Suppression of puffing during the graphitization of pitch needle coke by boric acid

Puffing of pitch needle coke was successfully suppressed by both impregnating boric acid and adding ferric oxide. The boric acid was impregnated into calcined coke and preheated above 870 K to convert boric acid to boron trioxide which melts above 850 K to get into the pore. Filled boron trioxide inhibits the binder pitch getting into the pore at the kneading and sublimes to open the pore above 1800 K at the early graphitization stage, through which liberated nitrogen can be released without puffing at the later graphitization. Boron trioxide reacts with carbon to produce CO and boron carbide, the latter substance enhancing the graphitization. The former reaction reduces the carbon yield. Hence there is an optimum amount to inhibit puffing sufficiently with least carbon loss.