Composition for depositing an alkanethiol monomolecular layer on a metallic surface and related methods

Abstract

A composition and methods for depositing a monomolecular layer of alkanethiol on a metallic surface are provided. The monomolecular layer of alkanethiol is applied using economical and reliable methods, such as by burnishing or ultrasonic bathing. The composition removes extra layers of alkanethiol to allow a single, even self-assembled monomolecular layer to form on the metallic surface, which enhances the tarnish-resistance of the surface and lubricates the surface.

Description

Composition for Depositing an Alkanethiol Monomolecular Layer on a Metallic Surface and Related MethodsFIELD OF INVENTION

[0001] This invention relates generally to a composition and methods for inhibiting corrosion of metallic material by applying sulfur-containing organic inhibitors to a metal surface in danger of corrosion.BACKGROUND OF THE INVENTION

[0002] Tarnishing or discoloration of silver surfaces is a long-known but unsolved issue. Beautiful metal articles, such as coins, jewelry, and flatware, are easily and quickly tarnished if they are exposed to the normal atmospheric environment. Even if silver and gold articles are faithfully stored in a controlled environment tarnishing still occurs over time. For example, collectible silver coins are typically stored in plastic capsules to reduce tarnishing, yet after a few years the edges of coins begin to display a brown color. Even museum artifacts that are stored in a controlled environment will discolor as the years pass.

[0003] The tarnishing or staining of silver surfaces is caused by water, humidity, and particularly by sulfur in the environment. Sulfurization occurs because the silver easily reacts with H2S in the air to form silver sulfide. (Silver sulfide may transition to silver sulfate.) Even a very low concentration of the H2S in the air can cause the silver surface to tarnish. Oxidation on the surface can also be observed as dark discoloration or stain.

[0004] Tarnish or corrosion on gold surfaces, which often displays as small reddish dots, is a related problem, because the tarnish is known to be mainly silver sulfide. Silver sulfide can form because even the purest gold retains a tiny proportion of residual microscopic particles of silver embedded within the gold metal. Research has shown that even though the gold has a purity of 99.99% or higher, a tiny quantity of silver resides on the gold surface. It is this residual silver, which, over time, corrodes to become visible red dots of silver tarnish on the gold surface. These reddots cause gold buyers to suspect the purity of the material. Solving the problem of silver tarnishing remediates the gold tarnishing problem.

[0005] The coining industry has recently addressed another issue involving tarnish, but on cupronickel coins. For over a decade now, the coining industry has treated copper alloy coins with a benzotriazole (BTA) composition to form an anti-tarnish film on the cupronickel surface. The cupronickel anti-tarnish film that is created on the coin surface not only has anti-tarnish properties, but it also serves as a lubricant between the coin and the die. The use of this film, with its enhanced lubrication properties, has saved millions of dollars per year in the cupronickel coin industry. Though the anti-tarnish problem for cupronickel has been resolved by applying the BTA film, BTA does not react with silver or gold. Thus, the tarnishing of silver or gold coins (or other articles) and the lack of a suitable lubricant for non-cupronickel coins have remained problems.

[0006] In an attempt to address the problem of tarnish on silver, in recent years many chemicals have been screened to assess their anti-tarnish properties and to evaluate their bonding strength to silver surfaces. Alkanethiols were found to form an alkanethiol film that bonded strongly with silver surfaces in the laboratory and ideally would be able to cover the silver surface to block attack by corrosive molecules. Alkanethiols (or alkyl mercaptans) are thiols of the structure R-SH having a hydrophobic alkyl chain (R) attached to a sulfhydryl group (SH).

[0007] It is currently understood that the sulfhydryl group (SH) of the alkanethiol has an affinity for silver and serves as a surface anchor. The alkane chain tail of the alkanethiol molecule extends outwardly from the surface anchor, with the alkane chain tails of adjacent molecules aligning with one another. The force that promotes the ordering of this self-assembly is the hydrophobic, van der Waals interactions between the carbons of the alkane chains. In a well-ordered alkanethiol film, this interaction causes the alkane chains to pack tightly and to tilt approximately 30 degrees to maximize the interaction between the chain tails and to lower the overall surface energy. It is believed that in the alkanethiol film created, the hydrophobic interactions between the chains overcome the molecule’s rotational degrees of freedom.

[0008] The alkanethiol films created by currently known formulations and methods are often termed “self-assembled monolayers (SAM),” but it has been determinedthat the film coating produced by conventional means is not truly a monolayer, but is laid down, at least partially, in multiple layers of alkanethiols, which creates an uneven film surface. This film is not consistently an even, single layer or monolayer. When multiple layers accumulate, a dark stain will appear. This dark stain is not only unsightly, but it can also transfer to the coining dies, which causes unwanted results. The multiple layers also cause wearing of the die. Though termed “layers” of alkanethiols, the term “layers” may include actual layers, irregular clusters, or other unwanted gatherings of alkanethiols that are not part of the base single layer of alkanethiol film that is adjacent to the silver surface.

[0009] Testing has shown that when the alkanethiol is introduced to a silver surface, an initial poorly ordered stage of an alkanethiol film is formed quickly. It is far from well ordered, but instead has many awkward defects and areas of multiple layers, which are instigated by van der Waals interactions between the carbons of the alkane chains. In a few days, the initially poorly ordered alkanethiol film was found in testing to typically be able to self-assemble to become a somewhat well-ordered film. However, the conventional anti-tarnish formulations and methods produce a film which has areas of monolayer and areas of irregularities and / or clusters of alkanethiol molecules or layers of alkanethiol molecules. So, the conventionally produced alkanethiol film is not a true single layer or monolayer; it could be compared to the surface of a person’s skin that should be smooth, but that has warts distributed here and there. These clusters of alkanethiol molecules, over time, result in black (sometimes viewed as brown or dark blue) tarnished spots.

[0010] Therefore, the known compositions and methods for applying the alkanethiol film to the silver surface do not create a well-ordered, single layer film that can tightly cover the surface, which is needed to prevent tarnish over the long term. Using these conventional methods, although at first the surface does not tarnish, as time passes, black spots gradually appear. When analyzed, a high sulfur concentration was detected in the black spots, which were determined to be substantially silver sulfate. This points to the fact that, using currently known formulations and methods, an inferior alkanethiol film that is not a single layer is produced. Additionally, current formulations and methods require many days to create an alkanethiol film. In most research laboratories, it takes a few days after the samples are immersed in a sulfur-containing organic tarnish inhibitor solution togenerate an alkanethiol film covering the whole surface. For use in consumer products and for use in commercial applications, the alkanethiol film needs to be applied in a shorter amount of time.

[0011] Therefore, though alkanethiol films have been tested as an anti-tarnish treatment for silver surfaces with some degree of success, some key issues have not been solved, so the current use of self-assembled alkanethiol films is quite limited. Using conventional methods and treatment solutions, it has proved difficult to generate a thiol film on a silver or gold surface that is a true monolayer, and a poorly formed defective monolayer does not meet the needs of commercial or consumer usage. It would be advantageous to be able to create a closely packed well-ordered alkanethiol monolayer of an even, single-layer thickness. The protective film needs to be closely packed and single-layered to impede corrosive constituents and to fulfill its anti-tarnish function over time. A well-ordered single layer is also required to efficiently fulfill the lubrication function during coining to achieve a longer die life, to minimize blackening of the die, and to maintain a high coin surface quality. Additionally, a fully hydrophobic outer surface is needed so the coin blank or coins can shed rinse water to avoid forming water stains on their surfaces. Another problem is that the known formulations and methods form an alkanethiol film too slowly for commercial applications and undesirably slowly for consumer applications.

