Formation of Porous Structures in Metal–Hydrogen Systems

Abstract

Crystallization of hydrogen-saturated melts under controlled conditions enables one to obtain a new class of porous materials (gasars). The technological parameters of the process such as the partial hydrogen pressure, the total gas pressure, the temperature of the melt, and the crystallization rate affect the porosity, size and form of pores, which enables one to control the structure of gasars. Using methods of quantitative metallography, we determine conditions of its formation. The most homogeneous nickel ingots of gasars are obtained with increase in the total gas pressure in the system during crystallization of the melt and the decrease in the partial hydrogen pressure. The gas gap between the chill and the ingot appearing in the process of directional crystallization of hydrogen-saturated melts limits heat exchange and leads to a disturbance of the cooperative growth of gas bubbles and crystals. However, the negative influence of this process considerably decreases with increase in the partial hydrogen pressure, which also favors the production of homogeneous ingots of gasars.