Theoretical Approach of the Quartz Dissolution Rate under Various Temperature, pH and Applied Stress Conditions

Junghae Choi(최정해) 대한자원환경지질학회 2017 자원환경지질 Vol.50 No.6

일반적으로 석영은 지각을 구성하는 광물 가운데 가장 많은 부분을 차지하고 있으며, 이러한 석영의 용해와 침전에 대 한 이해는 암석의 풍화 매커니즘과 열수작용 및 변성환경에서의 암석과 물의 관계를 규명하는데 매우 중요한 역할을 한다. 본 논문에서는 석영의 용해와 침전에 영향을 미치는 다양한 물리화학적 환경을 수식을 이용해 재정리하였으며, 이전의 연구자들이 발표한 연구결과를 바탕으로 물리화학적 조건하에서의 석영 용해에 대해 이론적 접근을 실시하였다. 본 논문을 통해서 석영의 용해 및 침전이 다양한 환경에 영향을 받으며, 특히 이론적 접근을 통해서 석영에 작용된 압력보 다는 주변의 pH 및 온도 조건에 더 큰 영향을 받는다는 것을 확인하였다. Quartz is the most abundant mineral in the Earth’s continental crust. Therefore, understanding of quartz dissolution and precipitation is very important to know about weathering processes and interactions between rocks and water in hydro-thermal and metamorphic environments. This paper presents a basic review on the research about quartz dissolution mechanism under various physico-chemical conditions. We rearranged the relationship between each physico-chemical factor and dissolution mechanism from the results of previous researchers in this paper. From this result, we understood that quartz dissolution and precipitation are affected by each factor such as temperature, pH, and applied stress conditions at contact point. In particular, we recognized that the high pH and temperature conditions have different anion con-centrations on mineral’s surface. As a result, high pH and temperature conditions have a better effect than applied stress condition to the quartz dissolution mechanism.

Investigation of the 2013 Hadari Debris Flow in Korea Through Field Survey and Numerical Analysis

( Junghae Choi ) 대한지질공학회 2018 지질공학 Vol.28 No.3

Landslides can be caused by localized intense rainfall. The loss of human lives and damage to property from landslides is increasing. However, little information exists on the movement and flow of sediment material at the time of rapid landslides. In this study, a field survey was conducted of landslides that occurred in 2013 in the Hadari area of Yeoju city in Korea. This was followed by numerical analysis. The purpose is to analyze the characteristics of a consequent debris flow and its movement at the time of failure. The results of the field survey and numerical analysis are consistent with each other. The maximum velocity of the debris flow was ~9.335 m/s and the maximum sediment thickness ~4.674 m. The latter is similar to the traces of debris flow observed in the field.

Observation on Change of Physico-chemical Properties of Rock under Freezing-Thawing Experiment

( Junghae Choi ) 대한지질공학회 2019 대한지질공학회 학술발표회논문집 Vol.2019 No.2

Near the site where rocks are weathered by the freezing and thawing mechanism, both groundwater and surface water can be contaminated by the specific dissolved chemical species. In particular, there are many places where there is pollution for this reason in the mine area. To reduce these types of water pollution, it is necessary to investigate the effect of weathering by the freezing and thawing mechanism on how much the rock is weathered and what types of chemical species are created from the weathering. It is a general tendency that the physical conditions of a surface are changed by the freezing and thawing, and the void of rock increases on the weathered surface due to the chemical dissolution of the mineral. In this study, we used rock samples from the mine area and separated two types of samples, which were andesite and tuff. The changes of the physical properties of the rocks were observed by physical properties analysis, and the variation of chemical species in the used solution was analyzed by chemical analysis methods, such as Inductively Coupled Plasma (ICP), after freezing and thawing experiments. As a result, the porosity and the dry density of the rock samples showed a tiny change during the experiment. In terms of the chemical change, it was observed that the change of Electrical Conductivity (EC) and the concentration of species varied greatly with the progress of freezing and thawing cycle.

Suggestion for a mineral dissolution rate equation for physico-chemical factors

Junghae Choi 대한지질학회 2015 대한지질학회 학술대회 Vol.2015 No.10

동적 초미소 경도법에 의한 심도별 대전화강암 내 광물들의 역학적 특성

최정해(Junghae Choi),신주호(Juho Shin),장형두(Hyongdoo Jang),강성승(Seong-Seung Kang) 한국암반공학회 2017 터널과지하공간 Vol.27 No.3

