Patent Description:
Aircraft surfaces are typically made of a metal, such as aluminum or titanium. A primer can be coated on the metal surface to prevent or reduce corrosion. To further improve the adhesion of primers to the metal surfaces, adhesive coatings are typically disposed between a metal surface and a primer.

An adhesive sol-gel film can be disposed at the interface between the metal and primer. Adhesive sol-gel films typically contain greater than <NUM> wt% water and, often times, greater than <NUM> wt% water. Water as a solvent for sol-gels is environmentally benign, reduces the amount of waste generated, and has an ability to hydrolyze silanes present in a sol-gel. Typical sol-gels of this type are effective for corrosion resistance of metals such as titanium or nickel, but other materials, such as low-alloy steels, are not as resistant to corrosion in the presence of water-based sol-gels. Furthermore, there can be situations in which sol-gel should be applied in the near vicinity of water-sensitive materials or components, or in interior crevices or pocket regions where water exposure or water entrapment might be prevalent.

Therefore, there is a need in the art for new and improved adhesive sol-gel films suitable for use with steel substrates.

<CIT> relates to a non-aqueous coating composition obtained by mixing (A) at least one silane, such as phenyltrimethoxysilane, methyltrimethoxysilane; and (B) vinyltriacetoxy silane and/or colloidal aluminum hydroxide and/or at least one metal alcoholate. Optional additives include ethyl orthosilicate, ethyl polysilicate or colloidal silica in a lower alkanol and boric acid, which may be dissolved in a lower alkanol. Hard corrosion resistant coatings are obtained. These coatings may be applied to metallic or non-metallic surfaces.

<CIT> relates to an anti-corrosive sol-gel that is a combination of an organometallic salt, an organosilane, and a borate, phosphate, or zinc functional component. The organosilane component may be selected from a large group of equivalent compounds but is preferably an alkoxyzirconium salt, and most preferably Zr (IV) n-propoxide. The organosilane may also be selected from a large group of equivalent compounds, but is preferably <NUM>-glycidoxypropyltrimethoxysilane (GTMS). Combination of the components takes place in the presence of an organic catalyst, preferably acetic acid.

<CIT> relates to sol-gel coating compositions and related processes. An alkoxysilane is contacted with water and an inorganic acid to form a first composition. A zirconium alkoxide is contacted with an organic acid to form a second composition. One or more alkoxysilanes and an organic acid are contacted with a mixture of the first and second compositions to form a sol-gel composition, to which a photoinitiator is added. The sol-gel composition has a ratio of a number of moles of silicon to a number of moles of zirconium (nSi/nZr) ranging from about <NUM> to about <NUM>. The sol-gel composition is applied on a substrate (e.g., an aluminum alloy substrate) multiple times to form multiple sol-gel layers, and at least one of the sol-gel layers is cured by UV radiation. The multiple sol-gel layers are then thermally cured.

The present disclosure provides sol-gel films and substrates, such as vehicle components, having a sol-gel film disposed thereon.

In one aspect, there is provided a sol-gel formulation as defined in claim <NUM>.

In another aspect, there is provided a vehicle component as defined in claim <NUM>.

The present disclosure provides a sol-gel formulation having about <NUM> wt% or less water content based on the total weight of the sol-gel formulation and comprises an organosilane, a metal alkoxide, an acid stabilizer, and an organic solvent. One exemplary sol-gel comprises <NUM> wt% glycidoxypropyl-trimethoxy-silane, <NUM> wt% zirconium tetra-n-propoxide, <NUM> wt% glacial acetic acid, and about <NUM> wt% water.

The present disclosure provides a vehicle component comprising a metal substrate and a sol-gel formulation disposed on the metal substrate. The sol-gel formulation has about <NUM> wt% or less water content based on the total weight of the sol-gel formulation and comprises an organosilane, a metal alkoxide, an acid stabilizer, and an organic solvent.

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical aspects of this present disclosure and are therefore not to be considered limiting of its scope, for the present disclosure may admit to other equally effective aspects.

The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one aspect may be beneficially incorporated in other aspects without further recitation.

The present disclosure provides sol-gel formulations, sol-gels, and substrates, such as vehicle components, having a sol-gel (or sol-gel formulation) disposed thereon. At least one sol-gel formulation has about <NUM> wt% or less water content based on the total weight of the sol-gel formulation and comprises an organosilane, a metal alkoxide, an acid stabilizer, and an organic solvent. At least one vehicle component comprises a sol-gel coating system comprising a metal substrate and a sol-gel formulation disposed on the metal substrate. The sol-gel formulation has about <NUM> wt% or less water content based on the total weight of the sol-gel formulation and comprises an organosilane, a metal alkoxide, an acid stabilizer, and an organic solvent. Sol-gel formulations and vehicle components of the present disclosure provide improved corrosion resistance of substrates, such as vehicle components, having sol-gels of the present disclosure disposed thereon. For example, a steel vehicle component having a sol-gel having <NUM> wt% or less water content disposed thereon has improved floating roller peel resistance characteristics (ASTM D3167) as compared to a steel vehicle component having no sol-gel formulation disposed thereon.

The term "sol-gel," a contraction of solution-gelation, refers to a reaction product of 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. The 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)<NUM> rapidly forms. Zr(OH)<NUM> 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 may condense to colloidal particles or they may grow to form a network gel. The ratio of organics to inorganics in the polymer matrix is controlled to maximize performance of the sol-gel, such as adhesion capability, for a particular application.

Organosilane: In at least one aspect, a weight fraction (wt%) of organosilane in the sol-gel is from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%.

In at least one aspect, organosilanes of the present disclosure are represented by formula (I):
<CHM>
wherein:
each of R<NUM>, R<NUM>, and R<NUM> is independently linear or branched C<NUM>-<NUM> alkyl. C<NUM>-<NUM> alkyl includes methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, and icosanyl;
R<NUM> is selected from alkylene, cycloalkylene, ether, and arylene. Alkylene includes linear or branched C<NUM>-<NUM> alkylene. C<NUM>-<NUM> alkylene includes methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, tridecylene, tetradecylene, pentadecylene, hexadecylene, heptadecylene, octadecylene, nonadecylene, and icosanylene. Ether includes polyethylene glycol ether, polypropylene glycol ether, C<NUM>-C<NUM> alkyl ether, aryl ether, and cycloalkyl ether.

In at least one aspect, ether is selected from:
<IMG>.

wherein n is a positive integer. In at least one aspect, n is a positive integer and the number average molecular weight (Mn) of the ether is from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>.

