Energy Distribution Plot Research Articles

Study on nonreciprocal radiation and photothermal conversion of VO2-based tunable inverse opal thermal emitter

In this work, a novel tunable nonreciprocal thermal emitter, consisting of an InAs magneto-optic inverse opal film and a VO2 film, is designed to achieve strong and tunable nonreciprocal radiation in the mid-infrared band of 6.8–7.8 μm. A more appropriate Lorentz-Drude model is used to describe the material properties of InAs, and the nonreciprocal band in the mid-infrared range for doped InAs is obtained through the Lorentz-Drude model. The effect of different middle layers on the structure of films and inverse opals is investigated under a magnetic field at an incident angle of 26° The inverse opal structure is found to have better nonreciprocal properties, while VO2 has the role of replacing noble metals in the tuning of nonreciprocal radiation. In addition, the strengthening mechanism of the inverse opal structure and the physical mechanism of the nonreciprocal radiation are further analysed and revealed through electric field energy distribution plots and impedance matching theory. A comparison of the nonreciprocal radiation and the photothermal effect of three inverse opal structures with different pore distributions and porosities for different parameters shows that the simple cubic structure has the strongest nonreciprocal radiation performance and a relatively high photothermal conversion effect, which can further increase the radiation capacity of the thermal emitter over a range. Therefore, the designed inverse opal composite structure can be used for the fabrication of tunable thermal emitters with nonreciprocal effects, where the amount of light absorbed in one channel of the thermal emitter can be controlled to tune the radiation capacity of the other channel. Providing a degree of assistance in the development and application of nonreciprocal thermal radiation devices in the mid-infrared wavelength band.

Electrochemical noise studies on the effect of nitrogen on the pitting corrosion of stainless steel using wavelet analysis

ABSTRACT The effect of nitrogen on the pitting process is investigated using the electrochemical noise (EN) approach in 0.01 M FeCl3 for 24 h at a sampling frequency of 1 Hz. The EN signals were investigated using wavelet analysis on four alloys of 316L SS containing varying quantities of nitrogen (0.07, 0.12, 0.14 and 0.22 wt-% nitrogen). Using an energy distribution (ED) and standard deviation of partial signal (SDPS) plot, the primary corrosion process in various nitrogen-containing 316L SS was found. The ED plot showed that as the nitrogen percentage in the alloy increased, the energy of the low-frequency signal decreased, indicating that long-time transients were suppressed. The SDPS figure revealed a drop in pit density as nitrogen levels increased. For specimens containing 0.07, 0.11, 0.14 and 0.22 wt-% nitrogen, the pit density was determined to be 439 ± 8, 383 ± 6, 212 ± 6 and 108 ± 4 pits mm−2, respectively.

Corrosion behavior of WB36CN1 steel at different flow rates

Purpose This paper aims to study the effect of flow rate (0.42∼2.09 m/s) on the corrosion behavior of WB36CN1 steel pipe in the simulated secondary circuit water environment (170°C, 6 mg/L ethanolamine + 100 µg/L NaCl), for which an autoclave was used to simulate the secondary circuit environment for carrying out related experiments. Design/methodology/approach The corrosion behaviors were studied by electrochemical methods, morphological observations and elemental analysis. Findings As flow rate increases, the amplitude of the current noise fluctuates increased, noise resistance Rn and spectral noise resistance Rsn decreased, the shear stress on the surface of WB36CN1 steel increases, the oxygen content on the surface decreases, the roughness becomes smaller. Meanwhile, the energy of energy distribution plot is concentrated at high frequencies under the three flow conditions, the slopes of current power spectral density curve approach 0 db/decade. This means that the oxide on the surface becomes less and corrosion rate increases with increasing flow rate. The corrosion type of WB36CN1 steel was uniform corrosion; the degree of uniform corrosion is higher at high flow rate. Originality/value The effect of flow rate on the corrosion behavior of WB36CN1 steel pipe in the secondary circuit water environment was studied by using electrochemical methods in the laboratory. The effect mechanism of flow rate for corrosion behavior was obtained.

