Comments on coke quality characterization by tensile strength

Abstract

According to theoretical and experimental investigations, the indirect tensile test turned out to be applicable to coke qualities. It was stated that: The size of the sample to be tested must be kept constant because, according to the Weibull distribution, size affects tensile strength.The crosshead speed must be kept constant as well. The crosshead speed between 0.1 and 1.0 mm/min, however, has no influence on the tensile strength and should be agreed upon to read 1.0 mm/min for tests to be carried out within reasonable time. This corresponds to the results of BCRA13). Furthermore, it was stated: The true tensile strength of samples which failed under strong deformation, is not measurable. Approximately 100 to 150 samples are sufficient for the statistical evaluation of the tensile strength distribution: Mean and median value or Weibull parameters. (Sample preparation and carrying out of the indirect tensile test for one coke quality requires approximately 16 to 22 hours.) The tensile strength of the coke depends strongly on its porosity. This was stated for porous material in general. The correlation between tensile strength and porosity can be expressed by the Knudsen equation. The introduction of the Griffith model and, accordingly, the notion of the largest pore diameter, does not result in better correlation of tensile strength as a function of coke structure, however, it may be used for interpretation of the coefficients, since a mechanical model is used. For more exact explanation of the correlation between tensile strength and pore structure, further investigations should be carried out.