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The precipitation characteristics of hydrides in Zr-2.5% Nb pressure tube material were investigated for various hydrogen concentrations and homogenization temperatures. A surface hydride was formed using the electrolytic method and homogenized at various temperatures up to at 550 ℃. The homogenization treatment was carried out at 300-550 ℃ over 240 hours, and the hydrogen concentration in the Zr-2.5% Nb alloy varied from 28 to 144 ppm. Hydrides were observed by optical microscopy and the precipitation parameters of the hydrides were analyzed by MATLAB, quantitatively. This is the first achievement of quantitative analysis of hydrides in Zr-alloys. The length of hydrides increased linearly with hydrogen concentration when homogenized at or below 400 ℃. The area fraction of hydrides increased linearly with the hydrogen concentration regardless of homogenization temperature. The length and the ratio (length/thickness) of the hydrides decreased with increasing homogenization temperature at 350-475 ℃ in 81-86 ppm hydrogen. The changes in the precipitation behavior of the hydrides with homogenization temperature are considered to be due to microstructure changes, both the decomposition of β-Zr and grain growth of α-Zr. (Received December 26, 2018; Accepted February 8, 2019)

keyword : Zr-2.5%Nb alloy, homogenization, hydrogen concentration, hydride, microstructure

Aluminum alloys have been widely used for aerospace applications due to their high strength and lightweight. New demand is growing for aluminum alloys with high temperature mechanical properties that can sustain plastic deformation at high temperature. In this study, correlations among microstructure, tensile properties and Charpy impact properties were analyzed at high temperature in the 7xxx aluminum alloy. Microstructures were analyzed using optical and scanning electron microscopes at varying exposure temperatures and time. Tensile and Charpy impact tests were conducted after exposure at 93, 149, 204, and 260 ℃ (200, 300, 400, and 500 °F) for 0.5 and 10 hours, and the results were compared to those at 25 °C (77 °F). Yield strength decreased with increasing exposure temperature, while total elongation and Charpy absorbed energy increased. Above 149 ℃ (300 °F), yield strength sharply dropped due to coarsening of the η' or η phase, and Charpy absorbed energy dramatically increased due to thermal softening of the matrix. The effect of exposure temperature and time on the mechanical properties of the 7xxx aluminum alloy was further investigated by fractographic analysis. The fracture toughness at high temperature was predicted on the basis of yield strength and Charpy absorbed energy suggesting a relationship between them. (Received October 24, 2018; Accepted February 14, 2019)

keyword : 7xxx aluminum alloy, elevated temperature strength, Charpy impact properties, Fracture toughness

The additive manufacturing (AM) process is a production technology process that has recently attracted attention. Among AM processes, the binder jetting (BJ) method is advantageous because it allows both wide material selection and design freedom. However, the output arrangement, which determines the direction in which the binder is injected during layer stacking, may affect the final physical properties of the fabricated part. In this study, an experiment was conducted to confirm the relation between outputs with the same shape and binder injection direction, while the density of the powder bed was kept uniform. As a result, it was confirmed that the density of the powder bed was uniform at 60.76%, but the bending strength of the resulting part was anisotropic depending on the additive direction. (Received November 8, 2018; Accepted March 8, 2019)

keyword : binder jetting additive manufacturing, 420 stainless steel, anisotropic bending strength, thermal debinding process, carbothermic reaction

ASTM P91 steel (viz. 9Cr-1Mo steel) was hot-dip aluminized to form a ~70 μm thick coating, and was then corroded in N₂/0.1%H₂S gas for 50 h at 800 and 900 ℃, to study the effect of aluminizing on the corrosion resistance of P91 steel in highly corrosive H₂S environments. Before corrosion, the aluminized coating consisted of an Al-rich topcoat, an Al₁₃Fe₄ upper layer, and an Al₅Fe₂ lower layer from the surface. During corrosion, Al, oxygen, and sulfur diffused inwardly, while substrate elements diffused outwardly. Impurity oxygen in the gas reacted preferentially with Al to form α-Al₂O₃ at the surface, which increased the corrosion resistance significantly. Bare P91 steel corroded quickly, to form bi-layered, fragile, nonprotective FeS scales. The coating transformed into either a (Al₁₃Fe₄, Al₅Fe₂)-mixed layer, AlFe layer, AlFe₃ layer, and α-Fe(Al) layer when corroded at 800 ℃/50 h, or into a AlFe3 layer and α-Fe(Al) layer when corroded at 900 ℃/ 50 h. Interdiffusion that occurred during corrosion increased the total coating thickness, and transformed (high Al)-Fe phases to (low Al)-Fe phases. The corrosion accompanied the formation of voids and microcracks in the coating. (Received November 30, 2018; Accepted March 5, 2019)

