Radioactive or magnetic ceramic microspheres 20–30 µm in diameter are useful for intra-arterial radiotherapy or hyperthermia. Antibacterial ceramic microspheres can provide antibacterial activity for biomedical polymers such as dental resin. Bioactive ceramic microspheres with drug load/release properties are useful, moreover, as inorganic fillers for bone cement and can also be used in chemoembolization therapy. The author introduces some successes and challenges associated with the development of functional ceramic microspheres for biomedical applications.

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The volume thermal expansion coefficients (β) in 50–300°C of xZnO–yBi₂O₃–zB₂O₃ glasses (x = 10–65, y = 10–50, z = 25–60 mol %) were measured and the refractive index-based interionic interaction parameters A(n_o) were estimated from oxide ion electronic polarizabilities to acquire deeper insight into the relationship between the electronic polarizability and chemical bonding state of oxide glasses. The glasses have relatively large values of β = 210–289 × 10⁻⁷ K⁻¹, and the substitution of ZnO for B₂O₃ and the increase in Bi₂O₃ content result in an increase in β. The values of A(n_o) decrease with the substitution of ZnO for B₂O₃ and the substitution of Bi₂O₃ for ZnO. An almost linear correlation was observed between β and A(n_o), i.e., the volume thermal expansion coefficient decreases with increases in the interionic interaction parameter. A good correlation was also observed between A(n_o) and the refractive index-based optical basicity Λ(n_o). The interionic interaction parameter is helpful for understanding the chemical bonding state of oxide glasses.

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ZrB₂–SiC composite ceramics were fabricated by spark plasma sintering SiC powders with various mixtures of ZrB₂, Zr, Al and graphite components, toughening the ceramics through the in-situ synthesis of Zr–Al–C microstructures. Different microstructures of Zr–Al–C toughened ZrB₂–SiC (ZSA) composite ceramics were formed during the sintering process by varying the components ball milled with the ZrB₂ powders prior to sintering. When the milled ZrB₂-based powders contained Al, the major Zr–Al–C phase changed into Zr₃Al₄C₆ from the designed Zr₂Al₄C₅, and the layered Zr–Al–C grains formed with a large aspect ratio in the ZSA ceramics due to the formation of an Al-based coating layer covering the ZrB₂ powders during milling process. The Zr and Al co-milled ZrB₂-based powders further improved the toughness of composite ceramics through a more uniform distribution and the larger aspect ratio of Zr–Al–C grains. As a result, the ZSA ceramic made using the milled powders of ZrB₂, Zr and Al showed the highest fracture toughness of 5.96 MPa·m^1/2, about 10% higher than that of the ceramic made using milled ZrB₂ and Zr powders. The toughening mechanisms are shown to be crack deflection and bridging caused by Zr–Al–C grains. This work points to a possible pathway to control the microstructure of Zr–Al–C grains for toughening ZrB₂–SiC composite ceramics.

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Al₂O₃–SiC composites with different SiC contents of 0–10 wt % were fabricated and the effects on damage and wear resistance investigated. The composites were fabricated using spark plasma sintering at 1600°C in a partial vacuum (80 MPa). Hertzian indentation evaluations using a spherical indenter indicated that the hardness of the composite is improved by SiC addition. Wear resistance evaluated using the ball-on-disk method showed enhanced wear resistance for the composites, even when SiC addition was less than 2 wt %. Thus, Al₂O₃ ceramics exhibited significantly improved damage and wear resistance, even though SiC addition was as small as 2 wt %.

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The low-temperature melt-infiltration method using eutectic Si alloys is a novel process of fabricating SiC fiber-reinforced SiC-based matrix composites (SiC_f/SiCs) for high-temperature structural applications. SiC_f/SiCs were fabricated by the melt-infiltration method using a eutectic Si–8.5 at%Hf alloy to evaluate their dry oxidation behavior at 800–1200°C for times ranging from 10–100 h. The oxidation behavior of monolithic HfSi₂ (Monolith) fabricated by spark plasma sintering was also evaluated in dry air. The oxidation behavior of the composite matrix and Monolith obeyed the parabolic law in dry conditions. The steps to form the oxidation layer were expected to produce HfO₂ and Si, followed by SiO₂, and, finally, HfSiO₄. The oxidation rate of the matrix was similar to that of Monolith and 10²–10⁴ times larger than that of Si. The oxidation activation energy employed in oxidation of HfSi₂ was calculated as 258 kJ/mol in dry air.

