Electrical contact properties

The electrical-contact properties also depend on the dimensions of the particles. As particle size diminishes, for example, as styrene particles pass from 40 to 4 M, the electrical-contact properties move to the negative side of the series [429, 431]. In vibw of this the developing powder must be of a single particle size otherwise its electrical-contact properties will vary and hence so will the adhesion to the substrate and the quality of the image. 

Electrical-contact properties may also be varied by modifying the surface of the contiguous bodies (see 11). 

Dravin and Kirillova [432] developed a sorption method of tinting, enabling the electrical-contact properties of the pol3rmers to be varied. In order to displace the properties toward the negative part of the series, alcohol and fat-soluble dyes may be used, while for the positive part basic dyes are required. 

Lead Telluride. Lead teUuride [1314-91 -6] PbTe, forms white cubic crystals, mol wt 334.79, sp gr 8.16, and has a hardness of 3 on the Mohs scale. It is very slightly soluble in water, melts at 917°C, and is prepared by melting lead and tellurium together. Lead teUuride has semiconductive and photoconductive properties. It is used in pyrometry, in heat-sensing instmments such as bolometers and infrared spectroscopes (see Infrared technology AND RAMAN SPECTROSCOPY), and in thermoelectric elements to convert heat directly to electricity (33,34,83). Lead teUuride is also used in catalysts for oxygen reduction in fuel ceUs (qv) (84), as cathodes in primary batteries with lithium anodes (85), in electrical contacts for vacuum switches (86), in lead-ion selective electrodes (87), in tunable lasers (qv) (88), and in thermistors (89). 

Uses. In spite of unique properties, there are few commercial appUcations for monolithic shapes of borides. They are used for resistance-heated boats (with boron nitride), for aluminum evaporation, and for sliding electrical contacts. There are a number of potential uses ia the control and handling of molten metals and slags where corrosion and erosion resistance are important. Titanium diboride and zirconium diboride are potential cathodes for the aluminum Hall cells (see Aluminum and aluminum alloys). Lanthanum hexaboride and cerium hexaboride are particularly useful as cathodes ia electronic devices because of their high thermal emissivities, low work functions, and resistance to poisoning. 

Particulate fillers are divided into two types, inert fillers and reinforcing fillers. The term inert filler is something of a misnomer as many properties may be affected by incorporation of such a filler. For example, in a plasticised PVC compound the addition of an inert filler will reduce die swell on extrusion, increase modulus and hardness, may provide a white base for colouring, improve electrical insulation properties and reduce tackiness. Inert fillers will also usually substantially reduce the cost of the compound. Amongst the fillers used are calcium carbonates, china clay, talc, and barium sulphate. For normal uses such fillers should be quite insoluble in any liquids with which the polymer compound is liable to come into contact. 

Tin coatings are widely used in the electrical industry because of their good contact properties and in the food industry because of low toxicity. In addition to pure tin coatings a number of alloy coatings have been developed for special applications, e.g. tin-lead (terne plate), tin-zinc, tin-cadmium, tin-bronze and tin-nickel. Reference should be made to Section 13.5 and to the publication by Britton for data on the corrosion of tin and its alloys. 

Very hard, steel-gray metal. Hardens platinum. The International Prototype Meter in Paris consists of a Pt-Ir alloy. Its hardness and corrosion resistance is exploited in fountain-pen tips, spark plugs in powerful engines (airplanes), and electrical contacts. Used as a material in shells for nuclide batteries in satellites. Responsible for the iridescent properties of vapor-treated sunglasses. 

Poor choice of FR additives can lead to excessive loss of PBT molecular weight upon processing, hence leading to impaired mechanical properties (usually seen as part melt-viscosity (MV) drop and, if severe, part breakage). In some cases, generation of acidic halide species can cause mold or electrical contact corrosion. 

If the wafer is not fixed in the cell, a mechanical wafer support is advisable. The ohmic contact can be an integral part of such a sample fixture, as shown in Fig. 1.5 a. During formation of mesoporous silicon on highly doped substrates at low bias (0-1.5 V), it was found that such a contact can even be immersed into the electrolyte without a significant degradation of its electrical properties. It is remarkable that mesoporous silicon formation takes place under the contact, too, without significant degradation of the contact properties. 

Cellulosics are appreciated for their easy processability aesthetics transparency high gloss pleasant feel aptitude for colouring and decoration low electrostatic build up balance of fair mechanical properties and chemical resistance to oils, greases and aliphatic hydrocarbons possibilities of plasticization allowing very low moduli to be obtained fair electrical insulating properties fair performance/cost ratios food contact possibilities. 

For example, the small tolerance and low surface roughness of the plate in manufacture are critical for assuring the high electrical contact conductivity, low fluid flow resistance, and low water holdup to meet performance require-menfs of fhe plates. Moreover, to play the role of removing generated water in the cathode side—particularly to avoid flooding when fhe current density is high, the surface of the cathode plate may need hydrophobicity [11] so as to better adjust hydrophobic and hydrophilic properties of plate materials in cathode and anode plates. This area needs further study. 

Many published results on electronic transport properties of organic materials, where metal contacts are usually made by evaporation of metals, do not describe the quality of the organic/metal interface, and some exotic observed features may perhaps be ascribed to extrinsic effects such as metal diffusion. The relatively simple contact lamination technique may become an alternative, since it provides a means for establishing electrical contacts without the potential disruption of the organic material associated with metal evaporation. The method consists in bringing the organic layer into mechanical contact with an elastomeric element coated with a thin metal film, which can also be patterned. The contacts are robust and reversible... 

The conductance of MWCNTs is quantized. The experimental setup to measure the conducting properties involved the replacement of an STM tip with a nanotube fiber that was lowered into a liquid metal to establish the electrical contact. The conductance value observed corresponded to one unit of quantum conductance (Go = 2e /h = 12.9 kQ ). This value may reflect the conductance of the external tube because, for energetic reasons, the different layers are electrically insulated [150]. Finally, the conductance of semiconductor nanotubes depends on the voltage applied to the gate electrode their band gap is a function of their diameter and helicity [145] and the ON/OFF ratio of the transistors fabricated with semiconductor nanotubes is typically 10 at room temperature and can be as high as 10 at... 

The colour of gold adds to the attractiveness of the metal, and the liquid state of mercury allows the metal to be used over a wide range of temperatures in thermometers and electrical contact switches. These unusual properties are explicable in terms of relativistic effects. The relativistic effects on the 6s orbital are at a maximum in gold and are considerable in mercury. 

The hole conductor has a spiro-center (a tetrahedral carbon linking two aromatic moieties) that is introduced in order to improve glass forming properties and prevent crystallization. Crystallization is undesirable since it impairs the formation of a good electrical contact between the 2 surface and the hole transporting... 

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