TECHNICAL FIELD

The present disclosure generally relates to a field of material science and metallurgy. The present disclosure particularly relates to a method for providing anticorrosion coating on ferrous metals. More particularly, the disclosure relates to a method for providing fayalite coating on the surface of steel, wherein the said fayalite coating is stable, hard, non-toxic, impermeable, insoluble and corrosion resistant.

BACKGROUND OF THE DISCLOSURE
Steel is the widely employed material for various applications. Unfortunately, steel has a tendency to corrode over time. A variety of methods for controlling corrosion have evolved over the past several centuries, with particular emphasis on methods to extend the life of metallic substances in corrosive environments. These methods typically include protective coatings which are used principally to upgrade the corrosion resistance of ferrous metals, such as steel and nonferrous metals, such as aluminum, and to avoid the necessity for using more costly alloys. However, such protecting coating typically have several pitfalls.

Protective coating fall into two main categories. The largest of these categories is the topical coating such as a paint, that acts as a physical barrier against the environment. The second category consists of sacrificial coatings, such as zinc or cadmium, that are designed to preferentially corrode in order to save the base metal from attack. Further, there are proposed organic coatings including epoxy, phenolic, polyester, phthalic acid, fluorine and silicone. However, coatings generally have been unsatisfactory because they give only limited corrosion protection, are relatively soluble and/or result in a toxic waste disposal problem.

Phosphate conversion coatings are widely used to improve the corrosion performance of painted ferrous metals, particularly painted steel. The corrosion processes of painted steel involve high pH conditions at the paint-metal substrate interface. Since, phosphate coatings are unstable in an alkaline environment, phosphate steel are rinsed with solutions containing chromium or chromate ions to improve their alkaline stability. However, recent studies suggest the improvement is marginal. Although dry paint adhesion on chromated phosphate steel is good, wet paint adhesion is unacceptable. The bond between the paint-phosphate interface is weak when water or other corrosion species are present.

Chromate coating have been used to improve corrosion resistance of cold-rolled steel by minimizing red rusting and of galvanized steel by minimizing white rusting. Unfortunately, hexavalent chromium has carcinogenic properties. Because of their toxic nature, rinses containing chromate ions are undesirable for industrial usage.

It also has been proposed previously to improve corrosion resistance and paint adhesion of cold-rolled or galvanized steel sheet using organic polymeric coatings containing a silane or using inorganic coatings including a combination of silane and silicate.

It also has been proposed to improve alkaline corrosion resistance and paint adhesion of phosphate cold-rolled or galvanized steel sheet using a two-step process including rinsing the sheet in an alkaline waterglass solution to form a silicate coating and subsequently rinsing the silicate coated sheet in an aqueous silane containing solution.

As evidenced by the methods mentioned above, there has been a long felt need to develop a low cost, nontoxic, relatively insoluble, corrosion resistant coating for ferrous metals that is environmentally safe and that can be disposed of inexpensively.

SUMMARY OF THE DISCLOSURE
The present disclosure relates to a method for providing anticorrosion coating for ferrous metals. The disclosure particularly relates to providing anticorrosion coating on the surface of the ferrous metals, such as steel.

A principal object of the present disclosure is to provide a low cost, non-toxic, stable, hard, compact, impermeable and relatively insoluble corrosion resistant coating for ferrous metals.

Additional object of the present disclosure is to control the temperature and to control the carbon dioxide atmosphere during the method of the present disclosure so that the coating on the surface of ferrous metal is stable, hard, compact, impermeable, relatively insoluble and resistant to corrosion.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
For the purpose that the disclosure may be easily perceived 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 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 Scanning Electron Microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX) point analysis of uncoated steel substrate.

FIGURE 2 Scanning Electron Microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX)point analysis of silicate coated steel substrate.

FIGURE 3 illustrates the Tafel test results of- (a) bare steel; and (b) fayalite coated steel.

FIGURE 4 illustrates the electrochemical impedance spectroscopy (EIS) test results of- (a) bare steel; and (b) fayalite coated steel.

