Percolation resisting additives

In the equations a is a constant and the other terms have their usual significance. The Ep values can be conveniently evaluated from the use of the linear equation which has been done by different workers for their systems of percolating microemulsions both without and with additives. The values obtained are quite large, and are system and condition dependent. A generalization of the Ep values is yet to be found, the trends are system specific. For instance, it may not follow a trend with respect to additives either there can be a maximum, a minimum, or a different mode of variation with changing concentration of an additive [48,49,95,96]. It has been observed that the percolation-resisting additives may... 

A mean-field theory (Kirkpatrick176) manages to account for this percolation phenomenon. In the framework of the CPA, a real resistance is considered immersed in a perfect effective medium, with the requisite that this substitution will not induce, on average, an additional potential difference. The effective conductivity obtained in this way is very satisfactory It shows a percolation... 

Chemically resistant masonry joints in clay pipe are rigid. Ground movement, such as settlement, can therefore break the pipe. For this reason it is important that all industrial waste lines be laid with continuous support. No matter what opinion others may have of the stability of the soil in the area where the pipe is to be laid, this writer has never seen any trench excavation, no matter how well prepared, that did not require adjustment to attain the suitable smooth surface and slope after the trenching operation had been completed. These adjustments require fill in some spots and further surface removal in others. In addition bell excavations are required to provide working room to make the joints. After the line is in service, heavy rains, flooding and even percolation of groundwater can cause soil movement above and around the pipe, and eventually, without uniform support, movement will take place that breaks the pipe. 

The study of electroconductive polymer systems, based on conductive particles and polymer blends, has been quite intensive during the recent past. Gubbels et al. [149] studied the selective localization of CB particles in multiphase polymeric materials (PS and PE). According to these results, the percolation threshold may be reduced by the selective localization of CB. The minimum resistivity was obtained when double percolation (phase and particle percolation) exists in the PS-PE blend. In addition, it was found that the percolation threshold may be obtained at very low particle concentrations, provided that CB is selectively localized at the interface of the blend components. Soares et al. [150] found that the type of CB (i.e., different surface areas) does not affect the conductivity of the blend with 45/55 PS/PIP (polyisoprene) composition. 

In adding conductive filler to an insulating resin, the volume resistivity changes slowly until a critical level of filler is reached, called the percolation point. The percolation point occurs when the resistivity drops abruptly, then continues to drop slowly (Fig. 2.11). " Almost continuous linkage of metal particles occurs at the percolation point where typical filler volumes for silver flakes are 25-30%. According to the percolation theory, there is a minimum critical volume of filler required for electrical conductivity in a polymer at which each filler particle must contact two other particles. A misconception in the use of silver flakes is that increasing the number of contacts lowers volume resistivity. Actually, the converse is true because, once the percolation point has been reached, each additional contact adds resistance. Thus, increasing the particle size can increase conductivity since the total number of contacts for a fixed volume decreases." ... 

L/D ratio See screw length-to-diameter ratio, leach To extract a soluble component from a mixture by the process of percolation. See percolation, leachate A contaminated liquid that drains from landfills and must be treated before entering the environment. It can contain decomposed wastes, decomposition byproducts, heavy metals, or bacteria. See geomembrane, lead 1. The distance in an axial direction from the center of an element such as a screw flight at its outside diameter to the center of the same flight. See directional property. 2. A heavy metal, Pb is hazardous to one s health if inhaled or swallowed. Its use is restricted. In plastics it is found in certain products, such as additives. Pb can be used in safe environments since it has excellent performance properties, such as resisting attack by many corrosive chemicals and is impervious to x-ray and gamma radiation. See hazard x-ray. 

The films with nominal contents x = 0.55 and 0.60 have high electric resistance (about 100-150 m 2 cm vs. 60 p. 2 cm for the bulk alloy) and a giant tunnel magnetoresistance without anisotropic part [128]. Latter fact indicates additionally that these films are physically nonpercolated. The film with x = 0.70 reveals the simultaneous presence of tunnel and anisotropic magnetoresistance and, is probably partly percolated. 

In a real electrode, the required amount of the conductive carbon depends on both the nature of the carbon and the active electrode material as well as on their particle size distributions. For an optimum electrical resistivity, the conductive carbon might be used slightly above the percolation threshold. Usually, the practical concentrations of conductive additive are higher than the percolation thresholds due to other electrochemical parameters and electrode-processing factors. 

Fig. 5.1 Schematic presentation of a percolation curve ideally describing the effect of a conductive additive at various carbon concentrations on the electronic resistivity of an electrode...

Electrical properties Electrical properties of polymers include several electrical characteristics that are commonly associated with dielectric and conductivity properties. Electrical properties of nanofilled polymers are expected to be different when the fillers get to the nanoscale for several reasons. First, quantum effects begin to become important because the electrical properties of nanoparticles can change compared with the bulk. Second, as the particle size decreases, the interparticle spacing decreases for the same volume fraction. Therefore percolation can occur at lower volume fractions. In addition, the rate of resistivity decrease is lower than in micrometer-scale fillers. This is probably due to the large interfacial area and high interfacial resistance. 

IS measurements have been performed in the 253-333 K temperature range and the results from the measurement at 293 K are shown in Figure 3-43. The Argand diagram consists of two semidrcles which can be understood and represented by a best fit of the data to an ideal Debye resistance (/ 2)/capadtance (C2) parallel link (lower frequency process 2) in series with an additional Cole-Cole resistance (Ri)/CPE (constant phase element) parallel link (higher frequency process 1). From the fit data, a Cole-Cole parameter a = 2/3 results which is very typical for percolation mechanisms. The Ohmic part is the same for both processes Ri = and so = 2/ ,. The spedfic conductivity processes have Oi = 02 = 3.23 X 10 Q" m at 293 K. Since both processes are thermally... 

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