• Economic and Environmental Geology
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• v.49 no.2
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• pp.77-88
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• 2016

Chrysotile is a 1:1 sheet silicate mineral belonging to serpentine group. It has been highlighted studies because of uses, shapes and structural characteristics of the fibrous chrysotile. However, it was designated as Class 1 carcinogen, so high attentions were being placed on detoxification studies of chrysotile. The objectives of this study were to investigate changes of mineralogical characteristics of chrysotile and to suggest detoxification mechanism of chrysotile by thermal decomposition. Samples for this study were obtained from LAB Chrysotile mine in Canada. The samples were heated in air in the range of 600 to $1,300^{\circ}C$. Changes of mineralogical characteristics such as crystal structure, shape, and chemical composition of the chrysotile fibers were examined by TG-DTA, XRD, FT-IR, TEM-EDS and SEM-EDS analyses. As a result of thermal decomposition, the fibrous chrysotile having hollow tube structure was dehydroxylated at $600-650^{\circ}C$ and transformed to disordered chrysotile by removal of OH at the octahedral sheet (MgOH) (Dehydroxylation 1). Upon increasing temperature, it was transformed to forsterite ($Mg_2SiO_4$) at $820^{\circ}C$ by rearrangement of Mg, Si and O (Dehydroxylation 2). In addition, crystal structure of forsterite had begun to transform at $800^{\circ}C$, and gradually grown 3-dimensionally to enstatite ($MgSiO_3$) by recrystallization after the heating above $1,100^{\circ}C$. And then finally transformed to spherical minerals. This study showed chrysotile structure was collapsed about $600-700^{\circ}C$ by dehydroxylation. And then the fibrous chrysotile was transformed to forsterite and enstatite, as non-hazardous minerals. Therefore, this study indicates heat treatment can be used to detoxification of chrysotile.

• The Korean Journal of Malacology
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• v.31 no.4
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• pp.267-272
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• 2015

This study was conducted in order to elucidate the dissemination mechanism of P. olseni using field and laboratory experiments. For this purpose, we quantified the level of P. olseni infection in buried (healthy) and surfaced (gapped) R. philippinarum from a clam bed on Wi-do Island on the west coast of Korea. In addition, the levels of internal and released P. olseni cells from artificially infected (and later dead) R. philippinarum were monitored for 8 days using the RFTM-2 M NaOH lysis method. Our results indicate that P. olseni cells in buried R. philippinarum was $2,655,625{\pm}1,536,936cells/clam$; the level in gapped R. philippinarum was considerably lower, $28,203{\pm}24,889cells/clam$ (p < 0.05). In the laboratory experiment, the P. olseni cells remained in the host tissue 2 days after death was approximately 50% lower than the level of infection measured in living clams. The level dropped to 20% 4 days after death and to 1.5% 6 days after death; eight days after death, P. olseni cells were undetectable since the R. philippinarum flesh had completely decomposed. The level of released cells on the day of death was only 0.05% of the internal level in live R. philippinarum; however, the level increased to 2.3% 5 days after death then gradually decreased and no released cells were detected 8 days after death. Therefore, our laboratory experiment suggest that the low level of P. olseni infection observed in gapped R. philippinarum at Wi-do Island could be caused by lysis of the most of P. olseni cells during the decomposition of dead R. philippinarum tissues. Until the end of decomposition of R. philippinarum, 6.68% of the total amount of P. olseni was released within 8 days. Our study showed that the amount of P. olseni cells from dead host is a considerably higher level than naturally released from healthy R. philippinarum, suggesting that death of the host plays an important role in the dissemination of P. olseni.

• Journal of the Society of Disaster Information
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• v.10 no.1
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• pp.71-83
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• 2014

This study carried out an experiment in order to compare thermal characteristics after collecting dust generated in the process of disposing of waste tire, plywood flour in the process of manufacturing plywood, salicylic acid dust in the process of manufacturing functional soap, and dust in the process of manufacturing wheat powder, which has potential fire and explosion hazard. According to the results of experiment, the analysis showed that all samples subject to the experiment were in the condition where heat flux decreased and temperature decreased as the quantity of added talc was increased. This shows that decomposition rate decreased, and hazard decreased. However, in all of samples subject to the experiment, as heating rate increased, endothermic onset temperature moved to the low-temperature part, and the amount of absorbed heat was largely increased. This showed that the decomposition hazard of sample increased as heating rate increased, according to the analysis. Besides, TGA experiment results showed that thermal stability was secured because total weight loss decreased as the amount of talc was increased for all samples subject to the experiment regarding the ratio of weight loss. It is expected that the continuous research and supplementation of dust explosion mechanism in the future will contribute to the establishment of measures for the effective dust explosion prevention.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.2
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• pp.89-95
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• 2021

