GB2583191A

GB2583191A - Method and article

Info

Publication number: GB2583191A
Application number: GB2005583.6A
Authority: GB
Inventors: Trowsdale Andrew; Wilson Andrew
Original assignee: British Steel PLC
Current assignee: British Steel PLC
Priority date: 2019-04-17
Filing date: 2020-04-17
Publication date: 2020-10-21
Anticipated expiration: 2040-04-17
Also published as: GB2583191B; GB202005583D0; GB2593989A; GB202106837D0; GB201905492D0

Abstract

A method of providing a coating on a steel article comprises depositing a first porous layer formed from a metal on at least a part of the surface of the article, providing a second hydrophobic layer on at least part of the first layer by applying a composition comprising a carrier, and removing at least some of the carrier. The first layer preferably comprises one or more of zinc, aluminium or magnesium and the second layer preferably comprises one or both of a silane or a siloxane. The first layer is preferably deposited by thermal spraying, most preferably wire arc spraying. The composition of the second layer preferably comprises a solution, an emulsion or a dispersion, and may be applied by misting, spraying, painting or immersing. Removing the carrier may be performed by heating. The silane may be a triethoxysilane. A railway track installed in a tunnel may comprise the steel article of the invention, wherein the steel article is a rail.

Description

Method and article

Field

The present invention relates to a method of providing a coating on a surface of a steel article and a steel article having such a coating. Particularly, the present invention relates to a coating comprising a plurality of layers, including a first layer and a second layer, wherein the first layer comprises and/or is a porous first layer, having pores therein, formed from a metal and wherein the second layer comprises and/or is a hydrophobic second layer, overlaying the first layer.

Background to the invention

Generally, corrosion of railway rails reduces a longevity and/or an integrity thereof. The rails are typically exposed to moisture, which may be persistent, particularly in sheltered locations such as tunnels. For example, the foot of a rail may sit on wet ground and/or be exposed to a wet, damp or humid environment. Furthermore, the rails may be exposed to salts, elevated electrical potentials and/or temperatures. Hence, corrosion may be accelerated. It is known to apply protective coatings to steel rails. Coatings are typically used to protect against pitting, galling and general loss of section due to corrosion.

Some coatings, such as those based on glass flake epoxy resins or glass flake polyesters, can provide good corrosion protection. However, problems occur when coatings become physically damaged, for example chipped or pulled from the surface. This can occur during transport and handling of rails, for example when using heavy lifting equipment. If any flaws in the coatings are not spotted, they represent a weak point in the rail where corrosion can develop. Other coatings, such as those containing metals for example zinc, aluminium and/or nickel, may be less affected by physical damage but flaws in these coatings may also be problematic. Particularly, penetration of moisture into the flaws may cause localised and/or accelerated corrosion, resulting in blistering of these coatings, thereby increasing a number density and/or area density of flaws.

Hence, there is a need to improve coatings, particularly for rails.

Summary of the Invention

It is one aim of the present invention, amongst others, to provide a method of providing a coating and a steel article having a coating which at least partially obviates or mitigates at least some of the disadvantages of the prior art, whether identified herein or elsewhere. For instance, it is an aim of embodiments of the invention to provide a method of providing a coating that reduces penetration of moisture towards the steel article and/or improves a resistance of the coating to blistering, compared with conventional coatings. For instance, it is an aim of embodiments of the invention to provide a steel article having a coating having an improved corrosion resistance and/or adhesion, compared with conventional coatings.

A first aspect provides a method of providing a coating comprising a plurality of layers, including a first layer and a second layer, on a surface of a steel article, the method comprising: depositing the first layer on at least a part of the surface of the steel article, wherein the first layer comprises and/or is a porous first layer, having pores therein, formed from a metal preferably comprising Zn, Al and/or Mg; and providing the second layer on at least part of the first layer by applying a composition, preferably comprising a silane and/or a siloxane, in a carrier thereon and removing at least some of the carrier, thereby providing the second layer, wherein the second layer comprises and/or is a hydrophobic second layer, preferably comprising the silane and/or the siloxane.

A second aspect provides a steel article having a coating comprising a plurality of layers, including a first layer and a second layer; wherein the first layer overlays at least a part of a surface of the steel article and wherein the first layer comprises and/or is a porous first layer, having pores therein, formed from a metal preferably comprising Zn, Al and/or Mg; and wherein the second layer overlays at least part of a surface of the first layer and wherein the second layer comprises and/or is a hydrophobic second layer preferably comprising a silane and/or a siloxane.

A third aspect provides a railway track, preferably installed in a tunnel, including a steel article having a coating provided according to the first aspect and/or a steel article according to the second aspect, preferably wherein the steel article is a rail having a length in a range from 6 m to 360 m, for example from 15 m to 250 m, preferably in a relatively shorter range from about m to about 60 m for example about 18 m, about 36 m, about 50 m or about 60 m, and/or preferably in a relatively longer range from 60 m to 150 m, more preferably in a range from 90 m to 130 m, for example 108 m or 120 m.

A fourth aspect provides use of a silane and/or a siloxane as a hydrophobic layer on a metal surface such as a porous metal surface, for example wherein the porous metal surface is deposited by thermal spraying.

A fifth aspect provides use of a silane and/or a siloxane as a hydrophobic layer on a metal surface, for example wherein the metal surface is deposited by thermal spraying, electroplating and/or hot dipping.

Detailed Description of the Invention

According to the present invention there is provided a method, an article, a railway and a use, as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description that follows.

Method The first aspect provides a method of providing a coating comprising a plurality of layers, including a first layer and a second layer, on a surface of a steel article, the method comprising: depositing the first layer on at least a part of the surface of the steel article, wherein the first layer comprises and/or is a porous first layer, having pores therein, formed from a metal preferably comprising Zn, Al and/or Mg; and providing the second layer on at least part of the first layer by applying a composition, preferably comprising a silane and/or a siloxane, in a carrier thereon and removing at least some of the carrier, thereby providing the second layer, wherein the second layer comprises and/or is a hydrophobic second layer, preferably comprising the silane and/or the siloxane.

In this way, the coating inhibits penetration of moisture towards the steel article and/or improves a resistance of the coating to blistering, compared with conventional coatings.

Particularly, the hydrophobic second layer, overlaying the first layer, inhibits and/or prevents penetration (i.e. ingress) of moisture (for example, water) into the pores, thereby reducing corrosion of the first layer and/or of the steel article. Blistering conventionally results due to corrosion, for example localized corrosion, of the steel article and/or the metal, such as Zn, Al and/or Mg, for example at and/or proximal to the surface of the steel article. Particularly, the corrosion products, for example oxides, have relatively lower densities compared with Fe or these metals, thereby blistering the coating. However, the second layer reduces and/or eliminates such blistering, by inhibits and/or prevents penetration (i.e. ingress) of moisture (for example, water) into the pores, thereby reducing corrosion of the first layer and/or of the steel article.

Coating The method is of providing the coating comprising a plurality of layers, including the first layer and the second layer, on the surface of the steel article.

