Abstract:
An ionic transport material is disposed relative to a substrate and configured to establish an ionic connection between the substrate and a replaceable sacrificial anode. The replaceable sacrificial anode is electrically connected to the substrate and is provided to inhibit corrosion of the substrate.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to inhibiting corrosion in substrates (e.g., metals, elements, equipment, structures, and vehicles, aircraft, cars, trucks, etc.). 
       BACKGROUND 
       [0002]    Corrosion protection of substrates (e.g., structures, aircraft, cars, trucks, metal parts of equipment, etc.) from moisture in air is typically accomplished by coating such substrates with a protective coating using specialized materials (e.g., epoxies, paints, and urethanes). However, such coatings are known to be prone to environmental damage and, once damaged, can leave the underlying metal substrate susceptible to corrosion. Although continued protection with such coatings can be achieved by maintenance and reapplication of the coating, the reapplication process can be costly since it often involves removal of an equipment from service, complete removal of old protection layers, and/or application of a new protection layer 
         [0003]    Sacrificial anodes have been used in marine applications to protect corrosion of metal hulls and equipment that are immersed in water. In such applications, the water in which the parts are immersed functions as an ionic transport medium that facilitates electrochemical connection between the sacrificial anode and surfaces to be protected. However, such sacrificial anodes are not completely effective since, significant corrosion can occur in regions, commonly referred to as “splash zones,” where water is intermittently splashed on the surface but a consistent ionic connection cannot be established with the sacrificial anode to prevent corrosion of the surface. 
       SUMMARY 
       [0004]    Since the ionic transport medium established between the sacrificial anode and the substrate in water cannot be established in air, sacrificial anodes cannot be as easily used to protect substrates from corrosion in air. Although techniques involving dispersing small particles of a sacrificial anode material throughout the protective coating have been proposed, once the protective coating is damaged, it can leave behind an exposed layer that begins to corrode, with the corrosion working its way under the undamaged coating. Further, no readily available technique for recharging the protection has been proposed. 
         [0005]    Some embodiments of the present invention feature a method of inhibiting corrosion of a substrate. The method involves coupling an ionic transport material to the substrate and establishing an electrical connection between the substrate and a replaceable sacrificial anode. 
         [0006]    Some embodiments of the present invention feature a system for inhibiting corrosion of a substrate. The system includes a replaceable sacrificial anode that is disposed relative to the substrate and an ionic transport material that is coupled to the substrate. The ionic transport material can be inserted between the substrate and the replaceable sacrificial anode. 
         [0007]    Some embodiments feature a method of inhibiting corrosion of a substrate. The method involves establishing an electrical connection between the substrate and a replaceable sacrificial anode and coupling an ionic transport material to the substrate. The ionic transport material can establish an ionic connection between the substrate and the replaceable sacrificial anode. 
         [0008]    Certain embodiments feature a system for inhibiting corrosion of a substrate. The system includes a replaceable sacrificial anode that is electrically connected to the substrate and an ionic transport material that is disposed relative to the substrate and is configured to establish an ionic connection between the substrate and the replaceable sacrificial anode. 
         [0009]    In other examples, any of the aspects above, or any apparatus or method described herein, can include one or more of the following features. 
         [0010]    In some embodiments, the ionic transport material can be coupled to the substrate by adhering a continuous layer of the ionic transport material to the substrate. In certain embodiments, the ionic transport material is coupled to the substrate by applying the ionic transport material as a top-coat layer to the substrate. 
         [0011]    In certain embodiments, the electrical connection between the substrate and the replaceable sacrificial anode can be established by placing the replaceable sacrificial anode and the substrate in direct physical contact. In some embodiments, the electrical connection between the substrate and the replaceable sacrificial anode can be established using an electrical wire. In some embodiments, the electrical connection between the substrate and the replaceable sacrificial anode can be established using an electrical conductor included in the ionic transport material. In some embodiments, the ionic transport material can include multiple layers. Each layer of ionic transport material can have an electrical conductivity that is independent of the other layers. 
         [0012]    In some embodiments, the ionic transport can be arranged to mechanically support the replaceable sacrificial anode. In certain embodiments, the ionic transport material can include a nanoporous solid that supports ionic transfer between the substrate and the replaceable sacrificial anode. 
         [0013]    In some embodiments, the replaceable sacrificial anode can include at least one element less noble than the substrate. In certain embodiments, depletion of the replaceable sacrificial anode can be monitored and in the event the depletion exceeds a predetermined threshold, an indication can be issued to request replacement of the replaceable sacrificial anode. 
