US2078182A - Tungsten manufacture - Google Patents

Description

Patented Apr. 20, 1937 UNITED STATES aware: I TUNGSTEN MANUFACTURE Albert E. MacFarland, Millburn, N. J.,-assignor to Sirian Wire and Contact Company, Newark, N. 1., a corporation of Delaware N. Drawing. Application August 9, 1935, Serial 29 Claims.

This invention relates to refractory metal manufacture.' More specifically, the invention pertains to a refractory metal such as tungsten in coiled filamentary form and a process for making the same. The invention has particular application to electric lamps. 1

In the use of refractory metals such as tungsten in filamentary form for electric lamps difficulties have arisen from the fact that at the high temperatures at which these lamps are operated the filaments are subjected to structural changes which cause offsetting and "sagging. By offsetting is meant a faulting or bodilyshifting of the material of the filament,-causing a break in the filament. This is believed to be due to the gradual crystallization of the metal along a plane which so weakens the strength of the material as to permit lateral or side slipping or shifting between the grain surfaces and final separation of the material. By the term sagging" is meant the gradual displacement of the material causing a lengthening of the filament between its supports and consequent deformation of the coil. This is disadvantageous,

as the sagging modifies the electrical and light giving characteristics of the filament disadvantageously and in a manner not easily predictable from the original lamp filament dimensions.

Various means have been proposed to overcome these dificulties'in lamp filaments, such as the formation of the metal into a single elongated crystal, or the introduction into the filament during the process ofmanufacture of certain foreign substances such as thoria or silica, which supposedly have an effect upon the crystalline growth of the tungsten in such'manner as to tend to resist the development of offsetting or sagging. These various methods, while useful, have not been effective to completely over- 40 come the mentioned difiiculties.

Accordingly, it is one of the important objects of the present invention to provide means for obtaining improved results as regards sagging and offsetting in refractory filaments for electric lamps. A further object is to provide a new type of filament which gives increased emciency in electric lamp operation. Further objects of the invention relate to improved manufacturing methods and to theproduction of a metal filament which retains, after high temperature heating, its original'elasticity. Various other objects will appear from the following description of my invention, which 'I will describe with particular reference to the use of tungsten metal in filamentary form for electric lamps.

As a primary source of the tungsten employed in the filament I use tungstic acid (H2WO4) in powdered form and in a chemically pure state. This acid is mixed preferably with potassium fluotitanate (KzTiFaHzO), although other ti- 5 tanium compounds such as titanium fluoride or titanium potassium oxalate may be used. In combining these substances the fluotitanate is' first dissolved in water and the powdered tungstic acid then added. This mixture is mechan- 10 ically stirred over a steam bath until the water is evaporated to dryness, and the resulting material is then crushed and loaded in fused silica crucibles and heated to a temperature somewhere in the neighborhood of 1,000" O. to bring 15 about dehydration of the constituent compounds. Alternately the crucible heating may be omit-' ted as not essential, the dehydration being accomplished as a preliminary phase of the subsequent reduction heating. I 20 The resulting product of the crucible heating is then pulverized and loaded into boats in a reduction furnace where itis subjected to a continuous heating for approximately three and one-third hours to bring about the reduction of 25 the tungstic anhydride (W03) and the initial development of the crystalline or grain structure of the tungsten. I employ a type of oven wherein nichrome tubing is heated externally by gas flames in at least three sections of more or less 30 uniform temperature, the first section being maintained at approximately 388 0., the second at 833 C., and the third at 1,000 C. The stoking time varies from ten to twenty-five minutes, and inasmuch as there are ten boats in the fur- 35 nace at a time, it is apparent that each boat receives progressively and uniformly the temperature of each heated section. While these boats are being passed through the tubing, hydrogen gas is drawn through the tubing in a 40 direction opposite to the movement of the boats in a quantity depending upon the speed of movement and the amount of charge of the boats through the furnace, an average flow being approximately cubic feet per minute. The 45 speed of movement of the boats and the rate of hydrogen flow and amount of charge are all important as affecting the grain size of/the resultant tungsten; the faster the movement for a maintained rate of hydrogen flow the larger the 50 crystalline size. Conversely provided the size of charge remains the same, an increased flow of hydrogen with the stoking rate remaining the same results in decreasing, or a maintaining of the hydrogen rate at a constant value and a 55 decrease in the stoking rate, will cause a diminution, in the crystalline size of the tungsten. The dryness of the hydrogen, i. e. the presence of water vapor, tends to increase, the crystal size. These factors are varied until the desired crystalline size is obtained which is satisfactory for the use to which the resultant product is subjected.

