N. Afify

Kinetics study of non-isothermal crystallization in Se0.7Ge0.2Sb0.1 chalcogenide glass☆

Abstract Differential scanning calorimetry data at different heating rates on Se 0.7 Te 0.3 chalcogenide glass are reported and discussed. From the heating rate dependence of values of T g , T c and T p , the glass transition activation energy, E t , and the crystallization activation energy, E c , were derived. The crystallization data are interpreted in terms of recent analyses developed for non-isothermic crystallization and also for the evaluation of E c and the characterization of a crystallization mechanism. The results indicate that bulk crystallization with two-dimensional growth occurs for this glass. The calculated E t and E c are 143 ± 3 and 174 ± 8 kJ/mol, respectively.

INVESTIGATION OF THERMAL PROPERTIES OF SOME BASALT SAMPLES IN EGYPT

This work aims in studying the temperature dependence of the thermal properties (thermal diffusivity, k, specific heat, Cp and thermal conductivity, λ) of some basalt group samples, collected from different regions in the eastern desert of Egypt. The thermal properties of these samples were measured in the temperature range from r.t. to 900 K. The average values of the thermal conductivity of these investigated samples lie in the range from 0.4·10−3 to 2.01·10−3 cal cm−1 s−1 K−1. This means that these samples are considered as thermal insulating materials. The thermogravimetric analysis (TG) confirmed that these investigated samples are dry rocks. X-ray fluorescence (XRF) and X-ray diffraction (XRD) confirmed that these rock samples have a crystalline phase, the peaks of XRD have a small change in their location as a result of heat treatment. This behaviour was attributed to the oxidation and firing of some minerals after the heat treatment.

Calorimetric study on the crystallization of a Se0.8Te0.2 chalcogenide glass

Results of differential scanning calorimetry (DSC) at different heating rates on Se0.8Te0.2 chalcogenide glass are reported and discussed. From the variation of heating rate (α) the crystallization fraction (ξ), heat flow differnce (Δq) and the crystallization peak temperature (Tp), the value of the effective activation energy for growth (EG) was evaluated by six different methods. The Se0.8Te0.2 chalcogenide glass has two crystallization mechanisms, one-dimensional and surface crystallization growth. The average value of EG for Se0.8Te0.2 chalcogenide glass is equal to (123.5±5.7) kJ/mol. All the methods used to evaluate the effective activation energy for growth (EG) are valid to discuss the results of glass-crystalline transformation but with differing accuracies.

Differential scanning calorimetric study of chalcogenide glass Se0.7Te0.3

Abstract Results of differential scanning calorimetric (DSC) under isothermal and non-isothermal conditions on Se 0.7 Te 0.3 glass are reported and discussed. By using the Johnson-Mehl-Avrami equation, the effective activation energies for crystal growth, E G , 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 E G is 150±7 kJ/mol.

Crystallization kinetics of overlapping phases in Se0.6Ge0.2Sb0.2 chalcogenide glass

Abstract 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.

DTA studies on the crystallization of InxSe1 − x chalcogenide glasses

Abstract Results of differential thermal analysis (DTA) under nonisothermal conditions on five chalcogenide glasses of the In x Se 1 − x system ( x = 0.05, 0.10, 0.15, 0.20 and 0.25 at.) are reported and discussed. The crystallization mechanism has been studied by using DTA, scanning electron microscopy (SEM) and X-ray diffraction. From the dependence of the glass transition temperature ( T g ), the onset crystallization temperature ( T c ) and the crystallization peak temperature ( T p ) on the heating rate (α), the glass transition activation energy ( E t ) and the crystallization activation energy ( E c ) were derived. The calculated E t for In x Se 1 − x varied between 246 and 309 kJ/mol. The results indicate that bulk crystallization with two-dimensional growth occurs for these glasses. The average activation energy of crystallization for In x Se 1 − x varied between 105 and 125 kJ/mol. In 0.10 Se 0.90 chalcogenide glass showed a minimum value of E c as well as ( T c - T g ), which represents the thermal stability of the glass, indicating that this composition has a tendency towards crystallization more than the other compositions.

Structural and crystallization kinetics studies of chalcogenide glass Se0.8 Te0.2

Using X-ray diffraction and differential scanning calorimetry (DSC) the structure and the crystallization mechanism of Se0.8Te0.2 chalcogenide glass have been studied. From the radial distribution function, the short-range order of the amorphous phase has been discussed. The lattice parameter of the crystalline phase has been determined by using the Cohen least-squares method. The results of the thermal analysis indicate that the crystallization process is a two-dimensional growth. The calculated value of the effective activation energy for crystal growth, EG, is 160.8±0.1 kJ/mol. The calculated lattice parameters a and c of the hexagonal crystalline phase are 0.4398±0.0014 and 0.5055±0.0021 nm, respectively.

Structural study of chalcogenide glass Se0.7Te0.3

Abstract Using X-ray diffraction and differential scanning calorimetry (DSC), the structure and the crystallization mechanism of Se 0.7 Te 0.3 chalcogenide glass have been studied. By means of the radial distribution function, the short-range order of the amorphous phase has been discussed. The lattice parameters of the crystalline phase have been determined by using the Cohen least-squares method. The cyrstallization mechanism and the activation energy have been investigated by using the Ozawa and the Takhor methods, respectively. The calculated lattice parameters a and c of the crystalline phase are 0.4380 ± 0.0015 and 0.5198 ± 0.0027 nm, respectively. On the other hand, the results of the thermal analysis indicate that the crystallization process is a two-dimensional growth. The calculated value of the activation energy for crystal growth E G is 161.7 ± 0.6 kJ/mol.

Investigation of the precipitation process in Al-Si alloys

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 degrees 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.

Investigation of the decomposition behaviour in supersaturated Al-Zn alloys

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.