Claims:The scope of the invention is defined by the following claims:

Claim:
1. Micropatterned surface in the form of grooves is prepared on the SS304 surface using the following machining technique:
a) Micropatterns on the surface are generated by an elaborate chemical etching process. Depending on the actual dimensions of the micropatterns desired, the etching process is determined with appropriate chemical solutions and abstractions.
b) Using 3D optical profilometer all the dimensions are actually measured and crosschecked with the images taken from scanning electron microscope (SEM).
c) By placing water droplet on flat and micropatterned surface manufactured by the method described above. We now measure wettability and conclude that our invention is successfully worked.
d) Using Electrochemical work station, we predicted corrosion parameters and conclude the invention successful.
2. As mentioned in claim 1, the desired physical measurement dimensions of the micropatterns are ridge width 55µm to 115µm and groove width 180µm to 270µm. From these combination of dimensions we invented the most optimum parameter to eradicate wettability and corrosion.
3. According to claim 1, solid fraction (F) of micropatterned surface was varied from 0.2 to 0.7 and found out 0.3 is optimum to minimize wettability and corrosion.
4. As per claim 1, exhaustive experimental study was conducted on wettability. For this purpose, we employed high speed photography and measurements were made from the images using Image J software (Contact angle was measured with an accuracy of 0.010). In our invention contact angles ?? and ?? to grooves increases upto 145.730 and 107.880 as against an angle of 77.720 on flat plate.
5. As per claim 1, our invention greatly minimizes corrosion rate (CR). In our invention we found that the CR of micropatterned surface was 0.047mm/year maximum and 0.025mm/year minimum whereas for the flat surface, CR is 0.121mm/year. Therefore, this invention nearly reduces corrosion rate (CR) to one-third.
6. As per claim 1, our invention significantly reduces wettability and simultaneously reduces liquid-mediated corrosion i.e. by saline water (sea water). The invention can also work to reduce corrosion by other liquids such as aqueous acids, etc.
7. As per claim 1, this invention has significantly reduced corrosion even under the presence of mechanical stresses, whereas normal coatings will peel off when the surfaces are stressed.
8. The claim also includes (1) micropatterned surfaces in the form of micropillars and microholes and (2) the invention is applicable to all metallic surfaces e.g. aluminium, copper, titanium etc. , Description:Hydrophobic Surfaces for Reducing Wettability and Corrosion of Steel Surfaces
Field of Invention
The present invention relates to, wettability and corrosion of the material pivot on the morphology of its surface. Through felicitous modification of the surface by fitting roughness, wettability and liquid-mediated corrosion characteristics of the material will be restrained.
The objectives of this invention
The objective of this invention is aggrandizing anti-wettability and corrosion resistance of steel by surface modification via micropatterned roughness in the form of grooves with its surface morphology, solid fraction ranging from 0.2 – 0.7 to appraise the observation.
Background of the invention
Micropatterning the surface have wide range of application in many fields especially in wettability study. Micropatterning refers to inducing patterned roughness on the surface which in turn depending upon the morphology of the roughness, the surface will act as either hydrophobic or hydrophilic. Hydrophobic surface inhibits wetting and opposes the degradation of the material caused by wetting of liquids where as hydrophilic surface is quite opposite to hydrophobic surface.
An attempt was made to correlate the effect of roughness parameter on corrosion behavior of the steel and found that corrosion rate of the steel will lead to decrease with respect to increase in average roughness Ra (0.010µm-0.419 µm). (A Y Kandeil & M Y Mourad [1989], Surface and Coatings Technology, 37,p 237-250). In this case the roughness induced was random roughness i.e. the morphology of the roughness was not well defined which leaves the problem unsolved. Another attempt was made to quantify the size effect of surface roughness to superhydrophobicity with different morphology of surface roughness. (Quanshuei Zheng et al. & Cunjing Lu [2014], Procedia IUTAM 10, p 462-475). According to their work, the surface will behave like superhydrophobic as long as Casie Baxter state is stable and described the wetting nature of surface dependent on different morpohology of roughness. In this case the correlation was done between modification of surface roughness and wettability not on corrosion related parameters. Across the globe several researchers working on optimizing the corrosion resistance of material by means of making the surface hydrophobic but they emphasize on coatings not on micropatterned roughness for fabricating the hydrophobic surface. (Dun Zhang et al. [2013], Corrosion Science, 69, p 23-30 and Jintao Tian et al. [2013], Electrochimica Acta, 97, p 409-419). The pitfall of coatings is that after a certain time period or at operating environment with the presence of mechanical/thermal stresses they begin to peel off.
