Ammonium paratungstate

The paratungstates are generally crystallised from slightly basic solutions. By far the most important salt is ammonium paratungstate [1311 -93-9] (NH 2o 12 40 known as the heavy form of commercial ammonium paratungstate. It is usually formed by crystallisation from a boiling... 

Traditionally, tungsten ore is chemically processed to ammonium paratungstate [1311-93-9] 5H20, and tungsten oxides, W O. These... 

Amine salts have been used for more than 25 years in the manufacture of pure ammonium paratungstate from sodium tungstate solutions obtained from the leaching of tungsten ores with alkali.211 Such solutions are produced by the leaching of scheelite with sodium carbonate solution at 190 to 225 °C... 

Ammonium paratungstate is recovered from the strip solution by evaporative crystallization, dried and calcined to produce blue oxide 208... 

Tungstic acid (HjWO. ), ammonium paratungstate [(NHJJW7O24] or WO3 reacts with Hj and CH4 at 850-1100°C to give W metal, which subsequently reacts to produce the carbides. The reaction is accelerated by Hj containing some HI This method is used to obtain finely divided WC for the production of cutting tools. 

The hydrate, 5(XH4)20.12W03.5H20 or 3(XHi)30.7W03.8Ha0, is obtained by evaporation of a solution of ammonium paratungstate at temperatures near the boiling-point. It yields small, glistening, monoclinie prisms,... 

The acid salt, 2(XH4) 0.5W03.5H20, is produced by cooling a hot saturated solution of ammonium paratungstate, when it separates in small octahedral plates with crv stallographic elements ... 

The normal barium salt, Ba4[SiCVV20-)s].27H20, is obtained as a fine crystalline powder by adding barium chloride to a boiling solution of ammonium paratungstate saturated TOth silicic acid gel, and allowing the oil which separates to remain in contact with the mother-liquor. 

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