Influence Of Micro-Sized CaCO₃Addition On Volumetric Stability, Strength And Thermal Shock Resistance Of Corundum Based Castables

The aim of this work is to generate uniform distribution of calcium dialuminate(CA2) and calcium hexaluminate (CA6) with micro-sized CaCO3addition andimprove the volumetric stability, strength and thermal shock resistance of thecastables after firing at high temperatures (1100C and1450C).In order to investigate the influence of micro-sized CaCO3contents and particlesize on the properties of castables after firing at high temperatures, the castablesamples with different amounts (0-3%) and different particle size (d50=18m, d50=11m) of CaCO3were prepared. And the influence of micro-sized CaCO3addition andparticle size on the performance of the castables was explored by measuring thepermanent linear change, strength and thermal shock resistance of castable samplesafter firing at1100C and1450C, respectively. The results indicated that micro-sizedCaCO3addition can improve the volumetric stability, strength and thermal shockresistance of the castable samples.To further investigate the relationship between the influence of micro-sizedCaCO3addition on phase composition and microstructure of the castable and theinfluence of micro-sized CaCO3addition on the properties of the castable, the matrixsamples were prepared according to the ratio of the matrix compositions of thecastables. And the matrix samples were cured, dried and fired as preparing thecastable samples.The results of XRD demonstrated that CA2was formed in the matrix sampleswith micro-sized CaCO3after firing at1100C and CA6was formed after firing at1450C. The volume expansion accompanying the formation of CA2and CA6contributed to the volumetric stability of the castable samples with0.5-1.5%mciro-sized CaCO3addition.The results of SEM indicated that CA2phase was formed in the matrix afterfiring at1100C. And the grains in the matrix were coalesced with the sintering necksof CA2to increase the connection between particles, leading to the increased strengthof the castables with0.5-2%mciro-sized CaCO3addition after firing at1100C. When the heating temperature reached1450C, interlocked CA6was formed in thecastable matrix. The binding ability of particles was increased because of theinterlocked CA6crystals among the grains, leading to the increased strength ofcastables with0.5-1.5%mciro-sized CaCO3addition after firing at1450C.Meanwhile, the thermal shock resistance of castables with micro-sized CaCO3addition was improved because the interlocked CA6phase can dissipate and absorbthe thermal stress generated from temperature fluctuation.In order to investigate the influence of particle size of CaCO3on the propertiesof castables after firing at high temperatures, the two kinds of the castables containingmicro-sized CaCO3and nano-sized CaCO3were prepared with different contents(0-1%) of CaCO3addition. And the influence of particle size of CaCO3on propertiesof castables was investigated by measuring the permanence linear change, strengthand thermal shock resistance of the castables after firing at1100C and1450C,respectively. The results indicated that micro-sized CaCO3addition can improve thevolumetric stability and thermal shock resistance to a higher degree, and nano-sizedCaCO3addition can promote the strength of the castable after firing at hightemperatures to a higher level.To further investigate the relationship between the influence of particle size ofCaCO3addition on phase composition and microstructure of the castable and theinfluence of particle size of CaCO3addition on the properties of castable, the matrixsamples with different particle size of CaCO3were prepared according to the samemethods and treatments as stated above.The results of XRD showed that CA2and CA6were formed in both matrixsamples with micro-sized CaCO3and nano-sized CaCO3after firing at1100C and1450C. Therefore, the influence of particle size of CaCO3addition on the propertiesof castables can not be explained by means of XRD analysis.The results of SEM indicated that small particles of nano-sized CaCO3filled thevoids among the grains and enhanced the sintering in the matrix, which wasbeneficial to the increased strength of the castables after firing at high temperatures.After firing at1450C, the platelet CA6grains grow on the surface of big grains in thematrix with micro-sized CaCO3addition. However, the clusters of CA6were formed among particles and coalesced the adjacent grains to form a closely connection. As aresult, volumetric stability and thermal shock resistance can be improved by theadditions of micro-sized CaCO3.