Silicate Electrolyte Research Articles

Corrosion and wear resistance of AZ31 Mg alloy treated by duplex process of magnetron sputtering and plasma electrolytic oxidation

In order to improve the wear and corrosion resistance of AZ31 magnesium alloy, a magnetron-sputtered Al layer with a thickness of 11 μm was firstly applied on the alloy, and then treated by plasma electrolytic oxidation (PEO) in an aluminate and silicate electrolytes, respectively. The performance of PEO coatings was investigated by dry sliding wear and electrochemical corrosion tests. The aluminate coating exhibits excellent wear resistance under both 10 and 20 N loads. The silicate coating only shows low wear rate under 10 N, but it was destroyed under 20 N. Corrosion tests show that the Al layer after magnetron sputtering treatment alone cannot afford good protection to the Mg substrate. However, the duplex layer of PEO/Al can significantly improve the corrosion resistance of AZ31 alloy. Electrochemical tests show that the aluminate and silicate coatings have corrosion current densities of ∼1.6×10−6 and ∼1.1×10−6 A/cm2, respectively, which are two orders lower than that of the un-coated AZ31 alloy. However, immersion tests and electrochemical impedance spectroscopy (EIS) show that the aluminate coating exhibits better long-term corrosion protection than silicate coating.

Tribological Behavior of Al2O3-MoO2-SiO2 Composite Ceramic Coating on Al-Zn-Mg-Cu Alloy

In order to enhance wear properties of Al-Zn-Mg-Cu alloy parts, Al2O3-MoO2-SiO2 composite ceramic coatings are formed on Al-Zn-Mg-Cu alloy by the DC micro-arc oxidation (MAO) method in the silicate electrolyte with sodium molybdate. Effects of sodium molybdate concentration on the structure characteristics and wear resistance of the composite ceramic coatings are analyzed by scanning electron microscopy, X-ray diffraction and the wear test, respectively. Analyses indicate that the composite coating consists of different states of Al2O3, MoO2 and mullite phase. With the addition of molybdate in the electrolyte, the morphology and structure are changed. The tribological behavior is greatly affected by the surface characteristics and hardness of the coatings. The composite coatings formed by adding 3 g/L of sodium molybdate electrolyte have the best wear resistance.

Preparation and characterization of micro-arc oxidation coating on hollow glass microspheres/Mg alloy degradable composite

Micro-arc oxidation (MAO) coatings on hollow glass microspheres (HGM) reinforced Mg alloy degradable composite were prepared in alkaline silicate electrolyte. The morphology, chemical composition and corrosion resistance of the coatings were investigated by SEM, EDS, XPS, XRD and electrochemical tests. The growth characteristics of the coatings and the effects of HGM on the MAO behavior were specially studied. The results showed that the main compositions of the coatings were MgO and Mg2SiO4 phases. The coatings possessed different growth behaviors on the different areas of the surface. The coatings exhibited faster growth rate on the α phase than the β phase. The HGM and Mg2Si particles hindered the growing of the coating in the early stage of MAO, but they would not disrupt the continuity of the coating, since they were gradually melted, reduced and disappeared, and translated into oxides of silicon and magnesium finally in the MAO process. The average thicknesses of the coatings obtained at MAO time of 10, 20, 30, and 40 min were 2.9 ± 0.9, 10.9 ± 0.8, 20.2 ± 1.2, and 22.7 ± 1.9 μm, respectively. Electrochemical tests showed the MAO coating obtained at MAO time of 30 min possessed the best corrosion resistance, the corrosion current density of which was approximately four orders of magnitude lower than that of the substrate.

