Combination Of Chemical Etching Research Articles

Different wettability surfaces composited by polydopamine-based SiO2/TiO2 coatings for efficient water collection and anti-corrosion application

Designing hybrid surfaces with superhydrophilic and superhydrophobic properties represents a promising approach for fog collection. Inspired by the adhesive properties of mussel proteins, a polydopamine (PDA) film was firmly attached to a brass surface through a combination of chemical etching and spontaneous dopamine polymerization. By harnessing the exceptional characteristics of PDA as a "double-sided adhesive," a hybrid surface with mixed wettability was created using a facile and cost-effective method involving SiO2 and TiO2 nanoparticles (NPs). The TiO2 NPs served as the hydrophilic sites for water capture, while the SiO2 NPs acted as the hydrophobic region to induce water droplet rolling. The resulting hybrid surface exhibited a significant improvement in water collection rate, measuring approximately 1.182 g/cm2/h, which was 1.84 times higher than that of the bare brass surface. This demonstrated a remarkable enhancement in fog collection capacity. Moreover, the hybrid surface demonstrated commendable corrosion resistance and remarkable durability, indicating its great potential for widespread application in practical scenarios.

Enhancement of water collection efficiency by optimizing hole size and ratio of hydrophilic-superhydrophobic area on hybrid surfaces

The scarcity of freshwater resources has had a significant impact on human life and wildlife survival. Fog harvesting has emerged as one of the most effective solutions to alleviate water scarcity in arid areas. At present, researchers have focused on optimizing hybrid surface designs to capture fog from the air and convert it into water droplets. Here, we prepared a hybrid surface for fog harvesting by a combination of chemical etching and surface modification with mechanical drilling. By adjusting the hole size and the ratio of hydrophilic-superhydrophobic area of the hybrid surfaces, the water collection efficiency was improved. The results indicated that the hole size affected the critical size of sliding water droplets, and the ratio of hydrophilic-superhydrophobic area affected the water droplet sliding speed and water collection frequency, thereby affecting the water collection efficiency per unit time. Therefore, by matching a specific hole size and ratio of hydrophilic-superhydrophobic area, the water collection volume and mobility of water droplets on the hybrid surfaces reached a dynamic equilibrium, achieving the optimal water collection efficiency. When the hole size was 1.0 mm, and the ratio of hydrophilic-superhydrophobic area was 1:4, the highest water collection rate was 805 mg/cm2/h, and the water collection efficiency was 17.5 %. By optimizing the hole size and the ratio of hydrophilic-superhydrophobic area, the water collection efficiency of the hybrid surface was maximized. This lays a solid foundation for promoting the practical applications of hybrid surfaces for fog harvesting.

Pool boiling heat transfer enhancement and bubble visualization on a microporous copper over CuO filmed surface through combination of chemical etching and electrochemical deposition

For high heat flux engineering application, a Microporous Copper over CuO Film Surface (MCCFS) is prepared to find out the Critical Heat Flux (CHF) and Boiling Heat Transfer Coefficient (BHTC). The bare Cu surface is modified into MCCFS through a combination of two chemical processes, i.e., chemical etching and electrochemical deposition. Various properties of the MCCFS, like porosity, wettability, and roughness, are also analyzed. The saturated pool boiling experiment is carried out by taking distilled water as the boiling liquid at atmospheric pressure. Results show that the CHF and the BHTC of the MCCFS are improved by 71% and 78%, respectively, than the bare Cu. This improvement is mainly due to the increased roughness and decreased wettability of the MCCFS. A visualization-based quantitative analysis of the bubble during boiling is also done to correlate the enhanced heat transfer from the MCCFS. Bubble characteristics like nucleation site density, bubble departure diameter, and bubble departure frequency are analyzed. The enhanced bubble site density, decreased departure diameter, as well as the enhanced departure frequency of the bubble supported the improvement of heat transfer from the MCCFS. A comparative analysis of the performance of heat transfer from the MCCFS is also presented.

