DESC:FIELD
The present disclosure relates to a process for electroplating a nickel coating
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.
Electrical impedance: The term “electrical impedance” refers to the measurement of the opposition that a circuit presents to a current when a voltage is applied.
Contact Potential Difference: The term “Contact Potential Difference” refers to the electrostatic potential difference between two metals (or one metal and one electrolyte) that are in contact and are in thermodynamic equilibrium. Specifically, it is the potential difference between a point close to the surface of the first metal, and a point close to the surface of the second metal (or electrolyte).
Pulsed electrodeposition: The term “Pulsed electrodeposition” refers to an electroplating process that involves the swift alternating of the potential or current between two different values resulting in a series of pulses of equal amplitude, duration and polarity, separated by zero current.
Grain refining: The term “grain refining” refers to the reduction in size of the grains inside a material. Grains are regions inside a material within which the atoms have a particular orientation. With grain refinement, more and more grains that are nearby are turned to have a different orientation.
Leveler: The term “leveler” refers to electroplating additives that aid in the deposition of smooth uniform coating on a substrate.
Brightener: The term “brightener” refers to electroplating additives that aid in obtaining the bright finish on the substrate.
Brightening efficiency: The term “brightening efficiency” refers to efficiency of a brightener to deposit bright fine-structure coating during the electroplating process.
Watts bath: The term “Watts bath” refers to a system used for depositing nickel metal on a substrate during an electrochemical process.
Porosity: The term “porosity” refers to the formation of pores in the nickel coating during nickel plating.
Duplex nickel plating: The term “duplex nickel plating” refers to the application of two coatings of nickel, the first being semi-bright, and the second being bright, which results in enhanced corrosion resistance.
Fermi Level: The term “Fermi level” refers to the top of the collection of electron energy levels at absolute zero temperature. This concept comes from Fermi-Dirac statistics. Electrons are fermions and by the Pauli exclusion principle cannot exist in identical energy states.
BACKGROUND
Electroplating a layer of nickel on a metal is carried out to protect the metal from corrosion, and wear and tear. In nickel electroplating, nickel is deposited onto a metal part that is clean and free of dirt. Generally, to clean and protect the part during the plating process a combination of heat treating, cleaning, pickling, and etching may be carried out. Once the part has been prepared, it is immersed into an electrolyte solution and is used as the cathode. The nickel anode gets dissolved into the electrolyte to form nickel ions. The ions travel through the solution and deposit on the cathode, Nickel electroplating is usually of two types – bright nickel plating and semi-bright nickel plating. Bright nickel plating having high luster is normally used for decorative purposes and corrosion protection, whereas semi-bright nickel plating is used where a high luster is not required. Bright nickel plating and semi-bright nickel plating can be achieved by Watts nickel plating baths using sulfur containing cyclic or heterocyclic organic brighteners. During electrolysis, the organic molecule breaks down into smaller molecules which are co-deposited along with nickel. However, co-deposition of sulfur along with nickel causes porosity in the nickel-coated layer. The degree of porosity in the nickel-coated layer depends on the amount of sulfur present in the electrolyte.
The thickness of the nickel-coated layer can be increased to about 20 microns to 30 microns to overcome the problem caused by porosity and to avoid corrosion. Use of a duplex layer of nickel is another way to overcome the porosity issue. In duplex layer of nickel, a first layer of nickel using sulfur free brightener is applied, followed by a second layer of bright nickel using sulfur containing brightener.
However, duplex nickel plating causes dimensional variation due to higher nickel thickness.
Therefore, there is felt a need to provide a process for electroplating a nickel coating 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 electroplating nickel on to an article.
Yet another object of the present disclosure is to avoid the formation of pores in the nickel coating during the electroplating of nickel.
Still another object of the present disclosure is to provide a thin nickel coating that provides corrosion protection.