It should be understood that the first layer overlays at least a part of the surface of the steel article and the second layer overlays at least a part of the first layer. In one example, the first layer overlays at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably at least 80%, most preferably at least 90%, for example at least 95%, 97.5%. 99% or 100% of the surface of the steel article, by area thereof. In one example, the first layer overlays at most 50%, preferably at most 60%, more preferably at most 70%, even more preferably at most 80%, most preferably at most 90%, for example at most 95%, 97.5%. 99% or 100% of the surface of the steel article, by area thereof. In one example, the second layer overlays at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably at least 80%, most preferably at least 90%, for example at least 95%, 97.5%. 99% or 100% of the first layer, by area thereof. In one example, the second layer overlays at most 50%, preferably at most 60%, more preferably at most 70%, even more preferably at most 80%, most preferably at most 90%, for example at most 95%, 97.5%. 99% or 100% of the first layer, by area thereof. In one example, the first layer overlays at least a part of the surface of the steel article exposed to moisture in use and/or subject to stress, fatigue and/or erosion. In one example, the steel article is a rail and the first layer overlays the foot or a part thereof, for example a bottom of foot and/or sides thereof, and optionally, at least a part of the web extending from the foot towards the head and/or at least a part of the head, for example sides thereof. In one example, the first layer does not overlay the running surface or a part thereof.

In one example, the first layer directly overlays at least a part of the surface of the steel article, without any interlayers therebetween. In one example, one or more interlayers are provided between the surface of the steel article and the first layer.

In one example, the second layer directly overlays at least a part of the first layer, without any interlayers therebetween. In one example, one or more interlayers are provided between the first layer and the second layer.

In one example, the second layer is an outermost layer, without any further layers thereover. In one example, one or more layers are provided on the second layer.

Depositing the first layer The method comprises depositing the first layer on at least a part of the surface of the steel article, wherein the first layer comprises and/or is a porous first layer, having pores therein, formed from a metal preferably comprising Zn, Al and/or Mg.

In this way, the metal of the first layer provides galvanic protection of the steel article. More generally, in one example, the first layer is formed from a metal having a lower electrode potential than the steel article.

Metal Potential with respect to a Cu:Cu804 reference electrode in neutral pH environment (V) Carbon, Graphite, Coke +0.3 Platinum 0 to -0.1 Mill scale on Steel -0.2 High Silicon Cast Iron -0.2 Copper, brass, bronze -0.2 Mild steel in concrete -0.2 Lead -0.5 Cast iron (not graphitized) -0.5 Mild steel (rusted) -0.2 to -0.5 Mild steel (clean) -0.5 to -0.8 Commercially pure aluminium -0.8 Aluminium alloy (5% zinc) -1.05 Zinc -1.1 Magnesium Alloy (6% Al, 3% Zn, 0.15% -1.6 Mn) Commercially Pure Magnesium -1.75 Table 1: Simplified galvanic series to select the metal In one example, the first layer provides a contiguous or a semi-contiguous boundary or interface with the surface of the steel article. Bonding of the first layer with (i.e. to) the steel article (i.e. the surface thereof) may not be complete and/or uniform. In one example, the first layer bonds at least 50%, preferably at least 60%, more preferably at least 70%, even more preferably at least 80%, most preferably at least 90%, for example at least 95%, 97.5%. 99% or 100% of the surface of the steel article overlaid by the first layer, by area thereof. In one example, the first layer bonds at most 50%, preferably at most 60%, more preferably at most 70%, even more preferably at most 80%, most preferably at most 90%, for example at most 95%, 97.5%. 99% or 100% of the surface of the steel article overlaid by the first layer, by area thereof.

In one example, the metal comprises Cu and/or Ag. Cu and/or Ag may provide an antibacterial effect and thereby reduce or prevent bacterial corrosion of the steel. In one example, the metal additionally and/or comprises Zn. ZnO may provide an antibacterial effect and thereby reduce or prevent bacterial corrosion of the steel.

In one example, the metal comprises Zn in an amount of at least 50 wt.%, preferably at least 60 wt.%, suitably at least 70 wt.%, for example at least 75 wt.% or at least 80 wt.%. In one example, the metal comprises Al in an amount of at least 1 wt.%, preferably at least 3 wt.%, suitably at least 5 wt.%, preferably at least 7 wt.%, for example at least 8 wt.% or at least 10 wt.%. In one example, Zn and Al together comprise at least 80 wt.% of the metal, preferably at least 90 wt.%, suitably at least 95 wt.%, for example at least 99 wt%. In one example, the metal comprises from 70 to 95 wt.% Zn and from 5 to 25 wt.% Al, preferably from 80 to 90 wt.% Zn and from 10 to 20 wt.% Al, for example about 82 to 88 wt.% Zn and from about 12 to 18 wt.% Al such as about 85 wt.% Zn and about 15 wt.% Al. In one example, the metal consists essentially of Al and Zn.

In one example, the metal consists of from 5 wt.% to 25 wt.% Al, optionally from 0 to 10 wt.% Mg, optionally from 0 to 5 wt.% Cu, optionally from 0 to 5 wt.% Ag, balance Zn and unavoidable impurities.

The above amounts refer to the content of the metal before deposition and/or as deposited on the steel article. It should be understood that the metal may comprises a different ratio of Zn and/or Al, for example, before deposition, depending on the deposition method. For example, if the metal is applied by thermal spraying, a proportion of a more volatile element may be lost during the deposition.

The metal may be applied to the steel article as an alloy and/or as a pseudo alloy, for example by co-thermal spraying. However, other compounds may form as part of the depositing and/or thereafter. Further compounds which may be present in the coating include oxides, hydroxides, carbonates and/or mixtures thereof. For example, the further components may include: an oxide, for example zinc oxide, aluminium oxide and/or mixed zinc -aluminium oxide; a hydroxide, for example zinc hydroxide, aluminium hydroxide and/or mixed zinc -aluminium hydroxide; a carbonate, for example zinc carbonate, aluminium carbonate, and/or mixed zinc -aluminium carbonate; and/or mixtures thereof.

In one example, depositing the first layer comprises thermal spraying, preferably arc spraying (also known as wire arc spraying), the metal onto the surface of the steel article.

Generally, thermal spraying methods are processes in which melted (or heated) materials are sprayed onto a surface (i.e. of the steel article). The "feedstock" (coating precursor) is heated by electrical (plasma or arc) or chemical means (combustion flame). Thermal spraying can provide thick coatings (i.e. the first layer) (approximate thickness range is 20 microns to several mm, depending on the process and feedstock), over a large area and/or of a specific targeted area of a large article at high deposition rate as compared to other coating processes such as electroplating, physical and chemical vapor deposition. Coating materials available for thermal spraying include metals, alloys, ceramics, plastics and composites. They are fed in powder or wire form, heated to a molten or semimolten state and accelerated towards substrates in the form of micrometer-size particles. Combustion or electrical arc discharge is usually used as the source of energy for thermal spraying, for example high velocity oxy-fuel coating spraying (HVOF). Resulting coatings are made by the accumulation of numerous sprayed particles. The surface may not heat up significantly, allowing the coating of flammable substances. Coating quality is usually assessed by measuring its porosity, oxide content, macro and micro-hardness, bond strength and surface roughness. Generally, the coating quality increases with increasing particle velocities.

In one example, the thermal spraying is selected from a group comprising: plasma spraying, detonation spraying, wire arc spraying, flame spraying, high velocity oxy-fuel coating spraying (HVOF), high velocity air fuel (HVAF), warm spraying and cold spraying.

