US1981715A

US1981715A - Electrodeposition of metals

Info

Publication number: US1981715A
Application number: US621619A
Authority: US
Inventors: Atkinson Ralph Hall
Original assignee: International Nickel Co Inc
Current assignee: Huntington Alloys Corp
Priority date: 1931-07-11
Filing date: 1932-07-09
Publication date: 1934-11-20
Anticipated expiration: 1951-11-20
Also published as: GB381931A; FR738450A

Description

Nov. 2o, 1934. y R, H, ATKINSON 1,981,715

ELECTRODEPOS ITION OF METALS VFiled July 9, 1932 IN V EN TOR.

A TTORNEYS.

Patented Nov. 20, 1934 l i l -uNl'lllD STATES PATENT critici?.v

Emcrnonnposlriolv or METALS Ralph Hall Atkinson, Acton, England.` assignor to The International Nickel Company, Inc., New York, N. Y., a corporation of Delaware Application July 9, 1932, Serial No. 621,619 In Great Britain July 11, 1931 3 Claims. (Cl. 204-1) This invention relates primarily to electroplatin a non-diaphragm cell, but which in a diaing and the electro-deposition of metals and alphragmv cell, according to the invention', is formed lOyso only in the anolyte where its accumulation does It is an object of the invention to provide a bath not aiect the plating process because part of the 'Iwhich shall have a long life without the use of anolyte can be evacuated periodically. The pal- 30 a soluble anode'. ladium on the other hand, being wholly cationic, Other objects and advantages will become apmigruttes to the cathode and thus can easily be parent from the following description. kept-within the catholyte compartment. How- The invention consists essentially in the use of ever, the invention is not dependent on the acan insoluble anode in a diaphragm cell with an curacy of the above theory.

ammoniacal anolyte substantiallyfree from any The evacuation of part of the anolyte can be metal compound arid with a catholyte which comeiected in any convenient way either continuousprises an ammoniacal solution of a compound or, ly or peliOdiCa-lly- The anOlyte removed may be compounds of a, metal or metals and which is replaced either by water or by ammonia solution. l5 capable of yielding electro-deposits. In carrying out the process with palladosam- 70 The conunercial development of ammoniacal mine Chloride the Catholyte may Conveniently 00nelectrolytes has not received much attention besist 0f an aqueOus sOluifiOn eOntaiIiiIig about 5 cause previously baths of thistype lcould lhave grams of free ammonia and about grams of only a short life on account of the fact that most palladium per liter. The anOlyte may cOnSiStOf 20 metal anodes are insoluble in these electrolytes, an aqueous solution of ammonia containing for 76 with the consequence that 'the meta1 content-,0f example about 30 grams of ammonia ,per liter. the latter had to be maintained 'by periodical ad- Initially al COIidUCtin salt may be added t0 the `ditidns of salts thereby leading to undesirable anolyte, but the ammonium chloride formed duraccumulation of acid radicals' in the plating soins operation is suiiicient to maintain the conn lution, so that although in certain cases the presduCliiVW 1n Order t0, Prevent the formation' 0f 3 ence of the diaphragm may not affect the nature nitrogen trichloride which is very explosive, strong 0f the deposit, e. g. copper and nickel, it has ammonia (specinc gravity 0.880) should be added the advantage that it enables the electrolyte, suitat intervalsto the anolyte.v

ably replenished from time to time, to be used for In practice it is found that goed deposits may a very much longer time than would be possible be obtained Withatholytes containing as much 85 without a diaphragm. as about 30 grams per liter ammonium chloride. The invention is particularly applicable to pal- Any tendency of the concentration to increase too ladium and alloys thereof, although it ls ln no `much may be remedied by increasing the rate way limited to these. It is, therefore, most con-` 0f evacuation 0f the aIiOlyte. venient nrst to describe the application of. the ln- A system by means of which the catholyte may 90 vention to the deposition or palladium and then be fortified without interruption of the process to indicate some further applications. is illustrated'by way of exampleinthe accompanyi It is known to use for= plating purposes a S0111- ing drawing. In this drawing the reference chartion of palladosammine chloride (dichiaro-dialnacier l represents the aIlOlYte Chamber. 2 the 40 minopalladium) v`in ammonia in an ordinary elec- Cathelyte chamber, arid 3 the diaphragm. The 95f trolytlc cell, but although the inltlaldeposlts catholyte is continuously drawn on by ineens of a may be good the deposits are unsatisfactory after Siphon 4 which Serves t0 maintain the level f a. short time. In proceeding in accordance with the liquid in the cathulvte chambei- The Siphon the present invention, however,- the catholyte delivers to a vessel 5 in which'palladosammine consists of a solution in'amnionia of apalladiumchloride is dissolved. The solution passes to a ammino compound such as palladosammine chlofilter 6 and is then pumped to a feed vessel 'I and ride. The deposits produced are ythen found to supplies the catholyte chamber 2. The catholyte be consistently good.l g may also be agitated in the actual plating cell The improved results are believed to be main. as well as continuously simulated. i. 5o 1y due to the fact that when the palladiumP tet- The deposits of palladium obtained by this 105 'l rammine cation, which is present in an ammoniprocessV are bright up to a thickness of aboutacal solution of palladosammine chloride, decom- 0.00002 inch, but thicker deposits are somewhat poses into palladium and ammonia, the latter milky.- although they t adherent and suitableA `reacts at the anode with chlorine to form am: for buillng or other g operations. monium chloride which accumulates undeslrably The current density required to give the best n0 results varies with the other conditions, including the concentration of the metal salts and the temperature. As an example in palladium plating with a bath containing 15 grams of palladium per liter as tetrammine chloride the most suitable current densities at the specified temperatures were as follows:-

