Development of Prosopis juliflora carbon-reinforced PET bottle waste-based epoxy-blended bio-phenolic benzoxazine composites for advanced applications

An attempt has been made in the present work to develop hybrid blended composites using epoxy resin (PETEP) derived from waste polyethylene terephthalate (PET) bottles and bio-phenolic (cardanol)-based benzoxazine (CBz) reinforced with functionalized bio-carbon (f-PJC) obtained from Prosopis juliflora (PJ) for high performance applications. The molecular structure, thermal properties, thermo-mechanical behaviour, morphology, surface properties, and corrosion resistance of the composites were studied by different analytical methods, and the obtained results are reported. Dynamic mechanical properties such as the storage modulus (2.591 GPa), loss modulus (1.299 GPa) and cross-linking density (5.1 × 10⁷ J mol⁻¹ K⁻¹) were improved in the case of the 5 wt% f-PJC/PETEP–CBz composite compared to those of the PETEP–CBz blended matrix and the f-PJC/PETEP–CBz composites with other weight percentages. Among the studied bio-carbon-reinforced hybrid composites with different weight percentages, the 5 wt% f-PJC/PETEP–CBz composite shows a higher value of char yield (38.37%), with an enhanced glass transition temperature of 285 °C and an improved water contact angle of 111.3°. Results obtained from corrosion studies infer that these hybrid composites exhibit improved corrosion resistance behaviour and effectively protect the surface of mild steel specimens from corrosion. It is concluded that the present work can be considered as an effective method for utilizing waste products and sustainable bio-materials for the development of high performance value-added hybrid composites for thermal and corrosion protection applications.

Schematic representation of development of functionalised Prosopis juliflora carbon (f-PJC) reinforced PET-epoxy resin (PETEP) blended bio-phenolic (cardanol) based benzoxazine (CBz) hybrid composites for high performance applications.     

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.     

Synergistically assembled graphene/ZnO composite to enhance anticorrosion performance of waterborne epoxy coatings

In this work, waterborne epoxy resin and graphene/ZnO (Gr/ZnO) were employed as the matrix and nanofiller to construct composite coatings with enhanced anticorrosive performance. The corrosion protection properties of the coatings were significantly improved by the dispersed Gr sheets, as well as the parallelly assembled ZnO nanoparticles. The most remarkable improvement was achieved by adding 0.04 wt% of Gr and 0.4 wt% of ZnO in the Waterborne Epoxy (WEP) coatings, where the highest impedance was 200 530 Ω cm² on Gr_0.04–ZnO_0.4, far more than pure epoxy with 6186 Ω cm² after 7 days of immersion in electrolytes. Furthermore, the Gr_0.04–ZnO_0.4 coatings and corresponding corrosion products immersed in a 3.5% NaCl solution for 30 days were also characterized, which could further reveal anticorrosion mechanisms of the graphene modified WEP coatings and the passivated effect of ZnO. Through the mechanism analysis, we also found that ZnO could be employed as the barrier reinforcement to improve the dispersibility of graphene in WEP coatings, and the parallel assembly of graphene occurs spontaneously, leading to remarkable improvement of anticorrosion properties.

This is the first example of synergistically assembled Gr/ZnO sheets to improve the corrosion protection properties of WEP coatings, and Gr_0.04–ZnO_0.4 exhibited the highest impedance of 200 530 Ω cm² compared to pure WEP of 6186 Ω cm².     

The corrosion resistance,cytotoxicity, and antibacterial properties of lysozyme coatings on orthodontic composite arch wires

