US2160322A - Electrodeposition of tungsten alloys - Google Patents

Description

Patented May 30,1939

l-QUNlTEDY STAT nmc'raonnrosrrion or TUNGSTEN ALLOYS 4 vHarry Howard Armstrong and Arthur Burley Menefee, Beverly Hills, Galif., asslgnors to I Tungsten Electrodeposit Corporation, Washington, D. (3., a corporation of Delaware 1 o p Serial No. 28,187

" No Drawing. Application June 24, 1935,

19 Claims.

This invention relates to the electrodeposition. of tungsten alloys of variable tungsten content The present invention is part-a continuatlonofprior application Serial No. 14,372, filed April 2, 1935. The wide potential utility of the heavier refractory metals, such as those of the 5th and 6th groups, has long been recognized\ and considerable effort has been expended in attempting to electrodeposit such metals. Particularly valul5 able among such metals are tungsten and tantalum. These are each characterized by a very high resistance to chemical corrosion and are r most refractory; furthermore they present decidedly pleasing chromatic characteristics. Such 2o metals either alone or in the form of alloys pre- Consonant with the recognition of the inherent value of these metals in the several technological fields many suggestions have been. advanced as I, to methods ofelectrodepositing them. It has been proposed, for example, to produce pure tantalum by electrodeposition. This is, and has been, recognized as difficult' of achievement becauseof the fact that compounds of tantalum hydrolyze relatively readily in water,-giving rise to the formation of insoluble or very sparingly soluble salts. To evade this difliculty it has been proposed toplate tantalum from a non-aqueous or anhydrous bath. Thus it has been suggested to dissolve a suitable tantalum, compound, such as tantalum chloride, in an organic solvent, such as toluene, to electrodeposit pure tantalum from the resulting solution. Similarly it has been suggested to dissolve tantalum compounds in anhydrous liquid ammonia and subsequently to electro-deposit tantalum from this solution.

ature required, the very low inherent conductivity and the high solution resistivity of such organic baths. In some circumstances these difllculties All such methods involving the utilization of 55 are further accentuated by the. physical or mechanical difllculties, such in the case of anhydrous ammonia, for example, as the problem of f retaining the ammonia in the liquid phase.

Similarly, as pointed out in our prior application'above referred to, comparable difllculties ob- 5 tain in the electrodepositionof tungsten. Thismetal is difflcult to electrodeposit because'of the tendency of tungsten to oxidize and deposit in the oxide condition, thus v giving rise to' impure and loosely adherent plates. By reason of the 10 I difliculty of reducing oxides of tungsten in aqueous solution, dueto active hydrolysis, it has been suggested to substitute an organic solvent for the water bath. Such methods however present the disadvantages enumerated above. 15

As fully disclosed in our copending application, we have found that it is not, only possible but is eminently feasible and practical to elec-' trodeposit tungsten containing alloys from aqueous baths. 1

We have now found that dense, lustrous. ad-

' herent alloy deposits containing tantalum may be obtained when employing aqueous baths. Improved results are secured, as will be seen, by codepositing other metals, such as tungsten and/or nickel, with the tantalum. When operating under the preferred conditions, smooth, even deposits of extremely small crystalline struc-' ture are procurable. Without advancing any definite statement as to the precise mechanism of the reactions involved, it would appear that-ionic complexes are formed which present sumcient stability to resistthe tendency of the tantalum, tungsten, and comparable metallic ions, to hydrolyze to form insoluble oxidesor salts.

A major object of the present invention, therefore, is to electrodeposit tantalum from aqueous electrolytes, s

Another object is to electrolytically produce alloys of tantalum. 40

Yet another object is to produce an aqueous electrolyte from which tantalum may be electrolytically deposited.

A further object is to produce, as-a new article of manufacture, a metal base plate having an adherent electrodeposit plate containing tungsten and tantalum.

Yet another objectof the invention is to elec- 3 trolytically produce alloys of tungsten and tantalum of variable content ratios.

