Experiments are reported on two techniques for melt-texture processing Ba2YCu3O6.5 by directional solidification from a semisolid melt containing particles of BaY2CuO5 and a copper-rich liquid. One of these employs an electric resistance furnace with ambient or oxygen enriched atmosphere; the other is a laser-heated furnace operating at 1.3 atm oxygen. Solidification interface morphologies and other structural features were examined in quenched specimens. Depending on growth rate and temperature gradient, three different types of growth morphologies of the growing 123 phase were observed: ‘‘faceted plane front,’’ ‘‘cellular dendritic’’ or ‘‘equiaxed blocky.’’ The interface temperature decreased markedly with increasing growth rate for the faceted plane front specimens. In the remaining specimens, solidification took place over a range of temperatures. The temperature of the ‘‘root’’ of the solidification front dropped, but temperature of the solidification front ‘‘tip’’ did not. A solidification model is developed and employed to interpret experimental observations. The model assumes limited diffusion of solute in the liquid during the growth of the superconducting phase. The model shows, in agreement with experiment, that growth rate of the low temperature solid phase has a strong effect on ability to obtain the desirable faceted plane front, and that thermal gradient has only a small effect. Interparticle spacing of the high temperature phase, BaY2CuO5, is also predicted to have a strong effect.

Surface phenomena, including wetting, have surely fascinated humans foi millennia. The breakup of a falling stream of water and the behavior of froths, both driven by surface energy, certainly caught the interest of people long before records were kept. The Phoenicians are credited with inventing that remarkable wetting agent, soap, in about 600 B.C., and a 2000-year-old soap factory was unearthed in the ruins of Pompeii.It is hard to pinpoint the first scientific studies of surfaces and wetting, but it is a good guess that the earliest scientists, or natural philosophers, were interested. In 1805 Young noted that in a system consisting of a liquid and a solid phase, the former will wet the latter to a degree dictated by the surface energies of the system. If a liquid drop rests on a solid substrate, as shown in Figure 1, the wetting angle, θ, characterizes the wetting of solid by liquid. The fundamental relationship between wetting angle and surface energy in equilibrium was given by Young as:where γsv is the surface energy of solid, γsl is the solid-liquid interfacial energy, γlv is the surface energy of liquid, and θ is the wetting angle.

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