Resistance, electrical bulk

The data indicate that the properties of the lower glass transition temperature metal ion modified polyimides are altered more than the properties of the higher glass transition temperature metal ion modified polyimides. Extraction removes both cobalt and chlorine from the films and slightly increases bulk thermal stability and both surface resistivity and bulk electrical resistivity. Details pertaining to the structure, analysis and properties of these novel gradient composites are discussed. 

One of the most desirable aspects of plastics and composites is the ability to make net-shaped parts. The same process that creates the material also creates the structure. The penalty for this advantage is that the process of curing a thermosetting plastic or composite part is irreversible. Any part that is not properly processed represents a loss of part, material and the money and time required to make that part, although larger parts are usually repaired if possible. Proper shape becomes a controlled property in addition to the bulk material properties, such as mechanical (stiffness or strength), physical (density, void content, etc.), chemical (degree of cure or carbonization, chemical resistance), electrical (resistivity, conductivity), or any combination of these. 

Electrical bulk properties of ionic solids can be rather inhomogeneous (Sec. 3.1). In the following it is shown that microelectrodes are a very useful tool to gain spatially resolved information on the conductivity of such inhomogeneous solids. Let us first consider the case of a spherical microelectrode (radius rme) atop a sample with homogeneous bulk conductivity Ubuik- The bulk resistance R between the microelectrode and a hemispherical counter-electrode of radius rce (Fig. 12a) can be calculated by integrating the infinitesimal resistances of hemispherical shells according to... 

In addition to silicon and metals, a third important element being deposited as thin films is diamond (Celii and Butler, 1991 May, 2000). For many years, diamonds were synthesized by a high pressure/high temperature technique that produced bulk diamonds. More recently, the interest in diamonds has expanded to thin films. Diamond has a slew of properties that make it a desired material in thin-film form hardness, thermal conductivity, optical transparency, chemical resistance, electrical insulation, and susceptibility to doping. Thin film diamond is prepared using chemical vapor deposition, and we examine the process in some detail as a prototypical chemical vapor example. Despite its importance and the intensity of research focused on diamond chemical vapor deposition, there remains uncertainty about the exact mechanism. 

Figure 9 shows the evolution of the electrical resistivity of the as processed films as a function of their carbon content. Resistivity of bulk Ni (6.84 pQ cm) is also reported for comparison. Error bars show deviations both among different samples with the same carbon content, and among different positions within... 

Direct current electrical resistivity determinations (bulk and each surface) of polyimide films either containing in situ generated Co O or SnO have proven valuable toward gaining information concerning the microstructure of these systems. The field and time dependence of the electrical current as well as th i dependence of charge... 

Singjai, R Changsarn, S. Thongtem, S. Electrical resistivity of bulk multi-walled carbon nanotubes synthesized by an infusion chemical vapor deposition method. Mater. Sci. Eng., A 2007, 443, 42M6. 

The important properties of carbon fibers include mechanical stiffness (Young s modulus), tensile and compressive strength, thermal stability, thermal conductivity (along the fiber axis), thermal resistivity (of bulk fibers), low coefficient of thermal expansion, and electrical conductivity. 

Carbon nanotnbes are regarded as ideal filler materials for polymeric fiber reinforcement dne to their exceptional mechanical properties and cylindrical geometry (nanometer-size diameter). Polymer chains in the vicinity of carbon nanotubes (interphase) have been observed to have a more compact packing, higher orientation, and better mechanical properties than bulk polymers due to the carbon nanotube polymer interaction. The existence of interphase polymers in composite fibers, their strnctnral characterization, and fiber properties are summarized and discussed in the literature (Liu and Satish 2014). Besides improvements in tensile properties, the presence of carbon nanotubes in polymeric fibers also influences other factors (thermal stability, thermal transition temperature, fiber thermal shrinkage, chemical resistance, electrical conductivity, and thermal conductivity). 

FIGURE 6.15 Enhanced setup for measuring contact resistance and bulk resistance within one measurement. Bulk properties can be obtained from a separate potential measurement across two needles electrically insulated from the main circuit. (Adapted from Kreuz, C. 2008. Dissertation PEM-BrennstofFzellen mit spritzgegossenen Bipolarplatten aus hochgefiilltem Graphit-Composite, Gerhard-Mercator-University in Germany, 04/2008.)... 

Component modelling The modelling of the stabiliser trim system includes one-dimensional mechanics with elasticity, damping, inertia and friction hydraulics with bulk modulus, fluid density, turbulent and laminar flow and resistive electrics. One of the developed component models is explained below. 

In order to illustrate the principal elements of the model, a simple electrical scheme is shown in Figure 6. The bulk of the specimen is taken to be purely resistive. The bulk resistance Rg is in series with a contact impedance. The latter is depicted as a resistance R parallel with a contact capacitance C. A further elaboration is necessary before undertaking the task of identifying... 

Figure 5.11 Through plane electrical resistance as function of compression pressure for common carbon fiber paper used as gas diffusion layer in PEFCs. The gas diffusion layers typically have some fraction of PTFE added to promote liquid water removal, which increases electrical bulk and contact resistance. (Reproduced from Ref. [18].)...

F (A0I + A0ii). The term in the braces is Uqs- and refers exclusively to the sample, while A0i + A0II refers to the potential drops over the two ion conductor samples. If contact resistances also occur at other phase boundaries the drop in electrochemical potential does not equal zero in the stationary state it is given by the product of current and contact resistance. Since, on the time scale of the stoichiometry polarization, electrical bulk processes and charge transfer processes actually behave in a quasi stationary manner, we may write that U =. .. + SilRi, whereby i refers to all parts outside the sample. 

There are large-scale operations using direct-heat resistance furnaces. These are mainly in melting bulk materials where the Hquid material serves as a uniform resistor. The material is contained in a cmcible of fixed dimensions which, coupled with a given resistivity of the material, fixes the total resistance within reasonable limits. The most common appHcation for this type of direct-heat electric resistance furnace is the melting of glass (qv) and arc furnaces for the melting of steel (qv). 

The properties of high quaUty vitreous sihca that determine its uses iaclude high chemical resistance, low coefficient of thermal expansion (5.5 X 10 /° C), high thermal shock resistance, high electrical resistivity, and high optical transmission, especially ia the ultraviolet. Bulk vitreous sihca is difficult to work because of the absence of network-modifyiag ions present ia common glass formulations. An extensive review of the properties and stmcture of vitreous sihca is available (72). 

Total electrical resistivity of 99.999% pure or purer bulk silver. Impurities increase resistivity. 

Electrical Properties. Generally, deposited thin films have an electrical resistivity that is higher than that of the bulk material. This is often the result of the lower density and high surface-to-volume ratio in the film. In semiconductor films, the electron mobiHty and lifetime can be affected by the point defect concentration, which also affects electromigration. These effects are eliminated by depositing the film at low rates, high temperatures, and under very controUed conditions, such as are found in molecular beam epitaxy and vapor-phase epitaxy. 

The terms resistance and resistivity are both used when referring to the resistance of an object to current flow. Surface resistance is the measure of electrical resistance along the surface of an object. However, the current flow is not limited to the surface of the object. Some of the current passes through the bulk of the object from one electrode to the other electrode. Surface resistivity includes the dimensions of the object in its measurement (Eig. 2c). 

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