Experimental and theoretical investigations of benzoic acid derivatives as corrosion inhibitors for AISI 316 stainless steel in hydrochloric acid medium: DFT and Monte Carlo simulations on the Fe (110) surface

The inhibition efficiency of benzoic acid (C1), para-hydroxybenzoic acid (C2), and 3,4-dihydroxybenzoic acid (C3) towards enhancing the corrosion resistance of austenitic AISI 316 stainless steel (SS) has been evaluated in 0.5 M HCl using weight loss (WL), open circuit potential (OCP), potentiodynamic polarization method, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) analysis. The results obtained from the different experimental techniques were consistent and showed that the inhibition efficiency of these inhibitors increased with the increase in concentration in this order C3 > C2 > C1. In addition, the results of the weight loss measurements showed that these inhibitors followed the Villamil isotherm. Quantum chemical calculations and Monte Carlo simulations have also been used for further insight into the adsorption mechanism of the inhibitor molecules on Fe (110). The quantum chemical parameters have been calculated by density functional theory (DFT) at the B3LYP level of theory with 6-31G+(2d,p) and 6-31G++(2d,p) basis sets in gas and aqueous phase. Parameters such as the lowest unoccupied (E_LUMO) and highest occupied (E_HOMO) molecular orbital energies, energy gap (ΔE), chemical hardness (η), softness (σ), electronegativity (χ), electrophilicity (ω), and nucleophilicity (ε) were calculated and showed the anti-corrosive properties of C1, C2 and C3. Moreover, theoretical vibrational spectra were calculated to exhibit the functional hydroxyl groups (OH) in the studied compounds. In agreement with the experimental data, the theoretical results showed that the order of inhibition efficiency was C3 > C2 > C1.

The corrosion inhibition efficiencies of benzoic acid (C1), para-hydroxybenzoic acid (C2), and 3,4-dihydroxybenzoic acid (C3) have been evaluated in 0.5 M HCl toward protecting AISI 316 stainless steel (SS).     

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.     

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.     

Understanding the adsorption performance of two glycine derivatives as novel and environmentally safe anti-corrosion agents for copper in chloride solutions: experimental,DFT, and MC studies

The inhibition impacts of two non-toxic glycine derivatives, namely, bicine (N,N-bis(2-hydroxyethyl)glycine) and tricine (N-(tri(hydroxymethyl)methyl) glycine) on copper corrosion were investigated in 3.5% NaCl solutions. Surprisingly, there is no report on using bicine and/or tricine as corrosion inhibitors for Cu and its alloys in a seawater-like environment. The effects of bicine and tricine on the corrosion behavior of Cu in 3.5% NaCl were examined using the open circuit potential, Tafel polarization, and AC spectroscopy (EIS) techniques. The corrosion rate decreased as a function of the inhibitor dose. The Tafel and EIS parameters showed that the inhibitors decreased both the anodic and cathodic corrosion currents and inhibited the charge transfer process by adsorption on the Cu surface. The inhibition property was attributed to the adsorption of inhibitor molecules with the Langmuir model. Tricine showed a superior inhibition performance of more than 98% at a concentration of ∼5 mmol L⁻¹. The free energy of adsorption data revealed physical adsorption. The outcomes of Monte Carlo simulations and theoretical studies well supported the experimental data.

The inhibition impacts of two non-toxic glycine derivatives, namely, bicine (N,N-bis(2-hydroxyethyl)glycine) and tricine (N-(tri(hydroxymethyl)methyl) glycine) on copper corrosion were investigated in 3.5% NaCl solutions.     

