Methods for removal of reaction sites on metal surfaces and application of a nanotube containing protective coating

Abstract

A method of preparing and decontaminating a substrate surface to remove contaminants including the steps of applying a first dry or fluid composition having a pH of 4 or less comprising an acidifier and an oxidizer, allowing the first composition to remain on the substrate surface for a predetermined period of time, and rinsing the first composition from the substrate surface with a second composition having a pH of 8 or more comprising an alkaline material liquid mixture formed utilizing activated carbon filtered potable water to achieve a neutral pH condition on the surface, and then applying a nanotubes coating on the surface.

Claims

1. A method of decontaminating a metal substrate surface to remove contaminants and preparing the decontaminated substrate surface for subsequently applying a protective coating on the substrate surf ace, comprising the steps of: a. applying to the substrate surface a first composition having a pH of 4 or less comprising an acidifier and an oxidizer; wherein the acidifier comprises citric acid anhydrous and the oxidizer comprises sodium persulfate; wherein the first composition in dry form comprises about 75% to 85% by weight acidifier and about 0.1% to 10% by weight oxidizer; b. allowing the first composition to remain on the substrate surface for a predetermined period of time; and c. rinsing the first composition from the substrate surface with a second composition having a pH of 8 or more comprising an alkaline material liquid mixture formed utilizing activated carbon filtered potable water to achieve a neutral pH condition on the surface.

2. The method according to claim 1 wherein the first composition is a gel comprising a mixture of an acidifier, an oxidizer and a rheology modifier.

3. The method according to claim 2 wherein the rheology modifier is xanthan gum.

4. The method according to claim 1 wherein the acidifier is in a powder form, and then mixed on-site with an activated charcoal filtered water to form the first composition.

5. The method according to claim 1 wherein the acidifier in the first composition is selected from the group of mineral acids comprising phosphoric acid, sulfuric acid, boric acid, hydrofluoric acid, hydrobromic acid, perchloric acid, other acids and salts derived from one of these mineral acids, and combinations there from.

6. The method according to claim 1 wherein the acidifier in the first composition is selected from the group of organic acids which are short or medium chain organic acids and which are food grade acids.

7. The method of claim 6 wherein the organic acids are citric acid anhydrous, sodium bisulfate, derivative compounds of citric acid or sodium bisulfate, and combinations thereof.

8. The method of claim 1 wherein the oxidizer in the first composition is selected from the group consisting essentially of persulfates, perborates, percarbonates, derivative compounds containing a radical similar to that in persulfates, perborates, or percarbonates, and combinations thereof.

9. The method of claim 8 wherein the oxidizer in the first composition is selected from the group consisting essentially of sodium persulfate, a derivative compound containing a radical similar to that in sodium persulfate, and combinations thereof.

10. The method according to claim 1 wherein the first composition comprises a thickener.

11. The method according to claim 1 further comprising, after application of the first composition on the substrate surface, vibrating the substrate surface for a period of time.

12. The method according to claim 1 wherein the predetermined period of time is about 30 minutes to about 60 minutes.

13. The method according to claim 1 further comprising the step of repeating the applying of the first composition and rinsing of the first composition from the substrate surface utilizing activated carbon filtered potable water to remove any contaminates remaining after the repeated rinsing.

14. The method according to claim 1 further comprising the step of initially rinsing the substrate surface with activated carbon filtered potable water prior to applying the first composition.

15. The method according to claim 1 further comprising the step of applying a nano-structured particle-containing coating to the decontaminated and prepared surface.

16. A method of applying a protective coating to a metal substrate surface comprising: a. applying to the substrate surface a first composition having a pH of 4 or less comprising an acidifier and an oxidizer; wherein the acidifier comprises citric acid anhydrous and the oxidizer comprises sodium persulfate; wherein the first composition in dry form comprises about 75% to 85% by weight acidifier and about 0.1% to 10% by weight oxidizer; b. allowing the first composition to remain on the substrate surface for a predetermined period of time; c. rinsing the first composition from the substrate surface with a second composition having a pH of 8 or more comprising an alkaline material liquid mixture formed utilizing activated carbon filtered potable water to achieve a neutral pH condition on the surface; and d. applying a protective coating to the substrate surface.