With these and other equally important and related objects in view, the'invention comprehends the concept of producing elec'trodeposited We have found that, similarly to tungsten,

. readily available compounds of tantalum, such as ll the oxides, may be dissolved in suitable aqueous solutions. We have further found that when, to an electrolyte containing soluble tungsten and tantalum, there is added another metal, such for example as nickel, the alloy plates of these metals,

duced. We have found in particular that such a common tantalum compound as tantalum pentoxide (TazOa) may directly be .dissolved in a suitable aqueous solution, such as a solution ,of

ammonium acid fluoride (NaH4HFz). As has been disclosed in our prior application, common tungsten compounds, such as the oxides and tungstic acid anhydride, are likewise directly soluble-in ammonium acid fluoride. We have also :0 further found that such compounds are soluble within a relatively wide range and thus, by reason of the common solubility of compounds of the two metals in a single cheap aqueous solvent,

a most economic method of electrolytically proll ducing alloys of the metals is presented. The

advantages of the employment of simple, cheap.

and readily controllable aqueous, baths over the organic solvents heretofore suggested will immediately recommend themselves to those skilled so in the art.

As will appear more fully hereinafter, the bath of the present invention may be considerably modified with respect to such factors as the specific amounts of the respective metals dissolved in the bath, the acidconcentration, temperature and current density ranges, the character of the buffers and addition agents and the like. Similarly the anodes employed may be of the inert type or may comprise one or more. of the metals which are to be deposited, it being particularly understood that the invention comprehends the establishment of the desired metal ions in the bath by direct dissolution or anodic corrosion.

The invention will be more readily understood composition of typical electrolytes and the operative procedure.

proved bath from which an alloy plate may be deposited may be made up by simultaneously or.

sequentially dissolving tungstic acid, tantalum pentoxide and ammonium bifluoride in water while maintaining the water at a temperature of tween approximately 106 F. and 210 F. Thus, to, say oneliter of water maintained at the temperature stated,there is added approximately 85 grams of ammonium bifluoride, 40 grams of tungstic acid and grams of tantalum pentoxide.

After complete dissolution the solution is flltered and then there is added 60 grams of tartaric acid, 30 grams of citric acid, 60 grams of sodium fluorideand15-grams of a soluble nickel salt, such as nickel chloride. The solution is then adjusted to a pH of approximately 5.3 using sodium hyof widely varient ratios, may eiliciently be pro-- solved in 500 cc. of water.

from a consideration of the compounding and As a typical example an im- During the the bath. For example, an improved bath may be made up by dissolving 40 grams of tungstic acid, grams of ammoniiun bifluoride and 30 grams of tartaric acid in 500cc. of water maintained'at elevated temperature for a period of time sufliciently prolonged to insure comple'te dissolution. There is then separately prepared a 80-- lution of 35 grams of tantalum pentoxide, 40'

grams of ammonium acid fluoride, 30 grams or tartaric acid and 20 grams of nickel chloride dis This second batch was similarly heated to a temperature of the order of 160 F. until complete dissolution was effected; The two solutions were then mixed and '75 cc. of sodium hydroxide added. Upon electrolyzing, using brass, copper, steel or other suitable cathode and tungsten carbide and/or nickel anodes, dense acid resistant plates were produced.

This type of bath may be considerably modifled with respect to the acid concentration. Thus to the above *described bath there was added an v additional quantity in the amount of cc. of

sodium hydroxide and the bath electrolyzed, using a steel cathode and four tungsten carbide anodes. The bath temperature was maintained at 160 F. and an 8 sq. in. test plate was plated for fifteen minutes at 4 amps. and 3 volts. Upon analysis this plate was found to contain 25.8% tantalum,\39.8%"tungsten and-34.4% nickel.

