Bulk specific resistance

The probable mechanism for conductance in selected polymers is related to the difficulty of delocalizing electrons. Carraher and colleagues found that antimony polyesters derived from aliphatic diacids are weak semiconductors with bulk specific resistivities in the range of 10"10 ohm cm, whereas analogous polyesters derived from aromatic diacids are good semiconductors with bulk resistivities of about 10"4 ohm cm. The difference in electron conductivity is believed to be due to a difference in ability of the material to delocalize electrons the aromatic polyesters possess the ability to delocalize electrons throughout the polymer chain and thus are more conductive (lower resistivities). 

Fig. 4. (a) Yam resistance in n-cm vs amount of antistatic agent on the yam. The agent is the ethyl sulfate salt of an amine, (b) Resistance vs amount of nonionic, hygroscopic agent on the yam. Dotted lines are calculated from the specific resistance of the dry bulk solution soHd lines are experimental yam... 

Volume resistivity Or specific resistivity of a material, expressed in W/cm. Resistance to electrical current flow through the bulk of an object. 

For micro PS a decrease in the specific resistivity by two or three orders of magnitude is observed if the dry material is exposed to humid air [Ma8] or vapors of polar solvents, e.g. methanol [Be6]. This sensitivity of PS to polar vapors can be used to design PS-based gas sensors, as discussed in Section 10.4. This change in resistivity with pore surface condition becomes dramatic if the pores are filled with an electrolyte. From the strong EL observed under low anodic as well as low cathodic bias in an electrolyte it can be concluded that micro PS shows a conductivity comparable to that of the bulk substrate under wet conditions [Ge8]. Diffusion doping has been found to reduce the PS resistivity by more than five orders of magnitude, without affecting the PL intensity [Ell]. 

The bulk (or volume)-specific resistance is one of the most useful general electrical properties. Specific resistance is a physical quantity that may vary more than 10 in readily available materials. This unusually wide range of conductivity allows wide variety of electrical applications. Conductive materials, such as copper, have specific resistance values of about 10 fl-cm, whereas good insulators such as polytetrafluoroethylene and LDPE have values of about 10 fl-cm. Specific resistance is calculated from the following equation where R is the resistance in ohms, a is the pellet area in square centimeters, t is the pellet thickness in centimeter, and P is the specific resistance in ohm-centimeter ... 

Because the surface of rubbers may conduct electricity more easily than the bulk of the material, it is usual to distinguish between volume resistivity and surface resistivity. Volume resistivity is defined as the electrical resistance between opposite faces of a unit cube, whereas surface resistivity is defined as the resistance between opposite sides of a square on the surface. Resistivity is occasionally called specific resistance. Insulation resistance is the resistance measured between any two particular electrodes on or in the rubber and, hence, is a function of both surface and volume resistivities and of the test piece geometry. Conductance and conductivity are simply the reciprocals of resistance and resistivity respectively. 

Examples include the work function, specific resistance (resistivity), elasticity, and thermodynamic properties (e.g. specific heat capacity, melting point). Intrinsic properties are determined by crystallographic structure and are not susceptible to significant change by modification of the microstmcture. Some commonly used synonyms for intrinsic macroscopic properties include global, bulk, and continuum-level. As we might... 

It is considered that the bulk area specific resistance i o must be lower than l o = k/<7 = 0.15 Qcm, where L is the electrolyte thickness and a is its total conductivity, predominantly ionic [39]. At present, fabrication technology allows the preparation of reliable supported structures with film thicknesses in the range 10-15 pm consequently, the electrolyte ionic conductivity must be higher than 10 Scm. As shown in Figure 12.9, a few electrolytes (ceria-based oxides, stabihzed zirconias, and doped gallates) exceed this minimum ionic conductivity above 500 °C. 

Table 4.17 Charge of bulk materials with medium and high specific resistances [41]...

Worked example [using the data fi om Hermia 1993], reproduced below, calculate the pressure as a function of time needed to maintain a constant flow rate of 1 m mT h on candle fibers of radii 15 and 10 mm, and for a filter of planar geometry. Data pressure at end of precoating 0.1 bar, beer viscosity 0.003 Pa s, body feed dosage 1 kg mT precoat dosage 1.5 kg specific resistance lxlo m kg and filter aid bulk density 350 kg m.-. The maximum pressure available fi om the pmq> is 3.5 bar. Applying Equation (6.9) at various times provides the results tabulated in Table 6.4. 

Specific resistance of cake a Resistance of pre-coated medium, Rm Concentration of solids, c Liquid viscosity, p Bulk density of precoat layer Cost of filter aid... 

For automotive applications, there is a need to develop specific membranes with custom surface/bulk properties in order to meet kinetics requirements (in particular cold start and acceleration). As discussed in Section 18.3, the permeation mechanism consists of two main steps (i) a surface step characterized by a surface resistance Rg and (ii) a bulk (diffusion-controlled) resistance Rj). For permeation in transient conditions of flow, the ratio Rg/Ro (Rs is the surface resistance and R the bulk diffusion resistance) is critical because the two steps are connected in series. Schematically, Rg is rate-controlling in transient conditions and R is rate-controlling in stationary conditions of flow. The value of the surface resistance Rg is a function of surface state (chemical composition of surface and roughness factor defined as the dimensionless ratio of the surface of the true to the geometrical solid-gas interface). The value of the bulk resistance R is a function of bulk state (chemical composition and microstructure) and membrane thickness (5).Therefore, the development of metallic membranes with custom properties requires the adjustment of all these physical parameters. 

On the other hand, the values of the resistance per layer showed a definite increase with the thickness of the film. The specific resistance of the films thus determined from their values of the resistance per layer was ca. 10 fl. This was based on the results of capacity measuranents on some 75 samples. The capacitance measurements thus performed on stearate films (1-10 layers) led to e values between 2.1 and 4.2, with a bulk value of 2.5. 

Recently, much attention has been paid to the so-called anisotropic gap state superconductor. At T = 0, Cs(0)/yT<- exhibits (T/T ) temperature dependence in the case of gap function with point node, while (T/T<-) temperature dependence is observed in the case of gap function with line node. As low-energy excitation is possible, one can observe the power law T dependence at the low temperature in specific heat for p and d wave superconductors. The measurements of specific heat give extremely fruitful information about the superconducting gap complementary with other measurements, such as NMR. Even if a superconductor is not bulk, zero resistance may be observed when there is a continuous superconducting current path inside the sample. By using specific heat measurements, it is possible to determine whether superconducting behavior occurs in the bulk or not. We note that it is extremely important to check the bulk nature of pressure-induced SC by specific heat measurements imder pressure. 

In the early amplitude selection, the number of scan lines was 2-4, and the frame frequency /p was 50-60 Hz. Because of a frame inversion for the AC drive, the minimum driving frequency of the drive voltage applied to the LCD was H /p, which means 30 Hz. The effective dielectric constant under such low frequencies fluctuated because the ionic conduction mainly fluctuated which led to malfunctions. More than lO Q. cm were required as the specific resistance of the bulk liquid crystal material. 

Thus, knowing the cross-sectional area, the separation distance, the current flowing and the potential difference between two points, the bulk resistance, R above, can be computed, expressed as specific resistivityy p, in units of 0-cm. The bulk specific conductivity a, in units of Q -cm or Siemens (S) /cm, is then its reciprocal. The surface resistivity of a coating or film, in units of 0/D (square), is just pity with t the thickness of the coating/film. 

Resistivity See Sheet resistivity (thin film) Specific resistivity (bulk). 

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