An overview is given exploring possible extension of activities for the scientists and engineers in the community of powder technology to the expanding and promising world of nano-biotechnology. In spite of large discrepancy of the mentality of two entirely different fields, the author maintains good chance of cooperation between these two fields, by keeping the essence of the materials science of particulates and thin films in mind. Light was shed on the two corners of nano-biotechnology, i. e. use of magnetic nanoparticles for diagnostics and therapeutics by appropriate surface modification, and preparation and structural control of protein nanofilms, including author's own experimental works.

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Composite gel powders with a basic composition of 0.65 (Ba_0.7Sr_0.3) TiO₃ - 0.27 SiO₂ - 0.08 Al₂O₃ were prepared by a sol-gel method in different solvent systems. In the alcohol solvent system, the difference in gelation time caused little change in the crystallization behavior in which the perovskite phase was formed at 800°C from the gel, but a substantial change in the sintering behavior of the calcined composite powders. The TPD-MASS analysis showed that the densification of the green compacts could be closely related to CO₂ gas release from the calcined powders at 700∼800°C. In the case of the acetic acid solvent system, on the other hand, the composite powders prepared were characterized by a different crystallization behavior in which the fresnoite phase was metastably produced at 700°C and by the relatively large specific surface area of the calcined powders. They also revealed that an increase in the Al₂O₃ ratio in the glass composition (0.27 SiO₂ - 0.08 Al₂O₃) resulted in an increased ratio of the perovskite BST phase after sintering, leading to an enhanced dielectric permittivity of the fabricated glass-ceramic.

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Mechanochemical process with the peculiarity of forming La(OH)₃ and Sr(OH)₂ as the reactive grinding aids in grinding liquids has been applied to the synthesis of solid solution La_1-xSr_xMnO_3+δ. The other starting material γ-MnO₂ is kneaded into the grinding aids to form mixed precursors of ground and hydrated MnO₂ and the hydroxides. The precursor consisting of La (OH)₃ and MnO₂ · yH₂O (LM) can be converted to orthorhombic-LaMn^IIIO₃ in argon or rhombohedral-LaMnO_3.15 in air above 700°C. Hexagonal-SrMn^IVO₃ is obtained by the heat-treatment of the precursor consisting of Sr(OH)₂ and MnO₂ · yH₂O (SM) at 600°C in air. The reactions of the mixed precursors are promoted from LM and SM, forming amorphous products at 400-600°C and crystallized to the intermediate pseudo-cubic phase at 600-800°C. The pseudo-cubic phase is transformed into orthorhombic (x≤0.1 in Ar), rhombohedral (x≤0.4 in air, x=0.2 in Ar), tetragonal (x=0.5 in air) and cubic phase (x=0.6 in air, 0.3≤x≤0.5 in Ar) at 1000°C depending on the composition. The substitution of La³⁺ in LaMn^IIIO₃ with Sr²⁺ leads the increased fraction of Mn⁴⁺ and related shrinkage of MnO₆-octahedra, which results in the reduction of lattice volume. The solubility limit of Sr²⁺ into LaMnO₃ is evaluated as x=0.57 from the liner relationship between the composition x and the lattice volume.

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Spherical porous Mn₂O₃ powders were prepared by spray pyrolysis. Lithium and aluminum nitrate solution were immersed to porous Mn₂O₃ powders to obtain LiAl_XMn_2-XO₄ powders. Homogeneous LiAl_XMn_2-XO₄ powders were formed by the calcination at 800°C. SEM observation showed that they had spherical morphology with dense microstructure. XRD revealed that the spinel phase was formed by the calcination at 700°C. LiAl_XMn_2-XO₄ cathode obtained by this method exhibited higher rechargeable capacity and cycle stability than that of LiMn₂O₄. The rechargeable capacity of LiAl_0.05Mn_1.95O₄ exhibited 120 mAh/g at 1C and 90 mAh/g at 10 C, respectively. 91% of initial discharge capacity was maintained after 500 cycles at a rate of 1 C. The doping of aluminum ion was effective for the cycle stability of LiMn₂O₄ cathode at 50°C.

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We attempted to fabricate and evaluate various nanofibrous multi layer structures and composite structures by using a multiple-nozzle electrospinning under various AC high voltage. To electrospun fibers, we prepared two kinds of precursor solutions. One is an aqueous solution containing poly (vinyl pyrrolidonel) (PVP) and metal nitrates. Another is slurry containing alcohol, poly (vinyl butyral) (PVB, Woko, Mw=340000 g/mol) and oxide powder. This method enables to make a composite fibrous structure that consists of an intertwined nano fibers with different composition. Adjusting an alcoholic vapor pressure of the synthesized atmosphere can variously change the structure. Therefore, it might be effective in the production of electrodes with a high specific surface area necessary for the improvement of reaction efficiency of the electrochemical reactor.

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For developing a large-scale production process of calcium carbonate hollow particles by CO₂ gas bubbling method, effect of operational conditions such as pH, temperature, reactant concentration and CO₂ gas bubbling rate on the morphology and crystal phase of the calcium carbonate particle prepared has been investigated with employing of a 4-liter reaction vessel constructed in this study. Precipitate particles formed by CO₂ bubbling into CaCl₂ aqueous solution were observed by scanning electron microscopy and characterized by powder X-ray diffraction analysis. No hollow particle could be formed under constant pH conditions controlled by a continuous addition of ammonia water during CO₂ gas bubbling. It has been found that hollow particles of calcium carbonate with a highly pure vaterite phase can be successfully synthesized under conditions with decreasing pH by CO₂ gas bubbling. In the rage of this paper, an appropriate initial pH is ranging from 9.8 to 9.5 with CO₂ gas bubbling of 1.25 l / min. flow rate for 3 to 6 min. Initial pH higher than 10 gave dense particles with higher content of calcite phase and the pH lower than 9 resulted in dense particles with vaterite phase. Therefore, it is very important for producing the hollow particle selectively to set the appropriate initial pH and to control pH-decreasing rate during the CO₂ gas bubbling.

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Heterogeneous nucleation and nucleation period of calcium carbonate on the mica and the highly oriented pyrolytic graphite (HOPG) substrate have been investigated. Calcium carbonate was prepared by the reaction of calcium nitrate solution with sodium carbonate solution. In the reaction crystallization of calcium carbonate, calcite and vaterite were nucleated on the both substrates. We counted the number of crystalline calcium carbonate on the substrates obtained from various initial supersaturations of calcium carbonate. The number of crystals on the mica surface was much higher than on the HOPG surface. Additionally, the number of crystals on the mica was greatly affected by changing of initial supersaturation. In order to explain the difference between the mica and the HOPG surface, a possible model for the nucleation period of calcium carbonate has been discussed. The surface crystallization on the mica and the HOPG could be described by considering the supersaturation in the bulk solution and in the vicinity of substrate, separately.

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