Lifetime Of Electrode Research Articles

Some requirements for electronic properties of a material for MHD: Thermal emission of electrons

There have been significant advances in MHD (magnetohydrodynamics) conversion recently. Hower, the lifetime of electrodes remains too short due to degradation derived from several mechanisms. Electrical degradation is a consequence of an ionic conductivity contribution and of inefficient thermal emission of electrons. The last factor is analyzed for oxides. Point defects are important to understand the effect of the gaseous environment and influence mainly the preexponential term in electron emission expressions. A correlation between the electron affinity χ and the band gap Eg may help to determine a rough value of χ. Oxides with low electron affinity and appropriate doping appear attractive for further research.

Laser-induced photoelectrochemistry: time-resolved luminescence studies of cds electrodes

The luminescence lifetime of a tellurium-doped CdS electrode in alkaline sulfide electrolyte has been determined. The decay is not a single exponential; the nominal lifetime varies from ⩽ 10 to⩾ 250 ns as a function of laser power, wavelength, and electrode potential. The results are discussed relative to recent steady-state luminescence measurements and time-resolved coulostatic photoelectrochemicai measurements.

Potentiometry of alkoxylates

The response characteristics of barium ion-selective electrodes to various alkoxylates have been investigated in aqueous and aqueous-ethanol test solutions in the presence and absence of barium ions and in the presence of sodium and potassium salts.The observed potentiometric response is an increase in the e.m.f. of the barium ion-selective electrode of up to about 100 mV, according to the amount of added alkoxylate in the 2 × 10–5–10–3M range. The response is linear with log[alkoxylate], but is characterised by a break in the linearity, which is attributed to the critical micelle concentration (CMC) of this class of non-ionic surfactants.The alkoxylates studied include nonylphenoxypoly (ethyleneoxy) ethanols (NPs) of the Antarox CO series, namely, CO-430, -630, -730, -850, -880 and -890; octylphenoxypoly (ethyleneoxy)ethanols (OPs), namely, Antarox CA-620 and Triton X-100; a sorbitan-9-octadecanoate poly (ethyleneoxy)ethanol, namely, Tween 80; alkylpoly (ethyleneoxy)ethanols, namely, Dobanol 25–7, Lutensol AO7 and Synperonic 7; a fluoroalkyl poly(ethyleneoxy)ethanol, namely, Monflor 51; poly(ethylene glycol)(PEG) 1540; and poly(propylene glycol)(PPG) 1025. CMCs were characterised in all instances except for PEG 1540, where the increases in the e.m.f. values were smaller than for the other materials studied.Anionic surfactants gave small decreases in e.m.f., but the cationic surfactant, benzyldimethylhexadecylammonium chloride, gave a large increase in e.m.f. characteristic of a cationic response.Exposure to alkoxylates reduced the lifetime of the barium ion-selective electrodes.

Neutral carrier ion-selective microelectrodes for measurement of intracellular free calcium

This paper describes the making and testing of calcium-selective microelectrodes for measurement of intracellular [free Ca 2+] levels. Pipettes of tip outer diameter down to 0.4 μm were siliconized by a novel and easy method of vapor treatment. The tips were filled with a sensor mixture using the neutral ligand and solvent of Oehme et al. (Oehme, M., Kessler, M. and Simon, W. (1976) Chimia (Aarau) 30, 204–206) but with very hydrophobic cations replacing Na + in the salt component. This change improved electrode stability and greatly reduced hysteresis in the responses to changing [Ca 2+] levels. Lowering the Ca 2+ concentration in the internal electrolyte also increased electrode lifetime. Electrodes showed a Nernstian response to [Ca 2+] down to 1 μM free concentration in 0.1 M KCl, and usually a useful response to below 100 nM Ca 2+. Selectivity for Ca 2+ over Mg 2+ and H + was sufficiently high that typical free intracellular levels of Mg 2+ and H + caused negligible interference. Selectivity for Ca 2+ over Na + was adequate for cells with 10 −2 M free Na +, but higher levels could raise significantly the detection limit for Ca 2+. Preliminary measurements of [free Ca 2+] have been made in frog skeletal muscle, ferret ventricular myocardium, and early embryos of Xenopus laevis. Relative merits of Ca 2+ microelectrodes and optical indicators are discussed.

Lead dioxide-coated carbon paste electrodes

Lead dioxide electrodeposited under optimized conditions on carbon paste provides an electroanalytically useful electrode, with an anodic working range extending to 1.9 V. Voltammograms for sulphite are used to study electrode lifetime and reproducibility; calibration graphs are linear up to 10 -3M sulphite in 0.5 M sulphuric acid.