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
The present disclosure provides a process for electroplating a nickel coating on an article. The process comprises immersing the article after pre-treatment in an electroplating bath comprising an aqueous medium comprising triethanolamine, nickel sulfate, nickel chloride, and boric acid, of an electroplating unit having a nickel anode and the article as the cathode. A pulsed power supply having a duty cycle in the range of 1000 cycles/minute to 1500 cycles/minute is applied for a time period in the range of 5 minutes to 10 minutes across the anode and the cathode to obtain a nickel coating electroplated on to the article. The nickel coating has a Contact Potential Difference in the range of 5.30 eV to 5.40 eV, an Electrical Impedance in the range of 400 Z/Ohm to 600 Z/Ohm, hardness in the range of 260 Hv to 330 Hv, thickness in the range of 2 micron to 4 micron, and is devoid of sulfur moieties. The pre-treatment includes alkaline soaking, electro-cleaning and acid dipping.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The present disclosure will now be described with the help of the accompanying drawing, in which:
Figure 1 illustrates the comparison of Impedance Spectroscopy of a sample electroplated with nickel in accordance with the present disclosure and a sample electroplated with nickel using commercial brightener;
Figure 2 represents the comparison of Contact Potential Difference measurement of a control sample, a sample electroplated with nickel in accordance with the present disclosure and a sample electroplated with nickel using commercial brightener; and
Figure 3 illustrates the X-Ray diffraction pattern of a sample electroplated with nickel in accordance with the present disclosure.
DETAILED DESCRIPTION
Nickel is a silver colored metal often used in jewellery and products, such as watches and spectacles. Though nickel is resistant to corrosion, contact with human sweat over a period of time may result in corrosion of nickel jewellery. Human sweat mostly comprises water, with trace amounts of mineral, lactic acid and urea dissolved in it. The pH of human sweat is typically in the range of moderately acidic (4.5) to neutral (7). Therefore, nickel is prone to corrosion when in contact with human sweat. Normally, nickel electroplating of a metal is carried out to change the surface property of the metal in order to prevent corrosion.
Conventional electroplating of nickel is carried out using organic brighteners containing sulfur. However, during electrolysis, sulfur is also deposited on the metal along with nickel. Co-deposition of sulfur along with nickel creates active sites for corrosion, and results in porosity in the nickel-coated layer. The degree of porosity in the nickel-coated layer depends on the amount of sulfur present in the electrolyte.
One way of avoiding the formation of pores in the nickel plated layer is to increase the thickness of the nickel-plated layer. Use of a duplex layer of nickel is another way to overcome the porosity issue. In a duplex layer of nickel, a first layer of nickel using a sulfur free brightener is applied, followed by a second layer of bright nickel using sulfur containing brightener. However, duplex nickel plating causes dimensional variation due to higher nickel thickness.
The present disclosure envisages a process for electroplating a comparatively thin nickel coating that has enhanced resistance to corrosion.
In an aspect of the present disclosure, there is provided a process for electroplating a nickel coating on an article. The process comprises immersing the article with an electroplating bath, and applying a pulsed power supply across the electrodes to obtain a nickel coating electroplated on the article. The process is hereinafter described in detail.
An article after pre-treatment with alkaline soaking, electro-cleaning, and acid dipping is immersed in an electroplating bath comprising an aqueous medium comprising triethanolamine, nickel sulfate, nickel chloride, and boric acid, of an electroplating unit. The electroplating unit has nickel as an anode and the article as the cathode.
A pulsed power supply having a duty cycle in the range of 1000 cycles/minute to 1500 cycles/minute is applied across the anode and the cathode for a time period in the range of 5 minutes to 10 minutes to obtain a nickel coating electroplated on the article. Pulsed power supply is able to control of uniform grain growth and provide even distribution, as compared to conventional direct current (DC) for electroplating. The coating obtained using pulsed power supply is coherent, and non-dentritic deposits at higher current densities are possible as compared to direct current. Further, the accompanying over potential provides higher nucleation rates and thus better grain refinement.
The nickel coating is has a Contact Potential Difference in the range of 5.30 eV to 5.40 eV, an Electrical Impedance in the range of 400 Z/Ohm to 600 Z/Ohm, hardness in the range of 260 Hv to 330 Hv, thickness in the range of 2 micron to 4 micron, and is devoid of sulfur moieties.
Typically, the concentration of the components in the electroplating bath can be: triethanolamine in the range of 0.1 ml/L to 2 ml/L, nickel sulfate in the range of 250 g/L to 260 g/L, nickel chloride in the range of 75 g/L to 80 g/L, and boric acid in the range of 45 g/L to 50 g/L. Typically, the aqueous medium is water. In an embodiment, the concentration of triethanolamine is 1.5 ml/L.
