Patent Description:
Alloys require corrosion protection in aerospace applications. Conventional sacrificial corrosion inhibition coatings are based on aluminum-ceramic paints with hexavalent chromium compound additives as corrosion inhibitors. However, hexavalent chromium-containing compounds are considered environmental hazards by government agencies around the world. Chromium-free compounds can also lack sufficient corrosion inhibition properties.

Furthermore, cold working processes for aircraft components (e.g., shot peening) will not effectively impart improved mechanical properties to said components when high curing temperatures (e.g., about <NUM> or greater) are used. However, standard industry coatings for aircraft components, and their respective curing temperatures, include ALSEAL <NUM> (<NUM> to <NUM>), NOF Metal Coating GEOMET <NUM> (<NUM> to <NUM>), NOF Metal Coating DACROMET (<NUM> to <NUM>), and Praxair SermeTel W (<NUM> to <NUM>).

<CIT> discloses a chromium-free anticorrosion coating composition for protecting aircraft components, in particular aircraft engine components, comprising: a lithium-potassium silicate matrix; aluminium or aluminium-alloy particles dispersed in the matrix; and corrosion inhibitors. The exemplified coatings are cured at <NUM>.

Therefore, there is a need to develop a chromium-free corrosion inhibition coating, combatable with cold working processes, curable at low temperatures, and with equal or better corrosion inhibition properties as compared to conventional hexavalent chromium-containing compounds.

Embodiments disclosed below not falling under the claims are considered to be only illustrative, without extending the scope of protection solely defined by the appended claims. Disclosed is a corrosion inhibition coating, comprising: a base comprising a silicate matrix, wherein aluminum, an aluminum alloy, or a combination thereof, is present within the silicate matrix; and an inhibitor comprising: zinc molybdate, cerium citrate, magnesium metasilicate, a metal phosphate silicate, or a combination thereof, wherein a curing temperature of the corrosion inhibition coating is about <NUM> to about <NUM>, preferably about <NUM> to about <NUM>.

Also disclosed is a substrate coated with the corrosion inhibition coating.

Referring to <FIG>, a multilayer structure <NUM> includes a corrosion inhibition coating <NUM> coated on a substrate <NUM>. The corrosion inhibition coating <NUM> can comprise an inhibitor <NUM> coated on a base <NUM>. The base <NUM> and the inhibitor <NUM> can be two distinct layers as shown in <FIG>. Referring to the multilayer structure <NUM> of <FIG>, an inhibitor <NUM> can be mixed within a base <NUM> to form a corrosion inhibition coating <NUM> as a single layer. The corrosion inhibition coating <NUM> can be coated on the substrate <NUM>.

The corrosion inhibition coating <NUM> can be a chromium-free corrosion inhibition coating, for example, a chromate-free corrosion inhibition coating, with equal or better corrosion inhibition properties as compared to conventional hexavalent chromium-containing compounds. The corrosion inhibition coating <NUM> can function in a wide range of applications, environments, and temperatures. The corrosion inhibition coating <NUM> is also environmentally friendly. The corrosion inhibition coating <NUM> can inhibit the corrosion of metal, thereby extending the life-time of a substrate <NUM>.

As shown in <FIG>, for example, the corrosion inhibition coating <NUM> can comprise a base <NUM> comprising a matrix and a metal within the matrix. In the coatings disclosed herein, the base can comprise a silicate matrix, wherein aluminum, an aluminum alloy, or a combination thereof, is present within the silicate matrix. For example, the silicate matrix can comprise silicates with low curing temperatures (e.g., less than about <NUM>). For example, the silicate matrix can comprise an alkali metal silicate, for example, sodium silicate, ethyl silicate, potassium silicate, lithium silicate, or a combination thereof. The aluminum alloy present within the silicate matrix can comprise, for example, aluminum-zinc, aluminum-zinc-indium, or a combination thereof.

The corrosion inhibition coating <NUM> can also comprise an inhibitor <NUM>. For example, the inhibitor <NUM> can comprise zinc molybdate (ZnMoO<NUM>), cerium citrate, for example, trivalent cerium citrate (C<NUM>H<NUM>CeO<NUM>), magnesium metasilicate (MgO<NUM>Si), and a metal phosphate silicate. The inhibitor <NUM> can be in the form of a powder.

The corrosion inhibition coating <NUM> can comprise about <NUM>% to about <NUM>% base <NUM> by volume and about <NUM>% to about <NUM>% inhibitor <NUM> by volume. For example, the corrosion inhibition coating <NUM> can comprise about <NUM>% to about <NUM>% base <NUM> by volume and about <NUM>% to about <NUM>% inhibitor <NUM> by volume. The corrosion inhibition coating <NUM> can comprise about <NUM>% to about <NUM>% base <NUM> by volume and about <NUM>% to about <NUM>% inhibitor <NUM> by volume. The corrosion inhibition coating <NUM> can comprise less than or equal to about <NUM>% inhibitor <NUM> by volume. For example, the corrosion inhibition coating <NUM> can comprise less than or equal to about <NUM>% inhibitor <NUM> by volume.

The inhibitor <NUM> can comprise about <NUM>% to about <NUM>% zinc molybdate by weight; about <NUM>% to about <NUM>% cerium citrate, for example, trivalent cerium citrate by weight; about <NUM>% to about <NUM>% magnesium metasilicate by weight; and about <NUM>% to about <NUM>% of a metal phosphate silicate by weight. For example, the inhibitor <NUM> can comprise about <NUM>% to about <NUM>% zinc molybdate by weight; about <NUM>% to about <NUM>% cerium citrate, for example, trivalent cerium citrate, by weight; about <NUM>% to about <NUM>% magnesium metasilicate by weight; and about <NUM>% to about <NUM>% of a metal phosphate silicate by weight. For example, the inhibitor <NUM> can comprise about <NUM>% zinc molybdate by weight; about <NUM>% cerium citrate by weight; about <NUM>% magnesium metasilicate by weight; and about <NUM>% of a metal phosphate silicate by weight.

