Iron Substrate Research Articles

Synthesis of hexagonal boron nitride nanocoatings for corrosion prevention of iron substrates

Iron and its alloys have applications in diverse fields such as civil infrastructure, aerospace, and defense. Corrosion of these alloys in saline environments is a significant concern that causes huge environmental losses. The current study explores pulsed laser deposition technique to synthesize hexagonal boron nitride (hBN) films as protective coatings, directly on iron (Fe), to mitigate the corrosion. Microstructural, mechanical, wetting, and corrosion properties of hBN-coated Fe substrates were investigated at different deposition temperatures (25–800 °C) and varying thicknesses (35–115 nm). Raman spectra and transmission electron microscopy confirmed the presence of hBN in as-deposited films. Crystallinity and surface roughness of hBN coatings increased as deposition temperature increased. Electrochemical studies performed in 3.5 wt% NaCl solution showed that the 115 nm thick hBN coatings deposited at 600 °C resulted in lower corrosion rates and has ~6-fold higher corrosion resistance than bare Fe. Also, the corrosion rates decreased with an increase in hBN coating thickness. Overall results suggest that hBN nanocoatings reduced the corrosion activity and can potentially serve as a corrosion-resistant barrier coatings in saline environments.

Stable method for electrodepositing network-like magnesium hydroxide layer with superhydrophobicity and enhanced surface performance under structure direction of xanthan gum/glycerol

Investigation of magnesium hydroxide superhydrophobic layer would significantly improve the application of green and low-cost superhydrophobic materials, for the abundant source, low economic cost, nontoxicity and environment friendliness of magnesium hydroxide. In this work, an obviously developed method which is stable and easy for fabricating network-like magnesium hydroxide superhydrophobic layer on iron substrate has been rendered, simply by cathodic electrodeposition with magnesium nitrate aqueous solution under structure direction of glycerin cross-linked xanthan gum, and subsequent surface modification with 1H,1H,2H,2H-perfluorodecyltriethoxysilane. The preparation process could be carried out at tremendously wide range of bath temperature (from 15 °C to 75 °C), xanthan gum/glycerol dissolving temperature (from room temperature to 100 °C), and storage times (from 0 day to 30 days). The superhydrophobic layer obtained at 35 °C bath temperature with addition of xanthan gum/glycerol dissolved at room temperature and stored for 7 days, shows strong water repellency (160.1° water contact angle, 3.2° sliding angle), and excellent self-cleaning performance. The layer also demonstrates good mechanical property according to cross hatch adhesion and tape peeling test, and owns an inhibition current efficiency as high as 99.98%, taking advantage of its extremely high anti-corrosion resistance (Rct = 2.87 × 105 Ω cm−2, Rf = 1.49 × 109 Ω cm−2).

Investigation of Conditions for Preparation of Ordered Nanohole Arrays by Anodization of Iron Substrates with Depression Patterns

Ordered iron oxide nanohole arrays were fabricated by the anodization of iron substrates with depression patterns formed by Ar ion milling with alumina masks in an ethylene glycol electrolyte containing NH4F and H2O. It was found that the optimization of anodization voltage, NH4F and H2O concentrations in the electrolyte, and electrolyte temperature is necessary to achieve straight pore growth induced from the depression patterns in the depth direction. The optimization of the anodization conditions enabled the formation of ordered iron oxide nanohole arrays with aspect ratios exceeding 10. The resulting ordered iron oxide nanohole arrays with high aspect ratios are expected to be applied to various functional devices such as photocatalysts and solar cells.

Normal range and predictors of serum erythroferrone in infants.

