Rapid synthesis of manganese tetraboride (MnB4) using reactive spark plasma sintering

Abstract

In this work, we report a rapid synthesis method for polycrystalline transition-metal tetraborides using reactive spark plasma sintering (R-SPS). This method was demonstrated on the synthesis of manganese tetraboride (MnB₄) in a short time, 30 min. Starting powders with variable B/Mn molar ratios (4.1, 4.5, 5.0, and 8.0) were subjected to 12 h of high-energy ball milling (HEBM), followed by synthesis and consolidation in a single step using R-SPS in a dynamic vacuum atmosphere. Phase purity was confirmed by powder X-ray diffraction (PXRD); MnB₄ was obtained for B/Mn molar ratio of 4.5 and higher in the temperature range of 850 – 1080 °C, while the lower B/Mn molar ratio (4.1) resulted in a mixed-phase (Mn₃B₄ + MnB₄) sample. The crystal structure and lattice parameters estimated from PXRD agree well to those reported for single-crystal MnB₄. Thermogravimetric differential thermal analysis (TG/DTA) revealed that MnB₄ is stable in air up to 400 °C.