THE INVESTIGATION OF THE ELECTROLYTIC

BEHAVIOR OF TUNGSTEN

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By KURT THEURER, B.A., M.S.

The Ohio State University

1955

Approved by:

^ A J L V A t (.A C

Jo -Xdvi sera' Department of Chemistry ACKNOWLEDGEMENT

The author* wishes to express his sincere appreciation t o his advisors Dr. Thomas R. Sweet, and Dr. W i l l i a m M. MacNevin, for their generous assistance an d guidance in this investigation.

ii TABLE OF CONTENTS

Page

INTRODUCTION...... 1

HISTORICAL REVIEW...... 2 THE UTILIZATION OF RADIOACTIVE TUNGSTEN AS A TRACER 10

Experimental Procedure...... 11

Experimental Results and Discussion...... 14

Conclusi ons...... 21 THE ELECTROLYTIC BEHAVIOR OF TUNGSTEN WITH VARIOUS METALLIC IONS AND ELECTRODES...... 25 Part I Metallic Ions...... 25 Cobalt ...... 26 Zinc...... 30 Palladium...... 34 Rhenium...... 3$ Part II Metallic Cathodes...... 40 Platinum...... 40 Copper...... 41 Palladium...... 46 Zinc...... 46 Cobalt...... 49 Results and Conclusions...... 55 THE ELECTROLYTIC BEHAVIOR OF TUNGSTEN ON OXIDE AND OXIDE FREE TUNGSTEN ELECTRODES...... 5S The Effect of Cathode Oxides on the Rate of Deposition of Tungsten-Cobalt Deposits.. 59 1. Constant Current Density...... 59 Apparatus and Materials...... 59 Procedure...... 6l Results and Conclusions...... 62

iii Page

2. Constant Cathode Potential...... 62 Results and Conclusions...... 62 The Electrodeposition of Tungsten on an Oxide Free Tungsten Electrode...... 64

Apparatus and Materials...... 64- Pro cedure...... 69 Results and Conclusions...... 71

The Study of the Electrolytic Behavior of Tungsten from Current-Time Measurements... 71

1. Untreated Tungsten Surface...... 72 2. Flashed Tungsten Surface...... 72 3. Untreated Tungsten Surface at Atmospheric Pressure...... 73 4. Untreated Tungsten Surface.. 73 5. Flashed Tungsten Surface...... 34 6. Flame Oxidized Tungsten Surface...... 34 7. Electrolytically Oxidized Tungsten Surface...... 34 9. Deposition of Copper on a Flame Oxidized Tungsten Surface...... 35 10. Deposition of Copper on an Untreated Copper Surface...... 35

Results and Conclusions...... 35

SUMMARY...... 94

BIBLIOGRAPHY...... 95

AUTOBIOGRAPHY...... 93

iv LIST OF TABLES

Table Page

I Absorption Data for Cobalt-Tungsten Sample... 15 II Absorption Data for Tungstate Solution.. 16 III Absorption Data for Zinc-Tungsten Sample 19 TV Separation of Tungsten from Rhenium...... 22

V Cobalt Standardization...... 29 VI Electrolytic Data for Cobalt-Tungsten Deposits...... 31 VII Zinc Standardization...... 33 VIII Electrolytic Data for Zinc-Tungsten Deposits. 35 IX Absorption Data for Palladium-Tungsten Sample...... 36 X Activity Data for Rhenium-Tungsten Deposit... 39 XI Plating Conditions with Platinum Cathodes.... 41 XII Absorption Data for Platinum Cathode Deposits 42 XIII Plating Conditions with Copper Cathodes..... 42 XIV Aosorption Data for Copper Cathode Deposits.. 44 XV Plating Conditions with Palladium Cathodes... 46 XVI Absorption Data for Palladium Cathode Deposits...... 47 XVII Plating Conditions with Cobalt Cathodes..... 49 XvTIII Absorption Data for Cobalt Cathode Deposits.. 50 XIX Cathode Gain at a Constant Current Density... 63 XX Cathode Gain at a Constant Cathode Potential. 63

v Table Page XXI Current-Time Data for the Deposition of Tungsten on an Untreated Tungsten Surface...... 73 XXII Current-Time Data for the Deposition of Tungsten on a Flashed Tungsten Surface.. 74

XXIII Current-Time Data for the Deposition of Tungsten on an Untreated Tungsten Surface at Atmospheric Pressure...... 76 XXIV Current-Time Data for the Deposition of Tungsten on an Untreated Tungsten Surface...... 79 XXV Current-Time Data for the Deposition of Tungsten on a Flashed Tungsten Surface.. SO XXVI Current-Time Data for the Deposition of Tungsten on a Flame Oxidized Tungsten Surface...... Si XXVII Current-Time Data for the Deposition of Tungsten on an Electrolytically Oxidized Tungsten Surface...... 82 XXVIII Current-Time Data for the Deposition of Tungsten on an Untreated Copper Surface. 86 XXIX Current-Time Data for the Deposition of Copper on a Flame Oxidized Tungsten Surface...... 88 XXX Current-Time Data for the Deposition of Copper on an Untreated Copper Surface... 89

vi LIST OF FIGURES Figure Page 1 Absorption Curves of an Electrolytic Cobalt-Tungsten Deposit...... 17 2 Absorption Curve of a Standard Tungstate Soluti on...... 1^ 3 Absorption Curves of an Electrolytic Zinc-Tungsten Deposit...... 20 4 Growth Curve for Tungstate Fraction and Decay Curve for Rhenium Fraction...... 23 5 Absorption Curve of an Electrolytic Palladium-Tungsten Deposit...... 37 6 Absorption Curves of Electrolytic Tungsten Deposits on Platinum Cathodes...... 43 7 Absorption Curves of Electrolytic Tungsten Deposits on Copper Cathodes...... 45 & Absorption Curves of Electrolytic Tungsten Deposits on Palladium Cathodes...... 4d 9 Absorption Curves of Electrolytic Thungsten Deposits on Cobalt Cathodes...... *..... 51 10 Electrolytic Cell...... 60 11 Electrolytic Vacuum Cell...... 66

12 Vacuum System...... 6d 13 Current-Time Curves for „he Deposition of Tungsten on an Untreated Tungsten Surface and on a Flashed Tungsten Surface...... 75 14 Current-Time Curve for the Deposition of Tungsten on an Untreated Tungsten Surface at Atmospheric Pressure. 77 15 Current-Time Curves for the Deposition of Tungsten on Various Tungsten Surfaces.... S3

vii Figure Page

16 Current-Time Curve for the Deposition of Tungsten on a Copper Surface....,...... 67

17 Current-Time Curve for the Deposition of Copper on an Untreated Copper Surface and on a Flame Oxidized Tungsten Surface 90

viii THE INVESTIGATION OF THE ELECTROLYTIC

BEHAVIOR OF TUNGSTEN

INTRODUCTION

The purpose of this investigation was to study the conditions that inhibit the continued deposition of tungsten from an aqueous tungstate solution. The electrodeposition of tungsten, like that of molybdenum, tends to diminish rapidly or stop altogether as soon as a thin layer is deposited. No satisfactory explanation has been published.

Foremost among the questions to be settled is whether the formation and presence of oxide is responsible for cessation of the deposition. Deposition of metals capable of inducing codeposition of tungsten and simultan­ eous oxide formation were studied. The influence of cathode material on the deposition has also been determined.

1 HISTORICAL REVIEW

Electrolytic Deposition of Tungsten and Tungsten Alloys The problem of obtaining metallic tungsten by electrolytic reduction has been studied for almost a century. During this period many investigators have claimed success­ ful deposition of metallic tungsten. However the electro­ deposits were always so very thin that their chemical purity is questionable. The literature of tungsten plating goes back to 1367 when Zettnow (1) electrolysed a sodium tungstate solution and obtained a thin deposit of tungsten on an iron cathode. The electrolytic deposition of tungsten powder on a mercury cathode was successfully accomplished by Feree (2) In 1393, and by Jackson, Russell, and Merrill (3) in 1929. The electrolyte consisted of tungsten trioxide dissolved in hydrofluoric acid. A few milligrams of tungsten were deposited after eight hours. Fink and Jones (4) claimed successful deposition of tungsten from an alkaline carbonate bath. Holt (5) was able to show that a trace of "depolar­ ising metal" was necessary and that this metal was present as an impurity in the reagents used. Successful deposition of tungsten has been claimed from sodium hydroxide (6), citrate (7), and phosphate (3) solutions, but only very thin layers of metal were deposited. These layers were too thin to determine accurately the purity of the metal. A series of patents were issued to Armstrong and Menefee (9) which dealt with the deposition of tungsten from fluoride baths. A reaction product of tungsten trioxide or a derivative in an alkaline bifluoride bath constituted the electrolyte. Harford (10) deposited tungsten from an aqueous solution of an alkyl hydrocarbon polyamine (diethylene triamine), but attempts to repeat this work have been unsuccessful (11). Broughall (12) plated tungsten from liquid ammonia solutions, but Merlub-Sobel (13) was unable to repeat this work. Two patents were issued to Wolfram-Lampen AG, one for plating tungsten from pertungstic acid (WO^HgOg-HgO) dissolved in water, alcohol, or ether (14)> and the other for plating tungsten from acetone solutions of the hexa- chloride (15). Neuman and Richter (16) obtained small amounts of tungsten from a solution of tungsten hexachloride in glycerine. The melting points of pure alkali tungstates lie between 750 and 950°C. A mixture of these salts melts at a lower temperature so that electrolysis from a fused bath is possible without decomposition occurring. A eutectric mixture of lithium, sodium, and potassium tungstates was electrolysed at 400°C. by Leimpt (17), Leo and Shen (Id) o electrolyzed a fused phosphate bath at 950 C. The elextrolysis of tungsten from fused baths usually results 4 in a dark powder, rather than a deposit with metallic properties. The codeposition of tungsten with other metals to form binary alloys has been much more successful than the deposition of tungsten alone. A series of papers were published by Holt and co-workers on the codeposition of tungsten with cobalt, nicke3., and iron from a boric acid solution (19,20,21), and from an ammoniacal citrate solution

(22,23,24)* Shiny metallic alloys were obtained with as much as 603C tungsten present* Tungsten has also been codeposited with copper (25), platinum (26), and chromium (27) to form binary alloys, the percentage of tungsten being considerably lower* Also reported as such tertiary alloys

as Ni-Co-W (26), Fe-Co-W (11), and Co-W-Mo (29), deposited from citrate solutions.

Mechanisms for Deposition of Tungsten and Tungsten Alloys Various mechanisms have been offered to explain the failure of electrolytic reduction of tungsten in aqueous solution and also the remarkable ability of cobalt, iron, and nickel to codeposit appreciable quantities of tungsten. Glazunov and Jolkin (30) found that a very thin film of tungsten was deposited on a copper electrode from a concentrated aqueous carbonate tungstate solution electro- o lyzed at a temperature of 115 C. and at a high current density. After one-half hour of electrolysis the deposition

of tungsten stopped and the deposited tungsten began to 5 redissolve. Glasunov (31) proposed that the primary process was the deposition of a lower valent oxide on the cathode which is reduced to the metal by atomic hydrogen. This reaction is stopped by the accumulation of tungsten ions of higher valence which react with the deposited metal as shown by the equations:

W ♦ W +^ ______^ 2W+2, W + 2W+6 ----- > 3W+4.

