Two Peaks in the Internal Friction as a Function of Temperature in Some Soda Silicate Glasses

Measurements of the internal friction of the glasses 17% Na 2 O‐83% SiO 2 , 25.6% Na 2 O‐74.4%, SiO 2 , and 34% Na 2 O‐66% SiO 2 were made as a function of temperature, composition, and frequency in the range 1 to 3 cycles per second and from –90° to 500°F. The internal friction as a function of temperature revealed two distinct peaks for each glass tested. One peak occurred in the temperature range −55° to +50°F. and the other in the range 300° to 500°F. All the observed peaks were found to be best represented by an assumed Gaussian distribution of heats of activation with the high‐temperature peaks exhibiting a much wider distribution than the low‐temperature peaks. It was therefore concluded that none of the peaks was a manifestation of a single heat of activation. The temperatures at which all peaks occurred increased with increasing frequency. From this shift of “peak” temperatures with frequency, the most likely heats of activation associated with each peak were calculated. The temperature dependence of the dynamic shear modulus for each glass was used to calculate the “relaxation strength” of the relaxation process for each peak. An analysis of all these data strongly indicated that the high‐temperature peaks as well as the low‐temperature ones were related to cooperative action among sodium ions.