Role of in-situ Formed Nonoxides Bonded Phases in Property Improvement of Alumina ULC Castables

In order to enhance performance of pre-cast shapes of alumina based castables,the present work explored the approach of forming in-situ bonding phases by incorporating Si powders and then heating in carbon embedded atmosphere. Using tabular alumina as aggregates,tabular alumina,SiC powders,Si powders,calcium aluminate cement,microsilica and ultrafineα-Al2O3 powders as matrix, alumina based ultra low cement（ULC） castables were prepared.Influences of Si powder addition at O, 4%,6%,8%and 10%（in mass ） on regular properties, cold modulus of rupture（CMOR）,hot modulus of rupture（HMOR）,thermal shock resistance（TSR） and microstructure of the castables after carbonization were investigated. After incorporation of Si powders and carbon embedded heating,the in-situ mullite and nonoxide phases such as SiAlON and SiC can be formed by oxidation, nitridation or carbonization reaction.HMOR and TSR of the castables with in-situ nonoxides bonding are obviously improved.After carbon embedded heating,the HMOR at 1 400℃increases from 1.6 MPa to 8.3 MPa,and the residual CMOR ratio after thermal shock increases from 64.9%to 137.9%when Si addition increases from 0 to 10%.