Introduction

Corrosion of aluminium alloys, particularly aluminium 5083, poses significant challenges in various industrial applications due to their widespread use in marine and structural environments. Statistics show that 10% of the world’s yearly metal production is lost to corrosion-related scrapping of metal equipment and materials1,2. One of greatest well-liked, reasonably priced, and effective methods for preventing metal corrosion is organic compounds coating3. Because of its high adherence to metal substrates, inexpensive and resistant to corrosion, epoxy resin is frequently employed in organic anti-corrosive coatings4,5. Nevertheless, the high fragility of epoxy resin typically causes fissures on the coated surface6,7. With its large certain surface regions, outstanding barrier qualities, exceptional chemically stability, and superior electric conductivity, graphene is a sheet-like structural material that is very successful in improving the capacity of anti-corrosive coatings8,9,10. Metal deterioration results from its high electrical conductivity, which speeds up electrochemical corrosion on the metallic surface11,12,13. In order to improve functionality and chemical compatibility in anti-corrosive purposes, GO is a well-known Graphene’s byproduct, has many chemically reactive functional groups on its external layer, such as carboxyl, hydroxyl, and epoxy groups. GO still maintains its sheet-like framework. The dispersion of GO in the coating is severely hindered by the high polymeric ability that GO generally shows between the layers14. The key to using GO practically in the anti-corrosion sector is therefore determining the way to get a proper dispersing of GO in the resin. Although GO has the potential to significantly enhance epoxy coatings’ qualities, a significant drawback is the potential to agglomeration. Poor dispersion inside the epoxy matrix results from this agglomeration, which is caused by strong van der Waals and electrostatic contacts among GO sheets. As a result, the coating’s performance may deteriorate, leading to decreased electrical conductivity, mechanical durability, and barrier efficiency.

It has been discovered by studies that putting inorganic nanoparticles on the GO surface may substantially improve GO sheet dispersion and decrease agglomeration15,16,17,18. A graphene-inorganic composite with a synergistic effect is created by supporting inorganic nanoparticles such as SiO2, TiO2, Fe3O4, ZnO, etc. on the graphene oxide surface. By depositing nanoparticles, graphene oxide can be given new functionality in addition to preventing its Nano sheets from restacking11,12. Titania has garnered a lot of interest due to its exceptional qualities which include non-toxicity, low density, providing self-cleaning and antifogging properties, and exceptionally corrosion-resistant properties19. Numerous investigations have confirmed that Titania can enhance the coating’s anti-corrosion efficiency when used as a binder20,21. To further enhance the efficiency of GO-based coatings, modifications and adaptation have been investigated. The addition of TTA (titanium tetra-acetoximate) as a precursor to generate TTA-GO framework during the crosslinking of the epoxy with hardner is a potential modification. The capacity of titanium-based organometallic precursors, including titanium tetra-acetoximate (TTA), to hydrolyze and condense into stable titanium oxides which serve as barriers against harsh environments has drawn attention. By offering active bonding sites and raising the crosslinking density of hybrid coatings, TTA not only acts as a source of titanium but also enhances compatibility with polymeric systems, according to published research22. The goal of this combination is to improve the coatings’ overall durability, adhesion, and corrosion resistance by utilizing the synergistic impact of GO and TTA (titanium tetra-acetoximate).

We used a modified Hummer’s method to synthesis GO for this investigation, and then incorporated it to the epoxy-based protective coatings both with and without TTA (titanium tetra-acetoximate) compounds. Investigating how efficiently these composite coatings protected aluminium 5083 substrates from corrosion was the major objective. Through comprehensive characterization and investigation, including EIS, XRD, field emission scanning electron microscopy (FE-SEM), weight loss analysis, salt spray testing, and FT-IR, we aimed to identify how effectively these coatings provided improved corrosion protection.

By showing how GO and TTA compound changes can greatly increase the ability of aluminium materials to withstand corrosion, this research contributes to development of progressive coating technologies. The results provide important information for developing high-performance protective coatings for challenging applications in harsh environments.

