• Korean Journal of Materials Research
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• v.26 no.12
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• pp.751-756
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• 2016

Graphite was diffusion-bonded by hot-pressing to W-25Re alloy using a Ti interlayer. For the joining, a uniaxial pressure of 25 MPa was applied at $1600^{\circ}C$ for 2 hrs in an argon atmosphere with a heating rate of $10^{\circ}C\;min^{-1}$. The interfacial microstructure and elemental distribution of the W-25Re/Ti/Graphite joints were analyzed by scanning electron microscopy (SEM). Hot-pressed joints appeared to form a stable interlayer without any micro-cracking, pores, or defects. To investigate the high-temperature stability of the W-25Re/Ti/Graphite joint, an oxy-acetylene torch test was conducted for 30 seconds with oxygen and acetylene at a 1.3:1 ratio. Cross-sectional analysis of the joint was performed to compare the thickness of the oxide layer and its chemical composition. The thickness of W-25Re changed from 250 to $20{\mu}m$. In the elemental analysis, a high fraction of rhenium was detected at the surface oxidation layer of W-25Re, while the W-25Re matrix was found to maintain the initial weight ratio. Tungsten was first reacted with oxygen at a torch temperature over $2500^{\circ}C$ to form a tungsten oxide layer on the surface of W-25Re. Then, the remaining rhenium was subsequently reacted with oxygen to form rhenium oxide. The interfacial microstructure of the Ti-containing interlayer was stable after the torch test at a temperature over $2500^{\circ}C$.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.7
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• pp.23-29
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• 2010

We propose an optical gas sensor, which consists of a hollow core photonic bandgap fiber (HC-PBGF) and fiber Bragg grating (FBG), for the detection of acetylene gas. The gas detection scheme is uniquely characterized by modulating the Bragg wavelength of the fiber Bragg grating around a selected absorption line of gas filled in the photonic bandgap fiber. In the measurement, a 2m-long HC-PBGF and FBG with a Bragg wavelength of 1539.02nm were used. The FBG was modulated at 2Hz. We demonstrated that the optical fiber gas sensor was able to selectively measure the 2.5% and 5% of acetylene gases.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2006.04a
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• pp.54-56
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• 2006

Single-well-gas-sparging tests were developed and evaluated for assessing the feasibility of in-situ aerobic cometabolism of trichloroethylene (TCE), using propane as a growth substrate. To evaluate transport characteristics of dissolved solutes [sulfur hexafluoride (SF6) or bromide (non-reactive tracers), propane (a growth substrate), ethylene, propylene (nontoxic surrogates to probe for CAH transformation activity), and DO], push-pull transport tests were performed. Mass balance showed about 90% of the injected bromide and about 80% of the injected SF6 were recovered, and the recoveries of other solutes were comparable with bromide and slightly higher than SF6. A series of Gas-Sparging Biostimulation tests were performed by sparging propane/oxygen/argon/SF6 gas mixtures, and temporal ground water samples were obtained from the injection well under natural gradient 'drift' conditions. The decreased time for propane depletion and the longer time to deplete SF6 as a conservative tracer indicate the progress of biostimulation. Gas-Sparging Activity tests were performed. .Propane utilization, DO consumption, and ethylene and propylene cometabolism were well demonstrated. The stimulated propane-utilizers cometabolized ethylene and propylene to produce ethylene oxide and propylene oxide, as cometabolic by-products, respectively. Gas-Sparging Acetylene Blocking tests were performed by sparging gas mixtures including acetylene to demonstrate the involvement of monooxygenase enzymes. Gas substrate degradation was essentially completely Inhibited in the presence of acetylene, and no production of the corresponding oxides was also observed. The Gas-Sparging tests supports the evidences that the successive stimulation of propane-oxidizing microorganisms, cometabolic transformation of ethylene and propylene by the enzyme responsible for methane and propane degradation.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1025-1028
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• 2008