The inhibitor <NUM> can comprise about <NUM>/<NUM> zinc molybdate by weight; about <NUM>/<NUM> magnesium metasilicate by weight; and about <NUM>/<NUM> of a metal phosphate silicate by weight. The inhibitor <NUM> can comprise about <NUM>% zinc molybdate by weight; and about <NUM>% cerium citrate, for example, trivalent cerium citrate, by weight. The inhibitor <NUM> can also consist of only four components, namely, the zinc molybdate, the cerium citrate, the magnesium metasilicate, and the metal phosphate silicate. For example, the corrosion inhibition coating <NUM> can comprise <NUM>% magnesium metasilicate. The corrosion inhibition coating <NUM> can also comprise <NUM>% chromium.

The metal phosphate silicate of the inhibitor <NUM> can comprise aluminum phosphate silicate, zinc phosphate silicate, calcium phosphate silicate, strontium phosphate silicate, or a combination thereof.

The inhibitor <NUM> can be mixed within the base <NUM>, for example so as to form a single layer <NUM> as shown in <FIG>. For example, the matrix of the base <NUM> can serve as the matrix for the inhibitor <NUM>. The base <NUM> and the inhibitor <NUM> can also be unmixed, for example so as to form two distinct layers as shown in <FIG>. In the case where the base <NUM> and the inhibitor <NUM> form two distinct layers, the inhibitor <NUM> can be coated on the base <NUM> and is thus further from the substrate <NUM> than the base <NUM>.

In the case where the base <NUM> and the inhibitor <NUM> form two distinct layers, the inhibitor <NUM> can further comprise a second matrix. For example, the inhibitor <NUM> can comprise about <NUM>% to about <NUM>% zinc molybdate by volume; about <NUM>% to about <NUM>% cerium citrate, for example, trivalent cerium citrate by volume; about <NUM>% to about <NUM>% magnesium metasilicate by volume; and about <NUM>% to about <NUM>% of a metal phosphate silicate by volume, mixed within the second matrix. For example, the second matrix can be greater than or equal to about <NUM>% by volume of the inhibitor <NUM>. For example, the second matrix can comprise silicate, epoxy, ceramic, or a combination thereof. For example, suitable ceramics can include alumina, beryllia, ceria, zirconia, carbide, boride, nitride, and silicide.

The curing temperature of the corrosion inhibition coating <NUM> will vary depending on the particular matrix used. For example, curing temperatures can be different for silicate, epoxy, and ceramic matrices. Curing duration can also vary with curing temperature. For example, if a higher curing temperature is used, less curing time is required.

In the case where the inhibitor <NUM> is mixed within the base <NUM> so as to form a single layer, the corrosion inhibition coating <NUM> can be cured at a single temperature, corresponding to the matrix used. In the case where the base <NUM> and the inhibitor <NUM> form two distinct layers, two different curing temperatures can be used, corresponding to the matrix used for each layer. For example, the base <NUM> can be cured at a first temperature, followed by addition of the inhibitor <NUM> and curing at a second temperature. For example, a curing temperature of the corrosion inhibition coating can be about <NUM> to about <NUM>, for example, about <NUM> to about <NUM>, for example, about <NUM> to about <NUM>.

The corrosion inhibition coating <NUM> can be coated onto a substrate <NUM>, wherein the substrate is a peened part. Shot peening can refer to a cold working process used to produce a compressive residual stress layer and modify mechanical properties of metals and composites. It can entail impacting a surface with shot (e.g., round metallic, glass, or ceramic particles) with force sufficient to create plastic deformation. Peening a surface can spread it plastically, causing changes in the mechanical properties of the surface. It can avoid the propagation of micro cracks from a surface. Such cracks do not propagate in a material that is under a compressive stress; shot peening can create such a stress in the surface.

The substrate <NUM> can comprise steel, aluminum, zinc, magnesium, alloys of these metals, or a combination thereof. For example, the substrate <NUM> can comprise alloys of these metals. The corrosion inhibition coating <NUM> can function in a wide range of applications and environmental temperatures. For example, the substrate <NUM> can be an aircraft component. For example, the aircraft component can be a propeller blade, a propeller shank, a propeller hub, a propeller barrel, a propeller tulip, a landing gear component, an engine gear, an engine disc, a shaft, for example, an engine shaft, a strut, or a counterweight.

Accordingly, the present disclosure provides a chromium-free corrosion inhibition coating, combatable with cold working processes, curable at low temperatures, and with equal or better corrosion inhibition properties as compared to conventional hexavalent chromium-containing compounds.

Claim 1:
A corrosion inhibition coating, comprising:
a base comprising a silicate matrix, wherein aluminum, an aluminum alloy, or a combination thereof, is present within the silicate matrix; and characterized by further comprising
an inhibitor comprising:
about <NUM>% to about <NUM>% zinc molybdate by weight,
about <NUM>% to about <NUM>% cerium citrate by weight,
about <NUM>% to about <NUM>% magnesium metasilicate by weight, and
about <NUM>% to about <NUM>% a metal phosphate silicate by weight,
wherein a curing temperature of the corrosion inhibition coating is about <NUM> to about <NUM>, preferably about <NUM> to about <NUM>.