Objective: The corrosion resistance of new orthodontic composite arch wires (CAWs), which have excellent mechanical properties in a simulated oral environment, must be improved. This study explored the susceptibility to corrosion, in vitro cytotoxicity, and antibacterial properties of lysozyme-coated CAWs. Methods: Lysozyme coating of laser-welded CAW surfaces was prepared by liquid phase deposition. Four groups of CAW specimens were prepared: uncoated CAWs and CAWs coated with 20, 40, and 60 g L⁻¹ lysozyme. The surface morphology of the lysozyme coatings was characterized by atomic force microscopy. The samples were immersed in artificial saliva (AS) for 2 weeks, and corrosion morphology was then observed by scanning electron microscopy. Corrosion behavior was characterized according to weight loss and electrochemical properties. The cytotoxicity and antibacterial properties of lysozyme-coated CAWs were assessed by cell counting kit-8 assay and a live/dead bacterial test, respectively. Results: Surfaces in the three lysozyme coating groups exhibited film-like deposition, the thickness of which increased with the lysozyme concentration. Surface pitting and copper ion precipitation decreased with increasing lysozyme concentration in coatings. The corrosion tendency declined as the corrosion and pitting potentials decreased. The corrosion morphology and electrochemical parameters together indicated that lysozyme coatings increased corrosion resistance. The coatings also reduced cytotoxicity to L-929 cells and increased anti-Staphylococcus aureus ability. Conclusions: Lysozyme coating of CAW surfaces by liquid phase deposition improved the corrosion resistance of CAWs. The protective coatings improved biocompatibility and endowed the CAW surfaces with certain degrees of anti-Staphylococcus aureus activity. Different lysozyme concentrations had different protective effects, with 40 g L⁻¹ maybe being the ideal lysozyme concentration for CAW coatings.

The corrosion resistance of new orthodontic composite arch wires (CAWs), which have excellent mechanical properties in a simulated oral environment, must be improved.     

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

Anticorrosive coatings are a useful approach for protecting steel structures/machinery against corrosion. Electrodepositions of zinc and zinc–nickel alloy films on steel substrates under various conditions from baths containing potassium citrate were studied. The effects of electroplating variables such as bath composition and current density on the coating composition, morphology, corrosion and mechanical properties were systematically investigated. The electrochemical and mechanical behaviour of Zn–Ni deposits obtained at 60 mA cm⁻² from the citrate bath exhibited a lower corrosion current (I_corr) and a less negative corrosion potential (E_corr) compared to pure Zn and Zn–Ni alloy coatings from the non-citrate bath. The crystallite size of the Zn–Ni coating deposited from the citrate bath was 35.40 nm, and the Ni content of the coating was 8.3 wt%. The morphological properties and crystalline phase structure of the alloy coating were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The topographical structure of the coatings was analyzed by atomic force microscopy (AFM). The dominant γ-NiZn₃ (815) and γ-Ni₂Zn₁₁ (330) (631) plane orientations in the zinc–nickel alloy films improved the corrosion resistance. Zn–Ni films with smaller grain size and uniform coating had an increased impedance modulus and improved corrosion resistance.

Anticorrosive coatings are a useful approach for protecting steel structures/machinery against corrosion.     

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.     

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.     

Effect of interlayer design on friction and wear behaviors of CrAlSiN coating under high load in seawater

In this paper, CrAlSiN coatings with different interlayer designs (without interlayer, Cr interlayer, CrN interlayer and Cr/CrN interlayer) were successfully obtained on 316L stainless steel and single crystal silicon by multi-arc ion plating technique. Coating microstructure, mechanical, anticorrosion and tribological behaviors in artificial seawater were systematically investigated by XRD, SEM, XPS, TEM, nanoindentation, electrochemical workstation and frictional tester system. Results showed that the CrAlSiN layer presented a typical nanocrystalline/amorphous structure, which consisted of CrN, AlN and Si₃N₄ phases. The Cr/CrN interlayer could obviously improve the adhesion, hardness and toughness of CrAlSiN coating. Compared with single CrAlSiN coating, the corrosion current density of Cr/CrN/CrAlSiN coating system was improved by 2 orders of magnitude and its inhibition efficiency was up to 98.82%. Under high applied load (15 N) condition, the CrAlSiN coating with Cr/CrN interlayer revealed the lowest COF (0.107 ± 0.009) and wear rate (7.3 × 10⁻⁸ ± 8.4 × 10⁻⁹ mm³ N⁻¹ m⁻¹) in seawater, which primarily attributed to the synergistic effect of ideal adhesion force, outstanding toughness and effectively barrier ability.

