Characterization of mixing performance in a microreactor and its application to the synthesis of porous coordination polymer particles

Here we quantitatively evaluated the mixing performance of a tailor-made microreactor with central-collision type through the iodide/iodate chemical test reaction, and applied the microreactor to the synthesis of zeolitic imidazolate framework-8 (ZIF-8), which is a subclass of porous coordination polymers (PCPs) or metal organic frameworks (MOFs). The chemical test reaction demonstrated excellent mixing performance of the microreactor with a characteristic mixing time shorter than 1 ms, which is approximately 100 times faster than those of a batch reactor and a millimeter-sized Y-shaped mixer. Taking advantage of the rapid and uniform mixing, the microreactor successfully produced ZIF-8 particles with high reproducibility by simply mixing aqueous solutions of zinc nitrate and 2-methylimidazole. The synthesis at room temperature resulted in ZIF-8 particles with chamfered cube shape, while a lower temperature of 5 °C produced raspberry-type spherical particles. We confirmed that prepared ZIF-8 particles have BET surface area of ～1500 m²/g and exhibit the gate adsorption behavior caused by the structural transition of the ZIF-8 framework.     

Fullerene Production in Tons and More: From Science to Industry

In the last decade, application of fullerenes has been proposed actively in a wide range of areas, and recent developments suggest that many of those applications are to be practical technologies. However, there has been no large-scale production enterprise for commercial usage of fullerenes. High production cost and limited availability of fullerenes have been the main obstacle in the development of the Fullerene Market. Improved flame-based technology leads to the most feasible process for mass production of fullerenes, since it is a continuous process and uses inexpensive hydrocarbons as its starting materials. In May 2003, we started fullerene production in tons and more to supply fullerenes with reasonable price as practical materials for industries.     

Structure and mechanical properties of nanocrystalline Ag/MgO composites

Nanocrystalline Ag/MgO composites were prepared by the ultrafine-powder-compaction method. The structure was investigated for the first time by high-resolution electron microscopy. Nanometre-sized Ag grains and MgO grains in the composites bonded directly without any intermediate phase layer. Certain preferred orientation relationships were observed between the Ag and MgO grains. The nanocrystalline Ag/MgO composites retained their grain size during annealing up to 873 K. Vickers microhardness measurements were performed on the as-compacted and annealed specimens. Generation and propagation of cracks were less active in the nanocrystalline Ag/MgO composites than in a single-phase nanocrystalline MgO. The Vickers microhardness of the nanocrystalline Ag/MgO composites remained up to 1073 K. Hot-pressing deformation tests showed that the nanocrystalline Ag/MgO composites deformed plastically at 1073 K.     

Out-of-Plane Negative Magnetoresistance of Bi2Sr1.6La0.4CuO6+δ Single Crystals in the Underdoped Region

In order to investigate a relationship between the carrier concentration and negative magnetoresistance in the underdoped region, we have performed out-of-plane electrical resistivity measurements for underdoped Bi ₂ Sr _1.6 La _0.4 CuO ₆₊ single crystals. Giant negative magnetoresistance has been observed in the most abundant carrier sample with = 0.12 in our experiment. The negative magnetoresistance reduces with decreasing carrier concentration.     

Intercalation of n-alkylamines into α-tin(IV) bis(hydrogenphosphate)

The intercalation reaction of n-alkylamines from methyl- to hexadecylamine into -tin(IV) bis(hydrogenphosphate) has been investigated. The reaction was conducted by mixing the phosphate and solutions of the amines dissolved in water or benzene. The amine/ phosphate molar ratios in the reaction mixtures were 0.43, 0.85, 1.71 and 3.41. The nitrogen/phosphorus atomic ratio in the intercalation compound was not changed by the amine/phosphate molar ratio. The interlayer distances of the intercalates obtained in the reaction mixtures with molar ratios of 3.41 and 1.71 increased with an increase in the number of carbon atoms in the alkyl chain of the amine. The slope of the straight line obtained in plot of interlayer distance versus number of carbon atoms in the alkyl chain of the amine indicates that the amine molecules form a double layer in the interlayer space of the phosphate and are inclined at an approximate angle of 67.7° to the phosphate layer. The interlayer distances of the intercalates of butyl- to nonylamines obtained at the molar ratio of 0.85 are smaller than those of the corresponding compounds from the molar ratios of 3.41 and 1.71, while those of decyl- to hexadecylamine intercalates lie on the previously discussed line. This behaviour is interpreted by assuming kink formation in the short alkyl chains between the phosphate layers.     

