Study On Effect Of Dispersants On Rheological Behavior Of The Matrix Slurry Of Corundum Based Castables

In this study, tabular alumina powder, microsilica, calcium aluminate cement, reactive alumina, xerogel powder and Al₂O₃ nano–powder were selected as main starting materials, trimeric sodium phosphate, sodium hexametahphosphate, sodium citrate, ammonium citrate, ADS, ADW, FS10 and FS20 were selected as dispersants. The effect of these dispersants on the rheological behaviour of slurries of three corundum-based castables matrix systems including tabular alumina powder - calcium aluminate cement– microsilica system, tabular alumina powder - xerogel powder -α-Al₂O₃ micro powder system and tabular alumina powder - xerogel powder -α-Al₂O₃ micro powder - Al₂O₃ nano–powder system was individually investigated. Based on the research results, the option and addition of the dispersants into different slurry were optimized. The corundum-based castables were tested to confirm the effect of the dispersants. This study include three major parts: electrokinetic characteristics of the micro powder slurries, the effect of dispersants on the rheological behavior of corundum-base matrix slurries and the application of dispersants on corundum based castables.In the study on the electrokinetic characteristics of the micro powder slurries, the change ofζ-potentials of four kinds of slurries including microsilica,α-Al₂O₃ micro powder, xerogel powder and Al₂O₃ nano–powder respectively under different pH were investigated. The effect of different dispersant additions (0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%) onζ-potentials for four kinds of slurries which including 8% microsilica, 15.6%α-Al₂O₃ micro powder, 18.75% xerogel powder, 3.1% Al₂O₃ nano–powder respectively was studied. The results showed that: 1)ζ-potentials ofα-Al₂O₃ micro powder and Al₂O₃ nano–powder were high under the conditions of both strong acid and strong basicity; microsilica showed highζ-potential under the condition of strong acid; the absolute value ofζ-potential for the xerogel powder was the highest when pH value was 10.5. 2) The isoelectric points of microsilica,α-Al₂O₃ micro powder, xerogel powder and Al₂O₃ nano–powder were reached when pH value were 1.95,7.78,5.5 and 8.72 respectively. 3) The dispersants of trimeric sodium phosphate, sodium hexametahphosphate and sodium citrate can increase theζ-potential of microsilica suspending liquid significantly. The dispersants of sodium hexametahphosphate, trimeric sodium phosphate, FS20, sodium citrate and ammonium citrate had great influence on theζ-potential ofα-Al₂O₃ micro powder slurry. It was found that the suspending liquid of xerogel was very stable, thus, the effect of dispersants on itsζ-potential was very small. The dispersants of trimeric sodium phosphate, sodium hexametahphosphate, sodium citrate, ammonium citrate and FS20 can significantly improve theζ-potential of the surface of Al₂O₃ nano particles; they could make theζ-potential from positive value to negative value. It was found that the effect of FS20 was the greatest. The research results of the effect of the dispersants on the rheological behavior of corundum-based matrix slurries showed that: 1) In the slurry of tabular alumina powder- calcium aluminate cement - microsilica system, when trimeric sodium phosphate and sodium hexametahphosphate were selected as the dispersants and keeping the water addition as 12%, the rheological behavior of this slurry exhibit a typical pseudoplastic fluid model under the condition of optimized addition of the dispersants. It was found that FS20 was the best dispersant for this system and its optimum addition was 0.1⁰.3%. 2) In the slurry of tabular alumina powder - xerogel powder -α-Al₂O₃ micro powder system, the dispersants of FS10, FS10 and ADW1 compound, and FS10 and ADS3 compound all had great influence on the rheological behavior of this slurry. When the addition of FS10 or FS10 and ADW1 compound was optimized, the rheological characteristics was close to Newtonian fluid. However, when the addition of FS10 and ADS3 compound was optimized, the rheological behavior exhibit a typical dilatant fluid model. 3) In the slurry of tabular alumina powder - xerogel powder -α-Al₂O₃ micro powder - Al₂O₃ nano–powder system, the compound dispersants of FS10 and FS20, FS10, FS20 and ADW1 or FS10, FS20 and ADS3 had remarkable influence on the rheological behavior for this slurry, furthermore the effect of compound dispersant was much more effective than single dispersant. It was found that the compound dispersant of FS10 and FS20 was the most effective. The optimized addition of FS10 for xerogel powder dispersion was about 1%. For Al₂O₃ nano–powder dispersion, the most effective dispersant was FS20.Based on the rheological behavior study, the effectiveness of dispersants on corundum-based castables was confirmed. It was found that for the system of tabular alumina - calcium aluminate cement– microsilica, the dispersant of FS20 can significantly increase the flowability of the castables: the flowability value reached 132 when the water addition was 3.84%. The castables sample reached high strength because of water reduction. The dispersant of FS10 had great dispersion effect on the castables system containing xerogel powder: when the water addition was 5%, the bulk density of the castalbe sample was high. The compound dispersants of FS10 and FS20 or FS10, FS20 and ADW1 had effective function of dispersion and water reducing on the nano-powder containing castables. The experiment results confirmed that the compound dispersant of FS10 and FS20 was most effective for the corundum-based castables.