Temperature of Current density catholyte amps. per dm I 3 C. 0. l to 0. 5 20 C. 0. 5 to l. 0 40 C. l. 0 to 1.5 70 C. 2. 0

' trite, uoride, acetate, tartrate, and citrate, may

with ammonium sulphate to fo be dissolved in ammonia to form catholytes which give good adherent deposits. Inv the case of the chloride, ammonium pallado-chloride (NH4) 2PdCl4 dissolved in aqueous ammonia yields the same electrolyte. Again, palladium may be deposited at about 50 C. from ammoniacal solu' tions of palladosammine oxalate. Ammoniacal solutions of diammino-dihydroxo-palladium or tetrammino-palladous hydroxide give particularly bright deposits. l

As an exampleof the use of tetrammine-palladous hydroxide the following may be given:-

A catholyte containing about 20 grams palladium and about 5 grams free NH3, both per liter, is prepared by adding excess-of ammonia. to an aqueous solution of dihydroxo-diammino-palladium made .by a known method and is allowed to stand for twelve hours. The anolyte contains 20 grams ammonium sulphate and 100 cc. ammonia solution (specific gravity .880) per liter. Gelatin about .05 gram per liter is added to the catholyte. The ordinary porous pot diaphragm is used. At room temperature, 2 volts, and a current density of 0.3 amp. per dm. bright adherent deposits (up to .0001 inch thick) are obtained with a current emciency of 94-97%.

As tetrammino-palladous hydroxide reacts rnistetramminopalladous sulphate, there isa tendency for the bath to lose its special character consequent on the diiusion of ammonium sulphate into the catholyte. removed from the cell and stored in another vessel when plating is not in progress.

Such separate storing of the catholyte may advantageously be adopted in all cases, but is especially desirable in the case of tetramminopalladous hydroxide.

The palladium ammino compounds may also be formed by using organic amines such as pyridine and ethylenediamine instead of ammonia. Thus, an aqueous solution of palladium chloride and excess of pyridine may be used as the catholyte in conjunction with an aqueous solution of pyridine hydrochloride as the anolyte. vAgain, an aqueous solution of palladium chloride and excess o! ethylenediamine hydrate may be used as the catholyte and an aqueous solution of ammonia and ammonium chloride at' the anolyte.

Therefore the catholyte should be The -invention may be applied advantageously to certain other metals capable of forming metalammines soluble in aqueous ammonia and capable of yielding eiectrodeposits, namely rhodium, platinum, iridium, nickel, copper, silver, zinc, cadmium and cobalt. As is well known iron is not precipitated from solutions of its salts in the presence of tartrates and citrates and such solutions may be used for the electro-deposition of iron. The ammoniacal solutions may also be used as catholytes in this invention. Tin may also be deposited from ammoniacal catholytes containing tin chloride and ammonium tartrate. Furthermore, the invention may also be used for plating with or depositing alloys of the said met- Ag2SO4, ZI1S04, CdSO4, NiSO4, COSOQ,

RhCLa, CuSO4 and Cu(NO3)1.

Platinum and iridium salts which may be used are :l

The rhodium, platinum and iridium baths should be maintainedat about C. during thev process in order to improve the current eiiiciency but .the baths of the other metals may be worked eith'er hot or cold.

Thus, as an example of the deposition of rhodium the following may be given: A solution containing about 7 grams rhodium as chloride and Iabout 16 grams of urea per liter is boiled until a test portion gives no precipitate on adding excess of ammonia. During the boiling it may be found necessary to add a little hydrochloric acid to remove turbidity. Finally, excess of strong ammonia solution (specific gravity .880) is added after which xthe solution is boiled. 'I'he anolyte contains 150 cc. oi' strong ammonia solution (specic gravity .880) and about 25 grams ammonium chloride per liter. At '10 C., 2 volts, and a current density of 0.3 amp. per dm2 this bath gives `bright adherent deposits of rhodium with a current emciency of 10%.