Two-dimensional lamellar polyimide/cardanol-based benzoxazine copper polymer composite coatings with excellent anti-corrosion performance

The economic loss and environmental damage caused by metal corrosion is irreversible. Thus, effective methods, such as coating technologies are used to protect metal surfaces from corrosion. In this work, cardanol-based benzoxazine (CB) was synthesized by a solvent-free method using cardanol, paraformaldehyde and n-octylamine. A cardanol-based benzoxazine copper polymer (CBCP) with good mechanical properties was then prepared by CuCl₂ catalysis and can be cured at room temperature. Subsequently, polyimide corrosion inhibitors with a two-dimensional sheet structure (pyromellitic dianhydride polyimide (PDPI) and 1,4,5,8-naphthalene tetracarboxylic dianhydride polyimide (NDPI)) were designed and prepared. Lastly, PDPI or NDPI was mixed with CBCP to obtain two-dimensional lamellar polyimide/cardanol-based benzoxazine copper polymer composite coatings. The Tafel curves and electrochemical impedance spectroscopy (EIS) measurements showed composite coatings with good corrosion resistance in different corrosive media. Compared to CBCP coating, the anticorrosion performance of the composite coatings improved obviously, especially the coating obtained with 0.5 wt% PDPI. It exhibits a high polarization resistance (3.874 × 10⁹ Ω), a high protection efficiency (99.99% and 97.98%) and low corrosion rate (3.376 × 10⁻⁶ mm year⁻¹). This work suggested a facile and eco-friendly strategy for preparing bio-based anticorrosive composite coatings from low cost and abundant cardanol and polyimide corrosion inhibitors, which will significantly promote their application in metal anticorrosion.

Room temperature cured two-dimensional lamellar polyimide/cardanol-based benzoxazine copper polymer composite coatings were successfully prepared, which exhibited excellent mechanical properties and anticorrosion properties.     

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)).     

Exploring corrosion protection properties of alkyd@lanthanide bis-phthalocyanine nanocomposite coatings

Organic coatings have been widely used to protect carbon steel pipelines from external corrosion; however, they often suffer from permeability and weak adhesion. Here we show that synthetic lanthanide bis-phthalocyanine complexes, LnPc₂ (Ln = lanthanide metal, Pc = C₃₂H₁₆N₈ denotes the phthalocyanine ligand) can be used to form new nanocomposite coatings to provide corrosion protection to the underlying carbon steel pipelines. Electrochemical studies (EIS and potentiodynamic polarization) showed that the incorporation of LnPc₂ compound (PrPc₂, SmPc₂ and HoPc₂) additives with alkyd coating, leads to a significant increase in the corrosion resistance of carbon steel in 0.5 M HCl solution. The alkyd@LnPc₂ nanocomposite coatings absorb very low water volumes, when compared to the neat alkyd coating. LnPc₂ compounds allowed enhancing the pull-off adhesion of coatings performance from 3.34 MPa to 19.94 MPa. The efficiency of alkyd@HoPc₂ coating appears higher than that of alkyd@PrPc₂ and alkyd@SmPc₂ coatings. The protective properties of alkyd@LnPc₂ coatings were confirmed by SEM, TGA, scratch hardness, impact resistance, bend test and contact angle analysis.

Organic coatings have been widely used to protect carbon steel pipelines from external corrosion; however, they often suffer from permeability and weak adhesion.     

Analysis of sodium generation by sodium oxide decomposition on corrosion resistance materials: a new approach towards sodium redox water-splitting cycle

In this study, the investigation of materials with corrosion resistance was carried out to prevent side reactions caused by sodium oxide (Na₂O) in the Na-redox thermochemical water splitting cycle, and essential operational conditions for sodium (Na) generation from Na₂O were also investigated. Thermal desorption spectroscopy and X-ray diffraction techniques at altered conditions were mainly used for the experimental investigation. Numerous types of materials were tested to find materials with high resistance towards corrosion and to understand essential thermal decomposition processes of Na₂O. In addition, under different temperatures and pressure conditions, the thermodynamic calculation of Gibbs free energy was performed to obtain experimental results. As a result, a Ti alloy showed significant resistance towards the corrosive reaction by Na₂O. The obtained experimental and simulated results support the direct decomposition of Na₂O to form Na and O₂ below 600 °C under low partial pressure conditions. The optimized conditions for Na generation with the Ti alloy sample can be used for low temperature water splitting.

In this study, investigation of materials with corrosion resistance was carried out to prevent side reactions by sodium oxide (Na₂O) in the Na-redox cycle, and essential operational conditions for Na generation from Na₂O were investigated.     

