Modulus and internal friction in phosphate-silicate bioactive glass

The real and imaginary parts of the dynamic shear modulus, G′ and G″, respectively, of a “bioactive glass” Na₂O, CaO, SiO₂, P₂O₅ have been measured from 10^?4 Hz to 1 Hz at temperatures from 160 K to 610 K. The mechanical loss tangent of the glass (T_g = 816 K) at 1 Hz shows two relaxation regions: one centred at 312 K and the second at 585 K. The low-temperature peak appears in the same region as the peak attributed to Na ion motion in silicate glasses. The modulus of the glass is 32 GPa at 295 K. The spectrum of the high temperature peak has a broad distribution of relaxation times with a half width of five decades of frequency, and Arrhenius “activation energy” of 164 kJ mol.^?1, and the amplitude of this relaxation decreases on cooling. The similarity of these features with those observed in rigid molecular and other types of glasses suggests that the relaxations observed in the bioglass may be more appropriately considered as an intrinsic property of the non-periodic arrangement of atoms or ions in a solid than as being due to the diffusion of specific types of ions in it. It is pointed out that isothermal and isochronal measurements of internal friction in glasses do not give the same relaxation rate at the same temperature, due mainly to a rapid decrease in the amplitude of relaxation with temperature. The shear, Young's and bulk moduli of the glass are, 31.9, 76.6 and 43.0 GPa, respectively, and the Poisson's ratio is 0.20.A sample of the same bioglass containing 0.05% more water showed a shoulder in its tan φ at ～ 400 K and a peak at ～ 560 K, with little change in its modulus or T_g. Thus the presence of water above a certain amount had less significant effect on the internal friction of the bioactive glass.