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The crevice-corrosion behavior of 304 stainless steel at several chloride concentrations was investigated with two types of specimens: plate and pipe joint. There is a good correlation of crevicecorrosion behavior between the plate specimen and pipe joint specimen. The crevice-corrosion of both specimens initiated when the chloride ion concentration exceeded 200 ppm. Four stages of crevice-corrosion were observed: isolated pits, coalescing pits, crystallographic attack, and polishing attack. Consequently, the critical chloride ion concentration of crevice-corrosion is affected by the intrinsic property of the material.

keyword : metals, joining, corrosion, image analysis, potable water

Electrotransport treatment is a new method to remove the hydrogen from inside metals. Potentiodynamic polarization tests, electrochemical impedance spectroscopy (EIS), and tensile tests were used to investigate the effect of electrotransport treatment on the anodic behavior and hydrogen embrittlement characteristics of Alloy 600. The hydrogen-charged specimen exhibited a higher anodic current than that of the uncharged specimen. In particular, the anodic current was reduced so that the electrotransport treatment had features similar to that of the uncharged specimen. The EIS results showed that the capacitance loop of the hydrogen-charged specimen was smaller than that of the electrotransport treatment specimen. Results regarding tensile behavior revealed that electrotransport treatment enhanced the mechanical property of hydrogen-charged specimens.

keyword : metals, deformation, hydrogen, tensile test, electrotransport treatment

Experimental flux cored wire with micro-addition of rare earth metal was manufactured and used to make 3-point bend CTOD specimens to assess the fracture toughness of the weld metal. The weld metal showed much higher CTOD value, 2.58 mm at 40 ℃, than the weld metal that contained no rare earth metal. Microstructural observations and fractography of the CTOD specimens indicated that the excellent fracture toughness of the weld metal is due to the microstructural modification of rare earth metal. Continuous cooling transformation diagrams showed that micro-addition of rare earth metal delayed the phase transformation of the weld metal during cooling, resulting in a larger amount of tough microstructure (acicular ferrite) instead of brittle microstructure(grain boundary ferrite). Nano-SIMS analysis showed that the reason for the delay of the phase transformation of the weld metal was the segregation of rare earth metal on the grain boundaries of austenite.

keyword : alloys, welding, toughness, SIMS, rare earth metal

The effect of PWHT time on the pitting behavior in NaCl solution was evaluated in the weld of Mod. 9Cr-1Mo steels. Specimens were fabricated using autogeneous gas tungsten arc welding (GTAW) and tested using various post weld heat treatment (PWHT) times (i.e., 30 min, 1 h, and 2 h). More retained δ -ferrite was produced adjacent to the fusion line than the weld center. The polarization curves shifted to low Ecorr and large Icorr, therefore decreasing the pitting corrosion resistance of the weld as the PWHT holding time increased. The ‘as-welded’ specimens showed random pitting at the martensite lath. With increasing PWHT time, pitting was also found at the δ-ferrite/tempered martensite (δ/TM) interface. This is because more coarse and dense Cr-rich M23C6 carbides were formed along the δ/TM interface than at the TM/TM interface as the PWHT holding time increased.

keyword : metals, welding, corrosion, transmission electrn microscopy, TEM, Mod. 9Cr-1Mo steel

The sulfuric acid leaching of electric arc furnace(EAF) dust was studied in an attempt to find a suitable hydrometallurgical method for the recovery of zinc. The effect of acid concentration, reaction temperature, stirring rate and solid-to-liquid ratio on Zn and Fe extraction from the solution was investigated. It was found that the leaching rate of Zn and Fe increased with increasing reaction temperature and sulfuric-acid concentration. Examination of data using a shrinking core model suggest that the leaching rate is controlled by mixture kinetics. The activation energy for the leaching reaction of Zn and Fe were calculated as 44.45 kJ/mol and 65.45 kJ/mol, respectively.

keyword : EAF dust, hydrometallurgy, sulfuric acid, leaching, zinc, kinetic

In this study, the solubility of Cu and Ni, which are the main metal components of waste PCB in a CaO-SiO2-Al2O3-MgO slag system, was investigated by the chemical equilibration technique in the temperature range 1673-1823 K, under a CO-CO2 atmosphere. The concentrations of Cu and Ni in the slag increased with increasing oxygen partial pressure and MgO content in the slag. The concentrations of Cu and Ni in the slag decreased with increasing temperature. The concentration of Cu in the slag decreased with increasing activity of CaO, but that of Ni increased. The dissolution mechanisms of Cu and Ni in the CaO-SiO2-Al2O3-MgO slag could be described by the following equations from the effect of oxygen partial pressure and slag basicity on Cu and Ni dissolution behaviors: From the results obtained, the enthalpy changes from dissolution of Cu into the CaO-SiO2-Al2O3-MgO slag were calculated to be -59.17 kJ/mol, and that for Ni was calculated to be -78.89 kJ/mol.

