Claims:1. A composition comprising core shell copper nanoparticle(s), a polymer matrix and boehmite,
wherein the said core shell copper nanoparticle(s) consisting essentially of
a) a core comprised of copper metal; and
b) a shell layer comprised of silica moiety that encapsulates the core.

2. The composition as claimed in claim 1, wherein the polymer matrix comprised of silane(s), preferably organic inorganic silane(s); and the silica moiety of a shell layer is selected from a group comprising a tetraethyl orthosilicate, tetramethyl orthosilicate, methyltrimethoxysilane or vinyltrimethoxysilane.

3. The composition as claimed in claim 1, wherein the silane(s) is selected from a group comprising (3-glycidyloxypropyl) trimethoxysilane, tetraethyl orthosilicate, vinyltriethxysilane, tetramethyl orthosilicate or 3-aminopropyltriethoxysilane or combinations thereof.

4. The composition as claimed in claim 1, having application as a coating, surface pretreatment or rust preventive composition.

5. The composition as claimed in claim 1 is a coating composition.

6. A process for making the composition as defined in claim 1, comprising
a) reducing copper oxide with hydrazine in ammonia solution to obtain copper nanoparticles;
b) mixing silicate solution to the copper nanoparticles to obtain core-shell copper nanoparticles; and
c) mixing the core-shell copper nanoparticles suspension, silane solutions and boehmite to obtain the composition as defined in claim 1.

7. A process for making the composition as defined in claim 1, comprising
a) reducing copper oxide with hydrazine in ammonia solution by heating at temperature ranging from about 50°C to 60°C for a time period ranging from about 45 minutes to 60 minutes to obtain copper nanoparticles.
b) mixing silicate solution to the copper nanoparticles to obtain core-shell copper nanoparticles; and
c) mixing the core-shell copper nanoparticles suspension at a concentration ranging from about 5 vol% to 15 vol%, silane solution at a concentration ranging from about 10 vol% to 25 vol% and boehmite at a concentration ranging from about 0.2 wt% to 2 wt% to obtain the composition as defined in claim 1.

8. The process as claimed in claim 6 and claim 7, wherein the silicate solution of step b) is prepared by adding tetraethyl orthosilicate in ethanol; wherein the silane solution of step c) is prepared by acid hydrolysis of ‘(3-glycidyloxypropyl) trimethoxysilane’ or ‘tetraethyl orthosilicate’ in presence of ethanol.

9. The process as claimed in claim 6 and claim 7, wherein the‘(3-glycidyloxypropyl) trimethoxysilane’ is used at a concentration ranging from about 10 vol% to about 30 vol%, preferably at a concentration of about 25%; ‘tetraethyl orthosilicate’ is used at a concentration ranging from 5 vol% to about 15 vol%, preferably at a concentration of about 10 vol% .

10. The process as claimed in claim 6 and claim 7, wherein the steps a) to c) are carried out in presence of solvent/medium selected from a group comprising gelatin solution, alcohol, aqueous ammonia solution or water or combinations thereof; and wherein the alcohol is selected from a group comprising ethanol, isopropanol, butanol or methanol or combinations thereof.

11. The process as claimed in claim 6 and claim 7, wherein the process described in step (b) and step (c) are carried out at a temperature ranging from about 20°C to about 30°C, and for a time period ranging from about 4 hours to about 24 hours.

12. The process as claimed in claim 6 and claim 7, wherein the steps a) to c) further comprise isolation and/or purification of the corresponding product; wherein said isolation is carried out by acts selected from a group comprising addition of solvent, quenching, filtration, extraction and combination of acts thereof; and wherein the purification is carried out using ion exchange resin.

13. A method of providing the coating to a substrate or an article comprising: (a) providing a substrate or an article, and (b) contacting the substrate or the article with a composition as defined in claim 1 to obtain a coated substrate or a coated article.

14. The method as claimed in claim 13, wherein the contacting is carried out by either dipping and spraying or combination thereof.

15. The method as claimed in claim 13 further comprising the step of curing to obtain a cross linked coating on coated substrate or a coated article.

16. The method as claimed in claim 13, wherein the said curing is carried out at a temperature ranging from about 100 °C to about 150°C, preferably at a temperature of about 120°C; and for a time period ranging from about 5 minutes to about 30 minutes.

17. The method of claim 13, wherein said substrate is a steel, galvanized or galvannealed or any combinations thereof.

18. The composition or the method claimed in any of the preceding claims, where the steel is selected from a group comprising mild steel, stainless steel, galvanized steel or tin plates.

