Electric Potential Drop Research Articles

Electric field and electrode potential drops of arcs and glow discharges in air

A simple experimental arrangement consisting of two arcs burning in series has been devised for measurement of the voltage gradient in the discharge column. The method is based on reciprocal variation of the length of the discharges so that the total length during the measurement is constant. Experiments have been performed in the current range between 20 mA and 4 A in dry air at pressures between 20 and 150 kPa. In the arc mode the current dependence of the field can be approximated by the power function E∝Iα, where the exponent α for pressures between 60 and 150 kPa is −0.54 and slightly higher at lower pressures. The pressure dependence (at constant current) can be expressed in similar form E∝pm with the exponent m equal to 0.15 and 0.24 for currents of 1 and 4 A, respectively, and for pressures above 40 kPa. Average values of the zero-length voltage were obtained in the arc and glow discharge modes, namely, 14.5 V in the case of the arc and 367, 346, 331, and 331 V for the glow discharge at pressures of 20, 60 100, and 150 kPa, respectively.

Sensitivity of the Potential Drop Technique for Crack Length Measurement in a Chevron‐Notched Specimen

It is shown that the electrical potential drop technique applied to the study of fracture in chevron‐notched specimens is insensitive to errors in the potential and current interprobe distance measurements. It is concluded, therefore, that the method is useful whenever the contact area between the probe and material is difficult to define, i.e., for metal‐ceramic surface contacts.

Grand canonical Monte Carlo simulation of double-layer capacity

Based on hard-sphere ions and on a chargeable wall the metal-electrolyte interface was simulated by a grand canonical Monte Carlo procedure. This method works with ion movements and with single-ion additions and subtractions, the latter two leading to higher transition probabilities than the usual ion-pair approach. Ion-ion and ion-wall interactions cause an enrichment of ions of both kinds at the interface, which is correlated with the drop in electrical and chemical potential with respect to the bulk electrolyte, as was previously claimed by an electrochemical adsorption model for the differential capacity of double layers. Its dependence on some potential determining parameters was investigated. Although no quantitative agreement with experimental data could be found, some features of the adsorption model are now better understood. For instance, from the equivalence of the calculated electrical and chemical energy near zero point of charge (ZPC) it is concluded that double-layer charging is an electrochemical reversible process near ZPC. For charging far beyond ZPC an additional energy consuming polarization or orientation process must be introduced.

Crack propagation under creep-fatigue interaction condition.

Crack propagation behavior was investigated under creep-fatigue interaction conditions. The interaction was classified into two types : (1) the interaction between creep damage and fatigue damage introduced at the same time in each cycle : (2) the interaction between pre-creep (or pre-fatigue) damage and fatigue (or creep) damage introduced in the following cycle. In order to discuss these interactions, three kinds of crack propagation tests were conducted. The results obtained were sumarrized as follows : (a) There was a remarkable effect of interaction (1) on the intensity of the stress (strain or strain rate) field in the vicinity of the crack-tip but little effect on the fracture criterion in the fracture process zone. (b) The pre-creep or the pre-fatigue damage had little effect on the following crack propagation. (c) The result (a) was supported by the detailed observation of the crack propagation in a cycle by means of a d.c. electrical potential drop technique. The observation also revealed that the pre-damage affected the following crack propagation when the damage was extremely large.

Small specimen fracture toughness tests of HT-9 steel irradiated with protons

A method to evaluate the fracture toughness, using the recrystallization technique and a small punch test, has been developed on miniaturized specimens of ferritic/martensitic steel HT-9. The recrystallization technique, to measure the plastic strain region formed with crack extension in precracked disk-shaped compact tension (DCT) specimens, made it possible to evaluate the specimen-size independent elastic-plastic fracture toughness in irradiated ferritic steels. The electrical potential drop and acoustic emission measurements were also applied to detect the crack extension together with load/displacement curves in DCT specimens. The small punch tests demonstrated a clear ductile-brittle fracture energy transition behavior and good ductile-brittle transition temperature (DBTT) correlation with the Charpy V-notch tests results. The effect of proton irradiation and/or hydrogen charging on-the fracture behavior of HT-9 was observed.

