Preparation of Blue Tungsten Oxide

Blue tungsten oxide (TBO) is an important raw material manufacturing of tungsten powder , tungsten oxide reduction due from tungsten powder blue easier to control the particle size and particle size composition , is conducive to the reduction process in the tungsten powder and mixed with other elements, so the TBO is gradually replace the tungsten trioxide production of special tungsten material as tungsten powder materials.

Blue tungsten oxide is an industrial product name , its composition mainly by WO2.9, WO3 and WO2.72 composed of several tungsten oxide , the proportion of each component depending on APT or restore the temperature calcination atmosphere and speed.

Preparation of blue tungsten oxide there are three main methods : APT sealed calcination , APT hydrogen reduction and inherent mild reduction . At present in China more industrial application is the first two methods .

Xue Kam et al APT decomposed under non-oxidizing atmosphere, blue tungsten oxide process of the study found that the decomposition experienced APT six stages :

First stage: the temperature between 90-180C , APT lose some water :

Second stage: temperature range of 180-260 ℃, ammonia begins to escape from ammonium paratungstate , the higher the temperature , the faster the loss of ammonia . Loss of ammonia product was obtained as ammonium metatungstate (AMT), soluble in water, reconstituted after preparation of high purity ammonium metatungstate products ;

Third stage: temperature range of 260-350 ℃, AMT decomposition, further loss of water and ammonia , ammonium decomposition products appeared tungsten bronze (ATB);

Stage IV : The temperature range 350-450C, at this time begins to decompose ammonia in the gas phase , to produce ammonia tungsten bronze (ATB), and to produce hydrogen and nitrogen from the gas phase can be detected in the product hydrogen. Decomposition of ammonia nitrogen and hydrogen atoms is first generated , the new ecological chemical activity of hydrogen atoms , ammonium tungsten bronze to the oxygen index ( tungsten compound in the x (O) / x (W) molar ratio ) decreases. Formation of ammonium tungsten bronze fixed composition , the ammonia content and oxygen index can vary , generally consisting of (NH4) xWO2.8 ~ 3.0;

Fifth stage: temperature range of 450-550 ℃, decomposition ATB ​​this stage , the hydrogen produced by decomposition of ammonia in the reaction , ATB decomposition products occurs WO3 and WO2.9, ATB under reducing atmosphere in the first section and then converted into the WO2 WO3.9in strong reducing atmosphere conditions , ATB will translate directly into W20O58 (WO2.9).

Stage 6: temperature range 550 N 650 ℃, decomposition products of this phase with the phase composition of systems vary considerably reducing the strength of the hydrogen to further participate in the reaction , so that the low priced tungsten oxide, tungsten oxide, transition , decomposition products , in addition to a small amount of ATB , there WO3, WO2.9 and tungsten oxide WO2.27 etc. , even WO2.


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