WO1997028292A1

WO1997028292A1 - Aluminum deoxidizing inhibitor, composition and process

Info

Publication number: WO1997028292A1
Application number: PCT/US1997/000202
Authority: WO
Inventors: Philip M. Johnson; Lawrence R. Carlson
Original assignee: Henkel Corporation
Priority date: 1996-01-29
Filing date: 1997-01-17
Publication date: 1997-08-07
Also published as: EP0877833A4; CA2242881A1; US5637252A; EP0877833A1

Abstract

A chromium-and-ferricyanide-free aqueous cleaner/deoxidizer for aluminum, the cleaner/deoxidizer having an etch rate on titanium that is low enough for practical use in processes where aluminum objects to be deoxidized are held on titanium racks or hangers during the process, combines boric acid, fluoborate anions, and an acid that is stronger than either of boric and fluoboric acids, usually also with an oxidizing agent such as hydrogen peroxide. Rates of etching of aluminum that are at least as much as 50 times the rates of etching of titanium under the same conditions can be achieved, and the deoxidizing of the aluminum is satisfactory for achieving corrosion resistance after subsequent conversion coating of the deoxidized aluminum surface.

Description

ALUMINUM DEOXIDIZING INHIBITOR, COMPOSITION AND PROCESS

Field of the nvention

This invention relates to inhibitors, compositions, and processes for deoxidizing and cleaning surfaces of aluminum and its alloys that contain at least 55 % by weight of aluminum (all such alloys being hereinafter to be understood as encompassed within the scope of the term "aluminum" unless the context requires otherwise), while minimizing the etching of titanium. "Deoxidizing" is to be understood herein as the removal from the surface of metals of oxide films and other adherent inorganic materials that would re¬ duce adhesion to subsequently applied protective coatings such as conversion coatings and/or paints and the like, and "cleaning" means removal of all other foreign materials, especially organic soils and poorly adherent inorganic substances such as metal dust and the like, that would reduce adhesion to such subsequently applied protective coatings. Statement of Related Art

With most deoxidizing agents, especially acidic aqueous liquid compositions with substantial hexavalent chromium and/or free fluoride ion contents, such compositions be- ing probably the most effective chemical classes of cleaners and deoxidizers for alumin¬ um now known, there is a perceptible but controlled etching or dissolution of the alumin¬ um, from its surface inward, while the deoxidizing agent is in contact with it. In the aero¬ space industry in particular, such deoxidizing is considered a necessity for achieving ad¬ equate corrosion resistance for many uses of aluminum. The aluminum parts being deox- idized are conventionally held by racks or other structures of titanium during the deoxi¬ dizing process, and etching of these titanium structures during the deoxidizing of alum¬ inum is very disadvantageous, as it decreases the lifetime of the titanium structures and would necessitate frequent replacement of these expensive items.

Hexavalent chromium-containing deoxidizing liquid compositions for the types of aluminum alloys most commonly used in aerospace have low etch rates for titanium. However, the pollution problems associated with hexavalent chromium have motivated efforts to eliminate or reduce its use as much as possible. Previously developed chromi¬ um-free deoxidizers for aluminum, however, have had unsatisfactorily high etch rates on titanium and/or have required at least one additional process step compared with conven¬ tional deoxidizing of aluminum with the use of hexavalent chromium containing deoxi¬ dizing liquid compositions, thereby making them unacceptable to most commercial users. DESCRIPTION OF THE INVENTION Object of the Invention

The primary object of the invention is to provide compositions and processes for deoxidizing and cleaning aluminum surfaces with little or no etching of titanium. Anoth¬ er object is to reduce pollution potential from aluminum deoxidizing compositions. Other objects will be apparent from the description below. General Principles of Description

Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, unless expressly stated to the contrary: per¬ cent, "parts of, and ratio values are by weight; the description of a group or class of ma¬ terials as suitable or preferred for a given purpose in connection with the invention im¬ plies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constitu- ents at the time of addition to any combination specified in the description, and does not necessarily preclude chemical interactions among the constituents of a mixture once mixed; specification of materials in ionic form implies the presence of sufficient counter¬ ions to produce electrical neutrality for the composition as a whole, and any counterions thus implicitly specified should preferably be selected from among other constituents ex- plicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to the objects of the invention; the term "mole" means "gram mole", and "mole" and its grammaucal varia¬ tions may be applied herein, mutatis mutandis, to ionic or any other chemical species with defined numbers and types of atoms, as well as to chemical substances with well de- fined conventional molecules; and the first definition of an acronym or other abbreviation applies to all subsequent uses of the same acronym or other abbreviation.. Summary of the Invention

It has been found that a combination of fluoboric and boric acids, together with a stronger acid and an oxidizing agent, provide a fully acceptable rate and quality of de¬ oxidizing aluminum with minimal etch of titanium exposed to the same deoxidizing com- position and process. Thus, one embodiment of the invention is an aqueous liquid com¬ position that comprises, preferably consists essentially of, or more preferably consists of, water and: (A) a component of dissolved acid with a larger ionization constant in water than that of either fluoboric acid or boric acid; (B) a dissolved source of fluoborate anions; and

(C) a dissolved source of boric acid; and, optionally, one or more of the following:

(D) a component of dissolved oxidizing agent that is not part of any of components (A) - (C) as recited above;

(E) a component of stabilizing agent for the oxidizing agent recited in part (D), the stabilizing agent itself not being part of any of components (A) - (D) as recited above;

(F) a component of surfactant that is not part of any of components (A) - (E) as recited above; and

(G) a component of dissolved aluminum cations. Various other embodiments of the invention include: (i) an inhibitor comprising, preferably consisting essentially of. or more preferably consisting of components (B) and (C) as described above; (ii) working compositions for direct use in treating metals, (iii) concentrates and partial concentrates from which such working compositions can be pre¬ pared by dilution with water and/or mixing with other chemically distinct concentrates, processes for cleaning and/or deoxidizing aluminum, and extended processes including additional steps that are conventional per se, such as rinsing, conversion coating, paint¬ ing, or the like. Articles of manufacture including surfaces treated according to a process of the invention are also within the scope of the invention.

Description of Preferred Embodiments For a variety of reasons, it is preferred that compositions according to the inven¬ tion as defined above should be substantially free from many ingredients used in compo- sitions for similar purposes in the prior art. Specifically, it is increasingly preferred in the order given, independently for each preferably minimized component listed below, that these compositions, when directly contacted with metal in a process according to this invention, contain no more than 1.0, 0.35, 0.10, 0.08, 0.04, 0.02, 0.01 , 0.001. or 0.0002 % of each of the following constituents: hexavalent chromium; ferricyanide; silica; sil¬ icates; thiourea; pyrazole compounds; sugars; gluconic acid and its salts; glycerine; α- glucoheptanoic acid and its salts; and myoinositol phosphate esters and salts thereof.

