•A novel PEO coating was prepared in the phosphate electrolyte containing K2ZrF6.•The obtained PEO coating was amorphous and comprised of Fe3O4, FePO4 and ZrO2.•The obtained PEO coating had characteristic of solid acid.•100% phenol could be degraded within 2 min under circumneutral pH.•The acid sites had a vital role in enhancing Fenton-like catalytic activity.Novel amorphous Fe3O4/FePO4/ZrO2 ceramic coatings as solid acid with porous structure were successfully synthesized in the phosphate electrolyte containing K2ZrF6 via plasma electrolytic oxidation (PEO) technique and characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The surface acidic property was investigated by NH3-TPD method. The results showed that the pore size and the intensity of pore interconnection of amorphous Fe3O4/FePO4/ZrO2 ceramic coating with solid acid property, increased with the increase of the K2ZrF6 dosage from 0.5 g to 2.0 g in the phosphate electrolyte. The Fenton-like performance of PEO coating catalysts was investigated by degradation of phenol under circumneutral pH. It was found that phenol removal efficiency decreased with the adding of K2ZrF6 amount from 0.5 g to 2.0 g except no catalytic activity of coating prepared without K2ZrF6, and Fenton-like PEO coating catalyst prepared with 0.5 g K2ZrF6 exhibited a superior catalytic activity which could degrade phenol thoroughly within 2 min under circumneutral pH. The strong acid sites played a dominant role in enhancing the Fenton-like catalytic activity. The excellent catalytic activity of PEO coating prepared in the phosphate electrolyte containing K2ZrF6 endowed it potential application in wastewater treatment.Download high-res image (242KB)Download full-size image

•C-TNTs film is obtained by gas thermal penetration method on TiO2 nanotubes.•Ti4+ is reduced to Ti3+ and the splitting organic products chemisorbed on the film.•The C-TNTs film's largest areal capacitance is up to 38.2 mF/cm2 at 10 mV/s.•The C-TNTs film's highest areal capacitance is 12.1 mF/cm2 at 125 μA/cm2•C-TNTs film keeps good stability and reversibility as supercapacitor electrode.In this work, we develop a novel carbon-modification method to improve the electronic conductivity and the electrochemical performances of TiO2 nanotubes electrodes for binder-free supercapacitor. The carbon modified TiO2 nanotubes (denoted as C-TNTs) is prepared by two-step process of anodic oxidation and gas thermal penetration method on a Ti plate. The structure and composition of C-TNTs was characterized by SEM, XRD, EDS, RAMAN, XPS and XANS, respectively. The electrochemical performances of C-TNTs were evaluated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and galvanostatic charging/discharging (GCD) tests. The C-TNTs film presents almost the same morphology as TNTs film and C is successfully deposited on the film in different forms. The largest areal capacitance of C-TNTs film is 38.2 mF/cm2 at the scan rate of 10 mV/s in CV curves, and 12.10 mF/cm2 at the current density of 0.125 mA/cm2 in GCD measurements, 21.1 times than that of TNTs film. The great improvement of the capacitance can be attributed to the increase of conductivity and the pseudocapacitance effect, which corresponds to the C deposition and Ti4+ reduction into Ti3+, and the chemisorbed CO and OH on the film surface, respectively. The galvanostatic charging/discharging cycle test indicates the good stability and reversibility of C-TNTs film as the electrode material in the application of supercapacitor.

•A binder-free C-TiO2 composite film was prepared by gas thermal penetration on pure Ti plate.•C-TiO2 composite films yields the largest specific capacity of 47.46 mC cm−2 at the scan rate of 10 mV s−1.•C-TiO2 composite films yields the largest specific capacity of 7.35 mC cm−2 at the current density of 0.075 mA cm−2.•Drop agent methanol provides the compounded carbon material for the film.•Gas thermal penetration provides an ideal reductive atmosphere for the formation of Ti3+ ions.In order to improve the capacitive properties of TiO2 materials for supercapacitors, the carbon-modified TiO2 (denoted as C-TiO2) composite films was synthesized by gas thermal penetration of pure Ti plate with methanol as the drop agent under the temperature of 550 °C. The structure and composition of C-TiO2 was investigated by SEM, XRD, RAMAN, XPS and XANES. The electrochemical performance of C-TiO2 was evaluated by electrochemical impedance spectra (EIS), cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) tests. Results show that the film is composed of a large amount of rutile TiO2 and a little anatase TiO2, and meantime the carbon is deposited on the film through the methanol decomposition during the gas thermal penetration, which greatly influences the electrochemical properties of the composite films. The prepared C-TiO2 yields the largest specific capacities of 47.46 mC cm−2 at the scan rate of 10 mV s−1 based on the CV curves, and 7.35 mC cm−2 at the current density of 0.075 mA cm−2 based on the galvanostatic charge/discharge curves, which compares favorably with many other similar modified TiO2 film materials reported nowadays. The excellent large charge storage properties of C-TiO2 films are attributed to the deposition of a certain amount of graphitized carbon and organic carbon containing hydroxyl groups and carbanyl groups and the formation of Ti3+ in the form of TiO1.5 under methanol reductive atmosphere be means of the improvement of the pseudocapacitance property and the conductivity of the composite films.

