The effects of partially or fully linked boron with a cross-linking structure of an organic precursor on the purity and morphology of ZrB₂ powder

From a chemical infrastructure perspective, it is important to ensure that all ions constituting a target product, e.g., Zr and B ions for ZrB₂, are fully linked with a cross-linking structure for synthesis via an organic precursor. In the present study, glycerol is used as a chelating ligand to prepare boron both partially and fully linked with the cross-linking structure of organic precursors by a sol-gel route. The results are far from expected, in that the more linked boron there is in the precursor, the purer the ZrB₂ produced. In the case of a partially linked cross-linking structure, the carbothermic reduction reaction for ZrB₂ is a multi-step process with an intermediary phase of ZrC, and then a high-purity prism-like ZrB₂ powder with a larger size is obtained. A minimum of 0.26 wt% for the oxygen content of ZrB₂ corresponds to a 0.67 molar ratio of glycerol to H₃BO₃. On the other hand, in the case with the boron fully linked, a single-phase of ZrB₂ cannot be obtained, and instead a double-phase is obtained. Therefore, the amount of impurity is greater, even though the size is smaller. The carbothermic reduction reaction is direct, and has only one step.