Natural extracts have been widely used to protect metal materials from corrosion. The efficiency of these extracts as corrosion inhibitors is commonly evaluated through electrochemical tests, which include techniques such as potentiodynamic polarization, electrochemical impedance spectroscopy, and weight loss measurement. The inhibition efficiency of different extract concentrations is a valuable indicator to obtain a clear outlook to choose an extract for a particular purpose. A complementary vision of the effectiveness of green extracts to inhibit the corrosion of metals is obtained by means of surface characterizations; atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy analysis are experimental techniques widely used for this purpose. Moreover, theoretical studies are usually addressed to elucidate the nature of the corrosion inhibitor—metal surface interactions. In addition, calculations have been employed to predict how other organic substances behave on metal surfaces and to provide experimental work with fresh proposals. This work reports a broad overview of the current state of the art research on the study of new extracts as corrosion inhibitors on metal surfaces in corrosive media. Most constituents obtained from plant extracts are adsorbed on the metal, following the Langmuir adsorption model. Electron-rich regions and heteroatoms have been found to be responsible for chemisorption on the metal surface, whereas physisorption is due to the polar regions of the inhibitor molecules. The plant extracts compiled in this work obtained corrosion inhibition efficiencies above 60%, most of them around 80–90%. The effect of concentration, extraction solvent, temperature, and immersion time were studied as well. Additional studies regarding plant extracts as corrosion inhibitors on metals are needed to produce solutions for industrial purposes.

中文翻译：

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植物提取物作为不同金属表面和腐蚀性介质的绿色腐蚀抑制剂：综述

天然提取物已被广泛用于保护金属材料免受腐蚀。这些提取物作为缓蚀剂的效率通常通过电化学测试进行评估，其中包括电势极化，电化学阻抗谱和失重测量等技术。不同提取物浓度的抑制效率是获得清晰的前景以选择特定用途提取物的重要指标。通过表面表征获得了绿色提取物抑制金属腐蚀功效的补充观点；原子力显微镜，扫描电子显微镜和X射线光电子能谱分析是广泛用于此目的的实验技术。此外，通常会进行理论研究，以阐明缓蚀剂与金属表面相互作用的性质。另外，已经使用计算来预测其他有机物质在金属表面上的行为，并为实验工作提供新的建议。这项工作报告了有关在腐蚀介质中金属表面上作为缓蚀剂的新型萃取物的研究现状的最新研究概况。按照Langmuir吸附模型，从植物提取物中获得的大多数成分都吸附在金属上。已经发现富电子区域和杂原子是金属表面化学吸附的原因，而物理吸附是由于抑制剂分子的极性区域引起的。在这项工作中汇编的植物提取物获得了60％以上的缓蚀效率，其中大多数约占80-90％。还研究了浓度，萃取溶剂，温度和浸泡时间的影响。为了生产用于工业目的的溶液，还需要进行其他有关将植物提取物用作金属腐蚀抑制剂的研究。