2 Electroconductivity

Electroconductivity a is one of the most important characteristics of foams. For solid foams it determines the reliabflity of a foam as an electrical insulator, for liquid foams it serves as a technological parameter which is used to monitor foaming and hardening kinetics of gas-filled polymers. 

A general expression for the electroconductivity of two-phase systems with a random arrangement of spherical particles of the disperse phase is given by Wagner 

Calculations of the generalized conductivity (electroconductivity, thermal conductivity, dielectric and magnetic permeability) of heterogeneous systems have been carried out by Kemer and Odelevsky For a matrix heterogeneous system with cubical inchtaons whose centers form a cubic lattice and whose faces are parallel, Odelevsky s relationship may be applied  

Provided that G Gp (for liquid foams x of solutions x of air) we obtain Eq. (39) from Eq. (41) by substitution of k instead of G. In contrast to Wagner s formula, Odelevsky s formula holds for all concentrations of the disperse phase (gas) and for all types of gas-filled systems gaseous emulsions (d 0.74), spherical (0.74 d 0.9) and polyhedral ( 0.9) foams. It requires isotropy of the matrix structures and equal diameters of the disperse phase inclusions. Therefore, the dependence of the ratio of the foam to the solution electroconductivity on the degree of foaming in the general form is given by equation 

Elucidation of the electroconductivity mechanism and accurate calculation of the electroconductivity of highly foamed RO systems is of considerable interest. Important relevant information is provided by electroconductivity studies of liquid foams with a high foaming degree, e.g. based on surfactants. 

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The purpose of the nondestructive control consists in detecting local modifications of the material parameters which, by their presence can endanger the quality of the half-finished or finished products. The electromagnetic nondestructive control permits to render evident surface and subsurface discontinuities in the electroconductive material under test. The present tendency of this control is to pass from a qualitative evaluation (the presence or absence of the material discontinuities which give at the output of the control equipment a signal higher or at least equal to that coming from a standard discontinuity whose shape and severity has been prescribed by the product standards) to a quantitative one, which enables to locate as exactly as possible the discontinuity and to make predictions over its shape and severity. 

Copolymers of diallyl dimethyl ammonium chloride [7398-69-8] with acrylamide have been used in electroconductive coatings (155). Copolymers with acrylamide made in activated aqueous persulfate solution have flocculating activity increasing with molecular weight (156). DADM ammonium chloride can be grafted with cellulose from concentrated aqueous solution catalysis is by ammonium persulfate (157). Diallyl didodecylammonium bromide [96499-24-0] has been used for preparation of polymerized vesicles (158). 

Some polymers from styrene derivatives seem to meet specific market demands and to have the potential to become commercially significant materials. For example, monomeric chlorostyrene is useful in glass-reinforced polyester recipes because it polymerizes several times as fast as styrene (61). Poly(sodium styrenesulfonate) [9003-59-2] a versatile water-soluble polymer, is used in water-poUution control and as a general flocculant (see Water, INDUSTRIAL WATER TREATMENT FLOCCULATING AGENTs) (63,64). Poly(vinylhenzyl ammonium chloride) [70304-37-9] h.a.s been useful as an electroconductive resin (see Electrically conductive polya rs) (65). 

The sulfur nitrides have been the subject of several reviews (206—208). Although no commercial appHcations have as yet been developed for these compounds, some interest was stimulated by the discovery that polythiazyl, a polymeric sulfur nitride, (SN), with metallic luster, is electroconductive (see Inorganic highpolymers) (208,209). Other sulfur nitrides are unstable. Tetrasulfur nitride is explosive and shock-sensitive. 

Transparent electroconductive coatings of stannic oxide are deposited on nonconductive substrates for electrical and strengthening appHcations. However, the agents used to deposit the oxide film are actually stannic chloride. More recently, some organotin compounds have been employed. 

Common conductive polymers are poly acetylene, polyphenylene, poly-(phenylene sulfide), polypyrrole, and polyvinylcarba2ole (123) (see Electrically conductive polymers). A static-dissipative polymer based on a polyether copolymer has been aimounced (124). In general, electroconductive polymers have proven to be expensive and difficult to process. In most cases they are blended with another polymer to improve the processibiUty. Conductive polymers have met with limited commercial success. 

The carbon blacks used in plastics are usually different from the carbon blacks used in mbber. The effect of carbon black is detrimental to the physical properties of plastics such as impact strength and melt flow. Electroconductive grades of carbon black have much higher surface areas than conventional carbon blacks. The higher surface areas result in a three-dimensional conductive pathway through the polymer at much lower additive levels of the carbon black. The additive concentrations of electroconductive carbon blacks is usually j to that of a regular carbon black (132). 

If pure, the carbides of Groups 1 and 2 are characterized by their transparency and lack of conductivity. The carbides of Group 3, ie. Sc, Y, the lanthanides, and the actinides, ate opaque. Some, depending on composition, show metallic luster and electroconductivity. The cation may exist in the MC2 phases of this group, and the remaining valence electron apparendy imparts pardy metaUic character to these compounds. 

