INTERNAL-FRICTION OF 16.3NA(2)O-CENTER-DO T-33.7MGO-CENTER-DOT-50.0SIO(2) GLASS

The internal friction of 16.3Na(2)O.33.7MgO.50.0SiO(2) glass was measu red with an inverted torsion pendulum in the frequency range 0.35-0.95 Hz, and the tracer diffusion coefficients of oxygen and magnesium wer e measured at temperatures below the glass transition point by use of stable isotopes 180 and Mg-26, respectively. The temperature dependenc e of the relaxation time of a high-temperature peak was represented by tau H.P.(S)=(2.04+/-0.05) x 10(-15) x exp[{183.8+/-5.7(kJ/mol)}/RT] T he temperature dependence of the tracer diffusion coefficients for oxy gen and magnesium was represented by the following equations: D-oxy(m( 2).s(-1))=(1.22+/-0.06) x 10(-10x) exp[{-150.2+/-5.1(kJ/mol)}/RT] D-Mg (m(2).s(-1))=(4.29(-1.15)(+1.57))x10(-6) (x)exp[{-195.3+/-1.9(kJ/mol)} /RT] The activation energy for the high-temperature peak (183.8 kJ/mol ) was smaller than that for magnesium diffusion (195.3 kJ/mol) by abou t 7% but greater than that for oxygen diffusion (150.2 kJ/mol). Compar ison of the results of the present study with those obtained by Hino e t al.(1)) led to the conclusion that the high-temperature peak was cau sed by the movement of magnesium ion under stress.