• The Journal of the Petrological Society of Korea
• /
• v.7 no.2
• /
• pp.132-145
• /
• 1998

The coal-bearing siliciclastic rocks of the Lower Permian Jangseong Formation, Samcheog coalfield, represent a megacyclothem which shows cyclic repetitions of sandstone, shale, coaly shale, and coals. Petrographic, geochemical, and SEM studies for sandstone samples, and XRD analysis for clay minerals were carried out to understand diagenesis in the sandstones of the Jangseong Formation. The Jangseong sandstones are composed of 60% quartz (mainly monocrystalline quartz) and 36% clay matrix and cement with minor amounts of feldspar, lithic fragments and accessory minerals (less than 4%). Jangseong sandstones are classified mostly as quartzwackes and partly as lithic graywackes according to the scheme of Dott(1964). The textural relationships between authigenic minerals and cements in thin sections and SEM photomicrographs suggest the paragenetic sequence as follows; (1) mechanical compaction, (2) cementation by quartz overgrowth, (3) formation of authigenic clay minerals (illite, kaolinite), (4) dissolution of framework grains and development of secondary porosity, and (5) later-stage pore-filling by pyrophyllite. We propose that these diagenetic processes might be due to organic-inorganic interaction between the dominant framework grains and the formation water. The Al, Si ions and organic acid, derived from dewatering of interbedded organic-rich shale and coals, were transported into the Jangseong sandstones. This caused changes in the chemistry of the formation water of the sandstones, and resulted in overgrowth of quartz and precipitation of authigenic clay minerals of kaolinite and illite. The secondary pores, produced during dissolution of clay and framework grains by organic acid and $CO_2$ gas, were conduit for silica-rich solution into the Jangseong sandstones and the influx of silica-rich solution produced the late-stage pyrophyllite after the expanse of kaolinite. The origin of the solution that formed pyrophyllite is not likely to be the organic-rich formation water based on the observation of fracture-filling pyrophyllite in the Jangseong sandstones, but the process of pyrophyllite pore-filling was indirectly related to organic-inorganic interaction.

• The Journal of Korean Academy of Prosthodontics
• /
• v.56 no.3
• /
• pp.206-211
• /
• 2018

Purpose: Recently, a method of forming a slot in the prosthesis lingual has been introduced to solve the occlusal and aesthetic disadvantages of screw-retained prosthesis in the manufacture of implant-fixed prosthesis and to ensure retrievability in cement retained prostheses. The purpose of this study is to investigate the effect of the internal gap on the removal of the prosthesis in the preparation of cement-retained implant prostheses with lingual slots. Materials and methods: Titanium abutment and internal gap of the zirconia prosthesis to be attached to the upper part were set to 30, 35, and $50{\mu}m$, respectively. Three for each type total 15 were produced for each type. The zirconia prosthesis formed a retrievable cement-type slot with a space of 1 mm at the location where the titanium abutment meets the shelf area. Autocatalytic resin cement was used for bonding of abutment and zirconia prosthesis, and the maximum removal stress value was measured in units of Ncm by using the customized equipment of the cemented specimen. The Kruskal-Wallis test was used to compare the three groups by statistical analysis (${\alpha}=.05$), modified by post hoc test the Mann-Whitney U-test and the Bonferroni correction method were used to compare the two methods (${\alpha}=.017$). Results: There was no statistically significant difference in removal stress between the $30{\mu}m$ group and the $35{\mu}m$ group in the internal gap (P = .032), and there was a significant difference between the $30{\mu}m$ group and the $50{\mu}m$ group, between the $35{\mu}m$ group and the $50{\mu}m$ group (P < .017). Conclusion: Thus, the internal gap of computer-aided design affected the retention between the zirconia prosthesis and the titanium abutment.

• Proceedings of the Korean Radioactive Waste Society Conference
• /
• 2005.06a
• /
• pp.110-120
• /
• 2005

For utilizing vitrification to treat low and intermediate level waste, industrial pilot plant was designed and constructed in October 1999 at Daejon, Korea through the joint research program among NETEC, MOBIS and SGN. More than 70 tests were performed on simulated IER, DAW etc. including key nuclide surrogate(Cs, Co); this plant has been shown to vitrify the target waste effectively and safely, however, some dust are generated from the HTF(High Temperature Filter) as a secondary waste. In case of long term operation, it is also concerned that pipe plugging can be occurred due to deposited dust in cooling pipe namely, connecting pipe between CCM(Cold Crucible Melter) and HTF. In this regard, we have developed the special complementary system of the off-gas treatment system to recycle the dust from HTF to CCM and to remove the interior dust of cooling pipe. Main concept of the dust recycling is to feed the dust to the CCM as a slurry state; this system is regarded as of an important position in the viewpoint of volume reduction, waste disposal cost and glass melt control in CCM. The role of DRS(Dust Recycling System) is to recycle the major glass components and key nuclides; this system is served to lower glass viscosity and increase waste solubility by recycling B, Na, Li components into glass melt and also to re-entrain and incorporate into glass melt like Cs, Co. Therefore dust recycling is helpful to control the molten glass; it is unnecessary to consider a separate dust treatment system like a cementation equipment. The effects of Dust Cleaner are to prevent the pipe plugging due to dust and to treat the deposited dust by raking the dust into CCM. During the pilot vitrification test, overall performance assessment was successfully performed; DRS and Dust Cleaner are found to be useful and effective for recycling the dust from HTF and also removing the dust in cooling pipe. The obtained operational data and operational experiences will be used as a basis of the commercial facility.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.28 no.2
• /
• pp.119-126
• /
• 2012