Subsequent to the heat treatment in the reduction or gas furnace the material is taken from the boats and tested for density, various volumetric tests being employed. For example, the tap test may be used in which a definite quantity of material is weighed out and then the holding receptacle subjected to -a series of taps followed by a measurement of the volume. The larger the grain size the less the volume. If the density is not appropriate to the uses desired the product is mixed with other charges of different density or crystalline size to develop a composite mixture of the required density.

The material is now compressed in a steel die a by a hydraulic press to form an ingot having a A amwavw-- size approximately %"x%"x16", which ingot is first baked in hydrogen at about 800 C. to permit handling and then inserted in a conduction type electric furnace where current is passed through the ingot for a period of about twentynine minutes in hydrogen flowing approximately 20 cubic feet per hour. By this'means the temperature is raised to about 90% of the fusion temperature for tungsten, at which point the temperature is held for about ten minutes and then permitted to drop to room temperature. This rate of increase of temperature of the ingot may be uniform or it may be in a series of steps, at each step the temperature being held constant for a time period to permit escape of the volatile constitutents and crystalline adjustment or growth. For example, I may raise the temperature rapidly to the maximum in two steps at and respectively of the melting point of tungsten, the temperature at these points being held for ten minutes or a sufiicient time to get the desired results in grain growth. Or I may raise the temperature by a number of steps of several hundred degrees, holding the temperature constant at the step points for approximately a minute. Generally speaking, the heat treatment is preferably such as to bring the metal close to the density of pure tungsten. In all heating methods, however, the total inclusive time, including the constant step points is approximately twenty-nine minutes. The resulting material, which is purified tungsten metal, is now ready for mechanical treatment, and where filamentary wire is desired the ingot is swaged and drawn to the desired diameter.

Where a coil-type filament is desired the filament is coiled over a mandrel of appropriate size and then strung from the lamp supports. A double coil filament, formed by recoiling the firstcoil over a second mandrel, and subsequently removing both mandrels as by chemical means, has been found, to form a stable and efiicient filament.

The filament resulting from this process of manufacture has both non-sag and non-offsetting properties which are an improvement over that at present known, resulting in greater durability and efiiciency when employed in lamp operation.

While the precise theory involved as to that which brings about the improvement in the properties of the tungsten filament hereinabove mentioned is not clearly understood, it appears that the results are due to the technical process including the heating treatment, and especially to the very intimate contact between the grains of the metal arising from the nature of the volatiles and the sequence of volatilization which takes place in the heating operations. As supporting this viewpoint it is pointed out that because of the refractory nature of tungsten it is exceed ingly dimcult in ordinary methods of treatment to insure a complete purity of metal so that interposed between the crystals of so-called pure tungsten actually exist foreign particles which tend to loosen the intercrystalline bond or in some manner disadvantageously afiect the nature of the crystalline growth under heat conditions. In the manner of the prior art it is proposed to overcome this inherent difficulty of tungsten by the addition of foreign substances such as various oxides, including silica, which modify the crystalline development of the tungsten and overcome the disadvantageous efiect of the native impurities. According to my process, however, absolute' purity of the intercrystalline surfaces is sought by a succession of volatilization reactions, the first proceeding in the lower zone of the region of greatest grain growth of the tungsten, and the other in a higher zone of this region; in other words, at temperatures within a range of 1,000 C. and 1,500 C. and a range of 2,000 C. and 2,500 0., respectively. This sequence of volatilization reactions takes place not only at different temperatures but at different stages of the crystalline development of the tungsten.

The nature of the cleansing action is understood to be partly mechanical in that the volatilization action in some manner facilitates the escape of the less volatile impurities present in the metal. However, there may be some chamical activity which assists in removing the impurities and effecting a cleansing of the intergrain surfaces. This cleansing brings about a material modification of the grain growth or intergrain activity which results in a marked resistance to sag as well as offsetting in the completed filament.

It is pointed out that the volatiles are most probably entirely eliminated below the germination point so that the final crystalline form is assumed under conditions of high metal purity.