•Sulfate functional Fe3O4/FeAl2O4 coating was successfully prepared.•Sulfate functional coatings had characteristic of strong solid acid.•Phenol could be rapidly degraded under wide range of pH (6–9) within 11 min.•The strong acid sites had a vital role in enhancing Fenton-like catalytic activity.A novel immobilized solid acid coating on Q235 carbon steel was successfully prepared via plasma electrolytic oxidation. Sulfate functionalized Fe3O4/FeAl2O4 was confirmed by XRD, TEM and XPS analysis and surface acidic property was verified by NH3-TPD measurement. Fenton-like degradation performance was evaluated by employing phenol as target pollutant. Fast phenol degradation under the wide range of pH (pH 6–9) was accomplished within only 11 min. Without sulfate functionalization, phenol could hardly be degraded by Fenton-like oxidation which meant that after sulfate functionalization the existence of acidic microenvironment on the catalyst surface not only provided an optimal circumstance for enhanced Fenton-like reaction, but also avoided adjusting pH of the treated wastewater. A reasonable Fenton-like degradation mechanism was proposed. This paper offered a novel design thought for synthesizing excellent Fenton-like coating catalyst under circumneutral pH.Download high-res image (249KB)Download full-size image

•Phytic acid-based network in nanoscale was formed on microarc oxidated Mg alloy.•Sealing microdefects improved corrosion resistance of microarc oxidation film.•The as-fabricated composite coatings had long-term corrosion protection.In order to improve the corrosion resistance of magnesium alloys, environmentally friendly anti-corrosive composite coatings were fabricated on AZ31B Mg alloy. Mg alloys were first treated by plasma electrolytic oxidation (PEO) technique and then modified by phytic acid/3-aminopropyltrimethoxysilane (PA/APTMS) hybrid. Besides, the technique parameters were optimized. The composition and structure of the composite coatings were characterized by SEM, EDS, IR and XPS, the corrosion resistance was evaluated by electrochemical tests in 3.5% NaCl solution and the possible corrosion resistance mechanism was proposed as well. The results showed that the composite coating's corrosion resistance was remarkably improved by two or three orders of magnitude, compared with Mg alloy substrate and the single PEO coating. The PA/APTMS hybrid in network structure and the stable covalent bonds within the composite coatings effectively restricted the penetration of a corrosive medium into the Mg alloy surface, representing an excellent corrosion barrier effect.

•The PEO coatings on Mg-Li alloys have porous structure with some bugles.•The PEO coatings on Mg-Li alloys are composed of crystallized Mg3(PO)4 and MgO.•The optimal technique parameters are 10 A/dm2, 20 min with 8.250 g/L phosphate solution.•The best PEO coating presents the lowest αS of 0.33 and the highest ε of 0.85.Plasma electrolytic oxidation (PEO) has been becoming an important method to prepare thermal control coating on valve metals. The aim of this study is to prepare high emissivity and low absorptance thermal control coatings on Mg–Li alloys in phosphate electrolyte system. The effects of technique parameters and electrolyte concentration on the coating structure and thermal control properties were investigated. The composition and structure of the coatings were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis (EDX). The thermal control properties containing absorptance (αS) and emissivity (ε) were investigated by ultraviolet–visible–near infrared spectrophotometer instrument and solar absorption reflectometer. The results show that the PEO coatings have typical porous structure with some bulges on the surface and are composed of crystallized Mg3(PO)4 and MgO. With the increases of the current density and the reaction time, the coating's thickness and Ra are increased because of the increase of the amount of micro-bulges and micro-cracks on the surface. As the concentration of the electrolytes increases, the number of micro-pores are decreased and the coating surface become uneven due to the increase of the conductivity of the electrolyte which enhances the spark discharging during the PEO process. The thermal control properties are related to the coating thickness and Ra, which can be adjusted by the technique parameters and the electrolyte concentration. In general, increasing the current density, extending the reaction time or modifying the electrolyte concentration, the absorptance is reduced whereas the emissivity is improved. The coating prepared at 10 A/dm2, 20 min in 8.250 g/L phosphate solution, presents the lowest solar absorptance (0.33) and the highest infrared emissivity (0.85) due to the large specific surface area and great thickness of the coating.