[0012] Accordingly, there is a need for an anti-tarnish composition that can be used to create an aqueous alkanethiol treatment solution into which the article with a metal surface can be immersed to deposit an even single-layered, alkanethiol monolayer on the surface to provide long-lasting anti-tarnish and / or lubrication properties. Additionally, there is a need for methods of application of the alkanethiol, for creation of the aqueous alkanethiol treatment solution, and for creation of a treated metallic article to which the anti-tarnish treatment can be applied quickly and efficiently in line with commercial manufacturing times for production of metallic objects, and yet in which the anti -tarnish composition forms a well-ordered monolayer of an even thickness in which defects and areas of alkanethiol clusters and / or multiple layers are minimized.BRIEF SUMMARY OF THE INVENTION

[0013] The present invention is directed to a fluidic anti-tarnish composition and an aqueous alkanethiol treatment solution created from the anti-tarnish composition and into which articles to be treated are immersed, which are used for depositing an alkanethiol monomolecular layer on a metallic surface. The present invention is also directed to methods for depositing the alkanethiol, for creating the aqueous alkanethiol treatment solution, and for creating metallic articles treated with the anti- tarnish composition. In the present invention, the anti-tarnish alkanethiol film is applied in a short number of minutes and is applied in an even, well-ordered monolayer. This short time accommodates production times in commercial facilities and facilitates usage by consumers. The inventive composition and methods provide the means to achieve an even monomolecular alkanethiol layer by at least removing any extra layers of alkanethiol that may have collected on the base alkanethiol monolayer. The self-assembled alkanethiol monomolecular layer produced reduces visible tarnishing of the metal surface and, in the coining industry, further serves as a lubricant between a die and the surface. Treatment with the anti-tarnish composition results in an evenly thick alkanethiol monomolecular layer. (Though this layer may have a color, it is not visible because it is only one thin layer thick.) Conventional anti-tarnish treatments result in an uneven surface with multiple layers, which is visible as a black stain.

[0014] The anti-tarnish composition is a solution comprising an alkanethiol, a water- soluble emulsifier, and an extra layer remover. The extra layer remover comprises a carboxylic acid or a salt thereof, and preferably comprises a tartaric acid or a salt thereof, in an amount that is effective to remove extra molecules of the alkanethiol beyond a tightly packed base monomolecular layer of alkanethiol. Though tartaric acid can also serve as an emulsifier, an additional emulsifier is preferably added. Most preferably, the emulsifier comprises polysorbate 80. In a preferred aspect of the invention, an anti -microbial agent may be added to the anti-tarnish composition, which allows longer storage and / or usage times. In another aspect of the invention, a surfactant may additionally be added.

[0015] The compounds of the fluidic concentrated anti-tarnish composition are dispersed in water to form an aqueous alkanethiol treatment solution. The alkanethiol is applied by burnishing or ultrasonic bathing of the article to be treated in theaqueous alkanethiol treatment solution. Due to the selected components of the inventive anti-tarnish composition and to the inventive methods used, a well-ordered mono-molecular layer is efficiently ordered on the surface with extra thiol layers removed in a very short time, such as in from one to ten minutes. Since conventional compositions and methods require hours or days to deposit an alkanethiol film, and since the inventive composition and methods require merely minutes to deposit an improved film, the inventive composition and methods solve the time problem currently experienced in commercial production facilities.

[0016] Though the fluidic alkanethiol composition (applied to the article to be treated in the form of the aqueous alkanethiol treatment solution) is herein particularly described for application to surfaces of silver and alloys thereof, it may also be used on other metal surfaces. The inventive alkanethiol composition can also be used to treat gold (and other metals) to both resolve the problem of the tarnishing of the residual silver and to provide lubrication for stamping or for other processes that may be used in manufacturing the metallic article. For example, gold surfaces can be treated so that the tiny portion of residual silver on its surface will not form the visible red dots of silver tarnish. Other metals may also have residual silver. Therefore, the inventive composition and treatment provides advantages in treating not only silver, but also gold and other metals.

[0017] The anti-tarnish treatment may be used before or after creation of the metallic article. For example, tests were performed in a coin minting facility in which the anti-tarnish treatment was carried out before stamping of a coin, after stamping of a coin, and both before and after stamping. Applying the treatment before stamping advantageously increases the lubrication and reduces the blackening of the die surface in addition to adding tarnish resistance. Applying the treatment after stamping provides tarnish resistance of the newly stamped metal surface. Applying the treatment before and after stamping provides both benefits, including improving the tarnish resistance beyond the tarnish resistance achieved by the before-stamping application.

[0018] In an aspect of the invention, the alkanethiol comprises hexadecanethiol. In another aspect of the invention, the alkanethiol comprises octadecanethiol. In a further aspect of the invention, the alkanethiol comprises a mixture of hexadecanethiol and octadecanethiol.

[0019] In an aspect of the invention, the emulsifier comprises polysorbate 80. In a further aspect of the invention, the emulsifier comprises Triton X-100. In another aspect of the invention, the emulsifier comprises a water-soluble nonionic surfactant.

[0020] In an aspect of the invention, the extra layer remover comprises a tartaric acid or a salt thereof. In an additional aspect of the invention, the extra layer remover comprises tartaric acid. In a further aspect of the invention, the extra layer remover comprises potassium tartrate.

[0021] In an aspect of the invention, the alkanethiol composition further includes an antimicrobial agent. In an additional aspect of the invention, the antimicrobial agent comprises didecyl dimethyl ammonium bicarbonate and / or didecyl dimethyl ammonium carbonate; this is sold under the brand name of CARBOSHIELD 1000.

[0022] In an aspect of the invention, the method of treatment includes bathing the metallic object to be treated in an ultrasonic water bath. In another aspect of the invention, the method of treatment includes bathing the metallic object to be treated in an ultrasonic water bath having two wave generators. In an additional aspect of the invention, the method of treatment includes bathing the metallic object to be treated in an ultrasonic water bath having two wave generators operating at different frequencies.

[0023] In one aspect of the invention the ultrasonic bath treatment time is under5 minutes. In a further aspect of the invention, the ultrasonic bath time is 1 minute. In an additional aspect of the invention, the ultrasonic bath time is between 1 and5 minutes. In another aspect of the invention the ultrasonic bath time is between 1 and 10 minutes.

[0024] In a further aspect of the invention, a monomolecular layer is applied in a portable household ultrasonic cleaning machine.

[0025] In another aspect of the invention, a monomolecular layer is applied onto the surface of a metallic object by a burnishing process in a burnishing machine using stainless steel media. In an additional aspect of the invention, a monomolecular layer is applied on coin blanks by a burnishing process by burnishing with stainless steel media.

[0026] In an aspect of the invention, the anti-tarnish composition is applied before the stamping of a coin. In another aspect of the invention, the anti-tarnish composition is applied after the stamping of a coin. In an additional aspect of the invention, the anti-tarnish composition is applied both before and after stamping of a coin. In a further aspect of the invention, the anti-tarnish composition is applied as a treatment on the surface of a metallic article after it is formed or shaped.

[0027] In a further aspect of the invention, a method for depositing an alkanethiol monomolecular layer on a metallic surface includes an environmental sulfurization test to evaluate the anti-tarnish properties.

[0028] In another aspect of the invention, a method for depositing an alkanethiol monomolecular layer on a metallic surface includes an accelerated sulfurization test to evaluate the anti-tarnish properties.

[0029] The object of the invention is to provide a composition for depositing an alkanethiol monomolecular layer onto a metal surface for tarnish resistance and / or lubrication and to provide methods related to the same, which give an improved performance over the above-described prior art systems and methods.

[0030] These and other objects, features, and advantages of the present invention will become more readily apparent from the attached drawings and from the detailed description of the preferred embodiments which follow.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0031] The preferred embodiments of the invention will hereinafter be described in conjunction with the appended drawings, provided to illustrate and not to limit the invention, where like designations denote like elements.

[0032] FIG. 1 is a top view of a reverse side of a 1993 US Mint Walking Liberty1 ounce silver coin before treatment using the anti-tarnish composition of the present invention.

[0033] FIG. 2 is a schematic of an ultrasonic water bath, wave generators, and an aqueous alkanethiol treatment solution formed from the anti-tarnish composition, schematically showing a 1993 US Mint Walking Liberty coin (not to scale) during deposition of an alkanethiol monomolecular layer of the present invention on a portion of the surface of the coin.

[0034] FIG. 3 is a top view of a reverse side of the 1993 US Mint Walking Liberty coin treated as shown in FIG. 2, which is illustrated after an accelerated sulfurizationtest, which shows tarnish only on the portion of the coin that was not treated with the alkanethiol monolayer film coating of the present invention.

[0035] FIG. 4 is a graph showing measured reflectivity test results comparing the uncoated / untreated reverse and obverse sides of a 2022 Sunshine Mint Route 66 silver round to the reverse and obverse sides of a 2022 Sunshine Mint Route 66 silver round that has been treated with the anti-tarnish composition of the present invention to form an alkanethiol monomolecular layer on the coin surface.

