DE1290410C2 - AQUATIC, ACID FLUORIDE IONS AND AN INORGANIC INHIBITOR CONTAINING SOLUTION, PRACTICALLY FREE OF CHLORIDIONS, AND METHOD FOR PURIFYING ALUMINUM AND ALUMINUM ALLOYS - Google Patents

Description

It is from "Chemisches Zentralblatt", vol. 1950/11, p. 2119: Referat über die USA.-Patent 2 507 314 (Aluminum Co. of America), and vol. 1959, p. 12,686: Referat über die French Patent specification 1 120 749 (Georgette War η a η t) known to add acidic aqueous solutions for pickling aluminum, chromic acid, chromates or dichromates as inhibitors. It is also from US Pat. No. 2,655,439, in particular Claims 5, 6, 7, 9 and 10, French Pat. No. 1 146482, p. 1, right column, paragraph 2, and p. 2, left column, Examples 1, 2 and 3, and the "Chemisches Zentralblatt" 1958, p. 1978/1979: Report on British patent specification 767888 and French patent specification i 119 649 (American Chemical Paint Co.) known acidic solutions for cleaning aluminum, the Fluoride ions and an inorganic inhibitor (CrO ₃ or hexavalent Cr compounds) should be used and that such fluoride ions and solutions containing an inhibitor may only contain traces of halogen ions (except F ions).

The invention is based on the object of using chromium compounds as inhibitors for acidic solutions to avoid cleaning of aluminum and aluminum alloys because they contain chromium To protect animal and plant life, wastewater is no longer drained into rivers may.

It has been found that, surprisingly, instead of chromium compounds, ferric ions are used as the inhibitor in aqueous solutions containing acidic fluoride ions, which are practically free of chloride ions can be used to clean aluminum and aluminum alloys.

The subject of the invention are aqueous, acidic fluoride ions and an inorganic inhibitor Solutions that are practically free of chloride ions for cleaning aluminum and aluminum alloys, characterized by a hydrogen

Ion concentration of 0.18 to 1.4 g / l, a ferric ion concentration of 2 to 17 g / l, a fluoride ion concentration of 0.4 to 3.3 g / l, a ratio of Hydrogen ion concentration to ferric ion concentration of 0.03 to 0.36 and a ratio of the fluoride ion concentration to the ferric ion concentration, which gives the values given by the curve AB for the corresponding ratios of the hydrogen Ion concentration does not exceed the ferric ion concentration. | _O

In the drawing, the relationship of the ratio of the maximum permissible fluoride ion concentration to the ferric ion concentration as a function of the ratio of the hydrogen-ion concentration to the ferric ion concentration is graphically represented in an aqueous solution of _J5; the ratio of the hydrogen ion concentration to the ferric ion concentration is plotted on the abscissa and the ratio of the maximum permissible fluoride ion concentration to the ferric ion concentration is plotted on the ordinate. The curve AB shows the relationship between the hydrogen ion concentration and the chloride ion concentration as a function of the ferric ion concentration.

It has been found that a maximum ratio of 0.23 fluoride ions to ferric ions in a Hydrogen-ion to ferric-ion ratio 0.0831. Because the highest possible concentrations of both hydrogen ions and fluoride ions are desired in the solutions in order to remove stains from aluminum or aluminum as quickly as possible. To achieve aluminum alloys, solutions with a fluoride to ferric ion concentration of not more than 0.2 is desirable, which is close to the maximum ratio and also a margin of safety against corrosion bit-iet.

Since both hydrogen and fluoride ions attack aluminum, the maximum permissible amount is Fluoride is inversely proportional to the hydrogen ion concentration.

A solution practically free of chloride ions contains no more than 0.1 g of chloride ions per liter. The hydrogen ion is a prerequisite for removing stains on aluminum or aluminum alloys, water-soluble salts are formed. Alloys containing significant amounts of silicon, however, require solutions that contain fluoride ions in addition to the hydrogen ions. The minimum or maximum amount Hydrogen ions per liter of solution amount to 0.18 and 1.4 g, respectively. Of the fluoride ions must each Liters are at least 0.4 g but not more than 3.25 g.

