Abstract
Specific surface free energy (SSFE) of natural calcium fluorapatite from the same mother rock and synthesized barium chlorapatite from the same lot was determined using contact angle of water and formamide droplets, compared with grown length of crystal face (h). The experimentally obtained SSFEs have different values even for the same index faces of the different crystals. The SSFEs also have wide distribution for each face of crystals. Observed SSFE is considered to be not only the SSFE of ideally flat terrace face, but also includes the contribution of strep free energy. Though the crystals we experimentally obtained were growth form, the relationship between SSFE and h was almost proportional, which looks like satisfying Wulff’s relationship qualitatively. The slope of SSFE versus h line shows the driving force of crystal growth, and the line for larger crystal has less steep slope. The driving force of crystal growth for larger crystal is smaller, which also means that the chemical potential is larger for larger crystal. The individuality of crystals for the same lot can be explained by the difference of the chemical potential of each crystal.
Highlights
Measurement of specific surface free energy (SSFE) of solid using contact angle of liquid is very popular and well accepted in the field of polymer science
The contact angles of liquid on inorganic crystal face have very wide distribution, and we need to take a lot of photographs to determine the average of contact angle
The length of the normal line from the center of the crystal to each face, hi, was obtained from the photograph and the hi was considered to be the grown length of the ith face
Summary
Measurement of specific surface free energy (SSFE) of solid using contact angle of liquid is very popular and well accepted in the field of polymer science. We determined the SSFE of ruby crystals from the contact angle of liquid droplet and discussed the relationship between the grown length of the crystal face [3]. The ruby crystals were growth shape, the relationship between the SSFE and h were almost proportional, which looks satisfying Wulff’s relationship. Wulff’s relationship should be satisfied for ideal equilibrium system, and the crystal face should be ideally flat At this time, we extended our experimental technique for natural mineral crystals in order to study the relationship between SSFE and h for the less ideal but more real system
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