Low Corrosion Research Articles

Experimental investigation of a mixed desiccant solution of potassium formate and ionic liquid

Liquid desiccant technology is a promising energy-efficient alternative to conventional temperature and humidity control systems. In the quest to identify the optimal fluid for liquid desiccant systems, alternative desiccant solutions have been explored in terms of their feasibility and compatibility in dehumidification systems. This study proposes and characterises a new type of less expensive mixture of potassium formate (HCO2K) and 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]). This novel desiccant solution was investigated in terms of corrosiveness to metals, moisture absorption and desorption ability, cost-effectiveness compared to conventional desiccant solutions. The corrosiveness of desiccant solutions to copper-nickel, copper and steel was tested at room temperature and at 60 °C. Experiments were conducted in a climatic chamber with temperatures of 25–31 °C and relative humidities of 80–90% for the absorption process and temperatures of 50–70 °C and relative humidities of 20–30% for the desorption process to assess the moisture absorption and desorption capacities and mass fraction variations of the desiccant solutions. The mixed desiccant of HCO2K/[EMIM][OAc] in the ratio 60/10% wt. showed a moisture absorption capacity of 0.146 gH2O/gsol (compared to 0.18 gH2O/gsol for aqueous lithium chloride at 33.3% wt.) for a temperature and relative humidity of the climatic chamber of 25 °C and 90%, respectively. Its low corrosiveness, good moisture absorption and desorption capacity and higher cost-effectiveness make it a promising alternative to conventional desiccants, such as aqueous solutions of lithium chloride.

Additive manufacturing of AA5083/TiN-Diamond hybrid nanocomposite parts via additive friction stir deposition: Metallurgical structure, mechanical, tribological, and electrochemical properties

Nano-diamond (ND) is a special ultrafine reinforcement whose agglomeration properties and weak interfacial bonding limit its application in aluminum matrix composites. This study used the additive friction stir deposition (AFSD) technique to produce AA5083-H321/2.5 wt% nano TiN/ND additive manufacturing deposition hybrid composite parts (AMDCPs) and a non-composite part (AMDNCP) was also deposited for comparative analysis. The aim was to improve the microstructure and examine the effect of the deposition process parameters, which include 900, 1250, and 1600 rpm rod rotation speed and 5 and 12 mm/min feed rate. The AFSD process parameters were used to calculate the heat input. The consumable rod and AMD parts were evaluated for their macrostructure, microstructure, macro-hardness, tribological, and corrosion properties. The microstructural features were examined using an OM, XRD, and SEM equipped with an EDS. The worn and corrosion surface morphology was investigated using SEM, and hardness was also evaluated as contour maps. The results show that defect-free deposited multilayer AA5083-nano TiN/ND hybrid composite parts were successfully manufactured, and analysis revealed a lower D/H ratio, well-bonded layers, homogeneously distributed TiN/ND and fragmented IMC components, and equiaxed refined grain microstructures. The deposited composites via AFSD showed a lower corrosion rate, higher hardness, and wear resistance than the deposited AA5083 consumable rod and AMDNCP. The AMDP C900-12 demonstrates an optimized deposition process parameter (900 rpm, 12 mm/min) with superior properties, including an increase in hardness by 9.3%, a reduction in grain size by 54%, and a decrease in corrosion rate by 45.2% related to the AMDNC part.

Processing and characterization of beryllium free Ni–Cr–Mo biomaterial doped with cerium, boron and titanium for dental applications

Dental restoration has been a major concern of healthcare since centuries. Several alloys are in use for dental prostheses including Ni–Cr–Mo alloy. The Ni–Cr–Mo alloy has advantage of economy and density over other alloys, while possessing equivalent corrosion and biocompatibility characteristics. However, beryllium in Ni–Cr–Mo dental casting alloys has associated health hazards, being carcinogenic. In this research Ni–Cr–Mo alloys with minor additions of boron (0.2 wt %), cerium (0.4 wt %) and titanium (2 wt %), to replace beryllium were developed through vacuum induction melting and investment casting technique. Manufacturing steps are detailed for the alloy development to have medically clean alloy, suitable for biomedical applications. The cast alloy samples were tested for microstructure, phases, melting temperatures, wear and corrosion characteristics. Corrosion and wear test results demonstrate that the composition with minor addition of cerium had a significant effect to have low corrosion rate (25.92 × 10−3 mills per year), low wear rate (0.04 × 10−4 mm3/N.m) and lowest coefficient of friction.

