Pyrolysis behaviour of stabilized self-sintering mesophase

A coal-tar pitch-based mesophase and a naphthalene-based mesophase were stabilized with air, using a multi-step temperature/time program from 200 to 300 °C. The extent of the stabilization was monitored by elemental analysis. The pyrolysis behaviour of the stabilized samples was studied by thermogravimetric analysis and differential scanning calorimetry. The results showed that the different chemical composition of parent mesophases affected the degree and effectiveness of stabilization, and consequently, the plasticity of the stabilized samples and the intensity of the exothermic effects during their pyrolysis. Naphthalene-based mesophase is more aliphatic and oxygen is taken more rapidly and in a larger amount than in coal-tar pitch-based mesophase. Consequently, the naphthalene-based mesophase stabilized more easily but stabilization was more difficult to control. Moreover, the variations in oxygen uptake and weight gain during stabilization reveal that in this sample, above 250 °C, degradation competes with stabilization. The pyrolysis behaviour of the mesophases is extremely sensitive to the changes produced by stabilization. In the coal-tar pitch-based mesophase the weight loss decreased, and the temperature of maximum rate of weight loss and temperature of initial weight loss increased with the severity of stabilization, while in the naphthalene-based mesophase this tendency was not observed. The competition between stabilization and degradation seems to be the responsible factor for this different behaviour. It was also found that the sinterability of the stabilized samples was mainly governed by their plasticity.