         [0014]    Other aspects and advantages of the invention can become apparent from the following drawings and description, all of which illustrate the principles of the invention, by way of example only. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The advantages of the invention described above, together with further advantages, may be better understood by referring to the following description taken in conjunction with the accompanying drawings. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
           [0016]      FIG. 1A  is a block diagram of a system for inhibiting corrosion according to some illustrative embodiments of the invention. 
           [0017]      FIG. 1B  is a block diagram of a system for inhibiting corrosion according to certain illustrative embodiments of the invention. 
           [0018]      FIG. 1C  is a block diagram of a system for inhibiting corrosion according to some illustrative embodiments of the invention. 
           [0019]      FIG. 2  is a schematic of a system for inhibiting corrosion of a substrate according to an illustrative embodiment of the present invention. 
           [0020]      FIG. 3  is a flow diagram of procedures for inhibiting corrosion of a substrate according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Some embodiments disclosed herein address the problem of corrosion of substrates (e.g., parts, structures, surfaces, equipment and airframes) through coupling an ionically conductive transport layer to the substrate and establishment of an electrical connection between a replaceable sacrificial anode and the substrate to be protected. The ionically conductive layer creates an electrochemical connection between the replaceable sacrificial anode and the substrate by allowing ions to flow between the replaceable sacrificial anode and the substrate. The replaceable sacrificial anode includes at least one element that is less stable than the substrate and, as such, when exposed to environmental conditions, is oxidized more readily than the protected substrate. During oxidation, electrons travel from the replaceable sacrificial anode to the surface to be protected, resulting in a reduction reaction, thereby preventing oxidation and corrosion of the surface. 
         [0022]    By using a replaceable sacrificial anode, embodiments disclosed herein offer rechargeable protection of the substrates through replacement of the replaceable sacrificial anode. The protection offered by the embodiments disclosed herein is versatile in that it can be applied to various surfaces and environmental conditions by adjusting the replaceable sacrificial anode size, adjusting the spacing between multiple replaceable sacrificial anodes, and adjusting the thickness of the ionically conductive layer. 
         [0023]    In some embodiments, the ionic conductive transport layer can include a metal organic framework (MOF) and/or polymer layer. The uniform nanoporous MOF can trap water and assist in solvation of the metal ions, thereby promoting ionic transport. Further, in some embodiments, the polymer can act as a binding agent that provides mechanical support and maintains the dimensional stability of the ionic transport layer. In certain embodiments, the ionic transport layer can be used to mechanically connect the replaceable sacrificial anode. 
         [0024]      FIG. 1A ,  FIG. 1B , and  FIG. 1C  are block diagrams of some embodiments of the invention that can be used for inhibiting corrosion of a substrate  110 . The substrate  110  can be any parts, structures, surfaces, equipment, and airframes that need to be protected against corrosion. The substrate  110  is coupled with an ionic transport material  120 . The ionic transport material  120  can be applied over existing paints that may have been previously applied to the substrate  110  and/or be designed to replace the existing paints. 
         [0025]    In some embodiments, the ionic transport material  120  can be applied as a top-coat layer to the substrate  110 . The ionic transport material  120  can include a nanoporous solid (e.g., MOF, molecular sieves, mesostructured glass, zeolites, etc.) that can trap water and ensure ionic conduction in presence of little to no moisture in the atmosphere. 
         [0026]    A replaceable sacrificial anode  130  can be disposed relative to the substrate  110 . Although a single replaceable sacrificial anode  130  is shown, depending on the application at hand, multiple replaceable sacrificial anodes  130  can be utilized. In some embodiments, a physical connection between the replaceable sacrificial anode  130  and the substrate  110  can be established using an external clamping mechanism (not shown). As shown in  FIG. 1B , in certain embodiments, the physical connection between the replaceable sacrificial anode  130  and the substrate  110  can be established using the ionic transport layer  120 . Connecting the replaceable sacrificial anode  130  to the substrate  110  using the ionic transport layer  120  is feasible since it simplifies system design by reducing the number of required parts. 
         [0027]    An electrical connection between the replaceable sacrificial anode  130  and the substrate  110  can be established in a number of ways. For example, as shown in  FIG. 1B , in some embodiments, the substrate  110  and the replaceable sacrificial anode  130  can be arranged such that they are in direct physical contact with each other. The physical contact established between the two mediums  110 ,  130  allows for transferring electrons through the physical contact point, resulting in establishing an electrical connection between the substrate  110  and the replaceable sacrificial anode  130 . 