Electric fields and currents in the earth's polar caps

A model for solar wind flow around the magnetopause incorporating a stagnation line at the frontside magnetopause is used to derive a formula for the electric field intensity and polar cap potential drop. These relationships are compared to experimental data from polar orbiting satellites. The relation between solar wind parameters and auroral arc velocity is also studied.

Tensile and shear fracture of an HSLA steel

Abstract : The purpose of this investigation was to characterize the mixed mode I - mode III fracture resistance of an HSLA steel, similar to ASTM A710 Grade A, of composition 0.04% C, 0.04% Nb, 1.17% Cu, 0.90% Ni, 0.70% Cr, 0.49% Mn, 0.27% Si, 0.20% Mo, 0.007% N, 0.010% P, 0.009% S, balance Fe. Plates of 12.7 mm thickness were heat treated according to two previously developed schedules to produce a ferritic structure containing either peak aged or overaged Cu precipitates. The compact specimen geometry and test procedures were identical to those used by Miglin et al with two exceptions. First, initial slots were inclined to the loading direction at angles of 90 (pure mode I), 75, 55, 45, and 35 degrees to produce varying ratios of mode III/mode I load components. Side grooves occupying a total of twenty percent of the section were also machined into the faces of the specimen prior to fatigue precracking to maintain crack propagation along the path of desired inclination angle. Without side grooves there are tendencies either for crack plane rotation or for double-shear formation during stable growth. Crack growth was monitored using the electric potential drop method.

In-plane fracture toughness of CFRP. 1st report Development of testing method.

A method for an in-plane fracture toughness test for CFRP is proposed in this paper. A new SEN tension specimen and loading grip system are developed for extremely anisotropic materials, such as CFRP. A personal computer program is developed in order to calculate the effect of anisotropy on the stress intensity factor, K, of the SEN tension specimen. The program is used to calculate KQ from the critical load at crack propagation. An a. c. electrical potential drop measuring system with a temperature compensation circuit is developed and applied to determine the crack initiation. Carbon/epoxy[0/90]laminates are used in the in-plane fracture toughness test. A procedure for the evaluation of fracture toughness, KC, is proposed based on the relation between KQ and the electrical potential drop at crack propagation.

Theory of the interface between a classical plasma and a hard wall

Abstract The interfacial density profile of a classical one-component plasma confined by a hard wall is studied in planar and spherical geometries. The approach adapts to interfacial problems a modified hypernetted-chain approximation developed by Lado and by Rosenfeld and Ashcroft for the bulk structure of simple liquids. The specific new aim is to embody self-consistently into the theory a “contact theorem”, fixing the plasma density at the wall through an equilibrium condition which involves the electrical potential drop across the interface and the bulk pressure. The theory is brought into fully quantitative contact with computer simulation data for a plasma confined in a spherical cavity of large but finite radius. It is also shown that the interfacial potential at the point of zero charge is accurately reproduced by suitably combining the contact theorem with relevant bulk properties in a simple, approximate representation of the interfacial charge density profile.

Hy‐wire measurements of atmospheric potential

A method of directly measuring the electric potential drop across the lowest portion of the atmosphere by using an apparatus called Hy‐wire is described. This tethered balloon‐borne system has been operated extensively at altitudes near 0.62 km at which voltages over 150 k V were measured with a high impedance device. Also described are measurements of system parameters such as system capacitance (5.6 pf/m), impedance (1010Ω), and response time (tens of seconds). Hy‐wire measurements from an around the‐clock experiment at Wallops Island, Va., having a characteristic repetitive diurnal pattern of variability exceeding 40% of the mean, are presented. This diurnal pattern is discussed in terms of both local and global current sources. A demonstration using Hy‐wire as a lightning channel model is also presented. These experiments have so far been conducted at mid‐latitudes but can also be flown from other locations in an effort to determine whether the lowest atmospheric electric circuit is affected by high altitude and possibly global current systems, and if so how much. The data presented in this paper are not definitive about the source of potential variations. The data are, however, representative of the new Hy‐wire technique and demonstrative of the potential usefulness of this technique.

