Experimental Research On Sintering Behavior Of XinJiang HeJing Magnesite

The reserves of XinJiang HeJing magnesite is rich,but the degree of its utilization is very low.In order to reveal its basic characteristics and prepare the magnesia with high performance and usability,its sintering behavior were investigated experimentally.Firstly,the raw magnesite was evaluated by chemical analysis,TG-DSC and XRD analysis.Secondly,the effect of heating rate on the thermal decomposition reaction of magnesite was investigated.The effects of calcination temperature?T?,soaking time?t?and particle size?d?of magnesite on the activity of caustic magnesia were studied using orthogonal experiment.Hence the optimal calcination conditions were determined.Lastly,The effects of molding pressure,sintering temperature and added micro silica on the bulk density and microscopic morphology of sintered magnesia were investigated.The crystalline phases and microstructure characteristics of specimens were studied by X-ray diffraction?XRD?and scanning electron microscopy?SEM?,respectively.The foundation for its application as refractory raw materials would be laid.The conclusions were drawn as follows.?1?The content of MgO is 46.75%,and the contents of impurities such as SiO2,Fe2O3,Al2O3 in the ore are very low.But the amount of CaO is relatively high,showing that it is the type of high-CaO and low-impurity magnesite.The main impurity phase is dolomite.Based on the results of TG and DSC,the magnesite began decomposing at about 450?,the decomposition rate can reach its high peak at 637.1?,the ore decomposed completely at about 750?.?2?At the same temperature,the decomposition rate of magnesite decreases withthe increasing of heating rate.And the decomposition temperature of magnesite increases with the increasing of heating rate.The higher heating rate could hinder the decomposition reaction.If the calcination temperature is in the range of 550⁶00?,the decomposition rate would reach 30% and the activation energy of the reaction would reach its high peak,the reaction occurs difficultly.The optimal heating rate is chosen as5?/min.?3?The calcination experiments show that the calcination temperature and particle size have greater influence than the soaking time on the activity of magnesia.And the optimal calcination conditions are that T=800?,t=120min,d=2mm.?4?The hydration reaction of sintered magnesia which was prepared by 20⁷0mm block magnesite using direct calcination method mainly occurs in the first 24 hours,and the rate of quality increases about 0.78%.With the extension of reaction time,the hydration rate increases and finally keeps steady.The sintered magnesia has good resistance to hydration.?5?The sintered magnesia show the optimal property using process parameters including molding pressure of 200 MPa,the sintering temperature of 1700?,the added silica powders content of 2%.The content of MgO reaches 93%.The bulk density is3.31g/cm3 and the apparent porosity is 1.95%.According to the microscopic morphology photos,it`s shown that the periclase grains develops well and has regular shape.The grain size is about 20?m with a few pores.The direct bonding degree of granular is higher.The adding silicon powders react with CaO and form dicalcium silicate?C₂S?phases being distributed around the periclase grains.