As will be appreciated and as indicated above, the nickel or tungsten content of the bath may be replenished. either by using tungsten containing and/or nickel containing anodes and producing the tungsten and nickel ions respectively by anodic corrosion. Similarly, if desired, replenish- '35 ment of the bath may be achieved by dissolvinga tungsten oxide or tungstic acid separately in ammonium acid fluoride and adding this in re quired amounts. The tantalum content is most readily replenished by making a replenishing solution comprising tantalum pentoxide dissolved in a solution containing ammonium bifluoride and an organic acid, such as tartaric.

Similarly in other experiments conducted it was found that tartaric acid may be replaced in whole or in part by equivalent amounts of citric and/or boric acid. These acids appear to function to prevent precipitation of the tungsten and tantalum from the bath. Sodium tartrate likewise has been found to be a useful and effective adjuvant.

It is further found that additions of ammonium phosphate improve the efficiency of the bath and the character of the ultimate plate.

As a result of considerable experimentation we have found that the plate may be produced over a'- wide pH range extending from a very acid to a definitely alkaline solution. This should be ad- 'justed to secure the desired results. Similarly the modification of the other factors, such as the current density, has a marked effect upon the character of the plate. Thus on plating an 8 sq. in.

test plateat 2 amps. a bright plate is produced which may be buffed to a very brilliant flnish. With the same bath and size test plate, plating at 4 amps. produces a less brilliant but more acid resistant plate. Again, when carrying out the plating at 8-amps. a plate is produced which is extremely hard to buff and which when buifed is not as brilliant as the plates described, but which is characterized by an extremely high resistance resistance of the plate applies generally whatever the character of the work or base plate.

We have found that the respective quantities ,to acid. This variation in the brilliancy and acid 1 metals in the bath. Furthermore the proportions of the several metals inthe plate may be varied 175, an adherent acid resistant plate is pmduring a given continuous plating operation by duced.

changin the current density and/or the tem- In commercial operations abath concentrate perature. It will be appreciated that the exmay be made up in the dry or liquid condition.v amples given aboveare presented as illustrative Thus a standardized liquid concentrate may be of the process and not as the exclusive methods made up, as will be appreciated, by dissolving 10 of either making up the bath or effecting the predetermined quantities of'a tantalum and tung- Y plating operation. Thus plates of the charsten compound in ammonium bifluoride and addacter described may be produced operating at pH ing to this the required mounts of "organic ranges from 1 to 8 or more. Likewise current acids, such as tartaric or citric, to maintain the density may be varied with good results from submetals in solution. Thus for subsequent use this 15 stantlally 6 to 500 or more amps. per sq. ft. of bath maybe diluted with water andadditional submerged cathode area. Also, while an optimum metal, such as nickel, by way of the soluble nickel temperature of 150 to 160 F. has been desalt, and the bath electrolyzed by aninert anode scribed, it is, to be. understood that this temperatungsten carbide and/or nickel or other metal ture may be varied over a range of from 80 F. containing anodes. p 20 or less to 180 F. or more. It will be appreciated that the'invention is not.

A striking, feature of the present invention is limited to the use of the particular tantalum comthe non-critical nature or flexibility of the'procpounds mentioned or to the described method of ess, especially with respect tothe solution concenbringing tantalum into 501M101! b fl p trations. Thus, employing the method described, hends any method by which the tantalum is made 25 ,namely by utilizing an ammonium bifluoride to available in an aqueous system. Thus improved solubilize the tungsten and tantalum a very high results are procuredv by dissolving freshly preconcentration of these metals may be obtained pared tantalum hydroxide in tartaric acid and in the bath. Forexample .a tungsten concentraadding this solution to a solution of a tungsten tion of up to 6 oz; per gal. of bath solution can compound in abifluoride, and utilizingthe resultbe obtained by dissolving tungstic acid or tungstic ing solution after adjustment ofthe acid conacid anhydride in a bifluoride solution. centration as'the plating bath.