Experimental

Materials required

Expanded graphite powder < 20 μm by Sigma-Aldrich, 98% conc. sulfuric acid (H2SO4), potassium permanganate (KMnO4) Rankem, 99% sodium nitrate (NaNO3) by HIMEDIA, 30% hydrogen peroxide (H2O2) by Rankem, 99.9% absolute ethanol (analytical grade), 37% hydrochloric acid (HCl), sodium chloride (NaCl) by Rankem, Toluene (sulphur free) C6H5CH3 by Rankem, Acetone (CH3COCH3) by Rankem, titanium tetra-acetoximate [Ti{(ONC)(CH3)2}4], Aradur-140 (polyamidoimidazoline) amine value of 370–410 mg KOH/g, H⁺ equivalent weight of ~ 95 g/eq, Araldite GY-250 (Diglycidyl ether of Bisphenol A) equivalent weight (EEW) of ~ 187 g/eq, and viscosity at 25 °C of 10,000–12,000 mPa s.

Sample preparation

The metal (Al5083) substrate (2 × 3 cm2) was used as the sample and by polishing the substrate with grit sandpaper 220 C to 1200 C, prepared by ultrasonic cleaning for 30 min. with acetone then drying it in a vacuum oven until it’s completely dried to provide a smooth and clean surface for further coating procedure.

GO preparation

A slightly modified Hummer’s approach was used to synthesis graphene oxide, as documented in the literature14. To do this, 120 ml of extremely pure H2SO4 were combined to 1 g of graphite powder and stirred for two hours using a mechanical mixer. Subsequently, under moderate mixing conditions, 1 g of NaNO3 was added gradually to the initial mixture. Lastly, a mixer was used to mechanically agitate the solution while adding 6 g of potassium permanganate. It was diluted with 600 ml of deionized water (DIW) in the icy water combination and stirred for half an hour after being combined for 72 h at ambient temperature. In order to stop the oxidation reactions and produce a dark yellow mixture, hydrogen peroxide was finally added to the diluted solution drop by drop. To get the precipitated product, the solution was maintained in a stationary state for 24 h. To exfoliate the GO sheets, the sediment was then rinsed three times with a 1 M HCl solution and three times with DIW using a series of sonication and centrifugation processes.

GO-epoxy composite coating preparation

For the composite GO-epoxy coating, take 0.02 g of graphene oxide into 10 ml acetone and sonicated (20 min.) it. After that, added epoxy resin into the solution and sonicate and stir until the liquid component dissolves the resin. When a uniform dispersion was reached, add the toluene (6 ml) into it and continuously stirring it by th e help of magnetic stirrer. Next, the epoxy and curing agent were mixed in a stoichiometric ratio of 100:50 (w/w), with a pot life of approximately 120 min at 23 °C, were added into the mixture. When a uniform and stable dispersion system was reached by the help of mechanical stirrer and ultrasonicator, coating was deposited on the object’s exterior with the help of spray coating machine. When the sample was coated, put it in the room temp. For 2 h and then put it in the oven for 24 h at below 50 °C.

GO-TTA-epoxy composite coating preparation

The sample was prepared according to Sect. 2.2. Composite epoxy coatings were prepared as follows: firstly, 0.02 g of graphene oxide into acetone (10 ml) and sonicate (30 min) it. In another beaker 0.02 g (titanium tetra-acetoximate) was added in 6 ml toluene and 20 min of sonication produced a homogeneous condition. Next, the homogenous solution was added into the previous solution of GO and sonicated. After that, added epoxy resin into the solution and sonicated for 30 min. then agitate it until the solvent fully dissolves the resin. Next, the epoxy and curing agent were mixed in a stoichiometric ratio of 100:50 (w/w), (with a pot life of approximately 120 min at 23 °C), were added into the mixture and the mixture was continuously stirred for 30 min. to ensure it was uniform. When a uniform and stable dispersion system was reached, coating was deposited on the specimen’s interface by the help of spray coating machine. When the sample was coated, put it in the room temp. up to 2 h and then put it in the oven for 24 h at below 50 °C. The thickness of the coatings was measured, and the average value obtained was 23.36 μm.

