Etch Tunnels Research Articles

Effects of current density on the growth of aluminum etch tunnels

The specific capacity of the anode material of medium and high voltage aluminum electrolytic capacitors is an important indicator of the capacitor, and the specific capacity is closely related to the number and growth length of tunnels. In this study, the influence of current density on the generation and growth of tunnels was analyzed by observing the corrosion surface morphology of aluminum foil and the cross-sectional morphology of the tunnel growth at different current densities. Current densities higher than 2 A/cm2 are conducive to the uniform development of tunnels but not for sustaining growth. Gradually decreasing the current during the growth process facilitates continuous tunnel growth.

Effect of Cetyltrimethylammonium Bromide Additives on Etched Tunnel Formation of Aluminum Foils

In this study, cetyltrimethylammonium bromide (CTAB) additive was introduced to adjust the tunnel etching behavior of aluminum foil. The distribution and growth of etched tunnels in solutions with and without CTAB additive of various concentrations were thoroughly investigated. Compared to the etched tunnels obtained in solutions without CTAB, those obtained in solutions with 1 wt% CTAB had obviously improved distribution and increased length, resulting in an enhancement of the specific surface area. These effects can be attributed to the improvement of wettability between aluminum surface and solution, which is helpful to increase the contact area and facilitate the mass transfer within tunnels. This work exhibits a facile way to improve the tunnel etching behavior of aluminum foil, showing a potential engineering value in industrial production.

Effects of the solution flow rate on the growth of aluminum etch tunnels

AbstractIncreasing the specific surface area of the anode foil of aluminum electrolytic capacitors is a research direction to improve the performance of capacitors. Industrial mass‐produced anode foil increases the specific surface area by electrochemical etching of the aluminum foil. However, the tunnels created by corrosion stop growing midway through this process. In this study, the effect of the solution flow rate on tunnel growth is investigated, and the growth of tunnels is analyzed using a new method of preparing oblique sections. Neater tunnels can be grown by increasing the solution flow rate to facilitate active tunnels.

Effect of Bipolar Electrochemical Process on Tunnel Etching Characteristics of Aluminum Foil

In this study, closed bipolar electrochemical etching was introduced to prepare etched tunnels on aluminum foils. The morphological evolution and tunnel etching behaviors of aluminum foils in the traditional electrochemical etching system and closed bipolar electrochemical etching system were thoroughly investigated using scanning electron microscopy and electrochemical measurements. Compared with the tunnels etched on the aluminum foil by traditional electrochemical etching, those by closed bipolar electrochemical etching had a larger diameter and a more uniform distribution of length. These characteristics are beneficial for improving the specific surface area of the etched aluminum foil. Furthermore, aluminum foils do not need direct electricity connection, thus offering a potential advantage in industrial production.

Distribution improvement of etch tunnels on aluminum foil coated by Al2O3 film doped with ZnO microspheres

In this paper, a Al2O3 film doped with ZnO microspheres was successfully fabricated on aluminum foil by the sol-gel method. In order to improve the distribution of etched tunnels, the effects of Al2O3 film doped with ZnO microspheres on the surface morphology and electrochemical properties of aluminum foil were investigated. The results showed that, with a suitable concentration of Al2O3 film and ZnO microspheres, uniform distribution of etched tunnels could be obtained on the aluminum foil after the electrochemical etching. When the concentration of Al2O3 film and ZnO microspheres are 0.1 mol/L and 0.02 mol/L, respectively, the specific capacitance of the etched aluminum foil achieved the maximum. The above beneficial results were attributed to the improvement in pitting initiation sites on the aluminum foil coated by Al2O3 film doped with ZnO microspheres, which was supported by the experimental results of surface morphology and electrochemical testing. The etching mechanism was related to the dissolution of ZnO microspheres, the replacement of Zn crystal nucleus and the formation of active sites for pitting corrosion. This paper provides experimental and theoretical insights into the distribution improvement of etch tunnels, showing a significant engineering value for process design and properties optimization for aluminum foils.

