Small Interelectrode Gap Research Articles

Characterization of 20 μm Dielectrophoretic Interelectrode Gap for Staphylococcus Aureus Rapid Detection Application

We propose an improvement of dielectrophoresis technique (DEP) by designing, simulating and experiment a 20 μm interelectrode gap for Staphylococcus aureus rapid detection application. In this paper, we use MyDEP simulation for DEP polarization Staphylococcus aureus on frequencies range. COMSOL simulation is utilized for comparison of 20 μm and 80 μm interelectrode gap based on trajectory and velocity of particles for Staphylococcus aureus application. We implied 20 μm interelectrode gap for Staphylococcus aureus application produced higher magnitude DEP force. Which gives accurate trajectory characterization and higher velocity of particle movement. DEP characterization using small interelectrode gap is capable of producing stable and optimum DEP value. It is demanding to distinguish the simulation Staphylococcus aureus using experimental method. DEP technique is important for analysis and characterization of the bacteria. The result show that 20 μm interelectrode gap has higher intensity of electric field which is 1.51 x 10^6 V/m in COMSOL simulation and produced 20.1 m/s for velocity of particle trajectories which is higher compared to 80 μm interelectrode gap. The DEP response was tested on 2.5 MHz, as crossover frequency response was observed on experimental and simulation. Thus, supportsthe capability of 20 μm interelectrode gap for Staphylococcus aureus rapid detection application. Furthermore, DEP characterization can be improvised by focusing on interelectrode gap for characterization among bacteria cells, critical for bacteria detection, manipulation, and isolation.

Fabrication of pyrolytic carbon interdigitated microelectrodes by maskless UV photolithography with epoxy-based photoresists SU-8 and mr-DWL

Maskless UV photolithography is increasingly used, especially in research environments where low turn-around time for new designs improves productivity. Here, we fabricate pyrolytic carbon interdigitated microelectrodes with small interelectrode gaps, good adhesion to the carrier substrate, high surface area and excellent electrochemical properties using maskless UV photolithography with two negative epoxy-based photoresists, namely the commonly used SU-8 and the recently developed mr-DWL. The minimum realizable trench width in 15 μm thick photoresist films is 2.4 ± 0.15 μm for mr-DWL 5 and 3.1 ± 0.10 μm for SU-8 2035. After pyrolysis, the two resulting pyrolytic carbon materials show similar electrochemical properties. However, shrinkage during pyrolysis is significantly lower for mr-DWL compared to SU-8, which is beneficial for the fabrication of interdigitated microelectrodes. Furthermore, delamination of the electrodes during processing and operation is prevented due to the introduction of poly silicon adhesion structures. This work provides valuable insights into maskless UV lithography as well as into the pyrolytic carbon process to increase the yield, performance and productivity for fabrication of microelectrodes.

Characteristics of evolution and collapse in spark-induced cavitation bubbles

Numerous scientists have thoroughly researched cavitation bubble dynamics using experimental methods such as tube arrest, underwater discharge, ultrasound, and laser focusing. In this study, with the aid of high-speed photography, the formation mechanism of the electrode-contact spark-induced cavitation bubble is discovered, i.e., electrolysis results in non-condensable gases wrapping the small inter-electrode gaps, and the non-condensable gases are broken down by discharge to form plasma, which then induces the cavitation bubble. Since the cavitation bubbles already contain a certain amount of non-condensable gases during the discharge process, the differences in the spatiotemporal evolution and collapse characteristics of the cavitation bubbles with varying amounts of non-condensable gases are further analyzed. The results show that underwater electrode-contact discharge system has an optimal voltage if the capacitance and discharge electrode size remain constant, and the cavitation bubbles generated under the optimal voltage condition are not only morphologically closest to the laser-induced cavitation bubbles, but also the change in radius over time during collapse is quite consistent with the Rayleigh bubble. Furthermore, compared to cavitation bubbles generated under varying voltages, those induced by the optimal voltage have a lower amount of non-condensable gases. This leads to the minimum first contraction radius and the maximum rebound radius being close to the corresponding values of the laser-induced cavitation bubbles. These new findings are of great significance for the improvement of experimental technology in the study of cavitation bubble dynamics, obtaining precise and dependable experimental data, and validating numerical simulations.

