US3245891A - Method for electrolytically shaping group 5b metals - Google Patents

Description

United States Patent 3,245,891 METHOD FOR ELECTROLYTICALLY SHAPING GROUP 53 METALS Simon P. Gary, Villa Park, Ill., assignor to Anocut Engineering Company, Chicago, 11]., a corporation of Illinois N0 Drawing. Filed Mar. 23, 1962, Ser. No. 182,118 8 Claims. (Cl. 204-143) This invention relates to an electrolyte for electrolytic shaping of a metallic workpiece.

The art of electrolytic shaping has been well developed for a variety of metals and alloys, but niobium and tantalum and alloys containing substantial proportions of these metals have been substantially impervious to such shaping treatment.

The process, as commonly practiced, consists of placing an electrode near a metallic workpiece and flowing an electrolytic solution rapidly through the gap between. The gap may range from .0002" to .02". The pressure driving the electrolyte through the gap will range from 30 to 300 pounds per square inch. The electrode is connected to constitute the cathode and the workpiece, the anode. An electrolyzing current is employed having a density of 500 to 8000 amperes per square inch at to 24 volts. The penetration rate is roughly .10 a minute per 1000 amperes per square inch current density.

The advantages of electrolytic shaping are likewise well known. Metal may be removed at a high rate of speed and leave a smooth and polished surface. The rapidity of metal removal is not dependent on the hardness of the material but rather on its chemical activity. It can form exceedingly complex shapes inconceivable under conventional machining methods. The application of this method, however, to the metals of group 5B of the periodic table has not hitherto been successful.

This inventon has as a major object a method for electrolytically shaping these metals and alloys containing them in suflicient quantity to be resistive to conventional electrolytic treatment, and the provision of an electrolyte whereby such shaping becomes possible.

The invention further includes as a major object the provision of an electrolyte suitable for such shaping which is relatively inexpensive.

The invention resides in the provision of an electrolytic material which will form bromide ions at the work piece anode. Material is removed in the form of niobium or tantalum bromides and is carried away by the stream of electrolyte from the working area.

A suggested source of the bromide ions is sodium bromide or potassium bromide, depending on which is the less expensive although calcium bromide or ammonium bromide will serve as well. The requirements of the material contributing the bromide ion are that it be highly soluble in water, that its cost be low, that it not hydrolize, and that the positive ion not plate out in the course of the shaping. Any ion more positive than uranium on the electromotive scale is suitable. The normal operating temperature of the electrolyte in the shaping of these materials is in the vicinity of 100 to 120 F. The temperature should be as high as possible consonant with an absence of cavitation or bubble production in the vicinity of the electric flow. (Some bubble formation is inevitable in that hydrogen is evolved from the anodic workpiece, but the rate of electrolyte flow should be sufiicient to sweep such bubbles away before they interefere significantly with the process.) This range of temperatures, however, successfully avoids such formation. On the other hand, this temperature is naturally maintained by the resistance heating thereof from the high current flow and, to a minor degree, by the frictional heating of the electrolyte in its passage through the working area.

The concentration of the bromide may vary widely. The concentration, of course, will affect both the quantity of bromide ions formed and the conductivity of the solution. A saturated solution of sodium bromide will permit an electrode penetration of the workpiece of about .05" per minute at a current density of 1000 amperes per square inch. This rate will remain substantially unchanged down to a concentration of about two ounces of sodium bromide per gallon. The rate will then dwindle progressively more rapidly as the concentration diminishes to a point where, with about one-tenth of an ounce of sodium bromide per gallon, the rate of removal is negligible.

A problem to be considered in the electrolytic shaping of these metals resides in the relatively high cost of sodium bromide as compared with conventionally employed electrolytic salts, notably sodium chloride. The bromides of the group 5B metals are unstable in aqueous solution and decompose into the hydroxides (or equivalent acids), but the decomposition takes place relatively slowly. Exhaustion of the free bromide ion, or at least a material reduction thereof, in the course of the chemical combination incident to the shaping must be considered. A further consequence of using a low concentration of sodium bromide is simply that desirable current densities under desirable voltages for this sort of operation cannot be obtained.

To meet these difficulties, it is proposed that a substantial proportion of sodium chloride or similar salt be incorporated in the electrolytic solution along with the bromide salt. The sodium chloride provides many advantages. It permits the use of a relatively low concentration of the more expensive bromide and at the same time keeps the conductivity of the electrolyte high. It provide a solution having high conductivity which is inexpensive enough either to avoid the necessity of recirculating the electrolyte or at least permit a great volume of electrolyte with reference to the flow rate of the electrolyte through the reaction zone so as to provide for a substantial period of time in which the metallic bromides formed may decompose and precipitate out to reconstitute the sodium bromide. The avoidance of recirculation generally is to be desired, or at least recirculation within a short period of time, not only because of the temporary exhaustion of the bromide ions by the reaction but also because of the possibility of plating out the group 5B metals on parts of the workpiece away from the reaction zone.

Although the invention is operative over a wide range of bromide concentration with or without an admixture of sodium chloride, the three following specific formulations will illustrate the nature of the electrolyte.

Example A Water gal 1 Sodium bromide (.07 N) oz 1 Example A is illustrative of an electrolyte using sodium bromide only. The sodium bromide may range from one quarter of an ounce to four ounces per gallon of water (.018 to .29 N). There is no advantage in going to a higher proportion of sodium bromide than four ounces and the effectiveness of the electrolyte falls off very fast below a quarter of an ounce per gallon. The rate of removal at a quarter of an ounce per gallon is slower than with the stated one ounce, on the order of one-half to three quarters of the rate, but may still be suitable for some purposes. At a quarter ounce, the concentration is near an exhaustible level of bromide ions.

