Description:FIELD OF INVENTION
[0001] The present invention relates to an electroplating composition having reinforcing-nano-composites and more particularly, to the electroplating composition having reinforcing-nano-composites selected from at least one of nano-TiO2 composites, or nano-SiO2 composites and method of preparing the electroplating composition.

BACKGROUND
[0002] Among surface coated steel strips, hot dip galvanized steel is the most popular coated steel product used in automotive segment. Recently, the need for improved corrosion resistance properties has been increased in some applications and it has been desired to enhance the corrosion resistance of Zinc coated steel. Conventional zinc coating can be modified to zinc alloy coatings to improve the corrosion resistance properties. However, hot-dip galvanizing has certain disadvantages like poor coating thickness control, and impossibility of single sided coatings etc. Another problem with the hot-dipping of zinc for high strength alloy steels is that they suffer from selective oxidation of alloying elements in the steel during annealing, resulting in poor wettability of molten zinc.
[0003] One of the ways by which these problems can be addressed is by electrodeposition of zinc (electro-galvanizing) instead of hot-dipping. Electrodeposition technology offers higher flexibility than hot dip technology to coat steel with variety of zinc alloys which can offer higher corrosion resistance along with better control over coating thickness (much lower thickness is possible), superior surface finish and possibility of only one-sided coating. Contemporarily, the electrodeposition process is being carried out using a direct current (dc) method or a pulsed current method.
[0004] There are many different electroplating compositions available which when utilized to coat steel using electrodeposition process improves the corrosion resistance. One such composition a zinc salt bath comprising additives such as benzylidene acetone, CTAB or a combination of CTAB and benzylidene acetone, when used to coat steel using pulsed current electrodeposition method provides a coating which provides better corrosion resistance than commercially available coats. However, these additives even though they provide better corrosion resistance properties, are very costly and increases the overall expense for the coating, which is undesirable.
[0005] The present disclosure is directed to overcome one or more limitations stated above or any other limitation associated with the prior arts.
OBJECTIVE OF INVENTION
[0006] It is an object of the invention to solve the problems of the prior art and provide an electroplating composition having reinforcing-nano-composites which is cost effective and provides a comprehensive coating solution where the multifunctional requirement of the automotive industry can be achieved through a low cost single coating system.
[0007] Another objective of the present invention is to develop the electroplating composition aimed to achieve Zn based composite coating system using DC and pulsed electrodeposition technology through physical dispersion of reinforcements for enhanced functional properties.
[0008] It is yet another objective of the present invention, to provide the electroplating composition having reinforcing-nano-composites selected from at least one of the nano-TiO2 composite particles, nano-SiO2 composite particles.
SUMMARY OF INVENTION
[0009] This summary is provided to introduce concepts related to the electroplating composition having reinforcing-nano-composites and method of preparing the electroplating composition. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0010] In one aspect of the present invention, an electroplating composition having reinforcing-nano-particles is provided. The electroplating composition having reinforcing-nano-particles comprises zinc sulphate, zinc chloride, boric acid, and reinforcing-nano-particles. The said reinforcing-nano-particles is selected from at least one of nano-TiO2 composite particles, nano-SiO2 composite particles. The electroplating composition has a pH of about 3-4.5.
[0011] In an embodiment, the zinc sulphate is present in an amount of about 200-300 g/L, the zinc chloride is present in an amount of about 5-8 g/L, the boric acid is present in an amount of about 22-35 g/L and the reinforcing-nano-particles are present in an amount of about 0.5-5 g/L.
[0012] In an embodiment, the zinc sulphate is present in an amount of about 250 g/L, the zinc chloride is present in an amount of about 6 g/L, the boric acid is present in an amount of about 30 g/L, and the reinforcing-nano-particles of TiO2 are present in an amount of about 1 g/L.
[0013] In an embodiment, the zinc sulphate is present in an amount of about 250 g/L, the zinc chloride is present in an amount of about 6 g/L, the boric acid is present in an amount of about 30 g/L, and the reinforcing-nano-particles of SiO2 are present in an amount of about 1 g/L.
[0014] In another aspect of the present invention, a method of preparing electroplating composition having reinforcing-nano-particles selected from at least one of nano-SiO2 composite particles, nano-TiO2 composite particles is provided. The method comprises adding and mixing zinc sulphate, zinc chloride, boric acid to demineralized water to obtain a first solution. The method also comprises stirring the first solution at a stirring rate of 250-350 rpm for a time duration of 1-1.5 hours to obtain a second solution. The method further comprises adjusting pH of the second solution to obtain a third solution. The method comprises adding reinforcing-nano-particles into the third solution to obtain a fourth solution. The method also comprises adjusting pH of the fourth solution to obtain a fifth solution. The method further comprises stirring the fifth solution for a time duration of at least 24 hours to obtain a seventh solution. The method also comprises ultrasonicating the seventh solution for a time duration of 20 - 40 minutes to obtain the electroplating composition having reinforcing-nano-particles.
