Enhancing bifunctional catalytic activity of cobalt–nickel sulfide spinel nanocatalysts through transition metal doping and its application in secondary zinc–air batteries

Developing large-scale and high-performance OER (oxygen evolution reaction) and ORR (oxygen reduction reaction) catalysts have been a challenge for commercializing secondary zinc–air batteries. In this work, transition metal-doped cobalt–nickel sulfide spinels are directly produced via a continuous hydrothermal flow synthesis (CHFS) approach. The nanosized cobalt–nickel sulfides are doped with Ag, Fe, Mn, Cr, V, and Ti and evaluated as bifunctional OER and ORR catalyst for Zn–air battery application. Among the doped spinel catalysts, Mn-doped cobalt–nickel sulfides (Ni_1.29Co_1.49Mn_0.22S₄) exhibit the most promising OER and ORR performance, showing an ORR onset potential of 0.9 V vs. RHE and an OER overpotential of 348 mV measured at 10 mA cm⁻², which is attributed to their high surface area, electronic structure of the dopant species, and the synergistic coupling of the dopant species with the active host cations. The dopant ions primarily alter the host cation composition, with the Mn(iii) cation linked to the introduction of active sites by its favourable electronic structure. A power density of 75 mW cm⁻² is achieved at a current density of 140 mA cm⁻² for the zinc–air battery using the manganese-doped catalyst, a 12% improvement over the undoped cobalt–nickel sulfide and superior to that of the battery with a commercial RuO₂ catalyst.

Transition metal-doped cobalt–nickel sulfide spinel (Ni_1.29Co_1.49Mn_0.22S₄) nanocatalysts for secondary Zn–air batteries with an efficient and stable electrochemical performance.     

Investigation on the composition and corrosion resistance of cerium-based conversion treatment by alkaline methods on aluminum alloy 6063

Cerium conversion coating (CeCC) and Ce–Mo conversion coating (CeMCC) were prepared on aluminum alloy 6063 (AA6063) by immersion in alkaline conversion baths. Surface morphology and composition of the conversion coatings were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). And electrochemical measurements were used to assess corrosion performance of the coatings. The SEM observations showed that CeMCC possessed a smoother and more uniform structure than CeCC, and the thickness of CeCC and CeMCC was about 0.8 and 1.2 μm respectively. The XPS depth analysis indicated that CeMCC contained a considerable amount of molybdenum and the cerium content was higher than that of CeCC at all coating depths. CeCC comprised of Al₂O₃, Ce₂O₃, CeO₂, and cerium hydroxides, and the composition of CeMCC also included MoO₂, MoO₃, Al₂(MoO₄)₃ and Na₂MoO₄ besides the above mentioned components. A potentiodynamic polarization (PDP) test revealed that the corrosion current density (i_corr) values for bare alloy and CeCC were 13.36 and 4.38 μA cm⁻² respectively in 3.5 wt% NaCl solution, while CeMCC exhibited the lowest i_corr value of 0.24 μA cm⁻², about two orders of magnitude lower than that of the substrate. Furthermore, the results obtained from both a cupric sulfate drop test and electrochemical impedance spectroscopy (EIS) characterization suggested that CeMCC possessed higher corrosion resistance in comparison with CeCC.

In contrast with the abundant research into acidic conversion treatment, cerium-based conversion coatings were prepared on AA6063 by alkaline methods.     

Correction: Electrochemical behaviour and analysis of Zn and Zn–Ni alloy anti-corrosive coatings deposited from citrate baths

Correction for ‘Electrochemical behaviour and analysis of Zn and Zn–Ni alloy anti-corrosive coatings deposited from citrate baths’ by Shams Anwar et al., RSC Adv., 2018, 8, 28861–28873, DOI: 10.1039/C8RA04650F.

