The Regulation Of MgO-Al₂O₃ Spinel Formation And Its Influence On The High-temperature Structural Stability Of Carbon-containing Refractories

The in-situ formation of MgO-Al₂O₃ spinel?hereinafter referred to as spinel?plays an important role on the service performance of carbon-containing refractories.The spinel formed in-situ can improve the bond in the matrix of carbon-containing refractories,but the volume expansion associated with the spinelisation reaction will also affect the thermal stability of the refractories.At present,there are few studies on the factors that affect the in-situ information of spinel in carbon-containing materials.So,in this paper,the influencing factors of the in-situ spinel formation were studied.In addition,the effect of secondary spinelisation reaction on the structure and performance of carbon-containing refractories were also discussed.Based on the former research,the formation of spinel is regulated by the ways in which the raw materials were coated with carbon.The main results are as follows:?1?With the introduced of magnesia to Al₂O₃-C refractories,the Al₂O₃-rich spinel is formed after heat-treatment at 1150°C.With the increase in heat-treatment temperature,the solid solubility of alumina in spinel increase,decreased caused the lattice parameters of spinel.After heat-treatment at 1650°C,the content of Al₂O₃ in spinel reaches about 94 wt%.The in-situ formation of spinel in the Al₂O₃-C refractories will significantly enhance the ceramic bond in the matrix and increase the strength of the material,which also causes volume expansion of the Al₂O₃-C refractories.?2?The holding time will affect the formation of spinel in Al₂O₃-C refractories.With the increase in the holding time,the alumina content in spinel increased and the grains of spinel developed more fully.After heat-treatment by 7-hours holding time,the content of Al₂O₃ in spinel reaches about 89 wt%.The grain size of spinel is2-4?m and the morphology of spinel is regular octahedron.?3?The particle size of magnesia will significantly affect the spinelisation reaction in the Al₂O₃-C refractories.The smaller particle size of the magnesia,the higher the spinelisation reaction degree,the more the spinels produced,the smaller the spinel grain size,and the content of Al₂O₃ in spinel.However,big particle size of magnesia will leads to its incomplete reaction.?4?With the introduced of the pre-synthetic spinel to Al₂O₃-C refractories,alumina will be sold dissolved into the spinel during the heat-treatment process,which will decrease the lattice parameters of the spinel.After heat-treatment at 1650°C for 5h,the content of Al₂O₃ in spinel reaches about 91 wt%.This effect of second spinelisation will also lead to volume expansion of the materials during the heat-treatment process.Meanwhile,the apparent porosity of Al₂O₃-C refractories is increased and the density is decreased.?5?With the introduced of the pre-synthetic spinel to MgO-C refractories,magnesia is also solid dissolved into the spinel during the heat-treatment process,which increased the lattice parameters of the spinel.Nevertheless the specimens didn't present obvious expansive effect during the heat-treatment process.?6?Alumina coated by carbon changes the in-situ formation of spinel and as a result the formation temperature of spinel is increased.As the solid phase reaction is weakened,the volume expansion associated with the spinelisation reaction is reduced,which shows that this method is an effective way to regulate the performance and micro structure of carbon-containing refractories.