Wire arc spray is a form of thermal spraying where two consumable metal wires are fed independently into the spray gun. These wires are then charged and an arc is generated between them. The heat from this arc melts the incoming wire, which is then entrained in an air jet from the gun. This entrained molten feedstock is then deposited onto a substrate with the help of compressed air, which solidifies as splat particles. This process is commonly used for metallic, heavy coatings.

Plasma transferred wire arc (PTWA) is another form of wire arc spray which deposits a coating on the internal surface of a cylinder, or on the external surface of a part of any geometry. It is predominantly known for its use in coating the cylinder bores of an engine, enabling the use of Aluminum engine blocks without the need for heavy cast iron sleeves. A single conductive wire is used as "feedstock" for the system. A supersonic plasma jet melts the wire, atomizes it and propels it onto the substrate. The plasma jet is formed by a transferred arc between a nonconsumable cathode and the type of a wire.

After atomization, forced air transports the stream of molten droplets onto the bore wall. The particles flatten when they impinge on the surface of the substrate, due to the high kinetic energy. The particles rapidly solidify upon contact. This is similar for all spraying processes.

The stacked particles make up a high wear resistant coating. The PTWA thermal spray process utilizes a single wire as the feedstock material. All conductive wires up to and including 0.0625" (1.6 mm) or larger can be used as feedstock material, including "cored" wires. PTWA can be used to apply a coating to the wear surface of engine or transmission components to replace a bushing or bearing. For example, using PTWA to coat the bearing surface of a connecting rod offers a number of benefits including reductions in weight, cost, friction potential, and stress in the connecting rod.

In one example, the first layer has a thickness in a range from 10 pm to 1000 pm, preferably in a range from 50 pm to 500 pm, more preferably in a range from 125 pm to 400 pm, even more preferably in a range from 175 pm to 375 pm, most preferably in a range from 225 pm to 325 pm, for example 250 pm.

It should be understood that the first layer comprises and/or is a porous layer, having pores therein.

In one example, the first layer is not fully consolidated (i.e. having a density less than the density of the metal), wherein the first layer comprises and/or is a porous layer, having pores therein. The presence of the pores may render the first layer pervious or semi-pervious to moisture and/or corrosive media, thereby reducing protection, for example galvanic and/or physical protection, due to the first layer of the steel article.

Porosity is a normal feature of thermal spray processes. Thermal spray is a very dynamic process, involving thermal, kinetic and chemical processes. There are some special issues with porosity in thermal spray coatings. Porosity, also referred to as void fraction, is a measure of the void space (or empty space, i.e. nothing) in a material. It is typically characterized as a percentage, between 0 and 100%, of the volume of voids within the total volume. It can take on a number of forms: open, closed, interconnected, elongated, etc. To understand the porosity associated with thermal spray processes, consider how the build is made. A coating is developed by the build-up of semi-molten spherical and irregular particles.

The build can be considered to follow the same type of dynamics associated with packing of spheres in a volume. For example, assuming that the powder is spherical, of uniform size and deposited such that a simple cubic lattice is developed, the packing density for this structure is 0.524. The porosity or void fraction is therefore 0.476 or 48%. If instead of a simple cubic lattice arrangement, a hexagonal or cubic close pattern is assumed, the calculated packing density is 0.7045, giving a porosity void fraction of 0.2955 or 30%. In the study of packing of spheres in a volume, it is possible to calculate the packing density of randomly stacked spheres in a volume. In this case, the packing density is 0.640, giving a void fraction of 0.360 or 36%. Generally, anything done to the coating from this point (non-spherical particles, nonuniform size, particle compression, etc.), reduces the porosity. For example, the porosity of closely packed, circular flat disks is 9%. The upper limit for porosity or void fraction for a thermal spray build is probably around 30%.

There are some other factors regarding the porosity in thermal spray coatings.

First, unlike the porosity in products such as Swiss cheese, which is uniformly distributed throughout, no matter which way you slice it, porosity in a thermally applied coating is layered. It is a lamellar structure. Think of the cross-section of a roll of bubble wrap where you have both closed cells and connected cells. Thermal spray builds layered coatings or structures with semi-molten particles, often trapping air or process gasses between particles into both closed singular cells and connected cells. In addition, the voids can take on a number of forms including cracks.

Second, thermal spray porosity is normally measured using a destructive test. A sample or coupon is prepared using the specified spray parameters and then destroyed in the measurement. Porosity of the end product is normally not determined.

Third, while porosity is a volumetric condition, in thermal spray coatings, it is usually measured as a two-dimensional property (area porosity). In some thermal spray operations, porosity is essential. For example, the hydroxyapatite (HA) coatings used for prosthetic implants depend on the open-pore structure for attachment by bone growth. For a thermal barrier coating (TBC) used in gas turbines, some of the insulating properties are due to the porosity of the coating which runs from 7% to 15%.

On the other hand, porosity can be a problem. For example, porosity can jeopardize the structural integrity of a coating. Corrosion protection coatings can fail if the porosity allows a direct path to the substrate. Highly polished coatings such as the tungsten carbide coating of plungers used in the manufacture of bottles can lead to flaws in the finished product.

Porosity is one of the most common quantitative parameters used to characterize the microstructure of a thermally sprayed deposit. This is even though the total porosity of the deposit does not have significant meaning from the viewpoint of quantitative interpretation of deposit properties".

The measurement of porosity is known to the skilled person. A number of means are available to measure porosity but the most popular for thermally sprayed coatings is Light Microscope Image Analysis. Besides porosity, this procedure allows for checking the thickness, interfaces, unmelted particles, any detachment and any contamination.

ASTM E2109-01 (2007), "Test Methods for Determining Area Percentage Porosity in Thermal Sprayed Coatings" covers procedures to perform porosity ratings on metallographic specimens. Specimens are prepared in accordance with ASTM E 1920.

While this is an area measurement, it is essentially equal to the porosity of the volume as long as the pores are small and uniformly distributed and/or sufficiently representative samples are obtained to avoid sampling bias, for example.

Preparation of the coupon includes sectioning, cleaning, mounting, grinding and polishing prior to microscopic inspection. Care is essential during preparation to avoid adversely influencing the results by smearing of material into voids or detaching singular particles.

Sample preparation for optical microscopy may be a destructive test and is therefore not always performed on the end product. The frequency of testing will vary according to the need.

In some cases, a single qualifying sample is sufficient. In other cases, a test coupon is sprayed concurrently with each part being coated.

Porosity determination can be by comparison to standard images or by the use of automatic image analysis equipment. One automatic image analysis technique is to first develop a gray scale image of the specimen, generate a gray scale histogram of the image, establish a gray scale threshold and determine the area percentage (percentage of pixels in the image) that is less than that threshold. Additionally and/or alternatively, line fractions of polished samples may be used for point counting.

Generally, porosity determination by infiltration of coatings is not practical and/or reliable. Mercury porosimetry may be performed according to ASTM D4284 -12(2017)e1, for example. Other methods of porosity determination of coatings are known.

Both the thermal spray process and the powder morphology can influence the porosity of the final coating structure. For example, the porosity of a coating from powder that is fused and crushed is generally lower than the porosity of a coating from powder that has been agglomerated and sintered. Also, HVOF coatings generally have a porosity that is lower than a coating produced by an electric arc process.

Post processing can also reduce coating porosity. In a sintering process, metal or ceramic particles are raised to an elevated temperature where, through diffusion driven by the reduction of surface energy, the pores reduce in size, leading to an overall decrease in porosity.

