Osram Sylvania Inc.

Global Tungsten & Powders Corp.

Henry J Stevens

Hans-Joachim Lunk

Michael Salmen

Thomas J Patrician

Dale E Benjamin

Ricky D Morgan

Harry D Martin, Iii

Tuan A Dang

Anna S Nached

Maria B Winnicka

Timothy A Frisk

The coating the tungsten powder particles with a ceramic barrier suppresses the leachability of tungsten in aqueous media. Preferably, the ceramic coating substantially encapsulates each particle of tungsten and has a thickness of at least about 30 nm and, more preferable, from about 200 nm to about 500 nm. Examples of ceramic coatings that may be used include, but are not limited to, aluminum oxide (alumina), aluminum oxyhydroxide (AlOOH), zirconium oxide (zirconia), cerium oxide (ceria), hafnium oxide (hafnia), and magnesium oxide (magnesia).

Ceramic-coated tungsten powder

There is described a method of making a nanocrystalline tungsten powder that comprises: (a) heating a tungsten-containing material in a reducing atmosphere at an intermediate temperature of from about 600&#xb0; C. to about 700&#xb0; C. for an intermediate time period; the tungsten-containing material being selected from ammonium paratungstate, ammonium metatungstate or a tungsten oxide; and (b) increasing the temperature to a final temperature of about 800&#xb0; C. to about 1000&#xb0; C. for a final time period.

Method of making nanocrystalline tungsten powder

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

It has been discovered that potassium retention in NS tungsten processing may be improved by double doping tungsten blue oxide (TBO) prior to reduction. The novel `double-doping` process consists of dry doping standard singly doped K--Al--Si TBO with potassium nitrate, KNO.sub.3, followed by the standard reduction, acid washing, sintering, rolling and drawing steps. In another aspect, the novel method includes an aqueous extraction of heteropolytungstate anion [SiW.sub.11 O.sub.39 ].sup.8- from a sample of the singly doped tungsten blue oxide to predict potassium retention.

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Athens, PA, United States of America

Henry J Stevens