Characterization

Characterizations of GO, GO-Epoxy, GO-TTA-Epoxy: With a spectral bandwidth 4000–500 cm− 1 and wavelength resolution is 0.8 cm− 1, the Fourier transform infrared spectra had been captured by a Bruker ALPHA instrument. It had two modes: universal mode (KBr pellets) and attenuated total reflectance (ATR). Viewing very tiny material structures is possible with the JOEL JSM-7610FPlus FESEM, an ultra-high resolution electron microscope. An EDAX energy dispersive x-ray analyzer is used in the JSM-7610 F chamber to evaluate elements at the micro-nano size. The autonomous multifunctional X-ray Diffractometer (model: SMARTLAB) from Rigaku is used to analyze the vibrations of structure in the nanoparticles. The ambient temperature range is 2θ between 20 °C and 80 °C, and the scanning rate is 1 s with a 0.05 interval. A Shimadzu DTG-60 H (230VAC) was used for TGA in order to evaluate the samples’ heat stability and decomposition behaviour. At a heating rate of 10 °C/min, measurements were made from room temperature to 800 °C. The active and barriers inhibiting corrosion properties of the particles were evaluated using the EIS method and Tafel polarization technique. To assess the active erosion restraint, all electrochemical tests were carried out at ambient humidity in a conventional three-electrode apparatus. Making use of an SP150 potentiostat that was managed by an appropriate computer, electrochemical evaluations were made. The measurements of EIS were conducted having AC amplitude of 10 mV and an OCP (open circuit potential) of 100 kHz to 10 MHz. The object being studied had been polarized to − 250 mV cathodically and + 250 mV anodically in comparison to the OCP at a scan count of 1 mV s-1 in order to ascertain the Tafel curves. Software called EC-lab V11.50 was utilized to fit and evaluate the impedance data. The inhibition efficiency (IE %) of GO and GO-TTA particles within the epoxy resin was calculated using Eq. (1):

$$\:IE\%=\frac{({i^\circ\:}_{corr}-{i}_{corr})}{{i^\circ\:}_{corr}}\:\times\:\:100$$
(1)

where icorr and iºcorr are the epoxy coating, GO-epoxy and GO-TTA-epoxy coating and bare aluminium samples corrosion current densities, respectively.

In order to evaluate the corrosion resistance of coated samples, salt spray testing was performed in a Korrox-III chamber by Presto. As required by ASTM B117, the test used a 5% NaCl solution at 35 °C.

Results and discussion

FT-IR

Figure 1 illustrates the structural characterization of GO, GO-Epoxy, and GO-TTA-Epoxy composites by the use of the FT-IR. For the hydroxide, carboxyl, and epoxide groups, the FTIR analyses of GO exhibit distinct main bands at 3391 cm− 1 (-O-H), 1734 cm− 1 (-C = O), and 1048 cm− 1 (epoxide -C-O-C). Peak absorbance in the medium bandwidth range, located at 1725 cm− 1 and 1626 cm− 1, are caused by the vibratory stretching of C = O and C = C of the carbonyl compounds and carboxylic acid present at the GO edges. Finally, the absorbed peak locations at 1213 cm− 1 and 1382 cm− 1 as well, indicate the stretching vibrations of the carboxylic acid’s C-O and C-OH. It is evident how the graphite has undergone oxidation when these oxygen-containing compounds are present. The C–O–C stretching vibrations and the = C–H stretching vibrations of the sp2 c-skeletons system are shown by the peaks at 1048 cm− 1 and 671 cm− 1, correspondingly, as can be seen in Fig. 1. The distinctive peak absorption regions of the GO-TTA spectra include the symmetrically and unsymmetrical stretching vibrations of the -CH3 and -CH2 molecules at 2924 cm− 1 and 2850 cm− 1, as well as the -NH and C-N stretching vibrations of amines at 1557 cm− 1 and 1236 cm− 1. Furthermore, a prominent Ti-O-Ti peak was visible in the low wavenumber area (631 cm− 1). Due to the presence of oxygen-rich functional groups (-OH, C=O, and C-O-C), which promote epoxy compatibility, the FT-IR study demonstrated that GO was successfully oxidized. After TTA was added, further peaks including -CH2, -CH3, -NH, and Ti–O–Ti peaks were found, confirming strong chemical bonds and the development of a hybrid organic–inorganic network These functional groups enhance interfacial bonding with the epoxy backbone and improve chemical crosslinking, contributing to structural integrity and barrier uniformity. The suggested mechanism explaining how graphene oxide (GO) and titanium tetra-acetoximate (TTA) interact inside the epoxy network in Fig. 3.1 (supplementary data).