Fabrication of functionalized coating with a unique flowery-flake structure for an effective corrosion performance and catalytic degradation

• Inorganic coating layers are hybridized with organic corrosion inhibitors. • Flowery-flake structures are formed by heterogeneous nucleation. • Crystal growth is formed via Layer by Layer self-assembly process. • Formation of stable coordination complexes via molecular orbital interactions. • Functionalized coating with catalytic activity and corrosion protection. The hybridization of organic compounds with inorganic layers would lead to the discovery of novel organic–inorganic hybrid materials with desired functional properties, which could open new avenues toward their state-of-the-art applications. In the present work, therefore, a hybrid organic–inorganic functionalized coating with unique flowery-flake structures was successfully deposited on the defective surface of plasma electrolysis (PE) coating via layer-by-layer self-assembly process of 1-azanaphthalene-8-ol molecules. Herein, two types of defective coatings obtained via PE treatments of AZ31 Mg alloy using either silicate or phosphate-based electrolyte systems were sealed additionally by ethanoic solution of 1-azanaphthalene-8-ol for 24 h. Although the formation level of unique flowery-flake structures has relied on the composition of the defective surface of PE coating, an organic–inorganic hybrid functionalized coating exhibiting high corrosion stability with a trade-off catalytic activity has been successfully obtained. Detailed analysis of the surface morphology of this coating suggested that the formation of stable coordination complexes, due to the molecular orbital interactions of azanaphthalene-8-ol molecules with the PE coating layer, would be the main reason for such performance. The roles of lone pairs and net charges of heteroatoms within 1-azanaphthalene-8-ol molecules during initial physisorption and chemisorptions are computationally analyzed. The mechanism underlying the heterogeneous nucleation and crystal growth of unique flowery-flake structures was discussed by impedance and computational analyses.

Fabrication of Ca and P containing niobium oxide ceramic coatings on niobium by PEO coupled EPD process

Abstract Surface modification of niobium (Nb) to develop Ca and P containing niobium oxide (Nb2O5) ceramic coatings by plasma electrolytic oxidation (PEO) coupled with electrophoretic deposition (EPD) in a single step process is reported in the present study. Four coatings were obtained in silicate and phosphate electrolytes with and without the addition of hydroxyapatite (HA) nanoparticles. The phase composition, surface and cross-sectional morphology of the coatings were analysed. The corrosion resistance of the coated samples and niobium substrate was analysed using potentiodynamic polarisation (PDP) method in simulated body fluid (SBF) solution. The cell-viability and the live and dead cell morphology on the substrate and the coated samples were evaluated using L-929 cells. The adherence and growth of the L-929 cells were estimated by the direct contact assay. The surface modification by the PEO process enhanced the corrosion resistance of niobium in a fluid body environment. Among the coated samples, the PEO-EPD samples obtained in silicate electrolyte exhibited better corrosion resistance (6.02 × 10−7 mA/cm2), optimal surface properties, lower contact angle (47°), higher surface energy (50 mJ/m2), good adhesion strength (Lc = 18.1 N) and better cell viability.

Rechargeable all-solid-state tin ion battery in a low-temperature environment

In this study, a Sn–7Mg alloy foil anode, a magnesium silicate electrolyte, and a Sn–40Cu alloy film cathode were fabricated and incorporated into an all-solid-state battery; then, the influence of operating temperature on the charge–discharge cycle characteristics was investigated. An intermetallic compound (Cu6Sn5) formed through metallurgy and heat treatment aided in suppressing the volume expansion of the electrode material. The results revealed that, when operated at room temperature, the battery exhibited the optimal charge–discharge cycle performance. Although the battery exhibited decreased capacity at a low temperature (−15 ​°C), its cycling stability remained applicable. By contrast, at a high temperature (55 ​°C), the battery had only a few charge–discharge cycles due to the escape of the interlayer water molecules form the electrolyte structure. Thus, this all-solid-state Sn battery is environmentally friendly and non-toxic, exhibits suitable capacity and stability, and shows potential for low-temperature energy storage applications.

Effect of NaOH concentration on microstructure and corrosion resistance of MAO coating on cast Al−Li alloy

Ceramic coating was prepared on cast Al−Cu−Li alloy by micro-arc oxidation (MAO) in a silicate electrolyte solution with additives including NaWO and NaOH. The effect of NaOH addition varying from 1 to 9 g/L on the microstructure and corrosion behavior of the coatings was investigated. The coating was characterized by XRD, XPS and SEM with respect to the composition and microstructures. The results show that NaOH promoted the formation of oxides in the reaction of MAO and contributed to the increase of layer thickness. Electrochemical tests (polarization curve and EIS) and mass loss test indicate that the corrosion resistance of the coated Al−Cu−Li alloy was improved with the increased addition of NaOH. Moreover, the results prove that the alumina coating formed in the electrolyte with 7 g/L NaOH showed the best corrosion resistance. The examination of the full immersion corrosion test presents the same result of corrosion resistance.

