Hydroxide Films Research Articles

Corrosion behavior and mechanism of dual phase Fe1.125Ni1.06CrAl high entropy alloy

This investigation explores the corrosion behavior and mechanism of as-cast dual phase Fe1.125Ni1.06CrAl high entropy alloy with low density (6.65 g/cm3) and high hardness (460.67 kgf/mm2) in 3.5 wt% NaCl solution. The microstructure, elemental distribution and corrosion behavior of high entropy alloys before and after the corrosion process were investigated via electrochemical quantitative analysis and then the corrosion mechanism of high entropy alloys was obtained by the first principles and experimental modeling approaches. The results show that quaternary Fe1.125Ni1.06CrAl high entropy alloy display spinodal decomposition microstructure of dual BCC phase with high hardness and distinguished corrosion resistance compared with other established alloys. The self-corrosion current density of 9.262 × 10−9 A/cm2 and corrosion potential of − 0.228 V are gotten for this alloy via potentiodynamic polarization measurements and the calculated parameters of high entropy alloys were analyzed by fitting equivalent circuit. Corrosive pits emerged on the alloy surface when the Fe1.125Ni1.06CrAl and Fe1.125Ni1.125CrAl specimens have experienced preferentially localized corrosion at the areas enriched in Ni and Al characterized by scanning electronic microscope and atomic force microscope. Oxides and hydroxides films of constitutional elements on the alloy surface are formed by X-ray photoelectron spectroscopy analysis, which indicates that corrosion properties of high entropy alloys possess. Chloride anions are easier to be adsorbed and attacked on the BCC2 phase surface based on the adsorption behavior analysis, accelerating the localized pitting and micro-galvanic corrosion processes.

In situ synergistic strategy of sacrificial intermedium for scalable-manufactured and controllable layered double hydroxide film

Layered double hydroxides (LDHs), a class of two-dimensional (2D) brucite-like layers, have been effectively applied in diverse fields. However, the current synthesis methods restrict the in situ scaling-up and tunable production of LDH-based materials. Inspired by the growing characteristic of “Bryophyllum pinnatum”, a sacrificial co-sputtered Zn−Al transition layer was introduced for the first time to in situ grow a scalable-manufactured and thickness-controllable LDH film on arbitrary substrate materials with flexible shapes through “partial dissolution” and “solution infiltration” processes. Diverse LDH films could be tailored by the creative regulation of the component, structure and surface state of the transition layer. Results showed that the as-prepared LDH film had strong mechanical robustness under harsh abrasion conditions due to its large thickness and multi-level microstructure. Moreover, a series of galvanic couple model experiments based on Zn/Al single-metal transition layers were designed to solve the real-time monitoring issue in the complex hydrothermal solution. This work not only develops a new strategy to design and grow in situ LDH films with multifaceted features, but also reveals sophisticated LDH formation mechanisms. Hence, the findings of this study may broaden the practical application of LDH-based materials toward advanced and smart devices.

Effect of Al surface oxide structures on oxidability of Al-peroxymonosulfate system

Al-peroxymonosulfate (PMS) system is an efficient way for removal of pollutants in aqueous solution. Al surface passive oxide film is a barrier to impede the electron transfer from inner metal Al to outside, whose compositions and phase structures are changed in different environment such as moisture or after recycling. In this work, for the first time, the effect of Al surface oxide structures on oxidability of Al-PMS system and its efficiency for removal of organic pollutant was investigated. It was found that if the passive oxide film on Al particles is hydrated and becomes hydroxides, the efficiency of Al-PMS system for degradation of bisphenol A (BPA) in aqueous solution decreases considerably, because the solubility of crystallized Al hydroxides is at least three orders of magnitude lower than that of amorphous Al oxides on pristine Al particles. Furthermore, the trace species in water have an influence on the hydration and structures of Al surface oxide film. For example, organics and F− ions in water will form complexes on Al particle surfaces and inhibit the hydration process, while Cl− ions corrode Al surface oxides and do not inhibit the hydration, based on the analyses of Al3+ ion concentration in their solution after BPA removal. It was also found that acid washing can remove the hydrated oxide film on Al surfaces and recover Al activity.

Enhanced Corrosion Resistance of Layered Double Hydroxide Films on Mg Alloy: The Key Role of Cationic Surfactant.