Fig. 1
figure 1

FT-IR spectra of GO, GO-epoxy coating, and GO-TTA-epoxy coating.

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XPS

The XPS spectra of GO-epoxy and GO-TTA-epoxy coatings are shown in Fig. 2. The XPS spectra indicate that the corresponding peaks including C1s, N1s, Ti2p, and O1s. Six common chemically shifted components can be seen in the C1s spectra of GO with peak-fitting curves in Fig. 2A-C1s: C = C (283.9 eV), C-C (284.0), C-OH (284.5 eV), C-O (285.09 eV), C = O (285.6 eV), and C(= O)-O (286.3 eV), in that order. In GO-TTA-epoxy, two new peaks appearance of C-N(285.3 eV) and C = N(286.2 eV) are seen in the spectrum of XPS of C1s (Fig. 2B-C1s), implying a reaction between TTA and GO. The O1s levels spectra of graphene oxide with peak-fitting curves in figure(C), shows four chemical shifted components; O-C = O (530.9 eV), C = O (531.6 eV), C-O (532.3 eV), C-OH (533.07 eV) respectively. After modification with TTA, Ti-O (529.1 eV) peak appear in O1s spectra; which indicate the successful modification of graphene oxide and also support the IR results. The N1s spectra of GO is fitted in C-N (399.8 eV), and N-H (398.6 eV) but in with modified TTA compound additional peak at C = N (401.9 eV) is also observed. The aforementioned XPS results further show that it is prepared successfully, which is in excellent compliance with FTIR.

Fig. 2
figure 2

XPS spectra of Graphene oxide-Epoxy coating (A,C,E,G), and Graphene oxide-TTA-Epoxy coating (B,D,F,H) on aluminium substrate.

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TGA

To ascertain thermal endurance of the materials and the breakdown of the compound at different temperatures, TGA is generally used. The TGA curves for GO-TTA-Epoxy, GO-epoxy, and GO coating are shown in Fig. 3. According to the thermal analysis of GO, the weight loss process occurred in three main steps: 60% between 30 and 170 °C due to the pyrolysis of OH moieties and the disappearance of physiologically consumed water; 18% between 170 and 320 °C due to the eliminating of carboxylic and epoxide components along with stable oxygen characteristics; and 22% between 320 and 440 °C due to the disintegration of GO’s fundamental carbon skeleton. When GO is thermally analyzed using epoxy The weight loss at the initial stage of resin decomposing (~ 300 °C) was greatly decreased by the GO addition. An effective physical interactions and enhanced thermal resistance of GO-epoxy cross-linked regions are associated to this phenomenon, which likely decreased the degree of C=C groups unsaturation brought on by water reduction. The thermodynamic phenomenon that is unique to nano-materials is also caused by this phenomenon, which reaches a maximum breakdown rate of 550 °C. Figure 2 shows that the framework undergoes an oxidative process in tiny molecule with GO-epoxy connections and entanglements. This is demonstrated by the volume loss increasing proportionately depending on the GO content during its decomposition stage at 550 °C. The incorporation of titanium compound to the coating significantly decreased the weight loss at the initial stage of decomposition (~ 380 °C) and increased thermal resistance. This enhanced thermal resistance is attributed to better GO dispersion and crosslinking induced by the presence of TTA, which stabilizes the composite structure. These results together show that adding TTA to the GO-epoxy matrix increases its thermal resilience and resistance to structural degradation at high temperatures, hence bolstering its usage in anticorrosive applications that are subjected to high temperatures.

Fig. 3
figure 3

TGA of GO, GO-epoxy coating, and GO-TTA-epoxy coating.

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Contact angle

The contact angle can vary depending on the specific formulation and surface treatment. In GO with epoxy coating the hydrophobicity is increased to compering to epoxy coating. In GO with TTA-epoxy coating the contact angle is indicates that the surface has low wetting and the hydrophobicity is increased to compering the bare Al and GO with epoxy coating. Average contact Angle Values of epoxy coating is 61.1°, GO with Epoxy is 64.2°, and GO with TTA-epoxy is 81.3° as shown in the Fig. 4 and Table 1. Bare aluminium is not as much hydrophobic as other composite coatings and the reduced contact angle suggests that there is a lot of wetting on the outer layer as well as the droplets of water are dispersed more widely.

