Conventional calorimetry has always the difficulty of choosing between near to equilibrium working conditions and high thermal
ramp rates. Thus, either the transport phenomena and sample homogeneities are good but the signals become weak due to thermal
losses, or the signals are sharp, but strong gradients across the sample lead to chemical and thermal heterogeneities. The
described pulsed fluidized bed technique, by strongly stirring the sample, allows good sample homogeneities even at high ramp
rates. Moreover, the permanently regenerated cover gas allows as well a good heat transfer towards the thermocouples as a
constant atmosphere composition leading to very precise onset temperatures.
Several DTA experiments followed by calorimetric works are reviewed here to emphasise the importance of complementary role
of both techniques. The thermal analysis is advantageous in the sense that it gives quickly the overall view of thermal behaviour
of a material under various conditions. Calorimetric work provides accurate heat capacity data which enable to derive thermodynamic
functions including the enthalpy and entropy. The latter quantity is especially important in judging whether the material
obeys the third law of thermodynamics. However, calorimetric work leads occasionally to an erroneous conclusion if the work
is not preceded by thermal analysis performed under various conditions. Sometimes, quality of information obtained by DTA
exceeds that obtained by laborious calorimetry.
Polymorphism of trilaurin mixed with 4% of cholesterol was studied with a setup coupling calorimetry and phase characterisation
by in-situ X-ray diffraction (Microcalix). Four polymorphic forms were identified. Monotropic and enantiotropic transitions
were identified from the reconstruction of Gibbs free energy diagram which allows the control of trilaurin polymorphism.
Calorimetry deals with the energetics of atoms, molecules, and phases and can be used to gather experimental details about
one of the two roots of our knowledge about matter. The other root is structural science. Both are understood from the microscopic
to the macroscopic scale, but the effort to learn about calorimetry has lagged behind structural science. Although equilibrium
thermodynamics is well known, one has learned in the past little about metastable and unstable states. Similarly, Dalton made
early progress to describe phases as aggregates of molecules. The existence of macromolecules that consist of as many atoms
as are needed to establish a phase have led, however, to confusion between colloids (collections of microphases) and macromolecules
which may participate in several micro- or nanophases. This fact that macromolecules can be as large or larger than phases
was first established by Staudinger as late as 1920. Both fields, calorimetry and macromolecular science, found many solutions
for the understanding of metastable and unstable states. The learning of modern solutions to the problems of materials characterization
by calorimetry is the topic of this paper.
The heat capacityCp of a sample can be considered as a frequency dependent quantity; its behaviour can reflect the dynamics of enthalpy fluctuations. In order to take into account the dynamic nature of the measured quantity, calorimetry can mimic experimental methods as those of dielectrometry, performing experiments in time domain or in frequency domain.
The paper gives a review on recent progress on new methods, instrumental innovations and new trends in low temperature calorimetry
as reported in the last five years in the literature. The paper refers to establishing strictly adiabatic conditions, improved
analysis of quasi-adiabatic experiments, high resolution adiabatic and isoperibol scanning calorimeters and microcalorimeters
for the study of µ-samples.
This paper explains why directly agitated test cells are sometimes required in order to obtain good adiabatic calorimetry data that can be used with confidence to predict large scale plant behaviour. Experiments for methyl methacrylate polymerisation are reported. Simple procedures are presented for calculating genuine thermo-kinetic parameters from data which includes energy dissipation from the stirrer drive system.
The research in thermal analysis and calorimetry, conducted by the author over the period 1964 to 1993, is summarised and
concisely reviewed. The major investigations have focussed on thermal analysis studies of coordination compounds, particularly
the metal dithiocarbamate complexes. A significant solution calorimetric study of some metal dithiocarbamate complexes has
also been undertaken. DSC has been applied to determine the sublimation enthalpies of many metal dithiocarbamate and metal
pentane-2,4-dionate complexes and solution calorimetry has been applied to study the thermochemistry of the latter group of
complexes. Thermal analysis investigations of several inorganic molten salt systems have been initiated. Thermometric titrimetry
has been applied to study metal-macrocyclic ligand systems in aqueous media and particularly those systems of environmental
significance. Temperature calibration standards for TMA have been proposed and TMA has been applied to study the mechanical
properties of several common inorganic compounds. DTA has been applied to study a wide variety of phenols and has subsequently
been applied as an analytical technique to determine the components of solid state phenol mixtures. Thermometric titrimetry
has been applied to determine the phenolic content of wines. A comprehensive thermal analysis study of Australian brown coal
has been undertaken, involving the DSC determination of coal specific energy, a TG/DTA study of the coal pyrolysis and combustion
processes and a TG/DTA and EGA study of the cation catalytic effect on the coal pyrolysis process. Thermal analysis and calorimetric
techniques have been extensively publicised and promoted by the publication of specialist reviews, the presentation of symposia
review papers and the oral presentation of short courses, particularly in the SE Asian region. This review essentially reveals
the diversity of possible application of thermal analysis and calorimetric techniques and the primary significance of thermodynamic
data in the fundamental rationalisation of chemical phenomena.
Materials with high surface areas and small particle size (nanophases), metastable polymorphs, and hydrated oxides are increasingly important in both materials and environmental science. Using modifications of oxide melt solution calorimetry, we have developed techniques to study the energetics of such oxides and oxyhydroxides, and to separate the effects of polymorphism, chemical variation, high surface area, and hydration. Several generalizations begin to emerge from these studies. The energy differences among different polymorphs (e.g., various zeolite frameworks, the - and -alumina polymorphs, manganese and iron oxides and oxyhydroxides) tend to be small, often barely more than thermal energy under conditions of synthesis. Much larger contributions to the energetics come from oxidation-reduction reactions and charge-coupled substitutions involving the ions of basic oxides (e.g., K and Ba). The thermodynamics of hydration involve closely balanced negative enthalpies and negative entropies and are very dependent on the particular framework and cage or tunnel geometry.