In this paper, CrAlSiN coatings with different interlayers (without interlayer, Cr interlayer, CrN interlayer and Cr/CrN interlayer) were successfully obtained on 316L stainless steel and single crystal silicon by multi-arc ion plating technique.     

Silane coatings modified with hydroxyapatite nanoparticles to enhance the biocompatibility and corrosion resistance of a magnesium alloy

The fast corrosion rate of magnesium alloys has restricted their use as biodegradable implants. Hence developing a practical approach to retard the corrosion rate of the AZ31 magnesium alloy, as well as promoting cell adhesion and proliferation is of great importance. Silane coatings were applied through dip coating, on samples pretreated in hydrofluoric acid. Samples were immersed in simulated body fluid at 37 °C, and the coating performance was assessed by electrochemical impedance spectroscopy. The coating morphologies of samples were investigated through field emission scanning electron microscopy and a cell viability/proliferation (MTT) test was performed to evaluate cellular response. A 2.2 μm-thick coating was accomplished, which increased the corrosion resistance to three orders of magnitude higher than that of the bare sample. Hydroxyapatite nanoparticles were added to the silane coating to improve biocompatibility and facilitate bone formation. Changing the concentration of hydroxyapatite nanoparticles not only helped to optimize the barrier properties of the silane coating but also ameliorated MG-63 osteoblastic cell growth. The findings showed great promise to enhance and maintain the corrosion barrier property and induce high osteoblastic differentiation by employing 1000 mg L⁻¹ of hydroxyapatite nanoparticles.

Incorporation of hydroxyapatite nanoparticles in silane coatings improves both corrosion resistance and cell viability on magnesium AZ31 implants.     

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.     

Preparation of epoxy/ZrO2 composite coating on the Q235 surface by electrostatic spraying and its corrosion resistance in 3.5% NaCl solution

The epoxy coating containing ZrO₂ nanoparticles modified with 3-aminopropyltriethoxysilane (APTES) was prepared by electrostatic spraying on the surface of Q235 mild steel. The effect of the concentration of APTES-modified ZrO₂ nanoparticles on the corrosion resistance of epoxy coating was characterized and tested by FTIR spectroscopy, scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The results show that nano ZrO₂ was successfully modified by a silane coupling agent. By adding an appropriate amount of APTES to modify nano ZrO₂ in epoxy coating could significantly improve the corrosion resistance of the Q235 surface. When the mass fraction of nano ZrO₂ is 2%, the composite coating shows the highest impedance value of about 1.0 × 10⁵ Ω cm² to achieve the best corrosion resistance.

Epoxy/ZrO₂ composite coating was prepared by electrostatic spraying. The best corrosion resistance in 3.5% NaCl solution was observed using 2 wt% ZrO₂.     

Performance evaluation of mercapto functional hybrid silica sol–gel coating and its synergistic effect with f-GNs for corrosion protection of copper surface

A nanocomposite coating comprising mercapto functional hybrid silica sol–gel coating and functionalized graphene nanoplates nanocomposite coatings with advanced anticorrosive properties was prepared by a sol–gel method. In this study, graphene oxide (GO) nanoplates were silanized using 3-aminopropyltriethoxysilane (APTES) to obtain functional graphene nanoplates (f-GNs). The f-GNs were characterized by FTIR, XRD, XPS, TEM, AFM and TGA techniques. The functionalized graphene nanoplates were chemically bonded to a sol–gel matrix and showed good dispersion in the sol. Then, silica hybrid sol–gel nanocomposites with raw GO and different amounts of f-GNs were applied on the copper surface. Uniform, defect-free and adherent sol–gel films were obtained. Various corresponding methods were used to investigate the nanocomposite coating''s properties. The corrosion resistance of copper significantly improved after being coated with mercapto functional hybrid silica sol–gel. The addition of f-GNs to the mercapto functional silica sol–gel coatings further improved the corrosion resistance due to a synergistic effect. Moreover, with an increase in the amount of f-GNs in the nanocomposite coating, the nanocomposite showed improved corrosion resistance. The nanocomposite containing 0.1 wt% f-GNs can efficiently protect the copper substrate from corrosion. This improvement was primarily attributed to the homogeneous dispersion of the f-GNs in the silica gel matrix and their effective barrier against corrosive molecules and ions. However, adding raw GO or excess f-GNs to the silica hybrid sol–gel coating had a negative effect on the corrosion resistance.