Holt and Vaaler (32) proposed a "catalytic reduction" theory to explain the electrolytic reduction of aqueous tungstate solutions in the presence of codepositing metals

such as iron, nickel, and cobalt. Two cathode reactions are suggested as being essential for the reduction process: M++ ♦ 2e ----- > M, (A) M W0£ + 8H+ + 6e ---- » W ♦ UH20. (B) Reaction (A) proceeds until the cathode is covered with a thin deposit of metal M, which acts as a catalyst for

reaction (B). When this metal catalyst is covered with a layer of tungsten, reaction (B) stops and reaction (A) proceeds again to give a new catalytic surface. In this way alternate layers of metal M and tungsten are deposited on the cathode. This mechanism was based on the following evidence: (1) Cathode potential studies showed that for the nickel-tungstate bath the cathode potential is less negative 6 than the cathode potential in a nickel bath. (2) Polarographlc studies Indicated no complex Ion formation between the metal and the tungstate, but did show a catalytic hydrogen wave for the nickel-tungstate bath. (3) The laminated structure of the electrodeposited alloys. This mechanism also explains why tungsten Itself will not deposit In appreciable quantities since reaction (B) stops as soon as a layer of tungsten is deposited. Because no metal M is available reaction (A) cannot proceed and tungsten oxides are deposited on the surface. Clark and Lietzke (11) further Investigated the mechanism of tungsten alloy plating. Absorption spectra indicated the possibility of cobalt-tungstate complexes in a citrate plating bath. Polarographlc evidence suggested the existence of tungstate-citrate complexes. Calculations for the energies of activation of iron-tungsten alloy deposition showed that tungstate reaches the cathode by diffusion rather than by migration. A radiochemical study showed that iron, cobalt, and nickel are no more effective as cathodes for tungsten deposition than other metals such as copper and platinum. Clark and Lletske concluded from these results that a very thin layer of tungsten or some tungsten compound is deposited on the cathode. This film is then cat&lytically reduced by hydrogen in the presence of freshly deposited iron, cobalt, or nickel. 7 Aikire (33) attempted to obtain tungsten from tungsten hexachloride dissolved in various organic solvents such as carbon tetrachloride, acetone, benzene, and dioxanei. Using potentials as high as 100 volts, he was unable to deposit tungsten on platinum electrodes. He concluded that the failure to deposit tungsten was not necessarily due to the presence of lower valent oxides but rather to the great stability cf lower valent tungstate ions. Conditions more extreme than obtained by electrolytic means may be necessary to reduce these lower-valent tungsten compounds.

Mechanisms for Deposition of Chromium and Molybdenum The Subgroup VI elements, chromium, molybdenum, and tungsten, show many properties coranon to each other. Among these are very high melting points, the ability to form acidic oxides, a maximum positive oxidation state of 6, high negative vali ss of their standard electrode potentials, and low hydrogen overvoltage values so that appreciable quantities of hydrogen gas are liberated during electrolysis. An understanding of the mechanism of chromium and molybdenum deposition may be helpful in comprehending the electro­ deposition of tungsten. For this reason a literature search was made of the proposed theories explaining the deposition of chromium and molybdenum. The deposition of chromium from aqueous solutions has been very successful and has found application in many s commercial processes. The bath usually contains chromic acid, and one or more acid radicals such as sulfate which act as catalysts for the deposition process. Sulfuric acid and sodium sulfate are the sulfate-bearing materials most widely used in the bath. Chromium cannot be deposited from a solution containing only chromic acid and water. Muller (34) suggested the formation of an insoluble film of chromium chromate, CrfOHjCrO^, on the cathode. This film prevents the deposition of chromium from a pure chromic acid solution.

The sulfate or other anions are able to alter or remove this film so that chromium deposition is possible. Ekwall

(35) concluded that sulfate has a greater tendency to form complexes with trlvalent chromium than with chromate, con­ sequently it reacts with newly formed trivalent chromium and prevents the formation of basic chromic chromate at the cathode. Kasper (36) showed that the basic chromium chromate is a colloid which the sulfate coagulates and thus prevents a film from forming on the cathode. Brenner and Ogburn (37) were able to show that chromium is deposited directly from the hexavalent state and not through an intermediate step involving trivalent chromium. They used radioactive chromium as a tracer in their work. The theories proposed to date are not able to offer a complete explanation for chromium deposition from chromic acid solutions. 9 The electrodeposition of molybdenum has been attempted with very little success. Numberous claims are found in the literature (3S|39»40), but attempts to repeat the work were usually unsuccessful. Fink (41) concluded that molybdenum exhibits "self-polarization," that is, it will not deposit on itself. The deposition ceases as soon as a monolayer of the metal is formed on the cathode. Ksychki and Yntema (4 2) claimed to have obtained shiny metallic molybdenum deposits from aqueous solutions of molybdic acid containing high salt concentrations of formates, acetates, propionates, or phosphates of sodium, potassium, or ammonium. The pH of the solution was 5.7-6.#, the current density 0.6 amp./cm. , the temperature 30 to 45°C., and the deposits weighed approximately 2 mg/cm. of cathode area. They suggested as a mechanism thafc lower-valent molybdenum states, formed during the step­ wise reduction from a valence of +6, were more soluble in the presence of a high concentration of anions than they were in water. Molybdenum thus was prevented from precipitating as a basic salt before final reduction to the metal. Molybdenum has been deposited with cobalt, nickel, and iron as a binary alloy from a citrate bath (43»44). McElwee and Holt (29) plated ternary alloys of cobalt, molybdenum, and tungsten. Because of the similarity to tungsten alloy deposition, the mechanism proposed for these molybdenum alloys was the same as for the tungsten alloys, a "catalytic reduction" process. THE UTILIZATION OF RADIOACTIVE TUNGSTEN AS A TRACER

Radioactive tungsten was used as a tracer to investi­ gate the electrolytic behavior of tungsten more efficiently.

The advantage of a tracer is that small amounts of tungsten can be readily determined. A suitable isotope of this investigation would be one which (1) was produced by an

(n,¥ ) reaction, (2) has a ganma energy, and (3) possesses a long half-life. Corrections for decay and self-absorption would be small or negligible with such an isotope.

Processed tungsten-135i produced in a neutron pile was chosen because of its 75 day half-life, 0.134 Mev. gamma energy, and availability from the Oak Ridge National Labora­ tory (45). Radioactive tungsten-131 with a half-life of

140 days and 0.03, 0.60, 0.30 Mev. gamma energies was present as an impurity. Since both of these isotopes have the same chemical properties no difficulty was expected. As the investigation proceeded, it became apparent that another radioactive isotope of short half-life was present.

It was identified as 16.9 hour rhenium-133, formed by a second (n,Jf ) reaction with stable tungsten-136. The presence of the rhenium isotope complicated the use of radioactive tungsten-135 as a tracer since rhenium has different chemical properties. Furthermore the rhenium is in transient equili­ brium with tungsten-133 and therefore cannot be permanently

10 11 separated. Special precautions must be taken when using tungsten-lS5 as a tracer, otherwise false observations will result.

Experimental Procedure

Apparatus The electrolytic cell is the same as described in the authorTs Masters thesis (46). Briefly it is a modified

Tracerlab E-16 electroplating cell 4 l/2w high, and ln in diameter to which a glass sidearm and a glass capillary tube with stopcock were added. A terminal located on the metal base provides electrical contact with a copper planchet electrode. The anode is a thin piece of platinum 0.5" x

1.75", bent similarly to a propeller and attached to a thin platinum rod. The glass sidearm, in conjunction with the rotating anode, provides a means for rapid and convenient removal of the radioactive solution.

Additional equipment for these experiments consisted of: Potter Predetermined Decade Scaler Model #341

Tracerlab SC-9C Shielded Manual Sample Changer

Tracerlab TGC-3 Geiger Muller Tube

Tracerlab SM-60A Electrical Stopclock

Tracerlab E-3A Aluminum Absorbers

Eberbach Electrolytic Analyzer Copper Disc Planchets (1" Diameter) 12 Stainless Steel Cupped Planchets (I*1 Diameter)

Beckman pH Meter, Model H-2

Reagents Radioactive Tungstate Solution. Processed tungsten-

1S5 was purchased from the U.S. Atomic Energy Commission, Isotopes Division, Oak Ridge, Tenn., as potassium tungstate solution. Approximately 3.0 Me. of this solution were transferred to a 2-liter volumetric flask and reagent grade sodium tungstate dihydrate added so that the final concen­ tration was 1.00 mg. of tungsten per ml. of solution.

All other chemicals were of reagent grade quality.

Absorption Curve for Tungsten-135-P A small amount of standard radioactive tungstate solution was evaporated in a cupped planchet. The activity was determined over the range of the aluminum absorbers.

Coincidence and background corrections were made on the observed activities.

Cobalt-Tungsten Electrolytic Bath The bath is similar to the one used by Clark and Holt

(24) in their deposition of cobalt-tungsten alloys. To 35 ml. of water are added 10 mg. of cobalt as cobalt sulfate, 1 g. of citric acid, and 10 ml. of the radioactive tungstate solution. The pH of the solution was adjusted to 7.5 with ammonium hydroxide. The solution was heated to B0°C., 13 introduced into the electrolytic cell, and electroplated for 15 minutes at 4.0 volts. The active solution was removed and the cell was rinsed with water. The copper planchet was washed with alcohol and allowed to dry in a 70°C. oven for 5 minutes. The activity was measured over the range of the aluminum absorbers. The samples were recounted once a day for a 3-day period. Background and coincidence corrections were made on all measured activities.

Zinc-Tungsten Electrolytic Bath The procedure was identical with that described above, except that 10 mg. of zinc, as zinc sulfate, replaced the cobalt.

Partial Separation of Tungsten from Rhenium To verify the presence of rhenium, a partial separa­ tion of tungsten from rhenium was made. Approximately 10 mg. of rhenium metal were dissolved in 10 ml. of 3% hydrogen peroxide. Then 10 ml. of the standard active tungstate solu­ tion, followed by 10 ml. of 1:1 hydrochloric acid were added. The mixture was digested at 90°C. until the tungstic acid had separated. Approximately 5 nil. of cinchonine solution (10j6 solution in 1:1 hydrochloric acid) were added, and the solution was further heated at 90°C. for 30 minutes. The precipitate was filtered, dried, and a portion transferred to a cupped planchet. A portion of the filtrate was trans­ ferred to a cupped planchet and evaporated to dryness. The 14 activities of both the evaporated filtrate and dried pre­ cipitate were measured with an aluminum absorber (225 mg. per 2 cm.) between the samples and the TGC-3 Geiger tube. The samples were recounted at short time intervals. All nec­

essary counting corrections were made.

