• The Journal of the Petrological Society of Korea
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• v.22 no.2
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• pp.83-115
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• 2013

Erroneous fission-track (FT) ages caused by an inappropriate calibration in the initial stage of FT dating were redefined by re-experiments and zeta calibration using duplicate samples. Revised FT zircon ages newly define the formation ages of Yucheon Group rhyolitic-dacitic tuffs as Late Cretaceous to Early Paleocene ($78{\pm}4$ Ma to $65{\pm}2$ Ma) and Gokgangdong rhyolitic tuff as Early Eocene ($52.1{\pm}2.3$ Ma). In case of the Early Miocene volcanics, FT zircon ages from a dacitic tuff of the upper Hyodongri Volcanics ($21.6{\pm}1.4$ Ma) and a dacitic lava of the uppermost Beomgokri Volcanics ($21.3{\pm}2.0$ Ma) define chronostratigraphies of the upper Beomgokri Group, respectively in the southern Eoil Basin and in the Waeup Basin. A FT zircon age ($19.8{\pm}1.6$ Ma) from the Geumori dacitic tuff defines the time of later dacitic eruption in the Janggi Basin. Based on FT zircon ages for dacitic rocks and previous age data (mostly K-Ar whole-rock, partly Ar-Ar) for basaltic-andesitic rocks, reference ages are recommended as guides for stratigraphic correlations of the Miocene volcanics and basements in SE Korea. The times of accumulation of basin-fill sediments are also deduced from ages of related volcanics. Recommended reference ages are well matched to the whole stratigraphic sequences despite complicated basin structures and a relative short time-span. The Beomgokri Group evidently predates the Janggi Group in the Eoil-Waeup basins, while it is placed at an overlapped time-level along with the earlier Janggi Group in the Janggi Basin. Therefore, the two groups cannot be uniformly defined in a sequential order. The Janggi Group of the Janggi Basin can be evidently subdivided by ca. 20 Ma-basis into two parts, i.e., the earlier (23-20 Ma) andesitic-dacitic and later (20-18 Ma) basaltic strata.

• Korean Journal of Mineralogy and Petrology
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• v.36 no.1
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• pp.73-94
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• 2023

We carried out the sensitive high resolution ion microprobe (SHRIMP) zircon U-Pb age dating and whole-rock geochemical analysis of granitoids and felsic porphyries in the Ssangyong Valley, Yongchu Valley, and Mungyeong Saejae geosites in the Mungyeong Geopark. The igneous rocks crop out in the western, northwestern and central parts of the Mungyeong city area, respectively, and intruded (meta)sedimentary successions of the Ogcheon Metamorphic Belt, Cambro-Ordovician Mungyeong Group and Jurrasic Daedong Group. The U-Pb isotopic compositions of zircon from two felsic porphyries and one granite samples in the Ssanyeong Valley yielded the Cretaceous intrusion ages of 93.9±3.3 Ma (tσ), 95.1±4.0 Ma (tσ) and 94.4±2.0 Ma (tσ), respectively. On the other hand, a felsic dike sample and a granite in the Yongchu Valley and a porphyritic granite in the Mungyeong Saejae had intrusion ages of 90.2±2.0 Ma (tσ), 91.0±3.0 Ma (tσ) and 88.6±1.5 Ma (tσ), respectively. Based on the average standard error calculated in combination with results of previous studies in this area (Lee et al., 2010; Yi et al., 2014; Aum et al., 2019), the geochronological results show that spatial variation in intrusion age of ~5 Myr between the Ssangyong (94.5±0.2 Ma) and Yongchu Valleys (89.7±0.4 Ma) is apparent. The geochemical compositions of major and trace elements in the samples showed an affinity of typical post-orogenic granite, indicating their petrogenesis during the late stage of Early Cretaceous magmatic activity possibly in association with subduction events of the Izanagi Plate.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.194-194
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• 2003

지르콘은 내침식성, 내마모성, 열 충격 저항성 및 기계적 물성이 우수하여 내화재료, 연마재료 등으로 다양하게 활용된다. 이러한 지르콘의 물성은 출발원료의 입도와 순도, 첨가제, 열처리 온도 등에 크게 의존한다. 본 연구에서는 출발 물질의 평균 입도를 각각 5$\mu\textrm{m}$와 3$\mu\textrm{m}$, l$\mu\textrm{m}$ 이하로 제어하였고, 시료의 열처리 온도를 135$0^{\circ}C$, 140$0^{\circ}C$, 145$0^{\circ}C$, 150$0^{\circ}C$, 155$0^{\circ}C$로 소결하였다. 각각의 지르콘 소결체는 미세 경도 측정, 결정상 분석, 밀도 측정, 미세구조 관찰을 통하여 특성 평가하였다. 미세경도 값은 140$0^{\circ}C$에서 소결된 지르콘의 가장 높았으며, 밀도는 150$0^{\circ}C$에서 소결된 지르콘이 가장 높으며, 155$0^{\circ}C$에서 소결된 지르콘은 과소결되어 전체적으로 물성이 저하되는 것을 관찰하였다.

