To provide analytical tools for the preparation and oxidation of pure bismuth, we have developed techniques for chlorine determination in bismuth and bismuth oxide: indirect, using atomic absorption spec trometry, and direct, using laser mass spectrometry, with detection limits of 1 × 10 -3 and 1 × 10 -5 wt %, respectively. The techniques were used to assess the purity of bismuth in the refining and oxidation steps.
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.
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