Surface Tension of Barium Chlorapatite Crystals Grown from Flux

Abstract

Abstract Large, well-formed crystals of barium chlorapatite [Ba5Cl(PO4)3] were grown from a sodium chloride flux. The prismatic crystals of Ba5Cl(PO4)3 were bordered by {(101-0)} and {(101-1)} faces. The crystals have a tendency to elongate in the <0001> directions. Contact angles of water, formamid, ethylene glycol, and diethylene glycol droplets on the Ba5Cl(PO4)3 crystals were observed. The surface tension, that is, the surface free energy of the grown crystals, was calculated in order to study the relationship between the morphology and the surface tension of the crystal. The contact angles of water, formamid, ethylene glycol, and diethylene glycol droplets on the ((101-0) ) face of a Ba5Cl(PO4)3 crystal were 40°, 37°, 30°, and 26°, respectively, and the contact angles of those liquids on the ((101-1) ) face were 20°, 18°, 16°, and 14°, respectively. The surface tension of the crystal faces were calculated from the observed contact angles using harmonic mean and geometric mean equations. The calculated surface tensions of the crystal faces were 58 ± 1 and 69 ± 1 mN/m for the ((101-0) ) and ((101-1) ) faces of a Ba5Cl(PO4)3 crystal, respectively. The fact that the surface tension of the ((101-0) ) face is smaller than that of the ((101-1) ) face indicates that the ((101-0) ) face is more stable than the ((101-1) ) face. The energetic stability of the ((101-0) ) face corresponds to the morphology of the Ba5Cl(PO4)3 crystal, which elongates in the <0001> directions.