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  • Author or Editor: P. K. Sinhamahapatra x
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Physicochemical properties of bismuth vanadate catalysts with varying compositions, e.g., Bi4V6O21-6 1/2H2O·12 1NH3; Bi6V2O14·3 H2O; Bi6V4O19·6 H2O have been studied by chemical analysis, differential thermal analysis, thermogravimetry, infrared, X-ray diffraction, surface area and magnetic susceptibility techniques.

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Thermal characteristics of the molybdates of magnesium (MgMoO4 · 2H2O), manganese (MnMoO4 · 1.5H2O) and silver (Ag2MoO4) have been studied by DTA and TG techniques. The thermal curves of MgMoO4 · 2H2O show two endothermic changes at 195° and 390° followed by an exothermic change at 420°C. The endothermic changes represent the stepwise dehydration of MgMoO4 · 2H2O to MgMoO4 · H2O and from MgMoO4 · H2O to MgMoO4. X-ray diffraction and IR studies, however, reveal that magnesium molybdate does not undergo any type of decomposition up to 900° and the exo-peak at 420° is clearly due to crystallization.

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Thermal characteristics of the vanadates of zinc, manganese and silver have been studied by DTA and TG techniques and the different transition products thus obtained have been characterised by IR, X-ray diffraction and magnetic susceptibility data. Chemical analyses indicate the following compositions of these vanadates: (1) Zn2V2O7.5H2O, (2) Zn3(VO4)2.3H2O, (3) Mn(VO3)2.2H2O and (4) Ag3VO4. The DTA curves indicate that zinc pyrovanadate undergoes endothermic changes at 110–195, 265, 365, 440, 660° and one exothermic change at 485°. This system is diamagnetic which becomes completely paramagnetic after 660°. Zinc orthovanadate exhibits a number of endothermic peaks at 300, 470, 700, 815 and 930° respectively. This system is feebly paramagnetic and retains this property up to 930°. Manganese metavanadate undergoes endothermic changes at 240, 280–590, 830 and 880° respectively. This vanadate is paramagnetic and paramagnetism increases appreciably at 590° and remains constant up 830°. Silver orthovanadate exhibits three endothermic changes at 180, 455 and 640°, respectively.

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