Honeycomb-like porous metallic glasses decorated by Cu nanoparticles formed by one-pot electrochemically galvanostatic etching

Pitting corrosion is a common localized corrosion phenomenon, which can lead to cracks and mechanical failure in structural metal materials. On the contrary, pitting corrosion could be a beneficial tool for generating large-area porous structures, which holds a great premise in a number of functional services, such as catalysis, sensing, storage, imprint lithography, and membranes. Herein we presents an electrochemical approach for creating a large-area honeycomb-like porous structure in Zr-based metallic glasses. A pitting process followed by subsurface tunnel etching in NaCl solution elicits to characteristic micrometer scale channels and nanometer size amorphous sidewalls decorated by Cu nanoparticles on the metallic glass substrate. A root-shape growing mechanism of tunnels initiated from pits and penetrating into alloy matrix is postulated. In addition, the effect of alloy composition on the microstructure of honeycomb-like porous metallic glasses is also investigated in detail.

Optimization of Initiation Sites of Tunnel Pits on Aluminum Foil Using Self-Ordered Concave Structures

The self-ordered concave structures fabricated on aluminum surface by aluminum anodic oxidation and oxide removal procedures were applied to control the pit initiation sites for tunnel etching of aluminum foil, where the tunnel pits would be correspondingly generated under the sites of self-ordered concave structures. The obtained sizes of the tunnel pits were 100–600 nm in width and 1.6 μm in length, which were mainly determined by the interpore distances of the concave structures and the tunnel etching conditions. Based on this process, the distribution of the tunnel pits on aluminum surface was improved observably, so that a high aspect ratio was successfully achieved.

Effect of Additive DCTA on Electrochemical Tunnel Etching of Aluminum Foil

The effect of additive DCTA (1,2-diaminocyclohexane-tetraacetic acid) to HCl + H2SO4 solution on electrochemical tunnel etching behavior of aluminum foil was investigated. The results show that DCTA can activate Al foil surface by decreasing the self-corrosion potential and breakdown potential, which may be attributed to that DCTA forms chelate with dissolved Al3+, thus suppressing the oxide film formation. The tunnel density and effective tunnel number as well as uniformity of tunnel length of etching foil can be increased after DCTA addition. Furthermore, the specific capacitance of etching foil can be enhanced with trace addition of DCTA.

Formation and effect of the branched layer during the tunnel etching of aluminum foil

In this study, branched layers formed under various conditions of the electrochemical etching of aluminum foils were observed. Tunnel clustering arose from the random distribution of high-density tunnels, greatly increasing the thickness of the branched layer; this occurred because the tunnel clustering increased the tunnel width, thereby facilitating electrolyte transport in vertical tunnels. In contrast, tunnel tapering blocked the branched tunnels generated at a certain depth. The thickened branched layer greatly reduced the foil thickness during tunnel widening, considerably reducing the surface area and the specific capacitance obtained for the etched aluminum foil.

Bushveld symplectic and sieve-textured chromite is a result of coupled dissolution-reprecipitation: a comparison with xenocrystic chromite reactions in arc basalt

Textures of Bushveld chromite from thin seams and accessory disseminations in the Platreef and the northernmost Waterberg Project area were compared with textures of xenocrystic chromite from mantle xenoliths found in Neogene basalt in the Kurile Island Arc. The sieve-textured to symplectic rims around the resorbed chromite in the Kurile samples resulted from the reaction between chromite and chromite-undersaturated basaltic melt, with the inclusions in chromite being entrapped during episodes of chromite primary growth, chemical dissolution, and reprecipitation or secondary growth. The relics of the lattice-oriented etch tunnels suggest that the dissolution preferentially developed along the crystallographic planes and defects. The Bushveld chromites exhibiting similar textures are interpreted as reaction-textured chromites, by analogy with the Kurile samples. The Bushveld sieve-textured, fish-hook to symplectic and amoeboidal to atoll-like chromites, are believed to have been formed due to coupled dissolution-reprecipitation of the earlier cumulus or xenocrystic chromite during interaction with chromite-undersaturated evolved melt. The electron backscattered diffraction data confirm the same single-crystal crystallographic orientation of all domains of the reaction-textured chromites as well as their clustered semi-dissolved relics. Therefore, Bushveld inclusion-rich chromite might have captured different populations of melt inclusions during its discontinuous out-of-equilibrium growth with fast episodic resorption and regeneration. The occurrence of reaction-textured chromites indicates a zone of interaction between dynamic magmatic influxes where chemical equilibrium was not achieved whereas a complete re-equilibration between chromite and the stagnant and sequestered interstitial liquid was attained during the formation of the massive chromitites.