Furthermore, in a process according to the invention that includes other steps than a cleaning and/or deoxidizing treatment with a composition as described above, when avoidance of environmental pollution is an important consideration, it is preferred that none of these other steps include contacting the surfaces with any composition that con¬ tains more than, with increasing preference in the order given, 1.0. 0.35, 0.10, 0.08. 0.04, 0.02, 0.01, 0.003, 0.001, or 0.0002 % of hexavalent chromium. On the other hand, the cleaning and/or deoxidizing process taught herein can be advantageously used prior to chromate conversion coating or anodizing in a chromate containing — or, of course, a non chromate containing — solution, where one of these types of treatment is needed. Strong acid component (A) is preferably supplied by nitric acid. Other strong and preferably inexpensive mineral or organic acids such as sulfuric, phosphoric, trichloroacetic, and oxalic acids can also be used. Acids that yield simple halide ions upon ionization in aqueous solution are generally less preferred, because of the danger of pitting corrosion attack on the aluminum being deoxidized. In a working composition according to the invention when component (A) is derived from nitric acid, the concen¬ tration of nitric acid preferably is at least, with increasing preference in the order given, 5, 10, 15, 20, 25, 30, 34, 38, 40, 42, 44, or 46 grams per liter of total composition (hereinafter usually abbreviated as "g/L") and independently preferably is, primarily for reasons of economy, not more than, with increasing preference in the order given. 200, 150. 100, 90, 80, 70, 60, 55, 50, or 48 g/L. If another acid than nitric is used, either alone or in a mixture, the preferred concentrations of component (A) in a working composition according to the invention are those that will result in the same pH values, in the complete working composition, as result from using the preferred amounts of nitric acid as specified above. Component (B), primarily for reasons of economy, is preferably derived from fluoboric acid, although salts of this acid can also be used. The stoichiometric equivalent as BF₄ anions of all sources of component (B) in a working composition according to the invention preferably is at least, with increasing preference in the order given, 0.4, 0.8, 1.2. 1.6. 2.0, 2.4, 2.8, 3.2, 3.30, 3.40, 3.50, 3.60, 3.70, or 3.80 g/L and independently preferably is, primarily for reasons of economy, not more than, with increasing prefer¬ ence in the order given, 20, 15, 10, 9.0, 8.0, 7.0, 6.0, 5.5, 5.0, 4.5, 4.1, or 3.9 g/L. Inde¬ pendently of the actual concentrations, the ratio of the concentration of the stoichiometric equivalent as BF₄" anions of all sources of component (B) to the concentration of com- ponent (A) when component (A) is nitric acid preferably is at least, with increasing pref¬ erence in the order given, 0.010: 1.0, 0.020: 1.0, 0.030: 1.0, 0.040: 1.0, 0.050: 1.0, 0.060: 1.0, 0.065: 1.0. 0.069: 1.0, 0.073 : 1.0, 0.077: 1.0, or 0.081 : 1.0 and independently preferably is not more than, with increasing preference in the order given, 0.50: 1.0, 0.40: 1.0, 0.30: 1.0, 0.20:1.0, 0.15:1.0, 0.13:1.0, 0.11:1.0, 0.10:1.0, or 0.090:1.0. If another acid or a mixture of acids is used for component (A), these ratios should be adjusted to provide the same pH in working compositions as do the above noted preferred ratios for component (A) when it is derived entirely from nitric acid.

Component (C) preferably is derived from direct addition of simple boric acid, i.e., H₃BO₃, but can also be derived from salts of this acid or of (actual or hypothetical) condensed boric acids. In a working composition according to the invention, the concen¬ tration as the stoichiometric equivalent as H₃BO₃ of all sources of component (C) prefer¬ ably is at least, with increasing preference in the order given, 0.4, 0.8, 1.2, 1.6, 2.0, 2.4, 2.8, 3.2.3.30, 3.40, 3.50. 3.60, 3.70, or 3.80 g/L and independently preferably is. primar¬ ily for reasons of economy, not more than, with increasing preference in the order given, 20, 15. 10, 9.0, 8.0, 7.0, 6.0, 5.5, 5.0, 4.5, 4.1, or 3.9 g L. Independently of the actual concentrations, the ratio of the concentration of the stoichiometric equivalent as H₃BO₃ of all sources of component (C) to the concentration of component (A) when component (A) is nitric acid preferably is at least, with increasing preference in the order given, 0.010:1.0. 0.020:1.0, 0.030:1.0, 0.040:1.0, 0.050:1.0, 0.060:1.0, 0.065:1.0. 0.069:1.0, 0.073 : 1.0, 0.077: 1.0. or 0.081 : 1.0 and independently preferably is not more than, with in¬ creasing preference in the order given. 0.50:1.0, 0.40:1.0, 0.30:1.0. 0.20:1.0. 0.15: 1.0, 0.13 : 1.0, 0.1 1 : 1.0, 0.10: 1.0. or 0.090: 1.0. If another acid or a mixture of acids is used for component (A), these ratios should be adjusted to provide the same pH in working com¬ positions as do the above noted preferred ratios for component (A) when it is derived en¬ tirely from nitric acid. Also, independently of the other preferences and of the actual concentrations, the ratio of the concentration of the stoichiometric equivalent as H₃BO₃ of all sources of component (C) to the concentration of the stoichiometric equivalent as BF/ anions of all sources of component (B) preferably is at least, with increasing prefer¬ ence in the order given, 0.1 :1.0, 0.3:1.0, 0.5:1.0, 0.60: 1.0, 0.70:1.0, 0.80:1.0, 0.90:1.0, 0.95: 1.0, or 0.99: 1.0 and independently preferably is not more than, with increasing pref- erence in the order given, 3.0:1.0, 2.5:1.0, 2.0:1.0, 1.8:1.0, 1.6:1.0, 1.4:1.0, 1.30:1.0, 1.20:1.0, 1.10: 1.0, or 1.01 :1.0.

