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Kodk IsIA4 Arseo lL4oratory

TECHNICAL REPORT

DEPOSITION OF ALWY BY CHEMICAL REDUCTION

my;

Jacob Knanishu

9 1 -.

DOV epWUtm t of the Army Project No. 593-32-006

Gvdm * Management Structure Code No 5010.11.810

port Mo. 61-4359 copy No._

IlL 1-9-100-9 Date 4 Dec~uber 1961

pICE 018U BY TCL THIS RXPWT MAY 13 DITHOYED WHENOiFFICE OfP TECHNICALL llZRVICZ8 No LOmGn REQUIREIm l II~GUs B. DEPARTMEW OF omuCQRWASHINGTON 250 D, C,

Report No. 61-4359

Copy No.

DUPOSITION O ALLOYS BY CNMICAL RWUCTION

co' - ushu

Approved by:

A. C. HANSONLaboratory Director

4 December 1961

Department of the Army ProjectNo. 593-32-006Ordnance Management Structure CodeNo. 5010.11.810

Rock Island ArsenalRock Island, Illinois

ASTIA Availability Notice:

Qualified requesters may obtaincopies of this report from ASTIA.

ABSTRACT

A literature survey was made on electroless plating anda historical report on its development is recorded.

The deposition of alloys of nickel, cobalt, and alloycombinations of nickel, chromium and Iron were explored, thebasis metal being steel, aluminum or magnesium.

Cobalt and nickel were successfully plated on steel andaluminum, as was the plating of nickel on magnesium. Stan-nate coating of magnesium was also undertaken with success.

i 61-4359

RAT IONS

Further investigation should be conducted In the fieldof electroleus plating. Testing of electroless metallic de-posits for hardness, corrosion resistance and Impact resis-tance should be explored.

1i 61-4359

DEPOSITION 0f ALWOYS BY C M ICAL REDUCTION

COUTN'r

Page No.

Object 1

Introduction 1

Procedure and Results 3

Discuss ion 7

Literature References 9

List of Prior Reports 11

Distribution 12

iii 61-4359

DEPOSITION OF ALLOYS BY CHEMICAL REDUCTION

OBJECT

The object of this work is to conduct a literature sur-vey and a laboratory evaluation of various electrolessplating processes.

INTRODUCTION

The study of the deposition of alloys by chemical re-duction was initiated so late in the fiscal year that littlemore than a literature survey was accomplished. Since thisproject was not funded for the following year, the literaturereview and preliminary tests are reported for record purposes.

A deposit of nickel by chemical reduction as now knownis actually an alloy of nickel and phosphorus. It is be-lieved possible, that by making modifications of the solutioncomposition, a family of alloys such as copper-nickel andnickel-chromium can be produced.

The deposition of cobalt by chemical reduction wasdeveloped by A Wurt.(1) at the same time as was nickel plat-ing by chemical reduction, but has not gained as much use.It is possible that by altering the nickel bath variousalloys could be electrolessly plated. This method of platingcan be used to advantage in protective coatings of parts usedin the electronic control compartments of rockets and missiles,space instrument packages, and radar equipment, where optimumprotection is imperative. Heat transmittance and surfacetexture of these coatings are important properties which canbe incorporated in the above instruments.

Many investigators have reported that by first dippingmagnesium in a molten bath of zinc, a coating by electrolessdeposition could more easily be accomplished. Properlyapplied, this method produces an adherent coating system onthe basis metal. This step (zinc immersion) makes the pro-tective process too complex to be used economically on aproduction basis, therefore, work has been done to eliminatethe immersion phase. However, the greatest problem con-fronting investigators in plating without a primary dip inzinc is the corrosive attack on the magnesium by the in-gredients in the nickel bath.

According to DeLong(6 ), the solution cannot contain morethan traces of sulphates and chlorides. Nickel acid fluoride,sodium hypophosphite, and a pH buffering compound are themain constituents of a successful solution.

