Tungsten Blue Oxide Used to Making Tungsten Metal Powder

We have found that tungsten metal powder doped with a fine dispersion of oxide particles can be formed by a wet chemical precipitation method. The doped tungsten metal powder can be used to form sintered tungsten bodies, or the elongated bodies formed by reducing the sintered bodies, having a fine tungsten grain size, and a fine distribution of oxide particles for pinning the grain boundaries.

The doped tungsten metal powder is formed from a tungsten oxide powder, the oxide being known as tungsten blue oxide and having the approximate composition WO3. Tungsten blue oxide powder particles can be formed, for example, by the decomposition of ammonium paratungstate in hydrogen. Such tungsten blue oxide particles are porous, consisting of agglomerates of very small oxide crystals, for example about 0.1 micron. The tungsten blue oxide powder can have an average particle size in the range of about 5 to 80 microns. Preferably, the tungsten blue oxide is milled to provide a uniform fine average particle size of about 2 to 7 microns.

The metallic tungsten powder is doped with an effective amount of the metal oxide to provide a fine tungsten grain size, pin grain boundaries, or improve the thermionic capability in sintered bodies formed from the powder. Tungsten powder comprised of greater than about 5 weight percent of the metal oxide can be sintered to form bars, but the bars are difficult to reduce to elongated rods or wires. The oxide is preferably in a range of about 0.5 to 3 weight percent, more preferably about 1 to 2 weight percent of the metallic tungsten powder.

The tungsten blue oxide powder is doped with a soluble salt solution of at least one of the metals from the group zirconium, hafnium, lanthanum, yttrium, and the rare earth's. A preferred rare earth is cerium. Suitable salt solutions can be formed by dissolving chlorides, oxy-chlorides, oxy-nitrates, or preferably nitrates of the metal in water, or the metal oxides can be dissolved in a hydrochloric, or nitric acid solution. The nitrates are preferred because the hydroxide precipitation products formed from precipitation of the metal nitrates, other than the metal hydroxide, are substantially removed by decomposition during reduction of the tungsten blue oxide. Precipitation products from the other salts that do not decompose during reduction of tungsten blue oxide to tungsten, such as chlorides or oxalates, can be washed from the mixture after precipitation of the hydroxides.

A sufficient concentration of the metal salt is dissolved to provide the desired weight percent of the metal oxide in the tungsten powder. Those skilled in the art can determine the quantity of salt solution needed to mix with the tungsten blue oxide to form a suspension, and the proportion of metal salt to tungsten blue oxide to give the desired weight percent of metal oxide in the tungsten metal powder.

Tungsten Powder Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten-powder.com
Tel.: 86 592 5129696; Fax: 86 592 5129797
Email: sales@chinatungsten.com
Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn

• < Prev
• Next >