Steel substrates including rare earth doped silica-alumina nanocoatings, coating compositions, and methods thereof

Abstract

The present disclosure provides a steel substrate comprising a rare earth doped silica-alumina coating, the rare earth doped silica-alumina coating comprising: a) from about 0.5 wt% to about 6.5 wt% Al; b) from about 0.5 wt% to about 6.5 wt% Si; and c) from about 0.1 wt% to about 11 wt% of a rare earth element. The rare earth doped silica-alumina coating is a nanocoating and provides very high corrosion resistance to the steel substrate and at the same time makes the steel substrate formable, weldable, paintable and fuel resistant. The present disclosure also provides a coating composition for depositing a rare earth doped silica-alumina coating on a steel substrate, wherein the coating composition comprises: a) an aqueous solution of an acid; b) a silane; c) aluminum isopropoxide; d) a compound of a rare earth element; and e) orthophosphoric acid or a derivative thereof. The present disclosure also provides a method for preparing the coating composition and a method for preparing a steel substrate including a rare earth doped silica-alumina coating.

Description

Technical Field

[0001] This disclosure relates to steel substrates including low-cost water-based nanocoatings, the water-based nanocoatings comprising silica and alumina doped with rare earth elements. In particular, this disclosure provides coated steel substrates, methods for preparing the same, and coating compositions for applying a coating to a steel substrate. Background Technology

[0002] Corrosion has a significant impact on a nation's environment and economy. The economic impact of corrosion on metallic structures is a critical issue. Steel is a common material used in many infrastructure projects due to its durability and affordability. However, steel is always susceptible to corrosion due to electrochemical reactions (spontaneous processes) in its service environment. Without proper care, significant economic losses can occur due to metal corrosion. Different methods exist to protect steel structures from corrosion, including: (i) passive isolation protection, (ii) active protection, (iii) sacrificial protection, (iv) electrophoretic deposition, (v) metallic coatings, and (vi) organic coatings. Different specialized coatings play a major role in mitigating corrosion. However, the choice of coating material depends on the substrate and its final application. In galvanized steel (GI), zinc is in direct contact with the steel (iron) substrate, providing sacrificial protection where preferential oxidation occurs on the zinc metal. Zinc is corroded due to its lower electrochemical potential compared to steel. In normal environments, the corrosion rate of zinc is generally slow. However, in the presence of ions (such as chloride ions) in coastal areas, this corrosion can be accelerated. Therefore, a secondary coating (organic / inorganic / hybrid) is required on the zinc surface to protect the zinc from corrosion and increase the lifespan of the entire structure.

[0003] Galvanized steel is primarily used in the construction industry. However, the surface of galvanized steel is prone to oxidation and darkening. Its forming behavior is also not ideal. To avoid these problems, the surface of galvanized steel is typically passivated with hazardous hexavalent chromates or a thin organic passivation layer. Hexavalent chromates are not environmentally friendly.

[0004] Motoaki Hara et al. investigated the use of colloidal silica coatings for chemical conversion treatment of galvanized steel as an alternative to chromate conversion. In this work, white rust appeared faster on the colloidal silicate film than on the chromate chemical conversion (CCC) film. However, the colloidal silicate coating offered more resistance to red rust compared to the CCC film. RV Lakshmi et al. have investigated the effect of cerium dioxide nanoparticle / cerium nitrate-doped silica-alumina hybrid sol-gel coatings on corrosion resistance. They observed that the cerium dioxide nanoparticle-doped coating showed better performance compared to the cerium nitrate-doped coating, due to the denser coating in the case of the cerium dioxide nanoparticle-doped coating.

[0005] Rust-preventive oils (RP oils) are also used on steel substrates (e.g., cold-rolled closed-annealed (CRCA), galvanized (GI), and alloyed galvanized (GA) substrates) to protect the steel from corrosion during transport to different end customers and during storage at the customer's location. These RP oils later need to be removed by degreasing followed by a seven-bath phosphate treatment. Phosphating pretreatment contributes to better adhesion of subsequent coatings. After phosphate pretreatment, these steel substrates undergo electrophoretic deposition (ED) of the coating, followed by primer and topcoat, respectively. These seven-bath processes are time-consuming and increase process costs. However, cost and process time can be reduced by using a single coating system (instead of phosphate, ED, primer, and topcoat) that provides all the required properties (corrosion resistance, formability, weldability, and post-coating properties).

[0006] Therefore, there is a need in the art to provide coatings that exhibit high corrosion resistance, formability, weldability, and post-coating properties, while simultaneously saving cost and time. This disclosure attempts to address this need. Summary of the Invention

[0007] This disclosure relates to a steel substrate comprising a rare earth-doped silica-alumina coating, wherein the coating comprises: a) about 0.5 wt% to about 6.5 wt% Al; b) about 0.5 wt% to about 6.5 wt% Si; and c) about 0.1 wt% to about 11 wt% rare earth elements.

[0008] This disclosure also relates to a coating composition for preparing a coated steel substrate, wherein the coating composition comprises: a) an aqueous solution of an acid; b) a silane; c) aluminum isopropoxide; d) a rare earth element compound; and e) phosphoric acid or a derivative thereof. In some embodiments, the coating composition comprises two silanes (e.g., TEOS and APTES), an organic green inhibitor, and a rust inhibitor.

[0009] This disclosure also provides a method for preparing a coating composition, comprising:

[0010] a. Preparation of the first solution, including:

[0011] A portion of the acid is added to softened water to obtain a first aqueous solution of the acid;

[0012] Add silane to the first aqueous solution of acid; and

[0013] After adding silane, rare earth element compounds are added to the first aqueous solution of the acid;

[0014] b. Preparation of the second solution, including:

[0015] The remaining portion of the acid is added to softened water to obtain a second aqueous solution of the acid;

[0016] Aluminum isopropoxide is added to a second aqueous solution of acid to obtain a second solution; and

[0017] c. Mix the first and second solutions, and then add phosphoric acid to obtain the coating composition.

[0018] In one embodiment, the coating composition comprises two silanes, an organic green inhibitor, and a rust inhibitor; the second silane is added to the mixture of the first and second solutions before the addition of orthophosphoric acid, and the organic green inhibitor and rust inhibitor are added to the second solution before the addition of the remaining portion of glycolic acid.

[0019] This disclosure also provides a method for preparing a steel substrate including the coating, wherein the method includes: a) applying a coating composition to a substrate to obtain a coated substrate; and b) drying the coated substrate at about 40 to 200 °C for about 2 to 20 minutes. Attached Figure Description

[0020] Figure 1 The results of salt spray test (SST) are shown for bare / uncoated GA substrates and bare / uncoated GI substrates.

[0021] Figure 2 The results of SST on the La-doped GA substrate with the coating are shown.

[0022] Figure 3 The results of SST on the La-doped GI substrate with the coating are shown.

[0023] Figure 4 The results of SST on the Ce-doped GI substrate with the coating are shown.

[0024] Figure 5 The impedance as a function of frequency is shown (Bode plot).

[0025] Figure 6 The results of adhesion (cross-cut) tests are shown for La-doped coatings of GA and GI samples.

[0026] Figure 7 The moldability test is shown on La-doped coated GA and GI samples.

[0027] Figure 8 The results of spot welding of GA / GI samples and their corresponding welding window diagrams are shown.

[0028] Figure 9 The (i) impact and (ii) cut bending tests are shown on the painted samples.

[0029] Figure 10 Scanning electron microscope and cross-sectional images of coatings (a, b) GA and coatings (c, d) GI are shown.

[0030] Figure 11 SEM-EDX images (coating GA and coating GI samples) with their corresponding elements are shown.

[0031] Figure 12 The self-healing behavior of coating GA is shown in (a) on day 1 and (b) on day 6 (after 120 hours of exposure to the ambient environment).