Also disclosed herein 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):
<CHM>
wherein R is selected from alkylene, cycloalkylene, ether, and arylene. Alkylene includes linear or branched C<NUM>-<NUM> alkylene. C<NUM>-<NUM> alkylene includes methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, tridecylene, tetradecylene, pentadecylene, hexadecylene, heptadecylene, octadecylene, nonadecylene, and icosanylene. Ether includes polyethylene glycol ether, polypropylene glycol ether, C<NUM>-C<NUM> alkyl ether, aryl ether, and cycloalkyl ether.

wherein n is a positive integer. In an example, n is a positive integer and the number average molecular weight (Mn) of the ether is from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>.

The organosilane used in the claimed sol-gel formulation is represented by compound <NUM>:
<CHM>.

In at least one aspect, an organosilane is selected from <NUM>-aminopropyltriethoxysilane, <NUM>-glycidoxy-propyltriethoxysilane, p-aminophenyltrimethoxysilane, p-aminophenyltriethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, n-(<NUM>-aminoethyl)-<NUM>-aminopropyltrimethoxysilane, <NUM>-aminopropyltriethoxysilane, <NUM>-aminopropyltrimethoxysilane, <NUM>-glycidoxypropyldiisopropylethoxysilane, (<NUM>-glycidoxypropyl)methyldiethoxysilane, <NUM>-glycidoxypropyltrimethoxysilane, <NUM>-(<NUM>,<NUM>-epoxycyclohexyl)ethyltrimethoxysilane, <NUM>-(<NUM>,<NUM>-epoxycyclohexyl)ethyltriethoxysilane, <NUM>-mercaptopropyltrimethoxysilane, <NUM>-mercaptopropyltriethoxysilane, <NUM>-methacryloxypropylmethyldiethoxysilane, <NUM>-methacryloxypropylmethyldimethoxysilane, <NUM>-methacryloxypropyltrimethoxysilane, n-phenylaminopropyltrimethoxysilane, vinylmethyldiethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, bis(trimethoxysilyl)ethane, bis(triethoxysilyl)ethane, bis[<NUM>-(trimethoxysilyl)propyl]amine, bis[<NUM>-(triethoxysilyl)propyl]amine, bis[<NUM>-(triethoxysilyl)propyl] disulfide, bis[<NUM>-(trimethoxysilyl)propyl] disulfide, bis[<NUM>-(triethoxysilyl)propyl] trisulfide, bis[<NUM>-(trimethoxysilyl)propyl] trisulfide, bis[<NUM>-(triethoxysilyl)propyl] tetrasulfide, and bis[<NUM>-(trimethoxysilyl)propyl] tetrasulfide.

In at least one aspect, 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. In at least one aspect, an organosilane of the present disclosure provides a sol-gel having reduced porosity and blistering as compared to conventional sol-gels.

Metal alkoxide: 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 +<NUM>. 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) tetra-isopentoxide, 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.

In at least one aspect, a weight fraction (wt%) of metal alkoxide in the sol-gel is from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%.

Corrosion inhibitor: A corrosion inhibitor useful to form sol-gels of the present disclosure provides corrosion resistance (to water) of a 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.

In at least one aspect, 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). In at least one aspect, a corrosion inhibitor is represented by the formula: R<NUM>--Sn--X--R<NUM>, wherein R<NUM> is H or an organic group, n is an integer greater than or equal to <NUM>, X is a sulfur or a metal atom, and R<NUM> is H or an organic group, wherein at least one of R<NUM> and R<NUM> is an organic group (preferably wherein R<NUM> and R<NUM> are both organic groups). One or both of R<NUM> and R<NUM> can include additional polysulfide groups and/or thiol groups. Furthermore, in at least one aspect, corrosion inhibitors include polymers having the formula -(R<NUM>--Sn--X--R<NUM>)q-, wherein R<NUM> is H or an organic group, n is a positive integer, X is a sulfur or a metal atom, R<NUM> is H or an organic group, and q is a positive integer and wherein at least one of R<NUM> and R<NUM> is an organic group (preferably wherein R<NUM> and R<NUM> are both organic groups). An organic group is a moiety comprising at least one carbon atom and optionally one or more non-hydrogen, non-carbon atoms. R<NUM> and R<NUM> each may be an organic group having <NUM>-<NUM> carbon atoms and/or non-hydrogen atoms. R<NUM> and R<NUM> (of a polymeric or monomeric corrosion inhibitor) may be independently selected from H or an organic group comprising optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, thiol, polysulfide, or thione, or combinations thereof (e.g. arylalkyl). In at least one aspect, R<NUM> and R<NUM> (of a polymeric or monomeric corrosion inhibitor) is independently selected from H, alkyl, cycloalkyl, aryl, thiol, polysulfide, and thione. R<NUM> and R<NUM> may be independently selected from H or an organic group selected from optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, heterocyclyl, or combinations thereof. R<NUM> and R<NUM> may be independently selected from optionally substituted alkyl, cycloalkyl, aryl, heteroaryl, and heterocyclyl. R<NUM> and R<NUM> may both be optionally substituted heteroaryl. Heteroaromatic examples of R<NUM> and R<NUM> groups include azoles, triazoles, thiazoles, dithiazoles, and/or thiadiazoles. Optional substituents of each of R<NUM> and R<NUM> can be independently selected from alkyl, amino, a phosphorous-containing substituent (such as -P(=O)(OR*)<NUM>, -P(=O)R*<NUM>,-P(=S)(OR*)<NUM>, -P(=S)R*<NUM>, -P(=O)(OR*)(NR*), -P(=O)(OR*)R*, -P(=CR*<NUM>)R*<NUM>,-P(=O)(OR*)R*, -PR*<NUM>), ether, alkoxy, hydroxy, a sulfur-containing substituent such as -SR*, -CH(SR*)(OR*), -CH(SR*)<NUM>, -SSR*, -C(=O)SR*, -S(=O)R*, -S(=O)<NUM>R*,-C(=S)R*, -S(=O)<NUM>(OR*), -S(=O)<NUM>(NR*), -S(OR*), a selenium-containing substituent (such as -SeR*, -SeSeR*, -C(=Se)R*, -Se(=O)R*, -Se(=O)<NUM>R*, -Se(=O)OH), and a tellurium-containing substituent (such as -TeR*, -TeTeR*, -C(=Te)R*, -Te(=O)R*,-Te(=O)<NUM>R*, -Te(=O)OH), wherein each R* is independently selected from H, alkyl, ether, aryl, heteroaryl, heterocyclyl, or combinations thereof, or two R* groups may together form a cyclic group. For example, optional substituents of R<NUM> and R<NUM> may be independently selected from alkyl, amino, ether, alkoxy, hydroxy, a phosphorus-containing substituent or a sulfur-containing substituent, or independently selected from alkyl, amino, ether, alkoxy, hydroxy and -SH, or independently selected from amino, hydroxy and -SH. In some embodiments, R<NUM> and R<NUM> are heteroaryl (for example, azole, triazole, thiazole, dithiazole, or thiadiazole, preferably thiadiazole) independently substituted by one or more moieties selected from alkyl, amino, ether, alkoxy, hydroxy or -SH, or independently substituted by one or more moieties selected from amino, hydroxy or -SH.

