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The interaction between particles and an advancing solid-liquid interface has been investigated both experimentally and theoretically. For each particular type of particle, a ``critical velocity'' was observed, below which the particles are rejected by the interface, and above which they are trapped in the solid. The dependence of the critical velocity on various properties of matrix and particle was investigated. A theory has been developed, based on the assumption that a very short-range repulsion exists between the particle and the solid. This repulsion occurs when the particle-solid interfacial free energy is greater than the sum of the particle-liquid and liquid-solid interfacial free energies. The particle is pushed along ahead of the advancing interface and becomes incorporated into the solid if liquid cannot diffuse sufficiently rapidly to the growing solid behind the particle. Reasonable agreement was obtained between the calculated and experimentally observed critical velocities.

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Single crystals of tin grown from the melt under a wide range of conditions are shown to exhibit a fibrous structure which manifests itself as parallel ridges ("corrugations") on the free surface of the specimen and as a hexagonal network ("hexagonal cells") on the growing solid–liquid interface. The center of each cell projects into the liquid. Segregation of impurities is shown to occur during solidification in a manner intimately related to the structure. The structure is suppressed by growth at low speeds or under a steep temperature gradient. The size and regularity of the elements of the structure depend upon speed of growth, temperature gradient, and impurity content. A theory is advanced which accounts for the origin and observed properties of the structure. This theory shows that the structure consists essentially of a particular distribution of impurities resulting from nonequilibrium solidification.

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