keyword : aluminizing, P91 steel, H₂S gas corrosion, hot dipping

Copper leaching from low-grade copper ore samples obtained from two active mines in the US, named conichalcite (sample A) and chalcopyrite (sample B), were studied under different leaching conditions using sulfuric acid and methane sulfonic acid (MSA). The conichalcite, sample A, is calcium-copper arsenite hydroxide [CaCu(AsO₄)(OH)] with small amount of gold and other metals. The copper grade is 0.41% with 0.48% arsenic and 2.04% sulfur. The chalcopyrite, sample B, was the main mineral with 0.60% copper grade with 0.73% sulfur and 0.032% molybdenum. Leaching systems utilized two oxidants (ferric ion and hydrogen peroxide) to investigate the kinetics of copper extractions. All leaching tests were performed by bottle roll leaching tests with 6.25% pulp density for 24 hours. Results showed that the leaching kinetics were relatively fast for oxidized sample A. Overall copper recovery was slightly affected by the oxidants and higher than 60% copper extraction was observed. Screen fractioned materials and the leached residue analysis showed that the copper grade in the residues are relatively consistent with 0.14-0.16% copper. This results showed that the ore samples contains readily leachable copper and refractory elements in all size fractions. The refractory portion seems to be relative uniform with wide range of easily leachable copper with 0.30 to 0.54%. Copper extraction from sample B using acids with ferric ion as an oxidant showed around 35% but it significantly increased over 80% using hydrogen peroxide as an oxidant. The copper extraction gradually increased up to 3.0 mol/L hydrogen peroxide content. (Received December 6, 2018; Accepted January 31, 2019)

keyword : conichalcite, chalcopyrite, leaching, hydrogen peroxide

We have developed an encapsulation technology for OLED devices using an LMPA sealing line to enhance barrier characteristics against moisture and oxygen penetration. To verify the potential of this technology for flexible OLED devices, three experimental factors were investigated in this study. First, the stability of the sealing line on the flexible substrate after repetitive bending was investigated by measuring changes in line resistivity. Secondly, temperature evolution and distribution on the flexible substrate during thermal processes were investigated. Thirdly, an OLED sample with the edge sealing line was manufactured and the lifetime was compared with a reference sample. The results showed the potential value of the LMPA sealing line to enhance the reliability and lifetime of flexible OLED devices. (Received October 1, 2018; Accepted February 11, 2019)

keyword : OLED(Organic light emitting diode), sealing, encapsulation, LMPA, Cu(Copper)

The effect of indium doping on zinc-tin oxide thin-film transistor was investigated using electrohydrodynamic (EHD) jet spray technology. EHD jet spray is a new and unique drop-on-demand patterning technology for printed electronics. After optimizing process parameters, the EHD jet spraying conditions were determined to be a voltage of 4.5 kV, a syringe speed of 0.032 μm/s, spraying time of 10 s, and a substrate temperature of 50 ℃. Indium doping increased metal-oxide formation in the thin-film, as confirmed by XPS. In addition, improved TFT electrical properties were obtained compared with non-doped TFTs by using EHD jet spray. A 0.1 M In-doped ZTO TFT showed a mobility of 7.40 cm²/V s, a threshold voltage of -3.4 V, an on-to-off current ratio of 1.87 × 10⁶, and a sub-threshold slope of 1.2 V/dec. Improved hysteresis behavior of the TFT was also achieved by indium doping. (Received January 22, 2019; Accepted March 5, 2019)

keyword : EHD jet, spray, ZTO TFT, Indium doping

Higher manganese silicides (HMSs) MnSi_1.74-1.75:Ge_m (m = 0.01-0.04) were prepared by solid-state reaction and hot pressing. The major phases of the HMSs were Mn₂₇Si₄₇ or Mn₄Si₇, and a small quantity of Si remained, but the intermetallic compound MnSi was not formed. The lattice constant increased with the substitution of Ge at Si sites. As the Ge content increased, the electrical conductivity increased, and the Seebeck coefficient decreased. The power factor was increased by Ge doping; however, the thermal conductivity also increased. Therefore, the dimensionless figure of merit (ZT) could not be increased significantly by Ge doping. For MnSi_1.74:Ge_m, a maximum ZT of 0.36 was obtained at 823 K for MnSi_1.74:Ge_0.03; for MnSi_1.75:Ge_m, a maximum ZT of 0.32 was achieved at 823 K for MnSi_1.75:Ge_0.01. (Received January 2, 2019; Accepted February 25, 2019)

keyword : thermoelectric, higher manganese silicide, HMS, doping, solid-state reaction, hot pressing

Recently, directly emitted NOx upon start-up has been spotlighted as a significant emissions problem. BaO loaded V₂O_5-WO₃/TiO₂ Selective Catalytic Reduction (SCR) catalysts were synthesized with various contents of barium which was a representative NOx adsorbent and their NOx adsorption, desorption, and removal efficiency were shown. The phase of BaO was changed to a BaO or BaCO₃ phase, which is capable of NOx adsorption when loaded on the TiO₂ support. The more BaO contents were increased, the higher the intensity of Ba²⁺, the NOx adsorption site, measured by FT-IR. Also, NOx storage capacities of the BaO loaded catalysts, which contained 5 wt% and 10 wt% of BaO, were calculated to be 12.59 μmol/g and 20.21 μmol/g at 200 ℃ respectively. The improvement in NOx storage capacity was explained by the increase in BaO content. And then the BaO loaded catalyst desorbed NOx in the temperature range of 345 to 360 ℃, which was the catalyst operating temperature. The NOx removal efficiency increased by reducing BaO content, and the catalyst loaded with 3 wt% of BaO showed 98% NOx removal efficiency at 350 ℃. The adsorbed NOx at 200 ℃ was desorbed at 300~400 ℃ and then removed by the SCR reaction. The synthesized NOx trap functional SCR catalyst can be applied to reduce the NOx generated at the time of equipment start-up at low temperatures. (Received January 7, 2019; Accepted March 8, 2019)

keyword : selective catalytic reduction, NOx Trap, NOx removal efficiency, NOx adsorption, NOx desorption