Experimental Results and Discussion

Corrections for self-absorption are negligible when only the 0.134 Mev. gamma energy of tungsten-165 is measured. 2 For this reason an aluminum absorber (223 mg. per cm.) was placed over the samples to absorb the 0.43 Mev. beta energy also present in the tungsten-165. On recounting an elec­ trolytic deposit it was observed that the activity had substantially decreased. In Figure 1 are the absorption curves for a cobalt-tungsten alloy counted over a 2 day period. An absorption curve for the tungstate solution before electrolysis is shown in Figure 2. The data for these curves are given in Table I and Table II respectively. A compari­

son of the graphs in Figure 1 and 2 indicates that elec­ trolysis has produced a shift in equilibrium resulting in a concentration of activity. This excess of activity decays until equilibrium has been re-established. This effect is more pronounced when sine replaces cobalt in the electrolytic

solution as shown by the data in Table III and by the ab­ sorption curves in Figure 3. The activity decays rapidly 15 Table I

Absorption Data for Cobalt-Tungsten Sample

Aluminum Absorbers Initial Activity Percent (mg./cm?)______(count s/min.) Activity 0.0 71736 100 10.5 44554 62.1 20.3 27646 33.5, 45.9 34393 4.36 70.0 30351 11.2 101 2131.0 2.97 1LB 1531.4 2.20 165 1493.9 2.03 223 1024.7 1.43 273 693.3 0.971 370 371.3 0.513 430 232.0 0.323 540 114.9 0.160 Aluminum Absorbers Activity After Percent , I rng t / c m f )______13.5 Hrs. (counts/kta) Activity 0.0 69171 100 10.5 42.335 62.0 20.3 26132 37.3 45.9 2365.5 3.42 70.0 6311.0 9.35 101 1145.0 1.66 143 329.0 1.20 165 746.6 1.07 223 0.763 273 0.529 370 191.0 0.276 430 139.7 0.202 540 67.5 0.0933

(continued on next page) 16 Table I (continued)

Aluminum Absorbers Activity After 44.5 Hrs. Percent (mg . /cm?)______(counts/min.)______Activity

0.0 68,335 10° 10.5 41539 60.8 20.3 250A5 36.6 45.9 1662.9 2.43 70.0 6079.3 3.83 101 572.1 0.836 148 395.1 0.57# 165 347.9 O .509 223 259.5 0.380 273 181.2 0.265 370 105.7 0.155 430 67.7 0.0994 540 30.1 0.0440

Table II

Absorption Data for the Tungstate Solution

Aluminum Absorbers Activity Percent (mg./cm?)______(counts/mi n.) Activity

0.00 214,200 100 10.5 141,300 66.0 20.3 35,520 39.9 45.9 19,721 9.21 70.0 4,473.3 2.09 101 942.0 0.440 143 560.2 0.262 223 332.3 0.179 297 262.6 0.122 370 164.2 0.0767 430 130.6 0.0610 540 67.0 0.0313 628 51.6 0.0241 750 45.4 0.0200 951 4 2 .0 0.0196 1160 39.0 0.0182 1600 39.6 0.0185 >oo< II

O Initial tim* A 163 hr* lattr □ 44.5 hr* lattr

IQO

i 50O|— o <

o £

IOO

0 5 0 0 —

0-100 J. J. -J 0 IOO 2 0 0 3 0 0 4 0 0 5 0 0 Aluminum (mg/cm2)

FIGURE I. ABSORPTION CURVES OF AN ELECTROLYTIC Co W DEPOSIT IUE . BOPIN UV O A STANDARD OF A TUNGSTATE CURVE ABSORPTION 2. FIGURE 0CC- C 005C OOKXX Percent octivity 0 .5 0 0 — 0 0 .5 0 500 100 10.0 LOO SOLUTION 0 0 3 "eo5 lmnm (mg/cm2) Aluminum ------§55— 1500 It 19 Table III

Absorption Data for Zinc•Tungsten Sample

Aluminum Initial Activity After Activity Absorbers Activity 24.5 Hrs. After i (mg./cm. ) (counts/min.) (counts/min.) (counts 0.0 153$.0 59$. 0 251.6

10.5 1463.6 567.$ 24$. 2 20.3 1452.1 553.9 239.2 45.9 1360.2 515.$ 223.0 70.0 122$.2 46$. 0 19$.4

101 1103.4 41$.4 169.6 14$ $30.0 336.2 141.4 223 552.4 217.2 90.4 276 421.2 161.2 65.6 370 216.2 $2.0 34.2 430 135.0 52.4 22.5 540 56.0 21.0 10.5 a.o

4 tim« 24 hr*. lot*r 46 hr& loter

IpOO

SOO

5 0

IOO 200 300 400 500 Aluminum (mg/cm2) FIGURE 3. ABSORPTION CURVES OF AN ELECTROLYTIC Zn W DEPOSIT 21 with a half-life of 16.9 hours. Lindner and Coleman (47*46) have shown that rhenium- 133 is produced from the neutron irradiation of tungsten-136 after a long period of time. They separated the rhenium from the tungsten by adding inactive rhenium carrier and precipitating it with tetraphenylarsonium chloride. In the present investigation the existence of rhenium- 133 was verified by adding inactive rhenium carrier and precipitating the tungsten with cinchonine. Figure 4 indi­ cates the effect when the transient equilibrium given by

133 Os Hours is disturbed. The tungstate fraction approaches equilibrium while the rhenium fraction decays with a half-life of 16.9 hours. The chemical separation does not leave the two fractions free from impurity. The data given in Table 17 were accordingly corrected. For the tungsten fraction there were 55.3 c.p.m. present before any activity was able to grow back. This activity was obviously rhenium and was subtracted frcm the remaining measurements. The rhenium fraction decayed to 77.0 c.p.m. which were subtracted to correct for the tungsten present.

Conclus‘on The presence of radioactive rhenium-133 has been proved in processed tungsten-135 obtained from Oak Ridge. 22 Table IV

Separation of Tungsten from Rhenium

Tungsten Fraction

Time After Initial Activity Activity

1.2 55.3 - 10.0 205.3 150.0

22.1 296.2 240.4

32.7 371.7 315.9

54.1 411.9 356.1 73.2 415.1 359.3

96.1 439.9 374.1

144.2 435.3 379.5

Rhenium Fraction

Time After Initial Activity Activity Separation (hours) (counts/min.) (corrected value)

2.5 233.5 211.5

9.5 233.0 161.0

22.5 176.2 99.2 33.0 141.0 64.0

54.5 103.2 31.2

73.5 77.9 -

102.5 76.0 - U S 1 77.1 _ 50 5 < o IUE . O: RWH UV FR UGTN FRACTION TUNGSTEN FOR CURVE GROWTH TOP: 4. FIGURE Activity (Counts/mi n) 100 50 10 I 0 2 150 120 0 9 0 6 30 0 ______OTM OCY UV FR HNU FRACTION RHENIUM FOR CURVE OECAY BOTTOM: I ______I ______i# (hours) Tim# io (hours) Timo I ______120 i ------J- ISO 24 This isotope interferes with the use of radioactive tungsten as a tracer in electrolytic investigations. The rhenium is

removed from the solution at a faster rate than the tungsten. This results in activity measurements which are not a true

indication of the actual amount of tungsten present in a sample. Furthermore, the 0.134 Mev. gamma energ listed as being present in tungsten-135 is too weak to be of any value in tracer work. This means that a correction for self­

absorption will be necessary when using tungsten-135 as a tracer. To obtain the activity of tungsten one must either wait several days until the transient equilibrium has been re-established, or recount the sample several days later

and correct for the rhenium activity mathematically. THE ELECTROLYTIC BEHAVIOR OF TUNGSTEN WITH VARIOUS METALLIC IONS AND ELECTRODES

Holt (49) studied the effect of various metals on the codeposition of tungsten from an alkaline carbonate bath* The results showed that cobalt, nickel, and iron codeposit tungsten to the greatest extent. Amounts as little as 0.1 mg. of meted, were sufficient to induce the electroplating of a shiny metallic tungsten alloy. Cadmium and tin codeposit tungsten to a smaller extent. The presence of tungsten in a sine deposit was questionable, and the metals Ag, Au, Hg, Pt, Al, As, and Pd gave negative results for tungsten on chemical analysis. Holt also studied the effect of various cathode metals such as brass, Cd, Cu, Ni, and Pt. These metals all behaved similarly in their ability to deposit tungsten.

Part I Metallic Ions The purpose of this phase of the investigation was to study the codeposition of tungsten with various metals from an ammonlacal citrate solution using radioactive tracers. It was hoped that additional information would be obtained so as to provide a better understanding of the mechanism for tungsten and tungsten alloy deposition. Cobalt, sine, palladium, and rhenium were the metallic ions studied. 25 26 Cobalt

Cobalt la one of the three metala with which tungeten la readily codeposited. Binary alloya are formed which contain 50 to 60£ tungsten. This strange behavior of cobalt haa no explanation other than the proposed "catalytic reduction1* mechanism.

Electrolytic Behavior of Cobalt

At the beginning of this research there were expecta­ tions of developing a rapid analytical procedure for tungsten baaed on the Isotope dilution method of analysis. In this method a cobalt-tungsten alloy Is deposited from a solution containing radioactive cobalt and radioactive tungsten. The relative amounts of cobalt and tungsten are determined by weighing the deposit and measuring the activities of the two isotopes. A gamma energy must be present in each of the radioactive isotopes for the development of a practical method. These energies must be sufficiently different so that one can be measured In the presence of the other.

Cobalt-60 has a 1.1 Mev. gamma, but the 0.134 Mev. gamma listed for tungsten-165 is present in such small amounts, if at all, that it cannot be detected. The first step in this Isotope dilution method would have been the preparation of a standard radioactive cobalt solution. This work was started before the tungsten-165 arrived from Oak Ridge. The results 27 suggested an explanation for the codeposition of tungsten with cobalt. The preparation of the standard radioactive solution consisted of adding radioactive cobalt-60 to a standard inactive cobalt solution. The activity per milligram of cobalt ( specific activity) was determined by electro­ plating a small amount of cobalt on a copper electrode, weighing the deposit, and measuring the activity. The electrolytic cell and other equipment were the same as described in the first section. A micro balance, manufactured by Christian Becker Inc., N.Y., was used to weigh the cobalt deposits. The inactive standard cobalt solution was prepared by dissolving 1 g. of spectrograph!cally standardised "Matthey Cobalt Sponge” in 100 ml. of dilute sulfuric acid. The solution was transferred to a 1 liter volumetric flask and diluted to the mark with distilled water. The cobalt was purchased from the Johnson Matthey and Company, London, England. The radioactive cobalt solution was prepared by adding 0.05 Me. of cobalt-60, as the cobalt chloride, to a 500 ml.- volumetric flask, and diluting to the mark with the standard inactive cobalt solution. The concentration of the final solution was 1.00 mg. of cobalt per ml. of solution. The radioactive cobalt was purchased from the U.S. Atomic Energy Commission, Isotopes Division, Oak Ridge, Tenn. 2d The plating bath was similar to the one used by Clark and Holt (24) In their deposition of cobalt-tungsten alloys. The electrolytic cell with a capacity of 45 ml. contained 10 ml. of the radioactive cobalt solution, lg. of citric acid, and enough ammonium hydroxide to adjust the pH to 7*5. All other plating conditions including changes In the above mentioned bath are summarized in Table V. The plating and counting techniques were the same as described in the first section. A comparison of the specific activities indicates that the specific activity decreases as the temperature Increases. This variation is independent of pH, concentra­ tion of cobalt and citric acid, the plating time, and the weight of the deposit. There is a smaller change in specific activity in each temperature group due to current density changes. As the current density decreases the specific activity increases. A lowering in the specific activity indicates the presence of an Impurity in the electrodeposit. Glasstone (50) reported that appreciable quantities of oxides have been found in nickel deposits due to the pre­ cipitation of hydrous oxides or basic salts. The discharge of hydrogen gas leaves the solution alkaline in the vicinity of the cathode so that precipitation occurs. This indicates that an increase in oxide precipitation should occur at the higher temperatures and current densities where the rate of 29 Table V

Cobalt Standardisation

Changes in Current - Temp. Plating Time No, Bath Content (Amn.xlO'* (°C.) (win.) _

1 none 100 2 33 2 none 23 2 45 3 20 mg. Co. 50 2 30 4 none 100 10 45 5 25 ml NHi OH pH 9.3 50 24 20 6 none 50 24 25 7 none 100 24 20 3 none 100 35 30 9 40 mg. Citric Acid 50 35 15 10 none 50 35 15

Rui Activity Specific No Deposit (mg.) (Counts per min.) Activity

1 1.690 4935.1 2949.3 2 0.966 2927.6 3030.5 3 2.740 7945.4 2399.6 4 1.247 3433.3 3753.7 1.397 4907.5 I 1.153 2943.0 2556.3 7 1.331 4655.4 2542.5 3 0.473 H31.0 9 1.359 4530.6 2464.0 1.013 2634.6 2444.0 30 hydrogen evolution ie greatest. The data show that under these same conditions the specific activities of the cobalt deposits are the lowest. It is apparent that this same effect which occurs with nickel has occurred with cobalt.

