Aluminum thermal conductivity

Alumina, or aluminum oxide [1344-28-17, has a thermal conductivity 20 times higher than that of most oxides (5). The flexural strength of commercial high alumina ceramics is two to four times greater than those of most oxide ceramics. The drawbacks of alumina ceramics are their relatively high thermal expansion compared to the chip material (siUcon) and their moderately high dielectric constant. 

Although beryllium oxide [1304-56-9] is in many ways superior to most commonly used alumina-based ceramics, the principal drawback of beryUia-based ceramics is their toxicity thus they should be handled with care. The thermal conductivity of beryUia is roughly about 10 times that of commonly used alumina-based materials (5). BeryUia [1304-56-9] has a lower dielectric constant, a lower coefficient of thermal expansion, and slightly less strength than alumina. Aluminum nitride materials have begun to appear as alternatives to beryUia. Aluminum nitride [24304-00-5] has a thermal conductivity comparable to that of beryUia, but deteriorates less with temperature the thermal conductivity of aluminum nitride can, theoreticaUy, be raised to over 300 W/(m-K) (6). The dielectric constant of aluminum nitride is comparable to that of alumina, but the coefficient of thermal expansion is lower. 

Cross-linked polyester composites have a relatively low coefficient of thermal conductivity that can provide beneficial property retention in thick laminates at high temperatures as well as remove the need for secondary insulation. The coefficient of thermal expansion of glass-reinforced composites is similar to aluminum but higher than most common metals. 

BeryUia ceramics offer the advantages of a unique combination of high thermal conductivity and heat capacity with high electrical resistivity (9). Thermal conductivity equals that of most metals at room temperature, beryUia has a thermal conductivity above that of pure aluminum and 75% that of copper. Properties Ulustrating the utUity of beryUia ceramics are shown in Table 2. 

The high electrical and thermal conductivities and corrosion resistance of copper combined with its workabiUty give the metal its very wide range of commercial appHcations. Unlike most metals, which are alloyed with other elements to enhance properties, for example, alloy steel and aluminum, copper is primarily used in its pure, unalloyed form. 

Copper is primarily alloyed to increase strength, however, electrical and thermal conductivities, corrosion resistance, formabiUty, and color are also strongly affected by alloying. Elements typically added to copper are 2inc, tin, nickel, iron, aluminum, siUcon, chromium, and beryUium. 

Aluminum and Alloys Aluminum and its alloys are made in practically all the forms in which metals are produced, including castings. Thermal conductivity of aluminum is 60 percent of that of pure copper, and unalloyed aluminum is used in many heat-transfer applications. Its high electrical conductivity makes aluminum popular in electrical apphcations. Aluminum is one of the most workable of metals, and it is usually joined by inert-gas-shielded arc-welding techniques. 

Copper and Alloys Copper and its alloys are widely used in chemical processing, particulany when heat and electrical conductivity are important fac tors. The thermal conductivity of copper is twice that of aluminum and 90 percent that of silver. A large number of cop-... 

Ting, J.M. and Lake, M.L., Vapor grown carbon fiber reinforced aluminum composites with very high thermal conductivity J. Mat. Res., 1995, 10(2), 247 250. 

The outstanding properties of copper-base materials are high electrical and thermal conductivity, good durabihty in mildly corrosive chemical environments and excellent ductility for forming complex shapes. As a relatively weak material, copper is often alloyed with zinc (brasses), tin (bronzes), aluminum and nickel to improve its mechanical properties and corrosion resistance. 

This is used widely for chemical and process plant applications where its resistance to corrosion and high thermal conductivity are desirable characteristics. The strength of aluminum can be increased by cold working, as shown in Table 3.29. 

Aluminum plates ASTM TllO of thermal conductivity 200 W m" K" . 

High thermal conductivity. Heat is carried through metals by collisions between electrons, which occur frequently. Saucepans used for cooking commonly contain aluminum, copper, or stainless steel their handles are made of a nonmetallic material that is a good thermal insulator. 

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