WO2016110840A1

WO2016110840A1 - Corrosion-resistant valve disc

Info

Publication number: WO2016110840A1
Application number: PCT/IL2016/050005
Authority: WO
Inventors: Michael Berger
Original assignee: Hakohav Valves Industries Metal (1987) Ltd.
Priority date: 2015-01-05
Filing date: 2016-01-05
Publication date: 2016-07-14

Abstract

A corrosion resistant iron-based substrate such as a valve disc, having a zinc/aluminum diffusion layer and a polymeric coating applied thereon, and articles-of- manufacturing containing same, are provided herein, as well as processes of preparing same. The substrates and articles-of-manufacturing are characterized as capable of withstanding intense flow of salt water and high hydraulic pressure.

Description

CORROSION-RESISTANT VALVE DISC

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to material chemistry, and more particularly, but not exclusively, to an anti-corrosive coating and to uses thereof in producing corrosion-resistant articles such as corrosion-resistant butterfly valve disc.

A common corrosive process is known as rusting of iron into iron oxide species. Corrosion degrades the physical and chemical properties of metals and structures comprising the same, including such properties as strength, surface morphology and reactivity with chemicals in the environment. Corrosion is most intuitively assessed visually, particularly when considering iron and iron-based substrates. In such iron- containing substrates, traces of red corrosion can be observed in accelerated corrosive conditions such as used in a salt spray test, whereas red corrosion traces indicate the beginning of iron-based substrate corrosion. Other methods include base metal mass loss and over-coating/paint peel tests.

Many metals and structural alloys corrode from exposure to moisture and air, but the process can be strongly affected by exposure to certain substances and microbes. Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as passivation and coating can increase metal corrosion resistance.

Anti-corrosive coating manufacturers have attempted to meet the more stringent coating corrosion resistance requirements by developing chemical additives and processes of manufacturing as well as coating compositions, all of which are aimed at increasing the corrosion resistance of their products, particularly when made of corrodible metals, such as iron. For example, some metal components which are used for marine piping, tapping and valves must fulfill the highest anti-corrosive property requirements, such as those stipulated in ASTM B-117 (salt spray test), which are measured by hours of corrosion resistance. Exemplary corrosion resistant metallic substances are duplex (ferritic-austenitic) stainless steels. These alloys have been developed to provide good corrosion resistance, particularly in sea water, and have been used for many years in various industrial equipment including heat exchanger tubes. In order to meet the highest requirements, the so-called "super duplex" stainless steels have been developed. See, for example, in U.S. Patent Application having Publication No. 2014/0003989, and U.S. Patent Nos. 4,765,953, 5,298,093 and 5,849,111; Vernhardsson, S., Corrosion 90, Apr. 23-27, 1990, Paper No. 164; and Lefebvre, G. et al, Proceedings of the First (1991) International Offshore and Polar Engineering Conference, pp. 224-232.

A corrodible base metal can be protected chemically against corrosion in two modes, forming a sacrificial protection layer and forming a barrier protection layer (non-conductive passivation). Sacrificial protection of a corrodible base metal against corrosion, also known as cathodic protection, is based on the electrochemical properties of the base metal and a sacrificial metal, and is effected by contacting the sacrificial metal which is more reactive than the base metal to an object made of the more reactive base metal. Commonly the corrodible base metal is iron and the sacrificial metal is magnesium or zinc, which will corrode before iron. Barrier protection or passivation of a base metal is based on coating the base metal with a substance that forms a physical, and in some cases also a chemical barrier between the base metal and a corrosive environment that contains corrosion factors such as water, ions and oxygen. Some highly corrodible metals, such as aluminum and chrome, are used to form a passivating and electrically-insulating layer of oxides and hydroxides that acts as a combination cathodic/barrier, by undergoing limited corrosion on the outer layer of the base metal, and sealing it from the corrosive environment.

U.S. Patent No. 3,642,457 discloses an exemplary methodology of cathodic protection of a base metal for the production of multi-metal diffusion coatings on metal articles. This methodology includes methods and compositions which provide prolonged cathodic protection against chemical or galvanic corrosion of the surface of the coated article during prolonged exposure to corrosive conditions, and particularly high-saline content marine atmospheres, especially where the protective coating is also subjected to mechanically erosive and abrasive environments. Chromate conversion coating is a type of conversion coating used to passivate aluminum, zinc, cadmium, copper, silver, magnesium, and tin alloys. It is primarily used as a corrosion inhibitor, primer, decorative finish, or to retain electrical conductivity. The process is named after the chromate found in the chromic acid used in the bath, more commonly known as hexavalent chromium. This type of bath is still the most widely used, however hexavalent chromium is toxic, thus, highly regulated, so new non-hexavalent chromium based processes have been developed. In the last decades several electrodeposition or electroplating processes have been developed for forming thin coatings composed of Zn-Fe, Zn-Ni, Zn-Co, or Zn-Cd alloys. By using chromate passivation, it became possible to maintain coating corrosion resistance of ferrous metal for 400 to 500 hours, before red corrosion traces appeared in the salt spray test. However, the added complexity and sensitivity of the electrodeposition or electroplating coating process led to a substantial increase in coating production costs. In addition, the addition of environmentally dangerous elements, such as Ni, Co, and Cd, in the coatings led to higher waste treatment expenditures.

Another commonly used method for applying a corrosion resistant zinc-based coating is the hot-dip (or galvanizing) process; in which treated metal articles are immersed in a molten zinc bath. This method is widely used for applying coatings onto large-sized products, and also for a continuous process of applying protective coatings on metal sheet and wire. However, the hot-dip zinc coating, thus applied, exhibits a relatively low corrosion resistance and high white corrosion susceptibility (corrosion products of zinc).

Hot-dip processes, known in Europe and the USA as Galfan, use a bath containing aluminum in addition to zinc. This type of coating contains 4.7-5.2 % by weight of aluminum. Galvalum Zn/Al hot-dip coating uses approximately 55 % by weight of aluminum. Adding magnesium and silicon to the zinc-aluminum-based coating composition further improved the corrosion resistance.

The modified hot-dip technology process, however, requires an extremely delicate multistage pretreatment of surfaces to be coated, fluxing, and in many cases, chromate passivation of finished coating as well. There are also problems in maintaining a constant melt composition in the bath, and, as a rule, the coating itself is applied in several steps. Another common drawback of zinc-based coatings, applied by both the electroplating and hot-dip processes, is their low adhesion to secondary coatings. The secondary coatings are applied to increase the corrosion resistance, to attain the required appearance of the product, and to obtain the specified technical characteristics, for instance, to increase or decrease the friction coefficient. White corrosion of zinc, developed in the vicinity of pores and defects of the second coating, leads to the mechanical destruction of the second coating. As the corrosion process advances, its products displace the second coating, which exhibits blistering.

Diffusive metal coatings were developed to overcome the above-mentioned process drawbacks. According to this technology, a substrate to be coated is placed into a powdered metal medium and heated up to a temperature, at which diffusion of atoms occurs between the substrate metal and the powder on the substrate surface. A particular version of this method widely used in industry is Sherardizing. According to the established understanding, Sherardizing is a process where iron-based parts are heated for several hours in a closed, usually rotating, container, together with zinc powder at temperatures of 370-450 °C. As a result of this process, two intermetallide Zn-Fe phases are formed on the substrate surface. The first phase is usually only several microns thick. It is adjacent to the base metal and contains approximately 20 % by weight of iron. The second phase, which forms the main part of the coating thickness, contains less iron, usually up to 12 % by weight of iron. To prevent the zinc powder from fusing and/or sticking to the substrates, the zinc powder is diluted with inert filler, such as sand, aluminum oxide, silica and the likes, or treated by a special hydrothermal method which creates a layer that prevents the zinc powder particles from fusing.

