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

The phenol-formaldehyde (PF) resin was modified by boron carbide (B4C). In order to investigate the modification effect of B4C, the residue values of pure PF resin and B4C modified PF resin were measured using thermal gravity. It was shown that the residue values of B4C 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 B4C additives and the oxygen-containing volatiles, such as CO and H2O, are demonstrated. The carbon and oxygen elements remained in the resin matrix in the forms of amorphous carbon and B2O3, 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.