Effects of mannitol on the synthesis of ultra-fine ZrB2 powders

ZrB2 particles were synthesized by a sol–gel method using zirconium oxychloride, boric acid, and mannitol as starting materials. Mannitol helps to form the Zr–O–B in the sol–gel system to improve the stability of the precursor. Mannitol acts both as a modifier, as well as carbon source. High purity of ZrB2 powder can be obtained with a molar ratio of B/Zr = 2.3, C/Zr = 6.6 after carbothermal reduction reaction at a low temperature of 1350 °C for 1 h. The yield rate of the modified ZrB2 precursor can be increased to 53.4%. Additionally, the ultra fine ZrB2 powder exhibits rod-like and well-crystallized particles morphology with a particle size of ~200–300 nm. For comparison purpose, sucrose or phenolic resin substituted for mannitol, acting as carbon source were carried out as contrast experiments. It revealed that mannitol helps to form chelate complex with H3BO3, which promotes the stability of the precursor, increases the yield of ZrB2, and reduce the preparation temperature of the ZrB2 powders. (a) SEM image of sample 3 heated at 1350 °C for 1 h. (b) XRD patterns of sample 3 heated at different temperatures for 1 h from 1000 to 1450 °C.