Erythroferrone (ERFE) has been identified as a hepcidin-regulating hormone synthetized by erythroblasts correlating to the erythropoietic activity and the needs for iron substrate in bone marrow of adults. The present study aimed to assess the ERFE serum concentrations and its predictors in infants. ERFE was explored at 4 time points during the first year of life in 45 healthy, breastfed, normal birth weight (NBW) infants, and 136 marginally low birth weight infants (LBW, 2000-2500 g) receiving iron (N = 58) or placebo (N = 78) between 6 weeks and 6 months of age. ERFE concentrations were low at birth, increasing gradually during the first year of life. In NBW infants, reference ranges (5th to 95th percentile) were at 6 weeks <0.005-0.99 ng/mL and at 12 months <0.005-33.7 ng/mL. ERFE was higher in LBW infants at 6 weeks but lower at 12 months compared to NBW and minimally affected by iron supplementation among LBW infants. Correlations of ERFE with erythropoietic and iron status markers were weak and inconsistent. The role of ERFE in the crosstalk of erythropoiesis and iron homeostasis remains unclear in infants and further studies on ERFE in infants and older children are warranted within the framework of the erythropoietin-ERFE-hepcidin axis. Normal range of erythroferrone in healthy infants is described for the first time. Erythroferrone in infants lacks correlation to iron status and markers of erythropoiesis. The findings indicate differences in infant regulation of iron homeostasis as compared to adults. The findings point to a need to study infant erythropoiesis separately from its adult counterpart. The findings may have clinical impact on management strategies of iron-loading anemia in infancy.

Tribological behaviour of HVOF-sprayed Ni-based self-lubricating composite coatings

ABSTRACT In the current investigation, the tribological behaviour of HVOF sprayed Ni-based self-lubricating composite coatings on cast iron substrate, which is a commonly used material for cylinders, was studied. Four different combinations of coatings materials, namely, Ni–10Mo–10Al, Ni–10Mo–10Al–10graphite, Ni–10MoS2–10Al and Ni–10MoS2–10Al–10graphite were deposited on a cast iron substrate. Then, the mechanical, morphological and tribological properties of the coated and uncoated samples were analysed by performing microhardness measurements, a scratch resistance test, a wear test (pin on disc), XRD and SEM/EDS. Results showed that among all coatings, Ni–10MoS2–10Al–10graphite coated cast iron sample has the highest microhardness of about 349.4 HV 111% higher than the substrate material and lowest average wear rate of about 1.1 × 10−4 g s−1.

The influence of Ce doping on catalytic oxidation of toluene over Co3O4/iron mesh monolithic catalyst

In this paper, CeCoOx/iron mesh monolithic catalyst (CeCoOx/IM) was successfully prepared by hydrothermal method. The preparation conditions such as Ce/Co ratio, hydrothermal temperature as well as nitrate/urea ratio of the catalysts were optimized systematically. The catalytic performance results showed that when the Ce/Co ratio was 0.4, hydrothermal temperature was 160 °C and nitrate/urea ration was 1:8, the obtained catalyst possessed the best toluene oxidation activity, and the temperature at 50% and 90% toluene conversion (T50% and T90%) was 248 °C and 256 °C, respectively, which was lower than that of Co3O4/IM (260 °C and 267 °C, respectively). In addition, the active component is closely combined with the iron substrate with an exfoliation rate of 0.07%. H2-TPR results showed that the existence of rich Co3+ species and the strong interaction between Co and Ce was one of the reasons for this improvement performance. The introduction of Ce can also improve the thermal stability, water resistance and cycling stability of the catalyst. The reaction kinetics analysis showed that the Ea value was significantly reduced by Ce doping, which reached to 71.3 kJ·mol−1 for the best performance catalyst. We hope this study can provide a theoretical support for the practical application of catalyst.

Use of Functionally Graded Material to Decrease Maximum Temperature of a Coating–Substrate System

A mathematical model for determining the temperature distribution in the system consisting of a coating deposited on the surface of substrate was proposed. The foundation material is homogeneous, while the coating is made of a functionally gradient material (FGM) with thermal conductivity increasing exponentially along the thickness. Heating processes of the outer surface of the coating were considered with a constant and linearly decreasing in time intensity of the heat flux. Such thermal loads are common in thermal problems of friction, particularly regarding frictional heating during braking. An exact (in quadrature) solution of the corresponding boundary-value problems of parabolic heat conduction was obtained. Asymptotic solutions to these problems were also found for small and large values of the Fourier number. Calculations were performed for a coating made of two-component FGM ZrO2-Ti-6Al-4V, applied on a cast iron substrate. In order to explain the effect of FGM on temperature, corresponding analysis was carried out for the coating made of a homogeneous (ZrO2) material.

