TECHNICAL FIELD
The present disclosure relates to the field of electroplating. Particularly, the present disclosure relates to electroplating compositions to provide zinc-iron-titania or zinc-iron-silica coatings, methods of preparing them, direct and pulsed current methods of depositing these electroplating compositions on steel substrates and steel substrates obtained therefrom.

BACKGROUND OF THE DISCLOSURE
Three types of coatings are deposited using electrodeposition, namely, pure metals, metal alloys and metal based composite coatings [1]. In case of pure metal deposition, one anode and one cathode are placed in an electrolyte solution and electricity is passed between these two electrodes [2,3]. Anode is generally a pure metal which is to be deposited on the cathode. The electrolyte is composed of the metal salt which is deposited on the cathode surface. When current is passed between anode and cathode, pure metal is deposited on the cathode surface. In the case of alloy deposition, the electrolyte solution is composed of the two-different metal salts at definite proportions which are intended for the alloy plating. Some additives are also present to obtain uniform co-deposition of the two metals. In the case of composite coatings, the electrolyte is composed of the salts of the metals along with reinforcement particles and surfactants. These surfactants are used to disperse the particles in the electrolyte solution [1].

A Zn or Zn-alloy composite coating with oxide reinforcement particles is a very promising coating material for providing higher corrosion resistance to steel compared to pure zinc or zinc-iron alloy. Moreover, composite coatings are known to have exceptional hardness and wear resistance properties compared to pure metal or alloy coatings [4-8]. Also, the passivation property is significantly improved by adding oxide particles in metal or alloy matrix [5].

A major challenge in co-depositing non-ionized oxide particles with different metallic ions from the electrolyte salt is the dispersion of nanoparticles in the electrolyte media. Nanoparticles agglomerate easily in the electrolyte because of their high surface energy. If these inert particles are not dispersed properly, co-deposition becomes very difficult [9-15]. The undispersed particles result in entrapment of large agglomerates in the coated matrix resulting in poor coating performance [12,13]. Two mechanisms are generally employed to disperse the nanoparticles in the electrolyte. One is by surface modification of the particles through surfactant treatments, and another is dispersing the particles with the help of mechanical shear forces through ultrasonication, magnetic stirrer or mechanical stirrer. The first method is termed as chemical dispersion [16] and the second one as physical dispersion [17].

Among all the oxide nanoparticles, titania and silica are used extensively in composite coatings. Titania particle has a very interesting property like semiconductivity and can act as a photo-catalyst [18]. Silica particle is used to improve wear resistance [19] and to provide barrier protection to underneath substrate [20,21].

Zinc-iron (Zn-Fe) coatings provide superior corrosion resistance, weldability and paintability over pure Zn coatings. Some studies have been conducted on improving the corrosion resistance property of Zn-Fe coatings by adding silica and titania in the Zn-Fe matrix [22-24]. Zn-Fe-TiO2 composite can be electrodeposited from alkaline bath where triethylamine (TEA) acts as a cationic surfactant [25]. Zn-Fe-SiO2 composite can be electrodeposited from sulphate where tri sodium citrate acts as a complexing agent and ascorbic acid acts as a reducing agent [22].

A Zn-Fe-oxide particles composite coating can be a promising coating that can provide excellent corrosion resistance to steel. However, a suitable electroplating bath, electrolyte preparation process and suitable particles dispersion process are yet to be developed to address the drawbacks of particles agglomeration, stability of electrolyte and uniformly dispersed oxide particles in the coating matrix. The present disclosure attempts to address this need.

STATEMENT OF THE DISCLOSURE
The present disclosure relates to an electroplating composition comprising zinc sulphate in an amount of about 200 g/L, ferrous sulphate in an amount of about 40 g/L, zinc chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, and titania or silica particles at a concentration of about 0.5-5 g/L, wherein the electroplating composition has a pH of about 3.5.

The present disclosure also relates to a method for preparing the electroplating composition described herein, comprising: a) adding boric acid to distilled water; b) after dissolution of boric acid, adding zinc sulphate to the distilled water; c) after dissolution of zinc sulphate, adding ferrous sulphate to the distilled water; d) after dissolution of ferrous sulphate, adding zinc chloride to the distilled water to obtain an electrolyte solution; e) after dissolution of zinc chloride, adding titania or silica particles to a portion of the electrolyte solution to obtain a titania or silica-containing solution; f) stirring the titania or silica-containing solution for about 30 minutes at a speed of about 300-400 rpm; g) ultrasonicating the titania or silica-containing solution after stirring to obtain an ultrasonicated solution; h) adding the ultrasonicated solution to remaining portion of the electrolyte solution; i) adding distilled water to obtain the electroplating composition; j) adjusting pH of the electroplating composition to about 3.5; k) stirring the electroplating composition for about 24 hours at a speed of about 300-400 rpm; and
l) ultrasonicating the electroplating composition for about 30 kHz for about 30 minutes.

The present disclosure provides direct current and pulsed current methods for depositing the electroplating compositions.

The direct current method for depositing the electroplating composition on a steel substrate, comprises: a) providing the steel substrate as a cathode; b) depositing the electroplating composition on the steel substrate at a constant current with a current density of about 180-200 mA/cm2 and at a stirring rate of about 300 rpm to provide a steel substrate comprising a zinc-iron-titania (Zn-Fe-TiO2) or a zinc-iron-silica (Zn-Fe-SiO2) coating.

The pulsed current method for depositing the electroplating composition on a steel substrate, comprises: a) providing the steel substrate as a cathode; b) depositing the electroplating composition on the steel substrate by employing a pulsed current with an average current density of about 190 mA/cm2, a duty cycle of about 50-75% and a frequency of about 75-200Hz to provide a steel substrate comprising a Zn-Fe-TiO2 or a Zn-Fe-SiO2 coating.

The present disclosure further relates to a steel substrate comprising a Zn-Fe-TiO2 coating, wherein the coating comprises about 0.04-0.08% by weight of titania. In some embodiments, the Zn-Fe-TiO2 coatings comprising about 0.04-0.08% by weight of titania exhibit a corrosion current density of about 2.8-3.5 µA/cm2.

The present disclosure also relates to a steel substrate comprising a Zn-Fe-SiO2 coating, wherein the coating comprises about 0.4-0.5% by weight of silica. In some embodiments, the Zn-Fe-SiO2 coatings comprising about 0.4-0.5% by weight of silica exhibit a corrosion current density of about 0.8-1.8 µA/cm2.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 shows the schematic of an exemplary method of preparing the electroplating composition.

Figure 2 shows the zeta potential values of titania and silica particles.

Figure 3 shows corrosion currents of Zn-Fe-TiO2 composite coatings obtained by the direct current method at varying titania nanoparticles concentration.

Figure 4 shows morphologies of the Zn-Fe-TiO2 composite coatings obtained by the direct current method at varying titania nanoparticles concentration.

Figure 5 shows wt.% of titania particles incorporated in the Zn-Fe-TiO2 composite coatings obtained by the direct current method at varying titania nanoparticles concentration.

