A NOVEL COMPOSITE LA-CONVERSION COATINGS FOR ENHANCED ANTI-CORROSION PERFORMANCE UNDER A HARSH AQUEOUS ENVIRONMENT

. The ceramic lanthanum nanoparticles with uniformly dispersed spherical nanostructures were successfully synthesized using sonication-assisted synthesis. The morphologies and phase compositions were assessed and investigated. The electrochemical impedance analysis potentio-dynamic polarisation measurements were used to calculate the corrosion protection properties of prepared ceramic lanthanum nanoparticles. The La 2 O 3 nanoparticles were added as a surface coating layer to enhance the corrosion resistance of low-carbon steel. The particles' impact on coating development, morphology, and corrosion inhibition efficacy were studied. After particle integration, results show a dramatic reduction in porosity and thickness, affecting corrosion resistance. Incorporating ceramic lanthanum nanoparticles into a coating reduces porosity and increases hardness, improving corrosion resistance; the result implies the suggested technique is viable for creating functionalized coatings on low-carbon-based materials. The results also demonstrated that these methods may increase the development and protectiveness of the coating. There was a crucial nano particulate La 2 O 3 level at which the conversion coatings exhibited the best protective qualities. As it increased the corrosion potential and lowered the anodic current, the composite La-conversion coatings may offer substantial corrosion protection for prolonged immersion in a 3.5% NaCl solution.


INTRODUCTION
One of the primary areas of focus is advancing organometallic or inorganic chemicals to facilitate the synthesis of nanoparticles.Using the novel molecule has potential benefits and presents a novel strategy for synthesizing nanomaterials, enabling control over nanocrystal characteristics such as size, shape, and dispersion [1].The decrease of particle size to the nanoscale scale yields a range of intriguing features when contrasted to the qualities exhibited by bulk materials.Due to their vast surface area, metal oxide and hydroxide nanoparticles significantly benefit traditional materials in several applications.Within the ever-evolving field of materials science and engineering, the continuous endeavour to discover innovative materials with unique characteristics persists as an enduring endeavour [2].The development of effective anti-corrosion coatings is one area that is of the utmost significance in this pursuit.These coatings are intended to safeguard essential infrastructure, industrial equipment, and consumer items from the persistent bombardment of corrosives.Corrosion, often known as the "silent adversary," has substantial economic and safety implications, resulting in yearly costs of billions of dollars and compromising the structural integrity of various infrastructures and equipment.In addition to its economic importance, corrosion has the potential to frustrate safety measures, resulting in severe breakdowns within essential systems, presenting environmental risks, and endangering the safety of people.To address this widespread issue, researchers persistently investigate novel carried out, and scanning electron microscopy was employed to examine the surface morphology following corrosion and wear tests [9].Some researchers concentrate on exploring the collaborative interplay between materials and coating technologies, shedding light on their joint contribution to enhancing the anticorrosive properties of superhydrophobic coatings.The analysis encompasses the impact of materials, spanning metallic, non-metallic, and hybrid classifications, each characterized by distinctive structural features and energy properties that enhance anticorrosive performance.Moreover, the review underscores the significance of dynamic fabrication strategies, emphasizing their crucial role in achieving improved corrosion inhibition activities [10].Researchers investigate and compare the tensile strengths of different samples comprised of aluminium alloy AA8011, both before and after experiencing corrosion.The study utilizes the Linear Radial Basis Function (LRBF) model to graphically represent and comprehend the data.It concludes that specimens subjected to a welding speed (WS) of 45 mm/min, a shoulder diameter (SD) of 21 mm, and a tool rotation speed (TRS) of 1200 rpm demonstrate the highest tensile strength among the specimens, both pre-and post-corrosion [11].
The present study aims to explore the synthesis of La2O3 by using sonochemistry as a unique method, focusing on its potential use in corrosion prevention.Moreover, this research extends the scope of investigation by utilizing three different acidic, basic, and neutral electrolytes (1 M KOH, 1 M HCl, and 3.5 wt.% NaCl) during the synthesis process, aiming to reveal the distinctive characteristics and performance variations of the resultant La2O3 coatings.Thus, the comprehensive investigation of the synthesis of La2O3 via sonochemistry and its application for anticorrosion purposes using three distinct electrolytes has been examined and investigated using several physicochemical techniques, with optical properties examined through ultraviolet (UV) spectroscopy and morphological analysis via scanning electron microscopy (SEM), along with EDAX and corrosion studies examined using different electrolytes and electrodes.