According to curve AB of the 5s drawing, the maximum amount of fluoride ions permitted in the solution also depends on the ratio of the hydrogen ion concentration to the ferric ion concentration. The ferric ion must be present in an amount of at least 2 g per liter; Quantities of 17 g per liter of solution are also possible.

The hydrogen ion can be replaced by sulfuric acid, sulfamic acid, nitric acid, acidic alkali metal salts such as acidic alkali metal sulfates and acidic ammonium sulfate, and can also be formed by a sulfonic acid or fluorosulfonic acid. Hydrogen fluoride can only partially can be used as a source of hydrogen ions, since the maximum content permitted in aqueous solutions of fluoride ions is 3.25 g / l. If this concentration of fluoride ions is exceeded, the aluminum metal is no longer protected against attack by the hydrogen ions. The solutions according to the invention contain at least 2 g of ferric ions, but not more than 17 g per liter. Larger quantities are of no advantage, since quantities of 100 g per liter require a long treatment time require. A high ion content also increases the solvency of the solution for the the compounds forming hydrogen and fluoride ions are too low.

When the ratio of the hydrogen ion concentration to the ferric ion concentration exceeds 0.36, the aluminum is attacked. This high ratio gives good stain removal in 0.5 to 2.0 minutes. With the minimum ratio of hydrogen to ferric ion concentration in question of 0.03, at 23.9 ° C, staining occurs in about 10 minutes. The ferric ion content is preferably about 8 g / l, and the preferred ratio of hydrogen to ferric ion concentration is about 0.084-

Because the ferric ions are reduced to ferro ions the higher the initial ferric ion content, the longer the solution can be used. When working with the preferred iron content and the preferred hydrogen-ferric-ion concentration ratio a solution can be used for uninterrupted operation for several months.

The ferric ion content can be determined by an or several of the following compounds are supplied: ferric fluoride, ferric formic acid ester, ferric nitrate and ferric fluorosilicate, preferably ferric sulfate; Ferrifluoride and ferrifluorosilicate cannot be used alone Source of ferric ions can be used, as to achieve the desired amount of ferric ions the maximum permissible content of fluoride ions for the solution would be exceeded.

The fluoride ion can be one or more the following water-soluble fluorides can be obtained: ferrifluoride, ferrifluorosilicate, alkali metal fluorides, Alkali metal fluorosilicates, alkali metal fluoroborates, aluminum fluoride, ammonium fluoride, acidic Alkali metal fluorides, acidic ammonium fluoride and hydrofluoric acid, preferably sodium fluoride.

In view of the above, solutions according to the invention can contain 0.7 g per liter Hydrogen ions, 8.37 g ferric ions and 1.6 g fluoride ions or 84 g acid sodium sulfate, 30 g Contain ferric sulfate, 3.6 g sodium fluoride and 2.4 g magnesium carbonate.

A solution according to the invention can also have a content of at least 0.6 percent by weight ionizable hydrogen, a ratio of hydrogen ion concentration to ferric ion concentration of about 0.08 and a ratio of fluoride ion concentration to ferric ion concentration be characterized by about 0.2.

It has also been found that it can be used for carrying out the process according to the invention It is important to continuously pass such an amount of air through the aqueous solution that one slight agitation of the solution occurs. Due to the oxygen in the air, some of the iron ion is in the Ferriform, which is easier than a married

mixed treatment of the solution with a liquid or solid oxidizing agent; after a long time However, when using the bath, it may be necessary to add an oxidizing agent.

The invention not only offers the advantage that chromate compounds no longer end up in wastewater, but also that solutions with much lower concentrations are used be able. From US Pat. No. 2,828,193 it follows that the known solutions are about 2.3 percent by weight Contains potassium dichromate.

While solutions containing chromate are refreshed after about 3 weeks must, the solutions according to the invention can be used continuously for several months.

The metal processing companies expediently provide the solutions for cleaning Aluminum or aluminum alloys from solid agents or liquid concentrates supplied by them here.

A solid agent contains at least one compound in each case.;. _T , Ht of the following groups: acidic alkali metal sulfates, acidic ammonium sulfate, sulfamic acid. Nitric acid, sulfuric acid, ferric sulfate. Ferrifluoride, ferric formic acid ester, ferric nitrate, ferric fluorosilicate and alkali metal fluoride, aluminum fluoride, ferric fluoride, ferrous fluorosilicate, ammonium fluoride, acidic alkali metal fluoride, acidic ammonium fluoride and / or alkali fluoroborate.

