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The present work studied aqueous extracts of castor beans as a natural inhibitor of the corrosion of mild steel in 1 M HCl using gravimetric tests, potentiodynamic polarization curves, linear polarization method, electrochemical impedance measurements, surface analysis by scanning electron microscopy (SEM) and chemical characterization by Fourier transform infrared spectroscopy (FTIR). Gravimetric tests showed that inhibition efficiency (IE) increased with immersion time and concentration of the extract, reaching 97.8% in the presence of 800 mg L−1 inhibitor after 24 h immersion time. For the gravimetric tests varying the temperature, a decrease of the activation energy (Ea) was observed, suggesting chemical adsorption of extract components on the metal surface. The extracts from the castor beans acted as a good corrosion inhibitor, and the macromolecules present in the high molecular weight fraction (HMWF) have a fundamental participation in this process since it presented 93.7% of IE for 200 mg L−1.

The effect of two papaya seed extracts (infusion and acid extracts) on the corrosion of carbon steel in 1 mol L-1 HCl was examined. The efficiency for inhibiting the corrosion of C-steel in 1 mol L-1 HCl increased with the extract concentration and decreased slightly with the temperature. The inhibitory property of the extract is discussed in terms of the mechanism by which its components adsorb onto the C-steel surface decreasing the active surface area. This adsorption process obeyed a Langmuir adsorption isotherm. The infusion extract which presented more phenolic compounds than the acid extract showed higher inhibition efficiency. The apparent activation energy (Ea) for the dissolution of C-steel slightly increased when the infusion extract was used.

The use of industrial painting is one of the methods for corrosion protection of metals and requires a suitable surface treatment on the metallic substrate for better adhesion between metal and paint film. In cases where the substrate presents low thickness (less than 2 mm), the phosphating pretreatment is widely used, despite of such process generates harmful residues to environment and human health. In this context, the sol-gel method has been highlighted as an easy and a cheap process, and less harmful to the environment. This work shows the development of carbon steel AISI 1005 pre-treatment by sol-gel method using niobium and/or aluminium-containing-resins, synthetized by Pechini method. Electrochemical and performance analysis were carried out in samples coated by the resins, which showed analogous behavior to phosphated systems. The proposed pre-treatment has potential for phosphating process replacement, because the morphology of the deposited layers enhanced the metallic contact surface with the organic coating, increasing its mechanical and polar adhesion. Such observation can justify its better anticorrosive performance, comparing to the untreated substrate.

The effect of two papaya seed extracts (infusion and acid extracts) on the corrosion of carbon steel in 1 mol L-1 HCl was examined. The efficiency for inhibiting the corrosion of C-steel in 1 mol L-1 HCl increased with the extract concentration and decreased slightly with the temperature. The inhibitory property of the extract is discussed in terms of the mechanism by which its components adsorb onto the C-steel surface decreasing the active surface area. This adsorption process obeyed a Langmuir adsorption isotherm. The infusion extract which presented more phenolic compounds than the acid extract showed higher inhibition efficiency. The apparent activation energy (Ea) for the dissolution of C-steel slightly increased when the infusion extract was used.

In the present work, two mixed oxides, namely, SiO2/Al2O3/Nb2O5 and SiO2/Al2O3/TiO2 (designated as SiAlNb and SiAlTi, respectively), obtained using the sol–gel method were used to immobilize chloroperoxidase. Hydrogen peroxide was quantified using potassium hexacyanoferrate(II) as a redoxmediator and amperometric measurements at 0.0 V vs. Ag/AgCl/Cl (3 M). The SiAlTi biosensor presented higher sensitivity than the SiAlNb biosensor, however, the first one did not present a good response regarding time. The developed biosensor using the SiAlNb mixed oxide provided good signal levels, good linearity, good stability (retaining approximately 70% of its original response after 6 weeks of usage), a low detection limit (3 цM), good sensitivity, a suitable working range (from 4 to 19 цM), fast response and good repeatability. The recovery of the amperometric method for the detection of hydrogen peroxide in synthetic samples was approximately 100 ±2%, and for Listerine® Whitening Pre- Brush Rinse samples fortified with 1, 2 and 3% (v/v) of hydrogen peroxide, it was 100 ±3%.