Figure 6 shows the corrosion current of Zn-Fe-TiO2 composite coatings obtained by the pulsed current method at varying titania nanoparticles concentration.

Figure 7 shows the top surface morphologies of the Zn-Fe-TiO2 composite coatings obtained by the pulsed current method at varying titania nanoparticles concentration.

Figure 8 shows wt.% of titania particles incorporated in the Zn-Fe-TiO2 composite coatings obtained by the pulsed current method at varying titania nanoparticles concentration.

Figure 9 shows the corrosion current of Zn-Fe-SiO2 composite coatings obtained by the direct current method at varying silica nanoparticles concentration.

Figure 10 shows morphologies of the Zn-Fe-SiO2 composite coatings obtained by the direct current method at varying silica nanoparticles concentration.

Figure 11 shows wt.% of silica particles incorporated in the Zn-Fe-SiO2 composite coatings obtained by the direct current method at varying silica nanoparticles concentration.

Figure 12 shows the corrosion current of Zn-Fe-SiO2 composite coatings deposited by the pulsed current method at varying silica nanoparticles concentration.

Figure 13 shows top surface morphologies of the Zn-Fe-SiO2 composite coatings deposited by the pulsed current method at varying silica nanoparticles concentration.

Figure 14 shows wt.% of silica particles incorporated in the Zn-Fe-SiO2 composite coatings deposited by the pulsed current method at varying silica nanoparticles concentration.

DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. 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 disclosure to achieve one or more of the desired objects or results. Throughout this specification, the word “comprise”, or variations such as “comprises” or “comprising” or “containing” or “has” or “having”, or “including but not limited to” wherever used, 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.

Reference throughout this specification to “some embodiments”, “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the present disclosure. Thus, the appearances of the phrases “in some embodiments”, “in one embodiment” or “in an embodiment” in various places throughout this specification may not necessarily all refer to the same embodiment. It is appreciated that certain features of the disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

As used herein, the term “electroplating composition” refers to an electroplating bath comprising electrolytes (Zn and Fe salts) and titania or silica nanoparticles. In some embodiments, the size of the nanoparticles ranges from about 20 nm to about 30 nm, including values and ranges thereof.

The term “titania” as used herein refers to titanium dioxide (TiO2). The term “silica” as used herein refers to silicon dioxide (SiO2).

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.

The present disclosure provides electroplating compositions for depositing Zn-Fe-titania (Zn-Fe-TiO2) or Zn-Fe-silica (Zn-Fe-SiO2) coatings on steel substrates. Further, the present disclosure provides an improved method for preparing electroplating compositions comprising Zn-Fe-oxides and titania or silica nanoparticles. The present disclosure also provides methods for depositing/electroplating said compositions on steel substrates by a direct current (DC) method and a pulsed current method. The coatings of the present disclosure show improved deposition kinetics, improved surface microstructure, higher titania or silica content, and/or improved corrosion resistance.

In some embodiments, the present disclosure provides an electroplating composition comprising zinc sulphate in an amount of about 200 g/L, ferrous sulphate in an amount of about 40 g/L, zinc chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, and titania or silica nanoparticles at a concentration of about 0.5-5 g/L, wherein the electroplating composition has a pH of about 3.5.

Titania or silica nanoparticles are present in the electroplating composition at a concentration of about 0.5-5 g/L, including values and ranges therebetween. For example, in some embodiments, titania or silica nanoparticles are present in the electroplating composition at a concentration of about 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, or 5 g/L, including values therebetween. In some embodiments, titania or silica nanoparticles are present in the electroplating composition at a concentration of about 0.5-4.5, 0.5-4, 0.5-3.5, 0.5-3, 0.5-2.5, 0.5-2, 0.5-1.5, 0.5-1, 1-5, 1-4.5, 1-4, 1-3.5, 1-3, 1-2.5, 1-2, 1.5-5, 1.5-4.5, 1.5-4, 1.5-3.5, 1.5-3, 1.5-2.5, 2-5, 2-4.5, 2-4, 2-3.5, 2-3, 2.5-5, 2.5-4.5, 2.5-4, 2.5-3.5, 3-5, 3-4.5, 3-4, 3.5-5, 3.5-4.5, or 4-5 g/L, including values and ranges therebetween.

In some embodiments, provided herein are electroplating compositions comprising zinc sulphate in an amount of about 200 g/L, ferrous sulphate in an amount of about 40 g/L, zinc chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, and titania nanoparticles at a concentration of about 1-2.5 g/L, wherein the electroplating composition has a pH of about 3.5.

In some embodiments, the electroplating composition comprises zinc sulphate in an amount of about 200 g/L, ferrous sulphate in an amount of about 40 g/L, zinc chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, and titania nanoparticles at a concentration of about 1 g/L, wherein the electroplating composition has a pH of about 3.5.

In some other embodiments, the electroplating composition comprises zinc sulphate in an amount of about 200 g/L, ferrous sulphate in an amount of about 40 g/L, zinc chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, and titania nanoparticles at a concentration of about 2.5 g/L, wherein the electroplating composition has a pH of about 3.5. In some embodiments, the electroplating composition comprising about 2.5 g/L titania nanoparticles provides a Zn-Fe-TiO2 coating comprising about 0.08% by weight of titania and exhibiting a corrosion current of about 3.5 µm/cm2, and a mixed morphology comprising basal and pyramidal microstructure.

In some embodiments, provided herein are electroplating compositions comprising zinc sulphate in an amount of about 200 g/L, ferrous sulphate in an amount of about 40 g/L, zinc chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, and silica nanoparticles at a concentration of about 4.5-5.5 g/L, wherein the electroplating composition has a pH of about 3.5. In some embodiments, the electroplating composition comprises zinc sulphate in an amount of about 200 g/L, ferrous sulphate in an amount of about 40 g/L, zinc chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, and silica nanoparticles at a concentration of about 5 g/L, wherein the electroplating composition has a pH of about 3.5. In some embodiments, the electroplating composition comprising about 5 g/L silica nanoparticles provides a Zn-Fe-SiO2 coating comprising about 0.43% by weight of silica and exhibiting a corrosion current of about 1.8 µm/cm2, and a very fine and compact pyramidal morphology.

Also provided herein is a method of preparing the electroplating compositions of the present disclosure. In some embodiments, the method broadly comprises dissolving boric acid, zinc sulphate, ferrous sulphate, and zinc chloride in this order in distilled water to obtain a main electrolyte solution; adding TiO2 or SiO2 to a small portion of the main electrolyte; stirring the electrolyte solution containing TiO2 or SiO2; ultrasonicating the electrolyte solution containing TiO2 or SiO2; adding the ultrasonicated electrolyte containing TiO2 or SiO2 to the main electrolyte solution; adjusting the pH to 3.5; stirring the main electrolyte solution for 24 hours; and again ultrasonicating the electrolyte solution briefly. In this method, TiO2 or SiO2 is ultrasonicated directly in a portion of the main electrolyte solution comprising boric acid, zinc sulphate, ferrous sulphate, and zinc chloride to obtain TiO2 or SiO2 nanoparticles. The electrolyte solution containing TiO2 or SiO2 nanoparticles is mixed with the remaining portion of the main electrolyte solution and the TiO2 or SiO2 nanoparticles are dispersed in the main electrolyte solution by stirring and ultrasonication, i.e., by physical dispersion. Chemical dispersion such as surface modification by surfactants or additives is not employed in the present method.

