Citric Acid Electrolyte Research Articles

Corrosion, wear and machinability studies on scrap aluminium alloy wheel based metal matrix composite

Recycled materials, especially scrap aluminum alloy wheels with reinforcement castings, are gaining applications in various fields such as aerospace, naval, military, and automobile. In this research, Honda car alloy wheels are stir-cast with 5% alumina as reinforcement and subjected to corrosion, wear, and machinability studies. Corrosion studies were conducted to evaluate the corrosion current density (ICorr), corrosion potential (ECorr), and corrosion rate for the cast aluminum metal matrix composite. The wear studies with different loads, i.e., 50 N, 60 N, 70 N, and 80 N, were performed on the specimen and investigated the coefficient of friction, frictional force, and pin temperature. The sliding load has a significant effect on wear performance, and for the sliding load of 80 N, the wear recorded was 2574.83 µm. The electrochemical machinability studies with voltage, duty cycle, and concentration of citric acid electrolyte are performed on the machining rate and surface corrosion factor. Analysis of the electrochemical machining process with PROMETHEE-II shows that 7 V, 60% duty cycle, and 30 g/L electrolyte concentration are estimated to be the best combination for a higher machining rate and a lower surface corrosion factor. KEY WORDS: Alumina, Machining rate, Nyquist plot, Electrochemical machining, PROMETHEE-II Bull. Chem. Soc. Ethiop. 2024, 38(4), 1163-1175. DOI: https://dx.doi.org/10.4314/bcse.v38i4.27

Electrochemical Characterization and Micromachining of Nitinol SMA by WECM Using Citric Acid Mixed H2SO4 Electrolyte

Nitinol shape memory alloy (SMA) is a tough material to machine because it is difficult to cut. The results of the current research work demonstrate how two different electrolytes affect the electrochemical behavior in relation to electrochemical machining performance of nitinol. Potentiodynamic polarisation (PDP) and electrochemical impedance spectroscopy (EIS) tests have been conducted using 0.1 M H2SO4 and mixed 0.1 M H2SO4 + 0.1 M citric acid electrolyte. Further, the experimental investigation on the machining characteristics of nitinol during wire electrochemical machining (WECM) has been conducted. It is revealed that the grooves width and depth increase with increase in applied pulse voltage and surface roughness increase with increase in groove depth. The minimum width overcut of machined groove was 18.10 μm in 0.1 M H2SO4 + 0.1 M citric acid at 5 V pulse voltage which is less compared to width overcut of 24.85 μm produced in 0.1 M H2SO4 electrolyte for same parametric machining condition. This specific mixed electrolyte produced average surface roughness (Ra) of 0.0631 μm at 5 V which is lower compared to 0.09055 μm produced using 0.1 M H2SO4 electrolyte. The fabrication of homogeneous average slit width of 92.234 μm using citric acid mixed H2SO4 electrolyte with minimum average surface roughness (Ra) of 0.0691 μm shows the capability of WECM.

Transparent and biocompatible In2O3 artificial synapses with lactose–citric acid electrolyte for neuromorphic computing

Electrolyte-gated synaptic transistors are promising for artificial neural morphological devices. However, few literatures have been reported regarding the manufacturing of electrolyte-gated synaptic transistors with low cost and biocompatible components. Here, the fully transparent synaptic transistors based on water-induced In2O3 thin films have been integrated by sol–gel method at low temperature, and lactose dissolved in citric acid solution is used as the gate electrolyte. The migration of the ions at the interface plays a crucial role in the potentiation and depression of the synaptic weight. In this work, the biological synaptic functions, including excitatory postsynaptic current, paired-pulse facilitation, high-pass filtering characteristics, short-term memory, and long-term memory, are mimicked. Meanwhile, based on the potentiation/depression behaviors of the synaptic transistor, a three-layer artificial neural network is applied for pattern recognition, and the recognition accuracy is as high as 94.6%. This study offers a possibility to realize fully transparent synaptic devices with biocompatible components at low temperature.