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.     

The low-temperature corrosion characteristics of alcohol-based fuel combustion

In this paper, the low-temperature corrosion characteristics of the four fuel combustions that include methanol, diesel, MF75 (the volume fraction of methanol is 75 ± 2%), and MF50 (the volume fraction of methanol is 50 ± 2%) were studied. MF75 and MF50 were modulated by methanol, diesel and a small amount of cosolvent. The quality indicators of four fuels were judged by the specific standard. The acid dew point temperature of the four kinds of fuel combustion flue gas was calculated and compared, and the acid ion in the condensate of the four fuel combustion products was analyzed and tested. Based on this method, the corrosiveness of four kinds of condensate was determined. The corrosion rates of five metals (brass, 304 stainless steel, 316 stainless steel, corten steel, and Q245 steel) were tested by two different methods (electrochemistry corrosion and static immersion corrosion). The experimental results show that the quality indicators of four fuels have all reached the relevant national standards. The dew point temperature of methanol, MF75 and MF50 are lower than that of diesel. The corrosion products on the surface of corten steel are relatively compact and easily accumulate dust, which is not conducive to the safe operation of the boiler. The corrosion resistance properties of 316 stainless steel is excellent, showing that it would be the ideal material choice for the low-temperature zone of a boiler flue.

Research on low-temperature dewpoint corrosion characteristics of boiler under four fuels (methanol, diesel, MF75 and MF50) combustion conditions.     

Nickel foam and stainless steel mesh as electrocatalysts for hydrogen evolution reaction,oxygen evolution reaction and overall water splitting in alkaline media

In this work, several commonly used conductive substrates as electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions were studied, including nickel foam (Ni foam), copper foam (Cu foam), nickel mesh (Ni mesh) and stainless steel mesh (SS mesh). Ni foam and SS mesh are demonstrated as high-performance and stable electrocatalysts for HER and OER, respectively. For HER, Ni foam exhibited an overpotential of 0.217 V at a current density of 10 mA cm⁻² with a Tafel slope of 130 mV dec⁻¹, which were larger than that of the commercial Pt/C catalyst, but smaller than that of the other conductive substrates. Meanwhile, the SS mesh showed the best electrocatalytic performance for OER with an overpotential of 0.277 V at a current density of 10 mA cm⁻² and a Tafel slope of 51 mV dec⁻¹. Its electrocatalytic performance not only exceeded those of the other conductive substrates but also the commercial RuO₂ catalyst. Moreover, both Ni foam and SS mesh exhibited high stability during HER and OER, respectively. Furthermore, in the two-electrode system with Ni foam used as the cathode and SS mesh used as the anode, they enable a current density of 10 mA cm⁻² at a small cell voltage of 1.74 V. This value is comparable to or exceeding the values of previously reported electrocatalysts for overall water splitting. In addition, NiO on the surface of Ni foam may be the real active species for HER, NiO and FeO_x on the surface of SS mesh may be the active species for OER. The abundant and commercial availability, long-term stability and low-cost property of nickel foam and stainless steel mesh enable their large-scale practical application in water splitting.

Efficient electrocatalytic overall water splitting is achieved with commercially-available and low-cost nickel foam and stainless steel mesh as cathode and anode electrodes.     

Investigation of corrosion characteristics of Cu-10Ni-1.2Fe-xMn (x = 0.53, 0.87, 1.19) alloy in 3.5% NaCl solution

Cupronickel alloys have been broadly utilized in various fields due to their excellent properties. In this paper, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) curves were used to study the impact of different Mn contents on the corrosion resistance of 90/10 cupronickel alloy. Surface morphology, electronic structure, and phase composition of the film formed on different Mn content 90/10 cupronickel alloy immersed in 3.5% NaCl solution for 30 days were investigated using SEM, EDS, Mott–Schottky, XRD, XPS, etc., revealing that adding an appropriate amount of Mn to the 90/10 cupronickel alloy can change the corrosion resistance of the alloy. The corrosion resistance first increases and then decreases with the addition of Mn content. Among them, the sample with 0.87% Mn addition has the best corrosion resistance, the corrosion product film is more complete, no cracks appear, and the corrosion product binding force is stronger. The addition of Mn promotes the filling of cation vacancies by Ni and generates more NiO, which enhances the stability of the corrosion product film.