[0036] FIG. 5A is a representation of a gold bar formed from a gold blank ultrasonically bathed in the aqueous alkanethiol treatment solution formed from the of the present invention showing a smoother surface than the un-treated gold bar of FIG. 5B.

[0037] FIG. 5B is a representation of a gold bar formed from a standard gold blank (without application of the anti-tarnish composition of the present invention).

[0038] FIG. 6 is a graph showing measured reflectivity test results for a variety of coins exposed to a sulfurization test, including, for comparison, a Route 66 Round treated with the aqueous alkanethiol treatment solution formed from the anti-tarnish composition of the present invention.

[0039] FIG. 7A is a schematic illustrating the surface contact angle of a water droplet on a metallic surface that has been treated with the anti-tarnish composition of the present invention, which can be compared to FIG. 7B.

[0040] FIG. 7B is a schematic illustrating the surface contact angle of a water droplet on a standard untreated metallic surface of the prior art, which is shown for comparison to the water droplet on the metallic surface of FIG. 7A.

[0041] Like reference numerals refer to like parts throughout the several views of the drawings.DETAILED DESCRIPTION OF THE INVENTION

[0042] Shown throughout the figures, the present invention is directed toward an anti- tarnish alkanethiol composition, which is a concentrated solution for mixing with water to create an aqueous alkanethiol treatment solution 10 that is used to deposit an alkanethiol monomolecular layer onto a metal surface 25 (particularly silver or gold or alloys thereof) of an object 20 to be treated. It is further directed to methodsrelated to creating the aqueous alkanethiol treatment solution 10, to applying the aqueous alkanethiol treatment solution 10 to form a self-assembled monomolecular alkanethiol film on the surface 25, to manufacture a tarnish -resistant article 20 having a metallic surface 25, and to test the anti-tarnish and lubricant properties of the metallic article 20 after treatment of the article 20 with the alkanethiol treatment solution 10.

[0043] The monomolecular alkanethiol film created by using the anti-tarnish composition (applied via the aqueous alkanethiol treatment solution 10) has been proven to be effective in minimizing the long-term effects of tarnishing and staining on gold and silver. The film has been shown to be stable and reliable. It has a low surface tension with a contact angle greater than 90 degrees. Advantageously, it can be applied to a silver surface in a few minutes.

[0044] The anti-tarnish alkanethiol composition, and the aqueous alkanethiol treatment solution 10 created from it, have many favorable characteristics for use in the coining industry and for consumer use. They are safe for industry workers and for home users. No special ventilation is required during usage. The anti-tarnish composition is easily and effectively applied using either of two methods (ultrasonic immersion and burnishing or mass finishing). And they can be safely and easily discarded after use.

[0045] The alkanethiol treatment solution 10 may be used to apply an alkanethiol monomolecular layer to the metallic surface 25 of an article 20 before, after, or before and after forming the metallic article; or the alkanethiol monomolecular layer may be applied to the surface of an article created months, years, or centuries ago, such as jewelry, silverware, or museum artifacts. Though new articles are often treated, and, in this case, pre-cleaning or tarnish removal may not be needed or wanted, the article 20 to which the alkanethiol monomolecular film is to be applied may optionally be cleaned before application. In an example, an old, tarnished silver bowl could be pre-cleaned to achieve a tarnish-free surface and then treated with the alkanethiol treatment solution 10 to prevent future tarnish. However, collectors sometimes prefer a patina developed over a period of time (such as a light discoloration around the edges of a coin or silver tray to suggest to the viewer that the article is antique), so, optionally, an article 20 with a light patina may be treatedIOto halt the tarnishing at an aesthetically pleasing state of tarnish and to prevent the development of a greater degree of tarnishing that would not be appealing.

[0046] The inventive composition and methods are suitable for improving the tarnish resistance of any of a variety of metallic articles 20, though in the exemplary discussion herein, the application of the monomolecular layer and the related methods are specifically discussed in relation to its application to silver and gold coins, and particularly silver coins. However, by using the disclosed inventive anti- tarnish composition incorporated into the aqueous alkanethiol treatment solution 10, new or older articles 20 of other shapes and types may also be advantageously treated. For example, the inventive composition and methods are suitable and useful for individuals who may have new or antique silver articles that are tarnished and would benefit from tarnish removal along with the application of an anti-tarnish monomolecular layer. Further, the inventive composition and methods disclosed herein are advantageously usable by restorers of museum artifacts that have a tarnished metallic surface to remove tarnish and to apply an anti-tarnish monomolecular layer to prevent or minimize future tarnish or discoloration.

[0047] The alkanethiol of the inventive tarnish retarding composition has the general formula R-SH, where SH is a sulfhydryl group and where R is an alkyl radical having from ten through twenty carbon atoms forming a hydrophobic alkyl chain. In one embodiment of the invention, the alkanethiol comprises octadecanethiol. In another embodiment of the invention, the alkanethiol comprises hexadecanethiol. In an additional embodiment, a mixture of hexadecanethiol and octadecanethiol is used. In further embodiments, other alkanethiols are used, and are within the scope of the invention.

[0048] The inventive fluidic anti-tarnish composition comprises an alkanethiol, an emulsifier, and an extra layer remover. The components of the anti-tarnish composition are combined with water, preferably deionized water, (and, optionally, other components) to form the aqueous alkanethiol treatment solution 10.

[0049] In one aspect of the invention, the aqueous treatment solution 10 is to be used to provide a lubricating and tarnish resisting coating to coin blanks. In this aspect, it may be placed in a burnishing machine and the coin blanks may be rotated and burnished with stainless steel media.

[0050] In another aspect of the invention the aqueous treatment solution 10 is disposed within the tank 13 of an ultrasonic water bath 12. In this aspect of the invention, the metallic article 20 or articles to be treated is / are supported and is / are bathed in the aqueous treatment solution 10 (into which the alkanethiol anti-tarnish composition has been mixed).

[0051] In both the burnishing and ultrasonic application methods, the purpose is to increase the collision between the molecules of the solution 10 and the metallic surface, which enhances the chemical reaction rate. It is a dynamic process as some material is removed from the surface while other molecules are adsorbed onto the surface, depending on the properties of the chemicals involved. Using either the burnishing or ultrasonic application methods, a self-assembled monomolecular layer of alkanethiol is deposited in a period of time measured in minutes as opposed to the days of time required by the conventional processes. Upon immersion in the aqueous treatment solution 10, the sulfur of the sulfhydryl group complexes with the silver atoms at the surface of the article being treated, and the large organic portion of the alkanethiol molecule forms a shield over the metal surface to protect it from atmospheric contaminants and to provide a lubricating effect. To achieve an even monomolecular layer quickly, the extra layer remover removes molecules of alkanethiol that are layered upon, clustered upon, or extend beyond a well-ordered base monomolecular layer of the alkanethiol. This effect of the extra layer remover allows an alkanethiol monomolecular layer with a thickness of under 100 nanometers to be deposited. In an aspect of the invention, the alkanethiol monomolecular layer has a thickness of between 20 and 100 nanometers. Preferably, the alkanethiol monomolecular layer or film is deposited in an even single layer having a thickness of 40 to 60 nanometers.

[0052] In addition to the alkanethiol, emulsifier, and extra layer remover, the anti- tarnish composition may include other components that are added to the composition to accomplish one or more of the following benefits: to assist in the removal of tarnish from the surface, to further aid in emulsification, to improve the viscosity of the fluid in the tank 13, to provide a stable product, to prevent growth of microbes in the solution 10, and / or to further assist in removing extra molecules and layers of the alkanethiol. For example, in addition to the alkanethiol, emulsifier, and extra layer remover, the composition may include any one or more of the following: one or moreanti-microbial agents, additional emulsifier(s), surfactant(s), rheology modifier(s), liquid diluent (s), and / or an additional extra layer remover(s). Optionally, the anti- tarnish composition may further comprise a coloring agent and / or an odorant.

[0053] The surfactant may be a nonionic surfactant or a cationic surfactant, but is preferably a non-ionic surfactant, such as glycerol monostearate.

