The thermophysical properties (thermal diffusivity a, specific heat Cp and thermal conductivity l ) of Bi1.5Sb0.5Te3 were measured in the temperature range 300-700 K. The results showed that the contribution of the charge carriers to the thermal conduction is negligibly small in com- parison with the contribution of phonons at high temperatures. On the other hand, the heat conduction due to the simultaneous thermal diffusion of electrons and holes is important as well as the lattice thermal conduction. The explanation of the results was supported by using electrical conductivity measurements and X-ray diffraction.

In the present work, the structure of Aso.3Seo.2So.4Geo.1 chalcogenide glass has been studied using the radial distribution function (RDF). Moreover, the effect of annealing temperature on the short range order of this glass has been investigated. The results revealed that the short range order structure of the as-prepared and annealed Aso.3Seo.2So.4Geo.1 chalcogenide glass is close to a regular tetrahedron. The medium range order of Aso.3Seo.2So.4Geo.1 chalcogenide glass is topology order. The topological structure of the medium range order can be described by the Phillips model. The structure of Aso.3Seo.2So.4Geo.1 chalcogenide glass is stable in the annealing temperature range 324-523 K.

Using X-ray diffraction and differential scanning calorimetry (DSC), the structure and the crystallization mechanism of Se0.7Te0.3 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 crystallization 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 EG is 161.7 ± 0.6 kJ/mol.

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.