1 61-4359

As mentioned above, A.Wurtz was the first to reducenickel compound solutions to nickel by the aid of hypophos-phites. The first effort at reduction of nickel produceda precipitate of black powdered nickel. The second trialproduced a nickel metal plating on any object that was im-mersed in the solution, plus a complete coating of the in-terior of the container that held the solution and object.

It was reasoned by Breteau(2) in 1911, during his ex-periments on nickel and cobalt, that the above reductionswere due to the catalytic influence of the metals themselves.

In 1916 F. G. Rouz(3) was granted a patent on a processsimilar to that of Breteau.

The potentials of these discoveries were not recognizeduntil 1944, 28 years later, after further wW;c had been donealong these lines, when Brenner and Riddell~' of the Bureauof Standards accidentally discovered that exfoliation of anickel-tungsten alloy was occurring on the interior surfacesof a tube where an insoluble anode was placed. Observingthe oxide formation on the anode prompted Brenner and Riddellto add various reducing agents to the solution in an effortto minimize this effect. When, according to Brenner, sodiumhypophosphite was used as the reducing agent, the interiorof the tube was completely plated. In this process, vigorousgassing occurred with a cathode efficiency of 120-130 percent.This led the researchers to believe that a chemical deposition,as well as electrodeposition, was taking place.

According to Brenner(5 ), the difference between theprocess developed by Brenner and Riddell and that of theearlier investigators, Breteau and Roux, was that while thelatter was a spontaneous and complete reduction, the formerwas a catalytic process so controlled that depositionoccurred only on the catalytic surfaces. By varying the con-centration of the hypophosphite, Brenner found that nickelcould be deposited on the surface of iron, nickel, gold,cobalt, palladium and aluminum in this manner.

More recently, with the advent of the use of lightmetals, considerable work has been done by H. K. DeLong(6)on the electroless plating of nickel on magnesium. In hispaper, delivered at the 1961 American 3iectroplaters'Society Convention in Boston, DeLong states that not onlydoes plating on magnesium produce good protection, but alsogood grounding, conductivity and solderability in the manu-facture and use of electronic equipment in the aircraft andmissile fields. He also states that tin, nickel, silver,gold and platinum can be applied advantageously as finalcoats for special uses.

2 61-4359

The method outlined by DeLong in him treatise on chemicalreduction of nickel onto magnesium appears to be the mostsuccessful and simplified method published to date. Pre-viously, many claims had been made in the superlative, butthey can hardly be accepted as practical and dependable on aproduction basis.

For several years, electroless plating of nickel, cobaltand chromium onto steel has been very successul, as noted byHarry J. West( 7 ) in a paper entitled, '%lectroless Nickel-Barrel Plating". He notes the importance of the pH, thetemperature, and the lining used in the plating tank. In a30 minute operation, an 0.00015 inch thickness deposit can beobtained.

In 1954, Harry J. West, the author of an article entitled"Electroles Nickel Plating On Non-Ferrous Metals", dealtwith the chemical reduction method of plating nickel directlyonto aluminum, brass, copper and titanium. The solution usedwas of the alkaline type with the pH held at approximatelyten.

Also, in 1954, John D. McLean and Seymour X. Farten(9 )reported that small fuse parts were successfully nickelplated by chemical reduction for Navy Ordnance. They claimedthat, since fumes have recesses and blind holes, the elec-troless method of plating was the perfect answer.

According to G. Gutzeit and R. W. Landon(10), the mainproblem in the earlier work of plating by chemical reductionwere to increase plating rates, produce a smooth lustroussurface, and a more stable plating solution.

Dr. Abner Brenner(ll) in a two-part report, concededthat, up to and including the year 1954, only nickel, cobalt,or nickel-cobalt alloys had been deposited by the elctrolessprocess in a manner capable of practical application.

In 1955, Harry J. West(1 2 ) reported that the corrosionresistance as determined by the salt spray (fog) test of athin film of chromium on steel deposited by the electrolessprocess, compared equally with the same coating thickness(0.0002 inches) of chromium on steel.

13 _CI_ A1D RESULTS

Since the time allotted for work on the electrolessplating project was short, attention was focused on magne-sium, because techniques of plating on magnesium are theleast known and are presently important.

