Thermal conductivity, alloys

Thermal energy is transported by two mechanisms in solids—electronic conduction and lattice or phonon conduction. An electrical analog for thermal conduction is shown in Fig. 2 [% The total thermal conductivity. A, is the sum of the electronic term and the lattice term. For pure metals and dilute alloys, thermal conduction is dominated by the electronic term, while for heavily alloyed metals, the phonon contribution is appreciable. 

Thermal Conductivity of Alloy Cast Irons Thermal Conductivity of Iron and Iron Alloys Thermal Conductivity of Aluminum and aluminum alloys Thermal Conductivity of Copper and Copper Alloys... 

Metal or alloy Thermal Conductivity near room temperature (cal / cm cm s °C) ... 

Alloy Thermal Conductivity, W/(m K) Thermal Expansion Gjefficient, 10 mm/(mm°C)... 

Copper/beryllium alloys (thermal conductivity 200 W/mK) and copper/cobalt/ beryllium alloys (225 W/mK) for nozzle casings and tips in applications up to aromid 280 C (see Figure 4.5a) (because of the mechanical strength of the alloy, which rapidly falls when the temperature rises). Treatment involving an overlayer of silicon carbide increases injection abrasion resistance with, for example, PA and GF. Nickel coating eliminates the influence of copper on the melt (electroless nickel plating) ... 

Copper alloys (thermal conductivity up to 350 W/mK) and aluminium alloys for heating jackets with embedded or wound heater element ... 

Titanium alloys (thermal conductivity around 7 W/mK) for sealing rings and insulating bushings for nozzle tips ... 

Pure silver has a brilliant white metallic luster. It is a little harder than gold and is very ductile and malleable, being exceeded only by gold and perhaps palladium. Pure silver has the highest electrical and thermal conductivity of all metals, and possesses the lowest contact resistance. It is stable in pure air and water, but tarnishes when exposed to ozone, hydrogen sulfide, or air containing sulfur. The alloys of silver are important. 

Silver s advantageous physical, chemical, electrical, and thermal conductive properties are used ia a variety of alloys. For example, (/) a 3.5% Ag,... 

Solders. In spite of the wide use and development of solders for millennia, as of the mid-1990s most principal solders are lead- or tin-based alloys to which a small amount of silver, zinc, antimony, bismuth, and indium or a combination thereof are added. The principal criterion for choosing a certain solder is its melting characteristics, ie, soHdus and Hquidus temperatures and the temperature spread or pasty range between them. Other criteria are mechanical properties such as strength and creep resistance, physical properties such as electrical and thermal conductivity, and corrosion resistance. 

A 99.5% Cu—0.5% Te alloy has been on the market for many years (78). The most widely used is alloy No. CA145 (number given by Copper Development Association, New York), nominally containing 0.5% tellurium and 0.008% phosphorous. The electrical conductivity of this alloy, in the aimealed state, is 90—98%, and the thermal conductivity 91.5—94.5% that of the tough-pitch grade of copper. The machinahility rating, 80—90, compares with 100 for free-cutting brass and 20 for pure copper. 

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. 

Electrical—Thermal Conductivities. Electrical conductivities of alloys (Table 5) are often expressed as a percentage relative to an International Annealed Copper Standard (lACS), ie, units of % lACS, where the value of 100 % lACS is assigned to pure copper having a measured resistivity value of 0.017241 Q mm /m. The measurement of resistivity and its conversion to % lACS is covered under ASTM B193 (8). 

Copper and its alloys also have relatively good thermal conductivity, which accounts for thek appHcation where heat removal is important, such as for heat sinks, condensers, and heat exchanger tubes (see Heatexchangetechnology). Thermal conductivity and electrical conductivity depend similarly on composition primarily because the conduction electrons carry some of the thermal energy. 

To a good approximation, thermal conductivity at room temperature is linearly related to electrical conductivity through the Wiedemann-Eran2 rule. This relationship is dependent on temperature, however, because the temperature variations of the thermal and the electrical conductivities are not the same. At temperatures above room temperature, thermal conductivity of pure copper decreases more slowly than does electrical conductivity. Eor many copper alloys the thermal conductivity increases, whereas electrical conductivity decreases with temperature above ambient. The relationship at room temperature between thermal and electrical conductivity for moderate to high conductivity alloys is illustrated in Eigure 5. 

---