[0015] In yet another aspect of the present invention, a method of preparing electroplating composition having reinforcing-nano-particles selected from at least one of nano-SiO2 composites particles, nano-TiO2 composite particles. The method comprises mixing zinc sulphate, zinc chloride, boric acid to demineralized water to obtain a first solution. The method also comprises stirring the first solution at a stirring rate of 250 - 350 rpm for a time duration of 1-1.5 hours to obtain a second solution. The method further comprises adjusting pH of the second solution to obtain a third solution. The method comprises separating the third solution into a fourth solution and a fifth solution. The method also comprises stirring the fourth solution at a stirring rate of 250 - 350 rpm to obtain a stirred fourth solution. The method further comprises adding reinforcing-nano-particles into the fifth solution to obtain a sixth solution. The method comprises adjusting pH of the sixth solution to obtain a seventh solution. The method also comprises stirring the seventh solution for a time duration of 15-20 minutes to obtain an eighth solution. The method further comprises ultrasonicating the eighth solution for a time duration of 1 hour to obtain the ninth solution. The method comprises adding the ninth solution to the stirred fourth solution to obtain a tenth solution. The method also comprises stirring the tenth solution for a time duration of at least 24 hours to obtain a twelfth solution. The method comprises ultrasonicating the twelfth solution for a time duration of 20 - 40 minutes to obtain the electroplating composition having reinforcing-nano-particles.
[0016] In an embodiment, the stirring rate is preferably about 300 rpm.
[0017] In an embodiment, a method for depositing the electroplating composition having reinforcing-nano-particles on a steel substrate is provided. The method comprises providing the steel substrate as a cathode. The method also comprises depositing the electroplating composition on the steel substrate at a constant current with a current density of about 170-190 mA/cm2 and at a stirring rate of about 250-350 rpm to provide the steel substrate comprising a zinc (Zn) coating with nano-SiO2 reinforcing composite particles or zinc (Zn) coating with nano-TiO2 reinforcing composite particles.
[0018] In an embodiment, the current density is about 180 mA/cm2. In an embodiment, the coating provided exhibits a corrosion current density of about 1 to 4 µA/cm2. In an embodiment, the coating exhibits a corrosion potential (Ecorr) of about -1.03 to -1.1 V. In an embodiment, the method provides a deposition rate of about 1.5 – 3.5 µm/min.
[0019] In an embodiment, a method for depositing the electroplating composition having reinforcing-nano-particles on a steel substrate is provided. The method comprises providing the steel substrate as a cathode. The method also comprises depositing the electroplating composition on the steel substrate by employing a pulsed current with an average current density of about 170-190 mA/cm2, a peak 30 current density of about 240-720 mA/cm2, a duty cycle of about 25%-75%, and a frequency of about 25-200 Hz. The electroplating composition having reinforcing-nano-particles is stirred at a rate of about 250 to 350 rpm during said depositing to provide the steel substrate comprising a zinc (Zn) coating with nano-SiO2 reinforcing composite particles or zinc (Zn) coating with nano-SiO2 reinforcing composite particles.
[0020] In an embodiment, the pulsed current has an average current density of about 180 mA/cm2, a peak current density of about 360 mA/cm2, a duty cycle of about 50%, a frequency of about 200 Hz, and wherein the electroplating composition is stirred at a rate of about 300 rpm.
[0021] In an embodiment, the pulsed current has ton of about 2.5 ms and toff of about 2.5 ms. In an embodiment, the pulsed current has an average current density of about 180 mA/cm2, a peak current density of about 240 mA/cm2, a duty cycle of about 75%, a frequency of about 25 Hz, and the electroplating composition is stirred at a rate of about 300 rpm.
[0022] In an embodiment, the pulsed current has ton of about 30 ms and toff of about 10 ms. In an embodiment, the coating exhibits a corrosion current density of about 0.5 – 4.5 µA/cm2. In an embodiment, the coating exhibits a corrosion potential of about -1.04 to -1.1 V. In an embodiment, the method provides a deposition rate of about 1 - 3 µm/min.