DETAILED DESCRIPTION
The present disclosure relates to a method for providing anticorrosion coating on the surface of ferrous metals.

The present disclosure particularly relates to a method for providing anticorrosion coating on the surface of ferrous metal, such as steel.

In an embodiment of the present disclosure, the anticorrosion coating provided on the surface of ferrous metal is fayalite (Fe2SiO4) which is stable, hard, compact, impermeable, non-toxic, relatively insoluble and resistant to corrosion.

In an embodiment of the present disclosure, the method for providing anticorrosion coating on the surface of ferrous metal, such as steel, comprises-
spraying silicate solution on the surface of ferrous metal at a controlled temperature and at a controlled atmosphere for providing anticorrosion coating on the surface of ferrous metal.

In an embodiment the controlled temperature during the method of the present disclosure is ranging from about 600°C to 870°C.

In another embodiment, the controlled temperature during the method of the present disclosure is about 600°C, about 620°C, about 640°C, about 660°C, about 680°C, about 700°C, about 720°C, about 740°C, about 760°C, about 780°C, about 800°C, about 810°C, about 820°C, about 830°C, about 840°C, about 850°C, about 860°C or about 870°C.

In an embodiment, the controlled atmosphere during the method of the present disclosure is maintaining carbon dioxide atmosphere at a pressure ranging from about 0.25 bar to 1 bar.

In another embodiment, the controlled atmosphere during the method of the present disclosure is maintaining carbon dioxide atmosphere at a pressure of about 0.25bar, about 0.30bar, about 0.35bar, about 0.40bar, about 0.45bar, about 0.50bar, about 0.55bar, about 0.60bar, about 0.65bar, about 0.70bar, about 0.75bar, about 0.80bar, about 0.85bar, about 0.90bar, about 0.95bar or about 1.0bar.

In an embodiment of the present disclosure the controlled temperature and the controlled carbon dioxide atmosphere during the method provides for stable, hard, compact, impermeable and relatively insoluble coating on the surface of the ferrous metal, such as steel.

In an embodiment of the present disclosure, the method for providing anticorrosion coating on the surface of ferrous metals, such as steel, comprises-
spraying silicate solution on the surface of ferrous metal at a temperature ranging from about 600°C to 870°C under carbon dioxide atmosphere having pressure ranging from about 0.25 bar to 1 bar.

In an embodiment of the present disclosure, the concentration of silicate solution employed in the method for providing anticorrosion coating is ranging from about solid concentration in the range of 6 wt% to 10wt%.

In an embodiment of the present disclosure, the silicate solution is selected from a group comprising ethylene silicate, ethyl silicate and sodium silicate.

In an embodiment of the present disclosure, the thickness of the anticorrosion coating provided on the surface of the ferrous metal is ranging from about 2 microns to 3 microns.

In an embodiment, the steel that is provided with an anticorrosion coating by the method of the present disclosure is a sheet, rebar or any other form of steel material that is capable of undergoing corrosion.

In an embodiment of the present disclosure the method for providing anticorrosion coating on the surface of ferrous metal further comprises curing the anticorrosion coating with a curing agent.

In an embodiment of the present disclosure the curing agent employed for curing the anticorrosion coating on the surface of the ferrous metal is selected from a group comprising, sodium and potassium silicate compounds. The concentration of the curing agent is ranging from about 6 wt% to 10 wt% of solid content.

In an embodiment, during the method of the present disclosure the sprayed silicate reacts with steel surface under the said controlled temperature and the said controlled atmosphere to form a fayalite coating on the surface of steel which is hard, stable, impermeable and insoluble. The said fayalite coating on the surface of steel has superior anticorrosion properties.

In an embodiment, the anticorrosion coating provided by the method of the present disclosure on the ferrous metal, such as steel has good bonding with cement admixture.