The authors regret a mistake in the author names of ref. 44. The correct reference is shown below as ref. 1.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Biological behavior exploration of a paclitaxel-eluting poly-l-lactide-coated Mg–Zn–Y–Nd alloy intestinal stent in vivo

As a new type of intestinal stent, the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd alloy stent has shown good degradability, although its biocompatibility in vitro and in vivo has not been investigated in detail. In this study, its in vivo biocompatibility was evaluated by animal study. New Zealand white rabbits were implanted with degradable intestinal Mg–Zn–Y–Nd alloy stents that were exposed to different treatments. Stent degradation behavior was observed both macroscopically and using a scanning electron microscope (SEM). Energy dispersion spectrum (EDS) and histological observations were performed to investigate stent biological safety. Macroscopic analysis showed that the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd stents could not be located 12 days after implantation. SEM observations showed that corrosion degree of the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd stents implanted in rabbits was significantly lower than that in the PLLA/Mg–Zn–Y–Nd stent group. Both histopathological testing and serological analysis of in vivo biocompatibility demonstrated that the MAO/PLLA/paclitaxel/Mg–Zn–Y–Nd alloy stents could significantly inhibit intestinal tissue proliferation compared to the PLLA/Mg–Zn–Y–Nd alloy stents, thus providing the basis for designing excellent biodegradable drug stents.

Mg–Zn–Y–Nd alloy stents coated with MAO/PLLA/paclitaxel coating were implanted into the New Zealand rabbits intestine to investigate the biocompatibility and degradation behavior.     

Crack resistance of a noble green hydrophobic antimicrobial sealing coating film against environmental corrosion applied on the steel–cement interface for power insulators

Due to their great load-bearing capabilities, steel–cement interface structures are commonly employed in construction projects, and power utilities including electric insulators. The service life of the steel–cement interface is always decreasing owing to fracture propagation in the cement helped by steel corrosion. In this paper, a noble crack-resistant solution for steel–cement interfaces utilized in hostile outdoor environments is proposed. A Ce-rich, homogeneous, and thick hydrophobic sealing coating (HSC) is developed on the steel–cement interface after 60 minutes of immersion in a 60 000 ppm CeCl₃·7H₂O sealing coating solution. The specimens treated with optimized HSC film demonstrate fissure filling, lowest corrosion current (I_corr) 2.3 × 10⁻⁷ A cm⁻², maximum hardness (109 Hv), oxide-jacking resistance (40 years), hydrophobic characteristics, carbonation resistance, and bacterial corrosion resistance, resulting in a crack-free steel–cement interface. This work will pave the way for a new branch of environmentally acceptable coatings for the construction and power industries.

Due to their great load-bearing capabilities, steel–cement interface structures are commonly employed in construction projects, and power utilities including electric insulators.     

Microstructural characterization and film-forming mechanism of a phosphate chemical conversion ceramic coating prepared on the surface of 2A12 aluminum alloy

Phosphate chemical conversion (PCC) ceramic coatings on the surface of 2A12 aluminum alloy substrate have been fabricated by a simple and inexpensive chemical conversion process in CrO₃–NaF–H₃PO₄ solution. Microstructure characterization showed that the average diameter of micro-pores and the thickness of the PCC ceramic coating were about 50 nm and 4 μm, respectively, and the ceramic coating was compact and uniform when the conversion time was 60 min. Meanwhile, we found that the PCC ceramic coating mainly consisted of AlPO₄, AlOOH, AlF₃, and a few amorphous phases (CrPO₄ and CrOOH) via EDS, XRD, XPS analyses. TG-DSC results indicated that the PCC ceramic coatings had excellent thermal stability. Significantly, the adhesion strength (178.55 N) between the PCC ceramic coatings and 2A12 Al substrate was remarkably improved owing to the strong chemical bond between the PCC ceramic coating and 2A12 Al substrate and the increase of surface roughness. Furthermore, a lower corrosion current density (1.382 × 10⁻⁷ A cm⁻²) and a higher corrosion inhibition efficiency (99.91%) confirmed that PCC ceramic coatings had fantastic corrosion resistance because of the presence of crystalline AlPO₄/AlF₃/AlOOH and amorphous CrPO₄/CrOOH as a barrier layer. Additionally, a possible film-forming mechanism of the PCC ceramic coating was proposed during the chemical conversion process, which could be divided into four stages: dissolution of 2A12 aluminum substrate and hydrogen evolution; crystallization of insoluble phosphates and formation of an amorphous phase; growth of insoluble phosphates and dissolution of PCC ceramic coatings; growth and dissolution of PCC coatings to dynamic equilibrium.