In at least one aspect, 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--R', wherein M is a metal and R<NUM> is an organic group. R<NUM> can include a disulfide group. Metal-thiolate complexes have the general formula M-(S--R<NUM>)n', wherein n' generally is an integer from <NUM> to <NUM> and M is a metal atom. Metals are copper, zinc, zirconium, aluminum, iron, cadmium, lead, mercury, silver, platinum, palladium, gold, and/or cobalt. R<NUM> may be as defined above in reference to the corrosion inhibitor formulae R<NUM>--Sn--X--R<NUM> and -(R<NUM>--Sn--X--R<NUM>)q-. In some embodiments, n' is <NUM> and/or M may be zinc.

In at least one aspect, the corrosion inhibitor includes an azole compound. Examples of suitable azole compounds include cyclic compounds having, <NUM> nitrogen atom, such as pyrroles, <NUM> or more nitrogen atoms, such as pyrazoles, imidazoles, triazoles, tetrazoles and pentazoles, <NUM> nitrogen atom and <NUM> oxygen atom, such as oxazoles and isoxazoles, and <NUM> nitrogen atom and <NUM> sulfur atom, such as thiazoles and isothiazoles. Nonlimiting examples of suitable azole compounds include <NUM>,<NUM>-dimercapto-<NUM>,<NUM>,<NUM>-thiadiazole, <NUM>-benzotriazole, <NUM>-<NUM>,<NUM>,<NUM>-triazole, <NUM>-amino-<NUM>-mercapto-<NUM>,<NUM>,<NUM>-thiadiazole, also named <NUM>-amino-<NUM>,<NUM>,<NUM>-thiadiazole-<NUM>-thiol, <NUM>-amino-<NUM>,<NUM>,<NUM>-thiadiazole. In at least one aspect, for example, the azole may be <NUM>,<NUM>-dimercapto-<NUM>,<NUM>,<NUM>-thiadiazole. In at least one aspect, the azole may be present in the composition at a concentration of <NUM>/L of sol-gel composition to <NUM>/L of sol-gel composition, for example, <NUM>/L of sol-gel composition. In some embodiments, the azole compound includes benzotriazole and/or <NUM>,<NUM>-dimercapto-<NUM>,<NUM>,<NUM>-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 <NUM>,<NUM>,<NUM>-thiadiazole-<NUM>,<NUM>-dithiol and thiadiazoles represented by formula (III) or formula (IV):
<CHM>.

The thiadazole of formula (III) may be purchased from Vanderbilt Chemicals, LLC (of Norwalk, Connecticut) and is known as Vanlube® <NUM>. The thiadiazole of formula (IV) may be purchased from WPC Technologies, Inc. ™ (of Oak Creek, Wisconsin) and is known as InhibiCor™ <NUM>.

A corrosion inhibitor of the present disclosure can be a derivative of <NUM>,<NUM>-dimercapto-<NUM>,<NUM>,<NUM> thiadiazole symbolized by HS-CN<NUM>SC-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 <NUM>,<NUM>-dimercapto-<NUM>,<NUM>,<NUM> thiadiazole (DMTD), and <NUM>,<NUM>-dimercapto-s-triazolo-[<NUM>,<NUM>-b]-<NUM>,<NUM>-<NUM>-thiadiazole, and trithiocyanuric acid (TMT). Other examples include N-,S- and N,N-, S,S- and N,S-substituted derivatives of DMTD such as <NUM>-mercapto-<NUM>-phenil-<NUM>,<NUM>,<NUM>-thiadiazoline-<NUM>-thione or bismuthiol II (<NUM>-Phenyl-<NUM>,<NUM>,<NUM>-thiadiazolidine-<NUM>,<NUM>-dithione) and various S-substituted derivatives of trithiocyanuric acid. Other examples include <NUM>,<NUM>' dithio-bis (<NUM>,<NUM>,<NUM> thiadiazole-<NUM>(<NUM>)-thione or (DMTD)<NUM>, or (DMTD), the polymer of DMTD; <NUM>,<NUM>' thio-bis (<NUM>,<NUM>,<NUM> thiadiazole-<NUM>(<NUM>)-thione; or (TMT)<NUM>, the dimer and polymers of TMT. Other examples include salts of DMTD of the general formula: M(DMTD)n, where n=<NUM>, <NUM> or <NUM>, 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(ll) (examples: ZnDMTD, Zn(DMTD)<NUM>, Bi(DMTD)<NUM>); similar salts of TMT, as for example, ZnTMT, in a ratio of <NUM>:<NUM>; 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=<NUM> or n><NUM>, m=<NUM>, <NUM>, or <NUM> and M is a metal cation such as M=Zn(II), Bi(lll), Co(ll), Ni(II), Cd(II), Pb(ll), Ag(I), Sb(III), Sn(II), Fe(II), or Cu(II). Typical examples are: Zn[(DMTD)<NUM>], Zn[(DMTD)<NUM>]<NUM>.

