Thermo-Raman investigations on thermal decomposition of (NH4)(6)Mo7O24 center dot 4H(2)O

摘要

An extensive study by thermo-Raman spectroscopy was carried out to understand the structural changes occurring during the thermal decomposition of (NH4)(6)Mo7O24. 4H(2)O in open air and under O-2 and N-2 flow. In addition, themogravimetry, differential thermal analysis and thermogravimetry coupled with mass spectrometry analysis were also carried out and a satisfactory decomposition mechanism has been proposed on a molecular level. The thermo-Raman investigations on the decomposition of (NH4)(6)Mo7O24. 4H(2)O or 12(NH4)(2)O .4(MoO3)(7). 16H(2)O, since there are four formulae in a unit cell, in open air indicated the formation of a rst intermediate 11(NH4)(2)O .4(MoO3)(7) in the temperature interval from 124 to 131 degreesC and a second intermediate 7(NH4)(2) O .4(MoO3)(7) from 174 to 239 degreesC, the coexistence of a third intermediate (mixed molybdena with residual volatile components) with MoO3 from 255 to 346 degreesC and the formation of MoO3 from 347 degreesC onwards. The present investigations indicated that during the thermal decomposition process from 25 to 250 degreesC, the (MoO3)(7) unit in (NH4)(6)Mo7O24. 4H(2)O remained intact and the collapse of (MoO3)(7) occurred to form MoO3 immediately subsequent to the loss of the remaining volatile compounds at 255 degreesC. The thermal decomposition of (NH4)(6)Mo7O24. 4H(2)O under O-2 and N-2 ow was also investigated in detail. [References: 34]