Research on the production of lithium hydroxide (LiOH) has been actively conducted in response to the increasing demand for high nickel-based positive electrode materials for lithium-ion batteries. Herein we studied the conversion of lithium oxide (Li2O) through thermal decomposition of lithium carbonate for the production of lithium hydroxide from lithium carbonate (Li2CO3). The reaction mechanism of lithium carbonate with alumina, quartz and graphite crucible during heat treatment was confirmed. When graphite crucible was used, complete lithium oxide powder was obtained. Based on the TG analysis results, reagent-grade lithium carbonate was heat-treated at 700℃, 900℃ and 1100℃ for various time and atmosphere conditions. XRD analysis showed the produced lithium oxide showed high crystallinity at 1100℃ for 1 hour in a nitrogen atmosphere. In addition, several reagent-grade lithium oxides were reacted at 100℃ to convert to lithium hydroxide. XRD analysis confirmed that lithium hydroxide (LiOH) and lithium hydroxide monohydrate (LiOH·H2O) were produced.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.5
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• pp.48-53
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• 2011

We investigated thermal stability improvement of exo-tetrahydrodicyclopentadiene (exo-THDCP) with thermal stabilizers (additives). The reaction products were sample during the reactions. The compositions of products were determined by gas chromatography-mass spectrometry (GC-MS) to measure thermal decomposition products of exo-THDCP and to specify mechanism for thermal stabilizers. Hydrogen donors (thermal stabilizers) such as 1,2,3,4-tetrahydroquinoline (THQ), benzyl alcohol (BnOH) increased thermal stability of exo-THDCP. These materials donated hydrogen to radical of exo-THDCP produced after initiation of exo-THDCP. We found that stabilization of exo-THDCP radicals decreased activity of primary products of exo-THDCP and lowered formation of secondary products (above-$C_{11}$ products).

• Korean Journal of Agricultural Science
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• v.43 no.4
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• pp.537-546
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• 2016

The development of models for agriculture systems, especially for crop production, has supported the prediction of crop yields under various environmental change scenarios and the selection of better crop species or cultivar. Crop models could be used as tools for supporting reasonable nutrient management approaches for agricultural land. This paper outlines the simplified structure of main crop models (crop growth model, crop-soil model, and crop-soil-environment model) frequently used in agricultural systems and shows diverse application of their simulated results. Crop growth models such as LINTUL, SUCROS, could provide simulated data for daily growth, potential production, and photosynthesis assimilate partitioning to various organs with different physiological stages, and for evaluating crop nutrient demand. Crop-Soil models (DSSAT, APSIM, WOFOST, QUEFTS) simulate growth, development, and yields of crops; soil processes describing nutrient uptake from root zone; and soil nutrient supply capability, e.g., mineralization/decomposition of soil organic matter. The crop model built for the DSSAT family software has limitations in spatial variability due to its simulation mechanism based on a single homogeneous field unit. To introduce well-performing crop models, the potential applications for crop-soil-environment models such as DSSAT, APSIM, or even a newly designed model, should first be compared. The parameterization of various crops under different cultivation conditions like those of intensive farming systems common in Korea, shortened crop growth period, should be considered as well as various resource inputs.

• Journal of the Korean Society of Costume
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• v.61 no.1
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• pp.109-123
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• 2011