[0023] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 illustrates a flowchart of a method of preparing electroplating composition having reinforcing-nano-particles selected from at least one of nano-TiO2 composites, nano-SiO2 composites, according to a first embodiment of the present invention;
[0025] Figures 2a and 2b illustrate a flowchart of a method of preparing electroplating composition having reinforcing-nano-particles selected from at least one of nano-TiO2 composites, nano-SiO2 composites, according to a second embodiment of the present invention;
[0026] Figure 3 illustrates a graph depicting a comparison between corrosion properties of a Zn-TiO2 coating deposited using DC method and electroplating composition prepared according to the first and second embodiments of the present invention, and conventional coatings;
[0027] Figure 4 illustrates morphologies of Zn-TiO2 coatings deposited using DC method and electroplating composition prepared according to the first embodiment of the present invention;
[0028] Figure 5 illustrates morphologies of Zn-TiO2 coatings deposited using DC method and electroplating composition prepared according to the second embodiment of the present invention;
[0029] Figure 6 illustrates a graph depicting a comparison between corrosion current of a Zn-SiO2 coating deposited using DC method and electroplating composition prepared according to the first and second embodiments of the present invention and conventional coatings;
[0030] Figure 7 illustrates morphologies of Zn-SiO2 coatings deposited using DC method and electroplating composition prepared according to the first embodiment of the present invention;
[0031] Figure 8 illustrates morphologies of Zn-SiO2 coatings deposited using DC method and electroplating composition prepared according to the second embodiment of the present invention;
[0032] Figure 9 illustrates a graph depicting a comparison between corrosion current of a Zn-TiO2 coating deposited using DC, pulsed methods and electroplating composition prepared according to the second embodiment of the present invention and conventional coatings;
[0033] Figure 10 illustrates morphologies of Zn-TiO2 coatings deposited using different pulsed current methods and electroplating composition prepared according to the second embodiment of the present invention;
[0034] Figure 11 illustrates a graph depicting a comparison between corrosion current of a Zn-SiO2 coating deposited using DC, pulsed current methods and electroplating composition prepared according to the second embodiment of the present invention and conventional coatings;
[0035] Figure 12 illustrates morphologies of Zn-SiO2 coatings deposited using different pulsed current methods and electroplating composition prepared according to the second embodiment of the present invention; and
[0036] Figure 13 illustrates a graph depicting a comparison between corrosion current of Zn-TiO2 and Zn-SiO2 coating deposited using DC, pulsed current methods and electroplating composition prepared according to the second embodiment of the present invention and conventional coatings.
[0037] The drawings referred to in this description are not to be understood as being drawn to scale except if specifically noted, and such drawings are only exemplary in nature.

DETAILED DESCRIPTION
[0038] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0039] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0040] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0041] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0042] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0043] As used herein, the term “electroplating composition” or “electrolyte composition” refers to an electroplating bath comprising electrolytes (Zn salts), reinforcing-nano-composites and any additives (optional). In the description below the terms “electroplating composition” and “electrolyte composition” are alternatively used.
[0044] The term “about” as used herein encompasses variations of +/-5% and more preferably +/- 2.5%, as such variations are appropriate for practicing the present invention.
[0045] The present disclosure provides electroplating compositions having reinforcing-nano-composites for depositing Zn coating (Zn- reinforcing-nano-composites coating) on steel substrates. The present disclosure provides electroplating compositions having two types of reinforcing-nano-composites. One electroplating composition is provided with nano-TiO2 composite particles and is used for depositing Zn-TiO2 nano-composite coating on steel substrate. Another electroplating composition is provided with nano-SiO2 composite particles and is used to deposit Zn-SiO2 nano-composite coating on steel substrate. The present disclosure also provides two different methods (100, 200) for preparing the electroplating compositions having reinforcing-nano-composites. Further, the disclosure provides two different methods (300, 400) for depositing/electroplating these compositions on steel substrates: a direct current method (300) and a pulsed current method (400).
[0046] The electroplating composition having reinforcing-nano-particles of the present invention comprises zinc sulphate, zinc chloride, boric acid, and reinforcing-nano-particles. The said reinforcing-nano-particles is selected from at least one of nano-TiO2 composite particles, nano-SiO2 composite particles. The electroplating composition has a pH of about 3-4.5. Herein the zinc sulphate is present in an amount of about 200-300 g/L, the zinc chloride is present in an amount of about 5-8 g/L, the boric acid is present in an amount of about 22-35 g/L and the reinforcing-nano-particles are present in an amount of about 0.5-5 g/L.
[0047] In some embodiments, the zinc sulphate is ZnSO4.xH2O where x is 0 to 7. In an exemplary embodiment, the electroplating composition comprises the heptahydrate form of zinc sulphate (ZnSO4.7H2O). In some embodiments, the pH of the electroplating composition is adjusted using sulfuric acid and/or sodium hydroxide.
[0048] In the preferred embodiment of electroplating composition having nano-TiO2 composite particles, the zinc sulphate is present in an amount of about 250 g/L, the zinc chloride is present in an amount of about 6 g/L, the boric acid is present in an amount of about 30 g/L, and the reinforcing-nano-particles of TiO2 are present in an amount of about 1 g/L.
[0049] In the preferred embodiment of electroplating composition having nano-SiO2 composite particles, the zinc sulphate is present in an amount of about 250 g/L, the zinc chloride is present in an amount of about 6 g/L, the boric acid is present in an amount of about 30 g/L, and the reinforcing-nano-particles of SiO2 are present in an amount of about 1 g/L.