19. The composition as claimed in claim 1, wherein the core-shell nanoparticle contains a cluster with a diameter of about 35 to 50 nm, and said shell has a thickness of about 0.5-20 nm.

20. A corrosion preventive, weldable and formable steel comprising the coating of the composition as defined in claim 1 on a steel.

Dated this 04th day of February 2020
Signature:
Name: Durgesh Mukharya
To: Of K&S Partners, Bangalore
The Controller of Patents Agent for the Applicant
The Patent Office, at Kolkata IN/PA No. 1541
, Description:TECHNICAL FIELD
The instant disclosure is in the field of chemical sciences and material science. The present disclosure generally relates to composition comprising core shell conducting copper nanoparticle(s), a polymer matrix and boehmite, wherein the said core shell copper nanoparticle(s) consisting essentially of a core comprised of copper metal; and a shell layer comprised of silica moiety that encapsulates the core. Further, the present disclosure provides a process for preparing said composition. Said compositions are nano- hybrid coating systems useful for providing a coat on a steel to provide both temporary corrosion resistance and spot weldability.

BACKGROUND OF THE DISCLOSURE
The zinc-based coatings have wide application as sacrificial corrosion resistive coating system on steel. But a higher coating thickness is needed to provide significant corrosion resistance since it is consumed rapidly under the corrosive environment. The application of paint or organic coating system was also popular to provide corrosion protection of steel. But these Zn and organic based coatings were not weldable and formable. This has triggered to look forward for the coating systems which are corrosion resistive, weldable, formable and paintable.
Several studies were carried out in the field of corrosion resistive, spot weldable and paintable coating system on steel. The cold rolled steel sheet is coated or treated with different coating system to make it corrosion resistive as well as weldable which is required for the downstream fabrication processes such as automobile panels. The Zn-alloy (e.g. Zn-Ni, Zn-Fe) coating systems on steel have significantly higher corrosion resistance with lower coating thickness. Miura et.al have developed Zn-Ni alloy, two-layer Zn-Fe electroplated and organic composite coating on steel which was of good corrosion resistance, weldable, formable and paintable. But these coatings are made of costly element (Ni) and consists of multilayers which makes the coating development process difficult.
The US patent 5,059,492 describes about the development of colored plated steel sheet which is highly corrosion resistant, weldable, press process able as well as suitable to further electrodeposition processes. The coating was basically an organic composite coating which was deposited on chromated Zn based steel surface.
The US patent 5,330,850 discloses about the synthesis of multilayer Organic-inorganic composite coating system on steel sheet for automobile panels application which has good formability, weldability and corrosion resistivity. The coating has two layers of zinc-alloy system which is followed by 3rd layer of chromating and final organic coating layer.

The US patent 5,397,638 also describes the development of resin coated steel sheet which was weldable and electrocoatable. The resin was modified with colloidal silica or silane coupling agent, phosphates of different elements and conducting fine powders. But this resin coating had chromated zinc alloy layer beneath the resin film.

The US patent 4,910,097 discloses the similar coating development where the zinc alloy plated steel sheet is chromated which is followed by organic coating on at least on side of the steel sheet. The organic coating is mainly composed of resins, colloidal silica, zinc powder, silane coupling agent and other additives which help to achieve the corrosion resistivity, spot weldability, printability and formability.

All the above discussed works basically focuses the development of corrosion resistive, weldable and formable coating systems on steel sheet which is made up of multilayer and comprises Zn-alloy, chromating and organic resin incorporated with fillers and additives. Chromate treatment is banned due to its carcinogenic effect. Also, the multilayer coating deposition makes the process much difficult. So, authors find here a scope to work on development of a single layer ecofriendly coating system which is capable to provide temporary corrosion protection as well as weldability.

The US application 2010/0098956 A1 describes the development of corrosion resistive and weldable coating system after the heat treatment of the coated steel above 800°C temperature. The coating was mainly organic binder based which was incorporated with electrically conducting fillers to make the coating suitable for welding. As a result of high temperature treatment, the coating generates electrically conducting compounds which develops spot weldability, corrosion resistivity and make it suitable as primer for further coating application.