[0054] The anti-microbial agent may be any standard anti-microbial compound. In a preferred aspect of the invention, an anti-microbial agent sold under the brand name of CARBOSHIELD 1000 is used. The active ingredients of CARBOSHIELD 1000 are didecyl dimethyl ammonium bicarbonate and / or didecyl dimethyl ammonium carbonate. The CARBOSHIELD 1000 component, in addition to its anti-microbial properties, also acts as a cationic surfactant and serves to inhibit corrosion. Because around 99% of the chemicals in the aqueous treatment solution 10 may be food grade, as time passes fungus will grow in the aqueous treatment solution 10, which can cause the aqueous treatment solution 10 to agglomerate (like the fat on the surface of a soup). By using an anti-microbial agent, the aqueous treatment solution 10 can be stored for a substantial length of time (which provides an advantage to industrial facilities and to consumer sales in which the alkanethiol composition in liquid form may spend time on the retail shelf) and can be used for a longer time in the ultrasonic bath 12 or burnishing tank.

[0055] The emulsifier of the anti-tarnish composition may be a nonionic emulsifier (such as polysorbate 80, polysorbate 20, glycerol monostearate, the polyethylene glycol derivative sold as TRITON X-lOo under the brand name TRITON, or the like). In a preferred aspect of the invention, the emulsifier of the anti-tarnish composition comprises polysorbate 80 (which may also serve partially as a surfactant).

[0056] Optionally, but in a preferred aspect of the invention, some components of the anti-tarnish composition are first mixed with a diluent before being introduced into the water of the ultrasonic bath 12 or a burnishing tank and / or before creation of a concentrate available to buy and / or before being packaged for consumer sales. The diluent may be a liquid such as water or a low molecular weight organic compound such as methyl alcohol, ethyl alcohol, propyl alcohol, or the like. The diluent may optionally be a mixture of the water and the low molecular weight organic compound or may be the organic compound mixed with a rheological dilatant fluid to carry thealkanethiol molecules as they shift and relocate along the metallic surface. In a preferred aspect of the invention, the diluent comprises propanol 91%.

[0057] In an aspect of the invention, the extra layer remover is a carboxylic acid or a salt thereof. In another aspect, the extra layer remover is tartaric acid or a salt thereof. In one aspect of the invention, the extra layer remover is a salt of tartaric acid, such as the potassium salt of tartaric acid, potassium tartrate. In a preferred aspect, the extra layer remover is tartaric acid, which is included in the inventive anti-tarnish composition in an amount (per weight) greater than has been provided or suggested in products or in published works before (although tartaric acid has been used along with other acids or for other purposes, such as to adjust pH). Many acids were experimentally tested, including citric acid, oxalic acid, and acetic acid. The other acids displayed various degrees of absorption or de-absorption, and may be used in the alkanethiol composition, but most preferably tartaric acid is used in the alkanethiol composition to remove extra layers. Optionally, other acids can be added to achieve additional purposes. For example, citric acid with its three acid groups can be added to the aqueous alkanethiol treatment solution 10 when etching (cleaning) is needed.

[0058] Tartaric acid is preferred because it provides several advantages. One beneficial effect is that it is a weak acid that can dissolve (which may also be termed “etch” or “clean”) chemicals weakly bonded to the silver surface (such as the emulsifier and / or anti-microbial agent and / or grease or the like) into the water of the aqueous treatment solution 10. Because the tartaric acid serves to disassociate any non-alkanethiol chemicals that may be loosely bound to the metal surface, it unblocks the metal surface to allow the alkanethiol molecules within the aqueous treatment solution 10 to reach the silver surface and to form a bond and / or a more uniform monomolecular layer. Advantageously, the tartaric acid cannot dissolve these alkanethiol-to-silver chemical bonds because these bonds are strong, so the tartaric acid does not remove the alkanethiol from the silver surface. Also, if there is a silver oxide layer, the tartaric acid can also remove it before the monomolecular film forms.

[0059] Additionally, as previously discussed, tartaric acid can disassociate any additional layers of alkanethiol molecules that are weakly bonded above the base monomolecular layer of alkanethiol. Thus, the addition of the tartaric acid in theranges provided removes any extra layers, which results in a single, monomolecular layer of alkanethiol. When the extra layers are not removed, silver sulfite is formed in the extra layers and in any clusters of alkanethiol, which appears to the viewer as dark tarnish or discoloration.

[0060] Yet another advantage of the tartaric acid is that the tartaric acid is a good emulsifier for the alkanethiol in the aqueous alkanethiol treatment solution 10.

[0061] Tartaric acid was tested at various concentrations. Concentrations of tartaric acid at or above 2% (in percentage by weight) can be used in the anti-tarnish composition. In an aspect of the invention, the concentration of tartaric acid is above 2%. In another aspect of the invention, the concentration of tartaric acid is above 4%. In an aspect of the invention, the concentration of tartaric acid is above 6%. In a preferred embodiment, the concentration is between 6% and 10%, which provides an improved, even, monomolecular layer. In one preferred embodiment about 8% tartaric acid is used.

[0062] In an embodiment the general formulation for the anti-tarnish composition to be mixed with water to create the alkanethiol treatment solution 10 is the following (in percent by weight):Alkanethiol = 0.1 to 5%;Emulsifier = 0.1 to 5%;Alcohol = 3 to 35%;Water (preferably deionized) = 1 to 95%; and Extra layer remover = 1 to 20%.

[0063] In another embodiment the general formulation for the anti-tarnish composition to be mixed with water to create the alkanethiol treatment solution 10 is the following (in percent by weight):Hexadecanethiol and / or octadecanethiol = 0.1 to 1%;Polysorbate 80 = 0.1 to 1%;Didecyl dimethyl ammonium bicarbonate and / or didecyl dimethyl ammonium carbonate (such as sold under the brand name of Carboshield 1000) = 0.1 to 1%;Propanol 91% = 4 to 12%;Water (preferably deionized) = 1 to 95%; andTartaric acid or a salt thereof = 4 to 12%.

[0064] In a further embodiment the general formulation for the anti-tarnish composition to be mixed with water to create the alkanethiol treatment solution 10 is the following (in percent by weight):Hexadecanethiol and / or octadecanethiol = 0.3 to 0.5%;Polysorbate 80 = 0.3 to 0.5%;Didecyl dimethyl ammonium bicarbonate and / or didecyl dimethyl ammonium carbonate (such as sold under the brand name of Carboshield 1000) = 0.3 to 0.7%;Propanol 91% = 6 to 10%;Water (preferably deionized) = 1 to 95%; and Tartaric acid or a salt thereof = 6 to 10%.

[0065] In a preferred embodiment the general formulation for the anti-tarnish composition to be mixed with water to create the alkanethiol treatment solution 10 is the following (in percent by weight):Hexadecanethiol = 0.3 to 0.5%;Polysorbate 80 = 0.3 to 0.5%;Didecyl dimethyl ammonium bicarbonate and / or didecyl dimethyl ammonium carbonate (such as sold under the brand name of Carboshield 1000) = 0.3 to 0.7%;Propanol 91% = 6 to 10%;Water (preferably deionized) = 75 to 90%; andTartaric acid = over 6%; or optionally, 6% to 10%; or optionally 8%.

[0066] In a solution / bath preparation method of the invention, such as may be used in the coining industry, an aqueous treatment solution 10 is formed by mixing the components of the disclosed anti-tarnish composition with water and is introduced into an ultrasonic bath 12 in preparation for receiving the article or articles to be treated. The concentration of the anti-tarnish composition in the solution 10 may be around 0.1 to 0.9%, may optionally be around 0.2 to 0.6%, may optionally be around 0.3 to 0.5%, and may be may optionally be about 0.4%.