Component (D) is normally preferably present in a composition according to the invention, unless components (A) - (C) have as much oxidizing power as when the pre¬ ferred amounts of component (D) as described below are used and component (A) is ni- trie acid. Component (D) most preferably is made up of hydrogen peroxide, although other peroxides and non-peroxide oxidizing agents can also be used. When only hydro¬ gen peroxide is used for component (D), the concentration of it in a working composition according to the invention preferably is at least, with increasing preference in the order given. 3, 7, 1 1, 15, 19, 23, 25, 27, 29, 30.0, or 31.0 g/L and independently preferably is, primaπly for reasons of economy, not more than, with increasing preference in the order given. 190, 140, 1 10, 90, 80, 70, 60, 50, 45, 40, 39, 37, 35. 34.0, 33.0, or 32.0 g/L. Inde¬ pendently of the actual concentrations, the ratio of the concentration of component (D) when it is constituted of hydrogen peroxide to the concentration of the stoichiometric equivalent as H₃BO₃ of all sources of component (C) preferably is at least, with increas- ing preference in the order given, 1.0:1.0, 2.0:1.0, 3.0:1.0, 4.0:1.0, 5.0:1.0, 6.0:1.0, 6.5 : 1.0. .9: 1.0, 7.3 : 1.0, 7.7: 1.0, or 8.0: 1.0 and independently preferably is not more than, with increasing preference in the order given, 50:1.0, 40:1.0, 30: 1.0, 20:1.0, 15:1.0, 13:1.0. 1 1 :1.0, 10.0:1.0, 9.0:1.0, 8.6:1.0, 8.4:1.0, or 8.3:1.0; independently of other pref¬ erences and of the actual concentrations, the ratio of the concentration of component (D) when it is constituted of hydrogen peroxide to the concentration of the stoichiometric equivalent as BF₄" of all sources of component (B) preferably is at least, with increasing preference in the order given, 1.0: 1.0, 2.0:1.0, 3.0:1.0, 4.0:1.0, 5.0:1.0, 6.0:1.0. 6.5:1.0, 6.9:1.0, 7.3:1.0, 7.7:1.0, or 8.0:1.0 and independently preferably is not more than, with increasing preference in the order given, 50:1.0, 40: 1.0, 30:1.0, 20:1.0, 15:1.0. 13:1.0, 11 : 1.0, 10.0: 1.0, 9.0: 1.0, 8.6: 1.0, 8.4: 1.0, or 8.3 : 1.0; and independently of other prefer- ences and of the actual concentrations, the ratio of the concentration of component (D) when it is constituted of hydrogen peroxide to the concentration of component (A) when component (A) is nitric acid preferably is at least, with increasing preference in the order given, 0.10:1.0, 0.20:1.0, 0.30:1.0, 0.40:1.0, 0.50:1.0, 0.55:1.0, 0.59:1.0, 0.62:1.0, or 0.65: 1.0 and independently preferably is not more than, with increasing preference in the order given, 4.0:1.0, 3.0:1.0, 2.0:1.0, 1.5:1.0, 1.3:1.0, 1.1:1.0, 0.90:1.0, 0.85:1.0.0.80:1.0, 0.75:1.0, 0.70:1.0, or 0.67:1.0. If another oxidizing agent or a mixture of oxidizing agents is used instead of only hydrogen peroxide for component (D), these concentrations and ratios should be adjusted so as to provide the same oxidizing power in the composi¬ tions as if they were made with the preferred amounts of hydrogen peroxide recited above; the oxidizing power of the composition may be measured for this purpose by the potential of a platinum electrode immersed in the composition, compared to some stand¬ ard reference electrode maintained in electrical contact with the composition via a salt bridge, flowing junction, semipermeable membrane, or the like as known to those skilled in electrochemistry. If another acid or a mixture of acids is used for component (A), any ratios involving component (A) should be adjusted to provide the same pH in working compositions as do the above noted preferred ratios for component (A) when it is derived entirely from nitric acid.

