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Corrosion characteristics of zinc coated SS304 stainless steel
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Corrosion characteristics of zinc coated SS304 stainless steel Adithya Pradeep Nair, Syed Arafat, Farhan, S. Vincent ⇑ Department of Mechanical Engineering, BITS Pilani Dubai Campus, Dubai, United Arab Emirates
a r t i c l e
i n f o
Article history: Received 26 November 2019 Received in revised form 22 January 2020 Accepted 28 January 2020 Available online xxxx Keywords: Stainless steel Coatings of zinc Corrosion resistance Passivity Linear polarization
a b s t r a c t Stainless Steel 304 (SS 304) is considered as one the most important material in the field of Bio-medical and various other applications. The corrosion properties must be looked into all these materials that constitute the medical applications. In the present investigation we determine the corrosion characteristics of zinc coated SS 304 steel in various acidic, neutral and basic solutions at different molar concentrations of chloride and different PH in alkaline solutions. The corrosion characteristics were then compared with uncoated SS 304 Steel. The corrosion resistance of the substance was tested by potentiodynamic polarization test. The various acidic, basic and neutral solutions tested are NaCl, NaOH, HCl in various molar concentrations that is at 1 M, 0.1 M, 0.01 M. Results indicate that Zinc coated SS304 Steel showed higher corrosion resistance when compared with uncoated steel indicating that coating was necessary to reduce the oxidation of the iron in SS304 Steel and a passive layer formed can increase its corrosion rate significantly. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
1. Introduction The failure by cracking is the reason for about 20% of the failures in the chemical process industry [1]. These come under the terms of localised and pitting corrosion. In a corrosive environment the stress level at which the failure occurs in steel is lower as compared to the non-corrosive environment. Good resistance to corrosion, good soldering ability and good frictional properties is the reason for substitution of Zinc coatings on various industries in comparison to nickel [2,3]. In the previous results it has been reported that zinc plated stainless steel is not good for storing Thiourea solution [4]. Some research has been done on zirconia or silica coatings to demonstrate the increase in corrosion resistance on stainless steel [5]. Other works have applied various other coatings like sol–gel and increasing the corrosion resistance on AISI 304 steel coated composite [6]. Lam et al. [7] recognized the corrosion attacks on SS304 and 316 stainless steel and found its corrosion resistance and crevice attack on both by testing it in a neutral media with the presence of Cl ions. Atik et al. [8], reported the corrosion resistant properties on SS3016 Steel by having sol–
⇑ Corresponding author. E-mail address: [email protected] (S. Vincent).
gel ZrO2 coatings was checked. All these experiments in some or the other way have explained that corrosion is a major problem in the SS304 steel. To improve corrosion resistance, various methods have been introduced. In this experimental procedure we will be comparing and checking the corrosion resistance in various acidic, basic and neutral media for both SS304 coated with zinc and the non-coated stainless steel. To the best of authors knowledge, reports on comparison between coating and uncoated stainless steel in acidic, basic or neutral solutions has not been reported. This study examines the corrosion resistance of a media in different environments such as acidic, alkaline and neutral with varying molar concentrations and comparative study between Uncoated and Coated SS304 is reported.
