Patent Application
20250236958
The present teachings relate generally to corrosion inhibition coatings and, more particularly, to corrosion inhibition coatings surface treatments including trivalent chromium conversion coatings.
The use of chromium-containing corrosion inhibitors has been widespread for decades because of its performance and durability with respect to the prevention of corrosion on steel, aluminum, and other alloys used in aerospace manufacturing. While the chromate-based compounds provide anti-corrosive properties, the use of chromium-containing corrosion inhibitors is being restricted by regulations on a global basis. Current conversion coatings contain hexavalent chromium.
New corrosion inhibitor coatings have been developed to replace the use of chromium for some applications. These corrosion inhibitor coatings, including trivalent conversion coatings have not exhibited results comparable to the traditional hexavalent chromium conversion coatings. Additionally, existing conversion coatings, both hexavalent or trivalent chromium, can be relatively non-robust, resulting in frequent manufacturing shutdowns or troubleshooting efforts during fabrication or service. Existing conversion coatings also do not possess properties comparable to MIL-A-8625 Type I or thin-film Type II anodize, and hence, cannot generally be used as a non-electrolytic, non-metal-fatigue-knockdown for anodize processes.
Thus, there is a need for providing corrosion inhibition compositions and application methods that address robustness issues and other desirable properties, while affording acceptable or improved adhesion and corrosion inhibition.
The following presents a simplified summary in order to provide a basic understanding of some aspects of one or more embodiments of the present teachings. This summary is not an extensive overview, nor is it intended to identify key or critical elements of the present teachings, nor to delineate the scope of the disclosure. Rather, its primary purpose is merely to present one or more concepts in simplified form as a prelude to the detailed description presented later.
A method of preparing a coated substrate is disclosed. The method also includes cleaning a substrate by exposing a surface of the substrate to a solvent; treating the surface of the substrate with a deoxidizing agent, and applying a sol-gel coating to the surface of the substrate, and where the sol-gel coating may include an inhibitor. Implementations of the method of preparing a coated substrate can include where the solvent may include isopropyl alcohol. The deoxidizing agent may include hydrogen fluoride and chromic acid. The inhibitor may include 2,5-dimercapto 1,3,4-thiadiazole (DMCT). Cleaning the substrate further may include flooding the surface of the substrate with an aqueous alkaline cleaning composition. The sol-gel coating includes no chromium. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.
A method of preparing a coated substrate is disclosed. The method of preparing a coated substrate includes cleaning a substrate by exposing a surface of the substrate to a solvent, treating the surface of the substrate with a deoxidizing agent, and applying a sol-gel coating to the surface of the substrate, where the sol-gel coating may include an inhibitor may include a mercapto-functional thiadiazole. Implementations of the method of preparing a coated substrate includes where the sol-gel coating further may include the mercapto-functional thiadiazole in an amount of about 1 wt % to about 15 wt % by volume of the sol-gel coating. The sol-gel coating further may include the mercapto-functional thiadiazole in an amount of about 3 wt % to about 10 wt % by volume of the sol-gel coating. The primer coating may include a metal. Applying the sol-gel coating may include mixing the inhibitor with an organosilane and metal alkoxide, where a volume ratio of organosilane to metal alkoxide is about 5% to about 20%, where the metal alkoxide has been pretreated with an acid. The inhibitor may include 2,5-dimercapto 1,3,4-thiadiazole (DMCT). The deoxidizing agent may include hydrogen fluoride and chromic acid. Cleaning the substrate further may include flooding the surface of the substrate with an aqueous alkaline cleaning composition.
An article is disclosed. The article includes a substrate, and a corrosion inhibitor coating composition disposed on a surface of the substrate, which may include a sol-gel formulation that may include an organosilane, a metal alkoxide, and an inhibitor may include a mercapto-functional thiadiazole. Implementations of the article can include where the sol-gel formulation may include the mercapto-functional thiadiazole in an amount of about 1 wt % to about 15 wt % by volume of the sol-gel formulation. The inhibitor may include 2,5-dimercapto 1,3,4-thiadiazole (DMCT). The substrate may include a metal, polymer, polymer composite, or combination thereof. The article is a component or part of an aerospace vehicle or a marine vehicle. The component or part of an aerospace vehicle or marine vehicle is an external surface thereof.
The features, functions, and advantages that have been discussed can be achieved independently in various implementations or can be combined in yet other implementations further details of which can be seen with reference to the following description.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present teachings and together with the description, serve to explain the principles of the disclosure. In the figures:
It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding of the present teachings rather than to maintain strict structural accuracy, detail, and scale.
Reference will now be made in detail to exemplary embodiments of the present teachings, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same, similar, or like parts.
The present teachings provide a method and multilayered composition to enhance the surface of trivalent chromium conversion coatings using a simple, non-chromium treatment, resulting in a conversion coating that exhibits properties superior as compared to trivalent and hexavalent chromium conversion coatings. The non-hexavalent conversion coating of the present teachings eliminates the use of hexavalent chromium and possesses properties that are superior to standard hexavalent chromium conversion coatings. The non-hexavalent conversion coating processes associated with the present disclosure are robust and can be performed successfully using wide ranges of critical process parameters. Additionally, the corrosion resistance and adhesion properties of the enhanced conversion coatings associated with the present teachings provide equal or better performance as consistent with meeting the requirements of MIL-DTL-81706 Class 1A. This allows for substitution of a simple conversion coating process for an anodize process, which eliminates a) the need for expensive, electrolytic processing equipment, b) the dangers associated with electrolytic processing, and c) the metal fatigue knockdowns associated with anodize processes.
Existing hexavalent conversion coatings used in corrosion resistance applications include hexavalent chromium. Existing trivalent conversion coatings do not have properties that are as good as or better than hexavalent chromium conversion coatings. Unfortunately, existing conversion coatings, hexavalent or trivalent chromium, can be relatively non-robust, resulting in frequent manufacturing shutdowns and troubleshooting efforts. Furthermore, existing conversion coatings do not possess properties comparable to MIL-A-8625 Type I or thin-film Type II anodize, and hence, cannot generally be used as a non-electrolytic, non-metal-fatigue-knockdown for anodize processes.
A commercial off-the-shelf (COTS) trivalent chromium conversion coating or corrosion inhibitor coating composition can be enhanced using a non-chromium, corrosion inhibited sol-gel treatment. In examples provided herein, various formulations have exhibited superior, stand-alone corrosion resistance in ASTM B117 neutral salt spray and improved adhesion properties due to the organic functionality in the sol-gel. This combination of several non-hexavalent chromium technologies, where each component provides different capabilities to the overall combination provides improved corrosion resistance and adhesion properties without the use of hexavalent chromium. Coatings and methods of the present teachings could also be used as a substitute for MIL-A-8625, Type I and thin-film Type II anodize processes. Furthermore, improvements in manufacturing robustness, worker safety, and critical environmental concerns can be realized.