Tribological properties of metal-organic framework nanosheets functionalized by oleic acid

<p indent="0mm">Terephthalic acid and copper acetate were used as raw materials, and copper-based metal-organic framework (Cu-MOF) nanosheets were synthesized by ultrasonic-assisted self-assembly. Afterward, oleic acid (OA) molecules were successfully modified on the surface of Cu-MOF by ultrasonic treatment to acquire Cu-MOF@OA nanosheets. The morphology of Cu-MOF@OA maintained its sheet structure; however, the size of the nanosheets was reduced, and the agglomeration problem was considerably alleviated compared with Cu-MOF nanosheets. The Cu-MOF@OA nanosheets exhibited good dispersion stability in <sc>500 N</sc> base oil. The tribological tests indicated that Cu-MOF@OA showed the best tribological properties at the addition concentration of 1.0 wt.%. Moreover, the friction coefficient and wear volume were reduced to 3/5 and 1/6 of the base oil, respectively. Finally, scanning electron microscopy and X-ray photoelectron spectroscopy were applied to characterize the morphology and characteristic elements of wear scar lubricated by Cu-MOF@OA nanosheets and explore the lubrication mechanism. The results indicated that complex tribochemical reactions occur among Cu-MOF@OA, base oil, and iron substrate under the action of load and shear stress during the friction experiment, forming a tribofilm composed of nitrogenous substances, carbonaceous substances, and iron oxides, which reduce the friction and wear of metal surfaces.

High temperature tribological and electrochemical behavior of heat-treated Al2O3-base hybrid coating sprayed by HVOF thermal spray technique

In the present study, the hybrid coating was developed by HVOF over the cast iron substrate. The hybrid coating material comprises Al2O3 (80% w/w) enriched with graphite, MoS2, and fumed silica in w/w of 5%, 10%, and 5% respectively. Microstructure and phase composition of prepared coated samples were analyzed by SEM-EDS, XRD and Raman Spectroscopy. The coated samples were heat-treated and their mechanical, electrochemical and tribological behavior was compared with the as-coated samples. There was a considerable change observed in the micro-hardness and anti-corrosion properties of the coated material after heat treatment. The residual stresses in the heat-treated sample decreased compared to the as-coated sample. The high-temperature tribological investigation was carried out in non-lubricated conditions at three different temperatures 30 °C, 150 °C, and 300 °C with a constant load of 40 N and variable sliding speed. The coefficient of friction and wear rate was calculated and it was found that there was a decrement up to 36% in the wear rate of the heat-treated samples compared to the as-coated sample. The SEM morphologies of the wear track showed the presence of small cracks, adhesion, abrasion and smear regions due to plastic deformation.

Multiwall Carbon Nanotubes for Solid Lubrication of Highly Loaded Contacts

When lubrication of rolling bearings with oil or grease is not possible, for example because the lubricant evaporates in vacuum, solid lubrication by multiwall carbon nanotubes (MWCNT) is a viable alternative. To understand the mechanisms underlying MWCNT lubrication of highly loaded contacts, we combine an experimental approach with large-scale molecular dynamics (MD) simulations. Tribometry is performed on ground iron plates coated with two different types of MWCNTs by electrophoretic deposition. Although structural differences in the MWCNT materials result in slightly different running-in behavior, most of the tests converge to a steady-state coefficient of friction of 0.18. The resulting wear tracks and tribolayers are subjected to structural and chemical characterization and suggest a tribo-induced phase transformation resulting in tribolayers that consist of MWCNT fragments, iron oxide, and iron carbide nanoparticles embedded in an amorphous carbon matrix. Covalent bonding of the tribolayer to the iron surface and low carbon transfer to the alumina counter body indicate sliding at the tribolayer/ball interface as the dominant mechanism underlying MWCNT solid lubrication. MD simulations of nascent a-C tribofilms lubricated by MWCNT bundles and stacks of crossed MWCNTs reveal two different sliding regimes: a low-load regime that leaves the MWCNTs intact and a high-load regime with partial collapse of the tube structure and formation of a-C regions. The critical load for this transition increases with the filling ratio of the MWCNT and the packing density of the stacks. The former determines the stability of the MWCNT, while the latter controls the local stresses at the MWCNT crossings. For both MWCNT materials, the high-load regime is predicted for the experimental loads. This is confirmed by a remarkable agreement between transmission electron microscopy (TEM) and atomistic simulation images. Based on the findings of this work, a multistep lubrication mechanism is formulated for MWCNT coatings rubbing against alumina on an iron substrate.