[0032] Figure 13 The self-healing behavior of coating GI is shown in (a) on day 1 and (b) on day 6 (120 hours of exposure to the ambient environment).

[0033] Figure 14 The XRD patterns of (a) powder coating (after drying), (b) bare GI and coated GI, and (c) bare GA and coated GA are shown.

[0034] Figure 15 The dynamic light scattering (DLS) spectrum showing the particle size distribution of the nano-coated sol is shown.

[0035] Figure 16 An exemplary schematic diagram of a process for preparing the coating compositions of this disclosure is shown.

[0036] Figure 17 The fuel / gasoline tolerance of the coated GA sheet is shown.

[0037] Figure 18 The FTIR spectra of the GI and GA coated samples are shown. Detailed Implementation

[0038] Regarding the use of virtually any plural and / or singular terms herein, those skilled in the art can translate them from plural to singular and / or from singular to plural as appropriate, depending on the context and / or application. For clarity, various singular / plural arrangements may be explicitly stated herein. The use of expressions “at least” or “at least one” indicates the use of one or more elements or components or quantities, as such use may be used in embodiments of this disclosure to achieve one or more desired objectives or results. Throughout this specification, wherever the words “comprise” or variations such as “comprises” or “comprising” or “containing” or “has” or “having” or “including but not limited to” are used, they will be understood to imply inclusion of the stated elements, integers, or steps, or groups of elements, integers, or steps, but not exclusion of any other elements, integers, or steps, or groups of elements, integers, or steps.

[0039] References to “some embodiments,” “one embodiment,” or “implementation” throughout this specification mean that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this disclosure. Therefore, the phrases “some embodiments,” “one embodiment,” or “in an embodiment” appearing in various places throughout this specification do not necessarily all refer to the same embodiment. It is understood that specific features of this disclosure described in the context of separate embodiments for clarity may also be provided in combination in a single embodiment. Conversely, various features of this disclosure described in the context of a single embodiment for brevity may also be provided separately or in any suitable sub-combination.

[0040] As used herein, the term "about" encompasses variations of + / -5%, and more preferably + / -2.5%, because such variations are appropriate for practicing the invention.

[0041] As used herein, the term "coated steel substrate" refers to a steel substrate having a rare-earth-doped silica-alumina coating. In some embodiments, the rare-earth-doped silica-alumina coating is a La-doped silica-alumina coating.

[0042] This disclosure provides a steel substrate comprising a rare earth-doped silica-alumina coating, wherein the coating comprises:

[0043] a) Approximately 0.5 to 6.5 wt% Al;

[0044] b) Approximately 0.5 to 6.5 wt% Si; and

[0045] c) Approximately 0.1 to 11 wt% rare earth elements.

[0046] In some embodiments, the rare earth element present in the coating is cerium (Ce), lanthanum (La), neodymium (Nd), praseodymium (Pr), or a combination thereof. In some embodiments, the rare earth element present in the coating is cerium (Ce). In some embodiments, the rare earth element present in the coating is lanthanum (La).

[0047] In some embodiments, the rare earth-doped coating on the steel substrate includes:

[0048] a) About 0.5 to 6.5 wt% Al, including its values ​​and ranges, for example, about 0.5 to 6 wt%, about 0.5 to 5 wt%, about 0.5 to 4.5 wt%, about 0.5 to 4 wt%, about 0.5 to 3.5 wt%, about 0.5 to 3 wt%, about 0.5 to 2.5 wt%, about 0.5 to 2 wt%, about 1 to 6.5 wt%, about 1 to 6 wt%, about 1 to 5.5 wt%, about 1 to 5 wt%, about 1 to 4.5 wt%, about 1 to 3.5 wt%, about 1.5 to 6.5 wt%, about 1.5 to 5 wt%, about 1.5 to 4 wt%, about 2 to 6.5 wt%, about 2 to 6 wt%, about 2 to 5.5 wt%, about 2 to 4.5 wt%, about 3 to 6.5 wt%, about 3 to 6 wt%, about 3 to 5 wt%, about 4 to 6.5 wt%. For example, Al at wt%, about 5 to 6.5 wt%, about 0.5 wt%, about 0.75 wt%, about 1 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 3.5 wt%, about 4 wt%, about 4.5 wt%, about 5 wt%, about 5.5 wt%, about 5.75 wt%, about 6 wt%, about 6.25 wt%, or about 6.5 wt%;

[0049] b) About 0.5 to 6.5 wt% Si, including its values ​​and ranges, for example, about 0.5 to 6 wt%, about 0.5 to 5 wt%, about 0.5 to 4.5 wt%, about 0.5 to 4 wt%, about 0.5 to 3.5 wt%, about 0.5 to 3 wt%, about 0.5 to 2.5 wt%, about 0.5 to 2 wt%, about 1 to 6.5 wt%, about 1 to 6 wt%, about 1 to 5.5 wt%, about 1 to 5 wt%, about 1 to 4.5 wt%, about 1 to 3.5 wt%, about 1.5 to 6.5 wt%, about 1.5 to 5 wt%, about 1.5 to 4 wt%, about 2 to 6.5 wt%, about 2 to 6 wt%, about 2 to 5.5 wt%, about 2 to 4.5 wt%, about 3 to 6.5 wt%, about 3 to 6 wt%, about 3 to 5 wt%, about 4 to 6.5 wt%. For example, Si at wt%, approximately 5 to 6.5 wt%, approximately 0.5 wt%, approximately 0.75 wt%, approximately 1 wt%, approximately 2 wt%, approximately 2.5 wt%, approximately 3 wt%, approximately 3.5 wt%, approximately 4 wt%, approximately 4.5 wt%, approximately 5 wt%, approximately 5.5 wt%, approximately 5.75 wt%, approximately 6 wt%, approximately 6.25 wt%, or approximately 6.5 wt%; and

[0050] c) Rare earth elements, including their values ​​and ranges, from about 0.1 to 11 wt%, from about 0.1 to 10.5 wt%, from about 0.1 to 10 wt%, from about 0.1 to 9.5 wt%, from about 0.1 to 9 wt%, from about 0.1 to 8.5 wt%, from about 0.1 to 7.5 wt%, from about 0.1 to 6.5 wt%, from about 0.1 to 5.5 wt%, from about 0.1 to 4 wt%, from about 1 to 11 wt%, from about 1 to 10.5 wt%, from about 1 to 9.5 wt%, from about 1 to 8.5 wt%, from about 1 to 7.5 wt%, from about 1 to 6 wt%, from about 2 to 11 wt%, from about 2 to 10.5 wt%, from about 2 to 10 wt%, from about 2 to 9.5 wt%, from about 2 to 9 wt%, from about 2 to 8.5 wt%, from about 2 to 8 wt%, from about 2 to 7.5 wt%. wt%, about 2 to 7 wt%, about 3.5 to 10.5 wt%, about 3.5 to 10 wt%, about 3.5 to 9.5 wt%, about 3.5 to 8.5 wt%, about 3.5 to 8 wt%, about 4 to 10.5 wt%, about 4 to 10 wt%, about 4 to 9.5 wt%, about 4 to 9 wt%, about 4 to 8.5 wt%, about 4 to 8 wt%, about 4 to 7 wt%, about 5 to 11 wt%, about 5 to 10.5 wt%, about 5 to 10 wt%, about 5 to 9.5 wt%, about 5 to 9 wt%, about 5 to 8.5 wt%, about 5 to 8 wt%, about 5 to 8 wt%, about 5 to 8 wt%, about 6 to 10.5 wt%, about 6 to 10 wt%, about 6 to 9.5 wt%, about 6 to 9 wt%, about 6 to 8.5 wt%, about 7 to 10.5 wt%, about 7 to 9 wt%. For example, rare earth elements in wt%, about 7.5 to 10.5 wt%, about 7.5 to 10 wt%, about 7.5 to 9.5 wt%, about 8 to 10.5 wt%, about 8 to 10 wt%, about 0.5 wt%, about 1 wt%, about 2 wt%, about 3 wt%, about 3.5 wt%, about 4 wt%, about 4.5 wt%, about 5 wt%, about 5.5 wt%, about 6 wt%, about 6.5 wt%, about 7 wt%, about 7.5 wt%, about 8 wt%, about 8.5 wt%, about 9 wt%, about 9.5 wt%, about 10 wt%, about 10.5 wt%, or about 11 wt%.