         [0028]    In some embodiments, the electrical connection between the substrate  110  and the replaceable sacrificial anode  130  can be established by connecting the two mediums using an electrical wire  140  and appropriate connectors (not shown). In the embodiments that employ electrical wires to connect the substrate  110  and the replaceable sacrificial anode  130 , further protection can be offered by monitoring the current that flows during oxidation of anode along this connection. In some embodiments, the data obtained from monitoring the current flowing between the substrate  110  and the replaceable sacrificial anode  130  can be used to provide a service alert to a user indicating when the replaceable sacrificial anode  130  should be replaced. A change in the potential difference between the sacrificial anode and substrate can signal significant loss of the sacrificial anode and, therefore, a need to replace the anode. In some embodiments, when operating in presence of stable electrical resistance, a change in the current flow can signal a reduction in the amount of sacrificial anode and a need to replace the anode. The amount of potential flow/change and/or current flow/change that is used to indicate the need for replacing the sacrificial anode can be a function of the system design and/or the application at hand. 
         [0029]    In certain embodiments, the electrical connection between the substrate  110  and the sacrificial anode  130  can be established through the ionic transport layer  120 . For example, as shown in  FIG. 1C , the electrical connection between the substrate  110  and the replaceable sacrificial anode  130  can be established by inclusion of a conductor  150  in the ionic transport layer  120 . In such embodiments, no additional wires are necessary. In some embodiments, the conductor  150  can be added under the replaceable sacrificial anode  130  or into the ionic transport layer  120 . In some embodiments, the conductor  150  can be added throughout the ionic transport layer  120 . By including the conductor  150  throughout the ionic transport layer  120 , the area of electrical connection to the substrate  110  can be significantly increased. This increased surface area reduces the required electrical conductivity of the composite conductor  150  and ionic transport layer  120 . 
         [0030]    In some embodiments, the ionic transport layer  120  can include multiple layers, each having an electrical conductivity or conductivity properties that can be different from the electrical conductivity or conductivity properties of other layers. For example, in one embodiment, two layers with distinctly different electrical conductivity or conductivity properties can be used. In some embodiments, the electrical conductivity of a layer (e.g., the top layer) can be maximized by addition of more conductors  150 . In some embodiments, the conductor  150  can be selected to maximize the conductivity of the layer along the surface of the layer, as compared to perpendicular to the surface of the layer. Further, in some embodiments, the electrical conductivity of a layer (e.g., the bottom layer) can be reduced relative to the other layers. In some embodiments, having multiple layers with varying conductivity levels, can serve to transfer the electrical charge in directions that may be desired/required. For example, when using a multi-layer ionic transport layer  120  that includes a top layer with increased conductivity (as compared to the other layers) and a bottom layer with decreased conductivity (as compared to the other layers), a electrical charge is first distributed across the surface of the conductor  150  and/or the ionic transport layer  120  and then more evenly down through the coating to the substrate. 
         [0031]      FIG. 2  is a schematic of a system for inhibiting corrosion of a substrate according to an illustrative embodiment of the present invention. In the embodiment illustrated in  FIG. 2 , a replaceable sacrificial anode  230  is directly connected to the ionic transport layer  220  and the substrate  210  to be protected, although, as noted previously, an electrical connection between the replaceable sacrificial anode  230  and the substrate  210  can be established in a number of ways (e.g., disposing the replaceable sacrificial anode  230  relative to the substrate  210  and running an electrical wire between the replaceable sacrificial anode  230  and the substrate  210 , placing the replaceable sacrificial anode on top of the ionic transport layer  220  and including a conductor in the ionic transport layer  220  to ensure electrical connection, etc.). 
         [0032]    As shown in  FIG. 2 , the cathodic action of the substrate  210  functions to reduce and extract oxygen (O 2 ) from the atmospheric air and form ions (OH − ) that in absence of the ionic transport layer  220  and the replaceable sacrificial anode can potentially cause corrosion of the substrate  210 . The ions (OH − ) are drawn along the conductive pathway created by the greater anodic potential of the replaceable sacrificial anode  230  and through the ionic transport layer  220  to the replaceable sacrificial anode  230  resulting in corrosion of the replaceable sacrificial anode  230 . The corrosion of the replaceable sacrificial anode  230  completes the electrochemical circuit created by the substrate  210 , ionic transport layer  220 , and the replaceable sacrificial anode  230 , inhibiting corrosion of the substrate  210 . 