In summary, porosity is used to characterize and qualify the microstructure of thermally sprayed coatings, it can be controlled and adjusted within some limits, there are difficulties in measuring it but outside lab services are available for determination of the porosity of a coating.

In one example, the first layer has a porosity in a range from1 % to 50%, preferably in a range from 1 % to 25 %, preferably from 5 % to 20%, for example 7 % or 10 % or 15 % by volume. Porosity of the first layer may be determined as described herein.

The liquid displacement method to evaluate bulk material density (ASTM B962 and B963) can be readily adapted to thermally sprayed coatings. An alternative liquid displacement method consists of producing coatings on a thin mild steel strip, after which the steel strip is dissolved away by immersion in an acid solution. The remaining strip is used for density measurement.

The strip is accurately weighed prior to being coated with a lacquer of known density, and again after coating. The coated strip is suspended in a beaker of de-mineralised and de-aerated water and weighed while immersed. The coating density can then been calculated.

It is often necessary to measure the porosity levels in a coating as well as the density. A cross section of the coated test piece is prepared (mounted and polished) and observed using an optical or scanning electron microscope (SEM). Pores and oxide area are determined using an image analyser, and the level of porosity calculated as volume fractions.

The porosity level can also be determined using commercially available mercury intrusion porosimetry (MIP). The method consists of evacuating the sample and immersing in mercury at low pressure. The mercury is then pressurised; corresponding volumes of intruded mercury are measured at a series of pressures. The pore diameter can be calculated. This method enables the total porosity and pore distribution to be determined.

B962 -Standard Test Methods for Density of Compacted or Sintered Powder Metallurgy (PM) Products Using Archimedes' Principle.

B963 -Standard Test Methods for Oil Content, Oil-Impregnation Efficiency, and Surface-Connected Porosity of Sintered Powder Metallurgy (PM) Products Using Archimedes' Principle.

Cleaning In one example, the method comprises cleaning the at least a part of the surface of the steel article before depositing the first layer thereon, for example by washing in hot water (from 70 °C to 95 °C, for example 85 °C) with a detergent and/or caustic additive and drying. In this way, the surface of the steel article may be degreased.

Roughening In one example, the method comprises roughening the at least a part of the surface of the steel article before depositing the first layer thereon, for example by blasting with suitable media such as steel grit and/or chilled iron grit, for example grit blasting such as using H grade grit, preferably after cleaning.

In one example, a surface root mean square (RMS) roughness of the surface of the steel article after roughening is from 1 to 100 pm. The RMS roughness may be determined from 3D surface texture measurements, for example.

In one example, cleanliness of the surface of the steel article after cleaning and/or roughening meets at least ISO 8501-1:2007 Sa 2, preferably Sa 2.5, more preferably Sa 3.

Providing the second layer The method comprises providing the second layer on at least part of the first layer by applying a composition, preferably comprising a silane and/or a siloxane, in a carrier thereon and removing at least some of the carrier, thereby providing the second layer, wherein the second layer comprises and/or is a hydrophobic second layer, preferably comprising the silane and/or the siloxane.

It should be understood that the silane refers to a compound having four substituents on Si, rather than SiH4.

Particularly, the inventors have determined that the hydrophobic second layer, overlaying the first layer, inhibits and/or prevents penetration (i.e. ingress) of moisture (for example, water) into the pores, thereby reducing corrosion of the first layer and/or of the steel article.

Without wishing to be bound by any theory, it is thought that the silane and/or the siloxane undergo hydrolysis and/or condensation reactions on the surface of the metal of the first layer, for example by reacting with Zn, ZnO, Al and/or A1203, leading to the formation of the second layer having inorganic metal-siloxane bonds and an organic Si-O-Si network, thereby providing the hydrophobic second layer and better protecting the metal and/or the steel article against corrosion. Particularly, it is thought that the composition penetrates into pores accessible from the outer surface of the first layer, including interconnected pores, for example by capillary action (i.e. wicking). Upon removal of the carrier, for example by evaporation, the silane and/or siloxane remains in the pores, particularly on the exposed surfaces thereof and undergo the hydrolysis and/or condensation reactions, as described above. In one example, applying the composition comprises entering, by the composition, at least some of the pores.

In one example, the composition comprises an acrylic resin, an epoxy, a urethane, a silane, a silicate, a siliconate and/or a siloxane.

Generally, silanes are saturated chemical compounds consisting of one or multiple silicon atoms linked to each other or one or multiple atoms of other chemical elements as the tetrahedral centers of multiple single bonds. By definition, cycles are excluded, so that the silanes may, for example, comprise a homologous series of inorganic compounds with the general formula SinH2,,÷2. Commercially available silanes are synthetically derived.

Each silicon atom has four bonds (either Si-H or Si-Si bonds), and each hydrogen atom is joined to a silicon atom (H-Si bonds). A series of linked silicon atoms is known as the silicon skeleton or silicon backbone. The number of silicon atoms is used to define the size of the silane (e.g., Siz-silane).

Related to silanes, for example, is a homologous series of functional groups, side-chains or radicals with the general formula SinH2n+2. Examples include silyl and disilanyl.

The simplest possible silane (the parent molecule) is silane, SiH4. There is no limit to the number of silicon atoms that can be linked together, the only limitation being that the molecule is acyclic, is saturated, and is a hydrosilicon.

In one example, the silane is a linear or a branched silane.

In one example, the silane is a triethoxysilane, for example selected from a group comprising triethoxy(octyl)silane (TEOS) (also known as Octyltriethoxysilane (OTES)), 3-aminopropyltriethoxysilane and triethoxy(2,4,4-trimethylpentyl)silane. TEOS is especially preferred, preferably in an aqueous carrier.

In one example, the silane is R1Si(OR2)3 wherein R1 is a lower alkyl group, a phenyl group or an N-(2-aminoethyl)-3-aminopropyl group, and R2 is a lower alkyl group.

In one example, the silane is RInSi(OR2)4_,, where R1 is a lower alkyl group, phenyl group, 3,3,3-trifluoropropyl group, y-glycidyloxypropyl, y-methacryloxypropyl group, N-(2-aminoethyl)-3-aminopropyl group or aminopropyl group, R2 is a lower alkyl group; and n is a number of 1 or 2.

In one example, the silane is R1Si(OR2)3 wherein R2 is a lower alkyl group, a phenyl group or a functional group, including at least one of vinyl, acrylic, amino, mercapto, or vinyl chloride functional group; and R2 is a lower alkyl group. As examples of silanes of formula R1Si(OR2)3 wherein R1 is an alkyl group or aryl group, mention may be made of, for example, methyltrimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxy silane, n-butyltrimethoxy silane, isobutyltrimethoxy silane, phenyltrimethoxy silane, preferably methyltrimethoxy silane. In the case where R1 is a functional group, mention may be made, for example, of N-(2-aminoethyl)-3-aminopropyltrimethoxy silane, 3-mercaptopropyltrimethoxy silane, 3-mercaptopropyltriethoxy silane, 3-aminopropyltriethoxy silane, 3-(meth)acryloxypropyl trimethoxy silane, 3-(meth)acryloxypropyltriethoxy silane, n-phenylaminopropyltrimethoxy silane, vinyltriethyoxy silane, vinyltrimethoxy silane, allyltrimethoxy silane, and any of the aminosilane catalysts.

