Immersion Test Research Articles

Assessing the effect of different biodiesels on corrosion of nickel alloy

This investigation explores the corrosion behaviour of Ni alloy (UNS718), which is a potential material for storing biodiesel and making engine components. The study also examines the connection between Ni alloy corrosion and biodiesel degradation. Immersion tests were conducted using in-house biodiesels to evaluate the corrosion rates of Used Cooking Oil (UCOB), Karanja oil (KOB), and Jatropha oil (JOB) biodiesels on Ni alloy (UNS718). The results highlighted the role of corrosion product morphology and the formation of corrosion-driven pitting, cracks, etc., on Ni alloy when exposed to different biodiesels such as KOB, JOB, and UCOB. The study utilized gravimetric techniques to measure the corrosion rate and advanced analytical tools such as FESEM, EDS, XPS, NMR and XRF. It revealed decreased corrosion rates of Ni alloys with prolonged biodiesel immersion. For example, after 2160 h, Jatropha biodiesel exhibited a corrosion rate of 0.000699 mm/year, while the corrosion rates of Ni alloy exposed to UCOB and KOB were 0.001398 mm/year and 0.001048 mm/year, respectively. The study also suggests a detailed mechanism of Ni alloy corrosion when exposed to different biodiesels such as Karanja, Jatropha, and Used Cooking Oil.

Research of two kinds of PANI@semiconductor based photocathodic coating corrosion protection effect and mechanism

PurposeThis study aims to report the development and experimental evaluation of two kinds of PANI@semiconductor based photocathodic anti-corrosion coating, for application on stainless steel substrates.Design/methodology/approachPANI was in situ chemical polymerized on TiO2 and BiVO4 particles, and FT-IR and SEM/EDS were used to understand the characteristics and elemental distribution of the composite particles. Composite coatings, which consisted of epoxy, PANI@TiO2 or PANI@BiVO4 and graphene, were prepared on the 304L stainless steel. Photoelectrochemical response measurement, electrochemical tests and immersion tests were used to assess the anti-corrosion performance of the prepared coatings in 45°C 3.5 wt.% NaCl solution. And the corrosion protection mechanism was further explained by combining with surface observation.FindingsThe photoelectrochemical response tests revealed the good photocathodic effect of the coatings, and the reversible oxidation-reduction properties of PANI (pseudocapacitive effect) leading to the repeated usage of the coatings. Consequently, the anti-corrosion mechanism of the composite coating is attributed to the physical barrier effect of the coating, the anodic protection effect of PANI and the photocathodic and energy store effect.Originality/valueThese kind coatings could prevent corrosion from day to night for stainless steel, which has great engineering application prospects on stainless steel corrosion protection.

Composite fluorescence probe towards a smart coating for early corrosion detection of carbon steel

Herein, a composite fluorescent probe was developed as a smart indicator in acrylic resin-based coatings for the early detection of steel corrosion. The Fe3+-sensitive Rhodamine B derivative probe (Rxbxja) was synthesized, and the SiO2 nanoparticle-supported probe S-Rxbxja was prepared through the hydrolysis of tetraethyl orthosilicate (TEOS). The successful synthesis of S-Rxbxja was confirmed using a variety of techniques i.e. SEM and FTIR. A fluorescence microscope was utilized to assess the self-reporting performance of coatings. EIS and seawater immersion tests were employed to evaluate the corrosion resistance of the coating. The fluorescence test results revealed the absence of premature fluorescence in the composite coating, owing to the exceptional compatibility between S-Rxbxja and the coating. The scratched area in the 0.5 wt% sensor-doped coatings exhibited fluorescent and colorimetric dual-channel signals after soaking in 3.5 wt% NaCl solution for 2 h before any visible corrosion phenomenon. The EIS results demonstrated that the |Z|0.01Hz value of composite coating maintained 107 Ω cm2 even after being immersed in a 3.5 wt% NaCl solution for 7 days, indicating the excellent anti-corrosion properties of the S-Rxbxja coating. Moreover, mechanical property tests showed that the S-Rxbxja coating had excellent mechanical properties due to the introduction of SiO2 nanoparticles.