[0067] The steps of the solution / bath preparation method comprise the following: a) Begin to prepare the ultrasonic bath by placing water (preferably deionized water) into the tank 13 of an ultrasonic bath 12.b) Heat the water in the ultrasonic bath 12 to 35°C to 65°C. c) Add the extra layer remover to the water. d) Activate the ultrasonic wave generator(s) 15 of the ultrasonic bath 12 to dissolve the extra layer remover into the water. e) Wait until the extra layer remover is completely dissolved in the water. f) In a separate container, such as a measuring tube, heat a diluent to 35 °C to 65°, such as by immersing the separate container in a warm water cup. g) Add the emulsifier into the diluent and stir, such as with a glass bar. h) Add any anti-microbial agent into the diluent and stir. i) Add the alkanethiol into the diluent and stir until all chemicals are dissolved to create an alkanethiol / diluent mixture. j) Activate the ultrasonic generator (s) 15 of the ultrasonic bath 12 to begin to produce ultrasonic waves. k) Pour the alkanethiol / diluent mixture into the in the water of the tank 13 of the ultrasonic bath 12. The generation of high-frequency waves within the water by the ultrasonic wave generator(s) 15 results in emulsification of the alkanethiol / diluent mixture into the water of the tank 13 and may result in some foaming. l) Maintain the generation of the ultrasound waves while stirring until any foaming disappears and the aqueous treatment solution 10 formed within the tank 13 has a uniform appearance. m) Introduce the article(s) to be treated.

[0068] In a preferred embodiment of the invention, the steps of the solution / bath preparation method comprise the following: a) Begin to prepare the ultrasonic bath by placing water (preferably deionized water) into the tank 13 of an ultrasonic bath 12. b) Heat the water in the ultrasonic bath 12 to 40°C to 55°C. c) Add tartaric acid or a salt thereof as an extra layer remover into the water. d) Activate the ultrasonic wave generator(s) 15 of the ultrasonic bath 12 to dissolve the extra layer remover into the water. e) Wait until the extra layer remover is completely dissolved in the water. f) In a separate container, such as a measuring tube, heat the alcohol to 45 °C to 55°C, such as by immersing the separate container in a warm water cup.g) Add the emulsifier into the alcohol and stir. h) Add the anti-microbial agent into the alcohol and stir. i) Add the alkanethiol into the alcohol and stir until all chemicals are dissolved to create an alkanethiol / alcohol mixture. j) Activate the ultrasonic generator(s) 15 of the ultrasonic bath 12 to begin to produce ultrasonic waves. k) Pour the alkanethiol / alcohol solution into the water within the tank 13 of the ultrasonic bath 12. The generation of high-frequency waves within the water by the ultrasonic wave generator(s) 15 results in emulsification of the alkanethiol / alcohol mixture into the water of the tank 13 and may result in some foaming. l) Maintain the generation of the ultrasound waves while stirring until any foaming disappears and the aqueous treatment solution 10 formed within the tank 13 has a uniform appearance. m) Introduce the article(s) to be treated.

[0069] In an embodiment of the invention, the steps of the solution / bath preparation method are modified with a concentrated fluidic anti-tarnish composition (comprising the alkanethiol, the extra layer remover, any emulsifier, any antimicrobial agent, any alcohol, and any surfactant) mixed into the water in the tank 13. Then the ultrasonic wave generator(s) 15 of the ultrasonic bath 12 is activated to dissolve the concentrated fluidic anti-tarnish composition into the water. Then high- frequency waves are generated within the water by the ultrasonic wave generator(s) 15 resulting in emulsification of the anti -tarnish alkanethiol composition into the water of the tank 13. The ultrasound waves are maintained until any foaming disappears and the aqueous treatment solution 10 formed within the tank 13 has a uniform appearance. The article(s) to be treated can then be introduced.

[0070] In one embodiment of the invention, the ultrasonic bath 12 is equipped with one ultrasonic wave generator 15 that produces ultrasonic waves of a first frequency, which may be in the range of about 25 to 60 kHz. The ultrasonic bath 12 is typically sold as an ultrasonic cleaner with a heater and with a digital timer that can be set to establish the length of time for which the ultrasonic wave generator 15 will be active. The ultrasonic bath 12 transforms low-frequency AC current into high-frequencysound waves, typically by using a piezoelectric transducer to create sinusoidal waves. These high frequency ultrasonic wave vibrations create microscopic spherical bubbles that implode violently causing cavitation by the formation and violent collapse of minute vacuum bubbles in the solution. These implosions are not overly harsh yet apply energy to every surface with which the solution makes contact, which improves the attachment of the alkanethiol to the surface and the evenness of the film created.

[0071] In another embodiment of the invention, the ultrasonic bath 12 is equipped with a sweep-frequency circuit. In this embodiment, the ultrasonic generator 15 produces ultrasonic waves of a first frequency, which may be in the range of about 25 to 60 kHz, but additionally sweeps the output frequency to the transducers by around 2-3 kHz to eliminate areas of inactivity between neighboring standing waves. The sweep frequency provides creates overlapping ultrasonic waves.

[0072] In a further embodiment of the invention, the ultrasonic bath 12 is equipped with two sweep-frequency ultrasonic generators 15, 17 that produce ultrasonic waves of a first and a second output frequency and that also sweep one or both output frequencies by around 2-3 kHz.

[0073] In a preferred embodiment of the invention, the ultrasonic bath 12 is a twodirectional two-frequency bath equipped with two ultrasonic wave generators 15, 17 that produce ultrasonic waves of a first frequency and of a second frequency, with both frequencies being in the range of about 25 to 60 kHz. In an example, one ultrasonic wave generator 15 may be disposed at the bottom of the ultrasonic bath tank 13, and one ultrasonic wave generator 17 may be disposed at the sidewall of the tank 13. In an aspect of the invention, the first generator 15 is a 200-Watt 40-kHz ultrasonic generator located under the tank, and the second generator 17 is a 200- Watt 20-kHz ultrasonic generator disposed adjacent to the sidewall of the tank 13.

[0074] Upon activation of both generators 15, 17, it was found that the generated cavitation bubbles were not spheres, but were instead elliptical balls, due to the different angles and / or frequencies provided by the two generators 15, 17. When an elliptical ball collapsed, the area of the pressure impacted was enlarged and the pressure was relatively uniform. The pressure spikes generated by the cavitation bubble collapse were blunted. For collectible coins, jewelry, or museum artifacts, this pressure modification is important. Any possible residual impact scars must beavoided. The two-directional (and, optionally, two-frequency) ultrasonic bath provides an excellent working environment to increase the chemical reaction rate but does not damage the initial surface feature. The processing time to completely apply a film to cover the solid surface was reduced from a few days to one to a few minutes. In one aspect of the invention the ultrasonic bath time is 1-10 minutes or under 10 minutes. In another aspect, the ultrasonic bath time is under 7 minutes. In a further aspect, the ultrasonic bath time is under 5 minutes. In an additional aspect, the ultrasonic bath time is under 2 minutes. In one aspect, the ultrasonic bath time is 1 minute.

[0075] Preferably, the temperature of the aqueous treatment solution 10 in the tank is controlled between 35 and 55 degrees C, optionally between 35 and 45 degrees C, and optionally at around 40 degrees C. Preferably, the coin or metal object 20 is directly immersed in the inventive solution without a precleaning cycle in the ultrasonic bath, because any cleaning process could damage the details on the object or coin.

[0076] When treating multiple coins or other articles 210 with a metal surface, they may be treated sequentially or simultaneously. In an aspect in which coins are being treated at a manufacturing plant, multiple coins may be supported within the tank 13 for treatment simultaneously to accommodate manufacturing time frames. In other aspects, such as the home ultrasonic cleaner containing the inventive aqueous treatment solution 10, jewelry pieces may be treated alone or in groups.

[0077] After immersion in the aqueous alkanethiol treatment solution 10, the coins or articles 20 are rinsed with water (preferably distilled). Preferably they are then sprayed to remove residual solution. Then they are air dried and / or they may be towel dried.

[0078] When the alkanethiol monomolecular layer is applied to the metal surface or coin blanks by burnishing, the standard burnishing process is used with the substitution of the inventive aqueous treatment solution 10 for the standard burnishing aqueous solution. The coin blanks to be treated, the inventive aqueous treatment solution 10, and stainless-steel balls are placed into the bowl of a burnishing machine. A rotor at the bottom of the bowl provides the mechanical agitation necessary to move the stainless-steel balls and coin blanks. The chemicalsof the alkanethiol composition within the aqueous alkanethiol treatment solution 10 react with the metal surfaces 25 when the many balls slide on the blanks.

