Technologies of hydrophobic coating on solid surface are important for various industrial items to impart functions such as antibeading, anti-rusting, anti-snow adhesion, self-cleaning, and lubrication. In recent, the demands of these functions are upgrading, and further improvements of performance are necessary. To meet today’s requirements, detailed understandings on the relation between solid characteristics (such as structure, chemical composition, and their arrangement) and static/dynamic hydrophobicity is indispensable. So far, the research on this relation has been conducted in the part of fluid mechanics, tribology, and surface chemistry. However, recent researches revealed that static and dynamic liquid droplet behaviors are affected by nano-scale surface characteristics on hydrophobic solids, and the importance of the viewpoint from materials science is gradually increasing in this topic. This paper presents a review of recent studies on the relation between solid characteristics and static/dynamic hydrophobicity, mainly of the past decade of our group.

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Basicity is defined as an electron donating ability of a material, and hence, an oxide material containing oxide ions with high electron density is regarded to be in high basicity. It has been demonstrated that basicity can be evaluated by binding energy of core level electrons, which is measured by X-ray photoelectron spectroscopy. Based on the experimental results obtained from a large number of oxide glasses, correlations among basicity, O1s binding energy, structure and properties of glasses have been investigated. In the present paper, some of the research outcomes are introduced.

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White light emission of rare earth (RE)-free Mn-doped SnO–ZnO–P₂O₅ glass is demonstrated. Glass transition temperature of the obtained glass is below 440°C, which assures the application to sealant of solid state light emitting devices. The RE-free transparent glass shows white light emission with a high value of quantum efficiency (QE) comparable to conventional crystalline phosphor by excitation of deep UV light. The broad emission of RE-free transparent glass can be continuously tuned by both the amount of activator and the composition of the glass without decrease of the QE value.

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We have succeeded in preparing Sr_0.5Ba_0.5Nb₂O₆ (SBN50)-precipitated ceramics by acid etching via a glass-ceramic process using SrO–BaO–Nb₂O₅–B₂O₃–ZnO–SiO₂ glasses. Although the mother glass has good resistance to acid etching, the phase separated glass-ceramic obtained by crystallization was easily etched. This phase separation process was favorable for removing the amorphous B₂O₃–ZnO phase and a superfluous crystalline phase. Addition of SiO₂, substituted for B₂O₃, was effective for maintaining the bulk structure of the SBN50-etched ceramic because of its ability to form a strong and chemically stable network. We have found that the SBN50-precipitated ceramic demonstrates photocatalytic activity, which is the first report on the activity of SBN50.

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Pure perovskite compound SrFeO₃ nanocrystals were successfully synthesized in molten NaNO₃–KNO₃ eutectic with Na₂O₂ from a mixture of strontium nitrate and ferric nitrate. The effect of metal precursors, salt medium, annealing temperature (mainly 400–800°C), and oxidizing properties of the melt on the phase composition, crystallite size and morphology of the resulting metal oxides were systematically studied by simultaneous TG/DSC, X-ray diffraction (XRD), scanning electron microscopy (SEM) methods. The results showed that the formation of the SrFeO₃ phase mainly depended on the nature of the metal precursor and salt medium. It was found that metal nitrates are the suitable precursors and NaNO₃–KNO₃ eutectic with Na₂O₂ is the suitable salt medium, which results in the formation of pure SrFeO₃ nanocrystals at a much lower temperature of 400°C.

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A pure phase of SiC was formed by microwave heating (2.45 GHz) a powder mixture consisting of SiO₂:carbon black in a 1:3 molar ratio at 1300°C for 0.5 h in a nitrogen atmosphere. In contrast, when the same powder mixture was heated at 1700°C for 0.5 h in a nitrogen atmosphere using a conventional electric furnace, low crystallinity SiC was formed with carbon black remaining as an impurity. The mechanism for the formation of SiC from a powder mixture of SiO₂ and carbon using microwave heating is discussed on the basis of chemical thermodynamics, and compared to that for conventional heating with a carbothermal reduction reaction. As a result, the advantage of carbothermal reduction reaction by microwave heating was confirmed.

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A PVP (Polyvinylpyrrolidone)-assisted TiO₂ film with thickness over 100 nm by one step dip coating was prepared by adding polyvinylpyrrolidone (PVP) to TiO₂ nano sol and heat-treatment at the relative low temperature (450°C). The maximum refractive index of PVP-assisted TiO₂ film was measured to be 1.8764 after 5th dip coating and heat-treatment in this work. As the amount of TiO₂ sol increased, it increased, while it decreased as the quantity of PVP increased. The crystalline phase by X-ray diffraction was identified to be anatase and the intensity increased with film thickness’s increase. The maximum thickness of pure TiO₂ film prepared without crack was 1.89 µm and U.V. absorption of PVP–TiO₂ nano hybrid film before heat-treatment was measured to be over 98% at 340 nm wavelength.

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The La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8 (LSGM) precursor powders with large size, hollow and thin wall structure are prepared by spray pyrolysis from the spray solution with ethylenediaminetetraacetic acid (EDTA). The precursor powders turned into the nano-sized powders after post-treatment and grinding processes. The pellets formed from the powders obtained from the spray solution with EDTA had pure LSGM phase, clean surface and dense structure with small pores after sintering at 1300°C. On the other hand, the LSGM pellet formed from the powders obtained from the spray solution without EDTA had small impurity phase, porous structure and rough surface. The conductivity of the LSGM electrolyte was 0.006 S/cm at a measurement temperature of 600°C.

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Transparent crystallized glass with a surface crystallization layer of sub-millimeter thickness was found in the glass compositions of 35BaO–15TiO₂–50GeO₂ (BTG50), 28BaO–18TiO₂–54SiO₂ (BTS54), and 35SrO–20TiO₂–45SiO₂ (STS45), and the precipitated fresnoite-type crystalline phase showed nonlinear optical properties. XRD measurements confirmed that BTS54 and STS45 crystallized glasses precipitate as a single phase of the fresnoite-type crystallites Ba₂TiSi₂O₈ and Sr₂TiSi₂O₈, respectively. On the other hand, BTG50 crystallized glass precipitated two phases with mainly fresnoite-type BTG, Ba₂TiGe₂O₈ and BaGe₄O₉. The results of the XRD analysis of STS45 crystallized glass demonstrated high crystal orientation in the (002) direction from the glass surface.

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