Thermal Conductivities of Selected Materials

C. Y. Ho, R. W. Powell, and P. E. Liley, Standard Reference Data on the Thermal Conductivity of Selected Materials, part 3, final report NBS-NSR05 Contr. CST-1346, Purdue University, Lafayette, Ind., Sept. 1968. 

Table 13.2 contains a listing of the thermal conductivities of selected materials. 

From Shackelford, J.F. and Alexander, W., CRC Handbook of Materials Science and Engineering, CRC Press, Boca Raton, FL, 2001, pp. 384-385. Data from Ho, C.Y., Powell, R.W., and Liley, P.E., Thermal Conductivity of Selected Materials, NSRDS-NBS—8 and NSRD—NBS-16, Part 2, National Standard Reference Data System-National Bureau of Standards, Part 1, 1966 Part 2, 1968. 

Table 13.3 Approximate values for thermal conductivities of selected ceramic materials...

The thermal conductivity of solids and fluids varies with temperature, and representative values should be selected for the temperature range of interest (Rg. 24.2). Measured thermal conductivity of porous materials is a combination of conduction and convection occurring within the pore fluids. The change in measured... 

By the same token, as the ambient temperature increases, the number of collisions increases, and the thermal conductivity of most materials decreases. A plot of the thermal conductivity versus temperature for several materials is shown in Fig. 4.9 One material not plotted in this graph is diamond. The thermal conductivity of diamond varies widely with composition and the method of preparation, and is much higher than those materials listed. Diamond will be discussed in detail in a later section. Selected data from Fig. 4.9 was analyzed and extrapolated into binomial equations that quantitatively describe the thermal conductivity versus temperature relationship. The data are summarized in Table 4.3. 

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. 

GP 1[ [R 1[ A change from aluminum to platinum as construction material results in reduced micro-reactor performance concerning oxidation of ammonia, decreasing N2O selectivity by 20% [28]. This is explained by the lower thermal conductivity of platinum, which causes larger temperature differences (hot spots) within the micro channels, i.e. at the catalyst site, e.g. due to insufficient heat removal from the channels or also by non-uniform temperature spread of the furnace heating. 

A typical measurement was performed as follows. The feeder was lowered into the crucible and the sample solution (seawater) was allowed to flow under an inert atmosphere with the suction on. A constant current was applied for a predetermined time. When the pre-electrolysis was over, the flow was changed from the sample to the ammonium acetate washing solution, while the deposited metals were maintained under cathodic protection. Ammonium acetate was selected for its low decomposition temperature, and a 0.2 ml 1 1 concentration was used to ensure sufficient conductivity. At this point the feeder tip was raised to the highest position and the usual steps for an electrothermal atomic absorption spectrometry measurement were followed drying for 30 s at 900 C, ashing for 30 s at 700 °C, and atomization for 8 s at 1700 °C, with measurement at 283.3 nm. The baseline increases smoothly with time as a consequence of an upward lift of the crucible caused by thermal expansion of the material. 

Of the three general categories of transport processes, heat transport gets the most attention for several reasons. First, unlike momentum transfer, it occurs in both the liquid and solid states of a material. Second, it is important not only in the processing and production of materials, but in their application and use. Ultimately, the thermal properties of a material may be the most influential design parameters in selecting a material for a specific application. In the description of heat transport properties, let us limit ourselves to conduction as the primary means of transfer, while recognizing that for some processes, convection or radiation may play a more important role. Finally, we will limit the discussion here to theoretical and empirical correlations and trends in heat transport properties. Tabulated values of thermal conductivities for a variety of materials can be found in Appendix 5. 

Thermal conductivity Ability of a material to conduct or transfer heat. Dimension W/cm K (Watt per centimeter Kelvin). For values of selected materials, see Section 9.1.1.4. 

The high thermal conductivity of SiC may turn out to facilitate new process designs for highly exothermic or endothermic reactions in which heat transfer must be carefully controlled. Furthermore, because the SiC can be formed from carbon in any shape or porosity due to the shape memory effect , a catalyst with good activity and selectivity in a particular reaction can be formed closer to a commercially acceptable form without an extensive development project. For all these reasons it is expected that research will accelerate rapidly in order to understand, improve and develop this novel material. 

---