Effect Of A Small Amount Of Andalusite Powder On The Oxidation Resistance Of Al₂O₃-SiC-C Castables For Iron Trough

The C and SiC used in the Al₂O₃-SiC-C castables for blast furnace iron runner are easily to be oxidized during high-temperature heating,which would deteriorate the properties of castables and shorten the service life.Previous studies have shown that the silica-rich glass phase extruded by andalusite mullitization can block the pores,thereby preventing the intrusion of external oxygen.Therefore,high amounts（19 wt%）of andalusite aggregates（8-5 mm、5-3 mm、3-1 mm）can improve the oxidation resistance of the castables.However,for andalusite aggregates with large particle size,only a small part of the silica-rich glass phase（about 20%）is extruded onto the surface of the particles to block the pores,while most of the silica-rich glass phase stays inside the particles,without participating in clogging the pores.Studies have shown that the reduction of andalusite particle size can promote its transformation and cause more silica-rich glass phase to be extruded to the particle surface.Therefore,the addition of small-sized andalusite powder may be more beneficial to improve the oxidation resistance of castables.So far,there are no relevant reports on whether the addition of small-sized andalusite powder is more conducive to improving the oxidation resistance of Al₂O₃-SiC-C castables for iron trough than large-sized andalusite aggregate,or whether the addition of a small amount of andalusite powder may have the same effect of improving the oxidation resistance of castables as the high amount of andalusite aggregate.In this work,the effects of a small amount of（1,2,3,5 wt%）andalusite powder(D₅₀=23μm and D₅₀=2μm)on the oxidation resistance and other properties of castables were studied.And it was analyzed whether the addition of a small amount of andalusite may have the same effect of improving the oxidation resistance of castables as the high amount of andalusite aggregate.At the same time,the effect of particle size change of small-sized andalusite powder on the oxidation resistance of castables was also studied.And on the basis of the above research,by fixing the addition amount（5 wt%）of andalusite powder(D₅₀=23μm and D₅₀=2μm)and changing the content（0,0.5,1.0,1.5 wt%）of antioxidant Si metal in the castables,whether the introduction of low-content andalusite powder can reduce the content of Si metal in the castables was also studied.The results of this work are as follows:The results show that the introduction of a small amount of（1,2,3,5 wt%）andalusite powder(D₅₀=23μm and D₅₀=2μm)can significantly improve the oxidation resistance of the castables,and the oxidation resistance of the castables increases gradually with the increase of andalusite powder content.For example,when the content of Si metal is the same（1.5 wt%）,the antioxidant index（43%）of the castables containing 1 wt%andalusite fine powder was significantly higher than that of the castables without andalusite powder（30%）.When the content of andalusite fine powder increased from 1 wt%to 5 wt%,the antioxidant index of the castables increased from 43%to 69%.This is because for the fired andalusite powder,the andalusite mullitization reaction is relatively complete,so more silica-rich glass phase will be extruded to the particle surface to block the pores and prevent the intrusion of external oxygen.In addition,the introduction of low-content andalusite powder also improves the strength,volume stability and thermal shock stability of the castables.Compared with previous studies on the enhanced oxidation resistance of andalusite aggregate,this work found that the introduction of low dosages（1,2,3,5wt%）of andalusite powder(D₅₀=23μm and D₅₀=2μm)can improve the oxidation resistance of castables,whose effect is similar to high amounts（19 wt%）of andalusite aggregates（8-5 mm,5-3 mm,3-1 mm）.For example,the antioxidant index（69%）of the castables containing 5 wt%andalusite fine powder(D₅₀=23μm)was significantly higher than that of the castables containing 19 wt%3-1 mm andalusite aggregate（60%）.The effect of low dosage（5 wt%）of andalusite powder(D₅₀=23μm and D₅₀=2μm)on the content of antioxidant Si metal in the Al₂O₃-SiC-C castables for iron trough was studied.The results show that,due to the above mechanism,compared with the andalusite-free castables with 1.5 wt%of Si,when the addition of Si metal in the castables containing 5 wt%andalusite powder is eliminated,the castables can still maintain sufficient oxidation resistance.For example,the antioxidant index of the castables without Si metal but with 5 wt%andalusite fine powder is 45%,which is significantly higher than that of the castables without andalusite powder and with high content（1.5 wt%）of the antioxidant Si metal（30%）.In addition,the castables containing 5 wt%andalusite powder and without Si also have high volume stability,thermal shock stability and strength.The influence of particle size variation of andalusite powder(D₅₀=23μm and D₅₀=2μm)on the oxidation resistance of castables was studied.The results show that,when the addition amount of andalusite powder and Si metal is the same,there is almost no difference between the effect of andalusite fine powder(D₅₀=23μm)and andalusite micro powder(D₅₀=2μm)on the oxidation resistance of the castables.This may be because that the particle size of andalusite fine powder(D₅₀=23μm)is already very small and it has been completely transformed in the fired castables,so the degree of andalusite mullitization is very high and more silica-rich glass phase has been extruded to the particle surface.Therefore,with the further decrease of andalusite particle size,the degree of mullitization and the content of silica-rich glass extruded to the particle surface do not change significantly.