The kinetics of the reactions (dissolution and precipitation) in Al- 8 at% Li alloy were investigated by difTerential scanning calorimetry (DSC). Analysis of nonisothermal DSC scans at difTerent heating rates was carried out to evaluate the overall activation energies associated with the transformation processes during continuous heating of the quenched alloys. An average activation energy associated with dissolution of Guinier - Preston zones was found to be 73.42 ± 5.41 kJ mol ", which implies that the dissolution process is controlled by the migra¬tion of lithium atoms through the aluminium matrix. The average activation energy of 8' phase precipitation was 62.65 ± 4.43 kJ mol-I. The activation energies of dissolution of the 8' phase and dissolution of the 8 phase or lithium in the matrix were 132.47 ± 4.03 and 398.40 ± 3.98 kJ mol ", respectively. The reaction order of all processes indicates that they occur three-dimensionally throughout the aluminium matrix. 8 and 8' phases have been detected in naturally (1800 min) aged specimens by x-ray difTraction

Results of differential scanning calorimetry, at different heating rates, a, on Ga5Se9S glass are reported and discussed. From the heating rates dependence of values of Tg and Tp, the glass activation energy, Eg and the crystallization activation energy, Ec' are derived. The crystallization results are interpreted in terms of recent analyses developed for non-isothermal crystallization and also for the evaluation of Ec. The crystallization mechanism is then characterized. From the obtained results, the glassy GaSSe9S has two-dimensional growth, the average value of the order of crystallization mechanism, n is 3. The average value of the glass activation energy, Eg and crystallization activation energy, Ec' for GaSSe9S glass are 189 ± 4 and 69 ± 5 kJ/mol, respectively.
© 2003 Elsevier Science Ltd. All rights reserved.
PACS: 6470 P; 6140; 6140 D

The Crystallization kinetics of chalcogenide glass M. 1. Abd-Elrahrnan '. I, A. A. Abu-Sehly', N. Afify', and G. Shuriet I Physics Department, Faculty of Science. Assiut University. Assiut 71516. Egypt Department of Science. Faculty of Education. Assiut University, New Valley Branch. New Valley. Egypt
Received 14 January 2002. revised 13 January 2003. accepted 7 February 2003 Published online 22 May 2003

PACS 61.10.Nz, 65.90.+i. 8140.Ef The crystallization kinetics of the Ge17.5 Te82.5 chalcogenide glass were obtained by using differential scanning calorimetry (DSC) under non- isothermal conditions. The fraction of crystallized material. calculated using the partial area analysis. revealed that the crystallization process of the Ge17.5 Te82.5, glass was two and three-dimensional. The crystallization of the Ge17.5 Te82.5 glass was confirmed by X-ray investigation of the as-prepared and annealed powder. The glass transition activation energy (Eol and the crystallization activation energy (E.) were calculated from the DSC thermograms using different methods.

This work aims in studying the temperature dependence of the thermal properties (thermal diffusivity, k, specific heat, Cp and thermal conductivity, A.) 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 thermo gravimetric 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 behavior was attributed to the oxidation and firing of some minerals after the heat treatment.

Based on the interference fringes in optical transmission spectra at normal incidence of different composition thin films As-S semiconducting glass, deposited by thermal evaporation, the direct analysis proposed by Swanepoel is applied for determining the real and imaginary parts of the complex index of refraction, and also the film thickness. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model, and the optical absorption edge is described using the 'non-direct transition' model proposed by Tauc. Likewise, the optical energy gap is derived from Tauc's extrapolation. Finally, the compositional trends of refractive index and optical band gap in different composition thin films As-S chalcogenide glass are interpreted in terms of the bond strengths of the chemical bonds present in the glass composition under study.
© 2006 Elsevier B.V. All rights reserved.

