• The Journal of Korean Academy of Prosthodontics
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• v.41 no.5
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• pp.656-673
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• 2003

Statement of problem : Long-term exposure of dental porcelain to saliva during temporary cementation of a porcelain-fused to metal (PFM) restoration could affect mechanical strength of dental porcelain if the restoration is refired. Purpose : This work was performed to verify the effect of water on the mechanical strength in aged dental porcelain. Material and method : 63 specimens(Vintage Metalbond opaque and opal powder) were distributed to three experimental groups ; non-water immersed control, immersed and pedried, and immersed and non-predired groups. The changes in flexural strength and fracture toughness after specimen refiring related to Fourier Transform Infrared (FT-IR) spectroscopy. Results : 1. The FT-IR reflectances assigned to molecular bonds of $H_2O$ were noted as significantly different between the first-fired group and three refired groups and between two water-immersed groups and control group after refiring(p<0.05). They were also significantly different between predried group and non-predried group after refiring(p<0.05) 2. For opal specimens, FT-IR absorbances for hydrogen bond of $H_2O$ and silanols were significantly higher in non-predried group than in predreid group(p<0.05). 3 Predried opal group showed the highest mean flexural strength(p<0.05). Non-predried group indicated higher mean flexural strength than control group(p<0.05). 4. The mean fracture toughness for predired group was higher than non-predried group(p<0.05). 5. The difference of leucite crystal size is noted between control group and water-immersed, predried group in scanning electron microscopic study(${\times}10000$).

• Journal of Conservation Science
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• v.27 no.1
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• pp.13-30
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• 2011

This study compared Pottery, Hwaecheongware, Buncheongware and Whiteware pieces excavated in Hakbong-ri of Chungnam analytically by observing their refined structures and estimating their firing temperature. As a result, base soil components of the specimens were mostly similar to those of typical Buncheongware, but the content of the fluxing agent was rather high, and it seemed that the Whiteware had been made with fairly different components from those of other sherds. Although the glaze showed less difference than base soil in general, the content of the glaze changed according to the decorating methods of Buncheongware. Based on the SEM-EDS analysis, it was found that the base soil components of the ceramics seemingly rather different were actually different and the analysis on the fine crystals of the base soil, the anorthite in the glaze and crystals in the ironing part, and the components and contents of white earth showed there were some noticeable points in the process of making each of the sherds. In the refiring experiment to estimate the firing temperature, mostly similar results were gained as $1150^{\circ}C$ to $1200^{\circ}C$ for pottery, $1100^{\circ}C$ to $1150^{\circ}C$ for Hwaecheongware, and $1100^{\circ}C$ to $1200^{\circ}C$ for iron-brown Buncheongware however, the results imply good quality Whiteware was burnt at above $1300^{\circ}C$ while bad quality Whiteware was burnt at a temperature far lower than that. Thus, there was clear difference between Whiteware sherds and other kinds of sherds.

• Economic and Environmental Geology
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• v.54 no.6
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• pp.671-687
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• 2021

This study investigated the firing temperature and thermal deformation process of roof tiles excavated from the connected stone-mound tomb in Seokchon-dong, Seoul, based on mineralogical and physical properties. A large number of roof tiles were excavated from the tomb site and some roof tiles were deformed by heat and were fired in uneven conditions. The colors of original roof tiles and their cores are mostly yellowish-brown, with high water absorption over 12%, containing fine-grained textures and some minerals such as quartz, feldspars, amphibole, and mica. It is estimated that the original roof tiles were fired below 900℃ in oxidation condition, showing loose matrices and mica layers by scanning electron microscopy. However, deformed roof tiles have the uneven surface color of reddish-brown and bluish-gray, and those cross-sections have sandwich structures in which dense reddish-brown surface and porous grey core coexist. They contained mullite and hercynite, so it was estimated to have been fired over 1,000℃, with 0.81~11% water absorption. In some samples, bloating pores by overfiring were observed, which means that they were fired at more than 1,200℃. In addition, the refirng experiments that the original roof tile was fired between 800℃ and 1,200℃ were carried out to investigate the physical and mineralogical properties of roof tiles compared to deformed ones. As a result, the water absorption decreased rapidly and the mineral phase started to change over 1,000℃. As the temperature gradually rises, the matrices are partially melted and recrystallized, resulting in similar thermal characteristics of deformed roof tiles. Therefore, the roof tiles from ancient tombs in Seokchon-dong seem to experience the secondary high temperature of 1,000 to 1,200℃ under uneven firing conditions, resulting in deformation characteristics such as shape transformation and mineral phase transition. It is considered to have been related to cremation rituals at the tombs of Seockchon-dong during the Baekje period.