• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.43-43
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• 2007

LTCC는 최근의 이동 통신 환경의 급격한 발전 속에 그 응용 및 특성 요구가 증폭되고 있다. 이러한 LTCC 소재는 주로 테이프 캐스팅에 의한 후막 공정으로 제품이 만들어지게 되는데, 캐스팅을 위해 제조되는 슬러리는 일반적으로 유변학적 의사가소성 거동을 하는 것으로 알려져 있다. 그러나, 슬러리 제조 조건에 따라 유변학적 거동이 다르게 나타나는 것이 관찰되었다. 이에, 슬러리 제조 조건을 다양하게 변화시키며, 유변학적 거동을 살며 보고 이렇게 변화된 유변학적 거동과 캐스팅된 시트 특성과의 관계를 검토해 보려 한다. LTCC 재료의 주 구성 요소인 glass와 세라믹 분말의 초기 조건 및 각각의 rheology 특성과 혼합 슬러리에서의 관계성 등을 고찰하려 한다.

• Journal of the Korean Ceramic Society
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• v.39 no.2
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• pp.164-170
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• 2002

Measurements of sedimentation, solid loading, zeta potential, and viscosity were employed to determine a proper dispersant and its amount for a well dispersed alumina powders in aqueous alumina tape casting using acrylate as a binder. Polycarboxylic acid was the most effective one among various dispersants considered in the present study and its amount was 0.23∼0.24 g per 100 g alumina for a dispersion. Better dispersion was obtained as an increase of dispersant addition. However, the dispersion was hindered as the amount of dispersant was higher than the optimum amount because of bridging or tangling of polymer chains. Excellent aqueous alumina tapes were prepared from the slurry containing the optimum amount of the polycarboxylic acid (0.2g), alumina powders(100 g), acrylate and Benzoflex as binder and plasticizer, respectively. The viscosity of the slurry was 570 cps and the alumina loading in the tape was 57 vol%.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.184-184
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• 2008

저온 동시 소성 세라믹(LTCC, Low Temperature Co-firing) 기술 중에서 테이프 캐스팅(tape casting)은 얇고 균일한 세라믹 그린 쉬트를 연속 성형할 수 있으며 성형된 쉬트의 밀도, 표면상태, 두께제어 등이 매우 중요하다. 얇고 균일한 세라믹 그린 쉬트를 제작하기 위해서 슬러리의 분산성과 레오로지 특성은 매우 중요한 요소이며 첨가되는 유기물 첨가제들의 종류와 함량비는 슬러리의 분산성과 점도에 큰 영향을 미친다. 본 연구에서는 유기물 첨가제의 종류와 함량에 따른 슬러리의 점도와 그린 쉬트의 밀도 및 두께 제어에 미치는 영향을 고찰하였다. 바인더로는 acryl, polyvinyl 계를 사용하였으며, 가소제는 glycol, phatalate 계를 사용하였다. 각각 2 종류의 바인더와 가소제의 함량에 따른 레올로지 거동과 그런 쉬트의 밀도를 측정하였다. 각 조성별로 준비된 슬러리를 사용하여 테이프 캐스팅 방법으로 제작된 그린 쉬트의 두께를 측정하여 유기물 첨가제 조성이 그린 쉬트의 두께제어에 미치는 영향을 평가하였다.

• Journal of Korea Foundry Society
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• v.23 no.3
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• pp.153-157
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• 2003

본 논문은 레오캐스팅용 AZ91 합금 슬러리를 제조하는 새로운 방법에 관한 것이다. 그 원리는 AZ91 합금 액상에서 Mn의 용해도차에 의해 생성되는 $Al_8(Mn,Fe)_5$ 정출물을 ${\alpha}-Mg$ 초정 생성을 위한 불균일 핵생성 자리로 사용하고자 하는 것이다. 제조된 슬러리의 미세조직 분석결과 $Al_8(Mn,Fe)_5$ 정출물이 ${\alpha}-Mg$ 내에 위치하고 있어, 이로부터 정출물이 효과적으로 불균일 핵생성 자리로 작용하고 있음을 알 수 있었다. 또한 Mn 함량의 증가는 $Al_8(Mn,Fe)_5$ 정출물 수를 증가시켜 고상분율이 일정할 때 슬러리 내 ${\alpha}-Mg$ 고상의 크기를 감소시키고 구형도를 향상시킨다. 이외에도 냉각속도 및 유지시간이 슬러리 미세조직에 미치는 영향에 대해서도 보고하였다.

