Interfacial resistance, determination

The deviation from a semicircle on the right provides information. One can obtain from its slope the value of i interface. There are two values in the real axis at which the plot (or its extrapolation) intercepts with the axis. The one at the high-frequency side of Fig. 7.47 turns out to give the solution resistance the low-frequency one gives the solution resistance together with the interfacial resistance (which can be determined later). The maximum of the semicircle must be associated with a certain value of and this value is 1 / DL intcrfaee. One can see that Cole-Cole plots provide a lot of information. 

Interfacial mass transfer of trace gases into aqueous pnase is investigated in a UV absorption-stop flow apparatus. For the first time, the mass accommodation coefficients are determined for O3 (5.3x10" ) and for SO2 (>2x10 2) The results are incorporated into a simple model considering the coupled interfacial mass transfer and aqueous chemistry in cloud drops. It is shown that dissolution of O3 into a drop is fast compared with its subsequent oxidation of dissolved S02 In addition, the conversion rate of S(IV) to S(VI) in aqueous drops by ozone reactions is not limited by interfacial resistance. 

In the second model, each filament carried the same fraction I/Ic of its critical current, and for this case hystersis loss depends upon I and higher powers of I/Ic. Whether or not an interfacial resistance exists at the filaments may be determined from the transverse conductivity, (7j, of the composite. An approximate expression for this conductivity, in the absence of interfacial resistance, is [ ]... 

It is possible in principle to break down the vertical resistances into as many regions as are desired. For example, it may be desirable to consider stratified layers of lakes such as the epilimnion or hypolimnion separately. An interfacial resistance could be invoked, but at the present state of knowledge its value is not accurately determinable. Liss and co-workers (77-/9) have recently shown that this effect tends to be most significant for gas-phase resistance-controlling systems. 

There is a temptation to multiply the resistivity by the half cell potential and present this as the corrosion current or rate. This is incorrect. The corrosion rate is usually determined by the interfacial resistance between the steel and the concrete, not the bulk concrete resistivity. The potential measured by a half cell is not the potential at the steel surface that drives the corrosion cell. Correlations between resistivity, half cell potential and corrosion rate may be found in similar samples in similar conditions in the laboratory but in the variability of the real ivorld any correlation is fortuitous. 

Thermal Conductivity. Conductivity measurements were made of tape candidates to determine whether or not they would satisfy the cable design requirements listed in Table I. The measurements were made for BNL by Jelinek of BCL using the apparatus illustrated in Fig. 7. The method was a modified steady-state conductivity technique where a temperature gradient was established between two copper plates separated by four layers of polymeric film. (Multilayer measurements were always made to approximate the series interfacial resistivity that would be present in lapped cable configurations.) One plate was attached to a controlled heat sink and a measured quantity of heat was added to the other plate by means of an electric heater. With the use of a liquid helium throttling dewar, the ambient temperature could be controlled to within 1 K. (Complete details of the conductivity measurement method are included in Appendix II of this paper.)... 

The order of the interfacial resistance of the SEI on lithium covered by native fdm in ImolL LiX/PC solutions was determined by Aurbach and Zaban [20 25] from Nyquist plots. For the different salts, the order of was LiPF LiBp4 > LiS03CF3 LiAsFg > LiNCSOj CF3)2 > LiBr, LiC104 [20]. The values for LiPF /PC and LiN(S02CF3)2/PC were about 800 and 23Qcm, respectively. The resistivity of the film was found to be directly proportional to the salt concentration, and the presence of CO2 in solutions considerably reduced the interfacial resistance. 

In Figure 5.11, we described the interplay between electron transfer and mass transfer and how both are required to observe a current from a G. sulfurreducens biofilm. It is difficult to determine the role of mass transfer in biofilms simply from cyclic voltammograms usually, certain electrochemical setups are required to investigate mass transfer via electrochemical methods. In our case, we used a combination of EIS and RDEs to study electron transfer and diffusional processes in G. sulfurreducens biofilms respiring on electrodes [50]. We tested the hypothesis that the RDE can be used as an electrochemical tool that controls diffusional processes when EABs are studied. We determined the film resistance, film capacitance, interfacial resistance, interfacial capacitance, and pseudocapacitance of G. sulfurreducens biofilms as shown in Eigure 5.23. The details of the calculations and experimental procedures are given in the literature [50],... 

