Carbon ber composites can be used to increase the

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Unformatted text preview: current can be conducted by the surrounding copper, which also effectively removes the heat. Figure 14.6–1 shows a close-up of a multifilament superconducting cable. Recently, superconducting materials containing copper, yttrium, barium, and oxygen have been developed with critical temperatures greater than 100 K (see Sections 10.2.9 and 12.9). This will allow superconducting behavior at liquid nitrogen temperatures. The wires made from these materials will also be composites. An unrefined example of such a wire is shown in Figure 14.6–2. Electronic package casings are another example of composites used in the electronics industry. With the revolution in integrated chip manufacturing, more-active devices are packaged in smaller and lighter packages (see Section 10.3.5). One factor that limits the density of active devices is the ability to rapidly remove heat. A 10 C rise in temperature can reduce a chip’s lifetime by a factor of 2.5 to 3. Thus, thermal conductivity of the casing | e-Text Main Menu | Textbook Table of Contents pg605 [R] G1 7-27060 / IRWIN / Schaffer iq Chapter 14 Composite Materials FIGURE 14.6–1 Close-up view of Nb-Ti multifilamentary superconducting cable. The superconducting Nb-Ti filaments are surrounded by a copper matrix. (Source: K. K. Chawla, Composites Material Science and Engineering, 1987, Springer-Verlag, New York. Reprinted with permission of Springer-Verlag, New York Publishers.) FIGURE 14.6–2 A picture of a Y-Ba-Cu-O superconducting composite wire fabricated by chemical vapor deposition of YBa2 Cu3 O7 x (light surface layer) onto a multifilament Al2 O3 fiber (darker core). (Source: Reprinted with permission from W. J. Lackey). | v v material (without the associated high electrical conductivity of metals) becomes critical. Carbon fiber composites can be used to increase the thermal conductivity of package materials. An additional design option to reduce thermal fatigue problems is tailoring the coefficient of thermal expansion of the composite casing to match that of the silicon. Thus, when silicon chips are mounted on the casing, the thermal stresses are low, extending the life of the package. Package casings are commonly made from either an iron-copper alloy called Kovar or a silicon carbide particulate-reinforced aluminum alloy. The composite casing has superior heat transfer characteristics and represents a significant weight reduction. | e-Text Main Menu | Textbook Table of Contents 13.01.98 plm QC3 rps MP 605 pg606 [V] G2 7-27060 / IRWIN / Schaffer Part III 13.01.98 plm QC2 rps MP Properties FIGURE 14.6–3 A picture of a eutectic in situ composite used as a low-voltage field emitter array cathode. Reprinted with permission from D. N. Hill.) (Source: Figure 14.6–3 shows a low-voltage field emitter array cathode for potential use in microwave amplifiers. It is made from a directionally solidified oxide-metal eutectic composite consisting of parallel arrays of continuous fibers of refractory metals such as W and Mo in an oxide matrix. The fibers range from 0.3 to 1 m in di...
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This note was uploaded on 02/25/2013 for the course PHYS 2202 taught by Professor Sowell during the Spring '10 term at Georgia Institute of Technology.

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