A family of calcite nanocrystal superstructures with unusual morphology were obtained from crystallization of calcite by the CO₂ gas diffusion technique in the presence of a bioinspired double hydrophilic block copolymer, polyethyleneglycol-block-poly (L-aspartic acid). From the typical calcite rhombohedra as a starting situation, the morphology can be systematically varied via various unusual porous mesocrystal morphologies to hemispheres composed of fine calcite triangles. The formation of mesocrystals is starting at a polymer concentration of only 10^-3 g/L and shows two remarkable results: (a) the reported bio-inspired block copolymer is the so far most active polymer for mesocrystal formation reported to our knowledge, and (b) the data prove that nucleation promoters exist, which can form nanocrystals for mesocrystal formation even without enhanced colloidal stabilization. This gives mesocrystal formation a much broader operation range than previously assumed.

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This review surveys recent advances in the synthesis of oxide materials, primarily as supported thin films but also in other forms such as free-standing films, mesoporous solids, and nanostructured fibers, from liquid (primarily aqueous) solutions. New studies using chemical bath deposition (CBD), liquid phase deposition (LPD), and successive ion layer adsorption and reaction (SILAR) to produce single- and multi-component oxide films, and the role that functionalized substrates can play in these deposition techniques, are surveyed. This review highlights significant new insights that have been gained in areas such as: nucleation and growth kinetics as they pertain to film growth in oxide systems; multicomponent films; the roles of polymers and other organic additives on the film deposition mechanism; and fabrication of patterned films and other advanced material morphologies.

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Novel hydrothermal solution processing routes covering conventional hydrothermal, solvothermal and supercritical hydrothermal techniques are becoming the most efficient routes for advanced nanomaterials processing including the high melting compounds. The importance of these novel hydrothermal solution routes has been discussed with appropriate examples. The current trends in the hydrothermal solution processing of materials, the importance of solubility study, thermodynamic calculations and the role of surfactants and chelates have been discussed in detail. The multi-energy processing of materials, instant hydrothermal system and the new concept in materials processing, viz. Chemistry at the speed of light have been highlighted here. The hydrothermal synthesis of nanomaterials of carbon polymorphs, rare earth vanadates, metal oxides and their nanocomposites have been discussed with an emphasis on the control of size and morphology.

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Hematite particles with various shapes have been synthesized through a simple hydrothermal reaction. The particle shape and size can be controlled by adjusting pH value in the starting solution. The products were characterized by X-ray powder diffraction patterns (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), high resolution transmission electron microscope (HRTEM), FT-IR, TG-DTA and mass spectrometry of gas species during TG-DTA. The TEM and HRTEM results revealed that large numbers of micropores ranging from 0.5-0.6 nm existed in the surface of spherical particles.

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Hydroxyapatite (HAp) precursors were prepared by chelation of calcium ions with organic phosphonic acid by using calcium nitrate hydrate (Ca(NO₃)₂·4H₂O) and 2-phosphonobutane-1.2.4-tricarboxylic acid (C₇H₁₁PO₉; PBTA) in distilled water in the temperature range of 60-130°C. HAp powder was then synthesized by heating the precursors at various temperatures. HAp precursors were pectized in a three-step reaction. First, calcium ions were chelated with carboxyl groups in PBTA in an early reaction. Second, chelation of calcium ions with phosphonic acid and/or the dehydrated condensation of carboxyl groups with phosphonic acid occurred at and above 80°C. Finally, dehydrated condensation of carboxyl groups proceeded in the range of 100-130°C. The homogeneity of the HAp precursors improved with an increase in their preparation temperature, which accelerated gelation. Powder obtained after heating the HAp precursor prepared at 130°C (preHAp-130) had a single crystalline HAp phase at 1000°C. In addition, the crystallization temperature of preHAp-130 was 200°C, which was lower than that of HAp precursors prepared using other polymerized complex methods. Powder obtained by heating HAp precursors at and below 800°C contained carbonate apatite, in which carbonate ions replaced hydroxyl and phosphate sites in the HAp crystal lattice. The Ca/P molar ratio of the HAp powder was higher than that in the stoichiometric composition of HAp (Ca/P = 1.67), because the organic components of the HAp precursors were not pyrolyzed; however, the powder obtained by heating preHAp-130 at 1000°C had stoichiometric HAp composition due to the thermal decomposition of the precursors. The particle size of the HAp powder prepared by heating preHAp-130 decreased with an increase in the heating temperature, and when the HAp particles were heated at and above 800°C, a three-dimensional network with micro and nanopores was formed.