A performance study of electrochemical micro-machining on SS 316L using suspended copper metal powder along with stirring effect

ABSTRACT Electrochemical micro-machining (ECMM) is widely used for machining small-sized components, intricate shapes, and hard materials. Fabrication of micro-holes in stainless steel 316L (SS 316L) can be effortlessly achieved by the ECMM process rather than other machining methods, owing to its favorable machining characteristics and advantages. This paper tries to elucidate the performance of ECMM on the machining of SS 316L using an eco-friendly citric acid as an electrolyte medium, and the results are compared with copper metal powder suspended in a citric acid electrolyte (suspended electrolyte) and copper metal powder suspended in a citric acid electrolyte with the assistance of a mechanical overhead stirrer (suspended electrolyte with stirrer effect). The output performance parameters such as MRR and overcut are calculated by varying the input response parameters such as machining voltage, duty cycle, and electrolyte concentration. From the experimental results at higher parameter levels, the highest MRR and moderate overcut are obtained for suspended electrolyte with stirrer effect. For suspended electrolyte, moderate MRR and the highest overcut are detected. The least MRR and reduced overcut are found for citric acid electrolyte. SEM and EDAX analysis have been carried out to see the machined micro-hole and the composition present in the specimen.

Effect of different electrolytes on electrochemical micro-machining of SS 316L

The use of stainless steel 316L (SS 316L) in the medical, marine, aerospace, bio-medical, and automobile sectors increases rapidly. Electrochemical micro-machining (ECMM) is the appropriate method for machining SS 316L due to its burr-free machining surface, no residual stress, and high precision. However, some limitations are found in using strong electrolytes, such as HCl, H2SO4, KOH, NaNO3, and NaCl, which reportedly face difficulties in disposing to the environment and handling issues. Hence, this paper addresses overcoming the disadvantages encountered in the ECMM process when using strong electrolytes to machine SS 316L. Therefore, different organic electrolytes such as tartaric acid (C4H6O6), citric acid (C6H8O7), and a combination of tartaric and citric acid (mixed electrolyte) are considered to select the best electrolyte. Process parameters like machining voltage, duty cycle, and electrolyte concentration are included in determining machining performance. The performance of ECMM is evaluated using material removal rate (MRR) and overcut. The overcut of tartaric acid electrolyte is 179% less than mixed electrolyte for the parameter combination of 12 g/l, 11 V, and 85%. On the other hand, the mixed electrolyte shows 114.2% higher MRR than the tartaric acid electrolyte for the parameter solutions of 25%, 11 V, and 20 g/l. Furthermore, the citric acid electrolyte shows the second-lowest overcut and higher MRR in all aspects of machining performance. Field emission scanning electron microscope (FESEM) studies are carried out to realize the effect of electrolytes on the machining surface.

Surface Enhanced Raman Scattering in Graphene Quantum Dots Grown via Electrochemical Process.

Graphene Quantum dots (GQDs) are used as a surface-enhanced Raman substrate for detecting target molecules with large specific surface areas and more accessible edges to enhance the signal of target molecules. The electrochemical process is used to synthesize GQDs in the solution-based process from which the SERS signals were obtained from GQDs Raman spectra. In this work, GQDs were grown via the electrochemical process with citric acid and potassium chloride (KCl) electrolyte solution to obtain GQDs in a colloidal solution-based format. Then, GQDs were characterized by transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy, respectively. From the results, SERS signals had observed via GQDs spectra through the Raman spectra at D (1326 cm−1) and G (1584 cm−1), in which D intensity is defined as the presence of defects on GQDs and G is the sp2 orbital of carbon signal. The increasing concentration of KCl in the electrolyte solution for 0.15M to 0.60M demonstrated the increment of Raman intensity at the D peak of GQDs up to 100 over the D peak of graphite. This result reveals the potential feasibility of GQDs as SERS applications compared to graphite signals.