The presence of grease, oil, corrosion products, dirt, or other material can affect the adherence, continuity, and durability of the electroplated deposits. Therefore, the process of electroplating can be preceded by pre-treatment steps, before immersing the article in the electroplating bath. The pre-treatment steps prepare the surface of the article to be electroplated by removing any defects or contaminants to aid in the electroplating process. The pre-treatment is achieved by the following steps:
Initially, the article to be electroplated with a nickel coating is soaked in an alkaline solution to obtain an alkaline-soaked article. Typically, the article is soaked in hot alkaline solution. In accordance with the embodiments of the present disclosure, the alkaline solution can comprise at least one alkali selected from the group consisting of potassium hydroxide, sodium hydroxide, phosphates, silicates and carbonates. Typically, the concentration of the alkali to the solution is in the range of 30 g/L to 60 g/L and the temperature of the alkali solution can in the range of 40 °C to 60 °C.
The alkaline-soaked article is then electro-cleaned to obtain an electro-cleaned article. Electro-cleaning involves introducing a controlled electric current to an electrolytic bath full of cleaning solution, which results in cleaning of the article immersed in the bath. Electro-cleaning is always used with DC current, and can be cathodic (direct), anodic (reverse) or periodic reverse (alternating anodic and cathodic currents). In an embodiment of the present disclosure cathodic electro-cleaning is used. In cathodic electro-cleaning, the article acts as the cathode within a direct-current system. The system generally uses an alkali cleaning solution. Hydrogen gas is liberated at the cathode (article to be cleaned), which helps to remove contaminants from the surface of the article.
The electro-cleaned article is further dipped in an acid solution to obtain an electro-cleaned acid-dipped article. In one embodiment, a dilute acid solution is used for the acid treatment. The acid dipping neutralizes the alkaline film on the metal surface, and removes the oxide layer present on the metal surface. The acids used can be selected from:
- Mineral acids: hydrochloric acid, sulfuric acid, and phosphoric acid;
- Solid acids: related to the sulfuric acid, e.g., Na- bisulfate, sulfamic acid; ferric sulfate or chloride, monosodium phosphate, ammonium persulfate, and bifluoride salts; and
- Organic acids: gluconic acid, citric acid, tartaric acid, lactic acid, ethylenediaminetetraacetic acid (EDTA), acetic acid, oxalic acid, and hydroxy acetic acid.
The article is typically washed/rinsed with water after every step.
The electro-cleaned acid-dipped article is electroplated using an electroplating bath to obtain the nickel electroplated article of the present disclosure.
The commercially available brighteners comprise sulfur, which result in the deposition of sulfur during the electroplating process. Also, when DC power supply is used during the conventional electroplating process, the nickel atoms are deposited on the cathode surface along with sulfur, which leads to voids or doped metal/organic molecules on the nickel plated surface, resulting in corrosion of the metal surface.
Triethanolamine (TEA) facilitates a controlled deposition of nickel on the metal to avoid formation of lumps of nickel atoms on the metal surface. The pulsed electroplating allows a uniform flow of nickel atoms towards the cathode surface. The remaining nickel atoms form complex with TEA. This results in a uniform thickness of the nickel electroplated coating and controlled grain growth.
It is possible to obtain thinner nickel coating using the process of the present disclosure. Use of TEA in electroplating, avoids deposition of sulfur in the nickel coating layer and hence pores are not formed, resulting in enhanced corrosion inhibition. The process also uses less expensive material making the process economic. The process of the present disclosure uses pulsed plating, which allows uniform grain growth as compared to conventional direct current electroplating. Further, lower thickness of the electroplated nickel coating results in less lead time (A lead time is the latency between the initiation and execution of a process) in production and hence higher productivity. TEA being a non-sulfur complexing agent can be used as a brightener for pulsed nickel electroplating. The hardness of the sample electroplated with TEA as a brightener is higher than the hardness of sample coated with commercially available sulfur containing brighteners. The brilliance and the colour value of the coating are comparable with the commercially available brighteners. TEA can further provide good corrosion resistance at very low thickness as compared to the commercial brighteners.