Electrochemical corrosion and tribocorrosion behavior of CrN and CrAlN coatings in artificial seawater

AbstractThis study investigated the corrosion and tribocorrosion behavior of CrN and CrAlN coatings deposited on steel through direct current magnetron sputtering. Additionally, the effects of Al addition on the microstructure, corrosion inhibition, and tribocorrosion behavior of CrN coatings were evaluated. Compared with the CrN coating, the CrAlN coating exhibited a denser columnar crystal structure and a higher hardness of 23.8 GPa. The CrAlN coating reacted with water to form Al2O3 and Cr2O3 films, which enhanced its corrosion resistance. Moreover, the addition of Al enhanced the wear resistance of the CrN coating and reduced the material loss due to corrosion, wear, and their synergistic effects. The CrAlN coating exhibited a low corrosion current density of 1.14 × 10−8 A/cm2, indicating a 92% reduction compared with the CrN coating. Furthermore, under either open circuit potential or anodic accelerated tribocorrosion conditions, the CrAlN coating featured significantly lower total material loss and synergistic material loss than the CrN coating, demonstrating higher corrosion and tribocorrosion protection.

Corrosion, wear and machinability studies on scrap aluminium alloy wheel based metal matrix composite

Recycled materials, especially scrap aluminum alloy wheels with reinforcement castings, are gaining applications in various fields such as aerospace, naval, military, and automobile. In this research, Honda car alloy wheels are stir-cast with 5% alumina as reinforcement and subjected to corrosion, wear, and machinability studies. Corrosion studies were conducted to evaluate the corrosion current density (ICorr), corrosion potential (ECorr), and corrosion rate for the cast aluminum metal matrix composite. The wear studies with different loads, i.e., 50 N, 60 N, 70 N, and 80 N, were performed on the specimen and investigated the coefficient of friction, frictional force, and pin temperature. The sliding load has a significant effect on wear performance, and for the sliding load of 80 N, the wear recorded was 2574.83 µm. The electrochemical machinability studies with voltage, duty cycle, and concentration of citric acid electrolyte are performed on the machining rate and surface corrosion factor. Analysis of the electrochemical machining process with PROMETHEE-II shows that 7 V, 60% duty cycle, and 30 g/L electrolyte concentration are estimated to be the best combination for a higher machining rate and a lower surface corrosion factor. KEY WORDS: Alumina, Machining rate, Nyquist plot, Electrochemical machining, PROMETHEE-II Bull. Chem. Soc. Ethiop. 2024, 38(4), 1163-1175. DOI: https://dx.doi.org/10.4314/bcse.v38i4.27

Sensitization characteristics for type 445 ultra-pure ferritic stainless steel with an electrochemical reactivation method

The sensitization characteristics of type 445 ultra-pure ferritic stainless steel (FSS) under different aging conditions were investigated by the optimized double loop electrochemical potentiodynamic reactivation (DL-EPR) test and microstructure observation. The solution 2 mol L−1 H2SO4 + 0.01 mol L−1 KSCN +0.5 mol L−1 NaCl and a scan rate of 100 mV min−1 are suitable for the DL-EPR test of 445 FSS. With the change of aging temperature from 500 to 900 °C, the degree of sensitization (DOS) slightly increases at first and then decreases, which reaches a maximum value at about 700 °C. Under the aging condition at 700 °C for 10 min to 2 h, the DOS value gradually increases, but it is less than 3% due to the low intergranular corrosion susceptibility. The aging treatment at 700 °C results in the precipitation of Laves phase and (Nb, Ti)(C, N), but no Cr-carbides. The sensitization may be related to the segregation of Cr atoms around (Nb, Ti)-precipitates at the grain boundaries.