Phosphate chemical conversion (PCC) ceramic coatings on the surface of 2A12 aluminum alloy substrate have been fabricated by a simple and inexpensive chemical conversion process in CrO₃–NaF–H₃PO₄ solution.     

An electrochemical study of pH influences on corrosion and passivation for a Q235 carbon steel in HNO3–NaNO2, HAc–NaNO2 and HCl–NaNO2 solutions

In this study, the influences of different pH values on the corrosion and passivation behaviors of a Q235 carbon steel in HNO₃–NaNO₂, HAc–NaNO₂ and HCl–NaNO₂ solutions were studied by electrochemical methods. The manifestations of the electrochemical characteristics were revealed and the variations in the electrochemical parameters were clarified. Moreover, for the Q235 steel in the three solutions with different pH values, the decrease in the corrosion current density (i_corr) and the increase in the charge transfer resistance (R_ct) in each solution, indicated a decrease in the corrosion rate. The decrease in the critical passivation current density (i_crit) and increase in the passive film resistance (R_f) suggested the reinforcement of passivation capability. On the other hand, in the three solutions at the same pH value, the corrosion rate increased and the passivation capability weakened in HNO₃–NaNO₂, HAc–NaNO₂ and HCl–NaNO₂ solutions. Simultaneously, the related electrochemical mechanisms of corrosion and passivation for Q235 carbon steel in acidic solutions containing nitrite anions (NO₂⁻) were also discussed.

In this study, the influences of different pH values on the corrosion and passivation behaviors of a Q235 carbon steel in HNO₃–NaNO₂, HAc–NaNO₂ and HCl–NaNO₂ solutions were studied by electrochemical methods.     

Removal of metallic coatings from rare-earth permanent magnets by solutions of bromine in organic solvents

Successful direct recycling routes are known for both Nd–Fe–B permanent magnets and Sm–Co permanent magnets. Often the magnets are coated by a nickel–copper–nickel coating to prevent corrosion of Nd–Fe–B magnets and chipping of Sm–Co magnets. However, this coating does not contribute to the magnetic properties and only ends up as a contamination in the recycled magnet powder, which in turn dilutes the magnet alloy and reduces the magnetic performance. One solution is the addition of virgin magnet alloy to the recycled powder, but this is not the best option from a sustainable point of view. Another option is to remove the coating prior to the magnet recycling. We developed a solvometallurgical process for removal of the metallic coating prior to direct recycling. In particular, a mixture of bromine in organic solvents was found to be very selective in the removal of the nickel–copper–nickel coating from both Nd–Fe–B permanent magnets and Sm–Co permanent magnets, without codissolution of the magnet alloy.

Rare-earth permanent magnets were treated with Br₂ in organic solvents to remove the Ni–Cu–Ni coating prior to direct magnet recycling by hydrogen decrepitation.     

Corrosion and biocompatibility behaviours of microarc oxidation/phytic acid coated magnesium alloy clips for use in cholecystectomy in a rabbit model

