Mixed Acid Solution Research Articles

Migration distribution and recovery of rare earth elements in the nitrophosphate process of fertilizer production

This work aimed to investigate the migration distribution and recovery of rare earth elements (REEs) of phosphate concentrate in the nitrophosphate process of fertilizer production. The nitrophosphate process was divided into three main stages, namely, acidolysis, frozen crystallization, and ammonia neutralization, to detect REE migration and distribution. By controlling the acidolysis stage parameters (55% HNO3; temperature, 60 °C; acid-to-phosphate concentrate ratio, 1.25; acidolysis time, 120 min), the leaching efficiency of REEs reached (95.4 ± 0.7)%. In the frozen crystallization stage, the crystallization temperature mainly affected the transition and distribution of REEs in the acidolysis liquid. By controlling the frozen crystallization temperature at −2 °C and time at 120 min, (4.49 ± 0.03)% of REEs co-precipitated with Ca(NO3)2·4H2O into the solid phase, and the majority of REEs stayed in the crystalline mother liquor. In the ammonia neutralization stage, the value of pH mainly influenced the extraction efficiency of REEs. By controlling the ammonia neutralization stage parameters (pH, 1.7; neutralization temperature, 60 °C; neutralization time, 180 min), the extraction efficiency of REEs in the crystalline mother liquor reached (87.6 ± 0.7)%. The ammonia neutralized precipitates were characterized by scanning electron microscopy, energy dispersive spectrum, X-ray diffraction, and X-ray photoelectron spectroscopy to verify the presence and forms of REEs. Finally, the HSC6.0 software was used to analyze the thermodynamic reaction process of phosphate concentrate decomposition with nitric acid and ammonia neutralization stage. Results showed that REEs in the form of REEH2PO42+, REENO32+, and REE3+ diffused into the mixed acid solution in the acidolysis and frozen crystallization stages, and REEs were precipitated in the form of REEPO4·nH2O, REEnCam(PO4)(3n+2m)/3, and REEF3 in the ammonia neutralization stage.

Effects of mixed acid solution on bromide epoxy vinyl ester and its glass fiber reinforced composites

Abstract As fiber reinforced plastics (FRP) have been increasingly widely used, they may sometimes come into contact with several corrosive media simultaneously, for example, the condensate in the smokestack liners of coal-fired power FGD systems. To study the long-term performance and degradation mechanism of FRP in these complicated environments, an accelerated aging test of bromide epoxy vinyl ester (Br-VE) and its glass fiber reinforced composites (GF/VE) in a mixed acid solution(H2SO4, HNO3, HF and HCl) at three different temperatures(25, 55 and 80 °C) for 180 days was carried out. Weight changes, flexural properties, Fourier transforming infrared spectra (FTIR), dynamic thermal mechanical (DMA), macroscopic and microscopic morphology were investigated. Results showed that immersion temperature has important effects on the corrosion behavior of specimens. The long-term weight change behavior of GF/VE at normal temperature was in accordance with Fick’s second law, but deviated at higher temperature. Flexural properties of GF/VE declined more drastically than those of Br-VE at elevated temperatures. The Tg of GF/VE decreased with rising temperatures. Results also indicted that Br-VE and GF/VE manifested varied degradation mechanisms when subject to the same mixed acid medium immersion. The degradation of GF/VE mainly involved plasticization, embrittlement, the hydrolysis of resin, an ion exchange between HF, H+ and Si-O-Si or alkali metal of the fiber as well as the debonding of the resin/fiber interface.