Silicate-Enhanced Heterogeneous Flow-Through Electro-Fenton System Using Iron Oxides under Nanoconfinement.

Herein, a silicate-enhanced flow-through electro-Fenton system with a nanoconfined catalyst was rationally designed and demonstrated for the highly efficient, rapid, and selective degradation of antibiotic tetracycline. The key active component of this system is the Fe2O3 nanoparticle filled carbon nanotube (Fe2O3-in-CNT) filter. Under an electric field, this composite filter enabled in situ H2O2 generation, which was converted to reactive oxygen species accompanied by the redox cycling of Fe3+/Fe2+. The presence of the silicate electrolyte significantly boosted the H2O2 yield by preventing the O-O bond dissociation of the adsorbed OOH*. Compared with the surface coated Fe2O3 on the CNT (Fe2O3-out-CNT) filter, the Fe2O3-in-CNT filter demonstrated 1.65 times higher kL value toward the degradation of the antibiotic tetracycline. Electron paramagnetic resonance and radical quenching tests synergistically verified that the dominant radical species was the 1O2 or HO· in the confined Fe2O3-in-CNT or unconfined Fe2O3-out-CNT system, respectively. The flow-through configuration offered improved tetracycline degradation kinetics, which was 5.1 times higher (at flow rate of 1.5 mL min-1) than that of a conventional batch reactor. Liquid chromatography-mass spectrometry measurements and theoretical calculations suggested reduced toxicity of fragments of tetracycline formed. This study provides a novel strategy by integrating state-of-the-art material science, Fenton chemistry, and microfiltration technology for environmental remediation.

Preparation of V doped lanthanum silicate electrolyte ceramics by combustion method and study on conductance mechanism

AbstractVanadium doped La9.33Si6−xVxO26+0.5x (x = 0.5, 1.0, 1.5) (LSVO) electrolyte powder was prepared by combustion method at 600°C for 5‐7 min. The powder was sintered at 1500°C for 3 hours to prepare LSVO ceramics. XPS, IR, XRD, and EIS analysis show that V5+ doping replaces Si4+ in [SiO4] to form [Si(V)O4] tetrahedron. With the increase in x, the lattice volume increase. When x = 2.0, the LaVO4 phase was formed, indicating that the limit doping amount of V5+ replacing Si4+ is x ≤ 1.5. The conductivity of LSVO increases significantly with the increase in x (x ≤ 1.0), which attributed to the defect reaction caused by V5+ doping. The addition of the interstitial oxygen Oi* in 63 channels and the increase of lattice volume leads to increased conductivity. When x = 1.0, the highest conductivity is 1.46 × 10−2 S·cm−1 (800°C). The doping enhancement conductivity mechanism is the Interstitial oxygen defect‐Lattice volume composite enhancement mechanism.

Investigation of the Characteristics of Ceramic Coatings Obtained by Microarc Oxidation on Direct and Alternating Currents in an Alkaline Silicate Electrolyte

This work presents the results of studies of structural and physicomechanical characteristics of oxide-ceramic coatings obtained on aluminum by microarc oxidation in an alkaline silicate electrolyte with various contents of silicate ions using alternating and direct currents.

Microstructure and biological activity of silicon‐doped composite coatings fabricated by micro‐arc oxidation on magnesium alloy

Among biomaterials, the mechanical properties of magnesium and its alloys are closest to those of human bone tissue, making these ideal materials for bone tissue repair and replacement. In order to further improve the biocompatibility and biological activity of the magnesium alloy AZ91D, micro‐arc oxidation with a constant‐current power supply mode was employed in this study in a silicate electrolyte solution. The resultant coating surface had a porous structure, and silicon was evenly distributed in it. Further, the results of in vitro experimental studies showed that the silicon‐doped magnesium coating on the surface of the magnesium alloys has no obvious cytotoxicity, and it can induce the proliferation of osteoblasts and promote actin stretching. In addition, it has good biological activity and biocompatibility. Thus, the novel method developed in this study improves the potential for clinical applications of magnesium alloys.

