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Ammonium uranates / Uranium oxides / Thermal decomposition SummaryAmmonium uranates (AU) were precipitated from a nuclearpure uranyl nitrate solution using ammonia liquor. Unwashed and washed uranate samples were heated at temperatures varying between 400° and 800°C and analysed thermally and by Xray diffraction analysis. The results indicated that amorphous uranium trioxide (A-UO,) is mainly formed in absence of carried ammonium and nitrate ions, whereas deamination of the retained ammonia leads to y?-U0 3 formation. The retained ammonium ions in the AU structure increased with the pH of precipitation and these ions lead to formation of two polymorphs of uranium octoxides.

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