W. F. Verkelst, Electroconductive Black—Possibilities andEimitations, Scandanavian Rubber Conference, Akzo Chimie, Copenhagen, Denmark, 1985. 

A new ionic polymeric polycarbamate was synthesized after steps of polyurethane chemistry using 3-iso-cyanatemethyl-3,5,5-trimethylcyclohexyl isocyanate, 2,5-dimethyl-2,5-dihydroperoxyhexane, 1,6-butanediol, 2,4-tolylenediisocyanate, and N,N -bis(j3-Hydroxy-ethyOpiperazine [27]. Modification of the nitrogen of the piperazine ring into quaternary ammonium salt by treatment with methyliodide gave the MPI high electroconductivity. 

On the other hand, fluorine s high electronegativity and its ability to form mostly ionic chemical bonds, provide materials with several useful properties. First, compared to oxides, fluoride compounds have a wide forbidden zone and as a result, have low electroconductivity. In addition, fluorides are characterized by a high transparency in a wide optical range that allows for their application in the manufacturing of electro-optical devices that operate in the UV region [42,43]. 

Molten salt investigation methods can be divided into two classes thermodynamic and kinetic. In some cases, the analysis of melting diagrams and isotherms of physical-chemical properties such as density, surface tension, viscosity and electroconductivity enables the determination of the ionic composition of the melt. Direct investigation of the complex structure is performed using spectral methods [294]. 

Electro-conductivity of molten salts is a kinetic property that depends on the nature of the mobile ions and ionic interactions. The interaction that leads to the formation of complex ions has a varying influence on the electroconductivity of the melts, depending on the nature of the initial components. When the initial components are purely ionic, forming of complexes leads to a decrease in conductivity, whereas associated initial compounds result in an increase in conductivity compared to the behavior of an ideal system. Since electro-conductivity is never an additive property, the calculation of the conductivity for an ideal system is performed using the well-known equation proposed by Markov and Shumina (Markov s Equation) [315]. 

Fig. 88. Thermal pattern and electroconductivity dependence of K2TaF7 (curves 1 - 3), heating thermal pattern of an equimolar mixture K2TaF7 - KF (curve 4) and crystallization of K3TaFg (curve 5) t = temperature in °C, % = conductivity in relative units.

N.N. Savvin, Mechanism of Adsorption of Atoms, Radicals and Some Simple Molecules on Metal Oxides According to the Data on Electroconductivity and IR-spectroscopy, PhD (Chemistry) Thesis, Moscow, 1980... 

V.I. Tsivenko, Studies of Adsorption Nitrogen Atoms and Nitrogen-Hydrogen Radicals on Oxide Adsorbents by Electroconductivity Technique, PhD (Chemistry) Thesis, Moscow, 1973 B.S. Agayan, I.A. Myasnikov and V.I. Tsivenko, Zhum. Fiz. Khimii, 47 (1973) 1292 - 1296... 

Fig. 6.7. The change in electroconductivity of a zinc oxide film due to hydrogen atoms emitted from the surface of the formed layers of platinum on the surface of fused silica during introduction of molecular hydrogen The arrow head indicates the beginning of evacuation of hydrogen...

Kariv-Miller, E., Pacut, R. I., and Lehman, G. K. Organic Electroconductions at Very Negative Potentials. 148, 97-129 (1988). 

Miyahara T and Kurihara K. 2004. Electroconductive Langmuir-Blodgett films containing a carotenoid amphiphile for sugar recognition. Journal of the American Chemical Society 126(18) 5684—5685. 

Some theoretical prerequisites for application of modified and expanded graphites, Si- and Sn-based composites and alloys, electroconducting polymers as active materials, catalysts and electro-conductive additives for lithium - ion batteries, metal-air batteries and electrochemical capacitors are considered. The models and the main concepts of battery-related use for such materials are proposed. 

The decay of 1,1-dimethylethyl hydroperoxide into free radicals under action of mineral acids was also established [229]. The similar kinetic equation was observed in this system and the rate of initiation was found to be propotional to the electroconductivity of the solution. The following mechanism of free radical generation was proposed [229]. 

The introduction of 0.5 mol L 1 pyridine into 1,1-dimethylethanol containing phenol and hydroperoxide increases the rate constant kn from 10-4 to 1.2 x 10 L mol-1 s 1 (353 K) [121]. At concentrations lower than 0.1 mol L 1, pyridine enhances the rate of the reaction of p-methoxyphenol with hydroperoxide in benzene at 353 K from almost zero to v = 3.7 x 10 2[ArOH][ROOH][C5H5N] [121]. The addition of pyridine to tert-butanol with p-methoxyphenol increases both the reaction rate and the electroconductivity of an ArOH solution. All these results are in agreement with the following reaction mechanism ... 

Katsumata, M. and Endo, M. J.,Epoxy composites using vapor-grown carbon fiber fillers for advanced electroconductive adhesive agents, J. Mater. Res., 1994, 9(4), 841 843. 

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