DE1290410B - Aqueous, acidic fluoride ions and an inorganic inhibitor containing solution, which is practically free of chloride ions, and processes for cleaning aluminum and aluminum alloys - Google Patents

Description

It is from "Chemisches Zentralblatt", vol. 1950/11, p. 2119: Referat über die USA.-Patent 2507314 (Aluminum Co. of America), and Jg. 1959, p. 12 686: Report on the French patent specification 1 120 749 (Georgette W a r η a η t) known acidic aqueous solutions for pickling aluminum chromic acid, Add chromates or dichromates as inhibitors. It is also from the USA patent 2 655 439, in particular claims 5, 6, 7, 9 and 10, of French patent specification 1 146 482, 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 767 888 and French patent specification 1,119,649 (American Chemical Paint Co.) known acidic solutions for cleaning aluminum, the Contain fluoride ions and an inorganic inhibitor (CrCfe or hexavalent Cr compounds), to use and that such fluoride ions and an inhibitor containing solutions are only traces of halogen ions (except F-Ioneri) may contain.

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

It has been found that, surprisingly, instead of chromium compounds, ferric ions are used as the inhibitor in aqueous solutions containing acidic fluoride ions that 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 containing solutions, which 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 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 does not exceed the values given by the curve AB for the corresponding ratios of the hydrogen ion concentration to the ferric ion concentration.

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 in an aqueous solution is shown graphically; 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 is 0.083ί. Because the highest possible concentrations of both hydrogen ions and fluoride ions in the solutions are desired to be one Achieving the fastest possible removal of stains from aluminum or aluminum alloys are solutions with a fluoride to ferric ion concentration of not more than 0.2, which is close to the maximum ratio, is desirable and also offers a margin of safety against corrosion.

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 that contain considerable 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.

The maximum permissible amount of fluoride ions in the solution also depends, according to curve AB in the drawing, on the ratio of the hydrogen ion concentration to the ferric ion concentration. The ferric ion must be in an amount of.

at least 2 g are present; 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.

If 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 of 0.03 in question, at 23.9 ° C, defatting occurs in about 10 minutes. The ferric ion content is preferably around 8 g / l _? and the preferred ratio of hydrogen to ferric ion concentration is about 0.084.

Since the ferric ions are reduced to ferrous ions, the solution can be used for longer the higher the starting ferrite ion content. When working with the preferred iron content and preferred hydrogen-ferric ion concentration ratio can a solution for an un-

interrupted 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 as the sole source of ferric ions, because for Achieving 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 can be characterized by about 0.2.

It has also been found that it can be used for carrying out the method 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 obtained what is easier than a chemical treatment of the solution with a liquid or is solid oxidizer; however, clogging can occur after prolonged use of the bath an oxidizing agent become necessary.

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 can. It follows from U.S. Patent 2,828,193. that the known solutions contain about 2.3 weight percent 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 metalworking 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 from each of the following groups: acidic alkali metal sulfates, acid ammonium sulfate, sulfamic acid, nitric acid, sulfuric acid, ferric sulfate, ferric fluoride, Ferric formic acid ester, ferric nitrate, ferric fluorosilicate and alkali metal fluoride, aluminum fluoride, Ferrifluoride, ferrifluorosilicate, ammonium fluoride, acidic alkali metal fluoride, acidic ammonium fluoride and / or alkali fluoroborate.

Sulfuric acid or nitric acid is expediently absorbed on other solid components so that the mixture is dry and solid.
Sodium sulphate is preferably used as the agent producing hydrogen ions; the 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 is preferably 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 desiccant such as magnesium carbonate.

A liquid concentrate contains at least one compound from each of the following groups: sulfuric acid, Nitric acid, hydrofluoric acid, ferric sulfate, ferric nitrate, ferrous form, ferrous fluoride, ferrous fluorosilicate and alkali metal fluoride, aluminum fluoride, ferrous fluoride, ammonium fluoride, ferrous fluorosilicate, Alkali metal fluoroborates, ammonium fluoroborate, acidic alkali metal fluorides, acidic ammonium fluoride and hydrofluoric acid.

Ferric sulfate or ferric nitrate is used as the preferred source of the ferric ion. Such a concentrate can also contain at least one of the following compounds as a source of part of the ionizable hydrogen: 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 sulfamic acid, sodium bisulfate and ammonium bisulfate. Any source of hydrogen ion that needs to be dissolved, however, will lower the solubility of the concentrate for the other required ingredients.

The concentration of the ionized or ionizable hydrogen in the liquid concentrate is generally 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 of sodium fluoride and 515 parts by weight of water.