In some embodiments, the method for preparing an electroplating composition of the present disclosure comprises: (i) adding boric acid to distilled water; (ii) after dissolution of boric acid, adding zinc sulphate to the distilled water; (iii) after dissolution of zinc sulphate, adding ferrous sulphate to the distilled water; (iv) after dissolution of ferrous sulphate, adding zinc chloride to the distilled water to obtain an electrolyte solution; (v) after dissolution of zinc chloride, adding titania or silica particles to a portion of the electrolyte solution to obtain a titania or silica-containing solution; (vi) stirring the titania or silica-containing solution for about 30 minutes at a speed of about 300-400 rpm; (vii) ultrasonicating the titania or silica-containing solution after stirring to obtain an ultrasonicated solution; (viii) adding the ultrasonicated solution to the remaining portion of the electrolyte solution; (ix) adding distilled water to the electrolyte solution to make up to a desired volume to obtain the electroplating composition; (x) adjusting pH of the electroplating composition to about 3.5; (xi) stirring the electroplating composition for about 24 hours at a speed of about 300-400 rpm; and (xii) ultrasonicating the electroplating composition for about 30 kHz for about 30 minutes to obtain the electroplating composition with a uniformly dispersed TiO2 or SiO2 nanoparticles.

Titania or silica is added to a portion of the electrolyte solution containing boric acid, zinc sulphate, ferrous sulphate, and zinc chloride. The titania or silica-containing electrolyte solution is stirred for about 30 minutes at a speed of about 300-400 rpm such as about 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, or 400 rpm. In some embodiments, the titania or silica-containing electrolyte solution is stirred for about 30 minutes at a speed of about 340-360 rpm. In an exemplary embodiment, the titania or silica-containing electrolyte solution is stirred for about 30 minutes at a speed of about 350 rpm.

After stirring, the titania or silica-containing electrolyte solution is ultra-sonicated to obtain titania or silica nanoparticles. In some embodiments, the ultra-sonication is carried out at a frequency of about 25-35 kHz for about 30 minutes. In some embodiments, the ultra-sonication is carried out at a frequency of about 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, or 35 kHz. In some embodiments, the ultra-sonication is carried out at a frequency of about 28-32 kHz for about 30 minutes. In an exemplary embodiment, the ultra-sonication is carried out at a frequency of about 30 kHz for about 30 minutes.

The ultra-sonicated titania/silica nanoparticles solution is added to the main electrolyte solution. The volume is adjusted with distilled water to a desired level. The pH of the electroplating composition is adjusted to about 3.5. After the pH adjustment, the electroplating composition is stirred for about 24 hours at a speed of about 300-400 rpm. The stirring facilitates uniform dispersion of titania or silica nanoparticles in the electroplating composition.

After 24 hours stirring, the electroplating composition is ultra-sonicated at a frequency of about 30 kHz for about 30 minutes to obtain the final electroplating composition/bath. The ultrasonication further facilitates uniform dispersion of titania or silica nanoparticles in the electroplating composition.

The present disclosure also provides methods for depositing the electroplating compositions described herein on steel substrates to provide substrates with zinc-iron-titania (Zn-Fe-TiO2) or zin-iron-silica (Zn-Fe-SiO2) coatings. In some embodiments, the electroplating compositions are deposited using a direct current (DC) method. In some embodiments, the electroplating compositions are deposited using a pulsed current method.

Direct Current (DC) Deposition
In some embodiments, a method for depositing the electroplating composition on a steel substrate comprises: a) providing the steel substrate as a cathode; b) depositing the electroplating composition on the steel substrate at a constant current with a current density of about 180-200 mA/cm2 and at a stirring rate of about 300 rpm to provide a steel substrate comprising a Zn-Fe-TiO2 or a Zn-Fe-SiO2 coating.

The inventors have found that the electroplating compositions of the present disclosure, when deposited by employing a constant current having a current density of about 180-200 mA/cm2, provide a higher rate of deposition compared to alloy coatings or commercially used Zn-Ni coatings. In some embodiments, the rate of deposition provided by the DC deposition method is about 3-3.5 µm/min, including values and ranges thereof. The rate of deposition of commercial coating is 1µm/min and Zn-Fe alloy coating is 2.91 µm/min.

In some embodiments, the current density employed in the DC method of deposition is about 180, 185, 190, 195, or 200 mA/cm2, including values and ranges thereof. In some embodiments, the current density employed in the DC method of deposition is about 185-195 mA/cm2, including values and ranges thereof. In an exemplary embodiment, the current density for the DC deposition is about 190 mA/cm2.

In some embodiments, an electroplating composition comprising about 200 g/L zinc sulphate, about 40 g/L ferrous sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 2.5 g/L titania nanoparticles and having a pH of about 3.5 is deposited on a steel substrate at a current density of about 190 mA/cm2 and a stirring rate of about 300 rpm to provide a steel substrate comprising a Zn-Fe-TiO2 coating.

In some embodiments, the DC method provides a Zn-Fe-TiO2 coating comprising about 0.08% by weight of titania and exhibiting a corrosion current of about 3.5 µm/cm2, and a mixed morphology comprising basal and pyramidal microstructure.

In some embodiments, an electroplating composition comprising about 200 g/L zinc sulphate, about 40 g/L ferrous sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 5 g/L silica nanoparticles and having a pH of about 3.5 is deposited on a steel substrate at a current density of about 190 mA/cm2 and a stirring rate of about 300 rpm to provide a steel substrate comprising a Zn-Fe-SiO2 coating. In some embodiments, the DC method provides a Zn-Fe-SiO2 coating comprising about 0.43% by weight of silica and exhibiting a corrosion current of about 1.8 µm/cm2, and a very fine and compact pyramidal morphology.

Pulsed Current Deposition
In some embodiments, a method for depositing the electroplating composition on a steel substrate comprises: a) providing the steel substrate as a cathode; and b) depositing the electroplating composition on the steel substrate by employing a pulsed current with an average current density of about 190 mA/cm2, a duty cycle of about 50-75% and a frequency of about 75-200Hz to provide a steel substrate comprising a zinc-iron-titania (Zn-Fe-TiO2) or a zin-iron-silica (Zn-Fe-SiO2) coating. The electroplating composition is stirred at a stirring rate of about 300 rpm during the deposition process.

