US1544451A - Electrodeposition of chromium - Google Patents

Description

Patented June 30, 1925.

UNITED STATES ,544,451 ATENT CARL HAMBUECHEN, OF MOUNT VERNON, NEW YORK, ASSIGNO'R TO IEJLE(HERO METALLURGICAL COMPANY, A CORPORATION OF WEST VIRGINIA.

ELECTRODEPOSITION OF CHROMIUM,

N Drawing.

To allwlaom it may concern: Be it known that I, CARL HAMBUEQHEN, a citizen of the United States, residing at .Mount Vernon, in the county of Westchester 5 and State of New York, have invented certain new and useful Improvements in Electrodepo si tion of Chromium, of which the 1 following is a specification.

I The invention is a process for electrodein positing chromium. The object is to provide an improved process easier of execution and capable of giving deposits of better quality. This object is attained by the use of an electrolyte of novel composition. A is novel arrangement of anodes is also included in the invention. v

As electrolyte I employ an aqueous solution of chromic acid to which has been added asmall quantity of a fiuorid, such as chromium, iron, ammonium or sodium fluorid. The electrolyte is preferably free from strong. mineral acids such as sulphuric and hydrochloric.

To prepare the electrolyte I merely dissolve pure chromic acid in water in the proportion of about 200 to 600 grams per liter 'of s'olution, and add about 10 to 50 grams of sodium .fluorid or an amount of another metal fluorid containing an equal quantity of fluorin to each liter of the solution. Very good results have been obtained .with an electrolyte containing 300 grams of CrO per literl The deposition may be carried out at room temperature or above. Temperatures below C.

.peres per square foot have given good '-results "If a small amount of sulphuric acid is added; to electrolyte prepared as described above,- the electrolyte does not become totally inoperative, but the current efiicienc'y is" fiuorin had been, added, in one 1 case; as

. sodium fluorid and in the other case as hydrofluoric acid were compared, "The-cursrent efficiency ofthe. sodium" -fluo'rid bath: 4 {was almost double-that o he t r h tawh'ile'the voltage required was much less Application filed. July 5, 1924. Serial No. 724,515.-

than half.

are preferred. Cathode current densities of 50 to 300 'am-.,

[cathode-surface.

claim! 1. Abath forelectrodepositing'chromium,

The bath containing hydro fiuoric acid accordingly consumed more than four times as much power per gram of chromium deposited. I

The electrolyte of my invention can be assure used in-conjunction with insoluble anodes of materials such 'as lead and lead peroxid.

It is of course necessary to replenish the bath from time to time with additions of chromic acid. In attempting to operate with chromium anodes, I have found that the current efliciency at the anode greatly exceeds that at the cathode, causing the chromium content of the bath to increase continuously, raising the voltage, and diminishing the current efficiency. The same effect has been observed with other electro-. lytes proposed for the deposition of chromium. I avoid this difficulty by the use of both insoluble anodes and soluble chromium anodes.

them in the bath simultaneously. It is impossible to state what ratio of insoluble anode surface to soluble anode surface will maintain the bath in constant conditionunder all circumstances, since this ratio may vary with the desired chromium concentrationin the bath, with the anode current density and its relation to the cathode current density, with the temperature of the bath, etc. The proper ratio for a particular arrangement is readily found by trial. With a chromium anode having a surfacev equal to the cathode surface, anode current eflicien cies about. six times' asgreat'as the cathode: current efliciency have often been observed.'

as lead, is therefore indicated, and has been approximately equal to the Having. now. described my invention, jI

containing I c'hromie aciv in ,e rcess anda soluble metal fluor1d, and be ng substans The replacement of about five-sixths of the anode surface with insoluble material, such tially free from acids other than chromic. 2. A bath for electrodepositing chromium containingper liter 200 to 600 grams. of

chromic acid and 10 to 50 grams of an alkali metal fluorid, and beingsubstantially free from acids other than chromic.

3. A bath for electrodepositing chromium containing chromic acid and 10 to 50' grams of sodium fiuorid per liter, and being subs stanti-ally free from acids other than chromic, and from sulphates.

4. Process of electrode ositing chromium from a bath containing 0 romic acid which comprises passing the depositing current into the bath through a soluble anode containing chromium, and an insoluble anode,

and adjusting the surfaces of the two anodes and the times of their immersion to main tain an efiicient concentration of chromium in the bath. 5. Process of electrodepositing chromium from a bath containing chromic acid which comprises passing the depositing current into the bath simultaneously-through a solubl e anode containing chromium, and an insoluble anode, and adjusting the surfaces of 7.. Process of electrodepositing chromium from a bath containing chromic acid and an alkali metal .fluorid, which comprises assing the depositing current into the ath through a soluble anode containing chromium, and an insoluhle anode, and adjust-- ing the surfaces of the'twoj anodes and the times of their-immersion to maintain an gflicientconcentration of chromium in the ath.

8; Process of electrode ositing chromium from a bath containing 0 romic acid and a metal fluorid, which comprises passing the de ositing current into the bath through a so uble anode containing chromium, and an insoluble anode, and adjustingvthe surfaces of the two anodes and the times. of their immersion to maintain an efiicient concen-v tration of chromium in the bath. H In testimony whereof I 'afiizrmy signature. I

CARL HAMBIIZJEOHEN.