Identifying sulfide stress cracking stages on a HSLA pipeline steel in H2S environment by electrochemical noise

Abstract Sulfide stress corrosion (SSC) in high strength low alloy (HSLA) pipelines was investigated in the work. Ultrasonic inspection and in-situ electrochemical noise (EN) measurements were carried out during stress corrosion experiments to monitor the progress of sulfide stress cracking in H2S environment. Moreover, the interrupt experiments were employed to reveal the evolution of corrosion morphology during SSC through the analysis for the EN signals. Microstructural characterization was also performed to identify the morphological evolution owing to the stress corrosion. It is found that the process of SSC is divided into three stages: uniform corrosion stage, pitting or local corrosion stage and cracks propagation stage. The period of time that the uniform corrosion transforms to the local/pitting corrosion is in the range of 12-24 h. The EN analysis results, such as time-domain curves, power spectral density (PSD) diagrams, energy distribution plots (EDPs) and current kurtosis, correspond to the microstructure observation and ultrasonic inspection. Especially, the recognition of crack initiation by current kurtosis curves correlate well with that by the ultrasonic inspection, which suggests that the current kurtosis analysis could provide the information for crack initiation in real time

CORROSION PROCESS OF MULTILAYER ALUMINUM-BRAZED SHEET BY EIS AND EN TECHNIQUES

The microstructures of AA4045/AA3003Mod./AA4045 aluminum-brazed sheet were observed and determined by stereoscopic digital microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS). The corrosion process of the brazed sheet in the exfoliation corrosion (EXCO) solution was investigated by electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) techniques. The results showed that the brazed sheet was composed of the Al-Si eutectic zone, the precipitates-free zone (PFZ), the band of dense precipitates zone (BDP) and the core material. With the immersion time increased, the capacitive time constant in EIS plot changed from one time constant through two unclear time constants to two clear time constants, and then went back to two unclear time constants again. The maximum relative energy in energy distribution plot (EDP) changed from small scales through middle scales to large scales, and then went back to middle scales. The corrosion process could be divided into four stages: the dissolution of the eutectic [Formula: see text]-Al in the resolidified clad in the form of pitting corrosion; the corrosion of the primary [Formula: see text]-Al grain boundaries in the form of intergranular corrosion (IGC); the corrosion of the BDP zone in the form of exfoliation corrosion; and the corrosion of the core material in the form of IGC.

A new hard X-ray-selected sample of extreme high-energy peaked BL Lac objects and their TeV gamma-ray properties

ABSTRACT Extreme high-energy peaked BL Lac objects (EHBLs) are an emerging class of blazars with exceptional spectral properties. The non-thermal emission of the relativistic jet peaks in the spectral energy distribution (SED) plot with the synchrotron emission in X-rays and with the gamma-ray emission in the TeV range or above. These high photon energies may represent a challenge for the standard modelling of these sources. They are important for the implications on the indirect measurements of the extragalactic background light, the intergalactic magnetic field estimate, and the possible origin of extragalactic high-energy neutrinos. In this paper, we perform a comparative study of the multiwavelength spectra of 32 EHBL objects detected by the Swift-BAT telescope in the hard X-ray band and by the Fermi-LAT telescope in the high-energy gamma-ray band. The source sample presents uniform spectral properties in the broad-band SEDs, except for the TeV gamma-ray band where an interesting bimodality seems to emerge. This suggests that the EHBL class is not homogeneous, and a possible subclassification of the EHBLs may be unveiled. Furthermore, in order to increase the number of EHBLs and settle their statistics, we discuss the potential detectability of the 14 currently TeV gamma-ray undetected sources in our sample by the Cherenkov telescopes.

Monitoring localized corrosion of Inconel 82 weld overlay on 304L SS weld by electrochemical noise

The manuscript presents the results from the electrochemical noise (EN) monitoring of Inconel 82 weld overlay on Type 304L stainless steel (SS) weld in 0.01M FeCl3. The microstructure of the weld overlay obtained from optical and scanning electron microscopy (SEM) showed an austenite structure, containing equiaxed dendrites and secondary phases at the interdendritic region. Energy dispersive spectroscopy (EDS) attached to SEM revealed the secondary phases to be Nb rich Laves phase. The electrochemical potential noise was monitored using a three identical electrode configuration. The acquired signals were detrended, and wavelet analysis was employed to encode useful information from the noise transients. Visual examination of the potential noise-time record contained distinct high amplitude transients typical of localized corrosion attack. The energy distribution plots (EDP) of the potential noise derived from wavelet analysis depicted maximum relative energy on D6-D8 crystals, which represent large time scale events such as those occurring from localized attacks. Also, repassivation events too could be divulged from the potential EDP. The micrographs of the post electrochemical noise experimented specimens revealed the occurrence of localized attacks along the interdendritic region and none inside the dendritic cores. The presence of secondary phases along the interdendritic regions was found to be detrimental in chloride medium, imparting inferior localized corrosion resistance to the weld overlay.

