US1795459A - Chromium plating - Google Patents

Description

Patented 10, 1931 UNITED STATES PATENT OFFICE Y LEoE a. WESTBROOK, or CLEVELAND HEIGHTS, orrro, A'ssrenoa, BY MESNE Assrcn- MEN'IS, moi-rim en ssELLI CHEMICAL COMPANY, OF CLEVELAND, 0310, A coaro- No Drawing.

' RATION or DELAWARE The only commercially successful chromium plating is up to. the present time obtained from a chromic acid bath-containing a small amount of a compound capable ofbright, and adherent plates are desired; The

common expedient of adding a more or less Y colloidal organic substance to the plating both as used in-the plating of other metals, is inoperative-in the case of chromium; the strongly oxidizing chromic acid bath would destroy most of the available organic materials.

My invention consists 'nowof a chromic acid electroplating bath containing certain inorganic addition agents.

, I The agents which I have found beneficial in a chromic acid bath containing small amounts of an anion are compounds of the metals contained in the groupcomprising molybdenum and vanadium. While these two metals are not generally considered to be closely related or to have very similar chemical properties, they have been found to act quite alike and different from any other heavy metal compound tested by me when one of their compoundsis contained in a chromic acid plating bath. While most any molybdenum and vanadiumcompound, soluble in the plating bath, will show a beneficial effect in the chromium plating bath, I prefer to use a bath containing the-negative radical cor-' responding to the higher, acid-forming oxides of these two'metals. The most convenient manner of preparing such a bath is to add a water soluble molybdate or vanadate to the chromic acid solution, or to dissolve M00 or V 0 in aqueous causticalkali and add CHROMIUM PLATING Application filed February 23, 1928. Serial No. 256,494.

possible explanation of the similar action-of the various soluble molybdenum and vanadium compounds when added toa c hrofniic acid bath.

The molybdate and vanadate' radicals do not replace the anion required in the bath for a successful chromium plating. Tlie presence of an anion for instance, S0; ",is

still needed to produce bright plates.v Further additions to my novel baths, such as ,chromimum chomate,-are not indicated and 7 do not seem to produce any effect on the plating process.

The following are two typical formulae of novel plating baths embodying my invent1on: I

1. Molybdate bath I liit e zs Gro i' 250 Nazsok M003 -A 3 NaOH 2' 2. Vanadate bath, i

V I 3 Na SO .3 205 NaO-H W if i The molybdenum and vanadium compounds were dissolved 'separately with the caustic soda in a littlewater and added'to the chromicacid, sodium sulfate solutions.

The anion, SO; therein is furnished bynthe' sodium sulfate: i

The followingtable-gives the conditions under which Commercially valuable, bright,

hard, adherent chromium plates have been obtained with the above baths; Its shows-the cathode metal current efliciency in 'per cent i at various temperatures and cathode current densities in amperes' per "square foot. For purpose of comparison a similar, plain bath, from which the addition agent has been omitted, is included- The plates obtained in the yanadate and molybdate baths have a somewhat improved :appearance, such as better brightness, hard-- ness, and adherence, than those from the plain bath. These figures show, however, an additional advantage in the baths containing the addition agent; the current efiiciency is less 5 dependent on the current density which in- T dicates an improved throwing power over the plain bath, I claim: 1. A chromium plating bath consisting of an aqueous solution of chromic acid containing a small amount of a compound capable of dissociating to yield an anion, and a small amount of a compound of a metal of the group comprising molybdenum and vanadium. a t g 2. A chromium plating bath consisting of an aqueous solution of chromic acid containing a small amount of SO;" radical and a small amount of the negative radical corresponding to the higher acid-forming oxides of one of the metals of the group comprising molybdenum and Vanadium.

3. A chromium plating bath consisting of an aqueous solution of chromic acid containing a small amount of S0 radical and a small amount of the negative radical corresponding to one of the acids of the group com-- prising molybdic and vanadic acid. In testimony whereof, I aflix my signature.

LEON n. w s'rBRooK,