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: Electroplating nickel coating on an article in accordance with the present disclosure
A polished brass article having 30 mm diameter and 2 mm thickness was first soaked in an alkaline solution using ultrasonic soak cleaner- USC 201 (procured from PS Galvasols, Bangalore). USC 201 is a commercially available cleaner used for alkaline cleaning comprising predominantly sodium carbonate. The concentration of the USC 201 used was 40 g/L. The brass article was soaked in the alkaline solution at a temperature of 55 °C for 5 minutes, to obtain the alkaline-soaked article. The alkaline-soaked article was rinsed in tap water, before further processing. The alkaline-soaked article was electro-cleaned by cathodic electro cleaner. Commercially available electro cleaning salt SSC 201 (procured from PS Galvasols, Bangalore) was used. SSC 201 comprises sodium carbonate and trisodium phosphate. The concentration of the SSC 201 used was 50 g/L. The electro-cleaning was carried out at a temperature of 55 °C for 5 minutes, to obtain the electro-cleaned article. The alkaline-soaked brass article was the cathode and the anode was stainless steel of the electro-cleaning system. The electro-cleaned article was rinsed in tap water, before dipping in acid. The electro-cleaned article was dipped in 10 % sulfuric acid for 5 minutes to obtain the electro-cleaned acid-dipped article. The electro-cleaned acid-dipped article was rinsed in demineralized water before being nickel electroplated using an electroplating bath comprising triethanol amine (1.5 ml/L) and water to obtain the nickel-plated article of the present disclosure. The bath used for nickel plating comprised of 250 g/L of nickel sulfate, 80 g/L of nickel chloride, and 45 g/L of boric acid. Electric supply in the form of pulsed power supply having a duty cycle of 1200 cycles/minute was applied for carrying out the nickel plating. The nickel plating was carried out for 5 minutes. The nickel coating had a thickness of 2 micron.
Different concentration of TEA (0.1 ml/L to 3.0 ml/L) was prepared in water and was used to study the effect of the different concentration of TEA on color value and hardness. However, there was no significant improvement in the brightness when the concentration of TEA was above 1.5 ml/L.
Experiment-2: Characterization of the electroplated nickel coating
Experiment-2a: Measurement of the luster and color of the nickel coating
Color value measurement using Konica minalto was performed and the results are summarized in Table-1 below.
Table-1
TEA Concentration L* a* b*
0.1 72.06 2.35 11.44
0.2 74.51 1.85 10.1
0.3 74.54 1.97 10.07
0.4 72.87 2.17 10.36
0.5 67.38 2.15 9.2
0.8 73.26 2.58 9.93
1 74.41 2.4 10.23
1.5 80.47 1.05 5.93
Sample nickel electroplated using commercial brightener 81.08 0.78 5.9

The L*a*b* color space was modeled after a color-opponent theory stating that two colors cannot be red and green at the same time or yellow and blue at the same time. As shown below, L* indicates lightness, a* is the red/green coordinate, and b* is the yellow/blue coordinate. Deltas for L* (?L*), a* (?a*) and b* (?b*) may be positive (+) or negative (-).
L* sample minus L* standard) = difference in lightness and darkness (+ = lighter, - = darker)
a* sample minus a* standard) = difference in red and green (+ = redder, - = greener)
b* sample minus b* standard) = difference in yellow and blue (+ = yellower, - = bluer)
It is seen from Table-1, that when TEA (1.5 ml/L) was used, the luster and color obtained was at par with the luster and color when commercial brighteners were used.
Experiment-2b: Measurement of the hardness of the nickel coating
The hardness of the nickel-coated layer was determined by Vickers hardness test and the results obtained are summarized in Table-2. The test shows the ability of the sample to resist plastic deformation from a standard source. 1.0 kg load was applied to the sample and a diamond indenter was used to make indents on the substrate. The diagonals of the indents formed were measured to determine the deformation.

Table-2
TEA Concentration ml/L Hardness Hv
0.1 268
0.2 279
0.3 280
0.4 290
0.5 299
0.8 304
1 315
1.5 328
Sample nickel electroplated using commercial brightener 316

However, there was no significant improvement in the hardness when the concentration of TEA was above 1.5 ml/L.
It is clearly seen from Table-2 that the hardness of the sample electroplated with nickel (using TEA) in accordance with the present disclosure is comparable with that of samples when commercial brighteners were used.