The inventors have found that the electroplating compositions of the present disclosure, when deposited by employing a pulsed current having an average current density of about 190 mA/cm2, a duty cycle of about 50-75% and a frequency of about 75-200Hz, provide a higher rate of deposition compared to alloy coatings or commercially used Zn-Ni coatings. In some embodiments, the rate of deposition provided by the pulsed deposition method is about 3-4 µm/min, including values and ranges thereof. In some embodiments, the rate of deposition provided by the pulsed deposition method is about 3-3.8 µm/min, including values and ranges thereof. In some embodiments, the rate of deposition provided by the pulsed deposition method is about 3-3.2 µm/min, including values and ranges thereof. In some embodiments, the rate of deposition provided by the pulsed deposition method is about 3.2-3.5 µm/min, including values and ranges thereof. In some embodiments, the rate of deposition provided by the pulsed deposition method is about 3.4-3.8 µm/min, including values and ranges thereof. In some embodiments, the rate of deposition provided by the pulsed deposition method is about 3.9 µm/min, including values and ranges thereof. The rate of deposition of commercial coating is 1 µm/min.

In some embodiments, the pulsed current has a duty cycle of about 50, 55, 60, 65, 70, or 75% and a frequency of about 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 192 or 200 Hz. In exemplary embodiments, the pulsed current has a duty cycle of about 75% and a frequency of about 200 Hz or a duty cycle of about 50% and a frequency of about 75 Hz.

In some embodiments, an electroplating composition comprising about 200 g/L zinc sulphate, about 40 g/L ferrous sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 1 g/L titania nanoparticles and having a pH of about 3.5 is deposited on a steel substrate by employing a pulsed current with an average current density of about 190 mA/cm2, a duty cycle of about 75% and a frequency of about 200Hz to provide a steel substrate comprising a Zn-Fe-TiO2 coating.

In some embodiments, the pulsed method provides a Zn-Fe-TiO2 coating comprising about 0.04% by weight of titania and exhibiting a corrosion current of about 2.8 µm/cm2, and a fine, compact pyramidal morphology.

In some embodiments, the pulsed method provides a deposition rate of about 3.2-3.5 µm/min for the titania-containing electroplating compositions. In some embodiments, the pulsed method provides a deposition rate of about 3.5-4 µm/min, about 3.8-4 µm/min or about 3.9 µm/min for depositing the electroplating composition comprising 1 g/L titania nanoparticles.

In some embodiments, an electroplating composition comprising about 200 g/L zinc sulphate, about 40 g/L ferrous sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 5 g/L silica nanoparticles and having a pH of about 3.5 is deposited on a steel substrate by employing a pulsed current with an average current density of about 190 mA/cm2, a duty cycle of about 50% and a frequency of about 75 Hz to provide a steel substrate comprising a Zn-Fe-SiO2 coating.

In some embodiments, the pulsed method provides a Zn-Fe-SiO2 coating comprising about 0.5% by weight of silica and exhibiting a corrosion current of about 0.89 µm/cm2, and a fine, compact pyramidal morphology. In some embodiments, the pulsed method provides a deposition rate of about 3-3.5 or about 3-3.2 µm/min for the silica-containing electroplating compositions.

The inventors found that the Zn-Fe-SiO2 coating deposited from an electroplating composition comprising about 200 g/L zinc sulphate, about 40 g/L ferrous sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 5 g/L silica nanoparticles and having a pH of about 3.5 by a pulsed current having an average current density of about 190 mA/cm2, a duty cycle of about 50% and a frequency of about 75 Hz shows superior corrosion resistance (e.g., a corrosion current of about 0.8-0.9 µm/cm2) compared to the commercial Zn-Ni coating and pulsed-deposited Zn-Fe alloy coatings.

The present disclosure provides a steel substrate comprising a zinc-iron-titania (Zn-Fe-TiO2) or zinc-iron-silica (Zn-Fe-SiO2) coating.

In some embodiments, the steel substrate comprises a zinc-iron-titania (Zn-Fe-TiO2) coating, wherein the coating comprises about 0.04-0.08% by weight of titania, including values and ranges therebetween. For example, in some embodiments, the steel substrate comprises a Zn-Fe-TiO2 coating comprising about 0.04%, 0.05%, 0.06%, 0.07%, or 0.08% by weight of titania. In some embodiments, the steel substrates comprising about 0.04-0.08% by weight of titania exhibit a corrosion current density of about 2.8-3.5 µA/cm2, such as about 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, or 3.5 µA/cm2. The Zn-Fe-TiO2 coatings exhibit a basal morphology, a pyramidal morphology, or a mixed morphology having basal and pyramidal microstructure. In some embodiments, the steel substrate comprising a Zn-Fe-TiO2 coating is obtained by the direct current method, wherein the coating comprises about 0.08% by weight of titania, has a corrosion current density of about 3.5 µA/cm2, and exhibits a mixed morphology having basal and pyramidal microstructure. In some embodiments, the steel substrate comprising a Zn-Fe-TiO2 coating is obtained by the pulsed current method, wherein the coating comprises about 0.04% by weight of titania, has a corrosion current density of about 2.8 µA/cm2, and exhibits a fine, compact, pyramidal morphology.

In some embodiments, the steel substrate comprises a zinc-iron-silica (Zn-Fe-SiO2) coating, wherein the coating comprises about 0.4-0.5% by weight of silica, including values and ranges therebetween. For example, in some embodiments, the steel substrate comprises a Zn-Fe-SiO2 coating comprising about 0.40%, 0.41%, 0.42%, 0.43%, 0.44%, 0.45%, 0.46%, 0.47%, 0.48%, 0.49%, or 0.5% by weight of silica. In some embodiments, the steel substrates comprising about 0.4-0.5% by weight of silica exhibit a corrosion current density of about 0.8-1.8 µA/cm2, including values and range thereof, such as about 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 1.8 µA/cm2. In some embodiments, the Zn-Fe-SiO2 coatings exhibit a corrosion current density of about 0.85-0.9 µA/cm2. In an exemplary embodiment, the Zn-Fe-SiO2 coating exhibits a corrosion current density of about 0.89 µA/cm2. In some embodiments, the Zn-Fe-SiO2 coatings exhibit a fine, compact pyramidal morphology. In some embodiments, the steel substrate comprising a Zn-Fe-SiO2 coating is obtained by the direct current method, wherein the coating comprises about 0.43% by weight of silica, has a corrosion current density of about 1.82 µA/cm2, and exhibits a fine, compact pyramidal morphology. In some embodiments, the steel substrate comprising a Zn-Fe-SiO2 coating is obtained by the pulsed current method, wherein the coating comprises about 0.5% by weight of silica, has a corrosion current density of about 0.89 µA/cm2, and exhibits a fine, compact, pyramidal morphology.

It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and not a limitation. While considerable emphasis has been placed herein on the particular features of this disclosure, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. Those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein. Similarly, additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein.

Descriptions of well-known/conventional methods/steps and techniques are omitted so as to not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for examples illustrating the above-described embodiments, and in order to illustrate the embodiments of the present disclosure certain aspects have been employed. The examples used herein for such illustration are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the following examples should not be construed as limiting the scope of the embodiments herein.

