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Thermogravimetry under quasi-equilibrium conditions utilized in the study of the thermal dissociation of compounds

I. Study of the kinetics of thermal dissociation for multi-stage reactions

Journal of Thermal Analysis and Calorimetry
Authors: V. Logvinenko, L. Myachina and G. Gavrilova

Study of the kinetics of multi-stage thermal dissociation reactions is a difficult task. Utilization of thermogravimetry under quasi-equilibrium conditions allows determination of intermediate phases, and if necessary their separation, in order to permit study of the kinetic stability separately. Parallel utilization of thermogravimetry under linear heating and quasi-equilibrium conditions allows detection of the existence of intermediate metastable phases.

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Abstract  

The thermal transformations of Pr and La carbonates, La, Ce, Pr, Nd, Sm, Eu and Gd fluorocarbonates, and La, Nd, Dy and Ho fluorooxalates were investigated. A Derivatograph Q-1000 (MOM, Hungary) was used for thermal analysis. The kinetics of the processes was studied in a flow reactor. The activation energies and preexponential factors for dehydration and decarbonization were calculated. Samples of Pr fluorocarbonate, Ho fluorooxalate, and Pr and La carbonates were exposed to γ-irradiation (dose from 6.2·106 to 6.1·107 rad). The influence of the irradiation dose upon the kinetic parameters (E a andA) of the processes was investigated.

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The mixed-ligand complex compoundscis- andtrans-[Cr(en)2(NH2CH3)2]Br(B10H10) were synthetized. It was demonstrated by IR spectroscopy that the hydrogen atoms of the anions B10H

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The decompositions of the clathrate compounds [M(NCS)2(4-MePy)4]·nG (whereM=Mn, Co, Ni or Cd;G=4-methylpyridine (4-MePy), benzene or xylenes) were studied on a Q-derivatograph under quasi-equilibrium conditions and with linear heating. These clathrates can be divided into two groups, in which the loss of guest is either (I) accompanied by destruction of the host complex, or (II) occurs before decomposition of the host complex. Kinetic parameters were obtained.

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CRTA for the thermoanalytical screening of volatile compounds

1. Calibration of standard Q-derivatograph sample holders vs. vapor partial pressures during quasi-isobaric quasi-isothermal heating

Journal of Thermal Analysis and Calorimetry
Authors: V. Logvinenko, G. Gavrilova, I. Karpova and P. Stabnikov

Abstract  

Quasi-equilibrium thermogravimetry (variant of CRTA) is utilized as a thermoanalytical screening method for volatile compounds, standard Q-derivatograph sample holders (platelike holder, open crucible, crucible with lid, and conical holder) were calibrated against the partial pressures of metal β-diketonate vapor (in sublimation and evaporation processes) in the range 0.0006–0.11 atm. The mathematical relationship between the vapor partial pressure, the holder construction, the vapor molecular mass, and the mutual diffusion coefficient of the gas was derived and considered. It is possible to obtain a roughp-T relationship for volatile compounds by using stabilized temperatures of sublimation (evaporation) processes in four pressure-calibrated sample holders.

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Thermal dissociation processes ofβ-diketonate adducts with the composition ML2 · 2B (L = acetylacetone and its substituted derivatives;M = Ni, Co;B = H2O, BuNH2CH3OH, Py, NH3) were investigated. Kinetics of dissociation were studied in a flow reactor. For dehydration processes a compensation relationship is observed (lgA=E+b), demonstrating analogous mechanisms.

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Thermal dissociation processes of compounds with the composition MoO2(C6H5CONHO)2.nA (A-polar organic solvent: alcohols, aldehydes, ketones, organic acids) were investigated. Kinetics of dissociation was studied in a flow reactor, the values of activation energy and preexponential factor were calculated. The influence of a solvent nature, of the length of included molecules and of the type of crystalline lattice was studied. The sequence of kinetic stability was obtained. It corresponds to the sequence of solvent activity with respect to H-binding up with the complex. For the series of alcohols nonmonotonous dependence of kinetic parameters on the length of chain (with the division into two groups: with even and oddn) was obtained. For all the compounds studied a compensation relationship is observed (lgA=aE+b).

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