Sulfuric acid or nitric acid is expediently c absorbed on other solid components so that the mixture is dry and firm.

As a means producing hydrogen ions Preferably acidic sodium sulfate is used: that Ferric ion is preferably obtained from ferric sulfate.

In order to achieve a free-flowing agent, it is advisable to add a drying agent to the mixture, such as lithium carbonate, calcium silicate or magnesium silicate in an amount of preferably 2 percent by weight, based on the mixture to be added.

A solid agent preferably consists of 70 percent by weight sodium bisulfate. 25 percent by weight ferric sulfate, 3 percent by weight sodium fluoride and 2 percent by weight of a drying agent such as magnesium carbonal.
A liquid concentrate contains at least one compound from each of the following groups: sulfuric acid, nitric acid, hydrofluoric acid, ferric sulfate, ferric nitrate, ferric formate, ferric fluoride, ferrous fluorosilicate and alkali metal fluorides, aluminum fluoride, ferrous fluoride, ammonium fluoride, ferric fluoride fluoride, ammonium fluoride, ferric fluorosilicate and ammonium fluoride, hydrofluoric acid, hydrofluoric acid, hydrofluoric acid, hydrofluoric acid.

The preferred source of ferric ion is ferric sulfate or ferric nitrate is used. Such a concentral can also be used as a source of part of the ionizable Hydrogen contain at least one of the following compounds: an acidic alkali metal sulfate, an acidic ammonium sulfate and / or sulfamic acid.

The liquid acids can have solid sources of ionizable oxygen dissolved in them, such as the

. Sulfamic acid, sodium bisulfate and ammonium bisulfate. Any source of the hydrogen ion that is dissolved must become. however, lowers the solubility of the concentrate for the other required ingredients.

The concentration of the ionized or ionizable hydrogen in the liquid concentrate generally amounts to about 0.5 percent by weight. The ratio of ionizable hydrogen to ionizable ferric ion is generally about 0.08, while the ratio of ionizable Fluoride to Ferri-Ion is about 0.2.

A liquid concentrate consists e.g. B. essentially from 250 parts by weight of sulfuric acid (60 Be). 210 parts by weight of ferric sulfate, 25 parts by weight Sodium fluoride and 515 parts by weight of water.

The invention is further described in the following examples, in which the best mode of carrying out is taken into account.

The aluminum alloys of types! 100 listed in the following examples. 2024, 6061 and 6063 had the following composition:

1100
2024
6061
6063

Si

Fe

1.0Si + Fe

0.50

0.40 to 0.8

0.20 to 0.6

0.50

0.7

0.35

Cu

0.20

3.8 to 4.9

0.15 to 0.40

0.10

Mn

0.05

0.30 to 0.9

0.15

0.10

1.2 to 1.8
0.8 to 1.2
0.45 to 0.9

Cr

0.10

0.15 to 0.35

0.10

Zn Ti 0.10 _ 0.25 - 0.25 0.15 0.10 0.10

aluminum

rest
rest
rest
rest

example 1

Panels consisting of aluminum alloys of types 1100, 2024, 6061 and 6063 were ^{pickled in an aqueous solution of 45 g / l sodium hydroxide at 66 °} C. for 10 minutes. The pickling resulted in heavy deposition of dirt on the surface of the aluminum alloys. The soiled or stained panels were then rinsed with cold water and immersed in aqueous solutions, which were dissolved in water at room temperature in the following amounts of 7.5, 15.0, 30.0, 120.0 and 240.0 g / l were obtained:

Table 1

component Weight percent Sodium bisulfate
Ferric sulfate
Sodium fluoride
Magnesium carbonate ... 70
25th
3
2

The solutions obtained had the compositions given in Table 2:

• solution H Table 2 of the components (g / l NaI- Ι NaHSOj 0.044 l'e 0.23 Ο, 102 Concentration of the 5.25 0.088 concentration 0.52 0.45 0.204 & i 10.5 0.175 1'C ₂ ISOJ., 1.05 0.9 0.407 7.5 21 0.35 1.88 2.09 1.8 0.815 15th 42 0.70 3.75 4.18 3.6 1.63 30th 84 1.40 7.5 8.35 7.2 3.25 60 168 15th 16.7 120 30th 240 60

During the immersion of the panels in the solutions given in Table 2, it was observed that whether hydrogen evolves, which indicates an attack on the metal. The observations are in the Table 3 reproduced:

Table 3

supply, d. H. within a period of 2 to minutes.

