• Carbon letters
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• v.15 no.1
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• pp.57-66
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• 2014

Three activated carbons (ACs) were prepared using NaOH (N) as an activating agent. Hydrofluoric acid pre-leached rice husk was used as a precursor. After leaching, the precursor was washed with distilled water, dried, crushed, and then sieved; a size fraction of 0.3-0.5 mm was selected for carbonization in the absence of air at $600^{\circ}C$. The carbonization product (LC) was mixed with NaOH at ratios of 1:2, 1:3, and 1:4 (wt of LC: wt of NaOH) and the produced ACs after activation at $800^{\circ}C$ were designated NLC21, NLC31, and NLC41, respectively. Surface and textural properties were determined using nitrogen adsorption at $-196^{\circ}C$, scanning electron microscopy images, thermogravimetric analysis, and Fourier transform infrared spectra. These ACs were used as adsorbents for lead(II) from aqueous solutions. The effects of the textural properties and the chemistry of the carbon surfaces were investigated and the impact of the operation conditions on the capacity for lead(II) sorption was also considered. Modification of NLC41 with $H_2O_2$ and $HNO_3$ gave two other adsorbents, $H_{NLC41}$ and $N_{NLC41}$ respectively. These two new samples exhibited the highest removal capacities for lead(II), i.e.117.5 and 128.2 mg/g, respectively. The adsorption data fitted the Langmuir isotherm and the kinetic adsorption followed pseudo-second order kinetics. The thermodynamic parameters have been determined and they indicated a spontaneous endothermic process.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.11
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• pp.865-871
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• 2017

In this paper, a gelatin layer was formed on the surface of the twisted fiber-optic couplers fabricated by hydrofluoric acid, which can be used to measure relative humidity. The proposed method of sensors has advantage of low cost compared with the sensors based on the conventional electronic devices and takes beneficial characteristics of optical fibers and light. The fiber-optic sensors presented in this study show a measurement from about 40% to 85% relative humidity, and the experimental results agree well with the calculated results. Based on the design presented in this paper, the structure will enable promising applications in the detecting humidity and various hazardous gases.

• Analytical Science and Technology
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• v.22 no.3
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• pp.247-253
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• 2009

Porous silicon films are electrochemically etched from crystalline silicon wafers in an aqueous solution of hydrofluoric acid(HF). Careful control of etching conditions (current density, etch time, HF concentration) provides films with precise, reproducible physical parameters (morphology, porosity and thickness). The etched pattern could be varied due to (1) current density controls pore size (2) etching time determines depth and (3) complex layered structures can be made using different current profiles (square wave, triangle, sinusoidal etc.). The optical interference spectrum from Fabry-Perot layer has been used for forensic applications, where changes in the optical reflectivity spectrum confirm the identity. We will explore a method of identifying the specific pattern code and can be used for identities of individual code with porous silicon based encoded nanosized smart particles.

• Journal of the Korean Institute of Gas
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• v.28 no.1
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• pp.35-43
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• 2024

With continuous advancements in industry, science, and technology, there is a steady increase in the number and utilization of new chemicals. The growing societal emphasis on chemical safety management is paralleled by an increasing public demand for robust safety measures. While various ministries at the government level oversee the safety management of chemical substances, the occurrence of accidents related to chemical substances remains frequent each year due to problems such as aging facilities and careless handling. Upon analyzing domestic chemical accident cases, incidents occurred predominantly in the sequence of leakage, explosion, fire, and others. The main causes of these accidents were examined, revealing facility defects and non-compliance with safety management as the primary contributing factors. In this study, Hazard and Operability Analysis (HAZOP) was employed to identify hazardous risk factors associated with the handling of hydrofluoric acid in workplaces, and a risk assessment was performed using Bow-Tie method. Based on the results of this study, it is expected to enhance safety management plans aimed at preventing chemical accidents in workplaces dealing with similar facilities. Ultimately, these insights contribute to the development of an advanced chemical safety management system, capable of proactively preventing potential chemical accidents.

• Journal of Wetlands Research
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• v.17 no.1
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• pp.45-52
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• 2015

We obtained the following results from investigation on vegetation damage from 5 to 6 August, 2013, about one year after an accident that hydrofluoric acid leaked from a chemical maker, Hube Globe in Gumi. Pinus densiflora and Pinus strobus showed very severe damage. Ginko biloba, Quercus acutissima, Pinus rigida, Salix glandulosa, Hibiscus syriacus, and Lagerstroemia indica showed severe damage. Quercus variabilis, Lespedeza cyrtobotrya, and Miscanthus sinensis showed moderate damage. Quercus aliena, Smilax china, Arundidinella hirta, Ailanthus altissima, Robinia pseudoacacia, and Paulowinia coreana showed slight damage. We did not find any plants without leaf damage around there. This result means that fluoride damage still persists in this area as was known that fluoride remains for a long time in air, soil and water and exerts negative effects at all levels of an ecosystem. In addition, fluoride content contained in plant leaf depended on the distance from a fertilizer producing factory and vegetation damage tended to proportionate to the concentration in the Yeocheon industrial complex. In these respects, a measure for removal or detoxification of the remaining fluoride is urgently required around the hydrofluoric acid leak spot. Fertilizing of dolomite containing Ca and Mg, which can trap fluoride, was prepared as one of the restoration plans. In addition, phosphate fertilizing was added in order to enhance soil ameliorating effects. Furthermore, we recommend the introduction of tolerant plants as the second measure to mitigate fluoride damage. As the tolerant plants to make a new forest by replacing trees died due to hydrofluoric acid gas damage, we recommended Q. aliena and S. china, A. hirta, etc. were recommended as plant species to add mantle vegetation to the forest margin to ensure stable interior environment of the forest.