동적 초미소 경도법의 압입시험, 하중-비하중 시험, 그리고 반복시험을 이용하여 심도별 대전화강암 내 광물들의 경도와 역학적 특성을 살펴보았다. 시험 결과 세 개 구간(Group-1, -2, -3)으로 광물 집단의 분류가 가능하였다. Martens 경도값은 세 가지 시험법 모두에서 41 m와 223 m 심도에 따른 차이가 크지 않았다. 그럼에도 불구하고, 그 크기는 반복시험<하중-비하중 시험<압입시험 순으로 나타났다. 광물 집단별 평균 Martens 경도, 탄성계수, indentation work 등을 고려해 볼때, 그들의 경계는 비교적 뚜렷하게 나타났다. 결론적으로 동적 초미소경도법의 세 가지 형태 시험법을 이용함으로써 광물들에 대한 비교적 정확한 경도값을 얻을 수 있었다. 또한 하중-비하중 시험과 반복시험으로부터는 광물들의 탄성계수와 광물들의 탄성적-소성적 성질 특성 파악도 가능하였다. The hardness and mechanical properties of the minerals in the Daejeon granite according to depths were investigated by indentation test, load-unload test, and cycle test of dynamic ultra-micro hardness. As a result of the tests, it was possible to classify into three mineral groups (Group-1, -2, -3). The Martens hardness was not significantly different between 41 m and 223 m depths in three mode tests. Nevertheless, they showed in the order of a cycle test<load-unload test <indentation test. Considering the average Martens hardness, elastic modulus, and indentation work for each mineral group, their boundaries were relatively clear. In conclusion, A relatively accurate hardness of minerals can be obtained by three mode tests of dynamic ultra-micro hardness. In addtion, it was possible to characterize the elastic modulus and the elastic-plastic properties of the minerals from the load-unload and cycle tests.

표토 훼손지역 평가를 위한 평가요소 분석

최정해(Junghae Choi),정교철(Gyo Cheol Jeong) 대한환경공학회 2021 대한환경공학회 학술발표논문집 Vol.2021 No.11

수치해석을 통한 춘천 산사태지역 토석류 거동 분석

최정해 ( Junghae Choi ) 대한지질공학회 2017 지질공학 Vol.27 No.1

최근들어 발생하는 강우는 지금까지의 강우특성과 비교하여 여름철에 단기간 집중적으로 내리는 형태로 바뀌고 있다. 2011년 강원도 춘천지역에서는 이러한 집중강우로 인해 많은 산사태가 발생하였으며, 이로 인해 재산피해와 인명피해를 야기시켰다. 본 연구의 목적은 강우에 의한 산사태 물질의 이동에 대한 특성을 분석하기 위해서 현장 자료와 수치해석 자료를 활용하여 시간에 따른 특성의 변화 및 강우량에 따른 특성의 변화를 분석하는 것이다. 본 연구에서는 항복응력 값의 변화를 통해서 강우량을 재현하였으며, 이를 통해서 어떠한 거동 특성을 보이는지 해석하였다. 그 결과 많은 강우에 의해 항복응력 값이 낮아지는 경우가 빠른 속도의 이동형태를 보이고 동시에 넓은 지역에 걸쳐 확산되는 특성을 확인하였으며, 이러한 결과는 현장에서 확인된 토석류의 흔적과 매우 유사하다는 것을 확인하였다. 본 연구를 통해서 산사태 발생 당시의 토석류 최대 속도 및 최대 두께 등을 파악하는 것이 가능하다. The characteristic of recent rainfall pattern in Korea is concentrated in summer season and it is very different compare with former characteristic. In 2011, there was heavy rainfall in Chuncheon city of northern part of Korea. Because of rainfall in short time, many landslides were occurred in narrow area and many people were killed by these landslides at that time. The purpose of this study is to calculate run-out distance of debris flow and analyze the movement properties of debris flow according to the elapsed time using numerical analysis method at that time. The debris 2D program, which is developed by prof. Liu in National Taiwan University, was used in this study. Run-out distance of debris flow was calculated under different yield strength conditions which were controlled by rainfall amount. The results reveal that absolute maximum velocity of the debris flow is about 8.1 m/s and maximum depth of debris flow is about 7 m when debris flow was occurred. The run-out distance after 500 sec is about 300 m from end of the valley. It is very well similar with actual debris flow run-out distance. From these results, we can presume the maximum velocity and depth of debris flow at that time.

Infrared and Radio observations of a small group of protostellar objects in the molecular core, L1251-C

Jungha Kim,Jeong-Eun Lee,Minho Choi,Tyler L. Bourke,Neal J. Evans II,James Di Francesco,Lucas A. Cieza,Michael M. Dunham 한국천문학회 2015 天文學會報 Vol.40 No.1

A New Decoding and Cell Selection Method for a PoRAM Sensing

Jungha Kim,Seunghyeok Choi,Sangsun Lee 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7

This paper propose a new decoding method and cell selection method using the switch for a PoRAM cell. The designed row-decoder operated as a 2- stage pre-decoder, and a master/salve D-F/F was inserted at the end of the decoder to eliminate glitch noise. The newly column-decoder structure is the same row-decoder but selected line applied low voltage. And MOS-switches are attached to the input port of each memory cell to select the proper line. The method generates the voltage drop of the selected cell that cell current flows to the sense amplifier input. This switch controls cell selection and current path for the memory cell sensing.

Lacquer Techniques in the Late Joseon Dynasty

( Junghae Park ),( Jaewan Choi ),( Uicheon Lee ),( Minji Kang ),( Soochul Kim ) 한국목재공학회 2023 목재공학 Vol.51 No.2

This study conducted scientific analyses on eight objects of wooden lacquerware to understand the manufacturing techniques of wooden lacquerware in the late Joseon Dynasty. The results of lacquer layer analysis with a microscope and scanning electron microscopy-energy dispersive X-ray spectrometry revealed that most samples were composed of 1-3 lacquer layers. Moreover, a red-colored layer was found to be red ocher and cinnabar, and Fourier-transform infrared spectroscopy analysis was carried out to determine the components of the lacquer layer. The detected components were mostly lacquer and partially cashew shell nut liquid.