• 한국세라믹학회지
• /
• 제44권8호
• /
• pp.445-450
• /
• 2007

A conversion layer of SiC was fabricated on the graphite substrate by a chemical vapor reaction method in order to enhance the oxidation resistance of graphite. The effect of boron carbide containing powder bed on the morphology of SiC conversion layer was investigated during the chemical vapor reaction of graphite with the reactive silicon-source at $1650^{\circ}C\;and\;1700^{\circ}C$ for 1 h. The presence of boron species enhanced the conversion of graphite into SiC, and altered the morphology of the conversion layer significantly as well. A continuous and thick SiC conversion layer was formed only when the boron source was used with the other silicon compounds. The boron is deemed to increase the diffusion of SiOx in SiC/C system.

• 한국세라믹학회지
• /
• 제34권6호
• /
• pp.636-644
• /
• 1997

The effect of various processing parameters, in particular the substrate and filament temperature, on the nucleation of diamond has been studied for the hot filament CVD process with a negative bias on the substrate. As far as the substrate temperature was maintained around the critical temperature of 73$0^{\circ}C$, the nucleation of diamond increased with increasing filament temperature. The maximum nucleation density of ~ 2$\times$109/$\textrm{cm}^2$ was obtained under the condition of filament temperature of 230$0^{\circ}C$, substrate temperature of 75$0^{\circ}C$, bias voltage of 300V, methane concentration of 20%, and deposition time of 2 hours. This nucleation density is about the same as those obtained in previous investigations. For fixed substrate temperatures, the nucleation density varies up to about 103 times depending on experimental conditions. This result is different from that of Reinke, et al. When the substrate temperature was above 80$0^{\circ}C$, a silkworm~shaped carbon phase was co-deposited with hemispherical microcrystalline diamond, and its amount increased with increasing substrate temperature. The Raman spectrum of the silkworm-shaped carbon was the same as that of graphitic soot. The silkworm-shaped carbon was etched and disappeared under the same as that of graphitic soot. The silkworm-shaped carbon was etched and disappeared under the deposition condition of diamond, implying that it did not affect the nucleation of diamond.

• 대한치과보철학회지
• /
• 제42권5호
• /
• pp.514-523
• /
• 2004

Statement of problem: All-ceramic restorations have been advocated for superior esthetics. Various post and core systems have been used to improve the strength of damaged teeth, but it is unclear whether they affect the final shade of finished all-ceramic restorations. Purpose: The influence of different types of post and core systems on light transmission through all-ceramic crowns was assessed by spectrophotometric analysis. Also the masking effect of different thickness of ceramic ingot was evaluated. Material and Methods : Forty-five sample disks (15mm in diameter) at several thickness(1.0, 1.5, 2.0mm) and value(shade 100, 200, 300) were made in heat pressed ceramic(IPS-Empress). Background specimens simulating gold-alloy cast posts(Type III casting gold alloy), metal posts(Ni-Cr casting alloy) and ceramic posts(CosmoPost) were fabrica-ted. Resin composite(Z250, A3 shade) was used as a tooth substrate reference. For each combination, the change in color was measured with a spectrophotometer. Readings were performed for 2 conditions (1) ability of ceramic to mask the core in relation to its thickness(1.0, 1.5, or 2.0mm) ; (2) influence of post and core types on the final color of the ceramic. Data were recorded according to the CIE $L^*a^*b^*$ systems and color difference($\Delta$E) was calculated. Results: 100 shade ingot: when ceramic thickness was 1.0mm, $\Delta$E value for ceramic post larger than 1 but $\Delta$E value for metal and gold post was larger than 2. For ceramic thickness of 1.5mm, only $\Delta$E value for metal was larger than 2, and the other samples' $\Delta$E value was smaller than 2. For ceramic thickness of 2.0mm, $\Delta$E values for all specimens was smaller than 2. 200 shade ingot: when ceramic thickness was 1.0mm, $\Delta$E value for ceramic post was smaller than 1 but $\Delta$E value for metal and gold post was larger than 2. For ceramic thickness of 1.5 mm, only the $\Delta$E value for metal was larger than 2, and the other samples' $\Delta$E value was smaller than 2. For ceramic thickness of 2.0mm, $\Delta$E values for all specimens was smaller than 1. 300 shade ingot: when ceramic thickness was 1.0mm, only $\Delta$E value for metal was larger than 2 and the other samples' $\Delta$E value was smaller than 2. For ceramic thickness of 1.5mm, $\Delta$E values for all specimens was smaller than 1. For ceramic thickness of 2.0mm, $\Delta$E values for all specimens was smaller than 1. Conclusion: The final esthetic result of the IPS-Empress glass-ceramic restoration was not affected by the presence of different core materials when the thickness was more than 2.0 mm. When ceramic thickness decreases to 1.5mm, it is advised to take the substrate aspects into consideration. If the ceramic thickness is less than 1.0mm, using the tooth color matched substrate is strongly recommended.

• 한국세라믹학회지
• /
• 제53권1호
• /
• pp.75-80
• /
• 2016

Ink-jet printing has become a widespread technology with the society's increase in aesthetic awareness. Especially, ink-jet printing using glazed ceramic ink can offer huge advantages including high quality decoration, continuous processing, glaze patterning, and direct reproduction of high resolution images. Recently, ceramic ink-jet printing has been rapidly introduced to decorate the porcelain product and the ceramic tiles. In this study, we provide an effective method to apply ceramic ink-jet decorations on the glass substrates using a oleophobic coating with perfluorooctyl trichlorosilane. The ink-jet printed patterns were much clearer on the oleophobically coated glass surface than the bare glass surface. The contact angle of the ceramic ink was maximized to the value of $64.0^{\circ}$ on the glass surface, when it was treated with 1 vol% PFTS solution for 1 min. The effects of the printing conditions and firing process on the ink-jet printed patterns on the oleophobically coated glass were also investigated.

