• Journal of the Korean Society for Nondestructive Testing
• /
• v.14 no.2
• /
• pp.122-131
• /
• 1994

Journal bearings in the rotating machineries are vulnerable to the contamination or the insufficient supply of lubricating oil, which is likely to be the cause of unexpected shutdown or malfunction of these systems. Various destructive and nondestructive testing methods had been used for the reduction of maintenance cost and the operational safety problems due to the accidents related to bearing damages. In this experimental approach, acoustic emission monitoring is employed to the detection of incipient failure caused by intervention of foreign particles most probable in the journal bearing systems. Experimental schedules for the intervention of foreign particles was composed to be more quantitative and systematic than last study in consideration of minimum oil film thickness and particle size. The experiment was conducted under such designed conditions as inserting alumina particles to the lubrication layer in the simulated journal bearing system. Several parameters such as AE rms level, waveform, AE energy distribution and other AE event parameters are used for analysis and characterization of damage source. The results showed that the history of damage was well correlated with the changes of AE rms level and the type of damage source signal can be verified using other informations such as waveform, distributions of AE parameters etc.

• Journal of Korean Society of Environmental Engineers
• /
• v.28 no.8
• /
• pp.836-842
• /
• 2006

Pine needle samples(1 year, 2 year, 3 year old) were collected in Seoul and Ansung to investigate the deposition characteristics of atmospheric PCBs depending on exposure periods. Total PCBs concentration of pine needle samples in Seoul and Ansung showed 2,429, 1,198 pg/g DW(dry weight), respectively. PCB homologs concentration of pine needle samples decreased with increasing chlorine-substituted compounds. It showed that higher chlorine- substituted compounds in existing particle phase compared to lower chlorine-substituted compounds existing in gaseous phase were difficult to accumulate lipids of the pine needles samples. The results of regression analysis between exposure periods in the atmosphere and concentration of total PCBs measured in pine needles at two sites showed significant levels($R^2>0.94$, p<0.01), which implies that atmospheric PCBs accumulated on pine needles with positive linearity depending on exposure periods in this study. Therefore pine needle samples can be used as passive air sampler(PAS) for monitoring air contamination for a long time in different sites.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.363-363
• /
• 2008

The development of dry etching process for sapphire wafer with plasma has been key issues for the opto-electric devices. The challenges are increasing control and obtaining low plasma induced-damage because an unwanted scattering of radiation is caused by the spatial disorder of pattern and variation of surface roughness. The plasma-induced damages during plasma etching process can be classified as impurity contamination of residual etch products or bonding disruption in lattice due to charged particle bombardment. Therefor, fine pattern technology with low damaged etching process and high etch rate are urgently needed. Until now, there are a lot of reports on the etching of sapphire wafer with using $Cl_2$/Ar, $BCl_3$/Ar, HBr/Ar and so on [1]. However, the etch behavior of sapphire wafer have investigated with variation of only one parameter while other parameters are fixed. In this study, we investigated the effect of pressure and other parameters on the etch rate and the selectivity. We selected $BCl_3$ as an etch ant because $BCl_3$ plasmas are widely used in etching process of oxide materials. In plasma, the $BCl_3$ molecule can be dissociated into B radical, $B^+$ ion, Cl radical and $Cl^+$ ion. However, the $BCl_3$ molecule can be dissociated into B radical or $B^+$ ion easier than Cl radical or $Cl^+$ ion. First, we evaluated the etch behaviors of sapphire wafer in $BCl_3$/additive gases (Ar, $N_2,Cl_2$) gases. The behavior of etch rate of sapphire substrate was monitored as a function of additive gas ratio to $BCl_3$ based plasma, total flow rate, r.f. power, d.c. bias under different pressures of 5 mTorr, 10 mTorr, 20 mTorr and 30 mTorr. The etch rates of sapphire wafer, $SiO_2$ and PR were measured with using alpha step surface profiler. In order to understand the changes of radicals, volume density of Cl, B radical and BCl molecule were investigated with optical emission spectroscopy (OES). The chemical states of $Al_2O_3$ thin films were studied with energy dispersive X-ray (EDX) and depth profile anlysis of auger electron spectroscopy (AES). The enhancement of sapphire substrate can be explained by the reactive ion etching mechanism with the competition of the formation of volatile $AlCl_3$, $Al_2Cl_6$ or $BOCl_3$ and the sputter effect by energetic ions.