Electrochemical Insight into the Role of H2O2 in Galvanostatic Passivation of AISI 316L Austenitic Stainless Steel in Citric Acid Electrolyte

Electrochemical Insight into the Role of H2O2 in Galvanostatic Passivation of AISI 316L Austenitic Stainless Steel in Citric Acid Electrolyte

Electrochemical Micromachining of Copper Alloy through Hot Air Assisted Electrolyte Approach

The industries like automobile, electronics, medical and biomedical sectors provide scope for various types of micro products/features made up of copper material. Due to the higher ductility of copper the electrochemical micro machining (EMM) is a prominent technique owing it’s no tool wear, high accuracy, burr free and non-contact machining surface. Although enhancing of EMM performance is significant work in the micro components manufacturing industry. Hence, in this present work the hot air is mixed with aqueous citric acid (C6H8O7) electrolyte (HAME) to machine high aspect ratio micro-holes (HAR micro-hole) and the results are compared with the dry air mixed electrolyte (DAME). The process parameters such as machining voltage (Mv), Duty cycle (Dc), and electrolyte concentration (Ec) are taken into account in evaluating the machining performance. The electrolyte temperature (Et) and frequency are kept at a constant level as 36 ± 1°C and 85 Hz respectively. The machining performances are estimated by means of material removal rate (MRR), overcut (OC) and taper angle of the HAR micro hole (TAHAR-micro-hole).The MRR shows 1.43 times improvement for HAME at the parametric combination of 20 g/L, 13 V, and Dc at 90% and reduced OC by 30.4% over DAME. The TAHAR-micro-holes are found to be 21.67° and 28.19° for the DAME and HAME respectively for the above parametric combinations. At parameters combination of 30 g/L, 13 V, and 90%, the MRR shows 2.87 times higher MRR compared to DAME. Furthermore, the use of citric acid as an electrolyte and mix of hot air contributes for higher MRR and reduced OC.The field emission scanning electron microscope (FESEM) analysis is done to understand the effect of hot air mixed electrolyte on the surface topography and inner machined surfaces of a micro-hole.

Effects and interaction of dietary electrolyte balance and citric acid on growth performance, intestinal histomorphology, digestive enzyme activity and nutrient transporters expression of weaned piglets.

Fifty-six piglets were weaned at 21days and randomly assigned to 1 of 8 dietary treatments with 7 replicate pens for a 14-day experimental period. The eight experimental diets were prepared via a 2×4 factorial arrangement with citric acid (CA; 0 and 0.3%) and dietary electrolyte balance (dEB, Na +K - Cl mEq/kg of the diet; -50, 100, 250, and 400mEq/kg). Varying dEB values were obtained by altering calcium chloride and sodium bicarbonate contents. Dietary CA significantly increased (p<.05) villus height (VH) and villus height:crypt depth (VH:CD) in the jejunum. Piglets fed a 250mEq/kg diet increased (p<.05) VH and VH:CD values in the duodenum. Jejunal VH and VH:CD increased (quadratic; p<.05), and ileal VH:CD (liner and quadratic; p<.05) decreased as dEB was increased in diets without CA, but no such effect was observed on the diets containing CA (dEB ×CA; p<.05). The CD in jejunum (quadratic; p<.05) increased as dEB was increased in diets containing CA, whereas it was decreased (linear; p<.05) in the diets without CA (dEB ×CA; p<.001). Dietary CA increased maltase activity and reduced the number of Ki67-positive cells (p<.05). Increasing dEB values in diets without CA increased sucrose and lactase activities (quadratic; p<.05), but no such effect was observed in the diets with CA (dEB ×CA; p<.05). An interaction effect between dEB and CA on the number of Ki67-positive cells was observed (p<.001). In conclusion, 250mEq/kg dEB diet with CA improved piglet intestinal digestion and absorption function by improving intestinal morphology and increasing digestive enzyme activities. However, these improvements were also observed in piglets fed the 100mEq/kg dEB diet without CA.