Raising the curtain: Bubble size measurement inside parallel plate electrolyzers

Alongside vertical gas-evolving electrodes, gas bubbles nucleate, grow, coalesce, detach, and ultimately form a bubble curtain, affecting the fluid dynamic, electrochemical reaction, mass transport, and ohmic drop. Due to the small inter-electrode gap in parallel plate electrolyzers, the size determination of detached bubbles inside the bubble curtain close to the electrodes is challenging. In particular, the size determination of detached oxygen bubbles needs to be addressed. We present an optical setup to record images from detached oxygen bubbles inside the bubble curtain of a membrane-separated, parallel plate electrolyzer. The images are postprocessed using an adopted region-based convolutional neuronal network to quantify the bubble sizes. Next, the electrolyte flow velocity, concentration, current density, and catalysts are varied, and the effect on the oxygen bubble size distribution is studied. The median size ranges from 140 to ▪, doubling values from literature measured in artificial electrolyzers.

A Diamond Terahertz Large Aperture Photoconductive Antenna Biased by a Longitudinal Field

The novel design of a terahertz large aperture photoconductive antenna (LAPCA) is reported. It features a longitudinal orientation of the bias electric field within the photoconductive substrate, and has the advantage of a small interelectrode gap, resulting in a higher field for the same applied voltage. The proposed LAPCA configuration has been tested with a nitrogen-doped (∼10 ppm) synthetic monocrystalline diamond, which is a promising material for high-intensity and high-power terahertz sources. Two antennas with different high-voltage electrode realizations were assembled, pumped by a 400 nm femtosecond laser, and tested for THz emitter function. The experimental data are found to be in good correlation with the numerical simulation results. The performance of antennas with the conventional transverse E-field configuration and the novel longitudinal configuration is compared and discussed.

Achieving high replicability for electrochemical machining via the stamp flushing method in stationary electrolyte

Traditional high-speed electrolyte flow for removing bubbles and sludges from the inter-electrode gap during electrochemical machining (ECM) usually results in the non-uniform distribution of temperature, bubbles, and sludges, thus deteriorating machining accuracy. Therefore, ECM performed in stationary electrolyte via an efficient flushing method may solve this problem. For this reason, the previous study proposed the stamp flushing method to squeeze out the bubbles and sludge from the inter-electrode gap by shortening the gap width. However, the effectiveness of the stamp flushing method in achieving high replicability has not been systematically investigated. In the present work, the stamp stroke motion was first optimized to improve the flushing efficiency of the stamp flushing method. To obtain higher stamping velocity and to avoid the damage due to the collision between the tool electrode and workpiece, a cushion mechanism was newly installed on the equipment. Based on the optimized stamp stroke motion, the periodical micropatterns fabricated on the tool electrode surface using wire electrical discharge machining (WEDM) were replicated onto the SK4 workpiece using ECM in stationary electrolyte. The dimensional deviation of the workpiece from the tool electrode after ECM was less than 4 μm in the feed direction and approximately 30 μm in the side direction when the initial width of the frontal gap was 10 μm. Outside the inter-electrode gap, the electrolyte flowing along the axial direction (EFAAD) was supplied to rapidly flush out the bubbles and sludge squeezed out by stamp motion to prevent them from backflowing into the inter-electrode gap during the widening phase of the gap after the stamp motion. Since the EFAAD does not affect the electrolyte in the inter-electrode gap, the ECM remains performed in a stationary electrolyte. High replicability was obtained uniformly over the working surface, which originates from the combined effect of small inter-electrode gap width and uniform distribution of temperature, bubbles, and sludge in stationary electrolyte. This work proves the potential of the proposed stamp-flushing method for manufacturing metal parts with high replicability.

