Electrical resistivity compounds

Concurrent bombardment during film growth affects film properties such as the film—substrate adhesion, density, surface area, porosity, surface coverage, residual film stress, index of refraction, and electrical resistivity. In reactive ion plating, the use of concurrent bombardment allows the deposition of stoichiometric, high density films of compounds such as TiN, ZrN, and Zr02 at low substrate temperatures. 

Borides have metallic characteristics such as high electrical conductivity and positive coefficients of electrical resistivity. Many of them, particularly the borides of metals of Groups 4 (IVB), 5 (VB), and 6 (VIB), the MB compounds of Groups 2(11) and 13(111), and the borides of aluminum and siUcon, have high melting points, great hardness, low coefficients of thermal expansion, and good chemical stabiUty. 

Compound Molecula r formula Densit T g/mL Mp, °C Micro hardness a Transvers e mpture strength, N/imn Compressio n strength, N/imn Modulus of elasticity, N/imn Heat conductivity, W/(cm-K) Coefficien t of thermal expansion, /3 X 10 Electrical resistivity, //n-cm... 

The calciaed or meta kaolin is used almost exclusively ia poly(vinyl chloride) wire iasulation because it enhances the electrical resistivity of the compound. 

The electrical resistance of most conductors, metals in particular, decreases as the temperature of the conductor decreases. For some pure metals and compounds of the metals, the resistance decreases with temperature as usual, but at some critical temperature the resistance drops identically to zero. The resistance remains zero as long as the material is maintained at a temperature below the critical temperature. Such a material is termed a supercon-... 

Chromium plating from hexavalent baths is carried out with insoluble lead-lead peroxide anodes, since chromium anodes would be insoluble (passive). There are three main anode reactions oxidation of water, reoxidation of Cr ions (or more probably complex polychromate compounds) produced at the cathode and gradual thickening of the PbOj film. The anode current density must balance the reduction and reoxidation of trivalent chromium so that the concentration reaches a steady state. From time to time the PbOj film is removed as it increases electrical resistance. 

Nonstoichiometry is relatively common among mixed metal oxides, in which more than one metal is present. In 1986 it was discovered that certain compounds of this type showed the phenomenon of superconductivity on cooling to about 100 K, their electrical resistance drops to zero (Figure 20.9). A typical formula here is YBa2Cu30 where x varies from 6.5 to 7.2, depending on the method of preparation of the solid. 

Table 2. Molecular weight, density (cf. [51, Table VII) and electrical resistance of the chemical compounds used in lead-acid batteries.

Thermal Conductivity Detector In the thermal conductivity detector (TCD), the temperature of a hot filament changes when the analyte dilutes the carrier gas. With a constant flow of helium carrier gas, the filament temperature will remain constant, but as compounds with different thermal conductivities elute, the different gas compositions cause heat to be conducted away from the filament at different rates, which in turn causes a change in the filament temperature and electrical resistance. The TCD is truly a universal detector and can detect water, air, hydrogen, carbon monoxide, nitrogen, sulfur dioxide, and many other compounds. For most organic molecules, the sensitivity of the TCD detector is low compared to that of the FID, but for the compounds for which the FID produces little or no signal, the TCD detector is a good alternative. 

Flammable atmospheres can be assessed using portable gas chromatographs or, for selected compounds, by colour indicator tubes. More commonly, use is made of explos-imeters fitted with Pellistors (e.g. platinum wire encased in beads of refractory material). The beads are arranged in a Wheatstone bridge circuit. The flammable gas is oxidized on the heated catalytic element, causing the electrical resistance to alter relative to the reference. Instruments are calibrated for specific compounds in terms of 0—100% of their lower flammable limit. Recalibration or application of correction factors is required for different gases. Points to consider are listed in Table 9.10. 

Rubber so compounded as to produce a vulcanisate having an electrical resistivity of about 107 to 109 ohm-cm. See Conductive Rubber. 

Dioxime cures yield vulcanisates with good ozone resistance and moisture impermeability and, as such, are frequently used for curing electrical insulating compounds. 

Calcined clays are hard clays which have been heat treated to remove the combined water. The removal of any surface bound entity from the clay particles improves the capacity to improve the electrical resistance of rubber compounds. Calcinated clays also reduce compound water... 

A well-known fact of fundamental solution science is that the presence of ions in any solution gives the solution a low electrical resistance and the ability to conduct an electrical current. The absence of ions means that the solution would not be conductive. Thus, solutions of ionic compounds and acids, especially strong acids, have a low electrical resistance and are conductive. This means that if a pair of conductive surfaces are immersed into the solution and connected to an electrical power source, such as a simple battery, a current can be detected flowing in the circuit. Alternatively, if the resistance of the solution between the electrodes were measured (with an ohmmeter), it would be low. Conductivity cells based on this simple design are in common use in nonchromatography applications to determine the quality of deionized water, for example. Deionized water should have no ions dissolved in it and thus should have a very low conductivity. The conductivity detector is based on this simple apparatus. 

Recalcitrant organic contaminants in the unsaturated zone, those that are difficult to remediate by vapor extraction, biodegradation, or other biological-chemical processes, can be removed via vitrification and electrical heating. This process involves heating the soil by electrical resistance or applied electrical fields to vaporize semi-volatile and volatile compounds, thermally to break down larger organic molecules, and (if heated sufficiently) to vitrify the mineral matter in the soil. 

MDCK Madin-Darby canine kidney (MDCK) cells have received attention as an alternative to Caco-2 cells for permeability measurements. When grown under standard culture conditions, MDCK cells develop tight junctions and form monolayers of polarized cells. The main advantage over Caco-2 cells is the shorter culture time to confluence (3-5 days). The transep-ithelial electrical resistance of MDCK cells is lower than that of Caco-2 cells and thus, closer to the TEER of the small intestine in vivo. The permeability coefficients of hydrophilic compounds are usually lower in Caco-2 cells than in MDCK cells, which is consistent with the lower TEER values for MDCK cell monolayers. The nonhuman (canine) and nonintestinal (renal) origin of MDCK cells is considered as a disadvantage. They have low expression levels of transporter proteins and low metabolic activity [34], MDCK cells that are stably transfected with P-gp/MDRl are often proposed as an alternative for Caco-2 cells to study bidirectional transport of compounds and, more... 

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