https://dspace.univ-guelma.dz/jspui/handle/123456789/677 2026-04-07T08:09:55Z https://dspace.univ-guelma.dz/jspui/handle/123456789/18602 Protection contre la corrosion de l’acier A9 en milieu acide par des inhibiteurs verts Seridi Abir, Benhamdi Naima This work is dedicated to the study of the effect of olive leaf extract (OL), marjoram oregano (MO), and their mixture (OL, MO) as green inhibitors on the corrosion of A9 steel in an acidic medium (1M HCl), using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and gravimetric measurements. To better understand how the inhibitor acts against corrosion, a thermodynamic study was conducted, along with the analysis of different adsorption isotherms. The results from the weight loss method and electrochemical techniques show that both extracts effectively inhibit steel corrosion, especially their mixture, which can reach up to 90% efficiency at a concentration of 50 ppm. This inhibitor behaves as an anodic inhibitor. The inhibitor molecules adhere to the steel surface according to the Langmuir isotherm, indicating the formation of a monolayer. Moreover, the activation energy values suggest that the adsorption is of the physisorption type. FTIR and UV-Vis spectra confirm the simultaneous presence of functional groups such as O-H, C-O, and C=O. The steel surface morphology was examined using optical microscopy. The findings show that olive leaf extract, marjoram oregano extract, and their mixture effectively inhibit the corrosion of A9 steel, form a protective film, and thus act as a good barrier against the penetration of the corrosive medium to the metallic surface. 2025-01-01T00:00:00Z https://dspace.univ-guelma.dz/jspui/handle/123456789/18561 Propriétés électroniques et optiques du GaN dopé : Une analyse par WIEN2k HADDAD, CHAIMA The analysis of the structural, electronic, and optical properties of pure gallium nitride (GaN) and GaN doped with aluminium (Al) and tallium (Tl) was carried out using the FP-LAPW method. The generalized gradient approximation (GGA-PBEsol) combined with the TB-mBJ potential, implemented in the WIEN2k code, was used for the calculations of the different properties. It was observed that doping GaN with Al at a concentration of 12.5% leads to the formation of wide-bandgap semiconductors, while the incorporation of Tl of the same concentration induces a reduction in the bandgap. The results also show that doping modifies the properties of GaN, particularly by shifting the absorption peaks toward blue and a red for Al and Tl dopants, respectively. This modification enhances light absorption, which could be beneficial for optoelectronic applications. 2025-01-01T00:00:00Z https://dspace.univ-guelma.dz/jspui/handle/123456789/18560 Transitions de phase et propriétés vibrationnelles du matériau LiBeP : Étude ab initio ELBEKRI, MERIEM A comprehensive study was conducted on the structural, electronic, vibrational and dielectric properties of the semiconductor compound LiBeP within the framework of density functional theory (DFT). We employed the pseudopotential method, implemented in the ABINIT code. The analysis examined five distinct candidate structural phases (polymorphs): included the cubic phase (AgMgAs), two hexagonal phases (LiGaGe) and (Ni2In), tetragonal phase (Cu2Sb), and orthorhombic phase (MgSrSi). The results of the equation of state showed a very good agreement with the experimental values and confirmed that the tetragonal (Cu2Sb) structure is the most stable. Under pressure, the compound transitions from the tetragonal structure to the orthorhombic structure at 11.43 GPa, and then to the hexagonal structure at 12 GPa. Electrically, in all three phases, the energy gap is indirect. To investigate the vibrational properties, density functional perturbation theory (DFPT) was used in conjunction with the previously mentioned computational method, confirming the dynamical stability of these phases by the absence of imaginary frequencies in the phonon spectra - a finding that was conclusively verified. The dielectric properties revealed that the hexagonal (LiGaGe) structure exhibits the highest dielectric polarization among the studied phases 2025-01-01T00:00:00Z https://dspace.univ-guelma.dz/jspui/handle/123456789/18559 Matériaux 2D pour la conversion d'énergie AYAICHIA, SANA The process of hydrogen production from water using two-dimensional (2D) materials represents a vital research field for the development of clean and sustainable energy sources. This study aims to explore the structural and electronic properties of selected 2D materials and their role in catalyzing water splitting for hydrogen production, through theoretical calculations based on first-principles using density functional theory (DFT). These materials exhibit unique characteristics, including large surface areas, tunable bandgap flexibility, and the ability to enhance the efficiency of photocatalytic and electrochemical water splitting. The findings reveal atomic-scale chemical and physical interactions that contribute to lowering the activation energy required for water dissociation, thereby improving hydrogen production efficiency. The study also highlights the strong correlation between the electronic structure of these materials and their catalytic performance, aiding in the design of advanced catalysts that meet industrial and environmental requirements. This research opens new avenues for developing hydrogen generation devices based on 2D material technologies, thereby supporting the transition to a sustainable energy economy. 2025-01-01T00:00:00Z