[0050] STRATEGY 1
[0051] Referring to Figure 1, the method (100) of preparing electroplating composition having reinforcing-nano-particles selected from at least one of nano-SiO2 composite particles, nano-TiO2 composite particles, according to a first embodiment of the present invention is illustrated. At step (102), the method (100) comprises adding and mixing zinc sulphate, zinc chloride, boric acid to demineralized water to obtain a first solution. In the illustrated example, the demineralized water is present in an amount about 500 ml/l.
[0052] At step (104), the method (100) comprises stirring the first solution at a stirring rate of 250-350 rpm for a time duration of 1-1.5 hours to obtain a second solution. At step (106), the method (100) comprises adjusting pH of the second solution to obtain a third solution. At step (108), the method (100) comprises adding reinforcing-nano-particles selected from at least one of nano-SiO2 composite particles, nano-TiO2 composite particles into the third solution to obtain a fourth solution. At step (110), the method (100) comprises adjusting pH of the fourth solution to obtain a fifth solution. At step (112), the method (100) comprises stirring the fifth solution for a time duration of at least 24 hours to obtain a seventh solution. In the preferred embodiment, the fifth solution is stirred for a time duration of 24 hours to obtain the seventh solution. At step (116), the method (100) comprises ultrasonicating the seventh solution for a time duration of 20 - 40 minutes to obtain the final electroplating composition having dispersed reinforcing-nano-particles. The preferred stirring rate in the method (100) is 300 rpm.
[0053] STRATEGY 2
[0054] Referring to Figure 2, a method (200) of preparing electroplating composition having reinforcing-nano-particles selected from at least one of nano-SiO2 composite particles, nano-TiO2 composite particles, according to second embodiment of the present invention is illustrated. At step (202), the method (200) comprises adding and mixing zinc sulphate, zinc chloride, boric acid to demineralized water to obtain a first solution. In the preferred embodiment, the demineralized water is present in an amount about 500 ml/l.
[0055] At step (204), the method (200) comprises stirring the first solution at a stirring rate of 250-350 rpm for a time duration of 1-1.5 hours to obtain a second solution. At step (206), the method (100) comprises adjusting pH of the second solution to obtain a third solution.
[0056] At step (208), the method (200) comprises separating the third solution into a fourth solution and a fifth solution. At step (210), the method (200) comprises stirring the fourth solution at a stirring rate of 250 - 350 rpm to obtain a stirred fourth solution.
[0057] At step (212), the method (200) comprises adding reinforcing-nano-particles selected from at least one of nano-SiO2 composite particles, nano-TiO2 composite particles into the fifth solution to obtain a sixth solution. At step (214), the method (200) comprises adjusting pH of the sixth solution to obtain a seventh solution. At step (214), the method (100) comprises stirring the seventh solution for a time duration of 15-20 minutes to obtain an eight solution. At step (218), the method (200) comprises ultrasonicating the eighth solution for a time duration of 1 hour to obtain the ninth solution. At step (220), the method (200) comprises adding the ninth solution to the stirred fourth solution to obtain a tenth solution. From the moment it is separated from the third solution, the fourth solution is constantly stirred at a stirring rate of 300 rpm till it is added to the ninth solution.
[0058] At step (222), the method (200) comprises stirring the tenth solution for a time duration of at least 24 hours to obtain a twelfth solution. In the preferred embodiment, the tenth solution is stirred for a time duration of 24 hours to obtain the twelfth solution. At step (226), the method (200) comprises ultrasonicating the twelfth solution for a time duration of 20 - 40 minutes to obtain the final electroplating composition having dispersed reinforcing-nano-particles. In the preferred embodiment, the ultrasonication of the twelfth solution is performed for a time duration of 30 minutes. The preferred stirring rate in the method (200) is 300 rpm.
[0059] The electroplating composition having reinforcing-nano-particles selected from at least one of nano-TiO2 composite particles, nano-SiO2 composite particles prepared using methods (100, 200) are deposited onto a steel substrate using methods (300, 400).
[0060] The strategy 1 and strategy 2 facilitate in dispersing the reinforcing-nano-particles within the electroplating composition and restricts/minimizes agglomeration of the reinforcing-nano-particles.
[0061] Direct Current (DC) Deposition
[0062] In some embodiments, the electroplating composition having reinforcing-nano-particles prepared using methods (100, 200) is deposited onto a steel substrate using method (300) which is direct current (DC) method (hereinafter alternatively referred to as DC method (300)).
[0063] The method (300) comprises providing the steel substrate as a cathode and a pure zinc plate as an anode in the electroplating composition having reinforcing-nano-particles prepared using methods (100, 200). The method (300) comprises stirring the electroplating composition at a stirring rate of about 250-350 rpm. The method (300) comprises passing a direct current between these two electrodes and depositing the electroplating composition having reinforcing-nano-particles on the steel substrate at a constant current with a current density of about 170-190 mA/cm2 to provide the steel substrate comprising a zinc (Zn) coating with nano-SiO2 reinforcing composite particles or zinc (Zn) coating with nano-TiO2 reinforcing composite particles. In the preferred embodiment, the current density is about 180 mA/cm2. In the preferred embodiment, the stirring rate is preferably about 300 rpm.
