Specific electrical resistivity

The specific electrical resistances usually depend on the material and the temperature [31]. For the most important pipe materials these are (in 10 Q cm) ... 

The specific electrical resistance of concrete can be measured by the method described in Section 3.5. Its value depends on the water/cement value, the type of cement (blast furnace, portland cement), the cement content, additives (flue ash), additional materials (polymers), the moisture content, salt content (chloride), the temperature and the age of the concrete. Comparisons are only meaningful for the... 

The cost and economics of cathodic protection depend on a variety of parameters so that general statements on costs are not really possible. In particular, the protection current requirement and the specific electrical resistance of the electrolyte in the surroundings of the object to be protected and the anodes can vary considerably and thus affect the costs. Usually electrochemical protection is particularly economical if the structure can be ensured a long service life, maintained in continuous operation, and if repair costs are very high. As a rough estimate, the installation costs of cathodic protection of uncoated metal structures are about 1 to 2% of the construction costs of the structure, and are 0.1 to 0.2% for coated surfaces. 

Zone I the E vsj linear curve corresponds to ohmiclosses j in the electrolyte and interface resistances a decrease of the specific electric resistance from 0.3 to 0.15 Dcm gives an increase in the current density j (at 0.7 V) from 0.25 to 0.4 A cm, that is, an increase in the energy efficiency and in the power density of 1.6-fold. 

The specific electrical resistance of an electrolyte solution is defined as the resistance of a cube 1 cm in length and 1 cm2 in cross-sectional area. 

In this section of the research, the aim is to investigate the optimal composition of the Ni(II)-containing solution as a function of the Ni(II) reduction rate, the total amount of Ni reduced, the fraction of NiS formed and PAN-hbre properties, such as specific electrical resistance. In Fig. 11.2, data are shown for the variation of Ni(II) and rongalite concentration as a function of time and temperature starting from a constant initial Ni(II) concentration, while the initial rongalite concentration was increased. It must be pointed out that in this section of the research, no fibre was immersed in the solution, so the pure kinetic parameters of the reduction reaction of Ni(II) by rongalite is studied. Similar experiments were performed with different initial Ni(II) concentrations. 

A first parameter to be studied is the applied potential difference between anode and cathode. This potential is not necessarily equal to the actual potential difference between the electrodes because ohmic drop contributions decrease the tension applied between the electrodes. Examples are anode polarisation, tension failure, IR-drop or ohmic-drop effects of the electrolyte solution and the specific electrical resistance of the fibres and yarns. This means that relatively high potential differences should be applied (a few volts) in order to obtain an optimal potential difference over the anode and cathode. Figure 11.6 shows the evolution of the measured electrical current between anode and cathode as a function of time for several applied potential differences in three electrolyte solutions. It can be seen that for applied potential differences of less than 6V, an increase in the electrical current is detected for potentials great than 6-8 V, first an increase, followed by a decrease, is observed. The increase in current at low applied potentials (<6V) is caused by the electrodeposition of Ni(II) at the fibre surface, resulting in an increase of its conductive properties therefore more electrical current can pass the cable per time unit. After approximately 15 min, it reaches a constant value at that moment, the surface is fully covered (confirmed with X-ray photo/electron spectroscopy (XPS) analysis) with Ni. Further deposition continues but no longer affects the conductive properties of the deposited layer. 

Table 11.9 Relative variations of amount of nickel and specific electrical resistance in individually cut PAN-fibre pieces obtained through chemical metallisation and galvanisation...

This reaction gives high yield of carbon (44-80%) and can be easily scaled. Purifying of the raw material includes treatment of it with sodium carbonate solution with following treatment with acid. Surface area of nanocarbons obtained was 64-500 m2/g, specific electric resistance of powder 0.02-0.07 Ohm.cm. 

Thermo-electromotive force and specific electrical resistance were measured by the standard 4-electrode method. 

Figure 5. Heating-cooling plots of specific electrical resistance p (1, 1 ) and thermoelectromotive force ET (2, 2 ) for PTFE-MWNT composite. Arrows indicate directions of temperature change.

The specific electric resistance of cobalt wires of great purity is 89-64 X 10 7 ohms per cm. cube, but this value increases enormously by the addition of small quantities of impurities. 

Temperature drop in reaction cell decreases along with increasing of cylidrical heater diameter (Fig. lb and lc). Material for heaters of various size has been chosen in such a way as to increase its specific electric resistance and decrease the thermoconductivity along with heater diameter increase. On practice it may be accomplished, for example, by variation of heater components ratio [5],... 

It is only the liquid phase in a foam that possesses electrical conductivity. That is why the specific electrical conductivity of a foam kf (or its specific electrical resistance pF ) depends on the liquid content and on its specific electrical conductivity Kl (or its specific resistance pi)... 

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