Electrolytic Behavior of Tungsten with Cobalt in an

Ammoniacal Citrate Bath Self-absorption effects make it impossible to deter­ mine quantitatively the plating conditions favorable for tungsten as an alloy. However qualitative conclusions may be obtained from this study. The procedure and bath concentrations have been described in the first section. The absorption curves for a typical cobalt-tungsten alloy, shown in Figure 1, illustrate the tendency of rhenium to electrodeposit at a faster rate than the tungsten. For this reason the deposits were recounted after a 10 day period. The results are summarized in Table VI. The samples were counted with 223 mg. of aluminum per cmf in front of the Geiger-Muller tube. The results showed that the percentage of tungsten in the deposited alloys was greater in the high temperatures. This conclusion was in agreement with Holt (24) who found the same effect. Zinc Holt (49) was unable to establish definitely whether tungsten was codeposited with zinc. This metal was studied 31

Table VI

Electrolytic Data for Cobalt-Tungsten Deposits

Run Current , Temp. Plating Time No. (amp.xlCK) l°cj. (mlnT) 1 25 2 60 2 50 2 45 3 100 2 45 4 25 80 90 50 80 60 I 100 80 60

Run No. Deposit Activity Activity (mg.) (counts per min.) 10 days later

1 0.889 2332.0 90.3 2 1.222 2080.9 *9.6 3 1.572 2227.7 60.4 4 0.864 4571.3 288.6 5 1.433 4660.1 755.4 6 2.583 5368.9 962.5 32 next in the present investigation to determine its potential­ ity as a codepositor. The behavior of electrolytically deposited cobalt and the availability of radioactive zinc in the laboratory suggested a study of the electrolytic behavior of zinc.

Electrolytic Behavior of Zinc The standard radioactive zinc solution was prepared by adding 0.05 Me. of zinc-65 to a 500 ml. volumetric flask containing reagent grade zinc sulfate so that on dilution a concentration of 1 mg. of zinc per ml. of solution was obtained. A 45 ml. portion of the electrolytic bath contained

10 mg. radioactive zinc, 1 g. citric acid, and enough ammonium hydroxide to adjust the pH to 7.5. The plating conditions and results are summarized in

Table VII. The results indicate that the specific activity of zinc is independent of temperature and current density. All the values are within the 2 % experimental error present in activity measurements.

Electrolytic Behavior of Tungsten with Zinc in an Ammoniacal

Citrate Bath The technique and chemical procedure were the same as for the cobalt-tungsten deposits. Experimental details were given in the first section. The absorption curves in Figure 3 33

Table VII

Zinc Standardization

Run Current * Temp. Platini Time No. (amp.xlCr) ( C.) (nin«i 1 20 2 30

2 50 2 30

3 20 do 30

4 50 do 30

Run Deposit Activity Specific No. A s k J ___ (counts per min.) Activity 1 0.493 22d.2 45^.2

2 0.796 359.1 451.1

3 2.927 1317.5 450.1

4 5.309 2390.3 450.2 34 illustrate that there is essentially no tungsten deposited with the zinc. Table VTII summarizes the results with zinc- tungstate solutions. The samples were counted immediately after deposition and recounted 10 days later. The activities were measured with 223 mg. of aluminum per cm? in order to minimize self-absorption effects. At the end of the 10 day period the activities had approached the background activity. This indicated that the amount of tungsten present in the deposit was negligible.

Palladium Palladium was chosen because it is a catalytically active metal with the ability to occlude large amounts of hydrogen during electrodeposition. Approximately 10 mg. of palladium, as the palladous chloride, were dissolved in dilute sulfuric acid, neutralized with ammonium hydroxide, and 1 g. of citric acid was added. To this solution 10 ml. of radioactive tungstate were added, and the mixture was diluted to 45 ml. The mixture was heated to S0°C. and electroplated on a copper planchet electrode for 20 minutes at 2.0 volts. The deposit weighed 7.9 mg., and the activity was 5.2 c.p.m. above background. The same procedure was repeated at 2°C. The results are tabulated in Table IX. The data in Table IX are plotted in

Figure 5. The same type of curve was obtained as with the zinc deposits. This indicated an absence of tungsten in the deposit. 35

Table VIII

Electrolytic Data for Zinc-Tungsten Deposits

Run Current.5 Temp. Plating Time No. (amp.xlO^) t°C.) (min.) 1 100 2 60 2 20 2 45

3 50 2 45 4 50 73 45

5 20 73 120 6 50 73 70

Run Deposit Activity Activity No^. (mg.) (counts per min.) 10 days later 1 0.233 1131.0 4.2 2 0.144 791.2 3.0

3 0.313 761.6 2.5 4 0.001 2207.5 2.3 5 0.009 1127.9 0.5 6 0.023 2002.£J 1.6 36

Table IX

Absorption Data for Palladium-Tungsten Sample

Aluminum Initial Activity Absorbers Activity 7 days (mg./cmf) (counts/min.) later 0 1310 45.0 20.3 1240 10.1 45.9 1130 70.0 1001 101 845.2 223 455.8

297 309.1 370 200.3 430 140.6

540 72.5 37

1,000

* 9 0 0

9 0

7 x ) Aluminum (m g/cm *)

FIGURE 9. ABSORPTION CURVE OF AN ELECTROLYTIC Pd - W DEPOSIT Rhenium The last metal studied In the Investigation was rhenium. This metal was studied because the electrolytic behavior of carrier-free amounts interfered with the use of radioactive tungsten as a tracer. The bath used was similar to the one developed by Voigt (51). A 45 ml, portion of the electrolyte contained 5 mg. of potassium perrhenate, 10 mg. of radioactive tungsten

10 ml. of ammonium hydrozide, and 4 g. of ammonium sulfate. The solution was electroplated on a copper planchet at £0°C. for one hour with an applied potential of 4.5 volts. A black non-metallic deposit was obtained. The activity of the sample was measured first without an absorber, and then with 223 mg. of aluminum per cm. The data are given in Table X. Absorption measurements were not made on the sample A comparison of the activity with and without the aluminum absorber clearly indicates that tungsten was present in the deposit. The activities measured without the aluminum remained constant (within experimental error) while the 2 activity measured with the 223 mg. of aluminum per cm, gradually decayed. This indicated that the rhenium codeposit tungsten, and that the activity effect from trace amounts of radioactive rhenium was substantially decreased by the addi­ tion of inactive rhenium carrier. 39 These results further showed that a small amount of activity can be expected in any deposit which contains radioactive carrier-free rhenium. This tungsten activity is so small that its presence may not be apparent until equilibri um has been re-established. This effect was observed with zinc-tungsten, and palladiura-tungsten samples. However the activity corresponds to such a minute amount of tungsten that it cannot be considered a tungsten alloy.

Table X

Activity Data for Rhenium-Tungsten Deposit

Aluminum Activity Activity Activity Absorber (counts 12 hrs. 36 hrs. (mg./cm?) per min.) later later

0 9149.6 9162.3 9124.5

223 35.2 23.1 25.1 40 Part II Metallic Cathodes The purpose of this phase of the investigation was to determine whether certain metallic cathodes were more effec­ tive than others in the electrodeposition of tungsten. Holt

(49) reported that the behavior of tungsten was independent of the cathode metal. He electrodeposited a tungsten alloy on various metals, and found that the weight of the deposit was independent of the cathode material, Clark and Leitzke

(11) carried out a radiochemical study using radioactive tungsten as a tracer. They added the tracer to the tungstate bath and electrolyzed the solution. Various metals were used as cathodes. Their conclusions were the same as Holt*s. Clark and Leitzke were unaware of the presence of radioactive rhenium in the tungsten tracer, and their results may be in error. Platinum, copper, palladium, zinc, and cobalt were the metallic cathodes studied.

Platinum Platinum planchets, 1 inch in diameter were used as

cathodes. The equipment and chemical procedure were the

same as described in a previous section. The electrolytic bath, 45 ml. in volume, contained 10 mg. of radioactive tungsten, 1 g. of citric acid, and enough ammonium hydroxide to adjust the pH to 7.5. This bath 41 was ussd with all metallic cathodes studied in this investi­ gation . A 1 ml. portion of the standard radioactive tungstate solution was evaporated on a copper planchet and the activity measured with and without an aluminum absorber. The activity of 1 mg. of tungsten was 107i-100 c.p.m. without aluminum, and 250 c.p.m. with 163 mg. of aluminum per cm. The plating conditions are summarized in Table II. The absorption data are given in Table XII, and plotted in

Figure 6.

