DESC:FIELD
The present disclosure relates to corrosion resistant ornamental articles.
DEFINITIONS
As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicates otherwise.
Sliding property: The term “sliding property” refers to the sliding movement of a fluid on a metal surface, such that the fluid is not retained on the metal surface.
Hydrophobicity: The term “hydrophobicity” refers to the physical property of any surface to repel water.
Columnar morphology: The term “columnar morphology” refers to a type of grain structure present in a coating.
Grain boundary: The term “grain boundary” refers to the interface between two grain or crystallites in a polycrystalline material. Grain boundaries are 2D defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. Most grain boundaries are preferred sites for the onset of corrosion and for the precipitation of new phases from the solid.
Low electrical resistivity: The term “low electrical resistivity” refers to the property of a substance that readily allows the flow of electric current.
Porosity: The term “porosity” refers to the formation of pores in the titanium nitride layer.
Microelectronics: The term “microelectronics” refers to the study and manufacture of very small electronic designs and components, such as, transistors, capacitors, inductors, resistors, diodes, insulators and conductors.
Ellipsometry: The term “Ellipsometry” refers to an optical technique for determining the dielectric properties (complex refractive index or dielectric function) of thin films.
BACKGROUND
The rising price of gold has led to increasing demand of artificial jewelry/ fashion accessories that resemble gold in color and in texture. The fashion industry prepare articles made of materials, such as, stainless steel or brass, which are coated with titanium nitride, followed by a thin coating of gold. The gold atoms occupy the pores present in titanium nitride and enhance the look and the feel of the artificial jewelry/ fashion accessories. Since, brass is a softer metal alloy as compared to stainless steel, a coating of nickel is applied to brass before being coated with titanium nitride. Titanium nitride is extremely hard, has high electrical resistivity, high wear resistance, excellent corrosion resistance and high thermal stability, and is also bio-compatible, making it an excellent coating agent.
However, during titanium nitride coating, pin holes are formed, which acts as a source for the corrodent to reach beneath the layer easily and to induce corrosion swiftly. Titanium nitride has a columnar structure and hence the grain boundaries are easily dissolved in corrosive environment, such as, contact with sweat, leading to corrosion of the artificial jewelry/ fashion accessories.
Therefore, there is felt a need to provide a process for protecting metals from corrosion that mitigates the drawbacks mentioned hereinabove.

OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
An object of the present disclosure is to ameliorate one or more problems of the prior art or to at least provide a useful alternative.
Another object of the present disclosure is to provide a process for preparation of a corrosion resistant ornamental article.
Yet another object of the present disclosure is to provide a corrosion resistant ornamental article that is capable of resisting corrosion from human sweat.
Still another object of the present disclosure is to provide corrosion resistant ornamental articles that resemble gold jewelry in look and in texture.
Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.
SUMMARY
In one aspect, there is provided a process for preparing a corrosion resistant article. The process comprises the steps, which are discussed hereinafter
An article prepared from a base metal is provided. The base metal is at least one metal selected from the group consisting of copper, brass, steel, and silver.
The article is then coated with a layer of nickel having a thickness in the range of 5 micron to 50 micron, to obtain a nickel-coated article.
The nickel-coated article is coated with a layer of titanium nitride having a thickness in the range of 0.1 micron to 2 micron, to obtain a titanium nitride-coated article.
Next, the titanium nitride-coated article is coated with a layer of gold having a thickness in the range of 0.01 micron to 0.2 micron, to obtain a gold-coated article.
A mixture comprising isotridecyl ethoxylate and a fluid medium is acidified separately to obtain an acidified mixture. The step of acidification is carried out using citric acid.
The gold-coated article is then treated with the acidified mixture to obtain a wet treated article.
The wet treated article is cured to obtain the corrosion resistant article.
In second aspect, there is provided a process for preparing a corrosion resistant ornamental article. The process comprises the steps, which are discussed hereinafter
An ornamental article prepared from a base metal is provided. The base metal is at least one metal selected from the group consisting of copper, brass, steel, and silver.
The ornamental article is then coated with a layer of nickel having a thickness in the range of 5 micron to 50 micron, to obtain a nickel-coated ornamental article.
The nickel-coated ornamental article is coated with a layer of titanium nitride having a thickness in the range of 0.1 micron to 2 micron, to obtain a titanium nitride-coated ornamental article.
Next, the titanium nitride-coated ornamental article is coated with a layer of gold having a thickness in the range of 0.01 micron to 0.2 micron, to obtain a gold-coated ornamental article.