In summary, .the process briefly consists in mixing tungstic acid with a solution of potassium fiuotitanate, evaporating to dryness, and dehydrating the mixture. This treatment is followed or is coincident with a heating in a reduction furnace of the gas type which reduces the tungstic anhydride and decomposes the fiuotitanate and also determines the initial crystalline size, and consequently the density of the substance. This is followed by a heating to high temperatures in ingot form to bring about successive volatilizations of the decomposition products of the potassium fiuotitanate and the formation of the desired grain structure.

As a specific example of the relative proportions of substances employed in a given'batch, I use 1,000 grams of tungstic acid in conjunction with 13 grams of potassium fluotita'nate. These amounts are approximate, as I may vary the quantities as follows:tungstic acid 1,000 grams, potassium fiuotitanate 6 to 20 grams, or in terms of percentages, 1 part of tungstic acid and 0.2% to 2.0% of potassium fiuotitanate by weight of the acid.

As a modification of the improved method of treating tungsten for lamp filament use I may include, in addition to the above materials, that is, tungstic acid and potassium fluotitanate, an aluminum compound which is introduced as a water soluble salt of aluminum in the original mixture and which decomposes to aluminum oxide in the reduction process. The action of this additional substance is such as to tend to prevent breakage of the filament due to vibration arising either from mechanical jar or from the passage of alternating current through the filament. In a typical batch I may combine the substances as follows: 1,000 grams of tungstic acid, 13 grams of potassium fluotitanate, and 1 gram of aluminum chloride, or in terms of limiting ranges, tungstic acid 1 unit, potassium fluotitanate 0.2% to 2.0%, and aluminum oxide 0.05% to 0.2%, the percentagesbeing in relation to the weight of tungstic acid. These substances are preferably chemically pure, and it is understood that the amounts mentioned are merely typical and do not necessarily limit me to the continued use of the stated amounts.

It is noted in connection with the process above described that the same results are not obtained by the use of potassium oxide and titanium oxide combined separately with tungstic acid, inasmuch as apparently there is not the intimate association of the substances and in the same relationship as occurs when these two compounds are introduced as potassium fluotitanate. A prerequisite also is that the compounds in their original condition must be such as to permit association by solution in order to insure this complete dissemination of the various substances. I have mentioned the temperatures such as have proven to be efiective in accomplishing the results of-my invention, but it is understood that these values, as well as that of others given in the above description, are approximate and not critical and limited.

It should be observed that the reduction heat is preparatory, the actual grain structure of the metal being determined in the final or ingot heat. The preparatory treatment is, however, important in that it insures the complete dissemination of the titanium compound through the tungsten metal and brings about the proper initial grain size of the metal. Throughout the claims and description the terms crystal and grain" are used synonymously.

The volatilization of the titanium, particularly in the form of its fluoride with or without the volatilization also of potassium or sodium oxide,

or hydroxide or fluoride, appears to scour the tungsten grains, resulting in the formation of a more satisfactory grain structure, which is highly resistant to sagging and offsetting. In accomplishing these results the titanium and alkali metal compounds are completely removed and vaporized away from the tungsten, a sufilciently high temperature being maintained for a sufilciently long time to accomplish this result. The form of fluorine or other compoundof titanium which exists in the reduced mixture has not been definitely determined, and for this. reason the compounds so formed may be potassium or sodium oxides, hydroxides, orfluorides, or titanium oxides or fluorides, or combinations of these sodium, potassium or titanium compounds.

While I have described specifically certain embodiments of my invention, I desire it to be understood that such embodiments are illustrative and that modifications may be made thereof within the scope ofthe present invention.

I claim as my invention:

1. The process of making tungsten metal having non-sag and non-offset properties which comprises the steps ofiorming a mixture of tungstic acid and a solution of potassium fluotitanate, dehydrating this mixture, and reducing the tungstic oxide and substantially completely volatilizing and thus removing the components of the fluotitanate in successive heat treatments in the presence of hydrogen.

2. The process of making ductile tungsten metal ingots having non-sag and non-ofiset properties which comprises the steps of forming a mixture of compounds of tungsten, titanium and water,

and successively dehydrating and pulverizing these compounds, reducing the powdered mixture in hydrogen to tungsten metal compacting the reducedmixture to form an ingot, baking the ingot-at a relatively low temperature in hydrogen to strengthen it, substantially completely removing the titanium compound by volatilization in separate temperature zones in the region of tungsten grain growth.