EXAMPLES

Example 1: Preparation of the electroplating composition
The electroplating bath/composition containing 200 g/L zinc sulphate, 40 g/L ferrous sulphate, 30 g/L boric acid as a buffering agent, 6 g/L zinc chloride as a pickling agent to increase the dissolution of Zn anode and 0.5-5 g/L titania or silica nanoparticles was prepared as shown in Figure 1. Specifically, 30 g boric acid was dissolved in 650 ml of freshly prepared distilled water to obtain a solution. After dissolution of boric acid, 200 g of zinc sulphate was dissolved in the solution. After dissolution of zinc sulphate, 40 g of ferrous sulphate was dissolved in the solution. After dissolution of ferrous sulphate, 6 g zinc chloride was dissolved in the solution to obtain the main electrolyte. 250 ml of the main electrolyte was taken in a separate beaker and 0.5-5 g of titania or silica particles were added to the 250 ml electrolyte solution. The titania/silica-containing electrolyte solution was stirred for 30 mins at a stirring rate of 350 rpm followed by ultrasonication at 30kHz frequency for 30 mins. The ultrasonicated solution was added to the main electrolyte. The volume was made up to 1L and the pH was adjusted to 3.5 followed by 24 hrs stirring at 350 rpm. The electroplating composition was again ultrasonicated at 30kHz frequency for 30mins. The detailed process is shown in Figure 1. No additional chemicals like surfactants or additives were added in the electrolyte for particle dispersion. Particle dispersion was achieved through ultrasonication and magnetic stirring.

Example 2: Zeta Potential Measurement
Zeta potential was measured using zeta-sizer instrument (Malvern Nano Sizer). 100ml of freshly prepared distilled water at pH 7 was taken. 1 g/l TiO2 or SiO2 were added in the solution. Agitation speed was maintained between 200-300 rpm. The pH of the solution was adjusted using HCl and NaOH solution. After 30 mins, 10µl solution was taken and injected into zeta-sizer cell. The zeta potentials were measured at 3, 6, 9 and 12 pH. The zeta potential values were noted for both the particles (TiO2 and SiO2) at different pH.

Zeta potential of titania particles was above +30mV at the operating pH (3.5) in the water media. Therefore, titania particles were well dispersed and can be deposited on the cathode surface. At the operating pH, zeta potential of SiO2 particles was in between +30mV to -30mV. Therefore, unlike titania particles, silica particles were not well dispersed. To deposit silica particles on cathode surface, stirring was employed.

Example 3: Direct current (DC) deposition of Zn-Fe-TiO2 coating
DC deposition was performed galvanostatically using a Potentiostat (Make: AMETEK) in a two-electrode setup. IF (interstitial free) steel sheet was used as a cathode and pure Zn (99.5% pure) as an anode. Prior to deposition, the IF steel samples were degreased to remove surface oil and then dipped in a dilute HCl solution to remove any oxide film which might be present. The samples were rinsed in distilled water and the deposition was carried out. The electroplating composition was deposited on the IF steel sheet substrate at a constant current with a current density of 190 mA/cm2 and at a stirring rate of about 300 rpm to provide the steel substrate comprising a zinc-iron-titania (Zn-Fe-TiO2) coating.

During deposition, the electrolyte was stirred at a constant rate using magnetic stirrer. The stirrer size was 5cm. The stirring rate was maintained at 300rpm. The current was supplied through a potentiostat. After plating/deposition, the coated samples were rinsed with distilled water and dried.

Various characterizations were performed on the coated steel substrate. Scanning Electron Microscope (SEM) (Make: Nova-Nano) study was conducted to observe the coating morphology, SEM-EDS to obtain wt.% of titania/silica in the coating at different current densities and potentiodynamic polarization test (Make: Gamry) was done to obtain the corrosion potential (Ecorr) and corrosion current density (ICorr) values using Tafel extrapolation.

The potentiodynamic polarization test results showing corrosion current densities of Zn-Fe-titania composite coatings at different particle concentrations are shown in Figure 3. Figure 3 also shows the corrosion current of the benchmark/commercially used coating (Zn-Ni passivated coating) and that of a Zn-Fe alloy coating deposited by a direct current at a current density of 190 mA/cm2 and a stirring rate of 300 rpm. The corrosion current was calculated using Gramry software (Version: 4.35) by Tafel extrapolation method. The corrosion current of the benchmark/commercial Zn-Ni passivated coating was 0.95 µA/cm2 and that of the DC-deposited Zn-Fe alloy coating was 1.1 µA/cm2. For the Zn-Fe-TiO2 coatings, at the lowest concentration of titania particles (0.5 g/L), the highest corrosion current (6.43 µA/cm2) was noticed. The lowest corrosion current (3.5 µA/cm2) was observed at a moderate concentration of TiO2 (2.5 g/L). As the titania concentration increased above 2.5g/L, the corrosion current started to increase again implying that corrosion resistance was decreasing. The corrosion potentials (-1.07V) were similar for all these Zn-Fe-titania composite coatings.

The particle concentration affects the morphology and the texture of the deposit which in turn affects the corrosion resistance properties of the coating. At the lowest concentration of particles (0.5g/L), finer structure was observed. For higher particle concentrations, relatively coarser structure was found. Also, some textural difference (based on alignment of basal plane morphology) was observed at different particle concentration. A mixture of pyramidal and basal morphology was seen for 1 and 2.5g/L of particle concentration whereas only basal morphology was observed at 5g/L of titania concentration. Pyramidal morphology is more corrosion resistive compared to the basal morphology. For this reason, superior corrosion resistance was observed for moderate concentration of titania particles. Very compact coating was noticed at all the concentrations of particles.

Titania wt.% in the final coatings was measured from cross-sectional area analysis using SEM-EDS. Titania wt.% in the final coating increased with the increasing concentration of particles in the electrolyte. The highest titania wt.% in the coating (0.08%) was observed at 2.5 g/L concentration leading to the lowest corrosion rate (3.5 µA/cm2) of the coating. A further increase in titania concentration in the electroplating bath beyond 2.5 g/L led to a reduction in titania wt.% in the coating. The lowest particle incorporation (0.01 wt.%) was observed at 0.5 g/L particle concentration in the electrolyte. Accordingly, the highest corrosion current (6.43 µA/cm2) was observed for 0.5 g/L of TiO2 concentration. Coating deposition kinetics measured through the rate of deposition (3-3.5µm/min) were similar at all the concentration of particles. The rate of deposition of commercial coating is 1 µm/min.

Example 4: Pulsed current deposition of Zn-Fe-TiO2 coating
The pulsed current deposition was performed galvanostatically using a Potentiostat (Make: AMETEK) in a two-electrode setup. IF (interstitial free) steel sheet was used as a cathode and pure Zn (99.5% pure) as an anode. Prior to deposition, the IF steel samples were degreased to remove surface oil and then dipped in a dilute HCl solution to remove any oxide film which might be present. The samples were rinsed in distilled water and the deposition was carried out. The electroplating composition was deposited on the IF steel sheet substrate by employing a pulsed current having an average current density of about 190 mA/cm2 and two different duty cycles/frequency parameters. P1 represents pulse 1 with 75% duty cycle and 200Hz frequency and P2 represents pulse 2 with 50% duty cycle and 75Hz frequency.

