Studies On The Preparation,microstructure And Properties Of Corundum-spinel Lightweight Refractories

Led by the innovation of“green development”,“energy conservation and emission reduction”and“industrial structure optimization and upgrading”have become the consensus of the high temperature industry and made great progress in recent years.During this period,the realization of lightweight refractories became much more urgent.Compared with high bulk density and high heat conductivity of traditional dense refractories,lightweight refractories usually possessed low bulk density and low thermal conductivity.When the lightweight refractories were used to working lines,it will be helpful to decrease heat dissipation in high temperature industries.At present,the research on lightweight refractories mainly focuses on the development of lightweight aggregate,which is based on the judgment that properly lightweight of aggregate will not significantly reduce the performance of refractories.Among them,lightweight aggregate is expected to increase its closed porosity,but at the same time inevitably leads to the increase of apparent porosity,which is not conducive to ensuring its slag resistance and mechanical properties dutring their application.In view of the above problems,the present work mainly includes:Firstly,the lightweight design of refractories with gradient density was proposed and applied to corundum-spinel refractories.The effects of matrix composition and preparation parameters on the lightweight and properties of the materials were studied.The formation mechanism of gradient density in the materials was explored.Secondly,the effect of strontium carbonate on the construction of interlocking structure in the matrix and the properties of the refractories were investigated.Thirdly,the effect of alumina bubbles addition on the performance of lightweight refractories was evaluated.Based on this,alumina bubbles were introduced into the dense refractories with higher content to realize the lightweight of refractories.Finally,the effect of alumina bubbles with Ai₂O₃coatings on the lightweight and properties of refractories was further studied.The main conclusions of this research are as follows:?1?With the protection of argon,carbonthermal reduction reaction of magnesia and graphite in the matrix occurred in high temperature,subsequently oxygen was inlet in the specific temperature.There existed a high density near the external surface and high porosity in the interior region in corundum-spinel refractory owing to the inherent competition between deposition reaction and mass transport of the gaseous species.The realization of the gradient density can effectively reduce the bulk density and realize the lightweight of refractories.This trend was more obvious with the increase of graphite and magnesia content in the matrix.The results of the parallel hot wire method showed that the thermal conductivity of the refractories decreased significantly.At the same time,the material has good mechanical properties and corrosion resistance to steel slag.?2?The addition of strontium carbonate and the decomposition during the firing were helpful to further achieve the lightweight of refractories.Meanwhile,the generated strontium oxide reacted with magnesia,alumina,and spinel in the matrix to produce the platelike MgSrAl₁₀O₁₇ phase with an interlocking structure.This structure is beneficial to further improve the mechanical properties of the lightweight refractories.However,according to the formation mechanism of MgSrAl₁₀O₁₇,it intensified the influence of gradient density on the thermal shock performance of lightweight refractories.?3?With introducing alumina bubbles into lightweight refractories,the trend of lightweight was further enhanced due to their unique spherical hollow structure,and the mechanical properties of lightweight refractories were also improved.But it also caused high apparent porosity,so the content of alumina bubbles should be kept at a reasonable level to ensure the gugranteed slag resistance.?4?With the introduction of alumina bubbles into dense refractories with high content,the lightweight of the refractories was directly and effectively realized.The thermal conductivity of the obtained lightweight refractories decreased significantly compared with that of dense refractories.The mechanical properties and slag resistance of the materials also decreased,but it could satisify the requirements of use performance.?5?The alumina bubbles with Al₂O₃ coatings were prepared by the pan granulation,and sintered at 1650°C.When they were added into lightweight refractories,it was found that better mechanical properties was achieved compared to the addition of alumina bubbles without coatings.Especially,the thermal shock resistance of lightweight refractories was significantly improved due to the Al₂O₃ coatings possessing an interlocking structure.?6?When alumina bubbles with Al₂O₃ coatings were added into the dense refractories,the lightweight of refractories can also be realized and ensured good mechanical performance.Compared with the direct addition of alumina bubbles,the specimens added with alumina bubbles with Al₂O₃ coatings possessed low porosity,which was helpful to ensure good steel slag resistance.