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Crystallographically oriented yet morphologically squiggly nanoscale ZnO architecture was produced through epitaxial growth by using a simple aqueous solution system. Specific adsorption of pyranine, an organic dye molecule having three sulfonic groups, suppressed regular growth in the c direction, and thus induced lateral growth of winding ZnO nanowires with diameters ranging from 20 to 100 nm on a single-crystalline ZnO (001) substrate. Although resultant wool-like structures consisted of tangled wires, the crystalline lattice of the whole architecture was found to be continuous and have six-fold symmetry originating from the single-crystalline substrate.

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To investigate color properties by inclusion of hematite in the iron zircon pigments, different samples were prepared by the sol-gel method without mineralizer. The starting amount of the ferric salt in the sol-gel reacting mixture was varied in order to obtain Fe₂O₃/Zr molar ratio in the range of 5-30%. Fe-ZrSiO₄ pigments of the sol-gel reaction were calcined the range 600-1300°C. The crystalline phases were determined by using X-ray diffraction(XRD). The process of inclusion of hematite in iron zircon pink color were studied by UV-Vis-NIR spectroscopy and FT-IR spectroscopy. It was found that the coral pink and reddish color in the iron zircon pigments is due to α-Fe₂O₃ particles incorporated in the zircon matrix.

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The Bi₄Ti₃O₁₂ powders were synthesized by a hydrothermal route. The influence of hydrothermal conditions on crystal structures and morphologies of Bi₄Ti₃O₁₂ particles was studied. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectroscopy and ultraviolet visible (UV-vis) spectroscopy. These results revealed that the Bi₄Ti₃O₁₂ powders prepared thus possessed a plate-like shape, a typical bismuth layered perovskite structure, and a wide UV-vis absorption peak. Additionally, the formation mechanism of the Bi₄Ti₃O₁₂ nanoplates was also discussed.

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Anatase was hydrothermally synthesized from transparent aqueous sols including layered titanate colloids. The reaction sols were prepared from titanium isopropoxide and different alkylammonium hydroxides (NR₄OH). The influence of the type of NR₄OH on the morphology of the anatase crystals and their aggregates was examined. We previously reported that although anatase has a tetragonal lattice, six-pointed starlike anatase aggregates were synthesized from the sols prepared using N(CH₃)₄OH. With increasing the alkyl chain length of NR₄OH, the number of the starlike aggregates decreased, and their arms became thicker and shorter. When N(C₄H₉)₄OH was used, needlelike anatase crystals elongated along the c-axis were formed rather than starlike aggregates. The use of NR₄OH with long alkyl chains were expected to retard stacking of the layered titanate during hydrothermal synthesis. The stacking and exfoliation of the layered titanate colloids may play an important role in the morphology of the resulting anatase crystals and their aggregates.

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Vanadium peroxo-citrate complex was used for the first time for synthesis of YVO₄:Eu red emission phosphor material by hydrothermal method. It was found that particles size can be efficiently controlled in the range of 60-400 nm by changing concentration of the solution utilized for the hydrothermal process. The nanocrystalline powders of YVO₄:Eu prepared at 200°C for 2 h with post-synthesis heat treatment at 1000°C exhibited high fluorescence intensity comparable or better than one of the best commercially available YVO₄:Eu phosphor synthesized by conventional solid state reaction method and having much larger grain size.

