Phase transitions of some sulfur-containing ammonium salts

• Phase transition of (NH4)2SO4 was originally detected near 370 °C.
• Melting parameters of NH4HSO4, of NH4SO3NH2, of (NH4)3H(SO4)2 were specified.
• Phase transitions parameters of (NH4)2SO4, of (NH4)3H(SO4)2 were determined.

For the first time high-temperature polymorphic transition of ammonium sulfate (NH4)2SO4 (Tpt ∼ 370 °C) was experimentally recorded and characterized by differential scanning calorimetry. Phase transitions parameters of (NH4)2SO4, of ammonium bisulfate NH4HSO4, of triammonium hydrogen disulfate (NH4)3H(SO4)2 and of ammonium sulfamate NH4SO3NH2 were clarified. Method of determining the phase transitions parameters for thermally unstable substances, in particular for the triammonium hydrogen disulfate (NH4)3H(SO4)2, was developed and tested with the help of differential scanning calorimetry.