Table XI

Plating Conditions with Platinum Cathodes

Run Current - Temp. Plating Time No. (amp.xlO^) (°C.) (min.) 1 100 30 30 2 100 2 30

Copper

Copper planchets, 1 inch in diameter were used as cathodes. The plating conditions are summarized in Table XIII. The absorption data are given in Table XIV and plotted in

Figure 7. 42

Table III

Absorption Data for Platinum Cathode Deposits

Run #1 Aluminum Absorbers Initial Activity Activity 5 days (mg./cm.)______(count a/min.) later 0 Id.7 do 20.3 16.1 70.0 11.1

101 9.5

Run #2

0 45.9 13.6

20.3 39.5 70.0 30.7 101 24.1

165 Id.5

Table IIII Plating Conditions with Copper Cathodes Run Current ^ Temp. Plating Time No*. (amp.xlCr ( C. ? _ (min 3 100 do 15 4 100 d0 40 5 100 2 35 6 50 2 30 FIGURE 6 . ABSORPTION CURVES OF ELECTROLYTIC TUNGSTEN TUNGSTEN ELECTROLYTIC OF CURVES ABSORPTION . 6 FIGURE Activity (C ounts/m in) 100 0 5 5.C 10 O EOIS N LTNM CATHODES PLATINUM ON DEPOSITS IOO Aluminum (mgAm* ) (mgAm* Aluminum 200 u n. 2 no. Run □ O R un no. I no. un R O 0 0 3 0 0 4 NJ 0 0 5 44 Table XIV

Absorption Data for Copper Cathode Deposits Run #3 Aluminum Absorbers Initial Activity Activity 5 days (mg./cm?)______(counts/min.)__ later

0 435.5 74.7 20.3 419.9 13.3 45.9 373.6 70.0 311.6 101 265.3 165 200.6 276 100.0 430 33.4 540 14.5 Run #4

0 964.4 140.1 20.3 396.4 29.9 70.0 735.1 101 627.0 165 433.1 276 234.6 430 75.4 540 31.9 Run #5 0 34.6 17.3 20.3 79.3 70.0 64.1 101 54.0 165 35.3 276 16.9 430 5.2

Run # 6 0 106.0 7.3 20.3 92.1 70.0 74.6 101 66.1 165 46.4 276 25.2 430 3.5 IUE . BOPIN UVS F LCRLTC TUNGSTEN ELECTROLYTIC OF CURVES ABSORPTION 7. FIGURE Activity (oounts/min) IpOO 900, 100 0 5 5.0 1.0 EOIS N OPR ELECTRODES COPPER ON DEPOSITS o o lmnm m/m ) (mg/cm2 Aluminum 0 0 9 0 0 2 A Run Run no. A 4 □ Run no. Run 5 □ • Run no. Run • 6 O Run Run no. O 5

HT 0 0 5 46 Palladium Palladium cathodes were prepared by dissolving palladous chloride in 30J& sulfuric acid, and electroplating on the copper planchets with an applied potential of 1.5 volts. The plating conditions are summarized in Table XV.

The absorption data are given in TableXVI and plotted in Figure 3.

Table XV

Plating Conditions with Palladium Cathodes

Current , Temp. Plating Time Run No. (amp.xlCr) (°C.) (min.)

7 100 30 30 3 50 30 30 9 50 2 30 10 100 2 30

Zinc The zinc cathodes were prepared by dissolving 20 mg.

of zinc oxide in dilute sulfuric acid, adding an excess of lOjt sodium hydroxide solution, and electroplating on copper

planchets with an applied potential of 3.5 volts. The radioactive tungstate solution at 30°C. was introduced into the electrolytic cell and a potential of 6.0 volts was applied. In 5 minutes the zinc deposit had 47 Table XVI

Absorption Data for Palladium Cathode Deposits

Run #7 Aluminum Absorbers Initial Activity Activity 5 days ( m g . / c m . 2 )______(counts/min.) later____

0 491.7 54.6 20.3 434.7 15.1 70.0 349.1 101 321.1 165 219.7 276 119.4 430 37.9 540 21.0 Run #8

0 144.1 29.7 20.3 124.7 9.2 70.0 105.3 101 55.0 165 62.9 276 37.4 430 14.9 Run #9 0 42.0 6.8 20.3 35.1 70.0 27.8 101 23.1 165 17.6 Run #10 0 242.2 18.5 20.3 211.2 6.8 70.0 180.2 101 166.1 165 122.1 276 58.2 430 24.2 540 10.0 FIGURE Activity (counts/m ini IOO 0 9 0 5 10 . BOPIN UVS F LCRLTC TUNGSTEN ELECTROLYTIC OF CURVES ABSORPTION 8. EOIS N ALDU CATHODES PALLADIUM ON DEPOSITS IOO lmnm mgc *) g/cm (m Aluminum 200 u n 10 no Run • Rn o 9 9 no. Run 6 no. O Run A O Run no. 7 7 no. Run O 0 0 9 0 0 3 0 0 4 4 9 dissolved from the copper planchet. This indicated a reaction between metallic sine and the tungstate ions. To verify this further, 45 ml. of the standard inactive tungstate solution (1 mg. of tungsten per ml.) were heated to dO°C. and intro­ duced to a cell equipped with another zinc plated copper cathode. The solution was stirred with the platinum anode and no potential was applied across the electrodes. In approximately 15 minutes the zinc had dissolved from the copper planchet. It was concluded that metallic zinc was able to reduce tungstate ions to a lower valence state.

Cobalt The cobalt electrodes were prepared by electroplating an ammoniacal cobalt sulfate solution on copper planchets with an applied potential of 3.5 volts. The plating conditions are summarized in Table XVII. The absorption data is given in Table XVIII and plotted in Figure 9. Table XVII

Plating Conditions with Cobalt Cathodes Run No . Current - Temp. Plating Time (amp.xlO3) (°C.) (min.) 11 100 2 30 12 50 2 30 13 100 do 30 14 100 do 15 15 100 do 70 50

Table XVIII Absorption Data for Cobalt Cathode Deposits

Run #11 Aluminum Absorbers Initial Activity Activity 5 days (mg /cm? (counts/min.)___ later

0 162.4 17,3 20.3 165.1 70.0 143.6 101 114.4 165 32.2 276 43.6 430 16.0 540 6.0 Run #12

0 164.0 12*3 20.3 151.6 70.0 114.6 101 104.0 165 72.2 276 36.0 430 14.4 540 6.1 Run #13

0 433.4 199*0 20.3 296.3 73.6 70.0 176.6 101 151.6 165 114.0 276 60.4 430 22.4 540 6.5 Run #14 0 360.0 200.1 20.3 240.0 66.5 70.0 109.7 101 96.1 165 77.0 276 44.7 430 15.2 540 6.3 IOOO O Run no II A Run no. 12 □ Run no. 13 50 0 x Run no 14 • Run no 15

IOO

50

5 0

1.0 DO 200 3 0 0 5 0 0 Aluminum (mg/cm*)

FIGURE 9. ABSORPTION CURVES OF ELECTROLYTIC TUNGSTEN DEPOSITS ON COBALT CATHODES 52

Table XVIII (continued)

Run #15

Aluminum Absorbers Initial Activity Activity 5 days (mg./cm./ M M i AIM " )\ (counta/min.) later

0 aid. 2 476.7 20.3 496.4 193.5 70.0 259.0 6.5 101 214.6 165 160.4 276 90.7 430 36.7 540 13.1

A comparison of the data and absorption curves indi­ cated that cobalt, at 30°C. was more effective in depositing tungsten than the other metals tested. The equilibrium activities measured in runs #13 and #14 corresponded approximately to 0.002 mg. of tungsten. The activity in run

#15 was equivalent to 0.004 mg. of tungsten. The activities at equilibrium for the copper cathodes (#3 and #4) were 140.1 and 74.7 c.p.m. respectively. These activities were higher than those obtained with platinum and palladium electrodes.

The higher activities could be considered indicative of tungsten deposition. Nevertheless, under identical plating conditions, the cobalt cathodes were at least twice as effective as the copper cathodes in the deposition of tungsten.

This behavior was proposed by Holt and Vaaler (32). Before this mechanism can be evaluated, another question to be answered is whether metallic cobalt reacts with tungstate ions. A standard radioactive cobalt solution was prepared. 53 The cobalt was electrodeposlted on 6 copper cathodes. All 2 activities were measured with 540 mg. of aluminum per cm. in front of the Geiger Muller tube to absorb any beta energies.

A 1 ml. portion of the radioactive cobalt solution was evaporated on a copper planchet, and the activity was counted.

The activity was 3635 c.p.m. per milligram of cobalt. The radioactive cobalt cathodes were used as follows:

Cathode #1: the activity was 3037.2 c.p.m. The electrolytic tungstate solution (80°C.) was added. No voltage was applied. In 15 minutes the cobalt deposit had dissolved.

Cathode #2: the activity was 2482.9 c.p.m. The in­ active sodium tungstate solution (80°C.) was added. The solution was stirred for 30 minutes with no voltage applied.

The activity on the cathode was 2181.3 c.p.m. The loss in activity was 301.6 c.p.m. which indicated that 0.1 mg. of cobalt had dissolved.

Cathode #3: the activity was 3611.3 c.p.m. The in­ active sodium tungstate solution (24°C) was added. The solution was stirred for 60 minutes with no voltage applied.

The activity on the cathode was 3477.3 c.p.m. The loss in activity was 134.0 c.p.m. which indicated that 0.04 mg. of cobalt had dissolved. This loss in activity could have been due to the handling of the cathodes, or to the stirring motion of the 54 electrolyte. A blank was run to eliminate these possibilities.

Cathode #4: the activity was 2363.3 c.p.m. A 3%

sodium sulfate solution (30°C.) was introduced into the cell.

The solution was stirred for 30 minutes and no voltage applied.

The activity on the cathode was 2336.0 c.p.m. The loss in

activity was 32.3 c.p.m. which indicated that less than 0.01 mg. of cobalt had dissolved.

Cathode #5: the activity was 5366.9 c.p.m. The

electrolytic tungstate solution (25°Cj was added. A current

of 100 milliamperes flowed for 30 minutes. The activity on the cathode was 2671.4 c.p.m. which indicated no loss in weight.

Cathode #6: the activity was 2660.3 c.p.m. The

electrolytic tungstate solution (25°C.) was added. A current

of 100 milliamperes flowed for 90 minutes. The activity on the cathode was 2671.4 c.p.m. which indicated no loss in wsight. These results indicated that metallic cobalt has a

tendency to react with tungstate ions. The activity loss by

cathode #4 was within the 2# allowable experimental error.

Cathodes #5 and #6 indicated that no cobalt metal is dis­

solved with an applied potential. Cathode #1 indicated that

the electrolyte containing citric acid and ammonium hydroxide

dissolves the cobalt metal with no applied potential. 55 Results and Conclusions The following information was obtained from this inve stigation: (1) The percentage of tungsten in cobalt-tungsten alloys is essentially a function of the bath temperature.

More tungsten is deposited at the higher temperatures. (2) Tungsten is codeposited with rhenium to a small extent. (3) Tungsten is not codeposited with zinc or palladium.

(4) Basic cobalt salts are precipitated during cobalt deposition. At the higher temperatures this effect is more pronounced. (5) Zinc does not show the same behavior observed with cobalt electrodeposition. (6) Metallic zinc spontaneously reacts with tungstate ions. (7) Metallic cobalt shows a slight tendenoy to spon­ taneously react with tungstate ions. (8) A cobalt electrode appears to be more effective in depositing tungsten than other cathodes metals such as palladium, platinum, or copper. These results explained the ability of cobalt to codeposit large quantities of tungsten. The tungstate ion or a lower valence state is precipitated with the basic cobalt salt8 during the electrodeposition. Clark and Lietzke (11) 56 have ehovrn the existence of cobalt-tungsten complexes.

According to this explanation, large amounts of tungsten ions are incorporated into the cobalt lattice. These are reduced by nascent or atomic hydrogen liberated during the plating process. Low overvoltage metals such as palladium and cobalt have strong hydrogen occluding properties. The reaction

H++ e — has been shown to occur within the metal for strong hydrogen occluders (52). The extent of cobalt precipitation as hydrous or basic salts is dependent on the temperature, as is the percentage of tungsten in the cobalt alloys. Holt (24) found that the percentage of tungsten in the binary alloys dropped from 50 to 35% as the temperature was reduced from 75 to 25°C. The ability of cobalt cathodes to deposit tungsten depends on a reaction between cobalt and tungstate ions which formed cobalt ions and a cobalt-tungsten complex. This complex is precipitated when the cobalt is redeposited.