EXPERIMENTAL
The precursor material used in the present experiment was lanthanum(III) nitrate hexahydrate (La(NO3)3.6H2O),whereas ammonia (NH4OH) was used as the reducing agent for the synthesis of ceramic lanthanum oxide nanoparticles.Furthermore, the washing process comprised ethanol and distilled water as solvents, in addition to the aforementioned compounds.

Synthesis of ceramic lanthanum nanoparticles
To produce the ceramic La2O3 nanoparticles, 100 mL of distilled water were given 0.1 M of lanthanum nitrate to dissolve.While vigorously stirring the mixture, the stoichiometrically appropriate quantity of lanthanum nitrate solution was added gradually.
As stated earlier, the solution was stirred for 30 minutes before ammonia was added to it progressively until it reached a pH of 10.Subsequently, the solution was transferred to a probetype sonicator operating at a frequency of 40 kHz.The sonicator was used to subject the solution to sonication for duration of one hour.The temperature of the solution reached a high of 50 ºC while it was being sonicated.After drying for 3 hours at 6 ºC in the air, the final product was finely ground.The ultrafine particles were calcined in a muffle furnace at 500 ºC for 3 hours [12], as shown in Figure 1(a).

Electrochemical measurements
The investigation evaluated the corrosion prevention properties of the synthesised ceramic La2O3 nanoparticles using a low-carbon steel (LCS) plate as the test substrate.The LCS metal plate was cleaned using acetone and then polished using silicon carbide grit sheets with a thickness of 1 mm.To create slurry, a mixture was prepared by combining ceramic La2O3 nanoparticles with N-methyl-2-pyrrolidone and polyvinylidene fluoride in weight proportions of 80:15:5.The coating of the slime onto the LCS plate was performed using the doctor blade technique [13].The plate that had been coated underwent a drying process lasting for 1 hour at 353 K temperature.Subsequently, it was cooled down, and corrosion experiments were conducted using electrolytic solutions that consisted of 1 M H2SO4, 3 M KOH, and 3.5 wt.% NaCl.The corrosion investigation used a potential window extending from -1.8 to -0.4 V at a scan frequency of 5 mVS -1 .

Characterization
The X-ray diffractometry was used to evaluate the phase clarity and assess the prepared ceramic La2O3 nanoparticles structural components.The assessment was performed on XRD analysis with Cu anode.The XRD patterns were obtained at a range of 2° to 80°.The FTIR study was conducted for functional group identification of the prepared ceramic La2O3 nanoparticles in the vicinity of 4000 to 400 cm -1 , using KBr in the ratio of 200:1.To know the average particle size distribution, a particle size analyzer study was performed, at a wavelength of 633 nm using a laser beam by light scattering technique.The technique was performed several times to get the optimized data to acquire an average particle size [14].To study the optical absorbance of ceramic La2O3 nanoparticles, UV-Vis spectroscopy was performed and DD water as a solvent in the electromagnetic spectral wavelength ranging from 180 to 800 nm.The bandgap of ceramic La2O3 nanoparticles is calculated with the results of UV-Vis spectroscopy by employing Tauc relations.Surface topology and morphological characteristics of ceramic La2O3 nanoparticles were considered using high resolution transmission electron microscopy at 200 kV in addition to energy dispersive X-ray spectroscopy (EDX) with elemental mapping analysis.Photoluminescence spectroscopy was used to investigate the electronic and optical properties of the synthesised ceramic La2O3 nanoparticles.The experimental setup for the electrochemical impedance studies (EIS) and corrosion tests included using platinum wire as the working electrode, saturated calomel electrodes as the counter electrode, and counter electrodes as the reference electrodes.The electrochemical measurements were conducted using a PGSTAT302N electrochemical workstation.The surface analysis of the pristine LCS plate and the ceramic La2O3 nanoparticles coated plate corrosion experiments in various electrolytes was conducted using scanning probe microscopy (SPM).

