Effect of Green Inhibitors on the Corrosion Rate of Mild Steel and Stainless Steel 304

Abstract

Corrosion is an inevitable process that affects metals in everyday life, requiring constant efforts to manage due to its technical, economic, and aesthetic significance. It refers to the degradation of metal surfaces caused by reactions with environmental elements. The damage caused by corrosion can be severe, leading to structural failure of metal components, increased repair and replacement costs, product losses, and even safety hazards, as well as environmental pollution. One effective method of mitigating corrosion is the use of inhibitors. These are chemical agents added in small amounts to reduce the corrosion rate. With growing awareness of environmental and health concerns, the focus has shifted towards developing eco-friendly, non-toxic corrosion inhibitors derived from natural sources. In this study, the inhibition of corrosion on mild steel and stainless steel in corrosive environments such as hydrochloric acid was explored using green inhibitors. These inhibitors were extracted from natural sources like Cinnamomum verum (cinnamon) and Aloe barbadensis (aloe vera) in the form of oils and gel. The study was conducted at room temperature using the weight loss measurement technique to assess the effectiveness of these inhibitors.

Introduction

Corrosion is a major issue in metal-based industries, leading to structural failures, economic losses, and safety risks. Among traditional prevention methods, corrosion inhibitors are widely used but many are toxic and environmentally hazardous. In response, there is a growing focus on green inhibitors—biodegradable, non-toxic substances derived from natural sources like plant extracts. This study investigates cinnamon oil and Aloe vera gel as green inhibitors for reducing corrosion in mild steel and stainless steel exposed to hydrochloric acid (HCl).

2. Literature Review

• Green Inhibitors work by adsorbing onto metal surfaces, forming protective films that block corrosive agents.

• The adsorption can occur via:

  • Physisorption (electrostatic interaction, reversible)

  • Chemisorption (chemical bonding, more permanent)

• Studies show:

  • Cinnamon oil (rich in cinnamaldehyde and eugenol) inhibits corrosion in stainless steel with up to 96% efficiency.

  • Aloe vera (containing amino acids, enzymes, polysaccharides) achieves up to 97% inhibition for mild steel.

• Plant extracts act as mixed-type inhibitors, reducing both anodic and cathodic reactions.

Challenges

• Variability in plant extract composition

• Lack of long-term performance data

• Limited understanding of adsorption mechanisms

3. Materials and Methods

• Metals Tested: Mild steel and stainless steel 304

• Corrosive Medium: 1.5M Hydrochloric Acid

• Inhibitors: Cinnamon oil and Aloe vera gel at concentrations of 0, 1, 5, 10, and 15 ml in 60 ml HCl solution

• Method: Weight-loss technique to assess corrosion rate and inhibition efficiency

• Metallography: Polishing and etching to observe microstructural changes

• Hardness Testing: Performed using standard indentation methods

4. Results and Discussion

• The study confirmed the effective inhibition of corrosion by both Aloe vera and cinnamon oil.

• Higher concentrations of inhibitors yielded greater protection.

• Aloe vera was especially effective for mild steel, and cinnamon oil showed strong results for stainless steel.

• SEM and electrochemical tests confirmed the formation of a protective film on metal surfaces.

• Adsorption behavior included both physical and chemical interactions, enhancing the stability of the protective layer.

Conclusion

1) This study aimed to evaluate the effectiveness of Aloe barbadensis miller and cinnamon oil as environmentally friendly corrosion inhibitors. 2) The results confirmed that both compounds successfully reduced the corrosion of stainless steel and mild steel in 1.5 M HCl solutions, with their inhibition efficiency increasing alongside concentration and immersion time. 3) Aloe barbadensis miller proved to be a highly effective inhibitor for mild steel in acidic environments, offering a potential alternative to conventional inhibitors containing harmful chemicals. 4) Aloe vera gel functioned as a mixed-type inhibitor, protecting the metal surface from both anodic and cathodic reactions. 5) Corrosion resulted in rough and irregular grain boundaries, resembling intergranular corrosion, which could weaken the material over time. 6) The hardness of the materials decreased after corrosion, but the presence of inhibitors significantly slowed this reduction, helping maintain the mechanical properties of the metals.

References

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Copyright

Copyright © 2025 Maloth Balaji, Smt. Palusa Pavani. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.