Other electrical measurements

Measurements of photoconductivity and of the Hall potential [367] are accurate and unambiguous methods of detecting electronic conduction in ionic solids. Kabanov [351] emphasizes, however, that the absence of such effects is not conclusive proof to the contrary. From measurements of thermal potential [368], it is possible to detect solid-solution formation, to distinguish between electronic and positive hole conductivity in semi-conductors and between interstitial and vacancy conductivity in ionic conductors. 

Measurements [113,368] of interfacial (contact) potentials or calculated values of the relative work functions of reactant and of solid decomposition product under conditions expected to apply during pyrolysis have been correlated with rates of reaction by Zakharov et al. [369]. There are reservations about this approach, however, since the magnitudes of work functions of substances have been shown to vary with structure and particle size especially high values have been reported for amorphous compounds [370,371]. Kabanov [351] estimates that the electrical field in the interfacial zone of contact between reactant and decomposition product may be of the order of 104 106 V cm 1. This is sufficient to bring about decomposition. 

The variations of dielectric constant and of the tangent of the dielectric-loss angle with time provide information on the mobility and concentration of charge carriers, the dissociation of defect clusters, the occurrence of phase transitions and the formation of solid solutions. Techniques and the interpretation of results for sodium azide are described by Ellis and Hall [372]. 

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Dielectric measurements, as a function of temperature, have been widely used to study the properties of semiconductors, insulation materials, plastics, elastomers, oil shales, inorganic substances, and others. The dielectric constant technique provides more insight into the segmental motions of the molecule and relaxation phenomena (1161 than does other electrical measurements such as electrical conductivity, resistivity, and so on. 

Electrical leads with terminating plugs (N) are contained within the cover for the extensometer, thermometer, and other electrical measurements which are to be made within the cryostat. 

All physical properties depend on defect concentration but some are far more sensitive than others. Electrical measurements are most often used in studying point defects. Transport properties tend to be more sensitive than equilibrium properties since defects often control diffusion or charge transport. Thus electrical conductivity is capable of detecting electrons, holes, and atomic point defects down to 10 /cm, far better than can be done by density measurements. In the latter, atomic defect concentrations of can be detected by compar-... 

Other methods attempt to probe the stmcture of the foam indirectly, without directly imaging it. Eor example, since the Hquid portion of the foam typically contains electrolytes, it conducts electrical current, and much work has been done on relating the electrical conductivity of a foam to its Hquid content, both experimentally (15) and theoretically (16). The value of the conductivity depends in a very complex fashion on not only the Hquid content and its distribution between films and borders, but the geometrical stmcture of the bubble packing arrangement. Thus electrical measurements offer only a rather cmde probe of the gas Hquid ratio, a quantity that can be accurately estimated from the foam s mass density. 

Signal Transmission and Conditioning. A wide variety of physical and chemical phenomena are used to measure the many process variables required to characteri2e the state of a process. Because most processes are operated from a control house, these values must be available there. Hence, the measurements are usually transduced to an electronic form, most often 4 to 20 m A, and then transmitted to the control house or to a remote terminal unit and then to the control house (see Fig. 6). Wherever transmission of these signals takes place in twisted pairs, it is especially important that proper care is taken so that these measurement signals are not cormpted owing to ground currents, interference from other electrical equipment and... 

As normally used in the process industries, the sensitivity and percentage of span accuracy of these thermometers are generally the equal of those of other temperature-measuring instruments. Sensitivity and absolute accuracy are not the equal of those of short-span electrical instruments used in connection with resistance-thermometer bulbs. Also, the maximum temperature is somewhat limited. 

Electromagnetic (EM) Conductivity Measures the electrical conductivity of materials in microohms over a range of depths determined by the spacing and orientation of the transmitter and receiver coils, and the nature of the earth materials. Delineates areas of soil and groundwater contamination and the depth to bedrock or buried objects. Surveys to depths of SO to 100 ft are possible. Power lines, underground cables, transformers and other electrical sources severely distort the measurements. Low resistivities of surficial materials makes interpretation difficult. The top layers act as a shunt to the introduction of energy info lower layers. Capabilities for defining the variation of resistivity with depth are limited. In cases where the desired result is to map a contaminated plume in a sand layer beneath a surficial clayey soil in an area of cultural interference, or where chemicals have been spilled on the surface, or where clay soils are present it is probably not worth the effort to conduct the survey. 

