Abstract: Thin films of Se_75-xTe₂₅Sb_x (x = 0, 3, 6, & 9) glassy alloys have been deposited onto a chemically cleaned glass substrate by thermal evaporation technique under vacuum. Glassy nature of the films has been ascertained by X-ray diffraction pattern. The analysis by absorption spectra, measured at normal incidence, in the spectral range 400-1100 nm has been used for the optical characterization of thin films under investigation. The optical constants (absorption coefficient (α), extinction coefficient (k)) and optical band gap (E_g) have been studied. It has been found that extinction coefficient (k) decreases with increase in wavelength (λ). The absorption coefficient (α) is found to increase with incident photon energy. Optical band gap (E_g) has also been calculated and found to decrease with Sb content in Se_75-xTe₂₅Sb_x (x = 0, 3, 6, & 9) glassy system. The decrease of optical band gap (E_g) with Sb concentration has been explained on the basis of Mott and Davis model.

Abstract: MgO hydration is an expansive process. It is used in cement to compensate for shrinkage, but it can be harmful at higher concentrations. First-principles calculations have been used to investigate the electronic properties of the steps of the hydration of MgO using the general gradient approximation GGA functional method within density functional method (DFT). The energy bands along high symmetry directions, energy of hydration and energy of dissociation cut through various planes are presented. The first principles band structure calculations reported here were carried out using Perdew, Burke and Ernzerhof (PBE) method. The calculations have been applied to investigate water adsorption on the (001, 110, 111 and 210) surfaces of MgO crystal. The hydrated MgO surfaces show a similar band structure that of brucite material. Both molecular adsorption and dissociative adsorption have been found to occur. The MgO surfaces have different tendency to interact with water molecules, and they differ in susceptibility disintegration of expansion. The results show that the safest surface is (001) group, while the harmful surfaces are (210) and (111) groups.

Abstract: The perovskite niobates (ANbO₃) constitutes an interesting structural family. Silver lithium niobate Ag_1-xLi_xNbO₃ (x = 0, 0.3, 0.5 and 0.7) mixed ceramic pellets were synthesized by the by solid-state reaction and sintering method. The lattice parameters of ceramic pellets were characterized by X-ray diffraction (XRD). The prepared samples show a perovskite structure and exhibit the orthorhombic symmetry at room temperature. Frequency dependent dielectric investigations, i.e., dielectric constant, loss tangent and electrical conductivity were carried out in the frequency range 10Hz-10MHz at room temperature.

Abstract: The ground heaving is a very complex phenomenon which utilizes a great number of intrinsic and surrounding parameters. It is the response of the ground to a gradient of potential of the water of this last. It appears initially by a water run-off within the meaning of Darcy, in the large pores of the ground, then by the hydration of the particles of clay. This phenomenon is related to two parameters of great importance: it water content initial of the ground which expresses the state of suction of the ground and which controls the rate of swelling that it is for the altered or intact grounds. it initial dry density or the index of the vacuums, which measures the quantity of material likely to inflate. Indeed, the curve which giving swelling according to time, reveals two quite distinct phases, one fast which starts with the flood of the sample, the other slow one which evolves/moves in time. According to Chen (1988), the first phase would be the result of a relaxation partial of the constraints in the partially saturated vacuums. This phase would correspond to a macroscopic swelling, compared to a water run-off within the meaning of Darcy, which is governed by the permeability of the medium and the gradient of suction, i.e. a water filling of the large pores separating the grains. The second phase would represent the process of progressive hydration of argillaceous minerals starting from water existing in the pores. Thus starting from this direction, our work, consists in plotting the curves of kinetics of swelling according to time for two natural clay soils of Algiers “Ouled Fayet and Cheraga” with the calculation of the pressures and rates of swelling of the latter in a first place, then by studying the behavior and the improvement of this swelling in this kind of the grounds by adding a hydraulic binder as being one stabilizing which is the lime of Saida.

Abstract: Mg-Al-LDHs with different Mg/Al mol ratio were studied. Adsorption of different organic substances on the layered double hydroxides (LDHs) of different composition was studied. Fatty alcohols, phenols and naphthalene derivatives were used as a sorbates. The structure changes, taking place because of this process, was explored by X-ray method. It has been found, that at the adsorption of such substances as alcohol and phenols the anion exchange take place. After the sorption the specific surface and inner distance of LDHs were measured. The mechanism of structure change was proposed.