Microstructure and properties of rare earth CeO2-doped graphene composite coatings prepared by MAO on AA7050

Abstract In this paper, ceramic coatings were prepared on the surface of 7050 high strength aluminum alloy using a micro-arc oxidation process in a silicate electrolyte combined with the rare earth element cerium or graphene. To analyze the surface morphology, roughness, phase composition, and corrosion resistance, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, and electrochemical measurements were used, respectively. It was shown that the micropore size of the composite coatings, which mainly consisted of α-Al2O3 and γ-Al2O3, decreases and the density improved with the simultaneous addition of 4 g · L-1 of CeO2 and 10 g · L-1 of graphene to the electrolyte. In addition, with the addition of CeO2 and graphene, the roughness was the lowest and the corrosion resistance was significantly improved.

Microstructure and properties of rare earth CeO2-doped graphene composite coatings prepared by MAO on AA7050

Abstract In this paper, ceramic coatings were prepared on the surface of 7050 high strength aluminum alloy using a micro-arc oxidation process in a silicate electrolyte combined with the rare earth element cerium or graphene. To analyze the surface morphology, roughness, phase composition, and corrosion resistance, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectrometry, and electrochemical measurements were used, respectively. It was shown that the micropore size of the composite coatings, which mainly consisted of α-Al2O3 and γ-Al2O3, decreases and the density improved with the simultaneous addition of 4 g · L-1 of CeO2 and 10 g · L-1 of graphene to the electrolyte. In addition, with the addition of CeO2 and graphene, the roughness was the lowest and the corrosion resistance was significantly improved.

Effect of microstructure and porosity of AlSi10Mg alloy produced by selective laser melting on the corrosion properties of plasma electrolytic oxidation coatings

In this work, PEO process was carried out on SLM samples of AlSi10Mg, characterized by different grades of porosity, in direct-current mode using high current densities and short time in a basic silicate electrolyte. For comparison, the PEO process was also performed on samples of conventional cast AlSi10Mg alloy. The microstructure and the composition of the coatings was evaluated with SEM and XPS, whereas the phase analysis was performed with XRD. The corrosion resistance was analyzed by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests.The parameters used for PEO process allowed to obtain a continuous coating on all SLM samples, but its morphology resulted strongly influenced by the initial microstructure of the substrate. The coatings more homogeneous and less porous were produced on the samples with initial lower porosity. The corrosion performances of all SLM samples improved after PEO treatment and the PEO coatings with lower porosity resulted the more corrosion resistant.

Microstructure, wear and corrosion performance of plasma electrolytic oxidation coatings formed on D16T Al alloy

The plasma electrolytic oxidation (PEO) coatings were produced on D16T Al alloy in the aluminate and silicate electrolyte with and without graphene. The phase composition, microstructure and elemental distribution of the coatings were tested by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). The wear and corrosion resistance of PEO coatings were evaluated by dry sliding wear tests and electrochemical impedance spectroscopy (EIS). The morphology feature of the wear tracks was compared and analyzed by SEM and three-dimensional microscope. The results demonstrate that the structure, wear and corrosion resistance of PEO coatings with graphene are better than that of PEO coatings without graphene. The coating fabricated in the aluminate electrolyte with graphene exhibited the lowest roughness. The coated samples formed in silicate electrolyte with graphene displayed the thickest, densest and the most compact coating. It exhibited the best wear and corrosion resistance due to the incorporation mode of graphene in the coatings. The mechanism of graphene improving the wear and corrosion resistance of PEO coating was further discussed. In summary, the comprehensive performances of PEO coatings formed in silicate electrolyte on D16T Al alloy are superior to that produced in aluminate electrolyte. Graphene incorporated in PEO coating in forms of embedded mode and spread mode filled the pores and cracks, and significantly improved the wear and corrosion resistance. That’s ascribed to the excellent structure of PEO coating produced in silicate electrolyte with graphene.

