US3625039A - Corrosion resistance of decorative chromium electroplated objects - Google Patents

Abstract

IMPROVED CORROSION RESISTANCE RESULTS IN DECORATIVE CHROMIUM PLATED OBJECTS HAVING CHROMIUM PLATED OVER NICKEL BY TREATMENT OF THE SURFACE CHROMIUM LAYER BY IMPINGEMENT OF SOLID PARTICULATE MATTER SO AS TO FORM MICROPORES IN SAID CHROMIUM LAYER. THESE MICROPORES EXTEND THROUGH SAID CHROMIUM LAYER TO THE UNDERLYING NICKEL LAYER. THE NUMBER OF MICROPORES PER SQUARE INCH SHOULD EXCEED 3,000 AND PREFERABLY BE IN THE RANGE OF 40,000200,000 PER SQUARE INCH FOR DECORATIVE CHROMIUM PLATED OBJECTS DEPENDING ON THE TYPE OF PARTICLE, SIZE OF PARTICLE, DENSITY OF PARTICLE AND MOMENTUM AT IMPINGEMENT. LIKEWISE, MULTIPLE NICKEL COATINGS CAN BE USED AND OTHER UNDERLYING METAL LAYERS SUCH AS COPPER CAN BE INTERPOSED BETWEEN THE SUBSTRATE AND THE NICKEL AND CHROMIUM SURFACE LAYERS.

Description

United States Patent 3,625,039 CORROSION RESISTANCE OF DECORATIVE CHROMIUM ELECTROPLATED OBJECTS Theo G. Kubach, Drosselweg 68, Leonberg-Silberberg,

Germany; and Werner H. R. Pritsch, Thomastrasse 57;

and Wilfried Bolay, Saumweg 29, both of Stuttgart,

Germany No Drawing. Filed Aug. 28, 1969, Ser. No. 853,977

Int. Cl. C216 7/06 US. Cl. 72-53 9 Claims ABSTRACT OF THE DISCLOSURE Improved corrosion resistance results in decorative chromium plated objects having chromium plated over nickel by treatment of the surface chromium layer by impingement of solid particulate matter so as to form micropores in said chromium layer. These micropores extend through said chromium layer to the underlying nickel layer. The number of micropores per square inch should exceed 3,000 and preferably be in the range of 40,000- 200,000 per square inch for decorative chromium plated objects depending on the type of particle, size of particle, density of particle and momentum at impingement. Likewise, multiple nickel coatings can be used and other underlying metal layers such as copper can be interposed between the substrate and the nickel and chromium surface layers.

IMPROVEMENT IN THE CORROSION RESISTANCE OF DECORATIVE CHROMIUM ELECTROPLAT- ED OBJECTS This invention relates to a means for improving the corrosion resistance of chromium electroplated objects. More particularly, this invention provides for enhancing corrosion resistance of decorative nickel-chromium electroplated articles by inducing microporosity in the chromium by means of impingement of solid materials on said surface chromium layer.

In the recent past, it has been discovered by various workers in the field, that decorative chromium can be improved, with respect to corrosion resistance by effecting the formation of micropores in the chromium layer. U.S. Pats. 3,298,802 and U .3. 3,449,223 illustrate examples of such decorative chromium of improved corrosion resistance. In US. 3,298,802 an object which may or may not be electrodeposited with other metal coatings, receives a continuous bright nickel electrodeposit. This bright nickel electrodeposit is followed by a thin electrodeposit of nickel which incorporates various solid particulate matter which is non-conductive into said thin nickel layer. Thereafter, chromium is electrodeposited on said particulate containing nickel layer. The particles in the nickel layer interfere with the flow of current during electrodeposition of the chromium layer and result in the formation of a microporous chromium deposit. US. 3,449,223 discloses a similar process which calls for a particulate containing bright nickel layer being plated directly on a substrate without the need for an underlying particle-free bright nickel layer.

Applicant has now discovered that this same improvement in corrosion resistance can be obtained in decorative chromium plated objects by forming micropores in the chromium surface after the final chromium layer has been electrodeposited on said object. The micropores are formed in the chromium surface by causing particulate materials of sufficient hardness to strike the surface of the chromium with sufficient force so as to form micropores.