Pool boiling heat transfer and bubble dynamics of modified copper micro-structured surfaces

In this work, hydrophobic copper micro-structured (HCM) surfaces are prepared to improve boiling heat transfer. A combination of chemical etching and heat treatment processes is employed to make the bare copper surface hydrophobic in nature. With the modification of wettability, a different micro-structured feature is developed on the surface. The static contact angle of the prepared hydrophobic surface is varied in between 114° to 140°. A saturated pool boiling experiment is conducted at atmospheric pressure by taking distilled water as the boiling fluid. The maximum heat transfer coefficient is 119.7 kW/m2K for the HCM surface with a contact angle of 140°. Due to its hydrophobic nature, the critical heat flux (CHF) of the HCM surfaces is a little smaller than the bare copper surface. Bubble dynamics are also observed during boiling. The surface roughness of the HCM surfaces is enhanced, which increases the active nucleation site of the HCM surfaces. The bubble departure diameter of the HCM surfaces is smaller than the bare copper surface, with a maximum reduction of 45% for the HCM-3 surface. It is also found that the micro-porous surface prepared by a combination of two conventional processes increases the heat transfer substantially.

Superhydrophobic palmitic acid modified Cu(OH)2/CuS nanocomposite-coated copper foam for efficient separation of oily wastewater

Developing an efficient, simple, and low-cost oil-water separation technologies is critical to address the challenges of oily wastewater treatment. In this work, a nanoflower-like CuS embedded into Cu(OH)2 nanowire arrays (Cu(OH)2/CuS) were grown on the surfaces of copper foam (CF) by combination of chemical etching and ion exchange methods, and subsequent modification with palmitic acid (PA) was performed to achieve superhydrophobic CF/Cu(OH)2/CuS-PA oil-adsorption materials. The reaction conditions of ion exchange such as the Na2S concentration and immersion time were demonstrated to be key factors to form hierarchical Cu(OH)2/CuS nanowire arrays, and thus further significantly influenced the hydrophobicity of the copper foam. Such superhydrophobic CF/Cu(OH)2/CuS-PA with a static water contact angle of 153.4° delivered a high separation efficiency of oil-water mixtures at 98.8%, and the separation efficiency was always up to 97.6% for various water-in-oil emulsions. After operating successive 30 cycles of oil-water separation, the high separation efficiency remained unchanged. The CF/Cu(OH)2/CuS-PA also presented high stability, good anti-corrosion and mechanical properties in harsh environments. Thus, this superhydrophobic copper foam offers a potentially promising three-dimensional adsorbent for practical application of spill oil recovery and oil/water separation.

Superwetting and photocatalytic Ag2O/TiO2@CuC2O4 nanocomposite-coated mesh membranes for oil/water separation and soluble dye removal

A novel oily wastewater treatment strategy of simultaneously removing insoluble oily compounds and soluble organic pollutants is highly desirable. Herein, a hierarchical Ag2O/TiO2 heterojunction-loaded CuC2O4 nanosheet-decorated copper mesh (Ag2O/TiO2@CuC2O4 CM) was rationally designed by a combination of chemical etching and solvothermal deposition methods to implement the strategy. The Ag2O/TiO2@CuC2O4 CM with hierarchical nanostructures derived from hydrophilic CuC2O4 nanosheets and belt-like Ag2O/TiO2 heterojunction was proven to exhibit superior superhydrophilicity, underwater superoleophobicity, and photocatalytic ability, which greatly improved the antipollution ability of the substrate mesh. The as-fabricated mesh with a reasonable mesh number can efficiently separate oil/water mixtures with an ultra-high flux (∼70 kL m−2 h−1) and surfactant-stabilized oil-in-water emulsions with an ultra-low residue oil content in filtrate (<60 mg L−1). More importantly, the loaded heterojunction on the CM showed a high photodegradation efficiency of about 94.1% toward soluble methylene blue and self-cleaning ability to regenerate oil-contaminated mesh within 60 min under visible light irradiation by photo-Fenton-like reaction. Besides, the favorable salt resistance, acid and alkali resistance, and stability of the CM for long-term use were also observed. Thus, this study provides a new way for the treatment of complex oily wastewater.

