US3825478A - Electrolyte and method for electrodepositing microporous chromium-nickel composite coatings - Google Patents

Abstract

AN AQUEOUS NICKEL ELECTTROPLATING BATH SOLUTION COMPRISING NICKEL IONS, A BATH SOLUBLE NITROGEN CONTAINING COMPOUND AND A BATH SOLUBLE METAL SALT WHICH IN THE BAHT WILL PRODUCE A METAL CONTAINING CATION WHOSE PH PRECIPITATION POINT IS LOWER THAN THAT OF THE PH PRECIPITATION POINT OF NICKEL IN SAID BATH.

Description

nited States Patent 3,825,478 ELECTROLYTE AND METHOD FOR ELECTRO- DEPOSITING MICROPOROUS CHROMIUM- NICKEL COMPOSITE COATINGS Richard J. Clauss, Allen Park, Thaddeus W. Tomaszewski, Dearborn, and Henry Brown, Huntington Woods, Mich., assignors to Oxy Metal Finishing Corporation, Warren, Mich. No Drawing. Filed Oct. 30, 1972, Ser. No. 302,170 Int. Cl. C23b 5/08, 5/50 US. Cl. 204-41 46 Claims ABSTRACT OF THE DISCLOSURE aqueous nickel electroplating bath solution comprising nickel ions, a bath soluble nitrogen containing compound and a bath soluble metal salt which in the bath will produce a metal containing cation whose pH precipitation point is lower than that of the pH precipitation point of nickel in said bath.

BACKGROUND OF THE INVENTION In previous cases, such as US. Pats. 3,152,971; 3,'152,- 972 and 3,152,973, it was disclosed that by dispersing certain very fine, bath-insoluble, essentially non-conductive particles such as aluminum oxide, titanium oxide, silicon dioxide, barium sulfate and the like in semi-bright and bright nickel plating baths, a multitudinous density of these particles was co-deposited, and that the subsequent thin, decorative chromium plate deposited on such composite nickel plate was made microporous. As a result of the consequence of the microporosity of the chromium plate, greatly improved corrosion protection of the underlying nickel plated metal resulted. This process occurs because the anodic corrosion currents in the pores of the microporous chromium plate are of much lower current density than if only the usual pores were present.

U.-S. 3,428,441 describes a composite metal coating wherein a nickel deposit is placed on top of a nickel substrate where a particle thickness of 0.0030.05 mils and containing LOGO-1,000,000 particles per square inch is obtained using various metallic salts such as aluminum trichloride, magnesium chloride and the like. In depositing the microporous structure, no solids are introduced. Further, the patentee describes electrodepositing a thin strike such as 0.0000050 of an inch onto a substantial nickel base which has solids in that electrodeposited nickel base.

Other patents which relate to electrodeposition of nickel for corrosion protective purposes are US. 3,449,223; 3,- 061,525, German Patent Specifications 2,045,890 and l,- 204,49l. German Patent Specification 1,000,311 describes obtaining a satin nickel finish wherein a salt of strontium is employed. British Patent Specification 1,074,389 describes obtaining a nickel plate with a tellurium compound present.

SUMMARY OF THE INVENTION It has been found that a bright nickel electrodeposit can be obtained from aqueous nickel solutions such as acidic nickel solutions when the bath contains bath soluble metallic salts wherein the metal containing cations of the salts have a precipitation point under the pH precipitation point of nickel in the nickel electroplating batth and further containing a bath soluble nitrogen containing compound such as an amine. When a bath of this nature is electrolyzed, thereby depositing nickel in a thickness generally greater than about 0.15 mil and the deposit is subsequently used as a substrate for the electrodeposition of a thin decorative chromium plate of at least about 0.01 mil thickness, greatly improved corrosion protection is obtained.