Example 2

The following solid concentrates were formed by mixing the specified ingredients:

<on7cntr; il pH S / l 125 C) 7.5 1.9 15.0 1.75 30.0 1.4 60.0 1.05 120.0 0.8 240.0 0.6

Extent of attack by the alloy concentrate

JJM

,Track
track
no
no
no
no

easy

no

no

no

no

no

6061

easy

track

no

no

no

no

6063

track
no
no
no
no
no

From Table 3 it can be seen that a concentration of at least 30.0 g / l is required. around to completely prevent the panels from being attacked by acid.

After immersion for 10 minutes, the panels were removed from the solutions and the amount of dirt removed is determined as a percentage. The results are shown in Table 4:

Table 4

pH dirt removed in "η des insiicsaml 6061 6063 ! ton rent nil (25 C) local filth 90 95 si 1.9 1100 y 2024 95 98 7.5 1.75 95 50 100 100 15.0 1.4 98 75 100 100 30.0 1.05 100 100 100 100 60.0 0.8 100 100 100 100 120.0 0.6 100 100 240.0 100 100

The observations show that at least 30 g / l of the concentrate are required to make the whole Remove dirt from all panels examined. It has been found, however, that there is a concentration from 120.0 to 240 g / l of the solid concentrate is required to completely remove the dirt of all alloys in the door through a continuous process in practically the shortest possible time

component

KHSO ₄
Fe ₂ (SO ₄ ).,
NaF
MgCO ₃

H ₂ NSO ₂ OH
Fe ₂ (SO ₄ I ₃
NaF
MgCO ₃

Sulfuric acid (98%)

Fe ₂ (SO ₄ I ₃

NaF

MgCO ₃

NaHSO ₄
Fe (NO ₃ J ₃ -9H ₂ O
NaF
MgCO ₃

NaHSO ₄

Ferric ammonium citrate

NaF

MgCO ₃

NaHSO ₄ .
Fe ₂ (SO ₄ I ₃
NaBF ₄
MgCO ₃

NaHSO ₄
Fe ₂ (SO ₄ I ₃
Na ₂ SiF ,,
MgCO ₃

NaHSO ₄
Fe ₂ (SOY ₃
NH ₄ F
MgCO ₃

Weight percent

72.5

22.9

2.8

1.8

65.7

28.6

3.4

2.3

49.3

42.3

5.1

3.3

57.5

38.3

2.6

1.6

50.5

45.8

2.2

1.5

70 25

70 25

70 25

Sheets made of aluminum alloys 1100, 2024, 6061 and 6063 etched in a solution of 45 g / l sodium hydroxide (98%) at 66C for 10 minutes, a thick layer of dirt formed on the surfaces of the panels. The dirty boards were carefully rinsed with cold water and dissolved in the solutions given in Table 5 below Concentrates A through H immersed at room temperature for 10 minutes. The crowd removed Dirt and the extent of the attack, if any, are in Table 5 Door each solution given. Each solution resulted in a complete removal of dirt from all Panels achieved without attack by the alloys.

Table 5

concentrate g / 1 % more distant
dirt Attack the A. 131 100 no B. 105 100 no C. 71 100 no D. 146 100 no E. 166 100 no F. 120 100 no G 120 100 no H 120 100 no

Example 3

Extruded pieces consisting of the aluminum alloys 6063 or 6351 were first cleaned in an alkaline cleaning agent in a concentration of 45 g / l water at a temperature of 60 ^° C. for 8 minutes; the detergent consisted of 70% borax, 17% tetrasodium pyrophosphate, 1% sodium gluconate and the remainder of a wetting agent. After cleaning, the aluminum parts were rinsed with cold water and etched in a solution of sodium hydroxide (98%) at a concentration of 60 g / l at a temperature of 54 ^° C. for 8 minutes. After the etching, the workpieces were rinsed with cold water and placed in a gently moving cleaning bath obtained by dissolving a granulated concentrate in water containing 70 percent by weight sodium sulfate, 25 percent by weight ferric sulfate, 3 percent by weight sodium fluoride and 2 percent by weight magnesium carbonate.