With the popularisation of laparoscopic cholecystectomy, ligation clips have been commonly used for ligating the cystic duct and cystic artery. However, non-degradable clips remain in the body long-term, which significantly increases the risk of the clip becoming detached. Thus, magnesium alloys have attracted tremendous attention owing to their biodegradability and good biocompatibility. However, the poor corrosion resistance hinders the clinical application of magnesium alloys with microarc oxidation/phytic acid (MAO/PA) composite coatings as protective coatings. Here, these alloys were used to hinder the rapid material degradation in aqueous solution. Electrochemical tests were conducted to evaluate the in vivo degradation behaviour in simulated body fluid (SBF) for Mg–Zn–Y–Nd alloys, and scanning electron microscopy (SEM) was used to observe the micromorphology of in vivo clip degradation. Cell toxicity, cell adhesion, and flow cytometry were performed in vitro to detect cytocompatibility. Biochemical detection of serum magnesium, serum creatinine (CREA), blood urea nitrogen (BUN), alanine transaminase (ALT), and alanine aminotransferase (AST), and haematoxylin–eosin (HE) staining of the heart, liver, and kidney tissues in vivo was conducted to determine the biocompatibility properties after surgery. Electrochemical measurements and SEM images revealed that the MAO/PA-coated magnesium alloy delayed corrosion in SBF. The apoptosis rate increased slightly with increased extract concentration. Nevertheless, MAO/PA-coated magnesium alloys still exhibited good cytocompatibility. No obvious abnormality was observed in the blood biochemical test or HE staining. Thus, MAO/PA-coated magnesium alloys exhibit better corrosion than bare magnesium. In addition, Mg–Zn–Y–Nd and MAO/PA-coated magnesium alloys exhibited no cytotoxicity, good adhesion, and biosafety.

Mg alloys with microarc oxidation/phytic acid composite coatings were tested as degradable ligation clips for ligating the cystic duct and cystic artery.     

Zinc–iron silicate for heterogeneous catalytic ozonation of acrylic acid: efficiency and mechanism

This research aimed at researching the degradation of acrylic acid (AA) in aqueous solution, by catalytic and non-catalytic ozonation processes performed in a semi-continuous reactor. Zinc–iron silicate was synthesized and characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) analysis, Fourier transformation infrared (FT-IR) and energy dispersive spectrometry (EDS). The characterization studies showed that Fe–Si binary oxide, Zn–Si binary oxide, ZnO and Fe₂O₃ deposits were formed on the surface of poor crystallinity zinc–iron silicate which contained abundant functional groups. Catalytic ozonation test results revealed that zinc–iron silicate exhibited high catalytic activity and stability in catalytic ozonation of AA in aqueous solution. The inclusion of zinc–iron silicate in the ozonation process enhanced AA decomposition by 28.7% and TOC removal by 20%, compared to the ozonation alone. The main AA removal mechanisms involved direct oxidation by ozone and indirect oxidation by hydroxyl radicals generated by the ozone chain reaction accelerated by zinc–iron silicate. The surface characteristics and chemical composition are significant factors determining the catalytic activity of zinc–iron silicate.

Zinc–iron silicate was synthesized, and exhibited high activity and stability for catalytic ozonation under semi-continuous conditions.     

Microstructure,friction and corrosion resistance properties of a Ni–Co–Al2O3 composite coating

Ni–Co–Al₂O₃ composite coatings were prepared by pulsed electrodeposition and electrophoresis–electrodeposition on aluminum alloy. The content of Al₂O₃ particles of the Ni–Co–Al₂O₃ composite coating prepared by electrophoresis–electrodeposition was significantly higher than the composite coating prepared by pulsed electrodeposition. The composite coating prepared by electrophoresis–electrodeposition exhibited a better anti-wear performance than that prepared by pulsed electrodeposition. The morphology, composition and microstructure of the composite coatings were determined by means of X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The hardness and friction properties of the samples were tested on the microhardness tester and the friction and wear loss tester respectively.

Ni–Co–Al₂O₃ composite coatings were prepared by pulsed electrodeposition and electrophoresis–electrodeposition on aluminum alloy.     

Composite protective effect of benzotriazole and 2-mercaptobenzothiazole on electroplated copper coating

Benzotriazole (BTAH) and 2-mercaptobenzothiazole (MBT) are mixed to passivate electroplated copper coatings. The growth process of passive films is comprehensively analyzed from the surface potential, microstructure and chemical composition by potential–time curve, FESEM and XPS. Meanwhile, the corrosion resistance of copper coatings with different passivation treatments is evaluated by potentiodynamic polarization curves and electrochemical impedance spectroscopy. During the composite passivation process of BTAH and MBT, the copper coating undergoes the following steps: chemical dissolution of the copper coating, preferential adsorption of MBT, formation of Cu(i)–BTA complex film and Cu₂O, and synergistic growth of Cu(i)–BTA and Cu(i)–MBT. A protective film with a thickness of about 233 nm, containing the inner layer of BTA–Cu(i) and MBT–Cu(i) and the outer layer of MBT–Cu(i) and Cu₂O, is formed on the copper coating after composite passivation. The composite passivation film significantly improves the corrosion resistance of copper coatings, and its corrosion inhibition efficiency for copper coatings reaches 90.7%, which is far better than that produced by using BTAH or MBT alone.

