DE1008542B - Chromic acid electrolyte - Google Patents

Description

GERMAN

The invention relates to an electrolyte for producing chromium coatings from an aqueous one Chromic acid solution.

Chromium baths have already been proposed, which contain silicofluorides as a radical foreign acid. Chromic acid electrolytes are also known which contain silicon fluorides in conjunction with strontium sulfate. The latter composition is intended to provide a self-regulating setting of the guide content at a certain level Cause CrOg concentration.

It has now been found that, unexpectedly, there is a surprising improvement in electrolytic properties Chromium deposition from aqueous solutions through the use of aromatic sulfonic acids or their Salts as a key component was achieved. The improvements achieved, for example, with a chrome plating bath the following composition:

CrO ₃ 250 g / l

C ₆ H ₄ (SO ₃ H) ₂ 40 g / l

under the following operating conditions:

Temperature 45 ° C

Cathodic current density 15 A / dm ²

Anodic current density 10 A / dm ²

Air injection approx. 0.5 m ³ / h

resulted in surprisingly good effects with regard to the depth effect. In addition, one was perfect Bud-free and burn-free precipitation increases with extremely long exposure times record.

With the same bath composition, hard, strong chrome coatings could be obtained under modified operating conditions. A hard chrome layer with a thickness of 200 μ and a hardness of 1050 ° Vickers was achieved at a temperature of 55 ° C., a cathodic current density of 50 A / dm ² and when air was blown in at 0.5 m ³ / h. Here, too, a surprisingly good depth effect and metal distribution was achieved, as well as a bud-free and smooth surface on edges and tips.

In order to be able to recognize the effectiveness of this bath even more clearly, comparative tests were carried out made in the Hull cell with chromic acid electrolytes of the following, known composition:

CrO ₃ 325.0 g / l

SrSO ₄ 9.7 g / l

K ₂ SiF ₆ 26.0 g / l

It was found that with a normal chrome plating time of 3 minutes in the Chromium bath according to the invention, the cathode sheet was completely provided with a chrome coating, while Chromic acid electrolyte

Applicant:

Dr. W. Kampschulte & Cie.,
Solingen, Schützenstr. 66-70

Dipl.-Chem. Dr. Leopold Bosdorf,
Düsseldorf-Oberkassel,

Karl Küll, Solingen,

and Adolf Schwedhelm, Düsseldorf,

have been named as inventors

In the tests with the known chrome bath, the cathode sheet is covered to 65% in the most favorable case was.

Another improvement has been made by using a chromic acid electrolyte other than aromatic Sulphonic acids still added silicon fluorides. The addition of silicon fluorides achieves that Power interruptions during electrolysis, gloss and adhesion of the deposited coatings are not influence. This is important; because power interruptions occur especially in mass chrome plants when rolling the items to be electroplated. CaI-ciumsilikofluorid have proven to be the most advantageous and potassium silicofluoride proven.

Another essential advantage of the aromatic sulfonic acids and the alkaline earth or alkali metal silicofluorides as catalytic lead components for chromic acid electrolytes is that these compounds can be added to the bath in excess. Due to the low degree of dissociation or the low. Solubility automatically sets the optimum catalytic conductivity at a certain CrO _{3 concentration.}

example 1

CrO ₃ 230 g / l

C ₆ H ₅ SO ₃ Na 35 g / l

K ₂ SiF ₆ 2 g / l

Example 2

CrO ₃ 250 g / l

C ₈ H ₄ (SOs) ₂ Ni 35 g / l

709 509/352

3 4

Example 3 O

CrO ₃ 280 g / l II

C ₆ H ₅ SO ₃ H 40 g / l R ₁ -SOR ₂

Example 4 s -L

ρ xT ³ / c 'Λ ·)' Mi 3 S e71, where R _{1 is} a ring system and R _{2 is} a

CaSiF ^{3 represents} 1 l / l hydrogen atom or a metal atom.

⁶ 2. electrolyte according to claim 1, characterized in that

lo draws that he also has hydrofluoric acid or their alkali and alkaline earth salts

Claims (1)

Patent claims: holds. 3. Electrolyte according to claim 2, characterized marked 1. Chromic acid electrolyte with self-regulating features that the salts of the silicofluoride Conductive salts, characterized in that they are more acidic than the solubility catalytically active component corresponds to a compound of these salts in the chromium bath, keep the general formula. © 70S 509/352 5. 57