Therefore, there is a need to identify a composition which provide the corrosion resistivity as well as weldability. The present disclosure tried to address said need to (i) provide the corrosion resistivity, and (ii) spot weldability by developing an unique composition which is developed as a nano- hybrid coating system.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
In order that the disclosure may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure where:
Figure 1 shows the FEG-SEM images of (a)synthesized pure copper nanoparticle, (b) Copper-silica core-shell nanoparticles and (c) Boehmite (AlOOH) particle.
Figure 2 shows (a-b) TEM images of copper nanoparticle, (c-f) EDS line scanning of copper nanoparticles.
Figure 3 shows (a-c) TEM images of core-shell copper-silica nanoparticle, (d-h) EDS line scanning of core-shell copper-silica nanoparticle.
Figure 4 shows XRD of Boehmite.
Figure 5 shows FTIR spectra of (a)liquid coating solution, (b) cured coated steel.
Figure 6 shows representative SEM image of coating surface for the composition C-1, C-2, C-3 and C-4.
Figure 7 shows comparison of Bode impedance plot of bare CRCA and different coated CRCA (C-1, C-2, C-3 and C-4) samples.

DESCRIPTION OF THE DISCLOSURE
The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the description of the disclosure. It should also be realized by those skilled in the art that such equivalent compositions and methods do not depart from the scope of the disclosure. The novel features which are believed to be characteristic of the disclosure, as to composition, method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure. Further, for the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification are to be understood as being modified in all instances by the term "about". It is noted that, unless otherwise stated, all percentages given in this specification and appended claims refer to percentages by weight of the total composition.

Thus, before describing the present invention in detail, it is to be understood that this invention is not limited to particularly exemplified compositions or process parameters or methods that may of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only and is not intended to limit the scope of the invention in any manner.

While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the disclosure. Thus, the use of examples anywhere in this specification including examples of any terms discussed herein is illustrative only, and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the case of conflict, the present document, including definitions will control.

It must be noted that, as used in this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a "solvent" may include two or more such solvents.

The terms "preferred" and "preferably" refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

As used herein, the terms "comprising" "including," "having," "containing," "involving," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Further, the terms “comprises”, “comprising”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a method that comprises a list of acts does not include only those acts but may include other acts not expressly listed or inherent to such method. In other words, one or more acts in a method proceeded by “comprises… a” does not, without more constraints, preclude the existence of other acts or additional acts in the method.

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.

Any discussion of documents, compositions, methods, acts, materials, devices, articles and the like that has been included in this specification is solely for the purpose of providing a context for the disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

A detailed description for the purpose of illustrating representative embodiments of the present invention is given below, but these embodiments should not be construed as limiting the present invention.

Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. The use of numerical ranges by endpoints includes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.80, 3, 3.75, 4, and 5) and any range within that range.

The present disclosure relates to a composition comprising core shell copper nanoparticle(s), a polymer matrix, and boehmite,
wherein the said core shell copper nanoparticle(s) consisting essentially of
a core comprised of copper metal; and
a shell layer comprised of silica moiety that encapsulates the core.

In an embodiment of the present disclosure, the polymer matrix comprised of silane(s), preferably organic inorganic silane(s).

In another embodiment of the present disclosure, the silica moiety of a shell layer is selected from a group comprising a tetraethyl orthosilicate, tetramethyl orthosilicate, methyltrimethoxysilane or vinyltrimethoxysilane.

In yet another embodiment of the present disclosure, the silane(s) is selected from a group comprising (3-glycidyloxypropyl) trimethoxysilane, tetraethyl orthosilicate, vinyltriethxysilane, tetramethyl orthosilicate or 3-aminopropyltriethoxysilane or combinations thereof.

In an embodiment of the present disclosure, the composition comprises core shell copper nanoparticle(s) at a concentration ranging from about 5 vol% to 15 vol%.
In another embodiment of the present disclosure, the composition comprises a polymer matrix at a concentration ranging from about 10 vol% to 25 vol%.
In another embodiment of the present disclosure, the composition comprises boehmite at a concentration ranging from about 0.2 wt% to 2 wt%.
In an embodiment of the present disclosure, the components/ ingredients of the composition are adjusted to constitute 100 wt% composition.

In an embodiment of the present disclosure, the composition as described above has application as a coating, surface pretreatment, or rust preventive composition.
In another embodiment of the present disclosure, the composition as described above is a coating composition.
The present disclosure also relates to a process for making the composition as defined above, wherein the said process comprising the steps of:
reducing copper oxide with hydrazine in ammonia solution to obtain copper nanoparticles;
mixing silicate solution to the copper nanoparticles to obtain core-shell copper nanoparticles; and
mixing the core-shell copper nanoparticles suspension, silane solutions and boehmite to obtain the composition as defined above.
The present disclosure also relates to a process for making the composition as defined above, wherein the said process comprising the steps of:
reducing copper oxide with hydrazine in ammonia solution by heating to obtain copper nanoparticles;
mixing silicate solution to the copper nanoparticles to obtain core-shell copper nanoparticles; and
mixing the core-shell copper nanoparticles suspension, silane solutions and boehmite to obtain the composition as defined above.
In an embodiment of the present disclosure, the process described in step (a) is carried out at a temperature ranging from about 50°C to about 60°C, preferably at about 50°C.

