Conventional and microwave-assisted sintering of ZnO-containing CAC-bonded alumina-based refractory castables
O.H. Borges, A.L.F. Cardoso, Murilo Henrique Moreira, R.F. Klein-Gunnewiek, V. C. Pandolfelli
Abstract
Recent studies have pointed out that ZnO can induce early spinel formation in alumina-based refractories, giving rise to gahnite (ZnAl 2 O 4 ). Besides that, the high microwave absorption of zincite enables the likelihood of applying this sintering technique to compositions comprising this oxide . In this work, microwave and conventional sintering were applied to ZnO-containing alumina-based refractory castables. Microwave-processed samples displayed higher densification, enhanced mechanical properties at RT, a faster sintering schedule, and 70%-lower energy consumption compared to the conventionally produced counterparts, which could be attributed to the higher heating rates and enhanced ion diffusion induced by the electromagnetic-assisted sintering. Moreover, thermodynamic and experimental analyses indicated that the oxidation of SiC used as microwave susceptors induced zinc volatilization, resulting in small (∼ 40 µm) pores in a densified refractory matrix. Although not necessarily detrimental to the castables’ properties, this volatilization was reduced by controlling the atmosphere of the microwave cavity during sintering.