During deposition, the electrolyte was stirred at a constant rate using magnetic stirrer. The stirrer size was 5cm. The stirring rate was maintained at 300rpm. The current was supplied through a potentiostat. After plating/deposition, the coated samples were rinsed with distilled water and dried.

Various characterizations were performed on the coated steel substrate. Scanning Electron Microscope (SEM) (Make: Nova-Nano) study was conducted to observe the coating morphology, SEM-EDS to obtain wt.% of titania/silica in the coating at different current densities and potentiodynamic polarization test (Make: Gamry) was done to obtain the corrosion potential (Ecorr) and corrosion current density (ICorr) values using Tafel extrapolation.

The potentiodynamic polarization results showing corrosion current densities of all pulsed deposited Zn-Fe-TiO2 composite coatings are shown in Figure 6. At P1 which corresponds to a higher duty cycle and a higher frequency, the lowest corrosion current (2.8 µA/cm2) was observed at a moderate concentration of TiO2 particle (1 g/L). As the titania concentration was further increased above 1g/L, the corrosion current started to increase. Corrosion potential was similar (-1.05V) for all the cases. The corrosion current of the benchmark coating was as noted in Example 3 (0.95 µA/cm2). The corrosion current of the Zn-Fe alloy coating deposited by the pulse 1 parameters was 1 µA/cm2. and that deposited by the pulse 2 parameters was 1.52 µA/cm2.

P2 represents lower duty cycles and lower frequency. Here also, the lowest corrosion current (3.66 µA/cm2) was observed at 1g/L of titania concentration and as the titania concentration increased above 1g/L, the corrosion current started to increase. The corrosion current was the highest at 0.5 g/L of TiO2 concentration. The corrosion current of the Zn-Fe alloy coating deposited by the pulse 2 parameters was 1.52 µA/cm2. Similarly, like pulse 1, corrosion potentials were comparable to each other (-1.06V).

The Zn-Fe-TiO2 composite coating deposited at the higher duty cycle and higher frequency showed superior corrosion resistance compared to the lower duty cycle and frequency at 1g/L titania particle concentration.

Figure 7 shows the top surface microstructures of pulsed current deposited Zn-Fe-TiO2 composite coatings at different particle concentrations. For P1, very compact coatings were observed for all the sets of particle concentrations. For 0.5g/L of titania concentration, hexagonal (basal) morphology was observed which correlates with the poor corrosion resistance seen at the lower concentration. For other sets of particle concentrations, pyramidal morphology and finer structures were noticed. Thus, better corrosion resistance was observed for moderate and higher concentration of particles.

For P2, very compact coatings were observed for all the sets of particle concentrations. Finer structures were observed for lower concentration of particles (0.5 and 1 g/L) and coarser structures started to form as the concentration of the particles increased. Also, textural difference was noticed from lower to higher concentration of particles. Pyramidal morphology was observed for 0.5 g/L and 1g/L of titania concentration whereas basal morphology was noticed in the case of higher concentration of particles (2.5 and 5g/L). This correlates with inferior corrosion resistance observed for higher concentration of particles.

Figure 8 shows the titania wt.% in the pulse current deposited composite coatings. The titania wt.% in the final coating was measured from the cross-sectional area analysis using SEM-EDS. For P1, a higher particle incorporation was observed for 1 g/L (0.04 wt.% titania) and 2.5 g/L (0.04 wt.% titania) of particle concentration. However, a hexagonal morphology was noticed for 2.5 g/L concentration. A superior corrosion resistance (corrosion current of 2.8 µA/cm2) was observed for 1 g/L of particle concentration that showed a pyramidal morphology. At lower concentration, less particles were incorporated in the coating. Accordingly, a high corrosion current was observed for 0.5 g/L of particle concentration. The highest deposition kinetics was observed for 1g/L of particle concentration (3.9 µm/min). For other concentrations, deposition kinetics were similar (3.2-3.5 µm/min).

For P2, a higher particle incorporation (0.07 wt.%) was observed for 1 g/L of particle concentration in the electroplating bath which correlates with the better corrosion resistance (3.66 µA/cm2) of the coating deposited at this titania concentration. Deposition kinetics were similar for all the concentration of particles with P2 parameters (3-3.8 µm/sec).

Example 5: Direct current (DC) deposition of Zn-Fe-SiO2 coating
Zn-Fe-SiO2 containing electroplating compositions were deposited by a direct current as described in Example 3 and various characterizations were performed.

The potentiodynamic polarization results showing corrosion current densities of Zn-Fe-SiO2 composite coating deposited by the direct current method are shown in Figure 9. The corrosion current of the benchmark/commercial Zn-Ni passivated coating was 0.95 µA/cm2 and that of the DC-deposited Zn-Fe alloy coating was 1.1 µA/cm2. With regard to silica-containing compositions, at a moderate concentration of silica particles, the highest corrosion current was noticed. The corrosion current decreased continuously from 1 g/L to 5 g/L silica concentration. The lowest corrosion current (1.82 µA/cm2) was observed at 5 g/L of silica nanoparticles concentration. After that, the corrosion current started increasing with the increasing particle concentration. The corrosion potentials were similar (-1.07V) for all these Zn-Fe-silica composite coatings.

Figure 10 shows the top surface microstructures of Zn-Fe-SiO2 composite coatings deposited at different silica nanoparticle concentrations. Very compact coatings were observed for all concentrations of silica particles. Apart from 7.5 g/L of particle concentration, no textural difference was observed. Hexagonal morphology was seen at the top surface for the Zn-Fe-silica composite coating with 7.5 g/L of particle concentration whereas only pyramidal morphology was observed for rest of the coatings. Accordingly, a higher corrosion current was observed when the particle concentration increased from 5 g/L to 7.5 g/L. Finer structures were noticed for composite coatings with 1g/L to 5g/L silica nanoparticle concentration.

Figure 11 shows the wt.% of silica in the final DC-deposited Zn-Fe-SiO2 composite coatings.
The lowest silica was incorporated (0.22 wt.%) at 1g/L of particle concentration. This explains the higher corrosion current (5.11 µA/cm2) noticed for Zn-Fe-silica composite coating with 1g/L particle concentration. As the particle concentration increased in the electroplating composition, more particles were incorporated on the cathode surface. The highest particles (0.43 wt.%) were incorporated at 5 g/L of silica particle concentration. Accordingly, the lowest corrosion current (1.82 µA/cm2) was observed for this concentration. The highest deposition kinetics was observed for 1 g/L of particle concentration (7.1 µm/min). For other concentrations, the deposition kinetics were similar (3.4-3.8 µm/min).

Example 6: Pulsed current deposition of Zn-Fe-SiO2 coating
Zn-Fe-SiO2 containing electroplating compositions were deposited by a pulsed current as described in Example 4 and various characterizations were performed.