In another embodiment of the present disclosure, the process described in step (a) is carried out for a time period ranging from about 45 minutes to one hour, preferably for a time period of about 60 minutes.

In an embodiment of the present disclosure, the process described in step (c) employs core-shell copper nanoparticles suspension at a concentration ranging from about 5 vol% to 15 vol%.

In another embodiment of the present disclosure, the process described in step (c) employs silane solutions at a concentration ranging from about 10 vol% to 25 vol%.

In yet another embodiment of the present disclosure, the process described in step (c) employs boehmite at a concentration ranging from about 0.2 wt% to 2 wt%.

The present disclosure relates to a process for making the composition as defined above, wherein the said process comprising the steps of:
reducing copper oxide with hydrazine in ammonia solution by heating at temperature ranging from about 50°C to 60°C for a time period ranging from about 45 minutes to 60 minutes to obtain copper nanoparticles.
mixing silicate solution to the copper nanoparticles to obtain core-shell copper nanoparticles; and
mixing the core-shell copper nanoparticles suspension at a concentration ranging from about 5 vol% to 15 vol%, silane solution at a concentration ranging from about 10 vol% to 25 vol% and boehmite at a concentration ranging from about 0.2 wt% to 2 wt% to obtain the composition as defined in claim 1.
The present disclosure also relates to a process for making the composition as defined above, wherein the said process comprising the steps of:
reducing copper oxide with hydrazine in ammonia solution in a closed capped glass bottle and maintaining the temperature at around 50°C for approximate time duration of 60 minutes to obtain copper nanoparticles.
mixing silicate solution to the copper nanoparticles to obtain core-shell copper nanoparticles; and
mixing the core-shell copper nanoparticles suspension at a concentration ranging from about 5 vol% to 15 vol%, silane solution at a concentration ranging from about 10 vol% to 25 vol% and boehmite at a concentration ranging from about 0.2 wt% to 2 wt% to obtain the composition as defined in claim 1.
In an embodiment of the present disclosure, the process as described above for preparing the composition, wherein the step (a) is carried out in a closed capped glass bottle without any inert gas purging.
In an embodiment of the present disclosure, the process as described above for preparing the composition, wherein the silicate solution of step b) is prepared by adding tetraethyl orthosilicate in ethanol;
In another embodiment of the present disclosure, the process as described above for preparing the composition, wherein the silane solution of step c) is prepared by acid hydrolysis of ‘(3-glycidyloxypropyl) trimethoxysilane’ or ‘tetraethyl orthosilicate’ in presence of ethanol.
In yet another embodiment of the present disclosure, the process described above employs the‘(3-glycidyloxypropyl) trimethoxysilane’ at a concentration ranging from about 10 vol% to about 30 vol%, preferably at a concentration of about 25%;
In still another embodiment of the present disclosure, the process described above employs ‘tetraethyl orthosilicate’ is at a concentration ranging from 5 vol% to about 15 vol%, preferably at a concentration of about 10 vol% .
In an embodiment of the present disclosure, the process of steps a) to c) are carried out in presence of solvent/medium selected from a group comprising gelatin solution, alcohol, aqueous ammonia solution or water or combinations thereof.
In another embodiment of the present disclosure, the alcohol is selected from a group comprising ethanol, isopropanol, butanol or methanol or combinations thereof.
In an embodiment of the present disclosure, the process described in step (b) and step (c) are carried out at a temperature ranging from about 20°C to about 30°C, and for a time period ranging from about 4 hours to about 24 hours.
In another embodiment of the present disclosure, the process of steps the steps a) to c) further comprise isolation and/or purification of the corresponding product; wherein said isolation is carried out by acts selected from a group comprising addition of solvent, quenching, filtration, extraction and combination of acts thereof.
The present disclosure provides a method of applying the coating to a substrate or an article comprising: (a) providing a substrate or an article, and (b) contacting the substrate or the article with a composition as defined in claim 1 to obtain a coated substrate or a coated article.
In an embodiment of the present disclosure, the method further comprises the step of curing to obtain a cross linked coating on coated substrate or a coated article.
In another embodiment of the present disclosure, the method of contacting is carried out by either dipping and spraying or combination thereof.
In yet another embodiment of the present disclosure, the curing is carried out at a temperature ranging from about 100 °C to about 150°C, preferably at a temperature of about 120°C; and for a time period ranging from about 5 minutes to about 30 minutes.
In an embodiment of the present disclosure, the substrate is a steel, galvanized or galvannealed or any combinations thereof.
In another embodiment of the present disclosure, the steel is selected from a group comprising mild steel, stainless steel, galvanized steel or tin plates.
In an embodiment of the present disclosure, the core-shell nanoparticle contains a cluster with a diameter of about 35 to 50 nm, and said shell has a thickness of about 0.5-20 nm.
The present disclosure relates to corrosion preventive, weldable and formable steel comprising the coating of the composition as defined above on a steel.