In an embodiment, the coating on the surface of the ferrous metal provided by the method of the present disclosure not only prevents the ferrous metal from corrosion but also prevents the ferrous metal from any other damaging reactions caused by the environment in which the ferrous metals are used.

In an embodiment, the method of the present disclosure makes the ferrous metal, such as steel resistant to corrosion, wherein the coated ferrous metal has a corrosion rate ranging from about 0.023mpy to 0.051mpy.

In another embodiment, the method of the present disclosure makes the ferrous metal, such as steel resistant to corrosion, wherein the coated ferrous metal has a corrosion rate of about 0.023mpy, about 0.024mpy, about 0.025mpy, about 0.026mpy, about 0.027mpy, about 0.028mpy, about 0.029mpy, about 0.030mpy, about 0.031mpy, about 0.032mpy, about 0.033mpy, about 0.034mpy, about 0.035mpy, about 0.036mpy, about 0.037mpy, about 0.038mpy, about 0.039mpy, about 0.040mpy, about 0.041mpy, about 0.042mpy, about 0.043mpy, about 0.044mpy, about 0.045mpy, about 0.046mpy, about 0.047mpy, about 0.048mpy, about 0.049mpy, about 0.050mpy or about 0.051mpy.

In an embodiment, the figure 3 illustrates the Tafel test results which demonstrate the dissolution/corrosion of steel material in an aggressive corrosive environment. The anticorrosion coating provided by the method of the present disclosure provides superior resistance against corrosion than the uncoated steel. Lesser Icorr and lesser corrosion rate of steel indicate better resistance against electrochemical corrosion of steel.
In an embodiment, the figure 4 illustrates the electrochemical impedance test results of coated steel and bare steel. The test results indicate that charge transfer resistivity and phase angle shift of the steel surface with the corrosive environment under different frequencies. More the resistivity and less phase angle shift of steel surfaces indicate better resistance against electrochemical corrosion of steel. As per the figure 4, the anticorrosion coating on ferrous metal provided by the method of the present disclosure provides superior resistance against corrosion than the uncoated steel, with increased resistivity and less phase angle shift.

Additional embodiments and features of the present disclosure will be apparent to one of ordinary skill in art based upon the description provided. The embodiments provide various features and advantageous details thereof in the description. Description of well-known/conventional methods and techniques are omitted so as to not unnecessarily obscure the embodiments. The examples provided herein are intended merely to facilitate an understanding of ways in which the embodiments provided may be practiced and to further enable those of skilled in the art to practice the embodiments provided. Accordingly, the following examples should not be construed as limiting the scope of the embodiments.

EXAMPLES

EXAMPLE 1: Preparation of anticorrosion coating on the surface of ferrous metal
About 6 wt% to 10 wt% of solid concentration of silicate solution was sprayed on the surface of steel at a temperature ranging from about 600°C to 750°C under carbon dioxide atmosphere having pressure in the range of about 0.25 bar.
Greyish coating was observed on the surface of steel, wherein the coating comprised of iron and oxygen. The coating that was formed was not compact and had an inferior resistance property towards corrosion with a corrosion rate of about 1.563mpy.

EXAMPLE 2: Preparation of anticorrosion coating on the surface of ferrous metal
About 6 wt% to 10 wt% of solid concentration of silicate solution was sprayed on the surface of steel at a temperature ranging from about 750°C to 870°C under carbon dioxide atmosphere having pressure in the range of about 0.25 bar.
Reddish coating was observed on the surface of steel, wherein the coating is fayalite (Fe2SiO4). The coating that was formed was compact and had an excellent resistance property towards corrosion with a corrosion rate of about 0.023mpy.

EXAMPLE 3: Preparation of anticorrosion coating on the surface of ferrous metal
About 6 wt% to 10 wt% of solid concentration of silicate solution was sprayed on the surface of steel at a temperature ranging from about 700°C to 800°C under carbon dioxide atmosphere having pressure in the range of about 0.5 bar.
Reddish coating was observed on the surface of steel, wherein the coating is fayalite (Fe2SiO4). The coating that was formed was compact and had an excellent resistance property towards corrosion with a corrosion rate of about 0.051mpy.

