• 연구논문집
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• 통권22호
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• pp.107-113
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• 1992

The $\alpha$-alumina/fused alumina/$\beta$"-alumina specimens were fabricated by addition of fused alumina to $\alpha$-alumina/$\beta$"-alumina system. The sintered densities with and without fused alumina were almost same. But, the bending strength was decreased due to the presense of defects caused by the inhomogeneous dispersion of large fused alumina particles. And the fracture toughness was also decreased because the crack propagated through the fused alumina particles due to the imperfection of $\beta$"-alumina coating around them.

• 한국세라믹학회지
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• 제33권5호
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• pp.547-555
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• 1996

Porous alumina ceramics were fabricated by pseudo-boehmite phydosol-gel process within/without commercial $\alpha$-alumina particles average 1 and 40 micron respectively. The pore characteristics of fired specimens were studied by the measurement of bulk density total porosity thyermal analysis pore volume pore distribution BET area XRD and SEM. with increasing of firing temperature pore volume and BET surface area were decreased and the average pore size was increased to approximately 146$\AA$ upto 80$0^{\circ}C$ by de-watering of [OH] and formation of $\alpha$-alumina. The fired relative density of the alumina-dispersed specimen with average 1 micron particle was increased with the amounts of dispersed particle by bimodal packing theory which is compared to the ones of specimen including of average 40 micron particle. It was confirmed that the percola-tion threshold in porous ceramics with coarser particle (40 micron) has formed between the transformed-alumina from hydrogel and dispersed-alumina of above 50 vol% particle and the total porosity was increased at the threshold point above.

• 한국세라믹학회지
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• 제25권3호
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• pp.193-200
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• 1988

침전법에 의해서 pH가 7, 9, 10, 11인 조건에서 생성된 알루미늄 수산화물을 출발물질로 하여 열처리에 따른 알루미나 분말의 특성을 연구하였다. $600^{\circ}C$에서 2시간 동안 열처리하였을 때 비정질 알루미늄 수산화물의 결정수가 탈수된 후에 생성된 최초의 상은 비정질 알루미나의 비표면적은 감소하였다. 비정질 알루미늄 수산화물을 제외한 나머지 알루미늄 수산화물로부터 결정수의 탈수는 비표면적을 증가시켰으며 AlOOH 형태의 수산화물의 존재비가 클수록 전이 알루미나 존재영역까지는 비표면적이 더 크게 나타났다. $\alpha-Al_2O_3$로의 전이속도는 동일온도에서 pH=7 > pH=10 > pH=9 > pH=11의 순서로 일어났으며, 생성된 $\alpha-Al_2O_3$ 분말의 morphology는 알루미늄 수산화물의 외형을 남긴 형골입자(skeleton particle였다. 또한, 열처리 온도의 증가와 $\alpha-Al_2O_3$로의 전이가 일어남에 따라 비표면적의 감소와 더불어 입자성장이 일어나다.

• 한국세라믹학회지
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• 제32권8호
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• pp.909-914
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• 1995

From alumina powder and TEOS, $\alpha$-Al2O3/SiO2 composite powder for reaction-sintered mullite was synthesized by heterogeneous coagulation and surface coating, and investigated the mullitization reaction and sintering behavor of these powders. In $\alpha$-Al2O3/SiO2 composite powder prepared by heterogeneous coagulation, each alumina particles were surrounded by silica particles of 50~60 nm in size. And the alumina particles in composite powder prepared by surface coating were coated by uniform silica layer with thickness of 50 nm. In both methods, mullitization reaction was completed at 1$650^{\circ}C$ for 3h, and specimen sintered above 145$0^{\circ}C$ was about 95% fo the theoretical relative density. Mullite grains formed from the reaction with composite powders showed spherical shape with a size of 1~2${\mu}{\textrm}{m}$.

• 한국세라믹학회지
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• 제31권1호
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• pp.1-10
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• 1994

Monodispersed alumina and Mg-doped alumina fine particles were prepared by controlled hydrolysis of alkoxides. Aluminium alkoxide and magnesium alkoxide were dissolved into complex solvent which was composed of hydrophobic n-octanol and hydrophilic acetonitrile. Hydroxypropyl cellulose(HPC) was used as a dispersant for the alumina particles. The size of these prepared powders was approximately 0.3 ${\mu}{\textrm}{m}$. In the case of sintering above 100$0^{\circ}C$, most of these prepared powders were transformed to $\alpha$-alumina. The relative density of the sintered body of these prepared powders at 1$600^{\circ}C$ was 98%. The sintered body of the Mg-doped alumina powder had more uniform grain size than that of the undoped alumina podwer.