Statistical analysis to examine the influence of thermal aging on hybrid glass epoxy polymer composites with fillers of multi‐walled carbon nanotubes

AbstractE‐glass fibers are widely preferred due to ease of processing and its low cost, which has substantial scope in the fields of electronics and electrical insulation applications. Because of its low strength and corrosion resistance, use of E‐glass fibers is limited in aerospace and automotive applications. There is a need for enhancing the properties of the composite to overcome such limitations. Therefore, an attempt is made to introduce multi‐walled carbon nanotubes (MWCNT) as fillers into E‐glass fibers to meet the industry needs. In the current study, woven glass fiber of 5 layers and multi‐walled nano carbon fillers of 2, 4 and 6 by wt%, LY556 epoxy resin, and HY951 hardener were used to prepare 4 different type of composites along with the neat epoxy glass fiber reinforced polymer composites (GFRP). The hand‐layup route was used in the composite preparation due to its low cost, technological feasibility, and simple process setup. The developed samples were characterized for mechanical properties via tensile, flexural and impact tests. Tribological characteristics were performed by air jet erosion test. Chauvenet's criterion is applied for identifying the outliers (if any) from the data of repeated test properties. Taguchi's (orthogonal array) is selected for obtaining optimal hybrid composite, which yield better mechanical properties. Empirical relations are developed for the material properties in terms of process variables. The sample (4 wt% MWCNT) exhibited enhancement of 17.27% in tensile strength, 6% of impact strength and 7.3% of flexural strength when compared with neat epoxy GFRP. This hybrid composite is considered for thermal aging and observed at 60°C, 8% increase in tensile, 7% increase of impact and 15% in flexural strength due to the precipitation on carbon nano tubes along the gain boundaries. The present study recommends 4% MWCNT fillers in developing hybrid glass epoxy polymer composites for use in aerospace, automotive and civil construction industries due to economic and technological feasibility.Highlights Utilize low‐cost E‐glass fibers in electronics and electrical insulation applications. Improve composite properties for aerospace and automotive industries. Develop hybrid glass epoxy composites with 2 to 6 wt% MWCNT fillers. Examine wear characteristics under air jet erosion and study the impact of thermal aging on mechanical properties. Apply Chauvenet's criterion for outlier identification in measured properties datasets.

Surface integrity and corrosion resistance of 18CrNiMo7-6 gear steel subjected to combined carburized treatment and wet shot peening

Typically, a cost-effective and versatile carburizing process is used to improve the surface integrity of high-value-added gear components. In this study, carburized treatment and wet shot peening (WSP) were applied to increase the corrosion resistance of 18CrNiMo7-6 gear steel. The surface integrity and corrosion resistance after carburizing and combined treatment (carburized treatment + WSP) were analyzed. The results indicated that the combined treatment converted the retained austenite surface layer within approximately 45 μm from the surface into the martensitic phase, with a 13.9 % reduction in equivalent grain size and a 23.6 % increase in dislocation density compared with carburizing. Furthermore, electrochemical experiments in a 3.5 wt% NaCl solution indicated that the combined treatment process increased the corrosion resistance compared with carburizing (55.4 % lower corrosion current density and a higher Fe2+/Fe3+ ratio). Despite the high surface roughness obtained with combined treatment, the improved corrosion resistance is primarily ascribed to the high compressive residual stress and dislocation density. This study provides insights into the surface strengthening design of 18CrNiMo7-6 gear steel for corrosive environments—particularly the synergistic strengthening effect of carburizing and WSP.

