Thermal transformations of the composition and structure of hexagonal molybdenum oxide

Abstract

Thermal transformations of the crystal structure and composition of the h-MoO 3 metastable phase with a transition to the α-МоО 3 stable modification are investigated. The study is performed using submicron phase-pure crystals exhibiting stability during their long storage in the air. By powder XRD, SEM, TGA, CHN, LMS, Raman and IR spectroscopy it is found: the composition of the deposited crystals is expressed by the general formula МоО 3 ⋅0.26H 2 O; the impurity cationic composition consists of 1.8 wt.% of ammonia groups and a sum of 15 elements detected at a level of 10 -4 wt.%. Thermal treatment of the crystals to T = 350 °C in the air results in the removal of adsorbed and structural water, ОН -, and 4 NH + groups with retaining the h-phase of hygroscopic МоО 3 ⋅0.08H 2 O. The h-МоО 3 ⋅0.08H 2 O crystals obtained show instability during the storage and transform into the α-МоО 3 stable modification. At T = 380 °C the h → α phase transition occurs with the removal of coordinated water and texture transformations resulting in the formation of α-МоО 3 hygroscopic crystals that at T = 650 °C acquire the platelet shape characteristic of the α-phase.

Phosphate Sensor Using Molybdenum

“…Furthermore, the rationality of phosphorus appeared at electrode surface can be confirmed by the result. This is also consistent with the fact that molybdenum is stable under normal circumstances and reacts in some special cases, 42 such as alkaline and other wet environment. Finally, the electrochemistry response mechanism of molybdenum electrode is based on the reaction between molybdenum and HPO 4 2− in alkaline condition.…”

The microstrain-accompanied structural phase transition from h-MoO3 to α-MoO3 investigated by in situ X-ray diffraction

“…Thermogravimetric results [ 23 – 25 ] indicate that the h-MoO 3 phase releases water molecules during heat treatment, suggesting that water molecules reside in the crystal structure of h-MoO 3 . To determine the crystal structures of h-MoO 3 and α-MoO 3 , slowly scanned XRD patterns were acquired from the carefully ground powders calcinated at 375 °C and 450 °C, respectively.…”