US2077873A - Tungsten metal and process for making the same - Google Patents

Description

Patented Apr. 20, 1937 PATENT OFFICE TUNGSTEN METAL AND PROCESS FOR MAKING THE SAME- Chester 11. Braselton, New York, N. Y., assignor to Sirian Wire and Contact Company, Newark, N. J., a corporation of Delaware No Drawing.

32 Claims.

This invention relates to a process of metal -manufacture and products resulting therefrom. More particularly, the invention pertains to treatment of tungsten and allied refractory metals so as to make them more suitable for use as filaments in lamps or other radiating devices.

Refractory metals such as tungsten when employed as filaments for electric lamps are subject to an internal alteration which brings about a deformation called sagging and which is detrimental to lamp efliciency. It has been proposed to remedy this defect by introduction of foreign substances which modify or control the crystal growth of the filament metal. Certain disadvantages result from this treatment, such as deposition of the foreign substance on the inner surface of the envelope.

I have discovered that resistance to internal alteration of the metal may be developed by introducing into the metal, particles of the same metal but derived from different sources so that in the completedmetal there is a structure composed or large and small particles of the same metal, all of the particles being intimately bound together. In addition I have found that if in the process of forming the final metal the particles are amalgamated by a chemically deposited bond of the same metal a marked improvement in resistance to deformation of the final structure results.

It is an object, therefore, of my inventionto provide a process for making metal for filaments and other uses which will not require introduction of foreign particles as permanent constituents of the metal; which introduces new methods of developing resistance against change of shape and structure of the metal when heated; which permits formation of particles of different size of the some metal without subjecting the particles 40 of the metal to diiferent heat treatment and which establishes an effective bond between the various particles of the metal.

Further objects of the invention are to provide 7 a refractory lamp filament, the desirable properties of which are not impaired by the manufacturing operation or by subsequent use, and to improve in general the efliciency and life 0 tungsten lamp filaments.

Still other objects are to provide a form of metal which is substantially independent of the crystalline structure for its physical permanency of shape; to provide a refractory filamentary metal which while homogeneous; isformed of particles of different size; and to provide a filament of tungsten, molybdenum or other refrac- Application December 29, 1934, Serial N0. 759,693

tory metal which is not subject to substantial impairment in physical or electrical properties when operated at-high temperature.

Further objects will be apparent on consideration of the following description of the process and of the product produced thereby.

In practicing my invention, which I will describe with reference to the metal tungsten, I employ as a primary source of this metal, tungsten trioxide (W03),- which in turn may be derived 10 from the hydrated tungstic oxide having a formula approximately H2WO4. As a secondary source of tungsten I may utilize any of the well known alkaline tungstates, such as the tungstates of potassium, lithium, sodium, rubidium and caesium. These tungstates may be in any of the various forms in which they occur, such as the normal or.ortho-tungstates having the formula generally accepted as M2WO4, the meta-tungstates having the formula M2W4Ol3'alld the para- 20 tungstates having the formula either M1oW12O41 or M6W7O24 where M stands for any alkaline metal.

For the purpose of illustrating the various steps of the process tungstic acid and potassium tungstate will be utilized in the description. These 25 compounds in chemically pure state are mixed together, the tungstic acid being added to a solution of the tungstate in distilled water and the mixture then heated to drive off the excess of water. As an example, I may use one kilogram 30 of tungstic acid and sixty-one and one-half grams of pure potassium tungstate or approximately six percent of the tungstate by'weight of the mix- 'ture.

This mixture of the tungstic acid and potassium 5 tungstate is then placed in a crucible and heated to a state of complete dehydration, the resulting product consisting of tungsten trioxide (W03) and postassium tungstate being ground and bolted through a 200 mesh per inch screen 40 I forming tungsten and water and the tungstate forming tungsten, water, and potassium hydrox- 50 ide (KOH).

The reduced product, which is in powdery form, is now mixed with other similarly made lots having somewhat difierent densities to obtain'a H mixture of desired density and then pressed hy- 5 draulically to form an ingot having a size approximately x x 16". The ingot is first baked in hydrogen at about 800 C. to permit handling and then suspended in a conduction 5 type electric furnace where current is passed through the ingot for a period of about twentynine minutes in hydrogen flowing twenty cubic feet per hour. By this means the temperature is raisedto about 90% of the fusion temperature fortungsten, at which point the temperature is held about ten minutes. and then permitted to a I drop to room temperature. In this operation the potassium hydrornde is melted and volatilized. The molten hydroxide being a ready solvent for tungsten and tungsten oxide carries tungsten in solution. This tungsten is derived from the tungsten oxide carriedv over from the initial lot or formed by oxidation of the pure tungsten between the heating steps. It is also derived from direct action on the tungsten particles. Accordingly when volatilization occurs the tungsten is deposited on the clean surface of the tungsten particles thus permitting a close bond or weld between the particles and a more solid mass. The 5 metal is now ready for mechanical treatment, and where filamentary wire is desired the ingot is swaged and drawn-to the desired diameter.