A study of the phase-structural engineering possibilities of coatings on D16 alloy during micro-arc oxidation in electrolytes of different types

The effect of electrolysis conditions with different electrolyte compositions on the growth kinetics, phase-structural state, and hardness of coatings obtained by microarc oxidation (MAO) on the D16 aluminum alloy (base – aluminum, main impurity Cu) was studied. An analysis of the results obtained showed that the choice of the type of electrolyte and the conditions for the MAO process makes it possible to vary the growth kinetics and phase-structural state of the coating on the D16 aluminum alloy within a wide range. For all types of electrolytes, with an increase in the content of KOH, Na 2 SiO 3 , or KOH+Na 2 SiO 3 , the growth rate of MAO coatings increases. It was found that in MAO coatings obtained in an alkaline (KOH) electrolyte, a two-phase (γ−Al 2 O 3 and α−Al 2 O 3 phases) crystalline state is formed. An increase in the KOH concentration leads to an increase in the relative content of the α–Al 2 O 3 phase (corundum). During the formation in a silicate electrolyte, the phase composition of MAO coatings with an increase in the content of liquid glass (Na 2 SiO 3 ) changes from a mixture of the γ−Al 2 O 3 phase and mullite (3Al 2 O 3 ∙2SіO 2 ) to an X-ray amorphous phase. The use of a complex electrolyte leads to a two-phase state of the coating with a large (compared to an alkaline electrolyte) shift of the γ−Al 2 O 3 →α−Al 2 O 3 transformation towards the formation of the α−Al 2 O 3 phase. It was determined that the value of hardness correlates with the content of the α−Al 2 O 3 phase in the MAO coating, reaching the maximum value of 1620 kg/mm 2 at the highest content (about 80 vol. %) of the α−Al 2 O 3 phase. Two types of dependences of the coating thickness on the amount of electricity passed were revealed. For the amount of passed electricity 10–50 A-h/dm 2 , the thickness dependence is determined as 4.2 μm/(A-h/dm 2 ), which suggests the basic mechanism of electrochemical oxidation during the formation of a coating. For the amount of electricity transmitted 50–120 A-hour/dm 2 , the thickness dependence is determined by a much smaller value of 1.1 μm/(A-hour/dm 2 ). This suggests a transition to a different mechanism of coating formation − the formation of a coating with the participation of electrolysis components

Role of the electrolyte composition in establishing plasma discharges and coating growth process during a micro-arc oxidation

Micro-arc oxidation (MAO) coatings were prepared on Al substrate in alkaline sodium hexametaphosphate, sodium silicate and sodium aluminate electrolytes, the breakdown voltage and responsive current respectively decreased and increased with increasing the electrolyte concentration. The behavior of electrolyte during MAO processes was analyzed and discussed based on the data of the coating microstructure, elemental and phase composition, and the carrier density and impedance of the coating. The behavior can be explained by a mechanism in which anions incorporated into the coating reduced the anion vacancies, thus reducing the carrier density and improving the impedance.

A study of the electrolyte composition influence on the structure and properties of MAO coatings formed on AMg6 alloy

