Generally, mesocrystals are known to be biological and bio-inspired mesoscale structures consisting of oriented nanometric crystalline units. In this article, mesocrystals are broadly categorized in a new family of crystalline materials as intermediate states between single crystals and polycrystals regardless of their unit size and degree of crystalline order. Here, the formation routes and the specific properties of a variety of mesocrystals and their related structures are described. Moreover, the potential of the novel crystalline materials having a high crystallinity and a high specific surface area is presented on the basis of their functions.

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Soft chemical synthesis of silicon nanosheets (SiNSs) and functionalized modified SiNSs are reviewed. Free standing SiNSs with sub-nanometer thicknesses have been prepared by exfoliating layered silicon compounds, and they are found to be composed of crystalline single-atom-thick silicon layers. SiNSs are new silicon nanomaterials, as are silicon nanoparticles and nanowires. Organic modified SiNS can be prepared by modifying a layered polysilane, which has an analogous structure to that of graphite, and this allows the properties of the SiNS to be controlled in order to make it suitable for particular applications. The potential applications of these SiNSs and organic modified SiNSs are also reviewed.

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Because of their excellent biocompatibility and osteoconductivity, ceramic biomaterials are clinically utilised as bone grafts for the reconstruction of injured bone tissues. Modification of the ceramic surface, leading to enhanced interaction with bone tissues, can improve the osteoconductive properties of bone grafts. Here, we explored the biophysical properties of bone tissue in order to develop a rationale for improved ceramic bone grafts. Material analyses revealed that the apatite minerals in bone tissues can store electrical energy generated by collagen fibrils in a piezoelectricity. Furthermore, we observed that bone, when polarized electrically by external voltage, depolarized by two mechanisms. Specifically, carbonate incorporation and electrical charges in bone minerals are important factors in bone piezoelectricity. These factors modulated osteogenic cell behaviours such as the osteoclastogenesis of peripheral mononuclear blood cells and the differentiation of mesenchymal stem cells into osteoblasts. Surface characteristics revealed that the electrical polarization increased the surface free energy and improved the surface wettability of the ceramic biomaterials. In addition, we applied the functionalized ceramic biomaterials to wound dressings and dental crowns. Composite materials, including polarized hydroxyapatite for wound dressing, enhanced epidermal recovery from full-thickness skin wounds. Surface modification by a combination of electrical polarization and chemical treatment improved bioactivity and durability of ceramics containing yttria-stabilized zirconia.

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The prepared [(Mg_0.7Zn_0.3)]_0.95Co_0.05]_1+δ(Ti_1–xSn_x)O_3+δ (δ = 0.02) (x = 0, 0.03, 0.05, 0.07, 0.09, 0.1 and 0.2) ceramics are sintered at 1175–1300°C, the needed sintering temperatures of [(Mg_0.7Zn_0.3)]_0.95Co_0.05]_1+δ(Ti_1–xSn_x)O_3+δ (δ = 0.02) ceramics slightly increased with the increase of Sn⁴⁺ content. The sintering characteristics of [(Mg_0.7Zn_0.3)]_0.95Co_0.05]_1+δ(Ti_1–xSn_x)O_3+δ (δ = 0.02) ceramics are developed by the X-ray diffraction patterns and SEM observations to find the influence of sintering temperatures and Sn⁴⁺ content on the crystal structure and the grain growth. The influence Sn⁴⁺ content and sintering temperatures on the quality values (Q × f) and the temperature coefficient of resonant frequency (τ_f values) of [(Mg_0.7Zn_0.3)]_0.95Co_0.05]_1+δ(Ti_1–xSn_x)O_3+δ (δ = 0.02) ceramics at microwave frequency are well developed in this study. As an optimal compose, [(Mg_0.7Zn_0.3)]_0.95Co_0.05]_1+δ(Ti_1–xSn_x)O_3+δ (δ = 0.02) successfully demonstrated a dielectric constant of 16.1, a Qxf of 300,000 GHz and a temperature coefficient of resonent frequency value of −53.8 ppm/°C after firing at a relatively lower sintering temperature of 1250°C.