U.S. Patent No. 7,241,350 provides an approach to minimize the corrosion producing effects of the electrochemical reaction between the substrate and the intermetallic Zn-Fe diffusion layer, which is one of the weaknesses of the Sherardizing process. In essence, the solution involves a sacrificial/self -pas sivating phase that protects Zn-Fe diffusion layer from a direct electrochemical reaction with the substrate material. Briefly, U.S. Patent No. 7,241,350 discloses diffusion metallic anticorrosive zinc-iron-aluminum coatings of iron and iron-based item surfaces, realized by heating of products at temperatures of 370-450 °C in a saturating powder mixture environment in a closed container. The coating compositions are multiphase-polymetallic, and comprise zinc, iron and aluminum, while other elements may be added to attain specific coating properties. This corrosion protection technology, referred to herein as zinc/aluminum diffusion treatment, coating or layer, exhibits a high corrosion resistance of at least a 700-hour corrosion resistance level in a standard salt spray test, a relatively high hardness level and good adhesion to secondary coatings.

U.S. Patent Application having Publication No. 2010/0215980 and U.S. Patent No. 8,398,788 teaches a thin zinc diffusion coating that includes an iron-based substrate, and a zinc-iron intermetallic layer coating the iron-based substrate.

Another approach to metal protection against corrosion, referred to above as secondary coating, is the application of a physical barrier that insulates the base metal from the environment. Unlike the barrier protection described above, which involves limited corrosion of a self-passivating second metal coating the base metal, a physical barrier typically involves coating the base metal with an organic or inorganic oily substance or with an organic or inorganic polymeric substance, that prevents corrosion factors from reaching the metal. For example, oiling a metal provides a very common short-term corrosion protection of metals. For longer terms, a polymeric coating can be applied in a form of a thin layer of an anti-corrosion paint, through thicker layers of polymeric layers to casting a polymeric encasement over the base metal.

U.S. Patent Application having Publication No. 2003/0049485 provides corrosion resistant coatings for metal substrates, which comprise a chemically stable mechanical attachment interface formed by coating a metal substrate with a seamless thermal spray metallic coating of a Ni-based alloy or stainless steel, and a polymer layer, made from polyether sulfone (PES), polyphenylene sulfide (PPS), poly ether ether ketone (PEEK), polyphenylene oxide (PPO), elastomers, fluoroelastomers, epoxy, nylon, chlorinated rubber, polyurethane, polyurea and, preferably, from a fluoropolymer such as PTFE, FEP, PFA, MFA, ECTFE (HALAR®); ETFE and PVDF, bonded to the metallic interface. These coatings are said to be highly suitable for resisting corrosive environments also in process chemistry vessels, furnaces and boilers, used for the coating process.

DE 102009030423 teaches zinc diffusion on metal member followed by powder coating by injection molding of a plastic coat over the zinc-treated metal member. Additional background art includes, for example, CA 1075980, EP 2230330, DE 102009030425, WO 2010129028, WO 2009076430, CN 201889934, GB 1091363, SU 1534091 and U.S. Patent No. 4,141,760. SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present invention there is provided an article of manufacturing comprising an iron or iron-rich substrate, the substrate comprising a diffusion layer formed on at least a portion of an exterior surface of the substrate, and further comprising a polymeric coating disposed on at least the portion having the diffusion layer and on top of the diffusion layer, wherein the diffusion layer comprises zinc and iron and discrete, laterally non-continuous aluminum-rich inclusions randomly distributed on or in the layer.

According to some embodiments of the invention, the polymeric coating comprises at least one polymer selected from the group consisting of a polyamide, a halopolymer, an epoxy resin, a silicone-based polymer, a sol-gel, low and high-density polyethylene, a polyurethane, an aliphatic polyester urethane resin, an aliphatic polycarbonate urethane resin, a hydroxy-functional polyacrylate, a poly(urethane acrylate) and a polyacrylate.

According to some embodiments of the invention, the polymeric coating comprises a polyamide.

According to some embodiments of the invention, the polyamide is nylon 11. According to some embodiments of the invention, the polymeric coating comprises a halopolymer.

According to some embodiments of the invention, the halopolymer is ethylene chlorotrifluoroethylene (ECTFE).

According to some of any of the embodiments of the invention, the polymeric coating further comprises a primer layer and a top polymeric layer.

According to some of any of the embodiments of the invention, the thickness of the polymeric coating ranges from 50 micron to 500 microns.

According to some of any of the embodiments of the invention, the polymeric coating is characterized by an adhesion to the substrate which is rated at least 3 on an NFT 58-112 scale. According to some of any of the embodiments of the invention, the polymeric coating is characterized by an adhesion to the substrate which is rated less than 2 mm on an EN 10310 scale.

According to some of any of the embodiments of the invention, the polymeric coating is characterized by a peel force of at least 10 MPa.

According to some of any of some embodiments of the invention, the article is configured to withstand a flow of salted water of at least 1.5 cubic meters per hour and/or a hydraulic pressure of at least 1 atmosphere for 100 days.

According to some of any of the embodiments of the invention, the article is a valve disc, and is some embodiments the article is a butterfly valve disc.

According to an aspect of some embodiments of the present invention there is provided an iron or iron-rich valve disc (e.g., butterfly valve disc) comprising a diffusion layer formed on at least a portion of an exterior surface thereof, the valve disc further comprising a polymeric coating disposed on at least the portion of the exterior surface having the diffusion layer and on top of the diffusion layer, wherein the diffusion layer comprises zinc and iron and discrete, laterally non-continuous aluminum-rich inclusions randomly distributed on or in the layer.

According to an aspect of some embodiments of the present invention there is provided an iron or iron-rich valve disc (e.g., butterfly valve disc) having a diffusion layer on at least a portion of an exterior surface thereof, wherein the diffusion layer comprising zinc and iron and discrete, laterally non-continuous aluminum-rich inclusions randomly distributed on or in the layer, the valve disc further comprising a layer of ECTFE coating at least the portion of the exterior surface having the diffusion layer.

According to some of any of the embodiments of the invention, the thickness of the diffusion layer ranges from 1 micron to 60 microns.

According to some of any of the embodiments of the invention, the diffusion layer further comprises at least one of element selected from the group consisting of tin, silicon and magnesium.

According to some of any of the embodiments of the invention, the thickness of the polymeric coating ranges from 50 micron to 500 microns. According to some of any of the embodiments of the invention, any of the article or the valve disc described herein exhibits a rate of corrosion of less than 5 mpy when fully immersed in a 3.5 % sodium chloride solution at a temperature of 25-33 °C for at least 50 days.

According to some of any of the embodiments of the invention, any of the article or the valve disc described herein exhibits a mass loss of less than 0.1 percent by weight when fully immersed in a 3.5 % sodium chloride solution at a temperature of 25-33 °C for at least 50 days.

According to an aspect of some embodiments of the present invention there is provided a process of preparing the article or disc valve presented herein, the process comprising:

subjecting the substrate or the iron or iron-rich valve disc to zinc/aluminum diffusion treatment essentially as described herein; and

applying the polymeric coating at least one portion of the article essentially as described herein, thereby preparing the article or valve disc.

Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

Implementation of the method and/or system of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of embodiments of the method and/or system of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

In the drawings:

FIGs. 1A-C present illustrations of a process by which a Zn-Fe diffusion layer, having Al-rich inclusions randomly distributed on or in the layer, according to exemplary embodiments of the present invention, is formed;

FIG. 2 presents an illustration of a portion of the outer surface of an iron-based substrate having Zn-Fe diffusion later and Al-rich inclusions randomly distributed thereon, and a layer a polymeric coating disposed thereon, according to exemplary embodiments of the present invention;

FIGs. 3A-C present photographs of three samples of cast iron valve discs which were fully immersed in a circulating 3.5 % NaCl solution at 30-33 °C for 14 days, wherein FIG. 3A shows the sample which was treated with Zn/Al without a polymeric coating, FIG. 3B shows the sample which was coated with Rilsan® nylon without being pre-treated with Zn/Al, and FIG. 3C shows the sample which was treated with Zn/Al and subsequently coated with Rilsan® nylon polymeric coating;

FIG. 4 is a table presenting color photographs of variously treated or non-treated valve discs exposed to salt solution for 50 days and subjected to a coating peel test, showing the effect of each anti-corrosion treatment and the effect of a combination thereof; and

FIGs. 5A-D present color photographs of variously treated valve discs after exposure to water at 80 °C for 24 hours, showing the superior adhesion of the RISLAN® coating on the Zn/Al diffusion layer (Figures 5A-B) compared to the inferior adhesion of the RISLAN® coating to the base metal (Figures 5C-D).

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to material chemistry, and more particularly, but not exclusively, to an anti-corrosive coating and to uses thereof in producing corrosion-resistant articles such as corrosion-resistant butterfly valve discs. Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

As described hereinabove, metal corrosion is an ever-present threat to metal articles in all common environments, and corrosion resistant metal articles are in high demand. Super-duplex metal alloys provide a satisfactory solution; however, these alloys are very expensive, difficult to process and brittle. Presently known solutions to corrosion protection of more cost-effective base metals, such as iron, include use of diffusion sacrificial layers, passivation layers, combination thereof (such as zinc/aluminum diffusion treatments), and physical isolation approaches, such as polymeric coating layers; however, each of these methods suffers from one or more problems, including the electrochemical reaction between the base metal (consisting mainly of iron) and the intermetallic Zn-Fe diffusion layer in the case of Sherardizing process, the depletion, oxidation, scratching and/or cracking of a sacrificial layer, passivating layer or combined layer approaches (as in the Zn/Al diffusion treatment); and peeling, cracking and/or scratching of a physical polymeric coating.

In a search for an improved corrosion protection methodology, that would supersede the currently practiced approaches, the present inventor has surprisingly found that while utilizing the sacrificial/passivating diffusion layer approach, referred to herein as the Zn/Al diffusion treatment, in combination with applying a polymeric layer over the base metal, a superior anti-corrosion effect is achieved, particularly when compared to each treatment when effected alone, in terms of retarding corrosion rate and improving polymeric layer adhesion, which allows the production of articles made of base metals, such as cast iron and iron-rich substrates, and yet provide a comparable yet more cost-effective solution to the expensive alloys, such as super-duplex.

Without being bound by any particular theory, it is assumed that the combined treatment approach of Zn/Al diffusion layer and a polymeric layer as provided herewith, is synergistically advantageous compared to the combined effects afforded by each of the anti-corrosion treatments when used alone, due to the improved adhesion of the polymeric layer to the Zn/Al diffusion layer on the surface of the base metal, which in turn is more protected from depletion, oxidation, scratches and cracks due to the physical/mechanical protection provided by the polymeric layer.

According to an aspect of embodiments of the present invention, there is provided an article of manufacturing, which comprises an iron or iron-rich substrate having a zinc and iron (Zn-Fe) diffusion layer on at least a portion of an exterior surface of the substrate, wherein the diffusion layer further includes discrete, laterally non- continuous aluminum-rich inclusions randomly distributed on or in the layer, the substrate further comprising a polymeric coating disposed on the portion of the substrate having the diffusion layer.

According to some embodiments of the present invention, the iron or iron-rich substrate is a cast iron valve disc, such as used in, e.g., a butterfly valve. Other iron or iron-rich elements used as, or as parts of, any article involving contact with water, and particularly used under corrosive conditions such as salt, heat and the likes, are contemplated. Exemplary substrates and/or articles of manufacturing comprising same, which are suitable for the anti-corrosion treatment presented herein include, without limitation, piping components, fluid control components and fluid containers.

In some embodiments, the substrates and/or articles-of-manufacturing described herein are configured for use as a part of a piping system for, e.g., salt water.

According to some embodiments of the present invention, inclusions of Al-Fe intermetallics and Zn-Al alloys, as described in U.S. Patent No. 7,241,350, which is incorporated by reference as if fully set forth herein, serve as the sacrificial/passivating phases.

Without being bound by any particular theory, it is assumed that the products of aluminum corrosion, stemming from the aluminum inclusions, exhibit low solubility in water, and precipitate on surface defects (cracks, pores, etc.), filling them and thereby considerably slowing down the corrosion rate. This effect of aluminum corrosion products filling is not reduced even after the sacrificed Zn/Al phase is consumed. Moreover, zinc corrosion products enhance this effect by precipitating on surface defects, and thus imparting the Zn-Fe diffusion layer with higher corrosion resistance under corrosive conditions. This suggested, non-limiting, mechanism may explain the higher resistance of the Zn/Al diffusion layer, according to embodiments of the present invention, compared with the Galfan type Zn-Al coating, wherein Zn-Al eutectics virtually permeate the entire coating thickness. Furthermore, it is assumed that the unique chemistry of the Zn/Al diffusion layer promotes adhesion of a polymer thereto, as further discussed hereinbelow.

The term "diffusion layer", as used in the context of the present embodiments, refers to a layer of an iron or iron-rich base metal having zinc and aluminum diffused into the exterior layer thereof, and being characterized by discrete, laterally non- continuous aluminum-rich inclusions randomly distributed on or in the layer. Thus, the "diffusion layer" can also be regarded as a Zn-Fe diffusion layer having discrete, laterally non-continuous aluminum-rich inclusions randomly distributed therein or thereon. The "diffusion layer" is referred to herein interchangeably as "Zn-Fe/Al inclusion layer" and "Zn/Al diffusion layer".

According to some embodiments of the present invention, the formation of the Zn-Fe diffusion layer having discrete, laterally non-continuous aluminum (Al)-rich inclusions randomly distributed therein or thereon, takes place at a temperature of about 400 °C, while using a saturating mixture containing about 85 % by weight of Zn and about 15 % by weight of Al. It is assumed that in the course of heating, zinc and aluminum interdiffuse between powder particles in the saturating mixture. Accordingly, in some embodiments of the invention, the powder grains used in the preparation of the Zn/Al diffusion layer contain from about 80 % to about 96 % by weight of Zn and from about 4 % to 20 % by weight of Al.

During the formation of the diffusion layer, it is assumed that zinc diffuses from the saturating powder environment and forms the layer of Zn-Fe intermetallics on the surface of the substrate. It is further assumed that the powder mixture becomes enriched with aluminum, and the reaction of aluminum with iron begins, forming Fe-Al intermetallics. This reaction occurs presumably due to diffusion of iron from the Zn-Fe intermetallic layer into the Zn-Al powder grains, forming Al-Fe intermetallic domains, referred to herein as "aluminum-rich inclusions". According to some embodiments of the present invention, the aluminum-rich inclusions are randomly distributed essentially on the Zn-Fe intermetallic surface. Figures 1A-C (background art) present illustrations of the process by which the Zn-Fe diffusion layer, having Al-rich inclusions randomly distributed on or in the layer, is formed.

According to some embodiments of the present invention, the multiphase diffusion layer is formed using various conditions which allow fine-tuning of the Zn/Al diffusion layer properties so as to arrive at desired properties. These include, for example:

1. The Zn quantity contained in the saturating powder mixture, which is used in the process, may be selected to correspond to the amount necessary to produce an intermetallide Zn-Fe layer of a desired thickness.

2. The particles of the saturating environment may be directed to essentially remain on the surface of the treated substrates. This feat may be achieved by constantly supplying powder particles to the substrate's surface, effected by, for example, conduct the process in a rotating container with wall-mounted mixing blades.

