DE1247116B - Process for the regeneration of aqueous, acidic chromating solutions - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

in the. Cl ,:

C23f

German ία .: 48 d I - 7/26

Number:
File number:
Anrnctdclag:
Auskgctag:

A 32784 VI h / 48 dl
3rd September 1959
tO. August 1967

The present invention relates to a method of repairing aqueous, acidic Chrotna transmission solutions for education voo pejra-free Coatings on aluminum. Aluminum is not only understood to mean metal, but rather it s this also includes the alloys in which aluminum lter main ingredient is.

It is known that decorative and corrosion-resistant, chemically bonded over aluminum surfaces can be obtained by treating the surface with aqueous, acidic solvents which, as essential components, contain fluoride, hexavalent chromium ion, phosphate and hydrogen ions. The known solutions, which are usually used, generally contain 0.15 to IV g / l of fluorocarbon, 2 to 60 g / l of sedimentary carbon (calculated as CrOJ or 2 to 285 g / l of phosphate (calculated) PO ₄ ) OiW have a pH of 0.8 to 4.5.Solutions of this type are described, for example, in British patents *> 632 102,632097 and 708937.

Ee is known to be the essential ingredients soldier solutions bra prolonged use of the solutions become exhausted and therefore need to be refreshed from time to time when the solutions are theirs Should retain the ability to negotiate.

Provided that the essential components of the coating solution are refreshed within are kept within the given limits, produce such excess resolution (c) even after prolonged use Coatings are not designed to be finely corrosive. If you do, »Ic mciit crfordcrlkh, the sifting out of the coatings remain gletchffirmtg should, it does not matter, the above-mentioned essential considerations "Divide the transfer from time to tent-" Tufrish and within the given limits hold, it is then also necessary to dnfiii to be careful that the concentration mi so-called active fluqrid held on a komtantca HlAe will. DitMConztntraticm an active Huorid * <in regardless of the absolute amount of total Fluoride, «'debes In the solution voilianden in. How the concentration of active fluoride measured «, ■ can be grounded, is in the British patent specification «03 405 described. «S

However, even if the concentration of active fluoride is regulated in a known manner, the coatings produced are not entirely satisfactory, in addition to their appearance. Although they are resistant to corrosion and are essentially uniform in color, there is a tendency that, after prolonged use and refreshing of the objects, processes for regenerating aqueous,
acidic chrutnationitSsungea

Register

Amchcm Product Inc, Ambler, Pa, (V. St. A.)

Represent

Drying. A. van der Wcrtfa, patent attorney,

Hamburg 90. Wiljtorfer S ». 32

Named as inventor:

Nctson James Nomhard, Jr., Orcland, Pe .;

David Ycats Dollman,

Lassdale Mounted Route, Pa. (V. Si. A.)

Claimed priority:
V. St. ν. America September 24, 1958
(762932)

the coatings are affected by a build-up of powder will. This powdery Ablofening forms I got on top of the coating and deteriorated thus not its corrosion resistance, but its appearance and its color binding properties. This formation of powdery chemicals bi thus a considerable disadvantage, and the object of the present invention is to provide powder-free coatings enable.

It has been found that the formation of powdery coatings can be attributed to the accumulation of other cations, in particular aluminum ions, in the water. In addition to the aluminum ions, however, other ions accumulate in the solutions, in particular the ions of the other alloy components and those ions that are brought in when the solutions are refreshed, and these ions can also be used to reverse the coatings, under the conditions prevailing in practice ^^ conditions, these ions tend to precipitate as insoluble sake on the Alumlaiumoberfichen, and thus give rise m to the surface vcrschmulzcndcn dci over the course of powdery deposits.

In order to be able to produce powder-free coatings even after prolonged use of the coating solutions,

ttffiOtSit

3 4

it is therefore necessary to collect an accumulation of sol- This was shown by the following comparison experiment

chen cations in the coating solution via a still exhibited:

allowable maximum amount to be removed. A bath was made from 14.8 g of CrO ₃ , 39.3 ml of H ₃ PO ₄

use of cation exchange resins for (75%) and water to make up to 11 made,

this purpose is obvious, but it was found that 5 0.25 g of aluminum as A1 (H _O PO ₄ ) ₃ was added,

that although such ion exchangers were successful and the solution was exchanged by a cation

Can be used to remove cations, such as sodium, seeing resin at a rate of

Potassium, ammonium and trivalent chromium ions, lÖÖ ml / min, conducted. The refresher solution and

to remove, they are unable, the concentration of the effluent were both based on active fluoride content

of aluminum ions in those strongly acidic, phosphorous tested (see German patent specification 1112 370); included

Phosphate solutions below the allowable maxi- must be an increase in the activity of the drain

to lower the value of about 1 g / l. via the refreshment solution an intake of

It has now been found that it is possible to display the aluminum through the cation exchanger

