US3866289A

US3866289A - Micro-porous chromium on nickel-cobalt duplex composite plates

Info

Publication number: US3866289A
Application number: US252495A
Authority: US
Inventors: Henry Brown; Thaddeus W Tomaszewski; Richard J Clauss
Original assignee: Oxy Metal Industries Corp
Current assignee: OMI International Corp
Priority date: 1969-10-06
Filing date: 1972-05-11
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18

Abstract

A firmly bonded laminated composite corrosion-protective metallic coating comprising as its essential layers three adjacently bonded layers of electrodeposits, the lower layer of which consists essentially of a metal selected from the class consisting of cobalt and cobalt-nickel alloy plate containing cobalt at least about 70% and having a thickness of about 0.1 mil to about 2 mils, an over-layer of metal selected from the class consisting of nickel and nickel-cobalt alloy plate containing at least about 50% nickel and having a thickness of about 0.02 to about 0.3 mil and an over-layer of densely porous chromium plate having a thickness of 0.005 to about 0.05 mil.

Description

United States Patent [1 1 Brown et a1.

[ MICRO-POROUS CHROMIUM ON NICKEL-COBALT DUPLEX COMPOSITE PLATES [75] Inventors: Henry Brown, Huntington Woods;

Thaddeus W. Tomaszewski,

Dearborn; Richard J. Clauss, Allen Park, all of Mich.

[73] Assignee: Oxy Metal Finishing Corporation,

Warren, Mich.

[22] Filed: May 11, 1972 [21] Appl. No.: 252,495

Related U.S. Application Data [63] Continuation-in-part of Ser. Nos. 864,156, Oct. 6, 1969, abandoned, and Ser. No. 865,520, Oct. 10, 1969, abandoned.

1 Feb. 18, 1975 Primary ExaminerL. Dewayne Rutledge Assistant ExaminerE. L. Weise Attorney, Agent, or Firm-B. F. Claeboe [57] ABSTRACT A firmly bonded laminated composite corrosionprotective metallic coating comprising as its essential layers three adjacently bonded layers of electrodeposits, the lower layer of which consists essentially of a metal selected from the class consisting of cobalt and cobalt-nickel alloy plate containing cobalt at least about 70% and having a thickness of about 0.1 mil to about 2 mils, an over'layer of metal selected from the class consisting of nickel and nickel-cobalt alloy plate containing at least about 50% nickel and having a thickness of about 0.02 to about 0.3 mil and an overlayer of densely porous chromium plate having a thickness of 0.005 to about 0.05 mil.

17 Claims, N0 Drawings MICRO-POROUS CHROMIUM ON NICKEL-COBALT DUPLEX COMPOSITE PLATES CROSS REFERENCE TO RELATED CASES This case is a continuation-in-part of US. Ser. No. 864,156 filed Oct. 6, 1969 and US. Ser. No. 865,520, filed Oct. 10, 1969 both now abandoned.

This invention relates to composite electroplates of highly porous, that is micro-porous chromium on top of nickel which is plated on top of cobalt plate. More particularly it relates to a method to obtain excellent corrosion protection of steel, zinc die castings, aluminum, magnesium and brass basis metals with decorative thin chromium plate and a minimum of nickel metal.

It has now been found that if a bright or semi-bright nickel plate or a bright or semi-bright nickel-cobalt alloy plate that contains particles as described in US. Pat. Nos. 3,152,971-2-3; 3,268,307-8; 3,268,423-4 etc., is deposited on top of a cobalt plate or of a cobaltnickel alloy plate that has a higher percentage of cobalt present than the plate above it containing the multitudinously codeposited bath-insoluble non-metallic particles, that excellent corrosion protection can be obtained in the CASS and Corrodkote accelerated corrosion tests, for the basis metals of steel, zinc'die castings, aluminum, magnesium, brass and metallized plastics. This is especially true if underneath the cobalt or high cobalt alloy plate an undercoat of essentially copper, brass, bronze or nickel plate is used, with copper the preferred undercoat and sulfur-containing bright the second choice. Of course, one can also use nickel under the copper or brass under-coat, or copper or brass under the nickel, etc. The thickness of thecopper, brass or nickel, etc. undercoats may be from about 0.02 to about 1 mil or even more.

