Effects Of Sintering Temperature And Holding Time On The Synthesis AlB₂

MgO-C refractoriy is an excellent material with good corrosion resistance, thermalshock resistance and other advantages, and is widely used in various types of furnacesas a lining material. To ensure the excellent performance of the MgO-C refractoryboride AlB2as an antioxidant added to the MgO-C refractory material not only preventthe oxidation of carbon, but also has advantages to improve thermal shock resistanceand erosion resistance. However, the current domestic and international research on thepreparation of AlB2is rare.In this paper, Al-B binary system phase diagram and thermodynamic calculationswere studied, and theoretical analysis was carried out. With Al powder and B powder asraw material, in terms of atomic ratio of Al: B=1:2,mixed powder was pressed toprepare a sample of6Φ36with a pressure molding machine. The samples weresintered to a temperature of700℃800℃,900℃,1000℃respectively, with Ar gas asprotective atmosphere and incubated under6h, and at800℃for three holding time (2h,4h,6h) sintered samples. Finally, XRD, SEM, EDX, analysis and other methods wasused to study the different effects of different sintering temperature and holding time onthe synthesis and micro structural features AlB2.DSC-TG was used to explore thephysical and chemical changes between Al powder and B powder. Ultimately theoptimal synthesis temperature and holding time of synthesis AlB2were determined.The results show that Gibbs free energy change of the reaction of Al and B isalways negative, the reaction can occur. As temperature increasing, the absolute value ofGibbs free energy change of the AlB2synthesis decreases, meanwhile，the absolutevalue that AlB2decompose into AlB12is increasing gradually. This proves that the riseof temperature is not conducive to AlB2,but easily generate AlB12by decomposition of AlB2. B and Al begin generating AlB2at700℃;there is maximum diffraction intensity,the highest concentrations at a temperature of800℃; AlB2phase of the sintered sampleis almost free at900℃; the sintered samples contains high-temperature phase AlB12at1000℃. AlB2phase is hexagonal structure rules by scanning electron microscopyobserving, where the molar ratio of Al: B is1:3，it is very close to AlB2. The DSC-TGshow that, Al and B mixed by ratio of1:2，are gradually heated under an argonatmosphere. When the temperature is660.5℃，there is an endothermic peak; After Almelts, there is a clear exothermic peak at758℃, because of generation of AlB2.Ascontinuous rising of the sintering temperature, diffraction intensity of AlB2phase in thesamples after sintering increase first, then weaken and disappear. Under the800℃,generated AlB2phase diffraction intensity is the highest, the highest content ofAlB2.With extend of holding time, diffraction intensity of AlB2phase in the samplesafter sintering gradually increases. Holding time is6h, the synthesis of AlB2phasediffraction intensity is the highest, content of AlB2is the highest.In summary，theoptimum process parameters of AlB2synthesized with Al and B is6h at800℃.