Aerodynamic Influence of Added Surfaces on the Performance Characteristics of a Sports Car

External aerodynamics plays a vital role in designing high-speed vehicles since a reduction in drag and positive lift generation are principal concerns in vehicle aerodynamics to ensure superior performance, comfort, and vehicle stability. In the present study, the effect of added surfaces such as NACA 2412 wings and wedge type spoiler at the rear end of a sports car are examined in detail using three-dimensional numerical simulations substantiated with lab scale experiments. The simulations are performed by solving Reynolds-averaged Navier–Stokes equations with a realizable k-e turbulence model using ANSYS Fluent software for Reynolds numbers 9.1 × 106, 1.37 × 107 and 1.82 × 107. The results obtained from simulations are validated with the experiments performed on a scale down model at the low-speed wind tunnel using a six component external pyramidal balance. The variation in the wake flow field of the vehicles with different added surfaces are demonstrated using pressure and velocity contours, velocity vectors at the rear end, and the turbulent kinetic energy distribution plots. It is observed that the positive lift coefficient of the base model is reduced drastically by incorporating a single wing at the rear end of the vehicle. The aerodynamics coefficients obtained from different configurations suggest that the two wing configuration has lesser drag than the wedge type spoiler though, the negative lift is higher with a wedge than the two wing configuration.

Adsorption and protective behavior of BTAH on the initial atmospheric corrosion process of copper under thin film of chloride solutions

The initial corrosion process of copper and the corrosion resistance mechanism of Benzotriazole under chloride-containing thin electrolyte layer (TEL) was investigated. After theoretical calculation and experimental characterization, the forming process of [Cu(I)BTA]n film was chemically adsorbed on copper surface by Cu-N bond tightly; corrosion rate increased as TEL thickness decreased. Whilst, energy distribution plot of electrochemical noise provided the validity of corrosion type, and the purported corrosion energy (Ec) deduced from electrochemical noise was approximately proportion to corrosion rate (1/Rct) with and without the anticorrosion film, which denoted the feasibility to determine corrosion rate by nondestructive on-line monitoring electrochemical noise progress.

Correlation between the corrosion rate and electrochemical noise energy of copper in chloride electrolyte.

An electrochemical noise technique has been applied to describe the corrosion process of copper. The results show that the sampling frequency clearly changes both the energy distribution plot and the power spectral density spectra, which should be taken into consideration strictly and logically before an electrochemical noise test. The corrosion energy, (Ec), deduced using the fast wavelet transform method showed a similar variation trend with corrosion rate. Hence, the proposed parameter Ec represents the corrosion rate or severity.

The effects of wall roughness on the methane flow in nano-channels using non-equilibrium multiscale molecular dynamics simulation

This paper presents a non-equilibrium multiscale molecular dynamics simulation method to investigate the effects of periodic wall surface roughness on the structure and mass transfer of methane fluid through the silicon nano-channels. In order to accurately capture the trajectories and microstructure of methane nano-fluidics, the present modification of OPLS fully atomic model is employed. Meanwhile, we introduce the corresponding coarse-grained model to solve the problem of wall–fluid interaction for methane Poiseuille flow within silicon atomic walls using the classical Lorentz–Berthelot mixing rules. The geometries of the upper wall roughness are modeled by rectangular waves with different amplitudes and wavelengths. The three-dimensional number densities of C (H) atom and kinetic energy distribution plots give a clear observation of the impacts of surface roughness on the localization micro-information of methane fluid. Moreover, the slip length of fluid over rough surface decreases with the increase in amplitude. The diffusion coefficients appear anisotropic, and the radial distribution functions decrease with the increase in the amplitude. These properties should be taken into account in the design of energy-saving emission reduction nano-fluidic devices. All numerical results also indicate that the presented method not only can well solve the issue of wall–fluid interactions, but also could accurately predict the micro-information and dynamic properties of methane Poiseuille flow.

Cohesive zone modelling of Mode III delamination using the edge crack torsion test

In the experimental studies of mode III delamination using the edge crack torsion test, the crack initiation and propagation measurement are always difficult. This information could be obtained through numerical modelling. The objective of this study is to propose a guideline to model mode III delamination behaviour using cohesive elements. Finite element models of an edge crack torsion specimen were developed based on the data from the literature. The delamination behaviour of the specimen along the pre-crack, which was located at the mid-Thickness location, was modelled using cohesive elements. Through parametric studies, it was found that for reliable numerical modelling, a mesh size of 0.5 mm was suggested, which provided three elements in the cohesive zone. As for the interface strength, it was recommended to choose 80 MPa. In addition, a viscosity parameter of 110-3 was found to be a good choice for reasonable computational time and converged numerical results. Besides, the interface stiffness was suggested to be 4106 MPa/mm. Furthermore, the fracture process zone contour revealed that the delamination was started at a normalised location of approximately 0.7. Not only that, the fracture energy and strain distribution plots have shown the delamination was mode III dominated within the normalised distance of 0.34-0.86. The results from this study suggested that cohesive zone modelling is a useful method for the detailed analysis of the mode III delamination of an ECT specimen. The numerical modelling approach suggested from this study could be applied to ECT specimens at various different initial crack lengths. It also has the potential to be used to simulate the mode III delamination of other various types of laminated composites.

