Curing mechanism of phenolic resin binder for oxide-carbon refractories

Abstract

Phenolic resin has been widely used as the binder of oxide-carbon refractories, and its curing process has a great effect on the bonding strength. In order to optimize the curing process, the curing mechanism, which involved the heat release reaction, weight change and chemical structure evolution, has been investigated in this study. The dehydration-condensation reactions of the curing started at 363 K. Then, the formation and volatilization of water began and accelerated the rate of weight loss of the binder. Meanwhile, these reactions led to the increase of the molecular size of the binder, which might cause the improvement of the binder's bonding strength. As the temperature increased up to 403 K, the exothermic reaction by the dehydration-condensations of the binder increased and the endothermic reaction by the volatilization of free molecules decreased. In the range from 403 K to 523 K, main dehydration-condensation reactions occurred. These reactions let the molecular size of the binder increase obviously and the bonding strength might be improved significantly. Therefore, a slow heating rate was needed. Above 523 K, the curing gradually approached the end and a higher heating rate was needed. Moreover, when the temperature reached 543 K, the curing was completed because the binder almost had the stable chemical structure, constant weight and very small exothermic reaction.