3. To minimize macro-heterogeneity of the layer's composition, which may lead to deterioration in the corrosion resistance thereof, the use of inert filler is minimized by, for example, using hydrothermal powder treatment, such as is described in Soviet Union (SU) Patent No. 1534091.

According to some embodiments of the present invention, the diffusion layer may further include other substances, for example metals such as tin, silicon, and magnesium.

According to some embodiments of the present invention, the saturating powder mixture, used in the making of the diffusion layer, contains from about 5 % to about 50 % by weight of aluminum, 0-15 % by weight of magnesium and other elements, such as, for example, tin and/or silicon, and the balance being zinc. It is noted that the initial size of powder grains should not exceed 150 micron, and according to some embodiments, the particle size is about 75 microns or less.

According to some embodiments of the present invention, the thickness of the diffusion layer ranges from about 1 micron to about 60 microns. According to some embodiments, the thickness of the diffusion layer is at least 5 microns, at least 10 microns, at least 20 microns, at least 25 microns, at least 30 microns, at least 35 microns, at least 40 microns, at least 45 microns, at least 50 microns, or at least 55 microns.

The finishing treatment of the treated substrate typically includes cleaning the treated substrate from the remaining powder and byproducts of the process, and optionally additional finishing operations such as polishing, pigmenting, oiling and applying surface organic and inorganic films.

According to embodiments of the present invention, the article of manufacturing presented herein further comprises a polymeric coating disposed on at least the portion of the substrate having the diffusion layer.

One of the advantages of having a secondary coating disposed on the substrate, in the form of a polymeric coating over the diffusion layer, is the provision of a physical shield against impact from foreign objects and friction against other parts of an article which comprises the substrate, such as a butterfly valve. Impact and friction against the inner walls of, e.g., a butterfly valve, may damage the sacrificial protection layer disposed on the substrate, namely the diffusion layer, and allow corrosion to set in the unprotected exposed external surface of the substrate. Without being bound to any particular theory, it is assumed that metal-to-metal contact points give rise to nucleation and propagation of corrosion, thus metal-to-metal contact points are being minimized in the iron-rich substrate provided herewith and subjected to corrosive conditions, thereby achieving maximal corrosion resistance therein.

The term "polymeric coating", as used in the context of embodiments of the present invention, refers to a layer of a polymeric substance applied on the exterior surface of a substrate. As used herein, the term "polymeric coating" means both a physical embodiment ("coating" as a noun) and functional embodiment ("coating" as a verb), namely the polymeric coating is the substance applied on the substrate and the function of coating the substrate with a polymer. Alternatively, the term "coating" is interchangeable with the term "disposed on". For example, a phrase such as "further comprising a polymeric coating at least one portion of an exterior surface of a substrate", should be read as "further comprising a polymeric coating, coating at least one portion of an exterior surface of a substrate", or "further comprising a polymeric coating, disposed on at least one portion of an exterior surface of a substrate". As used herein, the term "polymer" describes a large molecule made up of repeating units (monomers). Polymers may be classified by their repeating unit structure and may be linear, branched or, less commonly, cyclic. Copolymers contain two or more different monomers that can be arranged randomly or in repeating sequence blocks in the polymeric structure. In solution, entangled polymer chains can create networks, giving complex viscosity behavior. Generally, the term "polymer" as used herein encompasses, but is not limited to, homopolymers, co-polymers, such as for example, block, graft, random and alternating co-polymers, ter-polymers, and blends and modifications thereof, of various molecular weights. Furthermore, unless otherwise specifically limited, the term "polymer" includes all possible stereochemical configurations and conformations of the molecule. These configurations and conformations include, but are not limited to, isotactic, syndiotactic and atactic, cis and trans, and R and S and conformations.

Figure 2 presents an illustration of a portion of the outer surface of an iron-based substrate having Zn-Fe diffusion later and Al-rich inclusions randomly distributed thereon, and a layer a polymeric coating disposed thereon.

According to some embodiments, the polymeric coating disposed over the diffusion layer, comprises, without limitation, a thermally bonded polymer (which polymerizes and cures upon exposure to elevated temperatures, typically about 100 °C), a pressure bonded polymer (which polymerizes and cures upon exposure to elevated temperatures, typically about 30 psi), a chemically bonded polymer (polymerizes and cures upon activation and/or initiation by a radical forming agent, or initiator) and any combination thereof.

Exemplary polymers include, without limitation, a polyamide, a halopolymer, an epoxy resin, a silicone-based polymer, a sol-gel, low and high-density polyethylene, a polyurethane, an aliphatic polyester urethane resin, an aliphatic polycarbonate urethane resin, a hydroxy-functional polyacrylate, a poly(urethane acrylate) and a polyacrylate, and any combination of the foregoing.

In some embodiments, the polymer of the polymeric coating is a polyamide (nylon), such as nylon-6,6, nylon-6, nylon-6,9, nylon-6,10, nylon-6,12, nylon-11, nylon- 12 and nylon-4,6. In some embodiments, the polyamide is nylon-11, also known as the commercially available product Rilsan®. In some embodiments, the polymer of the polymeric coating is a polymer containing a halogen atom, such as a fluoropolymer. The term "fluoropolymer" typically refers to a fluorocarbon based polymer having a plurality of fluoro substituents bound to the main-chain via carbon-fluorine bonds, and is typically characterized by a high resistance to solvents, acids and/or bases. A non-limiting exemplary fluoropolymer, suitable in the context of some embodiments of the present invention, includes a polymer of chlorotrifluoroethylene, also referred to herein as ethylene chlorotrifluoroethylene (ECTFE) and known by the trade name Halar®, and a polymer of l,l,2,2-tetrafluorobutane-l,4-diyl also referred to as ethylene tetrafluoroethylene (ETFE) and also known by the trade name Tefcel®.

Exemplary commercially available high-density polyethylene anti-corrosion polymers include, without limitation, Alathon® and Petrothene®.

According to some embodiments, disposing the polymeric coating over the diffusion layer is effected with or without the use of a polymeric coating primer.

The term "primer", as used herein, refers to an undercoat layer which is applied as a preparatory coating on a material before coating the material with a main polymeric coating layer. Priming prior to coating improves adhesion to the surface of the substrate and durability of the subsequently applied polymeric coating, and provides additional protection for the material being coated. As used herein, the term "polymeric coating" further includes any optional intermediate polymeric layer or other layer that may be applied as a primer on the exterior surface of a substrate prior to the application of a top polymeric layer for increasing the adhesion thereof to the substrate. In such cases, the optional intermediate polymeric layer is referred to herein as a "primer layer" and the main polymeric layer which is applied thereon is referred to herein as a "top polymeric layer". Unless stated otherwise, the term "polymeric coating" refers to the combined primer layer and top polymeric layer.

According to some embodiments of the present invention, a primer is a substance that allows a top polymeric layer to adhere much better than if it was applied directly on the substrate or the Zn/Al-treated substrate. Hence, a primer is designed to adhere to the surface of the Zn/Al-treated substrate and to form an intermediate layer that is better prepared to receive the top polymeric layer. Typically the primer layer may be selected so as not to be durable as the top polymeric layer, and instead it can be characterized by improved filling and binding properties with respect to the Zn/Al- treated substrate. In some embodiments, the primer's filling and adhesive properties are achieved as a result of specific chemistry, and in some embodiments these properties are achieved through controlling the primer's physical properties such as porosity, tackiness, viscosity and hygroscopy. In some embodiments the filling and adhesive properties of the primer are achieve by utilizing both chemistry and physical properties.

