• Journal of Korean Society of Water and Wastewater
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• v.23 no.4
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• pp.471-479
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• 2009

A Nanoscale Zero-Valent Iron(NZVI) was modified to build a reactor system to treat nitrate. Shell layer of the NZVI was modified by slow exposure of the iron surface to air flow, which produced NZVI particles that are resistant to aerial oxidation. A XANES (X-ray Absorption Near-Edge Structure) analysis revealed that the shell consists of magnetite ($Fe_3O_4$) dominantly. The shell-modified NZVI(0.5 g NZVI/ 120 mL) was able to degrade more than 95% of 30 mg/L of nitrate within $30 hr^{-1}$ ( pseudo first-order rate constant($k_{SA}$) normalzed to NZVI surface area ($17.96m^2/g$) : $0.0050L{\cdot}m^{-2}{\cdot}hr^{-1}$). Ammonia occupied about 90% of degradation products of nitrate. Nitrate degradation efficiencies increased with the increase of NZVI dose generally. Initial pH values of the reactor systems at 4, 7, and 10 did not affect nitrate removal rate and final pH values of all experiments were near 12. Nitrate removal experiments by using the shell-modified NZVI immobilized on a cellulose acetate (CA) membrane were also conducted. The nitrate removal efficiency of the CA membrane supported NZVI ($k_{SA}=0.0036L{\cdot}m^{-2}{\cdot}hr^{-1}$) was less than that of the NZVI slurries($k_{SA}=0.0050L{\cdot}m^{-2}{\cdot}hr^{-1}$), which is probably due to less surface area available for reduction and to kinetic retardation by nitrate transport through the CA membrane. The detachment of the NZVI from the CA membrane was minimal and impregnation of up to 1 g of NZVI onto 1 g of the CA membrane was found feasible.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.3
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• pp.12-17
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• 2020

The mechanical properties of the propellant with yellow iron oxide were slightly increased compared to the propellant with red iron oxide. The propellant with yellow iron oxide used two types of AP. As the ratio of small particles of AP increased, the burning rate increased. The propellant may be applied to the propellant under operating conditions of 17.5 mm/sec or less having a pressure index of 0.5. The burning rate downs in the mixer scale-up. The stress at maximum load of propellant decreased and the strain at maximum load increased in the mixer scale-up. The yellow iron oxide did not affect the adhesive force between the insulation/liner/propellant.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.5
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• pp.332-339
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• 2011

Effects of powdered activated carbon impregnated by iron oxide nano particle (Impregnated PAC) on the microfiltration (MF) membrane system performance in NOM removal from water were investigated in this study. A fluidized bed column was employed as a pretreatment of MF membrane process. The Impregnated PAC bed was stably maintained at an upflow rate of 63 m/d without leakage of the Impregnated PAC particles, which provided a contact time of 29 minutes. A magnetic ring at the upper part of the column could effectively hold the overflowing discrete particles. The Impregnated PAC column demonstrated a significant enhancement in the MF membrane performance in terms of fouling prevention and natural organic matter (NOM) removal. Trans-membrane pressure of the MF membrane increased to 41 kPa in 98 hours of operation, while it could be maintained at 12 kPa with the Impregnated PAC pretreatment. Removal of NOM determined by dissolved organic carbon and UV254 was also enhanced from 46% and 51% to 75% and 84%, respectively, by the pretreatment. It was found that the Impregnated PAC effectively removed a wide range of different molecular-sized organic compounds from size exclusion analysis.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.8
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• pp.34-42
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• 2004

A new polishing technique for three dimensional micro/meso-scale parts is suggested using a micro quill and a magnetic chain structure. The principle of this method is to polish the target surface with the collected magnetic brushes at a micro tool by the non-uniform magnetic field generated around the tool. In a typical magnetic abrasive finishing process magnetic particles and abrasive particles are unbonded each other. But, to finish the three dimensional small parts bonded magnetic abrasive have to be used. Bonded magnetic abrasives are made from direct bonding, and their polishing characteristics are also examined. Alumina, silicon carbide and diamond micro powders are used as abrasives. Base metal matrix is carbonyl iron powder. It is found that bonded magnetic abrasives are superior to unbonded one by experiment. finally, the polished surface roughness is evaluated by atomic force microscope.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.3
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• pp.200-206
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• 1998

