The thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O was studied under isothermal conditions in flowing air and argon. Dissociation of the above complex occurs in three stages.
The kinetics of the particular stages thermal decomposition have been evaluated. The RN and/or AM models were selected as those best fitting the experimental TG curves. The activation energies,E, and lnA were calculated with a conventional procedure and by a new method suggested by Kogaet al. [10, 11]. Comparison of the results have showed that the Arrhenius parameters values estimated by the use of both methods
are very close. The calculated activation energies were in air: 96 kJ mol−1 (R1.575, stage I); 101 kJ mol−1 (Ain1.725 stage II); 185 kJ mol−1 (A2.9, stage III) and in argon: 66 kJ mol−1 (A1.25, stage I); 87 kJ mol−1 (A1.825, stage II); 133 kJ mol−1 (A2.525, stage III).
Simultaneous TG-DTG-DTA studies under non-isothermal conditions on [Co(NH3)6]Cl3, [Co(NH3)5]Cl2 and [Co(NH3)]2(C2O4)3.4H2O complexes have been carried out in air and argon atmospheres in the temperature range 293–1273 K. All the dissociation processes occur in three main stages. The kinetics of thermal decomposition of the complexes have been evaluated from the dynamic weight loss data, to determine the most probably mechanisms of the stages on the basis of statistical analysis. The decomposition of the compounds was controlled by diffusion and phase boundary reactions except stage III of the oxalate complex in argon (random nucleation). The activation energiesEa of the particular stages of the thermal decomposition were calculated.
The thermal decomposition process of mixtures of CoC2O4⋅2H2O (COD) or Co(HCOO)2⋅2H2O (CFD) or [Co(NH3)6]2(C2O4)3⋅4H2O (HACOT) with activated carbon was studied with simultaneous TG–DTG–DTA measurements under non-isothermal conditions in argon
and argon/oxygen admixtures. The results show that the thermal decomposition of the studied mixtures in Ar proceeds in the
same manner. It begins with the salt decomposition to Comet+CoO mixture followed by (T>680 K) the simultaneous reduction of CoO to Cometand carbon degasification. The final product of the thermal decomposition of COD-C and CFD-C mixtures, identified by XRD,
is β-Co. Cobalt contents determined in the final products fall in the range 71–78 mass%. The rest is amorphous residual carbon.
In Ar/O2 admixtures the end product is Co3O4 with ash admixture.
Simultaneous TG-DTG-DTA studies on [Co(NH3)5Cl]Cl2 under non-isothermal conditions were carried out in dynamic air and argon atmospheres in the temperature range 293–1273 K. Thermogravimetric measurements under quasi-isothermal conditions were also made. On the basis of the experimental data (weight loss, X-ray diffraction, reflectance spectroscopy and chemical analysis), the probable decomposition sequences are presented. The data indicate that the thermal decomposition of [Co(NH3)5Cl]Cl2 occurs in three stages in argon and four stages in air.
The thermal decomposition of [Co(NH3)5Cl]Cl2 was studied under non-isothermal conditions, in dynamic air and argon atmospheres. The kinetics of the particular stages of [Co(NH3)5Cl]Cl2 thermal decomposition were evaluated from the dynamic weight loss data by means of the modified Coats-Redfern method. TheDn andRn models were selected as the models best fitting the experimental TG curves. These models suggest that the kinetics and macromechanism of [Co(NH3)5Cl]Cl2 decomposition can be governed by diffusive and/or phase boundary processes. The values of the activation energy,Ea, and the pre-exponencial factor,A, of the particular stages of the thermal decomposition were calculated.
Using the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O as a basis, the paper presents results which show how computed values of kinetic parameters are influenced by experimental
conditions (ambient atmosphere, sample mass, linear heating rate) when using the non-isothermal methods and the Coats-Redfern
(CR) modified equation. It also illustrates the influence of the experimental methods i.e. non-isothermal and isothermal (conventional)
methods and also a quasiisothermal-isobaric one which can be recognised as equivalent to Constant Rate Thermal Analysis (CRTA).
The results obtained have confirmed the significant influence of the experimental parameters as well as that of the experimental
method used on the estimated values of kinetic parameters. The correlation between activation energy (E) and sample mass (m) or heating rate (β) is generally of a linear nature:E=a+bx
The thermal analysis of CoC2O42H2O, Co(HCOO)22H2O and Co(CH3COO)24H2O was carried out with simultaneous TG-DTG-DTA measurements under non-isothermal conditions in air and argon atmospheres.
The intermediates and the end products of decomposition were characterised by X-ray diffraction and IR and UV-VIS spectroscopy.
The decomposition of the studied compounds occur in several stages. The first stage of dissociation of each compound is dehydration
both in air and argon. The next stages differ in air and argon. The final product of the decomposition of each compound in
air is Co3O4. In argon it is a mixture of Co and CoO for cobalt(II) oxalate and cobalt(II) formate but CoO for cobalt(II) acetate.
Differential scanning calorimetry (DSC) was used to determine the molar enthalpies of dehydration and decomposition of CoC2O42H2O, Co(HCOO)22H2O and [Co(NH3)6]2(C2O4)34H2O. The first stage of dissociation of each compound is a single-step dehydration both in air and argon atmospheres. The next
stages are decomposition processes influenced by experimental parameters. The enthalpies of dehydration and decomposition
vary from compound to compound in each atmosphere. The obtained data have been related to the macromechanisms proposed for
the thermal decomposition and the parallel-consecutive decomposition-oxidation processes.