In this study, dense anticorrosion magnesium–aluminum layered double hydroxide (MgAl-LDH) films were prepared for the first time by introducing a cationic surfactant tetradecyltrimethyl ammonium bromide (TTAB) in the process of in situ hydrothermal synthesis of Mg-Al LDH films on an AZ31 magnesium alloy. Results of XRD, FTIR, and SEM confirmed that TTAB forms the MgAl-LDH-TTAB, although TTAB cannot enter into LDH layers, and MgAl-LDH-TTAB powders are much smaller and more homogenous than MgAl-CO32−-LDH powders. Results of SEM, EDS, mapping, and XPS confirmed that TTAB forms the MgAl-LDH-TTAB films and endows LDH films with denser structure, which provides films with better shielding efficiency. Results of potentiodynamic polarization curves (PDP) and electrochemical impedance spectroscopy (EIS) confirmed that MgAl-LDH-TTABx g films have better corrosion resistance than an MgAl-CO32−-LDH film. The corrosion current density (icorr) of the MgAl-LDH-TTAB0.35 g film in 3.5 wt.% NaCl solution was reduced to 1.09 × 10−8 A.cm−2 and the |Z|f = 0.05 Hz value was increased to 4.48 × 105 Ω·cm2. Moreover, the increasing concentration of TTAB in MgAl-LDH-TTABx g (x = 0.025, 0.05, 0.1, 0.2 and 0.35) provided denser outer layer LDH films and thereby increased the corrosion resistance of the AZ31 Mg alloy. Additionally, the |Z|f = 0.05 Hz values of the MgAl-LDH-TTAB0.35 g film still remained at 105 Ω·cm2 after being immersed in 3.5 wt.% NaCl solution for 168 h, implying the good long-term corrosion resistance of MgAl-LDH-TTABx g films. Therefore, introducing cationic surfactant in the process of in situ hydrothermal synthesis can be seen as a novel approach to creating efficient anticorrosion LDH films for Mg alloys.

Butynediol’s Role beyond Brightening Additive during Electrodeposition of Cobalt

Butynediol (2-Butyne-1,4-diol), a well-known type-II brightening additive, changes the interfacial pH resulting in the formation of porous cobalt hydroxide film of ca. 1 μm thickness over the copper substrate in a short duration of electrodeposition (2 min) and at a very low current density (−5 mA cm−2) from sulfate bath. In the absence of butynediol, a metallic cobalt layer was observed under identical deposition conditions. The choice of anions (sulfates, chlorides and nitrates) in the electrodeposition bath determines the kind of electrodeposited films obtained, viz., cobalt, cobalt/cobalt hydroxide, and compact cobalt hydroxide. The adsorption of butynediol enhances hydrogen evolution due to water reduction that facilitates the formation of porous microstructures of cobalt hydroxide. Competition for adsorption sites between butynediol and chloride and dissolution of cobalt hydroxide by diffusing protons result in a mixed metallic cobalt particle and porous cobalt hydroxide microstructure. The variations in the phases and microstructures of electrodeposits were evidenced through the difference in the magnetic and electrocatalytic properties.

The growth behavior and properties of orientated LDH film composited with reduced graphene oxide

Oriented reduced graphene oxide-MgAl layered double hydroxides (rGO-LDH) films were prepared on Mg alloy with pre-sprayed rGO-Al coating by in-situ growth method. Characteristics of orientated LDH films were detected through field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) and Raman spectroscopy. The orientation mechanism was dicussed. Corrosion behavior of the coatings was investigated using potentiodynamic polarization curves, electrochemical impedance spectroscopy and full immersion test. Ball on disc test was carried out for measuring the anti-wear performance. Results indicate that the nanosheets in LDH film tend to parallel to the substrate under low pH value, and nanosheets in LDH film tend to perpendicular to the substrate under high pH value. Parallel oriented LDH films exhibit excellent shielding and lubrication ability. And the rGO has a strong anchoring effect on perpendicular oriented LDH film, which results in higher anti-corrosion and anti-wear performance (load capacity) for the film. The orientation mechanism of films and the relationship between orientation and performance were discussed.