Molecular Dynamics Simulation of Interface Properties between Water-Based Inorganic Zinc Silicate Coating Modified by Organosilicone and Iron Substrate

The interface properties of Fe(101)/zinc silicate modified by organo-siloxane (KH-570) was studied by using the method of molecular dynamics simulation. By calculating the temperature and energy fluctuation of equilibrium state, equilibrium concentration distribution, MSD of layer and different groups, and interaction energy of two interface models, the influencing mechanism on the interface properties of adding organosiloxane into coating system was studied at the atomic scale. It shows that the temperature and energy of interface oscillated in a small range and it was exited in a state of dynamic equilibrium within the initial simulation stage (t < 20 ps). It can be seen from the multiple peak states of concentration distribution that the iron substrate, organo-siloxane and zinc silicate are distributed in the form of a concentration gradient in the real environment. The rapid diffusion of free zinc powder in zinc silicate coating was the essential reason that affected the comprehensive properties of coating. The interface thickness decreased from 7.45 to 6.82 Å, the MSD of free zinc powder was effectively reduced, and the interfacial energy was increased from 104.667 to 347.158 kcal/mol after being modified by organo-siloxane.

Facile method to activate substrate for oxygen evolution by a galvanic-cell reaction.

NiFe layered double hydroxide (NiFe LDH) is a promising material with multiple functions. In this communication, a novel method is used to prepare NiFe LDH. This synthesis method is achieved via galvanic-cell corrosion between nickel and iron substrates in aqueous solutions containing a halogen group anion (e.g., Cl) at ambient temperature. The as-prepared NiFe LDH electrodes are developed as electrocatalysts for the oxygen evolution reaction (OER) and exhibit excellent catalytic activities and durability. This work provides an energy-efficient, cost-effective, and scaled-up corrosion engineering approach for manufacturing NiFe LDH materials.

Fabrication of Fe-Fe1-xO based 3D coplanar microsupercapacitors by electric discharge rusting of pure iron substrates.

Iron oxides with advanced functional properties show great potential for applications in the fields of water splitting, drug delivery, sensors, batteries and supercapacitors. However, it is challenging to develop a simple and efficient strategy for fabricating patterned iron oxide based electrodes for supercapacitor applications. Herein, a facile, simple, scalable, binder-free, surfactant-free and conductive additive-free electric discharge rusting (EDR) technique is proposed to directly synthesize Fe1-xO oxide layer on a pure iron substrate. This new EDR strategy is successfully adopted to fabricate Fe-Fe1-xO integrative patterned electrodes and coplanar microsupercapacitors (CMSC) in one step. The CMSC devices with different geometries could be directly patterned by EDR, which is automatically controlled by a computer numerical control system. The fabricated Fe-Fe1-xO based 3D 2F-CMSC exhibits a maximum areal specific capacitance of 112.4 mF cm-2. Another important finding is the fabrication of 3D 2F-CMSC devices, which show good capacitive behavior at an ultra high scanning rate of 20 000 mV s-1. The results prove that EDR is a low-cost and versatile strategy for the scalable fabrication of high-performance patterned supercapacitor integrative electrodes and devices. Furthermore, it is a versatile technique which shows a great potential for development of next generation microelectronic devices, such as microbatteries and microsensors.

Sediment microbial fuel cells in oxidative sedimentary environments using iron substrate as voltage booster

The voltage variation of in situ sediment microbial fuel cells with the sedimentary environment hinders their practical applications. In this study, an iron substrate that provides equal cell voltage output regardless of the sedimentary environment, was used to elucidate the electron-transfer-mediating characteristics of soil organic matter. The cell exhibited voltages of 0.3 and 0.5 V in oxidative and reductive sediments, respectively. However, the addition of the iron substrate enabled the cell to output 0.8 V regardless of the sediment inoculum and alleviated its activation and concentration losses. The oxidative sediment with iron substrate showed relatively low ohmic loss, leading to a 1.3 × higher current than with the reductive sediment. Cyclic voltammetry revealed that the quinone-like moieties in the oxidation state influenced the redox reaction of the iron substrate by facilitating electron/proton transfer. In conclusion, the iron-substrate-based voltage-boosting strategy can help expand the utility of these cells as a power source, particularly in low-voltage aerobic sedimentary environments.

