Metal Protrusion Research Articles

High‐Temperature Oxidation Response of 444 Ferritic Stainless Steel in a Synthetic Automotive Exhaust Gas

The high‐temperature oxidation behavior of 444 ferritic stainless steel has been studied in cyclic oxidation experiments using synthetic automotive exhaust gas atmospheres at 950 and 1050 °C. The weight gain per unit area of the 444 ferritic stainless steel following oxidation at 950 °C for 100 h iss 85.7% lower than recorded at 1050 °C. The oxide scale at both temperatures consisted of Fe–Cr and Mn–Cr spinels in the outer layer and Cr2O3 in the inner layer. Nodule formation and spallation of the oxide scale are identified as the main causes of breakaway oxidation. The depth of the internal oxides gradually increases with the oxidation time. The nucleation and growth of internal SiO2 result in the formation of metal protrusions, which are eventually consumed in the formation of a SiO2 layer. The SiO2 layer is formed at the interface between the oxide scale and the substrate at 1050 °C. The nucleation and growth of internal SiO2, in combination with lateral growth of SiO2 at the Cr2O3 layer/substrate interface contributed to the formation of the SiO2 layer.

AC breakdown and decomposition products detection characteristics of eco-friendly insulating medium in gas insulated switchgear

Gas Insulated Switchgear (GIS) was a crucial electrical equipment that provides the safety and security of power systems, and finding the eco-friendly alternatives of sulphur hexafluoride (SF6) as insulating medium in GIS has been an urgent demand in past decades. However, few studies reported the specific dielectric strength under various electrodes and partial discharge (PD) decomposition products detection of applying the eco-friendly gas in GIS. In this paper, the insulation properties among C4F7N/CO2 mixtures, dry air and CO2 were explored under the reduced-scale gas-insulated experimental device. The relationship between AC breakdown voltage and gas pressure was gained under the different electrodes and gap distances, and 0.6 MPa 7% C4F7N/93% CO2, 0.9 MPa dry air, 0.9 MPa CO2 all possess the capacity to be the insulating medium in eco-friendly gas insulated switchgear. Furthermore, the partial discharge experimental was also carried out to realize the decomposition products detection of dry air, which designs three common defect types including metal protrusion defects, air gap defects, and metal contamination defects. The decomposition products detection result shows that the contains of CO2, CO, and NO2 linearly increase with the increasing applied voltages and times, and the partial discharge defects are distinguished according to the ratios of c(CO2 + CO)/c(NO2) and c(CO2)/c(CO). The results can provide the basis for the further development of eco-friendly gas insulated switchgear.

Electrochemical Embrittlement Accelerates Dendrite Growth in Ceramic Electrolytes

Although solid-state batteries with metal anodes promise to enable safer, higher energy density batteries, metal protrusions (dendrites) grow when charging faster than a critical current density[1,2]. It is generally believed that dendrites grow when plating-induced stresses exceed that required for fracture of the solid-electrolyte[2–4]. Although the electrolyte's fracture toughness is commonly taken as a constant[2–4], here we show that the effective fracture toughness depends markedly upon the metal deposition current density. Based upon operando birefringence microscopy[5], we directly measure dendrite-induced stresses and obtain the mechanical driving force for failure, as well as the electrolyte fracture toughness. We find that increasing current densities embrittle the solid electrolyte—diminishing the fracture toughness by as much as 70%. Cryogenic Scanning Transmission Electron Microscopy (Cryo-STEM) reveals decomposed electrolyte phases at the dendrite tip. This decomposition is associated with a volume contraction consistent with embrittlement of the electrolyte. All experiments were conducted on the most electrochemically stable Li-ion conducting solid electrolyte (tantalum-doped lithium lanthanum zirconium oxide); the fracture toughness of less stable electrolytes (e.g., agryodites) may be even more susceptible to such embrittlement. The collective results indicate that “electrochemical embrittlement” markedly weakens the electrolyte, enabling dendrite growth—even when such degradation has negligible effect on bulk electrochemical properties.