Regulating and intervening act of Cr chemical speciation effect on the electrokinetic removal in Cr contaminated soil in arid area

Heavy metals chemical speciation significantly effects the electrokinetic removal of heavy metals contaminated soil, but how to regulate and intervene the chemical speciation for improving the removal efficiency in the electrokinetic remediation of the contaminated soil is still an opened problem. In this study, we used increasing citric acid electrolyte concentration and soil pretreatment as regulating measures and the anolyte circulation and reduction wells as intervening act to explore the detailed transformation and migration of Cr speciation over time during electrokinetic remediation, the effect of the transformation and migration of Cr speciation in arid area contaminated soil on the removal efficiency. Based on the results of sequential extraction, the regulating measures can significantly improve the soil pH and the transformation of Cr speciation in arid areas, but the detailed transformation occurs in the early stage of remediation. The material flows showed that the transformation of other speciation to exchangeable (EXC) was higher than its migration to the electrode chamber and the EXC was not completely removed throughout the experiment. By adding HCl to the soil prior to the electrokinetic remediation, more Cr (III) can migrate to the cathode region. Regulating measure for pretreatment of real contaminated soil in arid area based on high concentration of citric acid and intervening act for the anolyte circulation could significantly reduce the bound to Fe/Mn oxides (FM), but the overall removal efficiency of the real contaminated soil (from 44.86% to 44.90%) was not improved, while the removal efficiency of artificially contaminated soil was higher. Furthermore, the multivariate linear regression analysis of the link between the five fractions and removal efficiency of Cr also shows that their correlation was much higher in artificially contaminated soils than in real contaminated soils. The scale effect would affect the transformation of the speciation, and the smaller the scale of the experiment is, the larger the influence on the migration and transformation of Cr speciation will be. The combination of regulating measures and intervening act provide a valuable reference for the specific transformation and migration of heavy metals speciation and the improvement of removal efficiency during EKR of contaminated soil in arid area.

Performance of magnetic field-assisted citric acid electrolyte on electrochemical micro-machining of SS 316L

ABSTRACT This paper throws light on machining stainless steel 316L (SS 316L) with the assistance of electrochemical micro-machining (ECMM) using an eco-friendly citric acid electrolyte. Investigation to produce micro hole on SS 316L is initially carried out by a bar magnet, which is placed in the citric acid electrolyte and the parameters like material removal rate (MRR), overcut are studied and the results are compared with the citric acid (C6H8O7) mixed with sodium chloride (NaCl) as a mixed electrolyte of various concentrations. Of the two machining conditions, mixed electrolyte performs 1.82 times faster in MRR for the parametric combination of 11 V,85% duty cycle and 20 g/l of electrolyte concentration. The overcut for the magnetic field-assisted citric electrolyte is found to be lower for the concentration in the range of 12 g/lit to 20 g/lit. The magnetic field-assisted citric acid electrolyte produces a 4.87% decrease in overcut for the parametric combination of 7 V, 85% duty cycle and 20 g/l of electrolyte concentration. Scanning electron microscopic (SEM) analysis has been performed in this study to illustrate the surface texture of the machined surface. Surface texture is found to be good in magnetic field-assisted citric acid electrolyte over mixed electrolyte.

Effects and interaction of dietary electrolyte balance and citric acid on the intestinal function of weaned piglets.

Fifty-six piglets (6.26 ± 0.64 kg BW) were weaned at 21 d and randomly assigned to one of the eight dietary treatments with seven replicate pens for a 14-d experimental period. The eight experimental diets were prepared via a 2 × 4 factorial arrangement with citric acid (CA; 0% and 0.3%) and dietary electrolyte balance (dEB, Na + K - Cl mEq/kg of the diet; -50, 100, 250, and 400 mEq/kg). Varying dEB values were obtained by altering the contents of calcium chloride and sodium bicarbonate. An interaction (P < 0.05) between dEB and CA in diarrhea score and the number of goblet cell in jejunum were observed. Ileum pH significantly decreased in weaned piglets fed 250 mEq/kg dEB diet compared with those fed -50 and 400 mEq/kg dEB diets (P < 0.05). Supplementation of 0.3% CA decreased the number of goblet cell in the ileal crypt (P < 0.05) and the relative mRNA expression of cystic fibrosis transmembrane conductance regulator, tumor necrosis factor-α, interferon-γ (IFN-γ), interleukin-1β (IL-1β), interleukin-10 (IL-10), zona occludens-1, and Claudin-1 (P < 0.05). Increasing dEB values increased the number of goblet cells in the jejunal crypt (P < 0.05). A 250-mEq/kg dEB diet decreased the relative mRNA expression of IFN-γ, IL-1β, and IL-10 (P < 0.05) than 100-mEq/kg dEB diet. The interaction between dEB and CA on the relative abundances of Cyanobacteria and Saccharibacteria was observed (P < 0.05). Supplementation of 0.3% CA increased relative abundances of and Streptococcus hyointestinalis. Piglets fed 250-mEq/kg diet increased relative abundances of Firmicutes and Lactobacillus rennini, and decreased the relative abundance of Proteobacteria, Veillonella, Actinobacillus minor, and Escherichia-Shigella.In conclusion, supplementation of 0.3% CA resulted in differential expression of inflammatory cytokines, ion transporters, and tight junction proteins, and changes in the microbial community composition. A 250-mEq/kg dEB diet reduced gastrointestinal pH and promoted the enrichment of beneficial microbes in the gut microbiota, thereby suppressing inflammation and harmful bacteria. However, the addition of CA to diets with different dEB values did not promote intestinal function in weaned piglets.