2. Experimental The corrosive behaviors of coated and non-coated stainless SS304 steel sample in acidic, neutral and alkaline solutions were determined using potentiodynamic polarization experiments using Metrohm Autolab 204 potentiostat. The specimens were cleaned in acetone and then with distilled water to remove the acetone on the surface and then dried with dry air. Tests were performed in a conventional three cell electrode with the specimen being the working
https://doi.org/10.1016/j.matpr.2020.01.508 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
2
A. Pradeep Nair et al. / Materials Today: Proceedings xxx (xxxx) xxx
electrode and platinum wire and the standard calomel (SCE) (USCE = 241 mV) was made as the reference and the counter electrodes respectively. The test was done in acidic, neutral and basic medium and the solutions prepared for that was 0.01 M, 0.1 M, 1M HCl, 0.01 M, 0.1 M, 1 m NaCl and pH 10, 12, 14 NaOH. Potentiadynamic polarization tests were performed with a scan rate of 0.0001667 mV/S and it was stabilized for 30 min. The polarization tests were done in a solution of 500 ml and the exposed area of the specimen was 1 mm2. The rest of the working electrode was insulated with thermoplastic resin so that only there required amount i.e. 1 mm2 is exposed to the electrolyte. The polarization tests were done at least 3 times to tests its uniformity in results. 3. Results and discussion Fig. 1 shows the comparison of the corrosion resistances when SS304 Steel was placed in the solution of 0.01 M HCl solution. The linear polarization tests were done and it was figured out from the graphs that coated stainless steel with Zinc had more corrosion resistance than the non-coated one which implied that in acidic medium the coated Zinc protects the surface of the SS304 Steel by a passive layer due to the reaction of zinc and the acidic HCl that protects the SS304 for corrosion and gives it a better corrosion resistance. To further prove its corrosion resistance in acidic medium, both the non-coated and the coated SS304 Steel was placed in the HCl solution of 0.1 M. The Fig. 2 shows the results which also indicate that Zinc coated SS304 Steel had lesser corrosion resistance as compared to non-coated steel in the terms of the potential applied but had higher resistance when it was compared on the basis of the current i.e. icorr. The values of Ecorr and icorr can be obtained from the Tafel extrapolation of polarization curves and by this method corrosion current density (Icorr) and corrosion potential (Ecorr) values were determined. Extracted icorr and Ecorr values for coated SS304 steel immersed in HCl, NaOH and NaCl solution for both coated and uncoated are listed in Tables 1 and 2 respectively. The corrosion resistance in acidic media was further checked with the help of 1 M HCl to further understand that Cl ions had a detrimental effect on the surface of the steel and its effect is reduced with the help of coating and is further proved by the help of Ecorr and icorr values and Fig. 3. The reaction with Zinc and HCl acid can be explained by this chemical formula [2]
Fig. 1. 0.01 M HCl comparison of both coated and uncoated steel.
Fig. 2. 0.1 M HCl comparison of both coated and uncoated steel.
Zn(s) + 2HCl(aq) ! ZnCl2 (aq) + H2 (g)
ð1Þ
This ZnCl2 acts as a passive layer for the further pitting corrosion by the Cl ions which initiate the pitting growth in surface of the stainless steel by adsorption. The Cl ions in the solution of HCl causes more pitting corrosion to occur when its concentration increases. This is shown in Figs. 4 and 5 for both uncoated and coated SS304 Steel respectively. It shows that 0.01 M HCl has the higher corrosion resistance than 0.1 M HCl and 1 M HCl. The value of Ecorr and icorr is higher for 0.1 M HCl than that of 1 M HCl and therefore it is determined from the following figures that Cl ions have some corrosion effect on the surface of the stainless steel. Fig. 6 shows the linear polarization curves when the sample of the steel (both coated and uncoated) is placed in a solution of neutral NaCl of concentration 0.01 M. It again shows the corrosion resistance has increased when the stainless steel was coated with Zinc. Since the attacking ions are same as that of the acidic media the passive layer formed is also the same. Zn reacts with the chloride ions to form a passive layer that can prevent sufficient amount of corrosion as compared to that of uncoated steel. The polarization bends is given in the Fig. 7 when both the coated and non-coated steel in placed in a solution of 0.1 M NaCl is compared. The values of Ecorr and icorr are provided in the table above which show a linear polarization current value of the order of 107 which shows that coated steel with Zinc is highly favorable for usage in areas where there is a high concentration of Cl ions. To test it in more concentration of the Cl ions, the test was done in a solution of 1 M NaCl and it also showed similar type of behavior indicating its increased corrosion resistance when it is coated with Zinc. The corrosion rate in units of mm/year for both coated and uncoated is given in Tables 1 and 2 respectively. The corrosion rate shows an order of 103 mm/year which shows that overall the stainless steel in neutral solutions are highly corrosion resistant in neutral solution even when it is not coated (Fig. 8). Even in neutral media the Cl ions still shows some effect for both the coated and uncoated steel and is given in the Figs. 9 and 10. The Cl ions like that of the acidic medium adsorbs on the surface of the stainless steel which initiates the formation of the pits. The adsorbed Cl ions get attached in between the crystalline matrix which then weakens the inter-crystalline bonds and increases the pit formation. The equation when Zinc reacts with a base like NaOH is given below [2].