3,825,478 Patented July 23., 1974 DESCRIPTION OF PREFERRED EMBODIMENTS The invention pertaining to this case is directed to a means of imparting corrosion protection to a metallic substrate by electrodepositing a bright nickel deposit onto the substrate and subsequently electrodepositing a thin chromium deposit thereon.

Nickel is electrodeposited onto the metallic substrate such as copper, zinc, steel, iron and the like. The metallic substrate that may be employed can be on top of a plastic such as polyvinyl chloride, polyvinylidene chloride, polypropylene, polyethylene, a acrylonitrile-butadiene-styrene (ABS) and the like. The metal is deposited onto the plastic substrate, normally pretreated by sensitizing the plastic substrate with a noble metal activating material such as that described in US. Pat. 3,011,920 or 3,672,938 and the like.

The nickel bath that may be employed in the present case is a normal aqueous acidic nickel electroplating bath containing nickel brighteners which are normally organic nickel brighteners. The nickel plating bath normally has a pH from about l-'5 and even more preferably about 25. The nickel is introduced into the nickel bath normally as a bath soluble salt such as the sulfate, chloride, sulfonate, fluoroborate or bromide and the like. Preferably nickel chloride and sulfate are used. The amount of nickel chloride that may be employed ranges from about 30- 300 grams per liter, preferably about 60 grams per liter while the nickel sulfate is employed in a range from about 100400 grams per liter, preferably about 225 grams per liter.

The temperature of the bath that may be employed in the present invention is one ranging from about 76- 170 F. preferably about -150 F.

It is to be appreciated that the nickel bath may contain appreciable quantities of cobalt, for example, up to at least as high as 50% cobalt which may be contained in the nickel containing electroplated layers. Portions of the nickel deposit can also be an iron-nickel alloy, prepared in accordance with US. Ser. 'No. 268,348, filed July 3, 1972, now abandoned. Preferably, however, it is desirable that the nickel containing electroplate be as pure nickel as possible.

The plating baths that may be employed in the present invention also contain other components such as wetting agents to prevent pitting, buffers such as boric acid, formic acid and the like.

The cathode current density of the plating baths ranges from about 5 to 200 amps per sq. ft. -(a.s.f.), while the anodic current density ranges from about 10 to 30 amps per sq. ft.

The metal containing cations that are introduced into the bath, in order to induce porosity in the bright nickel electroplate, are those that will have a pH precipitation point below that of nickel in the nickel electroplating bath. The precipitation point of any metal containing cation depends not only on the concentration of the hydroxyl ions but also the concentration of nickel. In other words, the lower the concentration of nickel, the higher will be the precipitation point for nickel. Stated otherwise, the bath soluble metal salt when in the solution produces a trivalent or tetravalent metal-containing cation in an amount of at least about 0.001 g./'1. to about 0.05 g./l. whose precipitation occurs at a pH which is lower than that of the nickel in the solution. Generally, the bath soluble metal salts that are introduced into nickel electroplating bath are those that are selected from Periodic Table Groups HI, V, and VI. The cations that may be employed are metal containing cations, wherein the metal may be aluminum, chromium, thallium, thorium, vanadium, uranium, lanthanum, or the various oxygenated metal cations such as uranyl, vanadyl and the like. Of the above enumerated cations the preferred metal containing cations are those that contain aluminum or chromium ions.

The nitrogen containing compound that may be employed in the present invention is preferably a bath soluble amino compound. A preferred amino compound is one containing the group of formula I.

Formula I )g( )1. wherein A preferred amino group is that of formula II,

Formula II *Rf' N(ERA) wherein R and A are as defined above;

R" is selected from the group consisting of hydrogen,

s is to 3; t is 0 to 3 and s+t=3; m is from 1 to 10, preferably 1 to 4; and v is from 1 to 20, preferably 1 to "10, provided that s is not 3 when R" is hydrogen.