Enhanced electrokinetic remediation of lead- and cadmium-contaminated paddy soil by composite electrolyte of sodium chloride and citric acid

The aim of this study was to inquire about the removal efficiencies of lead and cadmium in paddy soil by a composite electrolyte of sodium chloride and citric acid under electrokinetic remediation. The experiment was operated in a plexiglass tank, which was divided into one soil column (length × width × height = 20 cm × 5 cm × 5 cm) and two electrode chambers (length × width × height = 6 cm × 5 cm × 5 cm). In this paper, the composite electrolyte (sodium chloride + citric acid) which combined the merits of two different chemicals was investigated for electrokinetic remediation of lead- and cadmium-contaminated paddy soil under a voltage gradient of 1.5 V/cm during a 20-day treatment. The total concentrations of lead and cadmium in the initial soil were 940.83 and 4.51 mg/kg, respectively. As sodium chloride was solubilized in solution, a number of Na+, Cl−, OH−, and H+ ions were generated that could dissolve some of Pb and Cd in soil to form Cd–Cl and Pb–Cl. When the lead- and cadmium-contaminated paddy soil was implemented with 0.1 M sodium chloride, the total removal efficiencies of lead and cadmium were 23.10 and 27.94%, respectively, which were little higher than those implemented with deionized water. Citric acid was not only used to control pH, but it can also combine with metals to form soluble M-citrate. When sodium chloride was mixed with citric acid in electrokinetic (EK) remediation, high redox potential was obtained that forced most of the metals to migrate out from soil. The overall removal efficiencies of lead and cadmium were increased from 56.85 and 62.26% with single citric acid electrolyte to 80.37 and 90.86% with composite electrolyte of sodium chloride and citric acid, respectively. Eventually, the residual concentrations of lead and cadmium in the soil were only 184.70 and 0.41mg/kg, respectively, which met the demand of agricultural production and human health requirements. Citric acid + sodium chloride treatment poses less environmental risk than inorganic acid (HCl, HNO3, and H2SO4). There is good synergistic effect of sodium chloride and citric acid during the EK remediation process. Thus, citric acid + sodium chloride is considered as an effective electrolyte to remove lead and cadmium from paddy soil.

Manufacturing of highly ordered porous anodic alumina with conical pore shape and tunable interpore distance in the range of 550 nm to 650 nm

AbstractIn this work, highly ordered porous anodic alumina (PAA) with tapered pore structure and interpore distance (Dc) in the range of 550 nm to 650 nm were fabricated. To produce hexagonal close-packed pore structure a two-step process, combining anodization in etidronic acid electrolyte in the first step and high-concentration, high-temperature anodization in citric acid electrolyte in the second step, was applied. The Al pre-patterned surface obtained in the first anodization was used to produce regular tapered pore arrays by subsequent and alternating anodization in 20 wt.% citric acid solution and pore wall etching in 10 wt.% phosphoric acid solution. The height of the tapered pores was ranging between 2.5 μm and 8.0 μm for the PAA with Dc= 550 nm and Dc= 650 nm, respectively. The geometry of the obtained graded structure can be used for a production of efficient antireflective coatings operating in IR spectral region.