[0051] In some embodiments, the rare earth-doped coating on the steel substrate includes:

[0052] a) Approximately 0.5 to 6.5 wt% Al, including its values ​​and ranges, as described above;

[0053] b) Approximately 0.5 to 6.5 wt% Si, including its values ​​and ranges, as described above; and

[0054] c) Approximately 0.1 to 11 wt% Ce or La, including their values ​​and ranges, as described above.

[0055] In some embodiments, the rare-earth-doped coating on the steel substrate is a nano-coating. In some embodiments, the coating comprises nanoparticles or nanorods. The nano-morphology of the coating provides better coverage of the substrate, prevents water molecules and other corrosive ions (such as chloride ions) from penetrating through the coating, provides better corrosion resistance compared to conventional coatings, and provides properties such as the superior stain resistance and easy-to-clean properties of paints.

[0056] In some embodiments, the nanocoating has a particle size of about 35 to 500 nm (inclusive), such as about 35 to 450 nm, about 35 to 400 nm, about 35 to 350 nm, about 35 to 300 nm, about 35 to 275 nm, about 35 to 265 nm, about 35 to 250 nm, about 35 to 225 nm, about 50 to 500 nm, about 50 to 450 nm, about 50 to 400 nm, about 50 to 350 nm, about 50 to 300 nm, about 50 to 275 nm, about 50 to 265 nm, about 75 to 500 nm, about 75 to 400 nm, about 75 to 350 nm, or about 75 to 265 nm. In some embodiments, the nanocoating has a particle size of about 35 to 265 nm.

[0057] The adhesion of a coating to a steel substrate depends on the contact angle and surface energy. A low contact angle and high surface energy indicate that the coated substrate is hydrophilic, which contributes to better coating adhesion. In some embodiments, the coated steel substrate has a smaller contact angle and higher surface energy compared to the corresponding bare sample.

[0058] In some embodiments, the coated steel substrate has a contact angle of about 15 to 55° (inclusive), such as about 19 to 49°, about 20 to 45°, about 25 to 50°, about 30 to 50°, about 19°, about 20°, about 25°, about 30°, about 35°, about 40°, about 45°, about 49°, or about 55°. In some embodiments, the coated steel substrate has a contact angle of 19° or 49°. In some embodiments, the coated steel substrate is an alloyed zinc-plated (GA) substrate including the coating and having a contact angle of 19°. In some embodiments, the coated steel substrate is a zinc-plated (GI) substrate including the coating and having a contact angle of 49°.

[0059] In some embodiments, the coated steel substrate has a surface energy of about 50 to 75 mN / m (inclusive of values ​​and ranges), such as about 53 to 71 mN / m, about 55 to 70 mN / m, about 60 to 75 mN / m, about 65 to 75 mN / m, about 50 mN / m, about 53 mN / m, about 55 mN / m, about 60 mN / m, about 63 mN / m, about 71 mN / m, or about 75 mN / m.

[0060] In some embodiments, the coated steel substrate has a contact angle of 15 to 55° (inclusive of the above values ​​and ranges) and a surface energy of about 50 to 75 mN / m (inclusive of the above values ​​and ranges).

[0061] In some embodiments, the coated steel substrate has a contact angle of 19° and a surface energy of 71 mN / m. In some embodiments, the coated steel substrate has a contact angle of 49° and a surface energy of 53 mN / m.

[0062] In some embodiments, the X-ray diffraction pattern of the substrate before and after coating is similar, indicating that the substrate remains homogeneous after coating. The inventors observed that steel substrates (such as GA and GI substrates) are crystalline in nature before the coating is applied. After the coating is applied, the crystallinity of the substrate is reduced; however, most X-ray diffraction peaks remain intact after coating, and only a very small number of diffraction peaks are eliminated.

[0063] The coated steel substrate disclosed herein meets all four requirements—corrosion resistance, formability, weldability, and paintability. Therefore, this coated steel substrate is suitable for manufacturing products used in the automotive and electrical industries.

[0064] This coating provides high corrosion resistance to the steel substrate. In some embodiments, the coated substrate exhibits no white rust in salt spray tests of at least 200 hours, 300 hours, 400 hours, 500 hours, 600 hours, 700 hours, 800 hours, 900 hours, 1000 hours, 1200 hours, 1500 hours, 1800 hours, 2000 hours, 2300 hours, 2500 hours, 2800 hours, 3200 hours, 3500 hours, 4000 hours, 4500 hours, or 5000 hours.

[0065] In some embodiments, the coated substrate exhibits no white rust for at least up to 900 hours. In some embodiments, the coated substrate exhibits no white rust for at least up to 4500 hours.

[0066] In some embodiments, the coated substrate exhibits no white rust even after 900 hours. In some embodiments, the coated substrate exhibits no white rust even after 4500 hours.

[0067] In some implementations, the coated substrate exhibits increased impedance in electrochemical impedance spectroscopy (EIS) tests compared to the bare substrate, indicating that the coating is providing isolation protection.

[0068] In some implementations, the coating adheres well to the steel substrate and does not peel off from the substrate in a standard cross-cut adhesion test.

[0069] This coating provides formability to the steel substrate. In some embodiments, when tested by a dome test, the substrate shows up to 25 mm of coating without delamination or chalking, indicating that the coating is formable.

[0070] This coating also provides spot weldability to the steel substrate. In some embodiments, the coating shows a weld nugget diameter greater than 4.5√t in spot welding tests at a current of 5.5 kA or greater, where “t” is the thickness of the substrate, indicating that the weld quality is acceptable to automotive industry requirements.

[0071] The coated steel substrate of this disclosure exhibits very high corrosion resistance, for example, no white rust formation for more than 900 hours in some embodiments, or no white rust formation for more than 4,500 hours in some embodiments, and at the same time, the substrate is formable, weldable and paintable.

[0072] The coated steel substrates of this disclosure exhibit fuel resistance. In some embodiments, resistance to fuel (such as gasoline) is measured by exposing the coated substrate to fuel and observing rust formation over a specific time period. For example, in some embodiments, the coated substrates of this disclosure do not show rust formation after exposure to fuel for 450 hours, 500 hours, 750 hours, 1000 hours, 1250 hours, 1500 hours, 1750 hours, 2000 hours, 2250 hours, 2400 hours, 2472 hours, or 2500 hours. In some embodiments, the coated substrates of this disclosure exhibit good fuel resistance even after 2472 hours of fuel exposure. Accordingly, in some embodiments, the coated steel substrates of this disclosure can be used in fuel tank applications.

[0073] In some embodiments, the steel substrate is galvanized iron (GI), alloyed zinc (GA), aluminum zinc, zinc aluminum, magnesium zinc, or ultra-zinc coated substrate. In some embodiments, the steel substrate is GI substrate or GA substrate.

[0074] This disclosure also provides coating compositions for preparing coated steel substrates of this disclosure. In some embodiments, the coating composition includes:

[0075] a) An aqueous solution of an acid;

[0076] b) Silane;

[0077] c) Aluminum isopropoxide;

[0078] d) Compounds of rare earth elements; and

[0079] e) Orthophosphoric acid or its derivatives.