Enhanced corrosion resistance and cytocompatibility of zinc by Zn-Al layered double hydroxide films

Zinc (Zn) is promising candidate to construct biodegradable medical devices. However, the poor corrosion resistance limits its clinical application. Herein, Zn-Al layered double hydroxide (LDH) films were constructed. Results showed that Zn-Al LDHs films could effectively enhance the anti-corrosion ability and biocompatibility of the Zn substrate, which provided new insights in the surface modification of Zn.

Fabrication of uniform and anti-corrosion layered double hydroxides film on Mg-Gd-Y-Zn-Zr alloy through solution pH tailoring

Second phase is generally beneficial to the mechanical properties of magnesium (Mg) alloys. As an electrochemically heterogeneous structure, it leads to the formation of uneven chemical conversion films which are detrimental to corrosion protection. To address this problem for multiphase Mg alloys, a simple hydrothermal method was reported herein for fabricating a layered double hydroxides (LDHs) film with a uniform structure and superior corrosion protection upon Mg-Gd-Y-Zn-Zr alloy through tailoring solution pH. Morphology characterization reveals that high solution pH facilitates the production of LDHs nanosheets with dense and fine features, which is attributed to the high density of hydroxy groups on substrate as nucleation sites for LDHs growth. In addition, the uniformity of films depended on solution pH. The highest pH (13.5) of this study drove even distribution of OH− that in turn circumvented the micro-galvanic effect between second phases and α-Mg matrix. Immersion and electrochemical tests confirmed that corrosion resistance of the sample fabricated at pH of 13.5 outperformed those of the counterparts fabricated at pH 10−12. It is postulated that the high compactness of the LDHs film and the self-healing ability of RE(OH)3 were the driving forces.

Electrochemical degradation of methyl red in zinc hydroxide and zinc oxide thin films, physical and chemical activation

The experimental and ab initio results on structural, optical, and electronic properties of Zn(OH)2 and ZnO thin films (TFs) at various annealing temperatures are reported. The as-grown TF consists of Zn(OH)2 while annealing them at temperatures higher than 300 °C yields high-quality ZnO. The films were highly crystallized in a hexagonal structure with (200) orientation by XRD analysis. The evaluated optical band gap energies of Zn(OH)2 and ZnO TFs were 3.955 and 3.286 eV, respectively, and agree well with Vienna ab initio hybrid functional HSE06 density of states calculations. The material activation of ZnO and Zn(OH)2 TFs in electrochemical degradation catalyses of methyl red in water proven that ZnO TFs have higher decolourization efficiency than Zn(OH)2 TFs. The electrochemical circuit used was performed under experimental conditions of 12 V voltage difference and 0.3 A current.

Combining the 8-hydroxyquinoline intercalated layered double hydroxide film and sol—gel coating for active corrosion protection of the magnesium alloy

Combining the 8-hydroxyquinoline intercalated layered double hydroxide film and sol—gel coating for active corrosion protection of the magnesium alloy

Tribocorrosion performance of 316L stainless steel enhanced by laser clad 2-layer coating using Fe-based amorphous powder

To improve the tribocorrosion performance of 316L stainless steel (SS), multi-layer (1, 2 and 3 layers) Fe-based alloy coatings were manufactured by laser cladding Fe-based amorphous powder on 316L SS, and the corrosive wear behavior was investigated against Alumina ball in Ringer's solution. With the increase of cladding layer number, the content of body-centered cubic (BCC) phase increases, and the hardness also improved. The volume loss rate of SS at 5 N load decreased over 3 times by the 2-layer coating. Under 10 or 20 N loads, the 2-layer coating still presents the best tribocorrosion performance with the lowest values of friction coefficient and volume loss rate. The multi-layer cladding caused surface chemical composition change leading to the decrease of Cr accompanied with the increase of Mo and Y, which is responsible for the increase of BCC content and hardness as well as the formation of lubricant Fe–Cr hydroxide film. The friction induced lubricating film may facilitate to design new metallic coatings for the low carbon steels applied in corrosive environment.