Additional examples include ammonium-, aryl-, or alkyl-ammonium salts of DMTD, (DMTD)n, or <NUM>,<NUM>' thio-bis (<NUM>,<NUM>,<NUM> thiadiazole-<NUM>(<NUM>)-thione or <NUM>,<NUM>-dimercapto-s-triazolo-[<NUM>,<NUM>-b]-<NUM>,<NUM>-<NUM>-thiadiazole. Typical examples include: Cyclohexyl amine: DMTD, in ratios of <NUM>:<NUM> and <NUM>:<NUM>; Di-cyclohexyl amine: DMTD, in ratios of <NUM>:<NUM> and <NUM>:<NUM>; Aniline: DMTD, in ratios of <NUM>:<NUM> and <NUM>:<NUM>; similar salts of TMT, as for example Di-cyclohexyl amine: TMT, in a ratio of <NUM>:<NUM>. 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)<NUM> or <NUM>,<NUM>' thio-bis (<NUM>,<NUM>,<NUM> thiadiazole-<NUM>(<NUM>)-thione and TMT; Inherently conductive polypyrrole and/or polythiophene doped with DMTD, (DMTD)<NUM> and <NUM>,<NUM>' thio-bis (<NUM>,<NUM>,<NUM> thiadiazole-<NUM>(<NUM>)-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 <NUM>,<NUM>' thio-bis (<NUM>,<NUM>,<NUM> thiadiazole-<NUM>(<NUM>)-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. In some aspects, such inorganic matrixes include non-toxic anionic and cationic species with corrosion inhibitor properties, such as: MoO<NUM>-, PO<NUM>-, HPO<NUM>-, poly-phosphates, BO<NUM>-, SiO<NUM>-, NCN-, WO<NUM>-, 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)<NUM> 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, CeO<NUM>, ZrO<NUM>, and amorphous SiO<NUM>.

In at least one aspect, a corrosion inhibitor is a lithium ion, and a counter ion, which may 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). In at least one aspect, 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). Additionally, in at least one aspect, the counter ion includes various ions known to form salts with the other Group IA (or Group <NUM>) 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). In at least one aspect, for example, 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. Corrosion inhibitors of the present disclosure can include Cesium compounds.

Acid stabilizer: An acid stabilizer used to form sol-gels of the present disclosure provides stabilization of a metal alkoxide and a corrosion inhibitor (if present) 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) may also be used, such as glycols, ethoxyethanol, or H<NUM>NCH<NUM>CH<NUM>OH.

In at least one aspect, a pH of a sol-gel of the present disclosure is from about <NUM> to about <NUM>, such as about <NUM> to about <NUM>. In at least one aspect, a weight fraction (wt%) of acid stabilizer in the sol-gel is from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%. In at least one aspect, a wt% of acid stabilizer in a sol-gel is about <NUM> wt% and a weight fraction of metal alkoxide is about <NUM> wt% or greater. In another aspect, a wt% of acid stabilizer in a sol-gel is about <NUM> wt% and a weight fraction of metal alkoxide is less than <NUM> wt%. Preferably, a ratio of metal alkoxide to acid stabilizer in a sol-gel is from about <NUM>:<NUM> to about <NUM>:<NUM>, such as about <NUM>:<NUM>.

If a corrosion inhibitor is present in a sol-gel, a molar ratio of acid stabilizer to metal alkoxide can be from about <NUM>:<NUM> to about <NUM>:<NUM>, such as from about <NUM>:<NUM> to about <NUM>:<NUM>, such as from about <NUM>:<NUM> to about <NUM>:<NUM>, such as from about <NUM>:<NUM> to about <NUM>:<NUM>.

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 (if present), which reduces or prevents reaction of the corrosion inhibitor with, for example, a metal alkoxide.

One or more sol-gel components of the present disclosure may be dissolved in one or more solvents before being added to a mixture containing the other sol-gel components. Corrosion inhibitors, for example, generally have limited solubility in water and aqueous solvents. Corrosion inhibitors may be insoluble powders, insoluble materials (e.g., aggregates, solids, and/or liquids), hydrophobic compounds, heavy oils, and/or greases. Hence, sol-gel components may be dissolved in compatible solvents and may be suspended, emulsified, and/or dispersed within incompatible solutions and/or solvents. Suitable solvents for dissolving, suspending, emulsifying, and/or dispersing sol-gel components of the present disclosure are polar organic and/or non-polar organic.

Polar organic solvents are advantageous for dissolving sol-gel components, such as corrosion inhibitors. Additionally or alternatively, sol-gel components can be suspended, emulsified, and/or dispersed in a solvent. Examples of organic solvents for dissolving, suspending, emulsifying, and/or dispersing sol-gel components include at least one 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-<NUM>-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO). In at least one aspect, an organic solvent is selected from at least one of ethanol, n-propanol, isopropanol, <NUM>-butanol, <NUM>-butanol, <NUM>-pentanol, <NUM>-pentanol, <NUM>-pentanol, <NUM>-hexanol, <NUM>-hexanol, and <NUM>-hexanol. Organic solvents of the present disclosure can be anhydrous, e.g. greater than <NUM> wt% purity. In at least one aspect, a sol-gel formulation has an organic solvent content of from about <NUM> wt% to about <NUM> wt% based on the total weight of the sol-gel formulation, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%. Upon curing, e.g. heating, of a mixture containing the sol-gel components, some or all of the solvent(s) can be removed from the sol-gel/mixture.

In at least one aspect, a weight percent (wt%) of (metal alkoxide + organosilane + acid stabilizer) in the mixture is from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%.

Sol-gels of the present disclosure include an organic solvent and have a water content from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as about <NUM> wt% to about <NUM> wt%. In at least one aspect, a sol-gel has a water content of <NUM> wt% or less, such as <NUM> wt% or less, such as <NUM> wt% or less, such as <NUM> wt%. It has been discovered that a sol-gel having, for example, <NUM> wt% or less of water forms a sol-gel with sufficient adhesion ability to substrates, such as steel substrates, in addition to maintaining or improving corrosion resistance (e.g., reduced flash rust) as compared to conventional sol-gels that contain, for example, <NUM> wt% water or greater.

In at least one aspect, a weight fraction (wt%) of (metal alkoxide + hydroxy organosilane + acid stabilizer) in the sol-gel is from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%. A greater amount of (metal alkoxide + hydroxy organosilane + acid stabilizer) provides greater amounts of corrosion inhibitor to be present in the sol-gel. A weight fraction (wt%) of corrosion inhibitor in the sol-gel is from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt, about <NUM> wt%.

<FIG> is a side view of a corrosion-inhibiting sol-gel disposed on a substrate. A corrosion-inhibiting sol-gel system <NUM> comprising a sol-gel <NUM> is disposed on a material substrate <NUM>. Sol-gel <NUM> has corrosion inhibiting properties which provide corrosion protection of material substrate <NUM>. Sol-gel <NUM> promotes adherence between metal substrate <NUM> and a secondary layer <NUM>. Secondary layer <NUM> can be a sealant, adhesive, primer or paint, which can be deposited onto sol-gel <NUM> by, for example, spray drying.