• 한국전기전자재료학회논문지
• /
• 제29권1호
• /
• pp.30-34
• /
• 2016

In this paper, we report that selective etching on N-polar face by EC (electro-chemical)-etching effect on the reduction of bowing and strain of FS (free-standing)-GaN substrates. We applied the EC-etching to concave and convex type of FS-GaN substrates. After the EC-etching for FS-GaN, nano porous structure was formed on N-polar face of concave and convex type of FS-GaN. Consequently, the bowing in the convex type of FS-GaN substrate was decreased but the bowing in the concave type of FS-GaN substrate was increased. Furthermore, the FWHM (full width at half maximum) of (1 0 2) reflection for the convex type of FS-GaN was significantly decreased from 601 to 259 arcsec. In the case, we confirmed that the EC-etching method was very effective to reduce the bowing in the convex type of FS-GaN and the compressive stress in N-polar face of convex type of FS-GaN was fully released by Raman measurement.

• 한국세라믹학회지
• /
• 제38권9호
• /
• pp.846-852
• /
• 2001

2차원적 몬테 칼로 시뮬레이션을 사용하여, 화학적 기상 반응법에 의한 탄화규소 전환층의 생성에 미치는 온도의 영향을 조사하였다. 화학적 기상 반응법은 실리카의 열탄화 환원법에 근거하며, 흑연 기판의 탄소와 실리카 반응기체와의 화학적 반응에 의하여 탄화규소 전환층을 형성하는 방법이다. 탄화규소는 반응기체의 확산 및 반응과 같은 열적활성화 과정을 통하여 생성되기 때문에 탄화규소 전환층의 형성은 온도에 크게 의존함을 알 수 있다. 본 연구에서는 몬테 칼로법을 사용하여 삼각격자로 배열된 2차원적인 계에서 흑연 기판의 미세 기공을 따라 확산된 반응기체와 탄소와의 반응에 의해서 탄화규소가 형성되는 과정을 시뮬레이션을 행하였다. 반응 온도를 1900K, 2000K, 2100K, 2200K로 조건을 달리하여 시뮬레이션 하였으며, 그 계산 결과를 실험 결과와 비교하여 재현성을 검토하고 탄화규소 전환층의 두께와 화학적 조성 구배에 대한 반응 온도의 영향을 검증하기 위한 것이다.

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 1998년도 춘계학술발표회 초록집
• /
• pp.74-74
• /
• 1998

• 한국세라믹학회지
• /
• 제52권6호
• /
• pp.435-440
• /
• 2015

It is a challenge from an industrial point of view to fabricate silicon nitride substrates with high thermal conductivity and good mechanical properties for power devices from high-purity Si scrap powder by means of thick film processes such as tape casting. We characterize the residual carbon and oxygen content after the binder burnout followed by nitridation as a function of the temperature in the temperature range of $300^{\circ}C-700^{\circ}C$ and the atmosphere in a green tape sample which consists of high-purity Si powder and polymer binders such as polyvinyl butyral and dioctyl phthalate. The optimum condition of binder burnout is suggested in terms of the binder removal temperature and atmosphere. If considering nitridation, the burnout of the organic binder in air compared to that in a nitrogen atmosphere could offer an advantage when fabricating reaction-bonded $Si_3N_4$ substrates for power devices to enable low carbon and oxygen contents in green tape samples.

• 한국세라믹학회지
• /
• 제49권4호
• /
• pp.328-332
• /
• 2012

Etch rates of Si and high purity SiC have been compared for various fluorocarbon plasmas. The relative plasma resistance of SiC, which is defined as the etch rate ratio of Si to SiC, varied between 1.4 and 4.1, showing generally higher plasma resistance of SiC. High resolution X-ray photoelectron analysis revealed that etched SiC has a surface carbon content higher than that of etched Si, resulting in a thicker fluorocarbon polymer layer on the SiC surface. The plasma resistance of SiC was correlated with this thick fluorocarbon polymer layer, which reduced the reaction probability of fluorine-containing species in the plasma with silicon from the SiC substrate. The remnant carbon after the removal of Si as volatile etch products augments the surface carbon, and seems to be the origin of the higher plasma resistance of SiC.

• 한국자동차공학회논문집
• /
• 제10권2호
• /
• pp.40-47
• /
• 2002

Because UV wavelength lights can activate photocatalysts, plasma is used as a light source of a photocatalytic reactor. Even though plasma has good intensity for photo reaction, substrate of catalyst coating was limited by the geometry of plasma generator. Usually bead type substrate was used for a pack bed type reactor. Honeycomb monolith type substrate was used with UV lamps instead plasma, due to the light penetration the honeycomb monolith length was too short to show good activity In this study a photocatalytic reactor, which is using a honeycomb monolith substrate, was investigated with plasma as an activation light source. As a parametric study the effects of 1311owing factors on plasma generation and power consumption are examined; supply voltage, substrate length, environment condition, catalyst loading and ratio. Using the test results, the practicability test was done with simulated synthetic gases representing bad smells and automotive exhaust gases.