Articles written in Bulletin of Materials Science

• Influence of electrodeposition parameters on the characteristics of Mn–Co coatings on Crofer 22 APU ferritic stainless steel

Manganese–cobalt coatings are promising candidates for solid oxide fuel cell (SOFC) interconnection applications because of their high conductivity and good oxidation resistance. In the present study, manganese and cobalt are electrodeposited onCrofer 22APU ferritic stainless steel. The effects of current density, pH, sodium gluconate (NaC$_6$H$_{11}$O$_7$)concentration, cobalt sulphate concentration (CoSO$_4$·7H$_2$O) and deposition duration on the microstructure and cathodic efficiency are characterized by means of scanning electron microscopy, weight gain measurements and energy-dispersive X-ray spectrometry, respectively. Results show that increases in current density and deposition duration lead to decrease in current efficiency and deposition rate. Increasing the pH to 2.5 causes an initial rise of current efficiency and depositionrate, followed by subsequent decline. In addition, the increases in sodium gluconate and cobalt sulphate concentrations inthe electrolyte solution result in an increase in current efficiency and deposition rate. Moreover, the results demonstratethat the variations in the current density, pH, sodium gluconate (NaC$_6$H$_{11}$O$_7$) concentration, cobalt sulphate concentration (CoSO$_4$·7H$_2$O) and duration have a significant effect on grain size, uniformity and the adherence of the coating.

• Cyclic oxidation of Ni–Fe$_2$O$_3$ composite coating electrodeposited on AISI 304 stainless steel

Protective coatings can be applied to enhance the performance of interconnects in solid oxide fuel cells. In this study, AISI 304 steel was coated with a Ni–Fe$_2$O$_3$ composite to form a modified-Watt’s type electrolyte by the conventional electro co-deposition method. The characterization of the coatings before and after cyclic oxidation was performed by scanning electron microscopy and X-ray diffraction. In order to evaluate the oxidation behaviour, thermal cycling was carried out in a furnace at 850$^{\circ}$C. The results indicated that the coated steel had better oxidation resistance in comparison with the uncoated steel. After 60 cycles of oxidation, the Ni–Fe$_2$O$_3$ composite coating was converted to FeNi$_2$O$_4$, NiCrO$_4$, MnFe$_2$O$_4$ and Fe$_2$NiO$_4$. The Fe$_2$O$_3$/NiFe$_2$O$_4$ composite coating reduced the outward migration of chromium and the growth rate ofthe Cr$_2$O$_3$ layer.

• Effect of titanium oxide ceramic particles concentration on microstructure and corrosion behaviour of Ni–P–Al$_2$O$_3$–TiO$_2$ composite coating

Composite coatings are coatings that have been considered in terms of properties, such as corrosion resistance, oxidation resistance and excellent hardness. In this study, Ni–P–Al$_2$O$_3$–TiO$_2$ composite coating was made on AISI 316 steel using direct current deposition technique. The microstructure of the coating and its corrosion resistance were studied bychanging the amount of titanium oxide (1, 2, 3 and 4 g l$^{−1}$) in the bath. To investigate the morphology of the coating and the analysis of the coated material, a scanning electron microscope (SEM) and EDS microscopy were conducted, respectively. The results showed that in the bath containing 4 g l$^{−1}$ titanium oxide, the coating is perfectly uniform and continuous, while by reducing the amount of titanium oxide, it is not possible to form a suitable coating on the entire surface of the substrate. To investigate the corrosion resistance, the potentiodynamic polarization and electrochemical impedance spectroscopy testsin aqueous solution of 3.5% NaCl were carried out on coated and uncoated samples. The results of these tests were also correlated with microscopic images and showed that the coatings in a bath containing 4 g l$^{−1}$ titanium oxide has the highest corrosion resistance.

• Investigation of oxidation behaviour of AISI-430 steel interconnects in the presence of Ni–Co–CeO$_2$ composite coating for application of solid oxide fuel cells

AISI 430 stainless steels are used as interconnects in solid oxide fuel cells. One of the problems with these steels is the migration of chromium through the chrome shell and its transfer to the cathode, resulting in contamination andreduction in the efficiency of the fuel cells. To improve the oxidation resistance of these steels, a protective coating layer can be applied on the steel surface. In this investigation, AISI 430 stainless steel was electroplated with nickel, cobalt and cerium oxide. To investigate oxidation behaviour, isothermal oxidation and cyclic oxidation were performed at 800$^{\circ}$C. The coating on the steel surface was studied using scanning electron microscopy and X-ray diffraction. In isothermal and cyclic tests, the coated samples showed less weight gain than the uncoated samples due to the formation of NiFe$_2$O$_4$, CoFe$_2$O$_4$ spinels and NiCr$_2$O$_4$. These spinels prevented the outward diffusion of the chromium, improving the oxidation resistance of the steel substrate. Cyclical oxidation results showed that the coating formed on the steel surface resistedcracking and delamination.

• # Bulletin of Materials Science

Volume 44, 2021
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020