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Patented Feb. 27, 1934 1949,131

UNITED STATES PATENT OFFICE Y 1949,31 RODUMI Thomas P. Shields, Newark, N. J. No Drawing. Application November 14, 1932 Serial No. 642,685 5 Claims. (C. 204-1) The present application is a continuation in The plating which I illustrate part of my copending application Serial No. 490,- by specific examples hereinafter set forth, is one 335, filed October 21, 1930. of considerable stability. It can, therefore, be The present invention relates to a process of made up and placed in bottles of any convenient 5 preparing a solution containing a rhodiim Salt size, as for example one liter bottles, and then O adapted to deposit metallic rhodium on another shipped to the various manufacturers of jewelry, or in the form of a continuous, adher who may use it instandard apparatus. The chief ent coating or plate. The invention does not purpose of this solution is to produce a plate of contemplate the use of any novel apparatus, rath rhodium on a highly polished article, Which Will 0 er it provides a method whereby a rhodium plat not detract any of the luster or polish of the 65 ing may be applied to an article by Standard ap metal to be plated, while giving it a protecting paratuS. w coat. Hence, after plating with the above Solu The invention has particular reference to a tion in the manner indicated, the article plated process whereby rhodium is plated on articles of will require no polishing after the plating opera 5 jewelry in which the principal metal is tion. O , white , or the like. In the following examples certain proportions The and luster of rhodium are desirable in of ingredients and procedural steps are set forth, the art of jewelry making, but owing to the hard but it is to be distinctly understood that these ness and brittleness of this metal, and the dif Specific details are purely illustrative and are 20 ficulty of polishing, burnishing it or not to be construed as in anywise limiting the in s upon it, its use as a metal in the manufacture of vention. jewelry is impractical. An electrodeposit of this Eacample I metal in the form of a plating Which Would re quire polishing after it was applied, would not To pure distilled Water I add 20 grams of rhodi 25 be desirable or useful in the finishing of jewelry um Sulphate Rh2(SO4)3.12H2O, and then add 20 80 for the reasons Set forth above. grams of aluminum sulphate. I then The object of the present invention is to make acidify the Solution by adding 50 grams of 92% available to the plating industry and jewelry sulphuric . This solution is then made up the color and brilliance of rhodium by the manu to One liter by adding pure distilled water. The 30 facture of a practical solution by Solution is then placed in the usual deposition or which the industry, or trade may apply a finish, plating apparatus, the details of which are well or electroplate after the article is completely known. A yellow rolled gold article may be manufactured and polished. rhodium plated by the above solution, using a Among other attributes of rhodium which make voltage of 4% volts and a current of 2 35 it highly desirable as a coating or plate on jew amperes per square centimeter during a 90 elry are its color, which is silvery white, its re of five seconds. The rhodium plated rolled gold sistance to acidic, basic and Organic Solvents, and article will have a beautiful white appearance its resistance to atmospheric Oxidation. Its When taken from the deposition bath and after chemical inactivity, therefore, causes it to be non drying will require no polishing. The foregoing 4. Susceptible to tarnishing. method is particularly suitable for plating gold 95 It has also been found that a rhodium plating to be used as a setting. is much superior to a platinum plating as regards Eacample II color and hardness, since a rhodium plating has a whiter color than does platinum, and Wears much A Solution containnig about 1% of rhodium 45 longer than a platinum plating of the same thick chloride, about 10% of aluminum chloride and 00 SS about 10% of free in 1 liter of The invention is not limited to the coating of water was prepared. noble but includes also the coating or plat The above Solution was placed in an electro ing of base metals, Such as , , , plating apparatus and a Small gold pin was in 50 and the like. Hence it may be applied to mersed therein, the pin Serving as a cathode. 05 , hardware in automobile interior The said pin was plated by immersion in the furnishings and in fact on any article where a, above described solution during a period of one coating of varying degrees of thickneSS is desir half minute while employing a current density able, to protect a from the ravages of of 2 amperes per Square centimeter and a voltage 55 , A of about 4 volts, and maintaining the tempera 2 i,949,132 ture of the plating Solution at about 60 F. At acid is advisable; first to stabilize the Solution the completion of the plating operation the said and second, to increase the conductivity of the pin was removed from the bath, washed with Solution. The object of the or other Salt water and dried with a towel. The article thus is that since they are inert they will further