Plasma current analysis using discrete wavelet transform during plasma electrolytic oxidation on aluminum

Plasma electrolytic oxidation (PEO) was performed on commercially pure aluminum substrate at a constant applied potential of 520V in a solution composed of 0.05 M KOH, 0.04 M Na4P2O7 and 0.04 M NaAlO2 compounds. Orthogonal discrete wavelet transform (ODWT) was employed to analyze plasma currents at different time stages of the PEO process. The results of wavelet transform were presented in the form of energy distribution (ED) and standard deviation of partial signal (SDPS) plots. The variations of PEO coating morphology with processing time were also studied by scanning electron microscope (SEM). The comparison of the ED plots at different processing time stages indicated that the current transient shapes remained unchanged during the whole PEO process. Similarly, a detailed comparison of the SDPS plots indicated that the intensity and lifetime of plasma discharges increased and their frequentness decreased with processing time. The SEM micrographs of the surface and cross section of the coating supported the findings of wavelet transform in case of both pore size and population. It was also shown that the lifetime of B-type plasma discharges which were responsible for the dielectric breakdown phenomena and coating thickness enhancement, increased from ~80μs to ~160μs with time. In addition, increasing the intensity and lifetime of B-type plasma discharges led to regeneration of the interfacial voids and discontinuities, particularly in the last stages of the process.

Influence of aging treatment on the pitting behavior associated with the dissolution of active nanoscale β-phase precipitates for an Al–Mg alloy

The pitting characteristics of Al-5wt%Mg microelectrodes after various aging treatment have been investigated in a deaerated 0.6M NaCl solution (pH 3.5). The dissolution current of single and numerous active β-phase precipitates have been detected on the aged alloys under anodic potentiostatic polarizations. The results show that the metastable pitting rates depend on the size and number of β-phase precipitates. The pitting potential decreases and the average size of β-phase increases initially with the increase of aging time, while for long-time aged alloys, the energy distribution plot (EDP) obtained from wavelet analysis technique can distinguish their small microstructural differences.

Corrosion of AISI 1020 steel in crude oil studied by the electrochemical noise measurements

In this work, the corrosion process of AISI 1020 in crude oil, to which different amounts of sea water (0.5 and 4.0% v/v), naphthenic acid (500 and 3000ppm), and H2S (50 and 1000ppm) were added, was investigated using electrochemical noise at open circuit potential. The different oil samples were prepared using a 23 factorial design involving the three species described above. To analyze the obtained data, wavelet transform and energy distribution plot were used. Using this technique it was possible to separate the contributions of two types of corrosion, generalized and localized, in oil samples with different compositions and to analyze the effect of those variables on the changes that occurred during 55days of immersion in the experiment. The results showed an increase in pitting formation in those steel samples studied in oil containing H2S at 50ppm and 4.0% sea water. The contribution of generalized corrosion on the metallic surface is higher in oil containing 3000ppm naphthenic acid than in the other experimental conditions. The results were confirmed by morphological analysis of the corroded samples.

A Critical Appraisal of the Interpretation of Electrochemical Noise for Corrosion Studies

In this paper, procedures and parameters that enable identification of, or discrimination between, general and localized corrosion processes through electrochemical noise are critically discussed. Their relevant similarities, differences, and interdependences are indicated. In addition, the relation between different procedures and parameters with the underlying physicochemical processes is indicated. Consistent and reliable information can be obtained from electrochemical noise data when a data analysis procedure is selected, which on the one hand has a high discrimination ability and on the other hand yields a descriptive parameter that is directly associated to the underlying physico-chemical process. Procedures that meet these two requirements appear to be the Hilbert-Huang transform (Hilbert spectrum), wavelet transform (energy distribution plot), and the analysis of charge and frequency of corrosion events. In addition to the procedures that meet these two requirements, some of the descriptive parameters can be determined by different analysis procedures, which increase their reliability.