The cobalt plate or high cobalt-nickel alloy plate in which the cobalt is at least 70% is plated to, a thickness of 0.2 to 0.8 mil, although the range is from 0.1 mil to at least 2 mils may also be used. Also it is preferred that the underneath copper or nickel (bright or semi-bright) if the plate with the multitudinous codeposited nonmetallic particles is omitted and the usual thin chromium plate (0.005 to 0.05 mil) is applied directly to the cobalt plate or to the high cobalt-nickel alloy plate with cobalt at least about 70% cobalt which is applied on top of copper or nickel plate, then in CASS or Corrodkote wide surface corrosion pits are obtained in 16 hours CASS or Corrodkote testing. When for example, 0.2 mil of cobalt or 70% cobalt 30% nickel alloy is on top of 0.5 mil copper or bright or semi-bright nickel, the surface pits stop or slow down at the copper or nickel and proceed laterally with further corrosion exposure. In outdoor tests, both in marine and industrial atmospheres the same result occurred even with chromium plated cobalt-nickel alloy that was about 55-58% cobalt and plated as a thin plate on 1 mi] of bright nickel. These large surfacepits (l/l6- to 76-inch diameters) turned greenish and darkish in outdoor weathering and were very unsightly.

Thus, a method has now been found as described above to eliminate the large surface pitting when cobalt or high cobalt-nickel alloy plate (cobalt at least about 70%) is plated directly with the usual thin chromium plate and exposed outdoors in industrial or salty envibe between about 0.1 mil and about 1 mil. The top nickel or cobalt-nickel alloy plate containing the codeposited non-metallic particles can be from 0.02 mil to about 0.3 mil preferably about 0.02 to 0.15 mil, and the cobalt content is preferred to be less than about 50%. The final chromium plate can be 0.005 to about 0.03

mil thick and it will be micro-porous by virtue of its deposition on the plate containing fine codeposited nonmetallic particles.

For decorative, as well as corrosion protective uses, it is preferred that the top plate containing the codeposited particles be bright or semi-bright and contain approximately 0.08% sulfide sulfur to sulfur-free. The preferred codeposited particles are barium sulfate (0.1

to 3 micron size)'or polyvinylidene chloride (Saran) for low luster finishes, and the fine aluminum silicate, zirconium silicate, zirconium oxide, amorphous silica used alone or as mixtures for much higher luster finishes including brilliant finishes. For the highest brilliance, thin plates with the codeposited particles are plated on top of lustrous semi-bright or brilliant lustrous cobalt or high cobalt-nickel alloy plate. The use of lustrous bright undercoats'of copper or nickel or highly lustrous semi-bright coats also helps to attain any desired degree'of brilliancy or subdued brightness prior to the deposition of the final thin chromium plate.

ronments. This method uses a minum of nickel metal and yet excellent corrosion protection is obtained. This is very important during times when nickel becomes scarce. At these times, the top nickel plate containing the codeposited non-metallic particlesmay be about 0.1 mil and less, and the underlying cobalt plate may be 100% or close to 100% and only 0.2 mil or even less thickness on top of 0.3 mil to 1 mil copper plate.

The chromium that is applied to the final nickel plate or nickel-cobalt alloy plate can be conventional chromium plate obtained from chromic acid baths containing the sulfate catalyst, or mixed sulfate-silicofluoride or mixed other fluoride containing catalyst or organic acid catalysts may be used. It may be crack-free or micro-cracked. It may be plated from the trivalent chromium baths, as well as the hexavalent chromium baths, and its thickness may be from about 0.005 to 0.1 mil, preferably 0.005 to about 0.05 mils. When the chromium plate is a micro-cracked type as when mixed sulfate and silicofluoride catalysts are used or when selenium is used in the acidic hexavalent chromium baths or when trivalent chromium plating baths are used, then the top nickel or low cobalt nickel-cobalt alloy plate can be free or almost free from codeposited nonmetallic fine particles (by not having the particles dispersed in the bath), and an improved corrosion protective result can be obtained, though not nearly as good as when codeposited non-metallic fine particles are densely codeposited in the top nickel or nickel-cobalt alloy plate. If the chromium plate is not densely porous, that is, when the usual chromium plate is used on the nickel or low cobalt nickel-cobalt alloy plate that has no densely codeposited fine non-metallic particles, then very poor corrosion protection results.

