U.R.K. Rao

Thermal behaviour of (NH4)3VO2F4 and Na(NH4)2VO2F4

Abstract The thermal behaviour of (NH 4 ) 3 VO 2 F 4 and Na(NH 4 ) 2 VO 2 F 4 was investigated using TG, DTA and DSC techniques. The occurrence of a first order phase transition with the onset of decomposition in both the compounds is confirmed. The temperature, energetics and hysteresis of the transition are obtained. A possible path for the thermal degradation is given for both the compounds, and the residues are identified.

Fluorination of oxides of uranium and thorium by ammonium hydrogenfluoride

Abstract UO 2 , U 3 O 8 and ThO 2 were fluorinated by NH 4 HF 2 either alone or in conjunction with NH 4 F at room temperature to [NH 4 ] 4 UF 8 .2H 2 O, [NH 4 ] 3 UO 2 F 5 .H 2 O and [NH 4 ] 4 ThF 8 .2H 2 O respectively. The TG/DTA and powder XRD techniques were employed to study the thermal decomposition of these compounds and identify the final residues as UF 4 , UO 2 F 2 .2H 2 O and ThF 4 . This appears to be a simple route to the tetrafluorides.

On the preparation and thermal stability of (NH4)3 VOF6.1.5H2O and (NH4)3NbOF6.1.5H2O

Abstract (NH 4 ) 3 VOF 6 and (NH 4 ) 3 NbOF 6 were prepared by a simple solid state route and their thermolysis studied. It is concluded that both these compounds have water of hydration, their structures are different and they show first order phase transitions.

Thermal stability of CsH2PO4

Abstract The thermal behaviour of CsH2PO4 (CDP) was investigated using micro TG, DSC, X-ray and optical microscopy. The loss in weight commences at 508 K and levels off at 688 K. Although there is no water of hydration as such in this compound, the overall loss in weight corresponds to one molecule of H2O, giving CsPO3. Concomitant with this “dehydration”, CDP also undergoes a reversible polymorphic phase transition at 508 K, as evidenced by DSC and optical microscopic data. The process of “dehydration” might go through an intermediate, Cs2H2P2O7, as in the case of NaH2PO4.

Mode of thermal degradation of (NH4)3VO2F4·12H2O

Abstract Evidence in favour of the path of thermal degradation of (NH4)3VO2F4· 1 2 H2O, previously proposed involving three intermediate compounds, is presented by way of the thermal degradation of the intermediates themselves.

Phase transitions in ammonium oxyfluoro vanadates

Abstract Due to their potential as ferroelectric materials, we investigated the occurrence of phase transitions in several ammonium vanadium oxyfluoride compounds. In all the compounds studied two phase transitions, viz. one below and one above ambient temperature, were observed. The low-temperature transition is believed to be associated with electric dipoles.

Pyrolysis of sodium analogs of (NH4)3VO2F4

Abstract Three sodium analogs of (NH 4 VO 2 F 4 , viz., Na(NH 4 ) 2 VO 2 F 4 ( I ), Na 2 (NH 4 )VO 2 F 4 ( II ) and Na 3 VO 2 F 4 ( III ) were prepared by solid state synthesis and were subjected to thermal degradation. The nature of the residue was established and the possible course of thermal decomposition given in each case. It was inferred that as one goes from I to III , the Na + ions substitute the NH 4 + ions in an ordered fashion.

Preparation and thermal stability of the U(IV)(SO4)2-DMF complex

Abstract A new DMF complex of U(SO 4 ) 2 , i.e., U(SO 4 ) 2 ·2.2 DMF, was prepared and characterized using chemical analysis, X-ray powder diffraction studies, IR and measurement of magnetic susceptibility variation with temperature in the temperature range 77–300 K. Pyrolysis of the solvate was studied by means of TG under two different experimental conditions, and the actual thermal degradation path was deduced using a microthermobalance.

Thermal stability of K2U(SO4)3·H2O, a new double salt

Abstract K2U(SO4)3·H2O was synthesized and investigated by elemental analysis, X-ray powder diffraction, IR, TG and DTA techniques. By comparing its behaviour with that of its constituents, viz. K2SO4 and U(SO4)2, it was inferred to be a double sulphate.

Dimethyl formamide solvates of CaCl2

Abstract The water of hydration in inorganic salts plays a vital role in stabilising their crystal structures, as is evidenced by the fact that on dehydration the structures change radically. In order to understand further the role played by the solvent in the development of an ordered lattice, dimethyl formamide (DMF) solvates of inorganic salts have been prepared and studied. DMF is a good solvent and has a fairly high dielectric constant. Two compounds, viz. CaCl 2 · 2.5 DMF and CaCl 2 ·- 2 DMF, were prepared and were found to be moisture-sensitive. Their thermal stability was determined by micro-thermogravimetry. Both compounds started to lose DMF at 338 K and passed through an intermediate phase, CaCl 2 · DMF, which was stable in the temperature range 408–463 K. However, the differential thermogravimetric run showed four peaks which were also confirmed by differential scanning calorimetry. The X-ray powder diffraction pattern of both the solvates is also presented along with the chemical analysis. A comparative study of their thermal stability is presented.