• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.247-247
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• 2004

세라믹의 완전 소결체는 높은 경도와 취성을 가지기 때문에 연삭과 같은 입자가공이 행해지게 되어, 가공능률이 매우 낮고, 복잡한 형상 창성이 어렵다. 완전소결된 세라믹의 절삭가공에서는, 공구수명이 짧고, 가공속도가 매우 늦어 일반의 부품가공에 적용하기 어렵다. 또한 소결이 전혀 행해지지 않은 성형체의 절삭가공은 공작물의 강도가 약하기 때문에 가공속도, 가공능률, 부품의 척킹 및 치수 정밀도 등에 문제가 있다고 할 수 있다 이러한 문제 때문에 엔지니어링 세라믹의 고능률, 고품위 절삭에 관한 연구가 필요하다.(중략)

• Journal of the Korean Society for Precision Engineering
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• v.24 no.2 s.191
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• pp.33-40
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• 2007

In this study, presintered and full sintered low purity alumina ceramics were machined with various tools to clarify the effect of cutting fluid in machinability. The main conclusions obtained were as follows. When the presintered ceramics were wet machined with sintered diamond tool, the tool wear becomes extremely large, and higher cutting speed can be used than in the case of full sintered ceramics. The productivity of wet cutting with the sintered diamond tool is much higher than that of dry cutting. In the case of the CBN and ceramic tools, the tool wear were smaller at wet cutting than at dry cutting, especially exhibiting considerably larger grooved tool wear in wet cutting with ceramic tool.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.1
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• pp.39-46
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• 2005

In this study, unsintered, presintered and full-sintered low purity alumina ceramics were machined with various tools to clarify the machinability and the optimum cutting conditions. The main conclusions obtained were as follows. (1) Machined with alloy steel tool, the machinability of the presintered ceramics becomes better with the decrease of presintering temperature, but that of unsintered ceramics(white body) was extremely poor. (2) In the case of carbide, K01, the tool life in machining the white body was the longest, and the machinability of presintered ceramics becomes poorer with the increase of the presintering temperature. (3) The K01 tools exhibit longer life than the P10 tools in machining both the white body and the ceramics presintered at $1450^\circC$ or higher temperatures, but the P10 tools shows longer tool life than the K10 tools in machining of the ceramics presintered at temperatures below $1450^\circC$.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.1 s.178
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• pp.80-88
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• 2006

In this study, unsintered and presintered low purity alumina ceramics were machined with various tools to clarify the machinability and the optimum cutting conditions. The main conclusions obtained were as fellows. Machined with ceramic tool, the ceramics presintered at the temperature range of $1000\~1100^{\circ}C$ showed the best machinability due to the adhesion formed in weared surface within a certain cutting speed range. In the above combination and conditions, the ceramic tool showed the highest productivity through all experiments. The life of CBN tool was longer in machining of the ceramics presintered at $1000^{\circ}C$ than in the case of that presintered at $600^{\circ}C$, but the diamond tool showed adverse tendency. In machining of the ceramics presintered at $1000^{\circ}C$, the ceramic tool exhibits the longest tool life in high speed, the tool lives became extremely worse in the order of CBN tool and diamond tool. However, in the case of the ceramics presintered at $600^{\circ}C$, the diamond tool shows the longest tool life, the tool lives was much worse in the order of CBN tool and ceramic tool.

• Journal of the Korean Ceramic Society
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• v.37 no.11
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• pp.1078-1083
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• 2000

정전안정화 및 입체안정화를 동시에 적용한 복합안정화기구에 의하여 25 부피%의 나노 $Al_2$O$_3$슬러리를 제조하고, 이로부터 얻은 주입성형체, 원심성형체, 진공성형체의 기공구조 분석을 통하여 입자충전거동을 살펴보았다. 나노 알루미나 분말의 습식 성형체의 충전구조는 성형방법에 의하여 가해지는 외력의 영향을 크게 받지만, 반발력을 제공하는 표면장벽층의 상호작용에 의해서도 현저한 차이를 보이는 것으로 나타났다. 예비소결실험을 통하여 나노분말에서도 기공크기가 작고, 크기분포가 좁으며, 높은 밀도를 가진 균일성형체의 미세구조가 소결미세구조를 균일하게 하는데 필수적인 조건임을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.6
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• pp.1002-1012
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• 1997