An anticorrosion coating on copper consisting of mercapto functional hybrid silica sol–gel and f-GNs nanoplates with a synergistic effect was prepared.     

Different graphene layers to enhance or prevent corrosion of polycrystalline copper

Graphene was used as an anticorrosive coating for metals as it can effectively isolate the corrosion factors such as oxygen. However, we found that the anticorrosive and corrosive effects on metal surface were related to graphene layers and metal crystal faces. In this paper, we found that different layers of graphene had significantly different effects on the corrosion of polycrystalline copper during long-term storage under atmospheric conditions. Optical images and Raman spectra showed that single layer graphene (SLG)-coated copper had a higher degree of corrosion than bare copper. However, when covered with CVD in situ-grown bilayer graphene (BLG), the copper foil was effectively prevented from being etched as it exhibited a bright yellow color despite the differences in crystal faces. The surface potential differences measured by an electric force microscope (EFM) showed that a contact potential difference (V_CPD) between 30 and 40 mV existed between Cu/SLG and bare copper. The SLG-coated areas had a higher surface potential (SP), which meant that the (SLG)-coated copper was more prone to lose electrons to exhibit galvanic corrosion. The BLG coating made SP of underlying copper lower making it harder to lose electrons; thus, BLG successfully protected the copper from being corroded. These findings have a foreseeable significance for graphene as a metal anti-corrosion coating.

The degree of corrosion depends on the crystal faces and number of graphene layers, whereas BLG can be used as an anticorrosion coating.     

Synthesis and characterization of new polyimides from diphenylpyrene dianhydride and ortho methyl substituted diamines

Three new polyimides were synthesized via one-step polycondensation from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD) with two diamines with ortho methyl substitution (MBDAM and HFI) and one diamine without ortho substituents (BAPHF). The effect of diamine structure in DPPD based polyimides'' physical, thermal, mechanical and gas transport properties has been studied. The polyimide structure was confirmed by FTIR and ¹H NMR. All polymers show high thermal stability with decomposition temperatures above 493 °C, and glass transition temperatures above 336 °C. Changes in packing density of polyimide membranes were assessed by wide angle X-ray diffraction and correlated to fractional free volume FFV. Polyimides based on rigid DPPD dianhydride exhibited an improved gas permeability and selectivity when ortho methyl substituents are present in the diamine used for polyimide synthesis. DPPD-MBDAM polyimide showed the best gas productivity values with 565 barrer CO₂ permeability and a selectivity of 16 for CO₂/CH₄.

Three new polyimides were synthesized from 3,8-diphenylpyrene-1,2,6,7-tetracarboxylic dianhydride (DPPD) with two diamines with ortho methyl substitution (MBDAM and HFI) and one diamine without ortho substituents (BAPHF).     

Anticorrosive behavior of a zinc-rich epoxy coating containing sulfonated polyaniline in 3.5% NaCl solution

An epoxy zinc-rich composite coating containing self-doped conducting sulfonated polyaniline (SPANi) nanofiber was prepared and the corrosion resistance of as-prepared coatings on Q235 substrate studied by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET). Results suggested that a zinc-rich coating with addition of 1.0 wt% SPANi could enhance the cathodic protection time and barrier performance. To study corrosion diffusion, artificial scratch and adhesion strength were investigated via the salt spray test and pull-off test, respectively. Finally, the passivating action of coatings was demonstrated by analyses of corrosion products via X-ray diffraction spectroscopy.