When the top nickel layer is substantially all nickel and the next under layer is substantially all cobalt or high cobalt, for example, 70, 80, or cobalt, then drag-in of cobalt solution into the nickel bath containing the dispersed fine particles will cause the nickel plating bath to plate out nickel-cobalt alloy plate. Nevertheless, since the top nickel layer is preferably deposited from baths using nickel anodes, the cobalt content of the top plate can be easily controlled to keep it much under about 50% cobalt. Furthermore, even a rinse can be used between the two baths, but this wastes metal and is not needed..

The thickness of the cobalt or high cobalt cobaltnickel alloy layer for the most severe outdoor exposure need not be more than 2 mils thick, and the thickness of the underneath copper, brass or nickel layers need not be more than 2 mils thick, and actually about 1 mil thick for the cobalt and copper plates are about the highest thicknesses needed for very excellent corrosion-protective results.

Another method to obtain a porous chromium plate is to plate the usual thickness 0.005 to 0.02 mil chromium plate from the acidic hexavalent chromium baths on top of a thin highly stressed nickel plate or a highly stressed nickel-cobalt alloy plate that is relatively low in cobalt content. When cobalt or high cobalt content cobalt-nickel alloy plate is underneath the highly stressed or micro-cracked nickel, this top plate may have as high as at least about 0.1% sulfur and still have excellent corrosion-protective results with the composite plates of this invention. Thus, by using high chloride types of nickel baths where the chloride content as nickel chloride is over about 150 g/l and using either low concentrations of Class I compounds (benzene and naphthalene sulfonic acids, sulfonamides, sulfonimides, etc.) or none or even using low concentrations ofnegative valent organic sulfide compounds such as thioureas, etc. and using Class ll compounds (unsaturated alcohols, glycols, amines) as well as unsaturated acids (fumaric acid, acrylic acid, propiolic acid, etc.), saturated amines and nitro compounds, highly stressed and micro-cracked nickel results which causes microcracked chromium when thishighly stressed and micro-cracked nickel is plated with even the conventional chromium plate, especially if a hot water rinse or mild heat is used after chromiumplating. Also alkaline sion-protective composite plate of this invention results- The following examples illustrate plating baths which can be used for plating the firmly bonded composite plate of this invention on steel and zinc die casting the main commercial basis metals which are plated because they are susceptible to atmospheric corrosion. Other basis materials such as brass, copper, bronze, monel can be plated as shown-in the examples below just using a copper cyanide or brassstrike or a nickel strike or no strike and starting with the cobalt or high cobalt-nickel alloy plate (plating step 3 below), skipping the thicker copper plate (plating step 2). In the case of aluminum as the basis metal it is then chromium plated in a room temperature acidic hexavalent chromium plating solution preferably with interrupted current (5-7 seconds on, 1-2 seconds off) for about 3 to 6 minutes and then after thorough rinsing, transferred directly to a low pH nickel or cobalt strike as given in US. Pat. No.'3,047,939 and plated for l ,to 5 minutes and then transferred (with or without rinsing) to the cobalt or high cobalt alloy bath (plating step 3). If a zincate dip or other immersion coating is first applied to the aluminum surface, then after the immersion coating the copper cyanide or brass strike is employed preferably at room temperature and the composite coating as shown in the Examples below is applied. Magnesium needs pretreatments similar to the preparation of aluminum for plating. Non-conductive plastics, of course, require a surface metallizing preplate step before the composite plate is applied.

The examples following are representative examples of the highly corrosion-protective composite plates of this invention. By using standard 6 X 4 in. steel, panels for the accelerated corrosion tests of CASS and Corrodkote, the composite plate of this invention as illustrated in the examples will perfectly pass 5 Corrodkote cycles or 100 hours of CASS testing without showing any rusting or surface pits that would detract from appearance. This is also true when 6 X 4 in. standard zinc die cast panels are similarly plated and corrosion tested with no corrosion blisters or surface pits that would detract from appearance, occurring.

