Elementary thermochemical calculations show that in all cases of formation of solid product in the process of the congruent
dissociative vaporization of reactants, the equilibrium partial pressure of the main product greatly exceeds its saturation
vapour pressure, and therefore causes the appearance of vapour oversaturation. The oversaturation is responsible for the formation
and growth of nuclei, their shape and position, the transfer of condensation energy to the reactant, the existence of induction
and acceleration decomposition periods, the reaction localization, the epitaxial/topotaxy effects and the nanocrystal structure
of the solid product. Variations in the energy transfer explain an increase of the molar enthalpy with temperature and the
decelerating influence of melting on the rate of decomposition.
The effect of atmospheric water vapor on the kinetic rate behavior of the thermal decomposition of copper(II) carbonate hydroxide,
Cu2CO3(OH)2, was investigated by means of TG-DTA coupled with a programmable humidity controller. With increasing water vapor pressure
p(H2O) from 0.8 to 10.6 kPa, a systematic reduction of the reaction temperature of the thermal decomposition was observed as the
continuous trend from the previous works at the lower p(H2O). Through a comparative kinetic analysis of the reaction at different p(H2O), a catalytic action of the atmospheric water vapor on the nucleation process at the first half of the reaction was identified
as the possible origin of the reduction of the reaction temperature.
Authors:M. Suşeska, M. Rajiş, S. Matečiş-Mušaniş, S. Zeman, and Z. Jalový
TNAZ (1,3,3-trinitroazetidine) is a relatively new, powerful, steam castable, strained ring explosive. Owing these characteristics
it is of considerable interest to the energetic material community. A relatively high vapour pressure, volume contraction
and formation of shrinkage cavities in the solidification of its melt may be considered as some of its disadvantages. The
kinetics and heats of TNAZ sublimation and evaporation were studied by the non-isothermal and isothermal thermogravimetry
method. The activation energy of 94-102 kJ mol-1 was found for TNAZ sublimation, while the activation energy of 60-81 kJ mol-1 was found for TNAZ evaporation. The enthalpy of TNAZ sublimation at the melting temperature was found to be 95 kJ mol-1, and the enthalpy of TNAZ evaporation equals 66 kJ mol-1.
Authors:G. Golan, A. Axelevitch, B. Sigalov, and B. Gorenstein
Thermal effects in a low-pressure plane plasma discharge were obtained in a novel implementation of triode sputtering method.
This plane plasma discharge is formed in a relatively low vapor pressure of 0.03-0.65 Pa. Electron beam temperature and ion
beam concentration distribution, as well as their dependence on argon pressure within the plasma, were experimentally studied,
using the Langmuir probe technique. The influence of an external magnetic field on the ion beam concentration, and electron
beam temperature, were studied too. As a result of these studies, sputtering of various materials was done using the novel
plane plasma discharge method. This method enables the deposition of homogeneous thin film coatings. Analysis is done on Cu
sputtered layers with plane plasma discharge.
The vaporization enthalpies of two acetanilide pesticides, alachlor
(2’,6’-diethyl-N-(methoxymethyl)-2-chloroacetanilide) and metolachlor
were determined by processing non-isothermal thermogravimetry data according
to the Clausius-Clapeyron equation. The reliability of the procedure proposed
was tested carrying out some experiments at different heating rates using
acetanilide as a reference compound. A good agreement is found among the vaporization
enthalpies derived from all the multi-heating rate experiments as well as
with the one predicted from the vapor pressure data taken from literature.
The vaporization temperatures (Tvap=470±2
K and Tvap=479±2
K) and enthalpies (ΔvapH°(436
K)=85±1 kJ mol–1 and ΔvapH°(436 K)=70±1 kJ mol–1)
for alachlor and metolachlor, were selected, respectively.
Authors:K. Chatterjee, D. Dollimore, and K. Alexander
Hydroxy benzoic acids were subjected to rising temperature thermogravimetric analysis. After optimizing the procedural variables,
the kinetics of decomposition was determined and methyl paraben was taken as the calibration compound to characterize the
evaporation patterns for the ortho and meta derivatives. The Eact values for ortho, meta and para derivatives were 64.8, 78.2, and 119.1 kJ mol–1, respectively. The Antoine and Langmuir equations were utilized to determine the coefficient of evaporation k, which was 1245250.8, units being in the SI system. The vapor pressure plots were generated for the ortho and meta derivatives; ΔHvap for these two compounds were obtained as 66.7 and 80.4 kJ mol–1, respectively.
A thermobalance for studies of the high-temperature sulfidation of metals and alloys is described. This apparatus permits
the determination of mass changes in a sulfidized sample as a function of temperature and sulfur vapour pressure. The main
parts of this apparatus are the container with liquid sulfur and the reaction chamber with the quartz space and quartz spiral.
All parts of the apparatus are equipped with thermostating furnaces. The temperature within the apparatus is controlled with
an accuracy of 0.5 K. The quartz spiral (diameter 0.2 mm), consisting of 50 coils (diameter 30 mm), permits the recording
of mass changes in the sample (about 200 mg) with an accuracy of 10-5 g.
Besides heterogeneous kinetics measurements, it has been shown that the self- and chemical diffusion coefficients or the deviation
from stoichiometry of the metal sulfides can also be studied as functions of temperature and sulfur pressure by means of equilibration
Authors:E. Ukraintseva, V. Logvinenko, D. Soldatov, and T. Chingina
The thermal dissociation processes of clathrates [CuPy4(NO3)2]·2G (G=tetrahydrofuran, chloroform) were studied. Thermodynamic parameters (
G2980) of the processes, producing solid host complex [CuPy4(NO3)2] and gaseous guest (G), were determined from the strain measurements. These data are compared with previous data for clathrates of the host complex with benzene and pyridine. Quasi-equilibrium thermogravimetry was used to investigate the step-by-step character of the dissociation processes. Kinetic studies were carried out for clathrate [CuPy4(NO3)2]·2THF.
Authors:M. Wachsmuth, B. Eichler, L. Tobler, F. Hänssler, H. Gäggeler, and M Ammann
Selenium nuclides are available from thermal neutron induced nuclear fission of 235U at the gas-jet facility at the Swiss spallation neutron source (SINQ) at Paul Scherrer Institute, Switzerland. The formation of stable selenium compounds, their transport yields using the gas-jet system and their relative thermal decomposition temperature were investigated under oxidizing and reducing conditions in the target chamber. Using O2, H2, CO, and propene as additional gases, the selenium isotopes are suggested to form H2SeO3, H2Se, COSe, and C3H6Se, respectively, with overall 84Se yields of 1.5%, 4.7%, 6.3%, and 21.9%, respectively. Adsorption enthalpy, vapour pressure, solubility and acidity data for these species were collected from the literature or estimated from other known thermochemical properties. Carrier free bromine isotopes (84Br, 86Br) in the form of HOBr were obtained by thermally decomposing H2SeO3 and retaining elemental Se under oxygen rich conditions on quartz at 400 K.
Enthalpies and entropies of sublimation for N-acetylglycine amide (NAGA), N-acetyl-L-alanine amide (L-NAAA), and N-acetyl-D-leucine amide (D-NALA) were determined from the dependence of their vapour pressures on temperature, as measured by the torsion-effusion method.