Ammonium metatungstate and tungstic acid (or specifically ammonium tungstate) are distinctly different in terms of definition, properties, uses and production processes.
Definition and molecular formula
Definition and Molecular Formula of Ammonium Metatungstate
It is an inorganic compound, usually appearing as a white crystalline powder or slightly yellow, with the molecular formula H28N6O41W12 and molecular weight 2974.32. It is also known as ammonium metatungstate hydrate or ammonium (meta)tungstate hydrate (abbreviated as “AMT”). It is also known as ammonium (meta)tungstate hydrate (“AMT”).
Definition and molecular formula of tungstate
Tungstic acid does not refer to a specific compound, but is a class of multimeric compounds consisting of tungsten trioxide WO3 combined with each other and with water in different ratios and forms. It can be further categorized into xanthotungstic acid, scheelite tungstic acid, etc. However, if we refer to the specific compound of ammonium tungstate, its molecular formula is (NH4)10W12O41~xH2O, molecular weight is 3042.58, and it is a white crystalline powder.
Properties of Ammonium Metatungstate
It can dissolve in water, which is a main difference between it and ammonium paratungstate. In addition, ammonium metatungstate has important applications in the preparation of other tungsten compounds and petrochemical catalysts, as well as a raw material for the manufacture of tungsten metal, alloy steel and fireproof fabrics.
Properties of tungstic acid (ammonium tungstate for example)
It is also soluble in water, but insoluble in alcohol. At 100°C, ammonium tungstate loses four molecules of water of crystallization. In addition, its solubility in water at 20°C is less than 2%.
Uses of Ammonium Metatungstate
In addition to the applications mentioned above, it is widely used in the ceramic industry.
Uses of tungstic acid (or specifically ammonium tungstate)
It is an important intermediate for the preparation of other tungsten compounds, and plays an important role in the powder metallurgy of tungsten, the production of tungsten salts and the preparation of catalysts.
Production Process of Ammonium Metatungstate
There are various production methods, including taking ammonium tungstate or sodium tungstate as raw material, obtaining ammonium metatungstate solution by solvent extraction or ion exchange method, and then obtaining the product by evaporation and crystallization; or transforming ammonium sec-tungstate into ammonium metatungstate by heating, and so on.
Production process of tungstic acid (or specifically ammonium tungstate)
It is usually prepared by neutralization method, i.e. wolframite is synthesized into calcium tungstate by alkaline decomposition and action of calcium chloride, and then it is produced by acid decomposition and action of ammonia.
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