Method of and electrolyte for
US 2067534 A
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Patented Jan. 12, 1937 TATES METHOD OF AND ELECTROLYTE' FOR DEPOSITING BHODIUM Christian William Keitel, West Orange, N. J assignor to Baker & Co. Inc., Newark, N. J., a corporation of New Jersey No Drawing. Application September 19, 1931,
' Serial No. 563,885
This invention relates to an electrolytev for electrodepositing rhodium and the method of using the same.
One object of my invention is the provision of an acid electrolyte which produces very white deposits when used for electrodepositing rhodium.
Another object of this invention is the provision, of an electrolyte which may be .used to form a tarnish resisting coating on metal surfaces such as silver or the like, which are not tarnish resisting by themselves, and whereby the coating is of such a-whiteness that it cannot readily be distinguished from silver.
Further objects and advantages of my invention will be in part obvious and in part specifically pointed out in the description hereinafter contained, which discloses one embodiment of my invention, it being expressly understood, however, that various changes may be made in practice within the scope of the appended claims without digressing from my inventive idea.
According to my invention, a rhodium bath may be prepared in the following manner. Two grams of rhodium in the form of rhodium ammonium nitrite are suspended in 1000 cc. of 5% sulphuric acid, and the mixture is heated until solution is complete. The rhodium ammonium nitrite is a very insoluble salt, and the heating must be continued for a substantial length of time. given off, and the rhodium ammonium nitrite is apparently partially decomposed. When solution is complete, the bath is cooled until the temperature is about 50 C. and is used as an electrolyte. A voltage of about 4 volts and a current density of about to amperes per square decimeter are used.
The above proportions are merely given for the purpose of illustration of one form of my invention, and are not to be construed as limiting my invention to these proportions. Likewise the temperature and the voltage are not to be considered as invariable, as they may be varied, and the advantages set forth in connection with my invention may be obtained.
Another method of preparing my electrolyte is to boil rhodium ammonium nitrite in distilled water until the salt goes in solution. The heating takes about 10 to 30 hours. This solution contains a water soluble acid rhodium ammonium nitrite compound. The compound is a soluble alkali rhodium nitrite compound. Then prepare a solution of 50 cc. of concentrated sulphuric acid in one liter of distilled water and add 2 grams of rhodium in the form of the aqueous solution During the heating, brown fumes areprepared as above indicated. This bath is then used as an electrolyte for depositing rhodium at a temperature of about 50 C. The voltage used is about 4 volts and the current density is about 20 to 30 amperes per square decimeter.
My invention is not restricted to rhodium ammonium nitrite as other insoluble alkali rhodium nitrites may be used, as, for example, rhodium potassium nitrite .and rhodium sodium ammonium nitrite. These insoluble compounds are rendered soluble when treated in the manner above described in connection with rhodium ammonium nitrite.
In replenishing the bath it is only necessary to add rhodium ammonium nitrite in a quantity sufficient to bring the bath up to 2 grams of rhodium per liter, repeating either of the above described processes of bringing the rhodium salt in solution.
The electrolytes made according to my invention are used principally for tarnish proofing 20 metals which are not tarnish resisting by themselves, but may also be used for improving the color of precious metals. When a deposit of rhodium is made, the color of the deposit approximates the color of silver very closely, and whiter 25 deposits are obtained than the deposits heretofore obtained from electrolytes which are neutral or ammoniacal.
To my acid electrolytes I may add different conducting salts, as, for example, sodium sulphate, or the like. However, it is not absolutely necessary to add any conducting salts to my electrolyte. Other inorganic acids, such as nitric acids and also organic acids, such as citric, tartaric, oxalic, or chloracetic acid, may beused instead of the sulphuric acid, or admixed therewith.
By electrodepositing rhodium from my electrolytes, it is possible to obtain a coating which tarnish proofs jewelry articles, optical, frames, etc., the deposits being whiter than the deposits heretofore produced.
In some instances it may be desirable to deposit a flash coating or heavy coating of another metal on the silver article to be tarnish proofed before depositing the rhodium coating. I have found, for instance, that in certain cases a copper deposit under the rhodium allowed me to reduce the rhodium deposits to a minimum without being detrimental to the length of the life of the tarnish proofing. Other metals might be used for under plating, and I do not wish to limit myself in this respect.
Although particular and preferred forms of my invention have been described, it is to be expressly understood that various changes may be made in practice within, the-scope of the claims without digressing from my'inventive idea.
What I claim is:
1. An electrolyte for depositing rhodium, made by dissolving rhodium ammonium nitrite in an acid solution.
2. An electrolyte for depositing rhodium, made by dissolving a normally water insoluble alkali metal ,(includingl ammonium) rhodium nitrite compound in sulphuric acid.
3. An electrolyte for depositing rhodium, which comprises, the product obtained by dissolving rhodium ammonium nitrite in an acid solution containing sulphuric acid.
-4. Am electrolyte adapted for electrodeposit 8. The method of electrodepositing rhodium,
which comprises, passing an electric current through an electrolyte produced by dissolving rhodium ammonium nitrite in sulphuric acid.
9. The method of electrodepositing rhodium, which comprises, passing an electric current through an electrolyte containing an acid and a partially decomposed normally water insoluble alkali metal (including ammonium) rhodium nitrite compound.
10. The method of tarnish-proofing silver or the like, which comprises, immersing the article to be tarnish-proofed as the cathode in an elecolyte produced by dissolving a normally water insoiuble alkali metal (including ammonium) rhodium nitrite in an acid solution and passing an electric current through the same.
11. The method of tarnish-proofing silver or the like, which comprises, immersing the article to be tarnish-proofed in an electrolyte containing an acid and a partially decomposed normally water insoluble alkali metal (including ammonium)'\ rhodium nitrite and passing a current through the same.
12. An electrolyte adapted for electrodpositing rhodium, which contains an inorganic acid and a water soluble partially decomposednormally water insoluble alkali metal (including ammonium) rhodium nitrite compound.
. 13.- An electrolyte adapted for'electrodepositing rhodium, which contains sulphuric acid and a water soluble partially decomposed normally water insoluble alkali metal (including ammonium) rhodium nitrite compound.
CHRISTIAN WILLIAM KEITEL.