Optional component (E) is preferably present in a composition according to the invention when hydrogen peroxide is present therein, as the hydrogen peroxide is likely to decompose during storage in the absence of a stabilizer. Any of a wide variety of stab¬ ilizers for hydrogen peroxide that are known in the art may be used, unless they frustrate one of the objectives of the invention. Preferred constituents of component (E) are select¬ ed from the group consisting of molecules according to general formula (I):

RO(CH₂CH₂O)_y(CH₂CHCH₃O),H (I) where: R is a moiety selected from the group consisting of saturated-and-unsaturated straight-and-branched-chain-aliphatic-monovalent-hydrocarbon-moiety-substituent - bearing phenyl moieties in which the aromatic ring is directly bonded to the oxygen atom appearing immediately after the R symbol in formula (I); y is a positive integer; and z is zero, one, or two. More preferably, primarily for reasons of economy, the aliphatic por¬ tion of the R moiety preferably is saturated, and independently preferably is straight chain or is straight chain except for a single methyl substituent. Also, independently of other preferences: (i) the total number of carbon atoms in the R moiety preferably is at least, with increasing preference in the order given, 8, 10, 11, 12, 13, or 14 and independently preferably is not more than, wiύh increasing preference in the order given, 22, 21, 20, 19, 18, 17, or 16; z is zero; and x is at least, with increasing preference in the order given, 2, 3, 4, 5, 6, 7, 8, or 9 and independently preferably is not more than, with increasing preference in the order given, 15, 14, 13, 12, 11 , or 10. In a working composition accord¬ ing to the invention, the concentration of component (E) preferably is at least, with in¬ creasing preference in the order given, 0.02, 0.049, 0.077, 0.10, 0.13, 0.15, 0.17, 0.19, or 0.21 g L and independently preferably is, primarily for reasons of economy, not more than, with increasing preference in the order given, 1.3, 0.98, 0.77, 0.63, 0.56, 0.49, 0042, 0.35, 0.33, 0.31, 0.29, 0.27, 0.25, or 0.23 g/L.

If preferred component (E) as described above is present, optional component (F) is not normally needed, but may be valuable in certain instances, such as if the surfaces to be deoxidized are very irregularly wetted by a composition with components (A) - (E) only.

Optional component (G) of dissolved aluminum cations is not normally included in a freshly prepared working composition according to the invention, but usually accum¬ ulates during use of the composition on aluminum substrates.

One type of concentrate composition according to the invention preferably con- tains components (A), (B), and (C) as defined above in the same ratios to one another as are desired in the working composition(s) to be made from this type of concentrate com¬ position. In order to maximize the storage stability such a concentrate composition pref¬ erably contains not more than, with increasing preference in the order given, 25.0, 24.0, 23.0.22.0.21.0. or 20.7 % of HNO₃. Independently, even if hydrogen peroxide is desired in a working composition according to the invention, it preferably is not present in the same concentrate as any of components (A), (B), and (C) during storage of such a con- centrate. as these ingredients reduce the stability of the hydrogen peroxide. Therefore, the hydrogen peroxide preferably is provided in a second concentrate, which contains components (D) and (E) in the same ratio to each other as is desired in the final working composition s) to be made from the concentrates. In order to promote stability of such a hydrogen peroxide and stabilizer concentrate according to the invention. the concentra¬ tion of hydrogen peroxide therein preferably is not more than, with increasing preference in the order given, 50, 45, 40, 37, 34, 31, or 29 %.

