Solidification on spherical surfaces

Solidified spherical particles show a range of interesting surface patterns that are quite reminiscent of those seen in conventional casting. Given their immense practical importance (e.g., in making powders for metal 3D printing), understanding how these structures form during solidification remains an area of active interest. This work attempts to understand the dynamic evolution of surface morphologies on spherical surfaces using low-melting organic crystals. Container less solidification conditions are established to study the solidification dynamics of a single suspended drop using in situ imaging techniques. Complementary analytical and numerical calculations are also presented to help explain the nature and scale of the resulting patterns, as well as transitions between different surface morphologies. Quantitative differences in primary and secondary arm spacings with planar and cellular patterns are presented and discussed, based on which consequences for the development of structures on solidified metal drops are deduced. Our central deductions appear to be applicable to other, potentially unrelated, systems including micrometeorite dust, suggestive of common underlying physics.