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ZSM-5 and faujasite, which are aluminosilicate zeolites with different compositions, were synthesized without using organic structure-directing agents, and the changes in the medium-range order during the crystallization of ZSM-5 and faujasite were characterized by high-energy X-ray diffraction (HEXRD) technique. It is found that that the amorphous aluminosilicates have larger fraction of 4 membered ring (4R), compared to 6 membered ring (6R) that is the most dominant in amorphous silica. Furthermore, HEXRD measurements reveal that changes in the medium-range order are characteristic for each zeolite although crystallizations of both zeolites proceeded via a similar way: that is, the dissolution of amorphous precursors to solution followed by the nucleation and crystal growth of zeolite from the soluble species. In ZSM-5 crystallization, no major changes in the medium-range order are observed although slight decrease of the fraction of 4R is confirmed. On the other hand, clear changes in the medium-range order, especially on the ordering of 4R and 6R are confirmed in faujasite crystallization.

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The nitrogen-doped ZnO particles were prepared by heating a mixture of an ammonium salt and the aqueous sol of zinc peroxide nanoparticles. In the case that the sol of zinc peroxide nanoparticles were mixed with ammonium nitrate in the sol, nitrogen-doped ZnO particles were obtained by heating the mixture at 573 K for 1 h in the air. The obtained particles showed characteristic Raman peaks that can be assigned to the nitrogen-related local vibrational mode. The strength of the UV-VIS absorption peak, which corresponds to the nitrogen-related impurity state, also increased with increases in the mixed amount of ammonium nitrate (NH₄NO₃). The results of iodometric titration also showed the formation of acceptor states in the obtained nitrogen-doped ZnO particles. The nitrogen-doping successively occurred when the peroxo ions (O₂^2-) in the zinc peroxide did not react with the anions in the ammonium salts as an oxidizing agent.

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Effects of a silicon substrate on growth of ZnO in a wet chemical process were investigated. ZnO has been fabricated from base solutions composed of Zn(NO₃)₂, ammonia and polyethylene glycol at low temperatures by a wet chemical process. When a silicone substrate was immersed in the solution, flower-like ZnO was obtained on the substrate from the solution at pH = 10.4-10.9. In the case without the substrates, Zn(OH)₂ powders were obtained from the solution at pH = 10.4-10.9 and ZnO powders, which were not like flowers, were obtained from solution at pH ≤ 7.6.

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Silver nanoparticle/hydroxyapatite (Ag/HAp) hybrids were synthesized in an aqueous solution where silver ions were reduced by sodium tetrahydroborate in a slurry containing hydroxyapatite. The Ag/HAp hybrids contained silver nanoparticles with a size of approximately 12 nm existing on the surface of the hydroxyapatite. The number of silver nanoparticles in the Ag/HAp hybrids increased with increasing concentration of silver nitrate in the starting solution. The microstructure of the hydroxyapatite was the same both before and after hybridization with the silver nanoparticles. The hybrids free from surfactant were successfully synthesized through the hybridization process even without addition of surfactants. The use of a surfactant in the synthesis of the Ag/HAp hybrids did not influence the average particle size of the silver nanoparticles in the Ag/HAp hybrids, but the use of a surfactant made the silver nanoparticles form a monodispersion, and the number of silver nanoparticles deposited on the HAp decreased.

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The superhydrophobic property attracts many researchers in the both field of academe and industry. All of the superhydrophobic materials have the rough surface structure based on the Cassie-Baxter equation. The trapping of air into the rough surface structure caused the improvement of the superhydrophobic property. Therefore, the nanostructure control technique is very important. Of course, considering application in industry, the process cost of the superhydrophobic materials is very important. In this work, the superhydrophobic film is fabricated by the hot water treatment, which is one of the chemical bath deposition methods, of the metal aluminum. The hot water process of spattered Al film on the glass substrate results in the fabrication of the high transparent superhydrophilic film constructed by perpendicular nanosheet structure. After fluoroalkylsilanes coating, the resultant film shows the high transparent superhydrophobic property. Moreover, these processes can be applied to the commercial Al foil. So, we can easily obtain superhydrophobic film by using the hot water process.