Electrochemical Noise Analysis of Pitting Corrosion of Type 304L Stainless Steel

Electrochemical current and potential noise were simultaneously acquired from Type 304L stainless steel (UNS S30403) in 0.05 M ferric chloride (FeCl3) using a three-electrode configuration. Power spectral, statistical, and wavelet analyses have been used to know the uniqueness of the parameters proposed for the identification of various types of corrosion processes. Roll-off slopes derived from power spectral analysis and statistical parameters such as standard deviation, localization index, and kurtosis corroborated with pitting as the corrosion mechanism. Energy distribution plots (EDP) obtained from wavelet analysis of current noise was found to be useful to derive mechanistic information on the progress of corrosion. Discrete wavelet transform was used to decompose the signals into a D1, D2, D3…D8, S8 set of coefficients. The EDP showed that the contribution from the medium time scale crystal, D5, prevailed over the smaller time scale crystals and larger time scale crystals during the initial stages of immersion. With an increase in the time of immersion, the energy deposition on the larger time scale crystals increased and the maximum energy was concentrated on the D8 crystals, indicating that the dominant process occurring on the specimen surface was stable pitting. The results of the investigation are detailed in the paper.

Potentiostatic Electrochemical Noise Analysis of 2101 Lean Duplex Stainless Steel in 1 mol/L NaCl

The critical pitting temperature (CPT) of 2101 lean duplex stainless steel (DSS) in 1 mol/L NaCl was investigated. Potentiostatic electrochemical noise (EN) technique coupled with scanning electron microscopy (SEM) was used to study the corrosion process of 2101 DSS at different temperatures (15, 25, 28, and 35 °C) from below CPT to above CPT. The EN data were analyzed by wavelet technique based on orthogonal db4 wavelet. The results showed that, the patterns of current noises were different at different temperatures. The characteristics of energy distribution plot (EDP) obtained from wavelet analysis technique can be used as “fingerprints” of EN signal and can be used to interpret the corrosion process. With increasing solution temperature, the maximum relative energy defined in EDP changed from the region of crystal series coefficients with smaller scales through middle scales to larger scales, which indicated the process of initiation, propagation and growth into stable pitting of metastable pitting. The results were well confirmed by the corresponding morphologies.

Comparison between ED and SDPS plots as the results of wavelet transform for analyzing electrochemical noise data

Two valuable results of wavelet transform are energy distribution (ED) plot and standard deviation of partial signal (SDPS) plot. In this work, after brief review of theoretical basis of wavelet transform, the ED and SDPS plots are compared using both calculated and experimental signals. The experimental signals are obtained by recording electrochemical current noise of two Al alloys, AA2024 and AA5052. Both ED and SDPS plots can detect the predominant transients of each signal by the position of the maximum peak between d1 and d6 crystals and thereby may categorize several corroding systems according to the pit size. The slope value of the SDPS plot in the region after the maximum peak can be a measure of the frequentness of the predominant transients. Based on these slope values it might be possible to classify several corroding systems according to the pit density. The SDPS plot seems as an alternative tool to overcome the limitations of the ED plot in the corrosion monitoring applications. Employment of the ED plot along with the SDPS plot is recommended to provide a further insight into the electrochemical behavior of a corroding system.

Identification of the reinforcing steel's corrosion state in RC beams based on electrochemical sensor

PurposeThe purpose of this paper is to present a novel five‐electrode electrochemical corrosion sensor. Health degradation by the corrosion of steel in civil engineering is a persistent problem. Structural health monitoring (SHM) techniques, including embedded sensors, can greatly improve the quantification of the steel corrosion information, which can lead to promote assessments of structural safety and serviceability. To integrate the corrosion monitoring system in future, the corrosion sensor and the monitoring methods have been explored here in advance. Also, the corrosion monitoring system has been applied preliminarily in the investigation of reinforcing concrete (RC) beams.Design/methodology/approachFirst, a novel five‐electrode electrochemical corrosion sensor has been developed as the hardware to provide the platform for corrosion monitoring methods. Second, half‐cell potential of the RC beams has been measured before and after corrosion. Third, galvanostatic step method has been used to excite the steel‐concrete system, and the transient response of the system has been obtained and analyzed. Finally, wavelet transform algorithm has been established to analyze the electrochemical noise (EN) data of the steel bars in RC beams.FindingsThe results show that the corrosion sensor can be used effectively as the hardware to support the electrochemical measuring techniques. Much valuable information which is extracted by analyzing the potential response to the galvanostatic pulse excitation can be applied to determine the general corrosion state of the reinforcing steel. For pitting corrosion, the energy distribution plot of EN can be adopted as a benchmark method to identify the presence of the corrosion pit.Originality/valueThe paper provides the key techniques for a SHM system to realize corrosion monitoring of large‐scale RC structures in the future.