Hydroxide Films Research Articles

Alkali assisted water treatment of aluminum promoting the growth of hydrated oxide film for energy conservation

Aluminum anodizing process consumes a lot of energy for ions migration in solid phase. Commonly, the aluminum foil is treated by boiling water to form crystalline γ'-Al2O3 for reducing the energy consumption. In order to improve water treatment, the alkaline buffer solution was used for promoting the growth of hydrated oxide film and contributed to formation of crystalline alumina. As a result, the obtained samples consumed 12.08% less energy during anodizing process compared with that of water treated samples. The hydrated oxide film was detected by means of morphological and electrochemical analysis, which indicated the alkaline treatment promoted generation of hydrated oxide film as well as formed dense anodic oxide film after anodizing. Furthermore, the pretreated samples owned denser anodic oxide film verified by X-ray diffraction and electrochemical analysis, which implied less production of alumina on the same electrical performance. Therefore, the alkaline solution treatment of aluminum/hydrated oxide film has a good prospect for getting rid of the limitation of high energy consumption in electrolytic capacitors industry.

Discharge performance of the Al–Mg–Sn alloy anodes with different Sn content for Al-air batteries

In this paper, the discharge performance of the Al–Mg–Sn alloy anodes with different Sn content for Al-air batteries is investigated in 4 mol L−1 NaOH solution, and their microstructure, corrosion behavior and discharge properties are discussed in detail. It shows that Sn-rich phases in the Al matrix act as cathode to promote the anode dissolution of the Al matrix and increase the electrochemical activity. The electrochemical impedance spectroscopy (EIS) results reveal that the value of hydroxide film resistance (Rc) increases as Sn content increases to 0.5 wt%, indicating that Sn addition can improve the corrosion resistance and therefore reduce the hydrogen evolution rate (HER). As a result, the Al-0.6Mg-0.2Sn alloy shows good discharge performance at low current density and its peak energy density reaches 2858.6 mWh∙g−1 at 20 mA cm−2 with the discharge capacity of 2341.9 mAh∙g−1. The Al-0.6Mg-0.5Sn alloy presents good discharge performance at high current density and its peak anode efficiency reaches 93.21% at 40 mA cm−2. When Sn content is up to 0.8 wt%, excessive Sn-rich phases aggravate the hydrogen evolution corrosion and intergranular corrosion, which results in more weight loss. This is responsible for the unsatisfactory discharge performance of Al-0.6Mg-0.8Sn alloy at all current density.

Dual self-healing effects of salicylate intercalated MgAlY-LDHs film in-situ grown on the micro-arc oxidation coating on AZ31 alloys

Micro-arc oxidation (MAO) coatings only provide the passive protection of common Mg alloys (AZ31), especially causing severe localized corrosion under accidental damage. Herein, a novel MgAlY-Layered double hydroxides (LDHs) film loaded with salicylate is successfully prepared on flash-MAO coated AZ31 alloys, by the one-step hydrothermal and intercalation methods. The in-situ grown LDHs platelets seal the porous morphology, significantly improving the corrosion performance. Moreover, self-healing measurements (SVET) and characterizations (EDS, XRD, and FT-IR) demonstrate that the endowed active corrosion protection is attributed to the corrosion inhibition of anion-exchange reaction, and dual self-healing effects of yttrium oxide and Y(III) - salicylate complexes.

Electroactivity Variable Valence NiFe Layered Double Hydroxyde for Cl− Removal through Electrically Switched Ion Exchange

AbstractNiFe layered double hydroxide (LDH) films with different Ni/Fe molar ratios were successfully prepared on carbon paper (CP) by the potentiostatic method and were used for the removal of chloride ions (Cl−) by electrically switched ion exchange (ESIX) technology. The results showed that the Ni/Fe ratios had a significant effect on the adsorption performance of LDH for Cl−. The prepared NiFe LDH film with Ni/Fe molar ratio of 1 : 1 showed the best Cl− ESIX performance and the maximum adsorption capacity could reach 43.8 mg ⋅ g−1 at 1.4 V (vs. SCE) in 20 ppm Cl− solution. The excellent adsorption performance of LDH for Cl− was mainly due to the coupling of the interlayer anion exchange mechanism and the electroactivity‐variable valence mechanism. In addition, the Cl− regeneration rate remained above 95 % during five repeated adsorption/desorption experiments, and the charging capacity was still about 96 % of the initial capacity even after 1000 CV cycles. Therefore, the NiFe LDH film could be a promising electroactive material for the removal of Cl− from aqueous solution.