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Ni-Carbon nanotube (CNT)-Ni_0.5Zn_0.5Fe₂O₄ multiphase composites were sintered by spark plasma sintering (SPS) technique. Ni nanoparticles were in-situ formed due to the localized carbothermal reduction by CNTs and well distributed between grain boundaries in the composites. The electrical conductivity of the resultant multiphase composites was strongly dependent on the weight percentage of CNTs. In the SPS process, CNTs acted as “heating source” and improved the consolidation of the composites. The results indicate that the introduction of the CNTs can promote the sintering kinetics of the ferrite ceramics. However, the grain growth kinetics has been inhibited by SPS and the grain size becomes finer.

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The synthesis mechanism of Al₃BC₃ through carbo-thermal reduction process was investigated and the processing conditions were optimized using Al(OH)₃–B₂O₃–C as starting materials. The mass change and phase formation of the compacts were analyzed with varying temperature. Excess Al(OH)₃ and B₂O₃ were required compared to the stoichiometric composition due to the loss of the source materials by vaporization at 1,500–1,600°C. At 1,600°C, Al₂O gas began to actively react with carbon to form Al₄C₃ on the carbon particles. Al, Al₂O and B₂O₃ gases diffused through Al₄C₃ layer and reacted with carbon at and above 1,650°C to form Al₃BC₃. The formation of hexagonal terrace at the surface of synthesized powder indicated that the gases also reacted at the particle surface with carbon which diffused through the carbide layers. The reactions were completed after calcination at 1,725°C for 4 h or at 1,800°C for 1 h. Gas-solid reactions were the major synthesis mechanism. The optimum composition for the synthesis of the ternary compound was Al(OH)₃:B₂O₃:carbon = 0.7:1.4:0.25 by weight.

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Some glasses in the RE₂O₃–MoO₃–B₂O₃ system (RE: Gd, Sm, Dy) were prepared by using a conventional melt quenching method, and the self-powdering phenomenon of β′-Gd₂(MoO₄)₃ crystals, i.e., the breaking into small pieces during the crystal growth, was examined using polarized optical microscope observations in a heating stage. In Gd₂O₃–MoO₃–B₂O₃ glasses with Gd₂O₃/MoO₃ = 1/3 and with different B₂O₃ contents (15–30 mol %) such as 20Gd₂O₃–60MoO₃–20B₂O₃, β′-Gd₂(MoO₄)₃ crystals were formed and the self-powdering phenomenon was observed irrespective of B₂O₃ content. The crack formation radiating out from the center part was clearly observed in the inside of crystals (diameter >40 µm) formed at 570°C in the glasses with Gd₂O₃ or Dy₂O₃. But, any clear crack formation was not observed in the glass with Sm₂O₃. It was found that the base glasses have larger densities at room temperature compared with β′-RE₂(MoO₄)₃ crystals formed, which is a unique feature in the RE₂O₃–MoO₃–B₂O₃ system compared with the crystallization of other glass systems. Such differences in the density might induce the accumulation of extremely large stresses in the inside of crystals, eventually causing the breaking of crystals.

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Highly transparent zinc aluminate ceramics were fabricated by the solid-state reaction using a spark plasma sintering machine. The sintered body exhibited a microstructure consisting of submicron-sized grains and extremely low porosities. Annealing of the sintered body in air improved the transmission close to the theoretical limit in a wavelength range of 1–5 µm. The band gap energy estimated from the absorption coefficient was 4.3 eV. The Young’s modulus and the bulk modulus measured for the fully dense zinc aluminates were 282 and 211 GPa, respectively.

