The effect of polymer type on electric breakdown strength on a nanosecond time scale

Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength （EBD） on a nanosecond time scale is investigated, and a formula that qualitatively characterizes the relation between the electric breakdown strength and the polymer type is derived. According to this formula, it is found that the electric breakdown strength decreases with an increase in the effective relative dielectric constants of the polymers. By calculating the effective relative dielectric constants for different types of polymers, the theoretical relation for the electric breakdown strengths of common polymers is predicted. To verify the prediction, the polymers of PE （polyethylene）, PTFE （polytetrafluoroethelene）, PMMA （organic glass） and Nylon are tested with a nanosecond-pulse generator. The experimental result shows EBD （PTFE） 〉 EBD （PMMA） 〉 EBD （Nylon） 〉 EBD （PE）. This result is consistent with the theoretical prediction.

Patterning single-layer materials by electrical breakdown using atomic force microscopy

The development of nanoelectronics and nanotechnologies has been boosted significantly by the emergence of 2D materials because of their atomic thickness and peculiar properties,and developing a universal,precise patterning technology for single-layer 2D materials is critical for assembling nanodevices.Demonstrated here is a nanomachining technique using electrical breakdown by an AFM tip to fabricate nanopores,nanostrips,and other nanostructures on demand.This can be achieved by voltage scanning or applying a constant voltage while moving the tip.By measuring the electrical current,the formation process on single-layer materials was shown quantitatively.The present results provide evidence of successful pattern fabrication on single-layer MoS2,boron nitride,and graphene,although further confirmation is still needed.The proposed method holds promise as a general nanomachining technology for the future.

Preparation and Arc Breakdown Behavior of Nanocrystalline W-Cu Electrical Contact Materials

Nanostructured （NS） W-Cu composite powder was prepared by mechanical alloying （MA）, and nanostructured bulk of W-Cu contact material was fabricated by hot pressed sintering in an electrical vacuum furnace. The microstructure, electric conductivity, hardness, breakdown voltage and arcing time of NS W-Cu alloys were measured and compared to conventional W-Cu alloys prepared by powder metallurgy. The results show that microstructural refinement and uniformity can improve the breakdown behavior, the electric arc stability and the arc extinction ability of nanostructured W-Cu contacts materials. Also, the nanostructured W-Cu contact material shows the characteristic of spreading electric arcs, which is of benefit to electric arc erosion.

New Breakdown Electric Field Calculation for SF6 High Voltage Circuit Breaker Applications

The critical electric fields of hot SF6 are calculated including both electron and ion kinetics in wide ranges of temperature and pressure, namely from 300 K up to 4000 K and 2 atmospheres up to 32 atmospheres respectively. Based on solving a multi-term electron Boltz- mann equation the calculations use improved electron-gas collision cross sections for twelve SF6 dissociation products with a particular emphasis on the electron-vibrating molecule interactions. The ion kinetics is also considered and its role on the critical field becomes non negligible as the temperature is above 2000 K. These critical fields are then used in hydrodynamics simulations which correctly predict the circuit breaker behaviours observed in the case of breaking tests.

Electrical breakdown characteristic of a Ce-doped W-Cu contact material

W-Cu composite powder doped with Ce （1.5 wt.%） was prepared by mechanical alloying （MA）,and the W-Cu contact material was fabricated by hot pressing sintering in an electrical vacuum furnace.The microstructure,electric conductivity,hardness,and breakdown voltage of the Ce-doped W-Cu alloy were measured and compared with a conventional W-Cu alloy prepared by powder metallurgy.The results show that microstructural refinement and uniformity can improve the breakdown behavior and the electric arc stability of the Ce-doped W-Cu contact material.Also,the Ce-doped W-Cu contact material shows the characteristic of spreading electric arc,which is beneficial to electric arc erosion.

