Breakdown In Liquids Research Articles

Underwater Electrical Discharge with a Large Surface of Radiation

Breakdown and formation of surface electric discharge in a zone of turbulent agitation of water jet transverse to the axis of an electrode system are studied. The jet boundary is actually a two-phase medium favorable for electron breeding consisting of cavitation microbubbles up to 107 cm-3 in volume. These features differentiate the considered discharge from a low-voltage breakdown in a stationary liquid. Abnormal properties of electric discharge in a submerged water stream take place both at the initiation and at the stationary stage. The threshold voltages are reduced by several times at the stream velocities of about 30 m/s, simultaneously the duration of the prebreakdown stage is reduced by one to two orders of magnitude. At the arc stage of the discharge, there is a developed emitting surface with plasma shell thickness being about 1 mm. The change of initial water conductivity by four orders of magnitude does not lead to large changes in breakdown dynamics.

3-dimensional water display

A displaying technique of real 3D dynamic images inside a transparent liquid is demonstrated for the first time. Images were formed by micro-flashes generated by means of laser breakdown in liquid. Amongst several types of liquid tested, tap water was found to be an optimal medium for the displaying due to its lowest breakdown threshold power. Electronic color filter was exploited for dynamic coloring of flashes in synchronization with 3D steering of laser beam's focal point.

Logarithmic Fermi-liquid breakdown in [formula omitted

The d-electron low-temperature magnet NbFe 2 can be tuned to the threshold of magnetism by varying pressure, magnetic field or composition. In particular, it is possible to select between ferromagnetism, long-wavelength spin-density-wave (SDW) (helical) order or a paramagnetic low-temperature state by adjusting the precise stoichiometry within the Nb 1 - y Fe 2 + y homogeneity range. Preparing samples close to the composition where magnetic order vanishes—the quantum critical point—enables the first detailed investigation of the thermodynamic and transport signatures of Fermi liquid breakdown in a transition metal compound. We report measurements of the heat capacity C and of the resistivity ρ in stoichiometric and slightly Nb-rich NbFe 2 samples, including a single crystal with the composition Nb 1.02 Fe 1.98 , which on the phase diagram is located very close to the quantum critical point ( T N ≃ 2.8 K ) . Both the resistivity and the heat capacity of the nearly quantum-critical single crystal display striking, robust non-Fermi liquid temperature dependences: while the heat capacity coefficient γ = C / T diverges weakly as C / T ∼ log T from 4 K down to 0.1 K, in line with theoretical predictions for 3-D ferromagnetic quantum criticality, the resistivity follows a T 3 / 2 power-law, familiar from the case of MnSi and naively predicted for the proximity of an antiferromagnetic quantum critical point.

Probing Lithium and Alumina Impurities in Air- and Water Stable Ionic Liquids by Cyclic Voltammetry and In Situ Scanning Tunneling Microscopy

In this paper we report on some results on the electrochemical breakdown of ionic liquids at the cathodic limit of the electrochemical window and on the probing of inorganic impurities in ionic liquids (originating from the synthesis) at the interface electrode/electrolyte by in situ scanning tunneling microscopy on Au(111). It will be shown that the restructuring/reconstruction of Au(111) in ultrapure 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]Tf2N) leads to a transition from a wormlike surface structure to a surface with well defined terraces. Close to the cathodic decomposition of the liquid the quality of the STM pictures gets worse and at the onset of massive ionic liquid breakdown a film forms on the gold surface finally shielding completely the gold terraces. When the [Py1,4]Tf2N liquid, made by a metathesis reaction from [Py1,4]Cl and LiTf2N, is not thoroughly washed after the synthesis, the in situ STM pictures show in a wide potential range the same surface structures as with the ultrapure liquid, but in the cathodic regime the deposition of lithium in only a few monolayers is observed. In the respective cyclic voltammograms on Au(111) there is clear evidence for lithium deposition. We show furthermore that a spectroscopically ultrapure 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ionic liquid ([EMIm]Tf2N) can show unexpected behaviour at the electrode/electrolyte interface when after synthesis it is subject to an Al2O3 treatment with the aim to remove organic impurities. Al2O3 seems to be dissolved in the ionic liquid in low concentrations and deposited at the electrode surface. At lower electrode potentials the alumina seems to be reduced to metallic aluminium. Our results show that even ultrapure ionic liquids can contain inorganic impurities which are very difficult to probe with conventional analytical methods. Better synthesis routes will be necessary to make ultrapure ionic liquids for fundamental physicochemical studies.

