Transitions between pitting and intergranular corrosion in AA2024

The pitting and intergranular corrosion (IGC) behavior of various tempers of AA2024 was investigated in 1 M NaCl. The breakdown potentials associated with pitting or IGC were determined. The breakdown potentials were found to be almost independent of sample orientation for any given temper. Artificial aging had a strong effect on polarization behavior and localized corrosion morphology. The anodic polarization curves of AA2024 in the solution heat treated and water-quenched condition, T3, and T3+ tempers exhibited two breakdown potentials, whereas overaged AA2024-T8, T8+, and solutionized and furnace cooled AA2024 exhibited only one breakdown potential. When two breakdown potentials were observed, the more active one was found to be related to the transient dissolution of S phase Al₂CuMg particles leading to pitting while the noble one was thought to result primarily from initiation and growth of IGC. The breakdown potentials decreased with increasing aging time at 190 °C, and only one breakdown potential was measured for T8 and T8+ tempers. Unlike the T3 temper, no sharp IGC was found for these tempers. Selected granular attack from breakdown of the copper-depleted matrix was believed to be the cause for localized corrosion in the T8 and T8+ tempers. The effect of nitrate and sulfate ions on the localized corrosion behavior was also studied.     

Detection and Analysis of Aerosol Particles by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was evaluated as a means for quantitative analysis of the size, mass, and composition of individual micron-to submicron-sized aerosol particles over a range of well-characterized experimental conditions. Conditional data analysis was used to identify LIBS spectra that correspond to discrete aerosol particles under low aerosol particle loadings. The size distributions of monodisperse particle source flows were measured using the LIBS technique for calcium- and magnesium-based aerosols. The resulting size distributions were in good agreement with independently measured size distribution data. A lower size detection limit of 175 nm was determined for the calcium- and magnesium-based particles, which corresponds to a detectable mass of approximately 3 femtograms. In addition, the accuracy of the LIBS technique for the interference-free analysis of different particle types was verified using a binary aerosol system of calcium-based and chromium particles.     

The effect of inorganic particles on the breakdown strength and mechanical properties of EVA-based composites

Ethylene-vinyl acetate (EVA) copolymer was melt-blended with different inorganic particles, such as alumina trihydrate (ATH), montmorillonite-based organoclay (CLO15A) and organophilic silica (R202) to produce (nano)composites with outstanding electrical breakdown strength. The composites loaded with different amount of particles were characterized by dielectric, rheological, morphological and mechanical properties. The addition of the particles resulted in an increase of electrical breakdown strength, whose results depend on the nature and amount of filler. The addition of 1%–5% of ATH resulted in an increase of 50% of this property. Similar results were observed for the composites loaded with 7% of CLO15A and R202. All composites displayed low values of dielectric constant and dielectric loss, which is interesting for insulator applications. The presence of the filler did not exert great influence on the rheological properties of the composites, thus keeping the good processability of EVA matrix. Finally, the composites containing the organoclay presented the best mechanical response.     

Enhanced energy storage property of plate-like Na0.5Bi4.5Ti4O15/poly(vinylidene fluoride) composites through texture arrangement

The plate-like Na_0.5Bi_4.5Ti₄O₁₅ (P-NBT4) particles were synthesized by molten salt method and dispersed in a poly (vinylindene fluoride) (PVDF) matrix. The alignment of P-NBT4 particles in PVDF matrix perpendicular to the direction of applied electric field could bring to impressive dielectric performance and breakdown strength to the composites. On the one hand, the excellent dielectric property of the P-NBT4/PVDF composites is ascribed to the high capacitance that is consist of P-NBT4 particles micro-capacitances. On the other hand, a higher breakdown strength of the P-NBT4/PVDF composites is owing to that strong barrier layer was formed in the composites by P-NBT4 particles alignment, which bring difficulty to form a conductive pathway. Moreover, the textured P-NBT4/PVDF composites exhibit a high energy density (9.45 J/cm³) and energy efficiency (η) of 52.28% under the critical electric field of 300 kV/mm.     

