An adiabatic calorimetry was used for some investigations of equilibrium and non-equilibrium phase transitions. For one of
the substances studied (4,4′-di-n-heptyloxyazoxybenzene) it was possible to determine temperature dependence of an order parameter and number of clusters of
high temperature phase in a region of a phase transition. For another substance (liquid 3,4 dimethylpiridine) an anomaly on
the specific heat curves was interpreted as being responsible for a decay of molecules’ clusters.
Non-equilibrium phase transitions were investigated for some liquid crystal substances. The process of transformation between
metastable and stable phases was described quantitatively. The conclusions obtained concern the stability of metastable phases.
A model is proposed for AC calorimetry (ACC) at the first order phase transition point. The model is compared with the results of ACC around the melting point of ann-paraffin (C20H42). The observed frequency dependence of ACC is consistent with the model. A harmonic component of the temperature modulation with a frequency equal to twice the heating frequency was observed at the phase transition point. It is shown that the harmonic component can be explained on the basis of the proposed model.
Mukesh Chandra (extreme R) are also seen
It is giving me immense pleasure in introducing this special issue of the Journal of Thermal Analysis and Calorimetry based on the papers devoted to Indian Council of Chemists
Polyester yarn spun over a range of wind-up speeds has been characterized using differential scanning calorimetry. Samples prohibited from shrinking during the thermal analysis show slightly smaller heats of fusion and crystallization and reduced cold crystallization temperatures than samples that are free-to-shrink, particularly in the intermediate wind-up speed region. One critical observation made is that the cold crystallization temperature reaches a minimum at some relatively low overall molecular orientation (Δn ∼ 0.020) and fails to decrease further. A likely explanation is that crystallization continuously removes polymer from the melt in the spinline in regions where the local orientation reaches some critically high value.
Polyester yarn spun over a range of wind-up speeds and subsequently drawn at 373 K has been characterized by differential scanning calorimetry. Samples that are constrained from shrinking during the thermal scan respond differently than samples that are free-to-shrink. In the region of intermediate orientation, the constrained samples typically show a lower cold crystallization temperature: In the region of high orientation, the constrained samples typically show a higher melting temperature. The results are quantitatively similar to those based on fibers in which the orientation is imparted directly by high speed spinning.
The technique of heat flow calorimetry was used to study the thermal behaviour of different carbohydrates between 20°C and 270°C. The samples were analyzed by heating in sealed cells. The temperature range in which exothermic reactions, due to thermal decomposition, occurred varied widely depending on the type of carbohydrate investigated. Reaction enthalpies of 44 sugars and polysaccharides are given. Endothermic phenomena, such as fusion or vaporization of crystallized water, were also observed: fusion temperatures and enthalpies of 34 sugars and sugar alcohols are listed. Calorimetric curves showing crystallization of amorphous sucrose, cellobiose and lactose are also presented.
of the calorimetric continuous titration experiment is presented. The proposed
method is basing on the collection of larger number of experimental data points
than could be obtained from the classical isothermal titration calorimetry
experiment. After the deconvolution procedure resulting in the correction
for the calorimeter time response the pure power effect signal could be obtained.
The collected data enable the detailed analysis of the closely populated 2:1
and 1:1 weak complexes.
Results of the experimental thermodynamic investigations of the system Bi-Au2Bi obtained by using Oelsen calorimetry are presented in this paper. Activities, activity coefficients and partial molar quantities
for bismuth in the temperature interval 600-1000 K are determined. Based on the values of the thermodynamic parameters, negative
deviation from Raoult law was obtained for the investigated system. Also, bismuth activities and activity coefficients dependence
on composition and temperature is calculated by the nonlinear programming using gradient method.
The standard molar enthalpy of formation of crystalline dialkyldithiocarbamate chelates, [Pd(S2CNR2)2], with R=CH3 and i-C3H7, was determined through reaction-solution calorimetry in 1,2-dichloroethane, at 298 K. Using the standard molar enthalpies
of formation of the gaseous chelates, the homolytic (52618 and 66610) and heterolytic (269318 and 295710 kJ mol-1) mean enthalpies of palladium-sulphur bond dissociation were calculated.
Two geographical subspecies of the honeybee Apis mellifera, the European bee A. m. carnica and the Egyptian bee A. m. lamarckii, were investigated by direct calorimetry. Maximum, mean and minimum heat production rates were determined for groups of 6 bees as a function of temperature and daytime. Smaller Egyptian subspecies showed significantly higher mass specific metabolic rates than the European one. Maximum and mean heat production rates decreased exponentially with growing temperatures while the minimum values remained constant.