•Influences of parameters on structure and properties of coatings•The optimal parameters are 12 A/dm2, 30% of duty ratio and 100 Hz•The optimal coating has 0.237 of absorptance and 0.99 of emissivity.•The coating has good thermal stability and the electrolyte can be reused.The aim of this work is to analyze the thermal control performance of the coatings prepared on Ti6Al4V alloys by plasma electrolytic oxidation (PEO) under different electric parameters in zirconate electrolytes. The composition and structure of the coatings were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), thickness measurement gauge and roughness measuring instrument, respectively. The infrared emissivity and solar absorptance of the ceramic coatings were evaluated by the UV–vis–NIR spectrophotometer and infrared reflectometer. The results show that the coatings have typical porous structure and the main phase composition is KZr2(PO4)3 phase. With the increase of current density, extension of duty ratios and decrease of working frequency, the absorptance (αs) decreases and the emissivity (ε) increases, due to the increase of the real surface area for radiating energy of coating and the thicker coating composed of nonmetallic inhibiting the absorptance of solar energy. Besides, the thermal shock tests and repeated experiments show outstanding thermal stability of coatings and satisfactory reusability of the electrolyte. In general, the coatings have better thermal control performance than the other coatings in the previous reports, and the above results indicate that the coatings prepared in this work have significantly promising industrialization potential in spacecraft field.

•Two sorts of temperature control ceramic coatings were prepared on Ti alloy.•The intrinsic absorptance and emissivity of ZrO2 coatings are 0.92 and 0.76.•The intrinsic absorptance and emissivity of KZr2(PO4)3 coating is 0.62 and 0.91.•The lowest absorptance and the highest emissivity coating are 0.239 and 0.99.In order to reduce the effects of solar energy on the instruments and the apparatus in the outer space, two different kinds of ceramic coatings were prepared on Ti6Al4V alloys by plasma electrolytic oxidation (PEO) in zirconate electrolytes. The phase composition, microstructure, thickness, and roughness of coatings were examined by XRD, SEM, EDS, thickness measurement gauge, and roughness measuring instrument, respectively. The infrared emissivity and solar absorbance of the ceramic coatings were studied with the UV–vis–NIR spectrophotometer and infrared reflectometer. The results show that ZrO2 coatings are dense and deep gray–green, and mainly composed of m-ZrO2, t-ZrO2. In addition, a small amount of TiO2, ZrTiO4, and the amorphous compound containing P exists in the coating. The intrinsic solar absorbance and emissivity of ZrO2 coatings are 0.92 and 0.76, respectively. The KZr2(PO4)3 coating is rough, thick, and white with the main crystalline of KZr2(PO4)3. The intrinsic solar absorbance and emissivity of the KZr2(PO4)3 coating are 0.62 and 0.91, respectively. For both coatings, the absorbance decreases while the emissivity increases due to an increase in the real surface area of the coatings by increasing thickness and roughness of the coatings as the PEO time progresses. The porous structure of the KZr2(PO4)3 is proved to be ideal for high emissivity and low absorbance materials with the lowest solar absorbance (0.239), the highest infrared emissivity (0.99), and a corresponding balance temperature of the coating of 276 K.