Laser powder bed fusion of Mg–Zn–Zr alloy: Formability, microstructure evolution and biodegradation behavior

Laser powder bed fusion (LPBF) was used to fabricate Mg–Zn–Zr (ZK60) parts, with a thorough investigation of processability by varying laser power and scanning rate. The combined effect of these parameters, which determines laser energy density, significantly impacted the forming quality of LPBF ZK60. Dense parts (over 99%) free of visible defects such as pores and cracks were achieved at a laser energy density of 74.1 J/mm2. The formation mechanisms of pores and cracks were extensively analyzed concerning the characteristics of the molten pool and subsequent cooling behavior. The LPBF ZK60 parts exhibited extremely fine grains, with an average grain size of 3.2 μm. Both equiaxed and columnar grains were observed, with a central equiaxed zone in the melt pool and a perpendicular lamellar zone along its boundary. Additionally, the Mg7Zn3 eutectic phase precipitated within the α-Mg matrix of ZK60. Immersion and electrochemical tests indicated that the XZ plane displayed superior corrosion resistance, attributed to fewer deformation regions and lower dislocation density. Furthermore, in vitro cell experiments confirmed that the ZK60 alloy possesses good biocompatibility.

The influence of acid rain on asphalt and its mixture performance, simulation and micro-mechanism exploration

Acid rain will destroy asphalt roads and affect human production and life. Therefore, this study has designed a new indoor simulated acid rain erosion test, and explored the effects of acid rain on the properties of 70# petroleum asphalt, SBS asphalt and their mixtures and the acid rain erosion mechanism from the micro and macro perspectives. In this paper, the influence of acid rain erosion on the microscopic properties of asphalt has been revealed through microscopic experiments. Through the combination with the basic performance test of asphalt, the effect of acid rain erosion on the conventional properties of asphalt was studied. The effects of acid rain on the properties of road asphalt mixtures were studied by Marshall immersion and high-temperature rutting tests. The results show that there is no obvious chemical reaction between the two kinds of asphalt after acid rain erosion, but the surface structure and morphology have changed significantly. There was a mass loss, the decreases of the softening point and ductility, and an increase of the penetration; the residual stability and high temperature resistance of both asphalt mixtures were reduced. In the worst case, the quality of petroleum asphalt was lost by 82.2%, the softening point and ductility decreased by 9.6% and 16.9% respectively, the penetration degree increased by 3.1% and the residual stability and dynamic stability of petroleum asphalt mixture decreased by 8.82% and 27.9% respectively. The mass loss of SBS asphalt was 82.5%, the softening point and ductility decreased by 5% and 3.3% respectively, the penetration increased by 2.6%, and the residual stability and dynamic stability of SBS asphalt mixture decreased by 4.82% and 25.4% respectively. In general, under the action of acid rain, the performance of 70# oil asphalt, SBS asphalt and their mixtures are affected to varying degrees. The specific performance is to destroy the original shape of asphalt, resulting in the loss of quality of asphalt, the reduction of deformation resistance, high temperature stability and low temperature stability of asphalt, weakening the high temperature stability and water stability of asphalt mixture, and leading to the decline of road performance.

Improving shale hydration inhibition with hydrophobically modified graphene oxide in water-based drilling fluids

