Electricity conductivity through-plane

We can understand the differences in properties between the carbon allotropes by comparing their structures. Graphite consists of planar sheets of sp2 hybridized carbon atoms in a hexagonal network (Fig. 14.29). Electrons are free to move from one carbon atom to another through a delocalized Tr-network formed by the overlap of unhybridized p-orbitals on each carbon atom. This network spreads across the entire plane. Because of the electron delocalization, graphite is a black, lustrous, electrically conducting solid indeed, graphite is used as an electrical conductor in industry and as electrodes in electrochemical cells and batteries. Its... 

The following subsection will briefly discuss the main methods used to measure in-plane and through-plane electrical conductivity for diffusion layer materials. This parameter is critical for optimal fuel cell performance. 

The most typical way to measure the in-plane electrical conductivity of a diffusion layer is through the use of the four-point probe method. A small current is applied across the sample material a separate set of voltage measuring probes that are in touch with the material are used to measure the resulting voltage drop in order to calculate the resistance. With these values, the in-plane resistivity, p, can be calculated with the following equation [9,233] ... 

Through assumptions and the use of values for known resistances of the materials used in the apparatus, the actual bulk resistance of the DL material could be calculated. This resistance was then used so that the electrical conductivity could be solved. Nitta and colleagues noted that the in-plane conductivities of the DL materials were a linear fxmction of the compressed thickness (i.e., the conductivity increased when the thickness decreased with increased compression pressure). This resulted from a decrease in thickness that led to a loss of porosity in the DL materials and higher contact between fibers. 

Consider the plane wall with uniformly distributed heat sources shown in Fig. 2-8. The thickness of the wall in the x direction is 2L, and it is assumed that the dimensions in the other directions are sufficiently large that the heat flow may be considered as one-dimensional. The heat generated per unit volume is q, and we assume that the thermal conductivity does not vary with temperature. This situation might be produced in a practical situation by passing a current through an electrically conducting material. From Chap. 1, the differential equation which governs the heat flow is... 

FIGURE 1.1 One-dimensional heat conduction through a plane wall (a) and electric analog (b). 

Figure 5. Density influence on through-plane electrical conductivity from an array of experimental compositions.

The electrical conductivity for SiC/SiC is strongly affected by the matrix conductivity and in the fiber direction, it is usually dominated by conduction through the PyC (Pyrolitic Carbon) interphase By 2-probe DC (direct current) and AC (alternating current) and 4-probe DC methods, Youngblood et al measured the EC-values of 2D Hi-Nicalon S/PyC interphase/ICVI SiC matrix composites, and composites with the PyC interphase layer removed by oxidation (in plane) at temperatures up to 500 "C. It was found that by removing the PyC interphase, in plane EC of the composites decreased 30%. 

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