US1683064A - Electric conductor and process of making same - Google Patents

Description

Patented Sept. 4, 1928. I

a v. cerrcorro, or nnooxmm, NEW 12031:, ,nssmnoii 'ro :nu'nrnmn, ooiv'nnnsna T conromrron, A. oonronerrorf or DELAWARE.

nmwrmc 'connucron. AND rn'ooEss or MAKING s um No name.

This invention relates to improvementf in electric. conductors and process of making same; especially conductors designed to serve as electrodes in oscillating apparatus for communication b radio;

An object of t e invention is to rovide an electric conductor in the shape a filament capable of thermionic emission in vacuum tubes; filament being of novel composition, requiring relatively llttle power to cause it to become operative, and of relatively hi h efiici'ency and great durability.

A er object of the invention is to provide a filament of sucha character that it will remain uniform and homogeneous in its molecular structure under all conditions of use, and in which the liability of the oc-' currence of defective portions with consequent deterioration and danger of burning out, is practically eliminated.

A further obJect of the inventlon is to provide a method by which an electrical conductor or filament of the nature above outlined can be produced in an easy and slmplo manner. i

Other objects and advantages of this 1nvention will be clear from the following description, and novel'features of my 1n vention will be defined in the appended claims; but I do not wish to be limlted to the exact steps of procedure or other details herem set forth, since I may vary the specific process herein described for the sake of example, and to some extent the composition of the electrode or filament itself, without departing from the scope and spirlt of the invention.

A conductor in the form of a filament according to my invention is partlcularly adapted for high power vacuum tubes, but

by no means necessarilylimited to such de-' vices, as I may employ improved filament-s ment, a grid and a plate; the filament being made of some suitable conducting material and coated with a proper metallic oxide, so that it will emit electrons freely without consuming an unduly large quantity of cur- Applioation filed February 97, 1924. Serial No. 695,591.

rent, supplied to the filament to heat the same and raise it to a temperature at which it will glow and become active. In high power tubes when 'a tube having a coated 1 filament is employed in this way, the electric field generated by the anode or will often affect thefilament or catho e in such a way that theoutside coating of the filament will crack and flake oif, with the result that after such deterioration of the oxide coatingis continued for a certain period of time, the filament will become very late thin in one or more places along its length,

and when such thin places have developed to a material extent, current assing through the filament will cause the i rlament to flow more at such points than at others. Hence, the occurrence of so-called brightspots which are nothing more than the parts or sections of the filament whichhavebe'come' thinner than the rest of the filament, because the coating on such parts has been lost.

Under such circumstances, current passing through a filament in this condition, will heat 1t to a hlgher temperature at all of the thin portlons, and when the filament burns out, the burning out will take place at one of the points where the bright spots have been caused to appear.

In my invention, I aim to overcome this drawback by making a filament consisting of an alloy of certam rare metals'such as platinum and iridium, with such substances as barium carbonate (BaCO and strontium carbonate (SrCO or instead of the carbonates the oxides of barium and strontium can be taken.

By my method, the mixture of platinum and iridium is so treated that the filament produced therefrom, instead of being merely covered with a coating, envelope or film of metallio'oxide, is so treated that the barium and strontium, either in the form of metals or as oxides, are incorporated with the platinum and iridium and caused to permeate the entire mass thereof to such an extent as to be absolutely inseparable there a composition consisting of platinum and iridium or the like, and barium and strontium, present either as metals or as oxides in 1 the body of the product.

10" from. In fact, I believe the filament to have I proceed by taking some sponge platinum,

- grinding it into the form of powder, and

of 95% platinum to iridium. This mass can be pressed together to give it the form of a bar or ingot of convenient size for further working. The pressing of the powdered sponge platinum and iridium can be done in.

a small cylinder equipped with suitable means for exerting the necessary amount force upon the mixture so as to cause the articles to move together until. they cohere.

n this state, the p atinum'and iridium are removed from the cylinder for the next step in my process; and, obviously, before com- .pression is effected to produce the ingot, the

articles of sponge platinum and sponge iridium must be intermingled as. much as possible.