Anisotropic instability of dielectric liquids and decay to vapor-liquid system in strong electric fields

The results of a linear analysis for the stability of a homogeneous dielectric liquid with respect to density perturbations in a uniform electric field are presented. The electric field increases the instability increment for the stratification along the field and decreases this increment in the transverse direction. Thus, a strong electric field can induce anisotropic decay into liquid and vapor phases for a fluid that is initially both in a labile state and in a metastable or stable state. Theoretical calculations are confirmed by the results of numerical modeling of the fluid dynamics. The new regions of a low-density phase have the form of narrow cylindrical channels oriented along the field. This new mechanism of gas phase formation in strong local electric fields probably plays a key role in the inception and ultra-fast propagation of streamers during the breakdown in dielectric liquids in a nanosecond range.

Bubble departure in the direct-contact boiling field with a continuous liquid–liquid interface

Behavior of vapor bubbles was experimentally investigated in the boiling field where a volatile liquid layer of per-fluorocarbon PF5050 (boiling point 306 K) was directly in contact with an immiscible hot liquid layer of water above it. Heat was supplied to the continuous liquid–liquid interface by the impingement of the downward hot water jet. Vapor bubbles were generated not only from this continuous interface but from a large number of PF5050 droplets floating on it. According to precise observation, incipience of boiling did not occur at the liquid–liquid interface but in the PF5050 liquid close to the interface in both cases of continuous and dispersed interfaces. As a result, the bubbles broke up the thin PF5050 liquid film above them and rose up into the water layer. This bubble departure phenomenon, which does not occur in the ordinary pool boiling field on the solid heating wall, is very important to evaluate the heat transfer performance in the present direct-contact boiling system. For modeling this behavior, sizes of the bubbles were measured at the moment just after they were released into the water pool. Volumes of the bubbles were larger in the case of departing from the continuous liquid–liquid interface than from the droplets. This tendency could be explained by taking into account the buoyancy force acting on unit area of the thin PF5050 liquid film above the bubble before departure, which was one of the most important parameters for the liquid film breakdown.

Analysis of polarity effects in the electrical breakdown of liquids

Electrical breakdown simulations are carried out for liquids in response to a sub-microsecond (∼100–200 ns) voltage pulse. This model builds on our previous analysis and focuses particularly on the polarity effect seen experimentally in point–plane geometries. The flux-corrected transport approach is used for the numerical implementation. Our model adequately explains experimental observations of pre-breakdown current fluctuations, streamer propagation and branching as well as disparities in hold-off voltage and breakdown initiation times between the anode and cathode polarities. It is demonstrated that polarity effects basically arise from the large mobility difference between electrons and ions. The higher electron mobility leads to greater charge smearing and diffusion that impacts the local electric field distributions. Non-linear couplings between the number density, electric field and charge generation rates then collectively affect the formation of ionized channels and their temporal dynamics.

Decomposition of ionic liquids in electrochemical processing

The stability of ionic liquids with respect to high voltage differences is important for their use in electrochemical applications. Ionic liquids decompose when voltage differences larger than their electrochemical window (4–6 V) are applied. However, little is known about the decomposition mechanism and products. In this work the electrochemical breakdown of the ionic liquids 1,1-butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide and 1-butyl-3-methylimidazolium tetrafluoroborate on the cathode is predicted using quantum chemical calculations and validated by experiments. The quantum chemical calculations showed to be an excellent method to predict the electrochemical decomposition reactions and products.

Optical breakdown in a liquid: The slow phase of the dynamics of cavity collapse and a noncontact technique for pressure measurement in a liquid

It is demonstrated that, in the case of optically probing the breakdown region, a pulsed signal is formed due to the acoustic pulses produced by the breakdown and collapse of the cavitation cavity. The measured dependence of the delay time of the second pulse on the hydrostatic pressure in the liquid and the pressure of saturated vapor agrees well with the theoretical dependence corresponding to the hydrodynamic model of the cavity. On the basis of the optical cavitation effect, a technique is proposed for a noncontact measurement of hydrostatic pressure in a liquid enclosed in a sealed cell. The range of applicability of the technique is evaluated.

Microbubble-based model analysis of liquid breakdown initiation by a submicrosecond pulse

An electrical breakdown model for liquids in response to a submicrosecond (∼100ns) voltage pulse is presented, and quantitative evaluations carried out. It is proposed that breakdown is initiated by field emission at the interface of pre-existing microbubbles. Impact ionization within the microbubble gas then contributes to plasma development, with cathode injection having a delayed and secondary role. Continuous field emission at the streamer tip contributes to filament growth and propagation. This model can adequately explain almost all of the experimentally observed features, including dendritic structures and fluctuations in the prebreakdown current. Two-dimensional, time-dependent simulations have been carried out based on a continuum model for water, though the results are quite general. Monte Carlo simulations provide the relevant transport parameters for our model. Our quantitative predictions match the available data quite well, including the breakdown delay times and observed optical emission.