EXAMPLE I Plating Step 1 After cleaning and acid dipping the steel or zinc die castings, strike at 20 amps/sq.ft. from an alkaline cyanide copper bath for l-S minutes, and rinse.

Plating Step 2 Plate a thickness of about 0.5 mil copper in a bright acid copper sulfate plating bath, as for example, in the following bath.

Concentration grams/liter CuSO..5l-l,0 150 250 H 30 75 Polypropylene glycol, .05 0.2

(av. mol. wt. 350 750) Phenyl disulfide sulfonic acid .00l 0.005 Janus Green B .001 0.01 Temperature 75 F Av. Cathode Current Density 40 50 ampslsqft. Air-agitation Plating Step 3 After rinsing, the copper plated work is now plated in the following bright acidic cobalt plating bath with 0.5 mil of cobalt.

Concentration grams/liter CoCl,.6H,0 3B0; 40-80 (60 preferred) o-Benzoyl sulfimide 3 Allyl sulfonic acid 0.5 2 Z-Butynoxy-l .4-diethane 0.1 0.2

disulfonic acid Temperature [20 pH 2.8 3.5 Air-agitation Av. Cathode Current Density 40 50 ampslsqjt.

Plating Step 4 After rinsing the cobalt plated work, it is now plated in the following bright nickel bath for 2 minutes to give about an 0.06 mil bright nickel plate containing densely codeposited very fine non-conducting particles, in this case ultra-fine amorphous silica particles.

Cathode current density 40 50 .amps/sqft.

Plating Step 5 After rinsing, the work is now transferred to an acidic hexavalent chromium plating bath as, for example, the conventional one below and plated with 0.01 mil chromium which will be micro-porous by virtue of being plated on top of the nickel plate that contains multitudinous codeposited fine non-conducting particles.

Concentration grams/liter CrO, 250 l-I,SO. l.5 2.5 Temperature 115 l35F Cathode current density 200 300 amps/sqj't.

EXAMPLE II In Example I, instead of the straight cobalt bath in Plating Step 3, l020 g/l of nickel sulfate or nickel chloride can be added to this bath to plate a cobaltnickel alloy plate containing over 70% cobalt by weight. Also in Plating Step 4, about g/l of cobalt sulfate or chloride can be added to the nickel bath and a nickel-cobalt alloy plate will result with about 20% cobalt by weight average, and not higher than about 40% cobalt. The percentage of cobalt that plates out depends on the temperature, pH, ratio of cobalt to nickel in the bath and the degree of agitation of the bath. Instead of the ultra-fine silica as the particles dispersed in the nickel bath, very fine zirconium oxide (0.03 to 0.1 micron) .or zirconium silicate (0.05 to 0.1 micron, or aluminum silicate (0.05 to 0.15 micron size) powders may be used in concentrations of 0.5 to 2 g/l alone or together with the micronized silica hydrogels or precipitated silicas, and when used together, even about 20 g/l of the amorphous silica powders will give extensive codeposition.

It is to be understood that between each plating step, except transfers to similar baths as from Plating Step 3 to Step 4, rinses are used, and in some cases as after rinsing copper or brass strikes from alkaline baths,

acidic dips are often used. Also that a nickel strike may be used under the copper plate instead of cyanide copper or brass strikes.

Also, instead of the copper plate (Plating Step 2) from an acid bath, one from an alkaline cyanide or pyrophosphate bath can be used or a brass plate of similar thickness. Also, a nickel plate, bright or semi-bright, or a chromium plate may be used underneath the cobalt plate instead of the copper plate. The chromium plate may be as thin as 0.01 mil but preferably 0.03 to 0.1 mil as an underneath plate. The preferred plate underneath the cobalt or high cobalt nickel-cobalt alloy is, however, the copper plate.