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
3
A. Pradeep Nair et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 The corrosion potential (Ecorr) and corrosion current density (icorr) at different aqueous solution for coated stainless steel. Type of Solution
Concentrations
Icorr (lA/cm2)
Ecorr (V vs. SCE)
Corrosion Rate(mm/year)
HCl (acidic)
0.1 M 1M 0.01 M 0.1 M 1M 10 pH 14 pH
7.98E07 1.10E04 7.34E09 6.56E08 3.29E08 2.05E08 2.16E08
0.141 0.397 0.326 0.239 0.236 0.431 0.307
6.15E03 8.48E01 5.68E05 5.05E04 2.53E04 1.58E04 1.66E04
NaCl (neutral)
NaOH (alkaline)
Table 2 The corrosion potential (Ecorr) and corrosion current density (icorr) at different aqueous solution for uncoated stainless steel. Type of Solution
Concentrations
Icorr (lA/cm2)
Ecorr (V vs. SCE)
Corrosion Rate (mm/year)
HCl (acidic)
0.1 M 1M 0.01 M 0.1 M 1M 10 pH 14 pH
3.25E06 1.58E04 3.19E07 7.41E08 3.45E07 1.21E07 1.36E06
0.184 0.332 0.407 0.228 0.237 0.381 0.506
2.5E02 12.2E01 9.57E03 6.70E04 2.67E03 9.36E04 1.04E02
NaCl (neutral)
NaOH (alkaline)
Fig. 3. 1 M HCl comparison of both coated and uncoated steel. Fig. 5. Corrosion comparison of 0.01 M, 0.1 M, 1M HCl for coated steel.
Fig. 4. Corrosion comparison of 0.01 M, 0.1 M, 1M HCl for uncoated steel.
Fig. 6. 0.01 M NaCl comparison of both coated and uncoated.
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
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Fig. 7. 0.1 M NaCl comparison of both coated and uncoated. Fig. 9. Corrosion comparison of 0.01 M, 0.1 M, 1 M NaCl for uncoated.
Fig. 8. 1 M NaCl comparison of both coated and uncoated.
Fig. 10. Corrosion comparison of 0.01 M, 0.1 M, 1 M NaCl for coated.
Zn(s) + 2NaOH(aq) + 2H2 O(l) ! Na2 Zn(OH)4 (aq) + H2 (g) This equation indicates the usefulness of the coating of Zinc when the stainless steel is used in a highly basic environment. The linear polarization curves and the Tafel extrapolation of the Ecorr and icorr values also indicate the same. Fig. 11 shows the comparison when the two coated and non-coated steels are tested for its corrosion properties in 10 PH NaOH. Similarly to prove that coated Stainless steel with Zinc is much more resistant to corrosion as compared to non-coated steel, both these materials were kept in the solution of 12 and 14 PH respectively and it was found that coated steel forms a passive layer that protects the surface of the stainless steel from further attack of OH ions. The comparison was shown in the linear polarization graphs in Figs. 12 and 13 respectively. As the PH value increased the OH increased and its corrosion resistance decreased but not much compared to its decrease in the presence of Cl ions as
shown in figure Tables 1 and 2.The corrosion resistance in terms of mm/year was close to the range of 103 even with its PH value increasing which showed that it didn’t pose a greater corrosion threat to the surface of the steel than that of the acidic medium in the presence of Cl ions. To show the effect of OH on the surface of the stainless steel a comparison of the polarization curves were shown in Figs. 14 and 15 for within the uncoated and coated steel respectively. As from the figures an inference can be made that there is not much difference between the values of the corresponding icorr values of the peaks and there is an increase in Ecorr values as the value of OH ions decrease in the electrolytic solution for uncoated steel but an increase in the negative Ecorr values in the coated steel. This indicates that in a basic solution as the PH increases the coated
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
A. Pradeep Nair et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 11. PH 10 NaOH comparison of both coated and uncoated.
Fig. 12. PH 12 NaOH comparison of both coated and uncoated.
5
Fig. 14. Corrosion comparison of pH 10, 12, 14 NaOH for uncoated.
Fig. 15. Corrosion comparison of pH 10, 12, 14 NaOH for coated.
