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

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Carbonaceous materials including cokes, chars, and pyrolyzed coals were annealed at temperatures ranging from 973 K to 1773 K (700 C to 1500 C) in an inert atmosphere. Macro and microstrengths of original and annealed carbonaceous materials were characterized by the tensile strength and fracture toughness. Fracture toughness was determined for inert maceral-derived component (IMDC) and reactive maceral-derived component (RMDC) using ultramicro indentation. Experimental data obtained by tensile tests were processed using the Weibull statistical method to find "inherent" strength. Tensile strength of chars and coals was significantly increased by annealing at temperatures ranging from 973 K to 1373 K (700 C to 1100 C); further increase in annealing temperature to 1773 K (1500 C) increased their tensile strength only slightly. Tensile strength of cokes decreased with the increasing annealing temperature; the major effect was observed in the temperature range from 1573 K to 1773 K (1300 C to 1500 C). Fracture toughness of chars and coals was enhanced significantly by heat treatment at temperatures ranging from 973 K to 1373 K (700 C to 1100 C) as a result of pyrolysis, while that of cokes increased slightly by heat treatment. Fracture toughness of IMDC was higher than RMDC. Macrostrength of carbonaceous materials was strongly affected by their porosity and microstrength. The effect of pore geometry on macrostrength was marginal. Decreasing the porosity was more effective compared with increasing the microstrength in improving the macrostrength of carbonaceous materials. © 2013 The Minerals, Metals & Materials Society and ASM International

Effects of annealing on microstructure and microstrength of metallurgical coke

Two metallurgical cokes were heat treated at 1673 K to 2273 K (1400 C to 2000 C) in a nitrogen atmosphere. The effect of heat treatment on the microstructure and microstrength of metallurgical cokes was characterized using X-ray diffraction, Raman spectroscopy, and ultra-microindentation. In the process of heat treatment, the microstructure of the metallurgical cokes transformed toward the graphite structure. Raman spectroscopy of reactive maceral-derived component (RMDC) and inert maceral-derived component (IMDC) indicated that the graphitisation degree of the RMDC was slightly lower than that of the IMDC in the original cokes; however graphitisation of the RMDC progressed faster than that of the IMDC during annealing, and became significantly higher after annealing at 2273 K (2000 C). The microstrength of cokes was significantly degraded in the process of heat treatment. The microstrength of the RMDC was lower, and of its deterioration caused by heat treatment was more severe than IMDC. The degradation of the microstrength of cokes was attributed to their increased graphitisation degree during the heat treatment. © 2013 The Minerals, Metals & Materials Society and ASM International