An epoxy zinc-rich composite coating containing self-doped conducting sulfonated polyaniline nanofiber was prepared and the corrosion resistances of as-prepared coatings on Q235 substrate was studied by OCP, EIS and SVET.     

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.     

Preparation and performance of electrically conductive Nb-doped TiO2/polyaniline bilayer coating for 316L stainless steel bipolar plates of proton-exchange membrane fuel cells

A bilayer coating composed of an inner layer of Nb-doped TiO₂ obtained by the sol–gel method and an external polyaniline layer with small SO₄²⁻ groups obtained by galvanostatic deposition was prepared to protect 316L stainless steel bipolar plates of proton-exchange membrane fuel cells. The corrosion resistances of bare 316L and 316L with single polyaniline coating and Nb-doped TiO₂/polyaniline bilayer coating were investigated. The experimental results indicated that both single and bilayer coatings increased the corrosion potential and decreased the corrosion current density compared with bare 316L stainless steel. A thirty-day exposure experiment indicated that the Nb-doped TiO₂/polyaniline bilayer showed high stability, and it protected 316L more effectively from the penetration of the corrosive ions.

A bilayer coating composed of an inner layer of Nb-doped TiO₂ and an external polyaniline layer with small SO₄²⁻ groups was prepared; the bilayer coating could protect 316L more effectively from the penetration of corrosive ions.     

Effects of thermal treatments on the hydrophobicity and anticorrosion properties of as-grown graphene coatings

Graphene grown on metal substrates has been reported to provide efficient and robust hydrophobicity during water vapor condensation on metal surfaces. However, due to the intrinsic negative coefficient of thermal expansion (CTE) of graphene, the potential thermal stress in real application environments can cause CTE mismatch and then damage the protective graphene coatings, leading to loss of surface hydrophobicity and anticorrosion properties. In this study, the effect of thermal treatments on anticorrosion properties and subsequent hydrophobicity of the graphene surface has been investigated. The as-grown graphene on nickel (Ni–Gr) is explored in terms of survival under severe thermal cycling (up to 14.62 °C s⁻¹) and effectively maintains its surface properties. As a comparison, the as-grown graphene on copper (Cu–Gr) easily peeled off from the metal surface due to the thermal stress and intercalation of oxides. The thermal treatment at 200 °C under ambient atmosphere can elevate the corrosion rate 2.2 times and 29 times on the Ni–Gr and Cu–Gr surfaces compared to situations without thermal treatments, respectively. This study shows that the Ni–Gr surface is significantly more robust than the Cu–Gr surface as a sustainable hydrophobic surface in a complicated thermal environment.

Thermal treatments can significantly affect the anticorrosion properties and the subsequent surface hydrophobicity of graphene-metal systems with varied interfacial bonds.     

Atomic oxygen effects on silvered polyimide films and their surface modification by poly(siloxane amic acid) ammonium salts

The tolerance of silvered polyimide films synthesized by an in situ self-metalization method against atomic oxygen (AO) was evaluated. The results showed that the mass loss of R–Ag/PI was markedly increased as the AO fluence increased; Ag/PI showed an identical trend. SEM data showed that the silver particles on the surfaces of R–Ag/PI and Ag/PI disappeared. The surfaces achieved a “carpet condition” that was more obvious as the AO fluence increased. Poly(siloxane amic acid) ammonium salt was synthesized and made via imidization to produce a flexible organic coating that was characterized by ATR-FTIR, ¹HNMR, TGA, and XPS. This could be used to improve the tolerance of silvered polyimide films against AO. The AO resistance and the impacts on mass loss, surface morphology, and surface compositions were also evaluated after surface modification by poly(siloxane amic acid) ammonium salts. 20 wt% Foc/Ag/PI had a lower mass loss and smoother surface than the others due to the formation of a compact surface-SiO₂-type layer. This flexible organic coating can be produced via an environmentally-friendly method, and it maintains the inherent thermal stability of the polyimide which cannot be achieved by other anti-AO coatings.

Poly(siloxane amic acid) ammonium salt with good AO resistance was synthesized, and used to protect silvered polyimide films from AO erosion.     

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.