From Table-1 and Table-2 it is found that there was no significant change in the color value and hardness of the samples, when the concentration of TEA was above 1.5 ml/L. Therefore, the optimum concentration of TEA was 1.5 ml/L.
Experiment-2c: Corrosion resistance of the nickel coating
I. Measurement of Electrical Impedance
The comparison of Electrical Impedance of a sample electroplated with nickel (using TEA) in accordance with the present disclosure and a sample electroplated with nickel using commercial brightener was carried out and the results obtained are illustrated in Figure-1. It is clearly seen from Figure-1 that the sample (B) electroplated with nickel in accordance with the present disclosure exhibits more resistance (up to 600 Z/Ohm) to the electron flow as compared to the sample (A) coated with nickel using commercial brighteners. It is seen from Figure-1 that the sample electroplated with nickel in accordance with the present disclosure exhibits higher resistance to current conduction as compared to the sample electroplated with nickel using commercial brightener. The increased resistance to the flow of current in the sample electroplated with nickel in accordance with the present disclosure shows increased resistance to corrosion as compared to the sample electroplated with nickel using commercial brightener. Also, the increased resistance to electron flow delays corrosion, whereas free flow of the electron results in faster corrosion of the sample electroplated with nickel using commercial brightener. Therefore, from Figure-1 it can be concluded that the sample coated with nickel in in accordance with the present disclosure has more resistance to corrosion as compared to the sample where commercial brightener is used. The enhanced corrosion resistance is due to the fine grain refinement and the uniform thickness due to the pulsed power supply. The grains are closely packed, and resist penetration of the corroding electrolyte to reach the base material through the pores of the electroplated nickel coating.
II. Measurement of the Contact Potential Difference
The Contact Potential Difference was determined using Kelvin probe method. A control sample (without nickel coating: C), a sample electroplated with nickel (using TEA: B) in accordance with the present disclosure and a sample electroplated with nickel using commercial brightener (A) were analyzed and the results obtained are illustrated in Figure-2. The Kelvin probe method is a non-contact method that measures the potential difference (surface energy) of the samples. When two or more materials are brought together, the Fermi level equalizes the flow of electron from lower work function to higher work function. The work function is usually defined as being the least amount of energy required to remove an electron from a surface of an atom to infinity or equivalent to vacuum level. When a group of atoms or molecules are brought together to form a solid, the highest occupied energy level or Fermi level is called work function. The Kelvin probe measures the work function indirectly, and not by extracting electron by via equilibrium. The measurement of the flow of electron using vibrating tip in vacuum provides the corrosion resistance behavior of the samples under testing. The measurement was carried out for brass samples coated with commercially available grain refiners (A) using DC power supply and TEA as brightener (B). Brass was used as control sample (C). A higher potential difference of 5.33 eV is obtained in case of the sample (B) electroplated with nickel in accordance with the present disclosure, which used TEA and pulsed deposition of nickel, as compared to the sample (A: 5.11 eV) electroplated with nickel using commercial brighteners. A higher potential difference means that the energy required to remove electrons from the surface would be higher. The higher potential difference therefore corresponds to higher resistance to electron flow and hence a higher resistance to corrosion in case of the sample electroplated with nickel in accordance with the present disclosure. The higher contact potential of the TEA coated samples of the present disclosure is due to the higher resistivity of the surface to corrosion as indicated in Figure-3. This was further validated through subjecting the samples for continuous exposure to artificial sweat solution for 48.0 hours. No significant corrosion spots were noticed after 48.0 hours for samples electroplated with nickel in accordance with the present disclosure. Whereas, samples electroplated with commercial brighteners by conventional direct current subjected along with TEA exhibited corrosion spots on the surface.
Experiment-2d: Crystallinity of the nickel coating
X-Ray diffraction pattern of sample electroplated with nickel (using TEA) in accordance with the present disclosure was performed and the result obtained is illustrated in Figure-3. It is seen from Figure-3 that the sharp peaks are obtained at (1 1 1) and (2 0 0). The sharp peak obtained in Figure-3 indicates the high crystallinity of nickel. The fine crystallinity of nickel is clearly seen from Figure-3.
