US1154701A - Process of producing tungsten filaments. - Google Patents

Description

. gas is highly important for the purpose of F SS PROCESS OF PRODUCING TUNGS'IEN FILAMENTS.

No Drawing.

To all whom it may concern:

Be it known that I, ERNST AUGUST KRiirGER, a citizen of the German Empire, residing at Seehausen, Altmark, in Germany, have invented certain new and useful Improvements in the Process of Producing "sten with a small proportion of carbon and boracic acid or other compound of boron.

My invention consists in a particular manner of carrying out the process of manufacture with the raw material indicated.

According to the invention I first produce a rod consisting of powdered tungsten with a small proportion of carbon and a boron compound, preferably boracic acid, less than 1% of the latter being usually suflicient and only a small trace of carbon, about 0.1%. I may use the boracic acid in the form of powder. I moisten the mixture with water. I may also mix the tungsten powder and carbon alone, and form a rod of this mixture,by pressure, and then impregnate the rod in vacuo with a concentrated solution of boracic acid. The rod is then heated to about 1000 or 1200 C. whereby the boracic acid is caused to slowly swell and expel the air or other gas present from the minute interstices between the tungsten particles. This expulsion of obtaining nonporous wire. The melting boracic acid cements the metal particles to each other, and at the same time the superficial oxid layers dissolved by the boracic acid. Thus purely metallic tungsten particles come into intimate contact with each other, and can by subsequent treatment be sweated or fused together to produce a perfectly homogeneous structure. When the temperature reaches its higher values the boracic acid is probably reduced to boron, or causes carbid of boron to be formed, with the result that an alloy of tungsten and boron or boron carbid is obtained. This is accompanied by considerable shrinkage of the mass. After the rod has been kept for some time at the temperature mentioned, I heat it to a temperature between 1200 and 2000 C. by means of electric current, in a stream of hydrogen, whereby the, metal par- Specification of Letters Patent.

Patented Sept. 28,1915.

Application filed August 2'5, 1913. Serial No. 786,488.

ticles are fused together, and a very homogeneous structure, free from cavities or crevices, is obtained. The rod is then formed into wire by suitable mechanical treatment adapted for this purpose. The presence of the boron reduces the liability to attack by oxygen, so that there is no necessity for careful exclusion of atmospheric air in the course of the mechanical treatment. The rod being free from cavities, the wire obtained is free from those crevices which always occur in forming wire of pure tungsten.

The wire or filament obtained can be used in the manufacture of electric glow lamps.

Inasmuch as the filament of tungsten alloy is quite as efficient as pure tungsten filament, for glow lamp purposes, it is in general not necessary to eliminate the boron by special treatment. As-a matter of fact, the heating of the filament in the lamp to a large extent eliminates the boron, which does not blacken the bulb, but forms a thin transparent deposit. The expulsion of the boron from the filament in the bulb also improves the vacuum, the residual air being mechanically deposited, and perhaps in part chemically combined.

If it is desired to have a pure tungsten filament, I heat the filament to incandescence for a lengthy period, in vacuo, say to a temperature of 2000 or 2200 C. and then again hammer or roll and draw the filament, with heat. Y

The process described has very considerable advantages over the process of producing filament from pure tungsten. Particles of metallic tungsten are always coated with oxid, which renders it very difiicult to bake them together, and the result is that minute cavities are left, into which air penetrates and causes further oxidation. Ad-

mixture to the tungsten powder, such as silboron and a binding agent containing car-.-

bon, the mixture being heated to carbonize the binding agent, and then heated to white heat by current, in a stream of hydrogen. In this process only so much of the metal is used as will render the mixture conductive at ordinary temperatures, so that the whole of the tungsten or molybdenum becomes alloyed with boron.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

The process of producing a filament of tun sten or tungsten alloy, which consists in ormin'g, by pressure, a rod consisting of a mixture of powdered tungsten with a small proportion of carbon and boracic acid or other boron compound, heating said rod to a temperature of aboutlOOO to 1200 C.

at which the particles cake together, then heating the rod to incandescence by electric current in a stream of hydrogen, and then reducing the rod to wire by mechanical treatment. s a

In witness whereof I have signed this specification in the presence of two witnesses.

ERNST AUGUST KRUGER. Witnesses:

WOLDEMAB HAUPT, HENRY HAsrER.