State of problem: Cement-retained implant-supported prostheses are routinely used in dentistry. The use of high strength cements has become more popular with the increasing confidence in the stability of the implant-abutment screw connection and the high survival rates of osseointegrated implants. No clinical data on retention of metal copings using CAD/CAM. To evaluate retention of metal copings using CAD/CAM system bonded to short titanium abutment with four different cements and compare retentive strength of metal copings with sandblasting or without sandblasting before cementation. Forty titanium abutment blocks were fabricated and divided into 4 groups of 10 samples each. Forty metal copings with occlusal hole to allow for retention testing were fabricated using CAD/CAM technology. The four cements were Fujicem(Fuji, Japan), Maxcem Elite(Kerr, USA), Panavia F2.0(Kurarary, Japan) and Superbond C&B(Sunmedical, Japan). The copings were cemented on the titanium abutment according to manufacture's recommendation. All samples were stored for 24h at 37oC in 100% humidity and tested for retention using universal testing machine(Instron) at a crosshead speed of 1.0mm/min. Force at retentive failure was recorded in Newton. The mode of failure was also recorded. Means and standard deviations of loads at failure were analyzed using ANOVA and Paired t-test. Statistical significance was set at P<0.05. Panavia F2.0 provided significantly higher retentive strength than Fujicem, Maxcem Elite(P<0.05). Sandblasting significantly increased bond strength(P<0.05). The mode of failure was cement remaining principally on metal copings. Within the limitation of this study, Panavia F2.0 showed significantly stronger retentive strength than Fujicem, Maxcem Elite(p<0.05). The Ranking order of the cements to retain the copings was Panavia F2.0, Fujicem = Maxcem Elite. Sandblasting significantly increased bond strength(P<0.05). The retentive strength of metal copings on implant abutment were influenced by surface roughness and type of cements.

• The Journal of Korean Academy of Prosthodontics
• /
• v.47 no.4
• /
• pp.416-423
• /
• 2009

Statement of problem: The degree of light attenuation at the time of cementation of the PLV restoration depends on characteristics such as thickness, opacity and shade of the restorations, which interfere with light transmittance and, as a result, may decrease the total energy reaching the luting cement. Purpose: The purpose of this study was to compare the degree of conversion of light-cured resin cements measuring by FT-IR in regard to different thickness, light devices and curing time. Material and methods: In the control group, a clear slide glass (1.0 mm) was positioned between the light cured resin cement and light source. The specimens of ceramics were made with IPS Empress Esthetic. The ceramics were fabricated with varying thicknesses-0.5, 1.0, 1.5 mm with shade ETC1. Rely $X^{TM}$ Veneer with shade A3, light-cured resin cement, was used. Light-activation was conducted through the ceramic using a quartz tungsten halogen curing unit, a light emitting diode curing unit and a plasma arc curing unit. The degree of conversion of the light-cured resin cement was evaluated using FT-IR and OMNIC. One-way ANOVA and Tukey HSD test were used for statistical analysis ($\alpha$< .05). Results: The degree of conversion (DC) of photopolymerization using QTH and LED was higher than results of using PAC in the control group. After polymerization using QTH and LED, the DC results from the different ceramic thickness- 0.5 mm, 1.0 mm, 1.5 mm- did not show a significant difference when compared with those of control group. However, the DC for polymerization using PAC in the 1.5mm ceramic group showed significantly lower DC than those of the control group and 0.5 mm ceramic group (P<.05). At 80s and 160s, the DC of light-cured resin cement beneath 1.0 mm ceramic using LED was significantly higher than at 20s (P<.05). Conclusion: Within the limitation of this study, when adhering PLV to porcelain with a thickness between 0.5-1.5 mm, the use of PAC curing units were not considered however, light cured resin cements were effective when cured for over 40 seconds with QTH or LED curing units. Also, when curing the light cured resin cements with LED, the degree of polymerization was not proportional with the curing time. Curing exceeding a certain curing time, did not significantly affect the degree of polymerization.

