The DC electrical conductivity (s ) of powder compact specimens of the system Bi1-x Tex showed either metallic or semiconductor behavior depending on the range. of temperature of measurements. The transition from metallic to –semiconductor behavior for conduction was found to occur at a certain temperature depending on the conditions of sintering. The electrical conductivity also showed a continuous increase with increasing green density (po), as the compacts. Were sintered at 270 oC for 1.80 min. Measurements of the Seebeck coefficient (S) showed that the activation of holes decreases when enlarging the panicle size and increasing the compact green density (po). The specimens showed only p-type behavior. Over the whole considered range of the ambient temperature, the average particle size, the green density and both the temperature and time of sintering. Powder metall. Int. 20 (1988) [6].

The sintering behaviour of ceria pellets was studied to produce dense, sound and crack-free pellets. Ceria is prepared by the precipitation of ammonium cerous carbonate (ACeC). The precipitate of ACeC is dried and then calcined to produce ceria (CeO2) powder. The ceria powder is used to fabricate pellets which are sintered at 1200...1500 °C. It was found that higher density (more than 85 % of the theoretical), sound and crack-free ceria pellets can be obtained via calcination of ACeC powders at 600 °C for 2 h, pressing the obtained ceria powders into pellets at 550 N/mm2, and then sintering these pellets at 1500 °C for 3 h in air. powder metall. int. 21(1989) [1]

The thermoelectric power of bulk specimens of the system Bi1-xTex (0.3£ x £ 0.6 at.) was studied. The effects of Te content, temperature and time of annealing were considered. For most of the compositions considered, the activation of holes seemed predominant. The electron activations, as well as mixed activations, seemed dependent on Te content and the conditions of annealing. Compensation semiconductor behaviour could also be observed. However, both the value and polarity of the Seebeck coefficient seemed dependent on Te content, conditions of annealing and the temperature of measurement.

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.