Baths and processes for electrodepositing palladium

A process for electrodeposition of palladium is described wherein an electroplating bath comprising a palladium(II) compound is employed which electroplating bath is ammonia-free. The bath contains water and an amine of the formula ##STR1## wherein x=0 or 1 and when x=0: ##STR2## and when x-1: R.sup.1 =N(CH.sub.3) (CH.sub.2).sub. 3 NH.sub.2, NH(CH.sub.2).sub. 2 NH.sub.2, NH(CH.sub.2).sub. 2 NH(CH.sub.2).sub. 3 NH.sub.2, NH.sub.2, OH or C.sub.1-4 -alkoxy, R.sup.2, R.sup.3, R.sup.4 =H or CH.sub.3. The amine permits the electrodeposition of palladium at a current density above 2.5 A/dm.sup.2 and the resultant coatings are semi-glossy to glossy and are characterized by firm adhesion and freedom of pores. The coatings have only low internal tensions.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the use of an amine together with a palladium(II) 
compound for an ammonia-free, aqueous bath for electrodepositing palladium 
coats. 
2. Discussion of Prior Art 
German Patent 23 60 834 describes a bath for electrodepositing palladium 
coatings which bath contains palladium as complex with an amine of the 
general formula 
EQU NH.sub.2 --(CH.sub.2 CH.sub.2 NH).sub.n --CH.sub.2 CH.sub.2 NH.sub.2 with 
n.gtoreq.3. 
From this bath, at current densities between 0.1 and 2.5 A/dm.sup.2, 
glossy, palladium coatings, free of cracks and pores, can be deposited. 
During galvanizing, the pH of the bath remains constant, and in contrast 
to the slightly ammoniacal baths containing palladium as amine complexes 
no harmful vapors result. 
German Offenlegungsschrift 26 57 925 likewise describes an ammonia-free, 
aqueous bath for electrodepositing palladium. The bath contains palladium 
as diglycin palladium(II) complex and aminoacetic acid as complex former. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide amines for use together with 
palladium(II) compounds for ammonia-free, aqueous baths which can be 
operated also at current densities above 2.5 A/dm.sup.2 and give firmly 
adhering, pore-free and tension-free palladium coatings. It is also an 
object of this invention to provide a process for electrodepositing 
palladium from these baths. 
These objects are achieved according to the invention, by using an amine of 
the general formula 
##STR3## 
wherein x=0 or 1 and when x=0: 
##STR4## 
and when x=1: 
R.sup.1 =N(CH.sub.3)(CH.sub.2).sub.3 NH.sub.2, NH(CH.sub.2).sub.2 NH.sub.2, 
NH(CH.sub.2).sub.2 NH(CH.sub.2).sub.3 NH.sub.2, NH.sub.2, OH or C.sub.1-4 
-alkoxy, 
R.sup.2, R.sup.3, R.sup.4 =H or CH.sub.3 together with a palladium(II) 
compound for an ammonia-free, aqueous bath for electrodepositing palladium 
as a coating at a pH of 6 to 11, a temperature of 20.degree. to 70.degree. 
C. and a current density of 0.1 to 30 A/dm.sup.2. 
Besides 1-(2-aminoethyl)piperidine and 4-(2-aminoethyl)morpholine, there 
are used as amines in particular N,N,2,2-tetramethyl-1,3-diaminopropane, 
2,2-dimethyl-1,3-diaminepropane, N,N-dimethyl-1,3-diaminopropane, 
N-(2-aminoethyl)-1,3-diaminopropane, N-methyl-bis-(3-aminopropyl)-amine, 
N,N'-Bis-(3-aminopropyl)-1,2-diaminoethane, 
N,N,2,2-tetramethyl-3-aminopropanol, 2,2-dimethyl-3-aminopropanol, 
3-methoxy-propylamine and 3-butoxypropylamine. 
Preferred palladium(II) compounds are PdCl.sub.2, Pd(OH).sub.2, K.sub.2 
[Pd(NO.sub.2)].sub.4, Pd(NH.sub.2 SO.sub.3).sub.2, Pd(NH.sub.3).sub.2 
CL.sub.2 and Pd(NH.sub.3).sub.2 (NO.sub.2).sub.2. 
Preferably, the palladium concentration is 6-20 g/l and the amine is used 
in an amount which corresponds to a molar ratio of amine to palladium of 1 
to 1 to 3 to 1. 
Besides amines and palladium(II) compounds, the usual and known per se 
additions such as conducting salts, buffer salts, wetting agents and 
brighteners are used. 
The surprising advantage of the amines used according to the invention lies 
in the possibility of being able to operate the so-obtained ammonia-free, 
aqueous baths also at high current densities. Thus, the baths can be used 
also with processes that require a high rate of deposition, e.g. in tape 
galvanizing and in selective galvanizing. 
They furnish semiglossy to glossy palladium coatings that are of firm 
adhesion and free of pores and have only low internal tensions. 
The coatings are suitable for industrial purposes, electrical contacts for 
example, as well as for decorative purposes, jewelry for example. 
