New Borate Precursors for Boron Nitride Powder Synthesis

The thermal decomposition of guanidinium tetraborate, pentaborate, and nonaborate has been characterized under nitrogen and ammonia atmospheres, and conditions have been defined for bulk powder and aqueous aerosol transformations of these precursors to boron nitride (BN). The bulk pyrolyses under ammonia (600−1400 °C) produce micrometer- and sub-micrometer-sized platelet morphology particles with oxygen contents of 3−18 wt. %. Subsequent pyrolysis of these powders at 1600 °C under NH 3 reduces the oxygen contents to <1 wt. %. Pyrolysis of aqueous aerosols containing the guanidinium borates gives submicrometer spherical morphology BN particles. The chemistry and processing of guanidinium borates are compared with the behavior of alternative precursors.