US2145241A - Electroplating method and product - Google Patents

Description

Patented Jan. 31', 1939 UNITED STATES- PATENT OFFICE Harry Howard Armstrong Meneiee, Beverly Hills,

and Arthur Barley Calm, assignors to The n Electrodeposit Corporation, Wash- D. 0., a corporation ot ll'elaware No Drawing. Application April 2, 1935, Serial No. 14,372

11 Claims.

, Our invention relates to a process for electroplating tungsten alloys of variable tungsten content from aqueous solutions, as well as depositing other single metal deposits,and alloys of metals other than tungsten from the same type of elec- .trolyte, and is a continuation in part of our copending application Serial No. 744,566.

In our above mentioned application we have disclosed a method for the electrodeposition of tungsten alloy plate from an acid fluoride bath containing W02 ions produced either by dissolving the low oxide directly in the bath or by electrolyzing the said bath with a tungsten or tungsten bearing anode. While a substantially pure and uniform alloy plate of excellent quality may be produced by this method, further research has shown that tungsten alloys and other metals can be electrolytically deposited directly, from a fluoride solution of the oxides, tungstates, ,metatungstates, para-tungstates, tungstic acid, etc.

Heretofore, various methods and processes for electroplating tungsten have been proposed; ho cver, none of the prior art processes,.of which we are aware, produce a satisfactory plate and the methods per se are not commercially feasible. It has been suggested to provide a strongly alka line bath containing a tungsten complex radical but this has been found to be impractical because of the characteristic tendency of tungsten and similar metals to oxidize and deposit as sub-oxides, the resulting deposits being metallically impure and not firmly adhering to the cathode base. Because of the difllculty of reducing the oxides of tungsten in an. aqueous solution, due to the tendency of those tungsten ions which are produced by electrolysis to h'ydrolytically react with water, considerable study has been given to the possibility of utilizing non-aqueous and therefore non-oxidizing baths of tungsten salts 0r baths I containing'organic solvents, such as carbon bisulflde or acetone. These processes are not commercially practical because of the high working temperature required for a fused bath and because of the low cathode and high solution r sistivity when organic solvents are used.

Our present invention overcomes the inherent priorart methdifllculties existing in the known ods and in accordance with the improved process desscribed herein, we not only produce asatisfactory tungsten alloy plate, but also provide a method which is economical of operation and commercially feasible. V We have found that a dense metallic alloy deposit containing tungsten can be obtained from an acid bath containing W0; dissolved in a bisity of replenishing the bath by eiectrolyzing from 10 a tungsten or tungsten-bearing anode.

An object of our invention is the production of tungsten 'alloy plates, of dense, closely adherent qualitywhich are highly'resistant to the corrosive action of acids and salts, and withstand high 15 temperature;

Another object of our invention is to provide an electroplatingprocess capable of producing a satisfactory plate under varying operating con-v I ditions.

Yet another object of our invention is the formation of a solution bath from which substantially pure metallic tungsten may be produced by plating tungsten with a soluble or volatile" metal. I

Still another object of our invention is the formation oftungsten. complex ions of low valence which are chemically stable over a wide pH range.

A jurtherobject of our invention is the production of an electroplating bath solution containing a high metal concentration and low ion concentration 1 A still further object of our invention is to produce alloy plates of variable content ratios.

We have found as a result of considerablefexperiinentation that improved results in respect of the electrodeposition of tungsten and analogous meals may be secured by directly dissolving a suitable tungsten compound, such as unsstic acid anhydride, in an acid fluoride. Particular- 1y we have found that ammonium acid fluoride serves eflectively as a solvent for the acid anhydride. We have found additionally that the physical characteristics of the plate may be considerably improved by the use of certain ad- 'juvants in the bath for the purpose of controlling the acidity "or hydrogen ion concentration, the establishment and maintenance of complex ions and the like. Considered more specifically, we have determined that. an improved tungsten alloy plate of widely variant content may be elec-' trodeposited by immediately utilizing tungstic acid anirvdride, tungstates, meta-tungstates, para-tungstates, tungstic acid, etc., that is to say pH. value of the solution without the necessity of producing tungsten ions in the bath by means of anodic corrosion.

In preparing the improved bath, tungstlc acid anhydride and ammonium bifiuoride are dissolved in water at a temperature of substantially 106 F. to 210 F. and the solution filtered. Boric acid (HaBOa), sodium fluoride (Na?) and tartaric acid are then added and the resulting solution brought to a temperature of between 120 1''. and 140 I". or higher. At this stage in the preparation of the bath a soluble salt of the metal to be alloyed with tungsten is added. If nickel is desired as an alloy constituent, basic nickel carbonate (2NiCO:-3Ni(OH)z-4H:O) may be added. The resulting solution is then subjected to a current density of from 6 to amperes per square foot of submerged cathode area. We have found that good results are obtained by controlling the pH value of the solution within the range of fi'om substantially l to 10 or even higher during the plating operation.

