The effect of oxygen potential on the wetting behavior and interfacial energy between Cu and sapphire was studied using the sessile drop technique in a CO-CO, atmosphere. A linear relation was found between y5/, and logp0, (atm) from to atm y5/, approached a constant value asymptotically. A barrier surface layer was proposed to explain this change. The Gibbs adsorption equation was used to evaluate the characteristics of the interfaces. Formation of a Cu,O film at the liquid-vapor interface and a CuAIO, film at the solid-liquid interface is suggested. The work of adhesion reached a maximum at=O.Ol'at.% oxygen, corresponding to pO,=lO-~atm. Measurements of the basal radius as a function of oxygen content were used to evaluate the role of oxygen in promoting spreading. Spreading on sapphire is directly proportional to the logarithm of oxygen present in the molten Cu drops.Beyond

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The contribution of plastic flow to overall densification of a powder compact during hot-pressing was analyzed by incorporating the creep characteristics of materials at high temperatures into an equation applicable to hot-pressing conditions. When the particles are assumed to be spherical and when the effective stress acting at the points of contact under axial loading conditions is taken into consideration, the final form of the equation is:where CY, and p are geometric constants which can be calculated from the packing geometry, A and n are material constants, D is the relative density of the compact, and R is the radius of the spheres at any stage of deformation in arbitrary units. Computerized plots of D vs t were obtained for several materials. Experimental verification of these plots using hotpressing data for Pb2% Sb, Ni, and A1203 spheres and coarse irregular Al,O, particles showed that the experimental data fitted the theoretical prediction for orthorhombic packing well. A large deviation with respect to the initial packing density was encountered with very fine irregular ALO, powder, although its densification behavior with time was similar to that of the coarse particles.

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