Stable Zinc Electrode Reaction Enabled by Combined Cationic and Anionic Electrolyte Additives for Non-Flow Aqueous Zn─Br2 Batteries.

Aqueous zinc-bromine batteries hold immense promise for large-scale energy storage systems due to their inherent safety and high energy density. However, achieving a reliable zinc metal electrode reaction is challenging because zinc metal in the aqueous electrolyte inevitably leads to dendrite growth and related side reactions, resulting in rapid capacity fading. Here, it is reported that combined cationic and anionic additives in the electrolytes using CeCl3 can simultaneously address the multiple chronic issues of the zinc metal electrode. Trivalent Ce3+ forms an electrostatic shielding layer to prevent Zn2+ from concentrating at zinc metal protrusions, while the high electron-donating nature of Cl- mitigates H2O decomposition on the zinc metal surface by reducing the interaction between Zn2+ and H2O. These combined cationic and anionic effects significantly enhance the reversibility of the zinc metal reaction, allowing the non-flow aqueous Zn─Br2 full-cell to reliably cycle with exceptionally high capacity (>400mAh after 5000 cycles) even in a large-scale battery configuration of 15×15cm2.

Characterization of partial discharge decomposition of SF6/N2 gas mixture with different microwater contents

The SF6/N2 gas mixture as a preliminary alternative to SF6 is used in the power industry gas insulation medium. At present, the application of the 30% SF6/70% N2 gas mixture has made some progress, but the influence law of microwater content on its discharge decomposition characteristics is still unclear. In this paper, we simulate the defects of metal protrusions in the equipment through needle-plate electrodes, carry out SF6/N2 96hPD and its decomposition characteristic test under different microwater contents, and find that the increase of the microwater content in the SF6/N2 gas mixture will exacerbate the phenomenon of PD, resulting in the enhancement of the average discharge, and under the action of prolonged PD, more characteristic decomposition products will be generated, of which the SOF2 content is the highest, which can be as one of the characteristic components for fault severity judgment. This study provides a certain reference for the specific requirements of the microwater content of the SF6/N2 gas mixture in power equipment.

Discharge Evolution of Metal Protrusion Defects Observed at High Time Resolution

Discharge Evolution of Metal Protrusion Defects Observed at High Time Resolution

The Design, Fabrication, and Evaluation of a Phase-Resolved Partial Discharge Sensor Embedded in a MV-Class Bushing.

This paper proposes a novel phase-resolved partial discharge (PRPD) sensor embedded in a MV-class bushing for high-accuracy insulation analysis. The design, fabrication, and evaluation of a PRPD sensor embedded in a MV-class bushing aimed to achieve the detection of partial discharge (PD) pulses that are phase-synchronized with the applied primary HV signal. A prototype PRPD sensor was composed of a flexible printed circuit board (PCB) with dual-sensing electrodes, utilizing a capacitive voltage divider (CVD) for voltage measurement, the D-dot principle for PD detection, and a signal transducer with passive elements. A PD simulator was prepared to emulate typical PD defects, i.e., a metal protrusion. The voltage measurement precision of the prototype PRPD sensor was satisfied with the accuracy class of 0.2 specified in IEC 61869-11, as the maximum corrected voltage error ratios and corrected phase errors in 80%, 100%, and 120% of the rated voltage (13.2 kilovolts (kV)) were less than 0.2% and 10 min, respectively. In addition, the prototype PRPD sensor had good linearity and high sensitivity for PD detection compared with a conventional electrical detection method. According to performance evaluation tests, the prototype PRPD sensor embedded in the MV-class bushing can measure PRPD patterns phase-synchronized with the primary voltage without any additional synchronization equipment or system. Therefore, the prototype PRPD sensor holds potential as a substitute for conventional commercial PD sensors. Consequently, this advancement could lead to the enhancement of power system monitoring and maintenance, contributing to the digitalization and minimization of power apparatus.