As used herein, the expression "functional group" is intended to include any group, other than hydroxyl, (including alkoxy, aryloxy, etc.), which is hydrolyzable to provide, in situ, a reactive group (e.g., reactive hydrogen) which will react, in other than a condensation reaction, with the substrate (e.g., metal), itself, or other reactive components in or from the coating composition.

The functional groups, in addition to the hydroxyl group (by hydrolysis of the (OR2) groups), tend to form three-dimensional or cross-linked structure, as well known in the art.

Moreover, in the various embodiments of the invention, it is may be preferred to use mixtures of two or more silane compounds of formula R1Si(OR2)3. Mixtures of at least phenyltrimethoxysilane and methyltrimethoxysilane may be preferred for some applications.

Generally, total amounts of silane compounds of formula R1Si(OR2)3 will fall within the range of from about 40 to about 90 percent by weight, preferably from about 50 to about 85 percent by weight, based on the total weight of silanes, acid component and water.

Generally, a siloxane is a functional group in organosilicon chemistry with the Si-O-Si linkage.

The parent siloxanes include the oligomeric and polymeric hydrides with the formulae H(OSiH2),,OH and (OSiH2),1. Siloxanes also include branched compounds, the defining feature of which is that each pair of silicon centres is separated by one oxygen atom. The siloxane functional group forms the backbone of silicones, the premier example of which is polydimethylsiloxane. The functional group R3Si0-(where the three Rs may be different) is called siloxy.

In one example, the siloxane has the formula R2 0 Si -O R2 -n.

(i.e. a polysiloxane) wherein each RI is selected from a hydroxy group or alkyl, aryl, or alkoxy groups having up to six carbon atoms, each R2 is selected from hydrogen or alkyl or aryl groups having up to six carbon atoms, and where n is selected so that the molecular weight for the polysiloxane is in the range of 400 to 10,000.

In one example, the composition comprises more than one silane and/or more than one siloxane.

Generally, the silane is the smallest molecular compound of commonly available penetrating sealers for concrete. In contrast, the siloxane is the largest molecular compound of commonly available penetrating sealers for concrete. Surprisingly, the inventors have identified that penetrating sealers for concrete may be effective as the composition.

In one example, the composition comprises and/or is Rust-oleum (RTM) PREVOSIL SPECIAAL WB (i.e. a water based, WB, composition) (available from Rust-oleum Industrial, IL, USA) and/or ProPERLA (RTM) Water Repellent (available from ProPERLA UK Ltd), Stone Sealer LTP (available from httns://www ifo-online.co.uk/).

Section 3 of the Safety Data Sheet for Rust-oleum (RTM) PREVOSIL SPECIAAL WB (available from fillps:L/www,prpche0ilsg.euf5tatiOsgtety0eelinsgs_pleyosil wb wisicif; version 2.02; Date of issue/Date of revision 20/10/2017) states: 1SECTION 3: Composition/information on ingredients 3.2 Mixtures it Mixture There me ne additiona ngredients present vhIch, within the current knowledge of the supplier and in the concentrations applicable, are ctas-ified as hazardous to health or the environment, are PBTs. vPvBs. or Substaiees of equivalent concern, or have been assigned a workplace exposure limit and hence require repOrtitiG in this section.

SYSE

[1] Substance ciessified with a health or orivinmental hazard [21 Substance with a sitorkpieoe exposure limit [3] Substance meets the criteria for PST according to Reguiation EC) No. 190712006. Anne * Xi l 1:43 Substance Mean 'MG. Clitoris for vPvB according to Regiilation pEC) No 1907/200e, Annex [5] Substance of equivalent concern Occupational exposure Omits, if available, are listed in Section 8.

The Safety Data Sheet for ProPERLA (RTM) Masonry Crème (related to Water Repellent) (available from https://www.goog Ie. com/u rl?sa=t&rct=j&g =&esrc=s&so u rce=web&cd=l&cad=rja&u act=8&ved =22 hUKEwijttOpio7oAhVTfMAKHcsg B3sQ FjAAegQ IB BAB&u rl=https%3A%2 F/02 Fwww. prope da.co.uk%2Fwp-content%2Fuploads%2F2017%2F06%2FMasonry-Creme-Safetysheet. pdf&usg=A0vVaw0MCz6h7ROU62jgJn-leYnN; version: 1; Date of print: 24.02.2014), states: Safety Data Sheet (1907/2006/EC) In one example, a viscosity of the composition is sufficiently low to enable entrance of the composition into the pores.

In one example, the second layer has a thickness in a range from 1 to 250 nm, preferably 5 to 125 nm, more preferably in a range from 10 to 50 nm.

In one example, providing the second layer on at least part of the first layer by applying the composition comprises infusing, permeating, impregnating, soaking and/or saturating the composition into the at least part of the first layer, for example by misting, spraying, painting du rettient Moths. octylsitane EC: 2204341-2 CAS: 2943-75-1 ?Ai See Section 16 for the foil text of the H statements declared above, Manorial: MOPERIA -Masonry creme vs:sMon: l tato cC print: .nt.7014 26S-Iict 7 hydrocaretons 252.555"- ?,F,435-21-3 niethss447,4n-thinethv;pentyllsik ",.

and/or immersing the at least part of the first layer with the composition. In one example, providing the second layer on at least part of the first layer by applying the composition comprises penetrating the composition through at least part of the first layer towards the surface of the steel article, preferably to the interface between the first layer and the steel article (i.e. the surface thereof).

In one example, the composition comprises an acrylic resin, an epoxy, a urethane, a silane, a silicate, a siliconate and/or a siloxane, preferably a silane and/or a siloxane, in the carrier in an amount in a range from 0.5 wt.% to 50 wt.%, preferably in a range from 0.75 wt.% to 25 wt.%, more preferably in a range from 1.0 wt.% to 15 wt.%, most preferably in a range from 1.5 wt.% to 7.5 wt.% by mass of the composition.

In one example, applying the composition comprises misting, spraying, painting and/or immersing the at least part of the first layer with the composition, for example at a coverage (by area of the steel article) from 50 ml m-2 to 500 ml m-2, preferably from 100 ml m-2 to 300 ml m-2, more preferably from 150 ml m-2 to 250 ml m-2, for example 200 ml m-2 and optionally, allowing the composition to penetrate into the first layer.

In one example, the carrier comprises and/or is an aqueous carrier (i.e. water). In one example, the carrier comprises and/or is an organic carrier.

In one example, the composition comprises and/or is a solution, an emulsion and/or a dispersion, preferably an aqueous solution.

Aqueous carriers and/or aqueous solutions (i.e. water based) are preferred. Particularly, applying the composition proximal a thermal sprayer, for example, precludes and/or complicates use of compositions including flammable carriers.

In one example, removing at least some of the carrier is by evaporation of the carrier. In one example, removing at least some of the carrier comprises heating the second layer, for example using radiant lamps. In this way, removing of the carrier may be accelerated and/or an increased amount of the carrier removed.

In one example, the method comprises providing the second layer on at least part of the first layer comprises providing the second layer on at least part of the newly-deposited first layer. In this way, the second layer is provided on the newly-deposited first layer (i.e. immediately after, within 60 minutes, preferably within 30 minutes, more preferably within 15 minutes of depositing the first layer), before contamination thereof and/or moisture penetration therein.

The steel article may be as described with respect to the second aspect.