Application of SEM for monitoring morphological changes on the surface of secondary cell electrodes during cycling

A method for observing a specific region of an electrode during its lifetime is described, enabling morphological changes on the electrode surface to be monitored. The use of the present method is briefly illustrated using as an example a sintered cadmium electrode in an alkaline medium. Many changes occur within secondary cell electrodes during cycling, for example, growth and dissolving of crystals, etc. These changes have been observed by a number of authors using various techniques, inter alia by means of both light and scanning electron microscopy [1-3]. Also in the course of our studies [4, 5] of phenomena determining the service life and reliability of sintered cadmium e/ectrodes a consideration of morphological changes of the electrode active mass proved to be necessary. Besides some commonly used techniques (for example measurements of electrochemical properties of electrodes, changes in the value of specific surface area, chemical composition, free pore volume, observations of active mass migration, microscopic observations of electrode cross-sections, etc.) an exploitation of scanning electron microscopy was found to be very useful. In order to be able to evaluate more precisely the course of the above-mentioned processes on the dectrode surface, i.e. to observe a specific region of the surface during the whole electrode lifetime (for example an individual crystallite of the active mass) and thus to eliminate in part, the necessity of a statistical approach to observed phenomena (as is the case when interpreting common micrographs of a randomly chosen area of the electrode), we have developed a new experimental technique, which is described in the following paragraphs.* Model cells of the electrodes under investigation were assembled, enabling the removal of the cadmium electrode at a pre-determined stage of its lifetime, the performance of necessary microscopic observations on it, and afterwards re-assembly of the cell. The electrodes used were circular plates 23 mm in diameter and 0.75 mm thick; they were washed and dried before measurement by a standard procedure. Observations were performed on totally discharged electrodes. The above-mentioned method may be modified in various ways, however, for example if certain experimental conditions are fulfilled (preventing oxidation during washing and drying) it is also possible to observe charged electrodes with good results. A system of two rectangular coordinate axes was used for finding the identical region for examination. The axes were marked mechanically on the surface of the sintered plate. The coordinate system must be as accurate as possible (sharp lines) and stable during the impregnation and cycling processes. However, other methods of finding the identical region may be used as well. This system was used in order to always obtain an identical orientation of the specimen image on the scanning electron microscope monitor. It was then possible to f'md the identical region of the electrode with fairly good precision, using micrometric displacement of the specimen pedestal, even

A PVC-based electrode sensitive to DDA + as a device for monitoring the membrane potential in biological systems

A polyvinyl chloride (PVC)-based membrane electrode sensitive to dibenzyldimethyl ammonium cation (DDA +) was constructed, and operational parameters such as the selectivity coefficients, the detection limit, and the response time were obtained. In comparison with the selectivity coefficients obtained with the previous liquid-membrane electrode, significant improvement was not obtained, but the response time became pronouncedly shorter. Furthermore, the electrode lifetime was remarkably prolonged. With the electrode developed, the change in the membrane potential of liposomes containing dibutyl ferrocene which separated oxidizing and reducing agent solutions was measured. The DDA + uptake, U, and the membrane potential estimated from U changed in accordance with the redox potential in the medium when the concentration of internal ferricyanide was kept constant. The membrane potential collapsed when the uncoupler of oxidative phosphorylation was added. The ANS fluorescence measurement indicated that negative charges appeared on energization with oxidizing-reducing agent. The change in membrane potential of mitochondria during energization was also measured. It was found that the liposome described above is a good model for the generation of membrane potentials in mitochondria.

Dynamic scattering in nematic liquid crystals under dc conditions. II. Monitoring of electrode processes and lifetime investigation

The electrochemical properties of a pure liquid crystal are presented which lead to the conclusion that the nonreversible liquid crystal oxidation is the main cause of degradation in dc-driven devices. This phenomena is avoided by the use of electroactive dopants which fulfill the conditions established in Paper I. It is shown that very-long-term dynamic scattering is obtained which could afford the feasibility of dc-driven industrial devices.