Material substrate <NUM> can be any suitable material and/or can include any suitable structure that benefits from sol-gel <NUM> being disposed thereon. Metal substrate <NUM> may define one or more components (such as structural or mechanical components) of environmentally exposed apparatuses, such as aircraft, watercraft, spacecraft, land vehicles, equipment, civil structures, fastening components, and/or another apparatus susceptible to environmental degradation. Material substrate104 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 <NUM> 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. In at least one aspect, material substrate <NUM> is made of steel. Material substrate <NUM> can be a 'bare' substrate, having no plating (unplated metal), conversion coating, and/or corrosion protection between material substrate <NUM> and sol-gel <NUM>. Additionally or alternatively, material substrate <NUM> can include surface oxidization and/or hydroxylation. Hence, sol-gel <NUM> can be directly bonded to material substrate <NUM> and/or to a surface oxide layer on a surface of material substrate <NUM>. In at least one aspect, 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 <NUM> is disposed on a second surface <NUM> of sol-gel <NUM> opposite first surface <NUM> of sol-gel <NUM>. In at least one aspect, sol-gel <NUM> has a thickness that is less than the thickness of material substrate <NUM>. In at least one aspect, sol-gel <NUM> has a thickness of from about <NUM> (microns) to about <NUM>, such as from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>. Thinner coatings may have fewer defects (more likely to be defect free), while thicker coatings may provide more abrasion, electrical, and/or thermal protection to the underlying material substrate <NUM>.

In at least one aspect, secondary layer <NUM> includes organic material (e.g., organic chemical compositions) configured to bind and/or adhere to sol-gel <NUM>. Secondary layer <NUM> includes a paint, a topcoat, 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. In at least one aspect, secondary layer <NUM> 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 <NUM> 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).

In at least one aspect, material layer <NUM> is a pitch horn of a rotor blade. Rotor blades of the present disclosure comprise one or more rotor blade components. As described herein, "rotor blade component" comprises any suitable structure adapted, in combination with one or more other rotor blade components, to form a rotor blade. <FIG> is a perspective view of a rotor blade, according to some aspects of the present disclosure. As shown in <FIG>, rotor blade <NUM> of a main rotor assembly (not shown) is made of a root section <NUM>, an intermediate section <NUM>, and a tip section <NUM>. Root section <NUM> is coupled with pitch horn <NUM>. Each of sections <NUM>, <NUM>, <NUM> is any suitable geometry to tailor rotor blade aerodynamics to the velocity increase along the rotor blade span. Rotor blade tip section <NUM> comprises an angled geometry such as anhedral, cathedral, gull, and bent, among others. Rotor blade sections <NUM>, <NUM>, <NUM> define a span of rotor blade <NUM> between the axis of rotation A and a distal end <NUM> of tip section <NUM> along a longitudinal axis P between a first edge <NUM> and a second edge <NUM>.

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 <NUM> minute to about <NUM> hour, such as about <NUM> minutes. Additional organic solvent (e.g., from about <NUM> vol% to <NUM> vol% of total volume, such as <NUM> vol%) is then added to the metal alkoxide/acetic acid mixture. An organosilane is then added to the mixture and stirred for from about <NUM> minute to about <NUM> hour, such as about <NUM> minutes. Optionally, a corrosion inhibitor is added to the mixture. The mixture can be deposited onto a material substrate. The deposited mixture may be cured at ambient temperature or can be heated to increase the rate of curing/sol-gel formation.

<FIG> is a flow chart illustrating a method <NUM> of forming a sol-gel <NUM>. As shown in <FIG>, sol-gel <NUM> can be formed by mixing <NUM> one or more sol-gel components. Sol-gel components include two or more of organosilane, metal alkoxide, acid stabilizer, and optionally a corrosion inhibitor. Curing <NUM> the mixed components forms sol-gel <NUM>.

Generally, mixing <NUM> 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 <NUM> includes mixing the sol-gel components to form a mixture (e.g., a solution, a mixture, an emulsion, a suspension, and/or a colloid). In at least one aspect, mixing <NUM> includes mixing all sol-gel components together concurrently. Alternatively, mixing <NUM> 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 <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as about <NUM> wt% to about <NUM> wt%, such as <NUM> wt% or less, such as <NUM> wt% or less, such as <NUM> wt% or less, such as <NUM> wt%.

Mixing <NUM> can include dissolving, suspending, emulsifying, and/or dispersing the sol-gel 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 sol-gel 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-<NUM>-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO). In at least one aspect, an organic solvent is one or more of ethanol, n-propanol, isopropanol, <NUM>-butanol, <NUM>-butanol, <NUM>-pentanol, <NUM>-pentanol, <NUM>-pentanol, <NUM>-hexanol, <NUM>-hexanol, and <NUM>-hexanol. Organic solvents of the present disclosure can be anhydrous, e.g. greater than <NUM> wt% purity. In at least one aspect, a sol-gel formulation has an organic solvent content of from about <NUM> wt% to about <NUM> wt% based on the total weight of the sol-gel formulation, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%.

Additionally or alternatively, mixing <NUM> 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 <NUM> includes mixing solids, powders, and/or viscous liquids, mixing <NUM> can include mixing with a high-shear mixer (e.g., a paint shaker or a planetary-centrifugal 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 <NUM> can be diluted to control selfcondensation reactions and thus increase the pot life of the mixed sol-gel formulation. Mixing <NUM> can include mixing and a weight percent (wt%) of (metal alkoxide + organosilane + acid stabilizer) in the mixture is from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt%.

Mixing <NUM> can include mixing and a weight percent (wt%) of the corrosion inhibitor in the mixture is from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%, about <NUM> wt, about <NUM> wt%. In at least one aspect, a sol-gel formulation contains a corrosion inhibitor and mixing <NUM> includes mixing and a weight percent (wt%) of (metal alkoxide + organosilane + acid stabilizer) in the mixture is from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, for example about <NUM> wt%, about <NUM> wt%, about <NUM> wt%.

In at least one aspect, a molar ratio of acid stabilizer to metal alkoxide in a sol-gel formulation during mixing <NUM> is from about <NUM>:<NUM> to about <NUM>:<NUM>, such as from about <NUM>:<NUM> to about <NUM>:<NUM>, such as from about <NUM>:<NUM> to about <NUM>:<NUM>, for example about <NUM>:<NUM>.

