Mechanisms for puffing inhibition of coal tar based needle coke with disodium hydrogen phosphate (DHP) and boric acid Original Research Article

Puffing inhibition of coal tar based needle coke was effectively achieved regardless of the repeated impregnating and heating rate at the graphitization by impregnation with disodium hydrogen phosphate (DHP) and boric acid into the needle coke. Inhibitors were found dispersed into pores of the coke by impregnating and heat-treating the inhibitors on the coke. Such inhibitors in the pore prohibited the binder and impregnation pitches to penetrate into the pore at the kneading, baking and repeated impregnation. Such inhibitors vaporized or reacted with carbon in the pore at the early graphitization to leave some space between needle coke wall and binder pitch carbon, through which puffing causing species such as nitrogen and sulfur can liberate from the coke without expansion. The dispersion of inhibitors was observed in the pore of the coke by a computer-aided microanalyzer (CMA). Complete decomposition of DHP at the early graphitization may emphasize its inhibition activity compared to the activity of boric acid which is converted to boron carbide in the pore.