As used herein, the expressions “core shell copper nanoparticle(s)”, “core shell conducting copper nanoparticle(s)” and related terminologies are employed interchangeably within the instant disclosure and refer to the core shell copper nanoparticle of the present disclosure.

As used herein, the expressions “composition”, “nano-hybrid coating”, “nano-hybrid coating compositions”, “nano-hybrid coating system” and related terminologies are employed interchangeably within the instant disclosure and refer to the composition of the present disclosure comprising core shell copper nanoparticle(s), a polymer matrix, and boehmite.

Additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon description provided herein. The embodiments herein provide various features and advantageous details thereof in the description. 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
Materials:
Copper oxide (CuO), ammonia (NH3), gelatin and hydrazine were used to synthesize the copper nanoparticles. (3-Glycidyloxypropyl) trimethoxysilane (GPTMS) which was purchased from Sigma Aldrich and incorporated in coating formulation. Tetraethyl orthosilicate (TEOS) was also purchased from Sigma Aldrich and mainly used to make the silica shell outside of copper particles. TEOS also used as the part of main polymer coating matrix. The coating of present invention is composed of core shell copper nanoparticle where the core material is copper and the shell is made with silica moiety from TEOS-ethanol solution. The polymer matrix is made with the organic inorganic silanes (GPTMS and TEOS) along with the presence of synthesized Boehmite (AlOOH).
1.1 Synthesis
1.1.1 Synthesis of copper nanoparticles:
Copper nanoparticle was synthesized by the reduction of copper oxide with hydrazine in ammonia solution medium. A solution was prepared by adding copper oxide (1.25 wt%) and gelatin (1 wt%) in 100 ml aqueous ammonia solution (28%). Another solution was prepared by adding gelatin (1 wt%) into mixture of 10 ml of hydrazine and 100 ml of aqueous ammonia solution (28%). These two solutions were initially stirred separately at 400 rpm (by magnetic stirrer) maintaining temperature at around 50°C for 20 minutes. After that the two solutions were mixed with each other to develop the copper nanoparticles by reduction of copper oxide with hydrazine. Immediately after mixing the two solutions, the resultant mixture started to convert in red color from black. The overall mixture was stirred at 400 rpm for 40 minutes at 50°C in a closed capped glass bottle to get copper nanoparticle suspension. The final color of the copper nanoparticle suspension was red.
1.1.2 Core-shell Copper nanoparticle synthesis
The core-shell structure was given to copper nanoparticle to protect it from oxidation. A separate solution of tetraethyl orthosilicate (TEOS) was prepared by adding 25 vol% TEOS in 75 vol% ethanol for 30 minutes at room temperature under magnetic stirring at 400 rpm. 200 ml of this TEOS-ethanol solution was added to the previously synthesized copper nanoparticle suspension (200 ml) to make core-shell copper nanoparticles where core is the copper and the shell is formed by silica moiety which could prevent the oxidation or dissolution of copper nanoparticles. This core-shell copper suspension then used as a part of coating solution.
1.1.3 Preparation of Boehmite
The aluminium hydroxide was synthesized from aluminium nitrate hydrate (Al(NO3)3. 9H2O) by treating with caustic soda. 50 ml aluminium nitrate solution of 1(M) strength in aqueous medium was mixed with 50 ml 3(M) aqueous caustic soda solution and 120 ml distilled water. The whole mixture was stirred for 2 hours at 400 rpm at 60°C. Then the precipitate was filtered and washed with distilled water and dried in hot air oven at 60°C to get the aluminum hydroxide (Boehmite).
1.1.4 Synthesis of coating solution
GPTMS and TEOS were hydrolyzed separately in acidified water-ethanol medium and stirred for 24 hours in magnetic stirrer for stabilization of solution. The detail of these solution composition is shown in Table 1. Different compositions of coating were prepared from different combination of silane solutions, Boehmite and core shell copper nanoparticles which are listed in Table 2. Coating was deposited by simply dipping the steel coupon substrates into the coating solution. Curing was done at 120°C for five minutes to get a crosslinked coating on steel substrate.
Table 1: Solution composition
GPTMS/TEOS (ml) Water (ml) Ethanol (ml) Acetic acid
25% GPTMS GPTMS = 25 65 10 10 to 20 drops
10% TEOS TEOS = 10 10 80 10 to 20 drops