[0080] In some embodiments, the coating composition includes:

[0081] a) An aqueous solution of an acid;

[0082] b) Silanes (e.g., tetraethyl orthosilicate);

[0083] c) Compounds of rare earth elements;

[0084] d) Tannins (e.g., tannic acid);

[0085] e) Organic green inhibitors (e.g., anhydrous caffeine);

[0086] f) Aluminum isopropoxide;

[0087] g) a second silane (e.g., 3-aminopropyl)triethoxysilane); and

[0088] h) Orthophosphoric acid or its derivatives.

[0089] The coating composition is a water-based / aqueous coating composition.

[0090] The coating composition comprises an aqueous solution of an acid. In some embodiments, the acid is a carboxylic acid. In some embodiments, the coating composition comprises an aqueous solution of a carboxylic acid selected from lactic acid, formic acid, acetic acid, propionic acid, glycolic acid, benzoic acid, glutaric acid, hexanoic acid, butyric acid, valeric acid, fumaric acid, or combinations thereof. In some embodiments, the acid is glycolic acid.

[0091] In some embodiments, the acid is present in the coating composition at a concentration of about 2 to 40 wt% (including its value and range), for example, about 2 to 35 wt%, about 2 to 30 wt%, about 2 to 25 wt%, about 2 to 20 wt%, about 2 to 15 wt%, about 5 to 40 wt%, about 5 to 35 wt%, about 5 to 30 wt%, about 5 to 25 wt%, about 5 to 20 wt%, about 5 to 15 wt%, about 10 to 40 wt%, about 10 to 30 wt%, about 10 to 20 wt%, about 15 to 40 wt%, about 15 to 35 wt%, about 15 to 30 wt%, about 20 to 40 wt%, about 20 to 30 wt%, or about 30 to 40 wt%. In some embodiments, the acid is present in the coating composition at a concentration of about 2 wt%, 4 wt%, 5 wt%, 10 wt%, 12.5 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or about 40 wt%.

[0092] In some embodiments, the silane present in the coating composition is selected from tetraethyl orthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES), (3-aminopropyl)trimethoxysilane (APTMS), (3-glycidyl etheroxypropyl)trimethoxysilane (GPTMS), (3-glycidyl etheroxypropyl)triethoxysilane (GPTES), methyltrimethoxysilane (MTMS), or combinations thereof. In some embodiments, the coating composition includes TEOS as a silane. In some embodiments, the coating composition includes APTES as a silane. In some embodiments, the coating composition includes both TEOS and APTES as silanes.

[0093] In some embodiments, the silane is present in the coating composition at a concentration of about 3 to 30 wt% (inclusive of its value and range), such as about 3 to 27 wt%, about 3 to 25 wt%, about 3 to 20 wt%, about 3 to 15 wt%, about 3 to 10 wt%, about 5 to 30 wt%, about 5 to 25 wt%, about 5 to 20 wt%, about 5 to 15 wt%, about 5 to 10 wt%, about 10 to 30 wt%, about 10 to 25 wt%, about 10 to 20 wt%, about 15 to 30 wt%, about 15 to 25 wt%, about 20 to 30 wt%, about 20 to 25 wt%, about 25 to 30 wt%. In embodiments in which more than one silane is present in the coating composition, each silane is present at a concentration of about 3 to 30 wt% (inclusive of its value and range) as described above.

[0094] In some embodiments, aluminum isopropoxide is present in the coating composition at a concentration of about 5 to 40 wt% (inclusive of its value and range), for example, about 5 to 35 wt%, about 5 to 30 wt%, about 5 to 25 wt%, about 5 to 20 wt%, about 5 to 15 wt%, about 10 to 40 wt%, about 10 to 30 wt%, about 10 to 20 wt%, about 15 to 40 wt%, about 15 to 35 wt%, about 15 to 30 wt%, about 20 to 40 wt%, about 20 to 30 wt%, about 30 to 40 wt%, 5 wt%, 10 wt%, 12.5 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or about 40 wt%.

[0095] The coating composition comprises a compound of a rare earth element selected from cerium (Ce), lanthanum (La), neodymium (Nd), praseodymium (Pr), or combinations thereof. In some embodiments, the rare earth element compound is selected from rare earth element nitrates, sulfates, chlorides, phosphates, and hydroxides.

[0096] In some embodiments, rare earth element compounds are present in the coating composition at concentrations of about 0.05 to 10 wt% (including values ​​and ranges thereof), such as about 0.05 to 8 wt%, about 0.05 to 6 wt%, about 0.05 to 5 wt%, about 1 to 10 wt%, about 1 to 8 wt%, about 1 to 5 wt%, about 2.5 to 10 wt%, about 2.5 to 8 wt%, about 2.5 to 5 wt%, about 5 to 10 wt%, about 0.05 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 4 wt%, about 5 wt%, about 5.5 wt%, about 6 wt%, about 7 wt%, about 7.5 wt%, about 8 wt%, about 9 wt%, or about 10 wt%.

[0097] In some embodiments, the rare earth element compound present in the coating composition is cerium nitrate or cerium nitrate hexahydrate or cerium nitrate hydrate or cerium chloride or cerium chloride heptahydrate or cerium hydroxide or cerium phosphate or cerium sulfate or cerium isopropoxide or lanthanum nitrate or lanthanum nitrate hydrate or lanthanum nitrate hexahydrate or lanthanum chloride or lanthanum chloride or lanthanum chloride heptahydrate or lanthanum isopropoxide. In some embodiments, the rare earth element compound present in the coating composition is cerium nitrate or lanthanum nitrate.

[0098] The coating composition includes orthophosphoric acid or its derivatives. In some embodiments, orthophosphoric acid or its derivatives are present in amounts of about 5 to 50 wt% (inclusive of values ​​and ranges), for example, about 5 to 45 wt%, about 5 to 40 wt%, about 5 to 35 wt%, about 5 to 30 wt%, about 5 to 25 wt%, about 5 to 20 wt%, about 5 to 15 wt%, about 10 to 50 wt%, about 10 to 45 wt%, about 10 to 40 wt%, about 10 to 30 wt%, about 10 to 20 wt%, about 15 to 50 wt%, about 15 to 45 wt%, about 15 to 40 wt%, about 15 to 35 wt%, about 15 to 30 wt%, about 20 to 50 wt%, about 20 to 40 wt%, about 20 to 30 wt%, about 30 to 50 wt%, about 30 to 40 wt%, about 35 to 50 wt%, about 40 to 50 wt%, about 5 wt%, about 10 The coating composition is present at concentrations of about 12.5 wt%, about 15 wt%, about 20 wt%, about 25 wt%, about 30 wt%, about 35 wt%, about 40 wt%, about 45 wt%, or about 50 wt%. In some embodiments, the derivative of orthophosphoric acid is selected from phosphoric acid, phosphonic acid, pyrophosphoric acid, tripolyphosphoric acid, tetrapolyphosphoric acid, trimetaphosphoric acid, and phosphoric anhydride.

[0099] In some embodiments, the coating composition includes an organic green inhibitor, a rust converter, or both.

[0100] In some embodiments, the organic green inhibitor is selected from cysteine, folic acid, glycine, leucine, caffeine, alanine, tryptophan, methionine, or combinations thereof. In some embodiments, the organic green inhibitor is present at a concentration of about 0.05 to 10 wt% (inclusive of values ​​and ranges), such as about 0.05 to 8 wt%, about 0.05 to 6 wt%, about 0.05 to 5 wt%, about 1 to 10 wt%, about 1 to 8 wt%, about 1 to 5 wt%, about 2.5 to 10 wt%, about 2.5 to 8 wt%, about 2.5 to 5 wt%, about 5 to 10 wt%, about 0.05 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 4 wt%, about 5 wt%, about 5.5 wt%, about 6 wt%, about 7 wt%, about 7.5 wt%, about 8 wt%, about 9 wt%, or about 10 wt%. In some embodiments, the coating composition includes caffeine as an organic green inhibitor in any of the amounts described above.