(Invited) Anodizing of Metals for Fabrication of Functional Nanostructured Surfaces

Anodizing of metals, including aluminum, titanium, and iron, is a simple and const-effective process to form various nanostructured oxide films, such as nanoporous, nanotubular, and nanowire films. Such nanostructured anodic films have attracted much attention for many potential functional applications as well as fundamental interests on the mechanism of self-organized nanostructure formation. Here, our recent studies on the formation of nanostructured anodic films on aluminum, copper, and zinc and their application to controlled wettability will be outlined.Anodizing of zinc in KHCO3 electrolyte produces a nanowire-type anodic film on entire metal surface. The formation of the nanowire film involves the initial pitting corrosion; pits are developed on the zinc metal surface, and embryos of nanowires are formed within the pits. When the pits are covered with a thin air-formed or electropolishing film, the nanowire formation is promoted as a consequence of the increased concentration of dissolved zinc species within the pits. Then, the nanowires grow toward the outside of the pits and cover the entire metal surfaces. Because of this growth process, the nanowires grow radial direction before covering the entire surface. The nanowire surface is one of the promising geometry for superhydrophobicity. In fact, anodic nanowire film surface becomes superhydrophobic after fluoroalkylsilane monolayer coating.The anodic nanowire film is also developed on copper by anodizing in KOH electrolyte. The copper surface can be completely covered with the nanowires only for 30 s at a constant current density of 10 mA cm–2. The nanowires consist of a single crystalline Cu(OH)2 phase, and the nanowires on copper are formed uniformly without forming pits. The nanowires are reduced readily to copper metal with the nanowire morphology remaining almost unchanged, although the copper metal nanowires are polycrystalline. The copper metal nanowires are also superhydrophobic after fluoroalkylthiol monolayer coating. The copper substrate with the superhydrophobic metal nanowires maintain the high thermal conductivity and effectively removes the condensed water droplet, being very suitable for heat exchanger applications with high efficiency.Aluminum is the most suitable metal to control the surface morphology by wet process. The author’s group successfully fabricated hierarchically micro-/nano-porous aluminum surface by a combination of chemical etching and anodizing in acid electrolytes. Micropits are developed by chemical etching containing HCl solution and the HCl concentration control the size of pits. Nanopores are generated by anodizing in sulfuric acid or oxalic acid, the pore widening process can be applied to control the pore size and porosity. The hierarchically porous aluminum surface is used to form super-repellency even for low surface tension liquids, including rapeseed oil (surface tension of 35 mN m–1), hexadecane (28 mN m–1), octane (22 mN m–1), and even hexane (18 mN m–1). The nanopores can be used to infiltrate the self-healing agent of organic coating, so that self-healing super-liquid-repellency occurs repeatedly even if the thin organic coating is damaged. The porous aluminum surface is also suitable for fabricating the slippery liquid infused porous surface (SLIPS) by impregnating a lubricant liquid into the pores. The SLIPS on aluminum show excellent liquid slipping property, anti-snow-sticking property, and high corrosion resistance.References T. Inoue, A. Koyama, D. Kowalski, C. Zhu, Y. Aoki and H. Habazaki, physica status solidi (a), 1900836 (2020). K. Nakayama, A. Koyama, C. Zhu, Y. Aoki and H. Habazaki, Advanced Materials Interfaces, 5, 1800566 (2018). K. Nakayama, E. Tsuji, Y. Aoki, S.-G. Park and H. Habazaki, The Journal of Physical Chemistry C, 120, 15684 (2016).

