Melt rheology of zinc alkali phosphate glasses

R. L. Sammler a

The Dow Chemical Company, Ventures/Central Research and

Development, Midland' Michigan 48674

J. U. Otaigbe

Department of Materials Science and Engineering, Iowa State University,

3053 Gilman Hall, Ames, Iowa 50011

M. L. Lapham and N. L. Bradley

The Dow Chemical Company, Ventures J Centra Z Research and

Development, Midland, Michigan 48674

B. C. Monahan and C. J. Quinn

Science and Technology Group' Corning Incorporated, Corning,

New York 14831

(Received 16 August 1995; final revision received 18 December 1995)

Abstract

The melt rheology of two zinc alkali phosphate glasses was studied with oscillatory flow experiments to accelerate efforts to melt process them with organic polymers. The glasses differed markedly in chemical durability and melt viscosity. Melt viscosities were time independent at temperatures near their glass transition temperature. The omega dependence of the complex viscosity sigma star conformed excellently to predictions, h *( w ) = h 0 / (1 + i w t ) for Hookean dumbbells. Fit parameters h 0 and t were used to estimate a melt viscosity-average molecular weight M using a model reported by Ferry and co-workers [J. Applied Phys. 26, 359 (1955)]. Arrhenius activation energies D H* for viscous flow were consistent with those traditionally found for inorganic glasses. At higher temperatures, the melt viscosity of both glasses increased monotonically with time. The viscosity increase was exponential at long times, and the transition time to the exponential dependence was found to be strongly dependent on the shear strain. The steep viscosity rise is expected to cause significant processing challenges. Sample crystallization is thought to be responsible for this behavior.

a) Corresponding author.