[0101] In some embodiments, the rust converter is selected from tannic acid. In some embodiments, the rust converter is present at a concentration of about 0.05 to 10 wt% (inclusive of its value and range), such as about 0.05 to 8 wt%, about 0.05 to 6 wt%, about 0.05 to 5 wt%, about 1 to 10 wt%, about 1 to 8 wt%, about 1 to 5 wt%, about 2.5 to 10 wt%, about 2.5 to 8 wt%, about 2.5 to 5 wt%, about 5 to 10 wt%, about 0.05 wt%, about 1 wt%, about 1.5 wt%, about 2 wt%, about 2.5 wt%, about 3 wt%, about 4 wt%, about 5 wt%, about 5.5 wt%, about 6 wt%, about 7 wt%, about 7.5 wt%, about 8 wt%, about 9 wt%, or about 10 wt%. In some embodiments, the coating composition includes tannic acid as a rust converter in any of the amounts described above.

[0102] In some embodiments, the coating composition includes:

[0103] a) An aqueous solution of glycolic acid;

[0104] b) TEOS and APTES;

[0105] c) Aluminum isopropoxide;

[0106] d) Cerium nitrate or lanthanum nitrate; and

[0107] e) Orthophosphoric acid.

[0108] In some embodiments, the coating composition includes:

[0109] (a) An aqueous solution of glycolic acid;

[0110] (b) TEOS and APTES;

[0111] (c) Aluminum isopropoxide;

[0112] (d) Cerium nitrate or Lanthanum nitrate;

[0113] (e) Phosphoric acid;

[0114] (f) Caffeine; and

[0115] (g) Tannic acid.

[0116] In some embodiments, the coating composition includes:

[0117] a) An aqueous solution of glycolic acid, approximately 2 to 40 wt%;

[0118] b) Approximately 3 to 30 wt% TEOS and APTES;

[0119] c) Approximately 5 to 40 wt% aluminum isopropoxide;

[0120] d) Approximately 0.05 to 10 wt% of lanthanum nitrate or cerium nitrate; and

[0121] e) Approximately 5 to 50 wt% of orthophosphoric acid.

[0122] In some embodiments, the coating composition includes:

[0123] a) An aqueous solution of glycolic acid, approximately 2 to 40 wt%;

[0124] b) Approximately 3 to 30 wt% TEOS and APTES;

[0125] c) Approximately 5 to 40 wt% aluminum isopropoxide;

[0126] d) Approximately 0.05 to 10 wt% of lanthanum nitrate or cerium nitrate;

[0127] e) Approximately 5 to 50 wt% orthophosphoric acid;

[0128] f) Approximately 0.05 to 5 wt% caffeine; and

[0129] (g) Approximately 0.05 to 10 wt% tannic acid.

[0130] This disclosure also provides methods for preparing coating compositions. In some embodiments, the method for preparing a coating composition includes:

[0131] a. Preparation of the first solution, including:

[0132] A portion of glycolic acid is added to softened water to obtain a first aqueous solution of the acid.

[0133] Add a silane (e.g., tetraethyl orthosilicate) to a first aqueous solution of an acid; and

[0134] After adding silane, a rare earth element compound (e.g., a rare earth salt / hydroxide) is added to the first aqueous solution of the acid;

[0135] b. Preparation of the second solution, including:

[0136] The remaining portion of the glycolic acid is added to softened water to obtain a second aqueous solution of the acid; and

[0137] Aluminum isopropoxide is added to the second aqueous solution of the acid; and

[0138] c. The second solution is mixed into the first solution, and then phosphoric acid is added to obtain the coating composition.

[0139] In some embodiments, the coating composition comprises two silanes. In these embodiments, one of the silanes is added to a first aqueous acid solution before the addition of phosphoric acid, and the other silane is added to a mixture of the first and second solutions.

[0140] Before adding acid, in the step of preparing the second solution, an organic green inhibitor and a rust converter (if present) are added to the softened water.

[0141] In some embodiments, the method for preparing the coating composition includes:

[0142] (a) Preparing the first solution, including:

[0143] A portion of glycolic acid is added to softened water to obtain a first aqueous solution of the acid.

[0144] Add silane (tetraethyl orthosilicate) to the first aqueous solution of the acid; and

[0145] After adding silane, rare earth element compounds (rare earth salts / hydroxides) are added to the first aqueous solution of the acid;

[0146] (b) Preparing the second solution, including:

[0147] Tannic acid is added to softened water to obtain a second aqueous solution;

[0148] Add anhydrous caffeine to the second aqueous solution;

[0149] The remaining portion of glycolic acid is added to the second aqueous solution to obtain a second aqueous solution of the acid; and

[0150] Aluminum isopropoxide is added to the second aqueous solution of the acid; and

[0151] (c) The second solution is mixed into the first solution, and then a second silane (APTES) and phosphoric acid are added respectively to obtain a coating composition.

[0152] An exemplary schematic diagram for the preparation of the coating composition is shown in Figure 16 middle.

[0153] In the embodiments of the above methods, the concentrations or wt% of the components are as described in the embodiments of the coating composition. For the sake of brevity and to avoid repetition, each of those concentrations or wt% will not be repeated in the context of the method. However, each of those concentrations or wt% falls entirely within the scope of the method for preparing the coating composition.

[0154] The components of the coating composition are added to softened water or an aqueous acid solution at a temperature of about 25 to 60°C (inclusive). After each component is added, the components are mixed in the solution by stirring at a speed of about 100 to 1000 rpm (inclusive).

[0155] This disclosure also provides methods for preparing steel substrates including coatings of this disclosure. In some embodiments, the method for preparing a steel substrate includes: a) applying a coating composition described herein to a steel substrate to obtain a coated substrate; and b) drying the coated substrate at about 40 to 200 °C for about 2 to 20 minutes.

[0156] The coating composition can be applied to a steel substrate by dip coating or roll coating. After applying the coating composition, the steel substrate is dried at a temperature of about 40 to 200 °C (inclusive) for about 2 to 20 minutes (inclusive). In some embodiments, after applying the coating composition, the steel substrate is subjected to temperatures ranging from about 40 to 175 °C, 40 to 150 °C, 40 to 120 °C, 40 to 100 °C, 50 to 200 °C, 50 to 180 °C, 50 to 140 °C, 50 to 100 °C, 60 to 200 °C, 60 to 180 °C, 60 to 120 °C, 60 to 100 °C, 75 to 200 °C, 75 to 180 °C, 75 to 150 °C, 75 to 120 °C, 100 to 200 °C, 100 to 180 °C, 100 to 150 °C, or 150 to 200 °C. Dry at °C for approximately 2 to 20 minutes, 2 to 15 minutes, 2 to 10 minutes, 2 to 5 minutes, 5 to 20 minutes, 5 to 15 minutes, 5 to 10 minutes, 10 to 20 minutes, or approximately 15 to 20 minutes.

[0157] The steel substrate coated with this coating composition is dried in a hot air oven under the above-mentioned temperature and time conditions.

[0158] Substrates that can be coated with this coating composition include, but are not limited to, galvanized, galvanized, galume, galfan, magnesium zinc, or super galva substrates. In an exemplary embodiment, the substrate coated with this coating composition includes galvanized or alloyed galvanized steel substrates.

[0159] The above method can be used to obtain the performance characteristics of coated steel substrates, such as corrosion resistance, paintability, weldability, formability, adhesion, and fuel resistance.

