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APT is ammonium paratungstate for short. Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, with the chemical formula (NH4)10(H2W12O42)·4H2O.

 

Ammonium paratungstate is produced separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO3, tungsten (VI) oxide. From there, the oxide is heated in an atmosphere of hydrogen, reducing the tungsten to elemental powder, leaving behind water vapor. From there, the tungsten powder can be fused into any number of things, from wire to bars to other shapes.