• Polymer(Korea)
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• v.39 no.1
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• pp.114-121
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• 2015

Mutli-walled carbon nanotubes (MWCNTs) were surface-modified by a hydrofluoric acid solution to remove impurities and improve interfacial bonding and dispersion of nanotubes in an epoxy matrix. The crystallinity on the surface of treated MWCNTs was investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The mechanical properties were characterized by tensile test, and the enhancement of mechanical properties of the modified MWCNTs/epoxy composites was indicated by a 33% increase in tensile strength. The electromagnetic interference shielding effectiveness (EMI-SE) of modified MWCNTs/epoxy composites was improved with an increase in concentration of hydrofluoric solution, and EMI-SE showed the maximum increase with 25% HF. However, mechanical and EMI-SE properties didn't show further increase with over 50% HF concentration because the properties of MWCNTs were influenced by degradation of crystallinity and intrinsic properties of MWCNTs. The mechanical and electrical property enhancements of the polymer composites are attributed to the modification of MWCNTs which improve crystallinity of MWCNTs and dispersion in the epoxy resin.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.42-45
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• 2005

Accurate prediction of the fate and transport of contaminants in soils and sediments is very Important to environmental risk assessment and effective remediation of contaminated soils and sediments. The fate and transport of contaminants in subsurface are affected by geosorbents, especially carbonaceous materials including black carbon. Various physical and chemical treatment methods have been developed to separate different kinds of carbonaceous materials from soils and sediments. However, the effects of these separation methods on the properties of remaining carbonaceous materials including sorption capacity and linearity are unclear. The objective of this study is to determine if the chemical and thermal treatment methods previously used to separate different carbonaceous material fractions affect the properties of carbonaceous materials including longer term sorption capacity of hydrophobic organic contaminants. The results indicate that treatments with hydrochloric acid (HCl)/hydrofluoric acid (HF), trifluoroacetic acid (TFA), sodium hydroxide (NaOH) may not affect the sorption capacity of black carbon reference materials such as char and soot, however, treatments with acid dichromate $(K_2Cr_2O_7/H_2SO_4)$ and heat $(375^{\circ}C)$ for 24 hours in sufficient of oxygen) decrease the sorption capacity of them. The results of longer term sorption isotherm indicate that 2 days might be enough for trichloroethene (TCE) to equilibrate apparently with treated black carbon reference materials. The results suggest that acid dichromate and heat treatments may not appropriate method to investigate sorption properties of black carbon in soils and sediments.

• Journal of Integrative Natural Science
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• v.2 no.1
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• pp.37-40
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• 2009

Synthesis and characterization of alkyl-capped nanocrystalline silicon (R-n-Si) have been achieved from the reaction of silicontetrachloride with magnesiumsilicide. Surface of silicon nanocrystal has been derivatized with various alkyl groups (R=methyl, n-butyl, etc.). Silicon nanoparticles have been also obtained by the sonication of luminescent porous silicon. Former exhibits an emission band at 360 nm, but latter exhibits an emission band at 680 nm. In this study very sensitive detection of TNT (2,4,6-trinitrotoluene), DNT (2,4-dinitrotoluene), NB (nitrobenzene), and PA (picric acid) has been achieved in gas phase with porous silicon using photoluminescence quenching of the silicon crystallites as a transduction mode. Porous silicon are electrochemically etched from crystalline silicon wafers in an aqueous solution of hydrofluoric acid. We have characterized these silicon nanoparticles by Luminescence Spectrometer (LS 55).

• Journal of Korean Society of Environmental Engineers
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• v.33 no.10
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• pp.774-781
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• 2011

Nitric acid and hydrofluoric acid are used for acid pickling in zirconium alloy tubing manufacturing process. Nitrate and fluoride in the wastewater were treated by chemical coagulation and SOD (Sulfur Oxidation Denitrification) process. This study is investigated the effect of fluoride concentration and the optimal condition for SOD process. The limited fluoride concentration for SOD process was below 20 mg F-/L. The adjusted pH and alkalinity by NaOH and $NaHCO_3$ was shown to be more effective for removal of nitrate compared with using NaOH. Furthermore, the microbial activator mixed trace elements and ingredient for alkalinity did not only supplement with alkalinity but also enhance the growth and proliferation for sulfur-oxidizing bacteria. As a result, the inorganic industrial wastewater was successfully treated by the microbial activator in SOD process without continuous addition of seed sludge. Finally, SOD process was shown to remove nitrate in industrial wastewater and to contribute the microbial activator for activation of sulfur-oxidizing bacteria.

• Journal of the Korean Institute of Gas
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• v.27 no.4
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• pp.43-49
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• 2023

Hydrofluoric acid is a less acidic substance than hydrochloric acid, nitric acid, and sulfuric acid, but it is one of the most dangerous substances for humans. In recent years, it has become an indispensable substance in industries such as chemical plants and the semiconductor industry, and although it is a threat to the human body, its use is increasing for various purposes, and the amount of use is constantly increasing due to the expansion and development of the industry. The dangers of hydrogen fluoride have been highlighted since the 2012 accident, which led to a more than fivefold increase in management standards for handling facilities. Hydrogen fluoride converts to hydrofluoric acid when exposed to the air, which can be fatal to humans. This study simulates the effects of a release of a toxic substance in the workplace, even though a protection layer has been provided to minimize the damage caused by the released toxic substance, and recommend ways to control the risk to workers in the event of a release in the workplace.