A novel Cs4PW11O39Fe/Si composite material to achieve high photoelectric performance

Here we report a novel composite material Cs4PW11O39Fe/Si(Cs4PW11Fe/Si), which was prepared by combination of chemical etching and hydrothermal method. This composite material displays a superior photoelectric performance. A transient photocurrent density of 0.4 mA cm−2 and a maximum surface photovoltage of 0.043 mV as well as an maximum IPCE of 80.8% were obtained, much higher than those of the pristine p-Si or Cs4PW11Fe. The solar cell device ITO/Cs4PW11Fe/p-Si/Ag presents a PCE of 1.36% with a Voc of 0.78 V and a Jsc of 1.27 mA cm−2 as well as a FF of 68.5%. The improvement of the photoelectric performance results from the “mastoid” structure on the surface of material and the formation of p-n heterojunction between n-Cs4PW11Fe and p-Si. The “mastoid” structure and p-n junction are favorable to increasing light absorption and facilitating photo-generated carriers's separation and transfer.

Fabrication and investigation of superhydrophobic surface by dip coating

The present research work is focused on to fabricate and examine the characteristics of a superhydrophobic surface on copper (Cu) substrates by dip coating method. Three different samples of ‘Cu’ are set with chemical etching, mechanical rubbing and the combination of above two methods. The variations in the exteriorsurface morphologies have been examined by profilometer, scanning electron microscope and energy-dispersive X-ray spectroscopy. The adapted samples are immersed in a solution of silver nitrate follow by immersing in a combination of ethanol and perflurodecyltriethoxysilane for 10 min. The presence of leaf and dendrites assemblies have been observed on the surface, which are useful to trap the air between them and the entrapment allows water to roll off from the surface. The outcomes reveal that the modified substrates have a water contact angle (WCA) of 159° in the case of ‘Cu’ using combination of chemical etching and mechanical rubbing followed by immersion coating. The proposed methodology has the advantage of size compatibility and easy scale up for the development of superhydrophobic surface on copper in a cost and time effective manner.

Fundamental Understanding of Redox Characteristics of Defect-Rich Holey Graphene for Lithium Ion Energy Storage Devices

Graphene has received intensive research interest as a promising electrode material for energy storage applications because of its unique combination of properties including high intrinsic electrical conductivity, good mechanical flexibility, exceptional theoretical surface area and capacitance. The approaches to engineer graphene-based materials mostly involve functionalization, structural modification for the porous structure with abundant defective sites or incorporating other redox-active substances as the composite. Among various oxygen functional groups on graphene oxide, carbonyl group is regarded as the most active group to provide reversible redox reactions with Li ions.[1] The conservation of the redox-active carbonyl group during conventional chemical and thermal reduction processes of graphene oxide has so far shown only limited effect. Thus, the selective reduction process of oxygen functional groups on graphene oxide is a particularly promising strategy to enhance the charge storage performance on highly porous nanostructures. In this study, we prepared reduced holey graphene oxide with a combination of chemical etching and selective reduction processes, proposing a high performance cathode material for rechargeable lithium ion batteries. In addition, in order to further enhance the charge storage performance, a redox-active organic compound is introduced onto the holey graphene oxide structure. References T. Y. Liu, K. C. Kim, R. Kavian, S. S. Jang, S. W. Lee, Chem. Mater. 27, 3291-3298 (2015).

Polarity conversion of GaN nanowires grown by plasma-assisted molecular beam epitaxy

It is demonstrated that the N-polarity of GaN nanowires (NWs) spontaneously nucleated on Si (111) by molecular beam epitaxy can be reversed by intercalation of an Al- or a Ga-oxynitride thin layer. The polarity change has been assessed by a combination of chemical etching, Kelvin probe force microscopy, cathodo- and photoluminescence spectroscopy, and transmission electron microscopy experiments. Cathodoluminescence of the Ga-polar NW section exhibits a higher intensity in the band edge region, consistent with a reduced incorporation of chemical impurities. The polarity reversal method we propose opens the path to the integration of optimized metal-polar NW devices on any kind of substrate.

