Tungsten Products - Tungstic Acid H2W04

Tungstic acid, the most important intermediate in former tungsten chemistry, is today exclusively manufactured out of APT, in order to make use of the high purity APT level. For that purpose an aqueous APT slurry will b e treated with hydrochloric acid. By that tungstic acid is precipitated, and afterwards filtered, washed and dried. Tungstic acid has a very high active surface and is only used in small quantities for special purposes as there are: Production of ultrafine W and WC powders and production of tungsten chemicals.

 

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Tungsten Products - Tungsten Blue Oxide (TBO, VV03.X)

TBO is manufactured by calcination of APT under more or less reducing conditions which vary from producer to producer. TBO is not a chemically defined compound, but consists of various different constituents, like trioxide, tungsten bronzes and different lower tungsten oxides. The relative amount of the se compounds in TBO depends on the calcination parameters.

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Tungsten Products - Tungsten Trioxide (W03)

In a technical scale Tungsten trioxide is almost exclusively manufactured by calcination of APT under oxidizing conditions (in air), W03 is one of the most important, highly pure intermediates for the production of other tungsten compounds and tungsten metal powder. In the latter application it was substituted to a large extent by tungsten by tungsten blue oxide. Because of its bright yellow colour it is us e d as a pigment in oil and water colours. It is employed in a wide variety of catalysts, most recently in catalysts for the control of air pollution and industrial hygiene (DeNOx).

Tungsten trioxide particles are pseudomorphous to APT; that means the particles have the same shape and size as the former APT crystal s, but consist of very small W03 grains.

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Tungsten Products - Ammonium Paratungstate (APT)

Ammonium Paratungstate (NH4)[H2W12042J,4H20 is the most important precursor for the majority of tungsten products. Exceptions are only product s of melting metallurgy and Menstrum WC produce d directly from ore concentrates.

All other intermediates such as tungsten trioxide, tungsten blue oxide, tungstic acid and ammonium metatungstate ca n be derived from APT, either by thermal decomposition or chemical conversion.

APT is a white crystallized powder having average crystal size between 30 and 100 im, Especially crucial for the quality is the purity, Typical levels of todays commercial APT are (upper limits in pg/g): Al 1-7, As 5-10, Bi 0.5-1, Ca 1-10, C0 1-10, Cr 1-10, Cu 1-3, Fe 3-10, K 2-10; Mg l-7, Mn 1-10, M0 5-30, Na 5-10, Ni 1-7, P 5-7, Pb 1-5, S 5-7, Si 1-10, Sn 1-10, Ti 3-10, and U 3-10, APT is packaged in polyethylene-lined drums.

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Tungsten Products - Concentrates

They are also called Primary Tungsten Sources, Marketable ore concentrates of Scheelite and Wolframite contain typically 65 – 70 % W03, Off grade concentrates having lower W03 concentrations are seldom on the market and if so, only for a lower price. In fully integrated companies lower grades (6-40% W03) are often preferred, because upgrading to high concentrations is mostly combined with a lower yield.

Concentrates in former times have been the main trading product, but were substituted today by APT. Concentrates are packaged either in large polyethylene “big bags” (1 t0 2 tons) or, alternatively, in steel drums and individual packaging (50 t0 200 kg).

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Tungsten Intermediates - 4. Cast Carbide

By melting tungsten metal and tungsten monocarbide (WC) together, a eutectic composition of WC and W2C is formed. This melt is cast and rapidly quenched to form extremeIy hard solid partied s having a fine crystal structure. A tough, feather-like structure is preferred over the brittle, blocky structure obtained by insufficient quenching. The solids are crushed and classified to various mesh sizes.

Tungsten Intermediates - 3. Tungsten Carbide (WC)

Most of the tungsten metal powder is converted to tungsten carbide (WC) by reaction with pure carbon powder, e,g. carbon black, at  900- 2,200℃ in pusher or batch furnaces, a process called carburization.

Tungsten carbide is, quantitatively, the most important tungsten compound. Because of its hardness, it is the main constituent in cemented carbide (hardmetal).

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