keyword : waste electrical and electronic equipment, printed circuit board, copper, nickel, recycling

A Zn(BH4)2 sample was prepared by milling ZnCl2 and NaBH4 in a planetary ball mill under Ar gas. This sample contained NaCl. Then, 90 wt% MgH2-5 wt% Zn(BH4)2-2.5 wt% Ni-2.5 wt% Ti samples [named 90MgH2-5Zn(BH4)2-2.5Ni-2.5Ti] were prepared by milling in a planetary ball mill under H2 gas. The hydrogen absorption and release properties of the prepared samples were investigated. In particular, the variations of the initial hydriding and dehydriding rates with temperature were examined. SEM micrographs and XRD patterns of 90MgH2-5Zn(BH4)2-2.5Ni-2.5Ti after reactive mechanical grinding and after hydriding-dehydriding were also studied. Particle size distributions and BET specific surface areas of 90MgH2-5Zn(BH4)2-2.5Ni-2.5Ti after reactive mechanical grinding and after 11 hydriding-dehydriding cycles were analyzed. The 90MgH2-5Zn(BH4)2-2.5Ni-2.5Ti had an effective hydrogen storage capacity (the quantity of hydrogen absorbed for 60 min) of near 5 wt% (4.91 wt% at 593 K).

keyword : hydrogen absorbing materials, mechanical alloying/milling, scanning electron microscopy, SEM, X-ray diffraction, Zn, BH4, 2-added MgH2-based alloy

The Pressure-Composition-Temperature(PCT) curve of Mg(BH4)2 was studied by Sievert`` type apparatus. In order to understand the slope of the first plateau pressure, a thermal analysis technique was introduced. The PCT curves of the dehydriding reaction for Mg(BH4)2 are measured at 573, 598, 623, and 653 K, respectively. Under every temperature measured, the first plateau pressure shows slope but the second plateau pressure of MgH2 is clearly observed. The apparent enthalpy for the first plateau pressure from Mg(BH4)2 to MgH2 is roughly estimated. The equilibrium pressure at each temperature is determined to be the first plateau pressure where the hydrogen content is -5wt%. The apparent enthalpy for the first reaction from Mg(BH4)2 was estimated to be △H = 51.1 kJ mol-1 H2, and the apparent enthalpy for the dehydriding reaction from MgH2 was estimated to be △H = 90.0 kJ mol-1H2. The result of the thermal analysis shows three peaks. This means that it decomposes at least through the pathway of three reactions.

keyword : hydrogen absorbing materials, chemical synthesis, microstructure, thermal analysis, pressure-composition-temperature curve

Multi-layer graphene is considered to be a potential replacement of copper wiring for LSI (large-scale integration). PECVD (plasma enhanced chemical vapor deposition) is one of the most reliable synthesis techniques to manufacture high-quality, large-scale graphene at low temperature. Compared with thermal CVD graphene, the relatively lower quality of PECVD graphene is its main drawback. In order to suggest a solution for this problem, we studied the growth mechanism of multi-layer graphene deposited onto nickel by PECVD at 400 ℃. We found that both segregation and solution-precipitation models affect the growth behavior of multi-layer graphene. To support this, we analyzed the influences of Ni-film thickness, cooling rate, and plasma energy on multi-layer graphene growth. The results from this study would be useful for optimizing graphene growth conditions for many applications.

keyword : graphene, PECVD, growth mechanism, synthesis, nickel catalyst

We investigated the effect of CeO2 content on the catalytic behavior of (68-x)P2O5-32ZnO-xCeO2 (x = 0, 4, 8, 12, and 16 mol%) glasses. In addition, we confirmed the effect of the addition of B2O3 on the catalytic properties of (60-x)P2O5-32ZnO-8CeO2-xB2O3 (x = 0, 5, 10, 15 and 20 mol%) glasses. Using TGA, we confirmed that the catalytic activity of the (68-x)P2O5-32ZnO-xCeO2 glasses increased with CeO2 content. Furthermore, the catalytic activity of (60-x)P2O5-32ZnO-8CeO2-xB2O3 decreased until the B2O3 content attained 15 mol%, beyond which, it increased. The change in the catalytic properties in relation to the content of B2O3 and CeO2 was analyzed through FT-IR, XPS, optical band gap energy, and density.

keyword : glasses, solidification, optical properties, thermal analysis, catalytic properties