Concentration of aluminum ions in such areas. (The bath drainage also became the chemical one

train solutions at or below the still permissible 15 analysis to ensure the accuracy of the values

Upper concentration limit of 1 g / l thereby to confirm for active fluoride.) The results

hold that an exceeding excess showed that aluminum by the cation exchange

of aluminum ions in the form of potassium sodium shear.

fluoaluminate is precipitated. This precipitation can cause a second bath like the first,

by causing the coating solution to contain 3.39 g of NH ₄ FHF, and

Appropriate amounts of potassium and sodium ions as previously checked. While the active fluoride levels

to be absorbed. indicates a very low uptake of aluminum

Since it is predominantly aluminum ions which are th, no uptake was found when the ca-

accumulate in the coating solutions in an interfering manner, ion-exchanging resin from an acidic elution

may have been exposed to sodium and potassium 25 due to this addition. A third bath has been prepared

ions an improvement can already be achieved, like the second one, but with 1.0 g of aluminum in place

but this makes the elimination of others more troublesome of 0.25 g. The results confirmed those of the

Cations in the solution not yet reached in the second bath.

Conversely, the accumulation of other cations will The drain from the third bath was through the thereby increased even more. However, it has been found to pass 30 column used for the first bath. The Erdass these other cations in sufficient quantities showed that the fluoride-containing effluent was from by means of a cation-exchanging resin, essentially the whole of the third bath is created can be removed. The solution according to the invention hinders the cation exchanger from the first bath The task at hand thus requires the combined omitted aluminum absorption. These results are double-use both measures to both the 35 gene that although a cation exchange resin Aluminum ions as well as the other cations to aluminum in the absence of fluoride from a solvent. sung, it cannot do so in the presence of

The subject of the invention is thus a process fluoride can do, probably because aluminum

to regenerate aqueous, acidic chromatic and fluorine ions form an anionic complex,

Solution solutions for the formation of powder-free overburden 40 According to the present invention, therefore, there are two

trains on aluminum, such chromating various measures being applied at the same time,

solutions containing 0.15 to 12.5 g / l fluoride ions, 2 to namely, it becomes a cation-exchanging agent

60 g / l hexavalent chromium, calculated as CrO ₃ and resin, and on the other hand, sodium

Contains 2 to 285 g / l phosphate, calculated as PO ₄ , and potassium ions are added to the bath to take care of this

and have a pH of 0.8 to 4.5, aluminum dissolved from the solution in the form of a catalyst

ion-exchanging resin are passed, whereupon an insoluble alkali fluoaluminate is precipitated. A

the sodium and potassium ion solutions in such bath refreshing procedures, wherein

Amounts are added that aluminum cations by adding sodium and potassium aluminum in

precipitated as alkali fluoaluminates, form of sodium and / or potassium fluoaluminate

if the concentration of aluminum ions in the 50 is precipitated, is already the subject of the older pa-

Solution exceeds 1 g / l. tentes 1 096 712. In this older process,

In the older patent application (German interpretation but no cation exchanger additionally used 1194 674) is already a process for del, which is considered essential for the achievement of the ange-regenerate became known of the success aimed for by chromating solutions. In addition, in beat, which is characterized by the fact that the older patent excludes alkali as a permanent stock the chromating solutions that interfere with the part of the solution added from the start, and the Enriching cations with the help of a cation out-alkali content is constantly maintained. Derntauschers be removed, the addition of Η-ions min- opposite is according to the invention the addition of alkali only at least one more that does not interfere with the chromating - if necessary, carried out when the alumides and / or the desired concentration of 60 ions in the chromating bath has a predetermined limit cation in such a proportion that the value exceeds and only in such an amount, fresh chromating solution when passing through such as to reduce the aluminum ion concentrations through the exchanger is required even after prolonged contact. Samzeit in the coating solution remains in the effective pH range. It thus became firmly established in the method according to the invention made that when regenerating strongly acidic 65 no alkali ions. The inventively used phosphate and fluoride-containing solutions, so the cathode cation exchanger will not penetrate either ion exchanger is not able to load the alumi- added alkali ions, but remains free to remove nium ions to the extent necessary. for the removal of the other interfering cations.

1 247

The cation becomes enausiauscher in its function by intentionally added alkali ions if the conditions according to the invention are adhered to for this Alkali addition not affected.

The dissolved aluminum is precipitated in the form of elpasolite (K _{2 NaAlF 0} ), which is a potassium sodium fluoride aluminate which contains 2 moles of potassium and 1 mole of sodium for every mole of aluminum. The minimum amount of potassium and sodium to be added to the solution is therefore 2 moles of potassium and 1 mole of sodium for every mole of aluminum present in the solution. However, amounts of either potassium and / or sodium in excess of these minimum amounts are not detrimental because, as a result of the use of the cation exchange resin, any excess will be absorbed by the resin and hence there will be no undesirable accumulation of potassium and sodium ions in the bath.

