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The effect of the slab thickness (d) on the segregation behavior has been investigated for a phase separating system in a slab consisting of atomic planes parallel to the free surfaces. The calculations were carried out using the Fowler–Guggenheim approximation in the monolayer limit. It is shown, that by varying the surface fraction ξ, a surface phase transition can occur, similar to a semi-infinite system where a change in temperature can lead to a phase transition (S-shaped segregation isotherm). Furthermore, the existence of a minimum on the free energy curve versus d was examined. It was demonstrated that such a minimum can exist in the nanocrystalline region.

Abstract. Variable cryptocrystalline silica varieties occur en masse in the fractures and cavities of the andesite host rock, showing different genetic and morphological features of variable microbial activity. Four types of CL features characterized silica phases. Raman spectroscopy supported variable amorphous carbon phases in inhomogenous distribution.

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