Effects of temperature on electrochemical dissolution behavior of aluminum foil

Electrochemical dissolution behavior of aluminum foil in acid etchants was clearly investigated with different temperatures. Due to the electrochemical activation of temperature, the surface dissolution of aluminum foil in H2SO4 etchant slightly increased with the temperature. Even if NaCl was contained in the H2SO4 solution, the dissolution of aluminum surface and the value of Epit were dependent on the temperature. The rising temperature decreased the resistance of pitting on aluminum foil surface, which enhancing the density and uniformity of the tunnel pits. The surface dissolution and tunnel etching behavior of aluminum foil was discussed by a schematic diagram.

A Catalytic Etching-Wetting-Dewetting Mechanism in the Formation of Hollow Graphitic Carbon Fiber

Summary Hollow graphitic carbon nanofibers (HGCNFs) have great promise for many important applications, such as catalysis, sensors, energy conversion, gas storage, and electronic devices. Here, we report a catalytic etching-wetting-dewetting mechanism in synthesizing HGCNFs with both hollow spherical-like and tunnel-like pores. With in situ transmission electron microscope imaging, we show that the spherical pores are formed by the evaporation of encapsulated Ni on the surface of amorphous carbon nanofiber and that hollow tunnels are developed through continuous etching of the amorphous carbon under catalysis of Ni nanoparticles. Theoretical calculations and simulations reveal that continuous tunnel etching is driven by the wetting-to-dewetting transition of the Ni-tunnel wall interaction during the catalytic graphitization of the amorphous carbon wall. In a typical application, we demonstrate that the synthesized HGCNFs, with a capacity about three times higher than that of their non-hollow counterparts, are excellent potential candidates for CO 2 capture.

Effect of electrodepositing Ag on DC etching aluminum foils for electrolytic capacitor

Ag nuclei were electrodeposited on the surface of aluminum foil to induce tunnel etching. The effects of Ag nuclei on the surface and cross-section etching morphologies and electrochemical behavior of Al foil was investigated with SEM, polarization curve (PC) and electrochemical impedance spectroscopy (EIS). It is proved that the tunnels etched in this way are distributed more uniformly and the density of tunnels and pits are enhanced, leading to increase in specific capacitance of etched Al foil. These effects can be attributed to the mechanism that the Ag nuclei can serve as the favorable sites for tunnel initiation on aluminum foil surface owing to the formation of Ag–Al micro-batteries, in which Ag is cathode and Al is anode. This mechanism is supported by the SEM, PC and EIS.

Mechanical attrition assisted DC etching aluminum foils with enhanced capacitance

The aluminum foils for high voltage aluminum electrolytic capacitors were DC etched in HCl–H2SO4 hybrid acids and the effects of in-situ mechanical attrition on the etching were studied in this work. Compared with the conventional etching, the distribution of etch tunnels was, under in-situ mechanical attrition, more uniform with high density of etch pits and long tunnels, which expands the surface area of etched Al electrode and greatly increases its capacitance. This effect is probably due to the mechanical attrition effects which are beneficial for the breakdown of the protective film and reducing concentration polarization in the bulk etchant solutions, inducing higher pit and tunnel density and increasing the survival rate of tunnels.

Fabrication and Characteristics of High Capacitance Al Thin Films Capacitor Using a Polymer Inhibitor Bath in Electroless Plating Process.

An aluminum (Al) thin film capacitor was fabricated for a high capacitance capacitor using electrochemical etching, barrier-type anodizing, and electroless Ni-P plating. In this study, we focused on the bottom-up filling of Ni-P electrodes on Al2O3/Al with etched tunnels. The Al tunnel pits were irregularly distributed on the Al foil, diameters were in the range of about 0.5~1 μm, the depth of the tunnel pits was approximately 35~40 μm, and the complex structure was made full filled hard metal. To control the plating rate, the experiment was performed by adding polyethyleneimine (PEI, C2H5N), a high molecular substance. PEI forms a cross-link at the etching tunnel inlet, playing the role of delaying the inlet plating. When the PEI solution bath was used after activation, the Ni-P layer was deposited selectively on the bottoms of the tunnels. The characteristics were analyzed by adding the PEI addition quantity rate of 100~600 mg/L into the DI water. The capacitance of the Ni-P/Al2O3 (650~700 nm)/Al film was measured at 1 kHz using an impedance/gain phase analyzer. For the plane film without etch tunnels the capacitance was 12.5 nF/cm2 and for the etch film with Ni-P bottom-up filling the capacitance was 92 nF/cm2. These results illustrate a remarkable maximization of capacitance for thin film metal capacitors.