Aqueous solution deposition of indium hydroxide and indium oxide columnar type thin films

Abstract Crystalline In(OH)3 and UV-emitting In2O3 thin films with a unique columnar morphology have been successfully prepared for the first time via a simple aqueous solution deposition method. In the present study, sulfonate-terminated self-assembled monolayers on single-crystal Si wafers were used as substrates for the film deposition. Uniform In(OH)3 thin films formed on self-assembled monolayers in aqueous solutions of InCl3 · 4H2O at 60°C. These films, containing columnar In(OH)3 crystals, showed preferential growth orientation along the [100] direction. The current understanding of the film formation mechanism was discussed. After annealing in air at 400 °C, these films were converted to nanocrystalline In2O3 films without modification of the morphology. Photoluminescence emission from In2O3 films was reported at approximately 3.4 eV, which was ascribed to the near-band-edge emission.

Low-temperature synthesis of NaRE(WO4)2 films via anion exchange from layered rare-earth hydroxides (LRHs) films, phase/morphology evolution and photoluminescence

LRH films were prepared via electrodeposition within 10 minutes, and they were used as precursor templates to produce NaRE(WO4)2 films at pH ∼ 10. The obtained NaEu(WO4)2 and NaTb(WO4)2 films exhibit enhanced photoluminescence.

Fabrication of REVO4 films via sacrificial conversion from layered rare-earth hydroxide (LRH) films: the investigation of the transition mechanism and their photoluminescence.

Rare-earth orthovanadate REVO4 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Y) films were directly synthesized within 2 hours by sacrificial conversion from electrodeposited layered rare-earth hydroxide (RE2(OH)5NO3·nH2O) films at pH ∼ 10, without subsequent heat treatment. Detailed characterization of the products was achieved by combined X-ray diffraction, Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence excitation and photoluminescence. The mechanisms of phase and morphology evolution from Y2(OH)5NO3·nH2O to YVO4 were unveiled through systematic investigations into the influences of the concentration of the anion sources (Na3VO4) and the reaction temperature. The effects of lanthanide contraction on the phase structure and particle morphology of the REVO4 films were also clarified. Additionally, the photoluminescence of RE3+ activators (RE = Eu, Dy, and Eu and Dy) was elaborated with YVO4 as a representative host lattice, and the color-tunable emission and energy transfer from Dy3+ to Eu3+ were also investigated. Electrodeposition combined with a hydrothermal anion exchange technique established in this study led to the rapid synthesis of REVO4 films, and it might have wide implications for the generation of other types of inorganic functional films.

Microstructure Dependent Anticorrosion Performance of Layered Double Hydroxides Film on Steel

Microstructure Dependent Anticorrosion Performance of Layered Double Hydroxides Film on Steel

Corrosion-resistant Mg(OH)2/Mg-Fe layered double hydroxide (LDH) composite films on magnesium alloy WE43

BackgroundA new synthesis approach was developed for Mg-Fe layered double hydroxide (LDH) film on oxidised magnesium (Mg) alloy WE43 surface by cathodic electrodeposition. MethodsThe synthesised Mg(OH)2 surface layer provides essential divalent cations and a foundation for the direct growth of an Mg-Fe LDH film through the electrodeposition process with trivalent cations containing solution. FindingsThe cross-section analysis results disclosed that the Mg(OH)2 layer altered the typical morphology of LDH film, leading to structured LDH nanoplates with a thickness of approximately 3.5 µm. The formation of structured LDH nanoplates resulted from the perpendicular arrangement of the ab-faces of the crystallites to the WE43 surface, as seen from Field Emission Scanning Electron Microscopy (FE-SEM) images. Electrochemical tests in Hank's Balanced Salt Solution (HBSS) report the Ecorr value increased by 0.24 V and a decrease in icorr by one order of magnitude of Mg(OH)2/Mg-Fe LDH composite films against its substrate. Furthermore, the impedance modulus values of Mg(OH)2/Mg-Fe LDH composite films can achieve a magnitude of three times greater than its substrate. These results indicate that the Mg-Fe LDH film can effectively capture the corrosion anions during corrosion through the anion-exchange process, making it a promising surface modification for Mg alloy.

In situ growth of corrosion resistant Mg-Fe layered double hydroxide film on Q235 steel

HypothesisIn situ grown layered double hydroxide (LDH) is commonly used one of the anticorrosion ways for metal materials; Due to the dense growth of LDH on the metal surface, its special layered structure can effectively delay the corrosion rate of metal. MethodsIn this study, we use a hydrothermal method to successfully grow Mg-Fe LDH film on steel substrates based on self-supplied Fe3+ ions. The films were characterized by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectrometry. The potential corrosion resistance of the obtained Mg-Fe LDH film was confirmed using electrochemical impedance spectroscopy and polarization curves. FindingsAfter systematic adjustment and parameter optimization, it was found that Mg-Fe LDH film exhibited the best growth morphology and comprehensive performance with an initial pH value of 10, Mg2+/urea ratio of 1:4 and reaction time of 12 h. The SEM and electrochemical results further demonstrated that Mg-Fe LDH film play a good protection effect on carbon steel surface. This study provides an important reference for the processing of anticorrosion LDHs film.