3 61-4389

With the proper formulation and operation, acid andalkaline baths lend themselves well to the chemical reductionprocess. In plating directly onto magnesium, only the alka-line bath may be utilized, since acid causes extreme etchingand thus prevents an adherent coating from being formed.

Various combinations of composition materials were tried,with varying results. The increase or decrease in the temper-ature of the solutions resulted in variations of quality andquantity of coatings produced. Experiments w 9 baths simi-lar in composition to that proposed by DeLong s provedmost successful.

The specimen to be plated was first chemically etched ina chromic-acid-nitric-acid solution, shown in the tablebelow, until the surface was completely renewed, the amountof etching being proportional to the time of immersion.

Chromic Acid (Cr03 ) 60 gis/literNitric Acid (70%HNO3 ) 90 ml/liter

Immersion in the solution was followed by a water rinse,then a hydrofluoric acid immersion for 10 minutes as pre-scribed by DeLong. For high aluninum-magnesium alloy content,220 ml/liter of 70% hydrofluoric acid was used. For alloysunder 5%, a weaker solution (54 l/liter of 70% hydrofluoricacid) was used. After the specimen was thoroughly rinsed inwater, it was transferred to the plating solution. Good toexcellent results were obtained by using the above etchingprocedure and the electroless plating bath an follows:

Per Liter

Basic Nickel Carbonate (2NiCO3 • 3Ni(OH)2 • 4H20) - 10 gis

Hydrofluoric Acid (as 70% HF) 6 ml

Citric Acid (C6H507 ) 5.5 gis

amonium Acid Fluoride 15 gis

Sodium Hypophosphite (NaH2 PO2 • H20) 20 gis

Ammonium Hydroxide (30% NH4OH) 30 ml

pH Operational Range (colorimetric) 4.5-6.8

Operating Temperature 170-180 F

Agitation mild

Rate of Deposition (inches) about 0.0008/hr

4 61-4359

In the preparation of 1 liter of the solution, the basicnickel carbonate was slowly added to the hydrofluoric acidin approximately 100 ml of water to form the nickel acidfluoride. This step requires considerable agitation. Afterthe reaction was complete, the remainder of the chemicalswere added in the order they appear in the above table.

Water was added to effect dissolution. Additional waterwas then added to produce 1 liter of solution. The solutionwas adjusted to pH 6.5 and then filtered. Operating thebath at 1700 - 1800 F, the rate of deposition was found to be0.0006 inches per hour.

A bath similar to that employed by Brenner and Riddellwas prepared, and the plating of nickel onto steel andaluminum was performed with excellent results. Cobalt wassuccessfully deposited on steel panels by chemical reduction,using the solution f9lmulation and procedure outlined byBrenner and Riddell 'J.

An electroless chromium plating solution was then made.This solution waq similar in composition to that used byHarry J. West(12). In the operation procedure of electro-less chromium plating, catalytic initiation is necessaryto promote the plating process. This initiation was broughtabout by placing a catalyst metal, such as iron or aluminum,in the solution and allowing a momentary contact with thepart to be coated. Once this process has begun, the initialdeposit produced catalytic action, and plating continued.This method produced a satisfactory deposit. The formulationof the solution was as follows:

Chromium Fluoride 64 gums/gal of solutionSodium Chloride 4 gum/gal of solutionSodium Citrate 32 gus/gal of solutionSodium Hypophosphite 32 gms/gal of solutionWater - to make 1 gallon

of solutionTemperature 1600 - 1900 F

A stannate bath for the deposition of tin directly ontomagnesium was made, as follows:

Potassium Stannate 5%Potassium Pyrophosphate 5%Potassium Hydroxide .75 - 1.5%Sodium or Potassium Acetate 1%

The bath was operated for 20 minutes at 1950 - 2000 F.