Frequent wellbore instability issues caused by shale hydration and dispersion are encountered in water-based drilling fluids. In order to mitigate shale hydration, a hydrophobic graphene oxide (HGO) was prepared as a new shale inhibitor and characterized. The effectiveness of HGO in inhibiting shale hydration was evaluated through hydration expansion, hydration dispersion, and bentonite sheets immersion tests. The expansion height of bentonite in HGO (3.87 mm) was lower than that of commercial shale inhibitors potassium chloride (KCl, 4.64 mm) and polyether amine (PA, 4.33 mm). The shale recovery rate in HGO at 80 °C was 86.25 %, which was superior to KCl (46.60 %) and PA (78.25 %). Furthermore, the morphology of bentonite sheet remained more intact after immersion in HGO. Additionally, the inhibitory mechanism of HGO was studied in-depth, employing zeta potential, particle size, surface tension, wettability, capillary rise height, and scanning electron microscopy (SEM) tests. By virtue of electrostatic attraction, HGO could tightly adsorb to the shale surface, resulting in a hydrophobic blocking membrane, thereby greatly reducing water infiltration. Following interaction with shale at a concentration as low as 0.5 %, the water contact angle exhibited a notable enhancement, rising from 22.49° to 86.69°. And it could also decrease the capillary self-suction capacity of shale, further reducing water adsorption. Consequently, HGO exhibited significant potential for inhibiting hydration in shale drilling.

The effect of polylactic acid ordering on the long-term corrosion protection capacity of biodegradable magnesium alloys

The polylactic acid (PLA) coatings of different crystallinity were prepared on biodegradable Mg-2.2Zn-0.3Ca alloy wires to improve the long-term anti-corrosion properties. The composition characteristics and microstructure of the samples were investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscope (FTIR), wide angle X-ray diffraction (WAXD) and scanning electron microscope (SEM). The corrosion resistance of all samples was investigated by immersion tests and electrochemical techniques in vitro simulated body fluid (SBF). The results indicated heat treatment improved the crystallinity of PLA coating and heated-coating performed protective behaviors in the short and long-term immersion. The corrosion rate of heated samples was lower than that of unheated samples and exhibited superior long term protective effect for Mg alloy wires. The lifetime of heated sample (H2) increased significantly from 33 to 55 days. The initial electrochemical performance of unheated coating was better than heated coating, but it declined more rapidly during the long-term immersion. These results indicated that PLA coating could not ignore the effect of its crystallinity to anti-corrosion ability, and only the suit heat treatment makes PLA coating more ordering and achieves higher corrosion resistance in vitro immersion. Therefore, it has promising potential by controlling effectively the PLA ordering for surgical implant applications.

Evaluating the Performance of Recycled Concrete Aggregate in AC-BC Mixture Using Marshall Immersion and Cantabro Loss Tests

Evaluating the Performance of Recycled Concrete Aggregate in AC-BC Mixture Using Marshall Immersion and Cantabro Loss Tests

Corrosion behavior of 2A97 Al−Cu−Li alloys in different thermomechanical conditions by quasi-in-situ analysis

As a promising material in the aircraft industry, 2A97 Al−Cu−Li alloy exhibits high corrosion susceptibility that may limit its application. In the present work, to illustrate the influences of precipitate and grain-stored energy on localized corrosion evolution in 2A97 Al−Cu−Li alloy, cold working and artificial aging were carried out to produce 2A97 Al−Cu−Li alloys under different thermomechanical conditions. Quasi-in-situ analysis, traditional immersion test and electrochemical measurement were then conducted to examine the corrosion behavior of 2A97 alloys. It is revealed that precipitate significantly affects Cu enrichment at corrosion fronts, which determines corrosion susceptibility of alloys, whereas grain-stored energy distribution is closely associated with localized corrosion propagation. It is also indicated that quasi-in-situ analysis exhibits a consistent corrosion evolution with traditional immersion tests, which is regarded as a proper method to explore localized corrosion mechanisms by providing local microstructural information with enhanced time and spatial resolutions.

