US1779436A - Process of electrodepositing metals of the platinum group - Google Patents

Description

Patented Oct. 28, 1930 UNITED STATES PATENT OFFICE CHRISTIAN WILLIAM KEITEL, OF PERTH AMBOY, NEW JERSEY, ASSIGNOIR TO BAKER &'COMPANY, INC.. A CORPORATION OF NEW JERSEY PROCESS OF ELECTBODEPOSITING METALS OE THE IPLATINUH GBO UP Ho Drawing.

shipped as articles of merchandise; to secure such .salts from which an eflicient bath for electroplating can be readily prepared; to secure .salts none of whose ingredients will have deleterious action on the durability of IQ the solution, and will be harmlessely and readily decomposed even if large amounts of metal are deposited from the bath, and to obtain other advantages and results as may be brought out by the following description.

According to my invention, I make use of a salt of the metal to be deposited which when decomposed by electrolysis deposits its metal element upon the article to be plated, while the other elements of the plating salt are eliminated as gases so that the electrolyte does not accumulate deleterious products. I have found the ammino nitrite salts of platinum, palladium and rhodium to fulfill these requirements, and preferably I make use of the diammino nitrites. This salt is diiiicultly soluble in water, but is readily soluble in hot dilute ammonia whereby it is transformed into tetrammino nitrite which is very soluble in water.' By introducing such ammino salts into the bath for electrodepositing and keeping it ammoniacal, the metallic concentration of the solution can be kept constant without deteriorating the bath.

To prepare the diammino salt, taking platinum as an example. a concentrated solution of platinum chloride or sodium platinum chloride is taken and a slight excess of a concentrated solution of sodium nitrite is added. This causes a change of color from orange to light yellow or nearly colorless, and nitrous fumes are given off as a gas. Heat is applied until no more reaction-takes place, and after cooling, a slight excess of ammonia is added. The resulting precipitate is filtered and washed alkali free, and is. the desired salt, namely platinum. diammino nitrite.

To prepare an electroplating. solutionfrom the platinum diammino nitrite, 100 grams of a suitable conducting'salt, such as ammonium nitrate or ammonium sulphate, are

Application filed July 2, 1929. Serial No. 875,582.

dissolved in one liter of distilled water containing 5% ammonia. the platinum diammino nitrite are added, and on heating to boiling, the latinum diammino nitrite will go into inum tetrammino nitrite.

In the electrolysis 2.2 volts or more are used. The temperature of the bath should be 95 C. or more and the solution should be kept ammoniacal, the platinum diammino nitrite being added as needed to supply platinum. It

so ution as plat- Then 20 grams of v will be noted that the hath made as above described will contain no chloride or other halogen compound, to accumulate and cause the bath to deteriorate, and furthermore it will be noted that in replenishin as stated, a bath containing a chloride or ot er halogen compound, the same will not be increased above the original content.

Plating salts for other metals of the latinum group, such as palladium and rho ium, can be made in a way corresponding to that which has been described for platinum, using palladous chloride for palladium and rhodium trichloride for rhodium, the succeeding steps being the same as in the case of latinum, within the skill of a chemist, and t e solution or bath prepared similarly.

Other salts than chlorides vmay be used, such as sulphates, and other double salts than sodium chlorides, such as ammonium chlorides, all as will be understood by those skilled in electro-metallurgical chemistry, and the salts expressly mentioned are to be regarded merely as typical ones.

I have found that de osits from these solutions are very dense an that the metals can be deposited singly or an alloy deposit secured by mixing solutions suchas havebeen described, as for example if platinum and palladium solutions are mixed together a deposit of an alloy of the two metals will be obtained. Platinum and rhodium solutions mixed give a platinum-rhodium alloy deposit, palladium and rhodium solutions a palladium-rhodiumalloy, and so on.

By my invention'I obtain a salt which can be most conveniently shi ped and handled, in small bulk, as compared withthe ship in and handling ofliquid solution, and which can he simply added to the electrodeposition bath as needed to keep it at the desired strength, and withoutin any Way deteriorating said bath. The commercial importance ofthis process of renewing the metal being deposited from the bath is very great and it is of great commercial value.

I have found that it is possible to plate successfully from solutions that contain as little as one ounce and as much as ten ounces of plating salt per gallon.

' Various substitutions of equivalents can be made in carrying out my invention, and proportions varied, as will be understood by those skilled in the art, without departing from the spirit and scope of the invention, and therefore I do not desire to be understood as limiting myself except as required by the following claims when construed in the light of the prior art.

Having thus described the invention, what I claim is:

1. In the electrodeposition of metals of the group platinum, palladium and rhodium, the process of renewing the metal deposited from the solution by adding thereto an amino nitrite of the metal being deposited and keep ing the solution ammoniacal.

2. In th electrodeposition of metals of the group platinum, palladium and rhodium, the rocess of renewin the metal de osited from the solution by adding thereto a iammino n trite of the metal being deposited and keeping the solution ammoniacal. a5 3. In the electrodeposition of platinum, the process of renewing platinum in the solutiop y adding thereto an ammino nitrite of plannum and keeping said solution ammonlacal. 4. In the electrodeposition of platinum, the 40 process of renewing platinum in the solution by adding thereto a diammino nitrite of platinuzn and keeping said solution ammomacal.

5. Method for the preparation of an electrolyte for the electrodeposition of a metal is or alloy of the group comprising platinum, palladium and rhodium which comprises dissolving an ammino nitrite of the metal to be deposited in Water containing ammoniaand a suitable conducting salt. no CHRISTIAN WILLIAM KEITEL.