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Two different morphologies of ZnO synthesized by hydrothermal method were coated on quartz crystal microbalance (QCM). Field emission scanning electron microscopy and X-ray diffraction were used to analyze the morphology and crystal structure of ZnO. The humidity sensing behavior was examined by measuring the resonance frequency shifts of QCM in the whole humidity range from 11 to 95%. The kinetics of adsorption–desorption and mechanism of humidity sensing were studied. The results show that the morphology of ZnO greatly affects the humidity sensitivity of QCM sensor. Furthermore, the adsorption–desorption model is also dependent on the morphology of ZnO.

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The strain changes during temperature rise in a poled lead titanate zirconate rectangular parallelepiped specimen switched by compressive stress at room temperature are measured using an invar-specimen. First-order differential equations were derived by analyzing the observed polarization and strain data and solved to give an experimental formula for remnant polarization and remnant strain changes during temperature rise. Then the dependence of pyroelectric and thermal expansion coefficients on remnant state variables and the relations between reference remnant state variables were obtained through experiments. Using the relations and the experimental formula, the strain behavior during mechanical depolarization at a high temperature was predicted from a polarization behavior at the same temperature. It was found that the predictions compared favorably with the measured behavior.

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Tri-doped (Y_0.915Ho_0.01Yb_0.075Li_x)₂Ti₂O₇ (x = 0–15.0 mol %) nanocrystals were fabricated via a facile glycine–combustion approach. The crystal structure, morphology and up-conversion spectra of the as-obtained products were investigated using X-ray powder diffractometer (XRD), transmission electron microscope (TEM), spectrophotometer pumped by 980 nm diode laser, and Fourier transform infrared spectrometer. XRD results demonstrated that, owing to the flux effect of Li⁺ ions, the crystallization temperature of matrix Y₂Ti₂O₇ decreased when compared to Li⁺-undoped samples. TEM results showed the average particle of (Y_0.79Ho_0.01Yb_0.075Li_0.125)₂Ti₂O₇ nanocrystals calcined at 800°C for 1.0 h was estimated to be ∼50 nm. It was also found that up-conversion emissions were strongly dependent on the calcining temperature and Li⁺ ion concentration. Compared with the Li⁺-free Y₂Ti₂O₇:Yb³⁺/Ho³⁺ samples, the green and red emission intensity of nanocrystals tri-doped with 12.5 mol % Li⁺ was enhanced by 10.2 and 4.8 times, respectively. The emission increase should be mainly ascribed to the distortion of local symmetry around Ho³⁺ ions by Li⁺-doping. In addition, the pump power dependence of integrated intensity suggested that both green and red emission was two-photon population process.

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The effects of annealing temperatures on perovskite-type photovoltaic devices were investigated. CH₃NH₃PbI₃ photovoltaic devices doped with Cl were fabricated by the spin-coating method, and the microstructures of the cells were investigated by X-ray diffraction, optical microscopy and scanning electron microscopy. The current density–voltage characteristics and incident photon-to-current conversion efficiencies were improved by application of an appropriate annealing process, leading to improvement of the photoconversion efficiencies to 13.28%. Microstructure analysis indicated that the perovskite layer had a homogeneous morphology after annealing at 140°C, and that the devices provided stability in air.

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Super-hydrophilic titanium dioxide (TiO₂) photocatalysts with some mild oxidizing ability are favorable for the self-cleaning applications on plastic films. In this study, we have focused on brookite TiO₂ for such purposes. Brookite TiO₂ powders were synthesized by the hydrothermal conversion method using Mg₂TiO₄ as a precursor. Mg₂TiO₄ (1 g) and 1 M HCl (30 mL) were put into a polytetrafluoroethylene (PTFE)-lined autoclave. The hydrothermal conversion was conducted at 110–150°C for 24 h. The photocatalytic oxidizing properties of brookite TiO₂/silicone films on glass substrates, prepared by the flow-coating method, were measured by methylene blue decomposition, and the photo-induced hydrophilicizing properties were evaluated using the contact angle of water under UV irradiation. The brookite TiO₂/silicone film prepared from the sample treated at 150°C exhibited well-balanced properties for self-cleaning applications.

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Ta(V) nitride (Ta₃N₅) powders for non-toxic red pigments were prepared by heat-treatment of mixed powders of Ta(V) oxide, aluminum nitride and alkali fluorides in a nitrogen atmosphere without flowing ammonia. This synthetic method is environmentally friendly as compared with such conventional methods as ammonolysis with large amounts of flowing ammonia. In this study, the effect of mineralizers on formation of tantalum(V) nitride (Ta₃N₅) with heat-treatment of Ta₂O₅–AlN mixtures was examined. The results revealed that the formation of Ta₃N₅ was promoted by co-doping with potassium fluoride (KF) and lithium fluoride as mineralizers. Doping with KF led to improvement of the chroma of the powders by controlling the grain growth of Ta₃N₅ and developing the facets of the grains.

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