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The adsorption state and dispersion effect of an anionic polyelectrolyte (Dolapix CE64) dispersant on the stability of nanocrystalline ZrO₂ suspensions are studied by using adsorption isotherms, sedimentation, TGA, electrokinetic sonic amplitude (ESA) and Auger electron spectroscopy (AES) techniques. It was found that colloidal stability and surface properties of aqueous ZrO₂ suspension are closely related to coverage distribution of polyelectrolyte as a function of pH on nanocrystalline ZrO₂ particle surface. The amount of polyelectrolyte adsorbed on nanocrystalline ZrO₂ particle surface increases greatly with decreasing pHiep (pH 3.72) and increasing the polymer concentration. The results obtained from electroacoustic (ESA) technique and AES spectra of polyelectrolyte adsorbed on nanocrystalline ZrO₂ surface proved that both techniques are very effective ways to measure the distribution state of polyelectrolyte on nanocrystalline ceramic powder and reveal how the distribution affect the stability of the suspension. It was found that stabilization can be achieved only when conditions of both Dolapix CE64 ionization and ZrO₂ surface coverage are satisfied, suggesting an electrosteric stabilization mechanism. In conclusion, we hypothesized a stabilization model according to the model of two particles approaching to describe the influence of the adsorbed anionic polyelectrolyte configuration on particle surface and the stability of nanocrystalline ZrO₂ suspensions.

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The K₃Ta₃B₂O₁₂ photocatalytic material for water splitting was prepared by an aqueous solution-based process using a novel water soluble Ta-peroxolactate complex. Use of water as a processing solvent is essential to prevent formation of volatile boron compounds and to synthesize the stoichiometric single phase material by a solution technique. Photocatalytic activity of K₃Ta₃B₂O₁₂ for water splitting was the highest when a stoichiometric amount of lactic acid (LA) with Ta:La = 1:2 was used for preparation of the Ta-peroxo lactate complex. Additionally, activities of K₃Ta₃B₂O₁₂ in the photocatalytic water splitting have been improved when NiO was used as a co-catalyst. The highest photocatalytic hydrogen and oxygen evolution rates exhibited by the materials prepared in this work were H₂: 392 μmol/h and O₂: 192 μmol/h.

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Recently our research group has developed a new water-soluble silicon compound. In current work this compound was employed as a starting reagent for synthesis of Zn₂SiO₄:Mn²⁺ green emission phosphor by the hydrothermally induced gelation (HTG) method and by the polymerizable complex (PC) method. The sample obtained by the HTG method was composed of Zn₂SiO₄:Mn²⁺ single phase and showed two times higher emission intensity than a reference sample synthesized by the conventional solid-state reaction method.

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We investigated the resource recovery of phosphorus from aqueous media containing various inorganic phosphorus compounds by hydrothermal mineralization treatment. The hydrothermal treatment was carried out for the model wastewaters containing 2000 mg/dm³ of phosphorus in forms of P^VO₄^3-, P^IIIO₃^3-, P^IO₂^3- or a mixed aqueous solution of P^IIIO₃^3- and P^IO₂^3- with mineralizer Ca(OH)₂. The phosphorus concentration in the treated water, which contained P^VO₄^3-, was less than 0.1 mg/dm³. On the other hand, the hydrothermal mineralization treatments with solid-liquid separation under hydrothermal conditions were required for the treatment of P^IIIO₃^3- and P^IO₂^3-, in order to accomplish the national effluent standard of Japan (16 mg/dm³). In this case, the phosphorus concentration in the solution treated under the optimal conditions was 0.20 mg/dm³. Thus, the hydrothermal mineralization with Ca(OH)₂ is recommended as one of the detoxification and recovery techniques of phosphorus in aqueous solution.

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Nanocrystalline brookite titanium oxide was prepared by hydrothermal treatment of a water-soluble titanium complex with ethylenediaminetetraacetic acid (EDTA). In this work, we examined the effect of synthesis conditions such as reaction time, titanium concentration and solution pH on the brookite phase formation and its photocatalyitic performance. It was found that hydrothermal treatment of the titanium complex may yield anatase and brookite phases, and their ratio can be varied depending on titanium concentration. Single phase brookite could be prepared when titanium concentration in the starting solution was higher than 0.25 mol/dm³, while lower concentration favors formation of anatase. Remarkably, brookite could be synthesized from the Ti-EDTA complex in the wide range of pH including both acidic and basic media. The samples prepared from Ti-EDTA complex demonstrated higher photocatalytic activity in terms of NO gas decomposition than the brookite powders synthesized from Ti-glycolate complex or commercial TiO₂ photocatalyst P25. Higher photocatalytic activity of powders obtained from Ti-EDTA complex aqueous solution is explained by higher surface area of smaller but well-crystallized brookite particles that can be achieved when this new titanium complex is employed.

