• 한국기계가공학회지
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• 제10권2호
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• pp.135-141
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• 2011

In this study, the variation of the cutting forces generated in the machining process were evaluated experimentally. A material of $Al_{2}O_{3}$ ceramic and a tool of the dynamometer were used for the measurements of the cutting forces. With the constant rates of the feed and the tool rotation, the cutting forces were measured along three axial directions(X, Y, Z axis) for the various values of the hollow ratio. It was found that the cutting force be increasing linearly along the direction of Z axis, but along X, Y axis be not varied. Also from the viewpoint of the precesses of the hole drilling, the cutting force was found to be increasing sharply at the beginning process, but from the eighth process be increasing smoothly. As conclusions, the cutting force generated by machining for the material of $Al_{2}O_{3}$ ceramic are influenced more significantly by the feed rate and the hollow ratio than by the tool rotational speed.

• 대한치과기공학회지
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• 제43권1호
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• pp.6-12
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• 2021

Purpose: This study aimed to compare the shear bond strength between zirconia cores and veneer ceramics as per the sand blasting and liner treatments. Methods: The following 4 groups of zirconia-veneering ceramic specimens were prepared: (1) Group I, untreated; (2) Group II, with 110 ㎛ aluminium oxide (Al2O3) sandblasting; (3) Group III, with liner (IPS e.max ZirLiner; Ivoclar Vivadent); and (4) Group IV, with 110 ㎛ Al2O3 sand blasting and liner. Surface roughness was measured for all the prepared specimens, and the surface morphology was observed using a scanning electron microscope. All the samples (n=40) were fixed with measuring jigs, and shear bond strengths were obtained using a universal testing machine with a crosshead speed of 0.5 mm/min. The shear bond strength data were analyzed using one-way analysis of variance and t-test. The post hoc comparison was performed using the Tukey's test (α=0.05). Results: A significant difference in the surface roughness was observed between the specimens of groups I and II (p<0.05). Surface treatment with liner and sandblasting showed higher shear bond strength between zirconia core and veneering ceramic (p<0.05). Conclusion: The sand blasting and liner treatment increased the shear bond strength between zirconia core and veneering ceramic.

• The Journal of Advanced Prosthodontics
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• 제4권2호
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• pp.76-83
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• 2012

PURPOSE. Zirconia has been used in clinical dentistry for approximately a decade, and there have been several reports regarding the clinical performance and survival rates of zirconia-based restorations. The aim of this article was to review the literatures published from 2000 to 2010 regarding the clinical performance and the causes of failure of zirconia fixed partial dentures (FPDs). MATERIALS AND METHODS. An electronic search of English peer-reviewed dental literatures was performed through PubMed to obtain all the clinical studies focused on the performance of the zirconia FPDs. The electronic search was supplemented by manual searching through the references of the selected articles for possible inclusion of some articles. Randomized controlled clinical trials, longitudinal prospective and retrospective cohort studies were the focuses of this review. Articles that did not focus on the restoration of teeth using zirconia-based restorations were excluded from this review. RESULTS. There have been three studies for the study of zirconia single crowns. The clinical outcome was satisfactory (acceptable) according to the CDA evaluation. There have been 14 studies for the study of zirconia FPDs. The survival rates of zirconia anterior and posterior FPDs ranged between 73.9% - 100% after 2 - 5 years. The causes of failure were veneer fracture, ceramic core fracture, abutment tooth fracture, secondary caries, and restoration dislodgment. CONCLUSION. The overall performance of zirconia FPDs was satisfactory according to either USPHS criteria or CDA evaluations. Fracture resistance of core and veneering ceramics, bonding between core and veneering materials, and marginal discrepancy of zirconia-based restorations were discussed as the causes of failure. Because of its repeated occurrence in many studies, future researches are essentially required to clarify this problem and to reduce the fracture incident.

• 대한치과기공학회지
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• 제33권4호
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• pp.299-306
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• 2011

Purpose: This study aimed to investigate the shear bond strength by manufacturing the veneering porcelain on the IPS e.max $ZirCAD^{(R)}$ zirconia core, using the layering technique and heat-pressing technique, and to evaluate the clinical stability by comparing to the conventional metal ceramic system. Methods: The Schmitz-Schulmeyer test method was used to evaluate the core-veneer shear bond strength of zirconia core ceramic(IPS e.max $ZirCAD^{(R)}$) and their manufacture recommended two veneering ceramic systems(IPS e.max $ceram^{(R)}$, IPS e. max $ZirPress^{(R)}$). A metal ceramic system(Bellabond $plus^{(R)}$, VITA $VM13^{(R)}$) was used as a control group for the two all ceramic system test groups. The maximum loading and shear bond strength was measured. The average shear strength(MPa) was analyzed with the one-way ANOVA and the Tukey's test(${\alpha}$=.05). The fracture specimens were examined using Microscope to determine the failure pattern. Results: The mean shear bond strengths(SD) in MPa were MBSB control 43.62(2.13); ZBSB 18.65(1.76); ZPSB 18.89(1.54). The shear strengths of the zirconia cores were not significantly different(P>.05). Microscope examination showed that zirconia specimens presented mixed failure, and base metal alloy specimens showed adhesive failure. Conclusion: There was no siginificant different between the layering technique and the heat pressing technique in the veneering methods on the zirconia cores. None of the zirconia core and veneering ceramics could attain the high bond strength values of the metal ceramic combination.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.182-182
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• 2009