To overcome the above mentioned flaws the concept of micropatterning the roughness in the form of grooves on the surface of steel to eradicate wetting and corrosion is introduced. The micropatterned surface can sustain in the rugged environment more effectively when compared to the coatings.
Description of Prior Art
Conventional solution for optimizing corrosion resistance of the material is coatings. A key difference is by micropatterning the surface is that the life cycle of the material can be optimized operating in the extreme environmental condition even under the presence of external mechanical/thermal stress.
There are many types of corrosion resistance techniques available in the literature. One among them is making the surface hydrophobic i.e. increasing contact angle greater than 900 making the surface non-stick which attracts the researchers working on corrosion. The commonly used method for fabricating hydrophobic surface is coating and the researchers have suggested the various chemical combinations for coatings and observed the tremendous decrease in wetting of the surface (US005997943A & US006013724A). To increase the resistance to corrosion thickness of the coatings was also increased by making it as number of layers with different composition suitable for the proposed environment (US007427442B2). However in the above mentioned methods for fabricating hydrophobic surface the main disadvantage is over a certain period of time in the rugged working environment it will lead to peel off.
Instead of coatings hydrophobic surface can be fabricated by bonding gel to the surface. This is described in one of the Unites States patent (US006743467B1) and they observed the tremendous increase in contact angle more than 1650. The main disadvantage is that, if any load is applied on the gel i.e. on the surface, it will delaminate the gel from the surface. By means of incorporating very fine particles in powder form on the surface will lead to variation in surface morphology. If the incorporated particles supports hydrophobicity , them it means wetting on the surface will be minimum, on the other hand corrosion will be minimum (4701575). The incorporated particles may increase hydrophobicity but the main disadvantage is the incorporated particles create random roughness on the surface. Due to the random roughness on the surface, the hydrophobicity cannot be characterized accurately.
Summary of the invention
In the present innovative invention, the hydrophobic surface is fabricated through introducing patterned roughness in the form of microgrooves on the surface.
The main intention is to propose hydrophobic surface which can minimize wetting and eradicate liquid-mediated corrosion even in the presence of external mechanical stresses. Furthermore the relation between surface morphology, wetting and corrosion characteristics was revealed.
The striking features of this invention are for different groove geometries shifting from Wenzel to Casie- Baxter state was noted and its wettability and corrosion characteristics were observed.
Detailed description of the invention
Corrosion is the vital problem observed in most of the engineering structures. Stainless steel SS304 is one of the predominant materials in the structures because of its strength, adaptability, ductility and durability. There are several conventional techniques like coating, plating etc., are available to tackle corrosion. The serious disadvantage in the above mentioned conventional techniques was, they will not withstand in the corrosion environment with the presence of mechanical/thermal stress which kindles us to look for new innovative methods. Modifying the surface by inducing micropatterned roughness will help us to eradicate liquid-mediated corrosion even in the presence of mechanical/thermal stress and enhances the life cycle of the structures.
Micropatterns in the form of grooves were formed on the surface using chemical etching process with different geometry. The geometrical dimensions of the micropatterns were measured using 3D optical profilometer incorporated with Veeco software and counterchecked with the images taken using scanning electron microscope (SEM). The sample SEM image of the micropatterned surface is shown in Fig.1. The geometry of the micropattern was formed in the manner ridge width varying from 55µm to 115µm and groove width varying from 180µm to 270µm to obtain solid fraction (F) in the range between 0.2 to 0.7. The depth of the groove was kept constant at 41µm.
