Soon-Hyo Chung

Ab initio calculation of interfacial energies between transition metal carbides and fcc iron

An ab initio study was carried out on coherent and semicoherent interfacial energies for fcc Fe/MCs (NaCl structure, M = Ti, Zr, Hf, V, Nb, Ta) systems. The group V transition metal carbides have lower coherent and semicoherent interfacial energies than group IV transition metal carbides. Also, the coherent interfacial energies for fcc Fe/MCs systems are lower than those for bcc Fe/MCs systems. The difference between semicoherent and coherent interfacial energy for fcc Fe/MC systems becomes larger as the misfit increases. The semicoherent interfacial energies at relaxed interfaces Fe/TiC, Fe/ZrC, Fe/HfC, Fe/VC, Fe/NbC and Fe/TaC were 0.600?J?m?2, 0.661?J?m?2, 0.946?J?m?2, ?0.050?J?m?2, 0.320?J?m?2 and 0.380?J?m?2, respectively. In order to maximize precipitation strengthening effect in austenitic steel, VC is the most favorable precipitate under consideration.

An ab initio study of the energetics for interfaces between group V transition metal Nitrides and bcc iron

An ab initio study was carried out on interface energies, misfit strain energies and electron structures at coherent interfaces between bcc Fe and Nitrides (XNs) (NaCl structure, X = V, Nb, Ta). The interface energies at relaxed interfaces Fe/VN, Fe/NbN and Fe/TaN were −0.051 J m−2, −0.226 J m−2 and −0.643 J m−2, respectively. The influence of bond energy was estimated using the discrete lattice plane/nearest neighbour broken bond model. It was found that the dependence of interface energy on the type of nitride was closely related to changes of the bond energies between Fe, X and N atoms before and after formation of the interfaces Fe/XN. The misfit strain energies in Fe/VN, Fe/NbN and Fe/TaN systems were −0.052, 0.178 and 0.005 eV per 16 atoms (Fe 8 atoms and XN 8 atoms). The misfit strain energy became larger when the difference in lattice parameters between the bulk Fe and the bulk XNs increased.

Development of adsorbent for the simultaneous removal of organic and inorganic contaminants from aqueous solution

In this study, a modified adsorbent, alginate complex beads, was prepared and applied to the removal of mixed contaminants from wastewater. The alginate complex beads were generated by the immobilization of powdered activated carbon and synthetic zeolites onto alginate gel beads, which were then dried at 110 °C for 20 h until the diameter had been reduced to 1 mm. This dry technique increased the hardness of the adsorbent to assure its durability and application. The adsorption onto the alginate complex beads of organic and inorganic compounds, as target contaminants, was investigated by performing both equilibrium and kinetic batch experiments. From the adsorption isotherms, according to the Langmuir equation, the alginate complex bead was capable of effectively removing benzene, toluene, zinc and cadmium. From kinetic batch experiments, the removal efficiencies of benzene, toluene, zinc and cadmium were found to be 66.5, 92.4, 74.1 and 76.7%, respectively, for initial solution concentrations of 100 mg L(-1). The results indicated that the adsorbent developed in this study has the potential to be a promising material for the removal of mixed pollutants from industrial wastewater or contaminated groundwater.

Formation of FeMo2B2 phase in boron containing 9Cr-1.5Mo ferritic steels

Abstract The segregation and diffusion of boron during heat treatments were studied. The influence of boron contents, aging time and applied stress on FeMo 2 B 2 formation was also studied. Finally, the effects of boron contents and FeMo 2 B 2 formation on the high temperature strength were studied. Boron atoms were segregated to prior austenite grain boundary during normalizing treatment. And these boron atoms were slowly diffused into the grain interior during tempering and aging at 700 °C. The FeMo 2 B 2 phase was only formed after 1,000 h aging at 700 °C in alloy containing 196 ppm boron. The formation of FeMo 2 B 2 phase is accelerated by the applied stress. It was expected that the formation of FeMo 2 B 2 is closely related to the redistribution of boron atoms. The tensile strengths at 700 °C are increased with the increase of boron contents. However, the formation of FeMo 2 B 2 phase results in lower tensile strength.