Benzotriazole (BTAH) and 2-mercaptobenzothiazole (MBT) are mixed to passivate electroplated copper coatings.     

Wear and corrosion resistance of Co–P coatings: the effects of current modes

In this work, Co–P coatings were deposited from a chloride-based bath by direct current (DC), pulse current (PC) and pulse reverse current (PRC) methods, respectively. The effects of current modes on the microstructure, composition, microhardness, wear resistance and corrosion resistance of the Co–P coatings were explored. Results showed that the P content in the Co–P coatings increased and the surface roughness decreased in the sequence of DC, PC and PRC methods. The coatings with low P content deposited by DC and PC methods are crystalline with fcc and hcp structures, respectively, while the coating with high P content deposited by the PRC method is amorphous. Comparing to DC and PC methods, the PRC method can evidently improve the microhardness, wear resistance and corrosion resistance of Co–P coatings. The excellent wear and corrosion resistance of the Co–P coatings deposited by the PRC method could be attributed to its high P content, smooth surface and amorphous structure.

The P content in the Co–P coatings increased in the sequence of DC, PC and PRC methods. The PRC Co–P coating has better wear and corrosion resistance than DC and PC Co–P coatings.     

Synthesis of MOFs/GO composite for corrosion resistance application on carbon steel

Two unreported metal–organic frameworks [Cu(6-Me-2,3-pydc)(1,10-phen)·7H₂O]_n (namely Cu-MOF) and [Mn₂(2,2′-bca)₂(H₂O)₂]_n (namely Mn-MOF) were synthesized by a solvothermal method and their structures were characterized and confirmed by elemental analysis, X-ray single crystal diffraction, Fourier infrared spectroscopy and thermogravimetric analysis. Cu-MOF/graphene (Cu-MOF/GR), Cu-MOF/graphene oxide (Cu-MOF/GO), Mn-MOF/graphene (Mn-MOF/GR) and Mn-MOF/graphene oxide (Mn-MOF/GO) composite materials were successfully synthesized by a solvothermal method and characterized and analyzed by PXRD, SEM and TEM. In order to study the corrosion inhibition properties of the Cu-MOF/GR, Cu-MOF/GO, Mn-MOF/GR and Mn-MOF/GO composite materials on carbon steel, they were mixed with waterborne acrylic varnish to prepare a series of composite coatings to explore in 3.5 wt% NaCl solution by electrochemical measurements and results showed that the total polarization resistance of the 3% Cu-MOF/GO and 3% Mn-MOF/GO composite coatings on the carbon steel surface were relatively large, and were 55 097 and 55 729 Ω cm², respectively, which could effectively protect the carbon steel from corrosion. After immersion for 30 days, the 3% Mn-MOF/GO composite still maintained high corrosion resistance, the |Z| values were still as high as 23 804 Ω cm². Therefore, MOFs compounded with GO can produce a synergistic corrosion inhibition effect and improve the corrosion resistance of the coating; this conclusion is well confirmed by the adhesion capability test.

Two unreported metal–organic frameworks [Cu(6-Me-2,3-pydc)(1,10-phen)·7H₂O]_n (namely Cu-MOF) and [Mn₂(2,2′-bca)₂(H₂O)₂]_n (namely Mn-MOF) were synthesized and characterized. Cu-MOF and Mn-MOF all can form a three-dimensional structure.     