Are microbubbles necessary for the breakdown of liquid water subjected to a submicrosecond pulse?

Electrical breakdown in homogeneous liquid water for an ∼100ns voltage pulse is analyzed. It is shown that electron-impact ionization is not likely to be important and could only be operative for low-density situations or possibly under optical excitation. Simulation results also indicate that field ionization of liquid water can lead to a liquid breakdown provided the ionization energies were very low in the order of 2.3eV. Under such conditions, an electric-field collapse at the anode and plasma propagation toward the cathode, with minimal physical charge transport, is predicted. However, the low, unphysical ionization energies necessary for matching the observed current and experimental breakdown delays of ∼70ns precludes this mechanism. Also, an ionization within the liquid cannot explain the polarity dependence nor the stochastic-dendritic optical emission structures seen experimentally. It is argued here that electron-impact ionization within randomly located microbubbles is most likely to be responsible for the collective liquid breakdown behaviors.

Formation and propagation of waves during cavitation

The paper explores the collapse of a vapor bubble in a compressible fluid, accompanied by radiation from a divergent wave. The compressibility of a fluid is modeled using an isentropic equation of state of theta. The formation of a perturbation In the neighborhood of a bubble upon collapse, and then its propagation in surrounding the liquid upon re-expansion of the bubble. Divergent The wave is fairly accurately recorded in laser experiments breakdown of liquid, using sensors installed at some distance from the bubble. As for the formation of disturbances, in the literature there is a self-similar solution obtained for a liquid with equation Theta's state, which describes the final stage of the collapse. Based on this self-similar solution, a numerical scheme. After that, the numerical solution of the diverging wave is compared with available experimental data. Received good agreement with experiment.

Analysis of products from breakdown of liquid benzene, toluene and cyclohexane caused by Nd 3+:YAG pulsed laser irradiation

Products from liquid benzene, toluene and cyclohexane breakdown caused by strong Nd 3+:YAG fundamental pulsed laser irradiation were analyzed. Under nanosecond laser irradiation, hydrogen, methane, acetylene, ethylene, biphenyl, phenanthrene, anthracene and amorphous carbon were detected from liquid benzene and the laser intensity dependence of their yield was investigated. From laser intensity dependence of absolute quantity, it is suggested that biphenyl is produced by simple mechanism, while anthracene and phenanthrene are produced by diffusional collision of some kind of radicals via multi step reaction. In picosecond laser irradiation, the kind of products is same as those in nanosecond laser irradiation for liquid benzene, however yields of the products were higher because of stronger electric field. While in toluene and in cyclohexane same gaseous products as in benzene were detected. In particular, ethane was detected only from cyclohexane. In ultrasonic irradiation that is known as high pressure and high temperature reaction into liquid benzene and liquid toluene, results were different from those of laser irradiation. We could conclude that the reaction caused by near-infrared laser-induced breakdown is basically different from the reaction induced by high pressure and high temperature.

Breakdown of the Landau-Fermi liquid in two dimensions due to umklapp scattering

We study the renormalization-group (RG) flow of interactions in the two-dimensional ${t\ensuremath{-}t}^{\ensuremath{'}}$ Hubbard model near half-filling in an N-patch representation of the whole Fermi surface. Starting from weak to intermediate couplings the flows are to strong coupling, with different characters depending on the choice of parameters. In a large parameter region elastic umklapp scatterings drive an instability which on parts of the Fermi surface exhibits the key signatures of an insulating spin liquid (ISL), as proposed by Furukawa, Rice, and Salmhofer [Phys. Rev. Lett. 81, 3195 (1998)] rather than a conventional symmetry-broken state. The ISL is characterized by both strong d-wave pairing and antiferromagnetic correlations; however, it is insulating due to the vanishing local charge compressibility and a spin liquid because of the spin gap arising from the pairing correlations. We find that the unusual RG flow, which we interpret in terms of an ISL, is a consequence of a Fermi surface close to the saddle points at the Brillouin-zone boundaries which provides an intrinsic and mutually reinforcing coupling between pairing and umklapp channels.

