• Journal of the Korean Institute of Gas
• /
• v.22 no.2
• /
• pp.46-51
• /
• 2018

Hydrogen sulfide from landfill and sewage treatment plant is a major odor component and causes many civil petitions. Rapidly developing industries release hydrogen sulfide, an odorous gas, to the atmosphere. This study aims to develop a $10{\mu}mol/mol$ concentration level hydrogen sulfide primary standard gas for odor measurement. The hydrogen sulfide gas was prepared at a nominal concentration of $10{\mu}mol/mol$ in nitrogen using the gravimetric method described in ISO 6142. Replicate standard gases were produced in 4 aluminium cylinders, and their concentrations were verified by GC-AED. The uncertainty of production was less than 0.50 %, and the variation of the 4 replicates was 0.22 %. The wall adsorption of hydrogen sulfide in cylinders was 0.10 % at 1500 psi, and the concentration was estimated to be long-term stable for one year. The relative expanded uncertainty of the preparation consistency, adsorption and long-term stability of this hydrogen sulfide standard gas was less than 1.05 % (95 % of confidence level, k=2).

• Journal of the Korean Society of Propulsion Engineers
• /
• v.14 no.6
• /
• pp.31-37
• /
• 2010

This study was carried out to investigate the thermal decomposition and execute EIDS slow cook-off test for the propellant ingredients and 2 kinds of HTPE propellants. The thermal analysis of the propellant ingredients used in this study showed that the thermal stability of these materials decreases in the following order : AP > HTPE > AN > BuNENA. In addition, propellant HTPE 002 containing AN showed that an endothermic process at around $125^{\circ}C$ corresponding to the solid phase change(II$\rightarrow$I) of AN was followed by the exothermic process of BuNENA/AN mixture up to $200^{\circ}C$. In EIDS slow cook-off tests, HTPE 001 and HTPE 002 reacted at around $250^{\circ}C$ and $152^{\circ}C$ respectively, and both of them showed sudden temperature increase curves at $115^{\circ}C$. The critical temperatures, $T_c$, of thermal explosion for the propellants HTPE 001 and HTPE 002, were obtained from both the non-isothermal curves at various heating rates and Semenov's thermal explosion theory. Kissinger's method that was used to calculate $T_c$ was also employed to obtain the activation energies for thermal decompositions.

• Korean Journal of Materials Research
• /
• v.22 no.1
• /
• pp.54-60
• /
• 2012

The particle size of MgO was examined as a function of the Na content in $Mg(OH)_2$ powders and the calcination temperature. $Mg(OH)_2$ suspension was obtained by dropwise precipitation of $Mg(NO_3)_2{\cdot}6H_2O$ and NaOH solutions. The suspension was diluted by varying the dilution volume ratio of distilled water to $Mg(OH)_2$ suspension to change the Na salt concentration in the suspension. $Mg(OH)_2$ slurry was filtered and dried at $60^{\circ}C$ under vacuum, and then its $Mg(OH)_2$ powder was calcined to produce MgO with different amount of Na content at $500\sim900^{\circ}C$ under air. Investigation of the physical and chemical properties of the various MgO powders with dilution ratio and calcination temperature variation was done by X-ray diffraction, transmission electron microscopy, BET specific surface area and thermal gravimetric analysis. It was observed that MgO particle size could depend on the condition of calcination temperature and dilution ratio of the $Mg(OH)_2$ suspension. The particle size of the MgO depends on the Na content remaining in the $Mg(OH)_2$ powder, which powder was prepared by changing the dilution ratio of the $Mg(OH)_2$ suspension. This change increased as the calcination temperature increased and decreased as the dilution ratio increased. The growth of MgO particle size according to the increase of temperature was more effective when there was a relatively high content of Na. The increase of Na content lowered the temperature at which decomposition of $Mg(OH)_2$ to MgO took place, thereby promoting the crystal growth of MgO.