Experimental Study on Electrical Breakdown for Devices with Micrometer Gaps

The understanding of electrical breakdown in atmospheric air across micrometer gaps is critically important for the insulation design of micro ＆ nano electronic devices. In this paper, planar aluminum electrodes with gaps ranging from 2μm to 40 #m were fabricated by microelectromechanical system technology. The influence factors including gap width and surface dielectric states were experimentally investigated using the home-built test and measurement system. Results showed that for SiO2 layers the current sustained at 2-3 nA during most of the pre-breakdown period, and then rose rapidly to 10-30 nA just before breakdown due to field electron emission, followed by the breakdown. The breakdown voltage curves demonstrated three stages： （1） a constantly decreasing region （the gap width d 〈5 μm）, where the field emission effect played an important role just near breakdown, supplying enough initial electrons for the breakdown process; （2） a plateau region with a near constant breakdown potential （5 μm〈 d 〈10 μm）; （3） a region for large gaps that adhered to Paschen＇s curve （d 〉10μm）. And the surface dielectric states including the surface resistivity and secondary electron yield were verified to be related to the propagation of discharge due to the interaction between initial electrons and dielectrics.

Experimental Study on High Electrical Breakdown of Water Dielectric

By means of a coaxial apparatus, microsecond charging have been carried out with ferent ethylene glycol concentrations of ethylene pressurized water breakdown experiments with different surface roughness of electrodes and difglycol/water mixture. The experimental results about the breakdown stress and the effective time are presented. The breakdown stress is normalized to the situation that the effective time is transformed to 1 μs and analyzed. The conclusions are as follows： （1） the breakdown stress formula is modified to E = 0.561MA^-1/10teff^-1/^NP^1/8 ;（2） the coefficient M is significantly increased by surface polishing and ethylene glycol additive; （3） it is accumulative for the capacity of improving electrical breakdown strength for surface polishing, ethylene glycol additive, and pressurization, of which pressurization is the most effective method; （4） the highest stress of 235.5 kV/cm is observed in ethylene glycol/water mixture with an ethylene glycol concentration of 80% at a hydrostatic pressure of 1215.9 kPa and is about one time greater than that in pure water at constant pressure; （5） for pressurization and surface polishing, the primary mechanism to improve the breakdown strength of water dielectric is the increase in the breakdown time delay. Research results indicate great potential in the application of the high power pulse conditioning system of water dielectric.

Influence of Low Speed Rolling Movement on High Electrical Breakdown for Water Dielectric with Microsecond Charging

By means of a coaxial apparatus, high electrical breakdown experiments are carried out in the rest state and the low speed rolling state with microsecond charging and the experimental results are analyzed. The conclusions are： （1） the breakdown stress of water dielectric in the rolling state is in good agreement with that in Martin formula, and so is that in the rest state; （2） the breakdown stress of water dielectric in the rolling state is about 5% higher than that in the rest state; （3） the results simulated with ANSYS demonstrate that the breakdown stress of water dielectric decreases when the bubbles appear near the surface of electrodes; （4） the primary mechanism to increase the breakdown stress of water dielectric in the rolling state is that the bubbles are driven away and the number of bubbles near the surface of electrodes is decreased by rolling movement.

Applying Improved Electrical Breakdown Model to Study Insulating Property of c-C_4F_8/N_2 Gas Mixture

Perfluorocyclobutane(c-C4F8) has been recently considered as a potential alternative to SF6,because of its high electro-negativity and extremely low environmental effect.However,due to its high boiling point,c-C4F8 should mixed with buffer gases such as N2 or CO2 in order to avoid the liquefaction at low temperature.This paper investigates insulating properties of c-C4F8/N2 gas mixtures from two aspects including electrical strength,and Global Warming Potential(GWP).Moreover,improved electrical breakdown model of gas mixtures is founded.Breakdown temperature and breakdown electrical field in gas mixtures can be obtained from rigorous Townsend criterion expression according to gas mixtures ratio and cross section data of gas mixtures in this model.Under the condition of different gas pressure(0.1~0.4 MPa),gas mixtures ratio(0～30%),and electrode gap(2~10 mm),breakdown voltages of gas mixtures are calculated by using of this model.Insulation strength of SF6/N2 mixed gas is compared with c-C4F8/N2 mixed gas in the same conditions.Research results show that theoretical computation corresponds with experiment.If the content of c-C4F8 or SF6 in mixtures is less than 30%,insulation strength between c-C4F8/N2 and SF6/N2 is very close.Considering two indexes(breakdown voltage,GWP),it is suitable for c-C4F8 content being 15%～20% in c-C4F8/N2 gas

