The thermal behaviour of Ba[Cu(C2O4)2(H2O)]·5H2O in N2 and in O2 has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively
low temperatures (about 80°C), but continues until the onset of the decomposition (about 280°C). The decomposition takes place
in two major stages (onsets 280 and 390°C). The mass of the intermediate after the first stage corresponded to the formation
of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The
enthalpy for the dehydration was found to be 311±30 kJ mol−1 (or 52±5 kJ (mol of H2O)−1). The overall enthalpy change for the decomposition of Ba[Cu(C2O4)2] in N2 was estimated from the combined area of the peaks of the DSC curve as −347 kJ mol−1. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly
deceleratory and the α-time curves could be described by the three dimensional diffusion (D3) model. The values of the activation
energy and the pre-exponential factor for the dehydration were 125±4 kJ mol−1 and (1.38±0.08)×1015 min−1, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed
in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry
model withn=5. The other process was slow and could also be described by the contracting-geometry model, but withn=2.
The values ofEa andA were 206±23 kJ mol−1 and (2.2±0.5)×1019 min−1, respectively, for the fast process, and 259±37 kJ mol−1 and (6.3±1.8)×1023 min−1, respectively, for the slow process.
phenomenological, kinetic and mechanistic aspects of the nitrate, chloride,
bromide and iodide complexes of nickel(II) with1,2-(diimino-4’-antipyrinyl)ethane
(GA) have been studied by TG and DTG techniques. The kinetic parameters like
activation energy, pre-exponential factor and entropy of activation were computed.
The rate controlling process in all stages of decomposition is random nucleation
with one nucleus on each particle (Mampel model).
The conditions of thermal decomposition of hydrated scandium(III) chlorobenzoates were studied. On heating, the carboxylates
decompose in many steps. The hydrated complexes first lose water of crystallization in one or two steps and then anhydrous
compounds are transformed to Sc2O3 with formation of Sc2O(CO3)2 intermediate. The dehydration of the complexes is accompanied by an endothermic effect and the decomposition of anhydrous
complexes by strong endothermic effects. The anhydrous complexes are melted at 255–300°C.
Effect of 5% tartaric, succinic and citric acids on the decomposition of CaCO3 have been studied by TG-DSC and X-ray diffraction techniques. The decomposition temperature of CaCO3 is not decreased and at the same time particle size distribution and morphology of CaO are changed as determined by laser
granulometer and SEM studies.
The non-isothermal decomposition process of the powder sample of palladium acetylacetonate [Pd(acac)2] was investigated by thermogravimetric (TG) and the X-ray diffraction (XRD) techniques. Model-free isoconversional method
of Tang, applied to the investigated decomposition process, yield practically constant apparent activation energy in the range
of 0.05≤α≤0.95. It was established, that the Coats-Redfern (CR) method gives several statistically equivalent reaction models,
but only for the phase-boundary reaction models (R2 and R3), the calculated value of the apparent activation energy (E) is nearest to the values of E obtained by the Tang’s and Kissinger’s methods.
The apparent activation energy value obtained by the IKP method (132.4 kJ mol−1) displays a good agreement with the value of E obtained using the model-free analysis (130.3 kJ mol−1). The artificial isokinetic relationship (aIKR) was used for the numerical reconstruction of the experimental integral model
function, g(α). It was established that the numerically reconstructed experimental function follows R3 reaction model in the range of
α, taken from model-free analysis. Generally, decomposition process of Pd(acac)2 starts with initial nucleation which was characterized by rapid onset of an acceleratory reaction without presence of induction
Thermal decomposition of polyurethane, epoxy, poly(diallyl phthalate), polycarbonate, and poly(phenylene sulfide) was examined
using a combination of thermal and chemical analysis techniques. Thermal gravimetric analysis with simultaneous analysis of
evolved gases by Fourier transform infrared spectroscopy, differential scanning calorimetry, and gas chromatography coupled
with Fourier transform infrared spectroscopy were used to obtain rate data, determine enthalpy changes, and identify decomposition
products. Examination of the evolved decomposition products indicated a common set of chain scission mechanisms involving
the aromatic moieties in each of the polymer materials studied.
Authors:S. Halawy, N. Fouad, M. Mohamed, and M. Zaki
Non-isothermal decomposition of chromium chromate hexahydrate, Cr2(CrO4)3–6H2O, was studied on heating up to 600°C in different dynamic atmospheres of N2, O2 and H2, using thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). The results obtained at various heating rates (2–20°C min–1) were used to derive kinetic (Ea and lnA) and thermodynamic (
S parameters.It has been found that the activation energies of the dehydration and decomposition steps in N2 are generally larger than in H2 atmosphere, and the reverse is true for the enthalpy change of the decomposition. Thus, it has been concluded that the reductive decomposition (in H2) is easier than the thermal decomposition (in N2 or O2) of the chromate. Irrespective of the gas atmosphere applied, the eventual decomposition product was a mixture of -Cr2O3 and non-crystalline chromate species, -Cr2O3+x. Above 400°C in H2 atmosphere, more deoxygenation of the non-crystalline chromate takes place at high rates of heating to give -Cr2O3.
Authors:A. Coetzee, M. Brown, D. Eve, and C. Strydom
Both isothermal and programmed temperature experiments have been used to obtain kinetic parameters for the dehydrations and
the decompositions in nitrogen of the mixed metal oxalates: FeCu(ox)2·3H2O, CoCu(ox)2·3H2O and NiCu(ox)2·3.5H2O, [ox=C2O4]. Results are compared with those reported for the thermal decompositions of the individual metal oxalates, Cuox, Coox·2H2O, Niox·2H2O and Feox·2H2O. X-ray photoelectron spectroscopy (XPS) was also used to examinee the individual and the mixed oxalates.
Dehydrations of the mixed oxalates were mainly deceleratory processes with activation energies (80 to 90 kJ·mol−1), similar to those reported for the individual hydrated oxalates. Temperature ranges for dehydration were broadly similar
for all the hydrates studied here (130 to 180°C).
Decompositions of the mixed oxalates were all complex endothermic processes with no obvious resemblance to the exothermic
reaction of Cuox, or the reactions of physical mixtures of the corresponding individual oxalates.
The order of decreasing stability, as indicated by the temperature ranges giving comparable decomposition rates, was NiCu(ox)2>CoCu(ox)2>FeCu(ox)2, which also corresponds to the order of increasing covalency of the Cu−O bonds as shown by XPS.