Electrochemical milling of deep-narrow slots with a pulsating electrolyte flow field

Deep-narrow slots (DNSs) (width<4 mm and depth/width>2 mm) are inherent features in die-casting molds as heat-dissipating slots and turbomachinery components for seal slots. Electrochemical milling (EC-milling) is a flexible method to machine variety of structures by controlling the tool path. The process employs a tubular tool with a flat end face through which the electrolyte is supplied coaxially. However, owing to the small inter-electrode gap (IEG), the quantity and velocity of electrolyte flowing into the IEG are weakened during machining of DNSs. This reduces the machining quality and efficiency. Therefore, this paper proposes a method of EC-milling of DNSs with a pulsating flow field. A tubular tool with a wedge-shaped end face (WS-tube) is designed, and both the quantity and velocity of electrolyte flowing into the IEG will be changed with the rotation of WS-tube. Thus, a pulsating flow field is generated which can enhance the mass transport in the IEG. Consequently, both the machining efficiency and quality are improved. Flow-field simulation results indicate that as compared with the traditional flat end face tube (F-tube), WS-tube can generate a periodic pulsating flow field in both front and side IEG, and the peak electrolyte flowing velocity is also increased. The experiment results reveal that compared to that of 0.24 mm/min with F-tube, the maximum feeding speed reaches to 0.42 mm/min with WS-tube, and both the surface quality and taper are improved at the same time. Increasing the rotation speed of tube tool and pulse frequency further enhances the transport of electrolytic by-products, and the machining quality is improved. With the optimized parameters, a 5 mm deep DNS with width of 1.48 mm ± 0.02 mm, taper of 1.44° ± 0.27° and the surface roughness (Ra) of 0.7 µm has been successfully fabricated. • Pulsating flow field was proposed for electrochemical milling of deep-narrow slot. • A tube tool with wedge-shaped end face was designed to generate pulsating flow field. • With the rotation of wedge-shaped tube tool, pulsating flow field was generated in both front and side inter-electrode gap. • Both the machining quality and feeding speed of DNS were improved with pulsating flow field.

Single- and dual-channel nanosecond repetitively pulsed discharges at small and large spark gaps for turbulent premixed spherical flame initiation

This paper reports laminar/turbulent ignition probability (Pig,L/Pig,T) of single- and dual-channel nanosecond-discharge (SN and DN) at small and large inter-electrode gaps (dgap = 0.8 mm and 2.0 mm) using a lean n-butane/air mixture in a double-chamber fan-stirred explosion facility capable of generating near-isotropic turbulence over wide ranges of pulsed repetitive frequency (PRF = 1–100 kHz) and r.m.s. turbulence fluctuation velocity (urms = 0–4.9 m/s). The new DN configuration consists of two parallel anode electrodes with 2.6 mm apart and one central cathode electrode on the same vertical plane, which can generate two spatially separated and temporally synchronized discharges having an almost twice larger initial kernel size than the SN configuration. We apply the same total ignition energy Etot≈18 mJ via a train of 9 pulses/6 pulses for SN/DN experiments, each pulse having Eig≈2.2 mJ (SN) and/or 3.3 mJ (DN) except for the first pulse with the same 0.8 mJ regardless of PRF and dgap. Unlike the common notion that the larger ignition kernel leads to higher Pig,L, it is found that the DN configuration at small dgap = 0.8 mm is totally detrimental for spark ignition (SI) with Pig,L = 0% for all PRFs = 1–100 kHz, while the SN configuration at small dgap = 0.8 mm has its maximum Pig,L = 58% at PRF = 40 kHz showing the synergy effect. But the reverse is found at large dgap = 2.0 mm with Pig,L(DN) > Pig,L(SN). Moreover, when 1 m/s < urms < 4 m/s at PRF = 40 kHz and dgap = 2.0 mm, although both Pig,T(DN) and Pig,T(SN) decrease with increasing urms, Pig,T(DN) is noticeably higher than Pig,T(SN) showing ignition enhancement of dual-channel sparks at large dgap, Pig,T(DN) = Pig,T(SN) = 100% when urms < 1 m/s, and Pig,T(DN) = Pig,T(SN) = 0 % when urms ≥ 4.2 m/s. Finally, high-speed schlieren images of SN/DN kernel evolutions are used to comprehend these results that may be useful for the ignition strategy in lean-burn SI engines.