J LCHaOH 14a (HO O C-CHz) r-N-CHa-C Hn-N-CHz-CHz-N-(CHzCOOH),

Hr-COOH HO O C-CHzNHzi HO OC-CHnNHCHs;

H0O C-(CHaM-NHa;

HzP(O)( )zl Also useful are polyalkylenimine derivatives obtained by polymerizing a compound of the formula,

wherein X and Y may be hydrogen, lower alkyl or hydroxy substituted lower alkyl; and Z may be hydrogen, lower alkyl, hydroxy substituted lower alkyl, or cyano substituted lower alkyl, wherein alkyl is preferably 1 to 3 carbon atoms. The most preferred material is polyethylenimine. For other polyalkyleneimines, see US. 3,393,135.

It is to be appreciated that the acids that may be employed in the bath may be used as are expressed above i.e., as acids or may be employed as bath soluble salts such as the ammonium or the alkali metal salts thereof, such as, sodium or potassium, and the like.

When alkyl or alkylene is used above, it is preferred to use one containing 1 to 6 carbon atoms. When aryl is used above it is preferred to cover phenyl or naphthyl; alkylene as in polyoxyalkylene and hydroxy substituted polyoxyalkylene normally refers to lower alkylene, preferably from 2 to 4 carbon atoms. By alkylene is meant a saturated alkylene.

Using the nickel plating bath composition of the present invention, and employing the Dubpernell copper plating tests for estimation of the porosity of the decorative chromium plate deposited on above described bright nickel, a porosity count is obtained for a thickness of 0.15 mil nickel of as high as 10,000 pores per square inch, while for a thicker nickel plate it is much higher than this figure. When 0.3-0.5 mil of the nickel plate was used, the porosity count on the decorative chromium plate was often higher than 300,000 pores per square inch. In general with the additives of the present invention, the microporosity subsequently developed in the decorative chromium plate can reach about 60,000 pores per square inch without any appreciable dulling in the bright nickel deposit of 0.15 mil to about 2 mil thickness. For surfaces which have round contours, the pore count in the chromium can reach about 100,000 per square inch without serious dullness with a thickness of nickel of 0.15 up to about 2 mils.

The particular advantages of the present invention is that there is no requirement to have a separate bright nickel bath containing added dispersed fine bath insoluble non-conducting particles for the deposition of a thin (to avoid dulling) bright nickel plate containing co-deposited multitudinous fine particles on top of a thicker regular nickel plate of about 0.15- mil to about 2 mil thickness.

This latter method of employing particles will induce high microporosity in the final decorative chromium plate, but cannot be used in some automatic plating machines which have no provision or room for an additional nickel bath containing added dispersed fine particles.

If a water soluble aluminum or chromium salt such as the chloride, sulfate, fiuoborate or sulfamate is used without the aforementioned bath-soluble amino compounds such as EDTA (ethylene diamine tetra-acetic acid and its sodium, potassium, lithium, magnesium, iron, nickel or cobalt salts), asparagine, etc., then no beneficial results are obtained. In fact, harmful burning (lowered limiting cathode current density) can result if the concentration of aluminum or chromium ions in the nickel bath reaches about 0.5 g./l. and higher. Also without the regulating effects derived from the presence of the amino compounds, especially the amino compounds having acid groups, the formation of excessively large colloidal hydrophilic particles of aluminum and chromium hydroxides or their basic salts can cause visible unsightly speckling in the bright nickel deposits. It is mainly for this reason that the presence of aluminum and chromium salts in acidic nickel baths as foreign materials are considered impurities and are filtered out of the bath at pH values of about 3.5 to 5.5. Aluminum can enter the nickel baths when aluminum articles are nickel plated and some parts fall off the plating racks into the nickel baths. Chromium can enter a nickel bath from faulty plating racks that are cycled through nickel and chromium plating baths. In any case, with the usual filtration used with bright nickel baths, these ions are removed from the bath as hydroxides when the nickel bath pH is about 3 to 5.5.