Tungsten was deposited to a very slight extent on the cathodes tested in this investigation. Although cobalt was more efficient than the others in depositing tungsten, the effect was still small. If the amount of tungsten in these alloys was solely dependent on a catalytic hydrogen reduction mechanism, a catalytically active metal such as palladium would have shown a tendency to reduce tungstate ions. The research carried on with radioactive tungsten as a tracer did not indicate any such effect. 57 No infonnation was obtained from this work as to whether a layer of tungsten metal was deposited, followed by a gradual build-up of oxides, or whether only oxides were deposited. Since tungsten has a very strong affinity for oxygen, it would be reasonable to expect that the metallic layer never existed in an aqueous solution. Instead, oxides are deposited immediately at a rate dependent on the pH, temperature, concentration of tungstate ions, and applied potential. THE ELECTHOLYTIC BEHAVIOR OF TUNGSTEN ON OXIDE

AND OXIDE FREE TUNGSTEN ELECTRODES

The use of radioactive tracers in the present investi­ gation did not provide sufficient information to solve the problem of electrodepositing pure tungsten from an aqueous solution. An important question to be settled was whether the basic difficulty in the electrodeposition of tungsten was caused by the nature of the electrode surface, the be­ havior of the tungstate ion in an aqueous system, or a combination of both. The affect of an oxide covered surface on the electro­ deposition of tungsten was determined by measuring the rate of deposition from an electrolyte which contained a small amount of cobalt. The cobalt was necessary so that a weigh- able deposit may be obtained. At a later time the electrode o was reduced in hydrogen at 800 C., replaced in the same electrolytic bath, and the rate of deposition was measured again. Holt (24) had shown that cobalt-tungsten alloys contain oxides. This was confirmed by the present experiment. The experiment was performed at constant current density, and repeated at a constant cathode potential.

5$ 59 The Effect of Cathode Oxides on the Rate of Deposition of

Tungsten-Cobalt Deposits

1. Constant Current Density

Apparatus and Materials

The electrolytic cell was a divided compartment cell shown in Figure 10. The symbols marking the various parts are listed below:

A Large platinum gauze anode

B A 1B0 ml. tall form electrolytic beakers

C Rotating copper wire cathode, 10 cm. in length,

7 cm? in area

D Sintered glass disc separating the two compart­

ments.

The reduction apparatus consisted of a Vicor combus­ tion tube wrapped with nichrome and asbestos ribbons. The moisture in the tank hydrogen gas was removed by bubbling the gas through concentrated sulfuric acid. The temperature of the combustion tube was regulated with a variac and deter­ mined with a thermocouple which read directly in the Centi­ grade scale.

An Eberbach electrolytic analyzer was used. A mi Hi amine ter was placed in the electrical circuit so that the current could be nore accurately control]ed.

A semi-micro balance was used for all cathode weighings. 6 0

FIGURE 10. ELECTROLYTIC CELL 61 The electrolytic solution was similar to the bath used by Clark and Holt (24) in their deposition of cobalt-tungsten alloys. One liter of solution contained 35.7 g. of sodium tungstate dihydrate, 10 g. of citric acid, 100 mg. of cobalt as cobalt sulfate, and enough ammonium hydroxide so that the pH was 7*5. A 100-ml. portion of this solution contained 2.0 g. of tungsten and 10 mg. of cobalt. A 5# solution of sodium sulfate was prepared. All chemicals used were of reagent grade quality.

Procedure A 100-ml. portion of the electrolytic solution was transferred to the cathode compartment of the cell. A 100-ml. portion of the 5% sodium sulfate was placed in the anode compartment. The copper wire was initially treated with 1:1 nitric acid, washed with water and alcohol respectively, and allowed to dry in a 90°C. oven. The copper electrode was weighed on the semi-micro balance, and introduced into the cathode compartment. A constant current of 20 milliamperes was employed during the electrolysis. At frequent intervals, the cathode was removed from the solution and weighed. After the deposition had proceeded for several hours, the electrode was removed from the solution, weighed, reduced in hydrogen at 800°C., and reweighed. The electrode was replaced in the same electrolytic solution and the rate of deposition was measured again. 62 Results and Conclusions The data are summarized in Table XIX. These results show that the rate of deposition decreases with time. This decrease is related to the amount of oxide present in the deposit. On reduction of these oxides, the rate of deposi­ tion increased to its original value. These results indicated that the removal of oxides from the electrode further promotes the electrolytic deposition of tungsten.

2. Constant Cathode Potential The results obtained with a constant current density were checked by repeating the above experiment with a constant cathode potential. The apparatus was the same as described above except that a saturated calomel electrode was placed in electrical contact with the cathode compartment by means of a potassium chloride salt bridge. A portable student type potentiometer was connected across the cathode and calomel electrodes. During the electrodeposition the cathode potential was kept constant at 1.3 volts vs S.C.E. Results and Conclusions A summary of the data is given in Table XX. The

» results are the same as obtained with a constant current. The rate of deposition decreases with time. On reduction in hydrogen, the rate of deposition increased to it original value. This indicates that the presence of oxides on the 63 Table XIX

Cathode Gain at a Constant Current Density

Time Intervals Electrode Gain Rate of Deposition (hours)_____ (mg.)______(mg./hour)_____

1.33 1.33 1.36 1.36 1.34 1.34 1.14 1.14 7.40 0.67 0.18 0.18

Electrode Reduced in Hg at 800°C. 1.69 1.60

Table XX

Cathode Gain at a Constant Cathode Potential

Time Intervals Electrode Gain Rate of Deposition (hours) - (mg.)______------

0,83 1.09 1.31 0.50 0.40 0.80 0.50 0.41 0.82 2.50 1.60 0.64 1.17 0.79 0.68 11.50 6.00 0.52 1.00 0.25 0.25 1.00 0.25 0.25 1.25 0.20 0.16 Electrode Reduced at Hg at 800°C.

0.67 0.96 1.13 6 k cathode retards deposition.

The Electrodeposition of Tungsten on an Oxide

Free Tungsten Electrode

The interference of oxides suggested the preparation of an oxide-free electrode surface. On such a surface the rate of tungsten deposition should be at a maximum and a heavier deposit should be obtained. Tungsten was selected as the electrode material to avoid any interaction between the tungstate ions and the cathode. This made the behavior of the system solely dependent on the electrolytic behavior of the tungsten. Langmuir (53) made an extensive study of the removal of oxides from tungsten filaments. His work indicated that the oxides were volatilized when a tungsten filament was flashed at 2700°K for a few seconds in a good vacuum. His results were substantiated by thermionic measurements.

Apparatus and Materials An electrolytic cell was so constructed that:

(1) The tungsten filament was flashed in the absence of the electrolyte, (2) The electrolyte was brought into contact with the cleaned electrode, (3) All manipulations were carried out in a closed system. 65 The cell was of the divided compartment type shown in Figure 11. The symbols marking the various parts are listed below:

A Two t 34/45 female joints, B Sintered glass disc separating the two compart­

ments,

C Two $ 34/45 male joints in which the electrolyte

was frozen out during the flashing of the tungsten,

D Sidearm with a glass to metal seal providing

electrical contact for the anode,

£ Platinum (Slomin) gauze anode connected to the

sidearm lead with a metal collar,

F * 29/42 tungsten filament holder with two glass to

metal seals providing electrical contact. The

tungsten filament was connected to the 2 leads

with metal collars, G S 35/20 socket joint around which the cell rotated

ISO0 in order to flash the tungsten wire,

H Coiled tungsten wire cathode 25 cm. long, 0.02"

in diameter,

I Vacuum stopcock to prevent leakage during rotation

of the electrolytic cell,

J Vacuum stopcock for rapid evacuation of the anode

compartment. A D.C. source of 60 volts applied across the leads in F heated the tungsten wire to a temperature of 2750 - 50°K. The FRONT

FIGURE II. ELECTROLYTIC VACUUM CELL 67 temperature of the wire was measured with an optical pyro­ meter. During electrolysis the electrolyte in the cathode compartment was stirred with a magnetic glass coated stirring bar. The vacuum system built for this experiment is shown in Figure 12. The symbols marking the various parts are listed below: A Single stage mercury diffusion pump

B McLeod gauge to measure the vacuum

C Cold trap with liquid nitrogen to remove mercury

and water vapors from the system.

D Vacuum stopcock for admitting air into the system

E Ball and socket joint so that the electrolytic

cell could be rotated through a 130° angle after

flashing

F Electrolytic cell containing the tungsten

electrode and electrolytic solution.

The McLeod gauge was calibrated from the measurement of the cross-sectional area of the same capillary tubing used in the construction of the gauge. This value was calculated from the measurement of the volume occupied by mercury per unit length of the capillary bore. A pressure of 6x10"^ mm. of mercury was obtained during the flashing of the tungsten wire. <8

FIGURE 12. VACUUM SYSTEM 69 A 1 liter portion of the electrolyte contained 9 g. of sodium tungstate, 10 g. of citric acid, and enough ammonium hydroxide to adjust the pH to 7.5. A 40 ml. aliquot contained 200 mg. of tungsten.

Procedure

1. Weight Loss from Flashing

Several experiments were made to determine the loss in weight of the tungsten wire on flashing. The untreated weighed wire was bent to fit into the electrolytic cell. o The cell was rotated at an angle of 180 from the position shown in Figure 12. At 1:1 mixture of bee’s wax and rosin was applied to the ball and socket joint to prevent leakage.

The system was evacuated and the bottom half of the electro­ lytic cell was placed in liquid nitrogen. The cell was flame-heated several times to remove any moisture adsorbed on the glass surfaces. When the system had been sufficiently pumped out and the pressure had dropped to slightly better than 10"^ nm. of mercury, the wire was flashed for 3 seconds at 2700°K. The average loss in weight of the electrode was

0.3 mg. This loss was higher than the value calculated from the volatility of pure tungsten. This result indicated the presence of oxides and other volatile impurities.

2. Electrolysis of the Tungstate Solution

A 40-ml. aliquot of the electrolytic solution was transferred into each compartment of the electrolytic cell. 70

The weighed tungsten electrode and magnetic stirring bar were introduced into the cell. The cell was rotated at an angle of ld0° and the system was made air tight. Dissolved gases were removed from the electrolyte by freezing the solution with an acetone-dry ice mixture. During the freezing out process, the glass stirring bar was removed from the solution with a magnet to prevent cracking. The stopcock I in Figure 11 was opened and the system was evacuated for a short time. The stopcock was closed, the solution warmed to room temperature, and the freezing out process repeated to make certain that the dissolved gases were completely removed. The acetone-dry ice mixture was replaced with liquid nitrogen, so that the vapor pressure of the water was lower and a better vacuum was obtained. The system was evacuated for approximately

2 hours during which time the glass walls were flamed at frequent intervals. After flashing, the stopcock I was closed, the solution allowed to warm up, the cell rotated, and the electrolysis was started. The D.C. source for the electrolysis was a Sargent-Slomin electrolytic analyzer. A potential of 10 volts was applied to the system. The current, measured with a railliameter, was 20 ma. The electrolysis was continued for 1 hour. At this point the wire was removed from the system, washed, dried in a £0°C. oven, and weighed. In every determination there was a net loss in weight as a result of the flashing. In several determinations 71 the electrode was weighed after flashing, electrolysed for

1 hour, and weighed again. In no run was there any increase

in weight.