A mixture of sol-gel components can be incubated <NUM> for a period of time, such as from about <NUM> minute to about <NUM> minutes, such as from about <NUM> minutes to about <NUM> minutes, such as from about <NUM> minutes to about <NUM> 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 <NUM> hour to about <NUM> hours, such as from about <NUM> hours to about <NUM> hours, such as about <NUM> hours. Incubating <NUM> may be performed under ambient conditions (e.g., at room temperature) and/or at elevated temperature. Suitable incubation temperatures include from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>, for example about <NUM>.

In at least one aspect, method <NUM> includes coating <NUM> material substrate <NUM> with a mixture comprising sol-gel components and incubating <NUM> the mixture. Incubating <NUM> includes, after mixing the mixture comprising sol-gel components, allowing the mixture comprising sol-gel components to stand at room temp for about <NUM> minutes or more. Coating <NUM> can include wetting the material substrate <NUM> 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 <NUM>. 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 <NUM> for a few minutes (e.g., <NUM>-<NUM> minutes, <NUM>-<NUM> minutes, or <NUM>-<NUM> minutes) and, if necessary, excess, undrained mixture may be blotted off material substrate <NUM> and/or gently blown off material substrate <NUM> by compressed air.

In at least one aspect, coating <NUM> includes cleaning and/or pretreating material substrate <NUM> before wetting the material substrate with the mixture comprising sol-gel components. Generally, sol-gel <NUM> 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 <NUM> does not typically include coating metal substrate <NUM> with an undercoating or forming a chemical conversion coating on metal substrate <NUM>, unless the coating is applied to create a hydroxyl-rich or otherwise improved compatibility with the sol-gel. A material substrate surface can become hydroxyl-rich by depositing silica hydroxylates onto the material surface.

In at least one aspect, methods of the present disclosure include curing a mixture comprising sol-gel components. As shown in <FIG>, curing <NUM> can include drying a mixture comprising sol-gel components disposed on material substrate <NUM> and may be performed under ambient conditions, at room temperature, and/or at elevated temperature. In at least one aspect, a curing temperature is from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>, such as from about <NUM> to about <NUM>, for example about <NUM>, about <NUM>, about <NUM>. Curing <NUM> can be performed for a period of time, such as from about <NUM> minute to about <NUM> hours, such as from about <NUM> minutes to about <NUM> hours, such as from about <NUM> minutes to about <NUM> hours, such as from about <NUM> minutes to about <NUM> hours, for example about <NUM> hour.

After coating <NUM> and/or curing <NUM>, the sol-gel is suitable for exposure to an external environment and/or for application of a secondary layer <NUM>. As shown in <FIG>, depositing <NUM> a secondary layer <NUM> of organic material can be performed before curing <NUM> is completely finished, for example, depositing <NUM> a secondary layer <NUM> is performed at least partially concurrently with curing <NUM>. Depositing <NUM> can include painting, spraying, immersing, contacting, adhering, and/or bonding sol-gel <NUM> with the organic material to form secondary layer <NUM>. A secondary layer includes a paint, a fiber-reinforced plastic, or other suitable organic material.

The extent of protection provided by the present application is determined by the appended claims. Further examples of the disclosure are provided in the following clauses:.

It is to be understood that while the present disclosure has been described in conjunction with the specific aspects thereof, the foregoing description is intended to illustrate and not limit the scope of the present disclosure. Other aspects, advantages and modifications will be apparent to those skilled in the art to which the present disclosure pertains.

Experimental: Materials: <NUM>% AC-<NUM>-<NUM> kit was obtained from <NUM>. <NUM>% AC-<NUM> kit was obtained from <NUM>. <NUM>% AC-<NUM>-<NUM> and <NUM>% AC-<NUM> are each a non-chromate conversion coating for use on aluminum, nickel, stainless steel, magnesium, and titanium alloys. The kits have a Part A, which is an aqueous mixture of acetic acid and zirconium tetra-n-propoxide (TPOZ), and a Part B, which is GTMS. The two components are mixed together (Part A + Part B) and the molar ratio of silicon to zirconium in the mixture is <NUM>:<NUM>. A molar ratio of acetic acid to TPOZ in Part A is <NUM>:<NUM>. As used herein, the combination of (TPOZ/GTMS/ organosilane) is sometimes referred to as a "binder".

Glacial acetic acid (GAA) and glycidoxypropyl-trimethoxy-silane (GTMS) was obtained from Sigma Aldrich, UCT chemicals, Gelest, Inc. , and/or Acros organics. Zirconium tetra-n-propoxide (TPOZ; <NUM>% in n-propanol) was obtained from Sigma Aldrich or Gelest, Inc. A molar ratio of acetic acid to TPOZ is about <NUM>:<NUM>.

Sol-gel formulations were disposed onto a panel, such as a pitch horn of a rotor blade. The pitch horn of the rotor blades comprises steel. All panels were grit-blasted and blown using clean filtered air before depositing a sol-gel formulation onto the panel. The sol-gel formulation was then incubated and cured.

A crack growth test was performed according to ASTM D3762-<NUM> (<NUM>). The steel panels (<NUM>×<NUM>×<NUM> inch [<NUM>×<NUM>×<NUM>] <NUM> annealed steel panels) used in the crack growth test were grit blasted with #<NUM> aluminum oxide grit and compressed air was blown over the panels to remove grit residue. Sol-gel formulations were created and applied to fatigue blade pitch horns (i.e. the grid blasted steel panels) for one minute using drench spray application, followed by air drying for <NUM> minutes. The formulations possessed reduced amounts of water and acetic acid as compared to a standard <NUM>% <NUM> AC-<NUM> sol-gel formulation.

After processing the pitch horn for the first fatigue blade, a small amount of orange, rust-colored tint was visible on the pitch horn and test panels. Therefore, for the second fatigue blade, the amount of glacial acetic acid and the metal alkoxide were reduced to <NUM>% of the amounts of those present in the standard <NUM>% AC-<NUM> formulation. Table <NUM> illustrates the weight content of water, GTMS, TPOZ, and GAA, with remainder balance being reagent grade isopropyl alcohol. The examples in Table <NUM> are not presently claimed.

Solvay/Cytec BR6747-<NUM> epoxy primer was then applied to the surfaces of the steel panels, followed by curing for <NUM> hour at <NUM>°F (<NUM>).

The prepared steel panels were subsequently bonded together using Solvey/Cytec <NUM> lb/ft<NUM> (<NUM>/m<NUM>) FM94 film adhesive, with a <NUM> inch (<NUM>) nonbonded region at one end of the panel to allow insertion of a wedge, followed by curing in an autoclave at <NUM>°F ± <NUM>°F (<NUM> ± <NUM>) and <NUM> psi ± <NUM> psi (<NUM> kPa ± <NUM> kPa). The bondline thickness of the resulting bonded steel panels was <NUM> inch ± <NUM> inch (<NUM> ± <NUM>).