Electrical Breakdown Characteristic of Nanostructured W-Cu Contacts Materials

Nanostructured （ NS ）W-Cu composite powder was prepared by mechanical alloying （ MA ）, and nanostructared bulk of W-Cu contact material was fabricated by hot press sintering in an electrical vacuum furnace. The rnicrostructure, electric conductivity, hardness and break down voltage of NS W- Cu alloys were measured and compared to those of conventional W-Cu alloys prepared by powder metallurg＇y. The experimental results show that microstructural refinement and uniformity can improve the breakdown behavior and the electric arc stability of nanostructared W- Cu contacts materials. Also, the wanostructured W- Cu contact material shows the characteristic of spreading electric arcs, which is of benefit to electric arc erosion.

Applying the Different Statistical Tests in Analysis of Electrical Breakdown Mechanisms in Nitrogen Filled Gas Diode

This paper presents the results of our investigations of breakdown mechanisms, as well as a description of their influence on the distributions of time delay distributions, for a gas tube filled with nitrogen at 4 mbar. The values of the time delay are measured for different voitages, and the values of the relaxation times and their distributions and probability plots are analyzed. The obtained density distributions have Gaussian distributions and exponential distributions for different values of relaxation times （Gaussian for small values and exponential for large values of relaxation time）. It is shown that for middle values of relaxation time the delay distributions have a shape between Caussian and exponential distributions, which is a result of the different influences of electrical breakdown.

Air breakdown induced by the microwave with two mutually orthogonal and heterophase electric field components

The air breakdown is easily caused by the high-power microwave, which can have two mutually orthogonal and heterophase electric field components. For this case, the electron momentum conservation equation is employed to deduce the electric field power and effective electric field for heating electrons. Then the formula of the electric field power is introduced into the global model to simulate the air breakdown. The breakdown prediction from the global model agrees well with the experimental data. Simulation results show that the electron temperature is sensitive to the phase difference between the two electron field components, while the latter can affect obviously the growth of the electron density at low electron temperature amplitudes. The ionization of nitrogen and oxygen induces the growth of electron density, and the density loss due to the dissociative attachment and dissociative recombination is obvious only at low electron temperatures.

The influence of pore characteristics on rock fragmentation mechanism by high-voltage electric pulse

High-voltage electric pulse(HVEP)is an innovative low-energy and high-efficiency technique.However,the underlying physics of the electrical breakdown within the rock,and the coupling mechanism between the various physical fields involved in HVEP still need to be further understood.In this study,we establish a 2D numerical model of multi-physical field coupling of the electrical breakdown of porous rock with randomly distributed pores to investigate the effect of pore characteristics(porosity,pore media composition)on the partial electrical breakdown of rock(i.e.the generation of a plasma channel inside the rock).Our findings indicate that the generation of a plasma channel is directionally selective and extends in the direction of a weak electrical breakdown intensity.As the porosity of the rock increases,so does the intensity of the electric field in the‘electrical damage’region—the greater the porosity,the greater the effectiveness of rock-breaking.As the fraction of pore fluid(S_(water)/S_(air))gradually declines,the generation time of the plasma channel decreases,and the efficacy of rock-breaking by HVEP increases.In addition,in this study,we conducted an indoor experiment utilizing an electric pulse drill to break down the rock in order to recreate the growth mode of the plasma channel in the rock.Moreover,the experimental results are consistent with the simulation results.In addition,the development of this type of partial electrical breakdown is confirmed to be related to electrode polarity and pore characteristics via the experiment of the symmetrical needle-needle electrode arrangement,which further demonstrates the mechanism of partial electrical breakdown.This research is significant for comprehending the process of electric impulse rock-breaking and gives theoretical guidance and technological support for advancing electric impulse drilling technology.

