Synthesis Of Corundum/Mullite/Cordierite Composites With Waste Slag Of Aluminum Factory

In this study,calcined waste slag of aluminum factory,kaolin and talc were used as raw materials to fabricate cordierite/mullite/corundum composites.The comprehensive utilization of solid wastes,such as waste slag of aluminum factory,is of great importance for economic and environment.The influence of formula,sintering processes,mineralizers addition and two step calcination method on the structures and properties of composites were investigated.The crystalline structure of sintered samples was examined by X-ray diffraction(XRD).The content of crystalline phases was calculated by Rietveld quantification analysis.The lattice parameters of crystalline phases were determined by Philips X’plus analysis.Microstructure of samples was examined by scanning electron microscope(SEM).The properties such as bulk density,porosity,water absorption,bending strength and retaining rate of bending strength after thermal shock were measured.The results show that the crystalline phases mainly consist of α-Al2O3(corundum),Al4.59Sl1.41O9.7(mullite solid solution)and Mg2Al4Si5O18(cordierite)phases with tiny amount of MgAl2O4(magnesium aluminate spinel)for all sintered samples.Needle and columnar shape mullite solid solution crystals are formed as a complete network structure.Corundum crystals are in the shape of deformed hexagonal sheet and cordierite crystals are irregular granules.No changes can be observed in the space groups of all crystalline phases,while tiny changes can be detected in their lattice parameters.The bending strength of samples increases with increase in content of talc,while the retaining rate of bending strength after one thermal shock and bulk density decreases.It can be determined that the relatively optimal composition consists of 34wt%calcined slag,52wt%kaolin and 14wt%talc.Raising sintering temperature and extending soaking time faciliates the solid-state reaction and sintering,resulting in the increase in bending strength and bulk density of samples.The optimal sintering processes are sintering at 1380℃ and soaking for 3h.The crystalline phases of sintered sample with the optimum processes consist of 29.54wt%a-Al2O3,23.66wt%A14.59Si1.41O9.7,43.77wt%Mg2Al4Si5O18 and 3.03wt%Mg2(SiO4).The bending strength,retaining rate of bending strength after one thermal shock,apparent porosity,water absorption and bulk density are 58.49MPa,57.55%,1.56%,0.64%and 2.44 g/cm3,respectively.With the addition of TiO2 and TiO2/ZrO2 complex mineralizers,the formation of Mg2Al4Si5O18 is promoted and the bending strength of samples is improved.ZrO2 addition facilitates the formation of Mg2AlSi5O18 and Al4.59Sii.41O9.7 and inhibits the grain growth of those two crystals.The optimal content of the Ti02,ZrO2 and TiO2/ZrO2 mineralizers are 2.5wt%,2.5wt%and(0.75wt%+ 0.75wt%),respectively.Using two step calcining process can reduce shrinkage and deformation of samples in the process of sintering,and improve their thermal stability.The relatively optimal composition is 80wt%synthetic cordierite and 20Avt%calcined sludge.The optimal sintering processes are sintering at 1400℃ and soaking for 3h.The corresponding bending strength and retaining rate of bending strength after one thermal shock are 51.91 MPa and 72.98%,respectively.