Zinc provides a better passive area as compared to when it has a lesser PH value. 4. Conclusion
Fig. 13. PH 14 NaOH comparison of both coated and uncoated.
The Ecorr and icorr values were determined by Tafel extrapolation and we can infer from the figure that for acidic, neutral or basic medium the value of the corrosion resistance for a coated SS304 Steel has higher values as compared to uncoated SS304 Steel. A further insight is obtained when the comparisons is done within the uncoated and coated steel to determine the solutions effect on the pitting corrosion on the surface of SS304 Steel. It was proved from the linear polarization curves that Cl ions have a more detrimental effect on the stainless steel as compared to OH ions. This result was the same whether it was tested on coated and uncoated steel. The corrosion rate in terms of mm/year was also determined and it can be concluded that owing to the passive layer formation of Zinc in acidic, neutral or basic media the coated SS304 Steel had lesser corrosion rate in terms of mm/year. The magnitude of the Ecorr and icorr values also did not differ from the result as we could see that a higher value of Ecorr was obtained
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
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when coated stainless steel was kept as a working electrode in the corrosion testing apparatus than the Ecorr obtained on uncoated Steel. CRediT authorship contribution statement Adithya Pradeep Nair: Writing - original draft, Investigation. Syed Arafat: Methodology, Validation. Farhan: Resources, Visualization. S. Vincent: Writing - Review and Editing, Conceptualization. Declaration of Competing Interest
References [1] E.A. Brandes, G.B. Brook, Smithells Metals Reference Book, seventh ed., 1996. [2] D.A. Schario, M.L. Klingenberg, E.W. Brooman, Elecrochem. Soc. 96–2 (1996) 398. [3] M. Pushpavanaman, Bull. Electrochem. 16 (2000) 559. [4] S. Rajendran, V. Agnes Brigita, J. Manivannan, J. Jeyasundari, Portugaliae Electrochim. Acta 27 (2009) 05. [5] K. Izumi, N. Minami, Y. Uchida, Key Engineering Materials, TransTech 150 (1998) 77. [6] D.C.L. Vasconcelosa, J.A.N. Carvalho, M. Mantel, W.L. Vasconcelosa, J. Non. Cryst. Solids 273 (2000) 135–139. [7] By Erin Mackey, Tom Seacord, Stephen Lam, Corrosion 10 (2013) 5991. [8] M. Atika, C.R. Kha, P. de Lima Neto, L.A. Avaca, M.A. Aegerter, J. Zarzycki, J. Mater. Sci. Letters 14 (1995) 178–181.
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Corrosion characteristics of zinc coated SS304 stainless steel Adithya Pradeep Nair, Syed Arafat, Farhan, S. Vincent ⇑ Department of Mechanical Engineering, BITS Pilani Dubai Campus, Dubai, United Arab Emirates
a r t i c l e
i n f o
Article history: Received 26 November 2019 Received in revised form 22 January 2020 Accepted 28 January 2020 Available online xxxx Keywords: Stainless steel Coatings of zinc Corrosion resistance Passivity Linear polarization
a b s t r a c t Stainless Steel 304 (SS 304) is considered as one the most important material in the field of Bio-medical and various other applications. The corrosion properties must be looked into all these materials that constitute the medical applications. In the present investigation we determine the corrosion characteristics of zinc coated SS 304 steel in various acidic, neutral and basic solutions at different molar concentrations of chloride and different PH in alkaline solutions. The corrosion characteristics were then compared with uncoated SS 304 Steel. The corrosion resistance of the substance was tested by potentiodynamic polarization test. The various acidic, basic and neutral solutions tested are NaCl, NaOH, HCl in various molar concentrations that is at 1 M, 0.1 M, 0.01 M. Results indicate that Zinc coated SS304 Steel showed higher corrosion resistance when compared with uncoated steel indicating that coating was necessary to reduce the oxidation of the iron in SS304 Steel and a passive layer formed can increase its corrosion rate significantly. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
1. Introduction The failure by cracking is the reason for about 20% of the failures in the chemical process industry [1]. These come under the terms of localised and pitting corrosion. In a corrosive environment the stress level at which the failure occurs in steel is lower as compared to the non-corrosive environment. Good resistance to corrosion, good soldering ability and good frictional properties is the reason for substitution of Zinc coatings on various industries in comparison to nickel [2,3]. In the previous results it has been reported that zinc plated stainless steel is not good for storing Thiourea solution [4]. Some research has been done on zirconia or silica coatings to demonstrate the increase in corrosion resistance on stainless steel [5]. Other works have applied various other coatings like sol–gel and increasing the corrosion resistance on AISI 304 steel coated composite [6]. Lam et al. [7] recognized the corrosion attacks on SS304 and 316 stainless steel and found its corrosion resistance and crevice attack on both by testing it in a neutral media with the presence of Cl ions. Atik et al. [8], reported the corrosion resistant properties on SS3016 Steel by having sol–
⇑ Corresponding author. E-mail address: [email protected] (S. Vincent).