As an example of thedeposition of iron the following may be mentioned: about 120 grams of ferrous ammonium sulphate crystals and about -80 grams of citric acid are dissolved in about 800 cc. water. After boiling and iiltering, the nltrate is allowed to cool and then made ammoniacal by adding about 120 cc. of strong ammonia solution (specific gravity .880); about 33 grams of ammonium sulphate are added and the volume made upto 1 liter. The anolyte contains about 40 grams ammonium sulphate and about 80 cc. of strong ammonia solution (,specinc gravity 0.880) per liter. l

At 60 C., 1.9 volts, a current density of 0.6 amp. per dm and a plating time of 30 minutes va hard adherent deposit of iron is obtained on copper with a current eillciency of 30% As an example of the deposition of copper the following may be mentioned: A catholyte istaken containing about 12.5 grams per liter of copper as nitrate, about 20 grams per liter of ammonium nitrate, and a small excess of ammonia solution.

' Ihe anolyte contains about 50 grams o! ammonium nitrate and 160 cc. of strong ammoni solution per liter.

- At room temperature, 3.1v volts, a current density of 1 amp. per dm2 and a plating time of 30, minutes, an adherent deposit 4of copper is obtained on an aluminium cathode with a current eiiiciency of 64%.

In the case of copper the presence of ammonium salts is essential for satisfactory deposition.

As an example of the deposition of an alloy containing 90% palladium and 10% cobalt the following may be mentioned: A solution containing about 50 grams of cobalt sulphate crystals per liter and about grams ammonium sulphate per liter is made ammoniacal and boiled with the addition of hydrogen peroxide for one hour. rllhe solution is next cooled and ltered, and theA ltrate mixed with an ammoniacal solution of tetrammino-palladous sulphate. The mixed s0- lution containing about 14.4 grams palladium, about 1.4 grams cobalt, and about 3.4 grams ammonia, all per liter, is used as the catholyte with an anolyte containing about 40 grams ammonium sulphate and 120 cc. of ammonia solution (specic gravity .880) per liter. At room temperature, 3 volts, a current density vof 1 amp. per

a precipitate on making the solution ammoniacal. This solution is mixed with an ammoniacal solution of nickel sulphate to give a catholyte containing about 11 grams of iron, about 6 grams of nickel, about 40 grams of tartaric acid and 11 grams of free NH3 per liter. About 20 grams of ammonium sulphate per liter is added as conducting salt. The anolyte contains about 50 tion of 1% of ethylenediamine hydrate renders.

palladium deposits less milky, while urea serves to increase the current efiiciency in the deposition of rhodium. Again, the addition of a small -quantity of gelatin, of the order ot about 0.05

gram per liter,` to a tetrammino-palladous hydroxide catholyte gives bright line-grained plates.

" porous hard rubber are both' suitable.

The preferred diaphragm consists of a porous pot of the same porosity and material as those used in Leclanch cells, but of course other porou: materials may be used provided they are notattacked by the electrolyte, e. g. alundum and 'I'he cliaphragm may consists of a porous pot surrounding either the anode or thev cathode or it may be a porous partition- (or partitions) separating the anolyte from the catholyte compartment (or compartments) v The anode may consists for example of lead, platinum, palladium or graphite'.

' The selection of the cathode metal will be determined yby the metal which is to be deposited upon it. When used as the cathode for palladium platingcopper, silver, palladium, lead, tin, nickel-silver", brass and pewter among others, all lead to the formation of good adherent deposits and other metals such as nickel and iron may be plated after preliminary plating or coating with other metals such 'as copper and tin. In addition to the usual cathode metals used for electro-deposition it has been found that aluminium can be plated satisfactorily with copper, possibly because an ammoniacal electrolyte has less tendency to attack aluminium than the acid or alkaline electrolytes used in other plating processes.

Generally the cathodes will be stationary but moving cathodes may also be used in suitable cases.

A'smentioned above, the invention is applicable to the electrolytic reduction of metals from their f 'si salts, such for example as the electrolytic recovery of silver from silver chloride or of palladium from palladosammine chloride. In such a case, of course, a cathode is preferably used from which the deposit may be easily stripped. For

example, a carbon cathode may be used yfor silver, while in particular cases metal cathodes on'which only aky deposits are obtained in plating may advantageously be used in the reduction ot metal salts.

1. A process for the electrodeposition of a metal or alloy which comprises establishing a porous pot diaphragm cell containing an ammoniacal anolyte substantially free from a metal compound, an insoluble anode, and a catholytev containing an ammoniacal solution of a metal to be electro-deposited; making an article to be plated a cathode in said cell; and,` passing a current through said cell to cause the electro# deposition `on said article `oi? metal from said ammoniacal catholyte.

2. A process for the electrodeposition of palladium which comprises establishing a porous pot diaphragm cell containing an anolyte of the group consisting of ammonia, organic amine and the like, an insoluble anode and a catholyte containing anA ammoniacal solution of a palladium ammino compound; making a'n article to be plated a cathode in said cell; and passing a cur-v rent through said cell to cause the electrodeposition in said article of palladium from said ammoniacal catholyte.

3. A process for the lelectrodeposition of palladium which comprises establishing a porous pot diaphragm cell containing an anolyte of the group consisting of ammonia, organic amine and the like, an insoluble anode and a catholyte containing an ammoniacal solution of palladosamf.

mine chloride; making an article to be plated a cathode in said cell; and passing a current e through said cell to cause the electrodeposltion