A primer is typically selected to correspond with the main polymer of the top polymeric layer, and may also be selected specific to the substance of the substrate. In general, the primer is characterized by one or more of the following traits: the primer comprises a polymer or a resin (about 20-30 % by weight) which may be the same as the polymer comprising the top polymeric layer or different; the primer comprises a solvent (about 40-80 % by weight); the primer comprises an optional adhesive agent (about 2-10 % by weight) which is typically a suitable polymer having higher tackiness the primer is having a glass transition temperature suitable for the intended use and substrate material; the primer is having a surface tension suitable for the substrate material; and the primer is having other properties which provide the finished top polymeric layer higher adhesions to the substrate. The primer may comprise a colorant to assist in determining sufficient application thereof and various optional additives.

A non-limiting example for a primer suitable for nylon top polymeric layer, such as the commercially available RILSAN® polymer, is the commercially available solvent-based RILPRIM® primer or the water-based PREVIGREEN® liquid primer by ARKEMA Inc., France. Another non-limiting example for a primer suitable for ECTFE and other fluoropolymers, such as the commercially available HALAR® polymer, is the commercially available BONDiT™ primer by RELTEK LLC, USA. It is noted that other primers for other top polymeric layer are contemplated and are within the scope of the present invention.

According to some embodiments, disposing the polymeric coating over the diffusion layer is afforded by dipping, spraying or brushing. When dipping the substrate in a polymer, the substrate may be dipped in a liquid or a dry powder form of the coating material.

According to some embodiments, disposing the polymeric coating over the diffusion layer is afforded by pre-heating the substrate to more than 100 °C, more than 200 °C, more than 250 °C, more than 280 °C, more than 300 °C or more than more than 400 °C.

According to some embodiments of the present invention, the thickness of the polymeric coating ranges from about 50 microns to about 1500 microns. According to some embodiments, the thickness of the diffusion layer is at least 50 microns, at least 100 microns, at least 150 microns, at least 200 microns, at least 250 microns, at least 300 microns, at least 350 microns, at least 400 microns, at least 450 microns, at least 500 microns, at least 600 microns, at least 700 microns, at least 800 microns, at least 900 microns, at least 1 mm, at least 1.1 mm, at least 1.2 mm, at least 1.3 mm, at least 1.4 mm or at least 1.5 mm.

A low friction coefficient of the polymeric coating, disposed on the diffusion layer of the substrate, according to some embodiments of the present invention, bestows advantageous characteristics to the finished article, particularly when the article is used as a moving part in a system, or having moving parts in a system come in contact therewith. The low friction coefficient further minimizes the occurrence of scratching, cracking and/or peeling the polymeric coating, and thereby further contributes to the synergistic anti-corrosive effect of the combined treatment provided herewith.

According to some embodiments, the polymeric coating disposed over the diffusion layer is selected as having a low dynamic and/or static friction coefficient (μ) as determined according, for example, the ASTM D1984 standard method. According to some embodiments, μ of the polymeric coating is less than 0.01, less than 0.02, less than 0.03, less than 0.04, less than 0.05, less than 0.06, less than 0.07, less than 0.08, less than 0.09, less than 0.1, less than 0.15, less than 0.2, less than 0.25, less than 0.3, less than 0.35, less than 0.4, less than 0.45 or less than 0.5.

It is noted that when coming to select a suitable polymeric coating, one should also consider the economic factors of producing cast iron disc valves. Hence, while some polymers provide chemical and mechanical advantages, other may balance some disadvantages with economic advantages. For example, while ECTFE coating may provide some mechanical advantages compared to nylon, it is significantly more expensive than nylon coating, making ECTFE coating less cost-efficient. Thus, while the zinc/aluminum diffusion treatment combined with a polymeric layer coating is effective for protecting cast iron products to an extent that is comparable to more expensive alternatives, such as "super-duplex", one way to extend this advantage is to use more cost-effective (cheaper) polymeric protective material for the coating of disc valves, such as nylon.

According to some embodiments of the present invention, an article of manufacturing comprising an iron or iron-rich substrate and having a diffusion layer and a polymeric later disposed thereon, as described herein in any one of the respective embodiments and any combination thereof, is characterized as capable of withstanding a flow of salted water of at least 1.5, 2, 3, 4, 5, 10, 20 or 30 cubic meters per hour or more and/or a hydraulic pressure of at least 1, 1.2, 1.5, 2, 3 or 5 atmospheres for more for at least 100 days before showing first signs of failure.

According to some embodiments of the present invention, an exemplary substrate having a diffusion layer and a polymeric coating disposed on the diffusion layer, as provided herein, is characterized by a low rate of corrosion.

The terms "corrosion rate" or "rate of corrosion", as used herein, refer to the speed at which a metal deteriorates in a specific environment due to corrosion. The rate, or speed, depends upon environmental conditions as well as the type, size (surface area) and condition of the metal. In order to calculate the rate of corrosion, the following information is collected: the decrease in metal weight during the reference time period (mass loss); density of the metal; total initial surface area of the exposed metal piece; and the duration of the exposure time period. In the United States, corrosion rates are normally calculated using Mils per year (mpy). Mils is a unit of measurement equal to one thousandth of an inch, which is used to gauge a corrosion rate. The compound' s mpy is commonly utilized to express the rate of corrosion, which can be beneficial to the monitoring and prevention of corrosion in most industrial applications.

Corrosion rate (C.R.) can be calculated following the G31-72 ASTM experimental standard, according to the formula C.R. = K x (W / DAT), wherein K = 3.45· 10^A6 representing units of 1/1000 milli-inch per year (mpy), W = weight loss in

3 2

milligrams, D = metal density in g/cm , A = area of sample in cm , and T = time of exposure of the metal sample in hours. In general, positive corrosion rate values represent loss of mass due to corrosion, and negative values typically represent the experimental error, adsorption or deposition of contaminants on the samples. Table 1 below presents typical values of the rate of corrosion of unprotected steel in various common environments.

Table 1

According to some embodiments of the present invention, the rate of corrosion characterizing a substrate or an article of manufacturing, such as a valve disc, as provided herein, in 3.5 % salt water (equivalent so sea water of about 599 mM of predominantly NaCl), is less than about 5 mpy, less than about 4.5 mpy, less than about 4 mpy, less than about 3 mpy, less than about 1 mpy, less than about 0.5 mpy, or less than about 0.1 mpy.

Accordingly, the loss of mass characterizing a substrate or an article of manufacturing, such as a valve disc, as provided herein, is less than 0.1 percent by weight, less than 0.05 percent, less than 0.01 percent, or less than 0.005 percent.

As discussed hereinabove, some of the advantages of combining a diffusion layer with a polymeric coating involve the synergistic corrosion-resistance effect achieved by a physical and corrosion-resistant polymer protecting a corrosion resistant substrate while reducing its friction coefficient and preventing a metal-to-metal contact between various parts of the valve.

While reducing the present invention to practice it was further uncovered that the Zn/Al diffusion layer as described herein provides an improved substrate for the polymeric coating in terms of adhesion, compared to other anti-corrosion treatment methods, such as zinc diffusion or nickel-chrome plating. It is postulated, without being bound by any particular theory, that the Zn/Al diffusion layer creates favorable conditions for adhesion of the polymeric layer by exhibiting an outer surface that is not conducive to the formation of loose oxides that otherwise would deteriorate the adhesion of the polymer (or a primer layer that precedes the polymeric layer) to the base metal. This advantage is observed when the treated and coated substrate is subjected to standard peeling tests. According to some of any of the embodiments of the present invention, the polymeric coating disposed over the diffusion layer exhibits adhesion thereto, as determined by a standard coating peel test according to, for example, the NFT 58-112 adhesion standard measured on a rating scale from 0 (low adhesion rating) to 4 (high adhesion rating), the EN 10310 standard for onshore and offshore metal pipelines, and the EN ISO 2409 suitable for adhesion tests using a cross-cut and a pull test. Alternatively the adhesion may be tested following Moon J-I. et al. [Polymer Testing, 2012, 31, p. 433-438], McKnight M.E. et al. [Journal of Protective Coatings and Linings, 1995, 12(5), p. 82-89] or the ASTM D 3359 standard method.