         [0033]    The ionic transport layer  220  can be applied to the substrate  210  as a standalone film layer. In some embodiments, the ionic transport layer  220  can have a resistivity of less than or about 20000 Ω-cm. In some embodiments, depending on the application at hand and the required level of protection, the thickness of the ionic transport layer  220  can be tailored to attain diverse levels of ion conductance. In some embodiments, the thicknesses of the ionic transport layer  220  can be in the range of 10 to 100 microns. In addition to the thickness of the corrosion medium, the corrosion protection offered by the ionic transport layer  220  can depend on the distance of the ionic transport layer  220  from the sacrificial anode  230  and size of any defects that may be present in the ionic transport layer  220 . 
         [0034]    In some embodiments, in the event multiple replaceable sacrificial anodes  230  are used, having lower values of resistivity for the ionic transport layer  220  can allow for larger spacing between the multiple replaceable sacrificial anodes  230 . The spacing between the replaceable sacrificial anodes  230  can be adjusted to provide efficient corrosion protection and can be varied to the desired level. In some embodiments, the spacing between the replaceable sacrificial anodes  230  can depend on a number of factors including the thickness of the ionic transport layer  220 , the conductivity of the ionic transport layer  220 , and the corrosion environment. For example, in one embodiment, when using a 15-20 micron thick ionic transport layer  220 , the ionic transport layer  220  and replaceable sacrificial anode  230  can offer effective corrosion protection up to about between 2-3 inches from the replaceable sacrificial anode  230 . In another embodiment, when using multiple replaceable sacrificial anode  230  and an ionic transport layer  220  having a thickness of about or more than 25 micron, greater ionic transport layer  220  effective protection can be achieved by placing the replaceable sacrificial anode  230  at 6 inch intervals of one another. The distance between the replaceable sacrificial anodes  230  can be increased by using a thicker ionic transport layer  220 . 
         [0035]    The ionic transport layer  220  and replaceable sacrificial anode  230  can further provide the substrate  210  with protection even in the presence of environmental damage, defect, or discontinuities  240  in the ionic transport layer  220 . Specifically, depending on the thickness of the ionic transport layer  220 , the corrosion protection offered by the replaceable sacrificial anode  230  and ionic transport layer  220  can extend into the damaged and/or scratched areas  240  of the ionic transport layer  220 . For example, in one embodiment, two millimeter wide defects in the ionic transport layer can be protected with a 60 micron thick ionic transport layer and with the potential to protect larger defects at this thickness. In some embodiments, the extent of the protection offered in a scratch  240  can be proportional to the thickness of the ionic transport layer  220 . 
         [0036]    In some embodiments, the ionic transport layer can be directly applied to the substrate surface to be protected. Depending on application and other factors such as the desired thickness of the ionic transport layer, various application techniques can be used. For example, the ionic transport layer can be applied by spraying, painting, or rolling the ionic transport layer to the substrate. 
         [0037]    In some embodiments, the ionic transport layer  220  can be formed by mixing together a nanoporous MOF and a polymer. The polymer can be polyacrylonitrile, polyimide, polyvinylidene fluoride, polyurethane, or other similar film forming polymers that effective at binding together particulates. In some embodiments, the ionic transport layer  220  can be developed by mixing of the MOF and one or more polymer solution to form a slurry. Since the ionic transport layer  220  is mechanically supported by the substrate, the ratio of the polymer to the nanoporous solid can be adjusted. For applications where the film is self-supporting and/or support roll-to-roll processing, additional polymer amounts can be used to allow for less adjustment in the nanoporous solid content. Adjustments in the ratio of the nanoporous solid content of the ionic transport layer  220  can impact the ionic conduction capabilities of the transport layer, causing the ionic transport layer  220  to be more (or less) conductive. The change in the conductivity level of the ionic transport layer  220 , in turn, can impact the thickness of the ionic transport layer  220  that may be required for a certain application and/or effect the sacrificial anode spacing distances that may be required for that application. 
         [0038]    In some embodiments, once the slurry is formed, it is applied to the substrate  210  and allowed time to dry. In certain embodiments, the replaceable sacrificial anode can be directly adhered during the application of the slurry or by pressing the replaceable sacrificial anode into the undried/wet ionic transport layer slurry. If applied to a wet ionic transport layer slurry, the replaceable sacrificial anode is adhered to the substrate  210  by the dried ionic transport layer  220 . 