[0064] In some embodiments, the method (300) for depositing the electroplating composition is carried out for about 3-8 minutes. In the preferred embodiment, the method (300) is carried out for about 5 minutes.
[0065] The coating deposited on the substrate by method (300) exhibits a corrosion current density of about 1 to 4 µA/cm2. The coating exhibits a corrosion potential (Ecorr) of about -1.03 to -1.1 V. The method (300) provides a deposition rate of about 1.5 – 3.5 µm/min.
[0066] Referring to Figure 3, graph illustrating a comparison between corrosion properties of a Zn-TiO2 nano-composite coating deposited using DC method and electrolyte composition prepared according to the embodiments (Strategy 1 and Strategy 2) of the present invention, and conventional coatings is depicted.
[0067] For Strategy 1, the concentration of the reinforcing-nano-particles in the electrolyte is varied from 0.25 to 10 g/l where all the reinforcing-nano-particles were added in the bath through strategy 1 and electroplated with the DC method (300). It has been observed that the corrosion current (Icorr) has defined trend with the TiO2 concentration in the coating. It was seen that at lower concentrations of reinforcing-nano-particles Icorr was very high and then it reduced to the optimum and then again increased beyond a certain point. The deposition kinetics of the coatings were mostly in the similar range signifying no impact of the concentration on the same. Based on the corrosion results of strategy 1, the optimum concentration has been selected for the study through strategy 2 with the optimum range of 0.25 to 5 g/l of TiO2 in the electrolyte, where all the reinforcing-nano-particles were added in the bath through strategy 2 and electroplated with the DC method (300). It has been further determined that through concentrated emulsion technique (i.e. strategy 2) better properties were observed at both lower (0.5 g/l) and higher concentrations (5 g/l) of TiO2 reinforcing-nano-particles as compared to strategy 1.
[0068] The optimized concentration range of 0.5, 1, 2.5 and 5 g/l in strategy 2 have been further studied for the best corrosion resistance properties of the composite coatings is shown in Figure 3. It has been observed that without any additive or secondary coatings only TiO2 nano-particles embedded in the metallic matrix were able to improve the corrosion properties and was even better than the benchmark that is the commercial Zn-Ni sample with surface passivation.
[0069] Referring to Figures 4 and 5, morphologies of Zn-TiO2 nano-composite coatings deposited using DC method and electrolyte composition prepared according to the embodiments (Strategy 1 and Strategy 2) of the present invention is depicted. In Figure 4, top surface morphologies of the Zn-TiO2 nano-composite coatings through strategy 1 has been depicted along with the corresponding TiO2 content in the coating. Top surface morphologies of the Zn-TiO2 nano-composite coatings through strategy 2 in the optimized range of 0.5 g/l to 5 g/l are shown in Figure 5. Though not much difference is observed through the morphologies, the incorporation of the reinforcing-nano-particles has refined the deposited grains. It has been observed that through Strategy 2 TiO2 content in the coating is more compared to the Strategy 1 indicating better incorporation of the particles.
[0070] Referring to Figure 6, graph illustrating a comparison between corrosion properties of a Zn-SiO2 nano-composite coating deposited using DC method and electrolyte composition prepared according to the embodiments (Strategy 1 and Strategy 2) of the present invention, and conventional coatings is depicted.
[0071] For Strategy 1, the concentration of the nano-SiO2 reinforcing composite particles in the electrolyte is varied from 0.25 to 10 g/l where all the reinforcing-nano-particles were added in the bath through strategy 1 and electroplated with the DC method (300). The corrosion properties along with the deposition kinetics and corrosion potential of the composite coatings are shown in Figure 6 where it has been observed that the corrosion current (Icorr) has defined trend with the SiO2 concentration in the coating. It is seen that at lower concentrations of reinforcements Icorr was very high and then it reduced to the optimum and then again increased beyond a certain point. The deposition kinetics of the coatings were mostly in the similar range signifying no impact of the concentration on the same.
[0072] Based on the corrosion results of strategy 1, the optimum concentration has been selected for the study through strategy 2 with the optimum range of 0.25 to 5 g/l of SiO2 in the electrolyte, where all the reinforcing-nano-particles were added in the bath through strategy 2 and electroplated with the DC method (300). It has been further determined to have better properties at all the concentrations of particles can be achieved through concentrated emulsion technique (strategy 2). The optimized concentration range of 0.5, 1, 2.5 and 5 g/l in strategy 2 have been further studied for the best corrosion resistance properties of the composite coatings is shown in Figure 6. It has been observed that without any additive or secondary coatings only SiO2 particles embedded in the metallic matrix were able to improve the corrosion properties.