Growth model for filamentary streamers in an ambient field

We have simulated the fast streamer stage of liquid dielectric breakdown as stochastic growth of a branching fractal tree. Breakdown and threshold properties of the fluid are represented in the random filter procedure. A range of fractal densities, from sparse to bushy, is approximated by the choice of power-law (4th-power to linear). The choice of threshold (cutoff) voltage also significantly affects the growth form. These parameters combine with the shape and concentration of the electric field, to regulate the distribution and directedness of the local discharge growth pattern. Inclusion of a voltage gradient along the streamer tree produces a secondary narrowing effect on the growth. A large grid (128 cubed) is used for the discretization. Diagonal growth paths to neighbor-vertices are included, increasing the choice of available directions for each discharge event. We use a combination of data-parallel programming and three-dimensional visualization. Complete growth histories, evolving from the voltage distribution, can be displayed in animation or in color banding against the "trials" variable, which simulates a time tick. Side views of the structures provide comparison against sub-microsecond snapshots from experiment. Results include sparse, directed trees evolving from a 4th-power-law filter; also dense trees from a linear filter, whose conical upper-envelope boundary is strongly influenced by the choice of threshold (cutoff) potential.

A new model for the primary process of electrical breakdown in liquids

A new model for the generation of electrical streamers in insulating liquids is proposed, It is based on the mechanical stress generated by the electric field and its influence on the cohesive properties of the liquid. In fields of 10/sup 8/ to 10/sup 9/ V m/sup -1/ the stress is sufficient to enhance significantly the thermal generation of sub-microscopic rupture surfaces (holes) in the liquid which has solid-like properties in the short time of streamer development. Using the well-known Griffith concept of mechanically-generated crack propagation in solids, it is then argued that, when the population of sub-microscopic holes becomes sufficiently large, the same stress encourages macro-crack development which has all the hallmarks of streamer growth, In this model electrical discharges do not have a traditional primary role although they will have an important secondary role once macro-cracks have developed.

Breakdown of liquids: area effect, volume effect or … particle effect?

It has been known for a long time that the electric strength of insulating materials decreased when the size of the material was increased. This size influence has been interpreted either as an “area effect” or as a “volume effect”. The controversy between the two effects still persists. From the physical standpoint, a clarification is desirable. This article states that conducting particles (omnipresent in liquids) are able to produce high local field enhancements and act as triggers which reduce the breakdown field of uniform and non-uniform gaps. Numerical computations of field distribution modified by the presence of a single particle (of different shape) are presented. From an analysis of typical data on particle counting and distribution size in transformer oils, associated with the present knowledge of streamer generation and propagation in oils, the author shows how particles present in the bulk of the liquid or at the electrode surface could trigger a breakdown.

Influence of dissolved gas on optical breakdown and small-angle scattering of light in liquids

It is demonstrated that the small-angle laser beam scattering pattern in liquid depends greatly on the dissolved gas content: the intensity of the scattering steeply drops after degassing doubly distilled water. It was experimentally found that the parameters or small-angle scattering of light correlate strongly with those of optical breakdown in liquid. Namely, the fractal dimension and the gyration radius of scatterers in aqueous KCl solutions behave similar to the optical breakdown probability in those liquids versus salt concentration, while the optical breakdown cannot be induced after degassing. The effect might be associated with the presence of stable gas microbubbles in liquid.

Spectroscopic measurements of streamer filaments in electric breakdown in a dielectric liquid

Emission spectroscopy has been utilized to provide information about the electron density and temperature in streamers and breakdown arcs in transformer oil. Recorded spectra include strongly broadened hydrogen Balmer- lines and vibration/rotation band profiles of the molecule. The origin of the observed broadening of hydrogen lines is discussed and it is concluded that it arises mainly from collisions with charged particles, so-called dynamic Stark broadening. By assuming that the broadening is due solely to dynamic Stark broadening, electron densities between and were obtained for the rear of positive streamer filaments during the later stages of propagation. For negative streamers we obtained an upper limit of and for breakdown arcs electron densities up to . The temperature information in the emission profiles and the intensity ratio of the hydrogen Balmer lines are discussed. Rough estimations of the temperature are presented both for positive and for negative streamers.

Size effect and statistical characteristics of dc and pulsed breakdown of liquid helium

Breakdown time lag in liquid helium is measured over a wide range of electrode sizes and pulsed electric field strengths. The breakdown time lag and dc breakdown strength are statistically analyzed by using the Weibull distribution function and weak link theory. It is found that the time lag depends on both electrical stress and the electrode surface area stressed above a critical level. It is supposed that breakdown triggering electrons are generated by field emission phenomena at small protrusion tips on the cathode surface. In higher external electric fields, a less sharper protrusion emits initial electrons with a shorter time lag and may become responsible for liquid breakdown. A theoretical equation is proposed to predict the electrode size and electrical stress dependency of the breakdown time lag, based on Fowler and Nordheim theory. It is shown that the equation is consistent with the Weibull distribution function under multiple stress of electric field and stressing time.