17. The method according to claim 16 wherein the alkaline material is selected from the group consisting essentially of sodium carbonate, sodium bicarbonate, derivative compounds of sodium carbonate or sodium bicarbonate, and fugitive alkaline compounds.

18. The method according to claim 17 wherein the fugitive alkaline compounds comprise dimethylethanolamine (DMEA).

19. The method according to claim 16 further comprising the step of blasting the substrate surface with an abrasive material after the initial rinsing and prior to applying the first composition.

20. The method according to claim 16 further compromising the step of applying a nano-structural particle containing coating to the protective coating.

Description

PREFERRED EMBODIMENTS OF THE INVENTION

(1) If the substrate surface is contaminated with organic compounds, soil or other similar type material that is adhered to the surface, it may be preferable to first rinse the substrate surface with water. In accordance with this invention it is preferred to use activated carbon filtered potable water that has been de-chlorinated to remove these materials before applying the first decontamination composition of this invention to the substrate surface. If desired, the de-chlorinated potable water can be sprayed on the substrate surface by a pressurized stream of the de-chlorinated potable water to remove any of these materials that may be adhered to the substrate surface.

(2) As indicated, the first step of the method of this invention utilizes a first composition comprising an acidifier and an oxidizer having a pH of 4 or less is applied to the substrate surface. If the substrate surface is significantly contaminated, particularly by mill scale or other scale buildup or similar compounds, it may be preferable to first utilize any of the known blasting or scraping methods to remove such mill scale or other scale buildup, smooth the substrate surface, and remove contaminates. If the surface is a hard metal then it is preferred the acid and oxidizer be selected to form a solution having a pH of less than 2. The first composition can be applied in powder form, gel form, liquid form, or a powder mixed with a liquid to create a solution. Typically, for cost savings reasons the first composition will be delivered to the treatment site in a powder form. If it is desired to apply the first composition in a powder form, it can be sprayed or sprinkled on the surface. However, in many cases the powder will be mixed at the treatment site with sufficient amounts of activated carbon filtered potable water to dissolve the powder in the de-chlorinated potable water to create a treatment fluid (or can be initially supplied as a fluid) and applied by any known method of applying liquids which include, but are not limited to: brush, roller, conventional pressure washer, air assisted application equipment, airless sprayer, conventional sprayer, garden sprayer, or spray bottle. Alternatively, the powder can mixed with a gel, such as xanthan gum, guar gum, smectite clay, organic polymer thickeners and silica based thickeners; and then applied to the substrate surface by any known conventional method.

(3) In order to get more thorough coating of the first component, the surface can be vibrated using various techniques known to persons ordinarily skilled in the art. For example, pneumatic, ultrasound, or mechanical methods can be used.

(4) The ability to utilize de-chlorinated potable water, which can be obtained from filtering onsite readily available potable water through an activated carbon filter, results in a substantial reduction in transportation costs through the elimination of transporting the large quantities of liquid necessary to provide the rinsing steps of the invention. In addition such de-chlorinated potable water is far less expensive than de-ionized water needed with current metal surface treatment methods.

(5) When treating a steel surface the first composition preferably comprises an acidifier chosen to form a coating of an oxidized form of iron, such as iron carbonate, on the steel surface. This coating is not a residue, but a desired result to passivate the metal surface; i.e., render the metal surface less reaction to atmospheric gasses, moisture, and contaminants. The passivation is achieved through the highly effective removal of contaminants and subsequent surface pH adjustment that results in greatly reduced, or no anodic/cathodic activity, and greatly reducing or eliminating bacterial metabolic byproduct content, such as iron sulfide, typically produced by sulfur reducing bacteria.

(6) There are numerous organic and mineral acids, as well as salts of organic and mineral acids, that serve to create a solution of low pH. However, it has been found that when using a liquid form or solution of the acid and oxidizer in powder form, the acid and oxidizer should preferably have a mesh size of at least 1180 microns to better ensure complete mixing with the de-chlorinated potable water used to form a liquid or solution of the first composition.