Comprehensive impacts of the presence of proton exchange membrane on the efficiency of Mg-air fuel cell to remove nutrients and recover struvite

Mg-air fuel cell (MAFC) can achieve simultaneous recovery of phosphorus and nitrogen from wastewater in the form of struvite while generating electricity. This article investigated the comprehensive impacts of the presence of proton exchange membrane (PEM) on the efficiency of MAFC in treating synthetic wastewater, including phosphate and ammonium removal, power generation, and struvite generation. The results showed that the PO43−-P was completely removed within 20 min in the dural-chamber (DC) cell and the removal rate was 6.30 mg-P·cm−2·h−1, which was 1.55 times that of the single-chamber (SC) cell. The removal rate of NH4+-N in the DC cell was 3.37 mg-P·cm−2·h−1, which was 2.70 times that of the SC cell. However, the SC cell produced 63.10 mW·h of electricity, which was 4.61 times that of the DC cell. The precipitates were confirmed to be struvite, with a purity of 99.31 %(DC) and 93.95 % (SC). The low corrosion potential of Mg leads to hydrogen evolution corrosion during the reaction, resulting in low current efficiency, but the current efficiency increased with reaction time. PEM accelerated the hydrogen evolution corrosion, aggravated the magnesium corrosion, increased the internal resistance, and impaired electrical generation capacity, but provided more Mg2+ and alkalinity for the precipitation of struvite. In conclusion, the DC cell had a great capacity for removing nutrients (PO43− and NH4+) and producing high-purity struvite, while the SC cell had a strong ability to generate electricity.

High-Resolution Ultrasound to Quantify Sub-Surface Wrinkles in a Woven CFRP Laminate.

Carbon fiber reinforced polymer (CFRP) composites are popular materials in the aerospace and automotive industries because of their low weight, high strength, and corrosion resistance. However, wrinkles or geometric distortions in the composite layers significantly reduce their mechanical performance and structural integrity. This paper presents a method for non-destructively extracting the three-dimensional geometry, lamina by lamina, of a laminated composite. A method is introduced for fabricating consistent out-of-plane wrinkled CFRP laminate panels, simulating the in-service wrinkle observed in industries that utilize thick structure composites such as the vertical lift or wind power industries. The individual lamina geometries are extracted from the fabricated coupon with an embedded wrinkle from captured ultrasonic waveforms generated from single-element conventional ultrasonic (UT) scan data. From the extracted waveforms, a method is presented to characterize the wrinkle features within each individual lamina, specifically the spatially varying wrinkle height and intensity for the wrinkle. Parts were fabricated with visibly undetectable wrinkles using a wet layup process and a hot press for curing. Scans were performed in a conventional immersion tank scanning system, and the scan data were analyzed for wrinkle detection and characterization. Extraction of the layers was performed based on tracking the voltage peaks from A-scans in the time domain. Spatial Gaussian averaging was performed to smooth the A-scans, from which the surfaces were extracted for each individual lamina. The extracted winkle surface aligned with the anticipated wrinkle geometry, and a single parameter for quantification of the wrinkle intensity for each lamina is presented.

Corrosion failure analysis and solutions of aluminum alloy gas path plate used in sanding device of high-speed train

During the maintenance of a high-speed train, it was frequently found that the anodized aluminum alloy gas path plates in the sanding device had different degrees of corrosion. In this paper, SEM, EDS, XRD and LAD-EDTEST spectrometer were used to analyze the macro and micro morphology, elements and phases of corrosion product, element compositions of the matrix and assembly problem of the gas path plates. The mechanism of delamination spalling corrosion caused by local pitting corrosion of anodized aluminum alloy gas path plate was described. In addition, the properties of the coatings produced by different surface treatment methods and different substrate materials were compared. The test results indicate that the corrosion protection level of the micro-arc oxide coating is higher than that of the anodic oxide coating, which is mainly composed of γ-Al2O3 and contains a certain amount of α-Al2O3. Compared with 2A12-T4 aluminum alloy, the micro arc oxidation (MAO) coating of 6082-T6 aluminum alloy has lower porosity, higher hardness, higher corrosion potential, lower corrosion current, and better corrosion resistance, and 6082-T6 aluminum alloy is more suitable for use as the gas plate material. Meanwhile, it is proposed that the MAO coating with 35 μm can obviously improve the corrosion resistance of the gas path plate.