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Organic compound/metal oxide composite thin films have been prepared by the liquid-phase deposition method in a one-step deposition technique. Organic dyes were added to the metal fluoro-complexes aqueous solution in order to entrap these dyes within the growing thin films of metal oxides, yielding organic dye/metal oxide hybrid materials. According to Raman spectroscopy and X-ray photoelectron spectroscopy, the formation of the materials in the case of cationic dyes can be explained by the electrostatic interaction between negative charge density at the fluorinated surface of metal oxides and the cationic dyes. UV-Vis results indicate that stilbazo and pyrocatechol violet (catecholate dye molecules) form a charge transfer complex with metal oxides through the catechol moiety with a bidentate linkage.

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A novel water-soluble silicon compound was synthesized by the reaction between tetraethoxysilane (TEOS) and propylene glycol. This compound is stable in aqueous solutions and miscible with water in any ratio. The potential of this new silicon reagent for synthesis of multicomponent silicate by solution based techniques was evaluated by preparation of the (Y,Ce,Gd)₂SiO₅ blue emission phosphor using a polymerizable complex method. Phase compositions and fluorescence properties of the prepared material was compared against reference samples prepared by either conventional solid state reaction or by a polymerizable complex method employing the other silicon reagents. It was revealed the application of new water-soluble silicon compound as a reagent for synthesis resulted in the formation of a single phase (Y,Ce,Gd)₂SiO₅ material at reduced temperatures and its fluorescence intensity considerably outperformed those of the phosphors prepared by the other methods in this work.

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The equilibrium reaction of H₂SiF₆ solution in the LPD method was investigated by the measurement of UV and IR spectroscopies, vapor pressure and electric conductivity. These measurements were carried out by adding the F^- scavenger such as H₃BO₃ and Al metal which shifts the equilibrium reaction. The experimental results strongly suggested the presence of SiF₄ and [SiF₆·SiF₄]^2- in H₂SiF₆ solution. These species were estimated to be involved in the LPD process as intermediates and important for controlling the deposition process of metal oxide.

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Hollow hydroxyapatite (HAp) microspheres a few tens micrometers in diameter were fabricated by precipitating HAp preferentially on the surface of an organic polymer template using enzymatically supplied precipitant. The template, poly-divinylbenzene (PDVB) microsphere encapsulating urease, was synthesized in W/O/W emulsion. HAp was precipitated on the surface of the template as ammonia was enzymatically supplied from inside of the template in a solution containing calcium ion, phosphate ion and urea. Within 21.6 ks, the surface of the template was covered with HAp. After the template was removed by calcination at 873 K, the HAp hollow microspheres were obtained. The size of the HAp microspheres reflected that of the template and the latter was easily controlled in a range from 10 to 200 μ m by the preparation condition of the W/O/W emulsion. The shell thickness of the HAp sphere was also regulated by the duration of the enzymatic reaction. This material can be a promising candidate for the carrier of the drug delivery system.

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Hollow magnetite (Fe₃O₄) microspheres a few tens micrometers in diameter were fabricated by calcining iron hydroxide precipitated on spherical polydivinylbenzene (PDVB) template with enzymatically supplied ammonia. Monophasic Fe₃O₄ hollow spheres were obtained by calcining the precursor at 1073 K for 3.6 ks in an equimolar mixed gas of CO₂ and H₂. The prepared Fe₃O₄ hollow spheres had smooth surfaces. The particle size and monodispersity of Fe₃O₄ spheres reflected those of the PDVB template, and the latter was controllable 10-30 μm in diameter during the process of the polymerization. The Fe₃O₄ spheres showed ferrimagnetic behavior. The use of urease to precipitate the precursor was found to be effective for preparing template-directed microspheres, and the Fe₃O₄ microspheres synthesized are considered to be promising thermoseeds for hyperthermic treatment.