Results and Conclusions The loss in weight of the tungsten electrode due to

flashing hindered the electrolytic study of tungstate ions on a flashed surface. Nevertheless these results indicated

that the electrolytic formation of tungsten oxides in an aqueous solution is such a rapid process that the deposition

of tungsten metal is negligible.

The Study of the Electrolytic Behavior of

Tungsten from Current-Time Measurements

The effectiveness of an oxide free surface in the electrolytic reduction of tungsten was not shown in the above

experiments because of the loss in the weight from flashing

and the small contribution from tungsten deposition. Another

approach to this problem is to measure the current as a

function of time. This method is more sensitive and inde­ pendent of the electrode weight losses due to the flashing

process. The current measurements were made by placing a standard resistance in series with the electrolytic system and measuring the voltage drop with a portable student type potentiometer. Below are listed a series of experiments for 72 the study of the electrolytic behavior of tungsten from

current-time measurements. The flashing and electrolytic

procedures were the same as described in the previous section.

1. Untreated Tungsten Surface

The untreated tungsten electrode was placed in the

cathode compartment of the vacuum cell. After the solution was degassed, the electrolysis was started. The potential drop was measured as a function of time. The data are tabulated in Table XXI and graphed in Figure 13.

2. Flashed Tungsten Surface On completion of the electrolysis described above, the electrolyte was degassed and frozen out. The same electrode was flashed at 2700°K. and the electrolytic pro­

cedure repeated. The data are tabulated in Table XXII and graphed in Figure 13.

A comparison of the curves in Figure 13 shows the

effect of electrolysis on the two surfaces. The increase in

current with time was unusual. A possible explanation for

this sharp current rise was the build up of gas pressure in

the closed electrolytic cell. After the tungsten wire was

flashed, the cell was closed, and the electrolyte was un­

frozen. Therefore the cell was at a reduced pressure which was equal in magnitude to the vapor pressure of the elec­

trolyte. After 1 hour of electrolysis the pressure in the 73 Table XXI

Current-Time Data for the Deposition of Tungsten on an Untreated Tungsten Surface

Time Potentiometer Current (min.) (millivolts) (ma.)

1 554 27.7 2 566 2d.3 3 572 2d.6

4 576 2d.d

5 580 29.0

7 592 29.6

9 602 30.1

10 609 30.5 12 626 31.3 14 640 32.0

15 636 31.8

16 642 32.1

17 647 32.4

id 653 32.7 20 660 33.0

22 654 32.7

24 655 3 2 .d 26 660 33.0

2d 665 33.3 30 670 33.5

32 675 33.8 74 Table XXII

Current-Time Data for the Deposition of Tungsten on a Flashed Tungsten Surface

Time Potentiometer Current (min.) (millivolts) Ima.J 1 607 30.4 2 580 29.0

3 572 28.6 4 573 28.7 6 580 29.0

8 586 29.3

10 594 29.7

12 594 29.7

13 599 30.0 15 601 30.1 17 608 30.4 20 612 30.6

25 622 31.1

31 644 32.2 36 660 33.0 40 676 33.6

45 700 35.0 55 696 39.6 60 692 39.6 IU E 3 CRETTM CRE FR THE FOR CORVES CURRENT-TIME 13.FIGURE Current (Milliomps) 35.0 31.0 - 0 4 3 0 9 2 0 9 2 0 7 2 N O A LSE TNSE SURFACE TUNGSTEN FLASHED A ONAND UG T N N N UNTREATED ANTUNGSTEN ON 20 O Untrsotsd surfocs surfocs Untrsotsd O Fahd surfacs AFlashtd i* (minutes) Tim* 0 3 TUNGSTEN 0 5 DEPOSITION SURFACE 0 6

OF 76 Table XXIII

Current-Time Data for the Deposition of Tungsten on an Untreated Tungsten Surface at Atmospheric Pressure

Time Potentiometer Current (min .) (millivolts) (ma.) 1 760 36.0 2 768 39.4

3 794 39.7 4 809 40.5 5 626 41.3 6 820 41.0 7 831 41.6 9 843 42.2 11 846 42 ..3

13 845 42.3 15 651 42.6

17 854 42.7 20 655 42.6

22 845 42.3 25 836 41.6

30 833 41.7 35 830 41.5 40 631 41.6

45 634 41.7 50 829 41.5 60 826 41.3 Current (milliomps) 0 5 4 0- .0 4 4 .0 1 4 IUE 4 CRETTM CRE O TE EOIIN OF DEPOSITION THE FOR CURVE CURRENT-TIME 14. FIGURE 0 0 4 0- .0 2 4 .0 9 5 370 AT UGTN N N NRAE TUNGSTEN UNTREATED AN ON TUNGSTEN TOPEI PRESSURE ATMOSPHERIC 20 ie (minutes) Time 30 40 50 60 SURFACE SURFACE 77 73 electrolytic cell was still lower than the atmospheric pressure. Therefore the hour long electrolysis was carried out in a system which gradually built up pressure from the liberation of hydrogen and oxygen. 3. Untreated Tungsten Surface at Atmospheric Pressure The effect of the pressure build up in the electrolytic cell was studied by electrolysing an untreated tungsten sur­ face at atmospheric pressure. The data are given in Table

XXIII and shown graphically in Figure 14. These results indicated that the pressure was independent of the observed current rise. Another factor which may have contributed to this behavior was the position of the tungsten electrode in the cell. In the above experiments the electrode was perpendicu­ lar to the sintered glass disc. This position created a current density gradient along the cathode surface. The two compartment cell shown in Figure 10 was used in the remaining experiments. 4. Untreated Tungsten Surface The untreated tungsten electrode was placed parallel to the glass disc, so that the current density was uniform over the length of the electrode. A magnetic stirrer was used in the cathode compartment. The data are tabulated in Table XXIV and shown graphically in Figure 15. 79 Table XIIV

Current-Time Data for the Deposition of Tungsten on an Untreated Tungsten Surface

Time Potentiometer Current (min.) (millivolts) (ma.)

1 606 30.3

2 602 30.1

3 596 29.9

4 596 29.6 6 592 29.6

6 566 29.3

10 562 29.1

12 576 26.6

14 570 26.5 20 560 26.0

22 546 27.4

24 546 27.6 23 542 27.1

30 540 27.0

31 574 26.7

34 610 30.5 40 630 31.5

50 640 32.0

60 646 32.4 do Table XXV

Current-Time Data for the Deposition of Tungsten on a Flashed Tungsten Surface

Time Potentiometer Current (min.) (millivolts)

1 637 31.9 2 620 31.0

3 596 29.9 4 56$ 29.3

5 5d6 29.3 6 590 29.5

10 602 30.1 12 60d 30.4

14 614 30.7 16 620 31.0 id 62d 31.4 20 636 31.d 22 635 31.6

24 634 31.7 26 633 31.7 2d 632 31.6

30 631 31.6 61

Table XXVI

Current-Time Data for the Deposition of Tungsten on a Flame Oxidized Tungsten Surface

Time Potentiometer Current (min.) (millivolts) (ma.)

1 652 32.6 2 646 32.4

3 647 32.4 4 645 32.3

5 644 32.2

7 643 32.2 10 641 32.1

12 640 32.0

14 640 32.0 16 636 31.9

16 636 31-9

20 637 31.9 22 636 31.6

24 635 31.6 26 634 31.7 26 634 31.7

30 632 31.6

35 630 31.5 Table XXVII

Current-Time Data for the Deposition of Tungsten on an Electrolytically Oxidized Tungsten Surface

Time Potentiometer Current (min.) (millivolts) U a . ) 1 710 35.5 2 712 35.6 3 711 35.6 4 709 35.5 5 70S 35.4 6 70S 35.4 7 709 35.5 S 70S 35.4 10 710 35.5 12 709 35.5 14 70S 35.4 16 706 35.3

IS 704 35.2 20 702 35.1 Currtnt (milliompt) IUE 9 CRETTM CRE FR EOIIN OF DEPOSITION FOR CURVES CURRENT-TIME 19. FIGURE 0 . 0 2 0 9 2 - 0 7 2 31.0 O O UGTN N AIU TNSE SURFACES TUNGSTEN VARIOUS ON TUNGSTEN 0 2 is minutss) (m Tims 30 Flamsoxidizsd A Esurfocs l□ s e * r o l y t i co x i d i x s ds u r t o c s UntrsotsdO surfoct Floshsd• surfoe# 09 60 90 40

93

5. Flashed Tungsten Surface A flashed tungsten wire was placed parallel to the

glass disc and electroplated. The data are tabulated in

Table XXV and shown graphically in Figure 15*

6. Flame Oxidized Tungsten Surface

A tungsten electrode was placed in the oxidizing flame

of a Bunsen burner until the surface was covered with the

blue W20^ oxide. The oxide-covered surface was placed

parallel to the glass disc and electroplated. The data are

tabulated in Table XXVI and shown graphically in Figure 15.

7. Electrolytically Oxidized Tungsten Surface

A tungsten electrode was placed parallel to the glass disc and electroplated until it was covered with a layer of oxide. The electrode was washed with distilled water, placed into a new aliquot of the electrolyte, and

electroplated. The data are tabulated in Table XXVII and

shown graphically in Figure 15. S. Untreated Copper Electrode

A current-time study was made on a copper surface to determine whether the curves obtained in the previous experiments were characteristic only for the tungstate ions.

The data are tabulated in Table XXVIII and shown graphically in Figure 16. S5 9. Copper on a Flame Oxidized Tungsten Surface The conducting ability of a heavily flame oxidized tungsten surface was studied next in this investigation. A copper solution was chosen as the electrolyte because of its plating properties. A 100 ml. aliquot of this electrolyte contained 200 mg. of copper, as the copper sulfate, 3 ml. of

sulfuric acid, and 1 ml. of nitric acid. This solution was also placed in the anode compartment. At the end of 30 minutes 10 rag. of copper were deposited. The current-time data are tabulated in Table XXIX and shown graphically in

Figure 17. 10. Copper on an Untreated Copper Surface

In order to complete this study it was necessary to obtain information on the behavior of a metal depositing on its own metallic surface. Copper was again chosen. The electrolyte was the same as described above. The data are tabulated in Table XXX and shown graphically in Figure 17.

Result s and Conclusions A comparison of the curves in Figures 13 and 13 show the effect surface oxides have on the electrolytic behavior of tungstate ions in an aqueous system. The two sets of curves are not identical because the position of the tung­ sten electrode altered the current passing through the cell.

The current density gradient was at a miniraum when the regular two compartment cell was used with the electrode 66

Table XXVIII

Current-Time Data for the Deposition of Tungsten on an Untreated Copper Surface

Time Potentiometer Current (min.) (millivolts) (ma.)