High-temperature corrosion-resistant alloy for waste-to-energy plants: Alloy designing, fabrication, and possible corrosion-resistance mechanism

This study designed a novel high-temperature corrosion-resistant alloy through thermodynamic equilibrium computations. The strength was determined by the integration of precipitation-strengthening species of nickel boride and tungsten solid solution strengthening, while high-temperature corrosion-resistant property was realized through optimized compositional design. Phase stability was enabled by the presence of a face-centered cubic structure. The alloy was fabricated and its corrosion-resistance performance was experimentally compared with other commercially available nickel- and iron-based alloys under simulated municipal solid waste combustion. The designed alloy with a composition of Ni-5B-6W-28Cr-13Al showed a low corrosion rate of ∼72 % < 13CrMo4-5TS and 1.08 % > Inconel 625. Economic analysis showed that Ni-5B-6W-28Cr-13Al has a cost-effectiveness ratio of 1:1.57 with respect to Inconel 625 and 1:0.09 with respect to 13CrMo4-5TS. Corrosion-resistance mechanism was explored using scanning electron microscopy coupled with energy dispersive spectroscopy, x-ray diffractometer, and DFT computations. The corrosion resistance occurred through the formation of a uniform tungsten-chromium-oxide film which inhibits inward diffusion of corrosive chlorine species. These findings provide insights into the development of alloys for high-temperature technologies.

Corrosion behavior of Ni-W coatings with and without macroscopic defects under different corrosion conditions

High pressure and high temperature corrosion performance of Ni-W coatings with and without macroscopic defects were investigated successively in live acid at 100 ℃, spent acid and formation water containing CO2&H2S at 160 ℃ by using weight loss method, surface characterization and high temperature and high pressure electrochemical test. Additionally, the corrosion performance of C110 steels was comparatively studied. The results show that compared with C110 steels, Ni-W coatings have better resistance to each harsh corrosive environment with lower uniform corrosion rate, pit depth and decreased corrosion current density. The corrosion rate of Ni-W coatings in both live acid and spent acid are acceptable for oilfields, and its corrosion rate (0.0978 mm/y) in formation water is categorized as moderate-degree corrosion. The corrosion scale consisting of NiS, Ni3S2 or Ni3S4 and a small amount of Ni(OH)2 is stable, compact and closely combined with the substrate, thus effectively slowing down the corrosion rate of Ni-W coatings during long-term immersion. However, the preferential dissolution of Ni causes a W-rich layer on the top layer of Ni-W coating, probably forming WO2, which tends to crack and aggravates the coating degradation. For Ni-W coatings with artificial defects, the galvanic effect and the catalytic role of Cl- synergistically accelerate the corrosion of the C110 substrate at the defect, and its pit depth is over 100 μm after being corroded in formation water. Notably, the corrosion of the C110 substrate extends laterally and deeply along the coating/substrate interface, promoting the local corrosion disbonding of the coating. Therefore, macroscopic defects in Ni-W coatings should be avoided in their practical application.

Fabrication of bioinspired SnO2/Few layered rGO nanocomposite coating for preserving Zn metal assets in various environments

The current study inspected the effect of incorporating two nanomaterials, namely reduced graphene oxide (rGO) and Tin oxide (SnO2), synthesized by hydrothermal method, upon improving the corrosion resistance in Zinc metal plate under different electrolytes. The XRD results confirms the formation of SnO2 nanoparticles with a crystalline tetragonal structure with 23.1 and 31.89 nm crystalline size. FE-SEM images indicated that the rGO is well embedded into the SnO2 nanoparticles. The TEM images and elemental mapping show the presence of crystalline nanoparticles embedded within the layers of graphene. In addition, the corrosion resistance of both pure SnO2 and SnO2-rGO nanocomposite is assessed using electrochemical techniques. The substrate coated with nanocomposite is exposed to three distinct electrolytes utilizing a Zn metal plate. Adding reduced graphene oxide (rGO) to the composite material creates a barrier that protects against corrosion and improves the charge transfer efficiency, resulting in lower corrosion rates and increased stability. The composite's combined impact of SnO2 and rGO provides exceptional corrosion resistance and the findings lead to the development of innovative and efficient ways to prevent corrosion, thereby ensuring materials' long-lasting and dependable performance in various industrial settings.