A High Performance Copolyester with “Locked” Biodegradability: Solid Stability and Controlled Degradation Enabled by Acid-Labile Acetal

The gradual degradation of polyester in daily use causes unpredictable failure and restricts its reliable applications. The realization of excellent stability in use and controlled degradation in a specific environment is highly appreciated but still remains challengeable. Here, we demonstrate a new solution via introducing acetal units into poly(butylene succinate): “locking” the biodegradation of copolyesters by rigid spiro diacetal, which could be “unlocked” in strong acidic circumstances. In detail, a series of poly(butylene succinate-co-spirocyclic succinate) (PBSS) copolyesters containing different contents of spiroglycol (SPG) were prepared and characterized. Among them PBSS65 behaved as an excellent candidate for future application, which possessed a high elastic modulus (1.87 GPa) and tensile strength (46 MPa) and moderate elongation at break (252%). It kept stable after melt processing and pH 0–14 soaking, showing solid reliability in daily use. Its biodegradation was locked by the steric hindrance effect of SPG units. Only after treatment in acetone/H2O mixed acidic solution could the biodegradation be triggered. Moreover, it was found that the prolongation of the acid treatment time could accelerate the biodegradation process. The controlled degradation mechanism was proposed to be consisted of acid cleavage of SPG unit and enzymatic degradation of ester group.

Extraction and Characterization of Microfibrillated Cellulose from Discarded Cotton Fibers through Catalyst Preloaded Fenton Oxidation

With rapid developments in science and technology, mankind is faced with the dual severe challenges of obtaining needed resources and protecting the environment. The need for sustainable development strategies has become a global consensus. As the most abundant biological resource on Earth, cellulose is an inexhaustible, natural, and renewable polymer. Microfibrillated cellulose (MFC) offers the advantages of abundant raw materials, high strength, and good degradability. Simultaneously, MFC prepared from natural materials has high practical significance due to its potential application in nanocomposites. In this study, we reported the preparation of MFCs from discarded cotton with short fibers by a combination of Fe2+ catalyst‐preloading Fenton oxidation and a high‐pressure homogenization cycle method. Lignin was removed from the discarded cotton with an acetic acid and sodium chlorite mixed solution. Then, the cotton was treated with NaOH solution to obtain cotton cellulose and oxidized using Fenton oxidation to obtain Fenton‐oxidized cotton cellulose. The carboxylic acid content of the oxidized cotton cellulose was 126.87 μmol/g, and the zeta potential was −43.42 mV. Then, the Fenton‐oxidized cotton cellulose was treated in a high‐speed blender under a high‐pressure homogenization cycle to obtain the MFC with a yield of 91.58%. Fourier transform infrared spectroscopy (FTIR) indicated that cotton cellulose was effectively oxidized by Fe2+ catalyst‐preloading Fenton oxidation. The diameter of the MFC ranged from several nanometers to a few micrometers as determined by scanning electron microscopy (SEM), the crystallinity index (CrI) of the MFC was 83.52% according to X‐ray diffraction (XRD), and the thermal stability of the MFC was slightly reduced compared to cotton cellulose, as seen through thermogravimetric analysis (TGA). The use of catalyst‐preloading Fenton oxidation technology, based on the principles of microreactors, along with high‐pressure homogenization, was a promising technique to prepare MFCs from discarded cotton.

Separation of Pt(IV), Pd(II), and Rh(III) from Chloride Solutions by Multistage Extraction Using Nitrogen-Containing Extractants

This article demonstrates possible separation of Pd(II), Pt(IV), and Rh(III) ions from chloride solutions by solvent extraction in rotating coiled columns (RCC). The most common reagents used for extraction of platinum metals were selected as extractants: trioctylamine (TOA), methyltrialkylammonium chloride (MTAA), tributyl phosphate (TBP), and relatively new reagent—N,N,N',N'-tetra-n-octyldiglycolamide (TODGA). The completeness of extraction of platinum metals from individual and mixed hydrochloric acid and chloride solutions has been analyzed as a function of the essence and concentration of extractant, acidity of the analyzed solutions, and other factors. Optimum conditions of quantitative extraction of the metals from model hydrochloric acid and chloride solutions into the extractant phase have been determined, including subsequent selective separation at the re-extraction stage. A flowchart has been proposed for multistage extraction of Pd(II), Pt(IV), and Rh(III) using 0.05 M MTAA solution in toluene as a stationary phase in RCC. The flowchart includes extraction of Pd(II) and Pt(IV) ions from the solution (0.1 M HCl + 30 g/L Cl–) into the organic phase upon simultaneous separation of Rh(III) remaining in the aqueous phase and consecutive re-extraction of Pd(II) and Pt(IV) from the organic phase using 0.01 M solution of thiourea in 0.1 M HCl and 1 M solution of thiourea in 0.5 M HCl, respectively. The flowchart has been verified for separation of platinum metals in the production process of preset composition. The degree of metal extraction after processing by 0.05 M solution of MTAA in in toluene and consecutive re-extraction by solutions of thiourea is 99.5% for rhodium(III), 99.9% for palladium(II), and 97.4% for platinum(IV). The extracted aqueous phases of rhodium and platinum after output from the column did not contain impurities of other platinum metals. In the aqueous fraction of palladium, the platinum content was 0.5%.

