山田 修

Porous TiC ceramic powder was used as a novel substrate for the surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) analysis of various environmental pollutants. The porous TiC ceramic powder has a nano-structural morphology with a high surface area, an electrical conductivity, and a photoabsorption at the Nd:YAG laser band of 355 nm. These properties of the porous TiC ceramics suggest having a good compatibility as a substrate for SALDI-MS. Furthermore, the porous TiC ceramic powder can be used as an adsorbent for environmental pollutants. The porous TiC ceramic powder was added to a perfluorooctane sulfonate (PFOS) aqueous solution. The liquid was shaken for 2 h, and PFOS was adsorbed onto the TiC ceramics. The liquid was filtered, and the residue was dried. The obtained powder was fixed on a carbon tape and measured by SALDI-MS in the negative ion mode. As a result, the peak assignable to PFOS (C8F17SO3 −) was detected, and no other significant peaks at m/z 100–500 were observed. As for the other analytes, the ion peaks corresponding to the anions or cations derived from these compounds in the negative or positive ion mode were observed using the same treatments.

Combustion-synthesized titanium carbide ceramics uniformly disperse silver, producing silver ions and hydroxyl radicals in water. This generates antimicrobial activity against various bacteria. One such bacterium is Streptococcus mutans, a gram-positive anaerobic bacterium known as a major pathogen of dental caries. In this study, we analyzed the inhibition of oral biofilms and S. mutans by ceramic water in in vitro and human studies. S. mutans strains showed significantly lower antimicrobial and sucrose-dependent adhesion activity in the presence of ceramic powder compared with untreated culture medium. Confocal microscopy revealed that S. mutans biofilm structures with ceramic powder were thin and coarse. Twenty-seven volunteers (13 males, 14 females; 18-37 years old, mean 25.2 years) were enrolled for subsequent studies. After each meal, one group was asked to rinse with ceramic water while the other rinsed with untreated water for 1 week. After 1 week, the rinsing contents were switched between the groups and the same protocol was followed for an additional week. After rinsing with ceramic water, the average plaque score was 43.0 +/- 3.7, which was significantly lower than the baseline value (74.1 +/- 5.7, p < 0.001). However, no significant difference was observed when rinsing with untreated water. In addition, the total number of S. mutans in saliva was significantly reduced after rinsing with ceramic water compared with untreated water (p < 0.05). These results suggest that ceramic water possesses antimicrobial activity against S. mutans and inhibits biofilm formation. Rinsing with ceramic water can also inhibit dental plaque formation and S. mutans colonization in humans. (C) 2016 S. Karger AG, Basel

The aim of this study is to investigate the utilization of the powder of porous titanium carbide (TiC) ceramics as a novel adsorbent or a material for solid-phase extraction (SPE). The adsorption and elution of inorganic and organic pollutants, Pb(II), 2,4,6-trichlorophenol (TCP), perfluorooctane sulfonate (PFOS), and perfluorooctanoic acid (PFOA), to the material were evaluated. The cartridge packed with TiC ceramics powder was used for the extraction test of pollutants. The solution containing pollutants at 1.0 mu g mL(-1) was passed through the TiC cartridge, and the substances were almost quantitatively removed. Furthermore, the pollutants retained in the cartridge were eluted with 3 N HCl for Pb(II) and with methanol for organic pollutants. The recoveries of pollutants were over 80%. In addition, we used the TiC cartridge for the solid-phase extraction of water samples (500 mL each of the distilled water and the river water) by adding pollutants at determined concentrations. Every pollutant was adsorbed almost quantitatively, and eluted by 3 N HCl or methanol. From these results, we concluded that the powder of porous TiC ceramics is a useful reusable adsorbent for the water cleanup and solid-phase extraction. (C) 2010 Elsevier B.V. All rights reserved.

In this paper, we propose a new method of fabricating 3-D models of the high-temperature structural materials such as ceramics by selective laser sintering (SLS). To save the laser energy, we adopted the combustion synthesis which is the exothermic reaction between the raw materials. By adding chemical reaction heat to laser heat, the particles of the products of the reaction were bonded together by relatively low laser energy. The combinations of the raw materials and the laser scanning conditions for solidifying the products and laminating the solidified layers were investigated experimentally. Since burning in the furnace is unnecessary in the proposed method, it is possible to fabricate the models in a short time.

In this paper, we propose a new method of fabricating 3-D models of the inorganic materials having high melting points such as ceramics and intermetallic compounds by laser scanning. To save the laser energy, we adopted the combustion synthesis which is the exothermic reaction between the raw materials. By adding chemical reaction heat to laser heat, the particles of the products of the reaction were bonded together by relatively low laser energy. The combinations of the raw materials and the laser scanning conditions for solidifying the products of the reaction and laminating the solidified layers were investigated experimentally. By mixing the powdered binder with the reactive raw materials, the simple layered models were fabricated Since burning in the furnace is unnecessary in the proposed method, it is possible to fabricate the models in a short time.