Examples of the present disclosure provide the application of a non-chromium, corrosion inhibited sol-gel treatment to the surface of a trivalent chromium conversion coating to improve corrosion resistance and adhesion properties due to the compatible organic functionality in the sol-gel. Methods and application of a non-chromium, corrosion inhibited sol-gel treatment to the surface of a trivalent chromium conversion coating to improve corrosion resistance and adhesion properties. The method includes treating the metal substrate with a deoxidizer prior to application of the trivalent chromium conversion coating, and applying the non-chromium sol-gel which contains a mercapto-functional thiadiazole, such as, for example, 2,5-Dimercapto 1,3,4-thiadiazole (DMCT). Coated coupons were evaluated for corrosion resistance in salt spray test as per ASTM B117.
A trivalent conversion coating can refer to a type of surface treatment applied to an article having a metal or other substrate material to enhance corrosion resistance of the surface. The process can include the formation of a protective coating on the metal surface through a chemical reaction. A trivalent conversion coating indicates the presence of three valence states of a particular element, in this case chromium.
In general, trivalent conversion coatings offer several advantages, including improved corrosion resistance, improved environmental friendliness, and compliance with various regulations. These coatings can form a thin, protective layer on the metal surface, acting as a barrier against corrosion-inducing factors such as moisture and aggressive chemicals. Additionally, trivalent conversion coatings can provide a good base for subsequent paint, coating, or adhesive applications. These coatings can be utilized in industries such as automotive, aerospace, and other applications where corrosion resistance is desirable.
Teachings of the present disclosure generally relate to corrosion resistant sol-gels for aerospace applications. Sol-gels of the present disclosure include (or the reaction product of) an epoxy-containing organosilane, a metal alkoxide, an acid stabilizer, about 3 wt % to about 15 wt % corrosion inhibitor by volume of the total sol-gel coating, and a surfactant. In examples, the sol-gel can be made at a volume ratio from about 1% to about 99% by volume, or in some examples, from about 1% to about 10% by volume, or from about 3% to about 15% by volume, or from 20% to about 40% by volume. It has been discovered that a surfactant present in a sol-gel prevents or reduces porosity and blistering of a sol-gel/primer coating on a metal surface, providing a corrosion inhibiting ability of a sol-gel film because accumulation of water within the sol-gel is prevented or reduced. The surfactant also allows for increased wettability of the coating on the surface of the metal, improving coating adhesion and corrosion performance. Additionally, it has been discovered that the use of an organic primer disposed on a corrosion resistant sol-gel having a plurality of metal particles, e.g. aluminum, lithium, or the like, leads to enhanced corrosion protection of alloys (e.g., aerospace alloys). Solgels of the present disclosure have corrosion inhibiting ability, and, primers (disposed on the solgel) can be either non-chrome containing primers or chrome containing primers.
Methods for preparing a coated substrate of the present disclosure include applying a sol-gel coating to a metal substrate to form the sol-gel coating. The sol-gel coating comprises a corrosion inhibitor in an amount of about 3 wt % by volume of corrosion inhibitor to sol-gel coating to about 15 wt % by volume of corrosion inhibitor to sol-gel coating.
A metal substrate includes a metal aircraft surface, which can include steel or an alloy having a major component, such as aluminum. The metal substrate can include a major component and a minor component, known as an intermetallic. Intermetallics, for example, can contain copper metal which can be prone to corrosion. The metal substrate can include an aluminum substrate. The metal substrate can include an aluminum substrate with an intermetallic of copper. As a nonlimiting example, the metal substrate can be a 7075-T6 aluminum substrate or a 7178 aluminum substrate. In certain examples, substrates including at least a portion of one or more polymer composites or other materials can be used.
The term “sol-gel,” a contraction of solution-gelation, refers to a series of reactions wherein a soluble metal species (typically a metal alkoxide or metal salt) hydrolyze to form a metal hydroxide. The soluble metal species usually contain organic ligands tailored to correspond with the resin in the bonded structure. A soluble metal species undergoes heterohydrolysis and heterocondensation forming heterometal bonds e.g. Si—O—Zr. In the absence of organic acid, when metal alkoxide is added to water, a white precipitate of, for example, Zr(OH)2 rapidly forms. Zr(OH)2 is not soluble in water, which hinders sol-gel formation. The acid is added to the metal alkoxide to allow a water-based system. Depending on reaction conditions, the metal polymers can condense to colloidal particles or they can grow to form a network gel. The ratio of organics to inorganics in the polymer matrix is controlled to maximize performance for a particular application.
The sol-gel has a thickness of about 50 nm to about 10 μm, e.g., about 100 nm to about 2.5 μm, such as about 100 nm, about 200 nm, about 300 nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900 nm, about 1 μm, about 2 μm, about 2.5 μm, or the like. The sol-gel has a weight of about 30 mg/ft2 to about 1,000 mg/ft2, e.g., about 30 mg/ft2 to about 400 mg/ft2, or about 250 mg/ft2 to about 1000 mg/ft2, such as, for example, about 30 mg/ft2, about 100 mg/ft2, about 200 mg/ft2, about 300 mg/ft2, about 400 mg/ft2, about 500 mg/ft2, about 600 mg/ft2, about 700 mg/ft2, about 800 mg/ft2, about 900 mg/ft2, about 1000 mg/ft2, or the like.
A weight fraction (wt %) of organosilane in the sol-gel is from about 0.1 wt % to about 20 wt % by volume of the total sol-gel coating, such as from about 0.3 wt % to about 15 wt %, such as from about 0.5 wt % to about 10 wt %, such as from about 0.7 wt % to about 5 wt %, such as from about 1 wt % to about 2 wt %, for example about 1 wt %, about 1.5 wt %, about 2 wt %. Organosilanes of the present disclosure are represented by formula (I):
wherein:
An organosilane is a hydroxy organosilane. Hydroxy organosilanes are substantially unreactive toward nucleophiles, e.g., some corrosion inhibitors. Hydroxy organosilanes of the present disclosure are represented by formula (II):
The organosilane is represented by compound 1 or compound 2:
An organosilane is selected from 3-aminopropyltriethoxysilane, 3-glycidoxypropyltriethoxysilane, p-aminophenyltrimethoxysilane, p-aminophenyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, n-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropyldiisopropylethoxysilane, (3-glycidoxypropyl)methyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, nphenylaminopropyltrimethoxysilane, vinylmethyldiethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, bis(trimethoxysilyl)ethane, bis(triethoxysilyl)ethane, bis[3-(trimethoxysilyl)propyl]amine, bis[3-(triethoxysilyl)propyl]amine, bis[3-(triethoxysilyl)propyl]disulfide, bis[3-(trimethoxysilyl)propyl]disulfide, bis[3-(triethoxysilyl)propyl]trisulfide, bis[3-(trimethoxysilyl)propyl]trisulfide, bis[3-(triethoxysilyl)propyl]tetrasulfide, and bis[3-(trimethoxysilyl)propyl]tetrasulfide.