Thin film binary alloys of InxSe1-x (0.05£ X ≤0.30) have been prepared by the thermal evaporation technique. The optical transmission and reflection spectrum of these films were measured in the range 300-1100 nm. Both refractive index, 11 and extinction coefficient k have been determined from transmission and reflection measurements in terms of Murrnanns equations. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. The width of band tail is determined and the optical absorption edge is described using the 'non-direct transition' model proposed by Tauc. Finally, the relationship between the optical gap and chemical composition in InxSe1-x amorphous system is discussed in terms of the average heat of atomization H, and average coordination number Nc. The results of these calculations can be used rationalize the observed optical properties of these materials. Finally, the chemical bond approach has been also applied to interpret the decrease of the glass optical gap with increasing In content.
© 2007 Elsevier B.Y. All rights reserved

In this work, a new method to study the transformation kinetics is introduced. With this method, the activation energy, En for crystallization (phase transition or chemical reaction), the pre-exponential coefficient of effective overall reaction rate, k.; and the reaction order, n, can be determined. No approximation has been used in this method. This method can be used for isothermal and non-isothermal study. It is deduced from Avrarni's equation without any approximation. This new method has been tested to study the amorphous-crystalline transformation kinetics under isothermal and non-isothermal conditions in the context of glassy selenium. The source of error is discussed. The calculated values of Ee, under isothermal and non-isothermal conditions are 75.3 ± 2.5 and 79.4± 2.3 kl/rnol, respectively. The predominant crystallization mechanism of the amorphous phase of glassy selenium in isothermal or non-isothermal conditions is one-dimensional growth. The deduced values of k., were found to be 19.4 ± 0.9 and 20.8 ± 0.7 S-1 for isothermal and non-isothermal conditions, respectively. Resulting values of the parameter, n, are compared with values obtained from other known methods used to study the reaction kinetics in thermal analyses. The difference in the results obtained with this method and the results obtained with other known methods is acceptable or lie within the experimental error range.
© 2008 Elsevier Ltd. All rights reserved.

The fine-scale precipitates, that occurs during aging, the supersaturated AI-1.0 at.% Mg-x at.% Si (x = 0.6, 1.0 and 1.6) alloys have been investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques. The strength of the alloys increases as a high density of very fine W' coherent and 13' semicoherent precipitates nucleate. The precipitates compositions have been determined by analyzing the X-ray diffraction (XRD) charts, by using Scherrer equation. The obtained results showed that the 13" and 13' precipitates size lies in the nanometer range (from ~5 nm to ~32 nm). In addition, increasing Si concentration has exhibited an increase in the density of the precipitates, which fortifies the physical properties.

Different thickness of cadmium telluride (CdTe) thin films was deposited onto glass substrates by the thermal evaporation technique. Their structural characteristics were studied by X-ray diffraction (XRD). The XRD experiments showed that the films are polycrystalline and have a zinc-blende (cubic) structure. The microstructure parameters, crystallite size and microstrain were calculated. It is observed that the crystallite size increases and microstrain decreases with the increase in the film thickness. The funda¬mental optical parameters like band gap and extinction coefficient are calculated in the strong absorption region of transmittance and reflectance spectrum. The possible optical transition in these films is found to be allowed direct transition with energy gap increase from 1.481 to 1.533 eV with the increase in the film thickness. It was found that the optical band gap increases with the increase in thickness. The refractive indices have been evaluated in transparent region in terms of envelope method, which has been suggested by Swanepoul in the transparent region. The refractive index can be extrapolated by Cauchy dispersion relationship over the whole spectral range. which extended from 400 to 2500 nm. It is observed that the refractive index, n increases on increasing the film thickness up to 671 nm and then the variation of n with higher thickness lie within the experimental errors

Different compositions of amorphous Ge20Se80 and Ge20Se75M5 (M=Cd, Bi, or Zn) semiconducting films were deposited onto cleaned glass substrates by thermal evaporation method. The interference transmission spectra T(λ) at normal incidence for Ge20Se75M5 thin films were obtained in the wavelength range 400- 2500 nm. The direct analysis proposed by Swanepoel that is based on the use of the extremes of the interference fringes was used in order to derive the film thickness and the two parts of the complex refractive index (real part, n, and imaginary part, k,). The dispersion of n is discussed in terms of the Wemple-DiDomenico single-oscillator model. Furthermore, the optical band gap, Eg , has been determined from the absorption coefficient values using Tauc,s procedure. The obtained results of Eg were discussed in terms of the width of localized state Ee.