In the present work, the early stage of clustering and the subsequent precipitation of Si atoms in Al + 1.37, Al + 2.83 and Al + 6.81 at.% Si alloys have been investigated by means of electrical resistivity and microhardness measurements. The results showed that: (i) the interaction between the vacancy- type dislocations and the partially precipitated Si atoms is the predominant process during the initial stage (25-150 °C); (ii) as the large particles of Si precipitates are formed, they become no longer coherent with the Al matrix; (iii) the microhardness of the as-quenched specimens was found to increase linearly with increasing Si concentration in the alloy.

The crystallization kinetics of the chalcogenide glass Se0.8 Te0.2 was studied by means of differential scanning calorimetry. The variation in partial area (X) with temperature (T) revealed that the transition from the amorphous to the crystalline phase occurs in two dimensions. Activation energies were determined for both the glass transition (Et) and the crystallization (Ec). Et was calculated from the variation in Tg with the heating rate (a ). Ec was determined by three different methods: (i) variation in X with T, (ii) variation in Tp with a , and (iii) variation in Tc with a . Et and Ec have values of161.01±2.75 and 84.75± 8.21 kJ/mol, respectively.

From the DSC study, the Se0.6Ge0.2Sb0.2 chalcogenide glass has two amorphous phases and its crystallization takes place in two overlapping processes. By annealing as-prepared samples at 244°C for 2 h, the second phase can be observed. From X-ray diffraction measurements, the first phase identified is Sb2Se3 and the second phase is GeSe2. From the variation of the volume fraction of crystals with temperature, the crystallization mechanism for Sb2Se3 and GeSe2 phases are two dimensional and surface processes, respectively. The glass transition activation energy (Et) and the crystallization activation energy (Ec) of Sb2Se3 phase were calculated by different methods to be 234.4± 4.0 and 228.5± 13.2 kJ/mol, respectively. For the GeSe2 phase the corresponding values were 271.4± 3.8 and 245.2 ± 18.9 kJ/mol, respectively.

The high-temperature phase transition of K2SeO4 was studied by using differential thermal analysis. The Kissinger equation and the Mahadevan approximation were applied to evaluate the effective phase transition activation energy (E). The average value of E was 12.85 ±0.04 eV.

Results of differential scanning calorimetry (DSC) at different heating rates on Se0.7Ge0.2Sb0.1 glass are reported and discussed. From the heating rate dependence of glass transition, crystallization onset and peak crystallization temperatures values for the glass transition activation energy, Et, and the crystallization activation energy, Ec, were evaluated. The results are consistent with surface and one-dimensional crystallization for this glass. The calculated values of Et and Ec are 92± 6 and 134± 6 kJ/mol, respectively.

Results of differential scanning calorimetric (DSC) under isothermal and non-isothermal conditions on Se0.7Te0.3 glass are reported and discussed. By using the Johnson-Mehl-Avrami equation, the effective activation energies for crystal growth, EG, have been evaluated and the crystallization mechanism has been studied. The results indicate that the crystallization process is a two-dimensional growth. The average value of EG is 150± 7 kJ/mol.

Differential scanning calorimetry data at different heating rates on Se0.7Te0.3 chalcogenide glass are reported and discussed. From the heating rate dependence of values of Tg, Tc and Tp, the glass transition activation energy, Et, and the crystallization activation energy, Ec, were derived. The crystallization data are interpreted in terms of recent analyses developed for non-isothermic crystallization and also for the evaluation of Ec and the characterization of a crystallization mechanism. The results indicate that bulk crystallization with two-dimensional growth occurs for this glass. The calculated Et and Ec are 143± 3 and 174± 8 kJ/mol, respectively.

The temperature dependence of the electrical resistance and the spectral dependence of the optical absorbance of evaporated Ag10As30Te60 thin films were studied. It was found experimentally that the heat treatments cause significant changes in the electrical resistance and the optical absorbance of the chalcogenide film. The results obtained were correlated with the X-ray analyses.

The decomposition behaviour in supersaturated Al + (1-6.4) at% Zn has been investigated using electrical resistivity and microhardness measurements in the temperature range from room temperature to ~500° C. The experimental results showed that (i) both the temperature coefficient of resistivity and the relaxation time of the free electrons diminish as the concentration of Zn increases in the alloy; (ii) the early stage decomposition of the supersaturated alloys via Guinier-Preston zone formation is accompanied by an appreciable increase in the microhardness of about 80 MPa per 1 at % Zn; (iii) the obtained activation energy of 0.41 eV for the precipitation process of the dissolved zinc atoms is close to the migration energy of zinc in aluminium which indicates that the precipitation mechanism is characterized by the migration and coalescence of zinc atoms.

Crystallization kinetics of the Bi10Se90-x Inx glasses with x = 5, 10, and 20 at% have been studied under non-isothermal conditions. From the heating rate dependence of Tg and Tp, values of the activation energy for the glass transition (Et) and the activation energy for crystallization (Ec) are evaluated and their composition dependence discussed. DSC thermograms and X-ray diffractograms are useful in clarifying the role of In content on the crystallization phases and the electrical resistivity of these glasses. The results indicate that the crystallization mechanism involves several complex processes and that bulk crystallization with three-dimensional growth dominates over the other crystallization processes.