• Journal of the Korean Ceramic Society
• /
• v.52 no.5
• /
• pp.350-355
• /
• 2015

To develop ceramic composite anodes of solid oxide fuel cells without metal catalysts, a small amount of barium carbonate was added to an $(La_{0.8}Sr_{0.2})(Cr_{0.5}Mn_{0.5})O_3(LSCM)$ - YSZ ceramic composite anode and its catalytic effects on the electrode performance were investigated. A barium precursor solution with citric acid was used to synthesize the barium carbonate during ignition, while a barium precursor solution without citric acid was used to create hydrated barium hydroxide. The addition of barium carbonate to the ceramic composite anode caused stable fuel cell performance at 1073 K; this performance was higher than that of a fuel cell with $CeO_2$ catalyst; however, the addition of hydrated barium hydroxide to the ceramic composite anode caused poor stability of the fuel cell performance.

• Journal of the Korean Ceramic Society
• /
• v.52 no.4
• /
• pp.243-247
• /
• 2015

Si(Al)ON precursor was synthesized by formation of new Si-N bond using organoaluminum imine and liquid type poly(phenyl carbosilane). It was decomposed between $200-600^{\circ}C$, and the ceramic yield was 51% after pyrolysis. 150 - 200 nm in thickness of coating film was obtained by spin coating method. The precursor was easily oxidized during process because it was unstable in air. However the oxygen content was limited to 0.5 - 0.7 to silicon in heat treatment step. Even though the content of nitrogen was decreased by pyrolysis, Al-N and Si-N bonds were formed in ammonia atmosphere, and Si(Al)ON film was formed with 0.2 in content to silicon.

• The Journal of Korean Academy of Prosthodontics
• /
• v.28 no.1
• /
• pp.203-216
• /
• 1990

The purpose of this study was to evaluate the cervical margin fitness in the collarless metal ceramic crowns formed by different techniques. Specimens were divided as follows : the metal ceramic crowns with metal butt margin as group I, the collarless metal ceramic crowns formed with resin binder technique as group II, and the collarless metal ceramic crowns formed with shoulder powder mixed with phosphate-bonded investment liquids on a refractory die as group III. Each group was made of five specimens, and their marginal fitness on each epoxy die was evaluated under scanning electron microscope of x200 magnification at three measuring points : mesial, central, distal. The following results were obtained. 1. The metal ceramic crowns with metal butt margin exhibited significantly better marginal fitness than the collarless metal ceramic crowns. The marginal fitness in descending order was group I, III, II. 2. The collarless metal ceramic crown formed with resin binder technique had the worst marginal fitness & showed cervical color variation and dermacation between the corrected porcelain & the dentin porcelain. 3. The collarless metal ceramic crowns formed with shoulder powder mixed with phosphate-bonded investment liquids on a refractory die exhibited significantly better marginal fitness & sharper marginal configuration than the other collarless group.

• Ceramist
• /
• v.22 no.4
• /
• pp.332-349
• /
• 2019

Ceramic thin films are key materials for fundamental electronic devices such as transistors and capacitors which are highly important for the state-of-the-art electronic products. Their characteristic dielectric properties enable accurate control of current conduction through channel of transistors and stored charges in capacitor electrodes. The electronic conduction in ceramic thin films is one of the most important part to understand the electrical properties of electronic device based on ceramic thin films. There have been numerous papers dealing with the electronic conduction mechanisms in emerging ceramic thin films for future electronic devices, but these studies have been rarely reviewed. Another interesting electrical characterization technique is one based on electrical pulses and following transient responses, which can be used to examine physical and chemical changes in ceramic thin films. In this review, studies on various conduction mechanisms through ceramic thin films and electrical characterization based on electric pulses are comprehensively reviewed.

• Journal of the Korean Ceramic Society
• /
• v.54 no.3
• /
• pp.228-234
• /
• 2017

This work was achieved on the preparation of antimicrobial ceramic hybrid polyethylene films with natural chamomile extracts. The antimicrobial activity and various physicochemical properties of the prepared films were evaluated. Various natural products demonstrated antimicrobial activity. Among them, chamomile extracts showed strong activity and no cytotoxicity rather than that of the natural extracts. Porous ceramic materials were synthesized and demonstrated loading and controlled release of natural antimicrobial extracts. Furthermore, chamomile loaded ceramic hybrid films showed antimicrobial activity that was maintained for over 15 days.

• Journal of Powder Materials
• /
• v.18 no.6
• /
• pp.562-567
• /
• 2011

This paper reports the effect of sintering processes and additives on the microstructures and mechanical properties of $ZrB_2$-SiC composite ceramics. We fabricated sintered bodies of $ZrB_2$-20 vol.% SiC with or without sintering additive, such as C or $B_4C$, densified by spark plasma sintering as well as hot pressing. While almost full densification was achieved regardless of sintering processes or sintering additives, significant grain growth was observed in the case of spark plasma sintering, especially with $B_4C$. With sintered bodies, mechanical properties, such as flexural strength and Vickers hardness, were also examined.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.593-598
• /
• 2003

Ceramic plates containing many micro-holes are used in diverse applications such as MCP (Microchannel Plate). catalytic converters, filters, electrical insulators in integrated circuits, and so on. One of the efficient methods for machining many holes in ceramic plates is wet drilling of ceramic green bodies followed by sintering them. Since the strength of ceramic green bodies is much lower than the strength of sintered ceramic plate, ceramic green bodies can be drilled with high feed rate. The axial force during micro-drilling of ceramic green bodies increases rapidly at high feed rate, which induces the crack in workpiece. Therefore, the tool lift of micro-drill with respect to feed rate may be determined by the predicting increase of axial force. In this work, the axial force during micro-drilling was calculated using the chip flow model on the micro-drill tip. from which the tool life of diamond abrasive micro-drill during micro-drilling of ceramic green bodies was calculated.

