Authors:E. Aragon, K. Jardet, P. Satre, and A. Sebaoun
The Al–Ga–Zn ternary phase diagram presents two isobaric invariant reactions: a eutectic at 231C and a metatectic at 1231C
[1–3]. Calorimetric measurements on the two isobaric invariant reactions have been carried out. First the Tammann method has
enabled us to determine the composition of their limits on five isopletic cross sections. Then, the compositions of the invariant
phases have been determined.
A new calorimetric method and the results of determination of binary systems phase equilibria having a region of phase stratification
on the basis of calorimetric measurements are described in this paper. Isochoric heat capacity temperature dependence of binary
system of hydrocarbon-water has been studied by the method of high-temperature adiabatic calorimeter. Parameters of the phase
stratification region have been determined on the basis of revealed peculiarities of this dependence at phase transitions
liquid-liquid and liquid-vapour and phase diagram have been made.
For a great number of European safety groups, reaction calorimetry is the key technique for analysis of the main reaction in the risk assessment of chemical processes. A comparison of calorimetric studies of model reactions, the N-oxidation of two substituted pyridines with hydrogen peroxide, made by several European groups, can open the door to standardization of the methodologies used. However, the intrinsic experimental complexity of the model reactions, which included dosing at high temperature, a multiphase system and evaporation, and the different evaluation criteria, produced a considerable dispersion between the results obtained by the various groups.
Authors:C. Schick, M. Merzlyakov, A. Minakov, and A. Wurm
Quasi-isothermal temperature modulated DSC (TMDSC) were performed during crystallization to determine heat capacity as function of time and frequency. Non-reversible and reversible phenomena in the crystallization region of polymers were distinguished. TMDSC yields new information about the dynamics of local processes at the surface of polymer crystals, like reversible melting. The fraction of material involved in reversible melting, which is established during main crystallization, keeps constant during secondary crystallization for polycaprolactone (PCL). This shows that also after long crystallization times the surfaces of the individual crystallites are in equilibrium with the surrounding melt. Simply speaking, polymer crystals are living crystals. A strong frequency dependence of complex heat capacity can be observed during and after crystallization of polymers.
The measurement of the maximum glass transitionTg∞ of a thermosetting resin is usually performed by differential scanning calorimetry in the second scan (Tg2scan), after a previous scan by heating up the sample to a temperature where the exothermic curing reaction has been completed.
However, this method can eventually produce thermal degradation, decreasing the crosslinking density and theTg of the sample. Values ofTg2scan between 95† and 102†C were found in an epoxy resin based on DGEBA cured with phthalic anhydride. Thermal degradation effects
can be avoided if the measurement is performed by isothermal curing and further determination ofTg. ATg∞ value of 109†C is achieved, which is the maximum value ofTg according to the topological limit of conversion.
The role of calorimetry in adsorption is shortly reviewed. The differences between calorimetric adsorption heats and those
calculated from Clausius-Clapeyron equation for the systems ethanol-activated carbons are presented. Obtained results, together
with the results presented previously for other adsorbates, confirm that calorimetry is indispensable for a real thermodynamical
description of the adsorption process in this type of system.
In this paper, examples are given of how calorimetric values can give greater certainty to phase equilibria calculated from
thermodynamic data. Errors that may arise when phase diagram evaluations are carried out largely from the basis of Gibbs energy
information only are illustrated by reference to recent evaluations of the Ti−Si system and the resulting calculated oxidation
behaviour of titanium silicides. The importance of calorimetric values for calculation of metastable phase equilibria is demonstrated
by results of work on the AlN−TiN hard-metal coating system. Finally, suggestions are made with regard to areas of work where
calorimetric data are urgently needed.
Authors:E. Aragon, D. Vincent, A. Zahra, and A. Sebaoun
A systematic study of Al-Zn-Sn ternary alloys by using a Tian-Calvet calorimeter with slow heating and cooling rate was carried
out and supplemented by scanning electron microscopic observations.
The results have shown that crystallization coupled with dissolution of tin into the αss′ ternary solid solution on heating is an endothermic process, while melting coupled with tin expulsion on cooling is an exothermic
one. It seems that the thermal effects of phase transition are outweighed by much stronger ones due to a large composition
change of the αss′ ternary phase.