Within the limits of a comparative study of solid-state transformations induced by different constraints (thermodynamics, mechanics, electromagnetics, etc.), the authors present the phase-modifications brought about by the grinding of someoxalates (K2C2O4. H2O; CaC2O4. H2O; BaC2O4 ·n H2O withn=0, 1/2, 1 and 2). The water vapour pressure and temperature during the mechanical treatment were selected and fixed. The specificity of the mechanical constraint is discussed. This study mainly shows that (a) the grinding may or may not bring about dehydration, but it may also bring about rehydration; (b) the evolution of a hydrate during treatment, following a well-defined process, shows all the phases known from the most hydrated to the anhydrous form; (c) the mechanical dehydration may be stopped by a change in the grinding temperature and vapour pressure conditions.
Physical Chemistry in 1991 from Mumbai University. Her main area of work during the past 30 years has been determination of thermodynamic properties of nuclear materials using various techniques such as vapourpressure measurements, thermogravimetry
Binary systems with non-negligible vapour pressure may be described by theT-V-x diagram. The use of the volumeV as an independent variable makes it possible to show the part played by the vapour phase in binary systems. This first part deals with the experimental connection betweenT, V andx data measured by DTA with sealed silica ampoules. As an example the eutectic composition is used: the theoretical isothermal, isochoric and isoplethal sections are presented and compared to those of some former works.
The evaporation of benzene, cyclohexane, n-heptane, toluene, 2-xylene, 3-xylene and 4-xylene was studied in H2, He, N2 or CO2 as purge gases for control of the introduced methods of evaluation and the sensitivity limits of TG measurements. Ii as a function of (1−α) and the following equation proved very suitable for a quantitative comparison of 28 independent and
different TG measurements and for a very sensitive characterization of the thermal processes, even within an energy level
difference of 3 kJ mol−1, in spite of the known great inconsistency in the formal kinetic parameters:
The purge gases definitely influence the evaporation. The influence on the average vapour pressure is an exponential function
of the product of the molecular mass and the boiling temperature.
With regard to the number of factors in the TG measurement, and the great sensitivity of Ii and the above function, it can be supposed that these equations exhibit some multivariate regression character, besides their
natural parameter content.
The evaluation methods introduced help to extend the application of TG.
Authors:J. L. Fournival, J. C. Rouland, and R. Ceolin
The binary system water-phenobarbital is presented as a new example of systems with non-negligible vapour pressure. It is explained on the basis of aT- V- x diagram. Two invariant equilibria occur at very close temperatures: a peritectic equilibrium at 123 °C and a monotectic equilibrium at 125 °C.
at T = 298.15 K, of 2-acetyl-5-nitrothiophene and 5-nitro-2-thiophenecarboxaldehyde as −(48.8 ± 1.6) and (4.4 ± 1.3) kJ mol−1, respectively. These values were derived from experimental thermodynamic parameters, namely, the standard (po = 0.1 MPa) molar enthalpies of formation, in the crystalline phase,
measured by rotating bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from the temperature–vapour pressure dependence, obtained by the Knudsen mass loss effusion method.
The results are interpreted in terms of enthalpic increments and the enthalpic contribution of the nitro group in the substituted
thiophene ring is compared with the same contribution in other structurally similar compounds.
Non-isothermal dehydration of copper chloride dihydrate and nickel chloride hexahydrate were studied by using TG, DTG, DTA
and DSC measurements. The copper chloride salt loses its two water molecules in one step while nickel chloride salt dehydrates
in three consecutive steps. The first two steps involve the loss of 4 water molecules in two overlapped steps while the third
step involves the dehydration of the dihydrate salt to give the anhydrous NiCl2.
Activation energies (ΔE) and the frequency factor (A) were calculated from DTG and DTA results. We have also calculated the different thermodynamic parameters, e.g. enthalpy
change (ΔH), heat capacity (Cp) and the entropy change (ΔS) from DSC measurements for both reactants.
The isothermal rehydration of the completely dehydrated salts was studied in air and under saturated vapour pressure of water.
Anhydrous nickel chloride was found to rehydrate in three consecutive steps while the copper salt rehydrated in one step.
Authors:E. A. Ukraintseva, G. N. Chekhova, and D. V. Pinakov
, dichloroethane, methylene dichloride) was represented. For example, article [ 12 ] showed the decrease of equilibrium vaporpressure above CH 3 CN FGICs with decrease of fluorination degree x at fixed temperature (298 K). Thermodynamic properties for FGIC-1
Authors:V. M. Galogaža, E. A. Prodan, H. V. Peslyak, V. A. Sotnikova-Yuzhik, and S. A. Prodan
The kinetics of isothermal-isobaric dehydration of Li5P3O10·5H2O in vacuum (p=10−1 hPa) and in water vapour atmosphere (
=23·hPa) was investigated by TG in the temperature range 40–140°. It was shown that the initial non-degradation removal of 1/10 of the crystal water, the rate of which is sensitive to
, proceeds according to the laws of reversible topochemical reactions. In the next, irreversible degradation stage, where the bulk of the crystal water is removed, the kinetic characteristics of the process and the DSC effects exhibit a low sensitivity to the water vapour pressure. The peculiarities of Li5P3O10·5H2O dehydration were considered in comparison with the thermal behaviour of Na5P3O10·6H2O and K5P3O10·4H2O.
Authors:E. Gmelin, W. Hönle, Ch. Mensing, H. G. von Schnering, and K. Tentschev
The heat capacities of thecluster compounds [Ag6M4P12]Ge6 (M=Ge, Sn) have been measured in the temperature range from 2 K to 310 K. Thermal decomposition into the elements was carried out under Knudsen conditions on a thermobalance combined with a mass spectrometer. The thermodynamic functions standard entropy, enthalpy, and the Debye temperatures were calculated from the heat capacity data. The vapour pressure functions derived from the Knudsen effusion data, served to calculate the third law heat of formation.