Our process is flexible and susceptible of modification with reference to the constituents used and the procedure which may be followed in the preparation of the bath. As an illustration of one modification of our invention, tungstic acid anhydride, ammonium bifiuoride, sodium chloride and a soluble salt of the metal to be alloyed are added simultaneously to water. The solution is maintained at a temperature of 140 1". to 210 F. for approximately 30 minutes, and clarified by filtration. The pH value is adjusted to substantially 5.3. The resulting solution is maintained at a temperature of substantially 140 F., and a current of about 30 amperes passed through it from a tungsten carbide (W1C) anode to the cathode base to be plated, having an immersed surface of 1 square foot including its two faces.

in another modification of our process, which has been found particularly adapted for the production of -a tungsten alloy plate, fused ammonium bifiuoride and tungstic acid anhydride are dissolved in water at approximately 160 1''. and the resulting solution clarified by filtration. To this solution is added sodium fluoride, sodium chloride, and the soluble salt of the metal to be alloyed. The solution is maintained at a temperature of substantially 160 1''. and'electrolyaed at a current density of approximately 35 amperes per square foot of submerged cathode area. A platinum or tungsten carbide (W2C) anode'may be used. In addition an anode of the metal desired to be alloyed with the tungsten plate may be used either alone or in combination with the platinum or timgsten carbide anode.

The following examples of our process are presented as specific illustrations of the reaction quantities and operation conditions which have been found to give a plate of desirable quality.

Sample I 200gramsofWOzand240gramsofNHsHI": are added to one gallon of water and the solution raised to a temperature of between 160' I". to 210 1''. and clarified by filtration. grams of borlc acid, 60 grams of NaF and 60 grams of tartarie acid are added to the filtrate, the solution transferred to the plating vessel and heated to a temperature of between 120 F..and 1". If an alloy plate, as for instance a nickel-tungsten is desired, a soluble nickel salt is added; an excellent alloy plate is obtained by adding 10 grams of basic nickel carbonate to the bath. The

is then adjusted to between 53 and 8.8. During electrolysis a current density of between 6 and 100 amperes per square foot of submerged cathode areas is employed, using either a t mgsten or nickel anode" and any suitable metallic plating base as a cathode. Good results, however, may be obtained with a combination tungsten carbide and nickel anode or with a platinum anode.

Example II To one gallon of water raised to a temperature of between 140 F. and 210 F. the following admixed dry salts are added:

Grams W0: 120 N1CO:|.N1(OH)3.4H2O 60 NHdlF 240 NaF 240 The above temperature is maintained for about 30 minutes and the solution clarified by filtration. Adjusting the pH value as in Example I the batch I is placed in the plating tank and maintained at a temperature of substantially 140 F. during plating operations. Excellent results are obtained by electrolyzing with a tungsten carbide or nickel anode, or both, at a current density of about 30 amperes per square foot of submerged cathodic area.

, Example III zmcoa-auuonh-imb,

or a similarly suitable soluble salt of a metal desired to be alloyed with the tungsten plate. The pH value of the bath is adjusted as in Exampies I and 11. Excellent results are obtained by electrolyzing at a bath temperature of substantially F. A platlnum,tungsten carbide, or nickel anode has been found to give satisfactory results with a bath prepared in this manner when a current density of substantially 35 amperes or higher per square foot of submerged cathode area is used.

It will be appreciated that the above examples should not be construed as limiting our process as to the constituents used, the quantities employed or the operating conditions set forth. We have found that satisfactory tungsten deposits can be obtained with a pH range of from 1 to 10 or higher. The current density also may be varied with good results from substantially 6 to 500' or more amperes per square foot of submerged cathode area. A variation of temperature ranges from 80 1''. to F. or higher have been found to give satisfactory results.

The commercial value of our process, however, does not alone depend upon the flexibility or noncritical nature of the operating conditions. With our improved process it is possible to obtain wide variations of solution concentrations which are satisfactory for commercial plating operations. For example, a tungsten concentration up to '6 oz. per gallon of bath solution can be obtained by dissolving W0: in a bifluoride solution; a mixture of W0: and tungsten metal gives a relatively high tungsten content and fused wo=-'Nmrm also forms an exceptionally soluble compoimd producing high tungsten eoncentrationsin an 75 acid solution.