Advancements in Dendrite Suppression for Enhanced Energy Storage Technologies

Aqueous zinc batteries have emerged as promising alternatives to conventional lithium-ion batteries, offering an environmentally friendly and cost-effective solution to our growing energy storage needs. However, one of the critical obstacles to realizing their full potential lies in addressing the dendritic structure growth challenges within zinc batteries. These dendrites, unwanted metal protrusions that form during the charging and discharging cycles, can lead to adverse implications, including short circuits, reduced battery performance, and safety concerns. To overcome these challenges, researchers and engineers have been diligently devising strategies. This paper delves into the complexities of dendrite formation in aqueous zinc batteries, outlining their adverse implications for battery performance and safety. Various strategies to address the dendrite challenge are explored, with a focus on their effectiveness and limitations. One promising avenue involves developing innovative three-dimensional (3D) structural designs within the battery architecture to inhibit dendrite formation. Conclusively, harnessing the potential of aqueous zinc batteries hinges on the successful mitigation of dendrite formation through the concerted implementation of ingenious 3D structural designs and other innovative strategies, steering the pathway towards safer and more efficient energy storage solutions.

Generation Characteristics of Solid Byproducts of the C4F7N-CO2-O2 Gas Mixture under PD Fault.

With the gradual improvement of the requirements for the safe and stable operation of gas-insulated equipment (GIE), the eco-friendly insulating gas C4F7N-CO2-O2 has become the best choice to replace SF6 and apply it to various medium-voltage (MV) and high-voltage (HV) GIE. At present, the generation characteristics of solid decomposition products of the C4F7N-CO2-O2 gas mixture under partial discharge (PD) fault need to be studied. In this paper, a 96 h PD decomposition test was carried out by simulating metal protrusion defects in GIE with needle-plate electrodes to study the generation characteristics of C4F7N-CO2-O2 gas mixture solid decomposition products under PD fault and their compatibility with metal conductors. It was found that obvious ring-shaped solid precipitates appeared in the central area of the surface of the plate electrode under the action of long-term PD, mainly including metal oxides (CuO), silicates (CuSiO3), fluorides (CuF, CFX), carbon oxides (CO, CO2), and nitrogen oxides (NO, NO2). The addition of 4% O2 has little effect on the element composition and valence state of PD solid precipitates, but it can reduce their yield to a certain extent. The corrosion effect of O2 in the gas mixture on metal conductors is weaker than that of C4F7N.

Failure mechanisms of hybrid metal–composite joints with different protrusion densities under a tensile load

The mechanical behaviors of hybrid metal–composite joints with different protrusion densities were investigated by combining numerical and experimental methods. High-fidelity finite element models that considered the failure modes of all components were developed, and specimens based on metal additive manufacturing technology were tested under quasi-static tensile load to verify the numerical calculations. The results showed that the load capacity and the dominant fracture mode of joints were significantly affected by the metal protrusion density. The failure mechanisms of joints under different protrusion conditions exhibited a clear difference, which proved the possibility of an optimal and functional joint design.

Study on characteristics gases of metal protrusions partial discharge in 10‐kV air‐insulated switchgear

AbstractAir‐insulated switchgear plays an important role in distribution network and partial discharge (PD) is one of the common faults in its operation. The method of gas component analysis, which is to detect chemical gas products, is a novel one to discover PD. In order to study the feasibility of the method, the monitoring experiment of characteristic gases, comprising carbon monoxide (CO), nitrogen dioxide (NO2), and ozone (O3), of metal protrusion PD is carried out. This paper conducts the comparative experiments on three main factors affecting PD: voltage, air humidity and degree of protrusion, as well as studies how they affect the formation of characteristic gases. According to the experimental result, higher applied voltage promotes the formation of characteristic gases in the same conditions. In addition, with the increase of humidity from 40% to 75%, the generation of gases is inhibited. Furthermore, when the needle–plate distance is 30 mm, the gas concentration has almost no change within 6 h, which is different from that of 10 mm. In conclusion, the difference in gases concentration reveals the influence of three main factors on the generation of characteristic gases and provides an analytical basis for PD detection by gas composition analysis.

