Part 1: The effect of lattice defects on the sintering of lithium fluoride; Part 2: The morphology of calcium oxide from calcium carbonate decomposition

Our motivation for studying the effect of lattice defects on sintering kinetics came from a theory by Searcy concerning surface melting of solids. Surface melting has been shown to occur in ice, argon, and lead at temperatures below the melting point. While surface melting of this sort is an equilibrium phenomenon, Searcy has predicted that surface melting may also occur in a non-equilibrium situation -- when a solid is being rapidly heated and has a below-equilibrium concentration of vacancies for the temperature reached. To test the surface melting theory we have compared the density changes of two different types of powder compacts of lithium fluoride after subjecting both to the same fast-firing heat treatment. One type of compact consisted of powder originating from a crystal which he had quenched from a high temperature, and the other consisted of powder from a crystal which we had annealed at a lower temperature. When calcite is decomposed in vacuum, CaO is sometimes found in two distinguishable layers. Both layers are comprised of fairly uniformly sized, cylindrical rods on the order of 10 nm in diameter with the normal NaCl-type crystal structure. The outer layer consists of ∼1 μm diameter bundles of rods separated by ∼1 μm wide cracks. The second layer, adjacent to any undecomposed calcite -- the ''intermediate layer'' -- probably consists of rods which are relatively evenly spaced. Because sintering is negligible when calcite decomposition occurs below 700 degree C in a vacuum of 10-3 torr or less, the outer layer is probably formed by a diffusionless, cooperative re-packing of CaO rods first formed with the uniform spacing characteristic of the intermediate layer. 35 refs., 25 figs., 6 tabs