RESULTS AND DISCUSSION
The X-ray diffractometer was used to conduct a structural examination of the as-prepared and calcinated samples, as seen in Figure 1(b).The diffraction pattern indicates that all samples possess a cubic crystalline structure, as shown by the JCPDF card number 65-3185.The lattice parameters for these samples are determined to be a=b=c=4.74Å, with the angles α=β=γ=90⁰.The observed correlation between increased peak intensity and the corresponding increase in reaction time provides evidence for the enhancement of crystalline size in the samples.The absence of further impurity phases in the sample suggests that the produced samples exhibit high material purity.The ceramic La2O3 nanoparticles under investigation exhibited distinct diffraction peaks at specific angles of 31.7⁰,34.5⁰, 36.3⁰, and 56.7⁰, which corresponded to the (100), ( 002), (101), and (110) crystallographic planes, respectively.Furthermore, the prominent characteristic diffraction peaks at angles of 29.1⁰ and 45.3⁰ exhibited the most significant proportion of La2O3 compared to other phases.These peaks were correlated with the Miller indices of (321) and (440), respectively.The crystallite size of the ceramic La2O3 NPs was estimated using the Scherrer equations based on the X-ray diffraction data.The mean crystallite size of ceramic La2O3 NPs is determined to be 14.59 nm.Thus, it can be concluded that pure ceramic La2O3 NPs crystallite size increased with increasing sonication time and other synthesis parameters.The prepared ceramic La2O3 NPs are stable phase and high in purity.These ceramic nanoparticles are superiorly supportive for the anticorrosion application.The lattice parameter of the prepared ceramic La2O3 NPs was found to be a=b=c=4.74Å and α=β=γ=90⁰, volume V = 69.21Å 3 and the d-spacing value calculated with the following formula [11].

=
(1) The crystallite sizes, FWHM values, Miller indices and d-spacing for the prepared ceramic La2O3 NPs are tabulated in Table 1.The vibrational properties of the ceramic nanoparticles composed of La2O3 were examined using FT-IR spectroscopy which is an effective analytical technique that can potentially complement the findings obtained by XRD analysis.Figure 1(C) exhibits the synthesised samples' FT-IR spectra, covering a wave number range of 400 to 4000 cm -1 .It demonstrates the presence of La2O3 has a discernible impact on the intensity and shape of the significant absorption bands.The FT-IR spectral spectrum exhibits a distinct convergence of infrared (IR) lines, essential in forming various phases of ceramic La2O3 nanoparticles.The optical transparency of La2O3 exhibits a generally high degree, which may be attributed to the concentration of lanthanum and its potential correlation with enhanced scattering phenomena [15].The water and hydroxyl assign a weak absorption band at 3450 to 3380 cm -1 O-H stretching stretches.Similarly, a comprehensive and robust bond appeared at 1500 cm -1 to 1400 cm -1 due to O-H bending vibrations of water molecules.The bands observed at 2925 cm -1 arise concerning C-H bonding.The band at 2501, 1835 and 1087 cm -1 may appear from the absorption of atmospheric CO2 and other gas molecules.The absorption bands at 858, 746 and 471 cm -1 represent the metal-oxygen stretching (La-O stretch), confirming the formation of ceramic La2O3 nanoparticles and these findings are consistent with the results reported before [16] and reveals that the La2O3 had the highest intensity peaks, indicating its distinctive characteristics.
The evolving morphology of as-prepared ceramic La2O3 nanoparticles were investigated through SEM. Figure 2 (a and b) presents SEM pictures of the ceramic La2O3 nanoparticles captured at different magnifications.The ceramic nanoparticles of La2O3 exhibited distinct variations in their structural morphologies and revealed a uniform distribution of spherical La2O3 NPs.The presence of lanthanum ions promotes the process of crystal nucleation by facilitating the production of small grains.However, trapping these lanthanum grains poses a challenge to overall grain development.This could be due to stress formation during the synthesis process.The ultrasonication produces an enormous number of vibrations to the lanthanum ions.The results from the Field Emission Scanning Electron Microscopy (FESEM) analysis are consistent with the previously published data, indicating that the synthesis parameters significantly impact the behaviour of La2O3.These structural and morphological results from XRD and FESEM analysis show that the perfect method to produce ceramic La2O3 NPs is the ultrasonication process [17].Figure 2 (c) shows the TEM figures of the synthesized ceramic La2O3 NPs and the morphology of the sample was determined to be spherical.The existence of well-connected, easily dispersed, and uniformly distributed particles was indicated by the formation of assembled spheres of crystalline phase development [18].Figure 2(d) shows the EDAX spectra of the prepared ceramic La2O3 NPs.The inset table gives the elemental composition of ceramic La2O3 NPs.From the EDAX spectra, it can be concluded that the prepared ceramic nanoparticles are highly pure with no other traceable impurities.
