Browsing by Author "Adam A.M."

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    CHANGE OF THE ANTIMONY ANODIZING KINETICS BY COATING THE ELECTRODE WITH A THIN FILM
    (2023-01-01) Lilov E.; Lilova V.; Nedev S.; Kozhukharov S.; Adam A.M.; Girginov C.
    The present research work is dedicated on the processes kinetics description of the antimony anodization in potassium phosphate (K3PO4) aqueous solutions. The data have shown that the slope of the kinetic curves is dependent on the phosphate solution concentration. Besides, their mathematic approximation has revealed occurrence of a critical phosphate solution concentration of 0.11 mol dm-3. At this concentration, the slope of the kinetic curve tends to zero. Above this critical concentration, induction periods occur during the anodization. Additional experiments were performed with thin Sb2O3 layers preliminary deposited in vacuum. This approach has enabled to define the impact of such layers on the kinetic behavior during the anodization process. The results have shown that various stages of the process could be skipped. The final data analysis has confirmed the suggestion that the induction periods and voltage variations during the anodization process are caused by the formation of a thin Sb2O3 film, whose dielectric properties change with the film thickness increment.
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    Manipulation of thermal conductivity and thermoelectric power factor via Hf-doping in FeNbSb half-Heusler alloys for enhanced thermoelectric figure of merit
    (2025-12-01) Alsairy N.; Adam A.M.; El-Qahtani Z.M.H.; Petkov P.; El-Khouly A.
    Bulk samples of FeNb1-xHfxSb (x = 0.0, 0.10, 0.20) alloys have been prepared by successive induction melting and mechanical alloying (MA). Electrical and thermoelectrical characteristics have been investigated as functions of temperature in the temperature range 300 to 800 K. Electrical conductivity of the parent FeNbSb alloy and the low doped FeNb0.9Hf0.1Sb samples showed semiconducting behaviour with smaller electrical conductivity values. On the other hand, the most doped FeNb0.8Hf0.2Sb alloys showed a metal-like trend. The metallic behaviour indicated that typical acoustic phonon scattering dominates the charge transfer. Thermopower measurements revealed that Seebeck coefficients increase remarkably with the temperature increasing due to Hf-doping at the studied doping range due to the remarkable effect of Hf-doping on the carrier concentration. The relationship between temperature and thermoelectric power factor was evaluated and investigated. High thermoelectric power factor was achieved at 20 µWcm−1 K−2 for the highest Hf-doped alloy. Defects and electron–phonon scatterings reduced the lattice thermal conductivity and consequently improved thermoelectric figure of merit (zT). zT has significantly increased with temperature increasing providing evidence that half-Heusler materials are promising thermoelectric options in the mid to high temperature range. In addition, it can be concluded that higher Hf-content as dopant can simultaneously optimizes enhanced power factor besides significantly reduced thermal conductivity leading to better thermoelectric figure of merit. The maximum figure of merit (zT) was observed for the same sample with a value of 0.17, recorded at 700 K.
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    STRUCTURE, THERMAL, AND PHYSIC-CHEMICAL PROPERTIES OF SOME CHALCOGENIDE ALLOYS
    (2023-01-01) Adam A.M.; Abdel-Rehim W.M.F.; Petkov P.; El-Qahtani Z.M.H.; Alqannas H.S.; Alruqi A.B.; Hakamy A.; Ataalla M.
    Bulk products of crystalline Bi2Se3-xTex alloys (x =0.0, 0.1, 0.3, 0.5) were pre-pared using simple melting synthesis. Crystalline features, microstructure, and surface morphologies of the synthesized samples were examined via X-ray dif-fraction, scanning electron microscope, and energy dispersive X-ray spectrome-ter. Elemental distribution was studied by energy dispersive analysis of X-ray spectroscopy. Polycrystalline of rhombohedral crystal structure was observed for the concerned samples. Perfect crystallinity and micro-scalability of the prepared were also reflected by the physic-chemical properties of each sample. Thermal behavior was studied throughout differential scanning calorimetry and thermo-gravimetric analysis showing that the samples are of high stability over high temperature range. Physic-chemical properties were determined in terms of ex-perimental density. These properties were compactness value, molar volume and the percentage of free volume. Density of Bi2Se3 alloy was obtained at 7.37 gm/cm3. The Te doping enhanced the density of the Bi2Se3-xTex system. The most Te doped alloy showed density of 9.018 gm/cm3. All other physic-chemical prop-erties showed strong dependence on the Tea amounts in the system.