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Tham khảo tài liệu 'carbon materials for advanced technologies part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 190 5.3 Physical Properties Typical physical properties of our CFCMS monoliths are given in Table 3. The exact value of a particular property is dependent upon the fabrication route composition density etc. Consequently property ranges are given in Table 3 rather than absolute values. Table 3. Physical properties of CFCMS monoliths developed by ORNL UKCAER Property Value Density g cm3 0 2 - 0.4 0 4-1 0 Compressive strength MPa 1-3 Electrical resistivity mii cm 130 @ density of 0 25 g cm3 Thermal conductivity W m K 0.14 @ density of 0.25 g cm3 hot-pressed density range The effect of fiber binder ratio on the density and strength of the isotropic pitch derived fiber monoliths was exammed 23 in a study m which the ratio of P200 fibers was increased by factors of 2 3 or 4 from the standard fiber binder ratio. The density was seen to decrease from -0.38 g cm3 for the standard formulation to -0.36 g cm3 for the 4X formulation. A slight reduction in compressive strength from -1.9 to -1.7 MPa was observed to accompany the density reduction although the scatter in the data made it impossible to develop a density-strength correlation. During activation the carbon IS selectively gasified resulting m a mass loss m the monolith. The compressive strength o . IS degraded by this mass loss and follows the relationship 19 23 oc 1.843exp -0.01323x 9 where X is the fractional weight loss or bum-off. The electrical behavior of CFCMS IS shown in Fig. 17 a . The current-voltage relationship is linear and the electrical resistivity of the monolith in Fig. 17 a 2.5 cm in diameter and 7.5 cm in length was 130 mil cm 23 24 The resistivity of the monohth is considerably greater than that of the carbon fibers which according to the manufacturer s product literature IS 4-6 míỉ-crn. The poorer electrical conductivity of the monolith can be attributed to the large electrical resistance associated with the fiber bmder interface. A consequence of the passage of an electric current through the .