Figure 12 shows potentiodynamic polarization results depicting corrosion current densities of pulse deposited Zn-Fe-SiO2 composite coatings. In the case of pulse 1, the corrosion current for the Zn-Fe alloy coating was 0.91 µA/cm2. At the moderate concentration of SiO2 particles (2.5 g/L), the corrosion current was the lowest (2.4 µA/cm2). The maximum corrosion current was observed at 1g/L of silica concentration. Above 2.5 g/L, corrosion current increased again. Corrosion potential was similar at all the concentrations (-1.08V).

In terms of corrosion current, promising results were observed for pulse 2 deposits. In the case of pulse 2, the lowest corrosion current (0.89 µA/cm2) was observed at the highest particle concentration (5g/L). The corrosion current (0.89 µA/cm2) for 5 g/L silica concentration was also lower than that of the commercial Zn-Ni coating (0.95 µA/cm2) and pulsed Zn-Fe alloy coatings (1.94 µA/cm2). Like the P1 deposited coatings, the corrosion potential was similar for all the sets of pulsed current deposited composite coatings (-1.08V).

Figure 13 shows the top surface microstructures of Zn-Fe-SiO2 composite coatings deposited at different particle concentrations. Finer and compact structure was observed in the case of pulsed current deposited coatings. Similar top surface morphological appearance was observed for pulse 1 deposited coatings. A pyramidal morphology was observed for Zn-Fe-SiO2 composite coatings with particle concentrations of 0.5-2.5 g/L whereas a hexagonal morphology was observed for 5 g/L of particle concentration. Accordingly, an increase in the corrosion current was observed for 5 g/L particle concentrations for pulse 1.

For pulse 2, a pyramidal morphology was observed for all the coatings. Finer structure was observed for Zn-Fe-SiO2 composite coatings with particle concentrations of 0.5-5 g/L. The lowest corrosion current was observed at 5 g/L silica concentration as noted above. As the particle concentration increased above 5 g/L, coarser structure was observed. Hence, a higher corrosion current was observed for 7.5 g/L of particle concentration.

Figure 14 shows the silica wt.% in the pulsed deposited composite coatings. For Pulse 1, maximum nanoparticles (0.43 wt.%) were incorporated for 2.5 g/L of silica concentration. Therefore, the lowest corrosion current was observed for Zn-Fe-SiO2 composite coating with 2.5 g/L of silica concentration. As the concentration of particles in the electroplating composition increased or decreased from 2.5 g/L, lower particles were incorporated in the coating leading to an increase in corrosion current. Deposition kinetics were similar for all the concentrations (3-3.5µm/min).

In the case of pulse 2, silica wt.% in the final deposit steadily increased with increasing concentration of particles in the electroplating composition till 5 g/L and beyond that the silica wt% in the coating reduced further. The highest amount of particles (0.5 wt%) were incorporated at 5 g/L of particle concentration resulting in better corrosion resistance than others. Above 5 g/L of particle concentration, the particle incorporation was reduced. Therefore, the corrosion current again increased for 7.5 g/L of particle concentration. Deposition kinetics were comparable for all the concentrations (3-3.2 µm/min).

Zn-Fe-SiO2 composite coatings showed superior corrosion resistance when deposited at lower duty cycle and lower frequency (a duty cycle of 50% and a frequency of 75 Hz) compared to a higher duty cycle and frequency at 5 g/L particle concentration in the electroplating bath.

References
1. M.W. Losey, P.S.R.S., Electrodeposition. Reference Module in Materials Science and Materials Engineering, Materials Science and Materials Engineering 13, 1-20, 2017.
2. Jayakrishnan, D.S., Electrodeposition: the versatile technique for nanomaterials. Corrosion Protection and Control Using Nanomaterials, 2012, Book: Corrosion Protection and Control Using Nanomaterials (pp.86-125).
3. Zangari, G., Fundamentals of Electrodeposition. Encyclopedia of Interfacial Chemistry, 2018.
4. M. Sajjadnejad, M. Ghorbani, A. Afshar; Preparation and corrosion resistance of direct current and pulse current electrodeposited Zn-TiO2 nanocomposite coatings, Ceramics International 2014
5. Shirin Dehgahi, Rasool Amini, Morteza Alizadeh; Corrosion, passivation and wear behaviors of electrodeposited Ni–Al2O3–SiC nano-composite coatings,
Surface and Coatings Technology, Volume 304, 25 October 2016, Pages 502-511

6. H. Gu¨l, F. KilIc, S. Aslan, A. Alp, H. Akbulut, Characteristics of electro-co-deposited Ni– Al2O3 nano-particle reinforced metal matrix composite (MMC) coatings, Wear 267 [5–8] (2009) 976–990.
7. L. Chen, L. Wang, Z. Zeng, J. Zhang, Effect of surfactant on the electrodeposition and wear resistance of Ni–Al2O3 composite coatings, Mater. Sci. Eng. A 434 (2006) 319–325.
8. Q. Feng, T. Li, H. Yue, K. Qi, F. Bai, J. Jin, Preparation and characterization of nickel nanoAl2O3 composite coatings by sediment co-deposition, Appl. Surf. Sci. 254 (2008) 2262–2268.
9. J. Steinbach, H. Ferkel, Scripta Mater. 44 (2001) 1813.
10. A. Mo¨ller, H. Hahn, Nanostruct. Mater. 12 (1999) 259.
11. B. Mu¨ller, H. Ferkel, Nanostruct. Mater. 10 (1998) 1285.
12. S.C. Wang, W.C.J. Wei, Mater. Chem. Phys. 78 (2003) 574.
13. X.H. Chen, F.Q. Cheng, S.L. Li, Surf. Coat. Technol. 155 (2002) 274.
14. I. Garcia, J. Fransaer, J.P. Celis, Surf. Coat. Technol. 148 (2001) 171.
15. A.F. Zimmerman, G. Palumbo, K.T. Aust Materials Science and Engineering: A
Volume 328, Issues 1–2, May 2002, Pages 137-146
16. Arthi Jayaraman; Polymer grafted nanoparticles: Effect of chemical and physical heterogeneity in polymer grafts on particle assembly and dispersion, 07 February 2013, Journal of polymer science part B
17. Jamal M. A. Alsharefa , Mohd Raihan Tahaa, Tanveer Ahmed Khan; PHYSICAL DISPERSION OF NANOCARBONS IN COMPOSITES–A REVIEW, Sciences & Engineering), 2017
18. A. Fujishima, T.N. Rao, D.A. Tryk, J. Photochem. Photobiol. C: Photochem. Rev. 1 (2000) 1
19. T. J. Tuaweri and G. D. Wilcox, Influence of SiO2 Particles on Zinc-nickel Electrodeposition, Transactions of the Institute of Metal Finishing, 85, pp 245-253 (2007)
20. M. Abe, Y. Shiohara and A. Okado, Zinc-Based Steel Coating Systems, p. 171. The Minerals, Metals & Materials Society (1989).
21. M. Abe, S. Hashimoto, T. Nishimura and Y. Shiohara, Automotive Corrosion & Prevention Conference & Exposition, SAE 932356 (1993)
22. Yun-Ying Fan, Ying-Jie Zhang, Peng Dong; Preparation and Property of Electrodeposited Zn-Fe-SiO2 Composite Coating, Key Engineering Materials Vols 373-374 (2008) pp 212-215
23. A. Takahashi, Y. Miyoshi and T. Hada; Effect of SiO2 Colloid on the Electrodeposition of Zinc-Iron Group Metal Alloy Composites; Journal of electrochemical society; vlume141
24. WANG Yun-yan, PENG Wen-jie, CHAI Li-yuan, SHU Yu-de; Electrochemical behaviors of Zn-Fe alloy and Zn-Fe-TiO2 composite electrodeposition; 2003
25. WANG Yun-yan, PENG Wen-jie, CHAI Li-yuan, SHU Yu-de Electrochemical behaviours of Zn-Fe alloy and Zn-Fe-TiO2 composite electrodeposition J. Cent. South Univ. Technol. (2007)03-0336-04.