Steel article The second aspect provides a steel article having a coating comprising a plurality of layers, including a first layer and a second layer; wherein the first layer overlays at least a part of a surface of the steel article and wherein the first layer comprises and/or is a porous first layer, having pores therein, formed from a metal preferably comprising Zn, Al and/or Mg; and wherein the second layer overlays at least part of a surface of the first layer and wherein the second layer comprises and/or is a hydrophobic second layer preferably comprising a silane and/or a siloxane.

In this way, the steel article has a coating having an improved corrosion resistance and/or adhesion, compared with conventional coatings The steel article, the coating, the plurality of layers, the first layer, the second layer may be as described with respect to the first aspect.

In one example, the steel article comprises and/or is a rolled section, a hot-rolled rail section such as a rails or a profile including a sleeper, a drawn section such as bar, rod or wire, an extruded section, and/or a castings. In one example, the steel article is a railway track part (also known as a component). In one example, the steel article comprises a rail, a flat-bottom rail, a flat-bottom vignole rail, a crane rail, a tram rail, a grooved rail, a check rail, a conductor rail, a fish plate, a clip, a fastener, a base plate, a sleeper, a switch, a crossing and/or a switch blade.

In particular, steels that may be used in the present invention include steels according to rail standards and grades as detailed below and, commonly used structural steels such as EN 10025 grades S235, 5275, 5355, and S450, and equivalent standards and/or grades. Suitable steel compositions include those commonly used in rails according to standards such as UIC 860-0, EN 13674-1, EN 13674-2, IRS, British Steel standards, AREMA and/or EN 14811. For example, suitable steel compositions include UIC 860-0 Grades 700, 900A and 900B; EN 13674-1 grades R200, R220, R220G1, R260, R260V, R260Mn, R350HT, R350LHT and R370CrHT; EN 13674-2 grade R260Cr; IRS grades 880 and 1080HH; British Steel grades ML200, ML260, ML330, BLF320, BLF360, HP335, SF350, SFL350, MHH375 and MHH388; AREMA grades carbon standard, low alloy standard, low alloy intermediate, carbon high strength and low alloy high strength; EN 14811.

In one example, the steel article comprises 0.1 to 1.5 wt.% carbon, suitably from 0.2 to 1.3 wt.%, preferably from 0.25 to 1.25 wt.%, suitably from 0.3 to 1.2 wt.%, for example from 0.35 to 1.1 wt.%. In one example, the steel article comprises from 0.01 to 2.0 wt.% or 0.01 to 1.5 wt.% silicon, preferably 0.05 to 1.2 wt.%, preferably from 0.1 to 1.1 wt.%. In one example, the steel article comprises from 0.1 to 2.5 wt.% manganese, preferably from 0.25 to 2.2 wt.%, more preferably from 0.5 to 2 wt.%, suitably from 0.6 to 1.8 wt.%. In one example, the steel article comprises chromium in an amount of from 0.1 to 3 wt.%, for example from 0.5 to 1.5 wt.%. In one example, the steel article comprises less than 0.2 wt.% (by mass) chromium. Suitably the steel rail comprises less than 0.5 wt.% phosphorous, preferably less than 0.05 wt.% phosphorous. In one example, the steel article comprises less than 0.005 wt.% aluminium. In one example, the steel article comprises less than 0.25 wt.% vanadium. In one example, the steel article comprises less than 0.02 wt.% nitrogen. In one example, the steel article comprises 0.25 to 1.25 wt.% carbon, 0.05 to 1.2 wt.% silicon and 0.5 to 2 wt.% manganese.

In one example, the second layer overlays at least a part of the surface of the pores in the first layer.

In one example, the second layer at least partially fills the pores in the first layer.

In one example, the silane is a triethoxysilane, for example selected from a group comprising triethoxy(octyl)silane, 3-aminopropyltriethoxysilane and triethoxy(2,4,4-trimethylpentyl)silane.

In one example, the first layer consists of from 5 wt.% to 25 wt.% Al, optionally from 0 to 10 wt.% Mg, optionally from 0 to 5 wt.% Cu, optionally from 0 to 5 wt.% Ag, balance Zn and unavoidable impurities.

In one example, the first layer has a thickness in a range from 10 pm to 1000 pm, preferably in a range from 50 pm to 500 pm, more preferably in a range from 125 pm to 400 pm, most preferably in a range from 225 pm to 325 pm, for example 250 pm.

In one example, the steel article is a rail, a structural section or a profile.

In one example, the steel article is a rail having a length in a range from 6 m to 360 m, for example from 15 m to 250 m, preferably in a relatively shorter range from about 15 m to about 60 m for example about 18 m, about 36 m, about 50 m or about 60 m, and/or preferably in a relatively longer range from 60 m to 150 m, more preferably in a range from 90 m to 130 m, for example 108 m or 120 m.

The adherence of a coating to a steel article may be measured according to ASTM D4541 09 Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers or ASTM D4541 -17 Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers.

Suitably the adherence of the coating as measured according to ASTM D4541, as described above, is increased by at least 5%, suitably at least 10%, preferably at least 15%, for example at least 20% compared with a coating not including the second layer. The increased adherence of the coating to the steel article reduces the likelihood that the coating will be chipped or cracked during transport and installation. Therefore, the coating is more likely to be maintained for longer before breaching. As a result, there is a reduced likelihood of corrosion or failure of the steel. Suitably the adherence of the coating as measured according to ASTM D4541, as described above, is in a range from 3 to 30 MPa, in a range from 4 to 29 MPa, in a range from 5 to 28 MPa, in a range from 6 to 26 MPa, preferably in a range from 7 to 20 MPa.

The increased adherence of the coating to the steel article in this range reduces the likelihood that the coating will be chipped or cracked during transport and installation, as described above, while also permitting deliberate removal of the coating if desired, for example for preparation for welding, particularly in situ welding of installed rails. Some conventional coatings may require chemical removal such that preparation for in situ welding of installed rails is not possible and/or complex. Hence, by providing the increased adherence of the coating to the steel article in this range improves protection of the steel article due to the coating while facilitating joining and/or repair, if required.

The present invention may also provide one or more further benefits for example improved abrasion resistance, increased impact resistance, improved wear resistance, improved stray current resistance and/or improved prohesion performance compared with conventional coatings.

Railway track The third aspect provides a railway track, preferably installed in a tunnel and/or subject in use to accelerated corrosion conditions (i.e. moisture, flooding, corrosive liquids for example biological fluids such as excreted fluids including urine, including a steel article having a coating provided according to the first aspect and/or a steel article according to the second aspect, preferably wherein the steel article is a rail having a length in a range from 6 m to 360 m, for example from 15 m to 250 m, preferably in a relatively shorter range from about 15 m to about 60 m for example about 18 m, about 36 m, about 50 m or about 60 m, and/or preferably in a relatively longer range from 60 m to 150 m, more preferably in a range from 90 m to 130 m, for example 108 m or 120 m.

In one example, the steel article comprises a rail, a flat-bottom rail, a flat-bottom vignole rail, a crane rail, a tram rail, a grooved rail, a check rail, a conductor rail, a fish plate, a clip, a fastener, a base plate, a sleeper, a switch, a crossing and/or a switch blade. Use

The fourth aspect provides use of a silane and/or a siloxane as a hydrophobic layer on a metal surface such as a porous metal surface, for example wherein the porous metal surface is deposited by thermal spraying.