[0160] This disclosure provides a low-cost, water-based, rare-earth-doped silica-alumina nanocoating system for steel substrates with a low peak metallographic temperature (PMT) of 40 °C to 150 °C. The coating compositions prepared to provide this coating were found to be stable for over one year. This coating system is a reactive coating system for both GA and GI substrates. Performance studies were conducted on the coated substrates after homogeneous deposition and curing / drying of the coating composition. It was observed that the coated substrates exhibited superior corrosion resistance and other desired coating properties. For example, in some embodiments, the coating exhibited >4500 hours of white rust stability on GA substrates and >900 hours of white rust stability on GI substrates. This coating meets all four requirements (corrosion resistance, formability, weldability, and paintability) and also exhibits fuel resistance. Therefore, it is suitable for use in the automotive and electrical industries. The developed coating system is based on a silica-alumina system doped with rare-earth compounds / salts. Doping improves the overall corrosion resistance and conductivity of the coating system. The increased conductivity of the coating also facilitates post-welding processes. The developed coating is solderable due to the semiconductor properties provided by the doping of rare earth compounds. The low-PMT coating consumes less power compared to high-PMT coatings.

[0161] It should be understood that the foregoing descriptive content is an interpretation of this disclosure and is not intended to be limiting. While considerable emphasis has been placed on specific features of this disclosure herein, it will be understood that various modifications can be made without departing from the principles of this disclosure, and many changes can be made in preferred embodiments. Those skilled in the art will recognize that the embodiments described herein can be practiced with modifications to the spirit and scope of the embodiments described herein. Similarly, further embodiments and features of this disclosure will be apparent to those skilled in the art based on the description provided herein.

[0162] Descriptions of well-known / conventional methods / steps and techniques have been omitted to avoid unnecessarily obscuring the embodiments described herein. Furthermore, this disclosure provides examples illustrating the above embodiments, and specific aspects are employed to illustrate the embodiments of this disclosure. The examples used herein for such illustration are intended only to facilitate understanding of the practicality of the embodiments described herein and to further ensure that those skilled in the art can practice the embodiments described herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments described herein.

[0163] Example

[0164] Example 1: Synthesis of the coating composition and its application on a substrate

[0165] The coating composition is prepared in an aqueous acidic medium containing one or more of the following carboxylic acids: lactic acid, formic acid, acetic acid, propionic acid, glycolic acid, benzoic acid, glutaric acid, hexanoic acid, butyric acid, valeric acid, and fumaric acid. The concentration of these acids in the total composition varies from 2 wt% to 40 wt%. The acidic medium helps control sol growth and prevent precipitation. These acids can also form metal complexes with metals, thereby increasing the stability of the coating solution. Two silanes [tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES)] are used with aluminum isopropoxide. The concentration of the above silanes varies from 3 wt% to 30 wt%, and the concentration of aluminum isopropoxide varies from 5 wt% to 40 wt%. The coating composition is doped with rare earth element compounds (Ce / La / Nd / Pr, 0.05 wt% to 10 wt%) to improve the corrosion resistance and conductivity of the coating. Doping helps to make the coating easy to spot weld. One or more of the listed organic green inhibitors (cysteine, folic acid, glycine, leucine, caffeine, alanine, tryptophan, and methionine) were added to the coating composition at a concentration ranging from 0.05 wt% to 10 wt%, and a rust conversion agent (tannic acid, 0.05 wt% to 10 wt%) was added to make the coating robust. Orthophosphoric acid was added at a concentration ranging from 5 wt% to 50 wt%. The coating composition was applied to GA and GI substrates by dip coating and roll coating. After coating, the samples were dried in a hot air oven at 40 °C to 200 °C for 2 to 20 minutes. The samples were dried / cured at different temperatures / times, and the peak metallographic temperature (PMT) was found to be between 40 °C and 150 °C.

[0166] Example 2: Performance characteristics of coated steel substrates

[0167] Salt spray testing (SST) was performed on coated steel substrates (GA and GI) according to ASTM B117 to determine the corrosion resistance of the coating in a corrosive saltwater environment. To understand the effect of the coating on corrosion resistance, bare GA and bare GI samples were also subjected to SST.

[0168] Figure 1 The results of SST are shown. It was observed that both bare substrates corroded (i.e., formed white rust) after 6 hours of exposure in the SST chamber. However, in the case of the GA sample, red rust began after 48 hours.

[0169] Figure 2 The SST images of the GA-coated samples are shown after different time intervals. It was found that the coating on the GA substrate was very stable and showed no white rust even after 4500 hours.

[0170] SST images of GI samples in Figure 3The figures are shown at different time intervals. In this case, very little white rust (<1%, two spots) was observed after 960 hours. Therefore, the coating is stable on GI for 900 hours or longer. This high SST value is the first of its kind achieved for a galvanized substrate. According to previous studies, GA or GI substrates typically exhibit a maximum white rust stability of 200 hours in SST.

[0171] The corrosion resistance of Ce-doped coating samples was also tested. For GA and GI coated substrates, more than 10% white rust was observed after 264 hours of SST (see...). Figure 4 ).

[0172] The corrosion resistance properties of bare steel substrates and coated steel substrates (GA and GI) were investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). EIS studies were conducted in the frequency range of 0.01 Hz to 100 kHz. A three-electrode system was used, with the sample acting as the working electrode (1 cm⁻¹). 2 The exposed area was measured using a saturated calomel electrode (SCE) as the reference electrode and graphite as the counter electrode. A 3.5% aqueous NaCl solution was used as the electrolyte in all measurements. Figure 5 Semi-logarithmic plots (Bohr plots) of impedance versus frequency are shown for both GA and GI substrates. It is observed that the impedance of the coated samples (GA / GI) increases compared to the bare substrate, indicating that the coating provides isolation and protection.

[0173] Pass the standard cross-cutting test ( Figure 6 Adhesion tests were performed on the GA and GI coated samples. It was clearly observed that no coating was removed by the tape, indicating that the coating adhered well to both the GA and GI substrates.

[0174] Through impact, conical mandrel bending test and dome test ( Figure 7 The coating formability was examined. In the dome test, the coated samples were stretched up to 25 mm until fracture. No coating delamination or chalking occurred when the samples were stretched up to 25 mm. Dome test samples (GA and GI) with a height of 25 mm were exposed to SST, and no white rust was observed even after 144 hours of exposure. An impact test was performed using a 1 kg weight from a height of 100 cm (impact energy = 9.6 joules). No coating delamination or chalking was observed under this condition. These samples were held in the SST chamber, and it was observed that they remained stable in the SST chamber for over 500 hours without any white rust. Similarly, in the case of the conical mandrel bending test, no coating delamination or chalking occurred. These samples were also held in the SST chamber, which also showed a 144-hour SST life without any white rust.

[0175] Spot welding tests were conducted to examine the weldability of the developed coating system on both GA and GI substrates. Figure 8 a and Figure 8 b). Spot welding tests were performed with a 250ms power supply. The current was gradually increased from 0.5 kA to 6.5 kA. Current flow was observed even at low current levels (0.5 or 1 kA). A weld nugget formed even at low currents (1 and 1.5 kA), although the nugget size was small. The nugget diameter was measured after spot welding. A nugget diameter greater than 4.5√t, where "t" is the thickness of the steel sheet, was acceptable. The desired nugget diameter was formed when the current was 5.5 kA or greater. Spot welding process range tests were performed on both GA and GA samples, and the weld quality was found to be acceptable according to automotive industry requirements. Figure 8 c and Figure 8 d).

[0176] The sol-gel nanocoating samples were further coated / applied using an epoxy-polyester hybrid powder coating system. The powder-coated samples were then examined using various tests, such as (i) impact testing. Figure 9 a), (ii) cross-cut test, (iii) tapered mandrel bending test, (iv) cut-bending test Figure 9 (b) and (v) SST on cross-cut samples. It was observed that all the above tests passed without any stratification. The cross-cut samples also passed SST for over 1000 hours without any bubbling.