Qualitative and quantitative analyses of aloe-emodin, rhein, and emodin in qi yin granules by high-performance thin-layer chromatography

The aim of this study was to perform qualitative and quantitative analyses of aloe-emodin, rhein, and emodin in three prepared samples of compound qi yin granules by high-performance thin-layer chromatography (HPTLC) and to establish an analytical method. TLC was used to qualitatively analyze the three major components of the compound: aloe-emodin, rhein, and emodin. HPTLC was performed to determine the contents of the three components. HPTLC analysis showed that using Anhui Liangchen high-efficiency silica gel G plate was the optimal stationary phase and the upper layer solution of a petroleum ether–ethyl acetate–formic acid (15.5:5:1, V/V) mixed solution was the optimal developing agent. The composition of the samples for testing was basically the same, but the content was different. In summary, this study used HPTLC to qualitatively and quantitatively analyze aloe-emodin, rhein, and emodin in compound qi yin granules. It can lay the foundation for improving the quality control and standards of compound qi yin granules.

Electrodeposition of Ni-W/CNT Composite Plating and Its Potential as Coating for PEMFC Bipolar Plate

In this study, Ni-W/carbon nanotube (CNT) composite platings are electrodeposited onto steel plate as a possible coating material for the polymer electrolyte membrane fuel cell (PEMFC) bipolar plate, which requires high corrosion resistance under acidic environment and low contact resistance. The dispersibility of CNT in the plating bath is improved by surface modification of CNT through hydrothermal treatment in mixed acid solution. The change in electrodeposition behavior of Ni-W plating by CNT addition is investigated by cathodic polarization measurement. The corrosion resistance under acidic environment is evaluated using 0.5M H2SO4 solution and contact resistance of the composite platings is measured and compared with Ni and Ni-W plating. The surface modification of CNT through hydrothermal treatment is found to increase the CNT content in the Ni-W/CNT composite plating up to 0.33 mass.% and sufficient incorporation of hydrothermally treated CNT in Ni-W plating results in low contact resistance and enhanced corrosion resistance than pristine Ni-W plating.

Treatment of Coal Mine Acid Water Using Nf270 Membrane as Environmentally Friendly Technology

Ex-mining pond water is widely used for the daily needs of the people these days, such as bathing, washing, and even drinking. Over time, it turns out that coal mine acid water has polluted the environment. The use of membrane technology to produce water that meets drinking water quality standards by the Minister of Health Regulation No. 492 of 2010 can be a solution to this problem. The NF270 membrane is a membrane process between reverse osmosis and ultrafiltration, which has a lower flux and operating pressure below 0.2-1.53 Mpa compared to reverse osmosis. Membrane NF270 is used for the reclamation of wastewater, water purification and softening, seawater desalination, and others. Its high rejection of organic molecules with a molecular weight of 200-2000 Da ions and multivalent can remove suspended solids, natural organic matter, bacteria, viruses, salts, and divalent ions contained in water, including coal mine acid water. The purpose of treating acid mine drainage with the NF270 membrane is to remove COD, TSS, TDS, and Fe metals. The NF270 membrane was used in this study to treat the coal mine acid water of PT. Bukit Asam. The performance of the NF270 process was assessed from the effect of pressure (4, 5, and 6 bar) on the flux and rejection rate of each parameter in a single solution, mixed and aqueous coal mine acid solution. The optimum pressure of the NF270 membrane for all parameters was 6 bar. This optimum pressure was then used to compare the phenomenon of flux that occurred and the level of rejection produced in the original sample of coal mine acid water. In the original coal mine acid water, there was a significant decrease in flux due to fouling deposition on the membrane surface. This phenomenon of decreasing flux was caused by fouling and polarization concentration. The rejection rates produced for the parameters of COD, TSS, TDS, and Fe with NF270 membranes were 56.4-93.1%; 78.5-100%; 43-69.3%; 67-100% respectively. Treated coal mine acid water using NF270 membrane technology can be used as drinking water that meets the standards of the Indonesian Ministry of Health Regulation. Thus, NF270 membrane technology can be used to process coal mine acid water into environmentally friendly drinking water.

