| Bauxite-based homogenized grogs, as the main raw material of high aluminumrefractories, have developed rapidly in recent years in China. The bauxite-basedhomogenized grogs are still facing a series of problems, such as uneven compositionand fluctuat properties because of the difference raw materials and preparationprocess. In this paper, we investigated the composition, microstructure and propertiesof alumina-based homogenized grogs as to their status quo. Using70homogenizedbauxites as starting materials, the effects of sintering temperature, holding time andparticle size distribution on phase composition and microstructure of alumina-basedhomogenized grogs was investigated. The results are as follows:The composition, microstructure and properties of70homogenized grogs aresignificantly different due to the difference impurity content and preparation process.However, there were some similarities, for example, these homogenized grogs aremullite-corundum based; some amorphous phase coats on their surface, the crystals ofmullite formed the interlocking network structure; Most of the corundum crystalsdistributed among mullite crystals. On the other hand, the differences were obvious:the higher the content of R2O in the homogenized grogs, the higher the content ofglass phase. For example, R2O content of one homogenized grogs was2.01%, and itsglass content is up to27.57%, and the refractoriness under load is1550℃; R2Ocontent of another homogenized grogs is0.34%, and its glass content is only8.9%,and the refractoriness under load is1600℃. Due to the difference sintering process,the growth, the aspect ratio and content of mullite crystal are completely different.The highest mullite content in the homogenized grogs is up to85%, and its width isabout10μm; the lowest mullite content in the homogenized grogs is only60%, andits width is about2μm. In addition, some problems exist in all the70homogenizedgrogs, such as the imperfect growth of mullite, the agglomerated corundum crystaland unevenness distribution of the phase.70homogenized grogs was sintered in difference holding time0h,4h,6h,8h and10h at1650℃. With the increase of holding time, the volume density of homogenized grogs increases to2.72g/cm3and then keets stable, the porosity decreases to10%atfirst and then increased to13.58%, glass phase content decreases from7.6%to6.36%.These indicated that it is helpful to sintering when increasing the holding timeappropriately. In addition, with the increase of holding time, the content of mulliteand corundum in the crystal phase keeps stable. When holding time is10h,amorphous phase disappeared, and mullite crystal fully developed. The length ofmullite crystal is about10μm, and the width is about5μm. The glass phase is filled inthe interlocking network structure of mullite crystals.70homogenized bauxites were grinded to difference particle size (D50is150μm,100μm,68μm or44μm), and were sintered with holding time8h or10h at1630℃.With the decrease of particle size volume density increased gradually and apparentporosity decreased gradually. When Samples of150μm and44μm were sintered withholding time10h, only mullite crystals with the crossed reticular structure on thesurface can be observed, Corundum distributs among them. Glass phase was filled inthe gaps of mullite crystal. Amorphous phase is not observed.When the difference partical size samples was sintered with holding time0h,4h,6h,8h or10h at1650℃, with the holding time increasing to8h, mullite crystalincreased to the length of~10μm, and the width of~5μm. When holding timecontinues to increase, the crystal size of mullite kept stable. The size and content ofmullite in these samples crystal don’t change obviously with different particle sizedistribution in the same holding time. When sintered with holding time8h,amorphous phase disappeared in those samples that the particle size is44μm; Thereare clear interlocking network structure of mullites on the surface. |
PDF Full Text Request