Effects of Surface Microstructures on Superhydrophobic Properties and Oil-Water Separation Efficiency

In order to explore the effects of microstructures of membranes on superhydrophobic properties, it is critical, though, challenging, to study microstructures with different morphologies. In this work, a combination of chemical etching and oxidation was used and some copper meshes were selected for grinding. Two superhydrophobic morphologies could be successfully prepared for oil-water separation: a parabolic morphology and a truncated cone morphology. The surface morphology, chemical composition, and wettability were characterized. The results indicated that the water contact angle and the advancing and receding contact angles of the parabolic morphology were 153.6°, 154.6 ± 1.1°, and 151.5 ± 1.8°, respectively. The water contact angle and the advancing and receding contact angles of the truncated cone morphology were 121.8°, 122.7 ± 1.6°, and 119.6 ± 2.7°, respectively. The separation efficiency of the parabolic morphology for different oil-water mixtures was 97.5%, 97.2%, and 91%. The separation efficiency of the truncated cone morphology was 93.2%, 92%, and 89%. In addition, the values of the deepest heights of pressure resistance of the parabolic and truncated cone morphologies were 21.4 cm of water and 19.6 cm of water, respectively. This shows that the parabolic morphology had good separation efficiency, pressure resistance, and superhydrophobic ability compared with the truncated cone morphology. It illustrates that microstructure is one of the main factors affecting superhydrophobic properties.

Secondary carbides in high chromium cast irons: An alternative approach to their morphological and spatial distribution characterization

Secondary carbides precipitated in high chromium cast irons during thermal treatments were characterized by means of different characterization techniques, including scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscattered diffraction and a combination of chemical etching with confocal scanning laser microscopy. This set of techniques provides a full morphological, chemical and crystallographic description of the analysed phases.This work evaluated different methods for optimizing the image acquisition for a further image analysis (IA) based on the threshold binarization. Finally, the carbide size, distribution and morphology were determined after IA of the images acquired by aforementioned characterization techniques. Although the different techniques report some dispersion in the value for the average particle size, the particle inter-spacing and aspect ratio meet within the error value. The proposed characterization methodology provides statistically reliable data for a further evaluation of related physical properties in composites.

Peeling process of thin-film solar cells using graphene layers

A novel peeling process for thin-film solar cells using graphene layers was demonstrated. We fabricated amorphous silicon (a-Si) solar cells as substitutes for the undeveloped nanostructured silicon solar cells on graphene layers in order to investigate the solar cell performance after peeling for the first time. The graphene layers functioned as transparent electrodes after the peeling process, even though the series resistance increased after the peeling. Next, we fabricated a silicon nanowire (SiNW) array on graphene layers by a combination of chemical etching and thermal crystallization. Finally, we successfully peeled a SiNW array using graphene layers.

Combination of chemical etching and electrophoretic deposition for the fabrication of multi-scale superhydrophobic Al films

In this study, we reported a new method to fabricate superhydrophobic Al films by combination of HCl/H2O2 etching and electrophoretic deposition process. Through this two-step method, multi-scale hierarchical structures were successfully introduced on the surface. After hydrophobization, the resultant surface showed an excellent superhydrophobicity with a water contact angle of 169.6° and a sliding angle of ca. 1°. Furthermore, the surface exhibited excellent mechanical durability and could withstand abrasion tests under 8kPa for 60cm without losing superhydrophobicity. It also maintained superhydrophobicity when exposed to air or water for a long-term period. This work provides a cost efficient method to prepare mechanically robust and stable superhydrophobic Al alloy surface.

