Measurement of specific surface free energy (SSFE) of solid is very popular and well accepted in the field of polymer science.  On the other hand, the measurement of SSFE of crystals face is believed to be difficult.  Even though the significance of SSFE for crystal growth is well discussed, experimental determination of SSFE for crystal is very few.  We performed the first trial to determine the SSFE of barium chlorapatite using the contact angle of liquids and reported[1].  This time we are going to study the SSFE of some inorganic single crystals and discuss the morphology individuality of each crystal.

 Barium chlorapatite and ruby crystals were synthesized by flux method.  The contact angles of water and formamide droplet on (10-10) face and (10-11) face of barium chlorapatite and (11-23) face of ruby were measured by sessile drop method.  Contact angles were measured more than 300 times for each face.

 Distribution of contact angle was approximately normal distribution.  The average value of contact angle was nearly consistent with the angle of the highest frequency.  The value of SSFE can be calculated using the Fowkes approximation and Wu’s harmonic mean equations.  Wide distribution of the SSFE is considered to cause the distribution of step density on crystal surface.  The observed SSFE including step free energy was almost proportional to the grown length of the crystal, h.  In the same system, for example the same crucible, the crystal has different shape each other, but the shape of each crystal is the resulted from minimum of the surface free energy including the step free energy.

[1] T.Suzuki, K.Nakayama, S.Oishi, Bull. Chem. Soc. Jpn. 77 (2004) 109.

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