M.S. Chandrasekharaiah

Thermal decomposition of lanthanum formate

Abstract Thermal decomposition of lanthanum formate has been reinvestigated employing TG, DTA, GC, IR and X-ray diffraction techniques. Lanthanum formate was found to decompose according to the following scheme. The delineation of La2O(CO3)2 as an intermediate decomposition product is the main new finding in this investigation.

A simple method of determining the activation energy of an isothermal solid-state decomposition reaction

A simple approach to determine the activation energy (E) of solid-state decomposition reactions is described. The activation energy is calculated from the slope of the logarithm of the maximum peak height of the isothermal DTA trace versus the reciprocal of the absolute temperature. The proposed method is applied in the study of the kinetics of thermal decomposition of cadmium carbonate. The activation energy calculated from this method (90.8±2.2 kJ mole−1) is in very good agreement with the value (87.5±2.5 kJ mole−1) obtained by the conventional method.RésuméOn décrit une méthode simple dapproximation pour déterminer lénergie dactivation (E) des réactions de décomposition en phase solide. Le calcul de lénergie dactivation seffectue à partir de la pente du logarithme de la hauteur maximale du pic de la courbe dATD isotherme en fonction de linverse de la température absolue. On a appliqué la méthode proposée lors de létude de la cinétique de la décomposition thermique du carbonate de cadmium. Lénergie dactivation calculée à partir de cette méthode (90.8±2.2 kJ mole−1) est en bon accord avec la valeur (87.5±2.5 kJ mole−1) obtenue par la méthode conventionnelle.ZusammenfassungEine einfache Annäherung zur Bestimmung der Aktivierungsenergie (E) von Festphasenzersetzungsreaktionen wird beschrieben. Die Aktivierungsenergie wird aus dem Anstieg des Logarithmus der maximalen Peakhöhe der isothermen DTA-Kurve als Funktion der reziproken absoluten Temperatur errechnet. Die vorgeschlagene Methode wird zur Untersuchung der Zersetzungskinetik von Cadmiumcarbonat eingesetzt. Die hiernach berechnete Aktivierungsenergie (90.8±2.2 kJ mol−1) ist in guter Übereinstimmung mit dem durch die konventionelle Methode erhaltenen Wert (87.5±2.5 kJ mol−1).РезюмеОписано простое приб лижение для определе ния энергии активации тв ердотельных реакций разложения. Э нергия активации выч ислялась их наклона кривой в коор динатах логарифм максимума в ысоты пика и обратной абсолютной температуры. Предлож енный метод был применен дл я изучения кинетики термического разлож ения карбоната кадми я. Вычисленная по этому методу энергия актив ация (90.8+2.2 кдж.моль−1) находится в хорошем согласии со значением 87.5± 2.5 кдж.моль−1, полученным обычным м етодом.

Thermodynamics of liquid uranium vaporization

Abstract The vaporization of liquid uranium contained in single crystal cups of tantalum and tungsten was studied up to 3000 K using Knudsen effusion assembly. The flux of U(g) vapours effusing through the K-cell orifice was corrected for the solubility of Ta (or W) in liquid uranium and the equilibrium vapour pressure of liquid uranium was determined as: Log (P° u /aim) = (6.295 ± 0.164) - (2.642 ± 0.041) × 10 4 /T The sublimation enthalpy of uranium at 298.15 K was evaluated to be 126.3 ± 0.3 kcal/mol.

Thermal decomposition of europium formate and oxalate

Abstract A complete and consistent scheme of the thermal decomposition of europium (III) formate and europium(III) oxalate was elucidated from the results of microthermogravimetry supplemented by DTA, evolved gas analysis, IR and X-ray powder diffraction examination of the products. In addition to the previously known oxycarbonate, namely Eu 2 O 2 CO 3 another oxycarbonate, Eu 2 O(C0 3 ) 2 , was shown to be an additional intermediate of the decomposition reaction. The sequence of the decomposition reaction of the formate was shown to be

Thermal decomposition of cesium hexanitratouranium(IV)

Abstract As cesium hexanitratouranium(IV), Cs2U(NO3)6, has the same Cs:U stoichiometry as that of Cs2UO4, thermal decomposition of this nitrato complex in air and nitrogen was studied in detail as a possible alternate method of preparing pure Cs2UO4. The volatility of cesium nitrate, which is one of the intermediate products, changed this Cs:U ratio during thermal decomposition. Hence, only Cs2U2O7 was obtained on heating the sample to 775 K or higher. A scheme for the thermal decomposition of Cs2U(NO3)6 is given by combining the observed TG, XRD and IR data.

Containment of molten uranium alloys in powder metallurgical tungsten containers

Abstract Recently, in our laboratory, a necessity to contain molten uranium alloys such as URe 2 , UP, U-Nb etc., at temperatures of 2500 K arose. A systematic investigation of the compatibility of these alloys with tantalum and tungsten resulted in establishing that hot-swaged tungsten is a suitable container material. We have developed and experimentally demonsstrated the less expensive powder metallurgical tungsten containers of 98% + theoretical density as alternatives.