US1972136A - Precipitation of tungstic oxide - Google Patents

Description

Patented Sept. 4, 1934 PAT NT, orrice PRECIPITATION F 'ron s'rrc OXIDE Frank H. Briggs, Bloomfield, N. J., assignor to WestinghouseLamp Company, a corporation 7 of Pennsylvania v No Drawing. Application March Serial N0.'663,182. 4 Claims, (oi. 2s 2s) This invention relates to a metallic body and to amethod of producing the same. In its more specific aspect the invention is directed to a tungsten body of predetermined grain countyto tungsten particles of predetermined size and. to

an improvement in-the method of preparing the same. Y

Heretofore in the refractory metal body,. as for example tungsten, it has been customary to obtain a tungstate, as for example potassium tungstate, from a tungsten containing ore. The tungstate generally in a substantially pure condition is added toan acid, such as hydrochloric acid, with which it ;reacts to produce tungstic oxide and potassium chloride-according to the following equation:

' K2WO4+2HCl I-I2'WO4+2 KCl The hydrochloric acid employed was approximately 35% I-ICl by weight. 'To this hydrochloric acid the potassium' timgstate solution is slowly and continually added until the solution is slightly acid. This batchxof material is con tinually stirred throughout the addition step and I also stirred for a limitedpei'iod of time thereafter in order that complete'reaction' may take place between thetungstate and-thehydrochloric acid. At the, end of the reaction and when the solution is just slightly acid, the liquid containing potassium chloride in solution and the-tungstic oxide compound as a sludge is decanted leaving thewet sludge or tungstic oxide I-I2WO4 compound behind. The tungst'ic oxide is then subjected to a water washing operation. At 'this" stage the I tungstic oxide compound is subjected to 'a' drying operation carried out at an elevated temperature of about 100to120? C. This condition is maintaineduntil all of the excess moisture isevaporated therefrom. 1 i r The dried tungstic oxide I-IzWO4, which atthis period is in the form of relatively large lumps, is ground until the particle size thereofis of such dimensionsas to pass an 80 mesh sieve. These relatively small tungstic oxidei particles are 1 placed'in nickel boats. The boats containing the dried -H2WO4 are placed and rnaintainedjin.v the ordinary hydrogen furnace operating at a relatively high temperature until all of the oxide has been reduced to its metallic form; Ihave found that the individual particles of about 1 0 -o'fa'batch of metal particles so produced have diametrs' below' l rnicron and about on less ofa'micron' and that'the individual particles' 'of another 10% of said batch-have diametersfabove l4 microns 'and about-"' or more microns. The

process for producing a rare remaining 86% of the particles of this batch range in size between about 1 and 14 microns. -Thereafter. this batch-of tungsten particles is subjected to the usual pressing andsintering" operation in. order that-the same :may be'transformed into the ordinary tungsten barcwhich may be later mechanically treated in orderthat the same'may be. employed as the filament in' incandescent'lamps or the like. This sintered bar has a grain count of about four to five thousand per square mm. 1 Prior to the time of my invention it has been recognized that the grain size is an importantconsideration in an incandescent filament when pendent upon-the acidity ofthe hydrochloric acid at the time of tungstate addition and at'the time that the addition was terminated. As far as I am aware, I am'the first in this art to have discovered that-the size ofthegrains in sintered tungsten bars maybe predetermined and "controlled by controlling the acidity of the precipitant, HCI, and it'is with this particular discovery that my invention is specificallyconcerned. J

In the oour'se'of my experimentations with this problem, Ihave'found that I may provide a batch of tungsten'metallic particles of predeter mined sizes. By following out my processas hereinafter desc'ribedit is possible to obtain a batch of tungsten particleshaving less than one half of one per cent; of the quantity thereof comprised of individual particlesiwhose diameter is u one-half or less of amicron, and-less than-one half of one percent of the"quantity-thereof comprised of individualmetal' particles whose diameter is 14501 more microns. Because of thenature of my invention, it is possible to obtainabatch of metallic particlesof any particular smallrange ess for'p'roducing a batchfoftungsteniparticles with the individual particles thereof f redeterminedsize.-

An object of my invention is toprovideaproc$ Another object of my invention is to provide an improved step in the manufacture of incandescent lamps.

A still further object of my invention is the improved step of employing a batch of tungsten particles whose sizes are of such magnitude and within a certain range to provide a tungsten body which will have improved incandescent filament characteristics.

' per-cent HCLatthe initial precipitating step.

