US2307551A - Method of producing a white, platinumlike color chromium plate and the product thereof and bath therefor - Google Patents

Description

Pam-a Jan. 5, 1943 2,301,551 Ma'mon or raonucmo, a warm, rm'r- THEREFOR COLOR CHBOMIUM PLATE AND THE PRODUCT THEREOF ANDBATH Joseph John Trisha, Ea'st Elmhurst, N. Y., as-

signor, by direct and meme assignments, to

te Corporation, I eration of New York New York, N. Y., a cor- NoDrawing. Application August 19, 1939,

Serial No. 291,040

The present invention relates to an improved process for chromium plating articles of manufacture with an ornamental and/or protective plate having a white, platinum-like color and being substantially devoid of a bluish tint or purplishcast, to a product of such a process, and

" to a bath therefor.

It is well-known that thechromium plate produced by conventional electroplating processes possessed a highly objectionable bluish tint or purplish cast. In some industries, the bluish tint or purplish cast has been so objectionable as to reduce the value of the chromium plate or to render it unacceptable or unsalable. This has been particularly true in the Jewelry trade where white and platinum-like color has been'desired and has commanded a premium, while the bluish or purplish casts or tints of conventional chromium plating having been objected to by jewelers, merchants and the public. Even in the sanitary industry or plumbing trade, a demand has arisen for'a white chromium plate whereas the conventional bluish chromium plate has fallen into disfavor. Similarly, other industries wanting a "live plate have desired a white chromium plate instead of the "dead" plate of the customary bluish chromium plate. The shortcomings and disadvantages of the bluish chromium plate of prior art processes of chromium electro-plating including the Fink process (U. S. Patent No.

1,496,845), the Hambuechen process (U. S. Patent No. 1,544,451) and-other processes have been known to those skilled in the art. Although the investigators have been diligently endeavoring to solve the problem confronting the art, no wholly satisfactory and successful process has been proposed to produce an acceptable plate having a white and platinum-like tially devoid of a bluish I have discovered an improved process of electro-plating chromium which avoids the occurrence of a bluish or purplish plate and which pro duces an attractive white and platinum-like colored plate.

It is an object of the color which is substanor purplish cast.

present invention to provide an improved process of chromium plating on articles of manufacture with a white, platinum-like color. 7 It is another object of the present invention to provide a bath platinum-like colored chromium plating.

It is a further object to provide articles of manufacture plated with chromium having a white, platinum-like color devoid of a bluish or purplish tint.

.for electro-dcpositing white,

5 Claims. (Cl. 204-51) Other objects and advantages of the invention will become apparent from the following description.

Broadly stated. my invention comprises adding to any appropriate commercial or practical chromium plating solution metallic cadmium or an oxide of cadmium or a salt of cadmium, and then subsequently electrolyzing the plating solution to electrodeposit a white, platinum-like chrome plate.

It is to be observed that my new whitish, platinum-colored chromium plate is more resistant to rusting than the conventional chromium plate. This was shown by the results obtained by plating nails in the conventional chromium plating solution and plating similar nails in my improved chromium solution by my improved process and subsequently simultaneously exposing both groups of nails to the weather. Those nails plated with conventional chromium showed signs of rust before the end of a four month period while the others showed no signs of rusting.

For the purpose of giving those skilled in the art a better understanding of the following illustrative examples. are given.

Example No. 1

A chromium plating bath is made bydissolving about 300 grams chromic acid per liter or about 10 ounces of chromic acid in a quart of water, and adding about 3 cubic centimeters of concentrated sulfuric acid. When all of the diromic oxide is in solution about 10 to about 40 grams of cadmium metal or preferably about 15-20 to about grams of cadmium oxide or the equivalent amount of cadmium salt per quart are added. The solution is kept at the proper temperature (80 to 110 F.) and electrolyzed for a suitable period of time, depending upon current density and volume of the bath, preferably about three to about five hours for a 10,000 gallon bath, at a potential diil'erence of about five volts or until the cathode has been coated with a thin deposit. In order to determine whether or not the bath is in a condition permitting the deposit of a white,

The temperature is maintained at about F.

invention, the

to about 110 F. A chromium plate is obtained which has a white, platinum-like color practically devoid of bluish and purplish hues. The

throwing power of the present improved plating solution is increased over that of the conventional chromium plating solution. In some instances, an increase of throwing power up to Throwing Power of Chromium Plating Baths With the Cavity Scale Test Metal Cleaning and Finishing, October 1930, page 851.