Preparation of layered double hydroxide films using an electrodeposition and subsequent crystal growth method

AbstractThe surface coating of a gas reaction electrode with layered double hydroxides (LDHs) featuring various electrode catalyst activities was prepared via electrodeposition and the subsequent crystal growth of LDHs. LDH formation was confirmed by X-ray diffraction and Raman scattering measurements after subsequent crystal growth on respective electrodeposited precursor films in Ni-Fe and Zn-Al LDH systems. However, the crystal growth of LDHs in Ni-Mn and Cu-Mn systems was observed on the Mg-Al LDH-electrodeposited films. LDH films were also deposited on the surface of a carbon paper electrode with a rugged surface via electrodeposition and subsequent crystal growth. Using the prepared LDH-coated carbon paper electrodes, the electrode catalytic activity for the oxygen reduction reaction (ORR) was examined. For Ni-Mn, Ni-Al and Ni-Fe LDH-coated carbon paper electrodes, the threshold voltages of the ORR decreased. Hence, the LDHs electrodeposited on a gas reaction electrode have high electrochemical catalytic activity for the ORR.

A Novel Mg-Al-Co LDH/ MAO Composite Films on LA103Z Magnesium-Lithium Alloy and Its Active Anti-corrosion Performance

In order to further improve the corrosion resistance of the micro-arc oxidization (MAO) film on LA103Z magnesium-lithium alloy, a Mg-Al-Co layered double hydroxide (LDH) film was fabricated on MAO film by an in-situ hydrothermal method. The results showed that with the extension of hydrothermal treatment time, the dense LDH film sealed the micro-pores and cracks in the MAO film successfully. In addition, LDH film treated with a hydrothermal treatment at 90°C for 24 h has the best electrical insulation. The hydrogen evolution rates (mL.cm–2.h−1) of the LDH/MAO composite films rank as LDH/MAO-24 h ≈ LDH/MAO-30 h (0.12) < LDH/MAO-18 h (0.15) < LDH/MAO-12 h (0.16) < MAO (0.25). Meanwhile, the results of potentiodynamic polarization curves showed that the corrosion potential of LDH/MAO-24 h film increased from –1.5349 to −1.388 V, and the corrosion current density decreased by three orders of magnitude. Therefore, the LDH/MAO film has better corrosion resistance than a single MAO film and adds long-term corrosion resistance to the magnesium alloy, which owes to the sealing effect of LDH on inherent defects and trapping effect on corrosion ions.

Pure Mg-Al Layered Double Hydroxide Film on Magnesium Alloys for Orthopedic Applications.

Mg alloys are promising biodegradable orthopedic implants in the future. However, poor corrosion resistance and biocompatibility limit their wide applications. In this study, a pure Mg–Al layered double hydroxide (Mg–Al LDH) film on AZ31 was prepared through combining hydrofluoric acid pretreatment and hydrothermal treatment. Electrochemical analysis and the immersion test suggested that the as-prepared Mg–Al LDH-coated sample exhibited significantly enhanced corrosion resistance. The in vitro cell culture revealed that the Mg–Al LDH film was favorable for the alkaline phosphatase activity, collagen secretion, and osteogenesis-related gene expression of MC3T3-E1. Furthermore, the LDH-coated sample was beneficial for the migration, vascular endothelial growth factor secretion, and angiogenesis-related gene expression of human umbilical vein endothelial cells. The subcutaneous implantation test demonstrated that the Mg–Al LDH film could protect the substrate from corrosion and induce milder inflammation. The femur implantation demonstrated that the Mg–Al LDH sample showed better bone regeneration and osseointegration than bare AZ31. In summary, the as-prepared pure Mg–Al LDH film is able to enhance the in vitro and in vivo performances of AZ31, indicating a promising application in the orthopedic field.