Combination Of Electrode Materials Research Articles

Computation methods for one-dimensional bipolar charge injection

Kerr electrooptic field-mapping measurements have shown strong space charge effects in high-voltage stressed dielectrics, where the magnitude and sign of injected charge depends on electrode material. With appropriate choice of electrode material combinations and voltage polarity is possible to have uncharged, unipolar positively or negatively charged, or bipolar charged dielectrics. The bipolar homocharge case lowers the electric field at both electrodes due to space-charge shielding, and thus allows a higher voltage without breakdown. Using charge-transport analysis the authors consider the general case of charge injection from both electrodes and solve time and space dependences of the electric field and charge distributions and the time dependences of the terminal voltage and current. This analysis extends earlier work by including nonequilibrium charge dissociation and recombination so that the effective ohmic conductivity is not constant but varies with time and position due to local net charge density. Specific cases discussed are the open-circuit voltage decay of an initially charged capacitor, the charging and discharging by a Marx generator, and alternating voltage excitations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Photo-excited effects in impurity doped double layer chalcogenide films

Photovoltage of mono- and double-layer of chalcogenide glass films was studied. The photovoltage consists of the Dember effects, the built-in potential at the interface between electrode and chalcogenide films and “photo-induced” potential barrier. Suitable combination of electrode materials and two chalcogenide films in double-layer structures generated a relatively large photovoltage of 0.5 V as a result of co-operation of these three mechanism.

Dielectric properties of water and water/ethylene glycol mixtures for use in pulsed power system design

One class of modern pulse power generators use deionized water as an energy storage, switching and transmission dielectric. Water is chosen for its high dielectric constant and relatively high resistivity, which allows reasonably sized and efficient low-impedance high-voltage pulse lines where pulse durations are less than 100 µs. Water/ethylene glycol mixtures are being researched, so that rotating machinery, rather than the usual Marx generator, can be used as the primary energy store. The high resistivity and high dielectric constant of these mixtures at low temperature permit low-loss operation on millisecond time scales. Simple design criteria linking load parameters and charging circuit characteristics to the liquid dielectric are developed which show that the dielectric constant, breakdown strength, and relaxation time are the primary properties of interest to the pulse power engineer. On time scales greater than 100 µs, injection of space charge, with density q and mobility µ, affects the charging and discharging circuit characteristics, introduces the time constant of the time of flight for injected charge to migrate between electrodes, and increases the effective ohmic conductivity σ to σ + qµ. A drift-dominated conduction model is used to describe measured space-charge effects. Kerr electrooptic field mapping measurements show strong space-charge effects with significant distortions in the electric field distribution a few hundred microseconds after high voltage is applied. The injected charge magnitude and sign depends on the electrode material. Thus by appropriate choice of electrode material combinations and voltage polarity, it is possible to have uncharged liquid, unipolar-charged negative or positive, or bipolar-charged liquid. An important case is that of bipolar injection, which has allowed up to a 40 percent higher applied voltage without breakdown than with no charge injection, and thus a doubling of stored energy due to the space-charge shielding which lowers the electric field strengths at both electrodes. Although injected space charge increases the stored electric energy over the capacitive space-charge-free energy, (1/2)CV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , more energy is required from a source during charging and the energy delivered to a resistive load is reduced because of internal dissipation in the capacitor as the charge is conducted to the electrodes. However, it appears that this extra dissipation due to injected charge can be made negligibly small and well worth the price if the space charge allows higher voltage operation for long charging time or repetitively operated machines.

Electro-Optic Charge Injection and Tramsport Measurements in Highly Purified Water and Water/Ethylene Glycol Mixtures

Extensive Kerr electro-optic field mapping and voltage/ current measurements have been taken with highly purified water over the temperature range of T= 0 to 30°C using parallel plane electrodes with average field strengths up to 160 kV/cm. The Kerr constant of water B was measured to be B ?, 3.4 to 3.6x1O-14 M/V2 for free-space light wavelength 590 nm and varies only slightly with temperature over the measurement range. Photomultiplier tube measurements at 633 nm at ?10°C found water to have a Kerr constant B ? 2.7 to 2.9x10-14 m/V2 while ethylene glycol had a negative Kerr constant B ? -(.8 to .9)x1O-14 m/V2. Water/ethylene glycol mixtures had an essentially linear variation of Kerr constant between these limits as a function of weight fractions, having a zero Kerr constant at about 79% glycol/21% water by weight . With pure water, a HV step has no volume charge at t=0. For times greater than 500 ?s, stainless steel and copper electrodes generally inject positive charge although under some conditions with mixed electrodes they injected negative charge, aluminum electrodes only inject negative charge, while brass electrodes can inject either positive or negative charge. Thus, by appropriate choice of electrode material combinations and voltage polarity, it is possible to have uncharged water, unipolar charged negative or positive, or bipolar charged water. Generally, the bipolar case allows a higher applied voltage without breakdown, presumably due to the lower electric field strengths at the electrodes due to the space charge shielding.

Spontaneous electric current from metal 1-regenerated cellulose-metal 2 system induced by temperature change

Abstract An appreciable current has been found to be induced under short-circuit conditions by heating a system consisting of a regenerated cellulose (RC) film coated on both sides with metals (M1, M2). The magnitude and direction of current depend on the choice and combination of electrode materials. The direction of current is the same for heating and cooling. The current is reproducible in successive heatings. The magnitude of current was found to be higher when the amount of water content in the films was higher. A peak in the plots of current versus temperature is observed at 130°C which might be the glass-transition temperature of the amorphous region of regenerated cellulose. This peak is larger when the sample absorbs moisture. The observed current is suggested to be due to some electrochemical reaction at the metal-polymer interface.

Thermo-Induced Electric Current from Viscose Rayon Sandwiched Between Metal Electrodes

Viscose rayon sandwiched hetween metal electrodes has been found to generate electric current with temperature variation. The current is reproducible in successive heatings and is of electrochemical nature, since the magnitude and direction of current depend on the choice and combination of electrode materials. The glass rubber transition tempera ture of viscose is found to lie in the range 43-68°C, depending on the amount of sorbed water. The current is enhanced and glass-transition occurs at lower temperatures with increasing water content. Similarity between the plots of (1 R vs. T and (Is) vs. T, and constancy of the open circuit voltage difference at high temperature indicate that the metal viscose-metal system may be assumed to form a galvanic cell.