gel ZrO2 coatings was checked. All these experiments in some or the other way have explained that corrosion is a major problem in the SS304 steel. To improve corrosion resistance, various methods have been introduced. In this experimental procedure we will be comparing and checking the corrosion resistance in various acidic, basic and neutral media for both SS304 coated with zinc and the non-coated stainless steel. To the best of authors knowledge, reports on comparison between coating and uncoated stainless steel in acidic, basic or neutral solutions has not been reported. This study examines the corrosion resistance of a media in different environments such as acidic, alkaline and neutral with varying molar concentrations and comparative study between Uncoated and Coated SS304 is reported.
2. Experimental The corrosive behaviors of coated and non-coated stainless SS304 steel sample in acidic, neutral and alkaline solutions were determined using potentiodynamic polarization experiments using Metrohm Autolab 204 potentiostat. The specimens were cleaned in acetone and then with distilled water to remove the acetone on the surface and then dried with dry air. Tests were performed in a conventional three cell electrode with the specimen being the working
https://doi.org/10.1016/j.matpr.2020.01.508 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Peer-review under responsibility of the scientific committee of the 2nd International Conference on Recent Advances in Materials & Manufacturing Technologies.
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
2
A. Pradeep Nair et al. / Materials Today: Proceedings xxx (xxxx) xxx
electrode and platinum wire and the standard calomel (SCE) (USCE = 241 mV) was made as the reference and the counter electrodes respectively. The test was done in acidic, neutral and basic medium and the solutions prepared for that was 0.01 M, 0.1 M, 1M HCl, 0.01 M, 0.1 M, 1 m NaCl and pH 10, 12, 14 NaOH. Potentiadynamic polarization tests were performed with a scan rate of 0.0001667 mV/S and it was stabilized for 30 min. The polarization tests were done in a solution of 500 ml and the exposed area of the specimen was 1 mm2. The rest of the working electrode was insulated with thermoplastic resin so that only there required amount i.e. 1 mm2 is exposed to the electrolyte. The polarization tests were done at least 3 times to tests its uniformity in results. 3. Results and discussion Fig. 1 shows the comparison of the corrosion resistances when SS304 Steel was placed in the solution of 0.01 M HCl solution. The linear polarization tests were done and it was figured out from the graphs that coated stainless steel with Zinc had more corrosion resistance than the non-coated one which implied that in acidic medium the coated Zinc protects the surface of the SS304 Steel by a passive layer due to the reaction of zinc and the acidic HCl that protects the SS304 for corrosion and gives it a better corrosion resistance. To further prove its corrosion resistance in acidic medium, both the non-coated and the coated SS304 Steel was placed in the HCl solution of 0.1 M. The Fig. 2 shows the results which also indicate that Zinc coated SS304 Steel had lesser corrosion resistance as compared to non-coated steel in the terms of the potential applied but had higher resistance when it was compared on the basis of the current i.e. icorr. The values of Ecorr and icorr can be obtained from the Tafel extrapolation of polarization curves and by this method corrosion current density (Icorr) and corrosion potential (Ecorr) values were determined. Extracted icorr and Ecorr values for coated SS304 steel immersed in HCl, NaOH and NaCl solution for both coated and uncoated are listed in Tables 1 and 2 respectively. The corrosion resistance in acidic media was further checked with the help of 1 M HCl to further understand that Cl ions had a detrimental effect on the surface of the steel and its effect is reduced with the help of coating and is further proved by the help of Ecorr and icorr values and Fig. 3. The reaction with Zinc and HCl acid can be explained by this chemical formula [2]
Fig. 1. 0.01 M HCl comparison of both coated and uncoated steel.