Color-Tunable Nanosheet-structured Nickel–Cobalt Hydroxide and Oxide Thin Films

Color-Tunable Nanosheet-structured Nickel–Cobalt Hydroxide and Oxide Thin Films

Preparation and corrosion resistance of Ni-Fe layer double hydroxides superhydrophobic film on carbon steel

The nickel-ferric layered double hydroxides (NiFe-LDHs) film which are commonly used as catalysts was fabricated on Q235 steel in-situ via two-step hydrothermal method. And the superhydrophobic NiFe-LDH-PFDTES film was obtained by 1 H, 1 H, 2 H, 2 H-perfluorodecyltriethoxysilane (PFDTES) modification. To a certain extent, the application of NiFe-LDHs has been broadened. The structure and composition of NiFe-LDHs film and NiFe-LDH-PFDTES film were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and Fourier transform infrared (FT-IR). The wettability of films was analyzed by water contact angle testing. And the corrosion resistance of NiFe-LDHs and NiFe-LDH-PFDTES film in 3.5 wt% NaCl solution were measured by using potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS) techniques. The results show that NiFe-LDHs and NiFe-LDH-PFDTES film were successfully prepared on the surface of Q235 steel. By adjusting the preparation conditions, the NiFe-LDH-PFDTES film with optimal corrosion resistance was prepared in the condition containing the hydrothermal solution concentration is 1 unit and hydrothermal time for 6 h. The hydrophobicity changes little with the hydrothermal parameters, and all reach the state of superhydrophobic, the contact angle is greater than 150°, the sliding angle is less than 1°. For the superhydrophobic film, NiFe-LDHs has excellent synergy with PFDTES, covering of an "air film" on the rough structure of LDHs, blocking the solution from contact with the substrate, thereby providing corrosion resistance. NiFe-LDH-PFDTES film exhibits much better corrosion protective performance than NiFe-LDHs film in 3.5 wt% NaCl solution, the impedance modulus is increased about 4–5 orders of magnitude compared with Q235 steel, and the highest protection efficiency can reach 99.99%.

Comparative Study on Corrosion Resistance of Binary and Ternary Layered Double Hydroxide Films on Magnesium Lithium Alloy

Layered double hydroxide (LDH) (Mg-Al and Mg-Al-Co) films were prepared on the surface of LA103Z magnesium-lithium alloy by hydrothermal synthesis method. Corrosion resistance of binary and ternary LDH coatings was studied by comparison. Structures of the two films were characterized using XRD, FTIR, SEM and EDS, and the corrosion resistance of the films was evaluated by polarization curve, EIS, and hydrogen evolution rate during immersion in 3.5 wt% NaCl solution. Results showed that Mg-Al LDH film was tightly bonded to the substrate and had a large number of nanosheets growing perpendicular to the substrate, while Mg-Al-Co LDH film was thinner with a smaller size and fewer nanosheets. Electrochemical test results showed that the polarization resistance of Mg-Al and Mg-Al-Co LDH films was two orders of magnitude higher than that of the substrate. Hydrogen precipitation experiments showed that corrosion resistance of both the films was improved compared to the substrate, and the films played a protective role for the substrate, among which the corrosion resistance of the Mg-Al LDH layer was better than that of the Mg-Al-Co LDH layer.

Enhancing the Corrosion Resistance of ZnAl-LDHs Films on AZ91D Magnesium Alloys by Designing Surface Roughness

Zinc–aluminum layered double hydroxides (ZnAl-LDHs) film is a typical effective corrosion resistant film currently being explored. In this study, ZnAl-LDHs film was prepared on magnesium alloys with different surface roughness by means of metallographic preparation combined with the hydrothermal method. When the surface roughness Sa was at a minimum of 0.094 μm, the ZnAl-LDH films grew the most intensely, reaching 3.8 μm in thickness with a static contact angle of 84.34° and a minimum corrosion current density (icorr) of 1.12 × 10−4 A/cm2. After the neutral salt spray test, the sample mass was only increased by 0.0424 g. The results show that the size of ZnAl-LDHs nanosheets can be tailored by roughness of Mg alloy surface. The low roughness of magnesium substrate can accelerate the growth rate of ZnAl-LDH films, increase the thickness of films, and improve their corrosion resistance, but it is disadvantageous to the excellent hydrophobic properties of the surface. Finally, the possible growth and corrosion prevention mechanisms of LDHs films were proposed. This also provides a theoretical basis for the optimal processing parameters of magnesium alloy surface.