Recording the particle velocity spectrum at the time the shock wave reaches the surface of liquids of different viscosities

This paper presents the results of experimental studies of the cavitation breakdown of liquids in a wide range of shock-wave loading. The free surface velocity of liquids and the velocity spectrum of the cloud of particles and jets were measured using a laser heterodyne interferometer (photon Doppler velocimetry), and their size was determined. The spall strength of distilled water was determined.     

Enhanced dielectric response of ternary polymeric composite films via interfacial bonding between V2C MXene and wide-bandgap ZnS

Increasing the dielectric constant of polymer/sulfide ceramic composites by using wide-bandgap semiconducting sulfide ceramic fillers like ZnS is difficult because of their low interface polarization. To increase the dielectric constant, in this study, ternary polymer-based composite films were designed and fabricated using a hybrid filler consisting of shell-like ZnS particles and core-like V₂C MXene particles. First, V₂C MXene with a multi-layered structure was synthesized from the simplest raw materials followed by the in-situ hydrothermal growth of ZnS particles around the V₂C particles. Then, binary polymer/ZnS and ternary polymer/V₂C–ZnS composites were fabricated, and their dielectric, conductive, and electrical breakdown properties were investigated. Finally, the effect of interfacial bonding between the V₂C and ZnS phases was investigated by density functional theory calculations, and the contribution of V₂C/ZnS interfacial bonding to the higher dielectric constant of the ternary composites than that of the binary composites was explained. The ternary composites exhibited balanced electrical properties suitable for energy storage applications. The ternary composite with 10 wt% hybrid filler loading exhibited a high dielectric constant of ~52, a low dielectric loss of ~0.11 at 100 Hz, and a high electrical breakdown strength of ~202 MV m⁻¹. This study paves the way for the facile fabrication of high-performance composite dielectrics for application in advanced capacitors.     

Effects of alkyl/vinyl-modified nanosilicas on negative or positive high voltage direct current breakdown strength and tensile properties in silicone rubber nanocomposites

To develop silicone/nanosilica insulation materials for high voltage direct current (HVDC), hydrophilic surface of fumed nanosilica was changed to hydrophobic by modifying with various ratios of alkylsilane and alkylsilane/vinylsilane coupling agents and the effects of the modified nanosilicas on the HVDC breakdown strength under negative or positive polarities were studied. Dielectric and tensile properties were also studied. The surface modification was confirmed by Fourier-transform infrared spectroscopy (FT-IR) analysis and the weights of the alkyl and alkyl/vinyl groups on the modified nanosilicas were measured by thermogravimetric analysis (TGA). Silicone rubber nanocomposites were prepared by mixing a liquid silicone rubber (LSR) and the modified nanosilicas, in which the mixing ratio of the LSR to the nanosilicas was fixed to be 20 wt%. Transmission electron microscopy (TEM) was used to observe the even dispersion of the nanosilica particles in the LSR matrix, and it was found that the surface-modified nanosilicas were well dispersed in the form of nano-clusters with 20–60 nm in size. Electrical properties (±HVDC breakdown strength and dielectric properties) and mechanical properties (tensile strength and elongation-at-break) were estimated, and it was found that ±HVDC breakdown strength and tensile strength were maximal when the surface modification ratio of alkyl: alkyl/vinyl groups was 50: 50 wt%.     

