Application Of Spherical Mullite Aggregates In Low Bulk Density Castables

For many years,energy saving and emission reduction of high temperature industrial kilns have been paid much attention and studied by scientists and technicians,one of the effective ways to solve this problem is to use refractory castables with low density,low thermal conductivity and high strength as working lining materials of high temperature industrial kilns.Compared with traditional refractory aggregates,spherical aggregates have the characteristics of good fluidity,easy granularity control and easy compact accumulation.Therefore,the study of their properties and their application in refractory castables are of great significance for the development of refractories.In this paper,spherical mullite aggregates with BD of 1.40 g/cm³,1.56 g/cm³,1.73 g/cm³ and 2.03 g/cm³ prepared in laboratory are used as raw materials,and their properties are compared with those of spherical mullite aggregates with BD of 1.48g/cm³ produced by a company.The above five aggregates were used in castables.By using bauxite clinker,?-Al₂O₃ powder,SiO₂ powder and calcium aluminate cement as raw materials.The effects of the adding amount?53?%,57?%,60?%?of spherical mullite aggregates with BD of 1.48 g/cm³ on the properties of refractory castables,and the different BD of spherical mullite aggregate?the adding amount is 57?%?on the properties of castables were studied.At the same time,the calcination temperature?1100?,1200?and 1300?for 3 hours,respectively.?of the above castables on the properties of castables were studied.For the spherical mullite aggregate prepared in laboratory,with the increase of its BD,the AP decreases and the grain strength increases.Among them,the spherical mullite aggregate with BD of 2.03 g/cm³ has the highest grain strength?475.7 N?and the smallest pore size,which is below 60?m.The grain strength of spherical mullite aggregate with BD of 1.48 g/cm³ is the lower?112.7 N?,and its average pore size is the largest,some of which are up to 150?m.This is mainly due to the different preparation technology of the two aggregates.With the increase of the adding amount?53?%,57?%,60?%?of spherical mullite aggregate is added to the castables,mechanical properties at room temperature,high temperature performance,AP increase,thermal insulation and thermal shock resistance are improved.With the increase of calcination temperature,the CCS,CMOR and linear change of castables increase.When the adding amount of spherical mullite aggregate is 57?%,after drying at 110?for 24 hours,the CCS is31.0 MPa,the thermal conductivity?900??is 0.586 W/?m?K?,and the HMOR?1100?for 0.5 hour?is 5.0 MPa.The thermal conductivity of castable decreases slightly after calcination at 1300?for 3 hours,and the mechanical properties at room temperature and high temperature properties of castable are obviously improved,the thermal conductivity?900??is 0.551 W/?m?K?,the CCS is 40.6 MPa,the CMOR?1100?for 0.5 hour?is 5.9 MPa and the abrasion volume?1300??is 3.65cm³ after calcination at 1300?for 3 hours,which the comprehensive performance is the best.With the increase of the BD of spherical mullite aggregate,the BD,CCS,CMOR,HMOR and refractoriness under load of the castable increase,and the thermal conductivity increases,while the apparent porosity decreases.When the BD of 1.56g/cm³ of spherical mullite aggregate is added into the castable,the BD is 1.86 g/cm³,the CCS is 59.3 MPa,the linear change is about 0.2%,the thermal conductivity is0.556 W/?m?K?,and the abrasion volume?1300??is 4.96 cm³ after calcination at1300?for 3 hours.The sample not only has good mechanical properties,but also has low thermal conductivity,which can meet the requirements of working lining.This work studied the effect of spherical aggregates with different BD prepared in the laboratory on the properties of castables.These studies on the application performance of spherical aggregates can provide technical reference for the later technological improvement of spherical aggregates.