Hydrogen Production through Water Vapors using Optimized Corona-DBD Hybrid Plasma Micro-Reactor

Hydrogen as secondary energy carrier is one of the promising routes to meet renewable and sustainable energy demand. Hydrogen production using water plasmolysis, so far, has been considered as energy intensive. However, recent developments in the field of microplasmas has reduced energy requirement of water plasmolysis on par with electrolysis. However, there’s still room for improvement as water vapors dissociation efficiencies are less than thermodynamic and kinetic limits. One of the ways to do that is to split microchannel in plasma into sub-micron channels by packing beads inside the reactor. The current study investigates the plasmolysis of water vapours (steam) and argon gas with (1) empty channel plasma reactor and (2) glass beads packed plasma reactor. A custom-made Corona-DBD hybrid microplasma reactor has been designed and employed for water steam plasmolysis. This study aims to investigate the feasibility of water vapors dissociating into hydrogen at a relatively small interelectrode gap at atmospheric pressure. The minimum breakdown voltage has been found to be 3.7 kVpk-pk at 5 mA current. The maximum hydrogen production rate was observed 23.9 g/kWh at optimized conditions for the glass beads packed plasma reactor. So, in current study glass beads packed plasma microreactor yielded 23.9g of H2/kWh which is significantly higher than any previously published study

Surface Flattening of Directed Energy Deposited Parts through Jet Electrochemical Machining

For additive manufacturing (AM) processes, post-processing is usually needed before application, and electrochemical machining is considered a promising candidate for this purpose. Here, the possibility of using jet electrochemical machining (Jet-ECM) as a semi-finishing post-processing for directed energy deposition (DED) was investigated. The main purpose is to flatten the wave-like surface and improve dimensional accuracy. First, polarization, EIS, and current efficiency measurements were conducted, and it was found that the electrochemical dissolution behaviors of the DED-produced Inconel 718 alloy in NaNO3 solution were isotropic and irrelevant to the DED parameters, which can be attributed to the effect of the passive film. Pa and Pz values from the primary profile were considered more suitable than surface roughness for the characterization of the surface flatness. In the Jet-ECM experiments, the small inter-electrode gaps and high applied voltages were found to be beneficial to surface flattening, while the influence of the scanning speed was not evident. Multiple reciprocating scans could further improve the surface flatness, but most of the improvements were obtained in the first scan. This demonstrates the great potential of Jet-ECM in the post-processing of AM parts, and provide several essential guidelines for further researches.

Continuous Flow Electrochemical Oxidative Cyclization and Successive Functionalization of 2-Pyrrolidinones

2-Pyrrolidinones are important scaffolds found in numerous pharmacologically active compounds, such as brivaracetam and levetiracetam (antiepileptic drugs) or piracetam and pramiracetam (age-related memory impairment drugs). Among the numerous targets, nootropic agents represent an attractive class of compounds since they selectively improve cognitive functions. In this study, we report the successful translation of an electrochemical batch oxidative cyclization/functionalization of 2-pyrrolidinones, using the Kolbe reaction, from a batch type cell to a continuous flow electrochemical reactor. Combining organic electrosynthesis with continuous flow chemistry offers numerous advantages over batch electrolysis such as a faster reaction time and better mixing of the heterogeneous reaction. Moreover, due to the use of continuous flow electrochemical cells, which have a precise geometry, a small interelectrode gap, and large electrode surface area to reactor volume ratio, the productivity of organic electrosynthesis can be easily improved. Additionally, the translation of a batch electrochemical transformation to a continuous flow reactor is a critical step in the development of an electrochemical process given that flow chemistry is the most straightforward approach for the scale-up of this type of reactions. In this study, the application of continuous flow electrochemistry in our process allowed for an excellent productivity of 0.40 g/(h·mL) and an up to 81% yield of 2-pyrrolidinone within a loop-reactor setup (equipped with a 5 mL container).