High energy density nanocomposites based on poly(vinylidene fluoride‐chlorotrifluoroethylene) and barium titanate

Three series of poly (vinylidene fluoride‐chlorotrifluoroethylene)/barium titanate (BT) nanocomposites with varied compositions were fabricated via solution cast process followed by thermally treated in different ways. Quenching the composite samples at lower temperature could effectively enhance their dielectric constant, breakdown strength as well as the energy density. The highest energy density (13.6 J/cm³) is observed in the sample quenched from 200°C to ?94°C with 5 vol% BT, which is much higher than nanocomposites reported in the current literature. The addition of ceramic particles leads to the improvement of dielectric permittivity and energy density measured under the same electric field. However, the dielectric breakdown strength and the energy density measured at breakdown strength of the resultant composites are reduced as a function of BT content. The fixed maximum electric displacement and reduction of saturation electric field suggest that the addition of ceramic particles with high dielectric constant may help increase the energy density of composites under low electric field but not for high electric field. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.     

Aggregation and breakage kinetics of fresh cement paste

The influence of shear-induced forces on the microstructure of fresh cement pastes was studied. Aggregation and breakage kinetics of the paste matrix are highly influenced by the shear history. It was found that the kinetics of re-aggregation is relatively slow, and time scale for recovery is longer than the time needed for breakdown. When the aggregation kinetics dominates, network interactions among particles develop and the average floc size increases. When the breakage kinetics dominates, network interactions among particles are broken and are accompanied by a decrease in the average floc size. The results suggest that there is a limiting size to floc growth. Minor additions of clays can significantly impact the structural network development and result in a more flocculated structure. The flocs produced by the clays were highly stable flocs with strong interparticle bonds that were able to oppose floc breakage and floc erosion.     

Influence of the particle size and addition of K2O on the non-ohmic behaviour of ZnO praseodymium oxide varistors

The role of minor additions of K₂O in praseodymium oxide-doped ZnO varistors was investigated by changing the K₂O concentration on the one hand and the starting particle size of ZnO on the other. The results of this investigation show that up to 0·3 mol% K₂O effectively controls ZnO grain growth, especially with submicron powders, resulting in a considerable increase in the breakdown field. However, when the starting ZnO particle size is larger, higher K₂O additions are required in order to have an effective increase of the breakdown field. Hence it is possible to arrive at higher breakdown fields for praseodymium-doped zinc oxide, either by selecting zinc oxide particles in the submicron range or by the controlled use of additives such as K₂O.     

The effect of inorganic and organic nucleating agents on the electrical breakdown strength of polyethylene

Altering the morphology of polyethylene affects physical and electrical properties with reduced spherulite size correlating with higher electrical breakdown strength. Nucleating agents in polyethylene influence the final crystal morphology by increasing the number of spherulites and reducing spherulite size. Few studies are available that relate the nucleating activity to improved electrical breakdown strength. Although nanosilica is known to improve electrical breakdown strength of polyethylene in addition to serving as a nucleating agent, previous studies have not fully addressed the relationship between the improved breakdown strength and nucleating activity. In this article, direct current electrical breakdown strength and nucleation effects on morphology are assessed on a single set of controlled polyethylene compositions containing two types of surface treated nanosilica particles. The results are compared to composites with two types of organic nucleating agents 1,3:2,4‐bis(3,4‐dimethylbenzylidene) sorbitol or calcium 1,2‐cyclohexanedicarboxylate (CDA). CDA was the most effective organic nucleating agent and the hexamethyldisilizane treated nanosilica was the most effective inorganic nucleating agent in reducing spherulite sizes in low density polyethylene (LDPE). Reduced spherulite sizes in nucleated samples correlated with increased breakdown strength and lower conduction current compared to the neat LDPE. The LDPE sample with CDA also had the highest increase in crystallization temperature indicating stronger nucleating agent performance than the nanosilica and 1,3:2,4‐bis(3,4‐dimethylbenzylidene) sorbitol composite samples. The addition of these inorganic and organic nucleating agents all resulted in improvements in electrical breakdown strength. The results show that nucleation deserves more attention as a potential cause for improved breakdown strength observed with silica and organic nucleating agents. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46325.     