Brief description of the drawings

For a better understanding of the invention, and to show how exemplary embodiments of the same may be brought into effect, reference will be made, by way of example only, to the accompanying diagrammatic Figures, in which: Figure 1 schematically depicts a method according to an exemplary embodiment; Figure 2 is a photograph of a comparative example of a steel article (Comparative Example 1); Figure 3 is a photograph of a steel article according to an exemplary embodiment (Example 1); Figure 4 is a photograph of the steel article of Figure 3, in more detail; Figure 5 is a photograph of the steel article of Figure 3, in more detail; Figure 6 is a photograph of a comparative example of a steel article (Comparative Example 1) and steel articles according to exemplary embodiments (Example 1, Example 2) immersed in a heated and stirred water bath; Figure 7 is a photograph of a comparative example of a steel article (Comparative Example 1) after immersion in the heated and stirred water bath; Figure 8 is a photograph of a steel article according to an exemplary embodiment (Example 1) after immersion in the heated and stirred water bath; Figure 9 is a micrograph of a cross-section through the surface of a steel article according to an exemplary embodiment (Example 1); Figure 10 is a contrast-enhanced micrograph of a cross-section through the surface of a steel article according to an exemplary embodiment (Example 1), Figure 11 shows mass spectra of compounds included in a composition applied in a method according to an exemplary embodiment; and Figure 12 shows mass spectra of compounds included in a composition applied in a method according to an exemplary embodiment.

Detailed Description of the Drawings

Figure 1 schematically depicts a method according to an exemplary embodiment.

The method is of providing a coating comprising a plurality of layers, including a first layer and a second layer, on a surface of a steel article.

At S101, the first layer is deposited on at least a part of the surface of the steel article, wherein the first layer comprises and/or is a porous first layer, having pores therein, formed from a metal preferably comprising Zn, Al and/or Mg.

At S102, the second layer is provided on at least part of the first layer by applying a composition, preferably comprising a silane and/or a siloxane, in a carrier thereon and removing at least some of the carrier, thereby providing the second layer, wherein the second layer comprises and/or is a hydrophobic second layer, preferably comprising the silane and/or the siloxane.

Comparative Example

A rail (i.e. a steel article CE1), having a BS EN 13674-1:2011+A1:2017 60E1 profile and of grade R260, was cleaned and grit blast to Sa 3. A first layer was deposited by arc spraying using 85 wt.% Zn and 15 wt.% Al to deposit the first layer on all surfaces of the rail, except for the running surface, formed from a metal of about 85 wt.% Zn and about 15 wt.% Al, having a thickness of about 250 pm and having a porosity from 5 % to 20%. A second layer was not applied.

Example

A rail (i.e. a steel article El), having a BS EN 13674-1:2011+A1:2017 60E1 profile and of grade R260, was cleaned and grit blast to Sa 3. A first layer was deposited by arc spraying using 85 wt.% Zn and 15 wt.% Al to deposit the first layer on all surfaces of the rail, except for the running surface, formed from a metal of about 85 wt.% Zn and about 15 wt.% Al, having a thickness of about 250 pm and having a porosity from 5 % to 20%. A second layer was provided over the entire first layer and remaining surfaces of the rail (i.e. the running surface) by applying Rust-oleum PREVOSIL SPECIAAL WB (i.e. a composition) by spraying at a coverage of about 200 ml m-2 and allowing the composition to penetrate into the first layer. The water (i.e. a carrier) was removed by drying. The surfaces were touch dry within about 5 minutes.

Example 2

A rail (i.e. a steel article E2), having a BS EN 13674-1:2011+A1:2017 60E1 profile and of grade R350 HT, was cleaned and grit blast to Sa 3. A first layer was deposited by arc spraying using 85 wt.% Zn and 15 wt.% Al to deposit the first layer on all surfaces of the rail, except for the running surface, formed from a metal of about 85 wt.% Zn and about 15 wt.% Al, having a thickness of about 250 pm and having a porosity from 5 % to 20%. A second layer was provided over the entire first layer and remaining surfaces of the rail (i.e. the running surface) by applying Rust-oleum PREVOSIL SPECIAAL WB (i.e. a composition) by spraying at a coverage of about 200 ml m-2 and allowing the composition to penetrate into the first layer. The water (i.e. a carrier) was removed by drying. The surfaces were touch dry within about 5 minutes.

Figure 2 is a photograph of a comparative example of a steel article CE1 (Comparative Example 1). Particularly, water W applied to the surface of the steel article CE1 wets the surface.

Figure 3 is a photograph of a steel article El according to an exemplary embodiment (Example 1). Particularly, water W applied to the surface of the steel article El does not wet the surface.

Rather, the water W remains as droplets D on the surface.

Figure 4 is a photograph of the steel article El of Figure 3, in more detail. About 12 water droplets D are shown.

Figure 5 is a photograph of the steel article El of Figure 3, in more detail. The contact angle between the surface of the steel article and the droplets D is about 113, confirming that the surface is hydrophobic (repelling).

Results of immersion testing Figure 6 is a photograph of a comparative example of a steel article CE1 (Comparative Example 1) and steel articles El, E2 according to exemplary embodiments (Example 1, Example 2) immersed in a heated and stirred water bath.

The rails of Example 1, Example 2 and Comparative Example 1 were immersed in a heated and stirred water bath. The water was tap water, maintained at 30°C. The rails were observed every 500 hours. The bath was covered to reduce evaporative losses. After 2,500 hours, no blisters were observed for the rails of Example 1 or Example 2. In contrast, after 1,500 hours, hundreds of blisters were observed for the rail of Comparative Example I. Figure 7 is a photograph of a comparative example of a steel article CE1 (Comparative Example 1) after immersion for about 620 hours in the heated and stirred water bath. Profuse blistering B is observed, the blisters having an average diameter of about 3 -4 mm, with a mean number density of about 1.25 cm 2.

Figure 8 is a photograph of a steel article according to an exemplary embodiment El (Example 1) after immersion for about 620 hours in the heated and stirred water bath. No blisters are 25 observed.

Porosity Figure 9 is a micrograph of a cross-section through the surface of a steel article El according to an exemplary embodiment (Example 1), showing the steel substrate S and the coating C. The average Dry Film Thickness (DFT) of the coating C on the underfoot of the steel article El is about 200.5 pm. Similarly, the average DFT on the underfoot of the steel article CE1 is about 195.8 pm.

Figure 10 is a contrast-enhanced micrograph of a cross-section through the surface of a steel article El according to an exemplary embodiment (Example 1). The "solid" white is the steel substrate S and the coating C, while the black P is mostly void (i.e. porosity). Porosity measurements from 4 different samples on various positions on the cross-section taken are: Minimum: 6.44 % Maximum: 30.85 °A) Average: 15.52 % The porosity measurements were performed using software CeIIB (RTM) available from Olympus. The measurements are obtained by taking 9 line intensity measurements and taking the average of the 9 measurements. Using the contrast-enhanced micrograph, black and white picture ensures that the intensity measurements give data points of either maximum or zero value, with no intermediate points.

Composition Analysis of Rust-oleum PREVOSIL SPECIAAL WB and ProPERLA (RTM) Water Repellent by evaporation determined a solids content of triethoxy(octyl)silane (TEOS) of 3.9 wt.% and a solids content of 1.5 wt.%, respectively (contrasting with data sheet of claimed 15 wt.%).

