Firing mechanism of oxide-carbon refractories with phenolic resin binder

Oxide-carbon refractories, usually using phenolic resin as a binder, have been widely applied in metallurgical industry. Their firing has important effect on the properties, such as strength, porosity and thermal stability of the binder. Main processes occurring during the firing have been investigated. Below 750 degrees C, the binder decomposition was the main process. Its critical range was 400-600 degrees C, lots of functional groups decomposed, which caused a large amount of volatiles generated and many pores formed, leading to a fast decreasing of the strength by 50.1%. Above 750 degrees C, the binder shrinkage was the main process. At 750-800 degrees C, the crystallite size of the binder increased greatly, causing a rapid shrinkage and a fast decreasing of the porosity, which resulted in a significant increasing of the strength by 11.0%. As the temperature increased up to 950 degrees C, the shrinkage became slow, which leaded to that the porosity decreased slowly and the strength kept almost constant, implying that the thermal stability was good. Therefore, a slow heating rate was needed at 400-600 degrees C and 750-800 degrees C, and the firing temperature should exceed 800 degrees C.