Theoretical analysis of micro/nano electrochemical machining with ultra-short voltage pulses

The effect of pulse-on and pulse-off times on the efficiency of micro/nano ECM with ultra-short voltage pulses is theoretically analyzed. A new approximate analytical equation for the time of charging electrical double layer (EDL) is obtained. The equation takes into account all main parameters of the process. It enables one to determine the pulse-on time that provides a high localization of Faradaic process in the zones with small interelectrode gap and a high productivity of ECM process. The results of numerical calculations agree well with the data calculated by the proposed approximate analytical equation. The numerical calculations of the pulse-off time are performed. The effect of reverse voltage pulse imposed in the pauses on the EDL relaxation time is analyzed. The amplitude of reverse voltage pulse is limited by the condition of the absence of the tool-electrode wear. The proposed algorithm for calculating the pulse-off time and amplitude of reverse voltage pulse provides the required high coefficient of metal dissolution localization in the zone of small interelectrode gaps at a given pulse-on time.

Features of Electrostatic Fields and Their Force Action When Using Micro- and Nanosized Inter-Electrode Gaps.

The present work is devoted to assessing the influence of discreteness of electric charge distribution in the double electric layer on the characteristics of the electric fields and their force action in capacitor structures with small interelectrode gaps. Due to the fact that modern technologies often use submicron-sized interelectrode gaps, it is no longer possible to consider the electrodes uniformly charged because of the discreteness of the electric charge. The corresponding development of a mathematical and physical model for the study of a non-uniform electric field is suggested. Numerical calculations are carried out, expressions, criteria, and results that are convenient for practical evaluations are obtained. The physical and mathematical model for force characteristics of a non-uniform electric field is developed. With a sufficiently small size of the interelectrode gap, the integral force effect of discretely distributed charges can be significantly higher than with a uniform distribution of the same charge. At reasonable surface charge densities, these phenomena are usually observed at interelectrode gaps less than tenths of a micrometer.

Ultra-short pulse simulation for characterising oxide layer formation on stainless steel during μECM

Electrochemical machining is a controlled metal shaping process based on anodic dissolution performed by the electrode reactions. When pulse signals, in the micro-second or less range, are combined with a small inter-electrode gap, the process is referred to as Micro-Electro-Chemical machining or μECM. The application of using nano-second/micro second pulses for μECM for certain passivation metals can be very limited by the formation of an oxide layer that prohibits the penetration of ultra-short pulse durations due to the capacitive effect of the oxide layer. This paper will present findings from the development of a μECM numerical model that incorporates an advanced hybrid time stepping approach for representing nano-second pulse interactions with the physical phenomena of the electrolytic environment associated with μECM, thereby enabling the characterisation of the capacitive model of the formed oxide barrier layer. Experimental work was conducted using nano and micro-second pulses on the machining of 18CrNi8 and copper using NaNO3 electrolyte. The μECM simulation model contributed to quantifying the lack of faradic machining of 18CrNi8 that was experimentally observed. A particular solution, believed to be effective in breaking through the oxide film, is to directly pre-polarize the layer by super imposing a DC signal prior to the ultra-short pulses, such that its capacity has been already loaded when the short pulse signal is applied. However, too long of a DC signal application time can lead to machining damage. Through the development of an ultra-short pulse simulation model, this work has established, that we can numerically determine an optimal DC signal duration necessary to load the oxide layer just enough for facilitating anodic dissolution during physical μECM process, thus minimising machining damage.

Modeling of plasma temperature distribution during micro-EDM for silicon single crystal

In silicon single crystal micro-electrical discharge machining (Micro-EDM), the plasma channel and workpiece temperature field directly affect the machined parts. For Si single crystal, with short single discharge time and small inter-electrode gap, the temperature cannot be easily measured directly. Based on the theory of energy conservation and heat conduction, combined with Micro-EDM process, in this paper, thermodynamic analysis of plasma in Micro-EDM process is conducted, and a plasma temperature distribution model considering latent heat of fusion is established. Adopting Gaussian distribution heat flux boundary condition and the temperature field distribution of the workpiece surface is simulated by FLUENT. The relationship between material removal rate (MRR) and surface roughness (SR) corresponding to temperature distribution under different peak current and pulse width conditions is analyzed. The results show that plasma temperature has a positive correlation with peak current and pulse width. The increase of peak current and pulse width within the processing parameter range leads to the increase of MRR and SR. The experimental results verify the correctness of the model.