According to some embodiments, the polymeric coating adhesion to the Zn/Al diffusion layer described herein is at least 3 on the NFT 58-112 adhesion rating scale, or at least 4.

According to some embodiments, the polymeric coating adhesion to the Zn/Al diffusion layer, as measured by the EN ISO 2409 cross-cut method (pull test) is at least 8 Mpa, at least 10 Mpa, at least 12 Mpa, at least 14 Mpa, and at least at 16 Mpa.

The adhesion of the polymeric coating to the Zn/Al diffusion layer has been demonstrated and measured, as presented in the Examples section following below.

According to an aspect of some embodiments of the present invention, there is provided a process of preparing the articles of manufacturing provided herein, in any one of the described embodiments and any combination thereof, which is effected essentially by:

Immersing an iron or iron-rich substrate in a mixture of powders, comprising zinc, aluminum, and optionally powders of magnesium, silicon and nickel;

Heating the mixture of powders to a temperature of 400 °C in a sealed tumbling container for 1-24 hours;

Cooling and passivating the treated article in a passivation solution containing ZnO and orthophosphoric acid for 10 minutes at a temperature of 30-40 °C;

Coating the article with a polymeric coating.

In some embodiments, prior to immersing an iron or iron-rich substrate, the metal powders are subjected to hydrothermal treatment by adding water in the amount of 0.5-1 % by weight and keeping the mixture for one hour in a sealed reactor heated up to 300-350 °C. In some embodiments, prior to immersing an iron or iron-rich substrate in the metal powder mixture, the substrate is cleaned by, for example, sand blasting and/or washing in organic solvents.

In some embodiments, prior to coating the article with a polymer, the article is cooled and cleaned from excess metal powder and passivating solution.

It is expected that during the life of a patent maturing from this application many relevant iron or iron-rich substrate having a diffusion layer and a polymeric later disposed thereon will be developed, and the scope of the term "iron or iron-rich substrate having a diffusion layer and a polymeric later disposed thereon" is intended to include all such new technologies a priori.

As used herein the term "about" refers to ± 10 %.

The terms "comprises", "comprising", "includes", "including", "having" and their conjugates mean "including but not limited to".

The term "consisting of means "including and limited to".

The term "consisting essentially of" means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range. Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases "ranging/ranges between" a first indicate number and a second indicate number and "ranging/ranges from" a first indicate number "to" a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

As used herein the term "method" refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the chemical, pharmacological, biological, biochemical and medical arts.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.

EXAMPLES

Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non limiting fashion.

EXAMPLE 1

Zn/Al Treatment for Cast Iron Valve Discs

The cathodic treatment for an iron valve disc followed the procedure presented in U.S. Patent No. 7,241,350, which is briefly presented herein below. This anti- corrosion measure presented hereinbelow is referred to herein interchangeably as "zinc/aluminum diffusion treatment" or "zinc/aluminum cathodic treatment". The following materials for saturation and reagents for admixtures were used: Zinc powder (particles), supplied by Numinor Chemical Industries Ltd. (Israel), contained 93-96 % of zinc metal, having an average diameter size of less than 110 microns.

Aluminum powder, supplied by Zika Electrode Works Ltd. (Israel), contained

98.5 % of aluminum metal, having a particle size distribution: of 105-75 microns (5 % of the particles), 75-62 microns (15 % of the particles), and less than 44 microns (30 % of the particles).

Zinc oxide, supplied by Numinor Chemical Industries Ltd. (Israel), was pigment grade.

Magnesium powder, supplied by Zika Electrode Works Ltd. (Israel), contained 99.8 % of magnesium metal, having a particle size distribution of 420-297 microns (2 % of the particles, and less than 150 microns (97 % of the particles). The fraction of the particles greater than 75 microns, which was also used in the work, was isolated from this powder.

Silicon powder, supplied by Riedel-de Haen (Germany), contained 99 % of silicon metal, having a particle size distribution of 75-62 microns (34 % of the particles, and less than 44 microns (66 % of the particles).

Nickel powder (ME-040 grade), supplied by Zika Electrode Works Ltd. (Israel), contained 99.5 % of nickel metal.

Tin powder, supplied by Amdikat Ltd. (Israel), contained 99.88 % of tin metal, having a particle size distribution of 100-44 microns (5.8 % of the particles), and less than 44 microns (94.2 % of the particles).

Orthophosphoric acid solution, supplied by H.M. Chimilab Ltd. (Israel), contained 85 % of orthophosphoric acid.

Metal powders were subjected to hydrothermal treatment in compliance with Soviet Union Patent No. 1534091. Powders and water in the amount of 0.5-1 % by weight were kept for one hour in a sealed reactor heated up to 300-350 °C.

The process of diffusion saturation was carried out at a temperature of 400 °C, unless indicated otherwise, and a dwell time of 60 minutes for all saturating mixture compositions.

The coating process itself was performed as follows: A number of valve disc made of ductile cast iron (EN-GJS-400-15) weighing 750 grams were placed into a container, equipped with means for mixing the powders.

The container was filled up with a calculated amount of saturating mixture. The container was tightly sealed with an end cover and placed into a furnace equipped with a container-rotating device, which was rotated at 0.8 rpm. When the coating process was completed, the container was cooled down, and the dust remaining on the substrates was washed off using water.

Each treated valve disc was dried and passivated for 10 minutes at a temperature of 30-40 °C. The passivation solution contained 30 grams per liter of ZnO and 84 ml/1 orthophosphoric acid and formed a passivating layer of about 40 microns.

Weighing was accomplished using an A&D analytical balance, model HF-300G.

The coating thickness was determined using an Electromatic Equipment Co. magnetic thickness gauge, model DCF-900. Polished sections were analyzed using a Nikon microscope, model Optihot-lOOS.

Hardness was measured using a Buehler microhardness tester, Micromet 2100.

Chemical composition of coatings was determined by the XRF local microanalysis method using the JEOL-6400 instrument.

The corrosion resistance of the coating was determined in compliance with standard ASTM B 117 using the salt spray test. The quantitative measure of resistance is defined as the time elapsed before the appearance of white corrosion over the entire surface and red corrosion on 5 % of the specimen surface.

The mass loss in the salt spray test process was determined by weighing a specimen before and after testing, the corrosion products having removed from the specimen surface.

EXAMPLE 2

Polymeric Coating of a Treated Iron Valve Disc

Pristine valve discs, as well as valve discs which have been treated according to the procedure described in Example 1 hereinabove, were coated with a polymeric barrier layer using hot spraying or fluidization processes that afford highly reproducible thickness coating.

The valve disc samples were coated with HALAR® (an ECTFE polymer) according to the following procedure: The samples intended for coating with Halar® were cleaned by sand blasting and heated to about 300 °C for 15-45 minutes prior to coating. Various features on the samples were obscured in order to prevent their coating (threads and bores).

The cleaned and heated samples were sprayed with coating primer suitable for ECTFE overcoating, for example Halar® ECTFE 6614, to achieve a coat of about 100- 200 microns.

The primer-coated samples were heated to about 300 °C for 5 minutes and thereafter sprayed by or dipped in a polymer ECTFE solution, such as Halar® ECTFE 6014 for electrostatic spraying or Halar® ECTFE 6013 for dipping, to afford a polymeric coating of 150-200 microns over the primer layer, and the coated samples were kept heated for additional 5-15 minutes.

The previous step was repeated until the desired thickness has been achieved and allowed to cool at ambient temperature.

The valve disc samples were coated with Rilsan® nylon (a polyamide 11 polymer) according to the following procedure.