The granulated solid concentrate was used in an amount of 120 g / l and the solution was added.

ίο held 23.0 ⁰ C. The cleaning bath was made by dissolving 3180 kg of the dry powder concentrate in 26.498 liters of water. The workpieces were immersed in the solution for 15 minutes, removed from it, rinsed with cold water and then anodized.

After the solution was complete and during the cleaning process, the bath was continuously blown through moved by air. The cleaning bath was used continuously and it was usable for 7 months without having to refresh the solution. The tank containing the solution was made of acid solid steel, and after the long application; there was no attack by the tank. A complete ent Removal of dirt was noted on all extruded parts, and it could wedge Attack of the aluminum alloy can be detected at any time.

B e i s ρ i e 1 4

It became the minimum content of ferric ions. dc is required to attack the water site Ions on the alloys 2024 and 6063 to prevent ver, determined that from these Legic Existing cleaned panels were placed in aqueous * solutions at room temperature. di < Contained different amounts of sodium bisulfate and different amounts of ferric sulfate. A < Satisfactory inhibition was found when there was no attack on the immersed panels was put. Attack of the alloys was evidently evident either through the detection of a Ga «. development at the interface of the immersed egg

Board or by reducing the reflectivity of the board after immersion. Thieves Observations made for alloys 2024 and 6063 are shown in Tables 6 and 7, respectively

Table 6 Attack on an aluminum foil in 2024

NaHSO ₄
Conc 0.1 0.2 0.35 Fe ₂ (SO ₄ I ₃ Concentration ι 7.5 al 3.0 4.0 8.0 tration b easy no no no no g / l b b track 0.5 1.0 2.0 no no no 7.5 b b b no no no no no no 30.0 b b b no no no no no no 60.0 "b b b easy no no easy no no 120.0 b easy no 240.0 b b b

b = considerable.

Table 7 Attack on an aluminum foil 6063

NaHSOj 0.1 0.2 0.35 Conc b no no tration b b no "1 b b b 7.5 b b b 30.0 b b b '60, 0 120.0 240.0

Fe ₂ (SO ₄ ), concentration 7.5 g ¹

0.5 1.0 2.0 3.0 4.0 8.0 no no no no . no no no no no no no no b easy no no no no b easy track no no no b b b track no no

b = considerable.

Tables 6 and 7 show that at least for every 12 parts of acidic sodium sulfate one part of ferric sulfate is required. This corresponds to a hydrogen-ion to ferric-ion ratio of 0.359.

Example 5

The maximum permissible fluoride concentration in solutions was determined that had a sufficient Contains amount of hydrogen for quick cleaning and sufficient amount Ferri-ion to prevent corrosion by hydrogen ion, in a way that sodium fluoride until various cleaning solutions were added in small, increasing amounts a sufficient amount of fluoride was present to prevent the corrosion typical of fluoride on the test panels that were immersed in the cleaning solutions. The findings are shown in Table 8 refer to. In Table 8, the fluoride concentration given in grams per liter is the highest Fluoride content, after which a further addition of fluoride causes a fluoride attack on the body for each ratio of hydrogen ion to ferric ion concentration.

The cleaning used for these experiments

J5 solutions were given in a concentration of about 120 g / l produced, whereupon the sodium fluoride dissolved would. The "fluoride" corrosion was determined by the fact that that from the aluminum alloys 505; or 6061 existing panels were half immersed in the solutions. The corrosion was then determined by visual inspection.

The highest permissible ratio of fluoride to ferric ion concentration as a function of the ratio of hydrogen to ferric ion concentration is shown as curve AB in the drawing.