• Applied Chemistry for Engineering
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• v.10 no.5
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• pp.748-753
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• 1999

In gelcasting process of the Si powder slurry mixed with acrylamide monomers, it was characterized the effects of chemical parameters such as monomers and additives(polymerization initiator, catalyst and dispersant), Si powder and humidity at drying on processing parameters such as viscosity and idle time as well as on shrinkage and mechanical strength of green bodies. Generally, idle time decreased as initiator and catalyst amounts were increased, but rather depended on initiator. Idle times of the slurries greatly decreased to less than 1/2 time of the premix solutions in which gelation was delayed at higher MBAM portion as a crosslinking monomer. And fluidity of the slurries became worse at greater than 0.6 wt % dispersant. The green bodies showed only less than 7% of linear shrinkage without crack and distortion when dried for longer than 300 hrs under 98% humidity. Typically, the dried bodies containing 40, 50 vol % of Si powder displayed 64 and 36 Mpa in average, respectively.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.5 s.98
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• pp.98-103
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• 1999

The application field of porous mold is more and more expended. A mixture of alumina and cast iron is used for making porous mold using slip and vacuum casting method in this study. Slip casting is a process that slurry is poured into silicon rubber mold, dried in vacuum oven, debinded and sintered in furnace, In this procedure, slurry is composed of powder, binder, dispersion agent, and water. Vacuum casting is a technique for removing air bubbles existed in the slurry under vacuum condition. Since ceramics has a tendency of over-shrinkage after sintering, cast iron is used to compensate dimensional change. The results shows that sintering temperature has a great effect on characteristics of alumina-cast iron composite sintered parts. Finally ceramic-metal composite sintered mold can be used for aluminum alloy casting of shoe mold using this process.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.11
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• pp.62-67
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• 1999

The RP&M(Rapid Prototyping and Manufacturing) is the most appropriate technology for the small-lot production system, in which the production cycle is getting shorter owing to various needs from consumers. Recently RP products which are made of plastics, wax, and paper are used to verify the design of samples. But these products cannot be applied to the real mold because the strength enough to be a mold cannot be given by soft materials such as plastics. So RP products are copied to AFR(Al powder Filled Resin) molds or metal molds, which is called the RP&M. In this paper, RP&M is applied to a casting process. A porous casting mold, which is made from ceramic powder and binder, is used for rapid tooling of aluminum shoes molds.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.70-78
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• 1997

3Y-TZP/SUS316 Functionally Graded Material (FGM) was fabricated by slip casting method. Alumina mold was used to overcome problems of gypsum mold in slip casting process, and the optimal dispersion con-ditions of 3Y-TZP/SUS316 binary slurries was determined using electrokinetic sonic amplitude and a viscometer, and observing sedimentation behavior. The properties of the specimens casted by gypsum mold and alumina mold were compared in terms of changes in shrinkage rate, drying and sintering conditions, and microstructure. It was found that the specimens obtaine from the alumina mold showed a clean surface, easier thickness control of each layer, and higher productivity. Especially, no degradation was observed in the SUS316 prepared using alumina mold. Thus it is desirable to use porous alumina mold rather than gyp-sum mold for the slip casting of 3Y-TZP/SUS316-FGM.

• Journal of Korea Foundry Society
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• v.27 no.1
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• pp.31-35
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• 2007

In order to develop the semi-solid forming technology for magnesium alloy the rheological and thixotropic behavior of Mg alloy slurry with varying shear rates and cooling rates was investigated and simulated with considering the viscosity based on microstructures and processing variables. The viscosity of slurry of Mg alloy (AZ91D) in semi-solid region was exponentially increased with a solid fraction, and was decreased with increasing a shear rate. In order to analyze precisely the rheological behavior, the ANYCAST program modified with the Carreau model and the different heat transfer coefficient between the cast and mold was used to simulate the flow behavior of Mg semi-solid slurry during the injection into a casting mold in a high pressure diecasting machine. The simulated rheological behavior of Mg alloy slurry was matched well with the experimental results.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.871-877
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• 2002

Alumina slurriers, having various amount of alumina and ratio of organic additives, were prepared for tape casting. The relative viscosities were compared to investigate influence of composition on stability of the slurry and plotted as a function of powder fraction. They raised with increasing powder fraction of slurries, revealing a exponential function curve, which means that stability of slurry was not affected by amount and composition of organic additives. Cast green tapes were tested under tensile condition at room temperature. The increase in alumina ratio and binder ratio was found to decrease strain to failure of green tapes from 363% to 45% and from 68% to 25%, respectively. Tensile strength of green tapes increased abruptly with increasing alumina ratio, which showed its maximum at 1 MPa. On other hand, Tensile strength increased continuously from 0.5 MPa to 4 MPa with increasing binder ratio. Mechanical properties of them were affected seriously and lost their properties by elevating temperature from 20$^{\circ}C$ to 80$^{\circ}C$.