Richard M. Fulrath

Solubility of Gases in Glass. II. He, Ne, and H2 in Fused Silica

The statistical thermodynamics of the gas‐in‐glass system provides a basic model of both physical and chemical solubility. The physical solubility result is essentially equivalent to that for monatomic solubility. The chemical solubility result is dependent upon the specific system involved. The model was compared with experiment for a variety of systems. Helium and neon in fused silica were examples of the physical solubility of monatomic gases. Variations of the thermal history of the fused silica did not appear to have a measurable effect on physical solubility as evidenced in the helium data. Hydrogen in fused silica was an example of the physical solubility of polyatomic gases. Physical solubility was measured by a modified Seiverts technique and was characterized by a linear dependence on pressure. Binding energies for the physically dissolved species were of the order expected for van der Waals bonding. Vibrational frequencies were on the order of 1013 sec−1 with the heavier species having the lowe...

Solubility of Gases in Glass—A Monatomic Model

A statistical mechanical model of gas solubility in glass is presented. For equilibrium, the Gibbs free energy of the free gas is equated to that of the gas in solution. Expressions for the Gibbs energies are obtained from assumptions of the atomic motion in the free gas and dissolved states. The resulting solubility equations express the solubility (in atoms per cubic centimeter of glass) as a function of gas pressure, temperature, fundamental constants, and material parameters. An initial evaluation of the model is made by comparison with literature data for helium and neon in fused silica.

Direct observation of liquid-phase sintering in the system tungsten carbide-cobalt

The hot-stage of a scanning electron microscope has been used to observe liquid-phase sintering in the system tungsten carbide-cobalt. Densification behaviour and the mechanism for the first, fast stage of sintering have been determined; the influence of particle size and the amount of liquid phase has been investigated. In all samples the densification kinetics is that of a rearrangement process; direct observation confirmed this result.

Diffusivity of helium in fused silica

A statistical mechanical model of diffusion is applied to helium diffusion in fused silica. The number of gas atoms moving solubility sites is related to the number of atoms in those sites. The number of atoms in the excited state, between two adjacent solubility sites, relative to the number occupying solubility sites can be described by their partition functions. The process of diffusion is treated as a random walk process which results in a diffusion equation in terms of the temperature, fundamental constants, and material parameters. The model is compared to data reported in the literature on He diffusion in fused silica in order to determine the unknown parameters. The model also shows that absolute rate theory is not able to account for the nonlinearity observed in logD vs 1/T for this system.

DIRECT OBSERVATION OF LIQUID-PHASE SINTERING IN THE SYSTEM IRON-COPPER

The hot-stage of a scanning electron microscope has been used to observe liquid-phase sintering in the system iron-copper. The densification behaviour of compacts of Fe and Cu particles were determined. The influence of particle size of both components and the amount of liquid phase developed were investigated. In samples with about 20 vol % liquid phase, the densification kinetics as observed by direct observation shows that no rearrangement takes place. In samples with 40 vol % liquid phase and particle sizes of 10 to 20 µm, some rearrangement was observed.

Expansion during the reaction sintering of PZT

Abstract Expansion during the reaction sintering of PZT from PT and PZ constituents was studied at different molar ratios, for different particle sizes, and different temperatures: compositional and particle size effects were observed. The expansion is related to the size of the PT particles present and exhibits a maximum at 50 mole% PT for equal sizes of PT and PZ.

EFFECT OF SURFACE TREATMENTS ON STRENGTH OF PZT POLYCRYSTALLINE CERAMICS

In bending strength determinations of ceramics, the fracture usually initiates from the tensile surface or the edges. The edge effect could be minimized by carefully rounding off the edges of specimens subjected to four-point bending. The effect of tensile surface polishing, polishing and rounding off the edges, and the acid treatment of the polished surface on the strength of PZT polycrystalline ceramics was determined along with the failure mechanism.

Influence of mixing medium on sintering and coupling coefficient of PZT ceramics

Abstract Mixtures of PZT, PbO and a water solution of PVA were prepared with distilled water and isopropyl alcohol. Better cold pressing behavior and more uniform microstructures free of large pores were obtained with use of the alcohol. Nature of grain boundaries was essentially unaffected as indicated by K p measurements.