Turbulence-Model Predictions for a Flat Plate Boundary Layer

0.2 0.3 0^ TIME, msec Fig. 3 Typical oscillogram, photomultiplier current vs time. and the cathode was focussed on a photomultiplier. Periodic variation in the photomultiplier output signal would indicate the presence of a rotating spoke. Further discussion of the optical technique and equipment is given in Ref. 10. This investigation was carried out for argon mass flow rates of 0.04-0.12 g/sec, exhaust tank pressures of 2.0x 10~27.5xlO-2 torr, currents of 70-200 A, and magnetic field strengths of 0.0-0.24 tesla. Results and Discussion No periodic intensity oscillations, except those attributed to the 180 Hz power supply ripple, were observed for any combination of operating conditions. Specifically, no oscillations were present in the 25-300 kHz range expected for rotating spoke discharges. A copy of a typical oscillogram, showing luminous intensity as a function of time, is given in Fig. 3. These results were somewhat surprising in 'light of the previous reports which predicted critical magnetic fields in the 0.1-0.2 tesla range, with spoke rotational frequencies on the order of 50 kHz for the reported operating conditions. The possibility of insufficient oscilloscope response was checked by replacing the initial 300 kHz bandwidth instrument with another oscilloscope having an upper frequency limit of 150 MHz. Possible inhibition of spoke operation by relatively large power supply ripple was also considered. A capacitive filter was inserted in the power supply output circuit to reduce the ripple by approximately one order of magnitude. The additional experiments confirmed the absence of periodic oscillations for the range of operating conditions considered. The primary difference between the present experimental accelerator and those of the previously mentioned authors was in the cathode design. A consideration of the strong temperature dependence of electron emission and the thermal profile of the simple hollow cathode would suggest that this design would exhibit substantially more stable attachment than the more common conical design. We suggest that the observed cathode spot stability may have had a direct effect on the discharge mode, maintaining a uniform discharge in an operating region where spoke mode operation has been observed by previous authors. This result merits further study since the discharge mode may have a direct effect on the electrode lifetime and the operating efficiency of a plasma accelerator.

1081. Alloy for making parts of the cathode unit in electronic instruments: E M Savitskii et al, USSR Patent No 304642, appl 14 h Aug 1969, publd 15 th July 1971

Seven types of ion-selective chemical sensors based on poly(vinyl chloride) (PVC) as polymeric membrane, for determination of nitrate ion, have been prepared by using 3-nitro-o-xylene (NOX), tributylphosphate (TBP), bis-(2-ethylhexyl) sebacate (DOS), o-nitrophenyloctyl ether (o-NPOE), tris-2-ethylhexylphosphate (TEHP), dioctylphthalate (DOP) and dibutylphthalate (DBP) as plasticizers and tetradecil ammonium nitrate (TDAN) as ionophore. The response of each electrode was determined in relation to the lipophilicity of the plasticizer used, its rate of exudation to the aqueous phase, polarity, viscosity and its dielectric constant (εr). The experimental data was validated by calibrating the constructed electrodes against a reference Ag/AgCl electrode. The selectivity coefficient (KABPot) of the electrodes was determined by applying the standard mixed solutions method. No correlation between KABPot and εr of the plasticizer was found. ATR-FT-IR technique was used in order to evaluate the life-time of the polymeric membranes ion-selective electrodes (ISEs). The life-time of the electrodes was found to be limited fundamentally by the loss of the sensor and not due to the loss of the plasticizer. All the constructed ISEs showed Nernstian slopes with values of the practical detection limit (PDL) and lower limit of linear response (LLLR) in the range 10−6 to 10−5 mol/dm3. The electrodes constructed by using o-NPOE and/or DBP showed the longest life-time, this being longer than 6 months. The principal interfering anions were found to be ClO3−, BrO3−, Br−, Cl− and Bz− (benzoate). The selectivity loss of the sensors was found to be due to the loss of the ionophore by exudation. No correlation between the calculated values for KABPot of the electrodes and the dielectric constants of the plasticizers was observed.

A few instances, showing the possibility of applying the microscope to inorganic, qualitative analysis. A thesis

In this study, a novel interdigital electrode was employed during the laser percussion drilling of highly reflective materials. The main advantage of using interdigital electrodes is one-sided access for removing the charged particles in the plasma plume. Another benefit is the acceleration effect on the particles, which increases the drilling performance. Different configurations of interdigital electrodes were proposed and investigated in this work to provide a simple, low-cost method for expelling the laser-induced plasma plume generated during the laser percussion drilling process. Electrical fields with different electrode configurations applied to the charged particles carrying the ions were also simulated in this work. The results show that vaporized debris is expelled by applying an electrical field, and hence the penetration depth can be maximally increased by 84.9% through an optimal electrode configuration. Although the electrical field strength and drilling efficiency of interdigital electrodes show an underperformance compared with the plane electrodes, the lifetime of interdigital electrodes outperforms that of the plane electrodes owing to a less-scattered particle deposition.