A mixture comprising isotridecyl ethoxylate and a fluid medium is acidified separately to obtain an acidified mixture. The step of acidification is carried out using citric acid.
In accordance with an embodiment of the present disclosure, the fluid medium is deionized water.
The gold-coated ornamental article is then treated with the acidified mixture to obtain a wet treated ornamental article.
The wet treated ornamental article is cured to obtain the corrosion resistant ornamental article.
The corrosion resistant ornamental article is capable of resisting corrosion from human sweat.
In accordance with an embodiment of the present disclosure, the step of treating gold-coated ornamental article with the acidified mixture is carried out for a time period in the range of 1 minute to 10 minutes at a temperature in the range of 30 °C to 50 °C.
In accordance with an embodiment of the present disclosure, the step of is achieved by at least one of electro-deposition and vapor deposition.
In accordance with an embodiment of the present disclosure, the step of pH of said acidified mixture is in the range of 2 to 5.
In second aspect, there is provided a corrosion resistant ornamental article. The corrosion resistant ornamental article comprises a base metal layer, a nickel layer having a thickness in the range of 5 micron to 50 micron, deposited over the base metal layer, a titanium nitride layer having a thickness in the range of 0.1 micron to 2 micron, deposited over the nickel layer, a gold layer having a thickness in the range of 0.01 micron to 0.2 micron, deposited over titanium the nitride layer, and an acidified isotridecyl ethoxylate layer having a thickness in the range of 5 nm to 10 nm, deposited over the gold layer.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figures 1 illustrates a comparison of the corrosion activity of samples coated with an acidified mixture of isotridecyl ethoxylate and uncoated samples, exposed to artificial sweat solution; and
Figure 2 represents a SEM image of a nano polymeric layer of a sample coated with an acidified mixture of isotridecyl ethoxylate.
DETAILED DESCRIPTION
The demand for artificial jewelry/ fashion accessories that resemble gold in color and in texture is on the rise due to the increasing price of gold. Therefore, there is an increasing demand of artificial jewelry/ fashion accessories that resemble gold in color and in texture. However, corrosion of the artificial jewelry reduces the product life and also the aesthetic value of the product. The present disclosure envisages a corrosion resistant ornamental articles and a process for their preparation.
In an aspect of the present disclosure, there is provided a process for preparing a corrosion resistant ornamental article. The process comprises sequential coating of an ornamental article prepared from a base metal.
In one aspect, there is provided a process for preparing a corrosion resistant article. The process comprises the steps, which are discussed hereinafter
An article prepared from a base metal is provided. The base metal is at least one metal selected from the group consisting of copper, brass, steel, and silver.
The article is then coated with a layer of nickel having a thickness in the range of 5 micron to 50 micron, to obtain a nickel-coated article.
The nickel-coated article is coated with a layer of titanium nitride having a thickness in the range of 0.1 micron to 2 micron, to obtain a titanium nitride-coated article.
Next, the titanium nitride-coated article is coated with a layer of gold having a thickness in the range of 0.01 micron to 0.2 micron, to obtain a gold-coated article.
A mixture comprising isotridecyl ethoxylate and a fluid medium is acidified separately to obtain an acidified mixture. The step of acidification is carried out using citric acid.
The gold-coated article is then treated with the acidified mixture to obtain a wet treated article.
The wet treated article is cured to obtain the corrosion resistant article.
In second aspect, there is provided a process for preparing a corrosion resistant ornamental article. The process comprises the steps, which are discussed hereinafter
Initially, an ornamental article prepared from a base metal is provided. The base metal is at least one selected from the group consisting of copper, brass, steel and zinc.
The ornamental article prepared from a base metal is coated with a layer of nickel to obtain a nickel-coated ornamental article. The thickness of the layer of nickel is in the range of 5 micron to 50 micron. Usually, the ornamental article is prepared from a base metal, such as, brass which is an alloy made of copper and zinc. Brass is a comparatively softer alloy and hence it is coated with a layer of nickel before further processing.
The nickel-coated ornamental article is then coated with a layer of titanium nitride, to obtain a titanium nitride-coated ornamental article. The thickness of the layer of titanium nitride is in the range of 0.1 micron to 2 micron.
The titanium nitride-coated ornamental article is coated with a layer of gold, to obtain a gold-coated ornamental article. The thickness of the layer of gold is in the range of 0.01 micron to 0.2 micron.
