Temperature dependence of the potential

Figure 11. Temperature dependence of the potential of the two-phase plateaus in the Li-Sb and Li-Bi systems [41].

It is of interest to consider the temperature dependence of the potential of an electrochemical cell. For an isothermal reaction [Equation (7.26)]... 

A further source of uncertainty in the calculation of the enthalpy of activation, which is unique to electrochemistry, relates to the temperature dependence of the potential of the reference electrode. Thus, to obtain we determine log i versus MT at a constant... 

Counsell, C. J. R., Emsley, J. W., Heaton, N. J., and Luckhurst, G. R., Orientational ordering in uniaxial liquid crystals the temperature dependence of the potential of mean torque for 4-n-alkyl-4 -cyanobiphenyls, MoZ. Phys., 54, 847-861 (1985). 

The reference value for the Gibbs energy of ion formation is the hydrogen ion for standard conditions. The temperature dependence of the potential gives the correspKmding value of the ion formation entropy. The reference value is again the hydrogen ion. 

Corresponding partial molar Gibbs energies for 500 °C were calculated using Eq. (3.33). From the temperature dependence of the potentials partial molar entropies were calculated using Eq. (3.36). Finally, partial molar enthalpies were obtained using Eq. (3.37). Values of the partial molar functions of Ag as a function of composition are summarized in Table 3.5. 

The temperature dependence of the potential of AglAg(I) reference electrode was found to be in the range from 0.54 to 0.57 mV Using this AglAg(I) reference... 

They should exhibit a small temperature dependency of the potential. 

Comparable information on the Li-Bi and li-Sb systems was also obtained, and their room-temperature potentials are also included in Table 14.4. The temperature dependence of the potentials of the different two-phase plateaus is shown in... 

The potential difference between the Ag/ AgCl electrode and the RHE is experimentally measured in a H2 atmosphere. Fig. 4 shows the temperature dependence of the potential difference. It is clearly seen that the difference is less dependent upon the reaction temperature in comparison to the individual RHE. A potential difference of around 80 mV as the temperature is increased from 20 to 150 °C. The temperature dependence of their potential difference could be linearly approximated as follows ... 

An inherent source of uncertainty in the calculation of the enthalpy of activation, unique to electrochemistry, is related to the temperature-dependence of the potential of the reference electrode. Thus, in order to obtain AH, we determine logj versus 1/T at a constant metal-solution potential difference, A< ). Now, at any given temperature, A<[) is constant, as long as the potential with respect to a given reference electrode is constant. When the temperature is changed, this is no longer true, since the metal-solution potential difference at the reference electrode has changed by an unknown amount. 

Although the rate of a cathodic reaction involving an HaO ion considerably depends on potential (a - 0.2), which does not correspond to the simplest version of an activationless process, the activation energy of this reaction for a constant potential with respect to saturated calomel electrode (s.c.e.) was found to be practically equal to zero[435]. Taking into account the temperature dependence of the potential of s.c.e. and the estimate of the temperature coefficient of the absolute potential drop, we find that these two factors nearly compensate each other, i.e. the ideal activation energy is equal to zero[438]. It should, however, be taken into account that these measurements correspond to a constant concentration of HaO ions in the bulk of solution rather than at the... 

Figure B3.6.3. Sketch of the coarse-grained description of a binary blend in contact with a wall, (a) Composition profile at the wall, (b) Effective interaction g(l) between the interface and the wall. The different potentials correspond to complete wettmg, a first-order wetting transition and the non-wet state (from above to below). In case of a second-order transition there is no double-well structure close to the transition, but g(l) exhibits a single minimum which moves to larger distances as the wetting transition temperature is approached from below, (c) Temperature dependence of the thickness / of the enriclnnent layer at the wall. The jump of the layer thickness indicates a first-order wetting transition. In the case of a conthuious transition the layer thickness would diverge continuously upon approaching from below.

In addition, the temperature dependence of the diffusion potentials and the temperature dependence of the reference electrode potential itself must be considered. Also, the temperature dependence of the solubility of metal salts is important in Eq. (2-29). For these reasons reference electrodes with constant salt concentration are sometimes preferred to those with saturated solutions. For practical reasons, reference electrodes are often situated outside the system under investigation at room temperature and connected with the medium via a salt bridge in which pressure and temperature differences can be neglected. This is the case for all data on potentials given in this handbook unless otherwise stated. 

The strains needed to initiate cracks in both the annealed and the sensitised materials were obtained using tapered slow-strain-rate specimens and the data are given in Fig. 8.36. As can be seen, there is little temperature dependence of the strain needed to initiate cracks in sensitised material whereas the annealed material was most susceptible to cracking at about 250°C. These results indicate the complicated response of Type 316 stainless steel to applied potential and demonstrate that, even though environmentally-assisted cracking may be generated by severe test methods, in this case the slow-strain-rate test, the results obtained must be used with care. For instance, the cracking of the annealed material at low potentials... 

The lithium-tinsystem has been investigated room temperature and the influence of temperature upon the composition dependence of the potential is shown in Fig. 7. It is seen that five constant potential plateaus are found at 25 °C. Their potentials are listed in Table 4. It was also shown that the kinetics on the longest pla-... 

The temperature dependence of the inner-layer properties has been studied by Vaartnou etal.m m over a wide interval, -0.15°C < T< 50°C. The inner-layer integral capacitance Kh a curves have been simulated using the Parsons308 and Damaskin672,673 models. The experimental Kj, T dependence has a minimum at T = 20°C. The influence of the potential drop in the metal phase has been taken into account. 

Temperature dependence, for potential of zero charge on silver in contact with solution, 76 Temperature effects on the potential of zero charge, 23 upon polymerization, 406 Temperature variation of the potential of zero charge (Frumkin and Demaskin), 28... 

Figure 2.3. Catalysis (0), classical promotion ( ), electrochemical promotion ( , ) and electrochemical promotion of a classically promoted (sodium doped) ( , ) Rh catalyst deposited on YSZ during NO reduction by CO in presence of gaseous 02.14 The Figure shows the temperature dependence of the catalytic rates and turnover frequencies of C02 (a) and N2 (b) formation under open-circuit (o.c.) conditions and upon application (via a potentiostat) of catalyst potential values, UWr, of+1 and -IV. Reprinted with permission from Elsevier Science.

Metals and semiconductors are electronic conductors in which an electric current is carried by delocalized electrons. A metallic conductor is an electronic conductor in which the electrical conductivity decreases as the temperature is raised. A semiconductor is an electronic conductor in which the electrical conductivity increases as the temperature is raised. In most cases, a metallic conductor has a much higher electrical conductivity than a semiconductor, but it is the temperature dependence of the conductivity that distinguishes the two types of conductors. An insulator does not conduct electricity. A superconductor is a solid that has zero resistance to an electric current. Some metals become superconductors at very low temperatures, at about 20 K or less, and some compounds also show superconductivity (see Box 5.2). High-temperature superconductors have enormous technological potential because they offer the prospect of more efficient power transmission and the generation of high magnetic fields for use in transport systems (Fig. 3.42). 

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