Partial discharge induced decomposition and by-products generation properties of HFO-1234ze(E)/CO2: a new eco-friendly gas insulating medium

HFO-1234ze(E) is introduced as a new eco-friendly insulating gas for medium-voltage gas-insulated equipment (MV-GIE). However, there are few reports on the partial discharge (PD) induced decomposition and gaseous, solid by-product generation characteristics of HFO-1234ze(E)/CO2. Herein, the PD decomposition characteristics of HFO-1234ze(E)/CO2 were explored based on a needle-plate electrode that simulates the metal protrusion defect in MV-GIE. The partial discharge inception voltage, and phase-resolved partial discharge of HFO-1234ze(E)/CO2 under different mixing ratios, PD intensity and duration time at 0.15 MPa were obtained. Meanwhile, the PD-induced decomposition and generation of gaseous, solid by-products of HFO-1234ze(E)/CO2 were analyzed. A three-zone pattern that describes the gas–solid metal interface interaction was proposed for the first time. It is found that the increase of HFO-1234ze(E) content brings superior insulation performance, while the precipitation of gaseous (CF4, C2F6, CHF3, C3HF7) and solid by-products gradually aggravated. In order to avoid the negative impact of PD-induced decomposition on the insulation and service life of MV-GIE, the optimal HFO-1234ze(E) content of 30% is recommended. Based on the optimal mixing ratio (30% HFO-1234ze(E)/70% CO2), the effect of gas pressure and electrode materials on solid precipitation, breakdown voltage was also explored. This work guides the development of HFO-1234ze(E) based MV-GIE and understanding the solid by-products precipitation mechanism of eco-friendly insulating gas.

Direct Fabrication of Functional Shapes on 3D Surfaces Using Electrospinning.

In this work, we demonstrate the ability to simultaneously pattern fibers and fabricate functional 2D and 3D shapes (e.g., letters, mask-like structures with nose bridges and ear loops, aprons, hoods) using a single step electrospinning process. Using 2D and 3D mesh templates, electrospun fibers were preferentially attracted to the metal protrusions relative to the voids so that the pattern of the electrospun mat mimicked the woven mesh macroscopically. On a microscopic scale, the electrostatic lensing effect decreased fiber diameter and narrowed the fiber size distribution, e.g., the coefficient of variation of the fiber diameter for sample collected on a 0.6 mm mesh was 14% compared to 55% for the sample collected on foil). Functionally, the mesh did not affect the wettability of the fiber mats. Notably, the fiber patterning increased the rigidity of the fiber mat. There was a 2-fold increase in flexural rigidity using the 0.6 mm mesh compared to the sample collected on foil. Overall, we anticipate this approach will be a versatile tool for design and fabrication of 2D and 3D patterns with potential applications in personalized wound care and surgical meshes.

SF6 decomposition behaviour under partial discharge of typical insulation defects in gas‐solid insulated valve‐side bushing of converter transformer

AbstractIn this paper we investigated SF6 decomposition behaviour of typical insulation defects in gas‐solid insulated converter transformer valve‐side bushing under partial discharge (PD). Additionally, we compared the results with that of gas insulated switchgear (GIS). The results indicated that SF6 decomposition behaviour varies with the insulation defects type. For metal protrusion defects, the proportion ranking of CO2 and SO2 can be related to whether the needle tip is wrapped with epoxy resin‐impregnated paper (ERIP). The proportion of carbon‐containing products is much higher under contamination defect than under other defects. Moreover, the proportion of carbon‐containing components is higher under flashover condition than under PD condition and is accompanied by the appearance of H2S and CS2. However, the yield of SO2F2 is always low. Compared to negative DC voltages, positive DC voltages have a higher proportion of carbon‐containing components, mainly in the form of more CO2 and less SOF2. Compared to the PD decomposition behaviour of typical insulation defects in GIS, when PD involves ERIP, the proportion of carbon‐containing products, especially CO2, is significant higher, while the proportion of sulphur containing products, especially SO2F2, is lower.