2024 ALUMINUM OXIDE FILMS PREPARED BY THE INNOVATIVE AND ENVIRONMENT-FRIENDLY OXIDATION TECHNOLOGY

A kind of environment-friendly anodic oxidation technology was used to oxidize 2024 aluminum alloys from mixed acid solutions to effectively improve the anticorrosion and mechanical performances. The influences of anode oxidation method on surface morphology, microstructure, composition, electrochemistry parameter, anticorrosion property were studied. Aluminum alloy oxidation is actually a dynamic equilibrium process of the formation and dissolution of oxide film which is composed of porous and non-porous layer. With the treatment of anodic oxidation, [Formula: see text]-Al2O3 and [Formula: see text]-Al2O3 structures were obtained on the surface of aluminum alloys, which contributed directly to the increase of anticorrosion performance. The potassium dichromate solution was used to seal the surface of oxide films to further improve the anticorrosion property. The oxide films sealed with potassium dichromate were covered with leaf-like structures resulting in larger corrosion resistance that attributed directly to the decrease of corrosion current.

The aluminum current collector with honeycomb-like surface and thick Al2O3 film increased durability and enhanced safety for lithium-ion batteries

Durability and safety are main factors contributing to the market requirement of lithium-ion batteries (LIBs) in practical applications. The improvement of current collector has been proven as an effective approach to enhance comprehensive performance of LIBs. To achieve a sufficient electrical contact between the current collector and active materials, honeycomb-like surface of aluminum current collector is etched by direct current in sulfuric acid and phosphoric acid mixed solution. At the same time, a dense anodic aluminum oxide film is formed on the surface of aluminum current collector, which can protect LIBs from corrosion and thermal runaway. Experimental results show that the adhesion between the active material and aluminum current collector was improved by 23% after anodization. The corrosion resistance of alumina foil was promoted significantly in ethyl methyl carbonate and ethylene carbonate electrolyte with LiPF6. The corrosion current peak reduces to 0.022 mA/cm2 from 0.267 mA/cm2 after surface treatment. The capacity retention rate of the LiCoO2 electrode with an oxidation-treated aluminum current collector is 6.3% higher than with untreated aluminum foil at 5C after 500 cycles. What’s more, the nail penetration demonstrates that the aluminum current collector we prepared can reduce the temperature of the full batteries surface when the nail pierced, which improved the safety performance of LIBs.

Recycling of LiNi0.5Co0.2Mn0.3O2 Material from Spent Lithium‐ion Batteries Using Mixed Organic Acid Leaching and Sol‐gel Method