[0073] Referring to Figures 7 and 8, morphologies of Zn-SiO2 coatings deposited using DC method and electrolyte composition prepared according to the embodiments (Strategy 1 and Strategy 2) of the present invention is depicted. In Figure 7, top surface morphologies of the Zn-TiO2 nano-composite coatings through strategy 1 has been depicted along with the corresponding SiO2 content in the coating and the best properties were observed at 1 g/l SiO2 concentration in the bath. Top surface morphologies of the Zn-SiO2 nano-composite coatings through strategy 2 in the optimized range of 0.5 g/l to 5 g/l are shown in Figure 8. It has been observed that through strategy 2 SiO2 content in the coating is more compared to the strategy 1 indicating better incorporation of the particles thus improving the corrosion properties at both lower (1 g/l) and higher concentrations (5 g/l) of particles.
[0074] Pulsed Current Deposition
[0075] In some embodiments, the electroplating composition having reinforcing-nano-particles prepared using methods (100, 200) is deposited onto a steel substrate using method (400) which is pulsed current method (hereinafter alternatively referred to as pulsed current method (400)).
[0076] The method (400) comprises providing the steel substrate as a cathode and a pure zinc plate as an anode in the electroplating composition having reinforcing-nano-particles. The method (400) comprises stirring the electroplating composition at a stirring rate of about 250-350 rpm. The method (400) comprises passing a pulsed current between these two electrodes and depositing the electroplating composition on the steel substrate by employing the pulsed current with an average current density of about 170-190 mA/cm2, a peak 30 current density of about 240-720 mA/cm2, a duty cycle of about 25%-75%, and a frequency of about 25-200 Hz to provide the steel substrate comprising a zinc (Zn) coating with SiO2 reinforcing-nano-particles or zinc (Zn) coating with TiO2 reinforcing-nano-particles.
[0077] In one example (P1 conditions), the pulsed current has an average current density of about 180 mA/cm2, a peak current density of about 360 mA/cm2, a duty cycle of about 50%, a frequency of about 200 Hz, and the electroplating composition is stirred at a rate of about 300 rpm. The pulsed current has ton of about 2.5 ms and toff of about 2.5 ms.
[0078] In another example (P2 conditions), the pulsed current has an average current density of about 180 mA/cm2, a peak current density of about 240 mA/cm2, a duty cycle of about 75%, a frequency of about 25 Hz, and the electroplating composition is stirred at a rate of about 300 rpm. The pulsed current has ton of about 30 ms and toff of about 10 ms.
[0079] Exemplary parameters for depositing the electroplating composition are shown in Table 1.
Electroplating Parameter Value P1 Conditions P2 Conditions
Average Current Density of Deposition 170-190 mA/cm2 180 mA/cm2 180 mA/cm2
Peak Current Density 240-720 mA/cm2 360 mA/cm2 240 mA/cm2
Duty Cycle 25-75% 50% 75%
Frequency 25-200 Hz 200 Hz 25 Hz
Stirring Rate of Deposition 250-350 rpm 300 rpm 300 rpm
Table 1
[0080] In some embodiments, the method (400) for depositing the electroplating composition is carried out for about 3-8 minutes. In the preferred embodiment, the method (300) is carried out for about 5 minutes.
[0081] The coating provided exhibits a corrosion current density of about 0.5 to 4.5 µA/cm2. The coating exhibits a corrosion potential (Ecorr) of about -1.04 to -1.1 V. The method (400) provides a deposition rate of about 1 – 3 µm/min.
[0082] Referring to Figure 9, graph illustrating a comparison between corrosion properties of a Zn-TiO2 nano-composite coating deposited using DC method, pulsed current method (P1 parameters) and pulsed current method (P2 parameters), and conventional coatings is depicted. The electrolyte composition is prepared according to the second embodiment (Strategy 2) of the present invention.
[0083] The desired optimum concentration range of 0.5 g/l to 5 g/l of TiO2 reinforcing-nano-particles (as observed in the DC deposition) was taken for the pulsed deposition with the optimized parameters for the bath being at 50% duty cycle with 200 Hz frequency (P1) and 75% duty cycle with 25 Hz frequency (P2). It has been observed that at 1 g/l and 5 g/l both DC and pulse coatings are with excellent corrosion properties and with the pulsed deposition the properties have got further improved (Figure 9).
[0084] Referring to Figure 10, the top surface morphologies for all the concentrations of (0.5 g/l – 5 g/l) variations for both the pulse (P1 and P2) parameters are depicted. It has been observed that with increasing TiO2 reinforcing-nano-particles concentration, TiO2 content in the final coating has also got improved.
[0085] Referring to Figure 11, graph illustrating a comparison between corrosion properties of a Zn-SiO2 nano-composite coatings deposited using DC method, pulsed current method (P1 parameters) and pulsed current method (P2 parameters), and conventional coatings is depicted. The electrolyte composition is prepared according to the second embodiment (Strategy 2) of the present invention.