Postmodernism has affected general culture and arts as a powerful cultural image that has governed the later 20th century, and it is still a main subject as Zeitgeist representing modern society. Accordingly, this study is to verify the role and importance of the stage costume according to change of the art trend in the present age by clarifying relations between the postmodernism and the stage costume, and analyzing the postmodernism trend shown in postmodern classes. The postmodernism trend in costume is summarized as the deconstructionism, eclecticism and the populism. Hereunder is the conclusion of applying Postmodernism characteristics and creation mechanism commonly existing in theater and costume to the costumes of Korean theaters since 1990's. First, a deconsructionism trend of the Korean theater was visualized by the expression method of disembodiment and decomposition of stage costumes. Second, expression phase of interculturalism was concretely visualized through the stage costume, and it was considered that the postmodernism creation method. Third, a populism trend since 1990's was reflected to the stage costume, and deduced consensus with the audience and subculture familiar with the public as well as appeared as a phenomenon that emphasized a recreational elements. It is analyzed that this trend is a result that a concept of sportiveness was directly transferred through strong visual expression function of the stage costume. As a result of analyzing a Korean theater of the postmodernism disposition since 1990s, the costume reflected creational will of the postmodernism of works and played an important role as visual arts, created with a similar method and form.

• Transactions of the Korean Society of Automotive Engineers
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• v.20 no.6
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• pp.73-82
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• 2012

The main and side reactions of the three selective catalytic reduction (SCR) reactions with ammonia over a vanadium-based catalyst have been investigated using synthetic gas mixtures in the temperature range of $170{\sim}590^{\circ}C$. The three SCR reactions are standard SCR with pure NO, fast SCR with an equimolar mixture of NO and $NO_2$, and $NO_2$ SCR with pure $NO_2$. Vanadium based catalyst has no significant activity in NO oxidation to $NO_2$, while it has high activity for $NO_2$ decomposition at high temperatures. The selective catalytic oxidation of ammonia and the formation of nitrous oxide compete with the SCR reactions at the high temperatures. Water strongly inhibits the selective catalytic oxidation of ammonia and the formation of nitrous oxide, thus increasing the selectivity of the SCR reactions. However, the presence of water inhibits the SCR activity, most pronounced at low temperatures. In this study, the experimental results are analyzed by means of a dynamic one-dimensional isothermal heterogeneous plug-flow reactor (PFR) model according to the Eley-Rideal mechanism.

• Journal of Korean Society of Water and Wastewater
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• v.29 no.4
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• pp.481-491
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• 2015

The aim of this study was to evaluate the chemical quenching system for residual ozone and to determine the operating condition for the quenching system. Hydrogen peroxide ($H_2O_2$) and sodium thiosulfate ($Na_2S_2O_3$) were investigated as quenching reagents for ozone removal, and the tendency of each chemical was notably different. In the case of $H_2O_2$, the degradation rate of ozone was increased as the concentration of $H_2O_2$ increase, and temperature and pH value have a significant effect on the degradation rate of ozone. On the other hand, the degradation rate of ozone was not affected by the concentration of $Na_2S_2O_3$, temperature and pH value, due to the high reactivity between the ${S_2O_3}^{2-}$ and ozone. This study evaluates the decomposition mechanism of ozone by $H_2O_2$ and $Na_2S_2O_3$ with consideration for the water quality and reaction time. Furthermore, the removal test for the quenching reagents, which can be remained after reaction with ozone, was conducted by GAC process.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.31 no.5
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• pp.1-11
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• 1999

Wood components, cellulose and lignin, are degraded simultaneously and the general outline for the complementary character of carbohydrates and lignin decomposition as well as the existence of enzymatic systems combining these processes is still valid. The degradatiion of free cellulose or hemicellulose into monosaccharides has long been known to be relatively simple, but the mechanism of lignin degradatiion wasn ot solved very clearly yet. Anyway the biodegradation of woold constituents is understood at present as an enzymatic process. Kigninolytic activity has been correlated with lignin and manganese peroxidases. At present the attention is paid to laccase. Laccase oxidizes lignin molecule to phenoxy radicals and quinones . This oxidation can lead to the cleavageo f C-C or C-O bonds in the lignin phenyl-propane subunits, resulting either in degradation of both side chains and aromatic rings, or in demethylation processes. The role of laccase lies in the "activation" of some low molecular weight mediators and radicals produced by fungal cultures. Such activated factors produced also in cooperation with other enzymes are probably exported to the wood environment where they work in degradation processes as the ' enzyme messengers." It is worth mentioning that only fungi possessing laccase show demethylating activity. Thus demethylation, the process important for ligninolysis, is probably caused exclusively by laccase. Under natural conditions laccase seems to work with other fungal enzymes , mediators and mediating radicals. It has shown the possibility of direct Bjrkman lignin depolymerization by cooperative activity of laccase and glucose oxidase.