         [0039]    In one embodiment, an ionic transport layer can be used to protect a stainless steel substrate. The ionic transport layer can be placed (e.g., coated on as a topcoat) over a surface of a substrate (e.g., steel) in the form of a film and wetted to increase contact. A replaceable sacrificial anode (e.g., made of magnesium or zinc) is electrically connected to the substrate. Upon exposure of the substrate surface to a salt water (NaCl) solution, a potential difference between the surfaces confirms the electrical and ionic connection is established. Although corrosion in the substrate can occur in the surfaces that have not been coated with the ionic transport layer, the surface under the ionic transport layer is protected from corrosion due to the ionic and electrical connection established between the substrate and the replaceable sacrificial anode. Further, corrosion inhibition can be observed in the areas adjacent to the surface coated with ionic transport layer since, due to the anodic potential of the sacrificial anode, ions from such areas can be drawn to the sacrificial anode along the ionic transport layer. In some embodiments, protection to unprotected areas can extend to about 2 millimeter beyond the areas covered with the ionic transport layer. 
         [0040]    In one embodiment, in order to evaluate and compare the effectiveness of the ionic transport layer in providing a substrate protection against corrosion, a solution including synthetic sea water can be used. The synthetic sea water can be formed by adding approximately 50 grams of sodium chloride (NaCI), 22 grams of magnesium chloride (MgCl,2.6H20), 3.2 grams of calcium chloride (CaCh,2H20), and 8.0 grams of sodium sulfate (Na2S04) to approximately one liter of distilled water. The multiple substrate surfaces can be observed, of which some are left unprotected, some have been protected with urethane, some have been coated with a layer of the ionic transport layer, and some have been coated with both a layer of the ionic transport layer and a layer of urethane. The application of the urethane after the ionic transport layer provides additional abrasion resistance without inhibiting ion flow. 
         [0041]    A spray test solution can be prepared by adding approximately 2 milliliter of sulfurous acid (6.4 percent assay as SO2) to each liter of the synthetic sea water. The spray test solution can have a PH that is maintained approximately between 3.3 and 3.5. The substrate can be tested by mounting the substrate on a motor and spinning it around while spraying the substrate surfaces. The substrate can be tested for a number of hours (e.g., multiple hour long tests, conducted a few (e.g., four) hours apart from one another). Once the testing is completed, the substrate surface can be observed using an optical microscope to determine the extent of corrosion. 
         [0042]    Upon conducting such experiment, corrosion in uncoated surfaces can be observed rapidly. In the surfaces coated with urethane, due to the hydrophobic nature of urethane, corrosion is not observed even after a two hour long spray session. However, once scratched to expedite corrosion, corrosion in the surface initiates after about an hour and becomes more significant about after two hours into a spray session, and even continues to expand on storage. In contrast, substrate surfaces protected by the ionic transport layer, even when scratched, demonstrate no corrosion during or after corrosion testing. 
         [0043]      FIG. 3  is a flow diagram of procedures for inhibiting corrosion of a substrate according to embodiments of the present invention. An ionic transport layer can be coupled with a substrate surface (block  310 ). The ionic transport layer can be coupled with the substrate in a number of ways, for example by painting, rolling, etc. a layer of the ionic transport layer onto the substrate. 
         [0044]    Further, a replaceable sacrificial anode can be disposed adjacent to the substrate (block  320 ). The replaceable sacrificial anode includes at least one element that is less stable than the substrate and, as such, when exposed to environmental conditions, is oxidized more readily than the protected substrate. In some embodiments, more than one replaceable anode can be used. The replaceable sacrificial anode can be coupled to the substrate in a number of ways (e.g., using an external clamping mechanism or through the ionic transport layer). 
         [0045]    Corrosion in the substrate can be inhibited by establishing an electrical and ionic connection between the replaceable anode and the substrate (block  330 ). An electrical connection between the replaceable sacrificial anode and the substrate can be established in a number of ways (e.g., using an electrical wire, bringing the substrate and the sacrificial anode in direct contact, by including a conductor in the ionic transport layer). 
         [0046]    The electrical connection (e.g., current flow) between the substrate and the sacrificial anode can be monitored (block  340 ) to determine whether the anode has depleted. If the anode has depleted beyond a certain threshold, a user can be alarmed to replace the sacrificial anode (block  320 ). 
         [0047]    While the invention has been particularly shown and described with reference to specific illustrative embodiments, it should be understood that various changes in form and detail may be made without departing from the spirit and scope of the invention.