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The metastable phase of TiO₂(B), one of the polymorphs of titanium dioxide (TiO₂), was prepared by a hydrothermal treatment of a titanium glycolate complex ([Ti₄(C₂H₂O₃)₄(C ₂H₃O₃)₂(O₂)₄O₂]^6-) at 473 K for 1-72 h in the presence of H₂SO₄. Characterization by X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that the obtained samples were composed of single phase TiO₂(B) and the particles had plate-like morphology. After post-synthetic hydrothermal crystal growth (PHCG) applied to the as-prepared sample, thicker plate-like shaped particles were obtained. The photocatalytic activities of the samples obtained by the hydrothermal treatment and after the subsequent PHCG were evaluated in terms of methanol decomposition.

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Porous alumina monoliths with high thermal stability have been prepared using sol-gel processing from ionic precursors. Samples were synthesized from AlCl₃·6H₂O and LaCl₃·7H₂O dissolved in a H₂O/etanol solution containing poly(ethylene oxide) (PEO) via propylene oxide (PO) involved sol-gel reaction accompanied by phase separation. The heat-treated gels consist of controllable size of macropores and La-doped alumina skeletons. Doped lanthanum ions are homogeneously embedded in the gel matrix, which retards the phase transition from γ-alumina to α-alumina during the sintering. The 3 mol% La-doped aluminate exhibits the BET surface area of 55.3 m²/g, after the heat treatment at 1100°C for 24 h. Drying condition are also related to the thermal stability of obtained gels. Aluminate aerogels show higher thermal stability than corresponding xerogels due to relatively large mesopore size and high porosity. As a result, the 3 mol% lanthanum doped aluminate aerogel shows BET surface area as high as 82.5 m²/g even after heat treatment at 1100°C for 24 h.

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Layered double hydroxides (LDHs) are inorganic materials consisting of the hydroxide layers formed with at least two metallic elements and anions between the layers. In this study, we have investigated the functionalization of LDH coating films by modification of both sol-gel and aqueous solution processes. A binary oxide system, Al₂O₃-TiO₂, was used for the precursor gel films. Judging from XRD and SEM measurements, LDH crystals were generated for the wide range of gel composition. Therefore, coating films with composite structure of Zn-Al LDH and TiO₂ was obtained by simple process. The reconstruction of LDH, i.e., heat treatment and following incubation in aqueous solution, was also achieved. This process can be expected for the intercalation of functional molecules in LDH layers and crystallization of TiO₂ for these composite coatings.

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The hydrothermal technique was applied to the syntheses of ternary metal sulfides, AgCuS and Ag₃CuS₂, using silver, copper, and sulfur powders as starting materials. AgCuS was obtained as a single phase when the starting ratio of Ag:Cu:S was 0.9:1.1:1 in water above 120°C for 10 h except for synthesis condition at 120°C for 60 h and inductively coupled plasma (ICP) analysis revealed that experimental silver and copper contents in products were Ag_0.89Cu_1.10S. At 120°C for 60 h, some unidentified peaks were observed in the powder X-ray diffraction (XRD) pattern and plate crystals of new compound were found in addition to AgCuS particles from the field emission scanning electron microscopy (FE-SEM) image. Pure Ag₃CuS₂ was also prepared by a simple reaction of stoichiometric silver, copper, and sulfur powders above 90°C, and the composition of products was Ag_2.99Cu_1.00S.