Cupronickel alloys have been broadly utilized in various fields due to their excellent properties.     

4-Phenylpyrimidine monolayer protection of a copper surface from salt corrosion

4-Phenylpyrimidine (4-PPM) containing N heteroatoms can easily form compact and uniform layers on metallic surfaces. In this work, the protection of a copper surface from corrosion in 3 wt% NaCl by a 4-PPM layer was investigated by electrochemical impedance spectroscopy (EIS) and polarization methods. Under optimum conditions, the inhibition efficiency of a 4-PPM layer for copper corrosion reached 83.2%. Raman analysis in conjunction with calculations using density functional theory (DFT) based on the B3LYP/LANL2DZ basis set suggested that the 4-PPM molecule anchored on the copper surface via the N₁ atom to construct a uniform layer.

The efficiency of a 4-phenylpyrimidine monolayer optimally self-assembled on a copper surface against corrosion by a 3 wt% NaCl solution could reach 83.2%.     

Corrosion behavior and mechanism of ductile iron with different degrees of deterioration of cement mortar lining in reclaimed water pipelines

The deterioration of cement mortar lining (CML) has a significant impact on the corrosion of ductile iron pipes, and further affects the water quality of transported reclaimed water. In this study, the different coverage levels of CML (such as lined (100%), 90% and 50% lining coverage and unlined) were used for simulating different degrees of deterioration of CML. Electrochemical measurements, water quality testing and corrosion product microanalysis were carried out to monitor the corrosion process and investigate the corrosion mechanism. The results showed that the order of maximum corrosion rate under different conditions was: 50% lining coverage (0.159 mm a⁻¹) > unlined (0.110 mm a⁻¹) > 90% lining coverage (0.042 mm a⁻¹) > 100% lining coverage (0.007 mm a⁻¹). The complete lining can provide a higher pH to passivate the ductile iron to achieve perfect protection. When the damage of CML was very small, the self-healing of the lining can restore the protection ability to a great extent. The corrosion of the ductile iron with 50% lining was even more serious than the unlined ductile iron. The negative effect of the silicate dissolved from the lining on the crystal structure, growth and stabilization process of the corrosion products was considered to be the reason for the more acute corrosion of the pipeline with a large area lining spalling.

The influence of the degradation degree of cement mortar lining on the corrosion of the ductile iron pipe in reclaimed water.     

Biferrocenyl Schiff bases as efficient corrosion inhibitors for an aluminium alloy in HCl solution: a combined experimental and theoretical study

The corrosion inhibitive capabilities of some ferrocene-based Schiff bases on aluminium alloy AA2219-T6 in acidic medium were investigated using Tafel polarization, electrochemical impedance spectroscopy (EIS), weight loss measurement, FT-IR spectroscopy and scanning electron microscopic (SEM) techniques. The influence of molecular configuration on the corrosion inhibition behavior has been explored by quantum chemical calculation. Ferrocenyl Schiff bases 4,4′-((((ethane-1,2-diylbis(oxy))bis(4,1-phenylene))bis(methaneylylidene))bis(azaneylylidene))bisferrocene (Fcua), 4,4′-((((ethane-1,2-diylbis(oxy))bis(2-methoxy-1,4-phenylene))bis(methaneylylidene))bis(azaneylylidene))bisferrocene (Fcub) and 4,4′-((((ethane-1,2-diylbis(oxy))bis(2-ethoxy-1,4-phenylene))bis(methaneylylidene))bis(azaneylylidene))bisferrocene (Fcuc) have been synthesized and characterized by FT-IR, ¹H and ¹³C NMR spectroscopic studies. These compounds showed a substantial corrosion inhibition against aluminium alloy in 0.1 M of HCl at 298 K. Fcub and Fcuc showed better anticorrosion efficiency as compared with Fcua due to the electron donating methoxy and ethoxy group substitutions, respectively. Polarization curves also indicated that the studied biferrocenyl Schiff bases were mixed type anticorrosive materials. The inhibition of the aluminium alloy surface by biferrocenyl Schiff bases was evidenced through scanning electron microscopy (SEM) studies. Semi-empirical quantum mechanical studies revealed a correlation between corrosion inhibition efficiency and structural functionalities.

