The corrosion of metal is considered as one of the vital issues for steel structures when these structures are subjected to corrosion . Steel has high mechanical strength with low cost fabrication. Consequently, it is utilized in drilling equipment, ship building, and pipelines. In marines, corrosion results in 30% of the total failure thus needed to be repaired or replaced partially. In a marine environment, the corrosion of steel is influenced by salinity and alkalinity . Subsequently, coating was performed on steel faces to avoid the corrosion of new or existing steel construction. The corrosion of steel attracted many research interests as it is costly particularly in oilfield and marine environments . Recently, polymer composite liners to steel was used to decrease diffusion of oxygen and moisture. The protective organic coating as epoxy coating to metal is characterized by their excellent weather ability . Protected epoxy coating has attracted great attention in wet environment due to its very good toughness, durability and adhesion to metal substrates . However, the highly cross-linking density and the barrier behavior of the epoxy coating can be undesirably affected when exposed to corrosion. The polymer coating weakening results in the creation of holes and defects in the epoxy coating surface. During exposing to corrosive media, holes and defects become larger in width and depth. Holes are considered as conductive paths as the electrolyte diffuse in the polymeric coating . Moreover, the protective coating fails by the cause of delamination which is the separation at the polymeric coating/metal interface . The deterioration of polymeric coating decreases the barrier properties thus the mechanical properties of the polymeric coating . Therefore, it is essential to enhance the properties of epoxy resin by replacing epoxy with epoxy composite coatings to achieve the requirements of real applications .
Embedded of inorganic fillers to epoxy coating is one of the methods to enhance anti-corrosion characterization of organic polymeric coatings. Adding smaller filler particles in micron or nano size may improve barrier properties of the introduced polymeric coating. Size, morphology, shape, and the weight percentage of the fillers greatly affect the intrinsic characteristics of composite . Nanoparticles are considered as a good water barrier and thus effectively obstructs water absorption improving the service life of metals . Different nanomaterials are involved at various levels in the food industry having both positive and negative effects towards human health. Alumina can also be present due to contamination or migration from other food contact materials such as processing machinery, utensils, and devices . The coatings containing Al2O3 particles showed enhancement in scratch and abrasive resistance compared with that of polymer coating. This enhancement in scratch and abrasive resistance is attributed to the dispersion hardening of Al2O3 nanoparticles in polymer coatings . Enhancement in environmental impact can be attained utilizing nanosized particulates in polymeric coating and eliminating the requirement of toxic solvents . Nanoparticles embedded in polymeric coatings are well known for their outstanding physical, mechanical and thermal properties , .
Ramezanzadeh and Attar  investigated the corrosion resistance of the epoxy coating containing micron and nano sized ZnO fillers. The specimens were submerged in 3.5 wt% NaCl solution. The corrosion resistance of the coupons was significantly decreased after immersion for 15 days. The corrosion resistance of the epoxy coating was enhanced as reinforced with nano sized ZnO fillers. The results showed that the lowest reduction in cross-linking density and reducing hardness of the polymeric coating submerged in 3.5 wt% NaCl solution were attained as the epoxy coating was reinforced with the 3.5 wt% nano ZnO particles. Moreover, the adhesion was also increased at 3.5 wt%. Furthermore, Anaki and Xavier  studied the dispersability of reinforcing epoxy coating on mild steel with 2wt% of nano Al2O3. The resultant specimens has been submerged in 3.5% NaCl solution. The improved anticorrosion performance was conducted by the modified nanocomposite coating as compared to epoxy coating. The reinforced epoxy coating resulted in good adhesive strength, increasing in hardness, tensile strength, and better corrosion resistance than epoxy coating. In addition, Golru et al.  prepared epoxy/polyamide reinforced with 1, 2.5 and 3.5 wt% nano-alumina filler coted AA1050 substrate. The results showed that the nanofillers dispersed uniformly in the polymeric coating even when loading at high percentages. The polymeric coating corrosion resistance was more improved by increasing the weight percentage nanofillers.
In recent times, multilayered nanocomposites have gained a great attention due to their required characteristics as microwave absorbing, mechanical properties, permittivity constructed on the interfaces between adjacent layers and the synergistic impacts of fillers. Nevertheless, the application of multilayered of micro/nanocomposite coatings has not been reported yet . Al2O3 filler in micron size is commercially available and has a lower cost than Al2O3 in nano-size. So, the objective of the study is to develop multilayers of epoxy liners to steel filled with micro and nano Al2O3 particles with different percentage and differentiate between them. Three percentages of alumina micro and nanoparticles (1 wt%, 2wt%, and 3wt%) were introduced to epoxy with different configurations. The specimens were immersed in salt solution and in citric acid media. Barrier resistance and mechanical properties were investigated under dry and wet conditions.