Example B Water gal 1 Sodium bromide (.007 N) oz Sodium chloride oz 2 Example B illustrates the use of minimum quantities of sodium bromide together with a proportion of sodium chloride to provide sufiicient conductivity for the electrolytic shaping to take place. The proportions in Example B are minimal. With a reduction of either of the salts, the effectiveness of the solution falls off very rapidly. Again, the bromide concentration lies just above the point where bromide ion exhaustion is likely to appear. The penetration rate in Example B is about one-quarter to one-third of that possible with Example C.

Example C Water gal 1 Sodium bromide (.14 N) oz 2 Sodium chloride lb 1 simply more conductive ions and from the aspect that a sodium chloride solution is a better conductor than a Y sodium bromide solution. Example C recites a minimumcost, maximum-effectiveness proportion. In this proportion, a penetration rate has been obtained of .05" per minute at 1000 amperes per square inch or .10" at 2000 amperes per square inch. A reduction of sodium bromide will slow the rate of penetration. A greater amount will gain nothing other than added cost. The sodium chloride contributes the necessary conductivity for maximum penetration.

It will be appreciated from the foregoing description that an electrolyte has been devised which makes possible the electrolytic shaping of the group 53 elements of the periodic table, and more particularly niobium and tantalum, which is inexpensive and effective. It will be appreciated that any of a number of bromide salts may be employed, such as potassium bromide, calcium bromide or ammonium bromide. The requirements are that the salt be soluble so as to contribute enough bromide ions, that the metal ion of the salt not plate out and that it be cheap.

The sodium chloride is present, as stated, solely for purposes of conductivity. Any salt contributing like conductivity and free from side effects or reactions under the circumstances of the shaping will serve as well. The one distinguishing characteristic of sodium chloride is its cost.

Of the group 5B elements, niobium and tantalum have been discussed primarily because they are playing an increasing part, in relatively pure form, in high temperature technology. The third member of the group, vanadium,

is likewise relatively inert to electrolytic attack with a chloride electrolyte, and the presence of the bromide ion makes practicable electrolytic shaping of it to the same degree as the other two elements.

Although the concentration of the bromide has been stated generally in terms of ounces per gallon, obviously the significant factor is the ion concentration. The electrolyte, therefore, is defined in some of the claims herein in terms of a fraction of normal solution.

This invention, therefore, should be regarded as being limited only as set forth in the following claims.

I claim:

1. A method for the electrolytic shaping of a workpiece of the group 5B elements of the periodic table and their base alloys which comprises flowing an essentially purely aqueous electrolyte between an electrode and such workpiece which are in close proximity to each other,-.the electrolyte having a concentration of at least .007 normal of an ionizing, non-hydrolyzing bromide of a positive ion above uranium on the electromotive scale, and passing an electrolyzing high density current between the electrode and the workpiece in a sense to make the workpiece anodic.

2. The method as set forth in claim 1 wherein the bromide salt is taken from the group consisting of sodium, potassium, and ammonium bromides.

3. The method as set forth in claim 1 wherein the electrolyte is at least .018 normal.

4. The method as set forth in claim 1 wherein there is an ionizing salt in the electrolyte which is stable under the condition of the electrolysis and in the presence of the bromide salt, in sufficient concentration to impart to the electrolyte a conductivity to permit a current density of about 1000 amperes per square inch at about six volts between the electrode and the workpiece.

5. The method as set forth in claim 1 wherein the electrolyte is from .018 to .3 normal.

6. The method as set forth in claim 1 wherein the electrolyte contains from one-fourth to four ounces sodium bromide per gallon of water.

7. The method as set forth in claim 1 wherein the electrolyte includes, per gallon of water, from one-tenth to two ounces of a bromide taken from the group consisting of sodium, potassium, and ammonium bromides and from two ounces to one pound of a salt having generally the ionizing characteristics and the stability under the electrolysisand in the presence of the bromide salt of sodium chloride.

8. The method as set forth in claim 1 wherein the bromide salt is calcium bromide.

References Cited by the Examiner UNITED STATES PATENTS 2,742,416 4/1956 Jenny 204-141 2,863,811 12/1958 Ruscetta 204-141 2,920,026 1/1960 Kistler 204 143 3,130,138 4/1964 Faustetal 204 143 FOREIGN PATENTS 1,241,349 8/1960 France.

JOHN H. MACK, Primary Examiner.

JOSEPH REBOLD, Examiner.

Claims (1)

1. A METHOD FOR THE ELECTROLYTIC SHAPING OF A WORKPIECE OF THE GROUP 5B ELEMENTS OF THE PERIODIC TABLE AND THEIR BASE ALLOYS WHICH COMPRISES FLOWING AN ESSENTIALLY PURELY AQUEOUS ELECTROLYTE BETWEEN AN ELECTRODE AND SUCH WORKPIECE WHICH ARE IN CLOSE PROXIMITY TO EACH OTHER, THE ELECTROLYTE HAVING A CONCENTRATION OF AT LEAST .007 NORMAL OF AN IONIZING, NON-HYDROLYZING BROMIDE OF A POSITIVE ION ABOVE URANIUM ON THE ELECTROMOTIVE SCALE, AND PASSING AN ELECTROLYZING HIGH DENSITY CURRENT BETWEEN THE ELECTRODE AND THE WORKPIECE IN A SENSE TO MAKE THE WORKPIECE ANODIC.