Highly Enhanced Corrosion Resistance of Stainless Steel by Sol-Gel Layer-by-Layer Aluminosilicate Thin Coatings

Abstract

In this study, aluminosilicate sol-gel coatings were deposited on Type 430 stainless steel by multiple spin casting cycles. Amorphous aluminosilicate coatings, 65 nm thick, were prepared from precursor solutions with 50, 100, and 500 mmol dm −3 total concentrations of aluminum and silicon species (molar ratio of Al/Si = 1/4) by 10, 5, and 1 spin casting cycles, respectively. Although the obtained coatings had a similar composition with a molar ratio of Al/Si = 25/75, the coatings with increased density were formed by reducing the concentration of precursor solution. The pitting potentials of the coated stainless steels, measured by potentiodynamic polarization in 3.5% NaCl solution, increased remarkably (to 1.1 V vs Ag/AgCl) with a decrease in the concentration of precursor solution. Cyclic corrosion tests, consisting of 30 cycles of spraying of 5% NaCl solution at 35 • C for 2 h, drying at 60 • C for 4 h, and wetting at 50 • C and >95% relative humidity for 2 h, revealed highly improved corrosion resistance. Layer-by-layer sol-gel deposition using diluted precursor solutions is an effective way to obtain highly protective coatings. Metallic materials have been widely used in structural, marine, automobile, and aircraft applications. They are highly susceptible to corrosion in aggressive environments, and corrosion is one of the main contributors to materials loss in our society. Protective coatings have often been applied for corrosion protection. It has been well accepted that chromate coatings are the most effective, and have been applied as a suitable surface treatment of aluminum, magnesium, and steels. However, recent tighter regulations restrict the use of chromates due to their toxicity. As a consequence, the development of novel coatings with low environmental impact has attracted attention in the last decade.Sol-gel processing is one of the prospective candidates for the production of corrosion protection coatings with low environment impact. Sol-gel films usually have good adhesion to both metallic substrates and organic top coatings. The low temperature processing of the solgel method, compared with usual ceramic coatings, is important for the substrates that show mechanical degradation when exposed to environments at elevated temperatures. Thus, sol-gel processing has been extensively studied for corrosion protection of metals, including aluminum, magnesium, and steels.1 Sol-gel coatings based on SiO 2 , 2-6 ZrO 2 , 7-9 and Al 2 O 3 10,11 have been reported to provide good corrosion protection on various metals. However, there are still some drawbacks of inorganic sol-gel coatings: (i) it is difficult to form thick coatings (>1 μm) without cracking; 12 (ii) porosity usually exists in the coatings because the removal of organic components during heattreatment (usually at 400-600• C) introduces micropores in the coatings, through which corrosive solutions can penetrate to substrate. 13In order to overcome these drawbacks, increased interest has been directed toward organic-inorganic hybrid sol-gel sys...

Hybrid Sol–gel Coatings for Corrosion Mitigation: A Critical Review

“…The advantages and disadvantages of these materials, and the processing methods developed were discussed. Table 2 shows that numerous OIH sol-gel coatings for corrosion applications were developed [30,50,137,[191][192][193][194][195][196][197]. The number of reviews reported, only since 2016, clearly indicates that this field is still under development and is far from reach a matured stage.…”

Hybrid Sol-Gel Coatings: Smart and Green Materials for Corrosion Mitigation

“…In many instances, a dry gel needs further thermal treatment to be densified [20]. The sol-gel process versatility allows incorporation of additional components that introduce material's complementary functionalities, such as UV protection [21,22], anti-fouling [23,24], anti-reflection [25][26][27][28][29], moisture resistance [29][30][31][32][33], corrosion and adhesion protection [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53], along with the enhancement of mechanical, thermal, and optical properties, opening a wide range of application in several fields of science. Furthermore, this method allows the control of several experimental conditions leading to a simple sequence that may be tuned to the nature, final shape, and desired function.…”

Biomaterials Obtained by Gelation

“…The focus is here on the most interesting group, which are TiO 2 and SiO 2 -TiO 2 sol-gel biomaterials studied by a number of researchers (Li and de Groot 1993;Li et al 1994;Jokinen et al 1998;Peltola et al 2000;Areva et al 2004Areva et al , 2007Advincula et al 2006;Ä€ aritalo et al 2007;Wang et al 2012). However, other successful sol-gel oxide coatings on stainless steel were recently studied, including aluminosilicates (Habazaki et al 2014), ZrO 2 and SiO 2 -ZrO 2 -mixed oxides (Catauro et al 2014a;Śmieszek et al 2014).…”

“…But sol-gel TiO 2 enhanced the metal resistance to corrosion. Hence, it improved the implant biocompatibility, so that such coated implants are already in application Habazaki et al 2014;Śmieszek et al 2014).…”