New thermite type SHS process (TMSHS) is developed by combining the modified thermite reaction and the combustion synthesis reaction.The process enables to simultaneously synthesize and cast such intermetallic compounds as NiAl and Mo3Al without any external heat supply.<br /> The processing temperature can be varied arbitrarily to the appropriate temperature by changing the mixing ratio of reactant.This process would be also applicable for casting of many other intermetallics, ceramics and their composites.

本論文では、セラミックスや金属間化合物の合成と同時に緻密化を達成し、最終製品形状まで加工するための必要条件を洗いだし、それらを組み合わせて得た概念に基づいて、燃焼合成実験を行った結果、その基本概念の正当性が実証された。 比強度の大きいことから高温構造材料として有望視されているTiAl金属間化合物を中心として、その機械的特性や耐酸化性を向上させる目的で、非酸化物セラミックスを分散した複合糸を対象物質として選択している。

燃焼合成法は、2000Kから4000Kもの強い発熱反応によって化合物が自発的に生成する化学プロセスであり、この方法を用いてセラミックスや金属間化合物など、400種類以上の化合物が合成される。 燃焼合成の研究は、熱化学、熱物理、燃焼学、物理化学、固体化学、結晶成長、材料科学などを網羅した幅広い学際領域が対象となり、燃焼から合成に至るプロセスの本質的な解明には、総合的な理解を必要とする。ここでは化学プロセスとしての燃焼合成を簡単に記述し、多岐にわたる材料開発への応用と、これからの展望について概観した。

燃焼合成法は、2000Kから4000Kもの強い発熱反応によって化合物が自発的に生成する化学プロセスであり、この方法を用いてセラミックスや金属間化合物など、400種類以上の化合物が合成される。 燃焼合成の研究は、熱化学、熱物理、燃焼学、物理化学、固体化学、結晶成長、材料科学などを網羅した幅広い学際領域が対象となり、燃焼から合成に至るプロセスの本質的な解明には、総合的な理解を必要とする。ここでは化学プロセスとしての燃焼合成を簡単に記述し、多岐にわたる材料開発への応用と、これからの展望について概観した。

Solid solutions in the NbN－NbC sys－tem have been prepared by the combus－tion of niobium and carbon mixturesina pressurized nitrogen atmosphere oflO MPa．Starting with compositions ofO≦C／N≦0．8，the NbNl＿χCχ product exhibited good crystallinity with a NaCI struCture． The products were loosely sinteredand their particle morphology was sim－ilar to that of the starting Nb．The propagation velocities of com－bustion front and the maximum reactiontemperatures werein the range of O．4toO．05cm／s and 3000to2000K，respec－tively， which decreased withincreasingCarbon content．It is suggested thatthe formation of NbNI-χCχ is assisted by the heat of nitradization of Nb．The NbNI＿χCχ showed a superconductingtransition temperature of18．8K at χ＝0．4，Which is O．9K higher than thehighest reportedvaluein this system．

Much progress has been madein thestudy of Bl－NbN superconducting mate－rialforits very high criticalfield（Hc）and criticalcurrent density（Jc）． Using the SHS method，NbN plateand wire can be easily produced usingequipment thatisinexpensivein com－parison with chemicalvapour depositionand sputtering methods． They also have good superconductiveproperties with the transition temper－ature of16．4K．

化合物合成という立場からテルミット反応を見直し、新しいテルミット型燃焼合成法を開発した。基本的には燃焼合成法とテルミット反応を組み合わせたものであるが、標準生成熱を増加させ、断熱燃焼温度を上げることができる結果、今まで燃焼合成が困難であった化合物も合成可能とをった。 また適切を反応系（例えば6NiO＋8Ni＋18Al⇒14NiAl＋2Al203）を選択した場合、化合物が溶融するため、合成と同時に鋳造する応用技術分野も検討した

The role of high－purity silicain the fracture of Si3N4at high temperatures has beeninvestigated Microstructural Observations revealed that the glassy phase waslocalized atintergranular pockets when SiO2additions were over lOwt％． High strength at1673K despite the presence of a fairlylarge amount of glassy phaseis attributed to a high CaVitationthresholdinsuchglassypockets COnSisting of hidl－purity SiO2．

The influence of SiO2 addition on the densification and microstructural development of high－purity Si3N4 during HIP was studied．Analysis using a simple model shows that the enhanced densification was mainly due to the viscous flow of SiO2．The microstructure changed remarkably at between 10 and 20wt％ SiO2 additions．Analysis of the phase transformation kinetics suggests that the diffusion of Si3N4 through SiO2 glass is the ratecontrolling step for the transformation．

The role of high－purity silicain the fracture of Si3N4at high temperatures has beeninvestigated Microstructural Observations revealed that the glassy phase waslocalized atintergranular pockets when SiO2additions were over lOwt％．<br /> High strength at1673K despite the presence of a fairlylarge amount of glassy phaseis attributed to a high CaVitationthresholdinsuchglassypockets COnSisting of hidl－purity SiO2．