The aim of this study is to analyze the composition, structure and growth characteristics of plasma electrolytic oxidation (PEO) coatings through optical emission spectroscopy (OES). The PEO coatings were prepared on a magnesium–lithium alloy in a phosphate system at various frequencies. The composition and structure of the coatings were examined using X-ray diffraction (XRD), X-ray photo-electron spectroscopy (XPS) and scanning electron microscopy (SEM), as well as energy-dispersive X-ray (EDX). The discharge sparks of the PEO process were measured by optical emission spectroscopy. The results show that the PEO coating prepared at 50 Hz is composed of crystalline MgO and crystalline Mg3(PO4)2, and that the coating at 500 Hz is composed of crystalline MgO and amorphous Mg3(PO4)2. The coating prepared at 50 Hz has a greater degree of roughness than that prepared at 500 Hz, and the sizes of the micropores on the coating prepared at 50 Hz are considerably larger than that at 500 Hz, whereas the numbers of the micropores at various frequencies change in opposition to the pore sizes. The plasma temperature (Te) calculated with OES at 50 Hz is about 3100 K higher than that at 500 Hz. This means that more energy generated per cycle was applied to the electrode surface at 50 Hz than 500 Hz, which consequently influenced the structure and composition of the coatings. Based on the OES analysis, the growth characteristic of the PEO coatings was proposed to explain the changes of the coating roughness and the formation mechanism of crystalline or amorphous Mg3(PO4)2 at various working frequencies by the Te and the liquid-cooling effect, which was further proven by the experiments designed by changing the electrical parameters of the PEO process. This study also illustrates that the adjustment of the phase composition and structure by the electrical parameters can be well explained by OES. Besides, the corrosion resistance of the MAO coatings was evaluated by the polarization curves in 3.5 wt% NaCl solution. The corrosion resistance of the coatings is mainly determined by thickness and roughness, and the coatings prepared under 500 Hz generally present better corrosion resistance than those prepared under 50 Hz.

•The thermal control PEO coating is prepared on Ti alloy in K2ZrF6 solution.•Thermal control property is mainly related to thickness and roughness of the coatings.•The lowest absorptance and the highest emissivity are 0.34 and 0.9, respectively.•The absorptance increases whereas the emissivity decreases from the surface to the inner layer.Ceramic coatings with high emission and low absorptance were prepared on Ti6Al4V alloy by plasma electrolytic oxidation (PEO) in zirconate electrolyte. The effects of current density and working frequency on the structure and thermal control properties of the coatings were investigated. The phase composition, microstructure, thickness and roughness of coatings were examined by XRD, SEM, EDS, thickness measurement gauge and roughness measuring instrument, respectively. Thermal control properties of the coatings were studied with a UV–VIS–NIR spectrophotometer and an infrared reflectometer. The results show that the coatings are porous and composed of a large amount of KZr2(PO4)3, and a little monoclinic ZrO2, tetragonal ZrO2 and ZrP2O7 as well. The thickness of the coatings increases with the increase of the current density or the decrease of the working frequency while the roughness of the coatings increases with the increase of the current density and the working frequency. The increase of current density reduces the absorptance, but improves the emissivity; the increase of working frequency improves the absorptance, but does not change emissivity apparently. The coating prepared at 10 A/dm2, 50 Hz and 50 min, has the lowest solar absorptance (0.34) and the highest infrared emissivity (0.9).

•CNTs can decrease the size of Zn0.83Cd0.17S nanocomposites and improve the dispersity.•The absorption edges of Zn0.83Cd0.17S/CNTs red-shift with the increase of CNTs content.•S/C-2 sample shows the highest H2 production rate of 5.41 mmol h−1 g−1.•CNTs increase the photostability of Zn0.83Cd0.17S after photocatalytic recycling.Visible light photocatalytic H2 production from water splitting has received much attention for its potential application in converting solar energy into chemical energy. In this paper, carbon nanotube modified Zn0.83Cd0.17S nanocomposite was prepared by a solvothermal method. CNTS can efficiently suppress the growth of chalcogenide nanoparticles and improve the dispersity of the nanocomposite. The absorption edges of Zn0.83Cd0.17S/CNTs nanocomposites red-shift and the response of the visible-light region (500–800 nm) is strengthened with the increase of CNTs contents in the samples. The prepared Zn0.83Cd0.17S/CNTs nanocomposites exhibit an enhanced photocatalytic H2-production activity and an optimum amount of CNT is determined to be ca. 0.25 wt%, at which the Zn0.83Cd0.17S/CNTs displays the highest photocatalytic activity under the irradiation of Xe lamp, with an H2 production rate of 5.41 mmol h−1 g−1. Furthermore, the prepared Zn0.83Cd0.17S/CNTs nanocomposite is photostable and no photocorrosion was observed after photocatalytic recycling, compared with pure Zn0.83Cd0.17S photocatalyst.