Study on Microstructure and Properties of Mechanically Deposited Zn-Sn Coating

A Zn-Sn coating of ~30 µm thickness was prepared on an iron substrate by mechanical deposition using zinc and tin powders as raw materials. The Zn-Sn coating consists of zinc powder particles physically stacked with tin powder particles and filled with reduced tin, and the tin content in the coating is 20%–30%. The resulting Zn-Sn coating was characterized and analyzed with scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), polarization curves (Tafel), electrochemical impedance (EIS), and energy dispersive X-ray spectrometry (EDS). The results showed that the Zn powder was co-deposited with the Sn powder in a portable manner and the Sn powder was deflected and deformed to a great extent. The spot-flocculated reduced Sn also covered the surface of the Zn powder to fill the interstices of the coating to make the coating more compact. Compared with the pure Zn coating, the Zn-Sn coating has a positive shift of 68 mV in the self-corrosion potential in the polarization test, and the corrosion current was only 20% of that of the pure Zn coating. The reduced Sn had a shielding effect on the Zn powder and at the same time, in combination with inert tin powder, the polarization resistance of the plated layer increased to 1118 Ω/cm2. Furthermore, compared to the pure zinc layer, the time of white rust and red rust increased by 24 and 240 h, respectively. In addition, the XPS results showed that the Zn-Sn plating layer was clearly passivated, which was mainly due to the formation of Zn(OH)2 and Sn(OH)2. The results also emphasized that the tin element in the Zn-Sn plated layer can maintain the morphology of zinc powder, compact the plating layer, and prevent the release of corrosion products, thus improving the corrosion resistance of the Zn-Sn coating.

Construction of Superhydrophobic Coating on Iron Surface with Enhanced Anti-Corrosion, Anti-Adhesive and Anti-Bacterial Properties.

Superhydrophobic coatings on iron surface have a wide application potential in medical instruments, chemical industrial equipment, and house construction. In this work, we developed a multi-functional superhydrophobic coating on iron surface with a high air/water contact angle of 162.3° and a low sliding angle of 2.4°. The construction of superhydrophobic coating involves physical friction processing to fabricate micropatterns and structures, followed by annealing treatment and surface chemical modification with 1H,1H,2H,2H-tridecafluoro-n-octyltrimethoxysilane. The obtained organic-inorganic composite material exhibited considerable optimization potential to anti-condensation performance. The low surface energy of the superhydrophobic coating also leads to poor adhesion of water, dust, and blood platelets, which is beneficial for applications in medical devices. The electrochemical and impedance test results demonstrated that the superhydrophobic surface provided effective corrosion protection for the iron substrate, with an 84.63% increase in corrosion protection efficiency. The experimental results showed that the anti-bacterial ratios reached 90% for E. coli and 85% for S. epidermidis, while the anti-bacterial ratios of ordinary iron were only 8% for E. coli and 15% for S. epidermidis, respectively.

The Influence of Steel and Cast Iron as Substrate Materials on the Microstructure, Microhardness and Wear Resistance of Nickel-base Ti-Al Plasma Spray Coatings

This paper studies the influence of different substrate materials on the phase composition, microstructure, microhardness, and wear resistance of Ni-Cr-B-Si-C-Ti-Al plasma spray coatings. Two types of substrate metals were studied – AISI 1045 steel and Pig-P3 Si grey cast iron. It has been found that in the as-coated condition the surface layers have a phase composition of γ-Ni, Cr23C6, γ-TiAl, TiN, and α-Ti(N, O) on steel substrate, and γ-Ni, α-Ti, TiN, Ni3B, CrB, Cr23C6, α-Ti(N, O), Ni3Si on cast iron. The microhardness and wear resistance of the plasma sprayed Ni-Cr-B-Si-C-Ti-Al coatings is tested. The wear volume of the coatings has been tested for up to 60 min. The deposits on cast iron substrates demonstrate lower wear than those on the steel substrate.