The anticorrosion activity of biferrocenyl Schiff bases on AA2219-T6 in acidic medium were studied using Tafel polarization, electrochemical impedance spectroscopy, weight loss analysis, FT-IR spectroscopy and scanning electron microscopic technique.     

Design and synergistic effect of nano-sized epoxy-NiCo2O4 nanocomposites for anticorrosion applications

In the present work, we evaluated the corrosion inhibition properties of a ligand and mixed metal oxide nanocomposite. The ligand and mixed nickel–cobalt complex were synthesized using 1-naphthoic acid and aminoguanidine with the formulae [C₁₁H₇O₂(CN₄H₅)(CN₄H₆)]·H₂O and {Ni–Co[(CH₅N₄)₂(C₁₁H₇O₂)₂]}·H₂O, respectively. After their synthesis, physicochemical techniques such as CHNS analysis, infrared and UV-visible spectroscopy, thermal analysis, and X-ray diffraction (XRD) were employed to characterize both the synthesized ligand and nickel–cobalt complex. The metal oxide prepared from the decomposition of the metal complex was also characterized using several techniques to confirm its bonding and structure. In addition, the corrosion inhibition efficiency of the epoxy-ligand and epoxy-NiCo₂O₄ nanocomposite on mild steel (MS) in 3 M hydrochloric acid (HCl), 1.5 M sulfuric acid (H₂SO₄), and 0.5 M phosphoric acid (H₃PO₄) solution was examined and compared using weight loss measurements, Tafel plots, isotherms and electrochemical impedance spectroscopy (EIS). The results from the electrochemical studies disclosed that the epoxy coating of mixed metal oxides with 0.8 ppm concentration yielded excellent corrosion protection. The SEM images of mild steel and mild steel coated with epoxy-ligand/epoxy-NiCo₂O₄ in HCl confirmed the anti-corrosive behavior of the synthesized compounds. Hence, the as-prepared material can be a next-generation tool for sustainable anti-corrosive coatings.

This study reports the synthesis of nano-sized epoxy-NiCo₂O₄ nanocomposites and their anti-corrosive efficiency to attain sustainable development.     

Adsorption characteristics and inhibition effect of two Schiff base compounds on corrosion of mild steel in 0.5 M HCl solution: experimental,DFT studies,and Monte Carlo simulation

In this work, we report the synthesis of two Schiff bases of substituted gallic acid derivatives via amidation reaction and their characterization using ¹H-NMR spectroscopy to study their inhibition performance on the aggressive attack of HCl on mild steel (MS). The inhibitive performance was examined using chemical (weight loss) and electrochemical (Tafel and EIS) test methods. The results indicate that these derivatives significantly suppress the dissolution rate of mild steel via adsorption phenomena, which correlates to the Langmuir adsorption model. Tafel data display the mixed-type properties of these compounds and EIS results show that increasing Schiff base concentration not only leads to delaying the charge transfer (R_ct) of iron from 26.4 ohm cm⁻² to 227.7 ohm cm⁻² but also decreases the capacitance of the adsorbed double layer (C_dl) from 8.58 (F cm⁻²) × 10⁻⁵ to 2.55 (F cm⁻²) × 10⁻⁵. The inhibition efficiency percentage reaches the peak (90%) at optimum concentration of 250 ppm. The Monte Carlo simulations confirm the adsorption ability of the as-prepared compounds on the Fe (1 1 0) crystal. The SEM/EDX results revealed the presence of a protective film on the mild steel sample.

Structures of the synthesized Schiff bases inhibitor.     