The samples intended for coating with Rilsan® were cleaned by sand blasting and heated to about 300 °C for 15-45 minutes prior to coating. Various features on the samples were obscured in order to prevent their coating (threads and bores).

The nylon coating tank contained RILSAN 7443 T BLUE MAC (coating polymer) and RILPRIM P23V40 (coating primer) powder (5 % to 10 % primer in the mixture) by Arkema Inc.

The powder in the tank was aired by flowing 8 bars of compressed air into the powder from ventilation inlets throughout the heating and coating process.

The cleaned and heated samples were inserted into the powder in the tank for 2- 5 seconds.

The Rilsan coated valve disc samples were removed from the powder tank, cooled to room temperature, sand-blasted to remove excess powder and sprayed with "RILPRIM P23 V40" by Arkema Inc. to achieve a combined coating of 250-300 microns thick.

It is noted that other polymeric barrier coating are contemplated in the context of embodiments of the present invention. EXAMPLE 3

Corrosion Resistance Tests in Salt Water

A series of valve disc samples, treated with Zn/Al and coated with Rilsan® nylon or HALAR® ECTFE according to the procedures described hereinabove, were subjected to salt water exposure tests as described hereinbelow. The experiments for corrosion and electrochemical testing, both in the lab using 3.5 % NaCl in deionized (DI) water and in actual seawater at extreme conditions, were conducted for up to 100 days.

Prior to the salt water exposure tests, a cross pattern (two intersecting grooves) was made on one side of the disc so as to form a scratch in the sample through the polymeric barrier coating and deeper than the depth of the cathodic treatment (about 250-350 microns deep from the top layer). These scratches were thereafter used to observe the corrosive effect of the salt water on the exposed part of the disc (the unprotected bare metal).

For control, similar samples of valve disc, treated with only one type of protection, cathodic or one of the polymeric coating, were subjected to similar testing conditions.

Corrosion tests at constant temperature:

The experiments were conducted under the standard practice for laboratory immersion corrosion testing of metals (ASTM G31-72). Samples were placed in an immersion bath circulating 3.5 % NaCl solution at 25-35 °C in three positions, fully immersed, partially immersed and out of the salt solution. The experiments were conducted for up to 100 days during which the samples were removed periodically for observation.

Figures 3A-C present photographs of three samples of cast iron valve discs which were fully immersed in a circulating 3.5 % NaCl solution at 30-33 °C for 14 days, wherein Figure 3A shows the sample which was treated with Zn/Al without a polymeric coating, Figure 3B shows the sample which was coated with Rilsan® nylon without being pre-treated with Zn/Al, and Figure 3C shows the sample which was treated with Zn/Al and subsequently coated with Rilsan® nylon polymeric coating.

As can be seen in Figures 3A-C, while the sample which was treated with Zn/Al without a polymeric coating showed no red rust, the entire sample became discolored (grayed), the which was coated with Rilsan® nylon without being pre-treated with Zn/Al had clear signs of red rust in the grooves of the cross patter scratches, and the sample which was treated with Zn/Al and coated with nylon remained as if not exposed to the salt solution, did not exhibit discoloration or red rust, and overall seemed not to be affected by the corrosive conditions it was exposed to like the other samples.

Polymeric coat adherence:

In order to assess the effect of the Zn/Al diffusion treatment on adherence of the polymeric coat on cast iron valve discs, according to embodiments of the present invention, after experiencing mechanical damage and exposure to corrosive conditions, the cathodic treated-, polymer coated- and the cathodic treated and polymer coated- samples were subjected to manual peel tests at the area wherein intentional damage was inflicted (cross pattern scratches).

In this experiment six cast iron disc valves were tested. Two samples were subjected to zinc/aluminum diffusion, as described hereinabove, so as to form a layer of about 40 microns thick of cathodic protection; two samples were coated only with a layer of nylon, as described hereinabove; and two samples were treated with zinc/aluminum and coated with nylon. All samples were scratched in the center of the disc in a cross pattern, as described hereinabove, before exposure to salt solution. All samples were fully immersed in a 3.5 % sodium chloride solution, and the temperature of the solution was varied in a daily cycle between 33 °C for 12 hours to 25 °C for the remaining 12 hours for 50 days.

The coating of some of the above-mentioned samples was peeled in order to assess the coat adhesion at areas away from the coat scratching damage, and in order to assess the corrosion expansion under the protective coat. The peeling was effected so as to remove some of the polymeric coating to some extent so as to exposed the underlying base metal, regardless of the required force; hence these are not peeling test results in the standard sense of the term, as these tests do not provide a numeric value for adhesion.

Figure 4 is a table presenting color photographs of the valve discs exposed to salt solution for 50 days and subjected to a coat peeling, showing the effect of each of the Zn/Al diffusion treatment the effect of the polymeric coating, and the effect of a combination thereof. As can be seen in Figure 4, the visual inspection of the samples supported the results of the mass loss and corrosion rate experiments for the samples treated with Zn/Al diffusion only (samples 1 and 2), and local corrosion damage (red rust) was observed throughout the surface of the metal. Similar corrosion damage signs were also found along the entire surface of the metal in the samples nylon coated (samples 5 and 6). In contrast, for the samples which received both anti-corrosion treatments (samples 3 and 4), significant corrosion signs are not observed.

In addition to corrosion resistance, the fastness and adherence of the nylon coating was examine in valve disc samples treated with Zn/Al diffusion, nylon coating and both. It was found that the samples not treated for Zn/Al diffusion and coated with nylon only, exhibited relatively low coating adherence compared to the samples treated with both anti-corrosion measures.

Conclusions:

The combined anti-corrosion measures conferred superior corrosion resistance and coating adherence, compared to those observed in samples treated with each of the measures alone.

Components made of Zn/Al diffusion treated cast iron coated with nylon are significantly more cost effective, compared to components made of stainless steel. EXAMPLE 4

Nylon coating adhesion measurement

Comparative testing of the adhesion of nylon coating to the Zn/Al diffusion layer on a valve disc was conducted following the NFT 58-112 peel test, the EN 10310 scraping test and the EN ISO 2409 pull test, and compared to a valve disc not treated by Zn/Al diffusion.

The NFT 58-112 is rated from 0 to 4, where 4 is high level of adhesion. The EN 10310 test is rated by the distance in millimeters of exposed substrate from the center a cross pattern scratches when a corner of the cross pattern in the coating is pulled, where the longest distance indicates a low adhesion rating, whereas the pull force is also recorded to provide an additional adhesion strength parameter, where a higher force indicates better adhesion rating. Five discs were sand-blasted to clean-off any residuals, and three were subjected to Zn/Al diffusion treatment as described hereinabove while the remaining two discs were used as a control experiment. All the discs were thereafter coated with 200-400 μηι thick blue RILSAN® 5005/5010 (nylon- 11) coating, as described hereinabove.

The coating on all samples was subjected to cross pattern scratches at the center of each disc, and the adhesion tests were conducted before and after exposing the coated discs having a cross pattern scratches to water at 80 °C for 24 hours.

The results indicated that both the Zn/Al diffusion treated and RISLAN® coated samples and the samples having RILSAN® coating without a Zn/Al diffusion layer exhibited high adhesion (rating of 4 in the NFT 58-112 test and 1 mm in the EN 10310 test).

After the samples were subjected to water at 80 °C for 24 hours, the Zn/Al diffusion treated and RISLAN® coated samples exhibited a rating of 3.5-4 in the NFT 58-112 test, 1 mm in the EN 10310 test and a pull force of more than 12 MPa with a breaking region failure between the primer and the coating, as oppose to between the Zn/Al diffusion layer and the primer. The samples having RILSAN® coating without a Zn/Al diffusion layer exhibited a rating of 1.5-4 in the NFT 58-112 test, 2 mm in the EN 10310 test and a pull force of less than 6 MPa with a breaking region failure between the primer and the base metal.

