Growths of bubble/pore sizes in solid during solidification—an in situ measurement and analysis

The sizes of a bubble trapped in solid after nucleation on the solidification front during an upward freezing of water containing a dissolved oxygen or carbon dioxide gas are experimentally measured and quantitatively predicted in this work. The sizes of the bubble include the height, radius and contact angle of the cap on the solidification front and the length of the bubble in the solid. From in situ measurements of bubble shapes in solid at cold temperatures of −25° and −15°C, it quantitatively shows that pore formation can be divided into five regimes: (1) nucleation on the solidification front, (2) spherical growth, (3) solidification rate-controlled elongation, (4) disappearance of the bubbles, and (5) formation of the pores in solid. To interpret experimental results, equations incorporated with the growth rate of a spherical bubble and solidification rate to predict bubble shapes in the solid during the spherical growth and solidification rate-controlled elongation are successfully proposed. It is found that the time to reach the regime of solidification rate-controlled elongation corresponding to the maximum radius of the bubble is increased by decreasing solidification rate and increasing spherical growth rate of the bubble. Experimental data show the effects of initial gas concentration and solidification rate on geometries of the bubble in solid. Valuable database for more systematical studies of pore formation in solids are provided.