Toxicity and enzymatic mechanism of Citrus spp. essential oils and major constituents on Haemaphysalis longicornis (Acari: Ixodidae) and non-target Harmonia axyridis (Coleoptera: Coccinellidae)

Plant essential oils (EOs)-based acaricides have been recognized as environmentally-friendly alternatives to synthetic acaricides because of their low toxicity against non-target species. Despite this, there are knowledge gaps regarding the toxicity mechanisms of plant EOs against non-target species. Here, the toxicology and enzymatic mechanism of Citrus reticulata and Citrus lemon EOs were evaluated against the vector pest, Haemaphysalis longicornis, and non-target ladybird beetle, Harmonia axyridis. Both EOs were mainly composed of d-Limonene, followed by β-Myrcene and γ-Terpinene in C. reticulata, and (−)-β-Pinene and γ-Terpinene in C. lemon. Citrus reticulata and C. lemon EOs were toxic to Hae. longicornis, with 50 % lethal concentration (LC50) values estimated at 0.43 and 0.98 μL/mL via nymphal immersion test, and 42.52 and 46.38 μL/mL via spray application, respectively. Among the constituents tested, β-Myrcene was the most effective, with LC50 values of 0.17 and 47.87 μL/mL via immersion and spray treatment, respectively. A significant mortality of non-target Har. axyridis was found when treated by the EOs at concentrations two times greater than LC50 estimated against H. longicornis. The biochemical assay revealed that the EOs induced changes in the antioxidant enzyme activity of superoxide dismutases, catalase, and glutathione peroxidase in Hae. longicornis and Har. axyridis. The results demonstrated the acaricidal potential of citrus EOs and their major constituents for tick control, revealed the risk of the EOs to non-target species, and provided relevant insights into the mechanisms underlying their toxicity.

Corrosion shielding effect of polyaluminium sulphate on metallic aluminium during the solidification of radioactive incineration bottom ash by low alkalinity cement

Radioactive incineration bottom ash containing metallic Al is difficult to be directly solidified in the cement matrix due to the generation of hydrogen gas during the reaction of aluminium with alkali pore solution of cement paste. In this study, the simulated incineration bottom ash (SIBA) containing metallic Al was successfully and directly solidified by polyaluminium sulphate (PAS)-modified low alkalinity cement (LAC), and the mechanism of the corrosion shielding effect of PAS on metallic Al was characterized by a range of analytical techniques. The results indicate that the cement waste form containing 29.56 wt% SIBA achieved a compressive strength of 16.6 MPa at 28 days of hydration, which increased by 13.3 % and 36.1 % after freeze-thawing test and immersion test, respectively. The 42d cumulative fraction leached of Nd3+ and Ce3+ were 1.74×10−7 cm and 3.40×10−7 cm, respectively. The corrosion degree and corrosion rate of Al sheets in LAC with PAS addition was much lower than that without PAS at early and late age hydration, by transforming thick porous corrosion layer to thin dense one. The mineral phase of corrosion product remained as bayerite (Al(OH)3), regardless of whether PAS was added. The addition of PAS reduced the hydrogen gas generation and prevented the dissolution of Al(OH)4- from metallic Al sheet. The hydrolysis of PAS produced a large amount of Al(OH)4- in pore solution, which extended the pH range for Al(OH)3 passivation by preventing the transformation of Al(OH)3 protection layer on the Al sheet surface to Al(OH)4- in the pore solution, and accelerated the formation of ettringite to decrease the pH of pore solution. This study cast the light on the direct solidification of metallic-aluminium-containing incineration bottom ash or Al bulks by cement-based materials without the need for complex pretreatment processes.

Phytochemical investigation and in vitro and in vivo pharmacological activities of methanol extract of whole plant Argyreia capitiformis (Poir.) Ooststr

