Micro-structural evolution of phenol-formaldehyde resin modified by boron carbide at elevated temperatures

Abstract

The phenol-formaldehyde (PF) resin was modified by boron carbide (B 4 C). In order to investigate the modification effect of B 4 C, the residue values of pure PF resin and B 4 C modified PF resin were measured using thermal gravity. It was shown that the residue values of B 4 C modified PF resin are 71.9% and 68.4% after being pyrolyzed at 700 and 1000 °C, respectively, which are obviously higher than those of the pure PF resin (62.9% and 60.5% at 700 and 1000 °C, respectively). The microstructure evolution of the modified resin at high temperatures was also investigated by scanning electron microscopy and energy dispersive analysis of X-rays. By means of the microstructure characterization, the modification reactions between the B 4 C additives and the oxygen-containing volatiles, such as CO and H 2 O, are demonstrated. The carbon and oxygen elements remained in the resin matrix in the forms of amorphous carbon and B 2 O 3 , respectively, resulting in the improvement of residue values and stability of the PF resin at high temperatures. The distribution of modification particles became well-proportioned gradually at the elevated temperatures, and the shape of ceramic additives changed into white spherules due to the surface tension.