(7) Suitable mineral acids include hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric acid, hydrofluoric acid, hydrobromic acid, and perchloric acid, and other acids or salts derived from one of these mineral acids, as well as combinations of these mineral acids and their derivative salts and acids. Suitable organic acids are numerous and an exhaustive listing is impractical. It is only required that they can generate the desired pH values. Preferably, they will be short and medium chain organic acids and will be food grade acids due to their lower environmental impact. These organic acids would include citric acid, sodium bisulfate and other acids or salts derived from these organic acids. The most preferred acids include citric acid anhydrous and sodium bisulfate due to their low toxicity level, low cost, ease of acquisition, and favorable reactivity characteristics.

(8) The oxidizers are selected to react with non-water-soluble sulfides attached to the substrate surface. Oxidizers that can be used include, but are not limited to organic peroxides, inorganic peroxides, peracids, peresters, and combinations of these oxidizers. Commonly used oxidizers include persulfates, perborates, percarbonates, and combinations thereof. The oxidizers can also include the acid or salt derivitives of the above listed oxidizers. Preferred oxidizers include hydrogen peroxide and sodium persulfate due to their stability, cost and low environmental impact. If the first composition is to be a powder composition, then sodium persulfate is preferred; and wherein the oxidizer constitutes 0.1 wt. % to 10 wt. % of the first composition, and more preferably about 3.6 wt. %. When the first composition is in liquid form, it comprises the dry powder as defined herein mixed with a sufficient quantities of the de-chlorinated potable water to dissolve the dry powder in the de-chlorinated potable water.

(9) In another preferred embodiment the first composition can also comprise a rheology modifier to thicken the first composition to create improved adhesion of the first composition to a vertical surface (vertical cling) to better achieve and maintain a more complete coverage of the first composition on the substrate surface. When a rheology modifier is used as an optional constituent, the first component further serves as a barrier between the substrate and the atmosphere. This prevents the exposure of the acidified substrate surface to the moisture, oxygen or other atmospheric gasses, or air contaminants, thus preventing undesired reactions such as flash rust or recontamination of the surface.

(10) The rheology modifier can be in powder form, fluid form, or powder mixed with a liquid to create a solution. It is preferred that the rheology modifier be selected to create an oxygen barrier between the substrate surface and the atmosphere to aid in the efficacy of the method.

(11) Rheology modifiers that can be used include, but are not limited to xanthan gum, guar gum, smectite clay, organic polymer thickeners, silica based thickeners, and combinations thereof. The preferred rheology modifier is xanthan gum, which is desirable due to its ease of solubility, biodegradability, safety, and low environmental impact.

(12) In a preferred embodiment of the invention the first composition once applied to the substrate surface is allowed to sit on the substrate surface for a predetermined period of time (dwell time), to permit the first composition to react with the contaminates and facilitate their removal. This dwell time allows the elements of the first composition to react with contaminants on the surface of the substrate. In addition to the other contaminants discussed above, typical chemical contaminants on metal and concrete surfaces include, but are not limited to chlorine compounds, oxygen compounds, nitrogen compounds, and sulfur compounds.

(13) The dwell time can be adjusted by persons ordinarily skilled in the art to account for various factors which include, but are not limited to substrate composition, contaminant level, specific constituents used in the first component, volume of the first component used, atmospheric pressure, and temperature. However, a typical dwell time for metal surfaces can range from fifteen minutes to an hour, preferably thirty minutes to an hour, at ambient temperature, but also can vary greatly depending on the situation. A typical dwell time for concrete can range from fifteen minutes to an hour, preferably thirty minutes to an hour, at ambient temperature, but also can vary greatly depending on the situation.

(14) If the substrate surface is seriously contaminated, it is preferred that the first composition be re-applied to the substrate surface to better assure that any contamination on the substrate surface has been removed.

(15) In one or more embodiments, mechanical action, such as scrubbing, vibration, etc., can be incorporated in the methods to reduce the time and/or/chemical and/or pressure to remove surface contaminants.