In this invention, however, water-soluble salts of aluminum and chromium and other metal cations described above are purposely added and their concentration is maintained at an effective value by controlled continuous addition or by additions at regular intervals during plating, since it appears that a colloidal bath insoluble salt is slowly formed, these metal cations are continuously removed by filtration of the nickel solution.

Practically all bright solutions are filtered, and usually on a continuous basis. This is especially required for airagitated or mechanically agitated nickel baths. These methods of agitation are also the best methods to keep the colloidal hydroxides or basic salts of these metal cations dispersed as colloids in the nickel baths. The filtration which is necessary for the removal of contamination from air-borne dirt, particles from anodes and the like, also removes the colloidal particles formed as hydroxides or basic salts of the metal cations such as aluminum, chromium and others described above. The polyvalent cations can be present as low as 2 milligrams per liter while the concentration of the amino compound can be as low as 50 milligrams per liter and still provide an appreciable increase in the microporosity in the decorative chromium plate when the underneath bright nickel plate obtained from the baths containing these small concentrations of additives is in the upper thickness range of about 0.5- mils.

The average concentration used of the metal cations present in the nickel plating bath usually ranges from about 1 to 50 milligrams per liter, and the amino compound is used at about 0.5 to grams per liter (g./l.) when nickel plating thicknesses of 0.15 mil to 0.5 mil are employed and somewhat lower for thicknesses of bright nickel of about 1 to 2 mils such as 0.1 g./l. The useful range of the amino compound is from about 0.1 to about 10 g./l. The maximum microporosity induced in the decorative chromium plate occurs with the higher concentrations of the salts of the metal cations, and when the upper pH range (4 to about 5.8) of the nickel bath is used.

The most desirable organic amino compound, that is those that work conjunctively with the cations, are those that can be used over a broad range of concentrations without interfering with the regular brightening agents or detracting from the qualities or properties of the elecdrodeposit such as causing skipped plate in the low current density areas, or causing brittle plate. In this respect, the amino acids such as diethylene triamine pentaacetic acid, penta-sodium salt (DTPA), N-methyl taurine, ethylene diamine tetra-acetic acid and the like are especially good.

While some secondary brightening agents (Class H type nickel brighteners) having amino groups such as tetra ethylene pentamine or the quaternary pyridine propane sultone, are somewhat efiective in producing microporosity with the metal containin cations, the optimum concentration for achieving microporosity does not coincide with the concentration needed to produce bright, leveled electrodeposits.

Consequently, the preferred organic amino compounds are non-brighteners with a wide range of concentrations which are effective and which are practically neutral in their effect on brightness, leveling and the physical and mechanical properties of the deposit.

As has been mentioned above, the cations that are preferred to be present with the amino compounds are those from Periodic Tables III, V, and VI. However, it has further been found that if bath insoluble particles are introduced into the bath then a large number of other metal cations may be employed such as those from Periodic Table Groups I and II, in addition to the aforementioned III, V, and VI.

It was further found that if very finely divided amorphous silica powders in as low concentrations as about 10 mg./l. to, at the most, about 10 g./l. are dispersed in the bright nickel plating baths containing the additives of this invention, the microporosity induced in the decorative chromium plate becomes equal to that obtained with 20 to 60 g./l. of the same amorphous fine silica particles dispersed in regular bright nickel plating baths operated under the same conditions of bath agitation, pH, temperature and thickness of plate. With the highly increased codeposition of the very fine amorphous silicas, the bright nickel plate may now show a little too much'dulling when plate thicknesses greater than about 0.15 mil are used, especially when the concentration of the fine silica powder gigperjiad in the bright nickel bath is greater than about This is contrasted with the results obtained when substantially no particles (about 10 parts per million) are present in the bath but only the metal containing cation and the nitrogen containing compound. In this latter situation full bright heavy nickel depositions are obtained even when the nickel deposit is about 1-2 mils thick.