Morphological and chemical characterization of highly ordered conical-pore anodic alumina prepared by multistep citric acid anodizing and chemical etching process

Highly ordered, conical-pore anodic alumina (AAO) membranes with interpore distance (Dc) between ca. 530 and 620 nm and thickness ranging between 2.4 and 7.8 μm, were produced. In the fabrication process aluminum surface was first pre-patterned by the anodization in etidronic acid solution. Then, the regular arrays of Al concaves were used as nucleation sites to grow AAO during the second anodization, which was carried out in highly concentrated citric acid solution (20 wt%) and at relatively high temperature (33–35 °C). The conical pore shape was engineered by a multistep process combining anodization in the citric acid electrolyte and the subsequent chemical pore broadening in phosphoric acid solution. The morphological analyses has revealed that the geometrical parameters of the Al concaves were successfully transferred to the AAO membranes. Furthermore, FTIR spectra analysis confirmed that the electrolyte species, such as phosphonate and citric ions, are being embedded into the AAO framework during the anodization. The graded-index structure formed in AAO can be used for a production of antireflective coatings operating in a broad spectral range.

Template-Assisted Electrodeposition of Urchin-Like Ag-Nanoplate-Assembled Nanorod Arrays and Their Structurally Enhanced SERS Performance

An effective template-assisted electrodeposition approach is demonstrated for growing large-area, hexagonally arranged arrays of urchin-like Ag-nanoplate-assembled nanorods grafted on the polystyrene spheres (PSs) as homogeneous and sensitive surface-enhanced Raman scattering (SERS) substrates. The urchin-like Ag-nanoplate-assembled nanorod arrays are fabricated by first transferring the ordered hexagonally arranged PS colloidal monolayer onto the silicon wafer as the template, and then electrodepositing ZnO nanorods onto the surface of each PS, and finally assembling Ag-nanoplates onto each ZnO nanorod on the PSs via electrodeposition in silver nitrate and citric acid electrolyte. Because of the ordered arrangement of the PS arrays and the high-density sub-10 nm gaps between the neighboring building blocks, the hierarchical urchin-like Ag-nanoplate-assembled one-dimensional nanostructure arrays can offer uniform and abundant “hot spots” for sensitive and reproducible SERS effect. Using the urchin-like hierarchical Ag-nanoplate-assembled nanorod arrays as SERS substrates, 1 pM rhodamine 6 g (R6G), 10pM para-aminothiophenol (p-ATP), and 1 μM PCB-77 (one congener of polychlorinated biphenyl, a notorious member of persistent organic pollutant) are identified respectively, showing promising potentials in rapid detection of organic environmental pollutants.

Heat treatment effect on crystal structure and design of highly sensitive room temperature CO2 gas sensors using anodic Bi2O3 nanoporous formed in a citric acid electrolyte

The effect of annealing temperature on the crystal structure of anodic bismuth trioxide (ABO) layers prepared via anodization in a citric acid-based electrolyte was studied. The samples were annealed in air at temperatures ranging from 200 °C to 600 °C. Characterization of nanoporous ABO layers was carried out through x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–visible (UV–Vis) diffuse reflectance spectroscopy and photoluminescence (PL). Effects of heat treatment on crystallinity, morphology and gas-sensing properties were investigated in detail. The XRD measurements showed that a gradual phase change from beta to gamma occurs with an increase in annealing temperature. The beta to gamma transformation occurred between 500 and 600 °C. The changes in the average crystallite sizes of beta and gamma occurring during heat treatment of the ABO layers are correlated with the mechanism of gamma-phase nucleation. During the growth of the gamma phase, the grain size gets enlarged with a reduction in the total area of grain boundary. The pores’ formation and the pore diameter of both anodized and annealed samples were found to be in the range of 50 to 150 nm. The band gap of the ABO layer crystallines was determined using the diffuse reflectance technique according to the Kubelka–Munk theory. Results showed that the band gap of the ABO layer decreased from 4.09 to 2.42 eV when the particle size decreased from 58 to 24 nm. The CO2 sensing properties of the ABO were investigated at room temperature for 0–100 ppm concentration. The variations in the electrical resistances were measured with the exposure of CO2 as a function of time. The maximum value of the response magnitude of 77% was obtained for 100 ppm of CO2. These experimental results show that the ABO layer of nanoporous is a promising material for CO2 sensors at room temperature.