3. The process of making ductile tungsten metal ingots having non-sag and non-offset properties which comprises the steps of forming a mixture of compounds of tungsten, titanium and water, and successively dehydrating and pulverizing these compounds, reducing the powdered mixture in hydrogen to tungsten metal compacting the reduced mixture to form an ingot, baking the ingot at a relatively low temperature in hydrogen to strengthen it, substantially completely removing the titanium compound by volatilization in separate temperature zones in the region of tungsten grain growth and below the region of greatest tungsten grain growth.

4. The process of making tungsten metal having non-sag and non-offset properties which comprises the steps of forming a mixture of tungstic acid and potassium fluotitanate solution, dehydrating this mixture, and reducing the tungstic oxide and substantially completely volatilizing and thus removing the components of the fluotitanate in successive heat treatments in the presence of hydrogen, said heat treatments ranging successively from about 500 C. to above 2000 C., but at all times being below the melting point of tungsten.

5. The process of making ductile tungsten metal ingots having non-sag and non-offset properties which comprises making a mixture of compounds of tungstenand soluble compounds of titanium, dehydrating and pulverizing the mixture, reducing the powdered mixture in hydrogen to tungsten metal compacting the reduced mixture to form an ingot, baking the ingot at a relatively low temperature in hydrogen to strengthen it, and subjecting the ingot to graduated heating in a non-oxidizing atmosphere up to a temperature of approximately 90% of the melting point of pure tungsten to substantially completely volatilize and thus remove the titanium compound. a

6. The process of making ductile tungsten metal ingots having non-sag and non-ofiset properties which comprises making a mixture of a compound of tungsten and a soluble compound of titanium, dehydrating and pulverizing the mixture, reducing the powdered mixture in hydrogen to tungsten metal compacting the reduced mixture to form an ingot, baking the ingot at a relatively low temperature in hydrogen to strengthen it, and subjecting'the ingot to graduated heating in a reducing atmosphere up to a temperature of approximately 90% of the melting point of pure tungsten to substantially completely volatilize and thus remove the titanium com pound, the time of heat treatment above 1,000 C. being not more than half as long as the time of heat treatment below 1,000 C.

7. The process of making ductile tungsten metal ingots having non-sag and non-oilset properties which comprises making a. mixture of compounds of tungsten and titanium, dehydrating and pulverizing the mixture, reducing the powdered mixture in hydrogen to tungsten metal compacting the reduced mixture to form an ingot, baking the ingot at a relatively low temperature in hydrogen to strengthen it, and subjecting the ingot to heating in a reducing atmosphere up to a temperature of approximately 90% oi the melting point of pure tungsten to substantially completely volatilize and thus remove the titanium compound, said heating being in a series of temperature steps, the steps adjacent 1,000 C. covering a period exceeding two hours, and the higher temperature steps above 1,000 C. covering a period of less than one hour.

8. The process-of making ductile tungsten metal ingots having non-sag and non-offset properties which comprises making a mixture ofa compound of tungsten and a soluble compound of titanium, dehydrating and pulverizing the mixture, reducing the powdered mixture in hydrogen to tungsten metal compacting the reduced mixture to form an ingot, baking the ingot at a relatively low temperature in hydrogen to strengthen it, and subjecting the ingot to heating in a reducing atmosphere up to a temperature of approximately 90% of the melting point of pure tungsten to substantially completely volatilize and thus remove the titanium compound, said heating being in a series of temperature steps, the temperature being held approximately constant at the step points for a time period not exceeding two hours.

9. The process of making tungsten metal having non-sag and non-offset properties which comprises the steps of forming a mixture of tungstic acid and potassium fiuotitanate, dehydrating and reducing this mixture, and substantially completely volatilizing and thus removing the fluotitanate in successive heat treatments and at difierent temperatures.

10. The process of making tungsten metal having non-sag and non-offset properties which comprises the steps of forming a mixture of tungstic acid and potassium fluotitanate solution, dehydrating this mixture, and subjecting the resultant product to two successive heat treatments in the presence of hydrogen, the first treatment being at lower temperatures and over a long time period, and the second treatment being at higher temperatures and over a shorter time period, to volatilize and remove completely the potassium fiuotitanate.