Various particulate materials have been used with success in the instant process. These include round Ottawa sand (23-25 mesh), jagged sand (32-34 mesh), lead powder, polyethylene pellets x x A (Goodrich Geon Vinyl #8814 white), magnesium filings, glass beads (Blastolite BLXN-l6 General Steel Industries, St. Louis, Mo.), polystyrene pellets (.05" diameter), iron powder, nickel powder and powdered silica (320 mesh). Any solid particulate material would be useful in the practice of the present invention which has suflicient hardness to withstand the impact with the chromium surface at least to the extent of marring said chromium surface in the formation of a pore.

If small particulate matter is used in the practice of the present invention, such small particles must be given a higher velocity assuming equal density so that they possess sufficient force at impact to form micropores. Such smaller particulate matter may be successfully used in the practice of the instant invention by increasing the height from which such matter is dropped for impinging said particles on said chromium surface. Merely dropping such small particles short distances onto a chromium surface would not result in sufiicient momentum to effect such pore formation as required by the instant invention. It. on the other hand, large particles possessing excess momentum were employed, they would result in dulling or destruction of the chromium surface unless the impacts were precisely controlled which would not be commercial- 4 ly feasible. Should lead of the same mass be substituted for sand, for instance, the velocity of the lead particle would have to be somewhat above the velocity of the sand in order to accomplish the same results, this being due to the fact that lead is more malleable than silica and would absorb more of the force of the impact on the chromium surface.

Another factor which would influence the size, hardness and velocity of the particle is the chromium surface itself.

The size of the particles impinging upon the chromium surface so as to produce the microporous condition as indicated previously may vary widely. However, generally the particles would be in the size range of 15-400 mesh although larger or smaller particles can effect the same result under appropriate conditions.

In the practice of the instant invention, particulate matter is made to contact the chromium surface of the object which has an underlying nickel layer. The appropriate size particle utilizing the appropriate force is thereby used for a sufficient period of time to form pores in the chromium surface. To effect appreciable increases in corrosion resistance, the minimum number of pores formed should be at least approximately 3,000 per square inch, although lesser numbers of pores so formed effect some corrosion resistance improvement. The preferable pore density is in the range of 40,000 to 200,000 per square inch. The pore size can be anything up to approximately a few microns. The only upper limit on the pore concentration is that the pore formations should cease before the chromium electroplate shows dulling to the human eye. In determining the microporosity of the chromium layer, use is made of the Dubpernell test in which the composite electroplate is made cathodic in an acidic copper sulfate solution, preferably with a cell potential of about 0.2-0.3 volt. Copper is thus deposited only at the pores and not on the bulk of the surface where it is believed the chromium is covered by an oxide film. The frequency of microporosity is determined by using a microscope at -400 magnification.

The brightness of the finished article, that is after treatment of the. final chromium layer, depends on the number and size of the pores in the chromium layer. The limits could be determined by extensive laboratory work. However, this would appear to be an unnecessary expenditure of time and effort since visual observation of the chr0- mium layer during treatment foretells the finish one could expect on the final product. If the treated chromium layer is overtreated it visibly dulls and a satin finish thus results, whereas if it remains bright, a decorative chromium finish as contemplated by this invention will result. Thus, according to the instant invention, impingement of solid particulate matter on the chromium layer should be stopped before said chromium surface shows dulling to the human eye.

It is surprising that porosity of the chromium can be elfected With an insignificant effect on the brightness of the chromium surface as viewed with the naked eye. By use of an intense light and a non-treated surface for comparison, it is possible to see a slight haze in the surface of the treated sample. It is even more surprising when it is noted that similar but harsher treatments which are used for satinizing chromium or removing metal, lead to much reduced corrosion protection.

One important object which must be kept in mind in the practice of the instant invention is that the pores must extend through or almost through the chromium layer but may not extend entirely through the nickel layer underneath unless, of course, another layer of nickel underlies said pore containing layer. Likewise, additional metallic layers such as copper, nickel or the like can be interposed between the base material and the nickel-microporous chromium outer layers to further improve corrosion resistance and the like.

