Mixtures of 95vol% ultrafine γ-Al₂O₃ powder and 5vol% ultrafine SiC powder, with average particle size of 40nm, were mixed wet-ball milling and prepared by drying their slurry with a supercritical drying method and a microwave drying method. Al₂O₃ specimens dispersed with ultrafine-SiC particles as the secondary phase were hot-pressed, their powders being prepared by both the above drying methods. Difference between the superitical drying and the microwave drying method on the microstructure of Al₂O₃/5vol% SiC composites was investigated. Dense Al₂O₃/SiC composites were obtained at lower hot-pressing temperatures when the mixture was prepared by supercritical drying method. Influence of the drying method on the γ- to α-Al₂O₃ transition behavior was also examined. Al₂O₃/SiC powder dried by the supercritical drying method showed narrow particle size distribution and the formation of soft agglomerates. Al₂O₃/SiC composite sintered by hot-pressing the powder dried with the supercritical drying method indicated relatively higher strength, whereas the strength of Al₂O₃/SiC composite through microwave drying method was low and had the large scatter.

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Titania aerogels as a photocatalyst have been prepared by supercritical carbon dioxide drying followed by the sol-gel synthesis using titanium tetraisopropoxide as Ti source. The compositions of titanium tetraisopropoxide (TTIP), isopropanol (IPA), water, and hydrochloric acid as catalyst were optimized to find the best composition for the synthesis of crack-free alcogel by sol-gel synthesis. Supercritical carbon dioxide drying was performed at 40°C, 10MPa and 1 L/min of CO2 flow rate. Constructed supercritical drying process has been improved drying efficiency, and it conserves carbon dioxide for drying. The exponential decrease of the alcogel weight during drying process permits us to decide that the minimum CO2 weight is 70 times higher than the initial weight of the alcogel. Adjusting water content on the aerogel provide a crack-free aerogel when water content is greater than 3.6 as mole ratio. The mole fraction of water dominates the degree of polymerization of aerogel. Therefore, well-structured alcogel prepared by optimum water concentration. Titania aerogel was shown high-specific surface area but, photocatalytic activity needs to be improved.

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シリカウェットゲル表面にチタニアを被覆したもの、あるいはチタニア_-_シリカ混合ウェットゲルをすると、条件によりチタニアがアモルファスあるいはアナターゼとなったエアロゲルが得られ、その相はエアロゲルとして取り出し後空気中１０００℃程度の熱処理でも変化しない。この挙動を詳細に検討するため、シリカ_-_チタニア比の挙動への影響、ジルコニア被覆シリカとの挙動の比較、ＳＥＭ等による観察などを行い、またエアロゲル試料に時と同様の温度、圧力条件を再び加えた場合の相変化などを調べた。

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シリカ-チタニアゾル粒子をNa-モンモリロナイト層間に挿入し,粘土層間架橋多孔体を合成した。この架橋多孔体を加熱乾燥及びの二通りの方法で乾燥し,断熱性能と構造の関係について検討した.加熱乾燥した場合,静止空気以下の熱伝導率をもつ多孔体にはならなかったが,した場合,静止空気以下の熱伝導率を示す多孔体が得られた.加熱乾燥試料と試料とも空気の平均自由行程以下の細孔を持つため,空気部の熱伝導率は静止空気の熱伝導率よりも小さい.加熱乾燥試料と試の熱伝導率の差は,固体部の熱伝導率の差である.した場合,ケイ酸塩層同士がカードハウス構造を形成し,固体部の接触面積を減らし,固体部の熱伝導率が小さくなったと考えられる.また,試料において,今回検討した範囲では,ゾルの添加量が多いほど熱伝導率が低かった.これはカードハウス構造の形成が助長されることにより,固体部の接触面積が減少したためと考える.

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The survey deals with the preparation of ceramic powders by crystallizing in nonaqueous solvents and supercritical drying. The sintering behaviors and mechanical properties of sintered bodies are very much sensitive to the crystallizing conditions, since hard agglomerates formed when the precipitated gels were crystallized by normal calcination in air, whereas soft agglomerates formed when they were crystallized in water or organic solvents. CeO₂-ZrO₂ powders crystallized in methanol and water at 250°C were sintered to full theoretical density at 1100° and 1400°C, respectively, whereas that crystallized by calcination in air at 450°C was sintered to only 95.2% of theoretical density, even at 1500°C. Sintered bodies fabricated using the powders crystallized and dried using supercritical methanol possessed excellent mechanical properties.

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Organosiloxane (R_nSiO_(4-n)/2) gels can be prepared from organoalkoxysilanes using the sol-gel process. In general, however, formation of uniform networks from these precursors is strongly inhibited due to cyclization reactions. In addition, phase separation of hydrophobic condensates from polar solvent leads to inhomogeneous gels in these systems. A careful control of the hydrolysis and polycondensation reactions is therefore required to obtain a monolithic gel with desired properties. We have been trying to control the sol-gel reactions as well as phase separation in these systems to obtain unique porous materials particularly from methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS). Flexible aerogels and xerogels based on the methylsiloxane networks are discussed.