Table 2: Coating composition
Sample-ID Core-shell copper suspension (ml) 25% GPTMS (ml) 10% TEOS (ml) Boehmite (AlOOH)
(g) Ethanol
(ml)
C-1 15 100 75 1 15
C-2 15 100 75 NA 15
C-3 NA 100 75 1 15
C-4 10 100 75 1 15

1.2. Characterization:
Field Emission Gun Scanning Electron Microscopy (FEG-SEM):
The FEG-SEM analysis was carried out to understand the morphology of copper nanoparticles, core-shell copper nanoparticles and boehmite particles. It was also used to understand the morphology of coating surface. The EDS analysis of coating helped to understand the distribution of different phases throughout the coating surface.
Transmission Electron Microscopy (TEM):
TEM tests were mainly performed to confirm the core-shell structure formation for copper-silica particles. It also helped to understand the shape and size of the nanoparticles.
X-ray Diffraction study:
XRD with Cu-Ka radiation was used to identify the boehmite (AlOOH) phase synthesized from alkaline aluminum nitrate solution. The XRD scanning was performed in the diffraction angle range of 10° to 90° (2?) with step size 0.02. The XRD data was analyzed by xpert highscore software to identify the boehmite phase.
Fourier Transformed Infrared Spectroscopy (FTIR):
FTIR spectroscopy was performed to understand the formation of different chemical bonds during coating solution preparation and after the curing of coating.
Spot-weldability test:
The spot weldability test is necessary to check the weldability of coating. It is required to develop the weldability property of coating along with corrosion resistance property. A coating is called spot weldable only when the experimental nugget diameter is more than or equal to the theoretical nugget diameter. The theoretical nugget diameter of a coated steel sample is represented by the following formula-
Theoretical nugget dia.= 4vt (where t=thickness of steel substrate)
The spot-welding tests were carried out at different current flow from 7 to 8.5 kA with constant weld time of 267 milliseconds, constant force of 3.8kN, constant squeeze time of 450 milliseconds. After that the experimental nugget diameter was measured and compared with the theoretical nugget diameter to identify the spot weldability of coating. The steel substrate thickness for the weldability tests was 1.33 mm.
1.3. Corrosion measurement:
Electrochemical impedance spectroscopy (EIS):
EIS was performed to measure the corrosion resistance property and the mechanism of corrosion for different coating systems. All the EIS tests were performed in 3.5 wt% aqueous sodium chloride solution. A three-electrode flat cell was used to perform these tests where the sample (bare/coated CRCA) act as working electrode, saturated calomel electrode as reference electrode and platinum mesh as the counter electrode. The exposed sample area was 1 cm2 for all the electrochemical tests. The open circuit potential (OCP) was stabilized for 15 minutes to get the potential fluctuation less than 5 mV/second for at least 5 minutes. A sinusoidal potential perturbation of 10 mV was provided at stabilized OCP to record the impedance response in the frequency range of 10-2 to 105 Hz. The Bode plot were fitted with equivalent circuits and analyzed to understand the barrier property of coating.
1.4. RESULTS AND DISCUSSION
1.4.1 Microscopic analysis of synthesized nanoparticles:
Figure 1(a) shows the SEM image of copper nanoparticles produced by reduction of copper oxide with hydrazine. It reveals that most of the particles are hexagonal in shape and having 150 to 160 nm average particle size. Figure 1(b) indicates the copper-silica core-shell nanoparticles having average size in the range of 35 to 40 nm. The core-shell copper nanoparticles are spherical in shape. However, it is not possible to understand the formation of core and shell separately from the SEM images. Also, the size of TEOS coated copper nanoparticles are much less than the pure copper nanoparticles. The decrease in average particle size could be explained due to the re-dissolution of cooper into the ammonia solution which was used as the reaction medium. The Boehmite particles shown in the Figure 1(c) is very small in size (around 20 nm) and are present as a cluster.
Figure 2 (a-c) represents the TEM bright field image of pure copper nanoparticles. It shows that the copper nanoparticles (black colored) are hexagonal in shape with average particle size 150 nm which is matching with the SEM analysis where the shape and size obtained were similar. The EDS line scanning of the particles in Figure 2(c) confirms the presence of mostly copper (Figure 2(d-f)) particles.