With the assistance of thermal pyrolysis process for hydrocarbon gases, the formation and growth of particulate carbon was systematically investigated as a function of temperature in the gas phase. The yield and average size of pyrocarbon particles were found to increase with increasing pyrolysis temperature. The difference in the yield of carbon particles generated by pyrolizing acetylene and ethylene gas posed a question about the role of hydrogen in the pyrolysis of hydrocarbon gases. In order to reveal the role of hydrogen, controlled amount of hydrogen was added to the acetylene pyrolysis, and then hydrogen addition was observed to suppress the formation and growth of carbon particles. One can control the size of pyrocarbon particles by controlling the hydrogen gas addition.

• Polymer(Korea)
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• v.35 no.2
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• pp.176-182
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• 2011

Liquid crystalline aromatic polyesters (LCPs) are representative examples of thermotropic liquid crystalline polymers, whose structure-property relationships have been the subject of many researches. In this study, we synthesized organo-soluble liquid crystalline aromatic polyesters, and their composites with acetylene-terminated thermoset resins were prepared and characterized. Soluble LCPs were synthesized by employing 6-hydroxy-2-naphthoic acid, terephthalic acid, isophthalic acid, and 4-aminophenol as monomers via condensation polymerization based on transesterfication and transamidation. Acetylene-terminated thermoset resins were synthesized by the reaction of 4-ethynylaniline with terephthaloyl dichloride, isophthaloyl dichloride or 4,4'-biphenyldicarbonyl dichloride. We prepared the soluble LCP/thermoset composites by solution blending followed by thermal treatment. The thermal stability, thermal expansion coefficient, and dielectric properties of the composite were studied.

• Journal of the Korean Institute of Gas
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• v.20 no.1
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• pp.29-39
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• 2016

Electrical apparatuses for use in the presence of explosive gas atmospheres have to be special designed to prevent them from igniting the explosive gas. Flameproof design implies that electrical components producing electrical sparks are contained in enclosures and withstand the maximum pressure of internal gas or vapours. In addition, any gaps in the enclosure wall have to designed in such a way that they will not transmit a gas explosion inside the enclosure to an explosive gas or vapours atmosphere outside it. In this study, we explained some of the most important physical mechanism of Maximum Experimental Safe Gap(MESG) that the jet of combustion products ejected through the flame gap to the external surroundings do not have an energy and temperature large enough to initiate an ignition of external gas or vapours. We measured the MESG and maximum explosion pressure of propane and acetylene by the test method and procedure of IEC 60079-20-1:2010.When the minimum MESG is measured, the concentration of propane, acetylene in the air is higher than the stoichiometric point and their explosion pressure is the highest value.

• Journal of Soil and Groundwater Environment
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• v.22 no.6
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• pp.22-28
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• 2017

The accuracy of analytical results in response to the use of different additives ($NH_4Cl$, KCl, $LaCl_3$) and oxidant gases was evaluated and compared by using Atomic Absorption Spectrometry (AAS). Identification of spectroscopic interferences and possible improvements in Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) analysis were also discussed. The average accuracies of total chromium using Certified Reference Materials (CRMs) were found to be 72.1~94.2% in air/acetylene flame condition by AAS, and they were improved to 100.5~110.5% when the oxidants was changed to nitrous oxide rather than adding the additives. The field samples showed similar trends to CRMs, but chromium concentrations were highly variable depending on analytical conditions. The average accuracies using CRMs were estimated to be 89.3~166.1% by ICP-AES, and improved to below 121.7% after eliminating iron interference. Field samples with low chromium and high iron concentration were measured to be > 30% lower in total chromium concentrations by ICP-AES than AAS in nitrous oxide/acetylene flame. Total chromium concentrations in soil could be analyzed with better accuracy under nitrous oxide/acetylene flame by AAS because it was more effective to increase the temperature of the flame than to eliminate the chemical interference for maximizing atomization of chromium. When using ICP-AES, interference substances, total chromium levels, and analytical conditions should be also considered.