These Solutions, even though high in tunssten content, are substantially clear and free from undissolved materials, such as the oxrosion. The highest tungsten concentration which can be obtained by anodic corrosion is about 2 oz. of W per gallon. We have found, however, that when 40 grams of WOa-NH4HF2 are added to 200 cc. of water in equal quantities by weight, substantially 90% or more of the reaction compound will go in complete solution. We have found that depleted solutions caused by continuous plating operation, may be restored merely by adding W: and a bifiuoride in proper quantities to a heated portion of the electrolyte or by the more simple method of adding an aqueous solution of/WO: and the bifluoride tothe We have further discovered that the solubility of the woa-bifluoride mixture is not affected by the presence of other desirable salts such as; for instance, the alkali halides, citric,

tartaric and boric acids, sugars or soluble nickel,

salts. Two factors, therefore, (1) the high tungsten content of the bath solution and (2) the unaifected solubility of water soluble salts, of metals such as Ni which may be desired. to be alloyed with the tungsten, operate to provide great flexibility in the ratio range of tungsten and, for instance, nickel, in the solution. We

have produced satisfactory alloyplates from 'a' solution varying from substantially 15' parts tungsten to 1 part nickel to substantially 1 part tungsten to 1 part nickel. Alloy plates of this character can be produced by merely adding a soluble salt of the metal to be alloyed, to the WOa-bifluoride bath and electrolyzing with a suitable anode.

It is well known in the electroplating art that in order to obtain a line grain deposit the metal ion concentration of the bath solution must be low. 'It is also desirable in most cases to have a large amount of the metal bearing compounds dissolved in the solution so that a constant supply of metal ions will be supplied at substantially thesame rate that they are removed. We have obtained a bath solution of this character in that we have discovered a method of producing a water soluble. double salt of tungsten capable of supply- 1 ing stable complex ions.

'As suggested in our copending Serial No. 714,566, the double salts application 'WOzFr complex with a negative valence of two.

The even, small grained plate which is produced leads us to believe,

however, that we plate from 'a. reduced complex such as WOF: for, as iswell sknown, the lower the valence of the metal, the

more even the deposit.

The formation of stable complexes prevents;-

precipitation of the metal ions. Small amounts u of such organic compounds as tartratesvcitrates 'porated in the plate.

I follows that the com-- plexradical supplying thetungsten mass a 3 and acetates or their corresponding acids, have been found useful in forming the desirable complex tungsten radical. The presence of dextrose, probably because of its tendency. to act as a reducing agent, has also been found to be a desirable addition agent in that it aids in the formation of a fine grained and acid resisting plate.

" The addition of boric acid has been found advantageous as a pH regulator or bufler, for the reason that the resulting borates,being' weak .acid salts, prevent an appreciable variation of the hydrogen ion concentration caused by changes in anode and cathode efficiency. In lieu of boric acid we may employ a number of other materials as pH regulators,- as for example ammonium,

hydroxide, beryllium hydroxide, lithium hydroxide and lithiuin carbonate andthe like.

While the presence of NaF and NaCl increase the conductivity of the bath, the increase of halide ion concentration aids anodic corrosion-where a tungsten, tungsten carbide ,or nickel is used. This conclusion has been verified by solution tests showing an increased metal content when NaCl'and NaF were present. HF has also been found to aid anode corrosion.-

In lieu of employing nickel carbonate for supplying the nickel content, we may of course employ any other compound which will supply an available nickel ion, such for example as nickel chloride or nickel sulfate.

As indicated hereinbefore, the composition of a bath according to the presentinvention may be adjusted within a relatively wide range so as to secure tungsten alloy plates of specifically different compositions. also that the fundamental principles of the present invention may be utilized to prepare ternary alloys of tungsten, as for example by preparing a bath, as described, and adding thereto a soluble salt of nickel and a soluble salt of the third metal component which is desired to be incor- Similarly, as intimated hereinbefore, the invention is not limited to the utilization of nickel as the second component. As pointed out in the copending application refered to, any metals which form an acid fluoride, such as iron, nickel andcobalt, or those which form two fluorides, such as antimony, copper, etc., may be incorporated in the bath, as by way of a soluble salt, so as subsequently to be plated out with the tungsten.

It will'be appreciated that within the inventive principles-defined herein wide permissive variations in the composition of a specific bath, in the type and character of the ultimate plate and in the character of the anodes and cathodes (base plates) are' permissible. Thus,'as indicated in Example II, if desirable a so-to-speak bath concentrate maybe made up by admixing predetermined portiqns'of the salts soasito produce a standard dry mix which, upon addition to water, under regulated temperature conditions and It will be appreciated.

after adjustment of thehydrogen ion concentration, may be employed for plating. I