Wettability study was conducted on flat and micropatterned surface by measuring the wetting parameter i.e. static contact angle of water droplet placed on the surfaces. The images of the water droplets were captured using a high speed camera and characterized using Image J software. The images of the water droplet formed on the flat and patterned surface are shown in Fig.2. The morphology of the liquid droplet formed on the patterned surface varies from the image taken perpendicular to the grooves when compare to that taken parallel to the grooves, which is due to anisotropic wetting, as briefly described in one of the literature (Anand A.V. et al. [2017], Int. J. Surface Science and Engineering, p 174-190). The notable variation in contact angle (?) was observed between flat (77.720) and micropatterned surface (?? - 124.570-145.730 & ?? - 82.120-107.880). Wettability in micropatterned surface decreases up to solid fraction 0.3 and follows Casie Baxter model. After that wetting shifts to Wenzel state which leads to increase in wettability. To obtain minimum wetting in our invention we propose to fabricate micropattern surface with solid fraction (F) 0.3.
Meanwhile corrosion study was conducted on flat and micropatterned surface using electrochemical work station in saline water environment (i.e. saline water is the corrosive medium). The corrosion parameters were quantified using TAFEL plot. Micropatterned surface shows better corrosion resistance property when compare to flat surface. The corrosion rate observed on flat was 0.121 mm/year and in micropatterned surface ranges from 0.047-0.025 mm/year. The corrosion resistance of the micropatterned surface increases up to solid fraction (F) 0.3 then drop occurs. Other fitting parameters like corrosion potential, polarization resistance and corrosion current density also follow the same trend as corrosion rate. According to our invention micropattern surface with solid fraction (F) 0.3 shows better corrosion resistance property when compare to other geometrical dimensions of the micro groove patterns taken in our work.
Wetting and corrosion studies conducted in our invention proves that the strong correlation between surface morphology, wetting and corrosion resistance of steel. The corrosion resistance of the micropatterned steel surface increases with respect to the decrease in wettability. Microgroove patterned surface acts as hydrophobic surface and follows heterogeneous wetting where air pockets are formed between the grooves and opposes the penetration of water droplet inside the grooves (Casie Baxter state). This means that there will be a reduction in contact area available for the water droplet to wet on the micropatterned surface, which leads to decrease in wettability. Owing to the wetting of water droplet that follows Casie Baxter model, in micropatterned surface, the air cushion i.e. air trapped in between the microgrooves, repels the corrosive liquid-medium. The air pockets in between the grooves, opposes the penetration of corrosive liquid inside the grooves and minimizes the corrosion rate. The corrosive liquid touches only the top of the ridges in the case of the microgroove patterned surface, whereas in the case of the flat surface, the corrosive liquid makes contact with the entire surface. Thus, the microgroove patterned surface corrodes only at the top of its ridges, unlike in the case of the flat surface that gets corroded over its entire surface. Thus, as the area contacted by the corrosive liquid is lesser in the case of microgroove patterned surface when compared to that of the flat surface, corrosion rate reduces for the microgroove patterned surface when compared to that of the flat surface. The pictorial representation of the above statement is shown in Fig.3 for clear understanding. According to our invention micropatterned surface may stand as effective solution to alleviate wettability and liquid-mediated corrosion, and curtail liquid-mediated corrosion related failures in steel structures.
8 Claims & 3 Figures
Brief description of Drawing
In the figures which are illustrate exemplary embodiments of the invention.
Figure 1 SEM image of the Microgroove Patterned Steel Surface
Figure 2 Morphology of the Water Droplet Formed on a) Flat and Microgroove Patterned Steel Surface b) Perpendicular to the Grooves and d) Parallel to the Grooves
Figure 3 Schematic Illustration of Relation between Corrosion and Wetting

Detailed description of the drawing
As described above the present invention relates to aggrandizing anti-wettability and corrosion resistance of steel by surface modification using microgroove patterned surface.
The scanning electron microscope (SEM) image of the microgroove patterned surface is shown in figure 1. The measured geometrical dimension of the microgrooves using 3D optical profilometer was checked using SEM image and the deviations was observed within the acceptable level (deviation ± 1.27µm).
Morphology of the water droplet formed on flat and micropatterned surface captured using high speed camera is shown in figure 2. Due to heterogeneous wetting nature of microgroove patterned surface, morphology of the liquid droplet was captured in direction perpendicular and parallel to the direction of the grooves. The wetting parameter namely, contact angle (?) was measured from the captured image using Image J software.
Figure 3. illustrates the relation between wetting and corrosion. Due to hydrophobicity air pockets occupy the grooves and oppose the penetration of corrosive liquid medium, as a result corrosion rate will be decreased.