The reduction heat in which metallic tungsten is produced involves two tungsten compounds but these compounds do not reduce at the same temperatures, the oxide reducing before the tungstate. Hence. it is apparent that the microscopic structure of the tungsten particles obtained from the tungsten. trioxide will differ from that of the tungsten particles derived from the tungstate. This difference is evidenced in difierent crystal size, the smaller crystals apparently filling the interstices between the larger crystals so that there is built up a solid and 40 homogeneousmetal mass of approximately uniform density. I V The second or volatilization heat in the conduction furnace begins with all of the tungsten particles encased or surrounded by masses of potassium hydroxide. The action of the hydroxide apparently is very similar to a flux or cleaning agent on the one hand, and of a solvent on the other hand. In the fusedform the hydroxide dissolves the oxide and the tungsten itself on the surface ofthe particles etching and.

roughening the surface. Subsequently the tungsten is deposited from the volatilizing hydroxide and is fused into and between the roughened surfaces thus forming a more rigid mass than would otherwise be possible and definitely reducing deformation at high temperatures.

a duce ametal structure which at high temperatures deformation and hence maintains its original and normal physical and electrical properties. In this way the electrical efliciency of such a metalfor lamp filaments is improved and longer life is secured.

The cleansing power of the alkaline hydroxide on the particles of metal maybe utilized in a modified process which will now be described.

Instead of employing tungstic acid as the oxide constituent, tungsten metal may be used in par- 0 ticle form in conjunction with the alkaline tung state. In this modified process the tungstate such as potassium tungstate is dissolved in warm water and to this solution finely divided metallic tungsten or other refractory metal is added. The mixture is then stirred while the temperature is in filamentary form strongly resists- .2,o77,e7s

slowly raised bringing about evaporation of the water. This material is then placed in a tube furnace in a flow of hydrogen gas and heated for three or four hours until the tungstate breaks down to free tungsten and potassium hydroxide.

' This intermediate product is then removed,

pressed into an ingot, baked at a temperature in excess of 800 C. to give the material rigidity for handling, and then heated as described in' the preferred process to approximately of the fusion point of tungsten, thus volatiliz'ing the hydroxide and sintering and amalgamating the crystals of metal. A typical batch might include materials in the relation of 61 grams of .potassium para-tungstate to 793 grams'of tungsten.

A modification of the process just mentioned would be to use only the tungstate or an alkaline compound of another refractory metal and reduce the same in a hydrogen flow, continuing the heating process until the hydroxide component is removed leaving pure tungsten.

The same procedure may be utilized with a ,mixture of a. solution'of a hydroxide such as potassium hydroxide and finely divided tungsten or other refractory metal, the water of the solution being evaporated and the material formed into an ingot which is treated as previously described by first heating to a temperature in excess of 800 C; to obtain the ingot, and then placing the ingot in an electric conduction furnace wherein the ingot is raised to a temperature in excess.

of 2000 C. approaching 90% of the fusion point of tungsten. This final heat treatment volatilizes the hydroxide and sinters the tungsten particles to form a highly coherent body. These materials may be combined directly by a mechanical tumbling mill operation but the particles of metal are not as thoroughly coated by the hydroxide as where a solution is employed.

In either of the suggested modifications of the process above described instead of tungsten metal as one of the component elements other refractory metals such as molybdenum. titanium,

tantalum, zirconium or chromium may be used with the tungstate or hydroxide. In the case of the tungstate and a metal other than tungsten the result will be an alloy of the tungsten.

It'is emphasized that the strength and utility of filaments made according to any of the above processes arises from the apparent cleansing and solvent action of the hydroxide not only on for,- eign particles such as unreduced particles tungsten trioxide but also on minute particles of tungsten, thereby assuring a clean contact and intimate welding between particles. Further,

theuse only of compounds which by heat treat- The result of this process therefore is to proment ar either voiatilzed or reduced to metallic tungsten eliminates the difficulties arising from the presence oi. foreign matter'such as the silicates.

from 12 to 4'1, and indicating apparently that the absolute size is not the only determining factor in producing stability.