The invention is not limited to the employment While the invention has been described with of ammonium bifluoride. In lieu of this other respect to plating out the nickel alloys on common similarly acting bifiuorides, such as those, .-demetals, such .as steel, brass, copper and the like, 85

. scribed in the copending application referred to, it will beappreciated that it is equally applicable maybe employed. Again, if desired, sodium acid for purposes of overplating on. more expensive fluoride maybe utilized to'bring the tungsten into metals, such as overplating on an electrode: solution, as for example by dissolving sodiumposited nickel plate.- Thus the invention is sustungstate in hydrogen fluoride and thereafter ceptible of widemodiflcations with respect to the 0 adjusting the bath to the desired acid concentraingredients employed and \their method of com- 1 tion. It will be appreciated that-this process is pounding. The invention is considered to reside amenable to the general operative technique of broadly in the concept of'producing tantalum conthe plating art. Thus it is directly contemplated, taining electrodep'ositedplates from aqueous baths when desired, to utilize addition agents, such as and also in the production of a highly serviceable heavy molecular weight colloids ofthe character electrodeposited tungsten tantalum surface. I of glue, for enhancing the quality of the'plate. We claim:

Likewise for certain types of work the bath may 1. A method of producing tantalum containing be subjected to very fine clarification to remove electrodeposited plates which comprises electroundesired suspended matter, as for example by lyzing an aqueous acid solution of an alkali bim, treating the bath with aprecipitated colloid and fluoride containing dissolved tantalum and then filtering out the precipitated material. tungsten. i

It is particularly to beunderstood that the -.2. A method'of producing tantalumscontainprocess is not limited to the production of a ing electrodeposited' plates which comprises elec-' ternary alloy or an alloy containing nickel. Thus trolyzing an aqueous acid solution of an alkali u in lieu of nickel chloride, other nickel salts may bifluoridecontaining dissolved tantalum and be utilized in the bath. Similarly in lieu of ,nickel; 4 nickel any other metal which forms an acid 3. A method of producingprotective electrodefluoride may be employed, such for example as pbsited plates which comprises electrolyzing an iron, nickel, cobalt and the like. aqueous solution of an alkali bifluoride contain- '0 F 1 some p p 1' s a surface ombining 'ing dissolved tantalum, tungsten and nickel. the decidedly refractory characteristics of tung- 4, A method of producing surfacescontainins' sten and tantalum is desirable. In these cirt t tantalum and nickel which comprises ,cu ances t e p es t e d is available for dissolving tungsten containing and tantalum con h Production of a tungsten tantal m all y. taining compounds inahot aqifeous solution coni be produced by heating 20 grams of tantalum of the alloying components of the plate may be maintain the tantalum in solution. when elecwidely varied, as for example by adjusting the trolyzing the above solution, using a 4 sq. in. initial respective concentrations of the several copper cathode and tungsten carbide anode, at 9 amps. and 6 volts and maintaining the bath at taining an alkali bifluoride and citric acid; adjusting the hydrogen ionconcentration of the solution to substantially pH 5.3 and electrolyzing' the solution witha metal cathode and a tungsten containing anode.

Thus, for example, a plate of this character may pentoxide, 60 grams of tungstic acid and grams of ammonium bifluoride and 65 grams of tartaric acid in approximately 800 cc. of water. This may be adiusted'to the desired pH value, say a pH of 2.73. It has been found that in producing a tungsten and tantalum which comprises dissolv- 10 5. A method of producing surfaces containing resistant tungsten tantalum alloy the higher acid ing a tantalum containing compound in an aqueconcentrations are desirable, for at low acid conous solution of an alkali bifluoride, acidifying the centrations, of the order of pH. 6.2, it is dimcult to solution, electrolyzing the solution with a tungsten containing anode and coplating tungsten and tantalum upon a conductive cathode.

6. A method of producing surfaces containing tungsten and tantalum which comprises dissolving tungsten and tantalum containing compounds in an aqueous solution of an alkali bifluoride, acidifying the solution and electrolyzing" the solution with a conductive cathode and a tungsten carbide anode.