The coating steps mentioned above can be achieved by at least one of electro-deposition and physical vapour deposition
A mixture comprising isotridecyl ethoxylate and a fluid medium is separately acidified to obtain an acidified mixture. Typically, the mixture is acidified using at least one acid selected from citric acid and oxalic acid and the pH of the acidified mixture is in the range of 2 to 5. In one embodiment, the mixture is acidified using citric acid.
In accordance with an embodiment of the present disclosure, the fluid medium is deionized water.
The gold-coated ornamental article obtained is then treated with the acidified mixture to obtain a wet treated ornamental article. The treating step can be carried out for a time period in the range of 1 minute to 15 minutes at a temperature in the range of 30 °C to 50 °C.
Acidification results in enhancement of hydrophobicity and sliding property of the mixture. Enhanced hydrophobicity and sliding property ensure that liquids, such as, water and sweat is not retained on the ornamental articles and results in enhanced resistance to corrosion.
In accordance with one embodiment, the treating of the gold-coated ornamental article is carried out by dipping it in the acidified mixture for predetermined time.
The wet treated ornamental article is dried to obtain the corrosion resistant ornamental article. Curing is carried out at a temperature in the range of 100 °C to 120 °C. Curing the ornamental articles at the aforestated temperature range results in complete removal of water and the polymerization of the isotridecyl ethoxylate, so that a nano polymeric layer of isotridecyl ethoxylate is formed over the gold coated layer. The nano polymeric layer of isotridecyl ethoxylate is completely transparent and hence the ornamental articles retain the look and texture of gold. Further, the nano polymeric layer of isotridecyl ethoxylate does not undergo a reaction with the substrate and hence resists corrosion.
The present disclosure in another aspect provides a corrosion resistant ornamental article. The corrosion resistant ornamental article comprises:
a. a base metal layer;
b. a nickel layer deposited over the base metal layer. The thickness of the nickel layer can be in the range of 5 micron to 50 micron;
c. a titanium nitride layer deposited over the nickel layer. The thickness of the titanium nitride can be in the range of 0.1 micron to 2 micron;
d. a gold layer deposited over titanium the nitride layer. The thickness of the gold layer can be in the range of 0.01 micron to 0.2 micron; and
e. an acidified isotridecyl ethoxylate layer in the form of a nano polymeric layer deposited over the gold layer. The thickness of the nano polymeric layer can be in the range of 5 nm to 10 nm.
The corrosion resistant ornamental articles prepared in accordance with the present disclosure are capable of resisting corrosion due to human sweat. The enhanced sliding and hydrophobic property of the nano polymeric layer reduces the contact time of the ornamental article with fluids, such as, human sweat and water and thus provides increased protection from corrosion. Further, the look and the texture of the corrosion resistant ornamental articles are similar to that of gold jewelry and hence can be used as an inexpensive alternative to gold jewelry. Acidification of isotridecyl ethoxylate further increases the hydrophobicity and sliding property, resulting in enhanced corrosion resistance.
The present disclosure is further described in light of the following laboratory scale experiments which are set forth for illustration purpose only and not to be construed for limiting the scope of the disclosure. These laboratory scale experiments can be scaled up to industrial/commercial scale and the results obtained can be extrapolated to industrial/commercial scale.
Experimental Details
Experiment-1: Preparation of the corrosion resistant ornamental article in accordance with the present article
Step-1A: Preparation of gold-coated ornamental article
Brass coupons having a diameter of 30 mm and 2 mm thickness were prepared and were polished using emery sheet and diamond paste in a metallurgical polishing machine. A layer of nickel having a thickness of 12 micron was coated on to the brass coupons using the electroplating deposition technique, to obtain nickel-coated brass coupons. The nickel-coated brass coupons were coated with a layer of titanium nitride having a thickness of 0.5 micron to obtain titanium nitride-coated brass coupons. The titanium nitride-coated brass coupons were coated with a layer of gold having a thickness of 0.1 micron to obtain gold-coated brass coupons.
Step-1B: Preparation of the acidified mixture comprising isotridecyl ethoxylate
1.0 % mixture comprising isotridecyl ethoxylate and deionized water, was acidified using citric acid to obtain an acidified mixture. The pH of the acidified mixture was maintained at 3.5.
Among different pH values ranging from 3.0 to 7.0., the optimum hydrophobicity and sliding property was obtained for pH of 3.5. Further, acidification of isotridecyl
Step-1C: Coating with the nano polymeric layer of isotridecyl ethoxylate
The gold-coated brass coupons obtained in Step-1A were coated with a layer of the acidified mixture (obtained in Step-1B) by dipping the gold-coated brass coupons for a time period provided in Table 1, followed by drying at a temperature of 110 °C to obtain the corrosion resistant brass coupons having a nano polymeric layer of isotridecyl ethoxylate.