Fig. 2. 0.1 M HCl comparison of both coated and uncoated steel.
Zn(s) + 2HCl(aq) ! ZnCl2 (aq) + H2 (g)
ð1Þ
This ZnCl2 acts as a passive layer for the further pitting corrosion by the Cl ions which initiate the pitting growth in surface of the stainless steel by adsorption. The Cl ions in the solution of HCl causes more pitting corrosion to occur when its concentration increases. This is shown in Figs. 4 and 5 for both uncoated and coated SS304 Steel respectively. It shows that 0.01 M HCl has the higher corrosion resistance than 0.1 M HCl and 1 M HCl. The value of Ecorr and icorr is higher for 0.1 M HCl than that of 1 M HCl and therefore it is determined from the following figures that Cl ions have some corrosion effect on the surface of the stainless steel. Fig. 6 shows the linear polarization curves when the sample of the steel (both coated and uncoated) is placed in a solution of neutral NaCl of concentration 0.01 M. It again shows the corrosion resistance has increased when the stainless steel was coated with Zinc. Since the attacking ions are same as that of the acidic media the passive layer formed is also the same. Zn reacts with the chloride ions to form a passive layer that can prevent sufficient amount of corrosion as compared to that of uncoated steel. The polarization bends is given in the Fig. 7 when both the coated and non-coated steel in placed in a solution of 0.1 M NaCl is compared. The values of Ecorr and icorr are provided in the table above which show a linear polarization current value of the order of 107 which shows that coated steel with Zinc is highly favorable for usage in areas where there is a high concentration of Cl ions. To test it in more concentration of the Cl ions, the test was done in a solution of 1 M NaCl and it also showed similar type of behavior indicating its increased corrosion resistance when it is coated with Zinc. The corrosion rate in units of mm/year for both coated and uncoated is given in Tables 1 and 2 respectively. The corrosion rate shows an order of 103 mm/year which shows that overall the stainless steel in neutral solutions are highly corrosion resistant in neutral solution even when it is not coated (Fig. 8). Even in neutral media the Cl ions still shows some effect for both the coated and uncoated steel and is given in the Figs. 9 and 10. The Cl ions like that of the acidic medium adsorbs on the surface of the stainless steel which initiates the formation of the pits. The adsorbed Cl ions get attached in between the crystalline matrix which then weakens the inter-crystalline bonds and increases the pit formation. The equation when Zinc reacts with a base like NaOH is given below [2].
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
3
A. Pradeep Nair et al. / Materials Today: Proceedings xxx (xxxx) xxx Table 1 The corrosion potential (Ecorr) and corrosion current density (icorr) at different aqueous solution for coated stainless steel. Type of Solution
Concentrations
Icorr (lA/cm2)
Ecorr (V vs. SCE)
Corrosion Rate(mm/year)
HCl (acidic)
0.1 M 1M 0.01 M 0.1 M 1M 10 pH 14 pH
7.98E07 1.10E04 7.34E09 6.56E08 3.29E08 2.05E08 2.16E08
0.141 0.397 0.326 0.239 0.236 0.431 0.307
6.15E03 8.48E01 5.68E05 5.05E04 2.53E04 1.58E04 1.66E04
NaCl (neutral)
NaOH (alkaline)
Table 2 The corrosion potential (Ecorr) and corrosion current density (icorr) at different aqueous solution for uncoated stainless steel. Type of Solution
Concentrations
Icorr (lA/cm2)
Ecorr (V vs. SCE)
Corrosion Rate (mm/year)
HCl (acidic)
0.1 M 1M 0.01 M 0.1 M 1M 10 pH 14 pH
3.25E06 1.58E04 3.19E07 7.41E08 3.45E07 1.21E07 1.36E06
0.184 0.332 0.407 0.228 0.237 0.381 0.506
2.5E02 12.2E01 9.57E03 6.70E04 2.67E03 9.36E04 1.04E02
NaCl (neutral)
NaOH (alkaline)
Fig. 3. 1 M HCl comparison of both coated and uncoated steel. Fig. 5. Corrosion comparison of 0.01 M, 0.1 M, 1M HCl for coated steel.