Table 1 Contact angle with standard error of epoxy, GO-epoxy, and GO-TTA-epoxy coating (n = 3).
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Fig. 4
figure 4

Contact angle of (A) bare epoxy, (B) GO-epoxy coating, and (C) GO-TTA-epoxy coating measurements were performed using a 5 µL water droplet at room temperature.

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XRD

The synthesis of GO and its modified compound with titanium tetra-acetoximate (TTA) was also validated by XRD analyses. The obtained XRD patterns of GO and GO-Epoxy, and GO-TTA-Epoxy composite are shown in the Fig. 5. The Oxygen rich functional molecules on the sidewalls of the layers of the material GO exhibit 002 diffraction, which is responsible for the peak intensity of diffraction seen at a 2θ value at 9.48° in the XRD analysis of GO. At 13.97°, 16.88°, and 20.37°, respectively, the XRD peak values of GO was moved towards a higher 2θ value following the covalent interaction with epoxy and TTA chemical. A TTA and epoxide in the space between the layers of GO are responsible for the increase in interlayer spacing, which causes the shift in the XRD peak. When GO is exfoliated during sonication, the strength of the peaks that correspond to pure GO in GO-epoxy and with TTA-compound decreases. This change is especially important since it suggests that GO, epoxy, and TTA will interact covalently and crosslink, changing the interlayer distances and enhancing matrix compatibility. Better dispersion within the polymeric matrix is confirmed by the decrease in peak intensity following exfoliation and chemical treatment, which shows a disturbance of the GO stacking order. By reducing corrosive agent diffusion paths, such structural disorder and interlayer expansion improve the coating’s barrier effectiveness.

Fig. 5
figure 5

XRD pattern of GO, GO-epoxy coating, and GO-TTA-epoxy coating.

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SEM and EDX

The surface morphologies of all the nano composites coating on aluminium surface containing different coating of GO with or without TTA compound, and epoxy tiny particles were examined using instruments FE-SEM, as illustrated in Fig. 6. The morphology of every treated exterior of GO-TTA-epoxy coatings was found to show both the GO and TTA-compounds nanoparticle were evenly distributed throughout the epoxy matrix. Additionally, TTA coating samples showed no surface fractures, flaws, or phase separation when comparing epoxy and GO-epoxy coating specimens. However, in GO epoxy coatings the resulting coatings’ surface shape was different, and the addition of GO led to agglomeration. As a result, the nanoparticles’ dispersion inside the epoxy matrix was impacted. In this method, the surface morphological discrepancies between the mixed resins and the GO nanoparticle were clarified using the FE-SEM. As previously stated, the low surface wetting ability was caused by the graphene oxide coating with TTA providing smoothness on the coated surface due to its uniform coverage. One of the most important methods for ascertaining the elemental makeup of materials is Energy Dispersive X-ray (EDX) analysis Table 2 In GO-TTA-epoxy coatings, EDX may offer comprehensive details on the distribution as well as concentration of components such as titanium, carbon, and oxygen. The presence of Ti, which contributes to the barrier qualities on the Al surface, is confirmed by the GO-TTA coatings EDX. EDX can be used to providing thorough details on the concentration and distribution of elements including titanium, carbon, and oxygen in GO-TTA-epoxy coatings. The GO-TTA coatings EDX confirm the presence of Ti, which contribute the barrier properties on the al surface.

Table 2 GO-epoxy and GO-TTA-epoxy coating EDX on aluminium substrate.
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Fig. 6
figure 6

SEM images and elemental mapping of epoxy coating (A), GO-epoxy coating (B) and GO-TTA-epoxy coating (C) samples. (A) Epoxy coating, (B) GO-Epoxy coating, (C) GO-TTA-Epoxy coating.