One of the advantages of a deoxidizing composition according to the invention over most prior art is that a composition according to the invention is suitable for use at relatively low temperatures. In particular, primarily for reasons of economy, in a process according to the invention the temperature of the working deoxidizing composition ac¬ cording to the invention preferably is not greater than, with increasing preference in the order given, 50, 45, 42, 40, or 38 °C and independently, in order to achieve deoxidation in a reasonable time, preferably is at least, with increasing preference in the order given, 15, 17, 19, 21, or 23 °C.

Sufficiency of the deoxidizing effect has been found difficult to judge by any vis¬ ual indication or other quick method, and the primary practical method found successful so far is to measure the resistance to salt spray of an aluminum surface that has been de¬ oxidized according to the invention and then chromate conversion coated in a conven- tional manner, such as with products and processing conditions recommended in the Technical Process Bulletins for ALODINE® 600 and 1200S aluminum conversion coat¬ ing processes available from the Parker Amchem Division of Henkel Coφoration (here¬ inafter usually abbreviated as "PAD"), Madison Heights, Michigan, USA. Substrates of Type 2024-T3 aluminum deoxidized according to the invention and then processed ac- cording to one of these ALODINE® processes preferably should pass a 336 hour salt spray test. The time of deoxidizing preferably is sufficient to achieve this result. As a general guideline, with the most preferred working compositions according to the in¬ vention, a passing salt spray test can generally be achieved with no more than 10 minutes of deoxidizing, and sometimes with no more than 3 minutes. For reasons of economy, of course, the time is preferably not longer than necessary to achieve the required level of deoxidizing to meet performance requirements. Normally, before being deoxidized according to this invention. an aluminum sub¬ strate surface preferably is thoroughly cleaned in a conventional manner, such as with one of the RIDOLINE® cleaner/processes commercially available from PAD.

At least the most preferred compositions and processes according to the invention meet the deoxidizing requirements of U. S. Military Specification MIL-W-6858C, U 4.2. The practice of this invention may be further appreciated by consideration of the following, non-limiting, working examples, and the benefits of the invention may be fur¬ ther appreciated by consideration of the comparison examples.

EXAMPLES AND COMPARISON EXAMPLES Test panels of Type 2024-T3 aluminum sheet were subjected to the following process steps in the order shown:

( 1 ) Clean according to the RIDOLINE® 53L process as described in Technical Pro¬ cess Bulletin No. 1291, Edition of May 19, 1992, from PAD.

(2) Rinse with tap water. (3) Deoxidize by immersion in a composition as shown in detail below.

(4) Rinse with tap water.

(5) Conversion coat according to one of the ALODINE® 600 and 1200S aluminum conversion coating processes as noted above.

(6) Rinse with tap water, dry, and allow to sit for at least 72 hours. (7) Subject to salt spray testing according to American Society for Testing and Ma¬ terials Method B-l 17. Additional details are given in Table 1 below. Blanks in this table indicate that the ingredient shown at the top of the column was not added to the composition on the line where the blank appears. Etch rates and the results of salt spray testing are shown in Table 2 below. The results in Table 2 indicate that both bismuth oxide and fluosilicic acid are excellent selective inhibitors of titanium etching, but deoxidizing compositions containing only these materials as inhibitors do not achieve the level of salt spray resistance after sub¬ sequent conversion coating that is required for the most demanding aerospace applica- tions. These high levels of salt spray resistance are readily achieved by compositions ac¬ cording to the invention, such as those with identifying numbers 3. 4, 14, and 16 in Tables 1 and 2, that also have acceptably low etch rates for titanium.