AbstractA novel closed‐loop recycling system of mixed organic acid leaching and sol‐gel method re‐synthesis for LiNi0.5Co0.2Mn0.3O2 cathode material is designed. Mixed organic acid solution consisting of 0.4 mol/L DL‐malic acid and 0.1 mol/L ascorbic acid was applied to the leaching procedure. Under optimal conditions (temperature: 70 °C, time: 30 min, slurry density: 20 g/L), the leaching efficiency of Li, Ni, Co, and Mn is 99.06 %, 97.11 %, 96.46 %, and 97.22 %, respectively. DL‐malic acid has a stronger chelate tendency with metal ions in the mixed acid leachate, which is verified by the UV‐Vis spectra and FT‐IR spectra. Without adding extra chelating reagents to the leachate, LiNi0.5Co0.2Mn0.3O2 material is regenerated by the sol‐gel method directly. Electrochemical performances of the re‐synthesized LiNi0.5Co0.2Mn0.3O2 material exhibit an excellent initial charge and discharge capacity of 156.0 mAh g−1 and 145.2 mAh g−1 at 0.2 C, respectively. As an alternative to LIBs recovery, the advantages of this recovery method are low reagents consumption and environmentally benign.

Sustainable and efficient extracting of tin and tungsten from wolframite – scheelite mixed ore with high tin content

The separation and extration of tin and tungsten from wolframite – scheelite mixed ore with high tin content is urgently needed given the increasingly exhaustion of the high-grade tungsten ore. However, current tungsten hydrometallurgy technologies suffer from considerably drawbacks, such as low recovery of tin, high consumption of chemicals, and large sodium salt waste water discharge. In this study, a novel reduction melting pretreatment method was used for the thorough separation of tin in the purification process and to improve the recovery of tin and tungsten. In this process, tin was first separated from tungsten and recovered in the form of SnS. Approximately 99% of tin was volatilized under the optimized conditions of the [WO3]/[CaSO4]/[C] molar ratio of 1:2:4 after blowing nitrogen at a flow rate of 3 L/min for 15 min, and the tin content in the reduction melting products was less than 0.05%. Meanwhile, wolframite was converted to scheelite and ferric calcium tungstate that then were easily digested by the mixed sulphuric-phosphoric acid solution, and the leaching ratio of tungsten reached 99%. The leaching residue of calcium sulfate was reused as the sulfurizing reagent in the reduction melting process. The efficient separation and extraction of tin and tungsten of this technology indicated its potential for industrial application.

Improvement of the Surface Structure for the Surface Passivation of Black Silicon

Black silicon (B-Si) has been extensively applied in the photovoltaic field for its prominent light-trapping feature, but its large surface area also brings plenty of structural defects. In this article, a postetching treatment by using acid mixed solution consisted of HNO3/HF/H2O was adopted to balance the tradeoff between optical gain and electrical losses on metal-catalyzed chemical etching B-Si surfaces. We studied the effect of etching time on the reflectance and surface passivation of B-Si on polished and pyramid textured silicon substrates. The result shows that compared with the NaOH postetching applied in the industrial product line, the acid mixed solution could improve the surface passivation and low reflectance within the etching time of 3 min. Moreover, on the base of industrial anisotropic NaOH etch procedure, within etching time of 2 min, the reflectance and Seff decreased by 2.93% and 36.5 cm/s respectively. This fast and combined postetching treatment is a potential industrial method to obtain low reflectance and surface recombination loss.

Photometric determination of rhenium in mixed hydrochloric-nitric acidic solutions formed upon processing of molibdenite concentrate