Tye [38] explained that separator tortuosity is a key property determining the transient response of a separator (and batteries are used in a non steady-state mode) steady-state electrical measurements do not reflect the influence of tortuosity. He recommended that the distribution of tortuosity in separators be considered some pores may have less tortuous paths than others. He showed mathematically that separators with identical average tortuosities and porosities can be distinguished by their unsteady-state behavior if they have different distributions of tortuosity. 

Characteristically, the mechanisms formulated for azide decompositions involve [693,717] exciton formation and/or the participation of mobile electrons, positive holes and interstitial ions. Information concerning the energy requirements for the production, mobility and other relevant properties of these lattice imperfections can often be obtained from spectral data and electrical measurements. The interpretation of decomposition kinetics has often been profitably considered with reference to rates of photolysis. Accordingly, proposed reaction mechanisms have included consideration of trapping, transportation and interactions between possible energetic participants, and the steps involved can be characterized in greater detail than has been found possible in the decompositions of most other types of solids. 

Various techniques and equipment are available for the measurement of particle size, shape, and volume. These include for microscopy, sieve analysis, sedimentation methods, photon correlation spectroscopy, and the Coulter counter or other electrical sensing devices. The specific surface area of original drug powders can also be assessed using gas adsorption or gas permeability techniques. It should be noted that most particle size measurements are not truly direct. Because the type of equipment used yields different equivalent spherical diameter, which are based on totally different principles, the particle size obtained from one method may or may not be compared with those obtained from other methods. 

We will first describe the results obtained for n-type GaAs doped with silicon and then those on p-type GaAs and InP, trying to show how the spectroscopic results correlate with the electrical measurements to provide a consistent picture of the neutralization of dopants by hydrogen in III-V semiconductors. After considerations on the temperature dependence of the widths and positions of the H-related lines, we will discuss the occurrence and origin of other vibration lines associated also with hydrogen in as grown bulk and epitaxial III-V compounds. 

Method involves placing a specimen between parallel plate capacitors and applying a sinusoidal voltage (frequencies ranging from 1 mHz to 1 MHz) to one of the plates to establish an electric field in the specimen. In response to this field, a specimen becomes electrically polarized and can conduct a small charge from one plate to the other. Through measurement of the resultant current, the dielectric constant and dielectric loss constant for a specimen can be measured. The sharp increases in both the dielectric constant and the dielectric loss constant during a temperature scan are correlated with the occurrence of Tg... 

In addition to obtaining soil samples and transporting them to the laboratory, there has been research into on-the-go soil analysis. This is accomplished using sensors attached to implements in contact with the soil. A soil sample is taken, analyzed, and then returned to the field over a short period of time. In addition to specific sensors, reflection and conductance are other approaches used to obtain information about soil. Electrical measurements of soil are further discussed in Chapter 9. 

Wires and cables just carry the electric current and the electric network needs a multitude of other electric equipment including connectors, switches. .. electric power equipment motors and controls measuring and control equipment lighting and wiring equipment current-carrying equipment non-current-carrying wire devices pole line hardware. 

From Fig. 9.16, we obtain c/33 1.05 kN, a value consistent with the value listed in the catalog (1.27 kN). The value might be somewhat lower than the true value because the bonding of the tube ends is not perfectly rigid. If one end of the tube is free, or both ends are free, the deformation pattern varies significantly at the end(s). The net end effect is to reduce the value of the double piezoelectric response. Even if the end-bonding condition is unknown, an accurate measurement of the temperature or time variation of the piezoelectric constant can still be achieved. In other words, if the piezoelectric scanner is calibrated by a direct mechanical measurement or by the scale of images at one temperature, then its variation can be precisely determined by the electrical measurements based on double piezoelectric responses. 

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