Example No. 2

Into an electrolytic cell containing sumcient water and sufiicient chromium tri-oxide, an appropriate amount of sulfuric acid and of chromium hydroxideare introduced to bring the concentrations to about 250 grams of CrOs, about 3 grams of H2804 and about 6 grams Cr(OH)'a per liter; .When solution is complete, about 10 to about 40 grams of cadmium or about 12 to about 45 grams cadmium oxide or the equivalent of cadmium as. a salt are added per liter. The bath is "pretreated for a period of time, say for about one hour for a bath having a volume of 100 gallons, at the normal working temperature of the bath (about 80 to about 110 F.) at a potential difference of about 5 volts and a current density of about 0.75 amp. sq. in. or until a test strip immersed in the bath has deposited thereon a white, platinum-like deposit. The articles to be plated are then connected as a cathode and a coating of white, platinum-colored chromium is deposited at a current density of about 40 to about 110 amperes per square foot at a voltage of about 4 to about 6 volts. The temperature is maintained at about 80 F. toabout 110 F. or at the. working temperature of the bath. A chromium plate is obtained which has a white, platinum-like color substantially without any blue or purple hue.

Example N0. 3

For the purpose of depositing the new platinum-colored plate. of chromium by electrolysis of a solution containing chromium and cadmium, a fluoride bath similar to the fluoride bath of Hambuechen, etc. is made. About 800 grams of chromic acid and about grams of sodium fluoride or about 8 grams of hydrofluoric acid are addedto one liter of water or proportional quantities to larger volumes of water. When the solution of these ingredients has occurred about 10 to about 40 grams of cadmium or about 12 to about 45 grams of oxide of cadmium per quart or an equivalent amount of a soluble salt of cadmium are added. The solution is warmed until the temperature is about 36 to about 45 C. The bath is pretreated" as described heretofore. The articles to be plated are made the cathode in an electric circuit and plated with a white, platinum-like coating substantially devoid of a bluish or purplish cast or tint by passing a current through said electric circuit at a potential difamount of material plated, the deposit on the articles will have a tendency to become bluish or purplish. As soon as the bluish or purplish cast appears, the normal plating operation is discontinued. The color of the plating may be restored by replenishing the supply of cadmium in the bath. This may be done conveniently by placing, one or more sticks of cadmium metal in the bath or by the addition of suificient cadmium oxide to restore the metal concentration to the original one. In order to determine whether or not the bath is in a condition permitting the deposit of a white, platinum-like color chromium plate test strips are immersed from time to time during the "pretreatmen period. The bath is ready for use when a test strip is coated with a deposit of white, platinum-like color. I have found that in general the increase of the cadmium content of .the bath to a concentration above 45 grams of cadmium or its equivalent of cadmium compounds produces a gray deposit which is burned on the'edges. Simultaneously, the throwing power of the bath is reduced. The concentration of cadmium should preferably be controlled within critical limits for best results.

I have also found that the cadmium may be alloyed with the'anode material, for. example,

ference of from about 3 to about 6 volts at a longer or shorter periods depending upon the with the leadof the anode and in thatway cadmium may be introduced into the bath.

In producing my new whitish, platinum-colored chromium plating I have obtained satisfactory results with electrolytes containing cadmium and chromium as the major metallic constituents and containing as minor constituents mainly lead and antimony together with lesser amounts of zinc, tin, copper, manganese, magnesium, iron, aluminum, thallium. Lead and antimony present to the extent of a fraction of a percent to about 1% give satisfactory results. In practice I have employed cadmium oxide with a lead content of about 0.5% and an antimony content of about the same order of magnitude and obtained very satisfactory results.

