Fabrication of lotus-type silver with directional pores by unidirectional solidification in oxygen atmosphere

Lotus-type silver was fabricated by unidirectional solidification in mixture gas of oxygen and argon at high pressures. Two solidification methods were adopted in this study: the unidirectional solidification casting method and the Czochralski method. The directional pores were evolved by insoluble oxygen when silver melt dissolving oxygen was solidified. Non-uniform size distributions of pores in distorted shapes were observed in lotus-type silver fabricated by the unidirectional solidification casting method. On the other hand, round shape pores with good circularity and more uniform pore size were found in the cross section of the lotus-type silver made by the Czochralski method. The distortion of pore shape is attributed to the re-dissolution of oxygen gas in the pores to the molten silver during solidification.