Rapid solidification of Al2O3 was performed under pressurized hydrogen atmosphere. Many cylindrical pores that arranged in the direction of solidification was formed in the solidified film. The porosity remained constant and was independent of the hydrogen partial pressure. Even at a hydrogen partial pressure of 50%, the amount of hydrogen was sufficient for pore formation. The porosity of the samples prepared in this study was 35% at 0.1 MPa and 30% at 0.6 MPa. The porosity was higher than that of samples prepared by the unidirectional solidification method. The porosity did not depend on the total pressure either. The porosity decreased as the total pressure increased. Pressure is transmitted to the solid-liquid interface via the liquid phase, causing the pressure inside the pores to increase, which results in a decrease in pore size. As the hydrogen partial pressure increased, the thickness of the non-porous layer formed during the early stages of solidification increased slightly. The time required to reach a hydrogen concentration sufficient for pore formation at the solid-liquid interface increases as the hydrogen partial pressure decreases.
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