Heat capacities of U1–yLayO2 were measured by means of direct heating pulse calorimetry in the temperature range from 300 to 1500 K. An anomalous increase in the heat capacity curve of each sample was observed similarly to the case of U1–yGdyO2, found recently in our laboratory. As the lanthanum content of U1–yLayO2 increased, the onset temperature of an anomalous increase in the heat capacity decreased and the excess heat capacity increased. The enthalpy of activation (Hf) and the entropy of activation (Sf) of the thermally excited process, which cause the excess heat capacity were obtained to be 2.14, 1.63 and 1.50 eV and 39.4, 34.2 and 31.8 J·K–1·mol–1 for U0.956La0.044O2, U0.910La0.090O2 and U0.858La0.142O2, respectively. The values at zero La content extrapolated by using the data of Hf and Sf for U1–yLayO2 were in good agreement with the experimental values of undoped UO2 so far reported, similarly to the case of Gddoped UO2. The electrical conductivities of U1–yLayO2 (y=0.044 and 0.142) were also measured as a function temperature. No anomaly was seen in the electrical conductivity curve. It may be concluded that the excess heat capacity originates from the predominant contribution of the formation of oxygen clusters and from the small contribution of the formation of electron-hole pairs.
The response of a chemical reaction to temperature modulation has been examined experimentally in an epoxy thermosetting system.
The kinetic response appears in the imaginary part of the complex heat capacity determined by TMDSC. From the imaginary part
and the ‘non-reversing’ heat flow of reaction, the activation energy has been determined. The value of the activation energy
obtained is in good agreement with the value determined from Kissinger's plot utilizing the peak temperatures of the exothermic
reaction with different heating rates.
Authors:Y. Arita, T. Ogawa, B. Tsuchiya, and T. Matsui
Heat capacities, electrical conductivities and phase transition temperature of hafnium hydrides, HfHx (0.99≤x≤1.83), were studied using a direct heating pulse calorimeter and a differential scanning calorimeter from room temperature
to above 500 K. The heat capacity of HfH1.83 was larger than that of pure hafnium and showed no anomaly of heat capacity. In contrast, there were λ-type peaks for the
heat capacity and DSC curves for HfHx (1.1≤x≤1.6) near 385 and 356 K. The anomalies of heat capacity and electrical conductivity of HfHx (1.1≤x≤1.6) were considered the result of phase transition and order-disorder phase transition for hydrogen in the hafnium hydride
lattice for HfHx (1.1≤x≤1.3).
Authors:A. Toda, C. Tomita, T. Arita, and M. Hikosaka
The application of a periodically modulated driving force has been examined in the melting and crystallization kinetics of
ice crystals confined in a porous media. The kinetic response of transformation gives the real and imaginary parts of the
‘apparent’ heat capacity obtained with a temperature modulated differential scanning calorimetry (TMDSC). Based on a modelling
of the kinetics, the detailed examination of the frequency dispersion and its dependence on underlying heating/cooling rate
enables us to evaluate the transformation rate and the dependence of the rate coefficient on the driving force, i.e. the degree
of supercooling or superheating. The experimental results indicate that the transformation processes are limited by heat diffusion
from the growth interface of each crystallite to surroundings.