Browsing by Author "Ali, Ahmed I"

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    Influences of Ag-NPs doping chitosan/calcium silicate nanocomposites for optical and antibacterial activity
    (ELSEVIER SCIENCE BV, 2016-12) Youssef, Ahmed M; Abou Hammad, Ali B; Ali, Ahmed I; El-Nahrawy, Amany M
    Chitosan (CS)/calcium silicate nanocomposites pure and doped with Ag ions (1, 2 mol%) were prepared via sol gel method. The prepared CS/calcium silicate nanocomposites were investigated through X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The XRD results, indicating that after increasing the Ag ions in the CS/calcium silicate nanocomposite the crystallinity degree increased regularly in the prepared nanocomposites accompanying to the continuously rearrangement in the internal structure of nanocomposite under the effect of inorganic nanoparticles. Correspondingly, the optical properties of the prepared nanocomposites films were measured using UV/vis spectroscopy. The reflectance increased while the energy band gap decreased from 3.96 eV to 2.43 eV with Ag-ions concentration. More over the transition type changed from direct into indirect by adding Ag-ions, indicate that new band between valence and conduction band were formed. In addition, the optical parameters showed an increase in refractive indices and decrease in the surface and volume energies losses with increasing Ag-ions. Correspondingly, the prepared nanocomposites exhibited good antibacterial activity against gram positive (Staphylococcus aureus), gram negative (Pseudomonas aeruginosa) bacteria and fungi (Candidia albicans). The results suggested that the prepared CS/calcium silicate nanocomposites can be a promised candidate for optical sensors applications and smart packaging materials. (C) 2016 Elsevier B.V. All rights reserved.
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    Structure, magnetic and magnetocaloric properties of nano crystalline perovskite La0.8Ag0.2MnO3
    (ELSEVIER SCIENCE BV, 2019-06) AboZieda, Abd El-Rahman T.; Ghani, A. A; Ali, Ahmed I; Salaheldin, Taher A
    Nano crystalline La0.8Ag0.2MnO3 perovskite compound was prepared using sol-gel method. The synthesized nano compound was characterized using X-ray Diffraction (XRD) and High Resolution - Transmission Electron Microscope (HR-TEM). The magnetic and magnetocaloric properties were studied in a broad temperature range, and confirmed the presence of ferromagnetic-paramagnetic (FM-PM) transition around Curie temperature (T-C = 306 K). We reported a maximum magnetic entropy change vertical bar Delta S-M vertical bar(max) = 0.96 J/kg.K with relative cooling power (RCP) = 39.98 J/kg at magnetic field 2 T. Such results could be a significant practical application in magnetic refrigeration. The observed magnetic phase transition in the sample was testified a second order. The critical exponent analysis which define the magnetic transition revealed values 0.4025 for beta, 3.33 for delta and 0.93 for gamma. These values are closely related to those obtained by the mean field model. The second order magnetic phase transition is further confirmed by constructing a universal curve for variation of vertical bar Delta S-M vertical bar/vertical bar Delta S-max vertical bar vs rescaled temperature (theta) for various magnetic field values.
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    Synthesis, structural, magnetic and magnetocaloric properties of La0.8Sr0.2MnO3 nanoparticles
    (SPRINGER, 2019-04) Ali, Ahmed I; AboZied, Abd El-Rahman T; Ghani, AA; Salaheldin, Taher A
    In this work, we reported a detailed study on the synthesis, structural and magnetic properties of nanocrystalline La0.8Sr0.2MnO3. The synthesized nanoparticles were prepared using a sol-gel method and characterized using X-ray diffraction and high-resolution transmission electron microscope. The average particle size was found in the range from 40 to 45 nm. The magnetization versus temperature M(7) measurements as well as magnetization field dependence M(H) have been investigated using vibrating-sample magnetometer. The magnetization as a function of temperature M(7) indicated a broad second-order magnetic phase transition from ferromagnetic state to paramagnetic state in the Curie temperature region (320-340 K). The magnetocaloric effect of the sample has been estimated and presented a maximum magnetic entropy change vertical bar Delta S-M vertical bar(max) = 0.86 J kg(-1) K-1 with relative cooling power = 62.12 J kg(-1) at magnetic field (H) = 2T. Based on the result of magnetocaloric properties, the investigated sample could be considered as a good refrigerant material for near room temperature magnetic refrigeration.