• M S Gaafar

      Articles written in Bulletin of Materials Science

    • Study of rigidity of semiconducting vanadate glasses and its importance in use of coatings

      Yasser B Saddeek M S Gaafar

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      The elastic moduli of some multicomponent vanadate based glasses were analysed in terms of the bond compression model by some physical parameters such as, the density, average stretching force constant and average atomic ring size. These parameters were calculated for all the glass series and for all the glass composition to estimate the rigidity of these glasses. The results showed that the average force constant and the elastic moduli of these glasses are sensitive to the decrease in PbO content. This behaviour was attributed to the increase in the molar volume and the role of different modifiers. These parameters along with the coordination number of the glasses affect the glass transition temperature. The correlation between the elastic moduli and thermal properties of these samples showed that 0.25MoO3–0.25PbO–0.5V2O5 glass is the most rigid and has an applicable glass transition temperature for coating.

    • Acoustic relaxation of some lead niobium tellurite glasses

      M S Gaafar Y A Azzam

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      The longitudinal ultrasonic attenuation in 𝑥Nb2O5 −(1−𝑥)TeO2, 0.1PbO−𝑥Nb2O5−(0.9−𝑥)TeO2 and 0.2PbO − 𝑥Nb2O5− (0.8−𝑥)TeO2 tellurite glass systems was measured using the pulse echo technique at ultrasonic frequencies 2, 4, 6 and 8 MHz in the temperature range from 150 to 300 K. The absorption curves showed the presence of well-defined broad peaks at various temperatures depending upon the glass composition and operating frequency. The maximum peaks move to higher temperatures with the increase of operating frequency, indicating the presence of some kind of relaxation process. This process has been described as a thermally activated relaxation process, which happens when ultrasonic waves disturb the equilibrium of an atom vibrating in a double-well potential in the glass network structure. Results proved that the average activation energy of the process depends mainly on the modifier content. This dependence was analysed in terms of the loss of standard linear solid type, with low dispersion and a broad distribution of Arrhenius-type relaxation with temperature-independent relaxation strength. The experimental acoustic activation energy has been quantitatively analysed in terms of the number of loss centres (number of oxygen atoms that vibrate in the double-well potential).

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