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Corrosion control for metals has technical, economical, environmental, and aesthetical importance. The use of corrosion inhibitors from natural product is one of the best ways to slow the rate of corrosion of metals and alloys. The use of extract inhibitors from natural product is the best alternative because it does not contain heavy metals and is nontoxic, environmentally friendly, biodegradable, easy to obtain, inexpensive, and available in large quantities. The organic compounds contained in the extracts of natural products such as tannins, amino acids, phenolics, and alkaloids contain heteroatomic groups, which can inhibit corrosion rate and are interesting to study. With the development of science and technology, many methods are used to protect the corrosion, such as electroplating and coating, and organic inhibitor shows real promise such as Theobroma cacao peel extract. Although substantial research has been devoted to corrosion inhibition by plant extracts, reports on the detailed mechanisms of the adsorption process and identification of the active ingredient are still scarce. The addition of polar extract of cacao peel into a solution of HCl 1.5 M is very effective to reduce the attack surface corrosion on mild steel and can maintain its mechanical properties. This chapter consciously restricts itself mainly to plant materials, especially Theobroma cacao peel extract, as green corrosion inhibitors.

This study aims to investigate the effect of the electrophoretic deposition process (EPD) of natural HA (extracted from bovine bones) with various particle size on Ti-29Nb-13Ta-4.6Zr (TNTZ) coating surfaces. HA particles were refined from bovine bone powders using planetary ball mill and then sieving to separate the particle based on its size. The maximum size according to sieving mesh size is #25 µm, #63 µm and #125 µm. The coating process was conducted by using EPD apparatus with voltage and time process 10V and 5 minutes, respectively, for each sample. The coating layer morphology was observed with Stereo Microscopy, Scanning Electron Microscopy (SEM) and the thickness was measured with Thickness Gauge. The result shows that the size of the particle determines the coating layer characteristics. The best of HA coating quality according to the implant coating standard is obtained for the 25 µm particle size with the surface coverage is 99%. The thickness is 121 µm and the ratio of chemical composition Calcium and Phosphor Ca/P) is 1,49%. These may be concluded that, on the point of view physical characteristics, natural HA from bovine bone has potential enough as a coating layer to improve the bioactivity implant for biomedical application. However, the mechanical characteristic of the layer is still needed to determine the strength of coating layer for avoiding delamination during application.

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Effect of addition of theobroma cacao peels extract (TCPE), a new proposed green inhibitor, on tensile and hardness properties, and related microstructure of mild steel exposed in solution of 1.5M HCl was investigated in order to know the contribution of this kind of inhibitor in controlling mechanical properties, in addition to reducing corrosion attack. Corrosion behaviors including inhibition mechanism and adsorption process during exposure were then discussed. Corrosion rate and inhibitory efficiency of mild steel samples containing 0.3%C were determined using weight loss method. The samples were exposed in the acid solution with and without addition of 0.5-2.5% the TCPE. Tensile and hardness tests were subsequently performed on the samples to determine the change of mechanical properties of the metal prior and after addition of the extracts. Sample surface morphologies and chemical composition as well were observed by a scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (SEM-EDX). The results show that the strength, hardness and elongation of mild steel drop significantly due to heavy damage in the surface after immersion in the HCl solution for 32 days. However, these mechanical properties gradually increase with increasing concentration of the extract following the increase of surface coverage and inhibition efficiency. The increase of the tensile properties and hardness is due mainly to the ability of the inhibitor to cover mild steel surface through formation of metal-organo complexes protection layer in the surface of the mild steel. Although total carbon level in the surface of the mild steel also increases significantly, there is no any proof of carbon difussion into the mild steel. The addition of polar extract of theobroma cacao peels into a solution of 1.5 M HCl is, therefore, not only effective to minimize the degradation on the mild steel surface, but it also diminishes the mechanical properties reduction of the mild steel.