•The porous amorphous ceramic coating is prepared in silicate solution on Ti alloys.•The prepared coatings are of high emissivity and low absorbance character.•The best coating’s absorbance and emissivity are 0.39, 0.92, respectively.In this work, plasma electrolytic oxidation (PEO) technique is used for in situ preparation of high emissivity and low solar absorbance thermal control coatings on Ti–6Al–4V alloys. The thermal control ceramic coatings were characterized by SEM, EDS and XRD, respectively. The thermal control properties (αS and ε) were investigated by ultraviolet–visible–near infrared spectrophotometer instrument and solar absorption reflectometer. Meantime, the thermal shock properties of the coated samples were investigated as well. The results show that the prepared ceramic coating is porous with some big particles stacking around like large craters. The coating is mainly composed of O, Si, Ti, P and Na. The coating is not crystallized well and there is a great number of amorphous silicate in the coatings. The concentration of silicate and the current density influence the thickness and the roughness of the coatings, and consequently influence the thermal control properties. The absorbance and the emissivity are decreased first and then increased with the increase of the concentration. The absorbance is decreased while the emissivity is increased when increasing the current density. Thermal shock tests show not only that there is a good adhesion between the substrate and the coating, but also that the coating and its thermal control properties are stable and constant. When the concentration of the silicate is 10 g/L and the current density is 10 A/dm2, the best coating was obtained with the solar absorbance of 0.39, hemispherical emissivity of 0.92, and the balance temperature of 318 K, which presents a promising application prospect in the thermal control system of Ti alloys materials.

•The black thermal control ceramic coating is prepared on Ti alloy by PEO technique.•The doping of W and the increase of the PEO time improve the αS and ε of the coatings.•The highest values of αS and ε of the coating are 0.93 and 0.88, respectively.•The annealing treatment improves the crystallization of the coating and reduces αS.It is of great significance for the research of thermal control coatings on Ti alloys due to their wide applications in aerospace and satellites and many other fields. In this work, black thermal control coatings were prepared on Ti–6Al–4V alloy by plasma electrolytic oxidation (PEO) technique. The coatings were characterized by SEM, EDS and XRD, respectively. The thermal control properties (solar absorbance, αS and emissivity, ε) were investigated by ultraviolet–visible-near infrared spectrophotometer instrument and solar absorption reflectometer. Meantime, the thermal shock properties of the coated samples were investigated as well. The results show that the ceramic coatings are black and porous and the elements such as Fe, Co and Ni and W from the electrolyte incorporate into the coating and exist in the form of an amorphous state. The coatings are of high emissivity and high absorbance character, which are influenced by the doping of Na2WO4 and the PEO time. Increasing the concentration of Na2WO4, αS increases firstly and then remains constant while ε increases gradually. Extending PEO time, both αS and ε increase. The annealing treatment reduces the solar absorbance greatly, but does not influence the emissivity apparently, which may be due to the improvement of the crystallization of the coating. When the dosage of Na2WO4 is 7.5 g/L and the reaction time is 25 min, the best coating is obtained with αS and ε of 0.93 and 0.88, respectively. This work not only provides an effective method to prepare thermal control coating for Ti alloys as the engineering materials, but also expands the application range of PEO technique in the fields of functional coatings.

The sulfide solid solution has become a promising and important visible-light-responsive photocatalyst for hydrogen production nowadays. ZnxCd1−xS/CNT nanocomposites were synthesized to improve the dispersion, adjust the energy band gap, and enhance the separation of the photogenerated electrons and holes. The as-prepared photocatalysts were characterized by scanning electron-microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectra (UV-visible), respectively. And the effects of CNTs on structure, composition and optical absorption property of the sulfide solid solutions were investigated along with their inherent relationships. For Zn0.83Cd0.17S/CNTs, sulfide solid solution is assembled along the CNTs orderly, with a diameter of 100 nm or so. XPS analysis shows that there is bonding effect between the solid solutions and the CNTs due to the strong adsorption of Zn2+ and Cd2+ on the surface of CNTs. There are two obvious absorption edges for Zn0.83Cd0.17S/CNTs, corresponding to two kinds of sulfide solid solutions with different molar ratios of Zn/Cd. The hybridization of solid solutions with CNTs makes the absorption spectrum red shift. The photocatalytic property was evaluated by splitting Na2S + Na2SO3 solution into H2, and the highest rate of H2 evolution of 6.03 mmol h−1 g−1 was achieved over Zn0.83Cd0.17S/CNTs. The high activity of photocatalytic H2 production is attributed to the following factors: (1) the optimum band gap and a moderate position of the conduction band (which needs to match the irradiation spectrum of the Xe lamp best), (2) the efficient separation of photogenerated electrons and holes by hybridization, and (3) the improvement of the dispersion of nanocomposites by assembling along the CNTs as well.