Electromagnetic-Wave Mechanism of Formation and Propagation of Astrophysical Vortex Jets Generated in the Jumper of a Spiral Galaxy

An explanation of the mechanism of generation and acceleration of jets in outer space is given on the basis of experiments in the physics of electrical discharge. The presence of two arms in the spiral Galaxy gives grounds to assume that they have excess charges of the opposite sign. At the moment when the electric field strength between the tips of the arms becomes sufficient, an electrical breakdown occurs, which is accompanied by the movement of the current-plasma leader in the jumper between the tips of the arms. In the head part of the leader there is a flat electric domain of a strong field, which, during its inception, emits intense transverse electromagnetic waves in a direction perpendicular to the direction of the leader’s motion and to the plane of the accretion disk. The electric domain periodically appears and collapses due to the entry of neutral particles. Transverse electromagnetic waves capture charged particles from the discharge region and accelerate them in the direction of wave propagation. The crossed fields of an electromagnetic wave perform the functions of a multistage accelerator. The acceleration of the particles of the plasma produced in the discharge to relativistic energy values in the region of narrow vortex jets occurs under the action of forces caused by the components of the electromagnetic wave fields and the pressure gradient. The charged particles of a vortex jet acquire a significant rotational moment under the action of the Lorentz force. Explanations of the generation of microwave, bremsstrahlung and optical radiation from the region of the jumper between the arms of the Galaxy in the absence of electrical breakdown are also given.

Regulating local electric field to optimize the energy storage performance of antiferroelectric ceramics via a composite strategy

Electrostatic energy storage technology based on dielectrics is the basis of advanced electronics and high-power electrical systems.High polarization(P)and high electric breakdown strength(Eb)are the key parameters for dielectric materials to achieve superior energy storage performance.In this work,a composite strategy based on antiferroelectric dielectrics(AFEs)has been proposed to improve the energy storage performance.Here,AlN is selected as the second phase for the(Pb_(0.915)Ba_(0.04)La_(0.03))(Zr_(0.65)Sn_(0.3)Ti_(0.05))O_(3)(PBLZST)AFEs,which is embedded in the grain boundaries to construct insulating networks and regulate the local electric field,improving the Eb.Meanwhile,it is emphasized that AFEs have the AFE–FE and FE–AFE phase transitions,and the increase of the phase transition electric fields can further improve the recoverable energy density(Wrec).As a result,the Eb increases from 180 to 290 kV·cm−1 with a simultaneous increase of the phase transition electric fields,magnifying the Wrec to~144%of the pristine PBLZST.The mechanism for enhanced Eb and the phase transition electric fields is revealed by the finite element simulation method.Moreover,the PBLZST:1.0 wt%AlN composite ceramics exhibit favorable temperature stability,frequency stability,and charge–discharge ability,making the composite ceramics a promising candidate for energy storage applications.

Electrical breakdown of an acrylic dielectric elastomer: effects of hemispherical probing electrode’s size and force

Dielectric elastomers are widely investigated as soft electromechanically active polymers(EAPs)for actuators,stretch/force sensors,and mechanical energy harvesters to generate electricity.Although the performance of such devices is limited by the dielectric strength of the constitutive material,the electrical breakdown of soft elastomers for electromechanical transduction is still scarcely studied.Here,we describe a custom-made setup to measure electrical breakdown of soft EAPs,and we present data for a widely studied acrylic elastomer(VHB 4905 from 3M).The elastomer was electrically stimulated via a planar and a hemispherical metal electrode.The breakdown was characterized under different conditions to investigate the effects of the radius of curvature and applied force of the hemispherical electrode.With a given radius of curvature,the breakdown field increased by about 50% for a nearly 10-fold increase of the applied mechanical stress,while with a given mechanical stress the breakdown field increased by about 20% for an approximately two fold increase of the radius of curvature.These results indicate that the breakdown field is highly dependent on the boundary conditions,suggesting the need for reporting breakdown data always in close association with the measurement conditions.These findings might help future investigations in elucidating the ultimate breakdown mechanism/s of soft elastomers.