Synthesis and characterization of polyaniline–hydrotalcite–graphene oxide composite and application in polyurethane coating

In this paper, a composite from polyaniline and graphene oxide-hydrotalcite hybrid (PAN–HG) was fabricated by direct polymerization of aniline using ammonium persulphate as an oxidant in the presence of a HG hybrid. The structure and morphological properties of synthesized PAN–HG composites were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectra, and scanning electron microscopy (SEM) techniques. The electrochemical properties of the composite particles were also analyzed by potentiodynamic polarization curves to evaluate the corrosion inhabitation. The results were calculated by Tafel fitting and showed that the effective corrosion protection values were 73.11%, 88.46%, and 95.49%, corresponding to HG, 1PAN–HG, and 2PAN–HG. The influence of PAN–HG on the corrosion protection of the polyurethane coating applied on the CT3 steel was investigated. As a result, the PU containing 0.5% of 2PAN–HG showed the most effective protection of the CT3 steel substrate. The R_C of the coating was about 1.61 × 10⁷ Ω cm², and after immersion for 30 days, the R_C value was 0.17 × 10⁶ Ω cm². From all the analyzed results, PAN–HG has enhanced the corrosion protection and a complicated protection mechanism was also concluded and explained.

Corrosion protection: PAN–HG performed effect of 95.49% protection of CT3-steel in NaCl 3.5%. PU(PAN–HG) coating provides good corrosion protection with complex mechanism of high barrier, ion-exchange and e⁻ trapping to HG structure.     

Novel green manufacture of metallic aluminum coatings on carbon steel by sol–gel method

Industrial processes for fabricating hot-dipping aluminum coatings on carbon steels involve problems related to equipment complexity, environmental issues and high energy consumption. To address these problems, a novel method for manufacturing metallic aluminum coating on carbon steel Q235 at room temperature by sol–gel method was developed in this work. Both the single-layer coating (47 μm) and the double-layer coating (97 μm) specimens were prepared by spraying some aqueous silica sol slurries containing spherical and flaky micro metallic aluminum powders on the steel surface at room temperature and then drying them at 50 °C. When the two coating specimens were heated at 500 °C for 10 h, heated double-layer specimens were thus obtained. It was found that the double-layer and the heated double-layer specimens didn''t rust at all after being soaked in aerated 3.5 wt% NaCl for 30 days. The shielding effect of the compact top coating was the main anticorrosion mechanism of the double-layer coating based on some electrochemical impedence spectroscopies and potentiodynamic polarization curves. Both coatings comprised only one metallic Al phase based on XRD. A very small quantity of Al₂O₃ phase appeared only after heating both coating specimens at 500 °C in the air for 10 h. In both cases the coatings didn''t crack at all after being heated at 500 °C in the air for 15 h by SEM observation and the oxidation rates of the steel substrates under these conditions were reduced by over 72% owing to the presence of the coatings. The average adhesive strengths of the single-layer and double-layer Al coatings were 12.06 MPa and 11.23 MPa, respectively, which were much larger than the corresponding value (max 8 MPa) of an ordinary anti-rusting epoxy coating on Q235 steel. Compared to the conventional hot-dipping aluminum or aluminized process, this novel method eliminates all the high temperature processes and thus saves a lot of energy, eliminates the use of all hazardous fluorides or chlorides and explosive H₂, avoids the formation of the voids inside aluminized coating, reduces the hot-dipped Al coating defects, can be applied for the steel plates with over 0.8 mm thickness, and can be applied in situ to repair damaged Al or Zn coatings.

The novel double-layer specimen of Al coating had the ability to resist simulated seawater corrosion for 30 days and air oxidation at 500 °C for 15 h.     

