• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제54권12호
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• pp.561-566
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• 2005

This paper describes electrical resistivity, dielectric strength, thermal conductivity, thermal stability and tensile strength of mica sheet impregnated with silicone rubber resin or silicone rubber resin containing alumina powder. The mica sheet impregnated with silicone rubber resin had higher electrical resistivity, dielectric strength and tensile strength than those of virgin mica sheet. Electrical resistivity of mica sheet impregnated with silicone rubber resin containing alumina increased with increasing the amount of alumina. However, dielectric strength and tensile strength of mica sheet impregnated with silicone rubber resin containing alumina decreased with increasing the amount of alumina. The mica sheet impregnated with silicone rubber resin had lower thermal conductivity than that of virgin mica sheet. However, thermal conductivity of mica sheet impregnated with silicone rubber resin conatining alumina increased with increasing the amount of alumina. In the case of thermal stability, thermal degradation of virgin mica sheet and impregnated mica sheet with silicone rubber resin did not occur up to $1100^{\circ}C$ and $400^{\circ}C$, respectively.

• 한국세라믹학회지
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• 제52권3호
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• pp.192-196
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• 2015

Low soda alumina powder was fabricated using silica (${\alpha}$-quartz) as an agent for removing soda components in the alumina. Quartz powder 2 mm in size was added to aluminum hydroxide obtained through the Bayer process, and then the mixture was heated at various temperatures. Finally, the heat-treated powders were sieved for classification. In this study, the effects of the quartz amount and heating temperature on the mechanism of removing soda were examined. A minimum soda content of 0.005 wt% was observed at the conditions of 15 wt% quartz (based on $Al(OH)_3$ amount) heat-treated at $1600^{\circ}C$ for 8 h. The soda components, such as $Na_2O$, NaOH, and $Na_2CO_3$, in alumina were ionized and activated at high temperature, and this facilitated the reaction with quartz silica and alumina producing nepheline. The advantages of using quartz include low iron content and low cost in comparison with the conventional de-soda process using chamotte, another silicate mineral.

• 한국전기전자재료학회논문지
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• 제31권7호
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• pp.496-501
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• 2018

In this study, we prepared 40, 45, 50, 55, 60, 65, and 70 wt% content composites filled in epoxy matrix for two micro silica and three micro alumina types for use as a GIS heavy electric machine. As a filler type of epoxy composite, micro silica composites showed excellent AC breakdown strength properties compared to micro alumina composites in the case of electrical properties of micro silica and alumina. The electrical breakdown properties of micro silica composites increased with increasing filler content, whereas those of micro alumina decreased with increasing filler content. In the case of mechanical properties, the micro silica composite showed improved tensile strength and flexural strength compared with the micro alumina composite. In addition, mechanical properties such as tensile strength and flexural strength of micro silica and alumina composites decreased with increasing filler content. This is probably because O-H groups are present on the surface of silica in the case of micro silica but are not present on the surface of alumina in the case of micro alumina.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2017년도 제48회 춘계학술대회논문집
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• pp.412-415
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• 2017

본 연구에서는 금속을 담지한 alumina bead 촉매를 이용하여 ammonium dinitramide (ADN)기반 단일액상추진제 분해 성능 분석을 수행하였다. Alumina bead를 $1200^{\circ}C$에서 소성한 후, 회전 증발기를 이용하여 과량 용액 함침법 (Excess water impregnation)으로 alumina bead에 Pt 및 Cu 를 담지하였다. 자체 제작한 batch 반응기에서 ADN기반 단일액상추진제 분해 온도($T_{dec}$)를 측정하였다. Cu/$Al_2O_3$ 촉매가 Pt/$Al_2O_3$ 촉매에 비해 분해 온도가 더 낮게 나타났으며, $T_{dec}$ 는 약 $130^{\circ}C$이었다.

• 한국결정성장학회지
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• 제24권2호
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• pp.59-64
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• 2014

전해질로 $Na_2SiO_3$을 사용하여 A1050 알루미늄 판재를 pulse 폭 $ 2000{\mu}sec$, impulse 420 V, 400 ${\mu}$sec의 unipolar pulse로 플라즈마 전해 산화 코팅(plasma electrolytic oxidation coating)을 하여 산화 피막을 2, 5, 15, 30분에 따라 형성시킨 다음 산화피막을 분석하였다. 표면에 형성된 산화물의 결정상은 ${\alpha}-alumina$와 ${\gamma}-Alumina$로서 시간에 따른 변화는 없었다. 반응 초반에는 ${\gamma}-Alumina$가 많이 생성되었지만 시간이 갈수록 ${\gamma}-Alumina$의 양에는 변화 없이 ${\alpha}-alumina$가 많이 생겨남을 알 수 있었다. 이런 결과는 micro plasma에 의해서 ${\gamma}-Alumina$가 우선 생성되고, 이후 계속되는 micro plasma의 열에 의해서 ${\alpha}-alumina$로의 전이가 일어나기 때문으로 판단된다.