The aim of this work is to study the structure and the corrosion resistance of the plasma electrolytic oxidation ZrO2 ceramic coatings on Mg alloys. The ceramic coatings were prepared on AZ91D Mg alloy in Na5P3O10 and K2ZrF6 solution by pulsed single-polar plasma electrolytic oxidation (PEO). The phase composition, morphology and element distribution in the coating were investigated by X-ray diffractometry, scanning electron microscopy and energy distribution spectroscopy, respectively. The results show that the coating thickness and surface roughness were increased with the increase of the reaction time. The ceramic coatings were of double-layer structure with the loose and porous outer layer and the compact inner layer. And the coating was composed of P, Zr, Mg and K, of which P and Zr were the main elements in the coating. P in the coating existed in the form of amorphous state, while Zr crystallized in the form of t-ZrO2 and a little c-ZrO2 in the coating. Electrochemical impedance spectra (EIS) and the polarizing curve tests of the coatings were measured through CHI604 electrochemical analyzer in 3.5% NaCl solution to evaluate the corrosion resistance. The polarization resistance obtained from the equivalent circuit of the EIS was consistent with the results of the polarizing curves tests.Highlights► The ZrO2 ceramic coatings on AZ91D Mg alloys was prepared in tripolyphosphate and fluorozirconate solution. ► The double-layer structure with the loose and porous outer layer and the compact inner layer was analyzed by SEM and EIS technique ► The polarization resistance obtained from the equivalent circuit of the EIS was consistent with the results of the polarizing curves tests.

The aim of this work is to investigate the effects of cathode pulse under high working frequency on structure and composition of ceramic coatings on Ti–6Al–4V alloys by plasma electrolytic oxidation (PEO). Ceramic coatings were prepared on Ti alloy by pulsed bi-polar plasma electrolytic oxidation in NaAlO2 solution. The phase composition, morphology and element distribution in the coating were investigated by X-ray diffractometry, scanning electron microscopy and energy distribution spectroscopy, respectively. The coating was mainly composed of a large amount of Al2TiO5. As the cathode pulse was increased, the amount and grain size of Al2TiO5 were first increased, and then decreased. γ-Al2O3 in the coating was gradually decreased to nothing with the increase in the cathode pulse whereas rutile TiO2 began to form in the coating. As opposed to the single-polar anode pulse mode, the cathode pulse reduced the thickness of the coatings. However, as the cathode pulse intensity continued to increase, the coating then became thicker regardless of cathode current density or pulse width. In addition, the residual discharging channels were reduced and the density of the coating was increased with the appropriate increase of the cathode pulse.Research highlights▶ Al2TiO5 in the coating on Ti alloy by PEO treatment changes with the increase of the cathode pulse, regardless of the amount and the grain size. ▶ The cathode pulse brings about the decrease of γ-Al2O3 and the increase of rutile TiO2 in the coating. ▶ The appropriate cathode pulse during PEO process is beneficial to reduce residual discharging channels and improve the density of the coating.

The aim of this work was to investigate the effects of calcination/acid-activation on the composition, structure, and photocatalytic (PC) reduction property of an anodic oxidation TiO2/Ti film catalyst. The surface morphology and phase composition were examined by scanning electron microscopy and X-ray diffraction. The catalytic property of the film catalysts was evaluated through the removal rate of potassium chromate during the PC reduction process. The results showed that the film catalysts were composed of anatase and rutile TiO2 with a micro-porous surface structure. The calcination treatment increased the content of TiO2 in the film, changed the relative ratio of anatase and rutile TiO2, and decreased the size of the micro pores of the film catalysts. The removal rate of potassium chromate was related to the technique parameters of calcination/acid-activation treatment. When the anodic oxidation TiO2/Ti film catalyst was calcined at 873 K for 30 min and then acid-activated in the concentrated H2SO4 for 60 min, it presented the highest catalytic property, with the removal rate of potassium chromate of 96.3% during the PC reduction process under the experimental conditions.

