallic salt (here nickel acetate) plus sulfate (Samples Illa, lllb and lllc). Each sealing solution was operated at 212F for minutes. Sealing trials were conducted respectively at pHs of 5, 6 and 7. Each sample was desmudged by immersion for 3 minutes in 41% by weightnitric acid after the sealing step. Process effectiveness in terms of quality of desmudging by visual examination and quality of sealing by the acid dissolution test was determined.

The quantities of each of the sealing bath constituents, in each case, were determined on the basis of the amounts of either sulfate, nickel, or acetate present in a known effective sealing solution consisting of 4 g/l nickel acetate. Seals Illa, lllb, and lllc consisted of 4.0 g/l NiAc and the nickelous sulfate added yielded 750 ppm soluble sulfate. For Seals Ia, lb and lc the nickelous sulfate used was such that the S0 is equivalent to the quantity of acetate present in a 4 g/l NiAc solution. Seals Ila, IIb and He were the same as Seals Ia, lb and I0 but with an additional 750 ppm of S0 added.

The pH of each solution as made up was adjusted with acetic acid or sodium hydroxide in each instance to bring it from the original pHs for Samples Ia, lb and Ic of 5.05, for Samples Ila, Ilb and llc of 6.05 and for Samples Illa, lllb and lllc of 5.10 to the values shown in the following Table V.

While the invention has been described in terms of preferred embodiments, the claims appended hereto are intended to encompass all embodiments which fall within the spirit of the invention.

Having thus described our invention and certain embodiments thereof, we claim:

1. In a process for sealing anodized aluminum in an aqueous bath containing a hydrolyzable metallic salt followed by removal of smudge with a mineral acid, the improvement which comprises:

a. sealing said anodized aluminum in an aqueous bath consisting essentially of: 1. water, 2. at least one non-sulfate hydrolyzable metal salt,

and 3. 375-2,000 ppm soluble sulfate and b. thereafter removing smudge formed on said anodized aluminum by said sealing by treating same with a solution consisting essentially of: l. mineral acid, andv 2. water without adversely affecting the seal produced by said sealing.

2. The improvement of claim -1 wherein the nonsulfate hydrolyzable metal salt comprises at least about 1 g/l of said sealing bath.

3. The improvement of claim 1 wherein the soluble sulfate is supplied by at least one sulfate selected from the group consisting of sulfuric acid, nickel sulfate, aluminum sulfate and sodium sulfate.

4. The improvement of claim 1 wherein the mineral acid comprises at least one acid selected from the group consisting of nitric, hydrochloric, sulfuric, phosphoric and chromic.

5. The improvement of claim 1 wherein the concentration of the mineral acid is at least about by weight.

6. The improvement of claim 1 wherein the concentration of the mineral acid is at least about by weight.

7. The improvement of claim 1 wherein the nonsulfate hydrolyzable metallic salt is selected from the group consisting of nickel acetate and cobalt acetate.

8. In a process for sealing and desmudging anodized aluminum, the improvement which comprises:

a. sealing said anodized aluminum in a bath consisting essentially of: 1. water, 2. at least one non-sulfate hydrolyzable metal salt selected from the group consisting of nickel acetate and cobalt acetate comprising at least about 1 g/l of said sealing bath, and 3. 3752,000 ppm soluble sulfate selected from the group consisting of sulfuric acid, nickel sulfate, aluminum sulfate, and sodium sulfate, and b. thereafter removing smudge formed on said anodized aluminum by said sealing by treating same with a solution consisting essentially of: 1. water, and 2. at least about 15% by weight of a mineral acid selected from the group consisting of nitric, hydrochloric, sulfuric, phosphoric, and chromic acid, without adversely affecting the seal produced by said sealing.

Claims (22)

1. WATER,

1. WATER, AND

1. In a process for sealing anodized aluminum in an aqueous bath containing a hydrolyzable metallic salt followed by removal of smudge with a mineral acid, the improvement which comprises: a. sealing said anodized aluminum in an aqueous bath consisting essentially of:

1. water,

1. mineral acid, and

1. water,

1. water, and

2. at least about 15% by weight of a mineral acid selected from the group consisting of nitric, hydrochloric, sulfuric, phosphoric, and chromic acid, without adversely affecting the seal produced by said sealing.

2. at least one non-sulfate hydrolyzable metal salt selected from the group consisting of nickel acetate and cobalt acetate comprising at least about 1 g/l of said sealing bath, and

2. water without adversely affecting the seal produced by said sealing.

2. The improvement of claim 1 wherein the non-sulfate hydrolyzable metal salt comprises at least about 1 g/l of said sealing bath.

2. at least one non-sulfate hydrolyzable metal salt, and

2. AT LEAST ABOUT 15% BY WEIGHT OF A MINERAL ACID SELECTED FROM THE GROUP CONSISTING OF NITRIC, HYDROCHLORIC, SULFURIC, PHOSPHORIC, AND CHROMIC ACID, WITHOUT ADVERSELY AFFECTING THE SEAL PRODUCED BY SAID SEALING.

2. AT LEAST ONE NON-SULFATE HYDROLYZABLE METAL SALT SELECTED FROM THE GROUP CONSISTING OF NICKEL ACETATE AND COBALT ACETATE COMPRISING AT LEAST ABOUT 1 G/L OF SAID SEALING BATH, AND 3. 375-2,000 PPM SOLUBLE SULFATE SELECTED FROM THE GROUP CONSISTING OF SULFURIC ACID, NICKEL SULFATE, ALUMINUM SULFATE, AND SODIUM SULFATE, AND B. THEREAFTER REMOVING SMUDGE FORMED ON SAID ANODIZED ALUMINUM BY SAID SEALING BY TREATING SAMD WITH A SOLUTION CONSISTING ESSENTIALLY OF:

3. 375-2,000 ppm soluble sulfate (SO4 ) and b. thereafter removing smudge formed on said anodized aluminum by said sealing by treating same with a solution consisting essentially of:

3. The improvement of claim 1 wherein the soluble sulfate is supplied by at least one sulfate selected from the group consisting of sulfuric acid, nickel sulfate, aluminum sulfate and sodium sulfate.

3. 375-2,000 ppm soluble sulfate selected from the group consisting of sulfuric acid, nickel sulfate, aluminum sulfate, and sodium sulfate, and b. thereafter removing smudge formed on said anodized aluminum by said sealing by treating same with a solution consisting essentially of:

4. The improvement of claim 1 wherein the mineral acid comprises at least one acid selected from the group consisting of nitric, hydrochloric, sulfuric, phosphoric and chromic.

5. The improvement of claim 1 wherein the concentration of the mineral acid is at least about 15% by weight.

6. The improvement of claim 1 wherein the concentration of the mineral acid is at least about 20% by weight.

7. The improvement of claim 1 wherein the non-sulfate hydrolyzable metallic salt is selected from the group consisting of nickel acetate and cobalt acetate.

8. IN A PROCESS FOR SEALING AND DESMUDGING ANODIZED ALUMINUM, THE IMPROVEMENT WHICH COMPRISES: A. SEALING SAID ANODIZED ALUMINUM IN A BATH CONSISTING ESSENTIALLY OF:

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