Innovations in Corrosion and Materials Science (Discontinued) - Volume 4, Issue 1, 2014

The influence of hydrogen sulfide environment on corrosion - hydrogen - mechanical damage of structural materials was considered. The main regularities of 20 steel hydrogenation were analyzed. The blistering of 20 steel exposed to NACE solution was studied and duration of the blistering tests was defined. It is shown that loads applied to the hydrogenated metal allow the identification of places of hydrogen induced cracking (HIC) at the structural level. Hydrogen sulfide environment significantly changes the plasticity of structural materials. To establish the pipe steels properties degradation in hydrogen sulfide environments it is worth determining the change in the plastic properties, in particular the relative narrowing (ψ), since this characteristic is more variable and more informative because it assesses the resistance to metal deformation in the most weakened local cross-section, whereas the definition of δ takes into account the behavior of the deformable working part over its entire length.

The electrochemical corrosion properties of bulk nanocrystalline ingot iron (BNII) produced by severe rolling technique and as-received conventional polycrystalline ingot iron (CPII) in.0.1 mol/L H2SO4 + 0.25 mol/L Na2SO4 solution were studied by potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electron microscope at room temperature. The corrosion current density and capacitance of double electrode layer of BNII were one order of magnitude less than those of CPII respectively, the polarization resistance of BNII was one order of magnitude larger than that of CPII. These electrochemical corrosion results demonstrated that the corrosion resistance of BNII was enhanced in comparison with that of CPII in.0.1 mol/L H2SO4 + 0.25 mol/L Na2SO4 solution at room temperature. The enhanced corrosion resistance of BNII was attributed to the differences of valence electron configurations (work function, the density distribution of valence electrons and the binding energies of valence electrons) between BNII and CPII from electrochemical corrosion nature.

This work presents the dose/response functions from linear regression analysis of atmospheric corrosion statistical data from different sites of Mexico. During the last fifteen years atmospheric corrosion characterization was obtained from different sites, and the results were used as a database for statistical analysis and linear regression modelling, obtaining the Atmospheric Corrosion Dose/Response Functions presented here. The contribution of each relevant environment variable for steel, zinc, copper and aluminium atmospheric corrosion, were obtained. The models present good regression, correlation coefficients, depending on the variables considered in the analysis. Also, using experimental data, an example is presented for modelling and obtaining atmospheric corrosion iso-linear maps for different materials in the municipal area of the city of Cuernavaca, Morelos; Mexico for the prediction of atmospheric corrosiveness of sites with unavailable experimental data.

Titanium alloy is commonly used in dental implants as the material for the abutment that connects the crown to the screw drilled into the bone. During mastication, small fretting movements between the abutment and the screw can occur and saliva can enter in to the contact zone, causing fretting-corrosion (tribocorrosion) mechanisms in the abutment. These tribocorrosion mechanisms can lead to weakening and possible failure of the implant. This study will validate the use of a novel apparatus for tribologial studies. To confirm the accuracy of the apparatus, titanium type 5 (Ti6Al4V) alloy discs were polished and placed in a nonconductive basin with artificial saliva as the electrolyte. A potentiostat made by Biologic was used with a three electrode system. Two biomedical applications were considered for the pilot tests, i.e. Dentistry and orthopedics. Artificial saliva at pH of 6.5 and bovine calf serum (BCS) of pH 7.6 were used as electrolyte. The plate then underwent a tribological motion (fretting). Tribocorosion tests were conducted in a free potential mode. Potential and the coefficient of friction were monitored during the test. The tests were performed under loads of 2N and 5N. Electrochemical impedance spectroscopy (EIS) tests were conducted before and after the tribcorrosion tests (at Ecorr, 100 Hz to 0.05 Hz, ± 10mV). The value of the corrosion potential during fretting was within values of other corrosion potentials published by similar studies. This shows that the tribocorrosion apparatus constructed can be used in tribological studies and it can provide accurate electrochemical responses associated with tribological events. The apparatus could be used for different biomedical applications in dentistry and orthopedics.

Nickel is considered to be the primary cause of allergic contact dermatites. As a consequence, there is now a tendency to remove nickel of all manufacts designed to come into direct and prolonged contact with the human skin. However, the peculiar physical and chemical properties of nickel; i.e. very good corrosion resistance, white color and lustrous shining, make its substitution a very challenging task, especially for all the items requiring high aesthetical quality and durability. At present, the most diffused top finishing treatment for jewelry and fashion accessories is the electrodeposition (plating) of a thin layer of nickel alloyed with noble metals such as gold, rhodium and, mainly, palladium over a nickel intermediate layer. The presence of precious metals on the top layer creates the required aesthetical characteristics and, more importantly the Ni-content available for leaching results reduced. However, these solutions do not solve the problem since nickel is still present. In the long run, even these applications will have to be substituted with properly Ni-free technologies. The aim of this work is to characterize the corrosion resistance of Ni-free coatings constituted of a bronze intermediate layer and Pd/In and Pd/Fe top-coatings. The corrosion resistance of these systems was evaluated by means of electrochemical techniques, i.e. electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves (PD). The results evidenced corrosion resistance of these coatings similar to those of the traditional Ni-bearing ones. Finally, comparative free corrosion tests were carried out in neutral saline environment and artificial sweat solution in order to evidence the capability of the new Pd/Fe and Pd/In coating to constitute an aesthetically valuable “Ni-free” technology suitable for jewelry and fashion applications. The results showed that these new coatings have promising characteristics.

Changing of electrical properties during the manufacturing of the diffusion-junction and implanted-junction rectifiers in a heterostructure with porous epitaxial layer was considered. It was shown that, in spite of the inhomogeneity of the heterostructure, it is possible under specific conditions to increase the sharpness of diffusion-junction and implanted-junction rectifiers and at the same time to increase homogeneity of distribution of dopant concentration in doped area. It was shown that the porosity of epitaxial layer of heterostructure and the use of microwave annealing give the possibility to increase the two above effects. The influence of the variations of dopant concentrations upon electrical properties of p-n junction was also discussed by introducing an analytical approach to the model of mass transport.

A dynamic study was carried out using a fabricated stainless steel (SS-316) flow-through system. Biofilm (slime) formation and metallic corrosion are conventionally evaluated as separate, independent processes, however, in the present study both were monitored simultaneously. Relevant biofilm parameters were analysed and different types of bacterial population were assayed. In addition, scanning electron microscopy (SEM), EDAX and XRD techniques were used in the evaluation of the corroded specimen. After 165 days of operation, the SS-316 pipe developed leaks due to pipe punctures. Microbiological investigations substantiated the presence of iron bacteria, sulphate reducing and heterotrophic bacteria. Bacterial growth and biofilm formation at 45°C were negligible. SEM images showed many minor pits on the surface along with encrusted filamentous bacteria. Chemical analysis by XRD showed the presence of calcium, sulphur, silica, along with iron sulphide, iron carbonate and calcium carbonate. Based on the putative presence of corrosion causing bacteria and the detection of biologically mediated corrosion products by XRD analysis, it was concluded that the SS-316 tube failed due to microbiologically influenced corrosion (MIC).