Figures 5A-D present color photographs of the valve discs after exposure to water at 80 °C for 24 hours, showing the superior adhesion of the RISLAN® coating on the Zn/Al diffusion layer (Figures 5A-B) compared to the inferior adhesion of the RISLAN® coating to the base metal (Figures 5C-D).

As can be seen in Figures 5A-D, and reckoned from the numeric results, the Zn/Al diffusion treatment improves the adhesion of the polymeric coating to the metal disc. Figure 5A and Figure 5C show the results of the NFT 58-112 test, wherein Figure 5A exhibits a rough separation of the top polymeric layer from the primer layer, leaving the primer layer attached to the treated metal, while Figure 5C exhibits a "clean" detachment of the entire polymeric coating from the untreated metal. Figure 5B and Figure 5D show the results of the EN 10310 test, wherein Figure 5B exhibits a short peeling distance from the center of the cross pattern, while Figure 5D exhibits a longer peeling distance, exposing bare metal surface. Zinc hot dip coating, nickel plating and nickel/chrome electroplating were also conducted on cast iron valve discs, however, the polymeric coating adhesion to these samples was below minimal testing level, indicating that zinc coating by itself, nickel plating and nickel/chrome electroplating all provide a poor substrate for the subsequent polymeric coating in terms of adhesion strength (results not shown).

EXAMPLE 5

Accelerated Conditions in Salt Water Spray

Experimental description:

The accelerated extreme conditions salt water spray (fog) test follows the ASTM B 117 standard, and consists of atomizing a salt solution into uniform droplets on specimens supported or suspended between 15° - 30° from the vertical.

Briefly, the salt solution is a solution of 5 % by weight of sodium chloride (compared to sea water, which is 1.8 % to 3.5 %). The exposure zone of the salt spray chamber is maintained at 35 °C, and the pH of the salt solution is such that when atomized at 35 °C, the collected solution will be in a pH of 6.5 to 7.2. The exposure period is 1000 hours, not counting brief cessation of the exposure for weight measurements.

Iron-cast valve discs, each having about 4000 cm of exposed surface area, are divided into groups of 2-4 items each. Half of the members of each group is subjected to identical coating damage which is applied as a 1 mm deep cross pattern scratches at the center of each disc or al mm deep cut across the entire diameter and at the center of each disc.

Each group is subjected to the flowing treatment prior to exposure to salt spray:

Group No. Treatment

1. Sand blasting

2. Sand blasting; and

Zinc powder diffusion

3. Sand blasting; and

Zinc/ Aluminum diffusion

4. Sand blasting; and

RILSAN coating

5. Sand blasting;

Zinc powder diffusion; and

RILSAN coating 6. Sand blasting;

Zinc/ Aluminum diffusion; and

RILSAN coating

From each group, the same two items are removed periodically every 24 hours, dried in a 150 °C vacuum oven until reaching a stable weight, recorded for weight and photographed, and returned to the salt spray chamber.

At the end of the 1000 hours exposure to salt spray, all items are removed from the chamber, dried in a 150 °C vacuum oven until reaching a stable weight, recorded for weight and photographed.

Thereafter, the mass loss of each of the measurements is use to calculate the rate of corrosion for each item, and the average between the pairs of items exposed to identical conditions is use for comparing the corrosion rate for each group.

After mass loss measurements, each of the polymer-coated samples is subjected to a standard adhesion strength, using, for example, the NFT 58-112 peel test and/or the BS EN 10310 scraping test and/or the EN ISO 2409 pull test.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting.

Claims

WHAT IS CLAIMED IS:

1. An article-of-manufacturing comprising an iron or iron-rich substrate and comprising a diffusion layer formed on at least a portion of an exterior surface of said substrate, and further comprising a polymeric coating disposed on at least said portion of said external surface having said diffusion layer, wherein said diffusion layer comprises zinc and iron and discrete, laterally non-continuous, aluminum-rich inclusions randomly distributed on or in said layer, and further comprising a polymeric coating disposed on at least said portion of said external surface.

2. The article-of-manufacturing of claim 1, wherein a thickness of said diffusion layer ranges from 1 micron to 60 microns.

3. The article-of-manufacturing of claim 1, wherein said diffusion layer further comprises at least one element selected from the group consisting of tin, silicon and magnesium.

4. The article-of-manufacturing of any one of claims 1-3, wherein said polymeric coating comprises at least one polymer selected from the group consisting of a polyamide, a halopolymer, an epoxy resin, a silicone-based polymer, a sol-gel, low and high-density polyethylene, a polyurethane, an aliphatic polyester urethane resin, an aliphatic polycarbonate urethane resin, a hydroxy-functional polyacrylate, a poly(urethane acrylate) and a polyacrylate, and any combination thereof.

5. The article-of-manufacturing of claim 4, wherein said polyamide is nylon 11.

6. The article-of-manufacturing of claim 4, wherein said halopolymer is ethylene chlorotrifluoroethylene (ECTFE).

7. The article-of-manufacturing of any one of claims 4-6, wherein said polymeric coating comprises a primer layer and a top polymeric layer.

8. The article-of-manufacturing of any one of claims 4-7, wherein a thickness of said polymeric coating ranges from 50 micron to 500 microns.

9. The article-of-manufacturing of any one of claims 4-8, wherein said polymeric coating is characterized by an adhesion to the substrate rated at least 3 on an NFT 58-112 scale.

10. The article-of-manufacturing of any one of claims 4-8, wherein said polymeric coating is characterized by an adhesion to the substrate rated less than 2 mm on an EN 10310 scale.

11. The article-of-manufacturing of any one of claims 4-8, wherein said polymeric coating is characterized by a peel force of at least 10 MPa.

12. The article-of-manufacturing of any one of claims 1-11, configured to withstand a flow of salted water of at least 1.5 cubic meters per hour and/or a hydraulic pressure of at least 1 atmosphere for 100 days.

13. The article-of-manufacturing of any one of claims 1-12, being a valve disc.

14. An iron or iron-rich valve disc comprising a diffusion layer formed on at least a portion of an exterior surface thereof, the valve disc further comprising a nylon 11 coating disposed at least one said portion of said external surface, wherein said diffusion layer comprises zinc and iron and discrete, laterally non-continuous, aluminum-rich inclusions randomly distributed on or in said layer.

15. An iron or iron-rich valve disc comprising a diffusion layer formed on at least a portion of an exterior surface thereof, the valve disc further comprising a ECTFE coating disposed at least one said portion of said external surface, wherein said diffusion layer comprises zinc and iron and discrete, laterally non-continuous aluminum-rich inclusions randomly distributed on or in said layer.

16. The valve disc of any one of claims 14-15, wherein a thickness of said diffusion layer ranges from 1 micron to 60 microns.

17. The valve disc of any one of claims 14-15, wherein said diffusion layer further comprises at least one of tin, silicon, and magnesium.

18. The valve disc of any one of claims 14-17, wherein a thickness of said coating ranges from 50 micron to 500 microns.

19. The article-of-manufacturing of any one of claims 1-13 or the valve disc of any one of claims 14-18, exhibiting a rate of corrosion of less than 5 mpy when fully immersed in a 3.5 % sodium chloride solution at a temperature of 25-33 °C for at least 50 days.

20. The article-of-manufacturing of any one of claims 1-13 or the valve disc of any one of claims 14-18, exhibiting a mass loss of less than 0.1 percent by weight when fully immersed in a 3.5 % sodium chloride solution at a temperature of 25-33 °C for at least 50 days.

21. A process of preparing the article-of-manufacturing of any one of claims 1-13 or the valve disc of any one of claims 14-18, the process comprising:

applying said polymeric coating at least one said portion of the external surface, essentially as described herein.