7. A method of producing surfaces comprising tungsten tantalum and nickel which comprises dissolving tungsten, tantalum and nickel containing compounds in an aqueous solution of an alkali bifluoride, acidifying the solution, and electrolyzing the solution with a conductive cathode and tungsten containing and nickel containing anodes.

8. A method of producing tantalum containing surfaces which comprises dissolving tungsten tantalum compoundsin an aqueous solutionof an alkali bifluoride, adjusting the hydrogen ion con-' centration of the solution to between pH 1 and pH 8 and electrolyzing the solution with a metal cathode and a tungsten containing anode.

- 9. A method of producing adherent, acid re-' sistant tantalum containing electrodeposited plates which comprises dissolving tungsten and tantalum in an aqueous solution of an alkali biiluorlde, acidifying the solution, and electrolyzing the solution with a conductive cathode and a tungsten containing anode, and increasing the amperage in proportion to the desired degree in acid resistance of the electrodepositedplate' 10'. A method of producing tantalum containing surfaces which comprises dissolving tungsten and tantalum containing compounds in an aqueous solution of an alkali bifluoride, adding thereto an organic acid which acts to prevent the precipitation of ,theidissolved metals from the solution; adjusting the hydrogen ion concentration of the solution to between pH 1 and pH 8; ad-

justing'the temperature of the solution to between substantially F. and substantially F., electrolyzing the solution with a conductive cathode and a metal anode, and varying the cur-- byreacting a tantalum containing compound. with an alkali bifluoride. and dissolving in the solution a compound of a metal of a group consisting of tungsten, iron nickel and cobalt.

13. A method of producing tantalum-containing electrodeposited plates which comprises electrolyzing an aqueous acid solution of an alkali birluoride containing dissolved tantalum and a metal of the group consisting of tungsten, iron, nickel and cobalt and an organic acid of the group consisting of citric acid and tartaric acid, said acids being adapted to prevent precipitation of the metals from the solution.

14. An electroplating bath for electrodepositing tantalum comprising an aqueous solution formed by dissolving a tantalum containing compound and a compound of a metal coplatable with tantalum, said metal being chosen from the group consisting of tungsten, iron, nickel and cobalt,

in an aqueous acid solution of a bifluoride.

15 An electroplating bath for ele'ctrodepositing tantalum which comprises tantalum pentoxide and a tungsten containing compound dissolved in an aqueous solution of an alkali bifluoride, the bath containing a predetermined amount oi an organic acid .of the group consisting of tartaric and citric acids, adapted to prevent precipitation of the metals from the bath.

16. A method of producing tantalum containing'electrodeposited plates which comprises electrolyzingfla definitely acid aqueous'alkali bifluoride solution containing tantalum and tungsten ions. I

, 17. A method of producing tantalum containing-electrodeposited plates which comprises elec ftrolyzing an acid aqueous solution of 1 a fluoride containing dissolved tantalum, a metal coplatable with tantalum chosen from the group consisting of tungsten, iron, nickel and cobalt, and an organic acid of the group consisting of tartaric and citric acid, adapted to prevent precipitation of the metals from the solution.

18. ,A method of producing tantalum containing alloys which comprises dissolving an oxide of [tantalum in an alkali bifiuoride, adding an organic acid of the group consisting of tartaric and citric acids, adjusting the hydrogen ion concentration to between pH 1 and pH 8, electrolyzing the solution and depositing tantalum on an electrode.

19. A method of protecting metals which com prises immersing the metal in an aqueous alkali bifluoride electrolyte containing" dissolved tan,- talum and tungsten, adjusting the acidity to between pH 2.7 and pH 6.2, electrolyzing the solution and plating out tungsten and tantalum on the said metal.

HARRY HOWARD ARMSTRON. ARTHUR BURLEY MENEFEE.