The parsley extract (PLE) was prepared using absolute ethyl alcohol. The PLE and synergistic iodide were firstly utilized as efficacious corrosion inhibitors to slow down the corrosion rate of carbon steel-Q235 in 0.5 mol/L H₂SO₄ solution. The anti-corrosion performance was researched by weight loss method, electrochemical tests, surface analysis and quantum chemistry calculation. Results of electrochemical and weight loss tests show that the synergetic PLE and I⁻ exhibit the optimal corrosion inhibition efficiency 99%. The combined inhibitor displays the favorable long-term corrosion inhibition effect, and the inhibition efficiency can maintain more than 90% after 144 h immersion. The introduction of I⁻ makes carbon steel surface with higher negative charge amount, which could be beneficial to the interaction between corrosion inhibitor and Fe atoms. The adsorption behavior obeys the Langmuir isotherm adsorption, and involves chemical and physical adsorption. On the basis of electrochemical consequences and theoretical calculation, the adsorption process and anti-corrosion mechanisms are further explored.

Nowadays, the development of plant extracts as corrosion inhibitors to protect metals from corrosion is a popular research direction. However, given the vast diversity of plant species in nature, it is imperative to explore effective methods to improve screening efficiency in order to quickly identify the corrosion inhibition potential of plants. In this work, a new strategy for developing plant-extracted eco-friendly corrosion inhibitors based on the family and genus of plants is proposed. Three plants of different genera in the Asteraceae family, including Artemisia argyi extract (AAE), Chrysanthemum indicum extract (CIE), and Centipeda minima extract (CME), were selected and successfully prepared as novel corrosion inhibitors for Q235 steel in a sulfuric acid solution. The corrosion inhibition behavior and corresponding mechanism were systematically investigated by using some electrochemical tests (open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy) and surface characterizations (Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy). The experimental results illustrated that the main components of the three extracts were similar and that when combined with KI as mixed-type corrosion inhibitors, they could dramatically slow down the metal corrosion rate. The maximum value of the corrosion inhibition efficiency reached 96.29%, 96.50%, and 97.52%, respectively, at 200 mg/L and could increase to 98.64%, 97.65%, and 99.06%, respectively, with a prolonged immersion time. A synergistic effect exists between the three plant extracts and KI, leading to the firm adsorption of the three plant extract molecules onto a Q235 steel surface, thereby forming a robust protective film. This work demonstrated that plants of different genera in the Asteraceae family possessed similar corrosion inhibition capabilities, providing a novel way to select potential corrosion inhibitors from numerous plants based on family and genus classification.

In this work, the effect of heat flux on pitting corrosion behaviors and passive film properties of 304 stainless steel in 3.5 wt.% NaCl solution were investigated by the self-developed metal heat transfer surface testing system using electrochemical methods and surface analysis techniques. The results show that positive heat flux reduces the corrosion current density, inhibits the occurrence and growth of metastable and steady-state pitting corrosion, while the effect of negative heat flux is the opposite. The effects of heat flux on the semiconductor carrier concentration and the contents of Cr₂O₃ and NiO are not significant, but the effects on the contents of Fe (III) and Fe (II) in the outer layer of passive film are obvious. The positive heat flux increases the ratio of Fe (III) /Fe (II), thereby increasing the corrosion resistance of passive film, while the negative heat flux does the opposite.