Introduction to Corrosion Inhibition and the Role of Green Solutions
Corrosion remains one of the most significant issues in various industries that rely on metallic structures, especially mild steel, which is often exposed to harsh acidic conditions. In processes such as pickling, descaling, oil well acidizing, and tank cleaning, steel surfaces are subjected to corrosive acid solutions that can severely degrade their properties, shortening their lifespan and increasing maintenance costs. Traditionally, synthetic corrosion inhibitors have been employed to reduce these effects, but their environmental impact, toxicity, and cost have raised concerns in recent years.
In light of these challenges, there is an increasing demand for green corrosion inhibitors, substances derived from natural sources, which provide an environmentally friendly and sustainable alternative to synthetic chemicals. Among the most promising sources for green inhibitors are plant extracts, known for their biodegradability, non-toxicity, and low cost. The study conducted by Vanshika Singh, Sudesh Kumar, Ashish Sihmar, and their team in 2025, published in Scientific Reports, investigates the potential of Araucaria heterophylla, a species of evergreen conifer, as a natural, effective inhibitor against acidic corrosion on mild steel.
Understanding Araucaria Heterophylla and Its Corrosion Inhibition Potential
Araucaria heterophylla, also known as the Norfolk Island Pine, belongs to the Araucariaceae family and is known for its medicinal properties, including antibacterial, antioxidant, anti-ulcerogenic, and anti-cytotoxic effects. The plant's leaves contain a wide range of bioactive compounds, such as flavonoids, phenolics, alkaloids, and terpenoids, which have been identified in previous research as effective against various pathogens and illnesses. The research team aimed to evaluate whether these compounds could also provide protection against corrosion on mild steel exposed to acidic environments.
The study hypothesized that A. heterophylla extract could act as a green corrosion inhibitor for mild steel by forming a protective barrier on the metal surface, thereby reducing the corrosion rate. As an initial step, the plant’s leaves were extracted and subjected to various corrosion tests in a 1 M HCl (hydrochloric acid) solution, which is often used to simulate the corrosive environments that steel might encounter in industrial applications.
Experimental Methodology and Results: The Power of A. Heterophylla Extract
To assess the corrosion inhibition efficiency of A. heterophylla extract, the researchers employed several analytical techniques. These included weight loss measurements, potentiodynamic polarization, electrochemical impedance spectroscopy, and scanning electron microscopy to measure the corrosion rate and examine the formation of protective films on the steel surface.
Corrosion Inhibition Efficacy
One of the key findings of the study was that the A. heterophylla extract displayed significant corrosion inhibition, with an efficiency of 83.94% at a concentration of 1000 ppm (parts per million). After 12 hours of immersion in the acidic solution, mild steel samples treated with the extract exhibited dramatically lower corrosion rates compared to untreated samples. This was a clear indication that the plant extract was preventing the metal from reacting with the corrosive acid, thus preserving its integrity.
Electrochemical Analysis
The electrochemical analysis conducted during the study provided further insight into the protective capabilities of the extract. Potentiodynamic polarization measurements revealed a dramatic reduction in corrosion current density when A. heterophylla extract was added to the solution. The corrosion current density decreased from 1.08 μA/cm² in the untreated sample to 0.17 μA/cm² in the sample with 1000 ppm of the plant extract. This indicates that the inhibitor was effectively slowing down the corrosion process, preventing metal degradation.
Surface Morphology and SEM Imaging
Scanning electron microscopy was used to visually confirm the formation of a protective passive film on the steel surface. The SEM images revealed a smooth, uniform layer over the treated steel, which contrasted with the rough, corroded surface of untreated samples. This layer acts as a physical barrier, shielding the steel from further corrosion and contributing to the overall corrosion resistance observed.
Chemical Components of A. Heterophylla: What Makes It Effective?
To identify the active compounds responsible for the corrosion inhibition, the researchers utilized various chemical analysis techniques, such as Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography-Mass Spectrometry (GC-MS).
FTIR Analysis
FTIR analysis revealed the presence of several functional groups in the A. heterophylla extract that likely contribute to its inhibitory effects. These included:
• N-H stretching secondary amines (3337.07 cm⁻¹): indicative of nitrogen-containing compounds, which are known for their ability to bond with metal surfaces.
• CO–O–C–O stretching anhydride (1022.64 cm⁻¹): signaling the presence of oxygen-containing groups that can interact with metal surfaces, further enhancing corrosion protection.
GC-MS Analysis
The GC-MS analysis further confirmed the identification of several chemical components in the extract that are believed to be responsible for its corrosion-inhibiting action. These include flavonoids, alkaloids, and terpenoids, all of which have been previously noted for their antioxidant and metal-adhesion properties. These compounds work synergistically to form a protective layer on the steel, preventing the corrosive acid from attacking the metal.
Green Inhibitors: The Environmental and Economic Benefits
One of the major advantages of using plant-based corrosion inhibitors like A. heterophylla is their minimal environmental impact. Unlike synthetic corrosion inhibitors, which can be toxic to both humans and ecosystems, green inhibitors are biodegradable and non-toxic. This makes them a safer alternative in industrial settings, where toxic chemicals can contaminate water sources and soil, causing long-term environmental damage.
In addition to being safer, green inhibitors are also more cost-effective. The A. heterophylla extract, which can be obtained from naturally occurring plants, offers a sustainable and affordable solution compared to expensive synthetic alternatives. Moreover, the potential for large-scale cultivation of A. heterophylla for this purpose could further reduce costs and provide economic benefits to regions involved in its production.
The Future of Eco-Friendly Corrosion Protection
The study of Araucaria heterophylla as a corrosion inhibitor opens up new possibilities for sustainable materials protection. As industries increasingly turn to green chemistry and eco-friendly alternatives, plant-based inhibitors like A. heterophylla offer a practical solution to prevent corrosion without harming the environment. This research not only highlights the potential of this particular species but also paves the way for future investigations into other plant-based inhibitors.
In conclusion, the findings from this study suggest that Araucaria heterophylla extract holds significant promise as a natural, eco-friendly solution for preventing corrosion on mild steel in acidic environments. The combination of effective corrosion inhibition, environmentally benign properties, and low cost makes this green inhibitor a promising alternative to traditional synthetic chemicals, opening doors for more sustainable practices across various industries.
