International Business Machines Corporation

James M Vigar

Donald J Barclay

William M Morgan

A trivalent chromium electroplating solution containing trivalent chromium ions, a complexant, a buffer and an organic compound having a --C.dbd.S group or a --C--S-- group. The complexant is selected to give the chromium complex a stability constant, K.sub.1, in the range 10.sup.8 &lt;K.sub.1 &lt;10.sup.12 M.sup.-1.

Electrodeposition of chromium and its alloys

A trivalent chromium electroplating solution containing trivalent chromium ions, a complexant, a buffer and thiocyanate ions. The thiocyanate is of a molar concentration which is lower than the molar concentration of the chromium ions, and the chromium ion concentration being lower than 0.1 M. The stability constant, K.sub.1, of the solution's chromium complex is in the range 10.sup.8 &lt;K.sub.1 &lt;10.sup.12 M.sup.-1.

Bath and process for the electrodeposition of chromium

A trivalent chromium electroplating solution containing trivalent chromium ions, a complexant, a buffer and a sulphur species selected from sulphites and dithionites, the complexant being selected to impart a stability constant, K.sub.1, to the chromium complex which is in the range 10.sup.6 &lt;K.sub.1 &lt;10.sup.12 M.sup.-1. The chromium ion molar concentration is lower than 0.01M. The complexant is selected from aspartic acid, iminodiacetic acid, nitrilotriacetic acid, 5-sulphosalicylic acid or citric acid.

Trivalent chromium electroplating baths

A trivalent chromium electroplating solution containing trivalent chromium ions, a complexant, a buffer and a sulphur species having S--O or S--S bonds. The complexant is selected to give the chromium complex a stability constant, K.sub.1, in the range 10.sup.6 &lt;K.sub.1 &lt;10.sup.12 M.sup.-1.

A chromium electroplating solution in which the source of chromium comprises an equilibrated aqueous solution of chromium (III) - thiocyanate complexes having supporting electrolyte consisting essentially of potassium sulphate or, preferably, a mixture of potassium and sodium sulphates. The solution is employed as the catholyte in a plating bath in which the catholyte and anolyte are separated by a cation exchange membrane. This all-sulphate bath permits the use of lead anodes, has high efficiency and a good plating range.

Trivalent chromium electroplating solution and process

A process for plating thick chromium coatings for engineering applications comprises depositing a thin initial layer from a low concentration chromium III/thiocyanate bath and depositing the bulk of the remaining thickness from a relatively higher concentration chromium III/thiocyanate bath. Deposits produced by this two-stage process are more cohesive and smoother than those obtainable by plating the entire thickness from the high concentration bath alone.

Process for the deposition of thick chromium films from trivalent

A very low concentration (below 0.03 M) trivalent chromium plating bath in which the source of chromium is an equilibrated aqueous solution of a chromium (III) - thiocyanate complex gives a deposit of unexpectedly light color. Such a bath is employed to produce thin overcoatings of light colored chromium for decorative applications. The bath and process is also used to plate the initial layer of a thick (greater than 5 micron) deposit for engineering applications, the major part of which is plated from a higher chromium concentration bath. Such thick deposits from a higher concentration bath are more cohesive and smoother when plated over an initial layer from the low concentration bath.

Low concentration trivalent chromium electroplating solution and process

Generation of hydrogen cyanide at the anode in a chromium (III) - thiocyanate plating bath, resulting from oxidation of thiocyanate anions, is prevented by an additive to the electroplating solution which oxidizes at the anode in preference to the thiocyanate, and whose reaction products will not adversely affect the cathode reaction. Such an additive is potassium iodide.

Elimination of anode hydrogen cyanide formation in trivalent chromium

A method for brightening an electroplated chromium deposit wherein the deposited chromium is contacted with a solution having a constituent capable of forming complexes with chromium hydroxide species and of detaching the complexes so formed from the surface of an electroplated deposit. Preferably the solution is an alkaline ferricyanide solution or a solution of sodium dichromate in sulphuric acid.

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Winchester, United Kingdom

James M Vigar