Journal of Thermal Analysis

The thermal stability of solidified NaNO3 salts in bitumen and cement has been investigated for safety considerations in the field of solidification of radioactive waste. The thermal decomposition of bitumen and cement in presence of NaNO3 in a temperature range 22–650°C has been studied. The fraction decomposed of the pure samples and mixtures showed slow linear reactions followed by acceleratory and decay stages. Data are analyzed according to both Freeman-Carroll and Coats-Redfern kinetics to evaluate the activation energy and the order of reactions of all mixtures. It is found that the activation energies of bitumen and cement were 594 and 203 kJ mol-1, respectively. The order of reactions of bitumen and cement was 2 and 4, respectively. The addition of NaNO3 shortens the duration of the induction period in all mixtures. It was concluded that solidification of radioactive waste containing NaNO3 in bitumen and cement should be applied in the temperature range 22–300°C. At temperature higher than300°C solidification should be in cement.

We first introduce the latest experimental results, i.e., production of the fine nanostructured and near fully dense transparent Y3Al5O12 (YAG) bulks at high pressure and modest temperature (2.0–5.0 GPa and 300–500 °C). And then, we employ the first-principles plane wave pseudopotential density functional theory method to calculate the equilibrium lattice parameters and the thermodynamic properties of YAG. The obtained lattice parameters are consistent with the experimental data and the available theoretical data of others. Through the quasi-harmonic Debye model, the dependences of the normalized primitive volume V/V 0 on pressure P, the Debye temperature $$ \Uptheta_{\rm{D}} $$ , and the heat capacity C V on pressure P and temperature T, as well as the variation of the thermal expansion α with temperature and pressure are obtained successfully.

The Nernst–Planck equations with some additional assumptions was used in this study to investigate the forward kinetics and ion-exchange mechanism of heavy metal ions viz. Ni2+–H+, Cu2+–H+, Mn2+–H+ and Zn2+–H+ on the surface of carboxymethyl cellulose Sn(IV) phosphate composite nano-rod-like cation-exchanger. It was observed that heavy metals' exchange processes were imparted by the particle diffusion-controlled phenomenon. Some physical parameters i.e., fractional attainment of equilibrium U(τ), self-diffusion coefficients (D o), energy of activation (E a), and entropy of activation (ΔS*) were estimated. These investigations revealed that the equilibrium is attained faster at higher temperature probably because of availability of thermally enlarged matrix of carboxymethyl cellulose Sn(IV) phosphate composite nano-rod-like cation-exchange material. The physical parameters observed for this composite cation exchanger were also compared with other composite ion exchangers. The results showed that the ion-exchange phenomenon is more feasible on the surface of this composite cation exchanger as compared with the other ion exchangers which indicated the usefulness of this composite ion exchanger in various applications.

Differential scanning calorimetry was used to study crystallization behavior in selenium glass under non-isothermal conditions. The crystallization kinetics were described in terms of the Johnson–Mehl–Avrami nucleation-growth model; activation energies and kinetic parameter m JMA were determined. The study was performed in dependence with particle size, so that a novel approach to the evaluation of crystallization kinetics—the advanced interpretation of characteristic kinetic functions—could be employed. Extensive discussion of all aspects of a full-scale kinetic study for a complex crystallization process was performed within the framework of the introduced conception. The complexity of the crystallization process was found to be represented by very closely overlapping consecutive competing surface and bulk nucleation-growth mechanisms. Mutual interactions of both mechanisms as well as all other observed effects were explained in terms of thermal gradients, surface crystallization centers arising from the sample preparation treatments and a changing amount of volume nuclei originating from the combination of the pre-nucleation period and the actual glass preparation phase. The main objective of the study is to demonstrate the extent of so-far neglected information hidden in the characteristic kinetic functions and introduce a convenient tool for its acquisition.

The stability of Supersulphated Cement (SSC) is investigated at 95°C when subjected to relative humidities of 100, 53 and 11% of water vapour. Previously [1] investigations at 25, 50, 75°C under the same conditions of humidity reported the stability of ettringite, one of the initial hydration products. At 95°C, decomposition of ettringite, is found at all humidities and is rapid at 100% relative humidity. The hydration products of cement pastes at a water cement ratio of 0.27 were determined by thermogravimetry (TG) and X-ray diffraction (XRD). The formation of the hydragarnet, plazolite is recorded during the decomposition/dehydration process enhanced by possible carbonation. Rehydration studies on the products after storage for up to 9 months were carried out using distilled water and the samples tested for ettringite content. It is concluded that ettringite in SSC is inherently unstable at 95°C.

The coordination complex of Cu (II) with the Schiff base derived from 4-chloroaniline with salicylaldehyde have been synthesized and characterized by micro analytical data; FT–IR, UV–Vis, FAB-mass and thermal analysis studies. Thermal data show degradation of complexes. We carried out thermal analysis at three different heating rates viz. 5, 10 and 20 °C per min. The activation thermodynamic parameters, such as activation energy (E*), entropy of activation (ΔS*), enthalpy of activation (ΔH*) and Gibbs free energy (ΔG*) have been calculated with the help of TG, DTA and DTG curves using Coats–Redfern method. The stoichiometry of the complexes are in 1:2 (M:L) molar ratio. Synthesized complex has been tested for their reactivity and substitution behaviour.

To predict the isothermal course of a reaction from the dynamic DSC curves, the application of isothermal DSC curve transformation has been proposed. To perform such a transformation, it is sufficient only to determine the effective activation energy. To transform integral dynamic curves,α(T)), into isothermal ones,α(t), a better equation has been derived and its validity has been demonstrated on the example of two typical thermosetting systems. In addition, it has been shown that the transformation of differential curves, dα/dT (T), into isothermal ones dα/dt (α), readily allows determination of the kinetic function and rate constants. The procedure used to obtain information on the curing kinetics for thermosetting resins is characterized by simplicity and reliability and can work at E=E(α).

Studies on the three-component system Fe2O3-V2O5-WO3 have shown the occurrence of a new, compound with molecular formula FeVW2O10. Its X-ray characteristics and its melting temperature, 865±10 °C, have been established.