It is noteworthy also that the completed product consists entirely of tungsten. There are no' other foreign substances present which may gradually modify the metal characteristics during use. The alkaline hydroxide is volatilized at temperatures relatively low with reference to the Moreover, the intergranular crystal-- 1 line structure arising from tungsten crystals of group such as molybdenum may be used. Also,

not only may any of the various alkaline metal tungstates mentioned be used but also mixtures of these tungstates with each other. Further, other refractory metals such as, molybdenum, chromium, titanium, zirconium or tantalum may be produced from a mixture of the metalor oxide of the metal with a corresponding alkaline metal compound, for example, molybdenum or molybdenum oxide with an alkaline molybdate. In addition, while the specific values givenv are preferred, variations may be used. For example, the temperature of heat applied tothe metal in the final treatment is given as about 90% of the fusion point-of tungsten, but the range may vary according to the determination used. It may be preferable, therefore, to define this temperature as a temperature-in excess of 2000" C.

The alkaline metal compound left after the reduction in hydrogen of the tungstic oxide compound and the tungstate is probably either the oxide or the hydroxide which then subsequently is volatilized at a temperature up to above'2000 C., a portion of the alkali metal or hydroxide possibly being removed at temperatures below 2000" C. at least in part.

While I have described what now appears to be a preferred method of practicing my invention, setting down specified limits and values, it

should be understood however that these limits and values are merely illustrative as variations will occur dependent upon the purity of the material, time allowed for process, rate of flow or movement and other variables. I do not wish my invention therefore to be restricted only as required by the scope of the claims hereto appended.

What I claim is:

1. The process of obtaining tungsten metal which comprises reducing in hydrogen a mixture of dehydrated tungstic acid and alkali metal tungstate to tungsten and another alkaline compound, forming the resultant product into an ingot, substantially completely volatilizing in hydrogen the alkaline compound of theingot, and mechanically working the ingot to size.

2. The process of obtaining tungsten metal which comprises reducing in hydrogen by two successive heating steps a mixture of dehydrated tungstic acid and an alkali metal tungstate to homogeneous metallic tungsten, the tungstate being reduced to'a metal and an alkali metal oxide compound in the first heating step and then substantially completely volatilizing the alkali metal oxide compound.

3. The process of obtaining ductile tungsten metal in the form of aningot capable of producing a drawn tungsten filament with non-offsetting and non-sagging properties, said ingot consisting of large and small particles of the metal cemented together by thin layers of a chemical deposit of the metal which comprises reducing in hydrogen a dehydrated powdered mixtureof tungsten trioxide and an alkali metal tungstate, compacting the reduced powder to form an ingot, baking the ingot in hydrogen and substantially completely volatilizing the resultant alkaline compound.

4. The process of obtaining ductile tungsten metal in the form of an ingot capable of pro-.-

. ducing a drawn tungsten filament with non-oftsetting and non-sagging properties, said ingot consisting of large and small particles of the metal cemented together by thin layers of a chemical deposit of the metal which comprises reducing in hydrogen dehydrated powdered tungsten trioxide and potassium tungstate, compactmetal in the form of an ingot capable of producing a drawn tungsten filament-with non-oifsetting and non-sagging properties, said ingot consisting of large and small particles'of the metal cemented together by thin layers of a chemical deposit of the metal which comprises reducing in hydrogen dehydrated powdered tungsten trioxide and sodium tungstate, compacting the reduced powder to form an ingot, baking the ingot in hydrogen and subsequently substantially completely volatilizing in hydrogen the sodium compound formed from the reduction step.

6. The process of preparing ductile tungsten metal in the form of an ingot capable of producing a drawn tungsten filament with non-offsetting and non-sagging properties, said ingot consisting of 'large and small particles of the metal cemented together "by. thin layers of a chemical deposit of the metal which comprises reducing in hydrogen dehydrated powdered tungsten trioxide and caesium tungstate, compacting the reduced powder to form an ingot, baking the ingot in hydrogen and subsequently substantially completely volatilizing in hydrogen the caesium compound formed from the reduction step.

7. The process of preparing ductile tungsten metal in the form of an ingot capable of producing a drawn tungsten filament with non-offsetting and non-sagging properties, said ingot consisting of large and small particles of the metal cemented together by thin layers of a chemical deposit of the metal which comprises reducing in hydrogen a dehydrated powdered mixture of purified tungsten oxide and an alkali metal tungstate in predetermined quantities compacting the reduced powder to form an ingot, baking the ingot in hydrogen and finally elevating the temperature'after said reduction to a degree where the alkali. metal oxide will substantially completely vaporize, but below the fusion point of tungsten.