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Composites of silica aerogel and porous alumina were prepared by the supercritical drying method on autoclave of mixed solution of TMOS-MeOH-H₂O. Attempts to pack silica aerogels homogeneously in the pores of alumina and to increase the mechanical strength were successful. A linear relationship was found between the permeation rate of gas in composites and the inverse root of molecular weights from 298 to 523K. That is, the gas flow mechanism showed Knudsen flow rule. The mean pore diameters of composites were calculated to be 0.90-1.36nm by analysis of a linear relationship between permeation rate and mean pressure.

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SiCの耐アクティブ酸化性を向上させるために，ゾル-ゲル法を用いて厚いHfO2多孔質膜を多結晶SiC基板に被覆した。ポリマーを添加したHfO2前駆体溶液をSiC焼結体基板上にディップコートし，10MPa，300℃の超臨界CO2で乾燥し，空気中で300℃，400℃，550℃の 3 段階焼成を行った。前駆体溶液へのポリマー添加によって，単斜晶HfO2が生成する温度は低下し，焼成後の膜に発生する亀裂は少なくなった。を用いて作製したHfO2膜は多孔質構造を持っており，その膜厚は700nmとを用いない場合の約3.5倍であった。また，この厚い多孔質HfO2の被覆によって，Ar気流中におけるSiC多孔質材料のアクティブ酸化が抑制された。

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粘土層間架橋多孔体を利用してチタニアゾル粒子を粘土の二次元ケイ酸塩層間に保持し,二酸化炭素によって高気孔率のミクロボア多孔体を合成した。この多孔体に含浸法および光還元法の二通りの方法で白金を担持し,紫外線を照射して,乾式法(固-気反応系)による一酸化炭素の光触媒酸化を行った。白金無担持多孔体の光触媒活性は低いが,白金を担持することにより,光酸化触媒能は著しく向上し,特に光還元法により白金を担持した試料を用いると,日常生活環境下で上限と思われる濃度50ppmの一酸化炭素を室温で,ほぼ完全に酸化除去できた。電子顕微鏡観察および一酸化炭素吸着測定結果から推察して,光還元法白金担持試料の高い触媒活性は,粘土粒子間に高分散状態で存在するチタニア粒子上に,平均粒径6nmの白金超微粒子が効率的に担持されているためと考えられる。

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シリカウェットゲルをチタンアルコキシドの有機溶媒溶液に浸してからを行うことにより、チタニア被覆されたシリカエアロゲルを作製した。得られたエアロゲルの元素分析、粉末X線回折、透過型電子顕微鏡観察、比表面積・孔径分布測定などを行い、特性を評価した。チタニアの被覆量は通常20wt%程度で、有機溶媒の種類など処理法の違いにより制御が可能であった。透過型電子顕微鏡観察では、二酸化炭素では粒子の析出は観察されず、チタニアがシリカ骨格表面に被覆されていることが示唆された。比表面積は骨格のシリカエアロゲルのものと同等の600-700m2/gであり、チタニア単体エアロゲルのものより大きかった。クラスターの吸着特性、媒体の影響についても論じた。

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Surface-mount techniques primarily depend on soldering. However, soldering techniques have encountered some challenges in recent years. The reflow process in electronic assembly needs high-temperature processes, which result in undesired thermal damages and residual stress at a bonding interface. Therefore, there is an urgent requirement to attach electronic parts to circuit boards with good mechanical and electrical properties at room temperature. We recently developed a metallic nanowire surface fastener (NSF) to resolve the abovementioned problems. This fastener can connect electronic components on a substrate at room temperature using the van der Waals force between each nanowire. In this paper, we introduce a preparing method of a high-density nanowire array constituting the NSF. The NSF fabricated through the simple template method showed the room temperature bonding ability. The NSF’s adhesion strength and electrical properties were investigated by adjusting the nanowire parameters, such as diameter, length, density (number per area), preload, and shape. We also introduce some NSF applications, such as 64-pin NSF that behaves like a ball grid array for application to actual electronic devices and the fabrication of an NSF on a flexible substrate.

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きわめて気孔率が高く低密度の材料「エアロゲル」は湿潤ゲルのにより作製される。光学的に均質で透明であり,熱伝導度がきわめて小さいなどの特徴をもつため,透明断熱材などへの応用が期待され,特にシリカエアロゲルの研究が進められているが,実用化のためには強度や耐久性,製造コストの問題点が残されている。エアロゲルは構成粒子や孔径の小ささや比表面積の大きさという特徴ももち,これを活かして機能性材料への応用も期待される。この方面での研究はまだ緒についたばかりで基礎研究段階であるが,シリカ以外のエアロゲルの作製,各種物性の測定が行われている。これらのことについて解説を行った。

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