It should be emphasized that the best method by far to obtain the highly porous thin chromium plate in the most uniform and consistent manner (0.01 to 0.02 mil chromium) is by deposition on the nickel plate (or low cobalt nickel-cobalt alloy plate) containing the densely codeposited very fine non-metallic powders as described, and with this method and with the composite plate illustrated in Examples I and II, the optimum protection to the basis metal is obtained with the thicknesses of metal specified. Of course, thicker cobalt or copper plate would be even further improvement, but there is no need for outdoor exposures to use more than 2 mils of cobalt or copper,'and about 1 mil of each would normally be the highest required for severe outdoor exposure.

What is claimed is:

l. A firmly bonded laminated composite corrosionprotective metallic coating comprising as its essential layers three adjacently bonded layers of electrodeposits, the lower layer of which consists essentially of a metal selected from the class consisting of cobalt and cobalt-nickel alloy plate containing cobalt at least about and having a thickness of about 0.1 mil to about 2 mils, an over-layer of metalselected from the class consisting of nickel and nickel-cobalt alloy plate containing at least about 50% nickel and having a thickness of about 0.02 to about 0.3 mil and an overlayer of densely porous chorrnium plate having a thickness of 0.005 to about 0.05 mil.

2. A composite coating in accordance with claim 1 wherein said chromium is densely porous by virtue of micro-cracking.

3. A composite-coatingin accordance with claim 1 wherein said chromium is densely porous by virtue of the micro-porosity resulting from its deposition on the metal selected from the class consisting of nickel and nickel-cobalt alloy plate containing at least about 50% nickel, and said metal plate containing densely codeposited fine non-metallic particles. 3

4. A composite coating in accordance with claim 1 wherein the lower layer consisting of a metal selected from the class consisting of cobalt and cobalt-nickel alloy plate containing higher than about cobalt, has an underlayer of metal selected from the class consisting essentially of copper, brass, bronze and nickel plate of a thickness of 0.02 mil to about 1 mil.

5. A method'for electroplating from aqueous solutions a corrosion-protective composite metallic coating comprising as its essential layers three adjacently bonded layers of electrodeposits which comprises the steps of electroplating on a solid metal surface an adherent layer which consists essentially of a metal selected from the class consisting of cobalt and cobaltnickel alloy plate containing cobalt at least about 70% and having a thickness of about 0.1 mil to about 2 mils, an over-layer of metal selected from the class consisting of nickel andnickel-cobalt alloy plate containing at least about 50% nickel and having a thickness of about 0.02 to about 0.3 mil and an over-layer of densely porous chromium plate having a thickness of 0.005 to about 0.05 mil.

6. A method in accordance with claim 5 wherein said chromium is densely porous chromium by virtue of micro-cracking.

7. A method in accordance with claim 5 wherein said chromium is densely porous by virtue of the microporosity resulting from its deposition on the metal selected from the class consisting of nickel and nickelcobalt alloy plate containing at least about 50% nickel and said metal plate containing densely codeposited fine non-metallic particles.

8. A method in accordance with claim 5 wherein the lower layer consisting of a metal selected from the class consisting of cobalt and cobalt-nickel alloy plate containing higher than about 80% cobalt is deposited on an underlayer of metal selected from the class consisting essentially of copper, brass, bronze and nickel plate of a thickness of 0.02 mil to about 1 mil.

9. A composite coating in accordance with claim 1 wherein said chromium is densely porous by virtue of micro-cracking as a result of plating the chromium on top of a highly stressed and micro-cracking metal selected from the class of nickel and nickel-cobalt alloy plate containing at least about 50% nickel and having a thickness of about 0.02 to about 0.3 mil.

10. A method in accordance with claim 5 wherein said chromium is densely porous by virtue of microcracking as a result of plating the chromium on top of a highly stressed and micro-cracking metal selected from the class of nickel and nickel-cobalt alloy plate containing at least about 50% nickel and having a thickness of about 0.02 to about 0.3 mil.

11. The process for preparing a bright decorative chromium composite metal coating which comprises:

1. depositing on a basis metal a first layer of copper plate;

2. depositing on said copper plate a second thin layer of cobalt;

3. depositing on said layer of cobalt a third thin layer containing nickel having a thickness of 0.02 mils to 0.3 mils; and

4. electrodepositing on said third nickel-containing layer a fourth layer of bright decorative chromium.

