Measurements of electrical resistivity, X-ray diffraction and DTA were used to characterize the transport processes developed in an Fe-12.1 Cr-7.37 Ni (wt. %) stainless steel during heating from 300 to 980 K and subsequently during cooling to room temperature. The results revealed that this steel exhibits two transport regions during heating and only one during cooling. In case of heating, the first transition region (observed in the temperature range 650-730 K) is not to a structural but may be a magnetic transition. The second transition region (observed in the temperature range 885 - 915 K) is ascribed to the austenitic structural transformation. During cooling, a unique transition region was observed in the range 560-434 K. This was attributed to the martensitic transformation which may also be associated with a magnetic transition. From the DTA data, the effective activation energy for the austenitic transformation was determined to be 459.3 kJ mol-1. In the temperature ranges other than the transition regions the electrical resistivity fits a linear equation rather than the Bloch-Grüneisen equation.

The precipitation processes in quenched Al-2.4Li-1.16Cu-0.8Mg(wt.%) alloy (8090) from the solid solution state (Tq = 803K) have been investigated via the Vickers microhardness measurements, scanning electron microscopy and differential scanning calorimetry. On the basis of Kissinger's analytical equation of the DSC thermograms, the overall activation energies associated with the transformation processes are evaluated. The activation energy associated with the formation of the GPB zones and s ' phase is determined as 82.433kJ/mol. Whereas the energy of their dissolution is 139.78kJ/mol. The activation energy associated with the formation of the S' phase is determined as 106.88 kJ /mol. In addition, the microstructural examination of the samples after various aging temperatures revealed that the resultant precipitates are intergranular. PACS: 61.60.Dk

AI-C at% Mg alloys (C = 0.82, 1.84, 3.76, 5.74 and 12.18) have been selected for this study. From the electrical resistivity measurements it is concluded that the resistivity increment of Al-Mg alloys (in a solid solution state) is proportional to the atomic fractional constituents (Mg and Al) as D pall = 64.66 c(1 -c) m W cm. In addition, both the temperature coefficient of resistivity, a all and the relaxation time of the free electrons t all in the alloys diminish with increasing the solute Mg concentration. The increase of the scattering power, h , with increasing C is interpreted to be due to the contribution of electron-impurity scattering. The percentage increase due to electron-impurity scattering per one atomic percent Mg has been determined as 12.99%. The Debye temperature q decreases as the Mg concentration increases. The microhardness results showed that the solid solution hardening obeys the relation D HVs = 135.5C0.778 Mpa which is comparable to the theory of solid solution hardening for all alloys; D HVs = C0.5-0.67 MPa. PACS. 61.66.Dk Alloys

A series of Al1-x at % Mgx alloys (x = 3.76, 5.74 and 12.18) has been selected in order to study the mechanisms of the decomposition and precipitation processes which take place as a result of heating of the supersaturated solid solutions. Techniques of differential scanning calorimetry and scanning electron microscopy prodded with an energy dispersive x-ray spectrometer have been used for this purpose. The basis of the Johnson-Mehl-Avrami equation has been applied to characterise the kinetics of the transformations that occur during heating of the supersaturated alloys. Accordingly, an average overall activation energy of 0.51 eV has been determined for the dissolution of Guinier-Preston zones. The kinetics are controlled by the migration of magnesium atoms three- dimensionally in the aluminium matrix. The average activation energies associated with the precipitation of b phase (Mg5Al8) and its redissolution have been determined as 2.42 and 5.695 eV respectively. The reaction order of the precipitation process indicates that the precipitation occurs through the bulk of the alloy in three dimensions and these precipitates grow on pre-precipitated tiny nuclei.

The present work is a study of the electrical resistivity and thermal properties during continuous heating from room temperature up to 773 K of Al100-x Lix (x=0.5, 1, 2, 3, 6 and 8) alloys. From the electrical resistivity measurements at room temperature it is concluded that the resistivity increment of Al-Li alloys (in solid solution state) is proportional to the fractional constituents (Li and Al) as D r all [m W .cm] = (94.10 ± (0.13)[m W .cm] c(1-c). In addition both the temperature coefficient of resistivity aall and the relaxation time of the free electrons tall of the alloys diminish with increasing the solute Li concentration. Using the measured variation of the specific heat, Cp , and thermal diffusivity, a, as a function of temperature, the precipitation processes can be followed. Both tools were found to be sensitive for precipitation evolution.

Variation of thermo physical properties of AI-Li (8090) quenched from the solid solution state (803 K) during heating (10 Kjmin) has been used to determine the temperatures at which the phase transformations take place. Transmission electron microscopic examinations were used to characterize the developed precipitates. It has been shown that the thermal properties can be used as a powerful tool for detecting phase transformations. Microstructural examinations after aging at 373, 438, 563 and 673 K revealed the formation of GP zones, 8'-(A13Li), TB-(A17Cu4Li) and T2-(AI6CuLi3) precipitates, respectively. 8'-particles and TB-(Al7Cu4Li) were observed to be nucleated intragranularly, whereas T r particles were observed to grow on the grain boundaries. © 2002 Elsevier Science B.V. All rights reserved.

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.