• Journal of the Korean institute of surface engineering
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• v.56 no.1
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• pp.94-103
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• 2023

The effects of carburizing pressure and gas ratio on vacuum carburizing properties (uniformity and surface characteristics) have been studied through the analyses of carbon concentration, hardness, surface color, surface roughness and type of carbon bonding. AISI 4115 steel specimens were carburized with various pressures (1, 5, and 10 Torr) at different locations (P₁, P₂, P₃, P₄, P₅, and P₆) inside a furnace held at 950 ℃. Since the carburizing pressure represents the density of the carburizing gas, it plays an important role in improving the carburizing uniformity according to locations in the furnace. As the carburizing pressure increased, the carburizing uniformity according to the sample location was improved, but the surface of the carburized specimen was discolored due to the residual acetylene gas, which does not contribute to the carburizing reaction. Therefore, the carburizing uniformity and surface discoloration have been improved by injecting acetylene gas (carburizing gas) and nitrogen gas (non-reactive gas) in a specific ratio.

• Korean Journal of Materials Research
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• v.32 no.12
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• pp.553-559
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• 2022

In this work, the ablation behavior of monolith ZrB₂-30 vol%SiC (Z30S) composites were studied under various oxy-acetylene flame angles. Typical oxidized microstructures (SiO₂/SiC-depleted/ZrB₂-SiC) were observed when the flame to Z30S was arranged vertically. However, formation of the outmost glassy SiO₂ layer was hindered when the Z30S was tilted. The SiC-depleted region was fully exposed to air with reduced thickness when highly tilted. Traces of the ablated and island type SiO₂ were observed at intermediate flame angles, which clearly verified the effect of flame angle on the ablation of the SiO₂ layer. Furthermore, the observed maximum surface temperature of the Z30S gradually increased up to 2,200 ℃ proving that surface amorphous silica was continuously removed while monoclinic ZrO₂ phase began to be exposed. A proposed ablation mechanism with respect to flame angles is discussed. This observation is expected to contribute to the design of complex-shaped UHTC applications for hypersonic vehicles and re-entry projectiles.

• Korean Journal of Soil Science and Fertilizer
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• v.20 no.2
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• pp.185-192
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• 1987

A green house experiment was conducted to find out the acetylene reducing and $N_2$-fixing activity from photosynthetic and aerobic heterotrophic nitrogen fixing microorganisms in submerged paddy soil under different agricultural locality, soil series, soil texture, soil type, and drainage condition in which samples taken from without nitrogen treatment plot of NPK trials on 16 sites of the farmer's field. The results obtained were summarized as follows: 1. The highest acetylene reducing activity was observed at 7 days after incubation in the light condition (photo synthetic microbes+heterotrophic bacteria) while it was observed at 35 days incubation in the dark condition (heterotrophic bacteria). 2. Among the soil series, photosynthetic nitrogen fixing activity was pronounced more in Jangae, Ogcheon and Hwadong series while lower was obtained in Buyong and Daejeong series. Aerobic heterotrophic nitrogen fixing activity was high in Buyong and Daejong series. 3. Estimated amount of $N_2$-fixation from acetylene reducing activity was equivalented to 3.0 mg in light condition and 4.9 mg/100g/105 days in dark condition. 4. Among the agricultural locality, photosynthetic nitrogen fixing activity was high in rather warm southern part while heterotrophic nitrogen fixing activity was predominated more in mountainous area and Chungcheong continental. 5. Photosynthetic nitrogen fixing activity was predominated in high productive soil while aerobic heterotrophic nitrogen fixing activity was pronounced more in crose coarse sandy soil. 6. The soils properties of high photosynthetic nitrogen fixing activity were constituted of poorly or imperfectly drained clay or clay loam soil while heterotrophic nitrogen fixing activity was pronounced more in well to moderately well drained sandy or sandy loam soil.