Electronic heating

Textile uses are a relatively stable area and consist of the lamination of polyester foams to textile products, usually by flame lamination or electronic heat sealing techniques. Flexible or semirigid foams are used in engineered packaging in the form of special slab material. Flexible foams are also used to make filters (reticulated foam), sponges, scmbbers, fabric softener carriers, squeegees, paint appHcators, and directly appHed foam carpet backing. 

Composites fabricated with the smaller floating catalyst fiber are most likely to be used for applications where near-isotropic orientation is favored. Such isotropic properties would be acceptable in carbon/carbon composites for pistons, brake pads, and heat sink applications, and the low cost of fiber synthesis could permit these price-sensitive apphcations to be developed economically. A random orientation of fibers will give a balance of thermal properties in all axes, which can be important in brake and electronic heat sink applications. 

It is observed that a decrease of the pressure (from p = 250 to 150 mTorr) mainly results in a decrease of the densities due to higher transport losses, and in an extension of the sheath due to a higher ion mobility. The electric field and the electron heating diminish slightly for lower pressure. The electron and Hj density, and consequently the HJ outflux, are much more influenced by the pressure decrease than the SiH+ and SiH ion densities and the SiH+ outflux. 

Thus, even at temperatures well above absolute zero, the electrons are essentially all in the lowest possible energy states. As a result, the electronic heat capacity at constant volume, which equals d tot/dr, is small at ordinary temperatures and approaches zero at low temperatures. 

In Table 12.1, the contributions to the heat capacity Csp of the addendum are shown specific heat data references are reported in ref. [20], A factor 1/3 was attributed to the heat capacity contribution of the elements linking the crystal to the frame [15], Note that the electron heat capacity of the NTD Ge 31 sensor was derived from the electron... 

Table 8.2. Debye temperature ( p in K) and electronic heat capacity coefficient (see Section 8.4) (yin mJ K-1 mol-1) of the elements.

Using this simple argument, the electronic heat capacity, CE, of a free electron gas is... 

The electronic heat capacity thus varies linearly with temperature and is often represented as... 

The electronic heat capacity for the free electron model is a linear function of temperature only for T Tp = p / kp. Nevertheless, the Fermi temperature Tp is of the order of 105 K and eq. (8.46) holds for most practical purposes. The population of the electronic states at different temperatures as well as the variation of the electronic heat capacity with temperature for a free electron gas is shown in Figure 8.20. Complete excitation is only expected at very high temperatures, T>Tp. Here the limiting value for a gas of structureless mass points 3/2/ is approached. 

Figure 8.22 Variation of the electronic heat capacity coefficient with composition for the alloys Rh-Pdand Pd-Ag [17]. Solid and dotted lines represent the electronic DoS for the 5s and 4d bands, respectively.

The electronic heat capacity naturally has a pronounced effect on the energetics of insulator-metal transitions and the entropy of a first-order transition between an insulating phase with y = 0 and a metallic phase with y= ymet at Ttrs is in the first approximation Ains met5m = 7met7trs. 

Collectively, the inherent defects outlined above allow mechanisms by which electrons, heat and other substances can penetrate and move through a lattice, thereby enhancing the reactivity of pyrotechnic compositions. 

Recall from Figure 1.15 that metals have free electrons in what is called the valence band and have empty orbitals forming what is called the conduction band. In Chapter 6, we will see how this electronic structure contributes to the electrical conductivity of a metallic material. It turns out that these same electronic configurations can be responsible for thermal as well as electrical conduction. When electrons act as the thermal energy carriers, they contribute an electronic heat capacity, C e, that is proportional to both the number of valence electrons per unit volume, n, and the absolute temperature, T ... 

It can be shown that the conduction electron net spin susceptibility is proportional to the temperature coefficient of the electronic heat capacity [cf. Eq. (4.42)] and, for free electrons in a single band, having the Fermi energy much lower than any band gap, is given by... 

We can now see why the experimental electronic heat capacity did not obey the classical result of fcB per electron. Following Pauli s exclusion principle, the electrons can be excited into only the unoccupied states above the Fermi energy. Therefore, only those electrons within approximately kBT of F will have enough thermal energy to be excited. Since these constitute about a fraction kBT/EF of the total number of electrons we expect the classical heat capacity of fkBN to be reduced to the approximate value... 

K, so that the electronic heat capacity at room temperature is dramatically reduced compared to the classical prediction for a free-electron gas. 

Fig. 7.7 A comparison of the theoretical and experimental 4d and 5d electronic heat capacities. The theoretical values were obtained directly from eqn (7.28) and Fig. 7.6, neglecting any changes in the density of states due to bandwidth variation within the 4d and 5d series.

Solid HjPMo o reduced by H2 at a lower temperature shows a very weak ESR signal intensity of Mo5 +, probably because most of the Mo5+ ions are not detectable due to the rapid hopping of electrons. Heat treatment, which eliminates oxide ions from the heteropoly anion, leads to development of the Mo5 + signal, indicating the localization of electrons (101, 102). Early reports of ESR spectra of reduced PMo C o are likely due to these species. Several different species are observed in highly reduced samples. 

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