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Low-cost clay-based membranes with an excellent flexural strength were successfully prepared by a simple pressing route using low cost starting materials, such as kaolin, bentonite, talc, sodium borate, and carbon black, and subsequent sintering at 1000°C. Carbon black was added as a template. The effect of carbon black content on porosity, flexural strength, pore size distribution, pure water permeability, oil rejection rate, and flux of low-cost clay-based membranes was investigated. It was found that the porosity and pore size of membranes increased with increasing carbon black content, whereas the flexural strength decreased with an increase in carbon black content. The pure water permeability increased with an increase in porosity. The oil rejection rate decreased with increasing applied pressure and carbon black content. Typical porosity, flexural strength, oil rejection rate, and flux of clay-based membranes sintered at 1000°C were 34%, 58 MPa, 96.7%, and 6.3 × 10⁻⁵ m³/m² s at an applied pressure of 101 kPa, respectively.

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The monodispersity of pseudocubic hematite particles, produced from a forced hydrolysis reaction of acidic FeCl₃ solution, were controlled by using five kinds of polyethylene oxides (PEO; Alkox^®; Mesei Chemical Works. Ltd.) (0–2 wt.%). Alkox^® possesses nominal formula of –(CH₂–CH₂–O)_n–. The fairly uniform pseudocubic particles was precipitated for PEO with low M_w value and narrow molecular weight distribution. However, POEs with large molecular weight and wide molecular weight distribution produced polydispersed pseudocubic hematite particles. The PEO with the largest molecular weight attained nearly spherical with large particle size distribution. From the calculation of crystallite size, all the pseudocubic hematite particles were regarded as a polycrystal as well as the large spherical hematite particles produced without Alkox^® (control system). This polycrystallinity of the particles provided an evidence that the particles are grown by aggregation of polynuclear (PN) primary particles. The specific surface areas of the particles (SSA) were ranged in 4–10 m²/g and no large difference can be recognized among five kinds of PEOs. Since the measured SSA values were corresponded to the SSA one calculated by assuming monodispersed cubic particle with 300 nm in edge length, the pseudocubic hematite particles are non-porous. The time resolved XRD, TEM, ICP-AES and TOC measurements employed on the systems produced for pseudocubic particles elucidated that the pseudocubic crystal habit was formed by the specific adsorption of PEO molecules together with chloride ions and/or chloro ferric complexes to the {012} faces, restraining the growth process through stacking of ultrafine PN particles in the direction of normal to the {012} faces but strictly restricting the growth and mutual fusion of PN ones. The uniform pesudocubic particles found to be effective photocatalytic material than spherical and/or polydispersed pseudocubic hematite ones due to their large size with uniform flat crystal faces.

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Patterns of the thermoelectric iron silicide were fabricated on alumina substrates with a continuous-wave ytterbium fiber laser. The laser irradiation process was further examined to construct an iron silicide device without damaging the substrates upon thermal shock. The multi-step irradiation process of powder mounting and irradiation demonstrated its performance as a thermoelectric device. Furthermore, the mechanism associated with the formation of an iron silicide layer was discussed.

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Compositions of (CaSrBa) orthosilicate phosphors were prepared by Liquid Phase Precursor method. The structural phase determinations were done systematically by powder X ray diffraction and Transmission electron microscopy. The PL emission was observed under 450 and 375 nm excitation and green–red and pure green emission was observed for the 4f⁶5d → 4f⁷ transition of Eu²⁺ ion. The luminescence nature of the samples is determined to vary with crystal field effect on the Eu²⁺ ion and has been studied with the change in the binary Ca–Sr, Ba–Sr and ternary Ca–Sr–Ba compositions.

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An equation for the hydration reaction developed by Tomozawa, which was originally applied to a single particle, was applied to the hydration process of Portland cement with a known particle size distribution. We also studied the theoretical change of porosity after hydration as affected by the water-to-cement ratio by using an equation of hydration that considers the particle size distribution. Consequently, we derived a correlation between the porosity and the reaction rate, which was in agreement with the experimental values.