Single ion activity coefficients based on the electrical double-layer model. Na 2SO 4 aqueous solutions

Single ion activity coefficients for Na 2SO 4 aqueous solutions have been determined by emf measurements of the cells: sce/Na 2SO 4 (aq., m)/SO 2− 4-reversible electrode and sce/Na 2SO 4 (aq., m)/Na +- selective electrode; coupled with electric potential difference measurements for the cell: Hg (σ = const)/Na 2SO 4 (aq., m)/ sce. The extra-thermodynamic assumption behind this approach is that the electric potential drop across the compact layer at the Hg/solution interface in the absence of ionic specific adsorption is strictly independent of the electrolyte concentration. Results show that γ + is higher than γ −, somewhat less than expected on the basis of the simple difference in ionic charge. γ + and γ − calculated with the aid of Stokes, Robinson and Bates' hydration theory have been found to deviate the other way round. In the light of these results some considerations can be made on the accuracy of Gouy—Chapman diffuse layer calculations.

MHD Pressure Drop of NaK Flow in Stainless Steel Pipe

An experiment on electric potential and pressure drop for NaK flow in uniform trnasverse magnetic fields was conducted. A test channel was constructed using 45.3 mm (or 28 mm) I.D. and 1.65 mm thick 304-SS circular pipe in the NaK-Blowdown MHD Experimental Facility of Osaka University. The experimental range covered had a driving gas pressure <8 bar, an applied magnetic flux density: B0=0.3∼1. 75 T, a mean flow velocity of NaK: U0=2∼ 15 m/sec, a Reynolds number Re=8×l04∼6.2×l05 and a Hartmann number: Ha=740∼4150.A theoretical analysis is given on the basis of a uniform-velocity thick-wall model. Good agreement between the theory and the experiment were obtained both for the potential and for the pressure drop, except a small deviation of the experimental pressure drop towards values lying above the theoretical ones in a weak B0 and high U0 region (Ha2/Re <15).

On the electrical potential analysis of a cracked fracture mechanics test specimen using the finite element method

The use of the finite element method to calculate electrical potential drop vs crack extension calibration curves for fracture mechanics test specimens is investigated. The influence of finite element mesh size and the use of singular elements at the crack tip are considered. Also, some of the details of the compact specimen geometry and electrical potential set-up are examined. Electrical potential solutions for very deep cracks in the compact specimen were obtained and extrapolated to a limiting case solution. A comparison of some of the solutions generated in this investigation with other available numerical solutions and experimentally measured data was very favorable.

A comparison of theoretical and experimental methods of calibrating the electrical potential drop technique for crack length determination

The calibration of the do pd technique for determining crack length in compact tension, corner notched and fin cracked test pieces is described. Good agreement is shown between finite element, conducting paper and specimen “beach marking” methods.

Plasma–wall transition in an oblique magnetic field

The effect of a magnetic field on the transition layer between a plasma and an absorbing wall is studied. A numerical model is used which simulates the motion of plasma particles in the electric and magnetic fields for a prescribed particle influx at the plasma boundary. Bohm’s condition for the existence of a monotonic profile of the layer is generalized. The transition layer proves to have a double structure comprising a quasineutral magnetic presheath preceding the electrostatic Debye sheath. The magnetic presheath scales with the ion gyroradius at the sound speed and with the angle of the magnetic field. The total electric potential drop between plasma and wall proves to be fairly insensitive to the magnitude and angle of the magnetic field.