The present invention is applicable to all standard bright nickel and chromium electroplating baths as an improvement in corrosion resistance results in each and every case over the equivalent untreated composite.

In determining the corrosion resistance, suitable accelerated tests which correlate well with longer service tests on commercial articles of manufacture were used. These include the Copper Accelerated Salt Spray (CASS) and Corrodkote tests. Using these accelerated tests, the enhancement of the corrosion resistance by the practice of the instant invention has been damatically shown.

It should be noted that when corrosion tests are made, two types of corrosive attack generally result. With conventional chromium-nickel systems, pinhole corrosion occurs in relatively few sites in which rapid penetration to the base layer generally occurs as shown by basis metal corrosion. If the base metal for the electrodeposited coatings is steel, rust will become evident in the pinhole points of attack although the remaining bulk surface of the object may remain bright and show little attack.

Where a nickel-chromium surface has been treated according to the instant invention, few if any pinhole rust spots will develop over long periods for normal thicknesses. However, shallow surface attack will occur at the pores in the chromium and the test object will tend to appear dull and stained in varying degree due to corrosion of the nickel at the pores. However, this stain can be removed by simple washing.

The following examples illustrate the practice of the instant invention.

EXAMPLE I 4" x 6" fiat steel panels (3 per set) were plated with 0.4 mil semibright nickel onto which were subsequently plated 0.2 mil of bright nickel. These electroplating baths used to plate the nickel were standard commercial baths and provided typical deposits well known to those skilled in the art. After the panels had been plated with the two layers of nickel, they were then chromium plated. The chromium deposit was 10 millionths of an inch thick and was deposited from a conventional chromium electroplating bath having a Gro /H 50 ratio of 100: 1. The panels were then treated by pouring various solid materials as hereinafter described over the surface of the panel to provide impingement of the solid materials on the panels at a 45 angle so as to form micropores in said chromium surface. Unless otherwise specified, 250 cc. of the solid were poured as uniformly as possible over the surface of 4 x 6" panel. One panel per set was Dubpernell tested and the pore count for the set determined. The remaining two panels were corrosion tested 48 hours CASS, then 20 hours Corrodkote. Corrosion test results are given below for the solid treated panels as well as untreated control panels and numbers given under the corrosion test headings refer to pinhole rust spots. All panels resulted in a decorative chromium finish with the surface being fully bright. Test parameters and results of such tests are as follows:

Drop Pinhole 21st spots ht., Pores per 32 hrs. 48 hrs. 20 hrs.

Test material inches Dubpernell test sq. in. CASS CASS Corrodkote 3 Fine mleroprosity 79,s00-s9,400 g Rounded, Ottawa Sand 2325 mesh 10 d0 104,000 1 4,000 g 1% is ...do 134,000-164,000 g g 36 do 22s,000-a7s, 000 2 8 i 3 Fine mler0poroslty 40, 000-45, 000 g 10 do 104, 000-134, 000 g i Jagge San 3 -34 e h 18 .do 492, 000-537, 000 36 .--..do 596, 000-640, 000 g g 10 Medium porosity 3, 300-5, 000 g5 Pb Powder 8 .....do 8,30011,600 g 36 .-...do 11, 600-16, 600 a g 10 Very coarse porosity 5%? 5388 X /ie" X l ie, P lyethylene pellets 2.8% T104 (Goodrlcdl 18 do g Geon Vinyl #8814, white). 36 undo n 0 Z 11 200 10 Coarse porosity g 5% 52%? M filin 18 do 83 538g 36 4 a 132 at: Ottawa Sand cc 10 Fine mleroporoslty 45,000-75, 000 g g 2 Ottawa Salldi 250 10 d0 104,000- ,000 13 Ottawa sand, 75 cc 4.... 10 415,000450000i 2 TABLE-Continued Pinhole rust spots Drop ht., Pores per 32 hrs. 48 hrs. 20 hrs. Test material inches Dubpernell test sq. in. CASS CASS Corrodkote 10 100 200 33 100 200 Untreated std. Cr (Controls) Edge maeroeracking 9 100 200 2 38 100 4 60 200 33 100 200 EXAMPLE H EXAMPLE V 15 In another test 4" x 6" steel panels (3 per set) were plated successively with 0.7 mil of semibright nickel, 0.3 mil of standard bright nickel and 0.02 mil of chromium. After plating, two of the panels were treated with Ottawa sand (250 cc.) as described in Example I using a drop height of 6 inches. The sand treatment resulted in the appropriate microporosity as shown by the Dubpernell test performed on the third panel. The sand treated panels as well as control panels (without the sand treatment) were CASS tested for 46 hrs. and then Corrodkote tested for 60 hrs. with the following results:

CASS Corrodkote System 16 hrs. 46 hrs. 20 hrs. 40 hrs. 60 hrs.

Std. Cr Control i o o 20 D 0 60 Std. Cr Treated 0 0 0 0 0 D0 0 0 0 0 0 EXAMPLE III -In another series of tests to determine the effect of the sand treatment on panels going directly into the Corrodkote test, 0.4 mil of semibright nickel, 0.2 mil of standard bright nickel and 0.02 mil of conventional chromium were electrodeposited consecutively. These panels were then sand treated as described in Example II above and then Corrodkote tested directly. Test results were as follows:

Commercially available automotive bumper wings, electroplated successively with 0.5 mil semi-bright nickel, 0.3 mil standard bright nickel and 20 millionths conventional chromium were sand treated by dropping Ottawa sand from approximately inches with distribution as uniform as possible over the surface with the following results:

Corrodkoto Bumper wing hrs. 40 hrs. 60 hrs Control 70 100 100 Sand treated 5 6 5 Plastic panel (3 /2 x 3") were pretreated by conventional means, given a thin coating of electroless nickel and then electroplated successively with 0.8 mil bright acid copper, 0.4 mil senribright nickel, 0.2 mil standard bright nickel and 0.01 mil conventional chromium. Panels were treated by dropping Ottawa sand from 12 inches, with the following results after the successive CASS, Corrodkote, CASS exposures indicated:

The corrosion spots represent pores through the chromium and nickel and green copper corrosion exuding to the surface.

All numbers in the foregoing examples under CASS corrosion tests indicate pinhole corrosion spots.

We claim:

1. A process of treating a bright decorative composite electroplate of nickel and chromium on a metal or plastic substrate to increase the corrosion protection of said substrate comprising impinging a solid particulate material against the surface of the chromium with a force sufficient to form micropores extending through the chromium layer but insufficient to penetrate through the nickel layer or to adversely affect the brightness of the electrodeposit.

2. A process as described in claim 1 wherein said chromium deposit is contacted with said solid particulate material until at least 3,000 micropores per square inch are formed through said chromium deposit.

3. The process of claim 1 wherein the solid particulate material is impinged on the substrate by dropping.

4. The process of claim 3 wherein the particulate material is dropped from a distance of between about 3 inches and 36 inches.

5. A process of forming micropores in the thin decorative chromium layer forming the top layer of a duplex nickel-chromium layer electrodeposited on a metallic substrate comprising contacting a chromium layer with a solid particulate material with a force and for a period of time that are sufiicient to form micropores through the chromium layer but insuflicient to penetrate through the nickel layer or to appreciably affect the brightness of the duplex layer.

6. The process according to claim 5 wherein the chromium layer is contacted with said particulate material for a sufficient length of time until at least about 3,000 micropores per square inch are formed in said chromium layer.

7. The process according to claim 6 wherein the chromium layer is contacted with said particulate material until between 40,000 and 200,000 micropores are formed per square inch.

8. The process according to claim 7 wherein said solid particulate material is dropped on to the chromium layer 8 from a distance of between about 3 in. and 36 in. above 3,298,802 1/1967 Odekerken 204-41 said layer. 3,382,159 5/1968 Reed 7263 9. The process according to claim 8 wherein the solid 3,410,124 11/1968 Makoto 7253 3,449,223 6/1969 'Odekenken 29194 particulate material is sand.

RICHARD J. HERBST, Primary Examiner US. Cl. X.R.

References Cited UNITED STATES PATENTS 2,248,530 7/1941 Ellesworth 29--DIG16 2,999,798 9/1961 Eisele et a1. "204-41 29DIG 36