Structural changes and Raman analysis of single-walled carbon nanotube buckypaper after high current density induced burning

Single-walled carbon nanotube (SWCNT) buckypaper (BP) was exposed to high temperatures with electrical current-driven thermal heating either in the air or a vacuum. High electrical currents generate Joule heating and then cause breakdown of the BP in the air at over 400 °C due to rapid oxidation. In the vacuum, electrical resistive heating can generate temperatures of more than 2000 °C for the samples. Structural changes of SWCNTs after electrical current heating were observed using electron microscopy and Raman spectra. After breakdown of BP, the disorder-induced D-band increased and a smaller diameter related radial-breathing mode was reduced in the high temperature region. Structural transformations of SWCNT to other carbon nanostructures were observed after current-driven high-temperature treatment in the vacuum. In addition, surface-enhanced Raman scattering with intensity enhancement more than ten times was observed in the BP with agglomerated Fe or Ti particles.     

Effect of volume loading and surface treatment on the thixotropic behavior of polypropylene filled with calcium carbonate

The rheological properties of calcium carbonate‐filled polypropylene were examined using a Rheometrics dynamic analyzer. The study included steady shear test, transient stress growth test with sequential deformation history, and two‐step dynamic oscillatory shear flow. Thixotropic behavior was observed in transient tests for highly filled compounds when volume loading exceeding a critical value at about 20%. The material responses of these viscoelastic thixotropic materials depend on the duration of shear as well as on the rate of shear. The effects of filler on the rheological behavior of highly filled compounds are dominant at low strain rates; however, the effects of activity of the filler are almost negligible at high strain rates because of complete breakdown of the filler network. The timescales for structural changes in filled systems often become long compared with the viscoealstic time constants of the unfilled melt. The magnitudes of rheological properties and the degree of hysteresis appear to increase with increasing volume loading of filler particles. Conversely, surface treatment of fillers, which presumably reduces interaction between filler particles and the extent of agglomeration, results in major reductions of both rheological properties and the degree of hysteresis. The diverse experimental observations are interpreted in terms of a system forming a filler network due to weak interparticle forces. The thixotropy resulting from breakdown and recovery of the filler network is dependent on the characteristic time of the individual test.     

Influence of dynamic cyclic extension on the electrical conductivity of fast extrusion furnace (FEF) black loaded rubber vulcanizates

The influence of dynamic cyclic extension on the electrcal conductivity (σ) of 100 parts FEF carbon black loaded rubber (NR and SBR) vulcanizates was studied. The conductivity showed an initial rapid decrease with increasing cyclic strain amplitude, indicating a probable breakdown of the carbon black structure, owing to the masking of carbon particles by insulating rubber layers. The conduction mechanisms in these composites in terms of both the number of strain cycles and the strain amplitude were also studied. In addition, the temperature coefficient of conductivity was calculated for different amplitudes. It was greatly affected by the magnitude of the strain amplitude.     

Preparation of nano‐Ag particles and their modification on the mechanical and dielectric properties of epoxy resin

Nano‐Ag particles stabilized by a hyperbranched polymer (HBP) template were prepared for modifying the epoxy resin. The effects of preparation condition on the size and size distribution of Ag colloidal particles were studied. The Ag@HBP particles were then compounded with the epoxy resin to obtain the Ag@HBP/epoxy composites and the mechanical and dielectric properties of these composites were investigated. Dynamic mechanical analysis results show that the composites have higher loss factors than does the unmodified epoxy resin, which indicate better dissipation of mechanical energy and hence better shock or impact resistance. Fracture morphology of the composite shows a toughness feature. From the dielectric test results, the breakdown strength and dielectric constant of the composites at room temperature are increased, which can be explained by the Coulomb block effect. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Enhanced breakdown strength and energy density of antiferroelectric Pb,La(Zr,Sn,Ti)O3 ceramic by forming core-shell structure