Modelling specific capacitance of D.C. etched aluminium foil for aluminium electrolytic capacitor

The morphology of etched aluminum foil was observed using scanning electron microscopy, which led to the establishment of a cubic tunnel etch model and a trench tunnel etch model. With these two modes, the theoretical maximum specific capacitance values for the anode foil used in aluminum electrolytic capacitors were calculated with Matlab at various formation voltages. The corresponding optimum values for tunnel size, density, distribution and geometrical shape were also given as a function of oxide thickness. The experimental and theoretical capacitance values are compared. It is concluded that the theoretical maximum specific capacitance for trench etch tunnel model is higher than that for cubic etch tunnel one at fixed formation voltage. Promoting tunnel-merging in rows rather than in clusters is preferred during electro-etching process, leading to formation of trench tunnels on the Al foil. For high formation voltages, measured capacitances approach the optimum values and enlargement of surface area by electrochemical etching was faced with the limit. But for low formation voltages, the experimental capacitance value obtained is far behind the optimized one and the tunnels size, distribution, shape and density must be optimized to achieve high capacitance.

Effects of electrodeposited Zn nuclei on tunnel etching behavior of aluminum foil

Zn nuclei were electrodeposited on the surface of aluminum foil to induce tunnel etching. It is proved that the tunnels etched in this way are distributed more uniformly, and both of the merging of tunnels and the reducing of the foil thickness are weakened. These effects can be attributed to the mechanism that the Zn nuclei can serve as the favorable sites for tunnel initiation on aluminum foil surface owing to the formation of Al–Zn micro-batteries, whereas the rest area of aluminum foil is passivated. This mechanism is supported by the initial potential transient and impedance spectra.

Anodizing of etched aluminum foil coated with modified hydrous oxide film for aluminum electrolytic capacitor

Prior to galvanostatical anodization in boric acid solution, aluminum capacitor foil with a tunnel etch structure is treated in a two-step process in which a non-dense hydrous oxide film is first formed on foil in neutral boiling water for 10 min [namely, conventional hydration (CH)] and the hydrous oxide is then modified in a 80 °C weakly acidic solution containing trace amount of citric acid for 3 min [namely, modified conventional hydration (MCH)]. After modification, the hydrous oxide film becomes dense and thin. Time variations in the anode potential during anodizing were monitored, and the structure and dielectric properties of the anodic oxide films were examined by transmission electron microscopy, X-ray diffraction and electrochemical impedance spectroscopy measurements. It was found that the MCH-induced hydrous oxide film results in a decreased power consumption during anodization and an increased crystallized anodic oxide film, which has a high specific capacitance and a low specific resistance, comparing with the CH-induced hydrous oxide film.

Effect of placement of aluminium foil on growth of etch tunnels during DC etching

The tunnel growth behaviour of aluminium foil etched in different placement has been investigated. The limiting length of tunnel of specimens in increasing order is: face-down, vertical, and face-up placement. Many sub tunnels branch on the wall surface of the main tunnel when aluminium is etched in face-down placement, while much fewer sub tunnels are formed when aluminium is etched in face-up placement. A novel etching model has been proposed to interpret the phenomenon, by considering the electrocapillary effect. It reveals that the status and transport of hydrogen bubbles inside the tunnel has a great influence on the tunnel growth.

Effects of polymer corrosion inhibitor on widening etch tunnels of aluminum foil for capacitor

We investigated the effects of polymeric corrosion inhibitor polystyrene sulfonic acid (PSSA) additive to 3% HNO3 solution on widening tunnels of pre-etched aluminum foil by electrochemical DC etching for aluminum electrolytic capacitors, using scanning electron microscopy and polarization curves. With trace PSSA, the dissolution of exterior surface of etch tunnels of Al foil is suppressed and the dissolution of interior surface of etch tunnels of Al foil is facilitated, respectively. The tunnels transform from circular cone to circular column in shape and pits-merging on the surface is weakened, leading to significant increase in the surface area and specific capacitance of the Al foil. The amounts of reduced thickness and weight of Al foil during the widening process of etch tunnels can be decreased if PSSA is employed.