발간논문

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Ferritic T22, T23, and T91 steels were corroded in Na2SO4 salt at 800 and 900 ℃, and their hot corrosion behavior was studied. The corrosion resistance increased in the order of T22, T23, and T91. The good corrosion resistance of T91 at 800 ℃ was mainly attributed to Cr, which led to the formation of thin scales. By contrast, the amount of Cr in T22 and T23 was not enough to form protective scales so that thick, porous, bi-layered scales formed on T22 and T23 at 800 ℃. Nonetheless, T22, T23, and T91 suffered rapid scaling and dissolution of scales into the salt at 900 ℃. Iron oxides were the major corrosion products in this study.

keyword : metals, casting, corrosion, X-ray diffraction, Na2SO4 salt

Abstract: The aim of this study is to characterize the microstructure and mechanical properties of aluminum metal matrix composites (MMCs) containing 20 vol% of silicon carbide particles (SiCp) with different particle sizes. The A359/SiCp MMCs sinterted specimens were respectively manufactured from a blended powder and composite powders by a hot press technique. The consolidated composite with the blended powder exhibited a clustered region of reinforcement particles in the matrix, which was due to the influence of the interfacial debonding of the SiCp/matrix during fracture. On the other hand, a homogeneous particle distribution of the composite powders and the SiCp was observed in the sintered specimens after fracture. Homogeneous distribution of the MMCs and SiCp was significantly affected by the method of the preparation or the powder materials. This phenomena was predominant elevation of the mechanical properties in these composites.

keyword : composites, powder processing, sintering, mechanical properties, scanning electron microscopy

Oxidation and precipitation of Co(II) in sulphate solution using Na2S2O8 as an oxidant was studied. The main factors affecting the oxidation of Co(II), the reaction time, temperature, pH of solution, agitation speed and amount of added Na2S2O8, were investigated. The results indicated that the oxidation rate of Co(II) was not affected by the agitation speed and the amount of the oxidant, but it increased obviously with an increasing pH of the solution and reaction temperature. The kinetics equation was established as .ln(1.X ) = k1.[H+].0.4755.exp ( 3800) .t with a first order reaction. The product precipitated by the oxidation T of Co(II) was CoOOH, and Co2O3 was obtained by calcination of CoOOH at 300 ℃ for 2 hours. The particle size of the precipitated product was influenced by the pH of the solution.

keyword : metals, purification, oxidation, cobalt

Platinum was recovered from the leaching solution of spent petroleum catalysts by solvent extraction. The spent catalysts were first roasted at 800 ℃ to eliminate volatile matter. Most of the platinum in the spent catalysts was dissolved at an optimum leaching condition in a mixture of HCl and H2O2. Separation of platinum from the leaching solution was accomplished by solvent extraction with Aliquat 336 after iron was removed by extraction with TBP. Platinum and iron were stripped from the loaded Aliquat 336 and TBP by using 1 M HClO4 and 0.1 M HCl, respectively. Finally, HCl in the raffinate was recovered by extraction with TEHA and then by stripping with water. The optimum conditions to dissolve platinum and to separate platinum by solvent extraction are reported together with the mass balance of the constituents of the spent catalysts in each step.

keyword : composites, recycling, oxidation, X-ray diffraction

In order to investigate the effects of homogenization treatment on microstructural change and high temperature deformation stability, a series of hot compression tests and homogenization treatment were conducted for as-cast and upset-forged 1Cr-1.25Mo-0.25V steels. Microstructural inhomogeneity like dendritic morphology and elemental segregation in as-cast steel was homogenized after 10 hours-holding at 1200 ℃, followed by the rapid grain coarsening up to about 700 μm after 20 hours-holding. However, upset- forged steel showed rapid grain coarsening even in the early stage of high temperature holding at 1200 ℃. Compression tests for the 1Cr-1.25Mo-0.25V steels showed that flow stresses of as-cast 1Cr-1.25Mo-0.25V steel were higher than those of the upset-forged at temperatures lower than 1000 ℃. By analyzing the compression test results based on a dynamic materials model, we concluded that the microstructural inhomogeneity diminished hot deformation stability of the as-cast 1Cr-1.25Mo-0.25V steel. It is clear that the microstructural homogenization of as-solidified steel prior to upset forging is essential for improving the hot deformation stability and soundness of hot forgings.

keyword : metals, homogenization treatment, hot working, microstructure, compression test