• Journal of the Korean Ceramic Society
• /
• v.47 no.5
• /
• pp.407-411
• /
• 2010

ALC was fabricated using cement, lime and quartzite by hydrothermal reaction. ALC has low strength and brittleness on account of inner pores. The studies for resolving these problems were driven by many researchers. Among these researches, the controls of quartzite fineness have been studied for unsuitable properties of ALC. This study experimented with variation of 90 ${\mu}m$ residue for obtain good physical properties. It was found that 90 ${\mu}m$ residue influenced on physical properties of ALC. The lower amount of 90 ${\mu}m$ residue, the higher compressive and bending strength. But the continuing decrease of 90 ${\mu}m$ residue did not cause the increase of strength. In order to application of these results in process, the states of process and hydrothermal products will be considered.

• Journal of the Korean Ceramic Society
• /
• v.51 no.6
• /
• pp.539-543
• /
• 2014

Foam type porous silicon carbide ceramics were fabricated by a polymer replica method using polyurethane foam, carbon black, phenol resin, and silicon powder as raw materials. The influence of the C/Si mole ratio of the ceramic slurry and heat treatment temperature on the porous silicon carbide microstructure was investigated. To characterize the microstructure of porous silicon carbide ceramics, BET, bulk density, X-ray Powder Diffraction (XRD), and Scanning Electron Microscope (SEM) analyses were employed. The results revealed that the surface area of the porous silicon carbide ceramics decreases with increased heat treatment temperature and carbon content at the $2^{nd}$ heat treatment stage. The addition of carbon to the ceramic slurry, which was composed of phenol resin and silicon powder, enhanced the direct carbonization reaction of silicon. This is ascribed to a consequent decrease of the wetting angles of carbon to silicon with increasing heat treatment temperature.

• The Journal of Advanced Prosthodontics
• /
• v.3 no.2
• /
• pp.57-62
• /
• 2011

MATERIALS AND METHODS. Ceramics have a long history in fixed prosthodontics for achieving optimal esthetics and various materials have been used to improve ceramic core strength. However, there is a lack of information on how color is affected by fabrication procedure. The purpose of this study was to evaluate the effects of various dentin ceramic thicknesses and repeated firings on the color of zirconium oxide all-ceramic system (LavaTM) fabricated using CAD/CAM technology. MATERIALS AND METHODS. Thirty disc-shaped cores, 12 mm in diameter with a 1 mm thickness were fabricated from zirconium oxide based all ceramic systems ($Lava^{TM}$, 3M ESPE, St Paul, MN, USA) and divided into three groups (n = 10) according to veneering with dentin ceramic thicknesses: as 0.5, 1, or 1.5 mm. Repeated firings (3, 5, 7, or 9) were performed, and the color of the specimens was compared with the color after the initial firing. Color differences among ceramic specimens were measured using a spectrophotometer (VITA Easyshade, VITA Zahnfabrik, Bad $S{\ddot{a}}ckingen$, Germany) and data were expressed in CIELAB system coordinates. A repeated measures ANOVA and Bonferroni post hoc test were used to analyze the data (n = 10, ${\alpha}=.05$). RESULTS. $L^{\ast}a^{\ast}b^{\ast}$ values of the ceramic systems were affected by the number of firings (3, 5, 7, or 9 firings) (P<.001) and ceramic thickness (0.5, 1, or 1.5 mm) (P<.001). Significant interactions were present in $L^{\ast}a^{\ast}b^{\ast}$ values between the number of firings and ceramic thickness (P<.001). An increase in number of firings resulted in significant increase in $L^{\ast}$ values for both 0.5 mm and 1.5 mm thicknesses (P<.01, P=.013); however it decreased for 1 mm thickness (P<.01). The $a^{\ast}$ values increased for 1 mm and 1.5 mm thicknesses (P<.01), while it decreased for 0.5 mm specimens. The $b^{\ast}$ values increased significantly for all thicknesses (P<.01, P=.022). As the dentin ceramic thickness increased, significant reductions in $L^{\ast}$ values (P<.01) were recorded. There were significant increases in both $a^{\ast}$ and $b^{\ast}$ values (P<.01) as the dentin ceramic thickness increased. CONCLUSION. The number of firings and dentin ceramic thickness have a definite effect on the final color of all ceramic system tested. The mean ${\Delta}E$ value increased as the dentin ceramic thicknesses increased for zirconium-oxide based all ceramic specimens tested. However, the mean ${\Delta}E$ values were less than 3.7${\Delta}E$ units which is rated as a match in the oral environment.