DE2237807C3 - Process for the production of micro-cracked chrome layers over intermediate layers - Google Patents

Description

The invention relates to a method for producing micro-cracked chorus layers over nickel, cobalt, Nickel-iron, nickel-cobalt, iron-cobalt intermediate layers, whereby the intermediate layers are made up first Baths containing ions of one or more of these metals, ammonium ions, chloride ions, at least an aromatic and / or aliphatic carboxylic acid or its salts and additionally at least 0.01 to 8 g / l contain a pyridine compound as a cracking additive, are deposited electrolytically and then the Chrome rails for the deposition of chrome layers With high internal stress and low elongation at break, conventional chrome baths are applied will.

In a known method of the type mentioned (US-PS 35 63 864) are in the interlayer baths very specific pyridine compounds. e.g. i, 2-bis- (i-pyndyiio) -ethane bromide, used. Regarding Corrosion resistance coatings that meet the highest demands can be achieved in this way cannot be achieved.

The invention has the object / igruncle that Process of the type mentioned at the beginning result in cracked chrome layers with a particularly high number of cracks and, at the same time, optimal crack distribution.

This means that covering layers that meet the highest demands in terms of corrosion resistance can be achieved.
The invention consists in that

-, isonicotinic acid hydrazide, pyridine-3-carbinol,

Pyridine-4-aldehyde, L-nicotine,
1 (3-pyridyl) -2- (4-pyridyl) ethylene.
4-pyridyl acrylic acid and / or pyridine-3-aldoxime

in used as cracking additives in the interlayer baths will.

The invention also relates to a bath for the electrolytic deposition of the intermediate layers, which the respective metal ions, ammonium ions,

ι-, chloride ions, at least one aromatic and / or aliphatic carboxylic acid or its salts and additionally 0.01 to 8 g / l of at least one pyridine compound contains as a cracking additive, which is characterized in that it contains the aforementioned pyridine compounds

.'D has bonds as cracking additives

The advantages achieved by the invention can be seen in the fact that when using the described Interlayer baths coatings are achieved that meet the highest demands in terms of corrosion resistance.

r> chen suffice.

The following is a basic working scheme for the process according to the invention specified:

A nickel bath of the composition

100-400 g / l,

preferably 220 g / l Ni Cl ₂ ■ 6 H ₂ O,
20-200 g / l,
preferably 80 g / l NH ₄ OOCCHj,

with organic cracking agents of the concentration specified below, with or without the addition of usual brighteners?. to improve gloss and with or without non-foaming wetting agents for pore-4 (i contraception is used with the following working conditions:

PH value

(set with HCI)

Current density

1 - 6, preferably 3 - 4

to 30, preferably

5- 15 A / dm ²
Temperature 20-70, preferably

40-45 ⁰ C
Exposure time 10 see-10 min,

preferably '. up to 3 min

With subsequent chrome plating in a sulfuric or mixed acid electrolyte, depending on the chrome layer thickness and working conditions of the chrome baths you get up to 1500 cracks per cm.

The following substances and concentrations can be used as organic cracking agents:

a) Isonicotinic hydrazide
0.1-0.3 g / l (up to 5 g / l),

b) pyridine-3-carbinol

0.4 g / l

(up to 5 g / l),

c) pyridine-4-aldehyde

0.2-0.4 g / l

(up to 5 g / l),

d) L-nicotine
0.2-0.4 g / l
(up to 5 g / l),

e) 1 - (3-pyridyl) -2- (4-pyridyl) ethylene
0.1 g / l

(up to 2 g / l),

f) 4-pyridyl acrylic acid
0.4 g / l

(up to 8 g / l),

g) pyridine-3-aldoxime
0.2-0.4 g / l

(up to 5 g / 1).

The following specific examples illustrate the result.

example 1

g / l NiCl ₂ -6 H ₂ O ₁ 60 g / l NH ₄ OOCCH ₃ , adjust to pH 3.5 with hydrochloric acid, 0.4 g / l 3-pyridinecarbinol with or without 1 ml / 1 butyn-2-diol -1, 4 with or without ml / 1 wetting agent, commercially available.

temperature
Current density
Exposure time
Crack density

35-45 ° C
5-15 A / dm ²
30 seconds to 10 min
up to 1500 cracks / cm

acid, citric acid, as well as organic additives from the series of pyridine derivatives to achieve extreme high tensile stresses with very low elongation at break.

attachment

The comparison tests described below were used to demonstrate technical progress carried out, whereby instead of lengthy and id costly corrosion test microscopic Evaluations of the crack network were made. According to the relevant prior art is namely an increased number of cracks is synonymous with improved corrosion protection.

Test depositions were made on brass-plated steel strips with a defined angle and a surface area of 0.7 dm ² . For this purpose, after a corresponding pre-cleaning, the tapes were placed in a customary bright nickel bath at 3.5 A (flowing) and a temperature of 58 ° C for ten minutes and then for 1.5 minutes at 6 A (flowing) and a temperature of 25 ° C or 40 ° C exposed to the bath of the following composition, which is usual for the generation of high-tension nickel deposits:

Example 2

g / l NiCI ₂ -OH ₂ O, 80 g / l NH ₄ OOCCH ₃ , adjust to pH 3-4 with hydrochloric acid, 0.2 g / l isonicotinic acid hydrazide with or without 1 ml / 1 butyn-2-diol-1, 4 with or without 1 ml / 1 mesh center ?, commercially available.

temperature
Current density
Exposure time
Crack density

5-15 A / dm ²
30r-c up to 10 min
up to 1500 cracks / dm

Example 3

g / _{l NiCI 2} , 50 g / l citric acid, 45 ml / l concentrated ammonia, pH 3.0 - 4.0 adjust with hydrochloric acid or ammonia, 0.1 g / l isonicotinic acid hydrazide with or without 1.0 ml / l Butyn-2-diol-1,4 with or without 2.0 ml / 1 wetting agent, commercially available.

temperature
Current density
Exposure time
Crack density

35-45 ° C
5-15 A / dm ²
30 see-10 min
up to 1500 cracks / cm

Example 4

g / l NiCl ₂ -OH ₂ O, 100 g / l NH ₄ OOCCH ₃ , adjust to pH 3.5 with hydrochloric acid, 0.4 g / l 4-pyridyl acrylic acid with or without 1.5 ml butyne-2-diol 1.4 with or without 1.5 ml wetting agent, commercially available.