This study investigated the effect of an intermediate process on the microstructure and mechanical properties of a ferritic-martensitic tube for a fuel cladding tube in a sodium-cooled fast reactor (SFR). Cold drawing and heat treatment of the HT9 tube (12Cr-1MoWV) below the tempering temperature without a normalizing process was conducted (Route 1), whereas conventional normalizing and tempering conditions were also used for a comparison (Route 2). The results showed that the microstructure gradually transformed into the work-hardened structure during the Route 1 process, maintaining higher hardness throughout the reduction step. On the other hand, the microstructure of the Route 2 process gradually turned into a tempered martensite structure, whose hardness gradually increased throughout the step. M23C6 type of precipitates were generated regardless of the manufacturing route, where the size of precipitates in the Route 1 process was controlled to keep the high temperature mechanical property.

keyword : metals, tempering, microstructure, hardness test, ferritic-martensitic steel

In order to improve the energy conversion efficiency (ECE) by increasing the surface area of counter electrode (CE), we prepared 500 nm-polystyrene (PS) beads on a flat glass substrate, deposited with 100 nm-thick ZnO and 34 nm-thick Ru nano thin film using ALD. A 34 nm-thick Ru CE on a flat glass substrate was also prepared using the same method for a comparison. Finally, a 0.45 cm2 dye-sensitized solar cell (DSSC) device with a glass/FTO/blocking layer/TiO2/N719(dye)/electrolyte/34 nm-Ru/100 nm-ZnO/ 500 nm-PS bead/glass structure was fabricated. The microstructure of the CE was examined by field emission scanning electron microscopy (FE-SEM). The photovoltaic properties, such as the short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), energy conversion efficiency (ECE) and impedance, were characterized using a solar simulator and potentiostat. The microstructure examined using a FE-SEM confirmed that 100 nm-ZnO/34 nm-Ru on 500 nm-PS beads increases the surface area by 70% compared to a glass substrate. The ECE of the device with the CE, the glass/Ru and 500 vnm-beads/100 vnm-ZnO/Ru, was 1.81%, and 2.91%, respectively. These results suggest that the surface area of the CE contributed to the increase in efficiency. Moreover, increasing of surface area through ZnO coating on PS beads was more suitable for increasing efficiency than the conventional flat glass substrates.

keyword : dye sensitized solar cells, ALD, surface, FESEM, polystyrene

Interaction between ZrAlSiN thin films and osteoblasts cells was conducted in vitro. Ti and ZrAlSiN films were deposited on glass coverslips by cathodic arc deposition. Ti, ZrAlSiN thin films and the bare glass coverslips were cultured with human osteoblast cells (hFOB). Cell morphology was observed with a confocal microscope in the bright field mode. Cell viability was assayed by MTT. Cell proliferation was fluorescent visualized at 10 X magnification. Cell cytoskeletons were analyzed by observing actin stress fiber organization. Focal contact adhesion was studied by investigation of the density of the vinculin. Cell viability, cell proliferation, developed actin stress fibers and focal contact adhesion were found better on ZrAlSiN thin films than on Ti thin films or glass surfaces.

keyword : biomaterials, deposition, surface, image analysis, ZrAlSiN

Abstract: In this study, mechanical properties of commercial carbon fibers were evaluated using a single filament tensile test with various fiber gauge lengths. Tensile strength increased significantly with a decreasing length of the test specimens possibly due to small defect sites. The compliance method provided more accurate moduli of the carbon fibers, removing system errors during the single filament tensile test. The Weibull modulus revealed that shorter specimens had an inhomogeneous defect distribution, leading to a higher tensile strength and its standard deviation. X-ray diffractograms of carbon fibers showed a similar crystallinity and orientation in spite of significant differences in the fiber modulus and strength, indicating that crystalline structure of the commercial carbon fibers used in the study was not attributable to the difference in their tensile properties.

keyword : carbon and graphite, fibers, tensile test, scanning electron microscopy, X-ray diffraction

In order to investigate the deformation behavior of TiC-(5-15) mol% Mo composites at high temperature, crystals of various compositions were grown by the radio frequency (r.f.) floating zone melt technique and were deformed by compression test at temperatures from 1273 to 2273 K and at strain rates from 4.9 × 10.5 to 6.9 × 10.3 s.1. The plastic flow behavior was found to be different among three temperatures ranges (low, intermediate and high) whose boundaries were dependent on the strain rate. From the observed behavior, it is inferred that the deformation in the low temperature range is controlled by the Peierls mechanism, in the intermediate temperature range by the dynamic strain aging and in the high temperature range by the solute-atmosphere-drag mechanism.

keyword : composites, deformation, strain rale, compression test, TiC, Mo