An organosilane useful to form sol-gels of the present disclosure provides an electrophilic silicon and/or epoxide moiety that can react with a nucleophile, such as a hydroxy-containing nucleophile. An organosilane of the present disclosure provides a sol-gel having reduced porosity and blistering as compared to conventional sol-gels.
A metal alkoxide useful to form sol-gels of the present disclosure provides metal atoms coordinated in a sol-gel for adhesive and mechanical strength. Metal alkoxides of the present disclosure include at least one of zirconium alkoxides, titanium alkoxides, hafnium alkoxides, yttrium alkoxides, cerium alkoxides, and lanthanum alkoxides. Metal alkoxides can have four alkoxy ligands coordinated to a metal that has an oxidation number of +4. Non-limiting examples of metal alkoxides are zirconium (IV) tetramethoxide, zirconium (IV) tetraethoxide, zirconium (IV) tetra-n-propoxide, zirconium (IV) tetra-isopropoxide, zirconium (IV) tetra-n-butoxide, zirconium (IV) tetra-isobutoxide, zirconium (IV) tetra-n-pentoxide, zirconium (IV) tetraisopentoxide, zirconium (IV) tetra-n-hexoxide, zirconium (IV) tetra-isohexoxide, zirconium (IV) tetra-n-heptoxide, zirconium (IV) tetra-isoheptoxide, zirconium (IV) tetra-n-octoxide, zirconium (IV) tetra-n-isooctoxide, zirconium (IV) tetra-n-nonoxide, zirconium (IV) tetra-n-isononoxide, zirconium (IV) tetra-n-decyloxide, and zirconium (IV) tetra-n-isodecyloxide.
The sol-gel includes a metal alkoxide content, in which the metal alkoxide content is the reaction product of the metal alkoxide that forms in the sol-gel. A weight fraction (wt %) of metal alkoxide content by volume in the total sol-gel coating is from about 0.1 wt % to about 10 wt %, such as from about 0.2 wt % to about 5 wt %, such as from about 0.3 wt % to about 3 wt %, such as from about 0.4 wt % to about 2 wt %, such as from about 0.5 wt % to about 1 wt %, for example about 0.2 wt %, about 0.5 wt %, about 1 wt %.
An acid stabilizer used to form sol-gels of the present disclosure provides stabilization of a metal alkoxide and a corrosion inhibitor of the sol-gel as well as pH reduction of the sol-gel. The pH value of the sol-gel (and composition that forms the sol-gel) can be controlled by use of an acid stabilizer. Acid stabilizers of the present disclosure include organic acids. Organic acids include acetic acid (such as glacial acetic acid) or citric acid. Less acidic acid stabilizers (e.g., pKa greater than that of acetic acid) can also be used, such as glycols, ethoxyethanol, or H2NCH2CH2OH.
A pH of a sol-gel of the present disclosure is from about 2 to about 5, such as about 3 to about 4. A weight fraction (wt %) of acid stabilizer by volume in the total sol-gel is from about 0.1 wt % to about 10 wt %, such as from about 0.2 wt % to about 5 wt %, such as from about 0.3 wt % to about 3 wt %, such as from about 0.4 wt % to about 2 wt %, such as from about 0.5 wt % to about 1 wt %, for example about 0.1 wt %, about 0.2 wt %, about 0.3 wt %, about 0.4 wt %, about 0.5 wt %. For example, and without limitation, wt % of acid stabilizer in a sol-gel is about 0.5 wt % and a weight fraction of metal alkoxide is about 0.6 wt % or greater. As a further non-limiting example, a wt % of acid stabilizer in a sol-gel is about 0.3 wt % and a weight fraction of metal alkoxide is less than 0.6 wt %.
A ratio of metal alkoxide to acid stabilizer in a sol-gel can be from about 1:1 to about 3:1, such as about 2:1. A molar ratio of acid stabilizer to metal alkoxide can be from about 1:1 to about 40:1, such as from about 3:1 to about 8:1, such as from about 4:1 to about 6:1, such as from about 4:1 to about 5:1.
Without being bound by theory, it is believed that acid stabilizer in these ratios not only contributes to stabilizing a metal alkoxide for hydrolysis, but also protonates thiol moieties of a corrosion inhibitor, which reduces or prevents reaction of the corrosion inhibitor with, for example, a metal alkoxide.
Without wishing to be bound by theory, a surfactant useful to form sol-gels of the present disclosure provides enhanced adhesion of the sol-gel to the metal substrate by increasing surface wettability of the coating on the surface of the metal. The surfactant can enhance the adhesion and quantitated according to a wet cross hatch adhesion per ASTM D3359. For example, and without limitation, the sol-gel having the surfactant can increase the wet cross hatch adhesion to a value of 10.
Without wishing to be bound by theory, a surfactant useful to form sol-gels of the present disclosure provides enhanced adhesion of the sol-gel to the primer. Surfactants of the present disclosure can include a surfactant capable of performing an alkoxylation reaction, in which an addition of an epoxide to a substrate occurs. The surfactant can include one or more alcohol ethoxylates, alcohol propoxylates, ethoxysulfates, polethoxylated amines, or the like. For example, and without limitation, the surfactant can be ethylene-oxide alcohol, propylene-oxide alcohol, ethylene-oxide-propylene-oxide alcohol, polyethoxylated tallow amine, ethanolamine, diethanolamine, triethanolamine, or the like.
A corrosion inhibitor useful to form sol-gels of the present disclosure provides corrosion resistance (to water) of the metal substrate disposed adjacent the sol-gel. Corrosion inhibitors of the present disclosure are compounds having one or more thiol moieties. Metal aircraft surfaces can comprise steel or an alloy having a major component, such as aluminum, and a minor component, known as an intermetallic. Intermetallics, for example, often contain copper metal which is prone to corrosion. Without being bound by theory, it is believed that the interaction of thiol moieties of a corrosion inhibitor of the present disclosure with copper-containing intermetallics on a metal surface (such as an aluminum alloy surface) prevents corrosion of the metal surface. More specifically, interaction of the thiol moieties of a corrosion inhibitor of the present disclosure with the intermetallics blocks reduction of the intermetallics by slowing the rate of oxygen reduction and decreasing oxidation of a metal alloy, such as an aluminum alloy.
A corrosion inhibitor of the present disclosure is an organic compound that includes a disulfide group and/or a thiolate group (e.g., a metal-sulfide bond). For example, the corrosion inhibitor is not an organometallic corrosion inhibitor. A corrosion inhibitor is represented by the formula: R1—Sn—X—R2, wherein R1 is an organic group, n is an integer greater than or equal to 1, X is a sulfur or a metal atom, and R2 is an organic group. One or both of R1 and R2 can include additional polysulfide groups and/or thiol groups. Furthermore, corrosion inhibitors include polymers having the formula —(R1—Sn—X—R2)q—, wherein R1 is an organic group, n is a positive integer, X is a sulfur or a metal atom, R2 is an organic group, and q is a positive integer. R1 and R2 (of a polymeric or monomeric corrosion inhibitor) is independently selected from H, alkyl, cycloalkyl, aryl, thiol, polysulfide, or thione. Each of R1 and R2 can be independently substituted with a moiety selected from alkyl, amino, phosphorous-containing, ether, alkoxy, hydroxy, sulfur-containing, selenium, or tellurium. Each of R1 and R2 has 1-24 carbon atoms and/or non-hydrogen atoms. For example, heterocyclic examples of R1 and R2 groups include an azole, a triazole, a thiazole, a dithiazole, and/or a thiadiazole.
