Papers by Keyword: Corrosion

Abstract: Bioleaching and biocorrosion are based on similar biochemical processes. Microbe-surface interaction, biofilm formation and concomitant extracellular polymeric substance (EPS) production gained increasing interest in the past decades. Nowadays it is generally accepted that biofilm formation and an accompanying formation of manganese oxides by manganese oxidizing bacteria such as Leptothrix spp. account for one type of pitting corrosion of stainless steel (SS). However, little is known about biofilm formation, EPS composition of manganese oxidizing microorganisms and their influence on microbiologically influenced corrosion. Consequently, we studied biofilm formation of Leptothrix discophora, the biooxidation of manganese in biofilms on floating filters as well as biofilm formation on stainless steel and the involved corrosion processes. Cells were visualized by epifluorescence (EFM) or confocal laser scanning –microscopy (CLSM). Additionally, the influence of biofilm formation and biooxidation of manganese by L. discophora on the open circuit potential (OCP) and pitting potential (E_pit) of stainless steel was measured using a 3 electrode setup. L. discophora grew well in biofilms on floating filters and on SS coupons and incorporated in both conditions Mn²⁺ in the form of MnO₂ from the bulk phase into the biofilm. OCP measurements of actively manganese-oxidizing biofilms on stainless steel showed a significant ennoblement of ≥200 mV.

Abstract: In this paper, 6 mm thickness dissimilar aluminium alloys of 5083 (H321) and 2219 (O) butt joints were fabricated successfully by friction stir welding process. The quality joints were obtained for the welding parameters of 35 mm/min and 650 rpm with the shoulder diameter to pin diameter ratio as 3. Macrostructure study shows that the interface between the weld nugget and TMAZ is smooth and clear with a flow arm extending towards the top surface of the weld in the 2219 side. The boundary on the 5083 side between the weld nugget and the TMAZ was irregular. The obtained joint efficiency is around 92.57% based on the UTS of the softer material (AA2219). The tensile test results showed that the specimens failed in the heat affected zone of the softer base material 2219. The hardness values in the stirred zone are higher than the softer base material of alloy 2219. The friction stir welded dissimilar joint 2219-5083 exhibited better general corrosion characteristics than the 2219-2219 weld and 2219 base material.

Abstract: Al6061 has immense use in manufacture of several internal combustion engine parts as well. However the internal parts of an IC engine manufactured using Al6061 are susceptible to corrosion. Water may condense on the cylinder walls or move across the piston rings owing to blow-by and thus be admitted into the crankcase. This usually occurs in cold environment or short duration drive since pertaining to these conditions the engine may still be not hot enough to get rid of this water by evaporation. Upon amalgamation of this condensed water with the sulphur present in considerable quantities especially in low-grade fuels, sulphuric acid is formed thereby leading to a localized corrosion enhancing corrosive environment. In this work, TiO₂ and Inconel 718 are plasma sprayed on Al6061 specimen and their ability to protect against corrosion is studied and observed that the corrosion resistance of specimen coated with TiO₂ has improved by a considerable margin.

Abstract: In the present study, the corrosion behaviour of the Al2219, Boron carbide and Graphite has been investigated. The Aluminium Metal Matrix Hybrid Composites were fabricated by two step stir casting technique. Corrosion tests were carried out with the natural sea water (3.5 wt % NaCl) according to standard procedure. The tests were conducted at room temperature by cyclic polarization technique for a definite time interval. After the test, material loss was calculated by weight loss method. The surface morphology of the specimen before and after corrosion was studied using the optical microscope images. The test result reviles that, the corrosion rate of the composite was greater than the base alloy, but the corrosion of the hybrid composite is the most compared to the alloy and monolithic composite.

Abstract: A new FeMnSi metallic alloy is proposed as biodegradable material with applications in medical field. The corrosion behavior in simulated body fluids is evaluated after immersion for 14 days. The metallic biodegradable material surface was analyzed with a SEM (2 and 3D)+EDAX equipment. The effects of the solution on the metallic surface present an area with pitting corrosions, marks around 10 µm in depth, and a different one with new chemical compounds form from biological solution with good stability on the surface. Even if is a new biodegradable material based on iron simmilar results about the surface behavior were obtain by other researchers on different FeMnSi chemical compositions.

Abstract: Surface modification of magnesium alloys by plasma electrolytic oxidation (PEO) and subsequent treatment with suspension of superdispersed polytetrafluoroethylene and tetrafluoroethylene telomeric solution are presented. Electrochemical, mechanical properties and wettability of obtained composite coatings were investigated. The polymer-containing coatings decrease the corrosion current and wear by orders of magnitude as compared to unprotected magnesium alloy and base PEO-coatings.

Abstract: Investigation results of the composite coatings obtained on MA8 magnesium alloy by plasma electrolytic oxidation (PEO) and post-treated by electrophoretic deposition of superdispersed polytetrafluoroethylene (SPTFE) are presented. Comprehensive research of electrochemical and mechanical properties of the obtained polymer-containing coatings on the magnesium alloy has been performed. It has been established that composite coatings to decrease the corrosion current density by three orders of magnitude (down to I_c = 2.0×10^-10 A/cm²) and the wear by two orders of magnitude (down to 1.2×10^-6 mm³/(N·m)), as compared to the basic PEO-coating.

Abstract: Most metallic constructions and equipment which come in contact with petroleum products are made of steel and are exploited at ambient temperature which can range between −50°C and +50°C in different regions of our planet. When metals and alloys are in contact with pure hydrocarbons (C_nH_m), they do not react with them. However, rust or different types of depositions can be observed in tanks and pipelines containing gasoline, naphtha, and gas oil. The complex phenomenon of contamination is described in this paper in order to demonstrate its importance, as the number of failures of steel components is growing every year. It is important to understand that the corrosion process proceeds at the interface of different phases. Water, H₂S, corrosion products, ions, phenols, organic acids, and other organic sulphur-, oxygen- and nitrogen-containing compounds dissolved in petroleum products are the contaminants that are responsible for the further destruction of the steel components.

Abstract: The purpose of this research is to investigate the corrosion rate of low carbon steel in saline environment. The influence of variety of conditions that represent the actual conditions in practice such as the flow velocity and solution composition, particularly Na+, Cl^- and SO₄^-2, content were performed. Weight loss test of low carbon steel in the lab was conducted to determine the corrosion rate data in stagnant and flowing seawater for comparison to investigate the effect of flow velocity of sea water on the corrosion behavior of the low carbon steel. Results show that the corrosion rate of low carbon steel is increased by increasing the flow of seawater, but at very high velocities the corrosion rate was recorded to be decreased. XRD results show that the corrosion products contain both Fe₂O₃ and FeO(OH).

Abstract: Copper-nickel alloys have been used in many applications in marine environments because of excellent corrosion and biofouling resistance. . This investigation is cover a review of many previous studies about the behavior of these alloys in marine environments with different environmental conditions including the effect of sulphur contamination, the effect of CO₂, the effect of chlorine, the effect of flow velocity, the effect of temperature and the effect of adding some alloying elements to the alloy itself. There have been conflicting results in the past about the corrosion rate values and the chemical analysis of the corrosion films in different environmental conditions. More research is needed for studying the behavior of these alloys in marine environments to provide good assessment of the corrosion resisting characteristics.