The dynamic light scattering (DLS) analysis was executed to evaluate the average particle size distribution of the synthesized ceramic La2O3 NPs.The histogram of DLS analysis, specifically revealed in Figure 3(a), illustrates the distribution of particle sizes in ceramic La2O3 nanoparticles.The observed particle sizes vary from 9 to 80 nm, with an average size of 24.93 nm.The histogram-derived frequency distribution reveals that about 75% of the particles possess a size below 60 nm.These results agree well with the FESEM and TEM images of ceramic La2O3 NPs.Due to the ultrasonication process, the structural modifications in nanoparticles may be attributed to the partial disruption of intermolecular hydrophobic bonds.When the particles experience shear stress and their aggregation speed increases, there is a corresponding increase in collision occurrences.As the application of ultrasonication therapy intensifies, there is a concurrent reduction in particle size, leading to a narrower range of particle sizes.The sonication process does not impact the surface charge of particles, but it does result in the formation of a new surface and a reduction in particle size.By reducing the size of the particles, there is an increase in the unrestricted area of the material.In this specific case, the particles undergo reduction due to the exerted cavitation forces.This encompasses the disintegration of agglomerates and aggregates [19].Ultrasonic cavitation is a highly efficient process that disrupts the cohesion of agglomerates, aggregates, and smaller particles by disrupting the vander Waals forces that hold them together.The findings derived from XRD, FESEM, and TEM analyses indicate that the fabricated La2O3 exhibit stability in solution and possess a high degree of dispersibility, which renders them advantageous for potential applications in corrosion prevention.The amount of light a material retains or transmits is a function of its electronic transition from the ground state to the excited state, which occurs within this electromagnetic spectrum.The prepared UV-Vis spectra of ceramic La2O3 NPs samples are revealed in Figure 3(b).Noticeably, the optical absorptance spectra of ceramic La2O3 NPs samples have appeared at only the UV range.The UV cutoff wavelength for ceramic La2O3 NPs samples was 197, 202, 216, and 224 nm.Based on the above findings, it is evident that the sample exhibits a minor increase in absorption and a slight decrease in transmittance after applying calculations.The observed correlation may be attributed to the decrease in particle size, as seen in SEM images.This reduction in particle size is expected to result in an enhanced surface-to-volume ratio, thereby enhancing the samples' capacity for absorption after the calcination process [20].The UV-Vis results are in correlation with the FESEM and XRD results.The sample ceramic La2O3 NPs with uniformly distributed spherical morphology show a higher absorption when compared to the earlier reports.This can be accounted for the large surface area expected to be offered by the spherical morphologies.The estimated bandgap of the as-prepared and calcined materials was determined by analyzing the Tauc curve shown in Figure 3(c), obtaining a value of 5.47 eV.The high bandgap nanomaterials are highly supported for anticorrosion applications.Contact angle measurements are a notable criterion used in the examination of thin layer deposition on the surface of low carbon steel (LCS).
