PREPARATION OF BORON NITRIDE AND BORON CARBIDE BY THERMAL TREATMENT OF BORIC ACID-GLYCERIN CONDENSATION PRODUCT AS A PRECURSOR.

Boron-containing ceramics were synthesized by the heat treatment of the condensation product of boric acid and glycerin in N//2 or Ar. The condensation product was a transparent, glassy solid. It was found that the dehydration was completed and the formation of a compound with the structure (C//3H//5O//3B)n containing B-O-C bonding was revealed. The heat treatment of the condensation product between 900 degree C and 1250 degree C yielded boric oxide and amorphous carbon regardless of gas used. When it was heated in N//2 above 1300 degree C, boron nitride (BN) and boron carbide (B//4C) were detected by XRD and IR analyses. The crystallinity of BN and B//4C increased with the rise of heating temperature. However, heating time affected only the crystallinity of BN. The crystallite size of BN calculated by the Scherrer equation was about 50 A at 1300 degree C and 100 A at 1400 degree C. When the condensation product was heated in Ar above 1300 degree C, the formation of B//4C and graphite was observed.