Variation in electrical resistivity

ISO 11907-2. 1995 [121] is a static method of lest used to determine the corrosivity of fire gases. The specimens (600 mg) in the form of granules or chips arc heated with an electric resistance wire (800 C) in a crucible. The effluent is contained within a closed cabinet of 20 liters volume maintained at 50 C and 65% rh. The corrosion detector consists of a resistance etched copper plated laminate, and the corrosivity is assessed as the variation in electrical resistance due to attack on the copper circuit. Two operating procedures are given, one for the condensing mode, in which the corrosion sensor is water cooled to 40 C. and one for the non-condensing mode, without water cooling to the sensor see Fig. 22. 

A thermoresistive flow sensor refers to the flow measurement element based on monitoring the thermal states of an electrically heated sensor whose dependence on the heat loss represents the flow rates of the surrounding fluid. The thermoresistivity of a sensor reflects its variation in electrical resistivity with temperature. A sensor element should usually have a sufficiently high-temperature coefficient of resistance (TCR). Typical sensor materials are platinum, nickel, or polysilicon with a specific TCR in the... 

In PAN based fibers, the electrical conductivity is low, is dominated by the microtextural defects, and has a semiconducting character. It increases when the fibers are stretched during the high temperature treatment and when the temperature is raised, i.e., when the microtexture becomes more and more ordered [1j. Interestingly, the variations in electrical resistivity of PAN based HM fibers appear to be a function of the inverse of the carbon layer size and obey a linear relationship ... 

Fig. 1. The variation in electrical resistivity (dashed line) and optical transmittance (solid line) as a function of hydrogen exposure time for a 300 nm yttrium film capped with 20 nm of Pd over layer on exposure to H2 gas at 10 Pa pressure at room temperature (Huiberts et al., 1996a Griessen, 2001).

Hu et al. showed a decrease in electrical resistivity of PVA by four orders of magnitude with a percolation threshold of 6 wt% [68], while biodegradable polylactide-graphene nanocomposites were prepared with a percolation threshold as low as 3 5wt% [46]. For polystyrene-graphene composites, percolation occurred at only 0.1 °/o of graphene filler, a value three times lower than those for other 2D-filler [69]. Figure 6.7(b) shows the variation of conductivity of the polystyrene-graphene composite with filler content. A sharp increase in conductivity occurs at 0.1 % (the percolation threshold) followed by a saturation. The inset shows the four probe set up for in-plane and trans-... 

Most rocks and soils conduct electric current only because they contain water. But the widely differing resistivity of the various types of pore water can cause variations in the resistivity of soil and rock formations, ranging from a few tenths of an ohm-metre to hundreds of ohm-metres. 

The resistivity of rocks and soils varies within a wide range. Since most of the principal rock forming minerals are practically insulators, the resistivity of rocks and soils is determined by the amount of conducting mineral constituents and the content of mineralized water in the pores. The latter condition is by far the dominant factor, and in fact, most rocks and soils conduct an electric current only because they contain water. The widely differing resistivity values of the various types of impregnating water can cause variations in the resistivity of rocks ranging from a few tenths of an ohm-metre to hundreds of ohm-metres (i2 m) as can be seen from Table 7.5. 

Figure 8-9. Variation of electrical resistance in niobium nitride fibers with temperature.

As was previously indicated, IS measurements can also be used to determined membrane modifications and Figure 9.13 shows Nyquist and Bode plots for PS-Uf and PS-Uf/BSA fouled membranes in contact with a NaCl solution. Here a significant increase in electrical resistance due to membrane fouling can be observed, but the electrolyte contribution hardly differs in both systems. In both cases, the equivalent circuit for the membrane-electrolyte system is given by (R,C,)-(RM that is, a series association of the electrolyte part, formed by a resistance in parallel with a capacitor and the membrane part, which consists of a parallel association of a resistance and a CPE or non-ideal capacitor (RmQm). Fitting the experimental data allows determination of the electrical parameters (resistance, capacitance) for the different NaCl solutions studied and their variation with electrolyte concentration is shown in Figure 9.13c, d, respectively. 

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