Joseph H. Simmons

Non‐Newtonian viscous flow in glass

The viscosity of a soda‐lime silica glass was measured at high strain rates. The data show non‐Newtonian viscous flow in this inorganic oxide glass with the viscosity values below the expected Newtonian value. Following the imposition of large, steady strain rates, the observed stress increases with time to a maximum and then decreases to a time‐independent value. A comparison of the viscosity behavior of this glass with the molecular dynamics results in a ’’Lennard‐Jones’’ glass shows a number of points of correspondence and suggests the interpretation of the non‐Newtonian behavior as resulting from structural rearrangements in the material. The combined data show that the sustained, steady‐state stress asymptotically approaches a maximum at very high strain rates. This limiting stress is interpreted as the actual cohesive strength of the material and is calculated to be 1.4×108N/m2 (20,000 psi) for the glass under study.

Aqueous corrosion studies of a fluorozirconate glass

The effects of aqueous corrosion on a fluorozirconate glass containing ZrF4, BaF2, AlF3, LaF3 and LiF were investigated using soaking solution analysis, infrared transmission and reflectance spectroscopy and scanning electron microscopy. The dissolution of the glass was nearly congruent. The leached surface of the glass was covered with hydroxide crystals of Zr and Ba. The outer leached layer was thick, highly hydrated and cracked while the glass below was also hydrated and cracked indicating that no protective surface layer was formed. Drying studies of leached samples showed the appearance of an infrared absorptance peak at 7 μm (1440 cm−1) caused by bridging oxygen bonds formed during dehydration.

Application of the Environmental Relaxation Model to the Temperature Dependence of the Viscosity

An equation relating viscous flow processes to local microstructure is applied to the viscosity of nine materials belonging to different classes of glass formers. It is seen that the model proposes the correct general behavior for the viscosity and the associated activation energy distributions. The model further explains this behavior in terms of a temperature‐dependent ordering process in the structure of the material occurring at low temperatures. Finally, a simultaneous fit of the viscosity and the conductivity of a molten salt yields parameters whose relationships are physically meaningful in terms of the viscous relaxation and conduction relaxation processes.

Corrosion mechanisms and chemical durability of glass media proposed for the fixation of radioactive wastes

Results from leach tests conducted on simulated wastes fixated in borosilicate and high-silica glasses are presented. During the leaching period, the dissolution rates of several waste components were monitored. These components included alkali metals, alkaline earths, transition metals, rare earths, and an actinide, and it is shown how they differ and how the measurement of leach rates of some of these components can be misleading regarding long-term behavior. The problems of applying the results to the prediction of long-term dissolution behavior are discussed; models are presented for reliable long-term predictions, and the essential tests which must be conducted to allow the formation of these reliable predictions for long-term behavior are listed.

Degenerate Excited State in the Structure of B2O3

A degenerate excited state is essential to the description of structural rearrangements which account for the relaxational heat capacity, thermal expansion, and compressibility of vitreous B2O3. These relaxational responses cannot be simultaneously described by a two‐state model, or by any model involving a single ordering parameter, as shown by the magnitude of the Prigogine—Defay ratio (π≠1). The apparent two‐state behavior of the temperature derivatives, Δα and Δcp, and failure of a two‐state model to predict a sufficiently large compressibility (pressure derivative), suggest an analysis of structural rearrangements in vitreous B2O3 in terms of a single ground state and a twofold degenerate excited state which is characterized by different volumes.

A flow model for the kinetics of dissolution of nuclear waste glasses

Abstract A model has been developed to give reliable long-term predictions for the rate of material loss from radioactive waste solids and glasses exposed to aqueous environments. The model takes into full account the effects of the interaction of the glass with the medium over the entire range of flow/dilution conditions expected in geological repositories. These effects include an increase in leach rate with decreasing rate of flow at the moderate flow region due to a pH excursion, and a subsequent decrease in leach rate at the low flow rate region due to growing saturation with respect to SiO 2 Al 2 O 3 , etc. The surface-to-volume ratio can be treated as a scaling factor. The model makes possible a direct calculation of the fractional annual loss which the waste form undergoes over the entire range of possible respository conditions. The necessary data-base is obtained from the steady-state leachate concentrations measured in short-term flow tests carried out at several easily attainable combinations of experimental S/ V ratios and flow rates.