Function Of Poling Time Research Articles

Characterization of PDIV, PDEV, and RPDIV in Insulated Wires Under Unipolar Repetitive Square Wave Excitations for Inverter-Fed Motors

The behaviour of partial discharge inception voltage (PDIV), partial discharge extinction voltage (PDEV) and repetitive partial discharge inception voltage (RPDIV) as a function of exposure/poling time under unipolar repetitive square wave excitations at atmospheric pressure (1013 mbar) is experimentally measured and investigated. The partial discharge (PD) tests are performed on two commercially available insulated wires: Glass fibre as Type II and Polyether Ether Ketone (PEEK) as Type I insulated wires used in inverter-fed motors. The impact of excitation polarity, pulse repetition frequency and rise time on the PD quantities (i.e., PDIV, PDEV and RPDIV) is studied as a function of stressing duration. In addition, the trend of RPDIV and PDIV dispersion levels are compared as a function of poling time under positive and negative unipolar excitations with two rise times (i.e., 80 and 800 ns) and two pulse repetition frequencies (i.e., 50 Hz and 2.5 kHz), relying on the shape/slope parameter of the Weibull distribution. The collected data shows that the electric field induced by the interface charge deposited by PD occurring during consecutive pulses and the space charge accumulation in the insulation bulk plays a decisive role in PD quantities’ variations under unipolar repetitive square wave excitations.

Evolution of Protrusions on Lithium Metal Anodes Stabilized by a Solid Block Copolymer Electrolyte Studied Using Time-Resolved X-ray Tomography.

Growing demand for rechargeable batteries with higher energy densities has motivated research focused on enabling the lithium metal anode. A prominent failure mechanism in such batteries is short circuiting due to the uncontrolled propagation of lithium protrusions that often have a dendritic morphology. In this paper, the electrodeposition of metallic lithium through a rigid polystyrene-b-poly(ethylene oxide) (PS-b-PEO or SEO) block copolymer electrolyte was studied using hard X-ray microtomography. In this system, protrusions were approximately ellipsoidal globules: we take advantage of this simple geometry to quantify their growth as a function of polarization time and electrolyte salt concentration. The growth of 47 different globules was tracked with time to obtain average velocities of globule growth into the electrolyte. The globule diameter was a linear function of globule height in the electrolyte with a slope of about 6, independent of time and electrolyte salt concentration.

Structure of Lipid Nanoparticles Containing siRNA or mRNA by Dynamic Nuclear Polarization-Enhanced NMR Spectroscopy

Here, we show how dynamic nuclear polarization (DNP) NMR spectroscopy experiments permit the atomic level structural characterization of loaded and empty lipid nanoparticles (LNPs). The LNPs used here were synthesized by the microfluidic mixing technique and are composed of ionizable cationic lipid (DLin-MC3-DMA), a phospholipid (distearoylphosphatidylcholine, DSPC), cholesterol, and poly(ethylene glycol) (PEG) (dimyristoyl phosphatidyl ethanolamine (DMPE)-PEG 2000), as well as encapsulated cargoes that are either phosphorothioated siRNA (50 or 100%) or mRNA. We show that LNPs form physically stable complexes with bioactive drug siRNA for a period of 94 days. Relayed DNP experiments are performed to study 1H-1H spin diffusion and to determine the spatial location of the various components of the LNP by studying the average enhancement factors as a function of polarization time. We observe a striking feature of LNPs in the presence and in the absence of encapsulating siRNA or mRNA by comparing our experimental results to numerical spin-diffusion modeling. We observe that LNPs form a layered structure, and we detect that DSPC and DMPE-PEG 2000 lipids form a surface rich layer in the presence (or absence) of the cargoes and that the cholesterol and ionizable cationic lipid are embedded in the core. Furthermore, relayed DNP 31P solid-state NMR experiments allow the location of the cargo encapsulated in the LNPs to be determined. On the basis of the results, we propose a new structural model for the LNPs that features a homogeneous core with a tendency for layering of DSPC and DMPE-PEG at the surface.

Modeling of the second harmonic generation in SiO2 sol–gel films doped with nanoscopic DR1 molecules as function of the poling time

A physical description for the second harmonic generation (SHG) intensity as function of corona poling time in SiO2:DR1 sol–gel films is shown. This model describes the poling time dependence of the SHG based on a damped oscillator description of the nanomolecules of DR1. Instead of an usual biexponential or polynomial model with meaningless parameters, all the parameters from our model have a physical interpretation. The model results have been experimentally verified in several SiO2:DR1 sol–gel films with different side-chain doping concentrations.

Poling of Ferroelectric PT/P(VDF-TrFE) 0-3 Composite

Thick-film composites with 5 % to 30 % volume fraction of nanocrystalline lead titanate (PT) ceramic particles dispersed in a 70/30 mol-% vinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] copolymer matrix were prepared by solution casting followed by compression moulding. The crystal structure of the PT particles and the microstructure of the composite were characterized by XRD and SEM, respectively. The composites were poled at elevated temperature to produce samples with only the ceramic phase polarized. The poling current was recorded during the poling process, and a roughly exponential decay has been observed with "time constants" in the order of 10 3 s. The pyroelectric coefficient has been studied as a function of poling time. The built-up of the pyroelectric coefficient is faster than the decay of the poling current. Among composites with different ceramic loading the polarization develops with a higher rate in the composites with higher ceramic volume fraction. The polarization profiles of the poled composites have also been studied using the laser intensity modulation method (LIMM). Composite films with 30 % ceramic volume fraction poled for 10 3 s show a uniform polarization profile along the thickness direction, except in regions very close to the surfaces. The poling state of the ceramic inclusions was investigated by XRD. Intensity changes in the (002) and (200) diffraction peaks after poling reflect 90 domain switching in the PT inclusions. The poling ratio was estimated from the intensities of the diffraction peaks. A higher poling ratio of the ceramic inclusions was obtained in composites with higher ceramic volume fraction.