Fiber template approach toward preparing one-dimensional silica nanostructure with rough surface

Silica nanofibers were grown on the surface of chitosan nanofibers used as templates by coating the surface with silica derived from the hydrolysis and condensation of tetraethoxysilane using ammonium hydroxide as a catalyst. This was followed by the decomposition of the chitosan template. The relationship between different processing factors (type of templates as well as amounts of catalyst and template) and the formation of silica nanofibers was examined. Varying the processing factors was found to be effective in controlling the morphology of the silica nanofibers. The use of chitosan nanofibers effectively led to the formation of one-dimensional silica nanofibers as the positively charged chitosan nanofibers promoted the deposition of the negatively charged silica nanoparticles through electrostatic attractive forces. Therefore, the chitosan nanofibers acted as good deposition sites for interacting with silica nanoparticles. Although a large amount of catalyst promoted the sol-gel reaction, the silica nanoparticles grew excessively in the solvent. Therefore, the surface structure of the prepared silica nanofibers could be controlled by varying the amount of chitosan template as this also varied the formation mechanism of the silica nanofibers. The resultant samples had a rough silica wall composed of densely assembled silica nanoparticles, with a high specific surface area (338 m²/g).     

Preparation and mesostructure control of highly ordered zirconia particles having crystalline walls

Mesostructured zirconia particles having monoclinic-type crystalline walls were prepared using a low-temperature crystallization technique. Crystalline zirconia particles with highly-ordered mesostructures were obtained through the sol–gel process of zirconium sulfate tetrahydrate at 333 K in the presence of molecular self-assemblies of cetyltrimethylammonium bromide (CTAB) or mixtures of CTAB and anionic molecules such as sodium dodecyl sulfate and sodium p-toluenesulfonate. Variations in the molar ratios of CTAB and the chemical species of anionic molecules led to the variations in the periods of highly-ordered zirconia having crystalline walls. Calcination of the mesostructured zirconia particles prepared using templates consisting solely of CTAB yielded crystalline mesoporous zirconia particles.     

Future prospect of remote Cat-CVD on the basis of the production, transportation and detection of H atoms

The future prospect of remote Cat-CVD, in which the decomposition and the deposition chambers are separated, is discussed on the basis of the absolute density measurements of H atoms. It is now well recognized that uniform deposition is possible on a large area without plasma damages by Cat-CVD. However, we may not overlook the demerits in Cat-CVD. One of the demerits is the poisoning of the catalyzer surfaces by the material gases, both temporary and permanent. One technique to overcome this problem is remote Cat-CVD. The question is how to separate the decomposition and deposition areas. If the separation is not enough, there should be back diffusion of the material gases, which will poison the catalyzers. If the separation is too tight, radicals may not effuse out from the decomposition chamber. These problems are discussed and it is shown that SiO₂ coating to reduce the radical recombination rates on walls is promising. The possibility of the polytetrafluoroethene coating by Cat-CVD is also discussed.     

Nitridation enhancing effect of ZrO2 on silicon powder

The nitridation behavior of silicon powder with added Zr compounds was studied in order to assess the catalytic effect of zirconium on the formation of reaction bonded silicon nitride, using high purity silicon powder and monoclinic zirconia as starting materials. Thermogravimetric analysis revealed that the addition of ZrO₂ to Si powder reduced the temperature of the main nitridation reaction, and increased the amount of silicon converted to silicon nitride at a given temperature. On the other hand, the nitridation rate at higher temperatures (1380-1400 °C) indicated similar values for both pure Si and Si with ZrO₂ additions.