Browsing by Author "Abd El-Aal, N. S."

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    Elastic and structural properties of vanadium-lithium-borate glasses
    (TAYLOR & FRANCIS LTD, 2008) Sidkey, M. A.; Abd El-Moneim, A.; Gaafar, M. S.; Abd El-Aal, N. S.; Abd El-Latif, L.; Youssof, I. M.
    The ternary xV(2)O(5)-(40 - x)Li2O-60B(2)O(3) glass system, where x = 1, 2, 3, 4 and 6 mol%, was prepared by normal quenching. Ultrasonic velocities and attenuation were measured at room temperature using a pulse-echo technique. Various parameters, such as elastic moduli, micro-hardness, Poisson's ratio and Debye temperature, were determined from the measured densities and velocities. The composition dependence of these parameters, in addition to the glass-transition temperature, suggested that vanadium ions were incorporated into these glasses as a network modifier, resulting in the reconversion of BO4 tetrahedra to BO3 triangles by the breaking of B-O-B linkages and the formation of nonbridging oxygens (NBOs). The outcome was a reduction in network connectivity and rigidity with increasing V2O5 content. The results are explained quantitatively in terms of fractal bond connectivity, average atomic volume, network dimensionality, packing density, number of network bonds per unit volume, cross-link density and atomic ring size. The Makishima and Mackenzie model appears to be valid for the studied glasses when the fate of BO4 tetrahedra and creation of NBOs are taken into account.