[0079] In an exemplary burnishing method, around 500 to 1000 one-ounce silver blanks are immersed in the inventive aqueous treatment solution 10 formed from about 300 to 500 ml of the anti-tarnish alkanethiol composition diluted into about4 liters of deionized water. The blanks are burnished and treated for about 2 to5 minutes at 30-50 degrees C or optionally at 35-45 degrees C, or optionally at about 40 degrees C. Then the blanks are rinsed for about 2 to 5 minutes. Finally, the blanks are towel dried using the standard Spaleck system.

[0080] The amount of anti-tarnish alkanethiol composition needed per burnishing tank varies depending on the material, so a burnishing test and an accelerated sulfurization test should be performed to determine the best amount of anti-tarnish alkanethiol composition to be mixed into the water of the burnishing tank. The reaction rate is faster in the burnishing than in the ultrasonic bath, so the concentration of the anti-tarnish composition in the burnishing tank can be lower.

[0081] When the alkanethiol monomolecular layer is used in a home or restoration business, the user will likely not want to proceed through the steps of the solution / bath preparation method disclosed above. In this case, the inventive aqueous alkanethiol treatment solution 10 can be prepared at the manufacturer and sold in containers (such as one-gallon, two-gallon, or five-gallon jugs or the like). In another aspect of the invention, the components of the anti-tarnish composition may be sold in a concentrated formula with instructions for the user to mix with water in a home or business ultrasonic bath to create the inventive aqueous alkanethiol treatment solution 10 to be used in the home or business ultrasonic bath. In another aspect of the invention, the components of the anti-tarnish composition may be sold partially pre-mixed with additional water to be added by the user. In a further aspect of the invention, the components of the anti-tarnish composition may be sold in a kit of multiple containers with preparation instructions provided to the user for mixing with water to create the inventive aqueous alkanethiol treatment solution 10 to be used in the home or business ultrasonic bath.

[0082] The process of applying the alkanethiol to the surface of the metallic object is a dynamic coating process in which the article to be treated is introduced into the aqueous alkanethiol treatment solution 10 and a well-ordered alkanethiolmonomolecular film is formed on the surface. The alkanethiol application method may be varied slightly depending on the device into which the article 20 to be treated is placed for treatment, since the aqueous treatment solution 10 can be used in the large ultrasonic bath 12 of the coining industry, a more modestly sized home ultrasonic cleaner (such as is sold for cleaning jewelry), or in a commercial burnishing cylindrical container.

[0083] In this dynamic coating process, continually and simultaneously, some molecules from the aqueous treatment solution 10 are absorbed onto the metal surface while other molecules are de-absorbed from the surface. Although in some conventional processes for applying a thiol film to the surface of metal, the thickness of the layers of molecules increased with time or increased with an increase of alkanethiol in the solution, when using tartaric acid in the specified range disclosed herein, the alkanethiol film thickness remains the same, even when the concentration of alkanethiol is increased in the solution 10 or when the length of the bath time is increased. This leads to better results in both commercial and consumer usages.

[0084] When using the anti-tarnish composition and methods provided herein, a manufacturer or restorer may need to confirm, ensure, or prove that the selfassembled monomolecular layer is present and is protecting the metal surface 25. Though an environmental test can be performed in which the H2S in the air is allowed to react with the silver to form silver sulfide, this can require months or years to see the results. To avoid waiting, an accelerated sulfurization system may be used in which the article 20 is exposed to a higher concentration of sulfur for a shorter time.

[0085] For example, in a mint or coin manufacturing facility, a production line moves quickly, so it is not possible to use a sophisticated instrument to measure the deposited alkanethiol film in the short timeframe of the production line. Therefore, an accelerated sulfurization system may be used to speed up the exposure to sulfur to provide test results. This will then allow the color and reflectivity of the coins to be used to evaluate the anti-tarnish properties of the self-assembled alkanethiol monomolecular layer in a short time frame.

[0086] Tests have been conducted to assure that the anti-tarnish composition and the methods of application using the aqueous treatment solution 10 produce an alkanethiol monomolecular layer that is deposited in a single well-ordered layer andthat forms an intact tarnish-resistant film. In one test shown in FIGS. 1-3, a 1993 US Mint Walking Liberty coin was used. FIG. 1 shows the 1993 US Mint Walking Liberty coin that has been stored in a protected environment and is relatively untarnished. FIG. 2 illustrates schematically (not to scale) that the coin is then partially suspended in the inventive treatment solution 10 so that only a portion is treated (in the illustrated test, the portion treated is over half of the surface of the coin). After treatment, the coin is rinsed with distilled water and air dried. No visible or measurable changes in reflectivity or color were seen on the treated portion of the surface. The coin was then placed in an accelerated sulfurization chamber for one hour, which equates to being exposed in the ambient atmosphere for several years. The result of the test is shown in FIG. 3 in which the treated portion of the coin remained in the original condition and the uncoated area on the coin reacted with the H2S in the accelerated sulfurization system and turned brown and dark blue with tarnish.

[0087] The results of the three-day sulfurization test are shown graphically in FIG. 4. (In this case the sulfurization test used H2S released from vegetables, although other accelerated sulfurization tests can be used.) The reflectivity was measured in the coated and uncoated areas of the 1993 US Mint Walking Liberty silver coin. For the coated area of the surface, after three days, the average reflectivity dropped from around 92% to around 89%. For the uncoated surface area, the reflectivity dropped to around 50-60%. The results prove that the monomolecular layer applied by the composition and methods of the invention can protect an unpolished surface of a coin and prove that the coin need not be freshly minted for the alkanethiol application. Therefore, for collectors who prefer that the surface be slightly sulfurized, the coin can be held at this favored coloration, and the sulfurization that would further tarnish the coin can be inhibited.

[0088] The results of another test are shown in FIG. 6. In this test, the alkanethiol was applied to one 2022 Sunshine Mint Route 66 silver round. The blank for this Route 66 silver round was burnished with the inventive alkanethiol treatment solution 10 before stamping and was ultrasonically bathed in the solution 10 for 1.5 minutes after stamping. This treated coin was compared to seven 1 -ounce silver coins from around the world. The eight coins were placed in the accelerated sulfurization system to evaluate the anti-tarnish properties of the applied alkanethiol film. At the start, thecolor and reflectivity were similar among the coins. Though some coins had frosted surfaces, and some had polished surfaces, the reflectivity was similar; the initial reflectivity was in the range of from 92% to 96%.

[0089] After only a one-hour accelerated sulfurization test, all the coins had changed color except for the Route 66 silver round. The details of the processes or chemical treatments of the various mints that produced the seven comparison coins are not known, but the results of the sulfurization test varied between the coins. The Britannia coin made by the Royal Mint showed it had the worst anti-tarnish protection. The reflectivity of the Route 66 silver round did not change at all. Therefore, the use of the inventive anti-tarnish composition and methods by coin manufacturers will preserve the initial reflectivity and color, thereby reducing or eliminating customer complaints about tarnishing issues.

[0090] After the sulfurization test, small water drops condensed on the coin surfaces. The water drops later evaporated but some left watermarks on the coin surface. However, no watermark was found on the Route 66 silver round, due to its low surface tension property.

[0091] Another test that can show that the anti-tarnish alkanethiol monomolecular layer is protecting the silver surface 25 is a test of the surface contact angle of a water droplet, as shown in FIGS. 7A and 7B. The treated Route 66 silver round is shown in FIG. 7A and the surface 25 of the Royal Mint Britannia coin is shown in FIG. 7B. The surface contact angle of the Route 66 coin was measured at 90.1 degrees, which was the highest contact angle measured of the coins compared in FIG. 6. The lowest surface contact angle was measured on the Royal Mint Britannia, which was 52.9 degrees. The values of the contact angles also correlate to the appearance of water spots on the coin surfaces after the sulfurization test. The Route 66 coin had no water spots.

[0092] Tests have also shown that the alkanethiol monomolecular layer provides a lubricant effect and lowers the coefficient of friction between the dies and the blanks during production. Thus, the inventive alkanethiol monomolecular layer increases die life and the coin surface quality.

[0093] Gold articles and coins can also benefit from the application of the alkanethiol monomolecular layer onto the gold surface, both through reduction or elimination of red tarnish spots and through increasing the smoothness of the gold surface duringstamping. Gold articles and coins can appear tarnished from the random red spots found on the surface caused by silver sulfide. Though a process of etching the gold surface with nitric acid for a relatively long time is known to reduce gold tarnishing, the inventive composition and process herein disclosed can be accomplished in a shorter amount of time and with less damage to the surface.