Experimental demonstration of virtual critical coupling to a single-mode microwave cavity

We present an experimental realization of virtual critical coupling in microwave, i.e., virtual perfect absorption of an incident wave by a resonant cavity, through transient time modulation of its amplitude. The design of a waveform matched to the ignition process of a plasma, characterized in a simplified way by two operating modes over time (plasma off/plasma on), motivates this first step in practical realization of virtual critical coupling in microwaves. We propose a time domain method for extracting necessary parameters for realization of virtual critical coupling, especially the complex frequency called zero of the S-matrix. To this end, we start from the experimental characterization of a single-mode and single-access microwave cavity including metal protrusions for future plasma ignition. Then, the method relies on the analysis of harmonic response of the overcoupled cavity during three time periods: the transient under excitation, the steady state under excitation, and the transient after excitation cutoff. Finally, an experimental demonstration of virtual critical coupling is performed.

Design of a compact ultra-high frequency antenna for partial discharge detection in oil immersed power transformers

Oil-immersed Power transformers are considered to be one of the most essential parts of the electrical system and partial discharges (PD) are one of the dangerous problems that face transformer insulation. PD is localized dielectric breakdown of an insulation degradation or defect in an oil power transformer. Ultra-high frequency (UHF) detection technique can be utilized in PD detection inside oil-filled power transformers, by capturing the electromagnetic waves generated by PD using an antenna. This research presents a design for a compact double layer printed UHF antenna to detect and discriminate various types of PD activity in a power transformer. PD activity in the transformer has been proposed in this paper by using four different artificial insulation defects, metal protrusion defect in air medium, metal protrusion defect in an oil medium, surface discharge defect, and oil-paper void defect. The presented design guarantees a small-size wideband antenna for detection. The designed antenna has small/simple size and ultra-wide frequency passband from 1.4 to 1.85 GHz, 2.2 to 2.65 GHz, and 3.2 to 3.4 GHz. The normalized power frequency spectra of the captured UHF-PD signals of the four defective models showed that every PD type has its signature, and this could help in the discrimination among different types on site.

Electrostatic field strength distribution inside metal silo during polypropylene powder loading by computer simulation

This paper investigates the electrostatic field distribution inside a grounded metal silo during the loading of large amounts of powder (up to 1000 kg) using a simulation and accurate experimental parameters. The commercial COMSOL Multiphysics 5.4 AC/DC module, which uses the finite element method, was used in this study. Using the simulation, 1000 kg of 3 mm polypropylene powder was loaded into an industrial scale silo that was created based on the actual silo dimensions used in the experimental tests. The space charge density value used in the simulation model was based on the values obtained from experimental tests. As for the result, it was found that the electrostatic field strength, Es, of the accumulated powder area (area B) was much stronger than that of the falling powder area (area A). The Es in area B was strongest in the following order: the silo side wall inside the deposited powder surface, the side wall of the silo at the surface of the powder heap, and the center portions of the accumulated powder. It was also observed that the Es increased as the amount of loaded powder increased. When 5 kg was first loaded, it was seen that the Es was strong enough to cause electrostatic discharges. Also, when a metal protrusion (4 cm in diameter) was attached to the silo, it was observed that the Es around the surface of the protrusion was the strongest, signifying that strong electrostatic discharge is likely to occur with the existence of metal protrusions. These results were supported by the results of the experimental test.

Study on insulation defect discharge features of dry-type reactor based on audible acoustic

The audible signal (20 Hz to 20 kHz) generated during the operation of a dry-type reactor is one of the key features to evaluate its operation state. However, at present, the time/frequency domain features of the audible signal under typical insulation defects are not clear, which makes it difficult to effectively carry out the fault diagnosis of the dry-type reactor based on audible signals. Based on this, the audible signal features under typical insulation defect discharge of the dry-type reactor are studied in this paper. Three typical insulation defect discharge models (metal protrusion defect, pollution defect, and metal foreign bodies defect) are simulated; then, the discharge acoustic signals are collected under the voltage of 8 kV. Analysis of acoustic signal features shows that the acoustic signal of metal protrusion defect discharge occurs in the positive half cycle of power frequency with the cycle of 20 ms. Both pollution defect discharge and metal foreign bodies defect discharge show intermittent discharge; during the discharge, the discharge acoustic signal of pollution defect has features similar to that of metal protrusion defect, while the discharge of metal foreign bodies defect shows randomness with a larger amplitude of discharge acoustic signal (up to 110 dB). Based on the frequency domain feature vectors’ extraction, it is found that the odd harmonic component of the metal protrusion defect discharge acoustic signal accounts for more than twice the even-order harmonic, and the high-frequency energy (12.5–25 kHz) is the main component. The discharge acoustic signal of the metal foreign bodies defect is mainly low-frequency energy, and the high-frequency energy proportion of pollution defect discharge acoustic signal is similar to that of low-frequency energy. In addition, the variance of high-frequency energy ratio (Rhf) of the metal foreign bodies defect discharge acoustic signal is 5.25 and 21 times that of the metal protrusion defect and pollution defect. This study provides some technical support for further detection and assessment of the operation state of the dry-type reactor based on audible signals.