The fine silica powders generally designated as microfine precipitated silicas, micronized synthetic silicas used in concentrations as low as 10 to 300 mg./l. are made much more effective in codeposition with the bright nickel in inducing extensive microporosity in the final decorative chromium plate by the addition of small concentrations of salts of the above described metal cations. This procedure is maximized in this respect by the addition of small concentrations of the amino acids such as EDTA, DTPA, etc. Thus, with the additives of this invention in the bright nickel bath, the use of about 0.3 to 2 g./l. of the amorphous fine silica particles will induce a very dense microporosity in the decorative chromium plate equal to that obtained with the same thickness of nickel with at least 20 g./l. of the same powder in the nickel bath. This is, the codeposition of the silica particles is so extensive that only a 1 to 2 minutes bright plate at 50 amps/sq. it. need be used to induce a microporous deposit that is as extensive in microporosity in the decorative chromium plate as with at least 20 g./l. of the same silica powder dispersed in a regular bright nickel bath. With the short plating times of 30 seconds to even 5 minutes at cathode current densities of about 40 to 50 amps/sq. ft. filtration is not needed, and it is therefore simpler to control the metal containing cation concentrations in the bath under these conditions.

It appears that the silica particles adsorb the polyvalent cations and acquire a positive charge and therefore the fine silica particles are more readily codeposited with the nickel. Without the metal cations, the silica particles in the nickel solution are almost of neutral charge. The amino acids also help in this effect of increasing the codeposition and especially with the polyvalent cations also present. The aluminum and chromium, as well as other metal salts of the amino acids can be used instead of having separate additions of the metal salts and the amino acids.

Furthermore, the silica powders can be added to solutions of these polyvalent cations with, or even without, the amino acids and on evaporation to dryness, the silica powders can be coated or partially coated with salts or hydroxides of the polyvalent metal cations and be of the same increased effectiveness in codeposition with the nickel. In fact, with the fine silica particles dispersed in the nickel baths, polyvalent metal cations such as those of cerous and cen'c salts, rare earth salts such as those of lanthanum, neodymium and praseodymium and the mixtures of rare earth salts known as didymium salts, which salts do not readily form hydroxides in nickel baths, significantly help the codeposition of the fine silica particles apparently by adsorption on the silica. Even concentrations of magnesium ions above 1 g./l. help in this respect. The evaporation technique mentioned above using iron salts with the silica powder makes the ferrous and ferric ions more effective than when added separately.

The methods discussed for improving the codeposition of the fine silica particles also help with the codeposition of fine particles of bath-insoluble silicates, and metallic oxides, even though the latter acquire a positive charge in the nickel bath without any special additives such as those of this invention. Nevertheless, it is with fine amorphous silica particles that the additives of this invention are most effective.

The amount of bath insoluble fine particles that may be employed ranges from 0.01 g./l. to g./l. while the size of the particles may range from about 0.015 to about 10 microns. Because of the significant carrying activity that the bath insoluble particles have, with the metal cations, very small amounts of bath insoluble particles need be employed. It should also be pointed out that the higher the concentration of the metal containing cation of this invention, the greater will be the need to increase the concentration of the amine to achieve the most desirable results.

In addition to the aforementioned bath insoluble particles, other bath insoluble particles that may be employed are polyvinylchloride, polyvinylidene chloride, polyethylene, polypropylene, talc, calcium carbonate, and others that are mentioned in US. 3,152,971; 3,152,972 and 3,152,973 which are hereby incorporated by reference.

Without limiting the generality of the foregoing, and to give added amplification of the invention, below are examples which show preferred embodiments. All temperatures are in degrees centigrade and all percentages are percentages by weight unless otherwise indicated.

EXAMPLE I (1) A test field installation was made with the following solution:

Nickel sulfate, 43.4 oz./gal. Nickel chloride, 9.2 oz./ gal. Boric acid, 7.2 oz./ gal.

Brighteners present were:

Bis benzene sulfonamide, 1.3 g./l. Sodium allyl sulfonate, 2.1 g./l.

