Magnesia-silica-hydrate bonded MgO castables: Fid-Bau Portal

Magnesia-silica-hydrate bonded MgO castables

Odegard, C. / Feldborg, H. / Myhre, B.

This investigation of MgO castables with respect to MgO source and additive has shown that both flow and set time is dependent on the MgO source, the amount and type of additive and the amount of microsilica. With the deadburned quality the set is quicker and so is the effect of increasing microsilica content from 6 to 8 wt%. The type and amount of additive is also influencing set and flow. VanisperseCB seems to be able to retard setting and provides sufficient self-flow. Some promising self flow values are also presented with use of Calgon S and Castament FS 10. To sum up: good flow values are obtained with several different additives and should be chosen to fit the raw materials used in the actual case. The most versatile is so far VanisperseCB, which combines adequate dispersion with a retarding ability. The additives also influence the hot-properties, with the phosphate there is some fluxing, and hence reduction of refractoriness. A slightly lower refractoriness is noted with deadburned MgO as compared to fused MgO, and above approximately 1660 deg C also by the microsilica. Below this temperature the R.U.L. curves of a silica-free mix and those with 6 wt% or 8 wt% microsilica are similar. It has been shown that the flowability and set of MgO based castables of different origin may be controlled by proper particle size analysis, use of MgO fines, microsilica content and additive. Some trial and error must be accounted for working with this system. However, it is concluded that casting is applicable with a number of different MgO sources. With use of a suitable deflocculant, microsilica and MgO mixes were cast at very low water levels. Further work is needed is the area of refractoriness and slag resistance, by modifying the forsterite bond by for example fine spinel, calsined aluminas or magnesia-rich spinels.