Fig. 4. Corrosion comparison of 0.01 M, 0.1 M, 1M HCl for uncoated steel.
Fig. 6. 0.01 M NaCl comparison of both coated and uncoated.
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
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Fig. 7. 0.1 M NaCl comparison of both coated and uncoated. Fig. 9. Corrosion comparison of 0.01 M, 0.1 M, 1 M NaCl for uncoated.
Fig. 8. 1 M NaCl comparison of both coated and uncoated.
Fig. 10. Corrosion comparison of 0.01 M, 0.1 M, 1 M NaCl for coated.
Zn(s) + 2NaOH(aq) + 2H2 O(l) ! Na2 Zn(OH)4 (aq) + H2 (g) This equation indicates the usefulness of the coating of Zinc when the stainless steel is used in a highly basic environment. The linear polarization curves and the Tafel extrapolation of the Ecorr and icorr values also indicate the same. Fig. 11 shows the comparison when the two coated and non-coated steels are tested for its corrosion properties in 10 PH NaOH. Similarly to prove that coated Stainless steel with Zinc is much more resistant to corrosion as compared to non-coated steel, both these materials were kept in the solution of 12 and 14 PH respectively and it was found that coated steel forms a passive layer that protects the surface of the stainless steel from further attack of OH ions. The comparison was shown in the linear polarization graphs in Figs. 12 and 13 respectively. As the PH value increased the OH increased and its corrosion resistance decreased but not much compared to its decrease in the presence of Cl ions as
shown in figure Tables 1 and 2.The corrosion resistance in terms of mm/year was close to the range of 103 even with its PH value increasing which showed that it didn’t pose a greater corrosion threat to the surface of the steel than that of the acidic medium in the presence of Cl ions. To show the effect of OH on the surface of the stainless steel a comparison of the polarization curves were shown in Figs. 14 and 15 for within the uncoated and coated steel respectively. As from the figures an inference can be made that there is not much difference between the values of the corresponding icorr values of the peaks and there is an increase in Ecorr values as the value of OH ions decrease in the electrolytic solution for uncoated steel but an increase in the negative Ecorr values in the coated steel. This indicates that in a basic solution as the PH increases the coated
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
A. Pradeep Nair et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 11. PH 10 NaOH comparison of both coated and uncoated.
Fig. 12. PH 12 NaOH comparison of both coated and uncoated.
5
Fig. 14. Corrosion comparison of pH 10, 12, 14 NaOH for uncoated.
Fig. 15. Corrosion comparison of pH 10, 12, 14 NaOH for coated.
Zinc provides a better passive area as compared to when it has a lesser PH value. 4. Conclusion
Fig. 13. PH 14 NaOH comparison of both coated and uncoated.
The Ecorr and icorr values were determined by Tafel extrapolation and we can infer from the figure that for acidic, neutral or basic medium the value of the corrosion resistance for a coated SS304 Steel has higher values as compared to uncoated SS304 Steel. A further insight is obtained when the comparisons is done within the uncoated and coated steel to determine the solutions effect on the pitting corrosion on the surface of SS304 Steel. It was proved from the linear polarization curves that Cl ions have a more detrimental effect on the stainless steel as compared to OH ions. This result was the same whether it was tested on coated and uncoated steel. The corrosion rate in terms of mm/year was also determined and it can be concluded that owing to the passive layer formation of Zinc in acidic, neutral or basic media the coated SS304 Steel had lesser corrosion rate in terms of mm/year. The magnitude of the Ecorr and icorr values also did not differ from the result as we could see that a higher value of Ecorr was obtained
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508
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when coated stainless steel was kept as a working electrode in the corrosion testing apparatus than the Ecorr obtained on uncoated Steel. CRediT authorship contribution statement Adithya Pradeep Nair: Writing - original draft, Investigation. Syed Arafat: Methodology, Validation. Farhan: Resources, Visualization. S. Vincent: Writing - Review and Editing, Conceptualization. Declaration of Competing Interest
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The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Please cite this article as: A. Pradeep Nair, S. Arafat, Farhan et al., Corrosion characteristics of zinc coated SS304 stainless steel, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.508