Eco-Friendly ECM in citric Acid electrolyte with microwire and microfoil Electrodes

In this research, eco-friendly electrochemical machining (ECM) characteristics for drilling and milling stainless steel using microwire and microfoil electrodes in citric acid electrolyte are investigated. According to cell configuration and applied pulse conditions, extraordinary phenomena such as tool electrode cut-off due to Joule heating followed by fractured tool welding to the work substrate, electrolyte capillary action around the tool electrode, and tool shaking by evolved bubbles are observed and their effects on micro ECM performances are discussed. Complex micro/nano textures were found on the inner wall of the drilled holes under strict pulse conditions and their generation mechanism is described. Metal structure formed on the bottom of the blind hole under weak electric conditions hinders further drilling. By adjusting electrochemical conditions, micro holes, 37 μm in diameter with 100 μm depth and 26 μm in diameter with 50 μm depth, are drilled using a 10 μm thick tungsten wire electrode. A complex micro hand pattern is fabricated by electrochemical milling on SS 304 substrate. Furthermore, high quality micro grooves with dimension of 34 μm wide and 17 μm deep are machined using 20 μm thick stainless steel foil electrode. Finally, micro electrochemical reverse drilling technique is newly suggested and its effectiveness on machining time reduction is validated.

Nanoporous Anodic Bismuth Oxide for Electrochemical Energy Storage

Electrochemical energy storage using nanostructured metal oxides has been a topic of intensive investigation among materials scientists and electrochemists. Several transition metal oxides such as TiO2, WO3, Fe2O3, and V2O5 in the form of ordered nanoporous or nanotubular structures have been considered as active electrode materials for battery and electrochemical capacitor applications. Bismuth oxide (Bi2O3), because of its reasonable conductivity, high dielectric constant, catalytic behavior, non-toxicity, and abundance finds applications in a wide range of areas like gas sensors, optical coatings, microelectronics, photocatalysts, solid state electrolytes, and superconductors. Electro-deposited bismuth oxide (on various substrates and in various morphologies) has been investigated as a super capacitor material. The specific capacitance of the electro-deposited Bi2O3 varies from 60 -160 F/g. In the present investigation, Bi2O3 nanoporous films were synthesized by electrochemical anodization in the electrolyte solutions containing citric acid, ethylene glycol and glycerol. Nanoporous bismuth oxide films were formed by anodizing bismuth circular discs of 3 mm thick and 12.7 mm diameter. Anodization was carried out at various potentials ranging from 3 V to 60 V for different time durations ranging from 0.5 to 2 h. After anodization, the samples were thermally annealed at 200 °C for 2h. The influences of anodization time, electrolyte concentration and applied voltages on morphology have been investigated in this study. The electrochemical energy storage of the anodic bismuth oxide was investigated by carrying out cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy (EIS), and Mott-Schottky measurements in different electrolytes in the pH range of 7-14.All the depositions were examined under a FEI Quanta 200F scanning electron microscope. Figure 1 shows the nanoporous morphology of the oxide layer formed at 3V for 30minutes in citric acid electrolyte. The diameters of the pores were in the range of 20 -50 nm and total thickness of the film was about 500nm. It was observed that pore diameter and film thickness changed with the change in applied potential, time and electrolyte concentration. The XRD analysis showed that the nanoporous anodic oxide film after annealing was tetragonal β-Bi2O3. The nanoporous Bi2O3 contained a defect concentration in the range of 7x1016 – 4x1018 cm-3 for various anodized conditions.Figure 2 shows the typical results of cyclic voltammetry of as-anodized bismuth oxide nanoporous in 1 M KOH at different scan rates in a wide potential range. Oxidation of Bi (III) was not observed until 1.0 VAg/AgCl. However, a reduction wave was observed at potentials more negative than -0.6 VAg/AgCl, which could be attributed to the hydrogen ion intercalation in the oxide. Figure 3 shows the potential transient profile during the galvanostatic charge-discharge that was carried out at 10 mA/cm2.The high current density resulted in a sharp potential drop. The capacitance was calculated to be 78 mF/cm2 and the charge retention efficiency was 92%. The capacitance reported for the electrodeposited α-Bi2O3 was in the range of 12 - 22 mF/cm2 [1]. The anodic nanoporous oxide layer showed at least four times higher capacitance than the electro-deposited bismuth oxide.A detailed discussion will be provided in the final presentation on the electrochemical behavior of the Bi2O3 nanoporous structure as a function of morphology, and defect and electronic structures.