Platings produced in a bath having the compositions indicated above have been found to contain small amounts of lead such as about 0.0001 to about 0.003%. Whether thenew results are dependentupon the presence of lead in the plating or whether the modifying elements combine to afiect the development of the crystals of the chromium plating has not been established nor has the verity of any other theoretical explanation been established. Nevertheless, my.-

new whitish, platinum-colored chromium plate is readily recognized whether in bright finish or matte finish or in other finishes by the practically total absence of reflection in the bluish or purplish range of light.

I have found that in order to obtain a whitish, platinum-colored chromium plate it is necessary to pro-treat or electrolyze a conventional chromium plating bath adapted to produce a chromium plate having bluish or purplish hues after modification by the addition of additional elements as described hereinbefore. The pretreatment may be carried out at various current densities and for periods of time correlated with the electrode area, the volume of the bath and the current density. Thus, for small baths having a volume of a liter or so, the "pretreatment may be carried out at a current density of about 0.5 amp/sq. in. At such a current density a pretreatment for a period of a fraction of an hour, say 20 minutes is suflicient. A commercial bath of, say, gallons capacity may likewise be converted from one producing a bluish chromium plate to a bath capable of producing my new whitish, platinum-colored chromium plate by pretreating after the addition of modifying elements at a current density of about 0.75 amp/sq. in for example, for a fraction of an hour, say, one half hour, to about an hour. Similarly, a 500 gallon bath after pretreatment for about 1.5 hours to about 2 hours at a current density of about 0.75 amp/sq. in. likewise may be employed for the production of my improved chromium plating substantially devoid of bluish and purplish hues. As illustrative which the pretreatment of a 1,000 gallon bath, modified as described hereinbefore, may be carried out is as follows: the current density employed may be about 0.75 amp/sq. in. and the bath electrolyzedfor about 2.5 to about 3 hours. I have also obtained satisfactory results by pretreating a conventional chromium bath of 10,000 gallons capacity and modified in accordance with the principles of the present invention for a period of about 3 hours to about 5 hours at a current density of about 2.5 amperes per square inch. From the foregoing it will be appreciated by those skilled in the art that various changes may be made in the conditions of pretreatment without departing from the spirit of the present invention provided the pre-treatment of a conventional chromium plating bath only capable of producing a bluish or purplish chromium plate results in the production of my whitish, platinum colored chromium plat ng. The extent and efficiency of any set of conditions of pre-treatment is clearly determined by means of a test strip.

When the deposit on a test strip plated in a conventional chromium bath modified in accordance with the principle of the present invention becomes a whitish, platinum-color the pre-treatment may be discontinued and commercial use of the bath proceed.

Certain modification in the procedure permit plating various finishes on various bases. For example, a matte finish may be obtained by interrupting the current during the plating 01 an article. A hard finish may be obtained by controlling the amount of sulfates in the bath. For example, it has been found that with about 250 grams of chromic oxide per liter that about 3-4 grams of H2804 per liter give hard deposits at a voltage of about 3.5 to 4 volts. On the other hand, a soft ductile pate may be obtained by operating at hi her than normal working temperatures, say at about 115 F., with normal current densities.

Iron or steel may be plated directly after conventional cleaning in acustomary manner or after applying a preliminary nickel or copper plate. Nickel or German silver can be plated directly after conventional cleaning, while brass, copper and bronze may be plated directly or after a previous nickel plate. Tin or silver is plated with my new white, platinum-like plate after preliminary plating with nickel. Silver when plated directly has a "matte finish. Zinc, a uminum and lead die castings can be plated with my new whitish, platinum-colored chromium coating after being made practically chemically clean and plated with copper, the usual current densities and temperatures.

