The Andalusite Performance And Its Aluminosilicate Castable Applied Research

In this pasper, the study on andalusite and its application in refractory industry werereviewed. The properties of four andalusites from South Africa, Xinjiang, Meixian Shaanxi,Dandong Liaoning which have been widely used in industry were studied. Based on the result ofabove studies, Xinjiang's andalusite was chosen for mullite and hard-clay castables. The effectsof andalusite content on physical properties, high temperature mechanical properties and slagcorrosion resistance of the castables were investigated.(1) The results of thermal expansion examination show that the andalusite from Meixiandisplay shrinkage with -0.6% at 400℃. XRD analysis on the samples fired at differenttemperatures show that a small amount of Al₂Si₂O₅ (OH)₄ and KAl₂Si₃Al_O10 (OH)₂were appeared in Meixian's andalusite, and crystal water of the mineral lost between300℃and 500℃.(2) Mullization of the four andalusite samples formed with≤0.074mm is found to start at1200℃. The mullization reaction of Meixian's andalusite was finished at 1400℃andthose of the others are at 1450℃.(3) The effects of andalusite on properties of low cement mullite and hard-clay castables havebeen investigated. The results show that the castables fired at high temperatures expandslightly. After firing at 1500℃, the linear change of the mullite castable with 64%andalusite is 0.38%, and that of the hard-clay castable with 64% andalusite is 0.23% afterfired at 1350℃. Adding andalusite has little effect on the two types of castable for thesamples'density and has some negative effect on the strength of the samples at roomtemperature.(4) For mullite castable, the thermal mechanical properties are improved by adding 42%andalusite. The hot modulus of rupture (HMOR =2.57MPa) at 1400℃is greatly higherthan that of the sample without andalusite. The refractoriness under load (1241℃)increase by 100℃for drying sample, and by 300℃for pre-heat treated sample at 1500℃.Thermal shock resistance (TSR) of the castables is remarkable improved by andalusite,showing that the MOR is 4.39 MPa after thermal shock (△T=1100℃, one time by watercooling), increased by 61% comparing to the sample without andalusite, and the residual strength ratio is 40%; residual strength (three times in water cooling cycle) is 2.3 MPa andits residual strength ratio is 19%.(5) For hard-clay castable, the andalusite has some negative effect on HMOR at 1300℃. TheRefractoriness under load of the sample with 64% andalusite after drying is 1271℃,increasing by 100℃, and by 170℃for pre-heat treated sample at 1500℃. TSR isnoticeably improved by andalusite. Its residual strength is 5.87MPa, increased by 110%comparing to the sample without andalusite, and the residual strength ratio is 61% testedafter one time in water cooling; residual strength (three times in water cooling cycle) is4.0MPa and its residual strength ratio is 42%.(6) Andalusite improves slag corrosion resistance of the castable samples. the depth ofpenetration layer of the mullite castable with 64% andalusite is 0.5mm, and its corrosionindex is about 37% of the andalusite-free sample. The depth of corrosion layer ofhard-clay castbale is about 0.5mm, and its corrosion index is about 20% of theandalusite-free sample, no penetration layer is found.(7) The improvement of thermal shock resistance of the castables with andalusite is attributedto the formation of microcracks formed by the mullization reaction of andalusite insamples at high temperature, which result in buffering thermal stress and toughening thetextures in samples. The increase of refractoriness under loadding is due to thecounteraction effect to sintering shrinkage by the expansion of andalusite at hightemperature. It attributes the improvement of slag corrosion resistance to mullization ofandalusite and higher viscosity glass phase formed from andalusite at high temperature,which led to dense structure and slowed down the slag corrosion.