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Weight loss

All the samples (2 × 3 cm2) were immersed in the NaCl solution at room temperature for 45 days before being cleaned and weighed. Figure 7; Table 3 displays the masses of the samples at the beginning and after 45 days. Each specimen was polished using an emery sheet graded from 100 C to 2000 C. Following that, the taken samples were cleaned with DIW, degreased with acetone, and then allowed to dry. These samples were finally carefully cleaned with distilled water, dried, and coated and specimens were weighted. After 45 days immersed sample were collected and washed and cleaned properly after that samples were weighted. All performed experiments, and the average weight decrease was recorded. The corrosion Rate Units is Desired in mm/y, then the value of K in CR Equ.is 8.76 × 104 and for aluminium Alloy 5083 the density is 2.66 g/cm3. The corrosion rate for each tested material is presented in Fig. 6. According to Table 3 data shows that following 45 days of immersing in NaCl solution (3.5%), the corrosion rate has the highest value in the case of the Bare Al, 0.518. Lower values were obtained for the Graphene oxide with compound epoxy coating materials, such as a value of 15–20 times lower was calculated in the case of the bare Al. The lowest value for the corrosion rate at 45 days of immersion was calculated for the GO-TTA-epoxy coating (0.025), a value is lower than that calculated for the Epoxy coating and GO-epoxy coated sample. It should be understood that water absorption, coating swelling, or partial delamination- all of which do not directly correlate to metal dissolution- may affect traditional weight-loss metrics for polymer-coated systems. Therefore, the weight-loss data are not the main foundation for assessing corrosion resistance; rather, they are simply utilized as a comparison and supporting signal. The primary evaluation of anticorrosive performance is based on salt spray test results and electrochemical impedance spectroscopy (EIS) characteristics, which have greater potential for coated systems.

Table 3 Weight variation at 45 days of aluminum.
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Fig. 7
figure 7

Corrosion rate and protection efficiency of weight loss samples of Bare Al, epoxy coating, GO-epoxy coating, GO-TTA-epoxy coatings.

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Pull-off test

The pull-off test was carried out to examine the coatings’ adhesion strengths. The binding of the coating layer on the exterior layer of the pre-treated specimen was another crucial characteristic that had to be examined when creating anti-corrosion coating samples. Figures 8 and 9 present the sample’s optical picture and Table 4 presents the quantitative results. In dry conditions, the results demonstrated that the GO-TTA coating with epoxy has significantly higher pull-off strengths than conventional coatings. In the blank sample, the lowest adhesion strength value was noted. As the electrolyte reaches the coating/metal contact, it is well known that the hydrolysis of adhesion bonds may cause the adhesion strength to diminish. Another factor that may contribute to the reduction in coating adherence is the formation of corrosion-related substances beneath the coating, such as iron oxy-hydrolysis and OH-ions. According to the results, the GO with TTA-epoxy coating has much higher pull-off strengths (7.79 MPa) in dry conditions than other coatings. The epoxy sample that was left blank had the lowest adhesion strength (6.20 MPa).

Fig. 8
figure 8

Results of adhesion testing (a) epoxy coating (b) GO-epoxy coatings (c) GO-TTA-epoxy coatings sample.

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The dry adhesion strengths are increased by the application of corrosion-inhibiting pigments. The measurement of dry adhesion appears to be influenced by atmospheric humidity as well. The enhanced dry adhesion strength is caused by a very thin covering of composite material that forms on the metal surface when water vapor penetrates the coating and partially dissolves the pigments. The pull-off strength demonstrates a clear correlation between corrosion inhibition and adhesion. This indicates that by strengthening the coating’s resilience to corrosion, GO-TTA-Epoxy can decrease coating adhesion loss and increase pull-off strength.

Table 4 Pull-off strength and standard error of epoxy, GO-epoxy, and GO-TTA-epoxy coating (n = 3).
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Fig. 9
figure 9

Pull-off strength (MPa) with standard error of (a) epoxy coating (b) GO- epoxy coatings (c) GO-TTA-epoxy coatings sample.