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

The aluminum alloys of types 1100, 2024, 6061 listed in the following examples and 6063 had the following composition

Si

Cu

Mn Mg

Cr

Zn

Ti

aluminum

1100 2024

1.0 Si + Fe
0.50 I 0.50

0.20

3.8 to 4.9

0.05

0.30 to 0.9 1.2 to 1.8

0.10

0.10
0.25

rest
Resi

continuation

Type Si Fe Cu Mn 0.15
0.10 Mg Cr Zn Ti aluminum 6061
6063 0.40 to 0.8
0.20 to 0.6 0.7
0.35 0.15 to 0.40
0.10 0.8 to 1.2
0.45 to 0.9 0.15 to 0.35
0.10 0.25
0.10 0.15
0.10 rest
rest

example 1

Made of aluminum alloys of types 1100, 2024, 6061 and 6063 existing panels were placed in an aqueous solution of 45 g / l sodium hydroxide Pickled 66 ° C for 10 minutes. The pickling resulted in a heavy deposition of dirt on the surface 15 sodium bisulfate of aluminum alloys. The stained or stained panels were then washed with cold water rinsed and immersed in aqueous solutions made by dissolving in water at room temperature

the following quantities of 7.5, 15.0, 30.0, 120.0 and 240.0 g / l were obtained:

Table 1 Weight percent component 70 Sodium bisulfate 25th
3 Ferric sulfate 2 Sodium fluoride Magnesium carbonate

The solutions obtained had the compositions given in Table 2:

Tabel

Concentration of the solution NaHSO ₄ H Concentration of the components (g / l) Fe NaF F. 5.25 0.044 Fe ₂ (SO ₄ I ₃ 0.52 0.23 0.102 7.5 10.5 0.088 1.88 1.05 0.45 0.204 15th 21 0.175 3.75 2.09 0.9 0.407 30th 42 0.35 7.5 4.18 1.8 0.815 60 84 0.70 15th 8.35 3.6 1.63 120 168 1.40 30th 16.7 7.2 3.25 240 60

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

Table 3 Table 4

concentrate pH Extent of attack on the alloy 2024 6061 6063 gi (25-C) 1100 easy. easy track 7.5 1.9 track no track no 15.0 1.75 track no no no 30.0 1.4 no no no no 60.0 1.05 no no no no 120.0 0.8 no no no no 240.0 0.6 no

55

60

From Table 3 it can be seen that a .Konzentration of at least 30.0 g / l is required to completely prevent acid attack on the panels.

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:

pH Dirt removed - present in% of the total 6063 concentrate (25 C) Filth 95 g'l 2024 98 1.9 1100 50 6061 100 7.5 1.75 95 75 90 100 15.0 1.4 98 100 95 100 30.0 1.05 100 100 100 100 60.0 0.8 100 100 100 120.0 0.6 100 100 100 240.0 100 100

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 shortest time practically possible for a continuous process, d. H. within a period of 2 to 10 minutes.

Example 2

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

concentrate component KHSO ₄ Weight percent A. Fe ₂ (SOA 72.5 NaF 22.9 MgCO ₃ 2.8 H ₂ NSO ₂ OH 1.8 B. Fe ₂ (SO ₄ I ₃ 65.7 NaF 28.6 MgCQ ₁ 3.4 Sulfuric acid (98%) 2.3 C. Fe ₂ (SO ₄ I ₃ 49.3 NaF 42.3 MgCO ₃ 5.1 NaHSO ₄ 3.3 D. Fe (NO ₃ I ₃ ■ 9H ₂ O 57.5 NaF 38.3 MgCO ₃ 2.6 . NaHSO ₄ 1.6 E. Ferriammonium citrate 50.5 NaF 45.8 MgCO ₃ 2.2 NaHSO ₄ 1.5 F. Fe ₂ (SQi) ₃ 70 NaBF ₄ 25th MgCO ₃ 3 NaHSO ₄ 2 G Fe ₂ (SO ₄ I ₃ 70 Na ₂ SiF ₆ 25th MgCO ₃ 3 NaHSO ₄ 2 H Fe ₂ (SO ₄ I ₃ 70 NH ₄ F 25th MgCO ₃ 3 2

concentrate g / l % more distant
dirt Attack of the board 5 D 146 100 no E. 166 100 no F. 120 100 ■ no G 120 100 no ίο Η 120 100 no

35

40

Panels made of aluminum alloys 1100, 2024, 6061 and 6063 were etched in a solution of 45 g / l sodium hydroxide (98%) at 66 ^° C. for 10 minutes, a thick layer of dirt forming on the surfaces of the panels. The soiled panels were carefully rinsed with cold water and immersed in solutions of the concentrates A to H given in Table 5 below at room temperature for 10 minutes. The amount of soil removed and the extent of attack, if any, are given in Table 5 for each solution. With each solution, complete removal of the dirt from all panels was achieved without attacking the alloys.

Table 5

concentrate 131
105
71 % more distant
dirt Attack of the board A.
B.
C. 100
100
100 no
no
no

Example 3

Extruded pieces consisting of the aluminum alloys 6063 and 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 cleaning agent 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 etching, the work pieces were rinsed with cold water and placed in a weakly held in movement cleaning, which was obtained by dissolving a granular concentrate in water containing 70 weight percent sodium sulfate, 25 weight percent ferric sulfate containing 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 maintaining the solution at 23.0 ⁰ C. The cleaning bath was made by dissolving 3180 kg of the dry powder concentrate in 26.4981 of water . The workpieces were immersed in the solution for 15 minutes , removed therefrom, rinsed with cold water and then anodized.

