The Use of Microsilica in Refractory Castables - Elkem

1601401200vol% reactive alumina25vol% reactive alumina50vol% reactive alumina75vol% reactive alumina100vol% r. al. (0.03% citric acid)Free flow [%]1008060402000 50 100 150 200 250Time [minutes]Figure 6: Free flow as a function of time and superfines composition. q=0.25, 0.5%cement. Fused alumina based castables with 13vol% water. Castables withoutretarder unless indicated.160140120Vibra flow [%]100806040200vol% reactive alumina25vol% reactive alumina50vol% reactive alumina75vol% reactive alumina100vol% r. al. (0.03% citric acid)00 50 100 150 200 250Time [minutes]Figure 7: Vibra flow as a function of time and superfines composition. q=0.25, 0.5%cement. Fused alumina based castables with 13vol% water. Castables withoutretarder unless indicated.With 6% cement, the pattern is similar, but this time most of the compositions had to beretarded with some citric acid. Citric acid (retarder) had to be added when reactive aluminawas used in the 6% cement compositions. Without the retarder, the castables would nottransform into the “wet” stage during mixing at this low water content. Figure 8 shows the freeflow of castables with a q-value of 0.25 and 6% cement (Table 3). This is essentially the samecastable as those presented in Figure 6 and 7, but this time with 6% cement. The increasedcement content necessitates use of retarder, and even then, the work time is much shorter than