Experimental Researches on Heterogeneous Nucleation Behavior with Different Surface Conditions

It is of great significance to study the density of nucleation sites on the surface of casting mould in the research of casting process.In the present paper,substrate surface energy was calculated by measuring the contact angle of water on the substrate and the roughness of the surface was quantitatively characterized by fractal dimension parameters.Effects of substrate surface roughness on the nucleation behaviors of NH4Cl crystal was analyzed experimentally,the results indicate that: surface energy and micro-morphology have significant influences on the wet ability and nucleation properties of the substrate.The etched LY12 substrate surface has a complicated micro-morphology and exhibits fractal characteristics apparently.The as-etched surface in a state of high surface energy exhibits super-hydrophilicity and gives a high nucleation density in the followed nucleation experiments.When the surface is treated with 1H,1H,2H,2H-Perfluorooctyltrime-thoxysilane,the surface energy of the substrate decreases,and the surface become super-hydrophobicity and gives a lower nucleation density in the nucleation experiments.