Growth Mechanism and Corrosion Resistance of a Co-Al Layered Double Hydroxide Film Grown In Situ on a Steel Substrate

The growth mechanism of layered double hydroxide (LDH) films grown in situ on steel via hydrothermal treatment is still unclear. In this study, the mechanism of Co-Al-CO3-LDH film grown in situ on a steel substrate was investigated in detail. During the hydrothermal reaction, the in situ growth process of Co-Al LDH on steel involved three steps: (1) hydrolysis of Al3+ and etching of the steel surface, (2) hydrolysis of urea and promotion of LDH nuclei, and (3) crystallization of LDH. More importantly, the generation of Al(OH)3 determined the integrity of the LDH film grown on the steel surface, and a suitable heating rate was also the key factor that affected the growth of the ordered and regular LDH nanoflakes. Therefore, this work provides a comprehensive understanding of the in situ LDH growth mechanism on steel and may facilitate optimal LDH film preparation.

Magnetite-facilitated growth of a layered double hydroxide film on steel for improved anti-corrosion

Layered double hydroxide (LDH) grown in situ on steel is an effective protective anti-corrosion coating. However, improving the anti-corrosion performance of LDH films through microstructure regulation is challenging owing to the limited understanding of the in situ growth mechanism. In this study, density functional theory (DFT) calculations revealed that Al(OH)3 could strongly adsorb to the (004) lattice plane of Fe3O4. Therefore, Fe3O4 was introduced on the steel surface through pretreatment with nitric acid. A dense and tightly bonded MgAl-CO32−-LDH film was successfully grown in situ on the surface of the Fe3O4-modified steel, and the film exhibited a high corrosion protection efficiency of 99.5%. The Fe3O4 played a vital role in the growth process of the MgAl-LDH film. The Al(OH)3 and Al-rich LDH with vacant sites provided dense nucleation sites for the growth of MgAl-LDH, which was the key to the formation of an effective film. This work elucidates the in situ growth mechanism of the LDH film on steel and provides an alternative method for improving the anti-corrosion performance of LDH films.

Influence of Li+/Al3+ on the corrosion behavior of Li-Al layered double hydroxides (LDHs) film on LA51 magnesium alloys

A hierarchical superhydrophobic Al-Li layered double hydroxide (LDH) films with different Li + /Al 3+ molar ratios of 1:1, 1:2, 2:1, pH value of 11.5 and reaction temperature of 125 °C, have been fabricated on the surface of Mg-5Li-1Al (LA51) alloys by hydrothermal method following the characteristics of controllable cation structure and exchangeable anion between layers. The properties of the films were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). XRD and SEM results indicate that the Al-Li LDH films are successfully prepared on LA51 alloys. The contact angle (CA) was measured to be about 100.7°, indicating that the surface wettability of the film converted from hydrophilic to hydrophobic by surface modification. The corrosion resistance of Al-Li LDH films was evaluated by Tafel polarization curve and electrochemical impedance spectroscopy (EIS). Surprisingly, Tafel polarization curve and EIS test reveal that the Al-Li LDH films prepared at the molar ratio of Li + /Al 3+ 1:2, pH 11.5 and temperature 125 °C have better corrosion resistance in 0.1 M NaCl neutral solution. In addition, the formation mechanism and corrosion mechanism of the films on the surface of LA51 alloy are also proposed. It provides innovative synthetic materials and novel design ideas for the preparation of high-efficiency anti-corrosion coatings on LA51 alloys, whose application can be extended in industrial fields.

Efficient electrooxidation of biomass-derived aldehydes over ultrathin NiV-layered double hydroxides films

Efficient electrooxidation of biomass-derived aldehydes over ultrathin NiV-layered double hydroxides films

Creation of self-hardening aluminum phosphate binders for manufacturing foundry cores

The aims of this publication is to study the physical and chemical conditions of formation of self-hardening aluminum phosphate binders based on orthophosphoric acid and fine-grained aluminum powder, research of its chemical structure and properties of core mixtures for foundry production.The methods used in the work are: X-ray phase analysis on the Rigaku Ultima IV, differential thermogravimetric analysis on the STA 449 C. Orthophosphoric acid 85% concentration and finely dispersed aluminum powder were used as materials. Samples of core mixtures were made on the basis of quartz sand with an average particle size of 0.2 … 0.3 mm.As a result of the experiments, it was established that in the system of orthophosphoric acid and finely dispersed aluminum powder, a chemical interaction occurs at ambient temperature, which leads to the formation of a phosphate binder. It has been confirmed that it is aluminum orthophosphate in the form of berlinite, and it does not undergo phase transformations, namely it is thermally stable when heated from 20 to 1000 оС. A significant advantage for core mixtures in foundry production is that the chemical interaction in this system does not begin immediately after mixing the components, but after 5 … 10 min, which is explained by the presence of protective oxide or hydroxide films on the aluminum particles. This ensures the period of technological suitability of the core mixture, and subsequently ensures its self-hardening.In contrast to previously known aluminum phosphate binders, which required heating from 200 to 300 оС for their hardening, a self-hardening aluminum phosphate binders and the core mixture based on it were created for the first time.With the amount of 2 … 3% of orthophosphoric acid and 1 … 2% of aluminum powder, after 1 h the strength indicators of the mixture based on quartz sand exceed 1 MPa, which is sufficient for the production of foundry cores.

