Papers by Keyword: Corrosion

Abstract: There is an intensive construction of sewage collectors in the cities. The main structural material used in the construction of collector tunnels is reinforced concrete. Services engaged in the operation of sewage systems, increasingly began to face the destruction of concrete of non-pressure sewer collectors as a result of gas corrosion. Concrete corrosion takes place only in non-pressure manifolds, in the protruding part of the water pipeline or tunnel. The maximum intensity of corrosion is observed in the area, adjacent to the axis of the arch. Сorrosion damage can occur intensively on the walls and in the zone of variable water level. The article analyzes the causes leading to corrosion of reinforced concrete in tunnels.

Abstract: Zn-Mg alloys containing up to 5.28 wt.%Mg were prepared by gravity casting. Light and scanning electron microscopy with energy-dispersive X-ray spectrometry were used to characterize their as-cast microstructure as compared to that of pure zinc. The alloy with 3.60 wt.%Mg was found to be eutectic. Phase identification by X-ray diffractometry suggested that the eutectic Mg-rich phase wasMg₂Zn₁₁ with two types of intermetallic compounds, including Mg₂Zn₁₁ and MgZn₂, present in the alloy with 5.28 wt.%Mg. The microhardness increased with increasing Mg content from 41 HV for pure zinc to 266 HV for the alloy with 5.28 wt.%Mg. The electrochemical behavior of the alloys was studied by potentiodynamic polarization test at room temperature using 8.5 M KOH solution as electrolyte. Hydrogen evolution was generally postponed for the cases of Zn-Mg alloys as compared to pure zinc. The corrosion potential (E_corr) was not significantly affected by Mg addition into Zn, while the corrosion current density (i_corr) was significantly increased, especially for the case of the alloy with 3.60 wt.%Mg, as compared to that of pure zinc. It can be proposed that, due to its relatively higher hydrogen overpotential and uniform corrosion in KOH solution, the eutectic alloy with 3.60 wt.%Mg can be an alternative to pure zinc for use as anode in applications related to alkaline electrolyte.

Abstract: The effects of destabilisation and tempering heat treatments on hardness and corrosion behavior in 28 wt.%Cr-2.6 wt.%C cast irons with up to 6 wt.%Mo addition were studied. The irons were destabilised at 1025 °C for 4 h and air cooled. Tempering was carried out at 450 °C for 4 h. Phase identification and microstructure were investigated by X-ray diffraction (XRD), light microscope (LM), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Vickers macro-hardness was measured. A potentiodynamic technique was used to indicate aqueous corrosion resistance. The results revealed that the as-cast microstructure of 28 wt.%Cr iron consisted of primary austenite dendrites with eutectic M₇C₃ carbides. In the irons with 6 wt.%Mo addition, eutectic carbides including M₇C₃, M₂₃C₆ and M₆C were found. After destabilisation, the microstructure contained secondary carbide precipitates within an essentially martensitic matrix. Vickers macro-hardness of the as-cast and destabilised irons increased from 500 HV30 and 736 HV30 in the 28 wt.%Cr iron up to 570 HV30 and 870 HV30 in the iron with 6 wt.%Mo addition. Tempering slightly increased the macro-hardness. The as-cast 28 wt.%Cr iron had the lowest values for critical current density and passive current density. The destabilised + tempered treatment gave the lowest corrosion resistance.

Abstract: Composite coatings have been obtained by plasma electrolytic oxidation method and subsequent treatment with fluorine-containing compound: suspension of superdispersed polytetrafluoroethylene. A method of formation of the protective coating by dipping into the suspension of organofluorine compound with subsequent heat treatment has been developed. The surface morphology of samples, their electrochemical and tribological properties, as well as wettability have been studied. Formed composite coatings reduce the corrosion current density and wear more than two orders of magnitude in comparison with the base PEO-coating. Additionally, composite layers have hydrophobic properties: for polymer-containing coatings the value of contact angle attains to 143±2°.

Abstract: Pre-sintering for removal of lubricants is one of the most important steps in processing of powder metallurgy materials to achieve corrosion resistance. This is often the most neglected step in the sintering process. Incomplete removal of these organic compounds may result in sensitization of sintered parts. The aim of this study is to investigate the effect of lubricant removal process on the corrosion resistance of sintered AISI 304 L stainless steel filters. Pre-sintering was carried out at 450° C and sintering at 1150° C. As lubricant, 1% wax was used. The corrosion resistance of sintered samples was evaluated by polarization and tests, optical and scanning electron microscopy. The results showed that lubricant removal was not complete and during sintering sensitization of the stainless steel occurred decreasing the localized corrosion resistance of the stainless steel.

