| In this paper,ultrafine ?-Al2O3 powders were synthesized using ammonium alumina carbonate hydroxide(AACH)as the precursor after the calcinations process.The precursors and alumina powders were prepared by two different methods using ammonium aluminum sulfate and ammonium hydrogen carbonate as the main raw materials.One approach is that the precursor prepared by liquid phase precipitation reaction using dilute solution of two raw materials was heat treated at a high temperature for a short time to prepare ?-Al2O3 powders.Because of excessive waste liquid and low yield of powders in this approach,it is difficult to achieve pilot scale production.Another method solved the problems posed by the first method by increasing solid content of the feedstock.This method also got ?-Al2O3 powders with good dispersion by ball milling or sanding treatment.The obtained precursors and final ?-Al2O3 powders were characterized in detail by XRD,SEM,TEM,TG-DSC,and particle size distribution analysis.The effect of experiment parameters and calcinations process on the properties of precursor samples and final?-Al2O3 powder was investigated.Thus we optimized the best preparation conditions which might provide a experiment basis for the industrial production and application of precursors and ?-Al2O3 powders with good performance.1.Preparation of ultrafine ?-Al2O3 powders using AACH as precursor synthesized by liquid phase precipitation reactionEmployed dilute solution of aluminum sulfate(NH4HSO4)and ammonium bicarbonate(NH4HCO3)as feed solution,ammonium aluminum carbonate precursor was prepared with a certain mole ratio by liquid phase precipitation reaction and ?-Al2O3 powder formed followed by a heat treatment at high temperature for a short time.And then,the precursor and corresponding product were characterized by XRD,TG-DSC,TEM,SEM,laser particle size distribution analysis,respectively.The aforementioned analysis showed the impact of aging time on crystallinity and morphology of the precursor,and addition of seed crystal as well as calcining methods on the final ?-Al2O3 powders.The results indicated that high crystallinity,uniform morphology particles of precursor can be obtained when aged 12-24h after reaction.The resultant ?-Al2O3 powder after calcination was found no significant worm-like hard agglomeration.In the preparation,a certain amount of ?-Al2O3 seed,average particle size 100 nm,can largely reduce the a-phase transition temperature of precursor,and powder morphology be improved as well,thus development of powder particle size distribution to the normal distribution can be achieved.The precursor calcined at short-time high temperature lead to better dispersion of ?-Al2O3 powders,compared with conventional calcination ways.2.Preparation and characterization of ultrafine a-alumina powders with ammonium aluminum carbonate as precursor synthesized under high solid content.AACH precursor was prepared using aluminum sulfate(NH4HSO4)and ammonium bicarbonate(NH4HCO3)solid particles as raw materials and ?-Al2O3 powders formed followed by a heat treatment.The powders got to the ultrafine ?-Al2O3 powders with good dispersion by ball milling or sanding treatment.The precursor and final ?-Al2O3 were characterized by XRD,TG-DSC,TEM,SEM,laser particle size distribution analysis,respectively.The influence of additives,mixing methods and post-processing after calcination on the precursor and ?-Al2O3 powders was investigated.The aforementioned analysis showed that the addition of ammonium sulfate solid and PEG and the stirring method of high-speed dispersion while ultrasounds can improve the dispersion of precursors and final ?-Al2O3 powders.The results also showed that the milling additives can raise the efficiency of ball milling and for optimal result that the average particle size was 0.603 ?m,it took 7 hours with 1%milling additives.Sanding can also achieve the same effect that average particle size and size distribution decreased. |
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