The aim of this work was to prepare ceramic coatings containing ZrO2 phase on Ti alloy and study their structure and corrosion resistance. Compound ceramic coatings were prepared on Ti-6Al-4V alloy by pulsed single-polar plasma electrolytic oxidation (PEO) in K2ZrF6 electrolyte. The phase composition, morphology of the coatings and the element distribution in the coating were investigated by X-ray diffractometry, scanning electron microscopy and energy dispersive spectroscopy. The corrosion resistance of the coated samples was examined through the potentiodynamic anodic curves in 3.5% NaCl solution. The coatings prepared for short PEO time was composed of m-ZrO2, t-ZrO2 and ZrTiO4 and a little ZrP2O7; while increasing PEO time, the content of ZrP2O7 was increased and became the main crystalline. The Ti content in the coating near the substrate was decreased sharply while the content of Zr was increased greatly. The thickness of the coating was increased with the PEO time, but the coatings turned rougher and more porous. The prepared coated samples had better corrosion resistance than the substrate. Among the coated samples, the coated sample prepared for 40 min had the best corrosion resistance.

The influence of the working frequency on the structure, morphology and corrosion resistance of ceramic coatings on Ti–6Al–4V by pulsed bi-polar micro-plasma oxidation in NaAlO2 solution has been studied. The produced coatings were composed of Al2TiO5, α-Al2O3 and rutile TiO2, of which Al2TiO5 was the main crystalline phase. An increase in frequency did not change the content of Al2TiO5, however, the content of rutile TiO2 increased gradually while the content of α-Al2O3 decreased drastically. The coating can be divided into two layers: a porous outer layer and a dense inner layer. The thickness of the coatings reduced as the frequency increased. The corrosion potential increased with decreasing working frequency. The corrosion current density of the coated samples decreased with decreasing working frequency up to 60 Hz and then increased with further decrease of the frequency. Therefore, the best corrosion resistance was attained in the coated sample, which was prepared under the frequency of 60 Hz.

Micro-plasma oxidation (MPO) technique has been developed quickly in recent years. The ceramic coatings produced by MPO are reported to possess fine properties and promising application prospects in many fields. The aim of this work was to study the specific corrosion resistance of Ti–6Al–4V with ceramic coating by MPO and the effects of the coating on the corrosion resistance through the comparison between the coated samples and the Ti–6Al–4V substrate. Compound ceramic coatings were prepared on Ti–6Al–4V alloy by pulsed bipolar micro-plasma oxidation in the NaAlO2 system. The phase composition and element distribution in the coating were investigated by X-ray diffractometry and JEOL SUPERPROBE 733 electron probe micro-analyzer, respectively. The corrosion resistance properties of the coated samples were examined by the weight loss tests in three sorts of acids, potentiodynamic anodic curves and polarizing curve in 3.5% NaCl solution, and the galvanic couple corrosion current of coated samples with LY12 aluminum alloy and H62 yellow brass, respectively. The ceramic coating is composed of Al2TiO5, α-Al2O0 and rutile TiO2, of which Al2TiO5 is the main crystalline, and the content of rutile TiO2 in the inner layer is more than that in the outer layer of the coating, while the content of α-Al2O3 in the inner layer is less than that in the outer layer of the coating. The coating is of double-layer structure with the loose and porous outer layer and the compact inner layer. The content of Ti in the coating is less than that of the substrate, and Ti in the inner layer is more than that in the outer layer. The content of Al in the coating is more than that of the substrate; Al in the coating first increases, and then decreases from the substrate to the surface. The corrosion resistance of the coated samples in H2SO4 and HCl was improved five times, compared with the Ti–6Al–4V substrate. Besides, the corrosion resistance of the coated samples was better than that of the Ti–6Al–4V substrate in 3.5% NaCl solution, whether considering the point corrosion resistance or the uniform corrosion resistance. Meanwhile, the galvanic corrosion resistance of the coated samples coupled with LY12 aluminum and H62 yellow brass, respectively, was also improved due to the insulated ceramic coatings grown on it.