Pulsed actuation avoids failure in dielectric elastomer artificial muscles

Dielectric elastomer actuators(DEAs)are a class of artificial muscles capable of large linear strains(well over 100%),and with high energy density,and low cost and weight.One of the most prominent failure modes of a DEA is electrical breakdown,which can damage the device permanently,limiting its deformation capability.Breakdown is also common,since to maximize energy output,devices often operate near the breakdown limit.Elucidating breakdown mechanisms,as well as finding ways to prevent it,are of intense research interest.We show that by applying short electrical pulses,one could minimize the exposure of the DEAs to high leakage current,which is one of the main mechanisms for electrical breakdown.This allows one to operate at significantly higher potentials than the DC breakdown voltage.By applying pulses,we demonstrate up to 81.7%area strain repeatedly,at voltages more than twice the DC breakdown limit,without the risk of failure.The pulsed operation mode of DEAs accommodating higher voltages than possible with DC represents an opportunity for potential applications,safer and simpler device designs,and a technique for further study of DEA breakdown mechanisms.

Degradation patterns of silicone-based dielectric elastomers in electrical fields

Silicone elastomers have been heavily investigated as candidates for the flexible insulator material in dielectric elastomer transducers and are as such almost ideal candidates because of their inherent softness and compliance.However,silicone elastomers suffer from low dielectric permittivity.This shortcoming has been attempted optimized through different approaches during recent years.Material optimization with the sole purpose of increasing the dielectric permittivity may lead to the introduction of problematic phenomena such as premature electrical breakdown due to high leakage currents of the thin elastomer film.Within this work,electrical breakdown phenomena of various types of permittivity-enhanced silicone elastomers are investigated.Results showed that different types of polymer backbone chemistries lead to differences in electrical breakdown patterns,which were revealed through SEM imaging.This may pave the way towards a better understanding of electrical breakdown mechanisms of dielectric elastomers and potentially lead to materials with increased electrical breakdown strengths.

Silicone rubbers for dielectric elastomers with improved dielectric and mechanical properties as a result of substituting silica with titanium dioxide

One prominent method of modifying the properties of dielectric elastomers(DEs)is by adding suitable metal oxide fillers.However,almost all commercially available sili-cone elastomers are already heavily filled with silica to reinforce the otherwise rather weak silicone network and the resulting metal oxide filled elastomer may contain too much filler.We therefore explore the replacement of silica with titanium dioxide to ensure a relatively low concentration of filler.Liquid silicone rubber(LSR)has relatively low viscosity,which is favorable for loading inorganic fillers.In the present study,four commercial LSRs with varying loadings of silica and one benchmark room-temperature vulcanizable rubber(RTV)were investigated.The resulting elastomers were evaluated with respect to their dielectric permittivity,tear and tensile strengths,electrical breakdown,thermal stability and dynamic viscosity.Filled silicone elasto-mers with high loadings of nano-sized titanium dioxide(TiO_(2))particles were also studied.The best overall performing formulation had 35 wt.%TiO_(2) nanoparticles in the POWERSIL®XLR LSR,where the excellent ensemble of relative dielectric permittivity of 4.9 at 0.1 Hz,breakdown strength of 160 V µm^(−1),tear strength of 5.3 MPa,elongation at break of 190%,a Young’s modulus of 0.85 MPa and a 10% strain response(simple tension)in a 50 Vμm^(−1) electric field was obtained.

Investigation on the Structure and Performance of Polypropylene Sheets and Bi-axially Oriented Polypropylene Films for Capacitors

Polypropylene(PP) sheets are cast with various chill roll temperatures and rates, which are studied with differential scanning calorimetry, wide angel X-ray diffraction, scanning electronic microscopy and dielectric withstand voltage test system. The results show that increasing the chill roll temperature and cast rate can promote the increase of crystallinity and the growth of β-form. The PP sheets have asymmetric skin layer structures. The lower the chill roll temperature, the thicker the skin layer, the smaller the spherulite size. The electric breakdown strength(Eb) of PP sheets is mainly affected by the crystallinity but not the morphology. The PP sheets are further stretched to prepare bi-axially oriented PP(BOPP) films with various heat setting time. Our results indicate that the structure of PP sheets affects the properties of BOPP films. The as prepared BOPP films from the sheets cast at high chill roll temperature and rate have the highest crystallinity and Eb. Heat setting time has profound effect on the crystallinity and Eb, which increase first and then decrease with the heat setting time. It is expected that our study can provide guidance for optimizing process parameters.