[0094] In a test, twenty-four gold bars were ultrasonically bathed in the alkanethiol treatment solution 10 disclosed above for 5 minutes. Then the bars were rinsed in 50- degree deionized water and towel dried. The bars were then directly struck on the press. Two phenomena were observed.

[0095] Firstly, the die surfaces of these treated bars were not blackened during the stamping. The clean die surface indicated that the alkanethiol monomolecular layer on the blank surface was monomolecular, and that there were no extra alkanethiol molecules to accumulate on the die surfaces strike after strike.

[0096] Secondly, the surface morphology was improved due to the low friction.While silver is a solid lubricant (so the stamped coin image appears substantially the same with or without the alkanethiol monomolecular layer between the coin surface and the die), gold is not a solid lubricant. With the alkanethiol monomolecular layer applied to the gold surface, the friction was lower. This lower friction caused a smoother stamped surface. A comparison of the whole gold bar with and without the alkanethiol monomolecular layer is shown in FIGS. 5A and 5B. The inventive alkanethiol monomolecular layer was applied to the gold bar shown in FIG. 5 A before stamping. The comparison gold bar without the alkanethiol monomolecular layer is shown in FIG. 5B. Most fine scratches were plastically smoothed on the surface of the treated gold bar, thus resulting in an improved surface over the standard gold bar of FIG. 5B.

[0097] Tests were also performed on gold bars that were tarnished. The inventive application of the alkanethiol monomolecular layer onto the tarnished gold bars caused the red tarnish spots to disappear. Additionally, the red spots did not reappear after an accelerated sulfurization test. This indicates that the inventive anti-tarnish composition and methods may be used for gold product lines to replace the nitric etching and to improve the surface smoothness.

[0098] The composition and methods of treatment presented herein produce a thin and even monomolecular film. If the thiol film is not very thin and very even, uponexposure to air for a few months, some very small black dots will appear. Analyzing the small black dots with a scanning electron microscopy, the sulfur concentration at the dot locations was observed to be high. The black dots were formed by multiple layers of alkanethiol on the surface 25, in contrast to the single layer of alkanethiol applied in the current invention. Thus, the inclusion of the effective extra layer remover (preferably tartaric acid in the ranges provided) is desirable. Not wishing to be bound by theory, it is believed that the extra layer remover functions as a soap and opens the bonds between the physical adsorptions, such as the Van der Waals force, but it cannot open the bonds of the chemical reaction products. Thus, the addition of the extra layer remover to the aqueous alkanethiol treatment solution 10 and the utilization of the ultrasonic bath (or the burnishing process) removes the extra physically adsorbed layers of alkanethiol and only a reacted monomolecular layer remains on the metal surface. In Fourier transform infrared (FTIR) spectrum measurement, the formed alkanethiol monomolecular film was proved to be a single layer.

[0099] The anti-tarnish composition of the present invention can be used to create an aqueous alkanethiol treatment solution into which an article 20 with a metal surface25 can be immersed to deposit an even alkanethiol monomolecular layer on the surface 25 to provide anti-tarnish and / or lubrication properties. The time frame for the application is short enough to be used in coin fabrication facilities. The anti- tarnish treatment may be used before, after, or before and after creation of the metallic article.

[0100] Since many modifications, variations, and changes in detail can be made to the described preferred embodiments of the invention, it is intended that all matters in the foregoing description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents.

Claims

CLAIMSWhat is claimed is:

1. An alkanethiol composition, comprising: an alkanethiol for forming an alkanethiol monomolecular layer; an emulsifier; and carboxylic acid or salt thereof in an amount that is effective to remove extra molecules of said alkanethiol beyond a base monomolecular layer of said alkanethiol monomolecular layer when said alkanethiol composition is mixed with water to create an aqueous alkanethiol treatment solution into which an article to be treated can be received; wherein said alkanethiol monomolecular layer is deposited on a metallic surface of said article to be treated.

2. The alkanethiol composition as recited in claim 1, wherein said alkanethiol consists of hexadecanethiol.

3. The alkanethiol composition as recited in claim 1, wherein said alkanethiol consists of octadecanethiol.

4. The alkanethiol composition as recited in claim 1, wherein said alkanethiol consists of a mixture of octadecanethiol and hexadecanethiol.

5. The alkanethiol composition as recited in claim 1, wherein said metallic surface comprises a silver surface.

6. The alkanethiol composition as recited in claim 1, wherein said metallic surface comprises a gold surface.

7. The alkanethiol composition as recited in any one of the claims 1 to 6, wherein said carboxylic acid comprises tartaric acid.

8. The alkanethiol composition as recited in claim 7, wherein tartaric acid is present in an amount greater than 4% by weight of said alkanethiol composition.

9. The alkanethiol composition as recited in claim 7, wherein tartaric acid is present in an amount greater than 6% by weight of said alkanethiol composition.

10. The alkanethiol composition as recited in claim 7, wherein tartaric acid is present in an amount of 6% to 10% by weight of said alkanethiol composition.

11. The alkanethiol composition as recited in claim 7, wherein tartaric acid is present in an amount of about 8% by weight of said alkanethiol composition.

12. The alkanethiol composition as recited in any one of the claims 1 to 11, wherein said emulsifier comprises a nonionic emulsifier.

13. The alkanethiol composition as recited in claim 12, wherein said nonionic emulsifier comprises one of polysorbate 80, polysorbate 20, glycerol monostearate, or the polyethylene glycol derivative sold as TRITON X-lOo.

14. The alkanethiol composition as recited in claim 12, wherein said nonionic emulsifier comprises polysorbate 80.

15. The alkanethiol composition as recited in any one of the claims 1 to 14, wherein said alkanethiol composition further comprises an anti-microbial agent.

16. The alkanethiol composition as recited in claim 15, wherein said anti -microbial agent comprises at least one of the following: didecyl dimethyl ammonium bicarbonate or didecyl dimethyl ammonium carbonate.

17. The alkanethiol composition as recited in claim 15, wherein said anti -microbial agent comprises CARBO SHIELD 1000.

18. The alkanethiol composition as recited in any one of the claims 1 to 17, wherein said alkanethiol composition further comprises a diluent.

19. The alkanethiol composition as recited in claim 18, wherein said diluent comprises at least one of the following: water or a low molecular weight organic compound.

20. The alkanethiol composition as recited in claim 18, wherein said diluent comprises a low molecular weight organic compound.

21. The alkanethiol composition as recited in claim 20, wherein said low molecular weight organic compound comprises an alcohol.

22. The alkanethiol composition as recited in any one of the claims 1 to 21, wherein said alkanethiol composition further comprises a surfactant.

23. The alkanethiol composition as recited in claim 22, wherein said surfactant comprises a non-ionic surfactant.

24. The alkanethiol composition as recited in claim 23, wherein said non-ionic surfactant comprises glycerol monostearate.

25. The alkanethiol composition as recited in claim 1, wherein said carboxylic acid comprises potassium tartrate.

26. The alkanethiol composition as recited in any of claims 1 to 25, wherein said article to be treated comprises a coin or coin blank.

27. The alkanethiol composition as recited in any of claims 1 to 25, wherein said article to be treated comprises a non-coin metallic article.

28. An aqueous alkanethiol treatment solution, comprising an anti-tarnish alkanethiol composition and water; wherein said anti-tarnish alkanethiol composition comprises: an alkanethiol for forming an alkanethiol monomolecular layer; an emulsifier; and carboxylic acid or salt thereof in an amount that is effective to remove extra molecules of said alkanethiol beyond a base monomolecular layer of said alkanethiol monomolecular layer; wherein said alkanethiol monomolecular layer is deposited on a metallic surface of an article to be treated.

29. The aqueous alkanethiol treatment solution as recited in claim 28, wherein said alkanethiol consists of hexadecanethiol.

30. The aqueous alkanethiol treatment solution as recited in claim 28, wherein said alkanethiol consists of octadecanethiol.

31. The aqueous alkanethiol treatment solution as recited in claim 28, wherein said alkanethiol consists of a mixture of octadecanethiol and hexadecanethiol.

32. The aqueous alkanethiol treatment solution as recited in claim 28, wherein said metallic surface comprises a silver surface.