A robust superhydrophobic PVDF composite coating with wear/corrosion-resistance properties

A robust wear/corrosion-resistant superhydrophobic polyvinylidene fluoride (PVDF)/fluorinated ethylene propylene (FEP)/carbon nanofibers (CNFs) composite coating with a water contact angle (WCA) of 164±1.5° and a slide angle of 5±0.2° has been fabricated through the combination of chemical etching and spraying technique. The WCA of the coating still maintains 141±1.2° after 10,000 times rubbing due to the designed internal nano/micro-structure and the slide angle increases from 5±0.2° to 20±0.5°. The prepared coating also demonstrates excellent corrosion-resistance property under strongly acidic or alkaline conditions for 15 days. The wear-resistance of the superhydrophobic coating is approximately 5 times higher than the pure PVDF coating and commercial fluorocarbon coating. These excellent mechanical properties are attributed to the new groups of CC and CC by dehydrofluorination of PVDF and the new β-phase of PVDF by recrystallization of the α-phase. Furthermore, the enhanced adhesive ability of the coating corresponds with Grade 1 according to GB/T9286, mainly because that the interaction force among PVDF macromolecules can be intensified by chemical cross-linking and the hydroxyl groups formed on the surface of the aluminum plate by etching. It is believed that this robust multifunctional superhydrophobic coating may have the potential values in large-scale application.

Excellent friction-reducing performance of superhydrophobic steel surface in dry sliding

Superhydrophobic micro/nano-engineered steel surfaces with friction-reducing properties were fabricated by the combination of chemical etching and stearic acid coating.

Ultra‐high aspect ratio Ni nanowires in single‐crystalline InP membranes as multiferroic composite

AbstractBy a combination of chemical etching, atomic layer deposition (ALD) and galvanic deposition it became possible to produce Ni nanowires (NWs) with ultra‐high aspect ratio (∼1000), embedded in a semi‐insulating, piezoelectric, single‐crystalline InP matrix. This Letter discusses the structural and magnetic properties of these Ni NWs. They are crystalline with a preferential growth direction of the grains in 〈111〉. For H ⊥ z, they show a very narrow hysteresis loop with a low coercivity (about 100 Oe) and a very low remanence squareness S of 0.08. So the combination of piezoelectric InP and magnetostrictive Ni forms a very promising multiferroic composite. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Properties of ultrafast laser textured silicon for photovoltaics

In this work, we report a detailed material study of ultrafast laser textured silicon surfaces to gain insight into the impact of ultrafast laser processing conditions on photovoltaic device properties. A comprehensive study of the ultrafast laser processed silicon is achieved by determination of crystal structure and elemental compositional changes using transmission electron microscopy, compositional mapping by energy dispersive X-ray spectroscopy and depth profiling compositional determination using X-ray photoelectron spectroscopy. We have observed material non-homogeneity, impurity incorporation and strained silicon, all limited to the surface. A combination of chemical etching and thermal annealing was used to remove the laser induced changes and the material was restored to its starting quality. Further, silicon solar cell devices on such defect-etched surfaces are fabricated. These devices are characterized through dark i– v analysis and Fourier transform deep level transient spectroscopy for defect analysis.

Surface treatment of NiTi shape memory alloy and its influence on corrosion behavior

Abstract Influence of various surface treatments of a NiTi alloy on its surface chemistry and corrosion resistance was studied. NiTi (50.9 at.% Ni) alloy was subjected to mechanical polishing (MP), chemical etching (CHE) in an acidic bath, combination of mechanical polishing and oxidation at 530 °C/10 min in air (MPO) and combination of chemical etching and oxidation at 530 °C/10 min in air (CHEO). Scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectrometry were used for the surface examination. Corrosion behavior was determined by measuring potentiodynamic curves and nickel release into a model physiological solution with pH = 2. It was shown that oxidation at 530 °C has a slightly retarding effect on the nickel release in the case of MP material. However, in the case of CHE material, oxidation negatively influences corrosion, i.e. it strongly accelerates the nickel release, despite that it produces a relatively thick Ni-depleted oxide layer. Chemical etching was evidenced to produce the best corrosion performance in terms of nickel release. By comparing the MP and MPO sample, it was evidenced that oxidation significantly enhances susceptibility to the pitting corrosion. The findings obtained in our work were discussed in relation to variations in the surface chemistry and structure after different treatments.