11. The process 01 making ductiletungsten metal ingots having non-sag and non-offset properties in filamentary form which comprises the steps of forming a mixture of a tungstic compound and a soluble compound of titanium, dehydrating and pulverizing the mixture, reducing the powdered mixture in hydrogen to tungsten metal compacting the reduced mixture to form an ingot, baking the ingot at a relatively low temperature in hydrogen to strengthen it, subjecting the resultant product to the action of a series of consecutive and constant heats in a reducing atmosphere and including temperatures below 500 0., 950 C. and 1,100 C., whereby metallic tungsten is reduced from its compound, and subjecting the metallic tungsten to temperatures increased from room temperature to approximately 90% of the fusion point of tungsten, said heating being sumcient to cause complete volatization and removal of the titanium compound. v r

12. The process of making ductile tungsten metal ingots having non-sag and non-oil'set properties in filamentary form which comprises the steps of forming a mixture of a tungstic compound and a soluble compound of titanium, dehydrating and pulverizing the mixture, reducing the powdered mixture in hydrogen to tungsten metal compacting the reduced mixture to form an ingot, baking the ingot at a relatively low temperature in hydrogen to strengthen it, subjecting the resultant product to the action of a series of consecutive and constant heats in a reducing atmosphere and including temperatures below 500 C., 950 C. and 1,100 0., whereby metallic tungsten is reduced from its compound, and subjecting the metallic tungsten to temperatures increased from room temperature to approximately 90% of the fusion point of tungsten, said final heat being accomplished in a series of steps, the step points not exceeding fifteen minutes in duration, said heating being sufllcient to cause complete volatilization and removal of the titanium compound.

13. The process of making ductile tungsten metal ingots having non-sag and non-offset properties in filamentary form which comprises the steps of forming a mixture of a tungstic compound and a soluble compound of titanium, dehydrating and pulverizing the mixture, reducing the powdered mixture in hydrogen to tungsten metal compacting the reduced mixture to form an ingot, baking the ingot at a relatively low temperature in hydrogen to strengthen it, subjecting the resultant product to the action of a series of consecutive and constant heats in a reducing atmosphere and including temperatures below 500 C., 950 C. and 1,100 C., whereby metallic tungsten is reduced from its compound, and subjecting the metallic tungsten to temperatures increased from room temperature to approximately 90% of the fusion point of tungsten, said final heat terminating in a constant heating of the material for a time period not exceeding fifteen minutes, said heating being suflicient to cause complete volatilization and removal of the titanium compound.

14. The process of making ductile tungsten metal ingots having non-sag and non-offset properties in filamentary form which comprises the steps of forming a mixture of a tungstic compound and a soluble compound of titanium, dehydrating and pulverizing the mixture, reducing the powdered mixture in hydrogen to tungsten metal compacting the reduced mixture to form an ingot, baking the ingot at a relatively low temperature in hydrogen to strengthen it, subjecting the resultant product to the action of a series of consecutive and constant heats in a reducing atmosphere and including temperatures below 500 0., 950 C. and 1,100 0,, whereby metallic tungsten is reduced from its compound, and subjecting the ,metallic tungsten to temperatures increased from room temperature to approximately 90% of the fusion point of tungsten, said final heat being accomplished in a series of short steps, the step points not exceeding "two minutes in duration, said heating being sumcient properties in filamentary form which comprises-1.

the steps of forming a mixture of a tungstic compound and a compound of titanium, dehydrating and pulverizing the mixturei e-rpducing the powdered mixture in hydrogen to tungston metal compacting the reduced mixture to form an ingot,

baking the ingot at a relatively low temperature in hydrogen to strengthen it, subjecting the resultant product to the action of a series of consecutive and constant heats in a reducing atmosphere and including temperatures below 500 0., 950 C.

.' and 1,100 (2., whereby metallic tungsten is reduced from its compound, and subjecting the metallic tungsten to temperatures increased from room temperature'to approximately 90% of the fusion point of tungstem'said final heat beingaccomplished in aserles of short steps, the intermediate step points not exceeding two minutes and the final step point not exceeding fifteen minutes in duration, said heating being sufficient to cause complete volatilization and removal of the titanium compound.

16. The process of making tungsten metal which comprises the steps of combining tungstic acid and potassium fluotitanate dissolved in I 90% of the melting point of tungsten is reached,

at which point the temperature is maintained relatively constant for a time period of approximately ten minutes, the total time period of heat treatment of the metallic tungsten not exceeding thirty minutes but being sufficient to remove the potassium fluotitanate completely.