Table 8 Permissible fluoride content of the solutions

H ⁴ Fe ₂ (SO ₄ ), Fe *** NaF F. ratio F "/ Fe ⁴ ** NaHSO ₄ 0.926 9.2 2.57 0.96 0.435 H7Fc ** ⁺ 0.170 110.8 0.910 10.9 3.04 1.2 0.543 0.359 0.178 109.1 0.856 17.2 4.80 2.04 0.922 0.299 0.192 102.8 0.807 23.0 6.42 3.0 1.36 0.177 0.212 97.0 0.736 31.6 8.83 4.44 2.02 0.126 0.229 88.4 0.65 42.0 11.72 5.35 2.42 0.0831 0.206 78.0 0.60 48.0 13.40 4.82 2.185 0.0555 0.163 72.0 0.50 60.0 16.7 4.92 2.23 0.0447 0.134 60.0 0.333 80.0 22.3 5.64 2.55 0.030 0.115 40.0 0.167 100.0 6.84 3.10 0.015 0.110 20.0 0.000

1 sheet of drawings

Claims (1)

Patent claims: 1. Aqueous, acidic fluoride ions and an inorganic inhibitor containing solution, the S is practically free of chloride ions, for cleaning aluminum and aluminum alloys, characterized by a hydrogen ion concentration from 0.18 to 1.4 g / l, a ferric ion concentration from 2 to 17 g / l, a fluoride ion concentration of 0.4 to 3.3 g / l, a ratio of the hydrogen ion concentration to the ferric ion concentration of 0.03 to 0.36 and a ratio of the fluoride ion concentration to the ferric ion concentration, which is given by the curve AB Does not exceed values for the corresponding ratios of the hydrogen ion concentration to the ferric ion concentration. 2. Solution according to claim 1, characterized by a ratio of the fluoride ion concentration to the ferric ion concentration of not more than 0.2. 3. Solution according to claim 1 and 2, characterized by 0.7 g of hydrogen ions, 8.37 g Ferric ions and 1.6 g fluoride ions per liter of solution. 4. Solution according to claims 1 to 3, characterized by about 84 g of acid sodium sulfate, 30 g ferric sulfate, 3.6 g sodium fluoride and 2.4 g magnesium carbonate per liter of solution. 5. Means for producing an aqueous, acidic fluoride ion and an inorganic inhibitor containing solution, which is virtually free of chloride ions, for cleaning aluminum and aluminum alloys, characterized by a content of at least 0.6 percent by weight ionizable hydrogen, a ratio of hydrogen ions to ferric ions concentration of about 0.08 and a ratio of fluoride ion to ferric ion concentration of about 0.2. 6. Means according to claim 5, characterized in that there is at least one connection in each case of the following groups contains: acidic alkali metal sulfates, acidic ammonium sulfate, sulfamic acid, Nitric acid, sulfuric acid, ferric sulfate, ferric fluoride, ferric formic acid ester, ferric nitrate, Ferrous fluorosilicate and alkali metal fluoride, aluminum fluoride, ferrous fluoride, ferrous fluorosilicate, Ammonium fluoride, acidic alkali metal fluoride, acidic ammonium fluoride and / or alkali fluorate. 7. Agent according to claims 5 and 6, characterized by 70 percent by weight sodium bisulfate, 25 percent by weight ferric sulfate, 3 percent by weight sodium fluoride and 2 percent by weight a desiccant such as magnesium carbonate. 8. Liquid concentrate for producing an aqueous, acidic, fluoride ion and an inorganic one Solution containing inhibitor, which is practically free of chloride ions, for cleaning of aluminum and aluminum alloys, characterized by about 0.5 percent by weight Hydrogen, a ratio of hydrogen to ferric ions of about 0.08 and a ratio from fluoride to ferric ions of about 0.2. 9. concentrate according to claim, characterized in that that it contains at least one compound from each of the following groups: Sulfuric acid, nitric acid, hydrofluoric acid, ferric sulfate, ferric nitrate, ferrous fluorosilicate and sodium fluoride, ammonium bifluoride, hydrofluoric acid, ferric fluoride, aluminum fluoride. 10. Concentrate according to claims 8 and 9, characterized in that it is used as a source Part of the ionizable hydrogen contains at least one of the following compounds: a acidic alkali metal sulfate, an acidic ammonium sulfate and / or sulfamic acid. 11. Concentrate according to claim 8, characterized in that it consists essentially from 250 parts by weight of sulfuric acid (60 ° Be), 210 parts by weight of ferric sulfate, 25 parts by weight Sodium fluoride and 515 parts by weight of water. 12. A method for cleaning aluminum using the solution according to the claims 1 to 4, characterized in that oxygen is continuously passed through the solution will.