The thermal properties of a number of zirconia gels, prepared with various precipitants, have been studied by thermogravimetry, differential thermal analysis and evolved gas analysis. The results obtained show that ligands derived from the various precipitants are incorporated in these gels and strongly influence their high temperature behaviour. The observed properties are interpreted on the basis of a defect structure involving O2- vacancies generated through the removal of these ligands at higher temperatures.

Thermal and related studies of some zirconia gels

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.

Physico-chemical properties of solid catalysts: Studies on thermal analysis of the molybdates of magnesium, manganese and silver

By thermolysis of hydroxide coprecipitates of Bi(III) and Ti(IV) at medium temperatures between 500 and 660° one has obtained the following mixed bismuth and titanium oxides: Ti8TiO14, Bi2TiO5, Bi4Ti3O12 and Bi2Ti3O9. The hydroxide coprecipitates were obtained in controlled conditions, starting from Bi(No3)3 and TiO(No3)2. The thermolysis of the coprecipitates and the formation of mixed oxidic phases were investigated by means of TGA, TDA. IR and X-rays analysis.



Darstellung von Wismut-Titan-Mischoxiden durch Thermolyse der Hydroxid-Mischfallungen



Die Thermolyse der gemeinsamen Fallungen von Bi(III)- und Ti(IV)-Hydroxiden aus Bi(NO3)3 und TiO (NO3)2 bei mittleren Temperaturen zwischen 500° und 660° folgende Bi- und Ti-Mischoxide: Bi8TiO14, Bi2TiO5, Bi4Ti3O12 und Bi2Ti3O9. Die Thermolyse der gemeinsamen Fallungen und die Bildung der Mischoxid-Phasen wurden mittels TGA, DTA, IR- und rontgenographisch untersucht.

Mixed Bismuth and Titanium Oxides obtained by thermolysis of hydroxide coprecipitates

Degradation of dibutyl phosphate (DBP) in aqueous solution was successfully demonstrated in this paper using nanoparticles of anatase titania. Nanocrystalline anatase titania employed for the degradation study was synthesized in house by solgel route under stirring mode using titanium ethoxide precursor. The catalyst was characterized using XRD, DRS, BET, TEM, TG–DTA and Raman spectroscopy to establish the catalytic activity and surface morphology. A cylindrical photoreactor was used for the photocatalytic experiments. 10 mg of nano anatase titania and 0.5 mL of 30 % H2O2 were used as catalysts for the degradation of 1,000 mL of 240 mg/L DBP. Ion chromatographic procedure was used for following the DBP degradation. More than 95 % of DBP degradation could be in less than 45 min and the kinetics of DBP was found to follow pseudo first order. It was demonstrated that the photocatalytic efficiency of the synthesized titania was better than P-25 titania.

Synthesis, characterization and evaluation of nanocrystalline anatase titania for the degradation of dibutyl phosphate

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.

Physico-chemical properties of catalysts: Thermal analysis, infrared spectroscopy, X-ray diffraction and magnetic susceptibility of the vanadates of zinc, manganese and silver

The authors have reviewed the salient features of the thermal behavior of the following systems:
 Excellent correlations have been obtained in most of the systems between the thermal characteristics of the solids, as revealed by DTA, and their specific surface areas and catalytic activity.

S. K. Bhattacharyya

Papers

The application of differential thermal analysis technique to the study of single, binary and ternary oxide catalyst systems