Figure 3 (a-c) represents the TEM bright field images of copper-silica core-shell nanoparticles. The dark copper nanoparticles are surrounded by the silica shell which is less dark in contrast. The EDS line scanning of the particles (Figure 3d) confirms the presence of copper in the center whereas the silicon and oxygen are at the circumference of the center copper particle (Figure 3(e-h)). This confirms the formation of core-shell copper-silica nanoparticle.
1.4.2 Structural analysis of Boehmite:
Figure 4 shows that the Boehmite has been formed after alkaline treatment of aluminium nitrate. The xpert highscore analysis confirms the presence of aluminium hydroxide formation (ICSD 98-010-8877).
1.4.3 Structural analysis of coating:
Figures 5 (a&b) are the representative FTIR spectra for coating composition C-1, C-3 and C-4. Figure 5(a) represents the FTIR spectra of liquid coating solution. The peaks at 1650 cm-1 and 3360 cm-1 signify the presence of water which is expected as the coating solution is water based and has not been cured yet. The peaks at 2894 and 2975 cm-1 are due to the C-H stretching frequency which comes from the hydrocarbon chain of GPTMS and TEOS molecules. The peaks at 1042 and 1084 cm-1 mainly represent the starting of Si-O-Si/Si-O-Al bond formation in the liquid form. The absence of broad peak at around 3360 for coated steel (Figure 5b) is attributed to the completion of curing of coating. The peak at 1630 signifies the adsorbed water on the cured coating surface which may come from the atmospheric moisture. The peaks at 796, 903, 1037, 1090 confirm the formation of both Si-O-Si and Si-O-Al bonds due to curing of the coating. Coating made from composition C-2 also shows the formation of Si-O-Si bond in the range of 1000 to 1100 cm-1 along with peaks for C-H stretching at the above-mentioned frequencies. Hence, the FTIR confirms that the crosslinking of Si-O-Si or Si-O-Al has occurred in different coating composition in significant extent upon curing of the coating which could make the coating more compact.
Figure 6 shows the representative SEM image of coating surface for the compositions C-1, C-2, C-3 and C-4. It reveals that the surface is covered by black and white colonies. The EDS result (Table 3) shows that the black area is basically the silicon and oxygen rich area. It suggests that the black colonies are mostly covered with the compounds of silicon and oxygen which is mainly silicon oxide chain (Si-O-Si) as it has also been confirmed by FTIR analysis (Figure 6b). The white colonies are rich in iron than the silicon. It indicates that the white colonies are mostly covered by iron oxides along with less amount of silicon oxide chain. Therefore, it can be said that the coating surface is ununiformly covered by silicon oxide chain along with iron oxides and hydrocarbon chain.
Table 3: EDS result of coating surface shown in Figure 6
Spectrum level 1 2 3 4 5 6
O 9.64 48.16 49.83 13.41 14.83 40.22
Al - 4.16 0.45 - - 1.42
Si 4.78 37.59 45.0 8.16 8.96 54.28
Fe 85.59 9.59 2.74 78.42 76.21 3.86
Cu - 0.5 1.98 - - 0.22
Total 100.0 100.0 100.0 100.0 100.0 100.0

1.4.4 Coating weldability:
Table 4 shows all the spot-welding parameters and the comparison of desired and experimental nugget diameters obtained from the spot welding tests for different coating systems. All the core-shell copper nanoparticle incorporated coatings (C-1, C-2 and C-4) show spot weldability only when the applied current is more than or equal to 7.5kA. The spot weldability may have achieved due to very low coating thickness as well as incorporation of core-shell copper nanoparticle which could have significant role to pass the current during welding. Also, the coating composition (C-3) having no incorporated core-shell copper nanoparticles, shows spot weldability at and above current of 7.5 kA. Therefore, the occurrence of spot weldability could be attributed to the low coating thickness only. A detail probe is needed to understand the effect of core-shell nanoparticles on spot weldability.
Table 4: Parameters of spot welding
Sample Current (kA) Weld time (ms) Force (kN) Squeeze time (ms) Experimental Nugget dia. (mm) Theoretical nugget dia. (mm)
C-1 7 267 3.8 450 5.64 4.61
7.5 267 3.8 450 5.05 4.61
8 267 3.8 450 5.59 4.61
C-2 7.5 267 3.8 450 4.86 4.61
8 267 3.8 450 5.08 4.61
C-3 7.5 267 3.8 450 4.99 4.61
8 267 3.8 450 5.31 4.61
8.5 267 3.8 450 5.48 4.61
C-4 7 267 3.8 450 4 4.61
7.5 267 3.8 450 4.23 4.61
8 267 3.8 450 5.09 4.61
8.5 267 3.8 450 5.58 4.61