The aim of this study is to investigate the effect of impurity level and fabrication processes on the strength, impact and fracture toughness of 7075, 7050 and 7175 aluminum alloy forgings. A specially processed 7175S-T74 aluminum forgings was superior to a conventionally processed 7075-T73, 7050-T74 and 7175-T74 aluminum forgings in both strength and toughness. The reduction of impurity level of iron and silicon has significantly diminished the size and volume fraction of second phase particles such as $Al_7Cu_2Fe$ and $Mg_2Si$. A further reduction of the amount of second phase particles has been observed by applying a special fabrication process. This phenomena result from the application of intermediate soaking at higher temperature and more sufficiant hot working temperature than that of a conventional processing.

• 한국연소학회:학술대회논문집
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• 2012.04a
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• pp.213-215
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• 2012

As one of the primary fuel sources, oxy-fuel combustion of coal is actively being investigated because of the climate changing problem such like the emission of green house gases. In this paper research about the pulverized coal technology, which is widely used in both power-generating and iron-making processes was studied to invesgate the ignition behaviour of pulverized coal particles during coal combustion as changing the ambient oxygen concentration of the particle. The ignition phenomenon of the coal particles fed into a laminar flow reactor was imaged with a Integrated charged-coupled device (ICCD) camera. The ignition points were determined throught the analysis of the images, and then the ignition delay times were able to be calculated. The experiment results show that a lower oxygen concentration increases the ignition delay time.

• KSTLE International Journal
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• v.1 no.1
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• pp.34-42
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• 2000

A method and results of classification of four different metallic wear debris were presented by using their color features. The color image of wear debris was used far the initial data, and the color properties of the debris were specified by HSI color model. Particles were characterized by a set of statistical features derived from the distribution of HSI color model components. The initial feature set was optimized by a principal component analysis, and multidimensional scaling procedure was used fer the definition of a classification plane. It was found that five features, which include mean values of H and S, median S, skewness of distribution of S and I, allow to distinguish copper based alloys, red and dark iron oxides and steel particles. In this work, a method of probabilistic decision-making of class label assignment was proposed, which was based on the analysis of debris-coordinates distribution in the classification plane. The obtained results demonstrated a good availability for the automated wear particle analysis.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.3
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• pp.274-279
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• 2011

In this study, new abrasives that were composed of iron powder and carbon nanotube (CNT) particle were attempted to be abrasives for magnetic abrasive polishing. Because the CNT particles itself are very small ones with high hardness and magnetic strength, these properties are effective for magnetic abrasive polishing of nonmagnetic materials. As an experimental result for evaluating the machining characteristics in magnetic abrasive polishing, the CNT particles showed better performance than the conventional abrasives such as Fe and CBN powder.

• Tribology and Lubricants
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• v.25 no.1
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• pp.49-55
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• 2009

The frictional properties of automotive brake pads with four different ceramic materials such as magnesia, hematite, alumina, and zircon were investigated. A Krauss type friction tester using gray iron disks was used to examine the friction coefficient, intensity of friction force oscillation, and the tribe-surfaces. Results showed that the friction coefficient increased as the hardness of abrasives increases. Friction oscillation was also increased with hardness of the abrasives. However, the friction materials containing less abrasive particles produced stable friction films on the sliding surface. The transition between two-body and three body abrasion during sliding also played a crucial role in destructing the friction film on the pad surface and in determining various frictional properties.

• Corrosion Science and Technology
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• v.22 no.6
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• pp.429-434
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• 2023

This study investigated the localized corrosion behavior of a UNS G41400 steel surface treated with manganese phosphate. The phosphate coating, primarily composed of oxygen (O), phosphorus (P), and manganese (Mn) elements, had an approximate thickness of 6 ㎛. The particles comprising the coating varied in size by several micrometers; smaller particles were mainly composed of O, P, Mn, and iron (Fe) elements, indicating incomplete formation of the manganese phosphate film. Potentiodynamic polarization curves revealed a decrease in anodic current after surface treatment and a shift in corrosion potential toward the noble direction after treatment. After immersion in a 3.5 wt% NaCl solution for 96 hours, localized corrosion was observed, with some regions retaining residual phosphate film. Even though localized corrosion occurred on the treated surface, it was less severe than that on the untreated UNS G41400 steel surface. These findings suggest that manganese phosphate coating improved resistance to localized corrosion.