The well-known divergence between the present ‘state of the art’ of thermogravimetry and industrial requirements is discussed.
Sources of errors are analyzed and the optimization of measuring conditions is discussed regarding the problems associated
with static and dynamic (flow) atmospheres, and interactions between materials and gases or vapors. Recommendations for gas-flow
control systems and vapor sources are given. Thermal stability and the kinetics of gas-evolving, reversible, thermal decompositions
of solids are discussed. The scope of TG-derived kinetics for practical use is examined. Some new characteristic points of
TG curves are proposed and defined, e.g. ‘procedure-independent decomposition temperature’ and ‘augmented decomposition temperature’
(obtained at pseudo-equilibrium conditions).
Authors:A. Souza, M. Oliveira, I. Santos, M. Conceição, L. Nunes, and J. Machado
The kinetics of thermal decomposition of solid In(S2CNR2)3 complexes, (R=CH3, C2H5, n-C3H7,i-C3H7, n-C4H9 and i-C4H9), has been studied using isothermal and non-isothermal thermogravimetry. Superimposed TG/DTG/DSC curves show that thermal
decomposition reactions occur in the liquid phase, except for the In(S2CNMe2)3 and In(S2CNPri2)3 compounds.
Authors:V. Logvinenko, L. Yudanova, N. Yudanov, and G. Chekhova
The thermal decomposition of salts (both normal and acid) of transition metals with carboxylic acids (maleic, ortho-phthalic
and terephthalic) was studied in inert atmosphere. The residues after pyrolysis (up to 450C) are composites including two
structural components: an organic polymer matrix and spherical conglomerates from metal grains coated with polymer. Thermal
decomposition of solid solutions of metal bimaleates (Co-Ni, Fe-Ni, Zn-Ni) was investigated. Thermogravimetric data (obtained
at different rates of linear heating) were processed with 'Netzsch Thermokinetics' computer program. Kinetic parameters were
calculated only for the first decomposition step, and the process is described by Prout-Tompkins equation of nth order with autocatalysis. Some properties of the resulting composites have been studied qualitatively.
analyses of thermal decomposition (pyrolysis, thermal dissociation and combustion)
of 9 different samples were carried out in dynamic conditions at different
heating rates. The kinetic parameters (E, A and km)
of thermal decomposition were determined and interrelations between the parameters
and heating rate q were analyzed. There
were also relations between Arrhenius and Eyring equations analyzed for thermal
decomposition of solid phase. It was concluded that Eyring theory is an element,
which interconnects used thermokinetic equations containing Arrhenius law
and suggests considering kinetic quantities in way relative to 3 kinetic constants
and km). Analysis
of quantities other than km (i.e. E, A, Δ+H, Δ+S) in relation to heating rate is an incomplete method
and does not lead to unambiguous conclusions. It was ascertained that in ideal
case, assuming constant values of kinetic parameters (E
and A) towards heating rate and satisfying
both Kissinger equations, reaction rate constant km
should take on values intermediate between constants (km)1
determined from these equations. Whereas behavior of parameters E and A towards q were not subjected to any rule, then plotting relation kmvs.q in the background of (km)1
made possible classification of differences between thermal decomposition
processes taking place in oxidizing and oxygen-free atmosphere.
A study has been carried out of the influence of sample dilution, the nature of the gas atmosphere, and the static or flowing conditions of this, on the DTA curves resulting from the thermal decomposition of solids. The results obtained seem to indicate that only the reversible reactions of solid thermal decomposition are seriously affected by such factors.
For the quantitative analyses of evolved CO2and H2O during the thermal decomposition of solids, calibration curves, i.e. the amounts of evolved gases vs. the corresponding
peak areas of mass chromatograms measured by TG-MS, were plotted as referenced by the reaction stoichiometry of the thermal
decomposition of sodium hydrogencarbonate NaHCO3. The accuracy and reliability of the quantitative analyses of the evolved CO2and H2O based on the calibration curves were evaluated by applying the calibration curves to the mass chromatograms for the thermal
decompositions of copper(II) and zinc carbonate hydroxides. It was indicated from the observed ratio of evolved CO2and H2O that the compositions of copper(II) and zinc carbonate hydroxides examined in this study correspond to mineral malachite,
Cu2CO3(OH)2, and hydrozincate, Zn5(CO3)2(OH)6, respectively. Reliability of the present analytical procedure was confirmed by the fairly good agreement of the mass fraction
of the evolved gases calculated from the analytical values with the total mass-loss during the thermal decompositions measured
Authors:Gisele Cristiane Becher Ribas, Gledison Rogério de Souza, and Fernando Luis Fertonani
Thermogravimetry (TG), energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), mapping surface and X-ray diffraction (XRD) have been used to study the reaction of mercury with platinum–rhodium (Pt–Rh) alloy. The results suggest that, when heated, the electrodeposited Hg film reacts with Pt–Rh to form intermetallic compounds each having a different stability, indicated by separate third mass-loss steps. In the first step, between room temperature and 170 °C, only the bulk Hg is removed. From this temperature to about 224 °C, the mass loss can be attributed to decomposition of the intermetallic PtHg4. The third step, from 224 to 305 °C, can be ascribed to thermal decomposition of solid solution composed of intermetallic species RhHg2 and PtHg2. Intermetallic compound such as PtHg4, PtHg2, and RhHg2 was characterized by XRD. These intermetallic compounds were the main products formed on the surface of the samples after partial removal of the bulk mercury via thermal desorption.
A study of the kinetics of the thermal dehydration of syngenite was carried out using the isothermal gravimetric method. Weight changes of the samples were followed by means of a Mettler Thermoanalyzer. The applicability of nine equations commonly used to describe the thermal decomposition of solids was investigated. The experimental results can be best represented, over the whole temperature range of the change, by the Avrami equation I
Results of the kinetic study of the thermal decomposition of ammonium thiocarbamate in vacuum (ca. 10−2 torr) in the temperature range 303–353 K are presented. Under these conditions ammonium thiocarbamate decomposes into gaseous products (NH4COSNH2→2 NH3 + COS). Fifteen general equations for the kinetics of thermal decomposition of solids were taken into consideration. The following equation describes the experimental results over the whole range of the degree of decomposition:
, little is known about the thermal decomposition kinetics of DPG. Kinetic studies of thermaldecompositionofsolids constitute one of the most important applications of thermal analysis, in which the most common experimental technique is TG under the