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Salt spray test

A common test used to ascertain if salt corrodes metallic objects is ASTM B117 standard. A specimen kept in a confined chamber is sprayed with saltwater to accomplish this. Testing for atmospheric corrosion can be done more quickly with this form. Here, for GO with TTA-epoxy coating sample got no white dust after 720 h that means there is zero corrosion on the surface of the metal surface are present and for bare aluminium sample after 288 h white dust are seen and the rating is less as comparing graphene oxide coating sample or with TTA-epoxy coating sample as shown in Fig. 10. In the optical images of salt spray test samples; White dust and pits observed in bare epoxy coating on Aluminium, Pits and white dust observed in graphene oxide with epoxy coating but in graphene oxide with TTA-epoxy coating surface was observed smooth. To further illustrate how corrosion developed during the course of the test, pictures of the coated panels taken at various exposure times have been included (in the supplementary data). In addition to the initial before and after photos, these updates offer a more visible and quantitative evaluation of coating performance.

Fig. 10
figure 10

Salt spray (Optical) images of epoxy coating (A), GO-epoxy coating (B) and GO-TTA-epoxy coating (C) on aluminium substrate after 1008 h. (A) Epoxy coating, (B) GO-epoxy coating, (C) GO-TTA-epoxy coating.

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Electrochemical studies

To explain the effects of percolating particles and coated framework, the equivalent circuit (Fig. 11) was used as a constant phase element (CPEC as Q1) was used to quantify the capacitive reactions at the barrier interface to account for the unsatisfactory capacitive responses. The solution resistance is represented by (RS as R1) in this model. The corroding interface of Aluminium was also characterized by a parallel combination of an interfacial charge transfer resistance (RCt as R3) and a double layer constant phase element (CPEdl as Q2). In addition to modeling the coating using a CPEC as Q1, the percolation structure of the coating layer was characterized using coating resistances (RCR as R2) and W4 Represents the Warburg impedance, which accounts for diffusion-controlled processes The Nyquist diagram shows that each specimen has a semicircle form, with GO-TTA-Epoxy having the biggest diameter. In Table 3.10.1 (supplementary data) provided the fitted data for GO-TTA-Epoxy coatings, GO-Epoxy coatings, epoxy coatings in 96 h.The result is shown in Fig. 11. Generally speaking, a lower corrosion rate is associated with a bigger semicircle diameter. It indicates the rate of corrosion of GO-TTA-Epoxy was extremely low when comparing GO-Epoxy coatings and epoxy coatings on Al. The impedance spectra for epoxy coating decreased after 96 h of immersion, and for GO-Epoxy coating samples, the impedance spectra remained stable for 72 h but also showed decreased protection after 96 h. In contrast, the GO-TTA-Epoxy coating samples showed the highest impedance in 24 h and continued to show stable impedance after 96 h. This indicates that even after 96 h of immersion in a 3.5% NaCl solution, the GO-TTA-Epoxy coating exhibited the highest and most stable impedance, demonstrating its strong anticorrosive properties. The GO-Epoxy coating displayed values in the middle, indicating inadequate long-term protection but partial reinforcing. As a result of rapid ionic diffusion via holes and polymer matrix degradation, the unaltered epoxy coating, on the other hand, showed the lowest impedance. This pattern makes it abundantly evident that adding titanium tetra-acetoximate improves GO nanosheet dispersion, fortifies epoxy network crosslinking, and decreases micro-defect routes for chloride ion intrusion.

There is a noticeable difference in the coatings’ ability to prevent corrosion, as seen by the Bode plot obtained following 96 h of immersion. Superior barrier integrity and resistance to electrolyte penetration are demonstrated by the GO-TTA-Epoxy coatings, which has the largest impedance magnitude throughout the frequency range, especially in the low-frequency region. This partial improvement of protective activity is shown by the GO-epoxy system’s modest impedance. The unaltered epoxy coating, on the other hand, has the lowest impedance, indicating substantial ionic diffusion and decreased efficacy. This pattern demonstrates how adding titanium tetra-acetoximate improves dispersion, fortifies the coating matrix, and increases overall corrosion resistance.

Similar to this, the phase angle plot following 96 h of immersion demonstrates that the GO-TTA-Epoxy coating maintained a broad and high phase angle throughout a broad frequency range, indicating consistent dielectric response and robust capacitive behavior. This implies that the coating maintained its compactness, adhesion, and resistance to deterioration brought on by the electrolyte. A moderate phase angle changes in the GO-Epoxy system indicated some structural defects in addition to partial improvement. The plain epoxy coating, on the other hand, showed a low and narrow phase angle, indicating inadequate corrosion protection and poor dielectric qualities. The epoxy coating, on the other hand, exhibits a low and narrow phase angle, which indicates inadequate protection and dielectric qualities. According to these findings, adding titanium tetra-acetoximate greatly improves coating integrity and resistance to electrochemical reactions.

