On the high-temperature phase transitions of NH4HSO4

✍ Scribed by Diosa, J. E. ;Fernández, M. E. ;Vargas, R. A. ;Torijano, E. ;Mellander, B.-E.

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 141 KB
• Volume: 202
• Category: Article
• ISSN: 0031-8965
• DOI: 10.1002/pssa.200520065

✦ Synopsis

Abstract

Modulated differential scanning calorimetry (MDSC), thermogravimetric analysis (TGA) and X‐ray diffraction (XRD) were used to study the phase behaviour of NH~4~HSO~4~ (AHS) above room temperature. For powder AHS measured during successive thermal cycles, the MDSC curves show an endothermic peak at 147 °C on heating scans and an exothermic peak at about 115 °C on subsequent cooling runs. However, after the second thermal cycle, a second endothermic peak starts to appear at about 135 °C on heating runs whose intensity increases on subsequent cycles. The thermogravimetric measurements on powder AHS show weight loss above 135 °C. X‐ray powder diffraction data for AHS heated to 140 °C during 24 hours, show the diffraction pattern for (NH~4~)~2~S~2~O~7~. We discuss the endothermic effect at 135 °C in terms of a partial dehydration setting in at reaction sites distributed on the surface of the crystals. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)