CC HgOC:H4O-CzH4 S oaNa C-CHr-O-CflEh-o-Cafl s oiNa, 60-90 mg./1. (hereinafter referred to as BDOES).

Additions were made of 1.8 g./l. microfine silica, 15 mg./l. Al+++ (as aluminum sulfate) and 1 g./l. diethylene triarnine pentaacetic acid (sodium salt).

The solution was operated at a pH of 3.8-4 and a temperature of -145 F. Air agitation was used.

Thin nickel deposits, approximately 0.05-0.1 mil in thickness were overplated on bright nickel and subsequently chromium plated to a thickness of about 0.01 mil.

Standard Dubpernell test for microporosity of chromium were made and the porosity found to be 256,600 pores/sq. in.

EXAMPLE II From the same test installation as in Example Number I; but containing as an additional brightener, 1.4 g./l. of o-benzoyl sulfimide additional porosity tests were made. These tests were made on deposits of substantially the same thicknesses as given in Example Number I.

The porosity by Dubpernell test was found to be 250,800 pores/sq. in.

In this test, the concentration of microfine silica was 1.9 g./l. and the Al+++ concentration was 13 mg./1. The amino acid concentration was 1 g./l.

EXAMPLE III Using a Watts type nickel solution of the following composition:

Nickel sulfate, 39.0 oz./ gal. Nickel chloride, 8.4 oz./gal. Boric acid, 5.6 oz./gal.

And containing the following brighteners:

(l) 1.5% by weight, mixture of saccharin (sodium salt) and a small amount (about 0.1 g./l.) of his benzene sulfonimide;

(2) 0.7% by weight, mixture of sodium allyl sulfonate (2.1 g./l.) and BDOES;

an air agitated solution at a temperature of 140-145 F. was used to conduct tests in a sixty (60) gallon volume.

(a) A bright nickel deposit about 0.4 mil thick was plated from this solution and subsequently plated with about 0.01 mil chromium. The porosity by Dubpernell test was less than that 100 pores/ sq. in.

(b) Then 0.2 g./l. diethylenetriamine penta-acetic acid (Na salt) and 12.5 mg./l. Al+++ were added to the solution and the solution agitated and electrolyzed over night. The solution pH was adjusted to 4.0.

A bright nickel deposit, about 0.4 mil thick, was plated from the solution and subsequently plated with about 0.01 mil chromium. The porosity by standard Dubpernell test was 36,250 pores/ sq. in.

(c) The pH of the solution given in example (b) was adjusted to 3.0 and the bright nickel-chromium plated in the same manner.

The microporosity of the chromium deposit was 22,500 pores/sq. in.

(d) To the solution described in (0) above was further added 5 mg./l. Cr+++, added as the sulfate.

A bright nickel-chromium deposit plated in identical fashion to those in examples (a), (b) and (c) showed a microporosity of 66,250 pores/ sq. in.

EXAMPLE IV Laboratory tests were made in the air agitated Watts type nickel solution of Example III at a solution pH of 3.8-4.2 and a temperature of F. Air agitation was used. The brightener concentrations were 2% Number 1 and 0.75% Number 2.

To this solution was added 25 mg./l. Al' (as aluminum sulfate), 0.5 :g./l. diethylenetriamine penta-acetic acid (Na salt) and 10 mg./l. microfine silica.

A bright nickel deposit was plated to a thickness of about 0.4 mil from this solution and overplated with about 0.01 mil chromium.

Porosity was measured by the Dubpernell test as 50,000 pores/ sq. in.

EXAMPLE V Additional laboratory tests were made in air agitated solutions of the following compositions ranges:

Nickel sulfate, 200-300 g./l. Nickel chloride, 40-120 g./l. Boric acid, 40 g./l.

(a) Al 41 mg ./1. Dlethylene triamine. 25,00041,000 pores/sq. in.

Penta-aeetic acid (N a Sa1t).5 g./1.