• 한국재료학회지
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• 제22권12호
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• pp.643-649
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• 2012

Coatings composited with alumina and Perfluoro alkoxyalkane (PFA) resin were deposited on stainless steel plate (SUS304) to further improve corrosion resistance. Plate (ca. $10{\mu}m$) and/or nanosize (27~43 nm) alumina used as inorganic additives were mixed in PFA resin to make alumina-fluoro composite coatings. These coatings were deposited on SUS304 plate with wet spray coating and then the film was cured thermally. According to the amount and ratio of the two kinds of alumina having plate morphology and nano size, corrosion resistance of the film was evaluated under strong acids (HF, HCl) and a strong base (NaOH). The film prepared with the addition of 5~10 wt% alumina powders in PFA resin showed corrosion resistance superior to that of pure PFA resin film. However, for the film prepared with alumina content above 10 wt%, the corrosion resistance did not improve with the physical properties, such as surface hardness and adhesion. The film prepared with plate/nanosize (weight ratio = 1/2) alumina especially enhanced the surface hardness and corrosion resistance. This can be explained as showing that the plate and the nanosize alumina dispersed in PFA resin effectively suppressed the penetration of cations and anions due to the long penetration length and fewer defects that accompany the improved surface hardness under a serious environment of 10% HF solution for over 120 hrs.

• 멤브레인
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• 제11권3호
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• pp.124-132
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• 2001

고온에서 수소 분리 회수를 목적으로 silica/alumina 복합 막을 합성하였다. 막의 선택 투과 성능을 향상시키기 위해, sol-gel법에 의한 silica 및 alumina층을 중간층으로 도입하고, 그 위에 강제유동 CVD법에 의한 silica를 합성하였다. Sol-gel법에 의해 ${\alpha}$-alumina tube에 합성한 ${\gamma}$-alumina 및 silica 막은 Knudsen 확산 영역의 많은 mesopore를 포함하고 있어서 수소 선택 분리 막으로는 적합하지 못했다. 하지만, sol-gel법에 의해 합성한 silica/${\gamma}$-alumina층에 강제유동 CVD법으로 silica를 합성한 결과, 질소 투과 영역의 세공이 완전히 제거되어, 높은 수소 선택성을 가지는 복합 막이 형성되었다. 그 막은 온도에 따라 수소 투과 속도가 증가하여 $450^{\circ}C$에서 $5.57{\times}10^{-8}molm^2s^LPa^1$의 수소 투과 속도와, 9.52 kJ/mol의 활성화 에너지를 나타냈다. 분자체 효과에 의해 질소 투과가 완전히 배제되고, 수소만 선택적으로 투과되는 silica/alumina 복합막이 성공적으로 합성된다.

• 열처리공학회지
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• 제31권3호
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• pp.120-125
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• 2018

The PMMA composited material mixed with alumina studied to find the optimal condition, the adequate ratio of mixing, for the associated mechanical properties such as anti-corrosive, weatherproof performance. The 80% of hardness and 52% of scratch coefficient improved according to increasing ratio of alumina, which is mostly 3 times higher than that of pure PMMA, on other hand 16% of tensile strength and 35% of flexural strength has lost while alumina was adding in. The most proper ratio, having the best availability in substantial production, of composite between pure PMMA and alumina is determined as 93 wt. % vs 7 wt. %. Results of related five properties had estimated by using of a pentagram.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전기설비전문위원
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• pp.261-262
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• 2008

Damaged glass insulator that is utilized the high-speed railroad in domestic try to find the cause. This paper is investigated on the characteristics of alumina cement as the binder of class insulator. The components of glass insulator ore stub(tin), rod(tin), shed(tempered glass), and alumina cement. If composition of alumina cement is not unified, crack of alumina cement generated. As these results, cracked marks of cement is appeared and composition of alumina cement is not unified. Therefore, it is estimated that main element of long-term degradation is a alumina cement.

• The Korean Journal of Ceramics
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• 제7권2호
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• pp.74-79
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• 2001

Alumina composite reinforced by chopped alumina fiber was fabricated by filter-pressing the fiber slurry followed by the infiltration of alumina slurry. The chopped fiber was coated with nickel by electroless plating method. The green samples were densified by hot-pressing. Microstructures were studied by SEM and the mechanical properties such as bending strength and fracture toughness were measured. The resulting mechanical properties were analyzed in relation with processing parameters such as preform density and resulting microstructures. The load-displacement curve of the specimen with Ni interlayer but without Ni inclusion showed brittle fracture mode due to the direct contact between matrix and fiber. The load-displacement curve of the specimen with Ni interlayer and Ni inclusion in the matrix which is introduced by high applied pressure during specimen preparation showed non-brittle fracture mode due to the fiber pull-out and dutile phases in the matrix.