According to my invention I may obtain a batch of any desired size of metal particles whose sizes are substantially all less than one micron, for example. For this purpose I employ concentrated hydrochloric acid 36% HCl by weight. One example of the method which may be followed for for this purpose when it is desired to treat about 1 kilogram of 2N potassium tungstate solution is x as follows: 1

About 5000 grams of concentrated hydrochloric acid 36% of HCl is placed in a container and maintained at a temperature of about ,C. The potassium tungstate solution is conducted to said container. The feed of said tungstate may be regulated so that therev is but a very small quantity thereof and in a dispersed condition in the form of a fine mist passing through a tube of appreciable diameter.

Close to the tungstate feed end of the tube there is projected against said moving stream a stream of concentrated hydrochloric acid 36% 301, also in the form of a mist with the quantity of hydro chloric acid solution admittedbeing ten times that of the admitted tungstate by weight. This mass of hydrochloric acid and the tungstate together with the reaction'products thereof travel of the hydrochloric acid in the container and that added to the tungstate feed should be so regulated that the acidity of the liquor after c0m-.

plete precipitation shall be no less than approximately 33% I-ICl. This sludge which is essential- I ly H2WO4 is subjected to water washing and the H2WO4 is dried by being elevated to a temperature of about -120 C.

. This dried mass maybe in the form of large lumps and is ground to reduce the size thereof so that it may pass an'80 mesh sieve. At this stage the ground mass is subjected to the usual elevated and'reducing-atmosphere to convert the H2WO4 to pure tungsten metal. This usually con- I sists in maintaining the temperature at 600-850 C. and passing through the furnace-100 cu. ft. hydrogen per hour. The rate of stoking of the tungsten is about 700 grams per hour.- The batch of metal particles so obtained has about 95-98% of the individual particles thereof no greater than 1 micronin diameter. 1

Similarly I may obtain 'a batch of tungsten particles with not over.10% of the quantity of the individual particles thereof by number having a diameter less than about 6 microns. For this purpose I follow the novel, method outlined above and employ hydrochloric acid whose acidity i515 during and at the. endof the, precipitation.

. 1 Thus it isreadily apparent that Imay obtain a batch of tungsten particles contaming what- 1161 percent by weight Approximate particle size Oxide No.

Microm Afurther specificaspect of my invention is the application of acid control during precipitation in the course of incandescent filament manufacture;

Instead of beginning with'a concentrated hydrochloric acid solution containing 36% E01 and adding potassium tungstate =thereto until the solution is just slightly acid, I prefer to carry outthe precipitation step with a different range of acid concentrations. One range that I have found suitable is beginning with a hydrochloric acid solution containing 25-26% HCl, stirring and adding a 2N potassium tungstate solution thereto until the concentration of HCl is about 7-8 per cent. This step is carried out with constant agitation, slow addition of the tungstate and maintaining the temperature of the solution at about 80, C.

By following this method I have found that the size of substantially all of the individual metal particles prepared in the usual manner from I-I2WO4 precipitate thus produced is ,between about 1 and 8 microns and that there is no appreciable percentage, and less than 5% of individual particles by number, that measure less than 1. micron or greater than 8 microns.

A batch of individual metal particles so produced may in the usual manner be pressed, sintered and subjected to other normal operations for 5 the preparation of incandescent filaments that may be employed in an incandescent lamp. The grain count of the sintered bar is between 16,000 and 20,000 per square mm. which may without the understanding of my invention be regarded as high, but which I have found to bee. factor in the production of a superior filament,

The invention is susceptibleto modifications and the scope thereof is to bejlimited only by the prior art. I

What is claimed: 1 1. A method of preparing a. batchof tungsten particles comprising treating a soluble alkali metal tungstate compound; with ;;hydrochloric acid whose HCl content is no greater-than about 26% and during said treatment maintaining said 1101 acid content between about26%=- and 7% 7 I 2. A step in themethod of manufacturing a tungsten filament comprising-to about 25-26% HCl solution addinga 2N solution of a water soluble alkali metal tungstate until the concentration of the HCl is about 7-8% and removing the precipitate therefrom. r r 1 A tep, n th .me h ier m n actu in a 4. A step in the method of manufacturing tungsten comprising to about 25-26% H01 solution, adding a 2N solution of potassium tungstate until the concentration of the HCl is about- 7 to 8%, agitating the admixture formed and maintaining the temperature thereof at about C.

FRANK H. DRIGGS.