• Food Science and Preservation
• /
• v.21 no.3
• /
• pp.334-340
• /
• 2014

The moisture sorption isotherms of corn powder prepared from corn kernels roasted for 20 min at 160, 180, 200, 220, and $240^{\circ}C$ were determined at $20^{\circ}C$ using the static gravimetric method over the range of water activities ($a_w$) of 0.11~0.90. The moisture sorption isotherms showed a typical sigmoid shape, and the equilibrium moisture content tended to increase with increasing $a_w$, and increased sharply at above 0.75 $a_w$. At above 0.53 $a_w$, the equilibrium moisture content of the roasted corn powder increased with the increase in the roasting temperature. Six mathematical models (Bradley, Caurie, Halsey, Henderson, Kuhn, and Oswin) were used to fit the experimental data. The Oswin, Caurie, Henderson, and Halsey models were found to have suitability for describing the sorption curves, and the Oswin model was the best fit model for all the roasting temperatures. Concerning the monolayer moisture content, the Guggenheim-Anderson-Boer (GAB) equation showed high significance. The monolayer moisture content increased as the roasting temperature was increased, to 0.043 and 0.053 kg $H_2O/kg$ solids in the corn powder roasted at $180^{\circ}C$ and $240^{\circ}C$, respectively. These results suggest that the roasting temperatures of the corn kernels affected the moisture sorption characteristics ($20^{\circ}C$) of the corn powder.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.16 no.3
• /
• pp.254-263
• /
• 2006

Manganese has a role as both toxic and essential in humans. Manganese is also an essential component in the welding because it increases the hardness and strength, prevents steel from cracking of welding part and acts as a deoxidizing agent to form a stable weld. In this study, manganese generation rate and its content was determined in flux cored arc welding on stainless steel. Domestic two products and foreign four products of flux cored wires were tested in the well designed fume generation chamber as a function of input power. Welding fume was measured by gravimetric method and metal manganese was determined by inductively coupled plasma-atomic emission spectrophotometer. The outer shell of the flux cored wire tube and inner flux were analyzed by scanning electron microscopy to determine their metal compositions. Manganese generation rate($FGR_{mn}$) was increased as the input power increased. It was 16.3 mg/min at the low input power, 38.1 mg/min at the optimal input power, and up to 55.4 mg/min at the high input power. This means that $FGR_{mn}$ is increased at the work place if welder raise the current and/or voltage for the high productivity. The slope coefficient of $FGR_{mn}$ was smaller than that of the generation rate of total fume(FGR). Also, the correlation coefficient of $FGR_{mn}$ was 0.65 whereas that of FGR is 0.91. $FGR_{mn}$ was equal or higher in the domestic products than that of the foreign products although FGR was similar. From the electron microscopic analytical data, we concluded that outer shell of the wire was composed mainly of iron, chromium, nickel and less than 1.2 % of manganese. There are many metal ingredients such as iron, silica, manganese, zirconium, titanium, nickel, potassium, and aluminum in the inner flux but they were not homogeneous. It was found that both $FGR_{mn}$ and content of manganese was higher and more varied in domestic flux cored wires than those of foreign products. To reduce worker exposure to fumes and hazardous component at the source, further research is needed to develop new welding filler materials that improve the quality of flux cored wire in respect to these points. Welder should keep in mind that the FGR, $FGR_{mn}$ and probably the generation rate of other hazardous metals were increased as the input power increase for the high productivity.

• Applied Chemistry for Engineering
• /
• v.18 no.2
• /
• pp.188-193
• /
• 2007

Semi-solvent type cleaning agents were prepared by mixing naphthenes, natural terpene oil, surfactant and water, and measured their physical properties. And also, cleaning efficiency for flux and grease was measured by gravimetric method. By measuring the physical properties, pH for cleaning agents were 6.0~6.7, surface tension, 27.4~28.4 dyne/cm, and wetting index, 8.65~12.46 (with water), 11.99~17.43 (without water). The cleaning agent composed of naphthene, 30 wt%, natural terpene oil, 45 wt%, surfactant, 13 wt%, co-surfactant, 12 wt%, and water, 0 wt% had the largest wetting index, and shown the most effective cleaning properties for flux (98.66%) and grease (93.44%). The conductivity with $0.5{\sim}0.9{\mu}s/cm$ to the cleaning agent containing small amount of water was found to form W/O type microemulsion.

• Applied Chemistry for Engineering
• /
• v.23 no.1
• /
• pp.105-111
• /
• 2012

Manganese (Mn) catalysts were generated using $CeO_2$ and $ZrO_2$supports synthesized by the supercritical hydrothermal method and two different Mn precursors, aimed at an application for a low-temperature selective catalytic reduction process. Manganese acetate (MA) and manganese nitrate (MA) were used as Mn precursors. Effects of the kind and the concentration of the Mn precursor used for catalyst generation on the NOx removal efficiency were investigated. The characteristics of the generated catalysts were analyzed using $N_2$ adsorption-desorption, thermo-gravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. De-NOx experiments were carried out to measure NOx removal efficiencies of the catalysts. NOx removal efficiencies of the catalysts generated using MA were superior to those of the catalysts generated using MN at every temperature tested. Analyses of the catalyst characteristics indicated that the higher NOx removal efficiencies of the MA-derived catalysts stemmed from the higher oxygen mobility and the stronger interaction with support material of $Mn_2O_3$ produced from MA than those of $MnO_2$ produced from MN.

