Thermal conductivity metals Table

TABLE 2-374 Thermal-Conductivity-Temperature Table for Metals ... 

A satisfactory theory of metallic bonding must account for the characteristic properties of high electrical and thermal conductivity, metallic lustre, ductility and the complex magnetic properties of metals which imply the presence of unpaired electrons. The theory should also rationalise the enthalpies of atomisation A/f tom of metallic elemental substances. A/f tom is a measure of the cohesive energy within the solid, and we saw in Chapter 5 how it plays an important part in the thermochemistry of ions in solids and solutions. The atomisation enthalpies of elemental substances (metallic and nonmetallic) are collected in Table 7.1. There is a fair correlation between A/Z tom an(J physical properties such as hardness and melting/boiling points. 

The elements on the left side and in the center of the periodic table are metals. These elementary substances have the characteristic properties called metallic properties—high electric and thermal conductivity, metallic luster, the capability of being hammered or rolled into sheets (malleability) and of being drawn into wire (ductility). The elements on the right side of the periodic table are noninetals, the elementary substances not having metallic properties. 

In appUcations in which electrical conductivity is required, metals, copper, tungsten, molybdenum, and Kovar [12606-16-5] are the preferred chip-carrier materials. Metals have exceUent thermal conductivities. Tables 2 and 3 Ust the various materials used for substrates, along with their mechanical, electrical, and thermal properties. 

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 physical properties of bismuth, summarized ia Table 1, are characterized by a low melting poiat, a high density, and expansion on solidification. Thermochemical and thermodynamic data are summarized ia Table 2. The soHd metal floats on the Hquid metal as ice floating on water. GaUium and antimony are the only other metals that expand on solidification. Bismuth is the most diamagnetic of the metals, and it is a poor electrical conductor. The thermal conductivity of bismuth is lower than that of any other metal except mercury. 

Electrical conductivity is comparatively easy to measure, whereas thermal conductivity is not. Electrical conductivity values for the important cast alloys are Hsted in Table 2. Eigure 1 schematically shows the electrical conductivity of cast copper-base alloys compared with various other cast metals and alloys. The equation Y = 4.184 + 3.93a gives an approximation of thermal conductivity in relation to electrical conductivity, where Tis in W/(m-K) at 20°C and X is the % lACS at 20°C. 

Table 2.8 Thermal conductivities and heat capacities of some metals and oxides...

The other principal thermal properties of plastics which are relevant to design are thermal conductivity and coefficient of thermal expansion. Compared with most materials, plastics offer very low values of thermal conductivity, particularly if they are foamed. Fig. 1.10 shows comparisons between the thermal conductivity of a selection of metals, plastics and building materials. In contrast to their low conductivity, plastics have high coefficients of expansion when compared with metals. This is illustrated in Fig. 1.11 and Table 1.8 gives fuller information on the thermal properties of pl tics and metals. 

The solid metals all have the fee structure, like their predecessors in the periodic table, Ni, Pd and Pt, and they continue the trend of diminishing mp and bp. They are soft, and extremely malleable and ductile, gold more so than any other metal. One gram of gold can be beaten out into a sheet of 1.0m only 230 atoms thick (i.e. 1 cm to 18 m ) likewise Ig Au can be drawn into 165 m of wire of diameter 20/um. The electrical and thermal conductances of the... 

As a comparison, Table 4.1 lists the coefficients of thermal conductivity (at room temperature) for some metals employed in heat exchangers, together with some minerals commonly found in boiler deposits. 

Table 4.1 Coefficients of thermal conductivity for some heat-exchanger metals and boiler deposits...

Silver is a white, ductile metal occurring naturally in its pure form and in ores (USEPA 1980). Silver has the highest electrical and thermal conductivity of all metals. Some silver compounds are extremely photosensitive and are stable in air and water, except for tarnishing readily when exposed to sulfur compounds (Heyl et al. 1973). Metallic silver is insoluble in water, but many silver salts, such as silver nitrate, are soluble in water to more than 1220 g/L (Table 7.3). In natural environments, silver occurs primarily in the form of the sulfide or is intimately associated with other metal sulfides, especially fhose of lead, copper, iron, and gold, which are all essentially insoluble (USEPA 1980 USPHS 1990). Silver readily forms compounds with antimony, arsenic, selenium, and tellurium (Smith and Carson 1977). Silver has two stable isotopes ( ° Ag and ° Ag) and 20 radioisotopes none of the radioisotopes of silver occurs naturally, and the radioisotope with the longest physical half-life (253 days) is "° Ag. Several compounds of silver are potential explosion hazards silver oxalate decomposes explosively when heated silver acetylide (Ag2C2) is sensitive to detonation on contact and silver azide (AgN3) detonates spontaneously under certain conditions (Smith and Carson 1977). 

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