Penetration behavior of calcium ferrite melts into hematite substrate

Effects of adding SiO₂ or Al₂O₃ on the penetration characteristics of calcium ferrite (CF) melts into hematite substrate with the different percentage of porosity were examined, and were discussed from the viewpoints of the relation to the solubility gap, δFe₂O₃ (mol%), viscosity and surface tension of the CF-based melts. In case of dense hematite substrate with 5% porosity, the penetration depth of CF melts into hematite substrate was depressed by the addition of SiO₂ or Al₂O₃, and the addition of SiO₂ was more effective than that of Al₂O₃. Moreover, the penetration of CF-based melts along grain boundaries into hematite substrate did not take place, and melts/hematite interface moved down by dissolution of solid hematite into these melts. The penetration depth of CF-based melts into hematite substrate was mostly determined by δFe ₂O₃ (mol%), which meant that the dissolution of hematite into melts was rate-determine. In case of porous hematite substrate with 15% porosity, the penetration of CF-based melts along grain boundaries into hematite substrate occurred, and the penetration depth was 10 times deeper than the case of dense hematite substrate with 5% porosity for each slag. The penetration depth of CF melts was increased by the addition of SiO₂ due to the decrease of melting temperature in the calcium ferrite system. The penetration depth of CF melts with the addition of Al₂O₃ was very similar to that of CF melts. These melts penetrated into hematite substrate with crystallization (solid) due to the increase of the melting temperature in calcium ferrite system by the dissolution of hematite into the liquid phase. The penetration depth of CFbased melts into hematite substrate was dominated by the ratio between the surface tension and viscosity of melts taking the suspension-corrected into consideration.