[0086] The desired optimum concentration range of 0.5 g/l to 5 g/l of SiO2 reinforcing-nano-particles (as observed in the DC deposition) was taken for the pulsed deposition with the optimized parameters for the bath being at 50% duty cycle with 200 Hz frequency (P1) and 75% duty cycle with 25 Hz frequency (P2). It has been observed that the corrosion properties were never better than the benchmark, but at 1 g/l with DC depositions the properties were better than the other concentrations of SiO2 particles and pulsed current method with (P1 and P2 parameters) of depositions (Figure 11).
[0087] Referring to Figure 12, the top surface morphologies for all the concentrations of (0.5 g/l – 5 g/l) variations for both the pulsed current deposition (P1 and P2 parameters) are depicted. It is evident for SiO2 particles at higher concentration the grains have got further refined though the corrosion property has not improved further.
[0088] Referring to Figure 13, the optimum bath with optimum parameters were studied with oxide reinforcing-nano-particles (SiO2 and TiO2) both for DC and pulsed deposition. The optimization is done in terms of the electrolytic composition and method of preparation (strategy 1 and strategy 2), concentration of the reinforcing-nano-particles in the bath and corrosion resistance and deposition kinetics of the coating.
[0089] The shortlisted electroplating baths along with the desired surface morphology is shown in Figure 13. Pure Zn with TiO2 reinforcing-nano-particles without any passivation has become the single coating solution through DC deposition and has given better corrosion property than the commercial Zn-Ni EG sample with Cr passivation.
[0090] The present invention provides Zn based composite coating system using DC and pulsed electrodeposition technology through physical dispersion of reinforcing-nano-composites (nano-TiO2 composite particles and nano-SiO2 composite particles) for enhanced functional properties. The disclosed electroplating composition having reinforcing-nano-composites is a cost effective and a comprehensive coating solution where the multifunctional requirement of the automotive industry can be achieved through a single coating system.
[0091] The Zn coatings (Zn-TiO2 and Zn-SiO2 reinforcing-nano-composites coating) show a uniform morphology and fine grain structure and have superior corrosion resistance. The Zn coating (Zn-reinforcing-nano-composites coatings) on steel substrates can be used in applications, for example, in automobiles, electric appliances, building material and the like because of its improved sacrificial corrosion prevention effect. Further, the electroplating compositions prepared using the method (100) (i.e. strategy 1) and the method (200) (i.e. strategy 2) have leaner bath chemistry than the conventional plating baths and have reduced cost additives concentration in the bath as compared to conventional baths.
[0092] The above work was carried out in 20 cm2 samples in a 500 ml electrolyte with a stirring rate of 300 rpm and a stirrer bid of size 3 cm length and 0.5 cm diameter to study the corrosion resistance properties and deposition kinetics.
[0093] In the above disclosure, the terms “nano-TiO2 composite particles”, “TiO2 nano-particles”, “TiO2 reinforcing-nano-particles”, “reinforcing-nano-particles of TiO2” are alternatively used, without limiting the scope of the invention.
[0094] In the above disclosure, the terms “nano-SiO2 composite particles”, “SiO2 nano-particles”, “SiO2 reinforcing-nano-particles”, “reinforcing-nano-particles of SiO2” are alternatively used, without limiting the scope of the invention.
[0095] Furthermore, the terminology used herein is for describing embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0096] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0097] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

Claims:CLAIMS
I/We claim:

1. An electroplating composition having reinforcing-nano-particles comprising zinc sulphate, zinc chloride, boric acid, and reinforcing-nano-particles, wherein the said reinforcing-nano-particles is selected from at least one of nano-TiO2 composite particles, nano-SiO2 composite particles, wherein the electroplating composition has a pH of about 3-4.5.
2. The electroplating composition having reinforcing-nano-particles as claimed in the claim 1, wherein zinc sulphate is present in an amount of about 200-300 g/L, the zinc chloride is present in an amount of about 5-8 g/L, the boric acid is present in an amount of about 22-35 g/L and the reinforcing-nano-particles are present in an amount of about 0.5-5 g/L.
3. The electroplating composition having reinforcing-nano-particles as claimed in claim 2, wherein the zinc sulphate is present in an amount of about 250 g/L, the zinc chloride is present in an amount of about 6 g/L, the boric acid is present in an amount of about 30 g/L, and the reinforcing-nano-particles of TiO2 are present in an amount of about 1 g/L.
4. The electroplating composition having reinforcing-nano-particles as claimed in claim 2, wherein the zinc sulphate is present in an amount of about 250 g/L, the zinc chloride is present in an amount of about 6 g/L, the boric acid is present in an amount of about 30 g/L, and the reinforcing-nano-particles of SiO2 are present in an amount of about 1 g/L.