A corrosion inhibitor includes a metal in a metal-thiolate complex. Corrosion inhibitors can include a metal center and one or more thiol groups (ligands) bonded and/or coordinated with the metal center with a metal-sulfide bond. A thiolate is a derivative of a thiol in which a metal atom replaces the hydrogen bonded to sulfur. Thiolates have the general formula M-S—R1, wherein M is a metal and R1 is an organic group. R1 can include a disulfide group. Metal-thiolate complexes have the general formula M-(S—R1)n, wherein n generally is an integer from 2 to 9 and M is a metal atom. Metals are copper, zinc, zirconium, aluminum, iron, cadmium, lead, mercury, silver, platinum, palladium, gold, and/or cobalt.
The corrosion inhibitor includes an azole compound. Examples of suitable azole compounds include cyclic compounds having, 1 nitrogen atom, such as pyrroles, 2 or more nitrogen atoms, such as pyrazoles, imidazoles, triazoles, tetrazoles and pentazoles, 1 nitrogen atom and 1 oxygen atom, such as oxazoles and isoxazoles, and 1 nitrogen atom and 1 sulfur atom, such as thiazoles and isothiazoles. Nonlimiting examples of suitable azole compounds include 2,5-dimercapto-1,3,4-thiadiazole, 1H-benzotriazole, 1H-1,2,3-triazole, 2-amino-5-mercapto-1,3,4-thiadiazole, also named 5-amino-1,3,4-thiadiazole-2-thiol, 2-amino-1,3,4-thiadiazole. For example, and without limitation, the azole can be 2,5-dimercapto-1,3,4-thiadiazole. The azole can be present in the composition at a concentration of 0.01 g/L of sol-gel composition to 1 g/L of solgel composition, for example, 0.4 g/L of sol-gel composition. The azole compound can include benzotriazole and/or 2,5-dimercapto-1,3,4-thiadiazole.
Corrosion inhibitors of the present disclosure include heterocyclic thiol and amines, which can provide elimination of oxygen reduction. Heterocyclic thiols include thiadiazoles having one or more thiol moieties. Non-limiting examples of thiadiazoles having one or more thiol moieties include 1,3,4-thiadiazole-2,5-dithiol and thiadiazoles represented by formula (III) or formula (IV):
The thiadazole of formula (III) can be purchased from Vanderbilt Chemicals, LLC (of Norwalk, Connecticut) and is known as Vanlube® 829. The thiadiazole of formula (IV) can be purchased from WPC Technologies, Inc.™ (of Oak Creek, Wisconsin) and is known as InhibiCor™ 1000.
A corrosion inhibitor of the present disclosure can be a derivative of 2,5-dimercapto-1,3,4 thiadiazole symbolized by HS—CN2SC—SH or “DMTD”, and of selected derivatives of trithiocyanuric acid (“TMT”) used for application as a corrosion inhibitor in connection with a paint. Examples include 2,5-dimercapto-1,3,4 thiadiazole (DMTD), and 2,4-dimercapto-striazolo-[4,3-b]-1,3-4-thiadiazole, and trithiocyanuric acid (TMT). Other examples include N-, S and N,N-, S,S- and N,S-substituted derivatives of DMTD such as 5-mercapto-3-phenil-1,3,4-thiadiazoline-2-thione or bismuthiol II (3-Phenyl-1,3,4-thiadiazolidine-2,5-dithione) and various S-substituted derivatives of trithiocyanuric acid. Other examples include 5,5′ dithio-bis (1,3,4 thiadiazole-2(3H)-thione or (DMTD)2, or (DMTD), the polymer of DMTD; 5,5′ thio-bis (1,3,4 thiadiazole-2(3H)-thione; or (TMT)2, the dimer and polymers of TMT. Other examples include salts of DMTD of the general formula: M (DMTD) n, where n=1, 2 or 3, and M is a metal cation such as M=Zn(II), Bi(III), Co(II), Ni(II), Cd(II), Pb(II), Ag(I), Sb(III), Sn(II), Fe(II), or Cu(II) (examples: ZnDMTD, Zn(DMTD)2, Bi(DMTD)3); similar salts of TMT, as for example, ZnTMT, in a ratio of 1:1; and, also, the comparable soluble Li(I), Ca(II), Sr(II), Mg(II), La(III), Ce(III), Pr(III), or Zr(IV) salts. Additional examples include salts of(DMTD) n of general formula M[(DMTD)n]m, where n=2 or n>2, m=1, 2, or 3 and M is a metal cation such as M=Zn(II), Bi(III), Co(II), Ni(II), Cd(II), Pb(II), Ag(I), Sb(III), Sn(II), Fe(II), or Cu(II). Typical examples are: Zn[(DMTD)2], Zn[(DMTD)2]2.
Additional examples include ammonium-, aryl-, or alkyl-ammonium salts of DMTD, (DMTD)n, or 5,5′ thio-bis (1,3,4 thiadiazole-2 (3H)-thione or 2,4-dimercapto-s-triazolo-[4,3-b]-1,3-4-thiadiazole. Typical examples include: Cyclohexyl amine: DMTD, in ratios of 1:1 and 2:1; Di-cyclohexyl amine: DMTD, in ratios of 1:1 and 2:1; Aniline: DMTD, in ratios of 1:1 and 2:1; similar salts of TMT, as for example Di-cyclohexyl amine: TMT, in a ratio of 1:1. Additional examples include poly-ammonium salts of DMTD or (DMTD) n and TMT formed with polyamines.
Additional examples include inherently conductive polyaniline doped with DMTD or (DMTD)2 or 5,5′ thio-bis (1,3,4 thiadiazole-2 (3H)-thione and TMT; Inherently conductive polypyrrole and/or polythiophene doped with DMTD, (DMTD)2 and 5,5′ thio-bis (1,3,4 thiadiazole-2 (3H)-thione and/or TMT.
Additional examples include micro or nano composites of poly DMTD/polyaniline, poly DMTD/polypyrrole, and poly DMTD/polythiophene; similar micro or nano composites with TMT; and with 5,5′ thio-bis (1,3,4 thiadiazole-2 (3H)-thione; DMTD or salts of DMTD or derivatives of DMTD and of TMT, as organic constituents of various pigment grade inorganic matrixes or physical mixtures. Such inorganic matrixes can include non-toxic anionic and cationic species with corrosion inhibitor properties, such as: MoO4−, PO4−, HPO3−, poly-phosphates, BO2−, SiO4−, NCN−, WO4−, phosphomolybdate, phosphotungstate and respectively, Mg, Ca, Sr, La, Ce, Zn, Fe, Al, Bi.