The thickness of the nano polymeric layer was determined by Ellipsometry technique. The refractive index of the coated and uncoated surface was determined and is summarized Table-1. The thickness of the nano polymeric layer was found to be 1.2 nm.
Table-1: Properties of samples
Samples Dipping time
(minutes) Thickness (nm) Refractive index at 550 nm Mean Square index (MSE)
1 2 3.26 0.97 26
2 4 1.2 0.8 26
3 6 1.5 1.4 71
4 8 2.0 1.11 53
5 10 Not measured 1.1 22
6 (Uncoated Sample) NA NA 0.56 -

The uncoated sample (6) contained only the gold layer at the top and did not had the coating of the nano-polymeric layer. The refractive index of the gold layer (0.56) was used as the base line. The refractive indexes to the coated samples (1 to 5) were determined with reference to the refractive index of the gold layer.
Samples 1 to 5 were coated at 40 °C for 2 minutes, 4 minutes, 6 minutes, 8 minutes and 10 minutes, respectively. Thickness of Coated-5 could not be measured by ellipsometry. One reason for Coated-5 not exhibiting a measurable thickness could be that due to the longer dipping time, the coated layer has dissolved back into the acidified mixture and hence does not form a measurable layer.
Experiment 2: Study of corrosion resistance of the ornamental articles of the present disclosure on exposure to human sweat
The corrosion resistance of the brass coupons was carried out as per the IS 3160 standard. As per IS 3160, samples exposed to artificial sweat solution at 36 °C should not develop any stains or pits within 24 hours (this is equivalent to 1 year of the product life).
The artificial sweat solution was prepared by first dissolving 20 g/L sodium chloride, 17.5 g/L of ammonium chloride, 5.0 g/L urea, 2.5 g/L acetic acid and 15.0 g/L lactic acid. The pH of the resultant mixture was adjusted to 4.7 using sodium hydroxide solution.
A glass desiccator having a capacity of 10 L kept in a water bath having a temperature of 40 °C was used as the test chamber.
The coated samples 1, 2, 3, 4 and 5 were prepared using the procedure of Experiment 1 by dipping the brass coupons in the acidified mixture comprising isotridecyl ethoxylate for 2 minutes, 4 minutes, 6 minutes, 8 minutes and 10 minutes. The coatings were carried out at three different temperatures, viz. 35 °C, 40 °C and 45 °C. Thereafter, the samples were dried at a temperature of 110 °C.
After drying, the samples were sprayed with the artificial sweat solution (36 °C), every 3 hours and the corrosion activity was observed using a microscope (Zeiss metallurgical microscope - Axiocam ERc 5s).
Figure-1 illustrates the corrosion activity of samples exposed to artificial sweat solution. The column on the extreme right side depicts the samples that were not coated with a nano polymer layer of isotridecyl ethoxylate. The 1st row depict the samples that were coated at a temperature of 35 °C, the 2nd to 5th rows depict the samples that were coated at a temperature of 40 °C and the 6th and 7th rows depict the samples that were coated at a temperature of 45 °C. Starting from left, the 1st column was coated for a time period of 2 minutes, the 2nd column for 4 minutes, the 3rd column for 6 minutes, the 4th column for 8 minutes and the 5th column for 10 minutes. It is clearly seen from Figure-1 that the sample that was coated at 40 °C for 4 minutes exhibited excellent resistance to corrosion.
SEM analysis of the nano polymeric layer was carried out and the result obtained is illustrated in Figure-2. Figure-2 clearly shows the presence of the carbon content on the nano polymeric layer. The nano polymeric layer is made up of simple organic aliphatic chain molecules and hence the presence of carbon in the top layer confirms the presence of the nano polymeric layer.
Further, it was observed that increased polymer concentration has also resulted in corrosion behavior. Therefore, the higher polymer concentration of polymer cannot provide corrosion protection to the desired level.

TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a process for preparing a corrosion resistant ornamental article. The corrosion resistant ornamental articles are capable of resisting corrosion due to human sweat, which can enhance the life and aesthetics of the jewelry.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression “at least” or “at least one” suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Variations or modifications to the formulation of this invention, within the scope of the invention, may occur to those skilled in the art upon reviewing the disclosure herein. Such variations or modifications are well within the spirit of this invention.
