Boundary resistance

The equivalent circuit of a section of this SEI is presented in Fig. 13(b). It was recently found [123, 124] that at temperatures lower than 90 °C, the grain-boundary resistance of composite polymer electrolytes and composite solid electrolytes based on Lil-A Ojis many times larger than their ionic resistance. At 30 °C / GB is several orders of magnitude larger than (the ionic resistance) and for 100 pm-thick CPE foils or Lil-A Oj pellets it reaches [125] 105-106Qcm2 (depending on CPE composition). 

It seems probable that a fruitful approach to a simplified, general description of gas-liquid-particle operation can be based upon the film (or boundary-resistance) theory of transport processes in combination with theories of backmixing or axial diffusion. Most previously described models of gas-liquid-particle operation are of this type, and practically all experimental data reported in the literature are correlated in terms of such conventional chemical engineering concepts. In view of the so far rather limited success of more advanced concepts (such as those based on turbulence theory) for even the description of single-phase and two-phase chemical engineering systems, it appears unlikely that they should, in the near future, become of great practical importance in the description of the considerably more complex three-phase systems that are the subject of the present review. 

Experimental data show that the thermal boundary resistance between solids is poorly reproducible [52-53], The experiments in fact demonstrated that the physical and chemical condition of the interfaces is a critical factor determining the thermal boundary resistance. For this reason, the study of the contact resistance has been carried out on evaporated surfaces in order to reduce the irregularities and make Rc more reproducible. 

In 1941, Kapitza [54] reported his measurements of the temperature drop at the boundary between helium and a solid (bronze) when heat flows across the boundary. More than ten years later, Khalatnikov (1952) presented a model, an approximation to what is now known as the acoustic mismatch model , to explain that a thermal resistance Rk (thermal boundary resistance) occurs at boundaries with helium [55],... 

In 1987, Swartz [73] measured the thermal boundary resistance between metal films and the dielectric substrates onto which the films were deposited, in the range 0.6-200 K. A typical example is the measurement of the thermal contact resistance between indium and sapphire [72]. To minimize the dependence on surface irregularities, indium was vacuum deposited onto the sapphire rods the two surfaces were then pressed together and annealed. Analogous measurements have been carried out also with lead and aluminium. In all these cases, it has been clear that the contact resistance was strongly dependent on the sample preparation. In particular, obtained data suggest that the contact between the two materials was not complete. 

E.T. Swartz Solid-solid thermal boundary resistance, Ph.D. Thesis, Cornell University, Ithaca, New York (1987)... 

FIGURE 1.35 Contribution of the grain-boundary resistance (Rgb) to the total resistance (Rt) for samaria-doped ceria [115]. 

Transport of Ag+ across the AgI/Ag2S boundary has been studied experimentally as a function of A g (which was determined with the help of microsensors of the type Ag/AgBr) [H. Schmalzried, et al. (1992)]. From flux vs. driving force curves, the exchange flux j° has been evaluated and found to be ca. 1 A/cm2 at 260 °C. Introducing this high value of j° into Eqn. (10.41) and noting that the boundary resistance is... 

The boundary resistance R is dominated either by the space charge resistance in the current direction or the proper charge transfer resistance through the boundary core (Part I, Section VI.6). (Resistance effects due to laterally inhomogeneous contact conditions are discussed in Section III.9). 

Figure 35. Impedance spectra of the cell 02, Pt I SrTi031 SrTi031 Pt, 02 as function of d.c. bias. Electrodes are parallel to the bicrystal boundary (Z5 tilt grain boundary, iron content 2 x 1018 cnT3). Both bulk and boundary resistances are predominantly electronic resistances.222 Reprinted from I. Denk, J. Claus and J. Maier, J. Electrochem. Soc., 144 (1997) 3526-3536. Copyright 1997 with permission from The Electrochemical Society.

Rgb, c grain boundary resistance between two large contact electrodes... 

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