Browsing by Author "Youssof, I. M."

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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.
Structural role of RO and Al2O3 in borate glasses using an ultrasonic technique
(PERGAMON-ELSEVIER SCIENCE LTD, 2006) Abd El-Moneim, A.; Youssof, I. M.; Abd El-Latif, L.
The ternary alkaline earth aluminoborate glasses RO-Al2O3-B2O3, where R = Mg, Ca, Sr, have been prepared by the normal quenching method. Ultrasonic velocities and attenuation were measured in these glasses using the pulse-echo technique to explore the structural role of RO and Al2O3 in these glasses. From the measured densities and velocities, various parameters such as elastic moduli, microhardness and Poisson's ratio have been determined. Results obtained are discussed in terms of the field strength of the interstitial cation, molar ratio (Al2O3/RO), fraction of four coordinated boron atoms, number of network bonds per unit volume, average cross-link density and fractal bond connectivity of the network. It was found that the network connectivity of these glasses increases in the order Mg > Ca > Sr. Makishima and Mackenzie theory has been applied to correlate the experimental and theoretical data and good correlation was observed. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.