Influence of open voltage and servo voltage during Wire-EDM of silicon carbides

The high cost of silicon carbide and its associated difficulties in machining due to high hardness have long been a major hindrance towards successful applications in various industries, ranging from marine to aerospace sectors. This imparts a need to identify a suitable machining process that can machine silicon carbides with ease and at the same time generate complicated profiles. Therefore, the present work is an effort to identify the possibility of machining silicon carbides with wire electrical discharge machining process. In the current work, the silicon carbides being fabricated by rapid hot-pressing technique led to in-situ graphene formation. This graphene particles, in turn, aid the electrical discharge machining process by imparting a higher electron transfer rate through the workpiece. The influence of open voltage and servo voltage on the overall machinability were thoroughly investigated with machining rate, kerf width and surface roughness as the output characteristics. The variation in the intensity of discharge energy with open voltages had a direct influence on the formation of discharge crater which in turn, affected the overall output characteristics. This led to a gradual increase in the machining rate and the associated surface roughness with an increase in the open voltage. On the other hand, the increase in the servo voltage from 25 V to 39 V led to an initial increase in the machining rate which again decreases when the servo voltage further increases to 51 V. This variation in the machining rate was mainly due to the varying concentration of discharge, open and arcing pulses with varying servo voltage, with arcing pulses more dominant in lower servo voltage and open pulses in larger servo voltage. A minimum kerf width in the range of 170 µm was obtained in the present study with a wire tool of diameter 150 µm when the servo voltage was maintained at 25 V. Further, the kerf width was observed to increase with an increase in the servo voltage throughout the considered range. This is mainly due to the higher discharge concentration in the transverse direction as compared to the machining direction with an increase in the servo voltages. Moreover, a rougher machined surface with high debris concentration was observed when machined with lower servo voltages for all the considered open voltages. This behavior is mainly attributed by the high arcing phenomenon and ineffective removal of the eroded debris across the small inter-electrode gap by the dielectric fluid.

Weibull analysis of atmospheric pressure plasma generation and evidence for field emission in microwave split-ring resonators

The generation of atmospheric pressure microplasmas using microwave resonators is promising for many applications due to the possibility of high electron densities and low electrode degradation. In particular, such plasmas may help enable reconfigurable metamaterials operating from GHz to THz. Since plasma metamaterials may require the generation of tens to hundreds of plasmas, it is important to find ways to reduce the power required for plasma breakdown. Here, we study gold and silver microwave split-ring resonators (SRRs) with a variety of materials near the interelectrode gap (Cu, CuO nanowires, aluminum oxide). We focus on those fabricated using a traditional thick film technique, screen-printing, and using fs- and ns-laser ablation. The use of laser ablation allows us to explore small interelectrode gap sizes (7–100 μm) and the use of different lasers and laser parameters enables us to produce a variety of microstructures. We utilize Weibull statistics to examine breakdown in atmospheric pressure Ar with and without deep ultraviolet illumination of SRRs. Fabrication methods and materials are shown to influence both Q-factor of the SRRs and breakdown voltage independently. It is found that superior performance in terms of breakdown voltage and consistency in breakdown is related to Weibull modulus. The power requirement for breakdown varied as widely as an order of magnitude depending on fabrication method and material used for the SRRs. Furthermore, we consider the performance differences seen between various resonators and relate this to microstructure/material which suggests that field-emission may play a role in providing the seed electrons required for breakdown. This need for seed electrons appears to be especially important for gap sizes of 40 μm and smaller.

The Fundamentals Behind the Use of Flow Reactors in Electrochemistry.