燃焼合成を用いて、種々のセラミックスや金属間化合物か合成された。これら化合物の特性は、燃焼合成反応を制御することにより改善される。そこで、燃焼過程に関する制御分野と合成過程に関する制御分野に大別して、それぞれ検討を行った。 燃焼過程の制御については、燃焼温度の増減や分解温度との関係および燃焼速度に及ぼす出発原料粒径の効果や雰囲気庄の影響について考察した。また合成過程の制御においては、微細組織観察や熱力学的検討から固相拡散、溶解析出、分解凝縮に分類して考察した。このほかに、不純物の影響や、相状態と加工成形法についても言及した。

物質を構成する元素同士を混合し、化合時の反応熱を使った燃焼合成法について、その反応機構の基礎解析とともに興味のもたれる応用技術分野を紹介した解説である。 まず、基礎として堺焼合成される化合物群や燃焼温度の求め方、反応の制御方法等に加えて現在までに判明している反応機構について記述し、燃焼合成法の特徴と応用の分野では合成同時焼結プロセスに必要な一軸加圧や等方加圧、遠心力方式および衝撃圧方式等の開発について記述した。

燃焼合成反応は大きく分けて固相一固相反応と固相一気相反応に分類される。ここでは固相一気相反応の代表例として、窒化物セラミックスについてその製造法や反応機構について報告している。窒化物セラミックスか融点を持つ場合は、熱力学計算から求めた断熱燃焼温度と生成物の融点の関係から整理できたか、昇華分解する場合には、雰囲気圧によって変化する分解温度を考慮しなければならないことかわかった。

A homogeneous cavitation theory is developed in this study.In the theory, when athermal defects like non-bridging oxygen in silicate glass are present, they are considered as cavitation sites associated with lower activation energy for critical cavity nucleus formation than in pure case. The analysis gives a reasonable explanation to the significant detrimental effect of trace impurities such as Fe in Si3N4 with intergranular glassy SiO2.

The TiB2-TiN,TiAl-TiB2 and NiB-Al2O3 Materials were fabricated from each mixed reactant of Ti+B in nitrogen gas,Ti+Al+B and NiO+Ni+B+Al powders by the combustion synthesis,respectively.In case of the 6TiB2-8TiN,the combustion temperature exceeded the melting points of the TiB2 and TiN. The 6TiB2-8TiN was self-densified by absorbing nitrogen gas in isolated pores and forming TiNx under gas-pressurized condition.This material can be called as ceramic alloy.The composites materials of TiAl-TiB2 and NiB-Al203 Were also melted during the combustion reaction.

Fine Si3N4-SiC composite powders were synthesized in various SiC compositions to 46 vol% by nitriding combustion of silicon and carbon. The powders were composed of α-Si3N4, β-Si3N4 and β-SiC. The reaction analysis suggested that the SiC formation is assisted by the high reaction heat of Si nitridasintered. The sintered bodies consisted of uniformly dispersed grains of β-Si3N4, β-SiC and a few Si2N2O.

The TiB2-TiN,TiAl-TiB2 and NiB-Al2O3 Materials were fabricated from each mixed reactant of Ti+B in nitrogen gas,Ti+Al+B and NiO+Ni+B+Al powders by the combustion synthesis,respectively.In case of the 6TiB2-8TiN,the combustion temperature exceeded the melting points of the TiB2 and TiN. The 6TiB2-8TiN was self-densified by absorbing nitrogen gas in isolated pores and forming TiNx under gas-pressurized condition.This material can be called as ceramic alloy.The composites materials of TiAl-TiB2 and NiB-Al203 Were also melted during the combustion reaction.

High-purity Si3N4 containing 2．5to 20wt％ SiO2 additions were fabricated by hot isostatic pressing．Addition of SiO2 promoted densification and delayed the α－β transformation rate． The fracture toughness was insensitive to the mocrostructure and glass content，but the Vickers hardness depended strongly on both．The room temperature strength decreased with SiO2，probably due to increase in the initial flaw size．

The microstructures and mechanical properties of Si3N4-SiC composites containing 8 to 46 vol% SiC, which were prepared from combustion synthesis and HIP sintering without additives, were studied and compared with those of Si3N4 prepared from conventional methods. Transmission electron microscopic observation revealed the existence of some small SiC particles within the Si3N4 matrix grains. The fracture toughness of the Si3N4-SiC composite was independent of SiC content, probably because the SiC grains were smaller than the critical size for effective toughening and the formation of elongated Si3N4 grains was not promoted by the SiC dispersions. But SiC additions modified the high-temperature strength of the Si3N4-SiC composites and increased the microhardness at all temperatures. © 1991, Japan Society of Powder and Powder Metallurgy. All rights reserved.