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The Influence of Al and Si Additives on the Microstructure and Mechanical Properties of Low-Carbon MgO-C Refractories
T.B. Zhu, Y.W. Li, S.B. Sang, S.L. Jin
Abstract
The mechanical properties of low-carbon MgO-C refractories strongly depend on the formation of ceramic phases (e.g. their amounts, distribution and morphologies) in the matrix. In the present work, the influence of Al and Si additives on the phase composition, microstructure and mechanical properties of low-carbon MgO-C refractories (1 wt% flaky graphite) was investigated by means of X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, three-point bending and thermal shock tests. The results showed that Al4C3 whiskers and MgAl2O4 particles formed in-situ in the specimens after firing at 1000 °C and 1200 °C when Al and Si additives were incorporated simultaneously into the specimens. Up to 1400 °C, many SiC whiskers and plate-like AlN as well as MgAl2O4 in the form of hollow MgO-rich whiskers and particles appeared. However, few SiC whiskers and many Mg2SiO4 particles existed in the specimen fired at 1200 °C and lots of Mg2SiO4 particles formed at 1400 °C when Si powder was used as the additive. These ceramic phases unquestionably influenced the mechanical properties of low-carbon MgO-C refractories. Improved mechanical properties and thermal shock resistance were achieved for the specimen with Al and Si additives compared with those of the specimen containing Si powder.
Keywords
In-situ-formed ceramic phases, mechanical properties, thermal shock resistance, MgO-C refractories
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