The results of spectrophotometric study of the system Re (VII) – HNO 3 – HCl – mercaptoacetic acid – Sn (II) are used to develop a sensitive and selective method of photocolorimetric determination of rhenium in acid nitrate-sulfate solutions formed upon decomposition of molybdenite concentrates with nitric acid and also to reveal trends in complexation of aliovalent rhenium with organic sulfur ligands. Ammonium perrhenate (AR-0) was purified on a Purolite C-100 cation exchanger. Solutions of mercaptoacetic (thioglycolic) acid were prepared from chemically pure Apolda chemical (Germany). Light absorption spectra were recorded on EPS-3T (Hitachi, Japan) and Specord M-40 (Carl Zeiss Jena, Germany) spectrophotometers; the optical density of the solutions was recorded on a KFK-2 (Russia) photocolorimeter. Optimal conditions for the formation of a colored complex compound with mercaptoacetic acid in a mixed hydrochloric-nitric acid solution were determined along with the composition and stability of the complex. The mechanism of redox reactions that occur during complexation is proposed. A technique for monitoring the rhenium content in the products of hydrometallurgical processing of molybdenite concentrates is developed. The procedure provides rhenium determination in the presence of accompanying elements (Mo, Cu, Fe, Ni, etc.) and oxidizing agents (>120 g/liter The developed procedure includes preliminary separation of molybdenum and other interfering impurities by selective sorption of ions on a strongly basic anionite (ChFO) followed by their desorption with a 5 M HNO 3 solution and subsequent photocolorimetric determination of rhenium in the eluate in the form of an orange-yellow (λ max = 460 nm) mixes-ligand complex of Re (III) of assumed composition [Re(L) 3 NOCl]–, where L — is mercaptoacetic acid anion. The developed method of rhenium determination was used in analysis of effluents of washing sulfuric acid taken from the sulfuric acid workshop of the copper smelting plant of Almalyk MMC JSC (Uzbekistan).

A Low-Cost and Facile Method to Recycle Silicon Carbide Particles from the Solar Grade Silicon Slicing Wastes

Solar grade silicon slicing wastes (SoG-Siw) are the byproducts of the photovoltaic industry, which are the precious sources of SiC particles and high-purity silicon. Herein, we report a low-cost and facile approach to recover the SiC particles by the methods of physical sedimentation and chemical technique. The effects of reaction time, reaction temperature, acid concentration, stirring speed and liquid-solid ratio on the purity of SiC were discussed in details. The results indicated that the optimal reaction conditions were as follows: mixed acid solution of 5 wt% HF and 8 wt% HNO3, reaction time of 2 h, temperature of 60 °C and liquid-solid ratio of 5:2. SiC particles with the purity of 98.54 wt% with grain sizes of 1.2 ~ 11.4 μm were obtained, which could match the standards of SiC abrasives. It is promising that the current work could provide a low-cost and facile method for recycling SiC particles from SoG-Siw, which could also reduce the cost for solar cells and facilitate the recycling of high-purity silicon from SoG-Siw.

Experimental investigation on the effect of mixed acids etched nickel foam electrode on performance of an alkaline direct ethanol fuel cell

The three-dimensional porous materials represented by nickel foam have broad application prospects in the fuel cell field due to their excellent physical properties (high conductivity, high porosity and high specific surface area, etc.). However, the smooth nickel foam skeleton not only limits the loadable amount of active materials, but also reduces the utilization efficiency of loaded active materials. Therefore, increasing the roughness of the nickel foam skeleton to improve the utilization of active materials has far-reaching significance for the practical application. In this paper, we used mixed acids solution to etch the nickel foam and investigated the effect of etched nickel foam electrode on the performance of an alkaline direct ethanol fuel cell. It was found that mixed acids etching treatment can significantly improve the roughness of nickel foam skeleton and had a great influence on the ethanol oxidation half-reaction (EOR), while the effect on the single cell performance can negligible. Therefore, we believe that the pretreatment method of nickel foam has little effect on the performance of high loading actual electrode.

High-Performance Anticorrosive Polyester Coatings on Mild Steel in Mixed Acid Mixtures Environments

Mild steel sample was selected from acid storage tanks used in industry as a substrate, and two advanced technological polymeric resin-based coatings were developed, designated as LAM-P resin based which is LAM-P/FR coating and LAM-V resin based which is LAM-V/FR coating. These coatings were applied over steel samples by using the hand lay-up process. FTIR test was conducted to confirm complete curing, and SEM analyses were used to investigate surface morphology. A series of electrochemical tests were performed in acidic environment (mixed acid solution 56% H2SO4 + 26% HNO3 + 18% H2O by weight). The results indicated successful development of LAM-P/FR and LAM-V/FR to obtain coatings with desirable characteristics such as anticorrosion, thickness, adhesion, stability, charge store and more resistance to acidic environments. EIS data for mixed acid storage media demonstrated that LAM-V/FR coating has higher strength in mixed acid solution, higher values of impedance and phase shift, higher value of Rpore, and low value of Cc; corrosion rate percentage reduction is 96% of LAM-P/FR and 99.96% of LAM-V/FR compared to bare mild steel sample. The outcomes of this study can lead to assist in design guidelines for anticorrosive coating for industrial applications.