Antiferroelectric Pb_0.97La_0.02(Zr_0.33Sn_0.55Ti_0.12)O₃@SiO₂ (with 5% mole of SiO₂) particles were synthesized by a citric acid sol-gel method. Transmission electron microscopy(TEM) results illustrated the formation of core–shell nanostructures with controllable shell thicknesses about 3–5?nm. X-ray diffraction(XRD) patterns displayed that a stable perovskite phase was preserved and no other crystallization peaks were discovered from the shell component. Scanning electron microscopy(SEM) and Energy Dispersive Spectrometer(EDS) investigations confirmed that core-shell structures were inherited from particles to ceramics after sintering. As a result, through the coating process, the breakdown strength of the ceramic increases by 95% from 12.2?kV/mm to 23.8?kV/mm and the recoverable energy density was greatly enhanced from 1.76?J/cm³ to 2.68?J/cm³. These results demonstrate a promising reaction method to enhance breakdown strength in antiferroelectrics for energy storage capacitor applications.     

Kombinierte Licht‐ und Radiowellenemission während des Bruches von Partikeln

The relationship between the light and radio impulses that appear during the stressing layers of glass particles was investigated. Particles were stressed between two metallic plates under applied high voltage. The emission of light appears during the development of the first cracks within the particle. The radio wave impulses were caused by electrical breakdown of a fragment layer. It appears after the light impulse. The delay between light and radio impulse of about a few micro seconds represents the characteristic time of size reduction.     

ESR study of silica‐filled SBR with different rubber/filler interactions

Silica‐filled styrene–butadiene rubber (SBR) unvulcanizates and their vulcanizates with different rubber/filler interactions were prepared by using several kinds of coupling agents. Tensile tests and electron spin resonance (ESR) measurements were carried out for both unvulcanized and vulcanized samples to get information on the effects of filler/rubber interactions on the breakdown of carbon–carbon (C? C) linkages in SBR and carbon–sulfur (C? S? C, C? S? S? C) linkages at the crosslinked points between rubber and sulfur by a tensile force. The combination of ESR results and stress–strain data suggested that with increasing the mechanical energy applied to the samples by the stretching, the carbon–sulfur linkages around silica particles were broken first, followed by the breakdown of carbon–sulfur and C? C linkages in the rubber matrix. The assignment of ESR spectrum was also discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The use of latex rubber-modified polystyrene as a model system for HIPS: Effect of particle size

The effect of particle size in high-impact polystyrene (HIPS) is difficult to determine because of a size polydispersity and changes in particle morphology during the HIPS synthesis process. In this study, poly(n-butyl acrylate) rubber core/polystyrene shell particles were made by emulsion polymerization methods such that the only difference was in particle diameter, which ranged from 0.4 to 6.2 μm. The latexes were subsequently incorporated into a polystyrene matrix to form a toughened composite that acted as a simple model for HIPS. Charpy impact energies (notched and unnotched) of the composites showed that there was no toughening for particle sizes less than 2μm in diameter. The optimal impact energy was obtained with particle diameters in the region of 2–3 μm at 8 wt % rubber loading. The results imply that craze stabilization is the most important aspect of the toughening process. A simple toughening model based on the crack opening displacement of craze breakdown between adjacent rubber particles is suggested, with interparticle distance as the most important variable. © 1993 John Wiley & Sons, Inc.     

Poly (vinyl chloride) processing morphology

This paper describes how morphology of PVC changes in the Brabender mixing head. At the range of temperatures used for PVC processing, the Brabender torque-time curve shows minimum torque and maximum torque. The minimum torque is associated with a breakdown of 150 μm PVC grains and 10 μm agglomerates resulting in the release of the 1μm primary particles. The torque increases from minimal interaction between primary particles to the point where primary particles agglomerate at maximum torque so that fibriles can be formed when PVC samples are swollen in acetone and sheard. Further heating reduces the viscosity resulting in lower torque even though residual primary particles still exist with much particle to particle interaction. Primary particle structure disappears at about 215° C with complete melting.