Thermal decomposition of ammonium molybdates

• Published in: Journal of thermal analysis and calorimetry Vol. 124; no. 2; pp. 1013 - 1021
• Main Authors: Kovács, Teodóra Nagyné, Hunyadi, Dávid, de Lucena, Alex Leandro Andrade, Szilágyi, Imre Miklós
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.05.2016; Springer
• Subjects: Ammonium molybdate; Analytical Chemistry; Annealing; Atmospheres; Calorimetry; Chemistry; Chemistry and Materials Science; Combustion; Decomposition; Hostages; Inorganic Chemistry; Measurement Science and Instrumentation; Physical Chemistry; Polymer Sciences; Thermal decomposition; Thermal properties; Ammonium molybdate; SEM; TG/DTA; XRD; MS; FTIR
• ISSN: 1388-6150; 1588-2926; 1572-8943
• DOI: 10.1007/s10973-015-5201-0

The thermal behavior of ammonium molybdates, i.e., (NH 4 ) 6 Mo 7 O 24 ·4H 2 O ( 1 ) and (NH 4 ) 2 MoO 4 ( 2 ), was studied in inert (N 2 ) and oxidizing (air) atmospheres by TG/DTA-MS, XRD, FTIR and SEM. The thermal decomposition sequence of 2 had similarities to 1 ; however, there were significant differences as well. When both of them were annealed, NH 3 and H 2 O were released parallel, and in air the as-evolved NH 3 was burnt partially into NO and N 2 O. In both atmospheres, while 1 decomposed in four steps, the thermal decomposition of 2 involved 5 steps. In the case of 1 , the intermediate products were (NH 4 ) 8 Mo 10 O 34 , (NH 4 ) 2 Mo 4 O 13 and h-MoO 3 . In contrast, the decomposition intermediates of 2 were (NH 4 ) 2 Mo 3 O 10 , (NH 4 ) 2 Mo 2 O 7 , (NH 4 ) 2 Mo 4 O 13 and h-MoO 3 . By both 1 and 2 , the final product was dominated by o-MoO 3 , accompanied with small amount of Mo 4 O 11 in N 2 , which was absent in air. Most decomposition steps were endothermic, except for the last step around 400 °C, where crystallization from the residual amorphous phase had an exothermic heat effect. In addition, the combustion of NH 3 also changed the DTA curve into exothermic in some cases. The morphology of the final products was characterized by 1–5 μm sheet-like particles, except for annealing 2 in N 2 , when 0.5- to 1-μm-thick and 5- to 10-μm-long needle-shaped particles were detected.