TAILIEUCHUNG - Carbon Materials for Advanced Technologies Episode 6

Tham khảo tài liệu 'carbon materials for advanced technologies episode 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 180 thefr study. The solid carbon thermal conductivity must be scaled to account for density and the fact that not all of the solid carbon contributes to the solid thermal conductivity. The temperature dependence of the thermal conductivity of graphite is typically modeled as Ằ A. T e 3 where A and E are fitting parameters with E usually being set to 1 for perfect graphite. For polygranular graphite which contains a significant numbers of point defects and other phonon scattering sites E is between and 1. Less graphitic carbons and graphites with lower graphitization temperatures that have a significant population of extended crystal lattice defects have E values of less than . For CBCF Dinwiddie et al. decided to modify Eq. 3 for the solid Xg XAJ V 4 where X and z are functions of the heat treatment temperature. A and e were determined by fitting the thermal conductivity data from as fabricated CBCF specimens Fig. 6 where x 1 z 0 and A and e were found to be and respectively. Combining Eq. 1 and 4 gives the functional form of the equation for the thermal conductivity of CBCF as Ằ XA T etZ X 10 nT3 5 Equation 5 was fitted to experimental data for the thermal conductivity of CBCF heat treated at various temperatures for 10 15 and 20 seconds and a linear relationship was determined for z and the heat temperature Tm which is given by Eq. 6 . z - X T m 6 z varies from to - over the heat treatment temperature range 2673 to 3273 K and the term e Z in Eq. 5 therefore varies from -0 to over the same temperature range. Equation 6 was then substituted back into eq. 5 which was used to refit the data to determine the relationship between X and the heat treatment conditions time and temperature Eqs. 7 and 8 . The empirical parameter X in Eq. 5 was found to be given by 181 X R exp Tm X 7 where R is a time dependent variable given by R X 10 5 X 1O 7 X t 8 where t IS the tune at the heat treatment .

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