Preparation Of Calcium-hexaluminate Light-weight Materials With High Strength And Low Thermal Conductivity

In recent years,the research of light-weight materials is diversified gradually due to its increasing application in high temperature industry.The properties of high strength and low thermal conductivity in light-weight materials have become research theme.In this work,calcium-hexaluminate light-weight materials with high strength and low thermal conductivity were prepared with active alumina powder and nano-meter calcium carbonate as raw materials and composite binder and foam as additives.This work could divided into three parts as follows:a)The reactions between nano-meter calcium carbonate and active alumina powder were studied by thermodynamic analysis of decomposition temperature of nano-meter calcium carbonate,X-ray diffraction in high temperatures of mixture,X-ray diffractions,true densities and microstructures of fired samples,which provided a theoretical research of CA₆ formation and growth route in this experiment.b)Calcium-hexaluminate light-weight materials were prepared by foam method.The physical properties,X-ray diffractions and microstructures of fired samples were studied.Based on those results,CA₆ forming dynamics was analysised.c)The effects of different microsilica amount on properties of calcium-hexaluminate light-weight materials were explored.The results were showed as follows:?1?Calcium-hexaluminate was formed by the reaction between calcium-dialuminate and alumina at 1300 oC,and formed vastly from 1450 oC to 1500 oC.Above 1500 oC,calcium-hexaluminate grains grew sequentially.Calcium-hexaluminate grains were regular hexagonal plates morphology.?2?Sintering temperature rise caused bulk densities and cold crushing strengthes decreased from 1450 o C to 1500 o C and then increased from 1500 oC to 1600 oC.True densities increased from 1450 oC to 1500 oC and then were nearly 3.72 g/cm³.As composite binder content increased,green shrinkage decreased.Cold crushing strength of specimen containing 10 wt% composite binder had the greatest value.As the foam amount increased,physical properties such as linear changes,bulk densities,cold modulus of ruptures,cold compressive strengthes and thermal conductivities decreased.The specimen containing 10 wt% composite binder and 400mL/kg foam fired at 1500 oC,the bulk density was 0.78g/cm³,cold modulus of rupture was 1.58 MPa,cold compressive strength was 6.64 MPa,and thermal conductivities were 0.167 w/?m�k??300 oC?,0.177 w/?m�k??600 oC?,0.187 w/?m�k??900 oC?.?3?The addition of microsilica enlarged bulk density of fired specimen,and then improved its cold modulus of rupture,cold compressive strength,thermal conductivity and elasticity modulus.As the microsilica addition increased from 0 wt% to 1.0 wt%,the bulk density growth ratio was 49%,yet,its cold modulus of rupture and cold compressive strength grew by 338% and 237%,respectively.Though high temperature elasticity modulus increased gradually with the microsilica addition rise,its stability reduced gradually.0.5 wt% microsilica addition in specimen gave obvious improvement and stability of high temperature elasticity modulus.