Additional examples include DMTD or salts of DMTD or derivatives of DMTD and TMT in encapsulated forms, such as: inclusions in various polymer matrices, or as cyclodextrin inclusion compounds or in microencapsulated form.
Pigment grade forms of DMTD include Zn (DMTD) 2 and Zn-DMTD (among other organic and inorganic salts of the former) with inorganic products or corrosion inhibitor pigments, such as: phosphates, molybdates, borates, silicates, tungstates, phosphotungstates, phosphomolybdates, cyanamides or carbonates of the previously specified cationic species, as well as oxides. Examples include: zinc phosphate, cerium molybdate, calcium silicate, strontium borate, zinc cyanamide, cerium phosphotungstate, ZnO, CeO2, ZrO2, and amorphous SiO2.
A corrosion inhibitor is a lithium ion, and a counter ion, which can include various ions known to form salts with lithium. Non-limiting examples of counter ions suitable for forming a salt with lithium include carbonates, hydroxides and silicates (e.g., orthosilicates and metasilicates). For example, the corrosion inhibitor includes a lithium carbonate salt, a lithium hydroxide salt, or a lithium silicate salt (e.g., a lithium orthosilicate salt or a lithium metasilicate salt). The counter ion includes various ions known to form salts with the other Group IA (or Group 1) metals (e.g., Na, K, Rb, Cs and/or Fr). Nonlimiting examples of counter ions suitable for forming a salt with the alkali metals include carbonates, hydroxides and silicates (e.g., orthosilicates and metasilicates). For example, and without limitation, the corrosion inhibitor includes an alkali metal carbonate salt, an alkali metal hydroxide salt, and/or an alkali metal silicate salt (e.g. an alkali metal orthosilicate salt or an alkali metal metasilicate salt). For example, some nonlimiting examples of suitable salts include carbonates, hydroxides and silicates (e.g., orthosilicates or metasilicates) of sodium, potassium, rubidium, cesium, and francium.
Corrosion inhibitors of the present disclosure include aluminum and magnesium rich compounds, which can provide cathodic protection of a material. Aluminum rich corrosion inhibitors include aluminum or aluminum alloys, in which the aluminum or aluminum alloys are greater than 50 wt % by volume of the corrosion inhibitor. Magnesium rich corrosion inhibitors include magnesium or magnesium alloys, in which the magnesium or magnesium alloys are greater than 50 wt % by volume of the corrosion inhibitor. Corrosion inhibitors of the present disclosure can include Cesium compounds.
A weight fraction (wt %) of corrosion inhibitor by volume in the total sol-gel is from about 1 wt % to about 15 wt %, such as from about 3 wt % to about 15 wt %, such as from about 1 wt % to about 5 wt %, such as from about 5 wt % to about 10 wt %, such as from about 10 wt % to about 15 wt %, such as from about 12 wt % to about 15 wt %, for example about 1 wt %, about 5 wt %, about 10 wt %, about 15 wt %. For example, and without limitation, a wt % of corrosion inhibitor by volume in the total sol-gel is about 3 wt % to about 15 wt % and a weight fraction of metal alkoxide is about 0.6 wt % or greater by volume in the total sol-gel. As a further non-limiting example, a wt % of acid stabilizer by volume in the total sol-gel is about 3 wt % to about 15 wt % and a weight fraction of metal alkoxide in the sol-gel is less than 0.6 wt % by volume in the total sol-gel. The corrosion inhibitor incorporated into the sol-gel provides an additional layer of corrosion protection adjacent to the metal surface. Additionally, this will promote corrosion protection when used with non-chromate primer coating stackups.
A primer of the present disclosure can be disposed on the sol-gel coating to enhance bond adhesion of aluminum surfaces and adhesion to subsequent epoxy primers. Primers of the present disclosure can be composed of a reactive polymer. For example, primers can be composed of an epoxy, e.g. an amine-cured epoxy. Primers of the present disclosure can be composed of a siloxane, e.g., a polysiloxane. Primers of the present disclosure can include about 0 to about 30 wt % of corrosion inhibitors by volume in the primer solution.
Primers of the present disclosure include organic primers having a plurality of metal particles capable of preventing fastener-induced corrosion and filiform corrosion. The metal particles can be sacrificial corrosion inhibits corrosion of the surface metal by undergoing oxidation prior to the surface metal. The metal particles can include an aluminum ion, and a counter ion, which can include various ions known to form salts with aluminum. Non-limiting examples of counter ions suitable for forming a salt with aluminum include carbonates, hydroxides and silicates (e.g., orthosilicates and metasilicates). For example, and without limitation, the counter ion includes an aluminum carbonate salt, an aluminum hydroxide salt, or an aluminum silicate salt (e.g., an aluminum orthosilicate salt or an aluminum metasilicate salt). The counter ion can include various ions known to form salts with the other Group 13 metals (e.g., B, Ga, In, Tl, Ho, and/or Es). Nonlimiting examples of counter ions suitable for forming a salt with the alkali metals include carbonates, hydroxides and silicates (e.g., orthosilicates and metasilicates).
The metal particles can include a magnesium ion, and a counter ion, which can include various ions known to form salts with magnesium. Non-limiting examples of counter ions suitable for forming a salt with magnesium include carbonates, hydroxides and silicates (e.g., orthosilicates and metasilicates). For example, and without limitation, the corrosion inhibitor includes a magnesium carbonate salt, a magnesium hydroxide salt, or a magnesium silicate salt (e.g., a magnesium orthosilicate salt or a magnesium metasilicate salt). The counter ion can include various ions known to form salts with the other Group 2 metals (e.g., Be, Ca, Sr, Ba, and/or Ra). Nonlimiting examples of counter ions suitable for forming a salt with the alkali metals include carbonates, hydroxides and silicates (e.g., orthosilicates and metasilicates).
The metal particles can include a lithium ion, and a counter ion, which can include various ions known to form salts with lithium. Non-limiting examples of counter ions suitable for forming a salt with lithium include carbonates, hydroxides and silicates (e.g., orthosilicates and metasilicates). For example, and without limitation, the corrosion inhibitor includes a lithium carbonate salt, a lithium hydroxide salt, or a lithium silicate salt (e.g., a lithium orthosilicate salt or a lithium metasilicate salt). The counter ion can include various ions known to form salts with the other Group IA (or Group 1) metals (e.g., Na, K, Rb, Cs, and/or Fr). Nonlimiting examples of counter ions suitable for forming a salt with the alkali metals include carbonates, hydroxides and silicates (e.g., orthosilicates and metasilicates).