Fig. 11
figure 11

Nyquist, bode and phase angle diagram of epoxy coating, GO-epoxy coatings, GO-TTA-Epoxy coatings, immersed in 3.5% NaCl solution, the experimental and fitted data are shown in the forms of markers and lines, respectively and equivalent circuit (A) used for fitting the data.

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Potentiodynamic polarization measurement

The anodic and cathodic regions of the Tafel graphs generate the cathodic (βc) and anodic (βa) slopes/plots, corrosion potential (Ecorr), and corrosion current density (icorr). The icorr can be produced by projecting the Tafel lines to a corrosion potential. Separate tests were conducted on the aluminium samples using various epoxy coating, GO-epoxy coating, GO-TTA-epoxy coatings. Figure 12 shows the usual potentiodynamic polarization curves for various materials as determined in an aerated 3.5% NaCl solution. The figure illustrates the coating’s anodic and cathodic polarization behavior. Each curve’s cathodic and anodic Tafel lines were extrapolated to get the related corrosion kinetic parameters Ecorr, βc, βa, icorr, and IE%. According to the data displayed in the Table 5, graphene oxide with TTA-epoxy coating exhibits a lower corrosion current density and greater inhibition efficiency in comparison to bare aluminum, epoxy coating, and GO-epoxy coating. According to this result, the kinetic characteristics of cathodic the chemical mechanisms are the main influence being studied. After being 7.064 µA cm⁻2 for bare aluminum, the corrosion current density (Icorr) dropped to 3.187 µA cm⁻2 for epoxy-coated aluminum and then to 1.135 µA cm⁻2 for GO-Epoxy coatings. With an Icorr of 0.178 µA cm⁻2, or a 97.48% inhibition efficiency (IE), the GO-TTA-Epoxy coatings were remarkably the lowest. The corrosion rate (CR) of bare aluminum was 3.109 mpy; epoxy coatings decreased this to 1.402 mpy, GO-Epoxy to 0.499 mpy, and GO-TTA-Epoxy to as low as 0.078 mpy. These findings unequivocally show that the GO–TTA–Epoxy combination minimizes electrochemical activity at the metal/coating contact to provide exceptional corrosion protection.

Table 5 Potentiodynamic polarization fitted data for bare Al, epoxy coatings, GO-epoxy coatings, GO-TTA-epoxy coatings in 3.5% NaCl solution.
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Fig. 12
figure 12

Potentiodynamic polarization curves for bare Al, epoxy coating, GO-epoxy coating, and GO-TTA-epoxy coating.

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By evaluating the current conclusion with the published literature on the area of the present research, the novelty of the study has been further examined (Table 6).

Table 6 Electrochemical measurment results are compared to previously publish comparable studies.
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Conclusion

To improve the corrosion resistance of aluminium substrates, a unique graphene oxide–titanium tetra-acetoximate (GO–TTA) modified epoxy coating was created in this work. By adding TTA, the dispersion of GO in the epoxy matrix was much enhanced, reducing the agglomeration problems that are frequently seen in GO-based coatings. Surface characterization verified that this change produced a smoother surface shape and enhanced coating integrity. The coating was enhanced with better mechanical strength, chemical stability, and interfacial adhesion qualities essential for long-term durability by the synergistic interaction between GO and TTA. Tafel analysis, bode graphs, and EIS showed how resistant the coating was to corrosive conditions. Also, the system’s strong anticorrosive performance was confirmed by salt spray testing for 1008 h in 5% NaCl, which showed no obvious evidence of white rust or surface damage. The GO-TTA-epoxy composite coating offers a high-performing, environmentally friendly way to protect aluminium in harsh settings. It has potential uses in a variety of sectors, including as infrastructure, electronics, automotive, marine, and aerospace, where lightweight metals need better corrosion protection. Future research should focus on expanding the coating’s functional qualities, exploring other titanium-based modifiers and adjusting the formulation for different corrosion-prone alloy systems in order to increase the coating’s practical application.