5 61-4359

The procedure followed was:

The test panels were degreased, then placed in a chromicacid cleaning solution, rinsed in water, and put into analkaline cleaning solution until a bright surface was ob-tained, the alkaline cleaning composition being:

Sodium Hydroxide 2-4 oz/galSodium Carbonate 3-4 oz/galWetting Agent 0.1 oz/gal

Operating Temperature 200OF ± 10OFImmersion Time 10-15 minutes

The panels were removed from the alkaline cleaningsolution after a 10-15 immersion, and rinsed thoroughly.They were then placed in the stannate solution for 20 min-utes. Excellent coatings were obtained. However, some ofthe panels showed a pearlescent color due to too thin acoating. It was noted that, in order to obtain a goodcoating, replenishing of the solution with tin salts, andmaintaining the optimum temperature range of 1950 - 20007was necessary. Mechanical agitation also favored gooddeposition.

Stannate coated panels were placed in the salt spray(20%) cabinet in order to compare the protection aff91gedthe magnesium base with that of the Dow 17 treatment sSome of the stannate coated panels were given variousorganic protective top coats, and they, too, were subjectedto the salt spray test. After 888 hours, the Dow 17 treatedpanels with an organic top coat showed no signs of a break-down. The stannate pretreated panels had failed at 508hours, and although the exposure time may be consideredgood, the comparative value of stannate pretreatment ismuch less than the Dow 17 treatment in anti-corrosionqualities.

The following bath(4 ) was used successfully to platenickel on to both steel and aluminum:

Nickel Chloride 30 gas/literSodium Hypophosphite 10 gu/literAmonium Chloride 50 go/literSodium Citrate 100 gus/literAmonium Hydroxide to apH of 8-10

Temperature 1900,

6 61-4359

,ictroless plating of cobalt was carried out in abath(J of the following composition and operating technique:

Cobalt Chloride COC12 6H20 30 gms/literSodium Hypophosphite NaH 2PO 2 . H20 20 gms/literSodium Citrate Na3 C6 H5 O7 • 5-1/2 H20 35 gms/literAmmonium Chloride NH4Cl 50 gsm/literAmmonium Hydroxide NK4 OH for neutralizing bathpH 9-10Temperature 190 0 -200OF

Catalytic initiation was necessary to start deposition.Less noble metals such as iron or aluminum can be used.

The nickel plating bath as formulated by DeLong is notonly tolerant to magnesium, but also to other metals such asaluminum, iron, stainless steel, copper, tin and brass. Itsability to plate on the above metals makes it a prospectiveplating solution when combination couplings of these metalsare already in an assembly prior to plating.

The quality of the coatings can be improved (1 5 ) byusing a heat treatment at 750 C or higher (1382 F). The highheat makes the coating compact and adherent and causes thediffusion of the iron and nickel to produce a nickel-ironalloy.

DISCUSSION

It is important that the constant decomposition of thesurface of the basis metal be avoided. Therefore, in orderto obtain a complete and continuous coating, the solutionmust be so formulated that it will deter the oxidation ofthe surface and still promote chemical reduction of themetal salts used in the plating bath. When magnesium isthe basis metal in a chemical reduction process, the nickelmust be in the form of nickel-acid-fluoride. Chloride orsulphate ions must be absent from the bath because theyproduce corrosion action on magnesium. Using a conventionalformulation for electroless nickel plating on magnesium, apoorly adherent and irregular coating was produced. Thiswas due to the corrosive action of the chloride ions duringdeposition. In the areas where the nickel plating wassomewhat continuous, the appearance was dull.

It has been shown(4 ) that hypophosphites are excellentreducing agents in the electroless plating process. In-vestigators have used this compound in many chemical reductionprocesses of various metals such as nickel, cobalt, tungstenand chromium. Its reducing action takes place in the presence

7 61-4359

of catalytic metals. In the electroless plating of nickel,

the following reactions occur:

NiC12 + N&H2PO2 + H20-- Ni + 2HC1 + NaH2PO3

NaH2PO2 + H20--4 NaH2PO3 + H2

In the presence of water, the hypophosphite undergoesoxidation and the nickel is reduced. Since these two in-gredients are constantly changing chemically, they must beadded as replenishing materials in order that the reactioncan continue. In an alkaline solution, the rate of nickeldeposition is only slightly affected by the concentration ofnickel ions. This rate of deposition is mainly a function ofhypophosphite concentration. The reaction which determinesthe deposition rate in alkaline solution is the reaction ofhypophosphite to produce hydrogen, ch in turn, reducesthe nickel on the catalytic surfaceAf.