in obtained was of a brilliant white color, having crease conductivity in the Solution, without in 80 the characteristic appearance of natural rhodium. creasing the acidity thereof, as would Sulphuric acid or other , with resultant at Eacample III tack of the article to be plated. A solution containing about 1% of rhodium The above described plating give O phosphate and about 10% of free phosphoric acid equally good results at 20° C. or 90° C., and may 85 in a liter of water was prepared. be boiled without any danger of decomposition. The above solution was placed ln an electro As an anode of rhodium is insoluble in this Solu plating apparatus and a Was immersed tion and Would be very expensive, any insoluble therein, the brooch serving as a cathode. The anode such as platinum, gold, Or an alloy of these 5 plating operation was caried out as in Example metals or may be used. 90 II with respect to current density, voltage, time The loss in rhodium due to the deposit of of immersion of the brooch in the plating bath rhodium may be compensated for by adding and temperature. rhodium hydroxide, or a concentrated solution In the foregoing examples equivalent quantities of rhodium sulphate, phosphate or chloride. The 20 of any mineral acid may be used. I may use any metallic content of the solution should be kept 95 simple rhodium salt which is soluble in water constant by the addition of rhodium hydroxide, in place of the above rhodium salts which have and when it is not desirable to increase the con been disclosed in the specific examples. Simi ductivity of the Solution, rhodium Sulphate Solu larly I may also use any Soluble aluminum Salt tion in concentrated form is added. When it is de 25 in place of the aluminum Sulphate or aluminum sirable to increase the conductivity. 00 chloride above disclosed. The above described methods provide means I find that rhodium may be electrolytically de whereby rhodium may be recovered from a solu posited from solutions, such as the above by us tion after the other metals of the platinum ing a voltage ranging from 3 to 13 volts, depend have been removed. ing on the concentration of rhodium salt, and I claim: 105 also that the Solution may be either hot or cold, 1. An adapted to deposit a bright, The plating solution is so compounded that lustrous layer of rhodium. On a metal, compris using the concentration of Example I it will func ing an of a Soluble rhodium tion and produce a good plate, when using a volt salt, a soluble aluminum salt and a free mineral 35 age of about three to four volts. By diluting with acid. 10 an equal volume of water it will function with 2. The method of plating rhodium. On a noble six to seven volts; by again diluting With an equal metal to produce a White, lustrous finish requir volume of water or a concentration of one in ing no subsequent polishing, comprising immers four, it will function at from ten to fifteen volts. ing the said in a solution contain 40 The preferred amperage is from about one to ing an inorganic rhodium Salt, a Soluble alu 115 two amperes per square centimeter. When the minum salt and an inorganic acid and a free concentration of the Solution equals twenty grams mineral acid and passing a current of electricty of crystallized rhodium sulphate a voltage of through the solution. from three to 4 and A volts, ten grams of rhodium 3. A rhodium plating Solution adapted to pro 45 sulphate (crystallized), six to seven volts, five duce a bright, lustrous plating on a noble metal, 120 grams of rhodium sulphate (crystallized), and 10 containing 5 to 20 grams of rhodium Sulphate to 15 volts are used. Similarly in the other exam per liter of Water and a mineral acid. ples, the voltage should be increased when the 4. The method of plating rhodium on a noble solution is diluted in accordance with the above metal to produce a white, lustrous finish requir 50 ratios, viz., the voltage should be approximately ing no SubSCquent polishing, comprising immers 125 double when the dilution is twofold and quad ing the said noble metal in a Solution containing rupled when it is fourfold. Hence, if in any 5 to 20 grams of rhodium Sulphate per liter of of the foregoing specific examples, it is desirable water and a mineral acid and passing a current to use a solution more dilute than that specified of electricity having a voltage of 3 to 15 volts and 55 therein, the voltage should be modified as above. a current density of about 2 amperes per square 130 By the above method of dilution which has the centimeter through said solution. effect of adding resistance to the solution, the 5. A rhodium plating Solution adapted to pro jeweler can purchase a concen duce a bright plating on a metallic surface con trated solution and use the same with his present taining approximately twenty grams of crystal 60 plating outfit, without the necessity of installing line rhodium sulphate, twenty grams of potas 135 new electrical generating equipment, which would sium aluminum sulphate and fifty grams of sul be required if this Solution WOuld. Only operate phuric acid per liter of Water. at a fixed voltage. An excess of sulphuric acid or other mineral THOMAS P. SHIELDS. 140

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