Abstract: Several beta titanium alloys are finding ever-increasing applications in biomaterials, due to the combination of its mechanical properties including low elasticity modulus, high strength, fatigue resistance and good ductility with improved corrosion resistance. In this regard, a new beta titanium Ti-12Mo-8Nb alloy was developed as an alternative to the traditional alloy Ti-6Al-4V. Studies have shown that the release of vanadium (V) and aluminum (Al) ions in the human body may cause cytotoxic effects and neurological disorders, respectively. Additionally, this new alloy presented higher ratio of hardness to elastic modulus, as compared to the commercial Ti-6Al-4V alloy. This paper presents the electrochemical behavior and mechanical properties of the Ti-12Mo-8Nb heat treated at 950 oC for 1h under high vacuum and then water quenched. The electrochemical behavior was carried through potentiodynamic polarization curves using Ringer's solution to simulate the body fluid. The Ti-12Mo-8Nb alloy presented a microstructure consisting of β phase with good mechanical properties and a passive layer was formed.

Abstract: The purpose of this paper was to investigate the effect of Al₂O₃ and TiO₂ nanoparticles contents on structural proporties, microhardness and corrosion resistance of Zn-Ni alloy coationg. Zn-Ni, Zn-Ni-Al₂O₃ and Zn-Ni-TiO₂ composite coatings were electrodeposited on steel substrate by direct current in sulphate bath.The structure of the coatings was studied by X-ray diffration and by scaning electron miroscopy. The results showed the appearance of Ni₅Zn₂₁ phases and that the incrorporation of Al₂O₃ and TiO₂ in the Zn-Ni coating refined the crystal grain size.The corrosion performance of coating in the 0.6M NaCl as a corrisive solution was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy EIS methods. It was found that the incorporation of nanoparticules in Zn-Ni alloy coating have better corrosion resistance and the values of Rct and Zw increase, while the values of Cdl decrease with increasing of nanoparticules.

Abstract: In this study graphene coatings were deposited on mild steel substrate using feasible and environmental friendly method. The successful synthesis of graphite oxide was carried by the modified Hummer’s method. Graphene oxide (GO) coatings were developed from GO/water suspension using electrophoretic deposition (EPD). The EPD parameters voltage and deposition time were varied to deposit uniform adherent coatings. The coatings were post heat treated at 200 °C in vacuum for 4h to assess the effect on coated samples. GO and GO-EPD coating morphology were characterized using Fourier transform infrared spectroscopy (FTIR), Atomic force microscopy (AFM) and Scanning electron microscopy (SEM). Linear polarization (LPR) and electrochemical impedance spectroscopy (EIS) tests were performed in saline solution to evaluate electrochemical response. Coatings were partially reduced due to removal of oxygen containing functional groups during EPD and post heat treatments. The GO post heat treated coating had better corrosion resistance ~2 times than that of bare mild steel and higher charge transfer resistance.

Abstract: It is the function of concrete cover to protect reinforcement against corrosion from environmental attack. However, reinforced concrete structures in most cases suffer from corrosion of steel reinforcement and their service lives will be reduced. The steel in concrete is always prone to corrosion attack, and the reason being that concrete cover is porous in nature. Fluids and dissolved ions can impregnate through pore space or through cracks and come in contact with reinforcement. Preventive maintenance is the best corrosion control mitigation measure for reinforced concrete structures. This paper highlights the causes of corrosion in non-coastal areas like Kigali in Rwanda. Condition assessment of two reinforced concrete buildings in Kigali has been made based on structural survey. It was found that Crack width varies up to 2mm in column and beams. It is also suggested that to improve the life span of the columns and beams by retrofitting with advanced materials and the new structures are to be constructed with corrosion monitoring systems.

Abstract: The corrosion characteristics of 316SS and 304SS in subcritical and supercritical aqueous systems including chloride of approximate 4600 mg/L at 25 MPa and 250 °C, 350 °C, 425 °C, and 520 °C are comparatively investigated. Some local corrosion areas occurred on the surfaces of SS316, not on that of 304SS, at 250 °C and 425 °C, while at 350 °C, all the sample surfaces were covered by large amounts of corrosion products and clay materials due to the predominant precipitation for the formation of the outer subscale. Whether in reducing subcritical and supercritical industrial sludge suspension or in oxidizing supercritical sludge system, 304SS owns better corrosion resistance than 316SS due to higher chromium concentration of former.