Nevertheless, an addition of potassium and / or sodium is of course in excess of what is necessary Minimum amount a waste of both the alkali metals and the cation exchanging Resin.

Since the molar ratio of potassium and sodium in Elpasolit is 2, the potassium should be preferred and sodium to the solution in a molar ratio of 1.9 to 2.1, preferably 2, added will.

A portion of the solution is preferably withdrawn continuously, via the cation-exchanging process Resin passed and returned to the bulk of the solution.

Of course, the cation-exchanging resins have to be regenerated in a known manner will.

The potassium and sodium ions are preferably added to the solution in the form of their fluorides, and in particular in the form of a mixture of 1 mol of sodium fluoride and 2 mol of potassium fluoride. It was found that the fluoride activity of the solutions is kept constant with such an addition, so that The coatings produced not only adhere tightly and are corrosion-resistant and powder-free, but also one have uniform color.

For a better understanding of the invention, the following comparative tests are also given.

example

A coating solution totaling 8 liters was made with the following ingredients and concentrations manufactured according to the following approach:

Hydrogen fluoride (HF) 2.18 g / l

(= 2.07 g / l F)

Chromic acid (CrO ₃ ) 14.20 g / l

Phosphoric acid (H ₃ PO ₄ ; 100%) 67.00 g / l

(= 64.95 g / l PO ₄ )

The solution produced in this way produced an etching on aluminum test pieces of 45.4 mg / 0.093 m ² with a half hour immersion time at 46 ° C. The solution was then divided into two parts, each of 4 liters, called bath A and bath B. .

Both solutions were heated to about 46 ° C, and separate rows of like aluminum specimens were treated successively in each bath for 5 minutes. During the whole treatment time a portion was continuously withdrawn from each bath, passed over a cation exchange resin and returned to the bathroom. Refreshing the baths in relation to the chromic acid and phosphoric acid content, if necessary, was carried out in the usual manner.

The fluoride ion concentration in bath A was at a substantially constant value periodic addition of hydrogen fluoride kept.

o Bath B, on the other hand, was periodically analyzed to determine the concentration of dissolved aluminum and its fluoride gel was then replenished by adding 1 mole of sodium fluoride and 2 moles of potassium fluoride to the bath for every mole of dissolved aluminum present. Initially, Baths A and B both produced excellent coatings. However, after a number of test pieces (equivalent to about 0.93 m ^{2 of} aluminum) had been treated, the coatings of Bath A, although uniform in color, became extraordinarily powdery. In contrast, Bath B continued to operate satisfactorily, producing not only uniformly colored but also powder-free coatings even after 7.44 m ^{2 of} aluminum had been treated. Periodic measurements showed that the etching power of Bath B remained essentially constant. After Bath A was used to treat 1.86 m ^{2 of} aluminum, another test was carried out. The bath was analyzed for the presence of dissolved aluminum and it then contained 2 grams of aluminum per liter. A precipitate was formed by adding 3.12 g of sodium fluoride and 8.6 g of potassium fluoride to the bath. Subsequent analysis showed that the aluminum had been essentially completely removed from the solution and was certainly less than 1 g / l. Etchability measurements taken before and after the addition of sodium fluoride and potassium fluoride showed that the addition did not increase the fluoride activity of the bath. Test pieces of aluminum subsequently treated in the bath received excellent powder-free coatings.

Claims (4)

Patent claims: 1. Process for the regeneration of aqueous, acidic chromating solutions for the formation of powder-free coatings on aluminum, such chromating solutions containing 0.15 to 12.5 g / l of fluoride ions, 2 to 60 g / l of hexavalent chromium, calculated as CrO ₃ and 2 to 285 g / l phosphate, calculated as PO ₄ , and have a pTTvöri 0.8 to 4.5, are passed over a cation-exchanging resin, since you rch geken "nz" eTc h net that sodium and potassium ions be added to the solutions in such amounts that aluminum catalysts are precipitated as alkali fluoaluminates if the concentration of aluminum ions in the solution exceeds 1 g / l. 2. The method according to claim 1, characterized in that the potassium and sodium ions in a molar ratio of 1.9 to 2.1, preferably 2, are introduced. 3. The method according to claim 1 or 2, characterized in that the potassium and sodium ions be added periodically as soon as 7 8 the concentration of aluminum ions is 1 g / l. 5. Method according to one of the preceding reaches or exceeds. Claims, characterized in that the 4. The method according to one of the preceding lium and sodium ions as fluoride salts zjuge- Claims, characterized in that a part is set, continuously withdrawn from the solution, via the 5 Cation Exchange Resin Headed and Re-Considered Older Patents: is returned. German Patent No. 1194 674. 709 620/514 7.67 © Bundesdruckerei Berlin