No abstract

NaNbO(3) thin films prepared by the sol-gel method had homogeneous microstructure with an average grain size of 15-25 nm and exhibited photoinduced hydrophilic conversion under UV irradiation. However, the films had little photocatalytic oxidation activity under UV irradiation. This is the first observation that NaNbO(3) undergoes photoinduced hydrophilicity under UV irradiation.

No abstract

Microstructural control of CaO–Al 2 O 3 –SiO 2 (CAS) glass ceramics (GCs) was achieved by oxidation and mixing with nucleation agents. CAS GCs were precipitated with hexagonal platy particles of metastable CaAl 2 Si 2 O 8 layered crystals (CAS GC-H), which are typically prepared under a reductive atmosphere that forms metallic Mo or W particles as nucleation agents. The average particle size of crystals decreased significantly from 50 to 11 μm when the CAS GC-H containing metallic W particles was prepared under an oxidative atmosphere. Compared to this CAS-GC-H, the crystal particle size increased from 8–20 to 10–30 μm when the CAS GC-H was prepared by mixing glass cullet containing metallic Mo and that containing metallic W particles. These results indicate that one microstructure of CAS GC-H is controlled on the micrometer scale from a parent glass with one composition by varying the experimental conditions related to the glass melting state.

The ratio of the intensity of Tb 3+ fluorescence at 543 nm because of an electric dipole transition ( 5 D 4 – 7 F 5 ) relative to that at 437 nm due to a magnetic dipole transition ( 5 D 3 – 7 F 4 ) was determined to be proportional to the amount of metastable CaAl 2 Si 2 O 8 crystals precipitated in CaO–Al 2 O 3 –SiO 2 glass. The present results indicate that Tb 3+ luminescence can be used as a probe to evaluate the crystallization of glass.

Effects of kaolinite layer expansion and impurities on the rapid formation of metastable CaAl2Si2O8 with the supression of byproduct formation were demonstrated based on the solid-state reaction of calcium carbonate with methoxy-modified kaolinite.

Porous ceramics with unidirectionally oriented pores have been prepared by various methods such as anodic oxidation, templating using wood, unidirectional solidification, extrusion, etc. The templating method directly replicates the porous microstructure of wood to prepare porous ceramics, whereas the extrusion method mimics the microstructures of tracheids and xylems in trees. These two methods are therefore the main focus of this review as they provide good examples of the preparation of functional porous ceramics with properties replicating nature. The well-oriented cylindrical through-hole pores prepared by the extrusion method using fibers as the pore formers provide excellent permeability together with high mechanical strength. Examples of applications of these porous ceramics are given, including their excellent capillary lift of over 1 m height which could be used to counteract urban heat island phenomena, and other interesting properties arising from anisotropic unidirectional porous structures.

The effect of the starting materials of the nucleation agents for glass-ceramics (GCs) was explored. The number of hexagonal platy particles of metastable-CaAl 2 Si 2 O 8 in CaO-Al 2 O 3 -SiO 2 (CAS) GCs was increased by changing the sizes of molybdenum oxide (MoO 3 ) and carbon particles used as starting materials of the nucleation agents. X-ray diffraction patterns indicated that all of GC specimens display reflections attributed to metastable-CaAl 2 Si 2 O 8 solely. In addition, scanning electron microscopy (SEM) revealed that, compared with the CAS GC with precipitated hexagonal platy particles of metastable-CaAl 2 Si 2 O 8 (CAS GC-H) prepared using MoO 3 particles with a Brunauer-Emmett-Teller (BET) surface area of 3.5 m 2 /g and 10-50 µm carbon particles, CAS GC-Hs prepared using MoO 3 particles with a BET surface area of 1.2 m 2 /g or carbon fibers 10-50 µm in length and ∼5 µm in diameter resulted in approximately a twofold increase in the number of platy particles of metastable-CaAl 2 Si 2 O 8 and a decrease in the average particle size from 13 to 11 µm. The microstructures of the CAS GC-Hs are closer looks. In addition, no major differences in volume fractions estimated using the binarized SEM images are observed between those GC specimens. These results indicated that the starting materials of nucleation agents affect the crystallization of CAS GCs.