Ion-triggered calcium hydroxide microcapsules for enhanced corrosion resistance of steel bars

Herein, we synthesized Ca(OH)₂ microcapsules with ion-responsive shells composed of cross-linked poly-ionic liquids (CPILs). By exchanging PF₆⁻ with Cl⁻ in water, the hydrophobic poly-ionic liquids (PILs) on the shell are converted to hydrophilic channels. The encapsulated Ca(OH)₂ can permeate through the hydrophilic channels and release OH⁻. Meanwhile, the Cl⁻ content can be reduced. The release rate of Ca(OH)₂ is influenced by the content of monomers and concentration of Cl⁻ ions in water. SO₄²⁻ can also trigger the release of Ca(OH)₂ from the microcapsule. With these microcapsules, Q235 steel exhibited promising corrosion resistance in simulated seawater. These results indicate that encapsulation of corrosion inhibitors is highly desirable for enhanced corrosion resistance of steel bars and the proposed approach can be used to encapsulate various corrosion inhibitors and functional materials for a wide range of applications.

By exchanging PF₆⁻ of the CPILs with Cl⁻, Ca(OH)₂ can penetrate out of the microcapsule through the formed hydrophilic channels.     

Efficient reclamation of carbon fibers from epoxy composite waste through catalytic pyrolysis in molten ZnCl2

Carbon fiber-reinforced polymer composites have been widely used in various fields and have inevitably produced large amounts of composite waste. The recycling of carbon fibers with high value has become an active research topic at related institutions and production enterprises. In this paper, the catalytic pyrolysis of T700 carbon fiber/epoxy composites in molten salt was studied. Due to the efficient solubility of molten ZnCl₂ for the epoxy matrix and catalytic fracture of the C–N bonds by the action of Zn²⁺ ions, the epoxy composites can be completely degraded at 360 °C in 80 min under standard pressure, and the reclamation efficiency was significantly enhanced compared with conventional pyrolysis reclamation without a catalyst. The types and contents of the main oxygen-containing functional groups on the surfaces of the fibers reclaimed with ZnCl₂ were similar to those of the virgin fibers, and the graphitization structure of the carbon fibers was not destroyed in the pyrolysis process. The tensile strength of a monofilament of the fibers reclaimed with ZnCl₂ was obviously higher than that of fibers reclaimed in air; it reached a high retention rate that was about 95% that of the virgin fibers. The fibers reclaimed with ZnCl₂ after sizing exhibited a desirable reinforcing effect on the flexure performance and interlaminar shear strength of unidirectional carbon fiber/epoxy composites which was close to the performance levels of composite samples containing commercial T700 carbon fibers. Therefore, efficient technology to reclaim high-quality carbon fibers from epoxy matrices has been devised.

Carbon fibers were efficiently reclaimed from epoxy composite waste for remanufacturing through a catalytic pyrolysis in molten ZnCl₂.     

Synergistic effect of potassium iodide and sodium dodecyl sulfonate on the corrosion inhibition of carbon steel in HCl medium: a combined experimental and theoretical investigation

Carbon steel is an important industrial material, but it usually suffers from serious corrosion in the service environment. Using corrosion inhibitors is an effective approach to mitigate corrosion. The synergistic inhibition behavior of sodium dodecyl sulfonate (SDS) and potassium iodide (KI) on carbon steel corrosion in hydrochloric acid medium was investigated by electrochemical test, surface morphology analysis, and molecular simulation approaches. Results show that the corrosion inhibition performance is significantly enhanced after the two substances are compounded, and the inhibition efficiency can reach approximately 96% at small doses. The Tafel polarization curves suggest that the mixtures can be classified as anodic corrosion inhibitors. Impedance tests indicate that the inhibitor molecules are adsorbed on the steel surface, resulting in an increase of charge transfer resistance but a decrease of electric double layer capacitance. The adsorption process follows the Langmuir adsorption isotherm. Molecular simulation calculations further reveal the active sites of SDS and the stabilizing effect that I⁻ plays in the inhibition process. The present research offers an economic, environmentally friendly and efficient measure of corrosion control, and provides theoretical guidance for the efficient use of carbon steels and the development of novel corrosion inhibitors.

Carbon steel is an important industrial material, but it usually suffers from serious corrosion in the service environment.