US1896606A - Purifying tungsten - Google Patents

Description

@atented Feb. 193$ entree stares entrant orator;

ES FRE DERICK LIAM BATES, 0F CLEVELAND HEIGHTS, OHIO, ASSIGNOB T0 TEE QHIO INSERUIKENT MANUFACTUBIH'G COMPANY, OF CLEVELAND, OHIO, A.

PURIFYING TUNGS'JEEN Ito Drawing.

This invention relates to the production and purification of tungsten, and to electric conducting elements made therefrom, especially those which become highly heated in use such as electrical make-and-break contact points, incandescent filaments, etc. In the production of tungsten articles the customary procedure is first to reduce tungstic oxide by hydrogen with the production or" a granular metallic powder, and next to sin ter the resulting granular substance together into the form of a somewhat porous rod or ingot by the use of a very high tem perature, after which the same is wrought by swaging, drawing, etc., the procedure being substantially the same as was employed in the making of wrought iron in the days when a sufficiently high temperature for the complete fusion of the iron was unattainable. l have discovered, however, that in the reduction of these oxides by hydrogen it is so diliicult as practically to be impossible to obtain a complete elimination of the oxygen, and the remaining oxygen, though only a small portion of that present originally in the oxide, seriously impedes the subsequent manipulation and use of the metal by interfering with the proper welding of the difierout parts together, by rendering the article brittle and non-homogeneous, by tending to produce offsetting or sagging in wires, and pitting in the spark points, and otherwise misbehaving.

l have discovered, however, that it is possible to obtain a complete elimination of the oxygen, with the avoidance of the disadvantages above mentioned, by impregnating the article at the outset with a more volatile metal, provided this metal be one whose combination with oxygen is either unstable or sufficiently volatile to be dissipated by the temperatures employed.

Such a metal is silver; and it is within my invention to mix finely divided silver with the previously reduced granular tungsten, and afterwards to compact and sinter the whole, finally raising the temperature to such a degree as wholly to volatilize the silver which takes with it all traces of oxygen. The resulting bar or ingot shows no trace Application filed November 5, 1928. Serial No. 317,493.

of silver but is more easily worked than when made in the usual manner, is more ductile, and shows less sagging or ofi'setting when made into wire.

Another way of securing the intimate admixture of metals necessary to the performance of this process is to reduce them simultaneously by hydrogen. One way in which this can be done is to mix silver chloride intimately with the tungsten or other oxide, prior to the reduction by hydrogen, since silven chloride is likewise reduced under these conditions. A still better way is to precipitate the silver compound into the tungstic oxide so as to obtainthe most complete incorporation at all stages of the process. For example in the production of tungsten, it is customary to precipitate sodium tungstate solution with dilute hydrochloric acid according to the formula NaQWO, 2HO1=2NaCl +WO B 0 To produce the desired silver salt it is only necessary to add the proper proportion of silver nitrate solution to one of the original solutions, it makes little dillerence which. If for example the silver nitrate solution and sodium tungstate solution be added simultaneously to dilute hydrochloric acid a mix ture of the two precipitates will occur. Another way is to add the silver nitrate solution to the sodium tungstate solution thus producing a brown, cloudy, precipitate of silver oxide which is converted by the hydrochloric acid into silver chloride.

No added precautions are necessary in the reduction or subsequent treatment of the metal, the steps of washing and drying the precipitate, reduction by hydrogen, pressing, sintering, swaging, and drawing being performed in the usual manner. At one temperature in the operation the sintercd bar will be found more or less covered with drops of molten silver driven out of the pores by the heat, but it is necessary for the proper welding of the tungsten particles together that the temperature be raised to such a degree that all of this silver is volatilized. However, the subsequent processes are much facilitated, the ductility and strength of the metal is increased, and the sagging of filaments is largely overcome.

When such tungsten is made into spark points, make-and-break devices, or arcing terminals its tendency to disintegration and pitting is much decreased, and this without the retention of any substances inside the article which increase its electricalresistance or tend to impede the formation of a clean contact.

Another advantage of this treatment is' found in the case of thoriated filaments. It is well known that the usual tungsten filament cannot be worked successfully with a thoria content appreciably above 1.5% although an increase in the thoria content enhances the emissivity. By the employment of silver as above described I have found it possible to increase the thoria content up to as much as 2 or 3% with corresponding improvement in' the properties mentioned, and without increasing the brittleness or hardness suiiiciently to preclude successful working. I effect this by an extension of the same process, namely by adding the desired amount of thorium nitrate solution to the mixture of tungstic oxide and silver chloride prior to the reduction by hydrogen. This reduction serves merely to change the thorium nitrate to oxide and I find that with the presence of silver as herein described I can work the resulting metal into filament form successfully even with a thoria content up to 3% although the silver is wholly volatilized during the sintering operation. This advantage is present whether or not special additional steps are taken to reduce the thoria to metallic form.

In the plain reduction and purification of tungsten for spark point or filament use I generally use an amount of silver equal to about 5% to 10% of the tungsten. There is no apparent advantage in using more, nor disadvantage except the added cost. In making thoriated filaments, however, I have found it desirable to increase the silverin proportion to the amount of thoria contained so as to keep the amount of silver about equal to that of the thoria. It has been suggested and certain observed facts appear to confirm the suggestion that the effect of the silver is in some way to reduce the thoria to metallic form, and certainly the physical condition of the resulting mass is notably altered by its use, its improved grain structure bein compacting the same, sintering at atempera-.

ture sufiiciently highto volatilize all the silver, and afterward swaging and drawing.

In testimony whereof I hereunto affix my signature.

(IHARLES FREDERICK WILLIAM BATES.

visible even to the naked eye, but as to this I offer no theory but state merely the result of actual experience.

Having thus described my invention what I claim is:

1. Process of producing tungsten articles which are free from included tungstic oxide