1.4.5 Corrosion measurement (Electrochemical Impedance Spectroscopy (EIS) Study):
EIS tests were performed to understand the corrosion resistance property and the mechanism of corrosion. The Bode impedance plot of Figure 7 reveals that the bare as well as all the coated CRCA steel samples have resistive behavior at the higher (103 to105 Hz) and lower (100 to10-2 Hz) frequency region. Only the intermediate frequency region (100 to103 Hz) shows the capacitive behavior. It is evident that all the coated CRCA have the higher impedance at lowest frequency which is a clear signature of better barrier resistance of coated CRCA than bare CRCA.
All the EIS data was fitted with electrochemical equivalent circuit (EEC) to get the values of all electrochemical parameters. The Bode impedance data of bare CRCA was fitted with simple Randles circuit (having one time constant) where the solution resistance (Rsoln) is in series with the parallel combination of constant phase element (CPEct) and charge transfer resistance (Rct) (Figure 8(a)). All the coated CRCA was fitted with EEC of two-time constants where (CPEctRct) is in parallel with (CPEcRpore) which is again in series with Rs (Figure 8(b)). The CPEcRpore has been incorporated to explain the contribution of coating in the electrochemical process whereas the CPEctRct represent the corrosion process of CRCA. Here, Rsoln, Rpore, Rct are the solution resistance, coating resistance and charge transfer resistance respectively. The CPEc and CPEct are the constant phase elements corresponding to the capacitance of coating film and double layer capacitance. The ideal capacitance is replaced by constant phase element to represent the inhomogeneous electrochemical behavior of surface. The CPE is defined by the following equation:
Z_CPE=1/(?(j?)?^p C)
Where, C is the capacitance, ? is the angular frequency (?=2pf rad s-1), j=v(-1) and p is the exponent (0=p=1). All the EIS data were fitted by corresponding EECs with the help of Gamry fitting software.
Table 5 shows the electrochemical parameters of bare and coated CRCA obtained after fitting the EIS data with the proposed EECs (Figure 8 (a&b)). The total resistance to corrosion (Rt) represent the corrosion resistance property of each samples. Higher value of Rt signifies better corrosion resistance than the lower. It is evident that all the coated CRCA substrates has the more Rt value than the bare, which represents the coated CRCA have more corrosion resistance than bare substrate. It can be observed that the coated substrates of composition C-1, C-3 and C-4 are comparable in terms of corrosion resistance since their total resistance to corrosion (Rt) values are almost comparable. But composition C-2 has less resistance to corrosion (having less Rt value) than other coated CRCA.
Table 5: Electrochemical parameters obtained by fitting the Bode impedance plot of different samples with the EECs
Samples Rs (? cm2) Rct (? cm2) Rpore (? cm2) CPEct
(S*s^n) n CPEc (S*s^m) m Rt= (Rct+Rpore) (? cm2) Goodness of fit
Bare CRCA 14 349 - 4.1910-4 0.87 - - 349 4×10-2
C-1 30 8380
10
6.64E-05
0.8 8.19E-07
0.9 8390 2.08E-03

C-2 17
3100
28
3.92E-05
0.86 1.58E-05
0.81 3128 1.23E-02

C-3 10 10400
304
6.92E-05
0.77 1.26E-06
0.64 10704 8.34E-03

C-4 13
10400
56
5.47E-05
0.78 4.30E-07
0.76 10456 1.36E-03

Additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based on the description provided herein. The embodiments herein provide various features and advantageous details thereof in the description. Descriptions of well-known/conventional methods and techniques are omitted so as to not unnecessarily obscure the embodiments herein.

The foregoing description of the specific embodiments fully reveals the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments in this disclosure have been described in terms of preferred embodiments, 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.

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. These and other modifications in the nature of the disclosure or the preferred embodiments will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the disclosure and not as a limitation.