(16) Once the first composition has completed its reaction time with the substrate surface, the substrate surface is rinsed with the second composition until the substrate surface is neutralized. Selection of the rinse is dependent upon a variety of factors. The second component is desirable to create a modified surface that greatly retards flash rusting, is less subject to undesirable chemical reactions due to contaminants, and has superior acceptance for coatings. Usage of the second component creates an alkaline layer upon the substrate. During drying, the second composition evaporates and leaves the surface with a generally neutral pH. The second component comprises an alkaline material, such as, sodium carbonate, sodium bicarbonate, and alkaline compounds that are derivatives of sodium carbonate or sodium bicarbonate, but preferably an unstable fugitive alkaline material, such as dimethylethanolamine (DMEA). By utilizing a fugitive material, there is no chemical residue left upon the substrate surface upon drying. In one or more embodiments, drying of a surface can be accelerated by heating, forced air circulation, or other methods known to persons ordinarily skilled in the art.

(17) Potable water that has been filtered through an activated carbon filter can be used to combine with either the first or second composition to create a liquid solution or to dilute the solutions to achieve the desire concentrations. It can also be used as a rinse in this method. Activated carbon filtered potable water includes any water suitable for drinking that has been filtered through an activated carbon filter to remove chlorine and other undesirable compounds that may be in the water. The use of activated carbon filtered potable water, rather than a de-ionized water, is significant in reducing costs and assuring availability at the treatment site.

(18) In some cases, for example when the surface of the substrate is oddly shaped, it may be desirable to submerge the substrate in a bath as opposed to applying the components. In this embodiment, the substrate can be submerged in an ambient or heated bath of the components and allowed a soak time as an alternative to applying the components and allowing a dwell time. Soaking the substrate in a bath has the added benefits of no exposure to atmospheric components, better coverage of the substrate with components, and increased ability to control component temperatures.

(19) In the embodiments that a bath is used, the fluid in the bath can be agitated by mechanical means, ultrasound, or vibration. The mechanical means can include a recirculation of fluid through stirring, or the use of fluid nozzles. Ultrasound can be applied to the bath, or to the object to agitate the bath. Further, vibration mechanisms can help to loosen contaminants in the bath.

(20) In a preferred embodiment the first composition in powder form comprises:

(21) TABLE-US-00001 COMPONENT PREFERRED RANGE MOST PREFERRED sodium persulfate 0.1 wt. %-10 wt. % 3.6 wt. % citric acid 75 wt. %-85 wt. % 82.2 wt. % sodium bisulfate 1.0 wt. %-5 wt. % 2.3 wt. % xanthan gum 10.0 wt. %-15 wt. % 11.9 wt. %

(22) Once the substrate surface has been decontaminated and prepared for acceptance of a protective coating, a coating comprising nanotube material will be applied to the substrate surface by any of the many known application methods, including, but not limited to, dipping, spraying, rolling, or brushing the coating on the substrate surface.

(23) The proposed nanotechnology-enhanced corrosion control coating will prevent and combat corrosion degradation by directly targeting the thermodynamic enablers to corrosion, namely the galvanic cell formed between the anode, cathode and electrolyte. The nanotechnology-enhanced coatings not only use covalent and ionic molecular bonds to link together the nano particles used in the surface coatings themselves, but also to link the coatings to the substrate. When the coating and substrate surface are bonded together the coatings form very hard structures; and the bonding between the coating and the substrate welds the substrate and the coating together as a single structure providing unsurpassed adhesion, such that the coating and the substrate form a union. The result means that the surface is more completely covered and protected. A preferred form of the nanotube is a nano-sized quartz particle.

(24) Under current application technology the nanotube coating is very thin (approximately 1 mil). If a more protective coating is desired, it is preferred that a first coating of non-nanotube coating material be first applied to the decontaminated and prepared surface. Then the nanotube coating is applied to adhere to the non-nanotube coating to provide a thicker and more protective coating. Such a dual coating application would be useful in ships and other water vessels to reduce friction between the vessel hull and the water the vessel is moving through. On the other hand if the primary purpose of the coating is to produce a lower friction surface or if it difficult for a non-nanotube coating to obtain a strong adhesive bonding to the substrate surface (such as when the substrate is stainless steel), one apply only the single nano-tube coating.

(25) Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.