Moreover, the surface degradation of LCS in different electrolytes, i.e., 1 M H2SO4, 3 M KOH and 3.5 wt.% NaCl can be evaluated from the contact angle measurements in the presence and absence of the prepared ceramic La2O3 NPs coating.The phenomenon of surface deterioration in the LCS has resulted in the formation of corrosion products and an accompanying increase in surface roughness.The assessment of surface deterioration of LCS may be conducted using 1 M H2SO4, 3 M KOH, and 3.5 wt.% NaCl basic electrolyte for both uncoated and ceramic La2O3 NPs coated LCS plates.This evaluation involves measuring water contact angle values, as outlined in the Experimental section.From earlier reports on contact angle measurements of LCS, the obtained reports show better contact angle values for uncoated LCS plates.This may occur due to the proper cleaning on the surface of the LCS by applying an ultrasonication process for LCS plate surface cleaning.The contact angle data of ceramic La2O3 NPs coated LCS (LCS-L) show an increase in contact angle.This may be due to the thin layer of ceramic La2O3 NPs coating.The coating repulses the aqueous contact from the surface of LCS.Based on the results obtained, it can be assumed that applying a thin coating of ceramic La2O3 nanoparticles on the surface of LCS led to a reduction in surface deterioration.This may be attributed to the creation of adsorbed thin film layers, which subsequently decreased surface roughness [21].Additionally, applying a thin layer of ceramic La2O3 nanoparticles on the surface of LCS enhances its hydrophobic properties, primarily attributed to the presence of hydrophobic octadecyl and oleyl tails.These factors contribute to an elevation in the contact angle.The corrosion inhibition efficiency of the thin layer of ceramic La2O3 NPs coating on the surface of the LCS metal plate can be evaluated using the polarization test and electrochemical impedance spectroscopy (EIS).The contact angle values of the LCS plate under various electrolytes used for electrochemical analysis are shown in Figure 3(d).The contact angle value of uncoated LCS is 74⁰, 73⁰ and 74⁰, for 1M H2SO4, 3 M KOH and 3.5wt.% NaCl as a testing base solution.But, the ceramic La2O3 NPs coating on the surface of LCS shows an increment in contact angle value, i.e., 86⁰, 92⁰, 81⁰ under the 3 M KOH, 1 M H2SO4 and 3.5 wt.% NaCl electrolytes, respectively.
The electrochemical impedance spectra or Nyquist plots for 1M KOH, 1M H2SO4 and 3.5% NaCl solutions are revealed in Figure 4 (a), (c), and (d), respectively, for LCS plates and ceramic La2O3 NPs covered LCS plates.At lower frequencies, a semicircular shape was seen in the Nyquist plot diagram, indicating a potential linear relationship between this shape and the charge transfer resistance linked to the corrosion process.However, it is evident that the radius of these loops varies when comparing coated and uncoated metal surfaces across all investigated electrolytes, namely 1 M H2SO4, 3 M KOH, and 3.5% NaCl solutions [22].The electrochemical impedance parameters of LCS plates derived from the Nyquist plot, ceramic La2O3 NPs coated LCS plates under 1 M H2SO4, 3 M KOH, and 3.5wt.%NaCl electrolytes are tabulated in Table 2.The ceramic La2O3 nanoparticles coated LCS plate's electrical properties exhibited greater significance than the bare LCS plate samples which indicates that the coated specimens have superior barrier capabilities in mitigating electrochemical corrosion.Remarkably, the Rct values of the ceramic La2O3 coated on the surfaces of LCS plates exhibited greater values in 3.5% NaCl and 3 M KOH solutions compared to 1 M H2SO4 solutions when compared to uncoated LCS plates.The LCS plates coated with ceramic La2O3 demonstrate significantly higher Rct values, highlighting enhanced corrosion resistance compared to the surfaces of uncoated LCS plates.The electrochemical impedance spectra obtained from the samples using three distinct electrolytes provide evidence that the ceramic La2O3 nanoparticles offer substantial resistance against electrochemical corrosion.To clarify, the observed inductive response at low frequency is likely attributed to the adsorption of corrosion products on the surface of the electrode.It is important to note that all values were derived from the high capacitive loops.This phenomenon is evident from the observed rise in Rct values, accompanied by a concurrent decline in the values of Cdl, as shown in Table 2.The augmentation of the double-layer thickness led to a drop in the doublelayer capacitance (Cdl), which in turn caused a reduction in the dielectric constant which are attributed to the displacement of adsorbed water molecules and the adsorption of extract (organic matter) onto the surface of the mild steel.Figure 5 shows the Bode modulus and phase angle plot obtained on the uncoated LCS and ceramic La2O3 NPs