Carbothermal reduction synthesis of ZrB2 nanofibers via pre-oxidized electrospun zirconium n-propoxide

Zirconium diboride (ZrB2) nanofibers with an average diameter of 297±103 nm were fabricated through combination of electrospinning method and carbothermal reaction. The solution for electrospinning was prepared by dissolving zirconium n-propoxide (Zr(OPr)4) and boric acid in glacial acetic acid and 2,4-pentanedione followed by mixing in PVP/ethanol solution. The influence of the supplemental source of carbon, pre-heat treatment of electrospun nanofibers in the air, and materials used for fabrication of the crucible in carbonization treatment under argon atmosphere were studied to optimize the experimental conditions for the synthesis of ZrB2 nanofibers. The synthesized nanofibers were then characterized by FE-SEM, EDS, DSC-TG, XRD and BET. The results showed that increasing of C/Zr ratio caused an increase in diameter of the as-spun fibers and reduction of ZrO2 impurities in the final product. Interestingly, PVP/Zr(OPr)4 hybrid nanofibers maintained its fibrous morphology after stabilization at 150 °C in air for 24 h, pre-oxidized at 350 °C in an ambient environment for 4 h followed by carbonization at 1350 °C in argon atmosphere, resulting in high crystalline ZrB2 nanofibers while using graphite as an external supplemental carbon source. The crystallite size of ZrB2 nanofibers decreased from 47 to 37 nm with increasing pre-oxidation heating rate. The specific surface area of the nanofibers, which was calculated by the multipoint BET-equation, was found to be 19.5 m2/g, and the mean pore diameter was 34 nm.