[0177] The surface morphology of the coating samples was examined using scanning electron microscopy (SEM), and protruding morphologies were observed. Figure 10 a and Figure 10 c). This morphology contributes to formability and post-coating adhesion. As observed in paintability studies, good coating adhesion is achieved, where the protruding structure helps increase mechanical coating adhesion as well as chemical interactions. Figure 10 b and Figure 10 As observed, the coating thickness was found to be 2 to 3 µm. Figure 11 The SEM-EDX data is provided.

[0178] The self-healing behavior of the (La-doped) coating was investigated using SEM-EDX. Cross-cutting was performed on both the GA and GA coating samples. Figure 12 a and Figure 13 a (with corresponding table) shows the SEM-EDX image and corresponding values ​​for the first day. Figure 12 b and Figure 13b (with table) shows the SEM-EDX image and corresponding values ​​on day six. It was observed that the Si content increased after 120 hours of exposure to the surrounding environment, indicating the self-healing behavior of the coating.

[0179] The crystalline / amorphous properties of bare GA / GI, coated GA / GI, and the (dried) powder coating were determined by X-ray diffraction (XRD) using a PANlytical Xpert pro diffractometer with a monochromatic Cr-Kα source (λ = 1.540598 Å) at 40 kV in steps of 0.03 in the range of 10° < 2θ < 90°. For bare GI, diffraction peaks were observed at 2θ = 36.19, 39.01, 43.17, 54.32, 70.03, 76.97, 82.07, and 88.52. Of these peaks, the peaks observed at 36.19 and 82.07 correspond to both Zn1 and O1Zn1 (wurtzite type), while the other peaks correspond to Zn [JCPDS: 98-065-3502(Zn) and 98-016-1836(ZnO)]. Similarly, for the diffraction peaks of bare GA, at 2θ = Observed at 35.51 (Fe0.911O1, Fe0.902O1, Fe1O1, Fe1.86O4Zn1.14, Fe1Zn13), 40.89 (Fe0.911O1, Fe0.902O1, Fe1Zn13), 42.24 (Fe0.902O1, Fe1O1, Fe1.86O4Zn1.14, Fe1Zn13), 43.17 (Fe1, Fe0.902O1, Fe1.86O4Zn1.14, Fe1Zn13), 64.92 (Fe1, Fe1.86O4Zn1.14, Fe1Zn13), 73.96 (Fe1, Fe1.86O4Zn1.14, Fe1Zn13) and 82.29 (Fe1, Fe1Zn13). See Table 1 below.

[0180] Table 1: X-ray diffraction peaks

[0181]

[0182] After coating, most of the peaks remained intact, while a very small number of peaks were not detected. Figure 14 Data in section a shows that the developed (La-doped) coating is amorphous in nature. The bare GA and GI samples are crystalline in nature. However, due to the amorphous behavior of the coating, the crystallinity decreases after coating. Figure 14 a and Figure 14 b). Overall, this data indicates that the coating does not affect the surface uniformity of the steel substrate.

[0183] The contact angle and surface energy of bare / coated GI / GA samples were investigated (Table 2). It was observed that the coated steel sheet had a smaller contact angle compared to the corresponding bare sample. Furthermore, the coated sample exhibited a higher surface energy compared to the bare substrate. In the case of post-coating, paint adhesion depends on the contact angle / surface energy. A low contact angle / high surface energy indicates that the coated sample is hydrophilic in nature, which contributes to better paint adhesion.

[0184] Table 2: Contact angle and surface energy of bare / coated GI / GA samples

[0185]

[0186] The particle size of the coated sol (Nanocoat sol) was studied using a particle size analyzer with dynamic light scattering (DLS) technology. A variation in particle size (hydrodynamic diameter) between 35 nm and 500 nm was observed. Figure 15 ).

[0187] Fuel / Gasoline Tolerance Study:

[0188] Four coated GA samples were immersed in four different fuel mixtures. Gasoline was the primary fuel, with 1% to 35% water or ethanol added by volume. Other components (formic acid, acetic acid, and chlorine) were at ppm levels relative to water. The fuel mixtures were prepared according to the combinations given in Table 3 below. Images of the coated sheets tested after 2472 hours are shown in... Figure 17 middle.

[0189] Samples A and B, respectively immersed in gasoline + water and gasoline + ethanol mixtures, were observed to remain in excellent condition even after 2472 hours of exposure. Samples C and D remained in highly corrosive fuel mixtures, where gasoline was mixed with water, formic acid, acetic acid, and chlorine at varying concentrations, as shown in Table 3 below. Samples C and D also exhibited fuel resistance. After 2472 hours of exposure, the coating was found to remain almost intact on the surface with minimal degradation. In the case of sample C, edge corrosion (red rust) was observed at the bottom after 500 hours of exposure (500-hour data not shown here) and in the case of sample D, after 48 hours of exposure (48-hour data not shown here), but the red rust did not worsen further due to the coating. Because the coating exhibits fuel resistance, it can be used in fuel can applications.

[0190] Table 3: Fuel mixtures used to test the fuel / gasoline tolerance of the coated GA samples.

[0191]

[0192] Fourier transform infrared spectroscopy (FTIR)

[0193] Fourier transform infrared (FTIR) spectra were recorded for coated GI and GA substrates. Figure 18 FTIR spectroscopy was used to elucidate the structural details of oxides of Si, Al, and La, and their interactions with Zn and Zn / Fe substrates of GI and GA, respectively. The FTIR spectra were observed in the range of 400 to 4000 cm⁻¹. -1 The spectra were measured within the wavelength range. The FTIR peaks obtained for both coatings GI and GA are given in Table 4 below.

[0194] Table 4: FTIR peaks of coated GI and GA samples.

[0195]

[0196] The foregoing description of the specific embodiments reveals the general nature of the embodiments described herein, and without departing from the general concepts, others can readily modify and / or adapt such specific embodiments for various applications by applying present knowledge, and therefore, such adaptations and modifications should and are intended to be understood within the equivalent meaning and scope of the disclosed embodiments. It should be understood that the phrases or terms used herein are for descriptive purposes and are not intended to be limiting. Therefore, although embodiments in this disclosure have been described according to preferred embodiments, those skilled in the art will recognize that modifications can be made to practice the embodiments described herein within the spirit and scope of the embodiments as described herein.

[0197] Throughout this specification, the terms “combinations thereof” or “any combination thereof” or “any combinations thereof” are used interchangeably and are intended to have the same meaning as commonly known in the field of patent disclosure.

[0198] The embodiments characterized in this specification are intended to be interpreted independently, as well as in combination with other embodiments. For example, in Embodiment 1, three alternatives A, B, and C are described; in Embodiment 2, three alternatives D, E, and F are described; and in Embodiment 3, three alternatives G, H, and I are described. It should be understood that, unless specifically mentioned otherwise, the specification explicitly discloses embodiments corresponding to combinations A, D, G; A, D, H; A, D, I; A, E, G; A, E, H; A, E, I; A, F, G; A, F, H; A, F, I; B, D, G; B, D, H; B, D, I; B, E, G; B, E, H; B, E, I; B, F, G; B, F, H; B, F, I; C, D, G; C, D, H; C, D, I; C, E, G; C, E, H; C, E, I; C, F, G; C, F, H; C, F, I.

[0199] Although specific features of this disclosure have been given considerable emphasis herein, it will be understood that various modifications and numerous changes may be made in preferred embodiments without departing from the principles of this disclosure. These and other modifications or preferred embodiments of this disclosure will be apparent to those skilled in the art based on this disclosure, and it should be explicitly understood that the foregoing descriptive matters should be construed as illustrative rather than limiting.