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The effect of colloidal silica (SiO₂; CS) addition on the formation of porous spherical α-calcium orthophosphate (α-Ca₃(PO₄)₂; α-TCP) agglomerates has been examined. The starting powder was prepared by the spray pyrolysis of calcium phosphate (Ca/P ratio = 1.50) solution containing 0.9 mol·dm^-3 Ca(NO₃)₂, 0.6 mol·dm^-3 (NH₄)₂HPO₄, CS (mean particle size; 14, 24 and 39 nm) and concentrated HNO₃ at 600°C, using an air-liquid nozzle; the amounts of CS in the spray-pyrolyzed powder were adjusted to be 0.1-0.4 mass%. The heat-treatment of spray-pyrolyzed power with 0.4 mass% of CS addition at 1200°C for 10 min showed that the transformation from β- to α-TCP was restricted as the diameter of CS decreased from 24 to 14 nm. The heat-treatment of spray-pyrolyzed powder containing 0.1 mass% of CS (mean diameter: 24 nm) at 1200°C for 10 min resulted in not only the complete transformation of β- to α-TCP but also preservation of original spherical framework. The immersion of porous spherical α-TCP agglomerates in simulated body fluid (SBF) brought about the rapid formation of hydroxyapatite, due to higher specific surface area (17.0 m²·g^-1) compared to that of commercial powder (10.9 m²·g^-1). The hardened body with the porosity of 66.3% could be fabricated by mixing the calcium-phosphate paste with 50 mass% of the present porous α-TCP agglomerates, using the malaxation liquid. Immersion of this hardened body in SBF at 37.0°C resulted in the formation of hydroxyapatite within three days.

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Porous titania (TiO₂) was synthesized under ultrasonic vibration via an anodic oxidation of titanium metal in various kinds of electrolyte such as HNO₃, H₂SO₄, and their mixture. HNO₃ resulted in amorphous or poorly-crystalline particles with mesopores while H₂SO₄ resulted in dense and crystalline film with macropores. Ultrasound in general decreased the maximum voltage, film thickness, and a rutile phase, while it increased the region for the formation of mesoporous structure. Role of ultrasound on the anodic oxidation is discussed.

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A halogen- and acid-free aqueous solution was developed to crystallize anatase TiO₂ nano-particles. Spinal or zigzag chains of TiO₆ octahedrons were formed from [TiO(C₂O₄)₂]^2- ions. They were then gradually transformed into rutile TiO₂ in the solutions. Rearrangement of octahedrons realized aqueous phase transition from anatase to rutile.

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(Sr_0.975Mn_0.02Ln_0.005)Ga₂S₄ (Ln = La and Ce) phosphor materials were synthesized by the sulfurization of oxide-carbonate precursors prepared using aqueous solution processes based on amorphous metal complex method or micro-gel freeze-drying method. As a group, multicomponent sulfide phosphors obtained from the amorphous metal complex precursors demonstrated stronger emission brightness than materials of the same composition synthesized by the micro-gel spray freeze-drying method. (Sr_0.975Mn_0.02Ce_0.005)Ga₂S₄ phosphor demonstrated blue emission intensity reaching 40% intensity of one of the best commercially available BAM phosphors excited by 408 nm light. (Sr_0.975Mn_0.02La_0.005)Ga₂S₄ red phosphor exhibited strong deep red emission when excited by 310 nm light, and in terms of emission intensity it outperformed Ba_1.59Sr_0.4ZnS₄:Eu²⁺. Nevertheless, the former material can not be excited by visible or near UV light.

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Hydrogen titanate nanowires were prepared by hydrothermal method in 10 M NaOH followed by ion-exchanging process. Titanate nanowire thin films were successfully obtained by spray Layer-by-Layer (spray LbL) method within a short time. Due to the good dispersion state of the nanowires in an aqueous suspension and their linear morphology, titanate nanowires effectively adsorbed on the glass substrate. As a reference, TiO₂-anatase nanoparticle thin films were also prepared by spray LbL method.

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Hydroxyapatite (HA) was synthesized by the hydrothermal treatment of octacalcium phosphate (OCP). Powder of OCP was hydrothermally treated with distilled water at 120-240°C for 3-24 h. Only diffraction lines assigned to HA were detected by X-ray diffraction (XRD) even after the treatment at 120°C for 3 h. The crystallinity of the formed HA increased with increasing the treatment temperature and period. Plate-shaped particles were split into small strip-shaped particles by the hydrothermal treatment and this phenomenon was obvious when the treatment temperature was high and the period was long. However, the plate-shape morphology was remained when OCP was transformed to HA at 120°C for 3 h. The hydrothermal treatment of OCP is useful to synthesize the plate-shaped HA particles in a short period.