(b) Al+++ 82 mg./l.

N-methyl taurinc (Na Salt) 1 g./1.

(c) 'Il2S04 100 mg./1.

(DTPA) 1 g./1.

(d) Sulfanilic acid 1 g./1.

A1+++ 8 mg./1.

298,000-478,000 pores/sq. in.

25,000 or more pores/sq. in.

25,000 or more pores/sq. in.

10-20 mg./l.

25,000 or more pores/sq. in.

1,825-55,000 pores/sq. in.

(e) Th+ (as thorium fluoborate).

(D'IPA) 40-80 mg./1.

(t) M2604): 0.5-1.0 g./1.

Mic/r10 fine silica (4 microns) 0.5-1.0

g. N[CHzfi(OH)z] 2.0 g./1. O 1

EXAMPLE VI A Watts type nickel solution was prepared and to it was added:

1.5 g./l. saccharin 2.8 g./l. sodium allyl sulfonate 60 -90 mg./l. BDOES The solution pH was 4 and the temperature 145 F. Air agitation was employed.

An addition of 0.5 g./ l. diethylene triamine penta-acetic acid (Na salt) together with 25 mg./ 1. Al+++ (as was made to the solution.

A deposit of about 0.4-0.5 mils of bright nickel was deposited and subsequently chromium plated to a thickness of about 0.01 mils.

A standard Dubpernell test was conducted to determine porosity of the chromium and a moderate microporosity determined.

An addition of 10 mg./l. of Fe+++ ion (as ferric chloride) was then added to the solution and the plating test, as described above repeated. The microporosity of the chromium was found to be improved over the previous test.

It should be pointed out that the thickness of the chromium electrodeposited coating may range from about 0.004 mils to about 0.08 mils.

What is claimed is:

1. An aqueous acidic nickel electroplating bath solution comprising nickel ions, a bath soluble amine in a concentration of about 0.1 g./l. to about 10 g. g./l., and a bath soluble metal salt which in the solution will produce a trivalent or tetravalent metal-containing cation in an amount of at least about 1.0 to about 50 mg./1. whose precipitation occurs at a pH which is lower than that of the nickel in said solution.

2. The bath of Claim 1, wherein the metal containing cation is independently selected from the group consisting of a metal from Periodic Table Groups III, V and VI.

3. The bath of Claim 2, wherein the amine has a group of the formula, N(RA) (R') wherein R is independently selected from the group consisting of alkylene,

arylene, hydroxy substituted alkylene, hydroxy substituted arylene, polyoxyalkylene, hydroxy substituted polyoxyalkylene and the chloro or bromo derivatives thereof; A is independently selected from the group consisting of -N(R') COOH; SO H and P(O) (OI-D and R is independently selected from the group consisting of hydrogen, alkyl; hydroxy substituted alkyl, polyoxyalkylene,

hydroxy substituted polyoxyalkylene and the chloro or bromo derivatives thereof; g is 0 to 2 and h is 0 to 2;

4. The bath of Claim 11, wherein the amine is an amine of the formula; R",-N(RA),;; wherein R and A are defined above; R is selected from the group consisting of hydrogen,

sis 0 to 3; t is 0 to 3 and s+t=3; m is from 1 to 10, and v is from 1 to 20 provided that s is not 3 when R" is hydrogen.

5. The bath of Claim 4, wherein A is --N(R)3- 6. The bath of Claim 4, wherein A is -COOH.

7. The bath of Claim 4, wherein A is SO H.

8. The bath of Claim 4, wherein A is P(O) (OHM.

9. The bath of Claim 4, wherein R is alkylene.

10. The bath of Claim 4, wherein R is RN BA L til. 11. The bath of Claim 4, wherein R is hydroxy alkylene.

12. The bath of Claim 4, wherein R" is 17. The bath of Claim 4, further comprising fine bath insoluble particles having a size of about 0.01 to 10 microns present in an amount ranging from about 0.1 to about 10 grams per liter.

