Small Interelectrode Gap Research Articles

Modeling of Material Removal Rate in Micro-ECG Process

Microelectrochemical grinding (micro-ECG) is a variant of electrochemical grinding (ECG) process, in which material is removed by a combination of electrolytic dissolution and abrasive action that take place in a small interelectrode gap. This paper discusses analytical modeling of the material removal phenomenon in micro-ECG process to predict material removal rate. In the model, the phenomena, which contribute to the material removal in the process by electrolytic and abrasive actions, have been considered; these include streaming potential in the electrochemical action and shearing forces due to the flow of electrolyte through interelectrode gap and the abrasive action of grinding wheel. Two configurations of the process, viz., surface and cylindrical micro-ECG, have been modeled. The results have been validated by CFD simulation in the case of surface micro-ECG process, and specific experimentation in the case of cylindrical micro-ECG process.

Radio frequency expanding plasmas at low, intermediate, and atmospheric pressure and their applications

Abstract We report on the operation and characteristics of radio frequency (RF) plasma beam sources based on the expansion of the discharge outside of limited spaces with small interelectrode gaps. The appropriate electrode configuration, combined with high mass flow values and appropriate power levels, leads to small- or large-size plasma jets, working stably at low, intermediate, and atmospheric pressures. The sources are promising tools for a wide range of applications in thin film deposition, surface modification, and cleaning, including the case of temperature-sensitive substrates.

Influence of tool vibration on machining performance in electrochemical micro-machining of copper

Electrochemical micro-machining (EMM) appears to be promising as a future micro-machining technique since in many areas of applications, it offers several advantages, including biomedical and MEMS applications. A suitable micro-tool vibration system has been developed, which consists of tool-holding unit, micro-tool vibrating unit, etc. The developed system was used successfully to control material removal rate (MRR) and machining accuracy to meet the micro-machining requirements. Micro-holes have been produced on thin copper workpiece by EMM with stainless-steel micro-tool. Experiments have been carried out to investigate the most effective values of process parameters such as micro-tool vibration frequency, amplitude and electrolyte concentration for producing micro-hole with high accuracy and appreciable amount of MRR. From the experimental results and SEM micrographs, it is evident that the introduction of micro-tool vibration improves EMM performance characteristics. Lower electrolyte concentration in the range of 15–20 g/l reduces stray current effects. Hertz (Hz) range of tool vibration frequency improves the removal of sludge and precipitates from very small interelectrode gap. The 150–200 Hz range of tool vibration frequency can be recommended for EMM, which provides a better electrochemical machining in the narrow end gap. Compared to kHz range, Hz range micro-tool's vibration improves the MRR and accuracy in EMM.

The influence of the electric field shape on the gas breakdown under low pressure and small inter-electrode gap conditions

The connection between nonhomogeneities of the electric field and the value of the breakdown voltage [direct current (dc), pulls] in gases (N/sub 2/, SF/sub 6/) under low pressure and small inter-electrode gap was investigated in this paper. The obtained results show that the values of the breakdown voltages for nonhomogenous fields are considerably higher than the values for homogenous fields. It was also established that there is some disagreement between experimentally and theoretically (numerically) obtained values of the dc breakdown voltages for nonhomogenous fields. These results could be explained by the small distance effect and by the combination of the gas and vacuum breakdown mechanisms.

Production of syngas plus oxygen from CO 2 in a gas-diffusion electrode-based electrolytic cell

Most of the research published in electrochemical CO 2 reduction has been reported for half-cells, with little consideration of the overall system. However, it is necessary to consider the eventual involvement of full cells. We conducted CO 2 reduction and water oxidation in a CO 2-reducing full cell with larger geometric surface area (2×2 cm 2) and with a relatively small inter-electrode gap (1–2 mm) in order to minimize ohmic losses. The result was an ca. 1:1 CO/H 2 (v/v) gas ratio at a current density of 10 mA cm −2 and a cell voltage of 3.05 V, producing O 2 at the counter electrode. Based on an enthalpic voltage of 1.36 V, this constitutes an overall energy efficiency of 44.6%.

Electrochemical removal of nickel ions from industrial wastewater

The electrochemical reduction of nickel ions in dilute industrial wastewater from a galvanic nickel plating plant was carried out on a three-dimensional electrode in a gas diffusion electrode packed bed electrode cell (GBC) and also on a rotating disc electrode. To explain the experimental results, concentration profiles for selected species were calculated during nickel deposition. It was found that, depending on the solution composition and electrolysis conditions, metallic nickel, nickel oxide and nickel hydroxide, as well as nickel oxyhydroxide, can be deposited. Metallic nickel dendrite formation and its growth towards and on the Nafion membrane were identified as a major problem in a cell with a small interelectrode gap due to the damage caused on the gas diffusion electrode (GDE) membrane assembly. Moreover, it was found that the nickel selectivity ratio depends on the total current density as well as on the Ni 2+ concentration, and that the surface of the rotating disc electrode can be completely blocked by green nickel hydroxide deposit.

Large-area interdigitated array microelectrodes for electrochemical sensing

Advanced photolithography developed for the semiconductor industry has been used to fabricate interdigitated microelectrode arrays that pass steady-state limiting currents of up to 230 nA/μM analyte — 2.5 times more than the most sensitive interdigitated array built to date, and exhibit response times of ∼5 ms. This performance results from the small interelectrode gap and the large active area of the device (4 mm 2), a combination enabled by advanced photolithography. We describe the fabrication of these arrays and the characterization of their performance in two environments: an aqueous solution of Ru(NH 3) 6 3+ and a dinitrotoluene solution in acetonitrile. The scaling of array performance parameters with device dimensions is also presented.

