Ammonium tungsten oxide generally refers to ammonium paratungstate (APT), a key compound in tungsten chemistry and industry. Its chemical formula is often represented as (NH₄)₁₀(H₂W₁₂O₄₂)·4H₂O or (NH₄)₁₀W₁₂O₄₁·5H₂O, signifying its complex polyatomic structure. APT appears as white or slightly yellow crystalline solids, typically in fine powder form.
(ammonium tungsten oxide)
Its primary significance lies as an essential intermediate in tungsten metal and tungsten carbide production. The compound is industrially produced by digesting tungsten ore concentrates (like wolframite or scheelite) in alkaline solutions, followed by precipitation using ammonium salts. This purification step effectively isolates tungsten from impurities.
A critical property of APT is its behavior upon heating. When calcined under controlled conditions, it undergoes thermal decomposition. This process involves losing ammonia and water molecules, ultimately transforming into tungsten trioxide (WO₃), a crucial precursor for tungsten powder reduction. The purity and particle size of the resulting WO₃, and thus the final tungsten powder, are heavily influenced by the starting APT characteristics.
(ammonium tungsten oxide)
Beyond metal production, APT finds use as a catalyst precursor in various chemical reactions, particularly in petroleum refining and oxidation processes. Its decomposition products or derived tungsten compounds exhibit catalytic activity. Research also explores modified ammonium tungsten oxides (like ammonium tungsten bronzes) for applications in electrochromic devices, where their ability to change color with applied voltage is exploited for smart windows and displays. Handling requires care as APT can decompose to release ammonia gas under certain conditions. Its stability and solubility properties make it a fundamental material in the tungsten value chain.
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