Influence Of Atmosphere On The Microstructure And Properties Of MgO-C Refractories

In this paper, the microstructure characteristics and properties of MgO-C refractories withadditives of Al、Al/Si、Al/B2O3、Al/TiO2were studied under different heat treatment atmosphere(nitrogen atmosphere and buried carbon atmosphere).after different heat treatment temperature,the cold modulus of rupture, cold crushing strength, hot modulus of rupture and thermal shockresistance of specimens were studied.; XRD and SEM techniques were carried out to study thephase transformation and microstructure characteristics of the specimens. The effects ofadditives and heat treatment atmosphere on the microstructure and mechanical properties at hightemperature of the specimens were investigated.The Influence of heat-treating temperature on composition、microstructure and propertiesof MgO-C materials were studied under reducing atmosphere. It is revealed that compared withspecimens with Al powder additive, The mechanical strength of specimens with Al/Si additive ishigher. The thermodynamic calculation results show that the carbide is a more stable phase, after1000°C heating treatment, the metallic Al has been reacted with C or CO, which results theformation of strip-like Al4C3and octahedral MgAl2O4. It is also found that the metallic Si has nottaken part in any reaction at this stage. After1200℃heating treatment, the reaction between Siand C or CO leads to the formation of plate-like SiC which are interlocked into magnesia matrix.This interlocked structure results in the increasing of the modulus of rupture and residualstrength after thermal shock test. After1400℃heating treatment, massive of AlN whiskers andlarge amount of SiC whiskers were formed within the skeleton structure, thus, the properties ofHMOR and thermal shock resistance of the samples are further improved.The Influence of heat-treating temperature on composition、microstructure and properties ofMgO-C materials were studied under nitrogen atmosphere. It is revealed that compared withspecimens with Al powder additive, The mechanical strength of specimens with Al/Si additive ishigher. The thermodynamic calculation results show that the nitrides is a more stable phase, After1000°C heating treatment, the metallic Al has been reacted with C (CO) or N2. Then the phasesof rip AlN and eight surface MgAl2O4were formed. However, the metallic Si has not taken part in any reaction at this temperature After1200℃heating treatment, Si begins to react with C orCO to form plate shaped SiC which are interlocked into Magnesite matrix. That would result inthe increasing of the modulus of rupture and residual strength after thermal shock test. After1400°C heating treatment, the amount of SiC whiskers and large amount of β-Si3N4whiskerswere formed within the magnesite skeleton structure. So the properties of HMOR and thermalshock resistance of the samples are much better improved.The effects of additives of Al、Al/Si、Al/B2O3、Al/TiO2on the microstructure andmechanical properties of the specimens were studied under reducing atmosphere.Theexperimental results show that the Al/Si、Al/B2O3、Al/TiO2additives can improve the coldcrushing strength of specimens, The cold crushing strength of specimens with Al/Si additive hasbeen obviously improved after900℃、1300℃heat treatment, The improvement on cold crushingstrength of specimens with Al/B2O3is better after1100℃heat treatment,The additive of Al/TiO2has a good effect on improve the cold crushing strength of specimens after1300℃heattreatment.