Carbothermal synthesis of zirconium carbide hollow microspheres from polyzirconoxane and phenolic resin by spray drying

Zirconium carbide hollow microspheres (ZrC HMs) were fabricated via spray drying process and polymer-derived ceramics technique. The stable and homogeneous ZrC precursor solution can be prepared by mixing polyzirconoxane (PZO), phenolic resin (PR), curing agent p-toluenesulfonic acid (TsOH) and solvent n-propanol. The precursor solution was spray-dried to form hollow precursor microspheres. During the spray drying process, morphology of the hollow precursor microspheres can be regulated by adjusting temperature of inlet hot N2, concentration of precursor solution and the amount of curing agent TsOH. The prepared hollow precursor microspheres were carbonized at 700 degrees C and then converted into ZrC HMs by carbothermal reduction reaction above 1500 degrees C. During the pyrolysis process, nanosized ZrO2 grains produced by PZO decomposition are evenly dispersed, so is the carbon produced by PR pyrolysis, as prevents overgrowth of ZrO2 grains in the following process, even when it is changed to ZrC. ZrC HMs maintained excellent spherical morphology at temperatures of 1500-1900 degrees C, with particle size Dv(50)=16.4-18.7 mu m, which enable their promising applications in ultra-high temperature insulation material. This preparation method is simple and can be prepared on a large scale.