Determining the proton diffusion coefficient in highly hydrated iridium oxide films by energy dispersive X-ray absorption spectroscopy

Charge transfer reactions in electrodeposited iridium oxide films (EIROF) are investigated by means of operando energy dispersive X-ray absorption spectroscopy (EDXAS), where oxidation and reduction conditions are selected to drive the Ir(III)/Ir(IV) and Ir(IV)/Ir(V) reactions in acidic solutions. The Ir(III)/Ir(IV) couple is related to a well-known electrochromic phenomenon, while the Ir(IV)/Ir(V) couple might play an important role in the catalysis of the oxygen evolution reactions (OER). In the experiments, current intensity and time-resolved X-ray absorption spectroscopy (XAS) are simultaneously recorded upon application of appropriate potential steps, leading to the independent determination of both the relevant reaction rates and the rate-determining steps. This is allowed by the fast acquisition time (∼10−2 s) at the ESRF Energy Dispersive XAS (EDXAS) ID24 beam-line, in combination with the highly hydrated amorphous iridium oxide electrode material, which in turn allows to maximize the fraction of Ir sites participating in the electrochemical processes. If the experimental conditions exclude the possibility of having either oxygen evolution (or reduction), the Degree of Reaction (DoR), determined by both electrochemistry and XAS, exhibits exponential time dependence, clearly pointing to diffusion-controlled processes. Vice versa, under concomitant OER + oxidation of iridium centers or ORR + iridium reduction, the electrochemical and XAS DoRs highlight different phenomena, providing fully complementary information of the ongoing electrode reactions. In all cases, data elaboration allows to determine the diffusion coefficient of H+ ions within the catalyst layer, that is compared and confirmed by data obtained by electrochemical impedance spectroscopy (EIS). The high values of D obtained for EIROF is compared to values obtained on other IrO2 materials can help in explaining the relevant high electrocatalytic activity.

Low-cost superhydrophobic coating on aluminum alloy with self-cleaning and repellency to water-based mixed liquids for anti-corrosive applications

This work seeks to develop a low-cost superhydrophobic coating on 5052 aluminum alloy using a combination of methods. First, top-down with acid etching with dilute HCl solution for a few minutes. Second, bottom-up by simple deposition of layered double hydroxide (LDH) film; Third, chemical modification of the surface with stearic acid. Through the applied methodology, it is possible to obtain superhydrophobic coatings with a contact angle of 164° and sliding angles of 1°. The obtained coating also shows high repellency and low sliding angle value for different commercial liquid foods such as orange juice, grape juice, chocolate milk, iced tea, isotonic, and cola-based soda. The Tafel method reveals that corrosion inhibition efficiency is 97.7 % and 97.4 % after 24 h of exposure in 0.6 mol/L NaCl solution and cola-based soda medium (pH = 2,5), respectively. The immersion test for 21 days (3 weeks) in distilled water and NaCl solution (0.6 mol/L) shows a change of the wettability characteristic on the coated specimens to hydrophobic and hydrophilic at the end of the experiment, respectively. Future work intends to incorporate harder particles that can further improve the mechanical durability of the LDH-based superhydrophobic coating, aiming at the application as food contact materials.

Microwave hydrothermal electrodeposition of nickel carbonate hydroxide/cobalt hydroxide film on nickel foam for cement-based structural supercapacitors