1'7. The process of making purified tungsten metal comprising heating the unpurified'metal with alkali metal and titanium compounds which are completely eliminated successively at different temperatures to a temperature approximately 90% of the melting point of tungsten, said titanium and alkali metal compounds, being volatilizable between about 1,000" C. and a temperature of about 90% of the melting point 01. tungsten. and said compounds being selected from the class consisting of oxygen compounds, fluorine compounds and decomposable salts. i 18. The process of makingpurified tungsten metal comprising heating the unpurified metal with alkali metal and titanium compounds which are completely eliminated successively at difierent temperatures to a temperature approximately 90% of the melting point of tungsten, and holdthe class consisting of oxygen compounds, fluorine compoundsand decomposable salts.

'19. The process of making purified tungsten metal comprising heating the unpurified metal with alkali metal and titanium compounds which are completely eliminated successively at different temperatures to a temperature approximately 90% of the melting point of tungsten, said compounds being volatilized below 2,600 0., said titanium and alkali metal compounds, being volatilizable between about 1,000 C. and a temperature of about 90% of the melting point of tungsten, and said compounds being selected from the class consisting of oxygen compounds, fluorine compounds and decomposable salts.

20. The process of making purified tungsten metal comprising heating the unpurifled 'metal with alkali metal and titanium compoimds which are completely eliminated successively at difierent temperatures to a temperature approximately 90% of the melting point of tungsten, one of said compounds being eliminated chiefly below 1,7 C. and the other compounds being eliminated chiefly above '2,000 C., said titanium and alkali metal compounds, being volatilizable between about 1,000 C. and a temperature of about 90% of the melting point of tungsten, and said compounds being selected from the class consisting of oxygen compounds, fluorine compounds and decomposable salts.

21. A drawn tungsten metal filament having non-offsetting,andnon-sagging properties, said filament being of pure tungsten metal, the intergrain surfaces of which have been freed of foreign matter and secured by the complete vo1atilization of a titanium compound in intimate association therewith.

22. A drawn, non-offsetting, non-sagging coiled filament of pure tungsten metal, said metal having a pronounced grain structure, and the surfaces of said grains being completely freed of foreign substances and scoured by a series of volatilization" reactions at different temperatures involving complete volatilization of alkali metal and titanium compounds included in said filament, said titanium and alkali metal compounds, being volatilizable between about 1,000 C. and a temperature of about 90% ofthe melting point of tungsten, and "said compounds being selected from the class consisting of oxygencompounds, fluorine compounds and decomposable salts.

23. A drawn, non-ofisetting, non-sagging filament for'electric lamps comprising a. coiled filament coiled in a helix, said filament consisting of a pure refractory metal having a pronounced grainstructure, and the surfaces of said grains being completely freed of titanium compounds, included therein, by volatilization.

24. A drawn, pure, non-offsetting, non-sagging tungsten filament of crystalline structure, the surfaces of the crystalline grains having been completely freed of titanium and alkali metal compounds, includedtherein, by volatilization,

said titanium and alkali metal compounds, being volatilizable between about 1,000 O. and a temperature of about 90% of the melting point of tungsten, and said compounds being selected from the class consisting of oxygen compounds, fluorine compounds and decomposable salts.

25. A drawn, non-offsetting, non-sagging pure tungsten filament ofcrystalline grain structure,

the surfaces of the grains having been cleansed by complete volatilizationofdecomposition products of potassium fluotitanate.

26. A drawn, non-offsetting,non-sagging pure tungsten filament of crystalline grain structure, the surfaces of the grains having been cleansed by complete volatilization of potassium fluotitanate.

27. A metal composition adapted for heat treat- .ment as an ingot in the manufacture of pure tungsten comprising tungsten metal grains and uniformly disseminated throughout the tungsten. f potassium fluotitanate. 29. A metal composition adapted for heat treat- 28. Ametal composition adapted for heat treatment as an ingot in the manufacture of pure ment as an ingot in the manufacture of pure tungsten comprising tungsten metal grains and 5 tungsten comprising tungsten metal grains and. titanium fluoride intimately mixed therewith. 5

potassium fluotitanate, said fluotitanate being v ALBERT E. MocFARLAND.