Glasses in the system xFeCl 3 ±10Fe 2 O 3 ±(90±x)P 2 O 5 have been prepared by the normal quenching method over a wide range of composition (x 15 up to 50 mol%). The glass structure has been investigated using IR spectral analyses which shows that the intermediate range order is affected by substitution of FeCl 3 for P 2 O 5 . Thermal expansion coefficient, glass transition temperature, density and dissolution rate in HCl were also investigated. The formation of P±O±Fe and P±Cl bonds at the expense of PO bonds is responsible for the good chemical durability of the studied glasses. Changes in other properties are interpreted in terms of the depolymerization of the glassy matrix by FeCl 3 .Y.M. Moustafa and A. El-Adawy: Structural and Physical Properties of Glasses

The elastic properties of the vitreous system Bi 2 O 3 -B 2 O 3 have been measured by ultrasonic pulse echo overlap technique at a frequency of 10 MH z and at room temperature. For the purpose of measuring the ultrasonic velocity with high accuracy, the McSkimin criterion for determining the correct cyclic overlap between echoes is used. The elastic properties of the present glass system as a function of composition are discussed on the basis of the elastic internal energy due to the deformation. Also presented is a full discussion of the Poisson's ratio; which is found to be rather sensitive to the glass composition.

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