Shedding Light on the Failure Factors of Subsea Critical Fastener Bolts

Offshore facilities, such as oil and gas rigs, wind turbines, and related subsea equipment, typically use flanges fastened using bolts and nuts as the main connectors. In this study, multidisciplinary parameters, namely the preload torque used to tighten bolts, simulated subsea water currents, water temperature, and impressed current cathodic protection, were applied to ASTM A193 B7 bolts. An experimental supervisory control and data acquisition system was designed to obtain measurements every 5 min throughout a 21-day experiment. Finite element analysis was performed to predict the structurally vulnerable areas of the bolts. A strong correlation was found between the reference electrode readings and the measured electrical current, tightening torque, and water temperature. As the water temperature rises during the day, the reference electrode reading becomes less negative and the electrical current decreases. Subsea water currents cause about a four-time increase in the bolt corrosion rate, with unprotected bolts suffering a nine-time-higher corrosion rate than protected bolts. A unique supply–demand interaction is observed; less protection is supplied to areas with lower corrosion rates (lower demand for protection). Finally, scanning electron microscopy examination reveals new insights into the failure mechanisms of subsea bolts.

Anticorrosion Method Combining Impressed Current Cathodic Protection and Coatings in Marine Atmospheric Environment

In this study, a new anticorrosion method combining impressed current cathodic protection (ICCP) with coatings that can be applied to marine atmospheric environments is proposed. As the corrosion medium fills the cracks and pores of the coating, an electrolyte film layer is inevitably formed on the metal surface. Therefore, a graphene conductive coating with excellent chemical inertness and shielding performance is selected as the intermediate coating to form an electrolytic cell system with a metal substrate serving as the cathode and a graphene coating serving as the auxiliary anode. By studying the surface corrosion morphologies and electrochemical signals of the coating samples at different protection potentials and coating thicknesses, the optimal potential is determined to be 0.6 V, and the optimal coating thickness is determined to be 20 μm. The samples protected by the joint method have lower corrosion rates and better anticorrosion performance than those protected by the coatings alone.

Effects of rare earth oxides on wear resistance and corrosion resistance of 316L/TiC composite coating by laser cladding

In this paper, 316L/TiC composite coatings with different kinds of REOs (Y2O3, La2O3, CeO2, PrO2, Nd2O3) at identical contents (2%) were prepared on S355 marine steel using the laser cladding technology. The surface morphology, phase composition, microhardness, coefficient of friction curve (COF), Tafel curve and electrochemical impedance spectroscopy (EIS) impedance of the test specimens were studied with such instruments as scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer, Vickers microhardness tester, friction and wear tester, and multi-channel electrochemical workstation. The results show that the coating with REO added owns increased thickness and is uniform and dense without such defects as crack, and hole. The microstructure evolution mechanism of the coating from the bottom up is as follows: Cellular crystal, planar crystal → columnar crystal → equiaxed crystal. The phase composition of the coating with REO added remains unchanged, and is still Ni–Cr–Fe austenite phase and TiC phase. Further comparison shows that the coating with Nd2O3 added owns improved hardness, with a mean hardness of 3 times that of the substrate, and has a COF decreasing to 0.69, with wear loss becoming small. The coating with Nd2O3 added has the largest Ecorr, the smallest Icorr, large Z value and phase angle, the greatest Rct, and an nct value of 1, indicating that the coating has dense passivation film and small corrosion tendency, with low corrosion rate. Therefore, this study provides reference experimental and theoretical bases for application of 316L/TiC composite coating with Nd2O3 added at 2% in surface strengthening and repair of steel for marine engineering equipment.