The ingot isthen placed in an alundum crucible where it is covered with a mixture of barium carbonate and strontium carbonate or a mixtureof the oxides of each of these two substances, .to such an extent that the ingot is completely buried therein. The action of heat is then resorted to and for this purpose I may employ either an oxyhydrogen flame, playing directly upon the gontents of the crucible, or I may place the crucible in a carbon furnace. -Then as the platinum and iridium melt, they will take up some of the ingredients of the mixture of barium and strontium compounds. When this stage of the process has proceeded far enough, the mass of 'mixed platinum and iridium is removed from the remainder of the mixture of the barium and strontium compounds, and upon. inspection willbe found to have a heavy coating of the barium and strontium compounds upon its outside surface. This coating will not be uniform in thickness or hardness and if the product was drawn to'wire in this condition, it would be of very inferior quality.

Hence. in order to cause the barium and .strontium in whatever form they occur in the mixture to be evenly distributed through 1 the mixed mass of platinum and iridium, I

take the ingot of platinum and iridium after heating and clean it thoroughly by scraping or otherwise, to remove as much of the coating as possible. The metal bar is then placed in a clean alundum crucible and remelted, being left to stand in its molten state for a number of minutes. To cause remelting, I can emplo an oxyhydrogen flame as before and the orce of this flame will so agitate the molten metal that currents will be set up in it, so that the barium and strontium will be thoroughly mixed with the iridium and platinum and pervade the mass thereof, the barium and strontium being distributed uniformly throughout the molten metal and when the metal is allowed to cool and harden it will be quite homogeneous in structure and composition. The mass of material which I have so selected and treated is then a novel and very useful product that can be drawn downto any desired size by the means ordinarily employed to transform platinum rods into wire. This operation can be performed by drawing through a perforated die; The'conductor is at first quite brittle. It therefore. has to be annealed of after having been pulled throu h every fivedies, as it is successively rawn down through intermediate stages to wire of the necessary thinness, for the filament.

.'In its final condition, when the filament {has been reduced to the size desired, it will be found tohave the same capacity for emission as that of the ordinary coated. filament,

but is much. more stable and more durable and can be operated with about half the current which a coated filament requires. The

filament so produced is of uniform composition throug out, as distinguished from fila- 'ments having a bod of one substance and a coatingthereon 0 another or others, and my filament, because it has no coating, can'- not deteriorate and become thin at any point through the loss or breaking off of the coating, and consequently, bright spots never appearand the occurrence of thin sections giving rise to the danger of burning out thereat is made impossible.

In the course of the method by which the filament is .produced, the utilization of heat when barium and strontium in the form of carbonates are employed to cover the platinum-iridium ingot 1s really the same in effect as the use of barium and strontium oxides; because heat causes the carbonates to break up very readily into the oxides, and the stage at WhlCh the strontium and barium are introduced and the subsequent stages cause the'formation of a product consisting principally of the platinumv and iridium,

with the barium andstrontium either as metals in the free state or as oxides-of these metals. In any case, the filament when finished is of'uniform molecular structure and of the same hardness and thickness throug out its entire length, so as to afford all of the advantages and which my invention aims to secure.-

Having described my invention 'what I believe to be new and desire to, secure and protect by Letters Patent of the UnitedStates '1s:

possess all of the qualities '1. A conductor comprising" a mixture of finely divided and intermingled platinum and iridium, and conta' barmm and strontium evenl distribu mass of thecon uctorf 2. The process of makin .a. which consists in intermingfiing conductor finely dithrough the mixture of finely divided platinum and iridium, the mixture containing compounds of barium and strontium distrlbuted through.- out its mass.

4. A conductive substance comprising a. mixture of finely divided platinum and iridium, the proportion ofplatinum being in v excess of that of iridium, themixture containing compounds of barium and strontium 20 distributed throughout its mass.

In testimony whereof I ailix my signature.

JAMES v. CAPIQOTTO.