The effect of Re-oxidation on the PTCR properties of Sm-doped barium titanate ceramics was investigated by means of impedance spectroscopy. Electrical properties such as resistance vs. temperature, I-V curve were measured and microstructure was observed with SEM photography. Sample was fabricated with thick film process such as tape casting of green sheet, screen printing of electrode pattern, stacking, firing in reduced atmosphere and re-oxidation, etc. As the temperature of re-oxidation increases, resistance jump as a function of temperature enhances but resistance at room temperature increases. These behavior of resistance as a function of temperature, dependent on the re-oxidation condition, is analyzed with Cole-Cole impedance plot and is shown to be related with the degree of oxidation of grain boundary regardless of grain core during re-oxidation process of sample.

• The Korean Journal of Ceramics
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• 제3권2호
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• pp.124-128
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• 1997

An attempt was made to understand the dissolution and reprecipitation behavior of the constituent phases such as TiC, TiN, and Ti(CN) in TiC-TiN-Ni system. During the liquid-phase sintering the TiC phase was found to dissolve preferentially in Ni binder. The solid-solution phase, Ti(CN), formed around the TiN phase, resulting in a core/rim structure. This result was reproduced when large TiC particles were used with fine TiN particles. The path for the microstructural change in TiC-TiN-Ni system was largely controlled by the difference in the interfacial energy of each phase with the liquid binder phase. The results were discussed with thermodynamic principles.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2011년도 추계학술발표대회
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• pp.3.1-3.1
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• 2011

Nanoengineered materials with advanced architectures are critical building blocks to modulate conventional material properties or amplify interface behavior for enhanced device performance. While several techniques exist for creating one dimensional heterostructures, electrospinning has emerged as a versatile, scalable, and cost-effective method to synthesize ultra-long nanofibers with controlled diameter (a few nanometres to several micrometres) and composition. In addition, different morphologies (e.g., nano-webs, beaded or smooth cylindrical fibers, and nanoribbons) and structures (e.g., core-.shell, hollow, branched, helical and porous structures) can be readily obtained by controlling different processing parameters. Although various nanofibers including polymers, carbon, ceramics and metals have been synthesized using direct electrospinning or through post-spinning processes, limited works were reported on the compound semiconducting nanofibers because of incompatibility of precursors. In this work, we combined electrospinning and galvanic displacement reaction to demonstrate cost-effective high throughput fabrication of ultra-long hollow semiconducting chalcogen and chalcogenide nanofibers. This procedure exploits electrospinning to fabricate ultra-long sacrificial nanofibers with controlled dimensions, morphology, and crystal structures, providing a large material database to tune electrode potentials, thereby imparting control over the composition and shape of the nanostructures that evolved during galvanic displacement reaction.

• Nuclear Engineering and Technology
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• 제44권1호
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• pp.9-20
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• 2012

A brief review on the thermal plasma synthesis of nano-sized powders is presented according to the application materials, such as, metals, ceramics, glasses, carbonaceous materials and other functional composites, such as, supported metal catalyst and core-shell structured nano materials. As widely adopted plasma sources available for thermal plasma synthesis of nanosized powders, three kinds of plasma torches, such as transferred and non-transferred DC and RF plasma torches, are introduced with the main features of each torch system. In the basis of the described torch features and the properties of suggested materials, application results including synthesis mechanism are reviewed in this paper.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2000년도 춘계학술대회 논문집
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• pp.886-889
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• 2000

This paper describes the machining characteristics of the MoSi$_2$-based composites by electric discharge drilling with various tubular electrodes. MoSi$_2$-based composites has been developed in new materials for jet engine of supersonic-speed airplanes and gas turbine for high- temperature generator. By combining a nonconducting ceramics with more conducting ceramic it was possible to raise the electrical conductivity. In drilling by EDM, the dielectric flushed down the interior of the rotating tube electrode, in order to facilitate the removal of machining debris from the hole. Various metal-coated tubular electrodes of which core are copper and brass are used to know the effect of coating material on machinability of ED drilling.

• 한국세라믹학회지
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• 제46권4호
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• pp.345-349
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• 2009

In Part II, the paper will describe a three-phase alumina-based nanoceramic composite demonstrating superplasticity at a surprisingly lower temperature and higher strain rate. One important factor in the processing of these nanocomposites was the use of the electrical field assisted sintering method, SPS. These improvements in mechanical properties were briefly discussed in the context of the results from the microstructural investigations. SPS forming approach provides a new route for low temperature and high-strain-rate superplasticity for nanostructured materials and should impact and interest a broad range of scientists in materials research and superplastic forming technology.