Poling of Ferroelectric PT/P(VDF-TrFE) 0-3 Composite

Thick-film composites with 5 % to 30 % volume fraction of nanocrystalline lead titanate (PT) ceramic particles dispersed in a 70/30 mol-% vinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] copolymer matrix were prepared by solution casting followed by compression moulding. The crystal structure of the PT particles and the microstructure of the composite were characterized by XRD and SEM, respectively. The composites were poled at elevated temperature to produce samples with only the ceramic phase polarized. The poling current was recorded during the poling process, and a roughly exponential decay has been observed with "time constants" in the order of 10 3 s. The pyroelectric coefficient has been studied as a function of poling time. The built-up of the pyroelectric coefficient is faster than the decay of the poling current. Among composites with different ceramic loading the polarization develops with a higher rate in the composites with higher ceramic volume fraction. The polarization profiles of the poled composites have also been studied using the laser intensity modulation method (LIMM). Composite films with 30 % ceramic volume fraction poled for 10 3 s show a uniform polarization profile along the thickness direction, except in regions very close to the surfaces. The poling state of the ceramic inclusions was investigated by XRD. Intensity changes in the (002) and (200) diffraction peaks after poling reflect 90 domain switching in the PT inclusions. The poling ratio was estimated from the intensities of the diffraction peaks. A higher poling ratio of the ceramic inclusions was obtained in composites with higher ceramic volume fraction.

XPS and STM Investigation of the Passive Film Formed on Cr(110) Single‐Crystal Surfaces

A combined ex situ x‐ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) investigation of the passive films formed on Cr(110) single‐crystal surfaces in 0.5M is reported. The composition, thickness, and structure of the passive films were studied as a function of polarization time and potential in the passive region. XPS measurements evidence the formation of a hydroxide layer of trivalent chromium in the outer part of the film, and of a layer of oxide of trivalent chromium in the inner part. Some amount of oxyhydroxide may be present in the inner part of the film. Aging of the passive film under polarization is critical for the development of the oxide inner part. The surface topography, assigned to the hydroxide layer, is characterized by disordered protrusions of 1 to 4 nm lateral dimensions and 4 to 8 Å vertical dimensions. Ordered domains of limited extension (≤3 nm), assigned to chromium oxide, are detected, showing the nanocrystalline character of the inner part of the passive film. These nanocrystals are separated by areas in which no order could be found on the surface and where no crystalline defects could be detected. The relationship between the measured structure of the passive film and the resistance to breakdown is discussed.

Second-order optical nonlinearity in corona-poled glass films

Several experiments were performed to elucidate the origin of the second-order optical nonlinearity χ(2) induced in the corona-poled Corning 7059 glass films. The values and the time decay of the second-harmonic coefficient d33 were measured for the glass films poled on several different kinds of substrates. The value of d33 was found to be dependent on the kinds of substrates. It was also observed that the glass films poled on a soda-lime substrate showed faster time decay of d33 than those poled on a Pyrex glass substrate. The glass films were also poled at room temperature, and the values of d33 were measured as a function of poling time. As a result, the value of d33 increased with the poling time and approached a value which was close to that obtained for the glass films poled at 100 °C. From the experimental results, it is speculated that the space charge formed in the vicinity of the interface between the glass film and the substrate contributes to the creation of the χ(2). The planar charge density at the glass-film–substrate interface is derived, and the experimental results are discussed.

Correlation between the piezoelectric constant d31 and b-axis distribution in polyvinylidene fluoride

Nuclear magnetic resonance linewidths are analyzed to provide information on dipole distributions in β-polyvinylidene fluoride as a function of poling time in order to establish the contribution of the dipole reorientation mechanism to the time evolution of the piezoelectric d31 constant. Results indicate that dipole reorientation proceeds continuously with time and is not uniquely associated with the initially rapid and subsequently slower evolution of d31 with time. It is observed that d31 correlates well with 〈cos 2δ〉, where δ is the angle between a typical b axis and the poling direction. The magnitude of 〈cos 2δ〉 and 〈4δ〉 which characterize the remanent polarization indicates that dipole alignment is far from perfect along the poling direction even in the most strongly poled material.

Room Temperature Poling of Poly(Vinylidene Fluoride) with Deposited Metal Electrodes.

High values of pyroelectric and piezoelectric activity in fully-electroded films of poly(vinylidene fluoride) were obtained by "conventional" (non-corona) poling at room temperature with sufficiently high fields. The avoidance of breakdown while obtaining high activity requires an understanding of the time dependence of both breakdown and activity. Time-to-breakdown as a function of field, and room-temperature pyroelectric activity (7-14 days after poling at 23.5 °C) as a function of poling time and field were obtained for 25-μm biaxially stretched films with evaporated aluminum electrodes. The highest activities were obtained by poling at the highest fields and poling to breakdown. A pyroelectric activity of 36 μCK-1m-2 was measured two weeks after poling with a nominal field of 550 MVm-1 for a nominal poling time of 10 s (reduced by multiple breakdown). The highest activity obtained with no apparent breakdown (31 μCK-1m-2) was measured a week after poling with a field of 400 MVm-1 for 10 s. These values are comparable with the highest that have been reported for this material using any poling temperature or using corona poling.