The melt rheology of two zinc alkali phosphate glasses was studied wit
h oscillatory flow experiments to accelerate efforts to melt process t
hem with organic polymers. The glasses differed markedly in chemical d
urability and melt viscosity. Melt viscosities were time independent a
t temperatures near their glass transition temperature. The omega depe
ndence of the complex viscosity eta conformed excellently to predicti
ons, eta(omega) = eta(0)(1+iw tau), for Hookean dumbbells. Fit parame
ters eta(0) and tau were used to estimate a melt viscosity-average mol
ecular weight M using a model reported by Ferry and co-workers [J. App
lied Phys. 26, 359 (1955)]. Arrhenius activation energies Delta H doub
le dagger for viscous flow were consistent with those traditionally fo
und for inorganic glasses. At higher temperatures, the melt viscosity
of both glasses increased monotonically with time. The viscosity incre
ase was exponential at long times, and the transition time to the expo
nential dependence was found to be strongly dependent on the shear str
ain. The steep viscosity rise is expected to cause significant process
ing challenges. Sample crystallization is thought to be responsible fo
r this behavior. (C) 1996 Society of Rheology.