Claims:We Claim:

1.An electroplating composition comprising zinc sulphate in an amount of about 200 g/L, ferrous sulphate in an amount of about 40 g/L, zinc chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, and titania or silica particles at a concentration of about 0.5-5 g/L, wherein the electroplating composition has a pH of about 3.5.
2. The electroplating composition as claimed in claim 1, wherein the titania particles are present at a concentration of about 1-2.5 g/L.
3. The electroplating composition as claimed in claim 1, wherein the silica particles are present at a concentration of about 5 g/L.
4. A method for preparing the electroplating composition as claimed in any one of claims 1-3, comprising:
a. adding boric acid to distilled water;
b. after dissolution of boric acid, adding zinc sulphate to the distilled water;
c. after dissolution of zinc sulphate, adding ferrous sulphate to the distilled water;
d. after dissolution of ferrous sulphate, adding zinc chloride to the distilled water to obtain an electrolyte solution;
e. after dissolution of zinc chloride, adding titania or silica particles to a portion of the electrolyte solution to obtain a titania or silica-containing solution;
f. stirring the titania or silica-containing solution for about 30 minutes at a speed of about 300-400 rpm;
g. ultrasonicating the titania or silica-containing solution after stirring to obtain an ultrasonicated solution;
h. adding the ultrasonicated solution to remaining portion of the electrolyte solution;
i. adding distilled water to obtain the electroplating composition;
j. adjusting pH of the electroplating composition to about 3.5;
k. stirring the electroplating composition for about 24 hours at a speed of about 300-400 rpm; and
l. ultrasonicating the electroplating composition for about 30 kHz for about 30 minutes.
5. The method as claimed in claim 4, wherein the titania or silica-containing solution is stirred for about 30 minutes at a speed of about 350 rpm.
6. The method as claimed in claim 4 or 5, wherein the titania or silica-containing solution is ultrasonicated at a frequency of about 25-35 kHz for about 30 minutes.
7. The method as claimed in any one of claims 4-6, wherein the electroplating composition is stirred for about 24 hours at a speed of about 350 rpm.
8. A method for depositing the electroplating composition as claimed in any one of claims 1-3 on a steel substrate, comprising:
a. providing the steel substrate as a cathode;
b. depositing the electroplating composition on the steel substrate at a constant current with a current density of about 180-200 mA/cm2 and at a stirring rate of about 300 rpm to provide a steel substrate comprising a zinc-iron-titania (Zn-Fe-TiO2) or a zinc-iron-silica (Zn-Fe-SiO2) coating.
9. The method as claimed in claim 8, wherein the current density is about 190 mA/cm2.
10. The method as claimed in claim 8 or 9, wherein the electroplating composition comprises titania particles at a concentration of about 2.5 g/L.
11. The method as claimed in any one of claims 8-10, wherein the Zn-Fe-TiO2 coating deposited by the method comprises about 0.08% by weight of titania.
12. The method as claimed in any one of claims 8-11, wherein the Zn-Fe-TiO2 coating provided by the method exhibits a corrosion current density of about 3.5 µA/cm2.
13. The method as claimed in claim 8 or 9, wherein the electroplating composition comprises silica particles at a concentration of about 5 g/L.
14. The method as claimed in any one of claims 8, 9, and 13, wherein the Zn-Fe-SiO2 coating deposited by the method comprises about 0.43% by weight of silica.
15. The method as claimed in any one of claims 8, 9, 13, and 14, wherein the Zn-Fe-SiO2 coating provided by the method exhibits a corrosion current density of about 1.82 µA/cm2.
16. A method for depositing the electroplating composition as claimed in any one of claims 1-3 on a steel substrate, comprising:
a. providing the steel substrate as a cathode;
b. depositing the electroplating composition on the steel substrate by employing a pulsed current with an average current density of about 190 mA/cm2, a duty cycle of about 50-75% and a frequency of about 75-200Hz to provide a steel substrate comprising a zinc-iron-titania (Zn-Fe-TiO2) or a zin-iron-silica (Zn-Fe-SiO2) coating.
17. The method as claimed in claim 16, wherein the electroplating composition comprises titania particles at a concentration of about 1 g/L.
18. The method as claimed in claim 17, wherein the pulsed current has a duty cycle of about 75% and a frequency of about 200 Hz.
19. The method as claimed in claim 17 or 18, wherein the Zn-Fe-TiO2 coating deposited by the method comprises about 0.04% by weight of titania.
20. The method as claimed in any one of claims 17-19, wherein the Zn-Fe-TiO2 coating provided by the method exhibits a corrosion current density of about 2.8 µA/cm2.
21. The method as claimed in claim 16, wherein the electroplating composition comprises silica particles at a concentration of about 5 g/L.
22. The method as claimed in claim 21, wherein the pulsed current has a duty cycle of about 50% and a frequency of about 75 Hz.
23. The method as claimed in claim 21 or 22, wherein the Zn-Fe-SiO2 coating deposited by the method comprises about 0.5% by weight of silica.
24. The method as claimed in any one of claims 21-23, wherein the Zn-Fe-SiO2 coating provided by the method exhibits a corrosion current density of about 0.89 µA/cm2.
25. A steel substrate comprising a zinc-iron-titania (Zn-Fe-TiO2) coating, wherein the coating comprises about 0.04-0.08% by weight of titania.
26. The steel substrate as claimed in claim 25, wherein the coating exhibits a mixed morphology having basal and pyramidal microstructure or a pyramidal morphology.
27. The steel substrate as claimed in claim 25 or 26, wherein the coating exhibits a corrosion current density of about 2.8-3.5 µA/cm2.
28. A steel substrate comprising a zinc-iron-silica (Zn-Fe-SiO2) coating, wherein the coating comprises about 0.4-0.5% by weight of silica.
29. The steel substrate as claimed in claim 28, wherein the coating exhibits a pyramidal morphology.

30. The steel substrate as claimed in claim 28 or 29, wherein the coating exhibits a corrosion current density of about 0.8-1.8 µA/cm2. ,