A primer coating (disposed on the sol-gel) has a thickness of about 0.3 mils to about 2.5 mils, e.g., about 1.0 mils to about 2.0 mils, such as about 0.3 mils, about 0.5 mils, about 1.0 mils, about 1.5 mils, about 2.0 mils, about 2.5 mils, or the like.
A top coat of the present disclosure can be disposed on the primer coating to form solgels of the present disclosure having corrosion resistance (to water) of the metal substrate disposed adjacent the sol-gel. The top coat can include an organic top coat such as a polymeric coating (e.g., an epoxy coating, and/or a urethane coating), a polymeric material, a composite material (e.g., a filled composite and/or a fiber-reinforced composite), a laminated material, or mixtures thereof. The top coating includes at least one of a resin, a thermoset polymer, a thermoplastic polymer, an epoxy, a lacquer, a polyurethane, a polyester, or combination(s) thereof. For example, and without limitation, the top coat is a polyurethane. The polyurethane top coat prevents water permeability through the coating to allow for increased corrosion protection. The top coat has a thickness of about 2 mils to about 3 mils, e.g., about 2.1 mils to about 2.9 mils, such as about 2 mils, about 2.1 mils, about 2.2 mils, about 2.3 mils, about 2.4 mils, about 2.5 mils, about 2.6 mils, about 2.7 mils, about 2.8 mils, about 2.9 mils, about 3 mils, or the like. For example, and without limitation, the top coat has a thickness of about 2 mils to about 3 mils and the primer has a thickness of about 0.3 mils to about 2.5 mils.
Material substrate 104 can be any suitable material described herein and/or can include any suitable structure that benefits from sol-gel 102 being disposed thereon. Material substrate 104 can define one or more components (such as structural or mechanical components) of environmentally exposed apparatuses, such as aircraft, watercraft, spacecraft, land vehicles, an aerospace vehicle, a marine vehicle, equipment, civil structures, fastening components, wind turbines, and/or another apparatus susceptible to environmental degradation. Material substrate 104 can be part of a larger structure, such as a vehicle component. A vehicle component is any suitable component of a vehicle, such as a structural component, such as landing gears, a panel, or joint, of an aircraft, etc. Examples of a vehicle component include a rotor blade, landing gears, an auxiliary power unit, a nose of an aircraft, a fuel tank, a tail cone, a panel, a coated lap joint between two or more panels, a wing-to-fuselage assembly, a structural aircraft composite, a fuselage body-joint, a wing rib-to-skin joint, and/or other internal component. Material substrate 104 can be made of at least one of aluminum, aluminum alloy, magnesium, magnesium alloy, nickel, iron, iron alloy, steel, titanium, titanium alloy, copper, and copper alloy, as well as glass/silica and other inorganic or mineral substrates. Material substrate 104 is made of steel. Material substrate 104 can be a ‘bare’ substrate, having no plating (un-plated metal), conversion coating, and/or corrosion protection between material substrate 104 and sol-gel 102. Additionally, or alternatively, material substrate 104 can include surface oxidization and/or hydroxylation. Hence, sol-gel 102 can be directly bonded to material substrate 104 and/or to a surface oxide layer on a surface of material substrate 104. The material is not water sensitive, but a sol-gel disposed on the material is capable of protecting other adjacent structures that might be water sensitive.
Secondary layer 106 is disposed on a second surface 110 of sol-gel 102 opposite first surface 108 of sol-gel 102. Sol-gel 102 has a thickness that is less than the thickness of material substrate 104. Sol-gel 102 has a thickness that is about 50 nm to about 4 μm, e.g., about 100 nm to about 2.5 μm, such as about 100 nm, about 200 nm, about 300 nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900 nm, about 1 μm, about 2 μm, about 2.5 μm, or the like. Thinner coatings can have fewer defects (more likely to be defect free), while thicker coatings can provide more abrasion, electrical, and/or thermal protection to the underlying material substrate 104.
Secondary layer 106 includes organic material (e.g., organic chemical compositions) configured to bind and/or adhere to sol-gel 102. Secondary layer 106 includes a paint, a primer, a top coat, a polymeric coating (e.g., an epoxy coating, and/or a urethane coating), a polymeric material, a composite material (e.g., a filled composite and/or a fiber-reinforced composite), a laminated material, or mixtures thereof. Secondary layer 106 includes at least one of a polymer, a resin, a thermoset polymer, a thermoplastic polymer, an epoxy, a lacquer, a polyurethane, and a polyester. Secondary layer 106 can additionally include at least one of a pigment, a binder, a surfactant, a diluent, a solvent, a particulate (e.g., mineral fillers), corrosion inhibitors, and fibers (e.g., carbon, aramid, and/or glass fibers).
Tertiary layer 112 is disposed on a proximal surface 114 of secondary layer 106 opposite second surface 110 of sol-gel 102. Tertiary layer 112 includes organic material (e.g., organic chemical compositions) configured to bind and/or adhere to secondary layer 106. Tertiary layer 112 includes a paint, a primer, a top coat, a polymeric coating (e.g., an epoxy coating, and/or a urethane coating), a polymeric material, a composite material (e.g., a filled composite and/or a fiber-reinforced composite), a laminated material, or mixtures thereof. Tertiary layer 112 includes at least one of a polymer, a resin, a thermoset polymer, a thermoplastic polymer, an epoxy, a lacquer, a polyurethane, and a polyester. Tertiary layer 112 can additionally include at least one of a pigment, a binder, a surfactant, a diluent, a solvent, a particulate (e.g., mineral fillers), corrosion inhibitors, and fibers (e.g., carbon, aramid, and/or glass fibers).
Methods of forming a sol-gel of the present disclosure include mixing a metal alkoxide, acetic acid, and an organic solvent, such as an anhydrous organic solvent, followed by stirring for from about 1 minute to about 1 hour, such as about 30 minutes. Additional organic solvent (e.g., from about 1 vol % to 20 vol % organic solvent to total volume, such as 5 vol %) is then added to the metal alkoxide/acetic acid mixture. An organosilane is then added to the mixture and stirred for from about 1 minute to about 1 hour, such as about 30 minutes. A corrosion inhibitor is added to the mixture in an amount of about 3 wt % of the corrosion inhibitor to the mixture to about 15 wt % of the corrosion inhibitor to the mixture. The mixture can be deposited onto a material substrate. The deposited mixture can be cured at ambient temperature or can be heated to increase the rate of curing/sol-gel formation. In examples of the present disclosure, some of the ingredients listed herein can be optional and are not included in the sol-gel coating or formulation in each and every example as described herein.
Prior to applying 206 a sol-gel coating to a surface of the substrate, the substrate is cleaned 202 by exposing the surface of the substrate to a solvent. This can be accomplished by spraying, wiping, rinsing, flooding, or other means of applying a solvent to a surface known in the art. Applicable solvents for cleaning a substrate surface can include an alcohol (e.g., ethanol or propanol), ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, ether (e.g., dimethyl ether or dipropylene glycol dimethyl ether), glycol ether, tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO). Additional cleaning compositions can be or include an aqueous alkaline cleaning composition or aqueous-based alkaline cleaning composition.