Corrosion Behaviour of a Cr2O3 Coating on Mild Steel in Synthetic Mine Water

The Cr2O3 coating on the surface of ASTM A516 Grade 70 mild steel substrates was developed using the thermal plasma spraying process for protection against corrosion and wear. The microstructural behaviours for both coating and substrate were analysed using SEM and XRD techniques. The corrosion behaviours of the coatings and substrate in synthetic mine water with varying pH values (6, 3, and 1) were evaluated according to ASTM standards for potentiodynamic polarisation measurements. Tafel plots were drawn to determine the corrosion rates. Vickers hardness of the coatings and substrate were measured. The Cr2O3 coating exhibited cracks due to the solidification and cooling process, as well as some pores between the top and bonding layers caused by unmelted or partially melted particles. The corrosion tests revealed that a decrease in pH levels led to increased corrosion rates in both samples. The Cr2O3 coating demonstrated superior corrosion resistance, ranging from 0.036±0.003 mm/year to 0.110±0.004 mm/year, compared to the mild steel substrate, which ranged from 0.262±0.021 mm/year to 0.336±0.026 mm/year, across all pH values. Moreover, it exhibited significantly greater hardness (1260±77 HV3) than the mild steel substrate (180±14 HV3). The lower corrosion rates and higher hardness of Cr2O3 coating than the mild steel substrate make it a suitable coating in applications where corrosion resistance and high hardness properties are essential.

Effects of heat treatment on the nano-indentation, corrosion and cavitation erosion behavior of 17-4PH stainless steel by laser surface melting

The effects of heat treatment on the microstructure, residual stresses, nano-indentation behavior, the resistance to the corrosion and cavitation erosion (CE) of 17-4PH stainless steel (17-4PH SS) by laser surface melting (LSM) were thoroughly investigated. Experimental results showed that the samples were mainly composed of martensite phase, and the NbC precipitations formed after heat treatment. The distribution of NbC precipitations was more uniform in the sample (S3) after solution treatment 3 h at 1040 °C + aging treatment 3 h at 480 °C. The grain size was increased for the samples after heat treatment. This heat treatment processing significantly reduced the residual stresses generated from the LSM process, and the nano-indentation behavior of the LSM samples after heat treatment was improved compared to that of the LSM sample without heat treatment. The S3 sample displayed the highest corrosion resistance as indicated by the low corrosion current density (icorr), high pitting potential (Epit) and high polarization resistance (Rp). The CE resistance of samples after heat treatment in 3.5 wt% NaCl solution was higher than that of the sample without heat treatment. Among them, the S3 sample exhibited the highest CE resistance, and its CE mass loss was only 59.5 % of the sample without heat treatment. The excellent CE resistance resulted from the appropriate combination of mechanical properties, corrosion resistance and self-recovery ability of the passivation film.

Experimental and ab initio studies of enhance photocatalytic efficiency of La-doped ZnO/g-C3N4 nanocomposites for bromothymol blue dye degradation

The ability of photocatalysis to clean up environmental contamination, notably in the treatment of water and air, has received extensive research. The composite materials synthesized by the coprecipitation method were made of ZnO and graphitic carbon nitride (g-C3N4) with various concentrations of lanthanum doping (La-ZnO). It was discovered that La metal ions were evenly distributed throughout the layered stacking structures of ZnO nanosheet, which had an impact on the band structure and increased the rate of electron-hole separation and visible light absorption. First-principles calculations show that La-doped ZnO-gC3N4 possesses a direct band gap and a type-II band structure with the conduction band minimum and the valence band maximum located in separate layers. A built-in electric field from the gC3N4 to the La-doped ZnO has been established through an analysis of charge density difference, Bader charge, work function, and band alignment. The electron-hole pair becomes spatially separated as a result, which increases the photodegradation activity. High interfacial charge transfer, efficient charge separation and migration, and high visible light optical absorbance were caused by the direct coating of ZnO on an ultra-thin g-C3N4 layer. The 0.6 % La-doped ZnO-gC3N4 degraded 97 % of the bromothymol blue (BB) dye, which was four times higher than the bulk ZnO, which could remove only about 21 % of the dye at the same time. The combined effects of lower photo corrosion, higher solar light usage owing to a hollow structure and heterostructured semiconductor photocatalysis contribute to this increased photocatalytic activity. The capacity of La-doped ZnO/g-C3N4 nanocomposite to effectively break down BB dye via photocatalysis suggests that it has the potential to address the problems associated with dye pollution in water systems.