Corrosion behaviour of micro-arc oxidation coatings on Mg–2Sr prepared in poly(ethylene glycol)-incorporated electrolytes

Microarc oxidized calcium phosphate (CaP) ceramic coatings were fabricated on Mg–2Sr alloy from silicate electrolytes with different concentration gradient poly(ethylene glycol) (PEG₁₀₀₀). The microstructure, phase and degradability of the ceramic coatings were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and simulation body fluid (SBF) immersion tests respectively. An electrochemical workstation was used to investigate the electrochemical corrosion properties of the coatings. It is found that microstructure, thickness, adhesive strength and degradation rate are influenced by PEG₁₀₀₀ incorporation through adjusting the electrolyte activity and then altering the coating growth mechanism. Similar thicknesses (39.0–42.2 μm) are observed in PEG₁₀₀₀-containing coatings while their PEG₁₀₀₀-free counterparts possess the maximum value (51.5 μm). The weight gain in the first two days of SBF immersion suggests that a new layer containing CaP apatites is generated. Results show that ceramic coatings prepared in the electrolyte containing 8 g L⁻¹ PEG₁₀₀₀ exhibits the highest corrosion resistance and lowest degradation rate.

The highest corrosion resistance and lowest biodegradation are observed on the ceramic coating prepared in electrolytes containing 8 g L⁻¹ PEG₁₀₀₀.     

Corrosion resistance of Ni–P/SiC and Ni–P composite coatings prepared by magnetic field-enhanced jet electrodeposition

To extend the working life of 45# steel, Ni–P and Ni–P/SiC composite coatings were prepared on its surface by magnetic field-enhanced jet electrodeposition. This study investigated the effect of magnetic field on the corrosion resistance of Ni–P and Ni–P/SiC composite coatings prepared by conventional jet electrodeposition. The surface and cross-sectional morphologies, microstructure, and composition of the composite coatings were determined by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD), respectively. The corrosion resistance was studied using a LEXT4100 laser confocal microscope. The introduction of a stable magnetic field was found to improve the surface morphology of the coatings, increase the growth rate, and reduce the agglomeration of nano-SiC (3 g L⁻¹, 40 nm) particles, thus significantly improving the corrosion resistance of the coatings. The corrosion potential of the Ni–P coating increased from −0.78 V (0 T) to −0.46 V (0.5 T), and the corrosion current density decreased from 9.56 × 10⁻⁶ A dm⁻² (0 T) to 4.31 × 10⁻⁶ A dm⁻² (0.5 T). The corrosion potential of the Ni–P/SiC coating increased from −0.59 V (0 T) to −0.28 V (0.5 T), and the corrosion current density decreased from 6.01 × 10⁻⁶ A dm⁻² (0 T) to 2.90 × 10⁻⁶ A dm⁻² (0.5 T).

We investigated the effect of magnetic field on Ni–P and Ni–P/SiC composite coatings prepared by jet electrodeposition.     

The corrosion behavior of 304 stainless steel in NaNO3–NaCl–NaF molten salt and vapor

Corrosion behavior of 304 stainless steel in molten NaNO₃–NaCl–NaF salt and NaNO₃–NaCl–NaF vapor has been studied at 450 °C. The results showed that the samples suffered weight loss, and surface oxides, i.e. Fe₂O₃ and FeCr₂O₄ characterized by XRD, were formed after corrosion. The surface oxide layer was about 1.1 μm in thickness after corrosion in molten NaNO₃–NaCl–NaF salt, which was relatively homogeneous and dense. Whereas, the distribution of surface oxides was not even, and a shedding phenomenon was observed after corrosion molten NaNO₃–NaCl–NaF vapor. This is mainly attributed to the existence of NO₂ and NO in the molten NaNO₃–NaCl–NaF vapor determined by thermogravimetric infrared spectroscopy, which affected the adherence between oxides and the matrix. Additionally, the corrosion rate of 304 stainless steel in molten NaNO₃–NaCl–NaF salt is almost close to that in solar salt, which demonstrates that the synergy influence of Cl⁻ and F⁻ on the rate of 304 stainless steel is not significant. This work not only enriches the database of molten salt corrosion, but provides references for the selection of alloy and molten salt in the CSP.

Surface micro-morphology of 304 SS before corrosion (a), after corrosion in molten NaNO₃–NaCl–NaF salt (b) and molten NaNO₃–NaCl–NaF vapor (c). (Local enlarged region of A1 (b-1), A2 (c-1) and A3 (c-2)).