• Restorative Dentistry and Endodontics
• /
• v.34 no.3
• /
• pp.177-183
• /
• 2009

The aim of this study was to evaluate the marginal and internal gaps in CEREC3 CAD/CAM inlays of three different preparation designs. CEREC3 Inlays of three different preparation designs (n=10) were fabricated according to Group I-conventional functional cusp capping/shoulder preparation, Group II-horizontal reduction of cusps and Group III-complete reduction of cusps/shoulder preparation. After cementation of inlays. the bucco-lingual cross section was performed through the center of tooth. Cross section images of 20 magnifications were obtained through the stereomicroscope. The gaps were measured using the Leica application suite software at each reference point. Statistical analysis was performed using one-way ANOVA and Tukey's test (${\alpha}<0.05$). The marginal gaps ranged from 80.0 to $97.8{\mu}m$ for Group I, 42.0 to $194.8{\mu}m$ for Group II, 51.0 to $80.2{\mu}m$ for Group III. The internal gaps ranged from 90.5 to $304.1{\mu}m$ for Group I, 80.0 to $274.8{\mu}m$ for Group II, 79.7 to $296.7{\mu}m$ for Group III. The gaps of each group were the smallest on the margin and the largest on the horizontal wall. For the CEREC3 CAD/CAM inlays, the simplified designs (groups II and III) did not demonstrate superior results compared to the traditional cusp capping design (group I).

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.8 no.4
• /
• pp.401-410
• /
• 2003

Three beaches of the Seogwang-ri coast in the western part of Wu Island, Jeju-do, are solely composed of rhodoliths (red algal nodules). The beach sediments are coarse sand to granule in size and they show the banded distribution according to size. Commonly the larger pebble-sized rhodoliths are concentrated near the rocky coast, resulting from the transportation of the nodules from shallow marine environments by intermittent typhoons. Based on the internal texture of the rhodoliths, it appears that crustose red algae, Lithophyllum sp., is the main contributor for the formation of the rhodolith. The coarse sand to granule-sized grains show that they started to grow from the nucleus as rhodoliths, but the surface was severely eroded by waves. However, the pebble to cobble-sized grains exhibit the complete growth pattern of rhodoliths and sometimes contain other calcareous skeletons. It is common that encrusting red algae are intergrown with encrusting bryozoan. The surface morphology of rhodolith tends to change from the concentric to domal shape towards the outer part. This suggests that the rhodolith grew to a certain stage by rolling, but it grew in more quiet condition without rolling as it became larger. Aragonite and calcite cements can be found in the pores within rhodoliths (conceptacle, intraskeletal pore in bryozoan, and boring), and this means that shallow marine cementation has occurred during their growth. Growth of numerous rhodoliths in shallow marine environment near the Seogwang-ri coast indicates that this area has suitable oceanographic conditions for their growth such as warm water temperature (about 19$^{\circ}C$ in average) and clear water condition due to the lack of terrestrial input of volcanoclastic sediments. Fast tidal current and high wave energy in the shallow water setting can provide suitable conditions enough for their rolling and growth. Typhoons passing this area every summer also influence on the growth of rhodoliths.

• Korean Journal of Dental Materials
• /
• v.44 no.1
• /
• pp.61-68
• /
• 2017

This study evaluated the effects of various cleaning methods on the shear bond strength of zirconia ceramics after saliva contamination. Eighty zirconia disk specimens were divided into 8 groups. All groups were treated with one coat of MDP primer. All specimens (except the negative control) were contaminated with human saliva on the zirconia surface. The positive control went through the bonding procedure immediately after contamination without any cleaning procedure. With the exception of control groups, the remaining six groups were rinsed with water and either applied with MDP recoating (WATER+MDP) or without MDP recoating (WATER). While some were cleaned with a Ivoclean with MDP recoating (IVOCLEAN+MDP) or not applied with MDP recoating(IVOCLEAN), others were cleaned with a 1% NaOCl solution with MDP recoating (NaOCl+MDP) or without MDP recoating (NaOCl). The shear bond strength of all specimens were measured after being stored in distilled water at $37^{\circ}C$ for 24 hours. The data was analyzed statistically by an analysis of ANOVA, Tukey's post hoc test and Student's t-test was used to compare the shear bond strength according to the re-coating of MDP after the cleaning procedure. The positive control group showed the lowest shear bond strength value, and the WATER group and NaOCl group showed no significant difference when compared to the positive control group. The IVOCLEAN group showed significantly higher shear bond strength when compared to Water group and NaOCl group but not with the group of negative control. After rinsing with water or the NaOCl solution, the comparison of the single coating of MDP and re-coating of MDP showed different shear bond strengths but there was no significant difference to the negative control. After rinsing with Ivoclean, there was no significant difference to the negative control regardless of the recoating of MDP. In conclusion, the shear bond strength was affected by the cleansing procedure and Ivoclean was found to be effective regardless of the re-coating of MDP. When water or the NaOCl solution is used to remove surface contaminants, the re-coating of MDP provides a positive effect on cementation.