BackgroundA. capitiformis (Poir.) Ooststr has a long history of usage as a medicinal cure for a wide variety of illnesses in many different cultures. Pharmacological properties and phytochemical characterization of the crude A. capitiformis whole plant are evalutted, in this paper.MethodsAntioxidant activity was tested by the DPPH free radical scavenging method. In vitro anti-arthritic, anti-inflammatory, and cytotoxic effects were assessed using Bovine serum albumin (BSA), protein denaturation method, and brine shrimp mortality assays, respectively with antihelmintic activity through Pheretima Posthuma worms. Acetic acid-induced writhing, hot plate and tail immersion testing assessed in vivo analgesia. CNS activity was evaluated through elevated plaze maize, open field, hole cross, and head dipping method.ResultsPhytochemiical investigation of A. capitiformis showed the presence of alkaloid, saponin, terpennoids, steroid and flavonoids etc. with the % yield of crude 2.04%.With an IC50 of 45.35 µg/ml, the whole plant methanolic preparation has antioxidant activity equivalent to ascorbic acid. Anti-arthritic protein blocking dropped from 74.25 ± 0.12% to 12.18 ± 0.12%. 1000 µg/ml extract demonstrated 54.05 ± 0.12*% anti-inflammatory activity with protein denaturation. In the cytotoxicity assay, the extract had 129.72 µg/ml LC50 and the positive group 34.67 µg/ml. Unlike Albendazole, the methanol extract triggered mature earthworms at 50 mg/ml. The extract’s analgesic efficacy at 200 and 400 mg/kg was statistically significant (p < 0.001) in the acetic acid writhing and tail immersion method. The hot plate technique yielded statistically significant results only at 400 mg/kg (p < 0.001). Only 400 mg/kg was statistically significant in the Elevated Plaze Maize and Hole Board Procedure (p < 0.01). The hole cross and open field methods yielded highly statistically significant outcomes at 200 and 400 mg/kg (p < 0.001).ConclusionIn this research, the whole crude methanol extract of A. capitiformis revealed phytochemicals, antioxidants, in vitro anti-inflammatory and anti-arthritic properties, cytotoxicity, anti-helminthic, in vivo analgesic, and CNS inhibitory activities.

Corrosion behavior of additively manufactured FeCrAl in out-of-pile light water reactor environments

Iron-Chromium-Aluminum (FeCrAl) alloys are candidate materials for the cladding of light water reactor (LWR) fuels. The FeCrAl alloys in general range in Cr composition from 12% (C26M) to 21% (APMT). In this work, the general corrosion behavior of Additively Manufactured (AM) C26M coupons was compared to the behavior of traditional Powder Metallurgy (PM) coupons. Immersion testing were conducted for 12 months at 288 °C and 330 °C in pure water containing either oxygen or hydrogen. Results show that the mass change of AM specimens in hydrogenated water was like the mass change of PM specimens. In oxygenated water, the mass change of AM coupons was higher and less reproducible than for the PM coupons. Porosity in the AM specimens makes their behavior less predictable in high-temperature water.

Fostering biomineralization and biodegradation: nano-hydroxyapatite reinforced iron composites for biodegradable implant application

Iron (Fe) is regarded as a candidate material for biodegradable metallic implants due to its biocompatibility and ability to degrade in physiological environemnt. However, the degradation rate in the physiological environment is too slow for clinical applications. It is necessary to accelerate the rate such that the degradation is compatible with tissue growth. Furthermore, the implant material needs to be bioactive for promoting osteointegration, osteoconductivity, cell proliferation and biological apatite formation. Nano-sized bioactive hydroxyapatite (nHA) was incorporated into a porous Fe matrix to enhance the bioactivity and degradation rate. Electrochemical studies in biomemtic NaCl solution, revealed that incorporation of nHA in porous Fe can increase the degradation by 2.5 times compared to the pure iron counterparts with similar porosity. Furthermore, immersion tests in simulated body fluid (SBF) revealed that nHA added samples displayed enhanced biomineralization and degraded at a rate three times faster than pure iron in this environment. The incorporation of nHA into the iron matrix aided in the formation of biomineralized hydroxyapatite. The composite surface promoted the cell adhesion and proliferation and the L929 fibroblast cells exhibited good cell viability. It is proposed that porous morphology incorporated with nHA can improve biomineralization and tailor the degradation rate of Fe-based materials in physiological environment.