8. The process of preparing ductile tungsten metal in the form of an ingot capable of producing a. drawn tungsten filament with non-oifsetting and non-sagging properties, said ingot consisting of large and small particles of the 'metal cemented together by thin layers of a which comprises mixing with tungstic oxide, tungstates of one or more alkaline metals, reducing the oxide and tungstates, forming the reduced substances in compact form, and subsequently heating the compacted product to temper-atures below the melting point of tungsten and above 2000 C.

10. The process of producing tungsten metal which comprises mixing tungstic oxide and an alkali metal tungstate, reducing the oxide and tungstate, heating the reduced product in successive stages to a temperature in the neighborhood of 90% of the fusion temperature of tungsten, maintaining said temperature for a period of approximately ten minutes, and subsequently working the metal to form.

11. The process of producing tungsten metal which comprises mixing tungstic oxide with an alkali tungstate, reducing the mixture by applying heat in fixed increments over a period of approximately twelve hours in a flow of hydrogen gas, subsequently pressing the reduced product to ingot form, substantially completely volatilizing substances foreign to the tungsten in a hydrogen atmosphere, and finally working the metal to the form desired.

12. A pure tungsten metal consisting of tungsten particles of considerably difierent sizes, and the particles of said tungsten being scoured by complete vaporization of alkali metal oxides in combination therewith up to an elevated temperature above 2000 C. and below the fusion point of tungsten, said tungsten in filamentary form having non-offsetting and non-sagging characteristics, said tungsten consisting of the hydrogen-reduction products of tungsten oxide and an alkali metal tungstate.

13. Pure tungsten metal, the particles of which are of considerably different sizes and intermixed to obtain a uniform metal density, and the particles of said tungsten being scoured by complete vaporization of alkali metal oxides in combination therewith up to an elevated temperature above 2000 C. and below the fusion point of tungsten,

said tungsten in filamentary form having nonoifsetting and non-sagging characteristics, said tungsten consisting of the hydrogen-reduction products of tungsten oxide and an alkali metal tungstate.

14. Pure metallic tungsten, the particles of which are of considerably different sizes and de-- rived from plural sources having a greater stability with greater density when in filamentary.

form than tungsten derived from a -singlesource,

and the particles of said tungsten being scoured by complete vaporization of alkali metal oxides in combination therewith up to an elevated temperature above 2000 C. and below the fusion point of tungsten, said tungsten in filamentary 80 form having non-ofisetting and non-sagging characteristics, said tungsten consisting of the hydrogen-reduction products of tungsten oxide and an alkali metal tungstate.

15. A pure non-sagging, non-offsetting tung- 5 sten filament having particles of considerably different sizes, said formations having been produced by the reduction of a mixture of tungsten oxide and an alkali metal tungstate in hydrogen with subsequent complete vaporization of the al- 70 kali metal oxide up to a temperature above 16. The process of producing tungsten metal which comprises mixing tungstic acid with less than ten percent by weight of normal potassium u tungstate, dehydrating the mixture, subsequently reducing the mixture in an atmosphere of hydrogen, substantially completely volatilizing the foreign ingredients, and working the metal to size.

17. The process of producing tungsten metal which comprises mixing tungstic acid with about three percent by weight of normal potassium tungstate, dehydrating the mixture, subsequently drated mixture of tungstic acid and an alkali tungstate in hydrogen, to form a metallic powder, compacting said powder to an ingot, baking the ingot in hydrogen, subsequently heating the resultant tungsten and alkaline compound until the alkali metal oxide compound is completely volatilized, and mechanically working the resultant metal to the form desired.

19. The process of preparing tungsten metal which comprises mixing together tungstic acid and an alkaline tungstate solution, heating the mixture until the same is dehydrated forming tungsten trioxide (W03) and the alkaline tungstate, reducing the mixed oxide and tungstate to form a mixture of tungsten and alkaline hydroxide, forming the mixed oxide and tungstate into an ingot under pressure, baking the slug to harden the same, substantially completely volatilizing the. alkaline hydroxide in the slug, and finally working the resultant metal to size.