coated LCS.The results show that the impedance values were higher for LCS plates coated ceramic La2O3 NPs than uncoated LCS plates in all electrolytes.As previously documented, the observed results may be attributed to the enhanced barrier characteristics and corrosion prevention capabilities.The ceramic La2O3 NPs coating on the LCS surface improved the corrosion protection due to increased film thickness or covering of the surface porosity.The phase angle plot is characterized by an individual time constant.A more comprehensive analysis of the electrochemical impedance spectroscopy (EIS) outcomes may be achieved by the use of numerical fitting techniques, using the equivalent circuit shown in the study which consists of an electrolyte resistance denoted as R and a coating capacitance represented as CP. Figure 6 (a, b,  and c) show the potentiodynamic polarization curves, also known as Tafel plots, for LCS plates and ceramic La2O3 NPs coated LCS plates immersed in 1 M H2SO4, 3 M KOH, and 3.5% NaCl electrolytic solutions, respectively.The electrochemical corrosion parameters, namely corrosion potential (Ecorr), corrosion rate (CR), corrosion current (Icorr), and polarisation resistance (Rpol), were determined using the Tafel plot method.These values are provided in Table 3.This study examines the electrochemical corrosion inhibition properties of LCS plates coated with ceramic La2O3 nanoparticles.The corrosion inhibition behaviours are analyzed for each electrolyte individually to facilitate interpretation and analysis.In a 1 M H2SO4 electrolyte medium, the corrosion potential (Ecorr) of LCS plates coated with ceramic La2O3 nanoparticles was greater than that of the LCS plates without any coating.The corrosion potential (Ecorr) of zinc (0.372 V) plates is shifted to -1.008 V as a result of the addition of a thin layer coating of ceramic lanthanum oxide nanoparticles.This decreases the ceramic La2O3 NPs coated LCS plates' corrosion current compared to uncoated ones.The application of a ceramic coating composed of La2O3 nanoparticles has been shown to have a considerable effect on the corrosion rate.The manifestation of this effect is evident through the reduction of the corrosion current (Icorr) at a particular corrosion rate.In comparison to uncoated LCS plates, those coated with ceramic La2O3 showed a markedly increased corrosion rate, approximately 160.7 mm per year.The polarization resistance of uncoated LCS (4.018 Ω) is notably lower than the values observed for ceramic La2O3 nanoparticles-coated LCS plates, which registered 16.80Ω in a medium containing 1 M H2SO4 electrolyte.Based on the findings acquired, it can be surmised that applying a ceramic coating composed of La2O3 nanoparticles may serve as a viable strategy for mitigating the corrosion rate in solid acidic environments such as H2SO4 and HCl.The inhibitory efficiencies of the ceramic La2O3 nanoparticles covering were determined to be 85.77%, as shown in Table 3.The Tafel polarization curves of LCS plates ceramic La2O3 NPs coated LCS plates under 3 M KOH are shown in Figure 6(b).Furthermore, in 3 M KOH medium, the corrosion potential of LCS plates ceramic La2O3 NPs coated LCS plates was roughly 1.033 V and 1.447 V, respectively.The potential corrosion values of coated plates exhibited a substantial rise as compared to those of pure LCS plates.The corrosion rate of the uncoated low carbon steel (LCS) plate in a 3 M potassium hydroxide (KOH) electrolytic solution was very high, measuring 117.37 mm/year.Moreover, the polarization resistance exhibited a relatively high value, measuring at 4.720 Ω.In contrast, it was observed that the corrosion rate of the coated plates was relatively low, measuring 5.72 mm/year and 65.706 Ω, respectively, for the surfaces of ceramic La2O3 nanoparticles-coated LCS plates.These findings underscore the significance of applying a thin layer of ceramic La2O3 nanoparticles to the LCS surface for achieving a reduced corrosion rate and enhanced electrochemical corrosion resistance.Table 3 illustrates a notable improvement of 95.12% in corrosion prevention characteristics for the ceramic La2O3 nanoparticles-coated plates compared to the uncoated LCS surfaces.Conducting potentiodynamic polarization experiments on LCS (low carbon steel) and LCS plates coated with ceramic La2O3 NPs immersed in a 3.5% NaCl electrolytic solution revealed an anodic polarization effect on the metal plates, as illustrated in Figure 6(c).Compared to their uncoated counterparts, the coated LCS metal plates exhibited a notable capability to effectively inhibit corrosion on the metal surfaces.The corrosion potentials (Ecorr) of LCS plates increased when coated with ceramic La2O3 nanoparticles (NPs) compared to uncoated LCS plates.The outcomes indicate a decrease in the corrosion rate of the coated LCS metal plates (2.40 mm/year) when contrasted