The influence of electrolysis conditions at different electrolyte compositions on the phase formation and properties of coatings obtained by microarc oxidation (MAO) on an aluminum alloy AMg6 was studied. For electrolysis, three types of electrolytes were used: alkaline electrolyte ((KOH) solution in distilled water), silicate electrolyte (with different percentages of Na 2 SiO 3 component) and complex alkaline silicate electrolyte with liquid glass (1÷12 g/l Na 2 SiO 3 ) and potassium hydroxide (1÷6 g/l KOH). An analysis of the results showed that the choice of electrolyte type and conditions of the microarc oxidation process allows a wide variation in the phase-structural state, thickness and properties of the AMg6 aluminum alloy. The criterion for the expected phase-structural state of the coatings as a result of microarc oxidation is the completeness of the γ–Al 2 O 3 →α–Al 2 O 3 transformation process during coating formation. The use of an alkaline electrolyte does not allow achieving a high hardness of the coating due to the formation of the γ-Al 2 O 3 phase and the absence of thermodynamic conditions for the γ–Al 2 O 3 →α–Al 2 O 3 transition. When using a silicate electrolyte, it is possible to significantly increase the growth rate of the coating, but at the same time, the presence of a large specific Si concentration stimulates the formation of mullite and an amorphous-like phase. The use of a combined alkaline silicate electrolyte (with different percentages of KOH+Na 2 SiO 3 ) with a low content (6 g/l) of Na 2 SiO 3 in solution stimulates the formation of mullite. This is manifested to the greatest extent with the lowest content (1 g/l) of the KOH component. At a higher content (2 g/l) of the KOH component, the processes characteristic of an alkaline electrolyte become dominant. This leads to an incomplete transformation reaction and the formation of only the γ-Al 2 O 3 phase. The achievement of the thermodynamic conditions of the γ–Al 2 O 3 →α–Al 2 O 3 conversion became possible with an increase in the specific Na 2 SiO 3 content in the electrolyte solution to 12 g/l. In this case, MAO coatings were formed on the AMg6 alloy with the highest hardness of 1500 kg/mm 2 and high electric strength of 12 V/μm

Preparation of zinc and alkaline earth metal co-doped apatite-type lanthanum silicate electrolyte ceramics by combustion method and mechanism of co-doping enhanced conductivity

The amorphous and high purity apatite-type lanthanum silicate La9.33A0.2Si5ZnO25.2 (LASZO, A=Ca, Sr and Ba) co-doped with zinc and alkaline earth metal has been successfully prepared at 600 °C in 7-9 min by employing the combustion method, along with revealing the combustion thermochemical mechanism. The LASZO ceramics were sintered at 1400-1500 °C after pressing molding. The XRD, IR, SEM and EIS analyses confirm that Zn2+ replaces Si4+ and A2+ replaces LaⅡ3+, along with the lattice volume increasing with the A2+ radius. The conductivity of co-doped La9.33Sr0.2(Si5ZnO24)OiOi*0.2VO·· at 1073 K is noted as 5.43 × 10-3 S·cm-1, which is higher than undoped, Zn2+ single-doped and A2+ single-doped ceramics. It is due to the generation of the oxygen vacancy VO·· by the Zn2+ doping, formation of an oxygen vacancy VO·· and increased lattice volume leading to a reduced space drag of the oxygen ion transport and A2+ doping increasing the concentration of the interstitial oxygen ions by introducing the additional interstitial oxygen ions Oi*. Therefore, the mechanism of co-doping driven increment in the conductivity is the oxygen vacancy defect-interstitial oxygen concentration-lattice volume composite enhancement.

Plasma electrolytic oxidation of Zircaloy-2 alloy in potassium hydroxide/sodium silicate electrolytes: The effect of silicate concentration

This study mainly investigated the effects of silicate concentration at the range of (16g/L to 56g/L) on the plasma electrolytic oxidation of Zircaloy-2 in potassium hydroxide/sodium silicate electrolytes in detail, including the growth behavior, wear and corrosion resistance of as-obtained ZrO2/SiO2 alloyed coatings. It was found that the coating thickness increased continuously on increasing the silicate concentration in electrolyte. Besides, the amount of t-ZrO2 in the coatings increased with increase of silicate concentration in electrolyte, while the amount of m-ZrO2 decreased. Comparative studies have shown that the coatings formed in electrolyte with high silicate concentration possessed superior wear and corrosion performance, which could be ascribed to heavy silica deposition associated with the presence of t-ZrO2 stabilized by SiO2. The results may provide guidance for obtaining high performance of ZrO2/SiO2 alloyed coatings. Besides, it is believed that the presence of Si species in zirconia endows the coatings with enhanced bioactivity like bioactive glasses and ceramics coatings and we envision that the as-prepared ZrO2/SiO2 alloyed coatings have great potential for biological applications.