12. The process as claimed in claim 11, wherein the second thin layer of cobalt has a thickness of 0.1 mil to 2 mils.

13. The process of claim 11, wherein the third thin layer containing nickel has a sulfur content ranging from sulfur free to 0.08% sulfide-sulfur.

14. An article bearing a bright decorative chromium composite metal coating wherein said coating comprises:

1. a first layer of copper;

2. a second thin layer of cobalt thereon;

3. a third thin layer containing nickel having a thickness of 0.02 mils to 0.3 mils; and

4. a fourth layer of bright decorative chromium electrodeposited on said third nickel-containing layer.

15. An article as defined in claim 14, wherein the third thin layer containing nickel has a sulfur content ranging from sulfur free to 0.08% sulfide-sulfur.

16. The article as claimed in claim 15, wherein the second layer has a thickness of 0.2 to 0.8 mil and the third layer has a plated thickness of 0.02 mil to about 0.3 mil.

17. The article as claimed in claim 15, wherein the third thin layer is a nickel matrix.

Claims

1. A FIRMLY BONDED LAMINATED COMPOSITE CORROSIONPROTECTIVE METALLIC COATING COMPRISING AS ITS ESSENTIAL LAYERS THREE ADJACENTLY BONDED LAYERS OF ELECTRODEPOSITS, THE LOWER LAYER OF WHICH CONSISTS ESSENTIALLY OF A METAL SECLECTED FROM THE CLASS CONSISTING OF COBALT AND COBATH-NICKEL ALLOY PLATE CONTAINING COBATH AT LEAST ABOUT 70% AND HAVING A THICKNESS OF ABOUT 0.1 MIL TO ABOUT 2 MILS, AN OVER-LAYER OF METAL SELECTED FROM THE CLASS CONSISTING OF NICKEL AND NICKEL-COBATH ALLOY PLATE CONTAINING AT LEAST ABOUT 50% NICKEL AND HAVING A THICKNESS OF ABOUT 0.02 TO ABOUT 0.3 MIL AND AN OVER-LAYER OF DENSELY POROUS CHORMIUM PLATE HAVING A THICKNESS OF 0.005 TO ABOUT 0.05 MIL.

2. a second thin layer of cobalt thereon;

2. depositing on said copper plate a second thin layer of cobalt;

3. A composite coating in accordance with claim 1 wherein said chromium is densely porous by virtue of the micro-porosity resulting from its deposition on the metal selected from the class consisting of nickel and nickel-cobalt alloy plate containing at least about 50% nickel, and said metal plate containing densely codeposited fine non-metallic particles.

4. A composite coating in accordance with claim 1 wherein the lower layer consisting of a metal selected from the class consisting of cobalt and cobalt-nickel alloy plate containing higher than about 80% cobalt, has an underlayer of metal selected from the class consisting essentially of copper, brass, bronze and nickel plate of a thickness of 0.02 mil to about 1 mil.

5. A method for electroplating from aqueous solutions a corrosion-protective composite metallic coating comprising as its essential layers three adjacently bonded layers of electrodeposits which comprises the steps of electroplating on a solid metal surface an adherent layer which consists essentially of a metal selected from the class consisting of cobalt and cobalt-nickel alloy plate containing cobalt at least about 70% and having a thickness of about 0.1 mil to about 2 mils, an over-layer of metal selected from the class consisting of nickel and nickel-cobalt alloy plate containing at least about 50% nickel and having a thickness of about 0.02 to about 0.3 mil and an over-layer of densely porous chromium plate having a thickness of 0.005 to about 0.05 mil.

7. A method in accordance with claim 5 wherein said chromium is densely porous by virtue of the micro-porosity resulting from its deposition on the metal selected from the class consisting of nickel and nickel-cobalt alloy plate containing at least about 50% nickel and said metal plate containing densely codeposited fine non-metallic particles.

10. A method in accordance with claim 5 wherein said chromium is densely porous by virtue of micro-cracking as a result of plating the chromium on top of a highly stressed and micro-cracking metal selected from the class of nickel and nickel-cobalt alloy plate containing at least about 50% nickel and having a thickness of about 0.02 to about 0.3 mil.