Treating 204 the surface of the cleaned substrate can be done with a deoxidizing agent, such as one described herein. Deoxidizing agents can include, among other ingredients, chromic acid, hydrogen fluoride, or a combination thereof. The step of treating can be conducted after cleaning 202 and applying 206 the sol-gel coating. Mixing of the sol-gel components is done to form a mixture (e.g., a solution, a mixture, an emulsion, a suspension, and/or a colloid). Mixing can include mixing all sol-gel components together concurrently. Alternatively, mixing includes mixing any two components (e.g., metal alkoxide and acid stabilizer in an organic solvent) to form a first mixture and then mixing the remaining components into the first mixture to form a second mixture. The first mixture and second mixture each have a water content from about 0.1 wt % of water to the mixture to about 10 wt % of water to the mixture, such as from about 0.1 wt % to about 5 wt %, such as from about 0.1 wt % to about 3 wt %, such as from about 0.1 wt % to about 1 wt %, such as about 0.1 wt % to about 0.5 wt %, such as 0.5 wt % or less, such as 0.3 wt % or less, such as 0.1 wt % or less, such as 0 wt %.
Generally, mixing of a sol-gel composition is performed by combining the sol-gel formulation components (e.g., dispersing, emulsifying, suspending, and/or dissolving) in an organic solvent, preferably an anhydrous organic solvent, and optionally stirring the sol-gel formulation. Mixing can further include dissolving, suspending, emulsifying, and/or dispersing the solgel components in an organic solvent before mixing with one or more of the other sol-gel components. Examples of solvents for dissolving, suspending, emulsifying, and/or dispersing solgel components include one or more of alcohol (e.g., ethanol or propanol), ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, ether (e.g., dimethyl ether or dipropylene glycol dimethyl ether), glycol ether, tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO).
Additionally or alternatively, mixing can include mixing one or more of the sol-gel components as a solid, an aggregate, and/or a powder with one or more of the other sol-gel components. Where, for example, mixing includes mixing solids, powders, and/or viscous liquids, mixing can include mixing with a high-shear mixer (e.g., a paint shaker or a planetarycentrifugal mixer or stirrer). A high-shear mixer can be advantageous to break and/or to finely disperse solids to form a substantially uniform mixture. For example, a high-shear mixer can dissolve, suspend, emulsify, disperse, homogenize, deagglomerate, and/or disintegrate solids into the sol-gel formulation. The sol-gel components during mixing can be diluted to control self-condensation reactions and thus increase the pot life of the mixed sol-gel formulation. Mixing can include forming a weight percent (wt %) by volume of (metal alkoxide+organosilane+acid stabilizer to the mixture) in the mixture from about 0.1 wt % to about 30 wt %, such as from about 0.3 wt % to about 20 wt %, such as from about 1 wt % to about 10 wt %, such as from about 1 wt % to about 5 wt %, such as from about 2 wt % to about 4 wt %, such as from about 2 wt % to about 3 wt %, for example about 1 wt %, about 1.5 wt %, about 2 wt %, about 2.5 wt %, about 3 wt %.
Mixing can include forming a weight percent (wt %) by volume of the corrosion inhibitor in the mixture from about 0.1 wt % to about 50 wt %, such as from about 0.2 wt % to about 40 wt %, such as from about 0.5 wt % to about 35 wt %, such as from about 1 wt % to about 30 wt %, such as from about 2 wt % to about 25 wt %, such as from about 3 wt % to about 15 wt %, for example about 4 wt %, about 5 wt %, about 7 wt %, about 10 wt, about 15 wt %. A sol-gel formulation contains a corrosion inhibitor and mixing 202 includes forming a weight percent (wt %) of (metal alkoxide+organosilane+acid stabilizer to the mixture) in the mixture from about 0.3 wt % to about 50 wt %, such as from about 1 wt % to about 45 wt %, such as from about 2 wt % to about 40 wt %, such as from about 3 wt % to about 35 wt %, such as from about 4 wt % to about 25 wt %, such as from about 8 wt % to about 22 wt %, for example about 10 wt %, about 12 wt %, about 15 wt %.
A volume ratio of organosilane to metal alkoxide in a sol-gel formulation during mixing is from about 5% to about 20%, e.g., about 9% to about 11%, in which the metal alkoxide has been pretreated with an acid. For example, and without limitation, the volume ratio of organosilane to metal alkoxide is about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, or the like. A higher ratio increases the % solids in the sol-gel coating and allows for a higher concentration of inhibitors to be mixed into the coating.
In examples, a mixture of sol-gel components can be incubated for a period of time, such as from about 1 minute to about 60 minutes, such as from about 5 minutes to about 30 minutes, such as from about 10 minutes to about 20 minutes. Furthermore, pot-life is the period of time from the mixing until the sol-gel is formed (e.g., the mixture becomes too viscous to be usable). The pot life can be from about 1 hour to about 24 hours, such as from about 2 hours to about 8 hours, such as about 4 hours. Incubating can be performed under ambient conditions (e.g., at room temperature) and/or at elevated temperature. Suitable incubation temperatures include from about 10° C. to about 100° C., such as from about 20° C. to about 70° C., such as from about 30° C. to about 50° C., for example about 40° C.
Method 200 includes coating or applying 206 the material substrate 104 with a mixture comprising sol-gel components after cleaning 202 the substrate by exposing the substrate external surface to a solvent. The cleaning step can further include wiping or mild abrasion of the substrate surface. In examples, after mixing the mixture comprising sol-gel components, the mixture comprising sol-gel components can be allowed to stand at room temp for about 30 minutes or more. Coating 206 can include wetting the material substrate 104 with a mixture comprising sol-gel components, for example, by spraying, immersing, brushing, and/or wiping the mixture comprising sol-gel components onto material substrate 104. For example, suitable forms of spraying include spraying with a spray gun, high-volume, low-pressure spray gun, and/or hand pump sprayer. The mixture comprising sol-gel components is allowed to drain from the wetted material substrate 104 for a few minutes (e.g., 1-30 minutes, 1-10 minutes, or 3-10 minutes) and, if necessary, excess, undrained mixture can be blotted off material substrate 104 and/or gently blown off material substrate 104 by compressed air.
Applying the sol-gel coating 206 includes cleaning and/or pretreating material substrate 104 before wetting the material substrate with the mixture comprising sol-gel components. The metal substrate can be pretreated 204 by immersing the metal substrate into a solution maintained between pH 3.7-3.95 using 1N H2SO4 or IN NaOH before applying the sol-gel coating. This immersion in the acidic solution can be beneficial for application of trivalent chromium coatings or treatments. The solution can include about 3 grams/liter to about 22 grams/liter of water-soluble trivalent chromium salt, about 1.5 grams/liter to about 11.5 grams/liter of an alkali metal hexafluorozirconate, about 0 grams/liter (e.g., 0.1 grams/liter) to about 10 grams/liter of a water-soluble thickener, and about 0 grams/liter (e.g., 0.1 grams/liter) to about 10 grams/liter of a water-soluble surfactant selected from the group consisting of a non-ionic surfactant, anionic surfactant, cationic surfactant, and combinations thereof, per liter of the solution.
