Direct preparation of magnesium borate (Mg2B2O5) ceramic from boron-bearing slag: Super-gravity separation and microwave dielectric properties

In this study, a novel method was developed for direct preparation of magnesium borate (Mg2B2O5) ceramic from boron-bearing slag. The amorphous boron was efficiently enriched into Mg2B2O5 via crystalline phase transformation in the condition of B/S (B2O3/SiO2) = 1.20 and wt.% (MgO) = 36.00. High-purity Mg2B2O5 crystals were fully recovered from molten slag by super-gravity separation at G ≥ 500 and t ≥ 240 s. The Mg2B2O5 ceramic was directly prepared at various temperature by using the recovered Mg2B2O5, and the Mg2B2O5 ceramic displayed a favourable microwave dielectric properties including the dielectric constant ( ε r ) of 6.05, the quality factor (Q × f) of 38,147 GHz and the temperature coefficient of resonant frequency (TCF) of -20.98 ppm/K. Compared with synthetic methods that use high-purity oxides, this study provides a green and economical method for direct utilisation of industrial slag to prepare microwave dielectric materials.