18. The bath of Claim 2 wherein the amine is a polyamine.

19. The bath of Claim 8, wherein the amine also contains an acid group.

20. The bath of Claim 2, wherein the metal is from Periodic Table Group No. III.

21. The bath of Claim 2, wherein the metal is from Periodic Table Group No. V.

22. The bath of Claim 2, wherein the metal is from Periodic Table Group No. VI.

23. The bath of Claim 2, wherein the amine has an acid group present in the molecule independently selected from the group consisting of carboxylic acid, sulfonic acid and phosphonic acid.

24. A method of producing a corrosion protective coating onto a metallic substrate comprising passing a current from an anode through an aqueous acidic nickel electroplating bath solution comprised of nickel ions, introducing into the solution a bath soluble amine in a concentration of about 0.1 g./l. to about 10 g./l., adding to the solution a bath soluble metal salt which when in the solution will produce a trivalent or tetravalent metal-containing cation in an amount of at least about 1.0 to about 50 mg./l. whose precipitation occurs at a pH which is lower than that of the nickel in said solution, and subsequently electrodepositing a chromium coating onto the nickel plated substrate, thereby producing a microporous chromium coating.

25. The method of Claim 24, wherein the metal containing cation is independently selected from the group consisting of metal from Periodic Table Groups III, V and VI.

26. The method of Claim 25, wherein the amine has a group of the formula; -N(RA) (R') wherein R is independently selected from the group consisting of alkylene, arylene, hydroxy substituted alkylene, hydroxy substituted arylene, polyoxyalkylene, hydroxy substituted polyoxyalkylene and the chloro or bromo derivatives thereof; A is independently selected from the group consisting of L n. L l1 s is to 3; t is 0 to 3 and s+t=3; m is from 1 to 10, and v is from 1 to 20; provided that s is not 3 when R" is hydrogen.

28. The method of Claim 27, wherein A is -N(R) 29. The method of Claim 27, wherein A is COOH. 30. The method of Claim 27, wherein A is -SO H. 31. The method of Claim 27, wherein A is 32. The method of Claim 27, wherein R is alkylene. 33. The method of Claim 27, wherein R" is L RA m 34. The method of Claim 27, wherein R is hydroxy alkylene.

' 12 35. The method of Claim 27, wherein R" is 36. The method of Claim 27, wherein the amine compound is ethylene diamine tetra acetic acid.

37. The method of Claim 27, wherein the amine compound is diethylene triamine penta-acetic acid.

38. The method of Claim 27, wherein the amine compound is N-methyl taurine.

39. The method of Claim 27, wherein the amine compound is N[CH -P(O) (OH) 40. The method of Claim 25, wherein the amine is a polyamine.

41. The method of Claim 40, wherein the amine also contains an acid group.

42. The method of Claim 25, wherein the metal is from Periodic Table Group Number HI.

43. The method of Claim 25, wherein the metal is from Periodic Table Group Number V.

44. The method of Claim 25, wherein the metal is from Periodic Table Group Number VI.

45. The method of Claim 25, wherein the amine has an acid group present in the molecule independently selected from the group consisting of carboxylic acid, sulfonic acid and phosphonic acid.

46. The method of Claim 24, wherein the electrodeposited chromium coating ranges in thickness from about 0.004 mils to about 0.08 mils.

References Cited UNITED STATES PATENTS 3,471,271 10/1969 Brown et a1 204-49 X 1,524,448 1/ 1925 Murphy 204-49 2,541,721 2/1951 Roehl et al 204-49 3,032,485 5/1962 Tsu et a1 204-43 T FOREIGN PATENTS 144,692 3/1962 U.S.S.R. 204-43 T 201,871 11/1967 U.S.S.R. 204-43 T 160,411 4/1963 U.S.S.R. 204-43 T GERALD L. KAPLAN, Primary Examiner US. Cl. X.R. 204-49