Morphology control of phase-separation texture by elongation of two-liquids immiscible melt in Fe₃O₄-SiO₂ system

The existence of a liquid-liquid miscibility gap in Fe₃O₄-SiO₂ system has been reported. In this study, phase-separated glasses of 5 Fe₃O₄·95SiO₂ (mol%) were prepared by melting sintered rods of the same composition at 1800°C (in immiscible region) using an infrared imaging furnace and, subsequently, quenching with elongation of the melts at a constant rate. The glass quenched without elongation exhibited a binodal type phase separation texture consisting of discrete spherical Fe₃O₄-rich particles. On the contrary, in the sample quenched with elongation, Fe₃O₄-rich particles were stretched and oriented along the direction of elongation. The length of the stretched particles was proportional to the elongation distance and was not independent of the elongation rate within short elongation distance. However, the stretching of the particles was less pronounced for the long elongation ranges. This suggests that the spherical particles grown by phase separation in the binodal region, were stretched by viscous flow in the early stage of elongation and the stretching in the latter stage was reduced by restoration due to viscoelastic behavior and/or to a steep increase of viscosity. The deformation and orientation of phase separation texture could be achieved in this process, though this deformation proceeded under non-equilibrium conditions. Therefore, the operated elongation process of two-liquid immiscible melts may enable one to fabricate high-functional composite materials owing to morphology control of phase separation texture.