H. Herrera-Hernández

Electrochemical Evaluation of Corrosion on Borided and Non-borided Steels Immersed in 1 M HCl Solution

In this study the corrosion resistances of AISI 1018 and AISI 304 borided and non-borided steels were estimated using polarization resistance and electrochemical impedance spectroscopy (EIS) techniques. Boriding of the steel samples was conducted using the powder-pack method at 1223xa0K with 6xa0h of exposure. Structural examinations of the surfaces of the borided steels showed the presence of a Fe2B layer with isolated FeB teeth on the AISI 1018 steel, whereas a compact layer of FeB/Fe2B was formed on the AISI 304 steel. Polarization resistance and EIS of the borided and non-borided steels surfaces were performed in a corrosive solution of 1xa0M HCl. The EIS data were analyzed during 43xa0days of exposure to the acid solution. Impedance curves obtained during this period for the borided and non-borided steels were modeled using equivalent electrical circuits. The results of both electrochemical techniques indicated that boride layers formed at the steel surfaces effectively protect the samples from the corrosive effects of HCl. The main corrosion processes observed on the boride layers were pitting and crevice corrosion.

Electrochemical Impedance Evaluation of Uracil and Thymine Pyrimidine Derivatives and its Nucleosides Compounds as a Non-Toxic Corrosion Inhibitors of Steels in 1M HCl

a Universidad Autonoma Metropolitana-Azcapotzalco, Departamento de Ciencias Basicas, Av. San Pablo 180. CP. 02200, Mexico D. F., Mexico b Universidad Autonoma Metropolitana-Azcapotzalco, Departamento de Materiales, Av. San Pablo 180. CP. 02200, Mexico D. F., Mexico c Universidad Autonoma del Estado de Mexico (UAEM), Centro Universitario Valle de Mexico). Blvd. Universitario S/N, Atizapan de Zaragoza, Mexico, C.P. 54500.

Electrochemical Impedance Spectroscopy Analysis of 2-Mercaptobenzimidazole (2MBI) as Corrosion Inhibitor in HCl 1M

This work presents the results concerning the effect of different concentrations of an organic heterocyclic compound that displays corrosion inhibiting properties, known as 2-mercaptobenzimidazole, 2MBI, in a system comprising samples of the steel type API 5L X52 exposed to HCl 1M. The impedance spectra revealed that there was a continuous increase of |Z| as a function of increasing inhibitor concentrations in the electrolyte. A 200 ppm 2MBI was tested also, however, the greatest corrosion inhibiting efficiency was attained 99%, IE, with much smaller concentrations of the compound. This is sufficient reason to consider it a good corrosion inhibitor in HCl, just as it was effective for H2SO4. Furthermore, the inhibition kinetics study undertaken indicated that the 2MBI added in a fairly large concentration of 200 ppm in 1M HCl maintains its effectivity up to 32 immersion days. Also, it was observed that the corrosion potential, Ecorr, became more negative as the 2MBI organic molecules concentration increased in the system, which suggests that this inhibitor may be acting on the cathodic and anodic sites, thus being considered a mixed type inhibitor, in agreement with the corrosion mixed potential theory.

Electrocrystallization mechanism of iron phosphate coatings onto mild steel electrode surfaces

Samples of mild steel AISI-SAE 1018, 1045 and 1080 were electrochemically phosphatised, both potentiodynamically and potentiostatically, in a concentrated H3PO4 aqueous solution. The conversion coating layers formed were characterised by means of scanning electron microscopy and energy-dispersive x-ray analysis. The kinetics and mechanisms of the electrocrystallization process of FePO4·2H2O(c) films were studied using the potential step technique. It was found that the mechanism governing the formation of FePO4·2H2O(c) anodic film was common for all the steel samples, namely, the overall electrodic process comprises four different simultaneous contributions to the overall current (j(t)). The individual contributions were: jad(t), the current density contribution due to H3PO4 adsorption; jd(t), the current density involved during electrodissolution of iron of the steel electrode in the zones which were not covered yet by the FePO4·2H2O(c) film; jg(t), the current density contribution due to 2D nucleation and growth of an insoluble FePO4·2H2O(c) conducting adlayer; and jf(t), the current due to the growth of the passive layer induced by electrodissolution of iron metal and transport of the resulting Fe(II) ions through the FePO4·2H2O(c) film. However, each stage contributed to the overall process in a different manner, depending upon the carbon contents. The results from voltammetry indicated that it is possible to establish the potential at which the FePO4·2H2O(c) film begins to form and that this was also a function of the carbon contents.

Microwave-Assisted Preparation of 2-(Benzylthio)imidazole and 2-(Benzylthio)benzimidazole and its Comparative Corrosion Inhibiting Performance with 2-Mercaptoimidazole and 2-Mercaptobenzimidazole

In this paper, the anticorrosive performance of four inhibitive organic heterocyclic compounds [2-Mercaptoimidazole (2MI), 2Mercaptobenzimidazole (2MBI), 2-(Benzylthio)imidazole (2BZMI) and 2-(Benzylthio)benzimidazole (2BZMBI)] were investigated using pipeline steel in hydrochloric acid media (1M HCl) and compared using electrochemical impedance spectroscopy, EIS. The last two organic compounds were obtained through non-conventional synthesis using microwaves. As the inhibitors concentration increased from 5-200 ppm, Z’re also increased continuously, thereby suggesting inhibitor adsorption onto the metal surface. Also, all the organic inhibitors studied showed acceptable corrosion inhibiting efficiency, IE, of about 9496% after adding 30 ppm to the acid system. Furthermore, at this concentration the better protection efficiency was attained for the inhibitor 2BZMBI. The four inhibitive organic compounds were classified as mixed inhibitors, in accordance with the corrosion mixed potential theory.