Effect of the evolution of phenol–formaldehyde resin on the high-temperature bonding

The novel high-temperature adhesives (HTAs) were prepared using phenol–formaldehyde (PF) resin as matrix and elemental silicon or boron carbide as modification additives. The bonding properties of the above adhesives were investigated by the bonding experiment on graphite substrate. The graphite joints were heat treated at high temperatures ranging from 200 to 1500 °C. It was shown that the degradation and the content of PF resin had important influences on the bonding properties of the HTAs. The pyrolysis and degradation of the organic resin led to the drastic volume shrinkage and the decrease of mechanical strength of resin matrix. It is the main reason leading to the failure of the joints treated at high temperatures, especially in the range of 400–650 °C. It is concluded that the satisfactory bonding property of the novel organic resin matrix HTAs lies in two aspects: (i) the selection of additives with good modification effect, and (ii) the optimized ratio between resin matrix and modification additives.