In principle, any one of these could be the rate-determining step (r.d.s.). However, it was foimd, by the use of a variety of experimental techniques, that ionic migration through the SEI is the rate-determining step for many systems. In addition, it was found that the rate of nucleation of the metal deposit is affected by the interfacial resistance. This transport process is a key factor in the operation of non-aqueous SEI batteries. 

Impedimetric biosensors for whole cells have demonstrated two mechanisms in response. Considering the overall impedance of a biological cell as including the resistance and the capacitance of the cell membrane, the presence of intact cell membranes on the electrodes would contribute to the sensor s capacitance and/or resistance, and would determine the current flow and thus the sensor signal. However, when cells are attached to the electrode surface, they are usually separated by a gap of 10 -20 run (up to several hundred nanometers). This aqueous gap between the cell membrane and the electrode surface prevents a direct influence of the cell membrane capacitance on the impedance of the electrode. Therefore, the cell membrane resistances of these attached cells act as resistors on the IME surface and affect the interfacial resistance. The interfacial resistance is best represented as electron transfer resistance in the presence of a redox probe (e. g., [Fe(CN)6] / ) and can be sensitively monitored. Figure 10a presents a representative group of Nyquist plots of the impedance spectroscopic responses of an IME-based biosensor to different cell numbers of E. coli 0157 H7 at 10a antibodies, 10b 4.36 x 10 CFTJ/ml,... 

There are three major points to be stressed. First, the Hquid/ceUular interface may contribute significantly to mass transfer limitations. Second, when mass transfer Hmitations exist the intrinsic biokinetics parameters cannot be determined. In biochemical reactor design, intrinsic parameters are essential to model adequately the system performance. Furthermore, without an understanding of the intrinsic biokinetics, one cannot accurately study transport mechanisms across biological membranes. The determination of passive or active transport across membranes is strongly affected by the extent of the Hquid/ceUular interfacial resistance. 

U02(N03)2 TBP complexes and evaluating the individual interfacial resistances. Likewise, Chaudry et al (35) determined the influence of experimental variables, such as the effect of the nitric acid concentration in the feed solution, the TBP concentration in the kerosene membrane, the stripping agent (sodium nitrate, ammonium carbonate) concentration, and the temperature on the uranyl flux. They elucidated the mechanism of uranium transport and the stoichiometry of the transported species. A novel phenomenon, the so-called solubility mechanism was experimentally observed and theoretically explained (36) for uranium transport from a feed solution of 0.01 M uranium in nitric acid at pH 0.7-1.5 through a liquid membrane of 0-100 % of DEHPA in the hydrocarbon solvent Shellsol 2046... 

Membrane-electrode interfacial compatibility is reflected by the interfacial resistance value. The measurement requires the interfacial resistance to be extracted from the total resistance of the fuel cell, especially that of the membrane. One way of determining the nonmembrane part of the cell resistance is from the intercept of a ceU resistance plot as a function of monbrane thickness (Fig. 8). The difference between the observed nonmembrane resistance and the electronic resistance of a single cell is the interfacial resistance. From the data shown in Fig. 8, it follows that... 

The penetration theory has been used to calculate the rate of mass transfer across an interface for conditions where the concentration CAi of solute A in the interfacial layers (y = 0) remained constant throughout the process. When there is no resistance to mass transfer in the other phase, for instance when this consists of pure solute A, there will be no concentration gradient in that phase and the composition at the interface will therefore at all Limes lie the same as the bulk composition. Since the composition of the interfacial layers of the penetration phase is determined by the phase equilibrium relationship, it, too. will remain constant anil the conditions necessary for the penetration theory to apply will hold. If, however, the other phase offers a significant resistance to transfer this condition will not, in general, be fulfilled. 

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