Claims

1. A steel substrate comprising a rare earth-doped silica-alumina coating, wherein the coating comprises: a. Approximately 0.5 wt% to approximately 6.5 wt% Al; b. About 0.5 wt% to about 6.5 wt% of Si; and c. Rare earth elements, approximately 0.1 wt% to approximately 11 wt%.

2. The steel substrate as claimed in claim 1, wherein the substrate has a contact angle of 15° to 55°.

3. The steel substrate as claimed in claim 1 or 2, wherein the substrate exhibits a surface energy of about 50 mN / m to about 75 mN / m.

4. The steel substrate as claimed in any one of claims 1 to 3, wherein the coating is a nano-coating and exhibits a particle size of about 35 nm to about 500 nm.

5. The steel substrate as claimed in any one of claims 1 to 4, wherein the X-ray diffraction pattern of the substrate before coating and the X-ray diffraction pattern after coating are similar.

6. The steel substrate according to any one of claims 1 to 5, wherein the rare earth element is selected from cerium (Ce), lanthanum (La), neodymium (Nd), praseodymium (Pr), or a combination thereof.

7. The steel substrate as claimed in any one of claims 1 to 6, wherein the substrate exhibits no white rust in a salt spray test of at least 200 hours.

8. The steel substrate as claimed in any one of claims 1 to 7, wherein the substrate exhibits increased impedance in electrochemical impedance spectroscopy (EIS) testing compared to a bare substrate.

9. The steel substrate as claimed in any one of claims 1 to 8, wherein the coating does not peel off from the substrate in a standard cross-cut adhesion test.

10. The steel substrate as claimed in any one of claims 1 to 9, wherein the coating exhibits no delamination or powdering up to 25 mm when tested by a dome test.

11. The steel substrate as claimed in any one of claims 1 to 10, wherein the coating exhibits a weld nugget diameter greater than 4.5√t in a spot welding test at a current of 5.5 kA or greater, where "t" is the thickness of the substrate.

12. The steel substrate as claimed in any one of claims 1 to 11, wherein the coating does not show substantial rust formation even after exposure to fuel for 2472 hours.

13. The steel substrate as claimed in any one of claims 1 to 12, wherein the substrate is formable, weldable and paintable.

14. The steel substrate as described in any one of claims 1 to 13, wherein the substrate is a galvanized, alloyed galvanized, aluminum-zinc coated, zinc-aluminized, magnesium-zinc coated, or ultra-zinc coated substrate.

15. The steel substrate as claimed in any one of claims 1 to 13, wherein the substrate is a galvanized iron (GI) substrate or an alloyed galvanized (GA) steel substrate.

16. A coating composition for preparing a coated steel substrate as described in any one of claims 1 to 15, comprising: a. Aqueous solutions of acids; b. Silane; c. Aluminum isopropoxide; d. Compounds of rare earth elements; and e. Phosphoric acid or its derivatives.

17. The coating composition of claim 16, wherein the acid is a carboxylic acid.

18. The coating composition of claim 17, wherein the carboxylic acid is selected from lactic acid, formic acid, acetic acid, propionic acid, glycolic acid, benzoic acid, glutaric acid, hexanoic acid, butyric acid, valeric acid, fumaric acid, or combinations thereof.

19. The coating composition according to any one of claims 16 to 18, wherein the acid is present at a concentration of about 2 wt% to about 40 wt%.

20. The coating composition of any one of claims 16 to 19, wherein the silane is selected from tetraethyl orthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES), (3-aminopropyl)trimethoxysilane (APTMS), (3-glycidyl etheroxypropyl)trimethoxysilane (GPTMS), (3-glycidyl etheroxypropyl)triethoxysilane (GPTES), methyltrimethoxysilane (MTMS), or combinations thereof.

21. The coating composition of claim 20, wherein the composition comprises TEOS and APTES.

22. The coating composition according to any one of claims 16 to 21, wherein the silane is present at a concentration of about 3 wt% to about 30 wt%.

23. The coating composition according to any one of claims 16 to 22, wherein the aluminum isopropoxide is present at a concentration of about 5 wt% to about 40 wt%.

24. The coating composition according to any one of claims 16 to 23, wherein the rare earth element is selected from cerium (Ce), lanthanum (La), neodymium (Nd), praseodymium (Pr), or a combination thereof.

25. The coating composition of any one of claims 16 to 24, wherein the rare earth element compound is present at a concentration of about 0.05 wt% to about 10 wt%.

26. The coating composition of any one of claims 16 to 25, wherein the orthophosphoric acid is present at a concentration of about 5 wt% to about 50 wt%.

27. The coating composition of any one of claims 16 to 26, wherein the composition comprises an organic green inhibitor, a rust converter, or both.

28. The coating composition of claim 27, wherein the organic green inhibitor is selected from cysteine, folic acid, glycine, leucine, caffeine, alanine, tryptophan, methionine, or combinations thereof.

29. The coating composition of claim 27 or 28, wherein the organic green inhibitor is present at a concentration of about 0.05 wt% to about 10 wt%.

30. The coating composition of claim 27, wherein the rust converter is selected from tannic acid.

31. The coating composition of claim 27 or 30, wherein the rust converter is present at a concentration of about 0.05 wt% to about 10 wt%.

32. A method for preparing a coating composition as described in any one of claims 16 to 31, comprising: a. Preparation of the first solution, including: A portion of the acid is added to softened water to obtain a first aqueous solution of the acid; The silane is added to the first aqueous solution of the acid; and After adding the silane, the compound of the rare earth element is added to the first aqueous solution of the acid to obtain the first solution; b. Preparation of the second solution, including: The remaining portion of the acid is added to softened water to obtain a second aqueous solution of the acid; Aluminum isopropoxide is added to the second aqueous solution of the acid to obtain the second solution; and c. Mix the first solution and the second solution, and then add phosphoric acid to obtain the coating composition.

33. The method of claim 32, wherein the second silane is added to the mixture of the first solution and the second solution prior to the addition of phosphoric acid.

34. The method of claim 32 or 33, wherein in the preparation of the second solution, the organic green inhibitor, the rust converter, or both are added to the softened water before the acid is added.

35. A method for preparing a steel substrate as described in any one of claims 1 to 15, comprising: a. Applying the coating composition as described in any one of claims 16 to 31 to the substrate to obtain a coated substrate; as well as b. Dry the coated substrate at about 40 °C to about 20 °C for about 2 minutes to about 20 minutes.

36. The method of claim 35, wherein the substrate is a galvanized, alloyed galvanized, aluminum-zinc coated, zinc-aluminized, magnesium-zinc coated, or super-zinc coated substrate.

37. The method of claim 35 or 36, wherein the substrate is a galvanized iron (GI) substrate or an alloyed galvanized (GA) steel substrate.

38. The method of any one of claims 35 to 37, wherein the application is performed by immersing the substrate in the coating composition or by roller coating.

39. The method of any one of claims 35 to 38, wherein the drying is performed in a hot air oven.

40. The method of any one of claims 35 to 39, wherein the coating provided on the substrate by the method exhibits no white rust in a salt spray test of at least 200 hours.

41. The method of any one of claims 35 to 40, wherein when tested by a dome test, the coating provided by the method exhibits up to 25 mm of no delamination or chalking.

42. The method of any one of claims 35 to 41, wherein the coating provided by the method exhibits a weld nugget diameter greater than 4.5√t in a spot welding test at a current of 5.5 kA or greater, where "t" is the thickness of the substrate.

43. The method of any one of claims 35 to 42, wherein the coating provided by the method does not show substantial rust formation even after exposure to fuel for 2472 hours.

44. The method of any one of claims 35 to 43, wherein the coating provided by the method is formable, weldable and paintable.

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