1 676 33.B

3 670 33.5 5 660 33.0

7 655 32.6

9 645 32.3 11 636 31.9 14 632 31.6

16 627 31.4 20 630 31.5

24 635 31.6 26 640 32.0

26 670 33.5

30 714 35.7

34 733 36.7 36 742 37.1

40 750 37.5

44 755 37.6

47 755 37.6 50 750 37.5

55 745 37.3 60 740 37.0 FIGURE 16 CURRENT-TIME CURRENT-TIME 16 FIGURE Current (milliomps) 0 . 4 3 310 - 0 . 2 3 370 F UGTN N CPE SURFACE. COPPER A ON TUNGSTEN OF 20 i# (minutes)Tim# CURVE 0 5 0 3 O TE DEPOSITION THE FOR 0 4 87 0 6

m

Table XXIX

Current-Time Data for the Deposition of Copper on a Flame Oxidized Tungsten Surface

Time Pot entiometer Current (min,) (millivolts) (maj

1 637 34. $

2 670 33.5

3 674 33.7

4 677 33. a

5 630 34.0 6 633 34.4

7 694 34.7

9 701 35.1

11 701 35.1

13 691 34.6

15 690 34.5

17 693 34.7

19 692 34.6

24 696 34.3

29 701 35.1

34 704 35.2

39 705 35.3

44 707 35.4

49 712 35.6

54 710 35.5 59 716 35.3 39

Table XXI

Current-Time Data for the Deposition of Copper on an Untreated Copper Surface

Time Potentiometer Current (min.) (millivolts) (ma.)

1 674 33.7 2 672 33.6

3 673 33.7 4 730 39.0

5 769 33.5 6 672 33.6

3 770 33.5

10 763 33.4

12 763 33.4

15 770 33.5 20 770 33.5

25 770 33.5

30 773 33.7

35 769 33.5 40 763 33.4

45 674 33.7 50 672 33.6

55 776 33.3

60 779 39.0 Currant (milliompa) IU E 7 CRETTM CRE FR H DEPOSITION OF THE FOR CURVES CURRENT-TIME 17.FIGURE .0 4 3 .0 3 3 .0 5 3 0 0 4 0 7 3 .0 6 3 0- .0 9 3 N FAE OXIDIZED SURFACE. FLAME TUNGSTEN A ON COPPER N N UNTREATED AN ON 20 ia Iminutaa) Tima O Untraotad coppar aurfoca aurfoca coppar Untraotad O Faa xdzd ugtn aurfoca tungatan oxidizad Flama A OPR SURFACE COPPER 0 6 AND 91 parallel to the anode. For this reason the majority of the work was done with this type of electrolytic cell. The flashed tungsten surface showed a sharp drop in current density during the first 4 minutes (Figure 15). This indicated that a clean tungsten surface was converted to oxide in a short period of time. The deposition of 10 mg. of copper on an oxidized tungsten electrode is evidence that the presence of an oxide does not prevent the electrolytic deposition of a metal. However, as was shown by the cobalt-tungsten experi­ ment, the rate of deposition may be considerably decreased when surface oxides are present. The curve obtained for the deposition of tungsten on copper (Figure 16) shows that this electrolytic behavior is characteristic for tungsten and independent of the electrode metal. The curve for the deposition of copper on tungsten (Figure 17) shows a slight drop in current during the first few minutes, whereas the deposition of copper surface (Figure 17) is a relatively straight line. These results were interpreted to mean that a drop in current occurred during the time interval the electrode became covered with the depositing material. For the flashed surface this drop was a rapid one. For the untreated electrode the decrease was slower, having reached its minimum value after 25 minutes of electrolysis. It seems that the surface should have been covered with the electrodepositing material in a shorter time interval than 92 25 minutes. However, the largest portion of the current was utilized in the liberation of hydrogen so that the efficiency for any other process was extremely low. For the electro- lytically oxidized tungsten surface no drop in the current occurred since the material depositing was the same as that already on the surface. The flame oxidized surface showed a gradual drop in current as the electrode surface was being changed. This investigation has shown that the basic problem in the electrodeposition of tungsten is the formation of oxides on the cathode surface during electrolysis. The presence of oxide layers on an electrode surface is not responsible for the prevention of a metallic deposit, as was shown by the deposition of copper on a flamed oxidized tungsten surface. If the tungsten behaved like copper in an electrolytic reduction process, the tungsten would readily be deposited on an oxide-covered surface. This indicates that the reduction process stops with the formation of a lower- valent tungsten oxide. The rapid drop observed with the flashed electrode indicated that no metallic deposit was obtained. The deposition of tungsten on a tungsten electrode should have given a current-time curve similar to that curve similar to that obtained from the deposition of copper on a copper surface (Figure 17). Future work suggested by this investigation is:

(1) To study the composition of the electrolytic

tungsten oxides with X-ray fluorescence as an analytical

means of measuring whether any tungsten is deposited,

(2) To carry out a series of experiments in a

completely oxygen-free system either organic or inorganic.

For the organic system, new tungsten-organic compounds would have to be prepared which would be soluble in a conducting organic solvent,

(3) To attempt to reduce the oxides as they are electrolytically formed in the aqueous system. A possible approach would be to generate atomic hydrogen photocherriically on the cathode in the aqueous system. SUMMARY

The results of this investigation may be summarized as follows: (1) A study of the electrolytic behavior of tungstate ions with oxide and flashed tungsten electrode surfaces indicated that the basic difficulty in depositing tungsten is the formation of lower valent tungsten oxides on the

electrode surface. A small amount of oxide on an electrode

surface will slow down an electrolytic process but will not necessarily inhibit the deposition of a metal, (2) A study of the electrolytic behavior of tungstate

ions with various metallic ions and cathodes suggested an

explanation for the ability of iron, nickel, and cobalt to cause the deposition of large quantities of tungsten. This

explanation is based on the precipitation of a cobalt-tungsten

complex in the vicinity of the cathode, which is followed by

the reduction of oxide within the crystal lattice of the deposit. (3) Radioactive tungsten-135 was found to contain radioactive rhenium-133 as an impurity. This isotope is in

transient equilibrium with tungsten-133. Consequently the

use of tungsten-135 as a radioactive tracer was complicated.

Special precautions had to be taken in order to utilize it

successfully in the present investigation.

94 BIBLIOGRAPHY

1. Zettnow, E., Pogg. Ann., 130. 5 (1367). 2. Feree, J., Bull. Soc. Chim., 1£, 213 (1393).

3. Jackson, K., Russell, A., and Merrill, J.f J. Chem. Soc., 2394 (1929). 4. Fink, C., and Jones, F., Trans. Electrochera. Soc., 461 (1931),

5. Holt, M., Trans. Electrochem. Soc., 66, 453 (1934). 6. Kashima, J., Waseda Applied Chem. Soc. Bull., 19. 69 (1942). 7. Yntema, L., J. Am. Chem. Soc., 3775 (1932).

3. Holt, M., and Kahlenburg, L., Quarterly Review Am. Electropl. Soc., 12, 41 (1933). 9. Armstrong, H., and Menefee, A., U.S. patents 2,145,745-6 (1939); 21,160,321-2 (1939). 10. Harford, C., U.S. patent 2,334,301 (1935). 11. Clark, W . , and Lietzke, M., J. Electrochem. Soc., 99. 245 (1952). 12. Broughall, L., British patent 320,313 (1923). 13. Booth, H., and Merlub-Sobel, M., J. Phys. Chera., 233 (1933). 14. Wolfram Lamnen AG, German patent 231,657 (1911).

15. Wolfram Lampen AG, German patent 237,014 (1911).

16. Neuman, B., and Richter, H., Z. Eiektrochem., 30, 474 (1924). 17. Leimpt, 7., Z. Anorg, Chem., 122, 175 (1922). 13. Leo, S., and Shen, T., Trans. Electrochem. Soc., 66, 431 (1934). 19. Holt, M., and Nielsen, M., Trans. Electrochem Soc., 32, 193 (1942). 96

20. Holt, M. and Black, R,, Trans. Electrochem, Soc., $2 , 20!) (1942). 21. Holt, M. Black, R., and Hoglund, P., Trans. Electrochem. Soc., IiJt, 353 (1943). 22. Vaaler, and Holt, to., Trans. Electrochem. Soc,, 20, 43 (1946). 23. Lietzke, M., and Holt, M . , Trans. Electrochem. Soc., 21, 25? (1948). 24. Clark, Wi, and Holt, M., Trans. Electrochem. Soc., 244 (194#). 25. GolTts, L., and Kharlamov, V., J. Appl. Chem. U.S.S.R., 2, 640 (1936). 26. Kegel, W +, German patent 666,613 (193&). 27. Rogers, I)., and Burr, A., J. Electrochem. Soc., 97, 67 (1950). 2 &. Hoglund, P., and Holt, M., Trans. Electrochem. Soc., 359 (1945). 29. McElwee, R., and Holt, M., J. Electrochem. Soc., 22, 4# (1952). 30. Glazunov, M., and Jolkin, V., C.A. 2k* 31#4 (1940).

31. Glazunov, to., Rev, met., 214 (1946). 32. Holt, K., and Vaaler, L., Trans. Electrochem. Soc., 94, 50 (194#). 33. Alkire, 0., Ph. D. Dissertation, The Ohio State University, (1943), 34. Muller, E., Z. Elektrochem,, j>0, 172 (1944).

35. Ekwall, P., Tek. Foren. i Finland Forh., 22.* 39, (1939). 36. Kasper, (3., J. Research Natl. Bur. Standards., 2» 353 (1932). 37. Brenner, A., and Ogburn, F., J. Electrochem. Soc., 26, 34? (1945). 97

36. Minin, A., Russian patent 59,663 (1941). 39. Paul, K., Russian patent 53,756 (1936). 40. Price, W., and Brown, 0., Trans. Electrochem. Soc., 20, 423 (1936). 41. Fink, C., and Eldridge, C., Canadian patent 274,429 (1927). 42. Ksycki, M., and Yntema, L., J. Electrochem. Soc., 26, 43 (1949). 43. Holt, M., and Seim, H., U.S. patent 2,599,176 (1952).

44. Seim H., and Holt, M., Trans. Electrochem. Soc., 26, 205 (1949). 45. Isotopes Catalog and Price List. Oak Ridge National Laboratory. 46. Theurer, K., Master^ Thesis, The Ohio State University (1952). 47. Lindner, M., Phys. Rev., 6/^, 2'+0 (1951). 46. Lindener, M., and Coleman, J., J. Am. Chem. Soc., 22, 1610 (1951). 49. Holt, M., Trans. Electrochem. Soc., 2i> 301 (1937). 50. Glasstone, S., An Introduction to ElectrochemLstry, (1942), p. 46TT7 51. Voigt, A., Z. Anorg, Chem. 2 4 9 , 225 (1942). 52. Smith, D., Hydrogen in Metals (1950) p. 146.

53. Langmui:-, I., J. Am. Chen. Soc., 2?96 (1932). AUTOBIOGRAPHY

I, Kurt Theurer, was b o m in Brooklyn, New York,

October 27, 192B. I received my secondary school education in the public schools of Brooklyn, New York. My under­ graduate training was obtained at Hofstra College, from which I received the degree Bachelor of Arts in 1950. From

The Ohio State University, I received the degree Master of

Science in 1952. While in residence at The Ohio State

University I was appointed teaching assistant during the years 1951-52 and 1953-54 and was appointed research assistant during the years 1952-53 and 1954-55. In the

Summer Quarter, 1955, I received an appointment as University

Scholar at The Ohio State University.

9S