B6O ceramic by in-situ reactive spark plasma sintering of a B2O3 and B powder mixture

A mixture of B2O3 and amorphous B with the mole ratio of 1:14 is shown to react and form B6O ceramic under in-situ spark plasma sintering (SPS) conditions. The optimum SPS temperature and time to obtain phase B6O are 1250°C and 30 min, respectively, and Rietveld refinement of the XRD patterns indicates that the oxygen occupancy of B6Ox is reasonably high at x = 0.89(99). However, to reach high density above 98%, SPS temperatures of 1700–1800°C are necessary and a one-step two-temperature in-situ reactive SPS was designed and applied. As-prepared B6O dense ceramic has Vickers hardness (36.7 ± 1.2 GPa) and fracture toughness (K1c = 4.2 ± 0.15 MPa.m1/2) comparable with the highest values reported in literature for the bulks obtained by processing routes of already reacted B6O powders (ex-situ routes).