MECHANOCHEMICAL SYNTHESIS OF MULLITE AND MULLITE-SILICON CARBIDE FROM SECONDARY MINERALRESOURCES USED AS AN AGGREGATE FOR FIREPROOF CONCRETES

Mullite (3Al2O3-2SiO2) is a promising material for modern technologies. With its melting point of 1850 °, it may be used as an aggregate for fireproof concretes. The feasibility of producing mullite by its synthesis from the industrial by-products is studied in the paper. The materials used were fireproof clay from stripping rocks of the coal cuts and spoil sludge from the abrasion works (high alumina product). To reduce the temperature of agglomeration from 1400 to 1200 °, mechanochemical activation of the mixture in planetary mills was applied. The fireproof clay was mostly kaoline with a small amount of quartz. The high alumina product contained above 80% Al₂O₃ (corundum). The initial products were mixed in the proportions corresponding to the following reaction equation: Al₂O₃ · 2Sid ·H₂O + 2Al₂O₃ = Al₂O₃ · 2SiO₂. The activation was carried out in two laboratory planetary periodic mills (AGO-2, AGO-3) and a continuous mill for 3 to 5 min and 2 periods, respectively. The control mixture was ground manually in a mortar. All four mixtures were annealed for 3 h at 1200 °. Mullite was obtained in all the mixtures but the initial one. The continuous mill produced the best result. On the basis of the synthesized mullite, mullitesilicon carbide compound was obtained, a superfireproof composite material consisting of 75% synthesized mullite and 25% silicon carbide production wastes (SiC), the latter containing above 50% SiC. The compressive and flexural strengths of a new material were 300 and 43 MPa, respectively. The results of the investigation show that the aforementioned materials can be used for producing mullite. The cost of mullite from the by-products is reduced by a factor of 1.5 to 2 compared with that for the mullite from natural resources.

• INTRODUCTION

• EXPERIMENTAL INVESTIGATIONS

• CONCLUSIONS

• REFERENCES