Anti-Corrosion Methods and Materials

The effect of heat treatment on element distribution and electrochemical properties of Al-Zn-In anodes : Table of Contents

Qi Gongtai, Qiu Yubin — Sat Nov 14 08:00:19 GMT 2009

Abstract:
Purpose – The purpose of this paper is to consider the effect of heat treatment on alloying element distribution and the electrochemical properties of Al-5Zn-0.03In anodes. Design/methodology/approach – The Al-5Zn-0.03In alloy anodes are treated at 510°C for 10?h, then cooled in water. Electron probe microanalysis of JXA-8800 and EDAX quantitative energy dispersive X-ray analysis is used to examine the microstructure of the anodes before and after heat treatment, and the electrochemical properties of the anodes are tested. Findings – By heat treatment, the solubility of Zn in aluminum is increased while the solubilities of Fe and Si are changed only slightly. The quantity of the Al-Zn intermetallic compounds is evidently decreased and the Al-Fe-Si intermetallic compound is preserved. Strip segregation along grain boundaries is changed to spherical particulates. The attack of aluminum anodes initiates and propagates in grain boundaries and interdendritic zones, which are enriched in In and Zn, so the current efficiency of the aluminum anodes is related to the degree of corrosion taking place at grain boundaries and the extent of exfoliation of grains. The greater the extent of Al-Zn metallic compounds that are present at grain boundaries, the more sensitive to grain boundary corrosion is the alloy and the greater the degree of desquamation of grains, the lower is the current efficiency of the aluminum anode. Originality/value – The results of this paper clarify the role of water-quenching affect on the microstructure and electrochemical properties of Al-Zn-In anodes.

The determination and identification of stray current source influences on buried pipelines using time/frequency analysis : Table of Contents

Krzysztof Zakowski — Sat Nov 14 08:00:19 GMT 2009

Abstract:
Purpose – The purpose of this paper is to detect the source of stray current interference on underground pipelines in urban areas using a joint time/frequency method of signal analysis. Design/methodology/approach – Investigations are performed on an underground pipeline located in the vicinity of the two direct current tractions: a tramway line and a train line. The results of the analysis are presented in the form of spectrograms, which illustrate changes in the spectral power density of the potential of the rails and of the potential of the pipe in the joint domain time-frequency. Findings – The comparison of the spectrograms can be used to evaluate if and which stray current source has influence on the investigated metal construction. Originality/value – The combined analysis in the domain of time and frequency can be used as a supplementary one providing new information useful in the evaluation of stray current corrosion hazard. In the presence of several electric field sources in urban areas, this method reveals the complete time-frequency characteristic of each stray current source and its interference on the investigated construction.

Effect of localized corrosion on the galvanic corrosion of nitinol and dental alloys : Table of Contents

Abdollah Afshar, Mohsen Shirazi, Masoud Rahman, Esmaeil Fakheri — Sat Nov 14 08:00:19 GMT 2009

Abstract:
Purpose – The purpose of this paper is to evaluate the galvanic corrosion of nitinol orthodontic wires with six dental alloys in artificial saliva and consider the effect of initiated localized corrosion and real surfaces of anode and cathode on galvanic current. Design/methodology/approach – Linear polarization and cyclic polarization curves for each alloy in de-aerated Duffo and Castillo's artificial saliva are obtained. Galvanic corrosion investigation is conducted by polarization curve intersection and mixed potential theory methods. In order to verify the initiation of localized corrosion, scanning electron microscopy is used. Findings – Initiation of localized corrosion on the anode increases the galvanic current up to 45 times and therefore considering the effect of localized corrosion on galvanic corrosion is necessary. Placing stainless steel brackets or Aristaloy amalgam in direct contact to nitinol arch wire is not recommended. Originality/value – In order not to underestimate the galvanic corrosion between two alloys, it is recommended to consider the effects of localized corrosion and anode/cathode surface area ratio. In this paper, an electrochemical method for estimating these factors is proposed.

Synergistic effect of chloride and NO2 on the atmospheric corrosion of bronze : Table of Contents

Xia Cao, Ning Wang, Ning Liu — Sat Nov 14 08:00:19 GMT 2009

Abstract:
Purpose – The purpose of this paper is to investigate the effect of chloride along with NO2 on the atmospheric corrosion of bronze using exposure tests. Design/methodology/approach – Surface tension tests and electrochemical impedance measurements together with scanning electron microscopy (SEM) with energy dispersive atomic X-ray, and X-ray diffraction are used to characterize the corrosion behavior. Findings – The results of the weight loss measurements show that the whole corrosion kinetics can be described approximately by: ?W=atb; the synergistic effect of chloride and NO2 is observed clearly, though no nitrate existed in the corrosion products. Originality/value – A new catalyst theory has been suggested in this paper, i.e. that NO2 acts as a catalyst during the corrosion process when significant quantities of chloride also are present.

In field electrochemical evaluation of carbon steel corrosion in a marine test environment : Table of Contents

Ya Nan Luo, Shi Zhe Song, Wei Xian Jin, Lei Han — Sat Nov 14 08:00:19 GMT 2009

Abstract:
Purpose – The purpose of this paper is to research electrochemical testing technology as applied to in field corrosion evaluation of metallic materials and to study the corrosion behaviors of the materials exposed in different marine regions. Design/methodology/approach – The electrode systems for in field electrochemical evaluation of metallic samples are designed and applied to monitor two types of carbon steel samples exposed both in the submerged zone and the tidal zone at a marine corrosion test station. Corrosion potential monitoring, potentiostatic square wave, electrochemical impedance spectroscopy, and electrochemical noise methods are used in the test. Findings – It is confirmed that the electrode systems could be used for electrochemical measurement of metallic samples during exposure in the submerged zone and the tidal zone of a marine corrosion test station for long-term test durations. The electrochemical measuring results reflect the changes and differences of the samples' corrosion behavior during exposure in different regions and they respond directly to the influence of marine environmental factors on the corrosion behaviors, especially the influence of temperature. Originality/value – In this paper, lots of consecutive and dynamic corrosion information is obtained from field exposures. The findings provide a foundation upon which to investigate and forecast the corrosion behaviors of materials in marine environments.

Hybrid corrosion-resistant coatings analyzed using electrochemical noise : Table of Contents

Sat Nov 14 08:00:19 GMT 2009

Abstract:
Purpose – The purpose of this paper is to study the corrosion of carbon steel without coating and when protected using three different hybrid coatings, i.e. a bi-component polyurethane with nano-particles of SiO2 with and without sacrificial anode particles, and a mono-component polyurethane with SiO2 particles. Design/methodology/approach – In this investigation three different nano-structured coatings are developed and applied to steel substrates and then tested for their corrosion resistance (defined as “Rn”), under a very aggressive medium (pH=1.5) in a dynamic system (loop reactor). Their performance is evaluated using an electrochemical noise (EN) resistance technique. The electrodes are connected to a potentiostat and measurements are recorded as per the EN technique over a 2,048?s duration at 0, 24, and 48?h intervals. Scanning electron microscopy (SEM) are obtained before and after the corrosion trials to characterize the control and the different coating systems. Findings – The results show that a bicomponent coating, made up of alkyd resin and silica nanoparticles demonstrated the best performance, whereas the coating formed by SiO2 nanoparticles and polyurethane resin showed relatively low corrosion resistance. The inclusion of zinc nanoparticles in a third coating as sacrificial nano-anodes led to segregation and resulted in moderate corrosion resistance. These results are confirmed by SEM observations. Originality/value – The results obtained in this paper provide an insight to the understanding of the anticorrosion properties of three different hybrid coatings in a dynamic system (loop reactor).