• 한국세라믹학회지
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• 제29권5호
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• pp.367-376
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• 1992

The powder characteristics of seeded alumina prepared from alkoxide by sol-gel method were studied. When ${\alpha}$-Al2O3 seeded powders used, these ${\alpha}$ phase transformation temperatures decreased than those of unseeded powders by 110$^{\circ}C$ and fine powders under 0.1 $\mu\textrm{m}$ could be obtained. When Fe-nitrate added powders used, fast transformation rate resulted from ionic effects of Fe3+, but hard aggregated morphology exhibited. When ${\alpha}$-Al2O3 and Fe nitrate simultaneously added, these powders represented lower transformation temperature but resulted in microstructure with aggregated particles.

• 한국결정성장학회지
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• 제5권2호
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• pp.122-128
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• 1995

알루미나 입자표면에 실리카 흡착층을 갖는 복합분말로 제조된 시편을 반응소결시켜 물라이트화 과정을 고찰하였다. 물라이트화 반응은 알루미나와 cristobalite의 계면에서 낮은 알루미나 함량을 갖는 비정질 aluminosilicated 상이 중간층을 형성하면서 시작되고 이 층을 통한 알루미나의 확산에 의하여 물라이트가 성장되었다. 물라이트는 알루미나의 입자의 표면을 따라 성장하였으며 확산에 의해 성장속도가 제어되었다

• 한국세라믹학회지
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• 제39권10호
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• pp.1007-1010
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• 2002

마이크로파 가열을 이용하여 ${\gamma}-Al_2O_3와\;Na_2SO_4$ 분말 혼합물로부터 알파 알루미나 판상체 입자를 합성하였다. 마이크로파를 이용하여 합성된 알루미나 입자의 크기와 입자분포를 마이크로파 이용 없이 동일한 혼합물로부터 합성된 분말과 비교하였다. 마이크로파를 이용하여 합성된 시료는 마이크로파 사용 없이 합성된 시료에 비하여 입자크기가 작고 입자분포가 좁음을 알 수 있었다.

• Nuclear Engineering and Technology
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• 제38권5호
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• pp.423-426
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• 2006

A developed neutron activation analysis(NAA) and gamma-spectrometry were applied to improve the analytical sensitivity and precision of impurities in electronic-circuit raw materials. It is well known that soft errors in high precision electronic circuits can be induced by alpha particles emitted from naturally occurring radioactive impurities such as U and Th. As electronic circuits have recently become smaller in dimension and higher in density, these alpha-particle emitting radioactive impurities must be strictly controlled. Therefore, new NAA methods have been established using a HTS(Hydraulic Transfer System) irradiation facility and a background reduction method. For eliminating or stabilizing fluctuated background caused by Rn-222 and its progeny nuclides in air, a nitrogen purging system is used. Using the developed NAA and gamma-spectrometry, ultra trace amounts of U(0.1ng/g) and Th(0.01ng/g) in an alumina ball and high purity silica used for an epoxy molding compound (EMC) could be determined.

• 전기학회논문지
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• 제65권9호
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• pp.1504-1510
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• 2016

The aim of this study is to improve properties both glass transition temperature($T_g$) and coefficient of thermal expansion(CTE) using epoxy/micro-nano alumina composites with adding glycerol diglycidyl ether (GDE:1,2,3,5g). This paper deals with the effects of GDE addition for epoxy/micro alumina contents (40, 50, 60wt%)+surface modified nano alumina(1_phr) composites. 20 kinds specimen were prepared with containing micro, nano alumina and GDE as a micro composites(10, 20, 30, 40, 50, 60, 70wt%) or a nano/micro alumina composites(1phr/40, 50, 60wt%). Average particle size of nano and micro alumina used were 30nm and $1{\sim}2{\mu}m$, respectively. The micro alumina used were alpha phase with Heterogeneous and nano alumina were gamma phase particles of spherical shape. The glass transition temperature and coefficients of thermal expansion was evaluated by DSC and TMA. The glass transition temperature decreased and coefficients of thermal expansion become smaller with filled contents of epoxy/micro alumina composites. On the other hand, $T_g$ and CTE as GDE addition variation(1,2,3,5g) of epoxy/micro-nano alumina composites decreased and increased respectively.