When the presintered ceramics are machined with ceramic tool, the tool life becomes extremely short. The CBN tool exhibits the best performance in dry machining of the ceramics presintered at $1450^{\circ}C$ among all cutting tests. The roughness of the machined surface of the ceramics presintered below $1350^{\circ}C$ is smaller than that of the ceramics presintered at $1450^{\circ}C$ While the performance of the cemented carbide and CBN tools is better in dry than in wet machining, the diamond tool shows adverse tendency. The tool life is not affected by the feed rate and depth of cut. During the following full-sintering after the machining of the presintered ceramics, the surface roughness decreases up to 62%. The finished surface in machining the presintered ceramics is much better than that in machining the full-sintered ceramic.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.5
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• pp.14-21
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• 2010

In this study, presintered low purity alumina ceramics were machined with various tools to clarify the effects of the tool material, cutting condition and tool geometry on machinability. The main conclusions obtained were as follows. (a)The wear of tungsten carbide tool becomes smaller with the increase of the feed and clearance angle, and with the decrease of rake angle, especially exhibiting considerably smaller wear with both the decrease of rake angle and the increase of clearance angle. (b) So far as turning the ceramic presintered at low temperature, the diamond tool shows the best performance with higher feed. (c) The effect on the tool wear of the feed, clearance angle and rake angle becomes smaller in turning the ceramic presintered at higher temperature. (d) The tool wear is not severely affected by the depth of cut.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.178-185
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• 1999

For the process control of silicon nitride gelcasting, the composition effect of acryamide system on the viscosity of slip and mechanical property of gelcast green body were investigated. The slip was prepared by ball milling of silicon nitride suspension prepared with acrylamide monomer and polyelectrolyte dispersant after premixing them by attritor. The slip mixed with initiator was vacuum deaired and cast into molds, and then polymerized. The consolidated green body was obtained by drying the gelated slip. The viscosity measument and the diametral compression test was done to evaluate the rheological behaviro of slip and mechanical property of gelcast body, respectively. Experimental results showed that the high solid loading of silicon nitride slip was obtained up to 46 vol% with a low viscosity. The mechanical property of gelcast body mainly increased with increasing the concentration of monomer. The gelcast body was machinable above the ∼3 MPa of tensile strength. The relative density of pressured-sintered body was 98.5% at 1760$^{\circ}C$, 3 h.

• Journal of dental hygiene science
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• v.15 no.5
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• pp.577-584
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• 2015

The purpose of this study was to evaluate the effect of metal chloride infiltration treatment on color and strength changes of the yttria-stabilized tetragonal zirconia polycrystals (Y-TZP). Fifty disc specimens were prepared with a Y-TZP powder (ZPEX; Tosoh, Japan). Thirty different metal chloride solutions containing 0.03~0.08 wt% chromium and 0.03~0.07 wt% terbium ions were prepared. Presintered Y-TZP specimens were soaked in metal chloride coloring liquids for 3 minutes and sintered in air at $1,450^{\circ}C$ for 2 hours. The color of the specimens was measured with spectrophotometer and color difference (${\Delta}E^*$) was obtained based on the CIE $L^*$, $a^*$, $b^*$ color coordinate values. To evaluate the effect of metal chloride infiltration strength changes, the biaxial flexural test was performed at crosshead speed 0.5 mm/min. Colors of the sintered Y-TZP showed the colors of Vita shade guide A1, A2 and A3 with the infiltration of chromium and terbium chloride solutions. Density of the sintered Y-TZP increased by the infiltration of chromium and terbium chloride solutions. Bi-axial flexural strength of the sintered Y-TZP did not show statistically significant differences by the infiltration of chromium and terbium chloride solutions (p>0.05). Chromium and terbium chloride did not affect the crystal phase of zirconia, and all specimens showed tetragonal phase. Accordingly, this study suggests that chromium and terbium chlorides can make colored zirconia while adding in a liquid form. The color of colored zirconia differ from that of vita shade guide but it can use all ceramic restoration as substructure in dental clinic.

• Membrane Journal
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• v.20 no.1
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• pp.69-75
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• 2010

Cermet membrane was fabricated with tantalum as hydrogen-permeable metal and $Y_2O_3$-stabilized $ZrO_2$ (YSZ) as ceramic supporter. Ta/YSZ cermet membrane was prepared through pre-sintering in He atmosphere and then main sintering under high vacuum and the impurities to originate from sintering and brazing could be removed by mechanical polishing. As-prepared membrane showed dense structure with continuous channel of tantalum. Hydrogen permeation experiment was conducted in the region of $200{\sim}350^{\circ}C$ using Ta/YSZ membrane coated with Pd for hydrogen dissociation. The crack in membrane was formed at $300^{\circ}C$ and the Pd coating layer has flaked off in spots. XRD results showed that tantalum reacted with hydrogen to form $Ta_2H$. The lattice expansion by $Ta_2H$ caused deterioration for membrane.