TABLE 1 : DEOXIDIZER COMPOSITIONS

Identifying Amount in Composition¹ of: Number

% by Volume of 42 g/L of g L of g L of g L of °Baume Nitric Acid HBF₄ H₂SiF₆ HjBO₃ Bi₂O₃

1 5 1

2 5 3

3 5 1 5

4 5 3 4

5 10 3 4

6 5 2

7 10 2

8 5 3 4 3

9 10 3 4 3

10 5 2 3

11 10 2 3

12 5 2 4 3

13 10 2 4 3

14 5 5 4

15 10 5 4

16 5 3 10

17 10 3 10

18 5 3 4

19 5 3 4

Footnote for Table 1

'In each instance the composition also contained from 30 to 32 g/L of H₂0₂ and a peroxide decomposition inhibitor, which for all except the last two compositions in the table was TRI¬ TON™ N-101, which was commercially supplied by Van Waters & Rogers, Inc.. Kirkland, Washington. USA and is reported by its supplier to be a condensation product between ethylene oxide and nonyl phenol having an average molecular weight of 616. TABLE 2: ETCH RATES AND RESULTS OF SALT SPRAY TESTING

Identifying Etch Rate in Micrometres/Hour on: Results of 336 Number Hours Salt Spray

2024-T3 Aluminum Titanium Testing¹

1 1.2-1.8 0.25 Pass

2 3.8-5.1 0.62 Marginal

3 1.2-1.8 0.15 Pass

4 2.5 - 3.8 0.25 Pass

5 2.5-3.8 0.05-0.13 Pass**

6 2.5-3.8 0.005-0.013 Fail

7 2.5 - 3.8 0.08 Fail

8 2.5 - 3.8 0.005-0.013 Fail

9 2.5-3.8 0.08 Fail

10 2.5-3.8 0.005 - 0.020 Fail

11 2.5 - 3.8 0.025-0.051 Fail

12 2.5-3.8 0.025 Fail

13 2.5-3.8 0.018-0.025 Not measured

14 4.1-5.1 0.011 Pass - Fail*

15 4.1 -5.1 0.015 Fail

16 2.5-3.8 0.030 Pass - Fail*

17 2.5-3.8 0.038 Fail**

18 2.5-3.8 0.08 Fail

19 2.5-3.8 0.08 Fail

Footnote for Table 2

'The results are for conversion coating by an ALODINE® 600 process, except results suffixed with a single asterisk are for conversion coating by an ALODINE® 1200S process only, and results suffixed with a double asterisk had the same result for both of these types of conversion coating.

Claims

CLAIMS:

1. An aqueous liquid composition that is suitable either as such, after dilution with water, or both as such and after dilution, for deoxidizing etching of aluminum surfaces by contact therewith, said composition comprising water and: (A) nitric acid;

(B) a dissolved source of fluoborate anions; and

(C) a dissolved source of boric acid, wherein components (B) and (C) are present in amounts having stoichiometric equiva¬ lents as boric acid for component (C) and as BF₄ ^" anions for component (B) with a ratio of stoichiometric equivalent as boric acid to stoichiometric equivalent as BF₄ ^' anions from 0.3:1.0 to 3.0:1.0.

2. A composition according to claim 1 that is a concentrate, wherein: nitric acid is present in an amount from 10 to 25.0 %; component (B) is present in a ratio of stoichio¬ metric equivalent as BF₄ ^" anions to nitric acid from 0.010: 1.0 to 0.50: 1.0; and component (C) is present in a ratio of stoichiometric equivalent as H₃BO₃ to stoichiometric equiv¬ alent as BF₄ ^' anions in component (B) from 0.3:1.0 to 3.0:1.0.

3. A composition according to claim 2, wherein: nitric acid is present in an amount from 15 to 20.7 %; component (B) is present in a ratio of stoichiometric equivalent as BF₄ ^" anions to nitric acid from 0.081 :1.0 to 0.090:1.0; and component (C) is present in a ratio of stoichiometric equivalent as H₃BO₃ to stoichiometric equivalent as BF₄ ^' anions in component (B) from 0.95: 1.0 to 1.10: 1.0.

4. A working composition according to claim 1 , wherein: nitric acid is present in an amount from 5 to 200 g/L; component (B) is present in an amount from 0.4 to 20 g/L; component (C) is present in an amount from 0.4 to 20 g/L; and the composition also comprises from 7 to 140 g/L of hydrogen peroxide.

