Osram Sylvania Inc.

Patent Treuhand Gesellschaft Fur Elektrische Gluhlampen Mbh

Patent-treuhand-gesellschaft Fuer Elektrische Gluehlampen Mbh

Michael Salmen

Hans-Joachim Lunk

Henry J Stevens

Martin Fait

Alfred-Georg Gahn

Bernhard Altmann

Burkhard Ziemer

Maria B Winnicka

Joachim Fuchs

Anna S Nached

A boron addition for making potassium-doped tungsten powder is described herein. Boron is added to a potassium-doped starting material, preferably in the form of boric acid, and then the mixture is reduced to form a potassium-doped tungsten powder. The boron addition results in increased potassium incorporation in the potassium-doped tungsten powder and also effects an increase in potassium retention in sintered compacts of the potassium-doped tungsten powder.

Boron addition for making potassium-doped tungsten

A method of making a potassium-doped tungsten powder is described comprising forming a mixture of ammonium paratungstate or ammonium metatungstate and a potassium-containing compound selected from a thermally unstable potassium-containing salt or a potassium tungstate, and reducing the mixture in a single step without adding additional dopants to form a potassium-doped tungsten powder. The potassium-doped tungsten powder produced by the method of this invention can be pressed, sintered and drawn to produce a non-sag tungsten wire.

Method of making non-sag tungsten wire for electric lamps

To essentially eliminate aluminum and silicon as contaminants in a doped tungsten wire, the tungsten wire is obtained by mechanical working of reduced tungsten blue oxide which contains as a primary or major constituent a special hexagonal ammonium tungsten bronze of the general formula (NH.sub.4).sub.X (NH.sub.3).sub.y WO.sub.3. A liquid doping step is carried out by adding a solution containing potassium nitrate, the special doped ammonium tungsten bronze forming preferably more than 70% by weight of the overall tungsten blue oxide. The special hexagonal ammonium tungsten bronze is made by decomposing ammonium paratungstate in an ammonium atmosphere, preferably at a temperature between about 400.degree. and 550.degree. C.

Method of manufacturing a non-sag tungsten wire for electric lamps

To dope ammonium paratungstate with potassium, essentially devoid of silicon and ammonium, an aqueous potassium containing solution, preferably potassium hydroxide is added to an aqueous solution of ammonium paratungstate (APW), in a mol relationship of potassium to ammonium of between 0.1 and 10. A doped ammonium potassium paratungstate (AKPW) is obtained. This ammonium potassium paratungstate is then converted to tungsten blue oxide, which is reduced, preferably in a hydrogen containing atmosphere and a tungsten powder is then obtained which will be doped with 40 to 120 ppm, preferably about 90 ppm of potassium. Lamps equipped with tungsten wire filaments drawn from so doped tungsten have lifetimes at least 10% more than lamps with conventional tungsten filaments.

Process of making a non-sag tungsten wire for electric lamps

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Munich, Germany

Michael Salmen