In the examples that follow, the preparation of baths using the said amines 
is described and the conditions for electrodeposition of palladium 
coatings from these baths are given. 
Adjustment of the pH of the baths is made with a suitable basic compound, 
preferably with the amine used, or with an acid, preferably with one whose 
anions are already present in the bath. pH adjustment can be effected by 
the addition of a base such as K.sub.3 PO.sub.4 or KOH. 
Alternatively, if necessary, an acid such as HCl, HNO.sub.3, H.sub.3 
PO.sub.4 or NH.sub.2 SO.sub.3 H can be employed. Salts can be included in 
the ammonia-free aqueous electroplating bath. These salts include: 
NaNO.sub.3, K.sub.2 SO.sub.4, KCl, KH.sub.2 PO.sub.4, potassium citrate, 
Na.sub.2 SO.sub.4 or K.sub.2 HPO.sub.4. Some of these salts can be 
employed for pH adjustment.

The examples which follow will serve to illustrate the invention without, 
however, limit it. 
EXAMPLE 1 
To the solution obtained from an aqueous solution containing 10 g/l Pd as 
K.sub.2 [Pd(NO.sub.2).sub.4)] and 60 ml/l 
N-(2-aminoethyl)-1,3-diaminopropane, 30 g/l NaNO.sub.3 and 5 g/l potassium 
citrate are added. 
At a pH of 8.9, 60.degree. C. and 20 A/dm.sup.2, firmly adhering, glossy, 
finger-insensitive palladium coats are deposited. 
EXAMPLE 2 
To the solution obtained from Pd(NH.sub.3).sub.2 Cl.sub.2 in an amount 
corresponding to 10g/l Pd, 20 ml/l 
N,N'-bis-(3-aminopropyl)-1,2-diaminoethane and water, 20 g/l NH.sub.2 
SO.sub.3 H and 20 g/l Na.sub.2 SO.sub.4 are added. 
At a pH of 7, 50.degree. C. and 5 A/dm.sup.2, firmly adhering, semiglossy 
palladium coatings are deposited. 
EXAMPLE 3 
To the solution obtained from an aqueous solution containing 10 g/l Pd as 
Pd(NH.sub.2 SO.sub.3).sub.2 and 30ml/l 
N,N,2,2-tetramethyl-1,3-diaminopropane, 25 g/l NH.sub.2 SO.sub.3 H are 
added. 
At a pH of 8.1, 50.degree. C. and 5 A/dm.sup.2, firmly adhering palladium 
coatings are deposited. 
EXAMPLE 4 
To a solution obtained from Pd(OH).sub.2 in an amount corresponding to 10 
g/l Pd, 10 ml/l 2,2-dimethyl-1,3-diaminopropane and water, 10 g/l KH.sub.2 
PO.sub.4 are added. 
At a pH of 7.5 60.degree. C. and 5 A/dm.sup.2, firmly adhering, semiglossy 
palladium coatings are obtained. 
EXAMPLE 5 
To a solution obtained from an aqueous solution containing 10 g/l Pd as 
Pd(NH.sub.2 SO.sub.3).sub.2 and 60 ml/l 2,2-dimethyl-3-aminopropanol, 35 
g/l Na.sub.2 SO.sub.4 are added. 
At a pH of 8.1, 50.degree. C. and 5 A/dm.sup.2, firmly adhering palladium 
coatings are deposited. 
EXAMPLE 6 
To a solution obtained from an aqueous solution containing 10 g/l Pd as 
K.sub.2 [Pd(NO.sub.2).sub.4 ] and 25 ml/l 
N-methyl-bis-(3-aminopropyl)-amine, 30 g/l K.sub.2 HPO.sub.4 are added. 
At a pH of 7.2, 60.degree. C. and 10 A/dm.sup.2, well adhering, glossy 
palladium coatings are deposited. 
EXAMPLE 7 
To the solution obtained from an aqueous solution containing 10 g/l Pd as 
Pd(NH.sub.2 SO.sub.3).sub.2 and 40 ml/l 3-methoxypropylamine, 75 g/l 
K.sub.2 SO.sub.4 are added. 
At a pH of 7, 50.degree. C. and 5 A/dm.sup.2, well adhering palladium 
coatings are deposited. 
EXAMPLE 8 
To a solution obtained from Pd(NH.sub.3).sub.2 Cl.sub.2 in an amount 
corresponding to 10 g/l Pd, 30 ml/l 4-(2-aminoethyl)-morpholine and water, 
30 g/l KCl are added. 
At a pH of 8.2, 50.degree. C. and 5 A/dm.sup.2, semiglossy palladium coats 
are deposited. 
EXAMPLE 9 
To the solution obtained from Pd(NH.sub.3).sub.2 Cl.sub.2 in an amount 
corresponding to 10 g/l Pd, 25 ml/l 1-(2-aminoethyl)-piperidine and water, 
40 g/l KCl are added. 
At a pH of 7.8, 50.degree. C. and 5 A/dm.sup.2, semiglossy palladium 
coatings are deposited.