After the solution had taken place and during the cleaning process, the bath was constantly agitated by blowing air through it. The cleaning bath was used continuously and it was usable for 7 months without the need to replenish the solution. The tank containing the solution was made of acid-proof steel, and no attack on the tank was evident after long-term use. Complete removal of the soil was observed on all of the extruded parts and no attack on the aluminum alloy could be observed at any time.

Example 4

The minimum content of ferric ions required to prevent the hydrogen ion from attacking the alloys 2024 and 6063 was determined by placing the various amounts of cleaned tablets made of these alloys in aqueous solutions at room temperature Contained sodium bisulfate and various amounts of ferric sulfate . A satisfactory inhibition was observed when no attack on the immersed panels was put festzu. Attack of the alloys was evident either through the detection of gas evolution at the interface of the immersed panel or through a reduction in the reflection

909510/1197

10

Property of the board after immersion. The observations made for alloys 2024 and 6063, respectively are given in Tables 6 and 7, respectively.

Table 6 Attack on an aluminum foil in 2024

NaHSO *
iionwn— 0.1 0.2 0.35 Fe ₂ (SOY ₃ concentration - 7.5 g / l 1.0 2.0 3.0 4.0 8.0 tration b easy no no no no no no g / l b b track 0.5 no no no no no 7.5 b b b no no no no no no 30.0 b b b no easy no no no no 60.0 b b b easy b b easy no no 120.0 b 240.0 b

b = considerable.

Table 7 Attack on an aluminum foil 6063

NaKSQ, 0.1 0.2 0.35 Fe ₂ (SO _{4 I 3} concentration - 7.5 g / l 1.0 2.0 3.0 4.0 8.0 Conc b no no no . no no no no tration
gil b b no 0.5 no no no no no 7.5 b b b no easy no no no no 30.0 b b b no easy track no no no 60.0 b b b b b b track no no 120.0 b 240.0 b

b = considerable.

Tables 6 and 7 show that at least for every 12 parts of acid 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 containing sufficient hydrogen to achieve rapid cleaning and sufficient ferric ion to prevent corrosion by hydrogen ion was determined in the manner that sodium chloride was added to various cleaning solutions in small, increasing amounts until a sufficient amount of fluoride was present to produce the corrosion typical of a fluoride on the test panels that were immersed in the cleaning solutions. The findings are shown in Table 8. In Table 8, the fluoride concentration given in grams per liter is the highest fluoride content after which a further addition of fluoride resulted in a "fluoride" attack on the alloy for every ratio of hydrogen ion to ferric ion concentration.
The cleaning solutions used for these experiments were prepared in a concentration of about 120 g / l, whereupon the sodium fluoride was dissolved. The "fluoride" corrosion was determined by immersing half of the panels made of aluminum alloys 5052 and 6061 in the solutions. The corrosion was then determined visually

The highest allowable 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.

Tabslla 3 Permissible fluoride content of the solutions

K ⁺ ε Fe, (SO ₄ ) ₃ Ί Fe ^{++ +} NaF F ~ relationship F7Fe ⁺ * ⁺ 0.926 9.2 2.57 0.96 0.435 H * / Fe ⁺⁺⁺ 0.170 nut 0.910 10.9 3.04 U 0.543 0.359 • 0.178 109 ,! 0.856 17.2 4.80 2.04 0.922 0.299 0.192 ! 02.8 0.177

continuation

H ⁺ g / l Fe ₂ (SO ₄ I ₃ Fe ^{++ +} NaF F- relationship F ^ ZFe ^{++ +} NnHSO ₄ 0.807 23.0 6.42 3.0 1.36 H ⁺ ZFe ^{++ +} 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 0.006

Claims (1)

Patent claims: 1. Aqueous, acidic fluoride ions and one Inorganic inhibitor-containing solution, which is practically free of chloride ions, for cleaning of 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 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 that is practically free of chloride ions. for cleaning aluminum and aluminum alloys characterized by eiiH'B 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. Center! 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, Ferrifluorosilicate and alkali metal fluoride, aluminum fluoride, ferrifluoride, ferrifluorosilicate, 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 preparing 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 8, characterized in that there is at least one in each case Compound of the following groups contains: sulfuric acid, nitric acid, hydrofluoric acid, Ferric sulfate, ferric nitrate, ferric fluorosilicate and sodium fluoride, ammonium bifluoride, hydrofluoric acid, Ferrifluoride, 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 sulphate, an acidic ammonium stilfate and / or sulphamic acid. 11. Concentrate according to claims, characterized in that it consists essentially of 250 parts by weight of sulfuric acid (60 ° B4), 210 parts by weight of ferric sulfate, 25 parts by weight of sodium fluoride and 515 parts by weight of water. 12. Process for cleaning aluminum inn using the solution according to claims 1 to 4, characterized in that oxygen is continuously passed through the solution. 1 sheet of drawings