Generally, sol-gel 102 adheres and/or bonds better with a clean, bare material substrate, substantially free from dirt, nonreactive surface oxides, and/or corrosion products, and preferably populated with a sufficient concentration of reactive hydroxyl groups or other chemically-reactive species. Material substrate surface preparation methods can include degreasing, an alkaline wash, chemical etching, chemically deoxidizing, mechanically deoxidizing (e.g., sanding and/or abrading) and/or other suitable approaches towards creating a sol-gel compatible surface. Coating 206 does not typically include coating metal substrate 104 with an undercoating or forming a chemical conversion coating on metal substrate 104, unless the coating is applied to create a hydroxyl-rich substrate or otherwise improved compatibility with the sol-gel. A material substrate surface can become hydroxyl-rich by depositing silica hydroxylates onto the material surface.
Methods of the present disclosure can include curing a mixture comprising sol-gel components. Curing can include drying a mixture comprising sol-gel components disposed on material substrate 104 and can be performed under ambient conditions, at room temperature, and/or at elevated temperature. A curing temperature is from about 10° C. to about 150° C., such as from about 30° C. to about 100° C., such as from about 50° C. to about 90° C., for example about 60° C., about 70° C., about 80° C. Curing 308 can be performed for a period of time, such as from about 1 minute to about 48 hours, such as from about 5 minutes to about 24 hours, such as from about 10 minutes to about 8 hours, such as from about 30 minutes to about 4 hours, for example about 1 hour.
After coating 206 and/or curing, the sol-gel is suitable for exposure to an external environment and/or for application of a secondary layer 106. As shown in
After coating, the sol-gel is suitable for exposure for application of a tertiary layer 112. Depositing such a tertiary layer can include painting, spraying, immersing, contacting, adhering, and/or bonding secondary layer 106 with the organic material to form tertiary layer 112. A tertiary layer includes a paint, a fiber-reinforced plastic, or other suitable organic material.
All 2024-T3 panels were cleaned as follows: Degrease for 10 min in Brulin 815 GD followed by alkaline clean for 12 min in Bonderite C-AK and deoxidized for 10 min in Nitric/HF solution. The cleaning procedure for the panels can include solvent wiping with using isopropyl alcohol (IPA), and/or immersion in an aqueous alkaline cleaner (COTS) followed by deoxidation. Alternatively, panels could be grit blasted with 180 grit brown fused alumina or abraded manually or with mechanical assistance using an abrasive or cleansing scouring pad to remove any residual coatings or surface contamination.
The various pretreatments and conversion coatings evaluated were SurTec 650V-a trichrome passivation from SurTec, Bonderite SmutGo-NC deoxidizer, and Henkel 6/16-a deoxidizer from Henkel.
The SurTec coating was be applied using an immersion process. The solution was made up using 5% vol. of the concentrate in aqueous solution. The solution was maintained between pH range of 3.7-3.95 using 1N H2SO4 or IN NaOH. Cleaned panels were immersed in the SurTec 650V tank for 3 min followed by two to three rounds of 15-30 sec tap water rinse followed by a 15 sec deionized water rinse. The panels were then dried using compressed shop air. The coating was clear and translucent after drying.
Corrosion resistant sol gel of the present disclosure was formulated and applied using a conventional HVLP gun followed by overnight drying at room temperature.
Any primer and topcoat can be applied the day after the panels were pretreated using the pretreatments described above. Both primers and topcoats were applied using a conventional HVLP gun. The topcoat can be applied within a 4 h window after application of the primer and the coatings are cured at room temperature for 2 weeks. After this two-week drying time, the panels can be scribed using a wide tool cutter. Primer and topcoat thickness can be measured from witness coupons sprayed concurrently with the panels. Primer and topcoat thickness can also be measured and recorded using a handheld Elcometer thickness gauge.
ASTM B117 Corrosion Testing with Corrosion-Resistant Sol-Gel Formulations
Now referring to
For each of the above samples, as required, the aluminum test panels underwent a three-minute immersion in SurTec 650V, at 9% volume and pH of 3.7, adjusted with 5% sulfuric acid (H2SO4). The SurTec tank was maintained at 85° F. during the immersion process. The sol-gel composition was applied in the same day as the SurTec application, and the panels were aged for 24 to 72 hours prior to placing in the salt spray chamber for testing. Prior to application of the SurTec coating, the panels were rinsed with a pH 4 rinse for one minute. After the Surtech is applied, the panel is rinsed then dried then sol-gel is applied.
While the preceding 168 h photos are for reference only, per MIL-DTL-81706 Class 1 A corrosion requirements include no pits with tails on five 10″×3″ corrosion panels after 336 h exposure per ASTMB117. The panels that are close to meeting this requirement are shown in
Methods and application of a non-chromium, corrosion inhibited sol-gel treatment to the surface of a trivalent chromium conversion coating to improve corrosion resistance and adhesion properties are described herein. The method includes treating the metal substrate with a deoxidizer prior to application of the trivalent chromium conversion coating, and applying the non-chromium sol-gel which can contain 2,5-Dimercapto 1,3,4-Thiadiazole (DMCT). Coated coupons were evaluated for corrosion resistance in salt spray test as per ASTM B117.
While the present teachings have been illustrated with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. For example, it may be appreciated that while the process is described as a series of acts or events, the present teachings are not limited by the ordering of such acts or events. Some acts may occur in different orders and/or concurrently with other acts or events apart from those described herein. Also, not all process stages may be required to implement a methodology in accordance with one or more aspects or embodiments of the present teachings. It may be appreciated that structural objects and/or processing stages may be added, or existing structural objects and/or processing stages may be removed or modified. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. Furthermore, to the extent that the terms “including,” “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” The term “at least one of” is used to mean one or more of the listed items may be selected. Further, in the discussion and claims herein, the term “on” used with respect to two materials, one “on” the other, means at least some contact between the materials, while “over” means the materials are in proximity, but possibly with one or more additional intervening materials such that contact is possible but not required. Neither “on” nor “over” implies any directionality as used herein. The term “conformal” describes a coating material in which angles of the underlying material are preserved by the conformal material. The term “about” indicates that the value listed may be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the illustrated embodiment. The terms “couple,” “coupled,” “connect,” “connection,” “connected,” “in connection with,” and “connecting” refer to “in direct connection with” or “in connection with via one or more intermediate elements or members.” Finally, the terms “exemplary” or “illustrative” indicate the description is used as an example, rather than implying that it is an ideal. Other embodiments of the present teachings may be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present teachings being indicated by the following claims.
This application claims the benefit of U.S. Provisional Patent Application No. 63/613,445, filed on Dec. 21, 2023, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63613445 | Dec 2023 | US |