5. A working composition according to claim 4, wherein: nitric acid is present in an amount from 45 to 50 g/L; component (B) is present in an amount from 3.70 to 4.1 g/L; component (C) is present in an amount from 3.70 to 4.1 g/L; the composition comprises from 29 to 34.0 g/L of hydrogen peroxide; and the composition also comprises at least 0.15 g/L of peroxide decomposition inhibitors selected from the group consisting of molecules conforming to general formula (I):

RO(CH₂CH₂O)_y(CH,CHCH₃0)_zH (I) where: R is a moiety selected from the group consisting of saturated-and-unsaturated straight-and-branched-chain-aliphatic-monovalent-hydrocarbon-moiety-substituent-bear- ing phenyl moieties in which the aromatic ring is directly bonded to the oxygen atom ap¬ pearing immediately after the R symbol in formula (I); y is a positive integer: z is zero or one; the aliphatic portion of the R moiety is saturated and straight chain, or straight chain except for a single methyl substituent; the total number of carbon atoms in the R moiety is from 14 to 17; and the average value of y is from 8 to 11.

6. A process of deoxidizing an aluminum surface, by contacting it for a deoxidizing effective time with a composition according to claim 4 or 5.

7. An inhibitor for a nitric-acid-containing aqueous liquid deoxidizing composition for aluminum, said inhibitor comprising fluoborate anions and a source of boric acid in amounts having a ratio of stoichiometric equivalent as boric acid to stoichiometric equivalent as BF₄ ^" anions from 0.3:1.0 to 3.0:1.0.

8. A process for deoxidizing and etching an aluminum surface that is in contact with a titanium surface, by contacting both the aluminum and the titanium surfaces with an aqueous liquid composition that spontaneously deoxidizes and etches the aluminum sur¬ face by chemical reaction therewith, wherein: the rate of etching of the titanium surface is not greater than 0.25 micrometres per hours; the aqueous liquid composition comprises water and:

(A) a component of dissolved acid with a larger ionization constant in water than fluoboric acid or boric acid;

(B) a dissolved source of fluoborate anions; and (C) a dissolved source of boric acid; and the aqueous liquid composition comprises not more than 0.35 % of hexavalent chromium.

9. A process according to claim 8, wherein, in the aqueous liquid composition: component (A) is nitric acid and is present in a concentration from 5 to 200 g/L; component (B) is present in a concentration that has a ratio to the concentration of component (A) within a range from 0.01 :1.0 to 0.50:1.0; and component (C) is present in a concentration that has a ratio to the concentration of component (B) within a range from 0.1 :1.0 to 3.0:1.0.

10. A process according to claim 9, wherein: the concentration of nitric acid is from 10 to 100 g/L; the ratio of the concentration of component (B) to the concentration of component (A) is from 0.030:1.0 to 0.20: 1.0; and the ratio of the concentration of component (C) to component (B) is from 0.50:1.0 to 2.0:1.0.

11. A process according to claim 10, wherein: the concentration of nitric acid is from 20 to 70 g/L; the ratio of the concentration of component (B) to the concentration of component (A) is from 0.060:1.0 to 0.15:1.0; and the ratio of the concentration of component (C) to component (B) is from 0.70: 1.0 to 1.6: 1.0.

12. A process according to claim 11 , wherein: the concentration of nitric acid is from 34 to 55 g/L; the ratio of the concentration of component (B) to the concentration of component (A) is from 0.073:1.0 to 0.13:1.0; and the ratio of the concentration of component (C) to component (B) is from 0.80: 1.0 to 1.3:1.0.

13. A process according to any one of claims 8 - 12, wherein the rate of etching of the titanium surface is not more than 0.15 micrometres per hour and the aqueous liquid com¬ position comprises not more than 0.10 % of hexavalent chromium.

14. A process according to claim 13 , wherein the rate of etching of the titanium sur¬ face is not more than 0.030 micrometres per hour..