A thermal field FEM of titanium alloy coating on low-carbon steel by laser cladding with experimental validation

Numerical simulation is an efficient method to study the laser cladding process via reconstructing the thermal field and analyzing the evolution of the microstructures. In this work, a novel 3D finite element model (FEM) of the laser cladding process is proposed for materials with significantly different thermo-physical properties, for example, a titanium alloy (TA1) coating on an iron (Q235) substrate. Multiple practical factors, like the coating geometry variation, powder preheating and laser energy attenuation, were considered in this model to ensure its high accuracy. For different laser scanning speeds, the transient temperature contours and their variations against time were simulated, and the calculation errors of the highest temperatures are <2 %. Based on the comparison of the binary phase (TiFe) diagram with the chemical composition of the coating, a new criterion, called the Tm criterion, was established for the coating solidification. Then, the solidification parameters of the moving solid-liquid interface, like the cooling rate, solidification rate and G/R (temperature gradient to solidification rate) ratio, were calculated to predict and analyze the solidification process and microstructure evolution of the coating. Finally, the simulation results were compared with the physical experiments, which proved the validity of the FEM and the rationality of the Tm criterion. Based on the numerical simulation and predicted microstructure evolution, this research provides an accurate, applicable and powerful analytical method for the laser cladding process with different materials, which can substantially improve the time and cost efficiencies of the process optimization.

Annular laser cladding of CuPb10Sn10 copper alloy for high-quality anti-friction coating on 42CrMo steel surface

Reducing the damage caused by friction and wear to components such as Al alloy parts could extend the service lives of parts in automobile and other industrial fields. An effective approach to this is improving the anti-friction properties of key surfaces. In this study, an annular laser cladding (ALC) method was designed, an energy absorption model of the ALC process was established, and the cladding of a CuPb10Sn10 copper alloy coating on a 42CrMo steel surface was studied experimentally. The effects of the ALC process parameters on the laser absorptivity, porosity, and microstructure of the ALC sample were analyzed, and the coating properties (e.g., microhardness and anti-friction properties) were evaluated. The results showed that laser cladding of a CuPb10Sn10 copper alloy coating or other coating materials with low absorptivity could be realized on the surface of 42CrMo steel using the ALC process. The ALC process increased the laser absorptivity to 58 %, and the porosity of the ALC sample was reduced to 0.39 %. The coating microstructure was divided into three layers, in which the top layer of the Cu-rich phase had a uniform structure and no macroscopic crack defects. The main anti-friction component Pb phase and other Cu, Pb, and Sn elements were uniformly distributed. The microhardness of the coating fluctuated, and the value of the top-layer Cu-rich phase was approximately 120 HV0.3. The shear strength of the coating was 194 MPa, and the friction coefficient of the coating decreased by approximately 50 % to 0.19. The ALC method effectively improved the laser absorptivity during the laser cladding of copper alloys on iron substrates, providing theoretical guidance for designing and manufacturing anti-friction functional components in the automotive industry and other fields.

Synergistic improvement of nitrogen and phosphorus removal in constructed wetlands by the addition of solid iron substrates and ferrous irons

Sanjiang Plain is intensively used for rice production, and ditch drainage diffuse pollution prevention is crucial. Groundwater, rich in Fe ions, is the main source of irrigation water in this region. In this study, pyrite and zero-valent iron (ZVI) (sponge iron and iron scraps) were used as substrates to identify the synergistic influence of exogenous Fe2+addition and solid iron substrates on pollutant removal in constructed wetlands. Based on the results, iron substrates hardly improved the ammonia removal, mainly because of the physical structure and oxidation activity. At a hydraulic retention time longer than 8 h, the pollution removal efficiency in the zero-valent iron (ZVI) substrate treatment increased significantly, and the removal of nitrate (NO3−-N) and total phosphorus (TP) in the iron scrap substrate treatment reached about 60% and 70%, respectively. The high-throughput sequencing results showed a significant increase in the abundance of microorganisms involved in denitrification and phosphate accumulation in biofilms on ZVI substrates. The highest diversities of such microorganisms in biofilms on iron scraps were found for denitrifying bacteria (Pseudomonas), nitrate-reducing Fe (II)-oxidizing bacteria (Acidovorax), and Dechloromonas with autotrophic denitrification and phosphate accumulation, with a 43% cumulative abundance. Dechloromonas dominated in the iron sponge substrate treatment. The highest relative abundance of Acidovorax was found in the mixed iron substrate (pyrite, sponge iron, and iron scraps) treatment. The addition of ZVI substrate significantly improved the removal of NO3−-N and TP and reduced the hydraulic retention time through the continuous release of Fe2+ and the promotion of microbial growth. When designing constructed wetlands for treating paddy field drainage, the appropriate addition of iron scrap substrates is recommended to enhance the pollutant removal efficiency and shock load resistance of CWs.