Nanoporous Anodic Bismuth Oxide Photo-Anodes

Metal-oxide semiconductors have received a wide attention as photo anodes since the demonstration of water splitting by TiO2 electrode under UV illumination [1]. Significant research efforts were focused on developing various semiconductors with band-gap engineering for efficient photo water splitting. Bismuth oxide (Bi2O3) with a band gap of 2.8eV is a promising photo anode which exhibits good electrical conductivity, oxygen ion conductivity, and high dielectric permittivity. Due to its distinctive properties, Bi2O3 finds applications in a wide range of areas like gas sensors, optical coatings, microelectronics, photocatalysts, solid state electrolytes, superconductors etc. In spite being a non-toxic material with appropriate band gap and valence band edge position (+3.13 V vs. NHE), Bi2O3 demonstrates a poor hydrogen evolution due to its lower conduction band edge position (+0.33 V vs. NHE). The general strategies employed to overcome these limitations were simultaneous doping and nano-sizing of the material. In the present investigation, Bi2O3 nanoporous films were synthesized by electrochemical anodization in the electrolyte solutions containing citric acid, ethylene glycol and glycerol. Nanoporous bismuth oxide films were formed by anodizing bismuth circular discs of 3 mm thick and 12.7 mm diameter. Anodization was carried out at various potentials ranging from 3 V to 60 V for different time durations ranging from 0.5 to 2 h. After anodization, the samples were thermally annealed at 200 °C for 2h. The influences of anodization time, electrolyte concentration and applied voltages on morphology have been investigated in this study. Potentiodynamic, potentiostatic, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analysis studies were carried out with and without illuminated conditions. All the depositions were examined under a FEI Quanta 200F scanning electron microscope. Figure 1 shows the nanoporous morphology of the oxide layer formed at 3V for 30minutes in citric acid electrolyte. The diameters of the pores were in the range of 20 -50 nm and total thickness of the film was about 500nm. It was observed that pore diameter and film thickness changed with the change in applied potential, time and electrolyte concentration. Photo electrochemical studies were carried out using a potentiostat (Gamry, Reference 600) with platinum as the counter electrode. Potential Vs current plots were constructed by scanning the potential of the sample from the open circuit potential to 0.5 V at a scan rate of 5mV/s in 1 M KOH solution. Potentiostatic measurements were carried out in 1 M KOH solution at 0.2 V and 0.5 VAg/AgCl. A solar simulator with an AM 1.5 filter was used for illuminating the samples. The thickness of the oxide layer increased with the increase in the anodization potential. The photo current density of the nanoporous bismuth oxide increased with increase in the thickness of the oxide. The dark current density decreased with the increase in thickness of the oxide layer. The maximum photo current density (Iilluminated-Idark) recorded at an applied potential of 0.5 VAg/AgCl was 1 mA/cm2 for the sample anodized at 20 V. The sample anodized at 60 V showed about 20 µA/cm2 dark current density and 0.8 mA/cm2 photo current density at 0.5 VAg/AgCl. The photo activity of the nanoporous bismuth oxide is comparable to that of nanotubular TiO2 oxide photo anodes. The nanoporous Bi2O3 contained a defect concentration in the range of 7x1016 – 4x1018 cm-3 under dark condition for various anodized conditions. Upon illumination, the defect density increased to values in the range of 4x1017 to 2x1019 cm-3. A detailed discussion will be provided in the final presentation on the photo electrochemical behavior of the Bi2O3 nanoporous structure as a function of morphology, and defect and electronic structures. References A. Fujishima and K. Honda, Nature 238 (1972) 37