The numerical values given for various physical parameters, dimensions and quantities are only approximate values and it is envisaged that the values higher than the numerical value assigned to the physical parameters, dimensions and quantities fall within the scope of the invention unless there is a statement in the specification to the contrary.
While considerable emphasis has been placed herein on the specific features of the preferred embodiment, it will be appreciated that many additional features can be added and that many changes can be made in the preferred embodiment without departing from the principles of the disclosure. These and other changes in the preferred embodiment of the disclosure will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.
,CLAIMS:WE CLAIM
1. A process for preparing a corrosion resistant article, said process comprising:
a. providing an article prepared from a base metal;
b. coating said article with a layer of nickel having a thickness in the range of 5 micron to 50 micron, to obtain a nickel-coated article;
c. coating said nickel-coated ornamental article with a layer of titanium nitride having a thickness in the range of 0.1 micron to 2 micron, to obtain a titanium nitride-coated article;
d. coating said titanium nitride-coated article with a layer of gold having a thickness in the range of 0.01 micron to 0.2 micron, to obtain a gold-coated ornamental article;
e. separately acidifying a mixture comprising isotridecyl ethoxylate and a fluid medium to obtain an acidified mixture;
f. treating said gold-coated ornamental article with said acidified mixture to obtain a wet treated article; and
g. curing said wet treated article at a temperature in the range of 100 °C to 120 °C while polymerizing said acidified isotridecyl ethoxylate to obtain said corrosion resistant article.
2. A process for preparing a corrosion resistant ornamental article, said process comprising:
a. providing an ornamental article prepared from a base metal;
b. coating said ornamental article with a layer of nickel having a thickness in the range of 5 micron to 50 micron, to obtain a nickel-coated ornamental article;
c. coating said nickel-coated ornamental article with a layer of titanium nitride having a thickness in the range of 0.1 micron to 2 micron, to obtain a titanium nitride-coated ornamental article;
d. coating said titanium nitride-coated ornamental article with a layer of gold having a thickness in the range of 0.01 micron to 0.2 micron, to obtain a gold-coated ornamental article;
e. separately acidifying a mixture comprising isotridecyl ethoxylate and a fluid medium to obtain an acidified mixture;
f. treating said gold-coated ornamental article with said acidified mixture to obtain a wet treated ornamental article; and
g. curing said wet treated ornamental article at a temperature in the range of 100 °C to 120 °C while polymerizing said acidified isotridecyl ethoxylate to obtain said corrosion resistant ornamental article,
wherein said corrosion resistant ornamental article is capable of resisting corrosion from human sweat.
3. The process as claimed in any one of claims 1 and 2, wherein said base metal is selected from the group consisting of copper, brass, steel, and silver.
4. The process as claimed in any one of claims 1 and 2, wherein said treating step (f) is carried out for a time period in the range of 1 minute to 10 minutes at a temperature in the range of 30 °C to 50 °C.
5. The process as claimed in any one of claims 1 and 2, wherein said coating in steps (b), (c), and (d) are achieved by at least one of technique selected from the group consisting of electro-deposition and vapor deposition.
6. The process as claimed in any one of claims 1 and 2, wherein said fluid medium in step (e) is deionized water.
7. The process as claimed in any one of claims 1 and 2, wherein the amount of isotridecyl ethoxylate with respect to said fluid medium is in the range of 0.5 wt% to 5wt%.
8. The process as claimed in any one of claims 1 and 2, wherein said mixture comprising isotridecyl ethoxylate and said fluid medium is acidified by adding citric acid.
9. The process as claimed in any one of claims 1 and 2, wherein the pH of said acidified mixture is in the range of 2 to 5.
10. A corrosion resistant ornamental article comprising:
a. a base metal ornamental article;
b. a nickel layer deposited over said base metal article, said nickel layer having a thickness in the range of 5 micron to 50 micron;
c. a titanium nitride layer deposited over said nickel layer, said titanium nitride layer having a thickness in the range of 0.1 micron to 2 micron;
d. a gold layer deposited over titanium said nitride layer, said gold layer having a thickness in the range of 0.01 micron to 0.2 micron; and
e. a polymeric layer of acidified isotridecyl ethoxylate deposited over said gold layer; said polymeric layer of acidified isotridecyl ethoxylate layer having a thickness in the range of 5 nm to 10 nm,
wherein said corrosion resistant ornamental article is capable of resisting corrosion from human sweat.