Electrical resistivity measurements

The electrical-resistance measurement has nothing to do with the electrochemistry of the corrosion reaction. It merely measures a bulk property that is dependent upon the specimens cross-section area. Commercial instruments are available (Fig. 28-5). 

Electrical resistivity measurements have also been performed on individual SWCNT and on bundles of SWCNT. In the latter case thermoelectric power measurements have been carried out very recently (cf. Sec. 5.3.2). 

In conclusion, wc have shown the interesting information which one can get from electrical resistivity measurements on SWCNT and MWCNT and the exciting applications which can be derived. MWCNTs behave as an ultimate carbon fibre revealing specific 2D quantum transport features at low temperatures weak localisation and universal conductance fluctuations. SWCNTs behave as pure quantum wires which, if limited in length, reduce to quantum dots. Thus, each type of CNT has its own features which are strongly dependent on the dimensionality of the electronic gas. We have also briefly discussed the very recent experimental results obtained on the thermopower of SWCNT bundles and the effect of intercalation on the electrical resistivity of these systems. 

Shown in Fig. 4a is the temperature dependence of the relaxation time obtained from the isothermal electrical resistivity measurement for Ni Pt performed by Dahmani et al [31. A prominent feature is the appearance of slowing down phenomenon near transition temperature. As is shown in Fig. 4b [32], our PPM calculation is able to reproduce similar phenomenon, although the present study is attempted to LIq ordered phase for which the transition temperature, T]., is 1.89. One can confirm that the relaxation time, r, increases as approaching to l/T). 0.52. This has been explained as the insufficiency of the thermodynamic driving force near the transition temperature in the following manner. 

Relative change of electrical resistivity measured for Ag-3.5at%Al system at aging period with falling and rising temperatures [38]. ... 

W. Pfeiler, Investigation of short-tange order by electrical resistivity measurement, Acta metall 36 2417... 

Willemer, H. Determination of freezing and freeze-drying data based on light optical micrographs and electrical resistance measurement, p. 9-15, 7lh International Freeze Drying Course, Lyon 1997... 

Electrical Resistance and Percent Llgnt Transmittance. Low frequency electrical resistance measurements were made on a conductivity bridge (Model RC-18, Industrial Instrument, Cedar Grove, N.J.) at a line frequency of 1 KC. Beckman conductivity cell with cell constant 1.0 cm was used. The percent transmission was also monitored for each of the mixtures at 490 nm (Spectronlc 20, Bausch Lomb Co., Rochester, N.Y.). 

Figure 1. Circuit for electrical resistance measurement of foils.

Several charge-transfer complexes of HMTTeF with TeNQs, p-quinone and other accepting re-acceptors have been prepared and electrical resistivities measured with compaction samples. 

During the entire coating process the coating thickness is continuously monitored with an optical measuring system or by means of electrical resistance measurement devices. The measured values are compared with the coating thickness setpoints in the system and the evaporator power is thus automatically controlled. 

On the other hand, some of Suhrmann s electrical resistance measurements on nickel and platinum films and Eischens observations, of the effect of Hj on the infrared spectrum of chemisorbed CO on platinum, referred to earlier, suggest electron-transfer from hydrogen to the metal, i.e., adsorption of positive ions. 

The non-stoichiometry <5 of Cu2- O has been extensively studied by various methods such as chemical analysis of a quenched sample, thermogravimetry, electrical resistivity measurement, and coulometric titration, but the results obtained are not consistent. 

Electrical Resistivity Measurements. Electrical resistances were measured by the voltage-current method. The powder sample was compressed into a pellet with a diameter of V4 in. at 5000 psi. The pellet was placed Detween two brass electrodes, and the electrical resistance of the sample was determined from the measurements of the current through the sample and the potential across the sample. 

The electrical resistance measurement (ERM) method relies on the fact that when an exposed probe corrodes, its cross-sectional area decreases while its electrical resistance increases. A current of 100 mA is passed through the probe element, and the voltage across it is measured extremely accurately. Probes are available in wire loop, tube loop, flush mount, and cylindrical element configurations. A temperature compensation element is also required. 

Since liquid does not completely wet the packing and since film thickness varies with radial position, classical film-flow theory does not explain liquid flow behavior, nor does it predict liquid holdup (30). Electrical resistance measurements have been used for liquid holdup, assuming liquid flows as rivulets in the radial direction with little or no axial and transverse movement. These data can then be empirically fit to film-flow, pore-flow, or droplet-flow models (14,19). The real flow behavior is likely a complex combination of these different flow models, that is, a function of the packing used, the operating parameters, and fluid properties. Incorporating calculations for wetted surface area with the film-flow model allows prediction of liquid holdup within 20% of experimental values (18). 

---