• Journal of the Mineralogical Society of Korea
• /
• v.21 no.1
• /
• pp.57-65
• /
• 2008

The geochemical partitioning of arsenic in contaminated soils from a of wet land and tailing of the abandoned mine is examined. Chemical analysis and sequential extraction method by ultrasound-sonication extraction are applied to investigate the mobility and chemical existence conditions of arsenic as well as heavy metals. The results of this study showed that heavy metals concentration of tailings showed as a following order: Fe > As > Cu > Pb > Cr. The highest metal concentration was recognized in samples less than $63\;{\mu}m$ fraction in their particle sizes. Exchangeable and carbonate fractions in soil samples showed following Cu > As > Pb > Fe > Cr for tailings, and Fe > Pb > Cu > As > Cr for reservoir soils, respectively. Arsenic was bound as exchangeable fraction in tailings and its concentration appeared higher than those of the other metals. Thus, As can be easily dispersed into soil and water environments. The obtained results can be used to design soil remediation plan in the study area and require further detailed study to investigate severe environmental pollution of surface water as well as rivers with respect to heavy metals in terms of speciation analysis of toxic elements such as As and Cr.

• Journal of the Semiconductor & Display Technology
• /
• v.4 no.4 s.13
• /
• pp.19-26
• /
• 2005

The process optimization of ozone concentration and half life time was investigated in ultra pure water and alkaline solutions for the wet cleaning of silicon wafer surface at room temperature. In the ultra pure water,. the maximum concentration (35 ppm) of ozone was measured at oxygen flow rate of 3 liters/min and ozone generator power over 60%. The half life time of ozone increased at lower power of ozone generator. Additive gases such as $N_2$ and $CO_2$ were added to increase the concentration and half life time of ozone. Although the maximum ozone concentration was higher with the addition of $N_2$ gas, a longer half life time was observed with the addition of $CO_2$. When $NH_4OH$ of 0.05 or 0.10 vol% was added in DI water, the pH of the solution was around 10. The addition of ozone resulted in the half life time less than 1 min. In order to maintain high pH and ozone concentration, ozone was continuously supplied in 0.05 vol% ammonia solutions. 3 ppm of ozone was dissolved in ammonia solutions. The static contact angle of silicon wafer surface became hydrophilic. The particle removal was possible alkaline ozone solutions. The organic contamination can be removed by ozonated ultra pure water and then alkaline solution containing ozone can remove the particles on silicon surface at room temperature.

• Ecology and Resilient Infrastructure
• /
• v.2 no.2
• /
• pp.167-176
• /
• 2015

The water quality of the Gulpo Stream flowing through Incheon, Bucheon, Seoul, and Kimpo is getting worse due to a slow flow rate and bank constructions by stream channelization as well as an inflow of pollutants from living-sewages and factory-sewages. Besides, a dry stream phenomenon caused by a lack of maintenance water upstream makes a self-purification system worse, and the water quality of the Gulpo Stream is currently at its lowest level. The accumulated sludge of the streambed is mostly formed by the deposition of particle pollutants due to the slow flow rate and an artificially straightened stream channel. This accumulated sludge adsorbs a great quantity of organic materials and heavy metals. Because of the internal contamination possibility by a re-gushing, even after the pollution source is removed, it can cause future water pollution. Without a total examination as previously recommended, it is considered difficult to accomplish practical efficiency. In conclusion, the management of periodic sediment management such as dredging would be necessary in the Gulpo Stream because sediment could be an internal pollution source of stream water under anaerobic conditions.

• Journal of the Korean GEO-environmental Society
• /
• v.12 no.5
• /
• pp.51-57
• /
• 2011

Generally, ready-mixed concrete(RMC) gets hardened by time, so the remaining concrete in the drum should be cleaned. But if the RMC waste water generated from this is discharged to soil without any treatment, the strong alkaline elements and heavy metals affect water and ecosystem pollution. Although about 10 to 15% of water used for cleaning in the RMC factory is discharged to soil or river, the concrete report of this affecting soil pollution has not been sufficient. Hence, in this study it was analyzed the extraction of cleaning water from RMC factories all over the country and heavy metal and pH components remaining in soil when this is penetrated to various soils having water permeability. The specimens used for the experiment are weathering soil and soils having different particle size, and it is made to be penetrated to those for 24 hours while fixed thickness of the layer is maintained. Cleaning water is divided into that before deposition treatment(sludge water) and that after deposition treatment(upper water) to be penetrated into soil, and according to the result of penetrating sludge water to soil, Cu and Mn, Fe, and Zn were found to be remained over 23 to 90%. However, it is analyzed that in upper water having deposition treatment, Cu and Mn remain as 60% or more only in weathering soil.