5. A method (100) of preparing electroplating composition having reinforcing-nano-particles selected from at least one of nano-SiO2 composite particles, nano-TiO2 composite particles, the method (100) comprising:
adding and mixing zinc sulphate, zinc chloride, boric acid to demineralized water to obtain a first solution;
stirring the first solution at a stirring rate of 250-350 rpm for a time duration of 1-1.5 hours to obtain a second solution;
adjusting pH of the second solution to obtain a third solution;

adding reinforcing-nano-particles into the third solution to obtain a fourth solution;
adjusting pH of the fourth solution to obtain a fifth solution;
stirring the fifth solution for a time duration of at least 24 hours to obtain a seventh solution; and
ultrasonicating the seventh solution for a time duration of 20 - 40 minutes to obtain the electroplating composition having reinforcing-nano-particles.
6. A method (200) of preparing electroplating composition having reinforcing-nano-particles selected from at least one of nano-SiO2 composite particles, nano-TiO2 composite particles, the method (200) comprising:
adding and mixing zinc sulphate, zinc chloride, boric acid to demineralized water to obtain a first solution;
stirring the first solution at a stirring rate of 250 - 350 rpm for a time duration of 1-1.5 hours to obtain a second solution;
adjusting pH of the second solution to obtain a third solution;
separating the third solution into a fourth solution and a fifth solution;
stirring the fourth solution at a stirring rate of 250 - 350 rpm to obtain a stirred fourth solution;
adding reinforcing-nano-particles into the fifth solution to obtain a sixth solution;
adjusting pH of the sixth solution to obtain a seventh solution;
stirring the seventh solution for a time duration of 15-20 minutes to obtain an eighth solution;
ultrasonicating the eighth solution for a time duration of 1 hour to obtain the ninth solution;

adding the ninth solution to the stirred fourth solution to obtain a tenth solution;
stirring the tenth solution for a time duration of at least 24 hours to obtain a twelfth solution; and
ultrasonicating the twelfth solution for a time duration of 20 - 40 minutes to obtain the electroplating composition having reinforcing-nano-particles.
7. The method (100, 200) as claimed in claims 5 and 6, wherein the stirring rate is preferably about 300 rpm.
8. A method (300) for depositing the electroplating composition having reinforcing-nano-particles as claimed in claims 5 and 6 on a steel substrate, the method (300) comprising:
providing the steel substrate as a cathode;
depositing the electroplating composition on the steel substrate at a constant current with a current density of about 170-190 mA/cm2 and at a stirring rate of about 250-350 rpm to provide the steel substrate comprising a zinc (Zn) coating with SiO2 reinforcing-nano-particles or zinc (Zn) coating with nano-TiO2 reinforcing composite particles.
9. The method (300) as claimed in claim 8, wherein the current density is about 180 mA/cm2.
10. The method (300) as claimed in claim 8, wherein the coating provided exhibits a corrosion current density of about 1 to 4 µA/cm2.
11. The method (300) as claimed in any one of claims 8-10, wherein the coating exhibits a corrosion potential of about -1.03 to -1.1 V.
12. The method (300) as claimed in any one of claims 8-11, wherein the method (300) provides a deposition rate of about 1.5 – 3.5 µm/min.
13. A method (400) for depositing the electroplating composition having reinforcing-nano-particles as claimed in claims 5 and 6 on a steel substrate, the method (400) comprising:
providing the steel substrate as a cathode;

depositing the electroplating composition on the steel substrate by employing a pulsed current with an average current density of about 170-190 mA/cm2, a peak 30 current density of about 240-720 mA/cm2, a duty cycle of about 25%-75%, and a frequency of about 25-200 Hz; wherein the electroplating composition having reinforcing-nano-particles is stirred at a rate of about 250 to 350 rpm during said depositing to provide the steel substrate comprising a zinc (Zn) coating with nano-SiO2 reinforcing composite particles or zinc (Zn) coating with nano-TiO2 reinforcing composite particles.
14. The method (400) as claimed in claim 13, wherein the pulsed current has an average current density of about 180 mA/cm2, a peak current density of about 360 mA/cm2, a duty cycle of about 50%, a frequency of about 200 Hz, and wherein the electroplating composition is stirred at a rate of about 300 rpm.
15. The method (400) as claimed in the claims 13 and 14, wherein the pulsed current has ton of about 2.5 ms and toff of about 2.5 ms.
16. The method (400) as claimed in claim 13, wherein the pulsed current has an average current density of about 180 mA/cm2, a peak current density of about 240 mA/cm2, a duty cycle of about 75%, a frequency of about 25 Hz, and wherein the electroplating composition is stirred at a rate of about 300 rpm.
17. The method (400) as claimed in the claim 16, wherein the pulsed current has ton of about 30 ms and toff of about 10 ms.
18. The method (400) as claimed in the claims 13-17, wherein the coating exhibits a corrosion current density of about 0.5 – 4.5 µA/cm2.
19. The method (400) as claimed in the claim 18, wherein the coating exhibits a corrosion potential of about -1.04 to -1.1 V.
20. The method (400) as claimed in any one of claims 13 – 19, wherein the method provides a deposition rate of about 1 - 3 µm/min. ,