After bonding, <NUM> inch (<NUM>) wide specimens were machined from the bonded panels. To create an initial crack within the bondline, a <NUM>×<NUM>×<NUM> inch (<NUM>×<NUM>×<NUM>) aluminum wedge was inserted <NUM> inch (<NUM>) into the specimen end.

<FIG> are images illustrating bondline crack growth of low alloy steel, process control test specimens, comparing a no sol-gel treated specimen (<FIG>) with a <NUM>% water version of the specimen (<FIG>), where the latter was used to prepare Test Blade #<NUM> for adhesive bonding. The examples shown in <FIG> were exposed at <NUM>°F (<NUM>) and <NUM>-<NUM>% relative humidity during the crack growth test.

The crack length was assessed at <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> hours and, at completion of the test, the test specimens were separated to reveal the extent of bond failure and crack growth. Panels having the cured <NUM> wt% water sol-gel disposed thereon exhibited significant reductions in crack growth and corrosion as compared to panels that were not treated with the formulation disposed thereon. Nonetheless, it was observed that panels having the cured <NUM> wt% water sol-gel disposed thereon exhibited some 'flash rust' on the steel substrate material after treatment with the sol-gel and prior to bonding.

<FIG> is a graph illustrating crack growth test results (according to ASTM D3762) comparing test coupons representing the sol-gel treatments of Table <NUM>, as used on Test Blade #<NUM> and Test Blade #<NUM>, with a grit blasted-only test coupon having no sol-gel disposed thereon (labeled HP9-<NUM> grit blast). As shown in <FIG>, the sol-gel containing examples have much less stress crack growth as compared to an untreated HP9-<NUM> grit blast sample, even though some 'flash rust' is observed on the sol-gel containing examples. The presence of "flash rust," even with the low (e.g., <NUM>%) water formulation, was one reason even lower water content formulations, including <NUM>% water formulations, were tested.

A floating roller peel test was performed according to ASTM D3167-<NUM> (reapproved <NUM>). The floating roller peel (FRP) test possesses several characteristics that are particularly advantageous for evaluating surface preparations for adhesive bonding. Results for FRP tests are shown as pounds per inch of width ("piw"). Adhesive bond failures typically initiate at localized, stress concentration regions in the bondline. The FRP test imparts a high stress-concentration load upon the bondline throughout the duration of the test, and therefore, possesses capability for detecting susceptibility of the bond when exposed to high stress concentrations. Considering that moisture resistance is a desired characteristic to be achieved using the sol-gel approach, the FRP test can also be modified to expose the bondline to moisture during the test.

The thin adherend used in the floating roller peel tests described here was a <NUM> inch (<NUM>), ½ hard <NUM> stainless steel panel. The thin adherend was prepared by: grit blasting with #<NUM> aluminum oxide grit; and applying sol-gel solution to the grit blasted surfaces, followed by air drying for <NUM> minutes; and applying Solvay/Cytec BR6747-<NUM> epoxy primer to the surface, followed by curing for <NUM> hour at <NUM>°F (<NUM>). The thick adherend was a <NUM> inch (<NUM>) <NUM>-T3 aluminum panel. The thick adherend was prepared via a chromic acid anodize process, followed by application of Solvay/Cytec BR6747-<NUM> epoxy primer to the surface.

The FRP test specimens were then assembled by bonding the thin and thick panels together using a Solvey/Cytec FM94 film adhesive possessing an uncured areal weight of <NUM> lb/ft<NUM> (<NUM>/m<NUM>), followed by curing in an autoclave at <NUM>°F ± <NUM>°F (<NUM> ± <NUM>) and <NUM> psi ± <NUM> psi (<NUM> kPa ± <NUM> kPa). After curing, the FRP test specimens possessed a bondline thickness of <NUM> inch ± <NUM> inch (<NUM> ± <NUM>).

In each of the experimental runs described here, three different FRP specimens were tested. One test was performed under standard, room temperature, dry (RTD) conditions to provide a reference RTD test value. A second, room temperature wet (RTW) test was performed using a constant, room temperature, deionized water squirt on the peeling bondline throughout the duration of the test. The third specimen was also tested using the water-squirt technique; however, to provide more evidence with respect to moisture resistance, this specimen was first soaked in <NUM>°F (<NUM>) water for one week, followed by a short room temperature water soak to allow the specimen to equilibrate at ambient temperature, and then tested using the RTW water-squirt peel test.

Table <NUM> illustrates sol-gel formulations of the present disclosure and floating roller peel test results of sol gels formed from the sol-gel formulations. As illustrated in Table <NUM>, sol-gel formulations having <NUM> wt% water can form sol-gels disposed onto steel substrates with excellent FRP properties and had no cloudiness, which indicates that Zr(OH)<NUM> has not formed in the sol-gel formulation. Precipitation and cloudiness in the sol-gel formulation will reduce a sol-gel's ability to bond to a metal surface. Interestingly, cloudiness and precipitation increased as water content was reduced from <NUM> or <NUM> wt% water content, but cloudiness and precipitation began to decrease as water content fell below <NUM> wt%, for example <NUM> wt%. Examples marked * are not presently claimed.

With the <NUM> wt% water sol-gel formulation in mind, additional sol-gel formulations (shown in Table <NUM>) were tested with varying amounts of metal alkoxide and glacial acetic acid. As shown in Table <NUM>, the amounts of TPOZ and GAA can be varied in sol-gel formulations containing <NUM> wt% water and, after curing, the sol-gels formed have excellent FRP properties. These data indicate that sol-gel formulations of the present disclosure provide improved moisture exposure capability, corrosion resistance, and better adhesive bond properties, even when the moisture exposure occurs at the bondline with a metal, as compared to conventional sol-gel compositions having greater water content.

<FIG> is a graph illustrating floating roller peel (FRP) test results comparing pitch horns having <NUM> wt% water sol-gel formulations disposed thereon to a grit blasted test blade having no sol-gel disposed thereon (labeled HP9-<NUM> grit blast). The floating roller peel test (ASTM D3167) was performed at the following test conditions:.