When the basis metal does not possess catalytic pro-perties, the reaction must be initiated by momentarily in-jecting into the solution a catalytic metal which contactsthe basis metal. Once this is done, plating begins and thedeposited metal takes over the role of a catalyst and platingcontinues as long an the solution is replenished with thesalts of the plating metal, and with a sufficient amount ofhypophosphite to reduce these salts.

8 61-4359

LITURATURI RIFXRNCB8

1. Abner Brenner, "Symposium on Zlectroless Nickel Plating",A.S.T.M. Spec. Tech. Publication No. 265, 1959, pate 1,line 8.

2. P. Breteau (ref. 21 of A.S.T.M. Spec. Tech. Bulletin No.265 1959), 'Reduction by Precipitated Palladium and SodiumHypophosphite", Bulletin des Societe.' Chemiques, Vol. 9,pp. 515, 518 (1911).

3. F. G. Roux, "Process for Producing Metal Deposits", U.S.Patent, 1,207,218, Dec. 5, 1916.

4. Abner Brenner and Grace Riddell, "Nickel Plating on SteelBy Chemical Reduction", Proceedings A.Z.S., Vol. 33,p. 16, 1946. 'Deposition of Nickel and Cobalt By ChemicalReduction", Proceedings A.N.S., Vol. 34, p. 156, (1947).

5. Abner Brenner and Grace Riddell, "Nickel Plating on SteelBy Chemical Reduction", Proceedings A.E.S., Vol. 33,p. 25 1 8,9, and 10, (1946).

6. H. K. DeLong, "Plating on Magnesium by Zlectrodepositionand Chemical Reduction Methods", Presented at the 1961American Zlectroplaters Society Convention in Boston,Mass., p. 16, line 6.

7. arry J. West, Ilectroless Nickel Barrel Plating", MetalFinishing, Mar. 1954, Vol. 52, No. 3, p. 64.

8. Harry J. West, 'lectroless Nickel Plating on NonferrousMetals", Metal Finishing, July 1954, Vol. 52, No. 7, p. 72.

9. John D. Maclean and Seymour M. Karten, "A PracticalApplication of Ilectroless Nickel Plating", 41st AnnualProceedings A.Z.S., 1954, p. 226.

10. 0. Gutzeit, and R. W. Landon, "A Large Scale ZlectrolessNickel Custom Plating Shop", 41st Annual ProceedingsA.Z.S., 1954, p. 256.

11. Abner Brenner, "Electroless Plating Comes of Age", MetalFinishing, Nov. 1954, Vol. 52, No. 11, and Dec. 1954,Vol. 52, No. 12.

12. Harry J. West, "Ilectroless Chromium", Metal Finishing,July 1955, Vol. 53, No. 1, p. 62.

9 61-4359

LIJTERATURE IUFUINC28 (Con t.)

13. H. K. DeLong, "Plating on Magnesium by Ilectrodepositionand Chemical Reduction Methods", presented at the 1961A.Z.S. Convention in Boston, Mass., page 17.

14. Abner Brenner and Grace Riddell, "Deposits of Nickel andCobalt By Chemical Reduction", Proceedings ASOS.,Vol. 34, p. 161, (1947).

15. W. H. Metzger, Jr., "Ulectroless Nickel Plating",A.S.T.M. Spec. Tech. Publication No. 265 citing G.Gutzeit and 2. T. Eapp, Kanigen, "Chemical Nickel Plat-ing", Corrosion Technology, Vol. 3, No. 10, October 1956,page 331 (London).

10 61-4359

LIST 0F PRIOR RIPORTS

R. I. A. DateLab. No. Issued Title

54-24 3-1-54 Porosity of Nickel Deposits By Auto-radiographic Techniques

11 61-4350

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