20. The process of preparing tungsten metal which comprises mixingv together a hydrated tungstic acid having the approximate formula H2WO4 and potassium tungstate K2WO4, dehydrating said mixture by heat, reducing said dehydrated mixture in hydrogen to tungsten and potassium hydroxide, substantially completely volatilizing the hydroxide by heating, and working the resultant metal.

21. The process of preparing tungsten metal which comprises reducing a mixture of tungsten trioxide and potassium tungstate to obtain tungsten and potassium hydroxide, forming the mixture into ingot form by pressure, heating the ingot to completely volatilize the hydroxide, and working the metal to the desired form.

22. The process of preparing tungsten metal which comprises reducing a tungsten oxide associated with an alkaline tungstate to a product containing tungsten metal and an alkaline hydroxide, forming an ingot of the resultant product, substantially completely volatilizing the hydroxide within the slug, and working the ingot to the desired form.

23. A pure tungsten metal consisting of reduction products of tungstic oxide and an alkali metal tungstate and formed of tungsten particles of considerably diiferent sizes welded by chemically deposited tungsten, said tungsten being deposited from a solution in an alkali metal oxide which has been completely vaporized at a temperature up to 2000 C., said pure tungsten in filamentary form being non-offsetting and nonsagging.

24. A pure tungsten metal consisting of reduction products of tungstic oxide and an alkali metal tungstate and formed of particles of tungsten of considerably different sizes bonded by chemically deposited tungsten, said tungsten besagging.

25. A process of preparing tungsten metal, which comprises providing a compacted mass of finely divided tungsten, the particles of which tungsten are coated with a volatile alkaline metal Y compound, and then heating the compacted mass in a reducing environmentto volatilize the alkaline compound at a temperature up to above about 2000 C. and below the melting point of tungsten,

26. A process of preparing metal tungsten, which comprises mixing a tungsten oxide with an alkaline metal compound of a tungsten oxide, reducing the mixture to metallic tungsten and an alkaline metal oxide, and then substantially completely volatilizing oil? the alkaline metal oxide up to a relatively hightemperature above 2000 C.

and below the melting point of tungsten.

, 27. A process of preparing tungsten, which comprises adding about 1000 parts of tungstic acid to a solution of about 60 parts of an alkali metal tungstate in water, dehydrating the mixture and then grinding the mixture to about 200 mesh, reducing the mixture in' a hydrogen atmosphere to tungsten and'the alkali metal,

oxide, pressing the reduced mixture to ingot form, baking theingot in hydrogen to about 800 C. and thensubstantially completely volatilizing away the alkali metal hydroxide up to a temperature above about 2000C. and belowthe melting point of tungsten.

28. A process of preparing metallic tungsten, molybdenum, titanium, tantalum, zirconium and chromium, which comprises mixing an oxide of one of said metals with an alkali metal salt of 40 said oxide in the presence of water, removing the 45 in hydrogen at about 800 water and grinding the dehydrated mass, reducingthe dehydrated mass to the metal and an alkali metal oxygen compound, pressing the reduced mixture .to ingot form, baking the ingot 0., and then substantially completely volatilizing away the alkali metal oxygen compound in a hydrogen atmosphere up to above about 2000 (Land below the melting .point of tungsten.

selected from the group consisting of tungsten, molybdenum, titanium, tantalum, zirconium and chromium, which comprises mixing an oxide of the metal with an alkaline metal compound containing the refractory metal, reducing the compound to obtain the metal and an alkali metal oxide compound, compacting the reduced mixture to form an ingot, and finally heating the metal,

and oxide compoundingot at a temperature in excess of the volatilization point of the oxide compound. j

30. r A process of producing a tungsten filament for electric lamps with non-sagging characteristics which comprises providing a compacted mixture of metallic tungsten and an alkali metal oxide compound which has been produced by the hydrogen reduction of tungsten oxide and an alkali metal tungstate, and completely vaporizing ed the alkali metal oxide compound up to a temperature above 2000 and below the melting point of tungsten and in a reducing atmosphere.

31. A pure molybdenum metal consisting of molybdenum particles of considerably difierent sizes, and the particles of said molybdenum being scoured by complete vaporization of alkali metal oxides in combination therewith up to an elevated temperature above 2000 C. and below the fusion point of molybdenum, said molybdenum in filamentary form having non-ofisetting and non-sagging characteristics, said molybdenum consisting of the hydrogen-reduction products of molybdenum oxide and an alkali metal molybdate.

32. A process of producing a molybdenum filament for-electric lamps with non-sagging char- 29. The process of treatingrefractory metal,-

acte'ristics which comprises providing a com- C ESTER H. BRASELTONi