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Fine barium titanate (BaTiO₃) powders were prepared by a microwave-assisted liquid phase process at ambient pressure. The process is simple, ecologically friendly, and economical. Titanium dioxide (TiO₂) and Barium hydroxide octahydrate (BaOH₂·8H₂O) were the only starting materials used, in order to avoid contamination. BaTiO₃ powders were obtained as a single cubic phase from both microwave-assisted and conventional liquid phase processes. BaTiO₃ powders synthesized by conventional liquid phase process were nonuniform in size. In contrast, BaTiO₃ powders made by the microwave-assisted process consisted of fine uniform particles with a narrow size distribution. TGA analysis revealed that the lattice OH group content in BaTiO₃ powders synthesized by the microwave-assisted process decreased with increasing reaction time.

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High purity α-nickel hydroxide/carbon composite has been synthesized by the liquid phase deposition (LPD) method. The purity of the as-prepared samples was confirmed by X-ray photon electron (XPS) survey spectra, which showed no other peak than that of the core levels Ni 2p, O 1s, C1s, Ni 3s and Ni 3p involved in the process. Scanning electron microscope (SEM) images showed carbon particles randomly embedded within the Ni(OH)₂ network. The amount of deposited nickel hydroxide can be controlled by the ratio between carbon and the quantity of the treatment solution, and the reaction time.

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12CaO·7Al₂O₃ (C12A7) crystal is a constituent of alumina cements and an electrical insulator having a wide bandgap of ∼7 eV. When high-density electrons were doped into C12A7 by replacing the O^2- ions in its crystallographic cages with electrons almost exclusively (C12A7:e^-), they exhibited metallic conduction with a small work function of ∼2.4 eV, making the C12A7:e^- attractive for use in electronic devices. This article focuses on comparing two fabrication methods for the C12A7:e^- thin films: ion implantation of inert gas ions and a reduction reaction using an oxygen deficient amorphous C12A7 layer. Further, their respective electrical and optical properties are discussed.

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The microwave dielectric properties and microstructures of Ba₂Ti₉O₂₀-based ceramics were investigated as a function of B₂O₃ content and sintered at 940°C for 2 h. Densities of the specimens were enhanced with an increase of B₂O₃ up to 3 mass% and then decreased. The specimens could be sintered at 940°C without the degradation of the microwave dielectric properties of the specimens. The results of X-ray diffraction (XRD) indicate the presence of five crystalline phases, Ba₂Ti ₉O₂₀, BaZr(BO₃)₂, BaZrO₃, BaTi₄O₉, and Zn₃B₂O₆, in the sintered ceramics, depending upon the amount of B₂O₃ addition. Moreover, the microstructure of Ba₂Ti₉O₂₀-based ceramic with 3 mass% B₂O₃ addition was analysed by using a transmission electron micrograph, which the composition of dendrite phase should be BaZr(BO₃)₂. The specimens with 3 mass% B₂O₃ sintered at 940°C for 2 h showed ε_r of 28.3, Q × f value of 10784 (Q = 1477), and TCF (τ_f ) of -8.2 ppm/°C.

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Li₂O-ZnO-Al₂O₃-SiO₂ (LZAS) glass-ceramic system was studied in the high temperature spray pyrolysis. Small amount of P₂O₅ was used as nucleation agent. Fine-sized Li₂O-ZnO-Al₂O₃-SiO₂ glass powders with amorphous phase and spherical shape were formed by spray pyrolysis at temperatures between 1300 and 1500°C. The mean size of the glass powders prepared at a temperature of 1500°C was 0.7 μm. The glass transition temperature (T_g) of the glass powders was 551.2°C. The two crystallization exothermic peaks were observed at 703.8 and 923.8°C. Densifications of specimens occurred at sintering temperatures of 800 and 900°C, in which interconnected network microstructure was formed by tiny dendritic crystals. The specimens sintered at temperatures of 600 and 700°C had LiAl(SiO₃)₂ crystal structure. On the other hand, the specimens sintered at temperatures between 800 and 1000°C had LiAlSi₂O₆ (β-spodumene) crystal structure.

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