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Sinterable Ti₃SiC₂ powder was synthesized from a powder mixture with a molar ratio of 1.0Ti:0.3Al:1.2Si:2.0TiC by heating at 1200°C in Ar flow. Almost single-phase peaks of Ti₃SiC₂ were observed in X-ray diffraction patterns. The powder was dispersed in ethanol using polyethylenimine (PEI) as the polymer dispersant. Textured dense Ti₃SiC₂ ceramics were successfully fabricated by slip casting in a strong magnetic field followed by pressureless sintering at 1400°C for 2 h. The relative density of these Ti₃SiC₂ ceramics was 99.4%, and the bending strength, fracture toughness and electrical resistivity were 623 ± 9 MPa, 5.9 ± 0.1 MPa·m^1/2 and 0.31 µΩ·m, respectively. Compared with those of nontextured pressureless sintered samples of almost full density, the bending strength and fracture toughness of the textured Ti₃SiC₂ ceramics were increased by factors of 1.6 and 1.4, respectively.

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In order to improve interfacial bonding strength between carbon nanofibers (CNFs) and SiC matrix in CNFs/SiC composites and to disperse CNFs uniformly in the matrix, SiC coating on surface of CNFs was performed in argon atmosphere in the temperature range of 1400 to 1800°C using SiO₂, SiO, and mixture of Si and SiO₂ powders (Si/SiO₂ powder) as silicon sources, and the modification and dispersibility of the treated CNFs were investigated. β-SiC particles were deposited on the surface of the CNFs in all the specimens at 1600–1800°C. So more SiC was formed by heating CNFs with SiO powder at 1600°C. However, the formed SiC was oxidized at higher temperature, practically, at 1800°C. This oxidation was advanced more by using SiO₂ and Si/SiO₂ powders as silicon sources and very fine carbon fibers were observed on the surface of CNFs. The dispersibilities of CNFs heated with Si/SiO₂ and SiO powders were superior to those of as-received CNFs, CNFs treated with NaClO₃ solution and CNFs heated with SiO₂ powder, which resulted from the advanced oxidation of CNFs and the silanol group (–SiOH) on surface of formed SiC.

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The oxidation behaviour of MgAlON–BN composite was investigated under the air atmosphere using thermogravimetry (TG), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques in the present articles. Non-isothermal experimental results indicated that the rate of oxidation can be neglected at low temperature and, with further increasing temperatures, an increase of the oxidation was observed. While BN addition promoted the oxidation above 1100 K, and the weight gain was observed to decrease due to the fast evaporation of boron oxide as the temperature was beyond 1580 K. Isothermal studies also clearly indicated the decrease of weight gain due to evaporation after a certain oxidation time. The oxidation mechanism was investigated, and the results showed the oxidation products were γ-Al₂O₃ at low temperature and transformed to α-Al₂O₃ as the temperature was above 1100°C. BN addition promoted the transformation from γ-Al₂O₃ to α-Al₂O₃. From the isothermal oxidations, the kinetics of oxidation and evaporation were evaluated, and the overall kinetics of oxidation and evaporation were studied, and the activation energy for evaporation of B₂O₃ and for the oxidation of MgAlON–15 vol %BN at the later stage are 115.4 and 196.1 kJ/mol, respectively. The present paper provides a way to deal with oxidation of composites containing evaporating component.

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The solubility of calcium phosphate aqueous solution decreases with increasing temperature. In this investigation, hydroxyapatite (HAp) thin films were deposited on the various substrates applying this calcium phosphate solubility depending on the solution temperature, the solution temperature was kept at 10°C and the substrate temperature was kept about 80°C. HAp thin film with a single phase was deposited on Si wafer and metal Ti substrates. HAp and β-tricalcium phosphate mixture phase was observed for the film on YSZ substrates. All the resulting films were very dense, and the deposition rates of the films on all the substrates were 10–15 nm/min.

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