Heating-rate dependence of expansion and contraction behaviors of formed green carbon

The linear expansion coefficients of two kinds of formed green carbons were measured under constant heating rates of 0.5 to 3 K/min up to 1200 K. Expansion and contraction peaks appearing below 700K were practically independent of the heating rate, while two contraction peaks appearing in the higher temperature range were dependent on the heating rate. The temperatures at which these two contraction peaks appear were found to linearly vary with the logarithm of heating rate. Our theoretical model representing the contraction mechanism of the formed green carbons can qualitatively explain such contraction behavior in the higher temperature range. On the basis of these experimental and theoretical results, approximate equations expressing the heating-rate dependence of the expansion/contraction-peak values and of the expansion/contraction-peak temperatures were presented. Comparison of our experimental results with existing previous experimental ones suggests that the equations for the contraction-peak temperatures are valid for other formed green carbons. The equations predict that the contraction-peak temperatures appearing under heating rates of the order of 10^-2 K/min in practical processes are about 100 K lower than those under our experimental condition. This finding is important to determine the heating pattern of practical processes.