DE1621151B2 - Process for the galvanic production of a micro-cracked chrome coating on intermediate nickel layers - Google Patents

Description

The invention relates to a method for the galvanic production of a micro-cracked chrome coating on intermediate nickel layers, which are optionally applied to a previously galvanically deposited metal layer, with a galvanic electroplating at a maximum bath temperature of 35 ⁰ C and a current density between 1 and 15 A / dm ^{2 prior to chrome plating} Nickel intermediate layer is applied with the aid of an aqueous, acidic nickel bath, which is known for its main component nickel chloride, nickel sulfamate or nickel fluorate, which additionally contains acetic acid, nickel acetate, gluconic acid, nickel gluconate, tartaric acid, nickel tartrate, formic acid, nickel formate, malonic acid, nickel malonate, lactic acid, citric acid Contains nickel citrate, succinic acid, nickel succinate, ammonium acetate or mixtures thereof, according to patent 14 96 974.5.

According to the teaching of the main patent, the baths contain essentially cracked nickel layers a nickel salt of a strong acid, such as nickel chloride, and a nickel salt of a weak one Acid, such as acetic, gluconic, tartaric, formic, malonic, citric or succinic acid. To the To reduce manufacturing costs of such baths and the cost of dragged-out bath components to reduce, attempts have been made to achieve a cheaper composition of these baths.

According to the invention, this object is achieved in that the nickel salts of the strong acids are added to the nickel bath a part and the nickel salts of the weak acids in whole or in part by ammonium or alkali salts the corresponding acids are substituted.

Are advantageous as ammonium or alkali salts

ίο the strong acids chlorides, fluoborates, sulfamates and Sulphates of sodium, potassium and ammonium or mixtures of at least two of these salts are selected. The ammonium or alkali salts of the weak acids are beneficial sodium, potassium and Ammonium salts of gluconic, tartaric, malonic, formic, lactic, citric and succinic acids as well the sodium and potassium salts of acetic acid or mixtures of at least two of these salts.

It is noteworthy that by changing the concentration of the components of the bath, in particular the proportion and type of weak acid, a closer or wider association of the Networks can be reached, to which the cracks are composed. The density of the cracks leaves sicfi also vary by changing the pH of the bath and the bath temperature. Furthermore, the Change in the content of dissolved nickel to achieve variable values of the current density, so that in Depending on the facilities available and the shape of the parts to be treated, the most economical Bath for the production of the micro-cracked chrome layers can be put together can.

From US-PS 23 51966 an electrolyte bath is

J5 is known to contain nickel chloride and nickel acetate. With A nickel layer should help this bath at a bath temperature of preferably between 55 and 65 ° C fine grain structure, good appearance and high toughness. So exist to present invention no points of contact. On the one hand, there are none with the known electrolyte bath cracked nickel interlayers are deposited and on the other hand the teaching is not given for reasons the economic viability of partially replacing the nickel salts with ammonium or alkali salts.

The replacement of ammonium or alkali salts of strong or weak acids with nickel salts same acids is in Gray / Dettner "Modern Electroplating Metal Deposition", 1957, page 280, paragraph 3 and 4. There is thus a reverse substitution to the present invention, with it alone is about adding chloride ions to the bathroom. These chloride ions have the task of improving the Anode solubility, higher permissible cathodic current density, smoother, finer-grained, harder and stronger Precipitation, less tendency to form pores, needles, etc. too. Especially the statement »lesser The tendency towards the formation of pores shows that a purpose contrary to the present invention is being sought will.

Finally, reference is made to FR-PS 8 30 993, which describes an electrolyte bath, the nickel chloride, formic acid and contains sodium chloride. Here, too, efforts are made to produce thick, homogeneous and tension-free coatings

h5 ge. You get this result by keeps the electrolyte bath slightly acidic by means of organic acids such as formic acid. In addition, the bath temperature is close to the boiling point

temperature.

Examples of bath compositions and process conditions for electroplating a micro-cracked chrome coating on intermediate nickel layers are listed below, with the The figures given are to be regarded as approximate values:

Example I.

Nickel chloride nickel acetate ammonium chloride pH value current density temperature duration

Density of cracks

Example Il

Nickel chloride gluconic acid ammonium chloride ammonia current density temperature duration

Density of cracks

150 g / l

50 g / l

120 g / l

1 to 10 A / dm ²

25 ° C

1 min.

about 300 cracks per cm

200 g / l

100 g / l

150 g / l

up to pH 3.5

Ibis 15 A / dm ²

25 ° C

1 min.

about 500 cracks per cm

Example III

Nickel chloride

Ammonium acetate

Ammonium chloride

PH value

Current density

temperature

duration

Density of cracks

Example IV

Nickel chloride

Ammonium acetate

Ammonium chloride

PH value

Current density

temperature

Density of cracks

Example V

Nickel chloride

Sodium acetate

Sodium chloride

PH value

Current density

temperature

Density of cracks

150 g / l

50 g / l

120 g / l

3.5 to

Ibis 10 A / dm ²

25 ⁰ C

1 min.

about 700 cracks per cm

150 g / l

50 g / l

120 g / l

3.5 to

1 to 15 A / dm ²

35 ° C

about 500 cracks per cm

150 g / l

50 g / l

150 g / l

Ibis 10 A / dm ²

25 ° C

about 300 cracks per cm

All the baths mentioned are compatible with suitable brighteners, as already indicated in the main patent are.

Claims (3)

Patent claims: 1. A process for galvanic production of a micro-cracked chromium coating on nickel intermediate layers are optionally applied to a previously electrodeposited metal layer, with before the chromium plating galvanically at a Badhöchsttemperatur of 35 ⁰ C and a / dm 1-15 A ² lying current density, a nickel intermediate layer With the help of an aqueous, acidic nickel bath, known per se in the main constituent nickel chloride, nickel sulfamate or nickel fluorate, which additionally contains acetic acid, nickel acetate, gluconic acid, nickel gluconate, tartaric acid, nickel tartrate, formic acid, nickel formate, malonic acid, nickel malonate, lactic acid, nickel lactate, citric acid Contains succinic acid, nickel succinate, ammonium acetate or mixtures thereof, according to patent P 14 96 974, characterized in that in the nickel bath the nickel salts of the strong acids are partly and the nickel salts of the weak acids entirely or partly by ammonium m- or alkali salts of the corresponding acids are substituted. 2. The method according to claim 1, characterized in that the ammonium or alkali salts strong acids chlorides, fluoborates, sulfamates and sulfates of sodium, potassium and ammonium or mixtures of at least two of these salts can be selected. 3. The method according to claim 1 and / or 2, characterized in that the ammonium or alkali metal salts of the weak acids sodium, potassium and ammonium salts of the gluconic, tartaric, malonic, Formic, lactic, citric and succinic acid as well as the sodium and potassium salts of acetic acid or mixtures of at least two of these salts can be selected.