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Effects of Clay and Fire Clay Additives on the Porosity and Strength of Magnesia-Forsterite-Spinel Refractories

Abstract

This study investigates the effects of adding clay and fire clay to magnesia refractories and on their physical properties, such as contraction, mechanical strength, bulk density, and apparent porosity. Domestic raw materials were used and samples were fired at 1350, 1450, and 1550°C for 2 h. Adding clay exhibits no significant effect on density and porosity, whereas adding up to 40% fire clay has a significant effect on shrinkage with a maximum of 20%. The porosity measurements support a minimum at samples with 20% fire clay. Nevertheless, the effects of clay and fire clay on the strength of magnesia are unnoticeable. X-ray diffraction results show that, after firing, the main phase compositions of the samples with clay are periclase and forsterite. Adding fire clay leads to the formation of magnesite spinel, which can be attributed to the high Al₂O₃ content of fire clay. Scanning electron microscopy shows that no liquid phase was formed, thus indicating that the sintering mechanism can be a solid-state reaction that results in forsterite formation.

Esmaeil Salahi*, Mohsen Ghaffari, Aida Faeghinia

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