As <FIG> illustrates, pitch horns having sol-gels formed from <NUM> wt% water sol-gel formulations disposed thereon have higher peel strength and are capable of retaining bond strength when exposed to moisture as compared to the grit-blast abrasion approach (HP9-<NUM> grit blast). These data show that sol-gel compositions of the present disclosure provide improved moisture exposure capability, corrosion resistance, and better adhesive bond properties, even when the moisture exposure occurs at the bondline with a metal, as compared to conventional sol-gel compositions having greater water content.

<FIG> are images comparing grit blasted <NUM> low alloy steel panels, including grit-blast-only panels (left, <FIG>), grit blast followed by a {<NUM> minute drench spray + air dry} with <NUM> AC-<NUM>-<NUM> sol-gel (center, <FIG>), and grit blast followed by a {<NUM> minute drench spray + air dry} with <NUM> wt% water sol-gel (right, <FIG>), according to at least one aspect of the present disclosure. During spraying, the panels were tilted so that the aqueous sol-gel or nonaqueous sol-gel would run downwards, so the top portion of each of the aqueous sol-gel panels is a little less corroded than the bottom portion of each of the aqueous sol-gel panels. The images of <FIG> were taken about <NUM> hours after the air dry with no additional humidity or heat exposure to the panels. As shown in <FIG>, corrosion developed on the low alloy steel when treated with the aqueous AC-<NUM>-<NUM> treatment. <NUM> wt% water sol-gel prevents corrosion from occurring on the steel panels (right, <FIG>).

The term "alkyl" includes a substituted or unsubstituted, linear or branched acyclic alkyl radical containing from <NUM> to <NUM> carbon atoms. In at least one aspect alkyl includes linear or branched C<NUM>-<NUM> alkyl. C<NUM>-<NUM> alkyl includes methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosanyl, and structural isomers thereof.

The term "cycloalkyl" includes a substituted or unsubstituted, cyclic alkyl radical containing from <NUM> to <NUM> carbon atoms. In at least one aspect, cycloalkyl is a C<NUM>-<NUM>cycloalkyl or a C<NUM>-<NUM>cycloalkyl.

The term "aryl" refers to any monocyclic, bicyclic or tricyclic carbon ring of up to <NUM> atoms in each ring, wherein at least one ring is aromatic, or an aromatic ring system of <NUM> to <NUM> carbons atoms which includes a carbocyclic aromatic group fused with a <NUM>- or <NUM>-membered cycloalkyl group. Examples of aryl groups include, but are not limited to, phenyl, naphthyl, anthracenyl, or pyrenyl.

The term "alkoxy" is RO-- wherein R is alkyl as defined herein. The terms alkyloxy, alkoxyl, and alkoxy may be used interchangeably. Examples of alkoxy include, but are not limited to, methoxyl, ethoxyl, propoxyl, butoxyl, pentoxyl, hexyloxyl, heptyloxyl, octyloxyl, nonyloxyl, decyloxyl, and structural isomers thereof.

The term "heteroaryl" refers to a monocyclic, bicyclic or tricyclic ring having up to <NUM> atoms in each ring, wherein at least one ring is aromatic and contains from <NUM> to <NUM> heteroatoms in the ring selected from N, O and S. Non-limiting examples of heteroaryl include, but are not limited to, pyridyl, thienyl, furanyl, pyrimidyl, imidazolyl, pyranyl, pyrazolyl, thiazolyl, thiadiazolyl, isothiazolyl, oxazolyl, isoxazoyl, pyrrolyl, pyridazinyl, pyrazinyl, quinolinyl, isoquinolinyl, benzofuranyl, dibenzofuranyl, dibenzothiophenyl, benzothienyl, indolyl, benzothiazolyl, benzooxazolyl, benzimidazolyl, isoindolyl, benzotriazolyl, purinyl, thianaphthenyl and pyrazinyl. Attachment of heteroaryl can occur via an aromatic ring or through a non-aromatic ring or a ring containing no heteroatoms.

The term "heterocyclyl" refers to a non-aromatic <NUM>- to <NUM>-membered monocyclic, bicyclic or tricyclic ring system, wherein at least one ring contains a heteroatom selected from oxygen, sulfur and nitrogen. Each ring may be saturated or partly unsaturated (i.e. comprise one or more double bonds), may comprise oxidized sulfur and/or nitrogen atoms, may comprise quaternized nitrogen atoms, and may be fused to a benzene ring.

The term "ether" refers to an organic group comprising two carbon atoms are separated by a bridging oxygen atom, for example, R'-O-R', wherein R' is alkyl, aryl, heteroaryl, heterocyclyl, or any combinations thereof (e.g. arylalkyl). An ether may, for example, contain more than one bridging oxygen atom. The term "hydroxy" and "hydroxyl" each refers to -OH.

A "nonaqueous" sol-gel includes a sol-gel having <NUM> wt% or less water content, such as a water content from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as from about <NUM> wt% to about <NUM> wt%, such as about <NUM> wt% to about <NUM> wt%, such as <NUM> wt% or less, such as <NUM> wt% or less, such as <NUM> wt% or less, such as <NUM> wt%.

Compounds of the present disclosure include tautomeric, geometric or stereoisomeric forms of the compounds. Ester, oxime, onium, hydrate, solvate and N-oxide forms of a compound are also embraced by the present disclosure. The present disclosure considers all such compounds, including cis- and trans-geometric isomers (Z- and E- geometric isomers), R- and S-enantiomers, diastereomers, d-isomers, l-isomers, atropisomers, epimers, conformers, rotamers, mixtures of isomers and racemates thereof are embraced by the present disclosure.

Claim 1:
A sol-gel formulation comprising:
an organosilane;
a metal alkoxide;
an acid stabilizer; and
an organic solvent, wherein the sol-gel formulation has <NUM> wt% or less water content based on the total weight of the sol-gel formulation,
wherein the sol-gel formulation has from <NUM> wt% to <NUM> wt% organosilane, from <NUM> wt% to <NUM> wt% metal alkoxide, and from <NUM> wt% to <NUM> wt% acid stabilizer based on the total weight of the sol-gel formulation;
wherein the organosilane is:
<CHM>
wherein the metal alkoxide is one or more of 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) tetra-isopentoxide, 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, zirconium (IV) tetra-n-isodecyloxide;
wherein the acid stabilizer is acetic acid; and
wherein the organic solvent is an alcohol selected from ethanol, n-propanol, isopropanol, <NUM>-butanol, <NUM>-butanol, <NUM>-pentanol, <NUM>-pentanol, <NUM>-pentanol, <NUM>-hexanol, <NUM>-hexanol, and <NUM>-hexanol.