Iranian Journal of Materials Science and Engineering

Electrochemical Properties for BaSr1-xGdxCo2O5+δ and Ba0.5Sr0.5-xGdxCoO3-δ as a Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

Sara Tafaroji

The structural and electrochemical properties of Gd-doped perovskite oxides were investigated to improve the performance of solid oxide fuel cell (SOFC) cathodes. Ba_0.5Sr_0.5-xGd_xCoO_3-δ and BaSr_1-xGd_xCo₂O_5+δ (BSGC) compounds were synthesized via a sol–gel thermolysis method to elucidate the effects of Gd incorporation on crystal structure, microstructure, and electrochemical activity. X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirmed the coexistence of simple and double perovskite phases, with Gd substitution leading to finer grains (down to 0.4 ± 0.14 μm) and improved phase homogeneity. Area-specific resistance (ASR) and conductivity measurements revealed a strong structure–performance relationship. The optimal composition, Ba_0.5Sr_0.3Gd_0.2CoO_3-δ, exhibited an exceptionally low ASR of 0.12 Ω cm² at 700 °C which further decreased to a minimum of 0.04 Ω cm² at 850 °C, significantly outperforming GdBaCo₂O_5+δ (GBCO), (1.76 Ω cm²). These findings demonstrate that rational structural design through rare-earth doping effectively enhances oxygen transport and electrochemical activity, providing a promising pathway for high-performance intermediate-temperature SOFC cathodes.

Thermomechanical Analysis and Optimization of Residual Stresses in SS316L Components Fabricated by Directed Energy Deposition

Farnoosh Turki

The Directed Energy Deposition (DED) process is very sensitive to thermal environments, tends to produce residual stresses and geometric distortion. It is important to understand the influence of processing parameters on these effects in order to enhance build quality. The objective of this study is to control residual stress and distortion in the DED process by investigating baseplate thickness, number of layers deposited before laser interruption, dwell time, and laser power by a full factorial experiment design. The numerical results were validated by experimental measurement of residual stress using the X-ray diffraction (XRD) technique. The optimized processing conditions resulted in a 43% reduction in residual stress and a 33% decrease in dimensional distortion compared to the baseline setup. Among the four factors, baseplate thickness had the most significant effect, whereas dwell time had the least impact. To the best of the authors’ knowledge, the combined effect of baseplate thickness, dwell time, number of layers deposited before laser interruption, and laser power on residual stress and distortion in DED has not been previously investigated. The findings of this study provide a mathematical basis for future research aimed at optimizing process and material parameters in DED process.

Effect of Aging Duration on Mineral Composition, Microstructure, and Texture in a Malachite based Co precipitate and its Composite (Metallic) Oxidic Derivatives

Hajar Ghanbari

This study deals with the dependence of mineral, microstructural, and textural properties on the duration of the indispensable yet easily controlled step of aging. For this purpose, a set of Cu/Zn/Al precursors were synthesized using a conventional constant‑pH method. The precipitates were aged for three different durations of zero, two, and four hours. The obtained precipitates, after several washing cycles and overnight drying, were then calcined at 623 K. Precursor and calcined samples were studied in terms of elemental composition, mineral composition, microstructure, texture, porosity, and metallic copper surface area. The results suggest that the dependence of precursor surface area on aging is realized by its dependence on phase composition. In the precipitate aged for two hours, the relative dominance of malachite leads to the highest pre‑calcination surface area of 57 m²/g. The individual thermal behaviors of the precursor phases and their pre‑calcination surface area values seem to conjointly determine the post‑calcination surface area of the samples. Such that a combination of ripened particle structure and susceptibility to calcination induced surface deterioration yields the lowest post‑calcination surface area after aging for four hours. The calcines derived from the unaged and the two‑hour‑aged precursors yield surface area values of approximately 57–58 m²/g, sensibly higher than that of the four‑hour‑aged sample. The Cu⁰ surface area values of the samples depend on aging duration through the effect it imparts on the Cu/Zn‑interdispersion of the precursor malachite phase. The highest Cu/Zn‑interdispersion is achieved in the two‑hour‑aged sample that finally exhibited a maximum Cu⁰ surface of 112 m²/g_Cu.

Design and Optimisation of Corrosion Behaviour of Mg-Zn-Ca Alloy System Using Thermodynamic and Statistical Simulation

M. Reza Aboutalebi

In recent years, Mg- based alloys have been considered as a biodegradable biomaterial for implant applications. However, the high corrosion rate and hydrogen gas evolution in an aqueous environment are the most important challenges for these alloys. This study has focused on optimizing the biocorrosion properties of bioalloys in Mg-Zn-Ca system, using a combined approach of thermodynamic simulations, and response surface methodology (RSM). In, Mg₂Ca and Ca_xMg_yZn_z precipitates have a significant effect on corrosion mechanisms. It is believed that, in the Mg-Zn-Ca alloy system, the Mg₂Ca secondary phase usually enhances corrosion rate with microgalvanic coupling mechanisms. The ternary phases Ca_xMg_yZn_z have less detrimental effects on corrosion resistance. To minimize harmful phases, CompuTherm’s PANDAT software was utilized for phase evolution prediction, with outputs directly validated against experimental measurements. Potentiodynamic tafel polarization experiments and long-term immersion tests were conducted to evaluate the corrosion rate. In order to design an alloy with the least detrimental phase, a statistical model (RSM) was developed based on predicted results from thermodynamic model. The results showed that the ZX31 (Mg-2.6Zn-1Ca) exhibited the highest corrosion potential (-1.6336 V_Ag/AgCl) and the lowest corrosion current density (216 µA/cm²), showing higher biocorrosion resistance compared to ZX24 (Mg-2.3Zn-4.0Ca) and ZX15 (Mg-1.3Zn-4.8Ca).