• Analytical Science and Technology
• /
• v.30 no.5
• /
• pp.287-294
• /
• 2017

As the demand for natural gas increases with industrial development, the supply of natural gas is expected to become unstable with a shortage of imported natural gas. It is hence necessary to meet this demand by introducing and developing various types of natural gas, such as pipeline natural gas (PNG) and substituted natural gas (SNG), in addition to liquefied natural gas (LNG). The components included in PNG as well as their concentrations must be measured accurately, and a standard gas should be developed to accurately measure hydrocarbons ($C_6-C_{10}$), which are trace components included in natural gas. The components in the primary standard gas mixtures (PSMs) developed in the present study were hexane, heptane, octane, nonane, and decane with concentrations of $10-30{\mu}mol/mol$ with methane as the balance gas. Standard hydrocarbon ($C_6-C_{10}$) gas mixtures were prepared in aluminum cylinders by a gravimetric method with traceability following ISO 6142 with raw material gases, for which the purity of each component was analyzed completely. The prepared standard gas mixtures were analyzed by to evaluate the preparation consistency between the standard gas mixtures, the adsorbability of the cylinders, the variation of the stability, and the uncertainty. The results showed that aluminum cylinders have little adsorptive loss on their internal surfaces with excellent long-term stability. The developed standard gas mixture, containing hexane, heptane, octane, nonane, and decane with concentrations of $10-30{\mu}mol/mol$, showed an uncertainty in a range of 0.79 % - 1.63 %.

• Journal of Life Science
• /
• v.19 no.8
• /
• pp.1088-1092
• /
• 2009

This study was conducted to determine an estimated value and change in TDF (total dietary fiber) binding major minerals (Ca, P, K Mg) of soybean sprouts depending on cultivation periods of 1, 3 or 5 days, and parts of cotyledon and hypocotyl. The compositions of TDF binding major minerals in soybean sprouts were evaluated by the enzymatic-gravimetric method developed by Prosky and adopted by AOAC. The content of TDF binding P ranged between 915.28 mg and 1037.82 mg per 100 g cotyledon. Average contents of Ca, K, and Mg in cotyledon ranged between 541.67 mg and 634.34 mg, 180.91 mg and 253.98 mg, 231.90 mg and 301.01 mg, respectively, on dry matter basis. The average contents of TDF binding Ca in hypocotyl per 100 g were between 454.36 mg and 540.33 mg, and other major minerals contents were between 149.24 mg and 186.21 mg for P, 164.17 mg and 182.78 mg for K, and 152.53 mg and 161.22 mg for Mg, respectively. The proportional changes of Ca, an estimated value in cotyledon, ranged between 5.58% and 30.98%, 47.18% and 59.10% for P, 95.24% and 95.50% for K, and 58.45% and 68.64% for Mg, respectively, based on dry matter. An estimated value of Ca, P, K, and Mg in hypocotyl ranged between 6.71% and 13.52%, 91.03% and 91.76%, 96.91% and 98.92%, and 61.03% and 66.37%, respectively, on dry matter basis.

• Composites Research
• /
• v.28 no.4
• /
• pp.168-175
• /
• 2015

Recently, the applications of carbon fiber reinforced plastics (CFRPs) have become broader than ever when it comes to such industries as automotive, ships, aerospace and military because of their lightweight-ness and high mechanical properties. Thermosetting plastics like epoxy are frequently used as the binding matrix in CFRPs due to their high hardness, wetting characteristics and low viscosity. However, they cannot melted and remolded. For this reason, thermosetting plastic wastes have caused serious environmental problems with the production of fiber reinforced plastics. Thus, many studies have focused on the carbon fiber reinforced thermoplastics (CFRTPs) and recycling carbon fiber. In this study, recycled carbon fiber (RCF) was prepared from CFRPs using a pyrolysis method, which was employed to separate resin and carbon fiber. The degree of decomposition for epoxy resin was confirmed from thermal gravimetric analysis (TGA) and scanning electron microscope (SEM). The RCF was cut and ground to prepare a carbon fiber composite sheet (CFCS). CFCS was manufactured by applying recycled carbon fibers and various thermoplastic fibers. Various characterizations were performed, including morphological analyses of surface and cross-section, mechanical properties, and crystallization enthalpy of CFCS at different cooling conditions.