with pure Zn metal plates (4.68 mm/year).An evident improvement in polarization resistance is noted for the ceramic La2O3 nanoparticles-coated LCS plate compared to the uncoated LCS samples.This improvement is likely associated with the reduction of La 2+ ions.The application of a thin layer of ceramic La2O3 nanoparticles on the LCS surface resulted in a diminished corrosion rate and enhanced electrochemical corrosion resistance, aligning with findings from previous research.Based on the results obtained from the Tafel plot, it was shown that the ceramic La2O3 NPs covered LCS plate exhibited a 48.71% increase in corrosion resistance compared to the uncoated LCS metal surfaces.The findings suggest that applying a ceramic coating composed of La2O3 nanoparticles is crucial in forming a durable and robust protective barrier on the material's surface.This coating can potentially enhance the susceptible material's corrosion resistance.Table 4 presents a comparative analysis of the corrosion-inhibiting properties of various metal oxide nanoparticles, together with the corresponding observed results.It may be inferred that using ceramic La2O3 nanoparticles has shown to be advantageous in augmenting the corrosion resistance of low-carbon steel plate surfaces when exposed to an aqueous solution.After conducting the electrochemical investigation on the LCS plates with various electrolyte solutions, a nano-indenter was utilized to determine the indentation hardness and the modulus for both the uncoated and ceramic La2O3-coated LCS plates.The load control method was utilized to measure the qualities of coatings utilizing a Berkovich-type indenter.The test was carried out in the order of loading, holding, and unloading, respectively.Plates were loaded until the maximum load of 1000 mN was attained to get the data shown in Figure 6(d) which depicts the plates' mean load vs. depth curves.The ceramic La2O3 NPs coating applied to the surface of the LCS plates caused a change in the curves toward more significant displacement values.The measured nanoindentation parameters of the uncoated and ceramic La2O3 NPs coated LCS plates includes displacement (nm), hardness (GPa), contact depth (nm), contact stiffness in micronewtons per nanometer, and roughness (nm).The formulation with ceramic La2O3 NPs coated LCS plates under KOH and NaCl electrolyte recorded the highest depth before and after the holding period.On the other hand, the uncoated plate under the NaCl electrolyte had the lowest recorded depth before and after the holding period of 30 seconds.It suggests that the ceramic coating applied to the LCS plate's surface lowered the load-bearing behaviour of the coatings.Under the influence of the KOH electrolyte, the uncoated LCS plate reached a depth of 1696.5 nm when subjected to the maximum load.The reduced stiffness caused by the ceramic La2O3 NPs coating on the LCS plate surface could cause a depth penetration change or decreased indentation resistance.The values of the uncoated LCS plates for 1 M H2SO4, 3 M KOH, and 3.5% NaCl electrolytes are 59.04 GPa, 14.13 GPa, and 74.46 GPa, respectively.Surprisingly, the electrochemical investigation reveals that the coated plates' hardness values have dropped due to their interaction with aggressive electrolytes.This demonstrates the uniformity and stability of the ceramic La2O3 Nanoparticles coating on the LCS plate's surface despite the surface coating not peeling off.

CONCLUSION
In the present work, ceramic La2O3 nanoparticles were used as an interfacial layer on the surfaces of low-carbon steel.The corrosion inhibitor characteristics of low-carbon steel were enhanced by applying a ceramic coating of La2O3 nanoparticles, as demonstrated by potentio dynamic polarization and EIS experiments.The EIS, contact angle and wettability investigations have additionally demonstrated that the incorporation of nanoparticles enhances the corrosion resistance of the interface of low-carbon steel.This improvement can be ascribed to the preferential movement of ceramic La2O3 NPs to the metal surface during the coating process, facilitated by a notable affinity between the nanoparticles and the low-carbon steel surface.It was also found that the ceramic La2O3 NPs significantly enhance the mechanical properties and increase the surface wettability under various aqueous electrolytes.This observation demonstrates the ability of ceramic La2O3 nanoparticles to enhance the corrosion resistance capabilities of lowcarbon steels in aqueous conditions.

Figure 5 .
Figure 5. Bode plot of uncoated and ceramic La2O3 NPs coated LCS plate under 1 M H2SO4 (a and b), 3 M KOH (c and d) and 3.5 wt.% NaCl (e and f), respectively.

Table 1 .
Crystallite sizes, FWHM values, Miller indices and d-spacing for the prepared ceramic La2O3 nanoparticles.

Table 4 .
Comparison of nanomaterial coatings on metal surfaces.