Electroactive electrode materials for cement-based structural supercapacitors suffer from poor interface contacts with ceramic electrolytes and current collectors due to their poor adhesive to the current collectors and severe reactions during cement hydration process, leading to their inferior capacitive performance relative to conventional supercapacitors. Herein, microwave hydrothermal electrodeposition was developed to deposit a robust composite film of Ni2(CO3) (OH)2/Co(OH)2 as an electroactive electrode material onto nickel foam. Effects of Ni/Co molar ratio of 0.5, 1, 1.5, and 2 on the microstructure and electrochemical properties of the film electrode were investigated in detail. Subsequently, the film electrode with the optimal electrochemical performance was compared with that by hydrothermal deposition with no microwave involvement. The results showed all the resultant films by microwave hydrothermal electrodeposition showed a crooked sheet morphology with a polycrystalline structure containing lots of dislocations. Among them, the film of a Ni/Co molar ratio of 1 presented the optimal capacitive performance (a specific capacity of 632.8 (1.88) C/g(F/cm2) at 1 (2.97) A/g (mA/cm2), a superlong cycling life of 30,000 cycles at 10 A/g with a capacity retention of 80.4%) and demonstrated better electrochemical and adhesive properties than that prepared by hydrothermal electrodeposition with no microwave involvement. Finally, this optimal film electrode was employed as the cathode, active carbon as the anode and polyacrylic acid (PAA)-KOH-aluminate cement as the structural electrolyte, an hybrid structural supercapacitor device was assembled, and exhibited a compressive strength of as high as 37.2 MPa and a ionic conductivity of 8.2 mS/cm, and deliver excellent electrochemical performance (specific capacitance of 415.31 mF/cm2 at 0.5 mA/cm2, and 80.1% capacitance retention of after 8000 cycles at 1 mA/cm2), which is the best capacitive performance among the reported cement-based structural supercapacitors in the form of civil engineering. Our experimental results reveal that microwave hydrothermal electrodeposition could be utilized to fabricate high-performance electrode materials on nickel foam for structural supercapacitors.

A highly sensitive and ecofriendly assay platform for the simultaneous electrochemical determination of rifampicin and isoniazid in human serum and pharmaceutical formulations

Simple fabrication of an electrochemical sensor for simultaneous determination of rifampicin and isoniazid based on electrochemical modification of SPCE surface with reduced graphene oxide and nickel hydroxide film (Ni(OH)2/rGO/SPCE) without using toxic chemical agents.

Oriented growth of stacking α-cobalt hydroxide salt continuous films and their topotactic-like transformation to oriented mesoporous films of Co3O4 and CoO.

Mesoporous metal oxide films composed of nanocrystal assemblies with an aligned crystallographic orientation are key nanostructures for efficient interfacial reactions; however, the development of a simple and versatile method for their formation on substrates still constitutes a challenge. Here we report the template-free centimetre-scale formation of novel cobalt oxide films of Co3O4 and CoO with a [111]-oriented mesoporous structure starting from stacking cobalt hydroxide continuous films. The cobalt hydroxide precursor is formed electrochemically on conductive substrates from a Co(NO3)2 aqueous solution at room temperature. A thorough characterization by means of scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis-NIR spectroscopy, IR spectroscopy and Raman spectroscopy analyses reveals that the precursor film is an α-type layered cobalt hydroxide salt (α-Co-LHS) containing interlayer nitrate and hydrated water, i.e., α-Co(OH) x (NO3) y ·nH2O, with a [001]-oriented stacking film structure. Heat treatment of the [001]-α-Co-LHS films using different conditions, i.e., under air at 550 °C or under vacuum at 500 °C, results in the selective formation of Co3O4 or CoO mesoporous films, respectively. A plausible explanation for the observed centimetre-scale topotactic-like transformation from α-Co-LHS[001] to Co3O4[111] or CoO[111] is given according to the atomic framework similarity between the hydroxide precursor and the final oxides.

Enhanced Bactericidal Effect of Calcinated Mg-Fe Layered Double Hydroxide Films Driven by the Fenton Reaction.

Osteogenic and antibacterial abilities are the permanent pursuit of titanium (Ti)-based orthopedic implants. However, it is difficult to strike the right balance between these two properties. It has been proved that an appropriate alkaline microenvironment formed by Ti modified by magnesium-aluminum layered double hydroxides (Mg-Al LDHs) could achieve the selective killing of bacteria and promote osteogenesis. However, the existence of Al induces biosafety concerns. In this study, iron (Fe), an essential trace element in the human body, was used to substitute Al, and a calcinated Mg-Fe LDH film was constructed on Ti. The results showed that a proper local alkaline environment created by the constructed film could enhance the antibacterial and osteogenic properties of the material. In addition, the introduction of Fe promoted the Fenton reaction and could produce reactive oxygen species in the infection environment, which might further strengthen the in vivo bactericidal effect.

Structural and Morphological Properties of Nanosheet-like Structured Cobalt Hydroxide Films with Annealing Treatment

Structural and Morphological Properties of Nanosheet-like Structured Cobalt Hydroxide Films with Annealing Treatment