The preparation of V2CTx by facile hydrothermal-assisted etching processing and its performance in lithium-ion battery

In this study, high-purity V2CTx MXene was successfully synthesized by etching V2AlC with fluoride and hydrochloric acid mixed solution using a hydrothermal-assisted method. This method is more concise and effective and has a low level of danger. The morphology and structure of the V2CTx MXene was characterized by X-ray diffraction, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The electrochemical properties were investigated as an anode material for lithium ion batteries. The results show that the prepared V2CTx had a higher purity and showed excellent electrochemical properties as an anode of lithium-ion batteries. And V2CTx prepared with different etching system can he obtained with high yield and excellent purity by changing the reactive conditions of the system. However, electrochemical performance of V2CTx MXene obtained at different etching system is quite different. V2CTx synthesized in the mixed solution of ammonium fluoride and hydrochloric acid has the best performance, which originates from more accessible active sites for ion in the enlarged interlayer distance, and the smaller impedance of V2CTx.

D.C. etching anode aluminum foil to form branch tunnels by electroless depositing Cu

Purpose The purpose of this study is to explore the mechanism of branch pits and tunnels formation and increase the specific surface area and capacitance of anode Al foil for high voltage electrolytic capacitor by D.C. etching in acidic solution and neutral. Design/methodology/approach Al foil was first D.C. etched in HCl-H2SO4 mixed acidic solution to form main tunnels perpendicular to the Al surface, and then D.C. etched in neutral NaCl solution including 0.5 per cent C6H8O7 and Cu(NO3)2 with different concentration to form branch tunnels normal to Al surface. Between two etching, Cu nuclei were electroless deposited on the interior surface of main tunnels by natural occluded corrosion cell effect to form micro Cu-Al galvanic local cells. The effects of electroless deposited Cu nuclei on cross-section etching morphologies and electrochemical behavior of Al foil was investigated with SEM, polarization curve and electrochemical impedance spectroscopy (EIS). Findings The results show that sub branch tunnels can form along the main tunnels owing to the formation of Cu-Al micro-batteries, in which Cu is cathode and Al is anode. With increase in Cu(NO3)2 concentration, more Cu nuclei can be electroless deposited and serve as the favorable sites for branch tunnel initiation along the whole length of main tunnels, leading to enhancement in specific capacitance of anode Al foil. Originality/value Cu nuclei were electroless deposited on the interior surface of main tunnels by natural occluded corrosion cell effect to form micro Cu-Al galvanic local cells, which can serve as the favorable sites for branch tunnel initiation along the main tunnels to enhance specific capacitance of anode Al foil.

Etching Anode Foil with Branch Tunnels for Aluminum Electrolytic Capacitors.

Al foil for high-voltage aluminum electrolytic capacitor was first D.C. etched in HCl-H₂SO₄ mixed acidic solution to form main tunnels and then D.C. etched in natural NaCl solution containing 0.1% H2C2O4 and different trace amounts of Zn(NO₃)₂. Between the two etching processes, Zn nuclei were deposited on the interior surface of the main tunnels by the natural occluded corrosion cell effect to form micro Zn-Al galvanic local cells. The effects of Zn nuclei on the cross-section etching and electrochemical behavior of Al foil were investigated using scanning electron microscopy, polarization curve measurement, and electrochemical impedance spectroscopy. The sub-branch tunnels can form along the main tunnels owing to the formation of Zn-Al micro-batteries, in which Zn is the cathode and Al is the anode. Increasing Zn(NO₃)₂ concentration increases the number of Zn nuclei that can serve as sites for branch tunnel initiation along the main tunnels, thereby enhancing the specific capacitance of etched Al foil.