• Journal of the Korean Ceramic Society
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• v.28 no.7
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• pp.549-555
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• 1991

Mullite-zirconia (0∼4 mol% yttria) composites were obtained by In-situ sintering of zircon and alumina mixture, and their mechanical properties were studied in conjuction with microstructure observation. Martensitic transformation temperature (Ms) of zirconia dispersed in the mullite matrix decreased with Y2O3 contents and was about 600$^{\circ}C$ for ZrO2 containing 4 mol% Y2O3. On cooling of this composites, tetragonal to monoclinic phase transformation induced microcracks at the grain boundary of mullite matrix. The microcracks seemed to absorb the fracture energy in stress field during mechanical tests. Therefore, toughening mechanisms of this composite were considered to nucleation and extension of microcrack, and crack deflection mechanism due to the difference of thermal expansion coefficient between matrix and dispersed phase.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1245-1247
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• 2005

Glass frit was selected to be a $Bi_2O_3-RO-R_2O_3$ system as a sealing material to replace the current PbO system in PDP. Fillers such as a zircon, cordierite and ${\beta}-eucryptite$ were added for the control of thermal expansion coefficient (CTE), flowability and strength for sealing. At $450-500^{\circ}C$, reaction of frit and filler and interface were evaluated by a flow button test and SEM observation. The composite (frit and filler) showed CTE in the range of 70-83 x $10^{-7}/K$ and flowability of 14-20mm. It can be a candidate for the replacement of PbO system.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.648-653
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• 2003

Optimized recovery of heavy minerals from the near shore sands of Korean Yellow Sea was investigated using physical processing technologies such as gravity concentration and magnetic separation. The head samples were subjected to the three stages effective separation; Head sample was first treated by a spiral separator to recover rough heavy mineral concentrates, which are contained minerals like ilmenite, zircon and rare earth minerals. Much higher beneficiation processes were subsequently taken by wilfley table and magnetic separation according to their magnetic field responses. Heavy minerals were effectively recovered by wilfley table and subsequent recleaning of heavy minerals by magnetic separations was conducted. Qualitative and relative-quantitative analyses of their constituent elements were doing using XRD and XRF.

• Proceedings of the Petrological Society of Korea Conference
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• 1999.06a
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• pp.63-63
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• 1999

• Journal of the Korean Ceramic Society
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• v.40 no.7
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• pp.667-671
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• 2003

Tape cast laminar composites with alumina/zircon(reaction-bonded mullite/zirconia) as an inner layer and alumina/zirconia or mullite/zirconia as an outer layer have been fabricated by hot-pressing. The mechanical properties(hardness and Young's modulus) and microstructure of laminar composites were examined using a nanoindentation technique and Scanning Electron Microscopy (SEM), respectively. The indentation load-displacement curve revealed the existence of residual stress in laminar composites.

• Journal of the Korean Ceramic Society
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• v.46 no.4
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• pp.397-404
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• 2009

Using rice husk ash as silica, the influence of the firing temperature and holding time on the color intensity of Pr-$ZrSiO_4$ pigments were investigated. The Pr-yellow pigments were calcined at 500, 700, 800, 900, 950, 1000, $1100^{\circ}C$ in a ceramic method. The synthesized pigments were characterized by DT-TG thermal analysis, X-ray diffraction, UV-Vis spectroscopy, and SEMEDAX analysis. The relationship between the zircon phase-formation growth and Pr-yellow color development was evaluated and the optimum firing conditions were determined. The color of the pigment samples was characterized on the grounds of the Commission Internationale de l'Eclairage (CIE) standard procedure (CIE $L^*a^*b^*$ measurement) after an application on the bisque ceramic tile.

• The Journal of Advanced Prosthodontics
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• v.12 no.1
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• pp.9-14
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• 2020

PURPOSE. The aim of this study was to investigate the effect of different numbers of heat treatments applied to superstructure porcelain on optical, thermal, and phase formation properties of zirconia. MATERIALS AND METHODS. Forty zirconia specimens were prepared in the form of rectangular prism. Specimens were divided into four groups (n = 10) according to the number of firing at heating values of porcelain. Color differences and translucency parameter were measured, and X-ray diffraction (XRD) analysis and differential scanning calorimetry (DSC) were performed. Data were analyzed with analysis of variance (ANOVA). RESULTS. There were no statistically significant differences in ∆E, TP, L, a, and b value changes of the zirconia specimens as a result of repetitive firing processes (P>.05). CONCLUSION. Although additional firing processes up to 4 increase peak density in thermal analysis, additional firing processes up to 4 times can be applied safely as they do not result in a change in color and phase character of zircon frameworks.