In more detail, both Rust-oleum PREVOSIL SPECIAAL WB and ProPERLA (RTM) Water Repellent appear to include only a single, but different, compound.

Rust-oleum PREVOSIL SPECIAAL WB includes triethoxy(octyl)silane (TEOS) with chemical formula C14H3203Si having molecular weight 276 Da: ProPERLA (RTM) Water Repellent includes triethoxy(2,4,4-trimethylpentyl)silane, also with chemical formula C14H32O3Si having molecular weight 276 Da: Figure 11 shows GC-MS mass spectra of compounds included in a composition applied in a method according to an exemplary embodiment. Samples of Rust-oleum PREVOSIL SPECIAAL W were diluted in propanol, with the peaks at 1 min corresponding to water and propanol, matching a blank sample. For library matching, the NIST17-1.lib library was used.

Particularly, Figure 11 shows a GC-MS mass spectrum for Rust-oleum PREVOSIL SPECIAAL W, including triethoxy(octyl)silane, (above) and for triethoxy(octyl)silane from the NIST17-1.Iib library (below). Rust-oleum PREVOSIL SPECIAAL W is thus concluded to include triethoxy(octyl)silane, in view the positive match with the library spectrum.

Figure 12 shows GC-MS mass spectra of compounds included in a composition applied in a method according to an exemplary embodiment. Samples of ProPERLA (RTM) Water Repellent were diluted in propanol, with the peaks at 1 min corresponding to water and propanol, matching a blank sample. For library matching, the NIST17-1.lib library was used.

Particularly, Figure 12 shows a GC-MS mass spectrum for ProPERLA (RTM) Water Repellent, including triethoxy(2,4,4-trimethylpentyl)silane, (above) for triethoxy(octyl)silane from the NIST17-1.lib library (middle) and for triethoxy(2,4,4-trimethylpentyl)silane (from DOI: 10.4028/www.scientific.net/KEM.680.477). ProPERLA (RTM) Water Repellent is thus concluded to include triethoxy(2,4,4-trimethylpentyl)silane, indicated particularly by the additional mass spectral peak at m/z = 205 Da.

Definitions Throughout this specification, the term "comprising" or "comprises" means including the component(s) specified but not to the exclusion of the presence of other components. The term "consisting essentially of or "consists essentially of means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention, such as colourants, and the like.

The term "consisting of or "consists of means including the components specified but excluding other components.

Whenever appropriate, depending upon the context, the use of the term "comprises" or "comprising" may also be taken to include the meaning "consists essentially of or "consisting essentially of", and also may also be taken to include the meaning "consists of or "consisting of'.

The optional features set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional features for each aspect or exemplary embodiment of the invention, as set out herein are also applicable to all other aspects or exemplary embodiments of the invention, where appropriate. In other words, the skilled person reading this specification should consider the optional features for each aspect or exemplary embodiment of the invention as interchangeable and combinable between different aspects and exemplary embodiments.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at most some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS1. A method of providing a coating comprising a plurality of layers, including a first layer and a second layer, on a surface of a steel article, the method comprising: depositing the first layer on at least a part of the surface of the steel article, wherein the first layer comprises and/or is a porous first layer, having pores therein, formed from a metal preferably comprising Zn, Al and/or Mg; and providing the second layer on at least part of the first layer by applying a composition, preferably comprising a silane and/or a siloxane, in a carrier thereon and removing at least some of the carrier, thereby providing the second layer, wherein the second layer comprises and/or is a hydrophobic second layer, preferably comprising the silane and/or the siloxane.
2. The method according to any previous claim, wherein applying the composition comprises entering, by the composition, at least some of the pores.
3. The method according to any previous claim, wherein applying the composition comprises misting, spraying, painting and/or immersing the at least part of the first layer with the composition.
4. The method according to any previous claim, wherein the carrier comprises and/or is an aqueous carrier.
5. The method according to any previous claim, wherein the composition comprises and/or is a solution, an emulsion and/or a dispersion.
6. The method according to any previous claim, wherein depositing the first layer comprises thermal spraying, preferably arc spraying, the metal onto the surface of the steel article.
7. The method according to any previous claim, wherein providing the second layer on at least part of the first layer comprises providing the second layer on at least part of the newly-deposited first layer.
8. The method according to any previous claim, wherein removing at least some of the carrier comprises heating the second layer.
9. The method according to any previous claim, comprising cleaning the at least a part of the surface of the steel article before depositing the first layer thereon.
10. The method according to any previous claim, comprising roughening the at least a part of the surface of the steel article before depositing the first layer thereon.
11. A steel article having a coating comprising a plurality of layers, including a first layer and a second layer; wherein the first layer overlays at least a part of a surface of the steel article and wherein the first layer comprises and/or is a porous first layer, having pores therein, formed from a metal preferably comprising Zn, Al and/or Mg; and wherein the second layer overlays at least part of a surface of the first layer and wherein the second layer comprises and/or is a hydrophobic second layer preferably comprising a silane and/or a siloxane.
12. The steel article according to claim 11, wherein the second layer overlays at least a part of the surface of the pores in the first layer.
13. The steel article according to any of claims 11 to 12, wherein the second layer at least partially fills the pores in the first layer.
14. The steel article according to any of claims 11 to 13, wherein the silane is a triethoxysilane, 20 for example selected from a group comprising triethoxy(octyl)silane, 3-aminopropyltriethoxysilane and triethoxy(2,4,4-trimethylpentyl)silane.
15. The steel article according to any of claims 11 to 14, wherein the second layer has a thickness in a range from 1 to 250 nm, preferably 5 to 125 nm, more preferably in a range from 10 to 50 nm.
16. The steel article according to any of claims 11 to 15, wherein the metal, for example the first layer, consists of from 5 wt.% to 25 wt.% Al, optionally from 0 to 10 wt.% Mg, optionally from 0 to 5 wt.% Cu, optionally from 0 to 5 wt.% Ag, balance Zn and unavoidable impurities.
17. The steel article according to any of claims 11 to 16, wherein the first layer has a thickness in a range from 10 pm to 1000 pm, preferably in a range from 50 pm to 500 pm, more preferably in a range from 125 pm to 400 pm, most preferably in a range from 225 pm to 325 pm, for example 250 pm.
18. The steel article according to any of claims 11 to 17, wherein the steel article is a rail, a structural section or a profile.
19. The steel article according to claim 18, wherein the steel article is a rail having a length in a range from 6 m to 360 m, for example from 15 m to 250 m, preferably in a relatively shorter range from about 15 m to about 60 m for example about 18 m, about 36 m, about 50 m or about 60 m, and/or preferably in a relatively longer range from 60 m to 150 m, more preferably in a range from 90 m to 130 m, for example 108 m or 120 m.
20. A railway track, preferably installed in a tunnel, including a steel article having a coating provided according to any of claims 1 to 10 and/or a steel article according to any of claims 11 to 19, preferably wherein the steel article is a rail having a length in a range from 6 m to 360 m, for example from 15 m to 250 m, preferably in a relatively shorter range from about 15 m to about 60 m for example about 18 m, about 36 m, about 50 m or about 60 m, and/or preferably in a relatively longer range from 60 m to 150 m, more preferably in a range from 90 m to 130 m, for example 108 m or 120 m.
21. Use of a silane and/or a siloxane as a hydrophobic layer on a metal surface such as a porous metal surface, for example wherein the porous metal surface is deposited by thermal spraying.