Temperature 35-50 ⁰ C

Current density 5-15 A / dm ²

Exposure time 30 seconds-10 min

RiD density up to 1500 cracks

se / cm

In addition to nickel, which is usually in the form of chloride, but also partially or completely as sulfamate, sulfate, boron fluoride, Fluoride, citrate and acetate can be present, the electrolytes contain salts of aromatic and aliphatic carboxylic acids, like ζ. Π. of acetic acid, tartaric acid, phthalic

220 g / l Nickel chloride NiCI ₂ 6 H ₂ ( 30 g / l Am monium acetate approx. 25 ml / 1 Glacial acetic acid 1-2 ml / 1 Brightener z. B. 0.4 g / l butynediol 0.5-1.0 ml / 1 commercial wetting agent (foam-free) PH value 4.0

In some cases, an additional 0.25 g / l isonicotinic acid hydrazide was added to the last-mentioned bath. At a Part of the steel strips treated in this way, the nickel layers were subjected to etching, to make the crack formation visible, using an etchant of the following composition became:

35 g / l NaOH,

35 g / l K ₃ Fe (CN) ₆ ,

temperature

Treatment time

90-95 ⁰ C
2 min

The other part of the steel strips was then placed in a common chrome electrolyte chromed:

Exposure time
temperature
Current (flowing)

4 min
48 ° C
8A

In order to better recognize the formation of cracks, the chrome layers were also coated with the aforementioned etchant 15 see etched.

For measuring the cracks which, at 300x magnification, both in brightfield and in If the dark field was carried out, the steel strips were straightened beforehand and measuring points 1 to 4 set.

Measuring point 1: 5 mm from the face

Measuring point 2: 20 mm from the face.

Measuring point 3: 34 mm from the front.

Measuring point 4: 39 mm from the front.

22nd shine Chip g / l iso- etching Ver 37 807 MeQpunkic 2 3 4th nickel potential nicotine- chro about 450 350-450 350-450 The following table shows the results: rich acid- mung 600-700 650-700 about 1000 sample Ni hydrazide X Cr- 1 350-450 about 350 300-350 X 25 ° C X Etching area 450-500 500-550 about 550 600-700 X 25 ° C 0.25 - 600-650 100-200 - - X 25 ° C X 350-450 about 500 about 450 about 550 5 1 X 25 ° C 0.25 X X about 500 about 100 - _ la X 40 ° C _ X - - 200-250 300-350 250-300 300-400 2 X 4O ⁰ C 0.25 _ - X about 450 2a X 40 ° C - X X 100-200 3 X 40 ° C 025 X - 300-400 3a - 4th X 4a X

In a further experiment, the process according to US Pat. No. 3,563,864 was reproduced. It was with Except for the deviations indicated below in the same way as for the previous ones Ver / ahren described comparative experiments. The tension-filled nickel deposit was with the following Bath generates:

240 g / i NiSO ₄ ■ 6 H ₂ O,

40 g / l NiCI ₂ 6 H ₂ O,

40 g / l H ₃ BO ₃ ,

0.2 g / ll, 2-bis (l-pyridylio) ethane bromide,
Working conditions 4.3 A / dm ² , 60 ° C

Exposure time 3 min

The subsequent chrome plating was carried out as follows:

25OgZlCrO ₃ ,

2.5 g / l H ₂ SO ₄ ,

5 mg / 1 Na ₂ SeO ₄ .

Working conditions 15 A / dm ² , 38 ° C

Exposure time 4 min

Surprisingly, no crack formation at all could be observed on the chromium layers obtained in this way will.

As a result, the method according to the invention is unambiguous to the methods known in the prior art

in superior.

Claims (2)

Patent claims: 1. Process for the production of micro-cracked chrome layers over nickel, cobalt, nickel-iron, nickel-cobalt, iron-cobalt intermediate layers, where first the intermediate layers of baths, which contain ions of one or more of these metals, Ammonium ions, chloride ions, at least one aromatic and / or aliphatic carboxylic acid or their salts and additionally 0.01 to 8 g / l of at least one pyridine compound as a cracking additive included, are deposited electrolytically and then the chromium layers are made for the Deposition of chrome layers with high internal stress and low elongation at break is common Chrome baths are applied, thereby characterized that isonicotinic acid hydrazide, pyridine-3-carbinol, pyridine-4-aldehyde, L-nicotine, 1 (3-pyridyl) -2- (4-pyridyl) -ethylene, 4-pyridylacrylic acid c and / or pyridine-3-α-doxime as cracking additives the interlayer baths are used. 2. Etad for the electrolytic deposition of intermediate layers by a method according to Claim 1, which the respective metal ions, ammonium ions, chloride ions, at least one aromatic and / or aliphatic carboxylic acid or its salts and additionally 0.01 to 8 g / l contains at least one pyridine compound as a cracking additive, characterized in that it Isonicotinic acid hydrazide, pyridine-3-carbinol, pyridine-4-aldehyde, L-nicotine, 1 (3-pyridyl) -2- (4-pyridyl) -ethylene, 4-pyridyl acrylic acid and / or pyridine-3-aldoxime as cracking additives.