The strength of tungsten powder compacts mainly results from particles of irregular surface for particle shape is one of the most important factors affecting strength of tungsten powder compacts. Ammonium paratungstate has great influence on the tungsten powder particle shape. The compact strength varies greatly under the same process and raw materials with different properties while producing high compact performance tungsten powder using ammonium paratungstate one step reduction. The features of ammonium paratungstate for producing high compact performance tungsten powder are summarized by the experiments.

 

The structure and morphology of ammonium metatungstate (AMT), (NH 4)6[H2W12O40] ·4H2O, and its thermal decomposition in air and nitrogen atmospheres were investigated by SEM, FTIR, XRD, and TG/DTA-MS. The cell parameters of the AMT sample were determined and refined with a full profile fit. The thermal decomposition of AMT involved several steps in inert atmosphere: 

(i) release of crystal water between 25 and 200 °C resulting in dehydrated AMT, 

(ii) formation of an amorphous phase between 200 and 380 °C, 

(iii) from which hexagonal WO3 formed between 380 and 500 °C,

(iv) which then transformed into the more stable m-WO3 between 500 and 600 °C.
 

 As a difference in air, the as-formed NH3 ignited with an exothermic heat effect, and nitrous oxides formed as combustion products. The thermal behavior of AMT was similar to ammonium paratungstate (APT), (NH4)10[H2W12O 42]·4H2O, the only main difference being the lack of dry NH3 evolution between 170 and 240 °C in the case of AMT.