33. The aqueous alkanethiol treatment solution as recited in claim 28, wherein said metallic surface comprises a gold surface.

34. The aqueous alkanethiol treatment solution as recited in any one of the claims 28 to33, wherein said carboxylic acid comprises tartaric acid.

35. The aqueous alkanethiol treatment solution as recited in claim 34, wherein tartaric acid is present in an amount greater than 4% by weight of said alkanethiol composition.

36. The aqueous alkanethiol treatment solution as recited in claim 34, wherein tartaric acid is present in an amount greater than 6% by weight of said alkanethiol composition.

37. The aqueous alkanethiol treatment solution as recited in claim 34, wherein tartaric acid is present in an amount of 6% to 10% by weight of said alkanethiol composition.

38. The aqueous alkanethiol treatment solution as recited in claim 34, wherein tartaric acid is present in an amount of about 8% by weight of said alkanethiol composition.

39. The aqueous alkanethiol treatment solution as recited in any one of the claims 28 to38, wherein said emulsifier comprises a nonionic emulsifier.

40. The aqueous alkanethiol treatment solution as recited in claim 39, wherein said nonionic emulsifier comprises one of polysorbate 80, polysorbate 20, glycerol monostearate, or the polyethylene glycol derivative sold as TRITON X-100.

41. The aqueous alkanethiol treatment solution as recited in claim 39, wherein said nonionic emulsifier comprises polysorbate 80.

42. The aqueous alkanethiol treatment solution as recited in any one of the claims 28 to41, wherein said alkanethiol composition further comprises an anti -microbial agent.

43. The aqueous alkanethiol treatment solution as recited in claim 42, wherein said antimicrobial agent comprises at least one of the following: didecyl dimethyl ammonium bicarbonate or didecyl dimethyl ammonium carbonate.

44. The aqueous alkanethiol treatment solution as recited in claim 42, wherein said antimicrobial agent comprises CARBOSHIELD 1000.

45. The aqueous alkanethiol treatment solution as recited in any one of the claims 28 to44, wherein said alkanethiol composition further comprises a diluent.

46. The aqueous alkanethiol treatment solution as recited in claim 45, wherein said diluent comprises at least one of the following: water or a low molecular weight organic compound.

47. The aqueous alkanethiol treatment solution as recited in claim 45, wherein said diluent comprises a low molecular weight organic compound.

48. The aqueous alkanethiol treatment solution as recited in claim 45, wherein said low molecular weight organic compound comprises an alcohol.

49. The aqueous alkanethiol treatment solution as recited in any one of the claims 28 to48, wherein said alkanethiol composition further comprises a surfactant.

50. The aqueous alkanethiol treatment solution as recited in claim 49, wherein said surfactant comprises a non-ionic surfactant.

51. The aqueous alkanethiol treatment solution as recited in claim 49, wherein said nonionic surfactant comprises glycerol monostearate.

52. The aqueous alkanethiol treatment solution as recited in claim 28, wherein said carboxylic acid comprises potassium tartrate.

53. A method for treating a metallic surface of an article comprising: treating said metallic surface with an aqueous alkanethiol solution comprising an anti-tarnish composition and water, wherein said anti-tarnish composition comprises an alkanethiol and tartaric acid or salt thereof; wherein said tartaric acid or salt thereof is in an amount that is effective to remove extra molecules of said alkanethiol beyond a base monomolecular layer of said alkanethiol.

54. The method as recited in claim 53, wherein said tartaric acid or salt thereof is present in an amount greater than 4% (in percentage by weight) of said anti- tarnish composition.

55. The method as recited in claim 53, wherein said tartaric acid or salt thereof is present in an amount of 6% to 10% (in percentage by weight) of said anti- tarnish composition.

56. The method as recited in claim 53, wherein said tartaric acid or salt thereof is present in an amount of about 8% (in percentage by weight) of said anti-tarnish composition.

57. The method as recited in any of claims 53 to 56, wherein said anti-tarnish composition further comprises an emulsifier.

58. The method as recited in claim 57, wherein said emulsifier comprises a nonionic emulsifier.

59. The method as recited in claim 57, wherein said emulsifier comprises one of polysorbate 80, polysorbate 20, glycerol monostearate, or the polyethylene glycol derivative sold as TRITON X-lOo.

60. The method as recited in claim 57, wherein said emulsifier comprises polysorbate 80.

61. The method as recited in any of claims 53 to 60, wherein anti-tarnish composition further comprises an anti-microbial agent.

62. The method as recited in claim 61, wherein said anti-microbial agent comprises at least one of the following: didecyl dimethyl ammonium bicarbonate or didecyl dimethyl ammonium carbonate.

63. The method as recited in any of claims 53 to 62, wherein said anti -tarnish composition further comprises a surfactant.

64. The method as recited in claim 63, wherein said surfactant comprises glycerol monostearate.

65. The method as recited in any of the claims 53 to 64, further comprising: leaving said metallic surface in said aqueous alkanethiol treatment solution for no longer than ten minutes.

66. The method as recited in any one of claims 53 to 65, wherein said treating said metallic surface with an aqueous alkanethiol treatment solution comprises: placing said aqueous alkanethiol treatment solution in an ultrasonic bath having an ultrasonic generator; immersing said metallic surface in said aqueous alkanethiol treatment solution in said ultrasonic bath;activating said ultrasonic generator; and leaving said metallic surface in said ultrasonic bath for at least one minute while said ultrasonic generator is activated.

67. The method as recited any one of claims 53 to 66; wherein said treating said metallic surface with an aqueous alkanethiol treatment solution comprises: placing said aqueous alkanethiol treatment solution in an ultrasonic bath having two ultrasonic generators; immersing said article in said aqueous alkanethiol treatment solution in said ultrasonic bath; activating both of said two ultrasonic generators; and leaving said article in said ultrasonic bath for at least one minute while said two ultrasonic generators are activated.

68. The method as recited in claim 67, wherein said two ultrasonic generators operate at different frequencies.

69. The method as recited in claim 67, wherein: one of said two ultrasonic generators is disposed at a bottom of said ultrasonic bath; and a second one of said two ultrasonic generators is disposed at a side of said ultrasonic bath.

70. The method as recited in any of claims 53 to 69, wherein said article comprises a coin blank and said metallic surface comprises a coin blank surface; and wherein said treating said metallic surface with an aqueous alkanethiol treatment solution comprises: placing said aqueous alkanethiol treatment solution in a burnishing machine comprising a motor and a bowl containing numerous stainless steel balls;introducing said coin blank into said bowl; activating said motor; and leaving said coin blank in said burnishing machine for at least one minute.

71. The method as recited in claim 70, further comprising: holding said coin blank for about 2 to 5 minutes in said bowl at about 35- 45 degrees C; rinsing said coin blank for about 2 to 5 minutes; and towel drying said coin blank.

72. The method as recited in any one of claims 53 to 71, wherein said base monomolecular layer is deposited in a thickness of between 20 and 100 nanometers.

73. A method for manufacturing a metallic object, comprising: forming a shaped article having a surface that is at least partially formed of metal; and surface treating said surface of said shaped article with an aqueous alkanethiol treatment solution comprising a fluidic anti-tarnish composition and water; wherein said anti-tarnish composition comprises an alkanethiol and an amount of tartaric acid or salt thereof that is effective to remove extra molecules of said alkanethiol beyond a base monomolecular layer of said alkanethiol.

74. The method for manufacturing a metallic object, as recited in claim 73, wherein said anti-tarnish composition further comprises an emulsifier.

75. The method for manufacturing a metallic object, as recited in claim 74, wherein said emulsifier comprises polysorbate 80.

76. The method for manufacturing a metallic object, as recited in any of claims 73-75, wherein said anti-tarnish composition further comprises an anti-microbial agent.

77. The method for manufacturing a metallic object, as recited in claim 76, wherein said anti-microbial agent comprises at least one of the following: didecyl dimethyl ammonium bicarbonate or didecyl dimethyl ammonium carbonate.

78. The method for manufacturing a metallic object, as recited in any of claims 73-77, wherein said anti-tarnish composition further comprises a non-ionic surfactant.

79. The method for manufacturing a metallic object, as recited in claim 78, wherein said non-ionic surfactant comprises glycerol monostearate.

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