Browsing by Author "Gaafar, M. 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.
Structural studies and mechanical properties of some borate glasses doped with different alkali and cobalt oxides
(ELSEVIER SCIENCE BV, 2013) Gaafar, M. S.; Marzouk, S. Y.; Zayed, H. A.; Soliman, L. I.; El-Deen, A. H. Serag
Mixed alkali borate glasses doped with CoO, have been prepared by the melt quenching technique. Elastic properties and FT-IR spectroscopic studies have been employed to study the role of CoO and the mixed alkali effect on the structure of the investigated glass system. Elastic properties and Debye temperature have been investigated using sound wave velocity measurements at 4 MHz at room temperature. The density, molar volume and glass transition temperatures were employed to investigate the structure of these glasses. Infrared spectra of these glasses revealed that the borate network is affected by the increase in the concentration of CoO content and the mixed alkali oxides. These results are interpreted in terms of the change in the topology of these glass structures. The elastic moduli are observed to increase with the increase of CoO content due to the increased average bond connectivity. (C) 2012 Elsevier B.V. All rights reserved.