Conduction and block by organic cations in a K+-selective channel from sarcoplasmic reticulum incorporated into planar phospholipid bilayers.

A collection of organic cations has been used to probe the gross structural features of the ionic diffusion pathway in a K+-selective channel from sarcoplasmic reticulum (SR). Channels were incorporated into planar phospholipid bilayer membranes, and single-channel currents were measured in the presence of ammonium-derived cations in the aqueous phases. Small monovalent organic cations are able to permeate the channel: the channel conductance drops sharply for cations having molecular cross sections larger than 18-20 A2. Impermeant or poorly permeant cations such as tetraethylammonium, choline, and glucosamine, among others, block K+ conduction through the channel. This block is voltage dependent and can be described by a one-site, one-ion blocking scheme. 19 monovalent organic cations blocks primarily from the trans side of the membrane (the side defined as zero voltage), and much more weakly, if at all, from the cis side (to which SR vesicles are added). These blockers all appear to interact with a site located at 63% (average value) of the electric potential drop measured from the trans side. Furthermore, block by 1,3-bis[tris(hydroxymethyl)-methylamino] propane (BTP) shows that the presence of a blocking ion increases the duration of the apparent open state, as expected for a scheme in which the blocking site can be reached only when the channel is open. The results lead to a picture of the channel containing a wide (at least 50 A2) nonselective trans entry in series with a narrow (20 A2) constriction.

Hydrodynamics of dielectric fluid films

We introduce a general hydrodynamic model to study the stability of lipid films against thermal fluctuations. As one novel aspect the model accounts before all for a complete intrinsic surface rheology of the film interfaces. Thus the rheological behaviour of the surface adsorbed lipids is modelled which screen the hydrophobic film interior against the aqueous exterior. For coloured films we demonstrate first the influence of electrical forces on the dynamics and film stability. For that we perform a linear stability analysis on a simplified mechanically symmetric film with i) symmetric surface charge distribution and ii) linear electric potential drop across the film. Based on the complete film model we then categorize the complete set of solutions of the linearized equations of motion and we study the growth rates of unstable film modes. Finally we discuss the stability properties of a black film after introducing a repulsive mechanism due to the steric hindrance of the interfacial lipids.

Mean spherical approximation for charged hard spheres near a charged hard wall in a neutralizing background

The distribution of charged hard spheres near a charged surface in a nonuniform neutralizing background is calculated using the integral equation method based on the mean spherical approximation for both bulk and surface direct correlation functions. The contact value of the distribution and the total electric potential drop are given and compared to the exact result. Various possible extensions of the model are discussed.

On the dynamic stability of fluid dielectric films

A simplified model of a fluid dielectric (hydrocarbon) film is introduced suitable for investigating the influence of electrical forces on the dynamics and film stability. Electrical and long range van der Waals interactions are treated as body forces. Linear stability analysis is carried through for a mechanically symmetric film with (i) symmetric surface charge distribution and (ii) linear electric potential drop across the film. Results in the limit of negligible viscosities call for special attention to repulsive interaction mechanisms in dielectric films free of charge.

Determination of single ion activities by relying on the electrical double layer model: NaF aqueous solutions

Single ion activity coefficients for aqueous solutions of NaF in the range m = 0.1 up to m = 0.9 mol kg−1 have been derived by measuring the potential difference of the cell Hg (σ = const)/NaF(m)/F−-selective electrode. The approach rests on the assumption that the electric potential drop across the Hg/solution interface is independent of the electrolyte concentration once the diffuse layer effects are accounted for by the Gouy–Chapman theory, provided specific adsorption of ions is absent. The derived γ− values have been compared with the "real" activity coefficients as determined by Rabinovich and Titov and with the predictions of the hydration theory of Bates and Robinson. It is shown that the latter do not agree with the present experimental observations. Possible reasons for this apparent discrepancy are discussed.