Process monitoring of electrochemical micromachining

Electrochemical micro-machining (ECμM), utilises very small inter-electrode gaps (<20 μm) in order to obtain the accuracies necessary. The narrow gaps make the control of the process much more complex than normal ECM. Furthermore, difficulty in gap flushing leads to an increased tendency to cause electrical discharges, which is highly detrimental to the process. In order to formulate spark prevention and gap control strategies, this paper investigates the discharge mechanism in narrow electrolytic gaps. A monitoring method using radio frequency emission is given, which together with the current and voltage signals, identifies more clearly the events occurring within the gap.

Microcell conductivity measurements of polymer electrolytes

A microcell method has been developed for conductivity measurements of polymer electrolyte samples of small size. Samples were deposited in thin films on a microfabricated electrode pattern with small interelectrode gaps. The conductivities, calculated in each case without reference to the film thickness, were found to equal those measured conventionally. Fast equilibration of the sample with a dry argon environment eliminated the possibility of water contamination and confirmed the validity of previous data for bulk samples of LiClO 4-doped poly[oxymethylene-oligo(oxyethylene)] (APEO). The utility of the method was demonstrated by new measurements of the conductivity of APEO doped with lithium TFSI and lithium methide.

Pulsed response of Ga0.47In0.53As photodiode structures with a submicron gap between interdigital electrodes

The effects of miniaturisation of optoelectronic devices makes simple size-scaling methods ineffective. A two-dimensional model demonstrates that the main problem in metal—semiconductor—metal (MSM) diode structures with small interelectrode gaps is the small depth of penetration of an electric field into the active region of a diode. This results in different rates of electron and hole collection at the contacts and delays the pulsed response of a photodetector. Self-consistent two-dimensional analysis is made of the photocarrier motion in the active region of an MSM diode structure and of the characteristics of the pulsed response of Ga0.47In0.53As MSM photodiodes. Ways of improving this response are discussed. The calculated results are compared with experiments.

Modelling and Monitoring Interelectrode Gap in Pulse Electrochemical Machining

Pulse electrochemical machining (PECM) provides an economical and effective method for machining high strength, heat-resistant materials into complex shapes such as turbine blades of titanium alloys. The dimensional accuracy of PECM can be improved if a small interelectrode gap is maintained. This paper presents an interelectrode gap model for estimating machining parameters for the minimum gap size under the limit of electrolyte boiling. A specially-built PECM cell and a high speed data acquisition system are used to acquire the pulse current signal for developing an on-line monitoring strategy. A stochastic analysis of the current signal indicates a linear correlation between the gap size and the variance of the filtered current signal. An on-line monitoring system based on this correlation is proposed for the PECM process.

Modelling and Analysis of Pulse Electrochemical Machining (PECM)

A small interelectrode gap in Electrochemical Machining (ECM) results in improved dimensional accuracy control and simplified tool design. However, using a small gap with conventional ECM equipment adversely affects the electrolyte flow or mass transport conditions in the gap, leading to process instability. The most remarkable breakthrough in this regard is the development of ECM using pulsed current. Pulse Electrochemical Machining (PECM) involves the application of a voltage pulse at high current density in the anodic dissolution process. PECM allows for more precise monitoring and control of machining parameters than ECM using continuous current. Small interelectrode gap, low electrolyte flow rate, gap state recovery during the pulse-off times and improved anodic dissolution efficiency features encountered in PECM lead to improved workpiece precision and surface finish when compared with ECM using continuous current. This paper presents mathematical models for the PECM process which take into consideration the nonsteady physical phenomena in the gap between the electrodes, including the conjugate fields of electrolyte flow velocities, pressure, temperature, gas concentrations, current densities and anodic material removal rates. The principles underlying higher dimensional accuracy and simpler tool design attainable with optimum pulse parameters are also discussed. Experimental studies indicate the validity of the proposed PECM models.

Theoretical study of parallel dual-cylinder microelectrodes with a small imposed constant potential difference in static electrolyte solutions containing a reversible redox couple

A total mass flux recycling model has been used to develop a theory for parallel dual-cylinder (PDC) microelectrodes held at a small constant potential difference in static solutions containing a reversible redox couple for the case of steady-state response. The bilinear transformation of coordinates in diffusion space has been used in the treatment. In the model used it is assumed that lines of mass flux and equiconcentration surfaces established between a microcylindrical anode and cathode are represented by orthogonal circular functions. It is shown that, using a PDC device with a very small interelectrode gap, data obtained from non-stirred ferri/ferrocyanide solutions are in good agreement with predictions of the established theory.

Computer simulation of Pulse Electrochemical Machining (PECM)

Pulsed Electrochemical Machining (PECM) involves the application of a voltage pulse at high current density in the Electrochemical Machining (ECM) process. PECM allows for improved monitoring and control of the machining process when compared with traditional, direct current ECM. PECM is also readily automated. The small inter-electrode gap, system rest states between voltage pulses, and low electrolyte flow rate encountered in PECM lead to improved precision and surface finish when compared with d.c. ECM. This paper develops a mathematical model for PECM and employs this model in a computer simulation of the PECM process. The reasons for improved accuracy of PECM versus direct current ECM are also discussed.