M L. Greene et al. / Carbon 40 (2002)1217-1226 05 different residence times reported imply that different production rates can be expected for the manufacture of carbon fibers with similar properties. For example, by graphitizing this precursor fiber at 3000C for 5.4s (K= 290 WmK ), fiber production can be increased by a factor of approximately six compared to graphitize- tion at 2700C(K=266Wm K ) and by a factor of 670 times compared to graphitization at 2400C (K=270 W The relative energy costs to produce (graphitize) an -o- Fiber A arbitrary unit length of fiber under these different con- -- Fiber B ditions can be estimated from the experimental data given -o- Fiber C in Table 2. The product of the furnace voltage and current and the furnace residence time VX10'XI(s)/3600 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 S/h, is the electrical energy consumption(in kwh) required to process a 3.5 inch (-0.09 m, the furnace hot zone) length of fiber in this laboratory furnace. The calculations 甲中 4. Carbon fiber density as a function of the degree of hitization for fibers heat treated at 2700 C for 2400, 2700, and 3000C may be used to estimate the relative energy costs for fiber production, ignoring other operating costs, such as cooling water and furnace mainte nance. This simple analysis suggests, perhaps contrary to expectations, that the best approach to reduce production costs does not lie in furnace operation at lower tempera greatly reduced residence times and higher throughput 7.00 S@ 00 We have investigated the effects of graphitization time and temperature on the properties of carbon fibers prepared from different mesophase pitch precursors. By using a 0500600.70 continuous mode processing paradigm, it was possible to investigate the effects of very short(sI s)residence times at elevated temperatures on the properties of the carbon Fig. 5. Electrical resistivity as a function of the degree of fibers. Significant variations in density, electrical resistin graphitization for fibers heat treated at 2700C ity, and degree of graphitization were all observed, as were residual effects of precursor type on each of these prop- from the furnace volt and amp requirements. Since fibers erties. The rapid development of desirable material prop- with identical thermal conductivities were not erties was consistent with the known thermal activation nilar conductivities( that ranged fro energy associated with graphitization [9]. Irrespective of 290Wm were used. The residence precursor type, significant densification and decreases in temperatures required to produce carbon fibers with these electrical resistivity were observed for all fibers at a properties(from precursor A)are shown in Table 2. The residence time of only 0.7 s. Corresponding thermal Table 2 290 Wm-i wergy requirements for the manufacture of carbon fibers from precursor fiber A with thermal conductivities between 266 and Heat treatment umace power Residence gy requirements urrent/voltage for production of 0.09 m of fiber (kwh) 165017.5 12.38 1900/9.5 3000 2150/11.1 5.3M.L. Greene et al. / Carbon 40 (2002) 1217 –1226 1225 different residence times reported imply that different production rates can be expected for the manufacture of carbon fibers with similar properties. For example, by graphitizing this precursor fiber at 3000 8C for 5.4 s 21 21 (k 5 290 W m K ), fiber production can be increased by a factor of approximately six compared to graphitiza- 21 21 tion at 2700 8C (k 5 266 W m K ), and by a factor of 670 times compared to graphitization at 2400 8C (k 5 270 21 21 W m K ). The relative energy costs to produce (graphitize) an arbitrary unit length of fiber under these different con￾ditions can be estimated from the experimental data given in Table 2. The product of the furnace voltage and current 23 and the furnace residence time, VI 3 10 3 t (s)/3600 s/h, is the electrical energy consumption (in kWh) required to process a 3.5 inch (|0.09 m; the furnace hot zone) length of fiber in this laboratory furnace. The calculations Fig. 4. Carbon fiber density as a function of the degree of for 2400, 2700, and 3000 8C may be used to estimate the graphitization for fibers heat treated at 2700 8C. relative energy costs for fiber production, ignoring other operating costs, such as cooling water and furnace mainte￾nance. This simple analysis suggests, perhaps contrary to expectations, that the best approach to reduce production costs does not lie in furnace operation at lower tempera￾ture, but furnace operation at higher temperature with greatly reduced residence times and higher throughput rates. 4. Conclusions We have investigated the effects of graphitization time and temperature on the properties of carbon fibers prepared from different mesophase pitch precursors. By using a continuous mode processing paradigm, it was possible to investigate the effects of very short (#1 s) residence times at elevated temperatures on the properties of the carbon Fig. 5. Electrical resistivity as a function of the degree of fibers. Significant variations in density, electrical resistiv￾graphitization for fibers heat treated at 2700 8C. ity, and degree of graphitization were all observed, as were residual effects of precursor type on each of these prop￾from the furnace volt and amp requirements. Since fibers erties. The rapid development of desirable material prop￾with identical thermal conductivities were not available, erties was consistent with the known thermal activation fibers with similar conductivities (that ranged from 266 to energy associated with graphitization [9]. Irrespective of 21 21 290 W m K ) were used. The residence times and precursor type, significant densification and decreases in temperatures required to produce carbon fibers with these electrical resistivity were observed for all fibers at a properties (from precursor A) are shown in Table 2. The residence time of only 0.7 s. Corresponding thermal Table 2 Analysis of energy requirements for the manufacture of carbon fibers from precursor fiber A with thermal conductivities between 266 and 21 21 290 W m K Heat treatment Furnace power Residence Thermal Energy requirements temp. current/voltage time conductivity for production of 21 21 (8C) (A/V) (s) (W m K ) 0.09 m of fiber (kWh) 2400 1650/7.5 3600 270 12.38 2700 1900/9.5 33.1 266 0.17 3000 2150/11.1 5.3 290 0.04