Metal-Fluoride Complex Stability Constant in Acid Solution as an Indicator to Identify the Corrosion Behavior of Metal Cations on Titanium

The Ti was immersed in 0.058 mol/L NaF containing 1.68 mol/L H2SO4 solution with different metal cations (Ca2+, Cu2+, Fe2+, Mg2+, Mn2+, Ni2+, Zn2+, Al3+, and Fe3+) for 7 d to identify the role of metal cations on corrosion behavior of titanium. To elucidate the role of metal cations on the corrosion behavior of Ti in acid solution, the standard electrode potential, E0, hardness of metal cations, X, and metal-fluoride complex stability constant, Kn, were chosen as the potential indicator. It is found that the mass loss fraction obtained from the immersion tests as a function of the metal-fluoride complex stability constant, Kn, has the highest correlation coefficient (0.92). The metal cations (Al3+ and Fe3+) with higher stability constant of the metal-fluoride complex in acid solution, (Kn &amp;gt; 3.27), show corrosion inhibition effect on Ti in acid solution. The Kn could be a suitable indicator to understand the role of metal cations on the Ti corrosion mechanism.

Enhanced anti-corrosion characteristics of epoxy-functionalized graphene oxide nanocomposite coatings on mild steel substrates

This experimental investigation focused on coating of functionalized graphene oxide (FGO) on the mild steel to minimize corrosion, using a new method. Prior to the coating, the fundamental chemical and morphological structures of FGO were studied with aid of some characterization techniques: X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Various epoxy/FGO coating formulations with 10, 20, 30, 40 and 50 ppm of FGO were prepared and coated on the mild steel substrate, adopting dip coating method. Immersion test was carried out to observe the corrosion inhibition efficiency of the graphene. The adsorption isothermal behavior was also studied using various models and compared with the data obtained from the experimental results. From the results obtained, the formation of irregular rough patches and separation of platelets like zebra lines indicated the formation of graphene nanoparticles, as observed through morphological analysis. The occurrence of sharp peak at 24.3° in the XRD pattern depicted the existence of graphene in nanoscale. Electrochemical impedance (EI) and potentiodynamic polarization (PP) studies reported the maximum corrosion inhibition efficiency of 87% at 50 ppm concentration of epoxy/FGO. It was evident that an increasing concentration of graphene exhibited significant corrosion resistance in both studies. The bonding energy of randomly oriented graphene platelets reduced the removal of metal, delaying the crack propagation in tortuous path on the coated surface. These results established the significance and applicability of this study in various relevant industries.

Tailoring the mechanical strength and corrosion resistance of aluminum matrix composites through biochar reinforcement at varied weight percentages

This study introduces an innovative approach to fabricate aluminum matrix composites strengthened with biochar, derived from renewable biomass sources. A systematic investigation of varying biochar weight percentages (0, 2.5, 5, 7.5, and 10 wt%) reveals substantial improvements in mechanical properties and corrosion resistance. Mechanical assessments, including compressive strength and hardness, demonstrate a significant enhancement in mechanical strength with biochar incorporation. In this study, it was discovered that the composite with 7.5 wt% biochar exhibits an optimal balance, displaying an 8.83% increase in compressive strength and a 15.15% rise in hardness compared to the base aluminum matrix. The study further evaluates corrosion behavior through electrochemical analyses and immersion tests in 3.5% NaCl corrosive environments, highlighting the superior corrosion resistance of biochar-reinforced composites. Corrosion rates decrease by 73% in the composite with 10 wt% biochar for the 24 h immersion time, affirming its protective barrier against corrosive agents. This research provides quantitative insights into tailoring mechanical and corrosion properties in aluminum matrix composites through biochar reinforcement, offering a promising avenue for sustainable material development. The resulting materials exhibit not only an 8.83% increase in mechanical strength but also a 73% reduction in corrosion rates, offering valuable uses in industries that need strong, eco-friendly solutions.

