TAILIEUCHUNG - Carbon Materials for Advanced Technologies Part 7

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 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 4-1 0 Compressive strength MPa 1-3 Electrical resistivity mii cm 130 @ density of 0 25 g cm3 Thermal conductivity W m K @ density of 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 g cm3 for the standard formulation to g cm3 for the 4X formulation. A slight reduction in compressive strength from to 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 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 cm in diameter and 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 .

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