Determination of Phase Equilibria among δ-Fe, γ-Fe and Fe2M Phases in Fe-Cr-M (M: Hf, Ta) Ternary Systems

Phase equilibria among δ-Fe, γ-Fe, and Fe2M phases in the Fe-Cr-M (M: Hf, Ta) ternary systems were determined using bulk alloys heat-treated at high temperatures. The final goal of this study is to develop novel ferritic heat resistant steels strengthened by precipitation of Fe2M phase on the eutectoid type reaction path: δ → γ + Fe2M. The phases present in heat-treated samples were identified by microstructural characterization and X-ray diffraction pattern analysis. The chemical compositions of the phases were analyzed by energy dispersive spectroscopy. A pseudo-eutectoid trough (δ → γ + Fe2M) exists at ~1220 °C at a Hf content of 0.1% and at ~1130 °C at a Ta content of 0.6% on the vertical section at a Cr content of 9.5% in each ternary system, respectively. A thermodynamic calculation with a database that reflects reported binary phase diagrams and the present study indicates that an increase in the Cr content decreases the temperature and the Hf/Ta contents of the pseudo-eutectoid troughs. The determined phase equilibria suggest that the supersaturation of Hf/Ta for the formation of γ phase is higher in the Hf doped system than in the Ta doped system, which is probably an origin of a much slower kinetics of precipitation on the eutectoid path in the latter system.

Electron Diffraction Study of the Space Group Variation in the Al–Mn–Pt T-Phase

Binary high temperature “Al3Mn” (T-phase) and its extensions in ternary systems were the subjects of numerous crystallographic investigations. The results were ambiguous regarding the existence or lack of the center of symmetry: both Pna21 and Pnam space groups were reported. Our research on the Al–Mn–Pt T-phase allowed concluding that inside a continuous homogeneity region, the structure of the Al-rich T-phase (e.g., Al78Mn17.5Pt4.5) belongs to the non-centrosymmetric Pna21 space group, while the structure of the Al-poor T-phase (such as Al71.3Mn25.1Pt3.6) is centrosymmetric, i.e., Pnam. Following metallurgical and crystallographic considerations, the change in the symmetry was explained.

Synergistic effect of sorption and photocatalysis on the degree of dye removal in single and multicomponent systems on ZnO-SnO2

The paper presents the photodegradation process of one-, two- and three-component dye mixtures by ZnO-SnO2 nanoparticles. After 60 min of running the processes, the dye removal efficiencies of 76.44, 72.69, 62.43, 77.00 and 92.46% for MB, RB, TB, MO and YQ degradation, respectively, were obtained. For binary and ternary systems, dye removal efficiencies for all cases exceeded 70%. When the binary and ternary dye mixtures were tested, the photodegradation efficiencies of ZnO-SnO2 were similar to those of the single mixtures, indicating that this material could be used in industrial applications in the future. The focus of the study was to investigate the effect of sorption on photodegradation efficiency and the presence of both cationic and anionic dyes on their degradation efficiency under UV light. The significance of the effect of sorption on the degradation efficiency allowing the interaction of the catalyst with the dyes removed was confirmed. The main factor influencing sorption and consequently photocatalysis was the nature of the dye. It was confirmed that the positively charged ZnO-SnO2 surface effectively sorbs the dyes and causes their degradation.

COPEX: co-evolutionary crystal structure prediction algorithm for complex systems

Crystal structure prediction has been widely used to accelerate the discovery of new materials in recent years. Up to this day, it remains a challenge to predict the stable stoichiometries and structures of ternary or more complex systems due to the explosive increase of the size of the chemical and configurational space. Numerous novel materials with a series of unique characteristics are expected to be found in this virgin territory while new algorithms to predict crystal structures in complex systems are urgently called for. Inspired by co-evolution in biology, here we propose a co-evolutionary algorithm, which we name COPEX, and which is based on the well-known evolutionary algorithm USPEX. Within this proposed algorithm, a few USPEX calculations for ternary systems and multiple for energetically-favored pseudobinary or fixed-composition systems are carried out in parallel, and co-evolution is achieved by sharing structural information on the fittest individuals among different USPEX sub-processes during the joint evolution. We have applied the algorithm to W–Cr–B, Mg–Si–O, and Hf–Ta–C, three very different systems, and many ternary compounds have been identified. Our results clearly demonstrate that the COPEX algorithm combines efficiency and reliability even for complex systems.