ПОЛІПШЕННЯ ЕКСПЛУАТАЦІЙНИХ ВЛАСТИВОСТЕЙ ДЕТАЛЕЙ МАШИН ХОЛОДНИМИ ПЛАСТИЧНИМ ДЕФОРМУВАННЯМ

The article discusses the direction of improving the operational properties of machine parts by the cold plastic deformation. Purpose – to develop methods of experimental research of regular reliefs, including equipment, tools and material of prototypes; to create a classification of regular reliefs by purpose; to determine the mechanics of deepening of the linear indenter in the metal sample; to develop technological recommendations and research tools. The object of research – regular reliefs on the surface of machine parts. Methods and devices for conducting experiments were selected: hydrogenated presses, linear indentors, optical microscopes, microhardness testers, research materials, instruments and measuring instruments. The materials were alloy and stainless steel, gray and malleable cast iron, bronze and brass, aluminum and titanium alloys. The classification of reliefs by purpose, obtained by cold plastic deformation and cutting, has been developed. The mechanics of deepening of a linear indenter into a metal sample has been developed, which combines the values of the depth of indentation with the geometrical parameters of the indenter, friction coefficient, contact stress and groove depth. Experiments on 8 typical representatives of structural materials confirmed the theoretical principles of the mechanics of deepening. Scientific results allowed to develop and test a sample of the tool on a tubular part made of duralumin D16 (2117). The following process of improvement of operational properties of details of cars is offered: preparation of a surface under indentation; indenter deepening; removal of metal protrusions by cutting. KEYWORDS: REGULAR RELIEF, COLD PLASTIC DEFORMATION, LINEAR INDUCTOR, SURFACE OF PARTS, MECHANICS OF DEEPING

Потенціал в області мікронерівностей поверхні металу, який працює в режимі катодного захисту

This effort presents the results of investigation of cathodic protection process of a section of the main pipeline, which has been operating in cathodic protection mode for a long time and which insulation has completely exfoliated from metal surface, and a cavity between is filled with water and salt impurities. In this case, a decisive factor is a fact that a metal surface is covered with microroughnesses in the form of protrusions with almost conical shape. The surface is immersed in electrolyte. At the electrolyte-metal interface, a potential difference is formed - a corrosion potential, which creates an unstable equilibrium among the potentials of metal and electrolyte. A mathematical model is designed and implemented into a numerical algorithm and computer program. A computational experiment has been carried out to calculate the potential around microroughness. The model describes a change in potential in this area at incomplete and complete cathodic protection of metal surface. The basis of computational model is a selection of one of metal protrusions of material microheterogeneity and placing it in a cylinder, which diameter coincides with that one of the lower base of this protrusion, and its upper part passes through the apex of the protrusion. Mathematical model equations with corresponding boundary conditions and their discrete implementation are presented. The solution of problems is obtained by iterative procedures based on reference values of protective potential taken from practice. The results of computational experiment are presented in the form of graphs: 1) potential distribution in the field of electrolytes; 2) changes in electrolyte potential at the border with protrusion at different values of polarization potential; 3) changes in polarization resistance in the area (calculated). The geometry of computational domain was also varied, and the values of protective potential were determined to ensure the absence of corrosion. Keywords: corrosion, microroughness, protective potential, plastic current density, electrolyte