ConspectusIn the past decade, research into continuous-flow chemistry has gained a lot of traction among researchers in both academia and industry. Especially, microreactors have received a plethora of attention due to the increased mass and heat transfer characteristics, the possibility to increase process safety, and the potential to implement automation protocols and process analytical technology. Taking advantage of these aspects, chemists and chemical engineers have capitalized on expanding the chemical space available to synthetic organic chemists using this technology.Electrochemistry has recently witnessed a renaissance in research interests as it provides chemists unique and tunable synthetic opportunities to carry out redox chemistry using electrons as traceless reagents, thus effectively avoiding the use of hazardous and toxic reductants and oxidants. The popularity of electrochemistry stems also from the potential to harvest sustainable electricity, derived from solar and wind energy. Hence, the electrification of the chemical industry offers an opportunity to locally produce commodity chemicals, effectively reducing inefficiencies with regard to transportation and storage of hazardous chemicals.The combination of flow technology and electrochemistry provides practitioners with great control over the reaction conditions, effectively improving the reproducibility of electrochemistry. However, carrying out electrochemical reactions in flow is more complicated than just pumping the chemicals through a narrow-gap electrolytic cell. Understanding the engineering principles behind the observations can help researchers to exploit the full potential of the technology. Thus, the prime objective of this Account is to provide readers with an overview of the underlying engineering aspects which are associated with continuous-flow electrochemistry. This includes a discussion of relevant mass and heat transport phenomena encountered in electrochemical flow reactors. Next, we discuss the possibility to integrate several reaction steps in a single streamlined process and the potential to carry out challenging multiphase electrochemical transformations in flow. Due to the high control over mass and heat transfer, electrochemical reactions can be carried out with great precision and reproducibility which provide opportunities to enhance and tune the reaction selectivity. Finally, we detail on the scale-up potential of flow electrochemistry and the importance of small interelectrode gaps on pilot and industrial-scale electrochemical processes. Each principle has been illustrated with a relevant organic synthetic example. In general, we have aimed to describe the underlying engineering principles in simple words and with a minimum of equations to attract and engage readers from both a synthetic organic chemistry and a chemical engineering background. Hence, we anticipate that this Account will serve as a useful guide through the fascinating world of flow electrochemistry.

Analysis of the flow field in counter-rotating electrochemical machining

In electrochemical machining (ECM), the electrolyte flow field has marked influence on the processing stability, efficiency and surface quality. This paper presented a new electrolyte flow mode to improve the flow field distribution in counter-rotating electrochemical machining (CRECM), in which the electrolyte flows into the processing zone from both sides and top of the fixture, and flows out from the bottom of the fixture. The flow field distributions were analyzed and simulated via computational fluid dynamics (CFD) software. The simulation results showed that the low-velocity area in CRECM was eliminated and the velocity distribution was more uniform by using the optimized flow mode. Experiments were also conducted using a specific fixture. The experimental results indicated that a stable machining process with a small inter-electrode gap could be achieved, and the ECM accuracy was remarkably improved. The sidewall taper angles and rounded corners of the machined convex structure were reduced to be only about -0.8° and 0.6 mm.

Modeling and experiment study on inter-electrode gap in electrochemical machining with a floating cathode for rotary parts

A small inter-electrode gap is necessary to improve the machining accuracy in electrochemical machining (ECM). In order to achieve a stable small gap processing, this paper proposes a new concept of ECM method with a floating cathode. Aiming at the problem of gap regulation in this method, the modeling and experimental research are carried out, taking the electrochemical machining with a large span floating cathode of dual round outlets for rotary parts as an example. A mathematical model of machining gap is established based on fluid mechanics and kinetics of electrode processes, from which the relationships between the gap and process parameters are analyzed. Through the experimental method, the influence law of the variation of process parameters on the gap is further studied, and the mathematical model is modified. Comparisons between the modified theoretical model calculation results and experimental results show that considering only the flow field conditions, the average error of the inter-electrode gap obtained by experiment and model during work-piece rest and work-piece rotation is 6.1% and 4.3%; considering the flow field and electric field conditions, the average error of the inter-electrode gap during work-piece rest and work-piece rotation is 4.1% and 5.1%. The study demonstrates that a stable inter-electrode gap can be formed in ECM through the liquid electrolyte to support the cathode, and the inter-electrode gap was correlated with the electrolyte flowrate, current, and electrolyte pressure, so it is a feasible method to regulate the gap by adjusting the electrolyte flow or the inter-electrode current during processing, which provides a new way for gap formation and control in high-precision electrochemical machining.