• Economic and Environmental Geology
• /
• v.56 no.4
• /
• pp.409-419
• /
• 2023

Acid mine drainage(AMD) treatment is classified as both passive and active treatment. During the treatment, about 5,000 tons of neutralization sludge is generated as a by-product per year in Korea. This study was conducted to evaluate the characteristics of sludge generated from physico·chemical treatment processes as an active treatment from 5 different sources (D, H, S, T, Y) and the possibility of the sludges being recycled. The sludges have a pH range of 5.86 ~ pH 7.89, and a water content range of 51% ~ 82%. Most of particle sizes were less than 25 ㎛. In analysis of inorganic elements, the concentration of Al, Fe, and Mn were between 1,189 mg/kg ~ 129,344 mg/kg, 106,132 mg/kg ~ 338,011 mg/kg, and 3,472 mg/kg ~ 11,743 mg/kg, respectively. The concentration of As and Zn in sludge-T, Cd in sludge-D, Ni in sludge-H, Zn in sludge-S, and Cd in sludge-Y exceeded the soil contamination standards of Korea. The results from 2 separate kinds of leaching test, the Korea Standard Leaching Test(KSLT) and Toxicity Characteristic Leaching Procedure(TCLP), showed that all the sludges met the Korea groundwater standards. From the XRD and SEM-EDS analysis, the peaks of calcite and quartz were found in the sludges. The sludge also had a high proportion of Fe and O, and the majority of the composition was amorphous iron hydroxide.

• Journal of the Korean Geosynthetics Society
• /
• v.14 no.4
• /
• pp.59-77
• /
• 2015

In order to meet the new requirements for landfill materials, this study planned a study to apply mixed soil of mixing bottom ash and coastal dredged soil to the dredged ground. Coal ash generated from thermal power plant is divided into fly ash and bottom ash. In the case of fly ash, many studies have been conducted because small particles causes permeability coefficient to be small during recycling so no problem has been raised in the environmental area but the utilization of bottom ash has been limited because environmental problems have been raised during recycling due to its larger particle size and greater permeability coefficient. According to recently published studies, however, the results of the study that conducted the water analysis of leachate generated in the ground improvement section using bottom ash showed that heavy metal contamination levels were found to be within the reference value and no significant environmental problems were found so utilization of bottom ash is evaluated to increase significantly in the future. This bottom ash has the particle size of sand and only transportation costs need to be considered when providing materials because the majority has been disposed and it is judged as the most suitable material in dredging landfill in the economic aspect because most thermal power plants are located in the coast and transportation costs can be reduced by ship. Also, research on mixed soil that can maximize the effect of the construction period and construction cost savings than dredged soil is determined as needed because the demand for coastal dredging reclamation is increasing such as Saemangeum project etc. Therefore, we studied self-weight consolidation characteristics depending on sample processing and mixing method of mixed soil by carrying out interior self-weight consolidation experiments on mixed soil of mixing bottom ash and Kaolinite according to the new development needs of recent coastal reclaimed ground and these result findings are expected to be used as basic data when applying the large coastal dredged ground in the future.

• Economic and Environmental Geology
• /
• v.47 no.5
• /
• pp.479-488
• /
• 2014

Naturally occurring asbestos (NOA) from disturbance of rocks and soils has been overlooked as a source of exposure that could potentially have a detrimental impact on human health. But, few researches on mineralogical characteristics of NOA occurred in soils have been reported in Korea. Therefore, the objective of this study was to investigate the mineralogical characteristics of NOA occurred in soils at Daero-ri area, Seosan, Chungnam Province, Korea. Sedimentation method was used for particle size separation of the asbestos-containing soils. XRD and PLM analyses were used to characterize mineralogical characteristics and mineral assemblages in soils. SEM-EDS and TEM-EDS analyses were used to characterize mineral morphology and chemical composition. Particle size analyses of the asbestos-containing soils showed they were composed of 26-93% sand, 4-23% silt and 3-70% clay. Soil texture of the soils was mainly sand, sandy loam, sandy clay, and clay. PLM analyses of the soil showed that most of the soil contained asbestiform tremolite and actinolite. The average content of asbestos in the soil was 1.5 wt. %. Therefore, the soil can be classified into asbestos-contaminated soils based on U. S. Environmental Protection Agency classification (content of asbestos in contaminated soil > 1%). Morphologically different types of tremolite such as long fibrous, needle-like, fiber bundle, bladed and prismatic forms co-existed. Prismatic tremolite was dominant in sand fraction and asbestiform tremolite was dominant in silt fraction. This study indicates that the prismatic form of tremolite transform gradually into a fibrous form of tremolite due to soil weathering because tremolite asbestos was mainly existed in silt fraction rather than sand fraction.