It will also be understood that in accordance with the present invention double dioxyiiuoride salts of the two metals to be plated may separately be prepared, which, upon dissolution in water and adjustment of the acidity, may be employed as the electrolytic bath. Thus, for example, the present method comprehendsthe direct utilization of" such compounds 'as NiFaWOnFz; COFaWOaFa; CuFz.WOzFz as well as mnwom; Nanwom, zxmwom and the -content can The invention also directly comprehends the production as a separate article oi manuiacture a dry composition or a liquid concentrate irom which the electrolytic bath may readily be made up. Similarly it will be appreciated that many oi the ultimate co' tuents oi the bath may be incorporated in the iorm oi an anode. Thus certain oi the bath constituents. as ior example the alkali acid fluoride and the tungstlc acid anhydride, be ius d (with or without the other adiuvants, such as the nickel salts) in combination or association with conductive material such as carbon or tungsten carbide. or tungsten nickel alloy and the like. In making .up such a composite anode a suitable binder may -beernployecl to bond the metallic or other conductive constituent oi the anode.

These and all other similar modifications or ramifications oi the method and oi the ingredicuts, or .their equivalents. oi the bath and the anode are considered to be comprehended within the present disclosure. The present invention is considered to reside broadly'in the concept oi plating a tungsten or similar metal alloy. either oi binary or polynary typ in'which the tun sten be varied over a wide range and in which the tungsten is made available ior electrodeposltion by the-direct utilisation of timgs salts in the manner indicated.

We claim:

1 A process oi coelectroplating wltn metals such as nickel and timgsten which comprises iorming an aqueous bath by adding an oxyiluoride oi tungsten and a soluble salt' oi nickel to water, adjusting the bath to a definite acidity.

and electrolyzing with a metal anode.

2. An-electroplating bath ior electrodepositins tungsten with other metals comprising a solution oi a tungsten-containing compound in aqueous alkali bifiuoride, together with a salt oi a metal chosen irom the group consisting oi iron. nickel. cobalt, antimony and copper.

3- An electroplatlngbath ior coelectrodepoaltins ll mn with other metals comprising a solution oi tungstic acid anhydride in aqueous ammonium bifiuoride, together with. a salt oi a metal chosen irom the group consisting oi iron. nickel, cobalt. antimony and copper.

4. An electroplatin bath ior coelectrodepositinstungstenwithothermetalscomprisingasolutlon oi a tungsten-containing compound. in aqueom alkali bliluoride and an alkali halide. such solution also containing a salt oi a metal chosen irom the iollowing group: iron. nickel. cobalt, antimony and copper.

5. An electroplating bath ior coelectrodepositing tungsten with other metals comprising a solutlon oi tungstic acid anhydride, in aqueous alkali bifiuoride, and an alkali halide such solution also containing a salt oi a metal chosen irom the following group: iron, nickel, cobalt. antimony and copper.

6. An electroplating bath ior coelectrodepositing tungsten and other metals which comprises a solution oi tungsten acid anhydrlde, in aqueous ammonium bifiuoride, and an alkali halide such solution also containing a salt oi a metal chosen from the group consisting oi iron, nickel, cobalt. antimony and copper.

"l. A method oi producing an electroplating bath ior electrodepositing tungsten alloys which comprises. iusing a tungsten-containing compound with an alkali bifiuoride, dissolving the resulting product in water and adding thereto an aqueous solution containing an alkali halide, boric acid, and a salt oi a metal oi the group consisting oi iron, nickel. cobalt. antimony and copper. i

8. An electroplating bath ior electrodepositing tungsten alloys comprising a solution oi tungstlc acid anhydride in aqueous alkali bifiuoride, 110-- gether with a salt oi a metal'chosen irom the group consisting oi iron, nickel. cobalt, and copper.

9. An electroplating bath ior eiectrodepositlng tungsten alloys comprising a solution oi a tungsten=containing compound, in aqueous ammonium bifiuoride and a salt oi a metal chosen irom the group consisting oi iron, nickel, cobalt. antimony and copper.

'10.- A method oi producing tungsten alloys oi variable tungsten content which comprises, reacting a tungsten-containing compound with an alkali bifiuoride, at elevated temperatures, dissolving the resulting product in water, adding to the solution a soluble salt oi a second metal to be alloyed with the tungsten. said metal being chosen irom the group consisting oi iron. nickel, cobalt, antimony and copper. and electrodepositing an alloy oi tungsten and one oi said metals upon a suitable metallic cathode by electrolyzing the bath with a plurality oi anodes. at least one of which contains tungsten and another oi which contains the said second metal to be coplated therewith.

11. A method oi producing an electroplating bath ior electrodepositln'g tun ten alloys comprising fusing a tungsten-containing compound with an alkali bifiuoride, dissolving the resulting product in water and adding thereto a soluble salt oi as metal chosen from the group consisting oi iron, nickel, cobalt, antimony and copper.

. HARRY HOWARD ARMSTRONG.

AR'I'EURBURLEY antimony