Effect of annealing on properties of carbonaceous materials. Part II: porosity and pore geometry

The pore structure of carbonaceous materials was studied using image analysis. The effect of annealing on the porosity and pore geometry of cokes, chars, and pyrolyzed coals (laboratory chars) was examined in the temperature range of 973 K to 1773 K (700 C to 1500 C). The porosity of chars and pyrolyzed coals significantly increased during annealing at temperatures below 1373 K (1100 C) due to volatile matter release. Further increasing of the annealing temperature from 1373 K to 1773 K (1100 C to 1500 C) caused marginal porosity evolution. The porosity of cokes was not affected by annealing at temperatures below 1573 K (1300 C) and slightly increased in the temperature range 1573 to 1773 K (1300 C to 1500 C). The increase in the porosity of chars and pyrolyzed coals during annealing at temperatures 1373 K to 1773 K (1100 C to 1500 C), and cokes at 1573 K to 1773 K (1300 C to 1500 C), was a result of reactions with oxides of their mineral phases. Annealing had a marginal effect on the pore shape (Feret ratio) of carbonaceous materials, but enlarged the pore size of chars and pyrolyzed coals and decreased their pore density.