Current density is a key factor during micro-plasma oxidation (MPO) process. Its influences on structure, morphology and corrosion resistance of ceramic coatings on Ti–6Al–4V by pulsed bi-polar micro-plasma oxidation in NaAlO2 solution were studied in this paper. The ceramic coatings are composed of Al2TiO5, α-Al2O3 and rutile TiO2, of which Al2TiO5 is the main crystalline. Compared with the condition of the same current density for both pulses, the rise of cathode current density led to an increase in the amount of rutile TiO2, decreased the thickness and made the coatings compact; whereas the rise of anode current density led to an increase in the amount of α-Al2O3, increased the thickness and made the coatings coarse and porous. Whether increasing anode current density or cathode current density, there were more micro-holes on the surface of the coatings than that of same current density for both pulses. Besides, the corrosion resistance properties of the coated samples were better than that of Ti–6Al–4V substrate, whether considering the point corrosion resistance or the general corrosion resistance. When the anode current density (Ia) and the cathode current density (Ic) were both equal to 8 A/dm2 (Ia/Ic=8/8 A/dm2), or Ia=8 A/dm2 and Ic=10 A/dm2 (Ia/Ic=8/10 A/dm2), the produced coatings had the best point corrosion resistance, and the latter was a little better than the former. When Ia/Ic=10/8 A/dm2, the produced coating's general corrosion resistance was best.

Hierarchical dendritic micro–nano structure ZnFe2O4 have been prepared by electrochemical reduction and thermal oxidation method in this work. X-ray diffractometry, Raman spectra and field-emission scanning electron microscopy were used to characterize the crystal structure, size and morphology. The results show that the sample (S-2) is composed of pure ZnFe2O4 when the molar ratio of Zn2 +/Fe2 + in the electrolyte is 0.35. Decreasing the molar ratio of Zn2 +/Fe2 +, the sample (S-1) is composed of ZnFe2O4 and α-Fe2O3, whereas increasing the molar ratio of Zn2 +/Fe2 +, the sample (S-3) is composed of ZnFe2O4 and ZnO. The lattice parameters of ZnFe2O4 are influenced by the molar ratio of Zn2 +/Fe2 +: Zn at excess decreases the cell volume whereas Fe at excess increases the cell volume of ZnFe2O4. All the samples have the dendritic structure, of which S-2 has micron-sized lush branches with nano-sized leaves. UV–Vis diffuse reflectance spectra were acquired by a spectrophotometer. The absorption edges gradually blue shift with the increase of the molar ratio of Zn2 +/Fe2 +. Photocatalytic activities for water splitting were investigated under Xe light irradiation in an aqueous olution containing 0.1 mol·L− 1 Na2S/0.02 mol·L− 1 Na2SO3 in a glass reactor. The relatively highest photocatalytic activity with 1.41 μmol·h− 1 · 0.02 g− 1 was achieved by pure ZnFe2O4 sample (S-2). The photocatalytic activity of the mixture phase of ZnFe2O4 and α-Fe2O3 (S-1) is better than ZnFe2O4 and ZnO (S-3).A hierarchical dendritic micro–nano structure ZnFe2O4 was prepared by electrodeposition and thermal oxidation, which exhibits photocatalytic activity for hydrogen production in the aqueous system with Na2SO3 and Na2S as sacrificial reagents under visible-light irradiation.Download high-res image (91KB)Download full-size image

The sulfide solid solution has become a promising and important visible-light-responsive photocatalyst for hydrogen production nowadays. ZnxCd1−xS/CNT nanocomposites were synthesized to improve the dispersion, adjust the energy band gap, and enhance the separation of the photogenerated electrons and holes. The as-prepared photocatalysts were characterized by scanning electron-microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance spectra (UV-visible), respectively. And the effects of CNTs on structure, composition and optical absorption property of the sulfide solid solutions were investigated along with their inherent relationships. For Zn0.83Cd0.17S/CNTs, sulfide solid solution is assembled along the CNTs orderly, with a diameter of 100 nm or so. XPS analysis shows that there is bonding effect between the solid solutions and the CNTs due to the strong adsorption of Zn2+ and Cd2+ on the surface of CNTs. There are two obvious absorption edges for Zn0.83Cd0.17S/CNTs, corresponding to two kinds of sulfide solid solutions with different molar ratios of Zn/Cd. The hybridization of solid solutions with CNTs makes the absorption spectrum red shift. The photocatalytic property was evaluated by splitting Na2S + Na2SO3 solution into H2, and the highest rate of H2 evolution of 6.03 mmol h−1 g−1 was achieved over Zn0.83Cd0.17S/CNTs. The high activity of photocatalytic H2 production is attributed to the following factors: (1) the optimum band gap and a moderate position of the conduction band (which needs to match the irradiation spectrum of the Xe lamp best), (2) the efficient separation of photogenerated electrons and holes by hybridization, and (3) the improvement of the dispersion of nanocomposites by assembling along the CNTs as well.