In this work, liquid plasma spraying is used to deposit composite coatings for potential use as cathodes in intermediate-temperature solid oxide fuel cells. A suspension containing well-distributed Gd-doped ceria (GDC) nanoparticles in a lanthanum strontium cobalt ferrite precursor solution was used as the feedstock, and GDC concentration was varied to study its effect on phase composition, microstructure, surface morphology, and electrochemical performance. The results are presented and discussed.

Thermally sprayed aluminum (TSA) has been used to protect offshore structures for many years at ambient temperatures. However, the melting point of aluminum, and the limited corrosion rate data indicate that they are likely to perform well in high temperature seawater as they tend to form calcareous deposits. Nonetheless, not much is known regarding the protection mechanism offered by TSA at elevated temperatures. This paper reports micro-scale surface characterization data on damaged TSA-coated carbon steel exposed to boiling synthetic seawater. The corrosion rate, calculated using linear polarization resistance (LPR) technique of TSA was ~10µm/year. This is very similar to the TSA corrosion rate observed at room temperature. The formation of a calcareous deposit which covers the exposed steel seems to reduce the corrosion rate. Detailed microstructural characterization of the calcareous was also carried out and the kinetic information regarding the rate of formation of calcareous deposits is also presented.

Corrosion rate determination is often based on linear polarization (LPR) technique, carried out on small specimens in a controlled environment. The current is measured when the specimen is polarized away from its corrosion potential and the corrosion current gives the corrosion rate using Faraday's law. An important parameter in this calculation is the specimen area exposed. When testing rough, porous specimens such as thermally sprayed aluminum (TSA), the geometrical surface area does not represent the real surface area and hence the corrosion rate is not the actual corrosion rate. To measure the actual corrosion rate aluminum was thermally sprayed onto glass and the surface was characterized using a confocal microscope. These specimens were exposed to seawater at 25, 50 and 100°C, and the linear polarization resistance was determined using a potentiostat at room temperature. This was converted to a corrosion rate based on geometric and the actual surface area.

Atmospheric plasma spraying is attractive for manufacturing solid oxide fuel cells (SOFCs) because it allows functional layers to be built rapidly with controlled microstructures. The technique allows SOFCs that operate at low temperatures (500 to 700 °C) to be fabricated by spraying directly onto metallic supports. However, standard cathode materials used in SOFCs have high polarization resistance at low temperatures, necessitating alternative materials. In this study, coatings of lanthanum strontium cobalt ferrite (LSCF) were fabricated on steel substrates using axial-injection atmospheric plasma spraying. Coating thickness and microstructure were evaluated and X-ray diffraction (XRD) analysis was performed to detect material decomposition and the formation of undesired phases in the plasma. The results define the envelope of plasma spray parameters for depositing LSCF coatings and the conditions in which composite cathode coatings can be produced.

Twin wire arc sprayed Zn, Al and Zn/Al 85/15 coatings were investigated for comparison of their corrosion resistance, electrochemical behavior. The Zn, Al and Zn/Al 85/15 coatings possess prominent electrochemical passivation behavior. Oxide formation mainly onto the coating surfaces were identified with energy-dispersive X-ray analysis and were believed to be responsible for the passivation phenomena observed in the electrochemical polarization. Zn and Al are more negative in electrochemical potential than iron. Zn coatings act as a sacrificial anode and providing cathodic protection. Aluminum shows passive corrosion protection according to stable oxide layer occurs on coating surface. Zn/Al 85/15 coating show two corrosion protection mechanisms together. In this study, steel samples were coated with Zn, Al and Zn/Al 85/15 in optimum conditions by wire arc spraying technique. These coatings were investigated behaviors of polarization and corrosion resistance with electrochemical test.

For electrical or thermal insulation, the porosity of an air plasma sprayed (APS) coating is an important property to control. Moreover in aggressive environment the interconnected porosity is responsible for the substrate corrosion. To solve, at least partially, this problem, deposition by mutitechniques (APS and a PECVD) was used to close interconnected and opened porosities. In this study, titanium alloy (TA6V) substrates were coated by alumina using either one or both deposition processes. Electrochemical characterization technique was used to evaluate the open porosity in alumina coatings. It consists of evaluating the polarization resistance of the reference sample surface (uncoated substrate) and to compare it to coated ones. After different tests for selecting the electrolyte solution, the influences of different parameters (thickness and relative position) of each deposition process on coating porosity were examined.

Thermal spray coatings as Cr 3 C 2 -NiCr obtained by high velocity oxy-fuel spraying (HVOF) are mainly applied due to their behaviour against aggressive erosive-abrasive and corrosive atmospheres and their thermal stability at high temperatures. In order to increase the corrosion protection that it offers to the substrate trying to close the interconnected pores, it is possible to apply a thermal treatment with the gun during the spraying of the coating. This treatment could be applied in different ways. One of these ways consists of spraying only a few layers of coating followed by thermal treatment and finally the spray of the rest of layers. This thermal treatment on spraying is studied related to the corrosion properties of the system. The study comprises the electrochemical characterisation of the system by open circuit potential (OC), polarisation resistance (R p ), cyclic voltammetry (CV) and impedance spectroscopy measurements (EIS). Optical and scanning electron microscopy characterisation (OM and SEM) of the top and cross-section of the system has been used in order to justify the electrochemical results.

This paper presents the electrochemical characterization of a chromium carbide-NiCr coating applied using high-speed flame spraying. It examines the behavior of the complete system, the steel, the steel coating, and the coating immersed in NaCl solution alone. The paper discusses electrochemical measurement methods such as the measurement of polarization resistance, anodic polarization, and open circuit potential. The tests are compared with each other and with results from metallographic examinations. The structure was characterized by light and scanning microscopy. In addition, an analysis of the residual water was carried out using an ICP technique. The paper also includes a study of the various mechanisms that could affect the behavior of such coating types in a corrosive environment. Paper includes a German-language abstract.