Flux-Assisted Thermal Conversion Route to Pore-Free High Crystallinity Magnesium Borate Nanowhiskers at a Relatively Low Temperature

Abstract

A flux-assisted thermal conversion route to the pore-free high crystallinity magnesium borate (Mg2B2O5) nanowhiskers with a length of 0.47−3.0 μm, diameter of 50−240 nm, and aspect ratio of 5−36 at a relatively low temperature of 650−700 °C (200−350 °C lower than that needed via the traditional method) was developed in this paper. Magnesium borate hydroxide [MgBO2(OH)] nanowhiskers were first prepared by a coprecipitation−hydrothermal approach at 240 °C for 18 h by using MgCl2·6H2O, H3BO3 and NaOH (or KOH) as the raw materials and then calcined to produce Mg2B2O5 nanowhiskers. The resultant NaCl (or KCl) in the coprecipitation served as the flux and played a key role in the thermal conversion of MgBO2(OH) nanowhiskers as the transport medium for the rearrangement of structural units of Mg2B2O5, leading to the final formation of the pore-free Mg2B2O5 nanowhiskers with uniform one-dimensional morphology, high crystallinity, and twin crystal structures.