Electrokinetic ageing

Electrical endurance data, including that for plastic insulation, are frequently analysed using a Weibull statistical technique (see Section 8.17). Three ageing models are used in the literature thermodynamic [29], space charge life [30] and electrokinetic endurance [31]. As summarised in [32], they share some similarities in that they assume that there are several stages in the ageing process and that the dominant one involves the rupture and repair of chemical bonds within the plastic. The space charge life and electrokinetic... 

E E(t) EDM EDTA EDX EHD EKI EO EOF ESI-MS Ez Activation energy Exit-age distribution function Electro-discharge machining Ethylene-diamine-tetraacetic acid Energy dispersive X-ray Electrohydrodynamic Electrokinetic instability Electroosmotic-Electroosmotic flow Electrospray ionization mass spectrometry Electric field... 

The above electrokinetic model has implicitly only considered endurance under a steady electric field. Obviously many applications of polymeric insulation concern alternating fields, and it is well known that AC conditions are much more conducive to ageing and treeing than are DC ones. Hence it is important to extend our considerations to alternating fields. 

With smooth, nonporous surfaces the zero-point of charge and the isoelectric point usually do not differ much from each other. However, when porous particles, e.g., of activated carbons, are measured, the surface of the grains or particles may be acidic in character due to ageing while the internal surface is stiU basic. As mentioned before, aging in narrow pores is very slow due to diffusion restrictions. The electrokinetically measured lEP is determined by the -potential of the particle surface while the PZC is determined by the much larger interior surface of the particles [21]. 

In many publications, the preparation of samples for electrokinetic measurements and the measurement itself are described in detail. In a few other papers, the description is limited to the type of instrument. The potential is unequivocally defined by the composition of the solution in contact with solid particles. Therefore, conditions such as the solid-to-liquid ratio, aging, and ultrasonication should not affect the lEP. The use of optimum conditions for electrokinetic measurements may improve the reproducibility of results, but the lEP under different experimental conditions will be the same. In fact, in only a few studies was the experimental protocol indeed optimized, and in many other studies the experimental protocol was copied from other publications or arbitrarily selected. When the potential and lEP depend on the experimental conditions, information on these experimental conditions is essential. Eor example, the acidic branch of the electrokinetic curves (using the Acoustosizer) reported in [307] was rather... 

Plaza. R.C. et al.. Aging effects in the electrokinetics of colloidal iron oxides, J. Colloid Intetf. 245. 86. 2002. 

Kulkarni, R.D. and Somasundaran, P, The effect of aging on the electrokinetic properties of quartz in aqueous solution, in Proceedings of the Symposium on Oxide-Electrolyte Intetfaces, Alwitt, R.S., ed., The Electrochemical Society, Princeton, 1973, p. 31. 

In the meantime, the formation of the main alkaloids in C. ipecacuanha under a variety of conditions has been extensively investigated emetine (1) in callus cultures (49) and under the effects of L-tyrosine supplementation (5t)) emetine (1) and cephaeline (2) in Panamanian ipecac (57), in Nicaraguan ipecac (52), in regenerates obtained by clonal propagation (53,54), in tissue cultures (55) and under the effects of exogenous feeding of shikimic acid and L-phenylalanine (55), in cell suspension and excised root cultures (57), in adventitious root cultures (58), and in callus cultures (56,59) and the effects of age and electrokinetic potential (60) ipecoside (7) in the roots (61) and the effect oi Azotobacter, leaf mold, and farmyard manure on alkaloid content (62). In addition, micropropagation systems for C. ipecacuanha have been developed (63-65). 

The above-described dried soil was spiked with phenanthrene (600mg/kg) and with metal solutions (1000 mg/L) of low mobility lead and mobile nickel. The soil was left for the aging process. The contaminated soil in the above-described way was placed in eight electrokinetic cells and compacted in several layers. 

R. D. Kulkami and P. Somasundaran. Effect of Aging on the Electrokinetic Properties of Quartz... 

Electrokinetic remediation is highly dependent on rife-specilic geochemical conditions, such as soil composition, native electrolytes, pollutant aging, and pollutant mixtures. Several studies have integrated electrokinetic approaches for effective remediation of challenging polluted sites. Many of these studies are limited to bench-scale studies, and more field studies are needed to determine cost and effectiveness in field applications. Although several technologies have been developed to remediate polluted sites. 

Electrokinetic measurements on BaSO also lead to the conclusion that and SO4— arc the potential-determining ions The ero point of charge seems to jbe dependent upon the age and origin of the specimen used ... 

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