EXAMPLE 4: Preparation of anticorrosion coating on the surface of ferrous metal
About 6 wt% to 10 wt% of solid concentration of silicate solution was sprayed on the surface of steel at a temperature ranging from about 650°C to 750°C under carbon dioxide atmosphere having pressure in the range of about 0.75 bar.
Reddish coating was observed on the surface of steel, wherein the coating is fayalite (Fe2SiO4). The coating that was formed was compact and had an excellent resistance property towards corrosion with a corrosion rate of about 0.034mpy.

EXAMPLE 5: Preparation of anticorrosion coating on the surface of ferrous metal
About 6 wt% to 10 wt% of solid concentration of silicate solution was sprayed on the surface of steel at a temperature ranging from about 600°C to 700°C under carbon dioxide atmosphere having pressure in the range of about 1 bar.
Brownish coating was observed on the surface of steel, wherein the coating is fayalite (Fe2SiO4). The coating that was formed less compact and had good resistance property towards corrosion with a corrosion rate of about 0.034mpy.

EXAMPLE 6: Preparation of anticorrosion coating on the surface of ferrous metal
About 6 wt% to 10 wt% of solid concentration of silicate solution was sprayed on the surface of steel at a temperature ranging from about 700°C to 870°C under carbon dioxide atmosphere having pressure in the range of about 1bar.
Greyish coating was observed on the surface of the steel, wherein the coating comprised of iron and oxygen. The coating that was formed was not compact and had an inferior resistance property towards corrosion with a corrosion rate of about 1.962mpy.

EXAMPLE 7: Analysis of the anticorrosion coated ferrous metal and bare ferrous metal.
The anticorrosion coated ferrous metal (steel) obtained in Example 2 and bare steel (without fayalite coating) was subjected to Tafel test and Electrochemical impedance test.

Figure 3 illustrates the Tafel test result, wherein it is demonstrated that the fayalite coated steel could provide much superior (excellent) resistance against corrosion with Icorr of about 50.70na and corrosion rate of about 0.023mpy when compared to bare steel which had Icorr of about 5.87µA and corrosion rate of about 2.681mpy, when both the coated steel and the bare steel was subjected to aggressive corrosive environment.

Figure 4 illustrates the electrochemical impedance test results, wherein it is demonstrated that the fayalite coated steel has more resistivity and less phase angle shift when compared to the bare steel. Thus, implying that fayalite coated steel has superior (excellent) resistance against corrosion when compared to bare steel.

Additional embodiments and features of the present disclosure is 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. 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, 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. 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 to the embodiments without departing from the principles of the disclosure. These and other modifications in the nature of the disclosure or the 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.

Claims:

1.A method for providing anticorrosion coating on surface of ferrous metal, comprising-
spraying silicate solution on the surface of the ferrous metal at a temperature ranging from about 600°C to 870°C and at a carbon dioxide pressure ranging from about 0.25bar to 1bar, for providing anticorrosion coating on the surface of the ferrous metal.
wherein the anticorrosion coating is fayalite.

2. The method as claimed in claim 1, wherein the silicate solution is at a concentration ranging from about 6 wt% to 10 wt%.

3. The method as claimed in claim 1, wherein the silicate solution is selected from a group comprising ethylene silicate, ethyl silicate and sodium silicate.

4. The method as claimed in claim 1, wherein the anticorrosion coating has a thickness ranging from about 2 microns to 3 microns.

5. The method as claimed in claim 1, wherein the ferrous metal is steel.

6. The method as claimed in claim 1, wherein anticorrosion coated ferrous metal has a corrosion rate ranging from about 0.023mpy to 0.051mpy.

7. The method as claimed in claim 1, wherein the method further comprises curing the anticorrosion coating provided on the ferrous metal.

8. The method as claimed in claim 7, wherein the curing agent is selected from a group comprising sodium silicate compound and potassium silicate compound.