The thickness of the deposit by the time taken for plating. For example, a good commercial deposit for the Jewelry trade may be obtained in about to minutes under normal conditions. For plating dies, tools, etc.,

of the conditions under.

duced consistently Type of finish Time for .Time for heavy light plate Scientific explanations sults obtained by at the present time. my white, platinum-like alloy finish can be proof the remarkable rethis pretreatment are unknown It sufiices, however, that upon a practical scale by the use of my pretreatment in conjunction with my novel electrolyte and process.

It is .to be observed that further modifications of my process can bemade. For example, boric acid, tartaric acid, citric acid, oxalic acid, and mono-sodiuni, di-sodium and trisodium phosphates may be added to commercial chromium plating solutions as. modifiers.- The addition of these modifying agents in amounts up to about 20 to about 30 grams per liter makes possible the addition of increasing amounts of cadmium oxide or other sources of cadmium. In the presence of from about 10-20 grams of boric acid per liter, for example, the quantity of cadmium oxide may be increased to about to about grams per liter without the deposit losing its white, platinum-like finish or showing signs of burning. Likewise with 10 to about 30 grams of oxalic acid and the other modifiers enumerated hereinabove the quantity of cadmium oxide which may be added without deleterious effect upon the finish may be increased to about 160 grams per liter. The phosphates noted herein above may be used separately or in combination with tri-sodium phosphate.

It was surprisingto find that the addition of hydrofluoric acid metal fluoride (NaF, KF, etc.) as a modifying agent to the conventional Fink sulfate bath permits the cadmium oxide content to be raised to about 160 grams per liter without deleterious effects.

It is to be observed that the present invention provides a chromium deposit which to the unaided eye does not reflect light of the wave length of blue or purple range of the spectrum.

shows the practically total absence of reflection in the blue or purple range. This may be assumed to be a result of grain size although I do not wish to be limited to this explanation. For, whatever may be the explanation of the cause of the absence of bluish and purplish hues from my new whitish, platinum-colored chromium plate, the fact nevertheless remains that any conventional, commercial, industrially practical chromium bath which is modified and pre treated in accordance with the principles of the present invention produces my new whitish, platinum-colored chromium plate.

Although the present invention has been described be understood that variations and modifications may be resorted to as those skilled in the art will readily understand. Thus, when a chromium skilled in the art. Furthermore various articles of manufacture may be plated including bracelets, chains, rings, vanity cases, lipstick cases, optical frames, cigarette cases, cigar lighters,

watch cases, hollow and tableware, jewelry and novelty work, surgical instruments, plumbing ware, ornamental iron and bronze fittings for show-windows, display fixtures, hardware, lighting fixtures, kitchen utensils, ofiice articles, inkstands, letter openers, automobile parts and accessories, reflectors, etc., etc.

the purview of the-present specification and the scope of the appended claims.

The present application is a continuation in partof :myco-pending application, Serial No.

