TiC Coating On Graphite Flakes By Self–Propagating High–Temperature Synthesis And Its Effects On Properties Of Refractory Castables

Due to the good chemical stability,high thermal conductivity and nonwettability against steel/slag melts,carbon materials are widely applied in the carbon–containing refractory materials.However,the poor water wettability of carbon material will make it difficult to disperse in the refractory castable.At the same time,carbon material is easy to oxidize,which will increase the porosity of refractory castables and limit its industrial application for carbon–containing castables.In this paper,graphite flakes were coated by titanium carbide（TiC）using titanium powders（Ti）by self–propagating high–temperature synthesis.The phase composition and microstructure of the products were investigated by X–ray diffraction（XRD）,scanning electron microscopy（SEM）and energy dispersive spectrometry（EDS）,and the synthesis mechanism of TiC–coated graphite flakes was revealed by the Combustion Front Quenching Technique.The water dispersibility and wettability of TiC–coated graphite flakes were evaluated by Zeta potential test,sedimentation experiment and water drop angle test respectively.Furthermore,the physical properties,oxidation resistance and slag corrosion resistance of Al₂O₃–Mg O refractory castables added by graphite flakes,graphite flakes–TiC mechanical mixing powder[GT–2,n（graphite flakes）:n（TiC）=1:1],TiC–coated graphite flakes（CT–2）and castables without graphite（labled as CGF,CGT,CCT,C0 respectively）were compared.The main results of the present paper are as follows:（1）Continuous,uniform and different thickness TiC coating on graphite flakes were prepared by self–propagating high–temperature synthesis with graphite flakes and Ti powder as raw materials,adjusting the graphite/Ti（C/Ti）molar ratio.It was found that when the C/Ti molar ratio was 1.5,the coating thickness was～1.31μm;when the C/Ti molar ratio was 2,the coating thickness was～763 nm;when the C/Ti molar ratio was 2.5,the coating thickness was～700 nm.With the increase of C/Ti molar ratio,the TiC coating on the surface of graphite flakes becomed more thinner.（2）Based on the combustion theory and thermodynamic calculation,through analyzing the phase composition and microstructure analysis of combustion front quenching sample,the synthesis mechanism of TiC–coated graphite flakes was investigated.It can be concluded that the synthesis mechanism of TiC–coated graphite flakes in C–Ti system was melting–reaction–precipitation mechanism,and the formation of the TiC coating is mainly controlled by the template growth mechanism,and the graphite flakes was used as template.（3）Compared to graphite flakes and graphite flakes–TiC mechanical mixing powder（GT–2）,TiC–coated graphite flakes（CT–2）had the highest Zeta potential value and increased with p H value,and no delamination phenomenon in water,and the water wetting angle with water was 26°,which was 50°lower than that of uncoated graphite flakes.The water wettability and dispersivity of the TiC–coated graphite flakes were improved owing to the presence of the TiC coating.（4）In the carbon–containing castables,after drying at 110℃,the apparent porosity of CCT castable was 13.4%,which is 39.37%and 11.26%lower than CGF and CGT castables,respectively,showing lower apparent porosity.At the same time,because the TiC coating effectively slowed the oxidation of CT–2,the decarbonized depth of CCT castable was 8.0 mm,which is 14.89%and 8.05%lower than CGF and CGT castables,respectively.The slag corrosion area of CCT castable was 29%,which is 19.44%、6.45%and 3.33%lower than C0,CGF and CGT castables,respectively.The castable exhibited good oxidation resistance and slag corrosion resistance.