Characteristics electrical resistivity

We can define the principal electrical properties of polymers in terms of four characteristics electrical resistance, capacitive properties, dielectric strength, and arc resistance. We can change the surface characteristics of a polymer by subjecting it to a corona discharge generated by a strong electrical field. Lastly, we must also consider the influence of other physical properties on the application of polymers in electrical applications. 

Biomolecules-functionalized CNTs can result in characteristic electric conductivity changes of CNTs (Hou et al., 2003), which may be developed into specific biosensor for ultrasensitive detection of biomolecules such as DNA molecules, bacteria and vims, etc. We also observed that oligo DNA-filled SWCNTs appeared as characteristic Electric Resistance peaks as shown in Fig. 9.22, which also may be used as biosensor to detect biomolecules or sequence DNA sequences. 

The experimental dependence between the current density and width of air channels of bipolar plate has been obtained [3, 4]. Based on these data optimal width of channels 0.4-0.7 mm and current transfer prominent elements 0.2-0.7 mm was prescribed (exact values are determined by technological and material aspects of bipolar plate production, and also by gas diffusion layer parameters (thickness, porosity, mechanical characteristics, electric resistance). 

An important dimensionless group in the field of electrochemical engineering is the Wagner number. The Wagner number is the ratio of the impedance of reaction to a characteristic electrical resistance of the solution. 

Polyimide. Polyimide is a biaxiaHy oriented high performance film that is tough, flexible, and temperature- and combustion-resistant. Its room temperature properties compare to poly(ethylene terephthalate), but it retains these good characteristics at temperatures above 400°C. Its electrical resistance is good and it is dimensionally stable. The principal detriment is fairly high moisture absorbance. The main uses are for electrical insulation, particularly where high temperatures are prevalent or ionizing radiation is a problem. The films may be coated to reduce water absorption and enhance... 

For many electronic and electrical appHcations, electrically conductive resias are required. Most polymeric resias exhibit high levels of electrical resistivity. Conductivity can be improved, however, by the judicious use of fillers eg, in epoxy, silver (in either flake or powdered form) is used as a filler. Sometimes other fillers such as copper are also used, but result in reduced efficiency. The popularity of silver is due to the absence of the oxide layer formation, which imparts electrical insulating characteristics. Consequently, metallic fibers such as aluminum are rarely considered for this appHcation. 

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. 

Thermal Methods Level-measuring systems may be based on the difference in thermal characteristics oetween the fluids, such as temperature or thermal conductivity. A fixed-point level sensor based on the difference in thermal conductivity between two fluids consists of an electrically heated thermistor inserted into the vessel. The temperature of the thermistor and consequently its electrical resistance increase as the thermal conductivity of the fluid in which it is immersed decreases. Since the thermal conductivity of liquids is markedly higher than that of vapors, such a device can be used as a point level detector for liquid-vapor interface. 

The performance of the unit involves the gas characteristics, analysis, velocity, flow rate, dust or liquid particle size and analysis, resistixdty and required final particle efficiency of removal. Some particle materials of high electrical resistivity prevent proper electrical operation. 

Contact with steel, though less harmful, may accelerate attack on aluminium, but in some natural waters and other special cases aluminium can be protected at the expense of ferrous materials. Stainless steels may increase attack on aluminium, notably in sea-water or marine atmospheres, but the high electrical resistance of the two surface oxide films minimises bimetallic effects in less aggressive environments. Titanium appears to behave in a similar manner to steel. Aluminium-zinc alloys are used as sacrificial anodes for steel structures, usually with trace additions of tin, indium or mercury to enhance dissolution characteristics and render the operating potential more electronegative. 

The precautions generally applicable to the preparation, exposure, cleaning and assessment of metal test specimens in tests in other environments will also apply in the case of field tests in the soil, but there will be additional precautions because of the nature of this environment. Whereas in the case of aqueous, particularly sea-water, and atmospheric environments the physical and chemical characteristics will be reasonably constant over distances covering individual test sites, this will not necessarily be the case in soils, which will almost inevitably be of a less homogeneous nature. The principal factors responsible for the corrosive nature of soils are the presence of bacteria, the chemistry (pH and salt content), the redox potential, electrical resistance, stray currents and the formation of concentration cells. Several of these factors are interrelated. 

Superconductivity is the loss of all electrical resistance when a substance is cooled below a certain characteristic transition temperature (Ts). It is thought that the low temperatures are required to reduce the effect of the vibrations of the atoms in their crystalline lattice. Superconductivity was first observed in 1911 in mercury, for which Ts = 4 K. Over the years, many other metallic superconductors were identified, some having transition temperatures as high as 23 K. However, low-temperature superconductors need to be cooled with liquid helium, which is very expensive. To use superconducting devices on a large scale, higher transition temperatures would be required. 

Archie, GE, The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics, Transactions of the American Institute of Mining Engineers 146, 54, 1942. 

Fig. 8.4 Plots of relative change in electrical resistance against tensile deformation of a CNT/epoxy composite (a) shows the various characteristics of the piezoresistivity of nanocarbon networks linear resistance change in the elastic regime, nonlinear region after inelastic deformation and the permanent electrical resistance drop due to plastic deformation (image adapted from [30]) ...

Graphite is midway between a semiconductor and a metal in electrical characteristics. The resistivity is very sensitive to impurities, and therefore to crystal perfection, and is directional, being two to three times greater in the basal plane than perpendicular to the plane. Properties measured in the hexagonal plane are independent of the direction within the plane, probably... 

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