With DC power supply, the nickel plating is continuous and hence the breakdown of the organic brightener and co-deposition of sulfur is unavoidable, resulting in corrosion. The pulsed power supply, and TEA as the complexing agent (brightener) used in the present disclosure (which does not have sulfur atom) inhibits corrosion of the electroplated nickel coating. The nickel atoms are aligned towards cathode (the article) uniformly for fine crystalline deposit as the power supply is pulsed as clearly seen from the sharp peak obtained in Figure-3. It is seen from the sharp peak of Figure-3 that the nickel atoms are closely packed, and is devoid of porosity, inclusions, and foreign material, resulting in increased resistance to corrosion.
The process of the present disclosure can be applied wherever lower thickness is required with higher corrosion resistance. Other substrates like zinc, steel can also be coated using this process.
TECHNICAL ADVANCEMENTS
The present disclosure described herein above has several technical advantages including, but not limited to, the realization of a cost-effective process for electroplating a nickel coating on an article. The deposition of sulfur in the electroplated nickel coating is avoided by the use of TEA in electroplating. Therefore, pores are not formed, resulting in enhanced corrosion inhibition. The process uses pulsed power supply, which allows uniform grain growth as compared to conventional direct current electroplating.
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 electroplating a nickel coating on an article, said process comprising:
- immersing said article after pre-treatment with alkaline soaking, electro-cleaning, and acid dipping, in an electroplating bath comprising an aqueous medium comprising triethanolamine, nickel sulfate, nickel chloride, and boric acid of an electroplating unit having a nickel anode and said article as the cathode; and
- applying a pulsed power supply having a duty cycle in the range of 1000 cycles/minute to 1500 cycles/minute across said anode and said cathode for a time period in the range of 5 minutes to 10 minutes to obtain a nickel coating electroplated on to said article.
2. The process as claimed in claim 1, wherein the concentration of triethanolamine is in the range of 0.1 ml/L to 2 ml/L, preferably 1.5 ml/L, the concentration of nickel sulfate is in the range of 250 g/L to 260 g/L, the concentration of nickel chloride is in the range of 75 g/L to 80 g/L, and the concentration of boric acid is in the range of 45 g/L to 50 g/L.
3. The process as claimed in claim 1, wherein said nickel coating has:
- a Contact Potential Difference in the range of 5.30 eV to 5.40 eV;
- an Electrical Impedance in the range of 400 Z/Ohm to 600 Z/Ohm;
- hardness in the range of 260 Hv to 330 Hv;
- thickness in the range of 2 micron to 4 micron; and
- is devoid of sulfur moieties.
4. The process as claimed in claim 1, wherein said pre-treatment steps, prior to immersing said article in said electroplating bath is achieved by:
a) soaking said article in an alkaline solution to obtain an alkaline-soaked article;
b) electro-cleaning said alkaline-soaked article to obtain an electro-cleaned article; and
c) dipping said electro-cleaned article in an acid solution to obtain an electro-cleaned acid-dipped article.
5. The process as claimed in claim 5, wherein said article is washed with water after every step.
6. The process as claimed in claim 5, wherein in step (a) said alkaline solution comprises at least one alkali selected from the group consisting of potassium hydroxide, sodium hydroxide, phosphates, silicates and carbonates, and the concentration of said alkaline solution is in the range of 30 g/L to 60 g/L.
7. The process as claimed in claim 5, wherein in step (a) the temperature of said alkaline solution is in the range of 40 °C to 60 °C.
8. The process as claimed in claim 5, wherein in step (b) said electro-cleaning is selected from the group consisting of anodic electro-cleaning, cathodic electro-cleaning, periodic-reverse cleaning, and interrupted-current cleaning.
9. The process as claimed in claim 5, wherein in step (c) said acid solution comprises at least one acid selected from the group consisting of mineral acids, solid acids, and organic acids.
10. An article obtained by the process as claimed in claim 1, having a nickel coating deposited thereon, wherein said nickel coating has:
- a Contact Potential Difference in the range of 5.30 eV to 5.40 eV;
- an Electrical Impedance in the range of 400 Z/Ohm to 600 Z/Ohm;
- hardness in the range of 260 Hv to 330 Hv;
- thickness in the range of 2 micron to 4 micron; and
- is devoid of sulfur moieties.