Comparison of the effects of different ageing tests on flexural properties of flax fibre composites

This study investigates the changes in the flexural properties and microstructure of flax fibre thermoset composites induced by accelerated and natural ageing methods. The reductions in flexural strength and modulus of composites, ranging from 14 %–48 % and 6 %–57 %, respectively or even an increase in flexural properties after the cyclic ageing test, show the diverse effects of the tests on the flax composites. Only small differences in the composites' performance were found between the natural ageing under the shade and natural ageing exposed to sunlight. The long-term moisture cycling did not cause progressive damage; instead, the composite's flexural properties increased, likely due to an improvement in both the fibre's and matrix's mechanical properties. The water immersion test seems to be predictive of the long-term durability of uncoated flax composites in natural conditions. Microstructure analysis supports composites' flexural test results, with flax/epoxy showing superior properties compared to flax/polyester. The results suggest that uncoated flax composites can withstand extreme humidity changes, but perhaps not in applications wherein composites come in contact with liquid water for long periods, likely due to the effects of leaching. The varied impacts of the different ageing tests on flax fibre composites underscore the need to thoroughly select testing protocols that simulate service conditions relevant to the composites' intended application.

Experimental Study on the Chlorine-Induced Corrosion and Blister Formation of Steel Pipes Coated with Modified Polyethylene Powder.

In this study, chlorine-induced corrosion and blister formation on steel pipes (SPs) coated with modified polyethylene powder (MPP) were evaluated through various tests, including chlorine exposure, wet immersion, and temperature gradient experiments. The results confirmed that the extent of corrosion and iron leaching varied with the coating type as expected. In batch leaching tests, no corrosion was observed on modified polyethylene-coated steel pipes (MPCSPs) within a chlorine concentration range of 0 mg/L to 10 mg/L; similarly, there were no significant changes in specimen weight or iron levels. In contrast, the control group with uncoated SPs exhibited significant iron leaching and corrosion, a trend consistent in sequential leaching experiments. SEM analysis after a month of chlorine exposure revealed no significant corrosion on MPCSPs, and SEM-EDX confirmed no major changes in the carbon bond structure, indicating resistance to high chlorine concentrations. Comparative analysis of wet immersion and temperature gradient tests between MPCSP and conventional epoxy-coated SP (ECSP) specimens revealed that MPCSPs did not develop blisters even after 100 days of immersion, whereas ECSPs began showing blisters as early as 50 days. In temperature gradient tests, MPCSPs showed no blisters after 100 days, while ECSPs exhibited severe internal coating layer blisters.

Effect of pH on the controlled release of benzotriazole from halloysite clay nanotubes for corrosion protection of mild steel

Due to the increase in severe consequences of mild steel corrosion, the development of coatings with improvement in corrosion-resistant properties has become very essential. In this work, benzotriazole (BTA) was encapsulated into halloysite nanotubes (HNTs) for inhibiting the corrosion of mild steel surface. The BTA-encapsulated HNT exhibits pH-responsive properties over a wide range of pH. It was found that a large amount of BTA was released at pH 3 (48 %), followed by pH 7 (30 %) and least in the case of pH 10 (20 %). At neutral pH, a rapid release of BTA was observed during initial exposure, reaching a steady-state later, with no significant release further. A salt immersion test was carried out after immersing mild steel (MS) substrates in BTA-HNT nanopowder dispersion in 3.5 wt% NaCl at different pH. SEM images and EDS maps confirmed that corrosion product formation on MS surface at pH 3 was significantly more with corrosion pits along with HNTs throughout the surface. At pH 7 and 10, corrosion pits were observed with very few halloysite nanotubes on the surface. An optimum amount of BTA is required to inhibit corrosion, excessive release may cause more Cl− ions to penetrate, leading to more corrosion. Electrochemical data also reveals the same trend, where the icorr value was maximum for pH 3 (1.09 × 10−5 A/cm2) > pH 7 (4.74 × 10−6 A/cm2) > pH 10 (3.43 × 10−6 A/cm2). Therefore, results suggest that BTA-encapsulated HNT can be efficiently incorporated into the coating matrix for their controlled release to provide corrosion protection under varying neutral and alkaline marine environments.