| Corundum-spinel purging plugs are widely used in various steel ladles because of their good hot strength,slag resistance and volume stability.At present,the castable purging plug is usually fired at high temperature,which requires high energy consumption,and is easy to peel off and spalling,which limited the improvement of their service life of the purging plug and the steel ladles.Recently,corundum-spinel unfired purging plug have been tried out by some manufacturers,and it’s found that there are some shortcomings including low strength at medium temperatures and poor volume stability,which easily lead to short life and lower blowing rate of unfired purging plug,and limit their application.In order to solve the problems existing in unfired purging plug,this paper firstly explores the effect of cement content on the properties and structure of corundum-spinel castable,and then the effect of zinc source（ZnO,Zn（OH）2,BZC）on the microstructure and properties of corundum-spinel castable were investigated.The results are listed as follows:As for cement-bonded corundum-spinel castables,with cement content increasing,the cold strength of the specimens fired at 600°C-1400°C reaches the maximum when the cement content is 6 wt%,cold strength of the specimens fired at1600°C reaches the maximum when the cement content is 2 wt%,hot modulus of rupture（HMOR）tested at 1400°C firstly increases and then decreases（the maximum is at 4 wt%cement,37.1 MPa）,and the thermal shock resistance（TSR）tends to decrease.When the cement content is 4 wt%,the sample has higher CMOR,HMOR,and better TSR.but the strength of the sample after firing at medium temperature（600°C-1000°C）noticeably decreases,the cold modulus of rupture（CMOR）after firing at 800°C is the lowest（4.5 MPa）,which is 49%of the strength after drying.Therefore,it is unrealistic to improve the strength after firing at medium temperature by increasing cement content in the castables.When ZnO is introduced into corundum-spinel castables,it is found that cold strength of the castables treated at 600°C-1400°C increases with ZnO content increasing,cold strength of the specimens fired at 1600°C reaches the maximum when the ZnO content is 0.6 wt%,HMOR increases from 36.29 MPa to 58.34 MPa,TSR of the sample is basically unchanged,the maximum permanent linear change（PLC）of the sample after high temperature sintering is reduced from 0.38%to0.25%.The cold strength of the samples sintered at medium temperature（600°C-1000°C）noticeably increases with ZnO addition,and the CMOR of the samples sintered at 800°C increases significantly from 3.06 MPa to 15.07 MPa.When the content of ZnO is 0.9 wt%,the samples sintered at different temperatures have higher CMOR,HMOR and TSR,and the volume stability is also improved.When Zn（OH）2 is used in the castables,it is found that with the increase of Zn（OH）2,cold strength of the specimens sintered at different temperatures increases gradually,HMOR firstly increases and then decreases（the maximum is 50.40 MPa at 0.6 wt%）,TSR of the specimens slightly changes,and PLC of the sample decreases from 0.4%to 0.26%after firing at high temperature.Zn（OH）2 can greatly improve the strength of the samples fired at medium temperature.The CMOR of the specimens sintered at 800°C increases from 3.19 MPa to 14.98 MPa.The samples with 0.6 wt%Zn（OH）2 sintered at different temperatures have higher CMOR,HMOR,and better TSR.When Basic zinc carbonate（BZC）is used in castables,with BZC content increasing,the cold strength of the samples dried at 110°C and fired at 600°C,800°C,1400°C reaches the maximum at 0.6 wt%,the cold strength of the samples fired at 1000°C and 1600°C reaches the maximum at 0.3 wt%,the maximum HMOR is 36.15 MPa at 0.3 wt%,the TSR of the sample is improved,and the PLC decreases by 0.1%after high temperature firing.The addition of BZC increases the cold strength of the sample after medium temperature firing,and CMOR of the specimens sintered at 800°C increases from 3.25 MPa to 7.58 MPa.When the content of BZC is 0.3 wt%,the specimens sintered at different temperatures have higher CMOR,HMOR.and the residual MOR and residual MOR retention rate（50.5%and 21.7%,respectively）after thermal shock are also higher.With adding ZnO,Zn（OH）2 and BZC in the castables,Zn Cr2O4 and Zn Al2O4are formed in the samples fired at 600°C and 800°C-1000°C,respectively,which significantly improves the strength of the samples fired at medium temperature,and the content of Zn Al2O4 increases significantly and grows well after high temperature firing（1400°C-1600°C）.The addition of the zinc salts promotes the sintering of the samples,effectively improves the volume stability of the samples after high temperature sintering,promotes the formation of aluminum-chromium solid solution and the growth of CA6 grains,thus improving the HMOR of the samples.When ZnO is used as the zinc source,the CMOR of the corundum-spinel castable fired at medium temperature increases by 400%,the PLC after high temperature firing decreases by 34%and HMOR increases by 48%.When Zn（OH）2is used as the zinc source,the CMOR of the samples after medium temperature sintering increases by 370%,the PLC decreases by 35%,and HMOR increases by57%.When BZC is used as zinc source,the increase of CMOR and HMOR is the smallest,the CMOR of the samples sintered at medium temperature increases by130%,and HMOR is slightly improved. |
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