119.628; filed in the U. S. Patent Oflice on Janj :1. A method for providingarticles with a chromium electroplating having a white, platinumlike color substantially devoid of bluish and purplish' hues which comprises preparing a chromium plating bath for the industrial electrodeposition of a conventional electroplate of bluish chromium, said bath containing chromic acid and a chromium plating catalyst comprising an acid radical and having immersed therein an electrode surface, adding at least about 13 to about 1'! grams to about 35 grams of metallic cadmium and up to about 1% of lead and antimony per liter to said bath, pretreating said bath by passing a current between an anode and a test cathode immersed therein at a current density of about 0.5 to about 2.5 amperes per square inch and at about 5 volts for a'period of time varying from a fraction of an hour to several hours until a test plate shows awhite, platinum-colored deposit of chromium substantially devoid of bluish and purplish hues, making an article to be plated with platinum-colored chromium the oathode of said. electrolyzed bath, passing an electric current through said electrolyzed chromium bath at a potential difference of about 3 to about 6 volts at a current density of about 40 to about 110 amperes per square foot while maintaining the bath at a temperature of about 80 to about 110 F., continuing to plate a succession of artides in said electrolyzed bath until an article being. plated begins to show bluish and pur-' plish hues, adding suiiicient metallic cadmium to said bath to bring the concentration of cadmium to at least about 15 to about grams to about 30 .grams of cadmium per liter, then continuing to plate the said bath and repeating the Such variation and modifications are considered to be within void of bluish and purplish hues, making an aring catalyst comprising an acid radical for industrial plating of conventional bluish chromium electroplating, including in said bath at least 13 grams per liter of cadmium, an effective amount up to about 1% of lead and antimony and an amount of modifier-up to about 30 grams per liter selected from the group consisting of boric acid, hydrofluoric acid, alkali metal fluorides and mono-, diand tri-sodium phosphates, whereby the amount of cadmium which may be included inthe aforesaid bath may be greater than 35 grams of metallic cadmium, said bath having an electrode surface immersed therein, pretreating said bath by passing a current between an anode and a test cathode immersed therein at a current density of about 0.5 to about 2.5 amperes per square inch and at about 5 volts for a period of time varying from a fraction of an hour to several hours until a test plate shows a white, platinum colored deposit of chromium substantially deticle to be electroplated with chromium the oathode of said electrolyzed bath, and passing an electric current through said electrolyzed bath at a potential difference of about 4 to about 6 volts at a current density of about 40 to about 110 amperes per square foot While maintaining the temperature of said bath at about to about F., whereby an article is electroplated with a white, platinum-like chromium electroplating containing cadium and substantially devoid of bluish and purplish hues.

3. An electroplating bath for use in electrodepositing white, platinum-like chromium electroplatings substantially devoid of bluish and purplish hues constituted principally of chromium comprising a solution containing chromic acid and a chromium plating catalyst comprising an acid radical in amount suflicient to produce commercial bluish chromium electroplatings, at least 13 grams per liter of cadmium, an eiiective amount of lead and antimony up to about 1% and an amount of modifier up to about 30 grams per liter adapted to make possible the addition of increased amounts of cadmium up to about grams per liter and being selected from the group consisting of boric and hydrofluoric acid,

alkali metal fluorides and mono-, di-, and trisodium phosphates, said bath having been pretreated by passing a current between an anode and a test cathode immersed therein at a current density of about 0.5 to about.2.5 amperes per square inch and at a. potential difference of about 5 volts for a period of time varying from a fraction of an hour to several hours until a test plate shows a white, platinum colored deposit of chromium substantially devoid of bluish and purplish hues and capable, only after such pretreatment, of electrodepositing white, platinum-like chromium platings substantially devoid of bluish and purplish hues.

4. An electroplating bath for use in electrodepositing chromium electroplatings constituted principally of chromium and cadmium in amount effective to produce a white, platinum-like deposit comprising a solution containing chromic acid, a chromium plating catalyst comprising the fluoride radical sufficient to deposit conventional bluish chromium electroplating commercially, an effective amount up to about 1% of lead and antimony and an amount of modifier up to about 30 grams per liter adapted to make possible the addition of increasing amounts of cadmium and at least 13 grams to about 160 grams of cadmium per liter, said bath having been pretreated by passing a current between an anode and a mium platings substantially devoid oi bluish and test cathode immersed therein at a current denpurplish hues.

sity of about 0.5 to about 2.5 amperes per square 5. As a new article of manufacture, an elecinch at a potential diflerence of about 5 volts for troplated article having a white, platinum-cola period of time varying from a fraction 01' an 5 ored plating of electrodeposited chromium conhour to several hours until the test plate shows taining about 0.0001 to about 0.003% lead, said a white, platinum colored electrodeposit of chroplating being substantially devoid of bluish and mium substantially devoid of bluish and purplish purplish hues.

hues and capable, only after such pretreatment, JOSEPH JOHN TRISKA. oi electrodepositing white, platinum-like chroi0