Hiromitsu Kozuka

Antibacterial silver-containing silica glass prepared by sol–gel method

Recently, various inorganic antibacterial materials containing silver have been developed and some of them are in commercial use. Colorless and more chemically durable materials which slowly release the silver ion for a long period are, however, desirable to be developed for medical applications such as composite resin for dental restoration. In the present study, Si(OC2H5)4, Al(NO3)3 x 9H2O, AgNO3, HNO3, C2H5OH and H2O solutions with various Al/Ag atomic ratios under a constant Si/Ag atomic ratio of 1/0.023 were kept at 40 degrees C for gelation and drying. Thus obtained gels were pulverized into fine powders with average particle size of approximately 10 microm and then heat-treated at 900-1000 degrees C for 2 h. For the composition Al/Ag = 0, a yellow-colored glass was formed, since the silver existed in the form of metallic colloids in the glass. However, for the compositions Al/Ag > or = 1, colorless glasses were successfully obtained, since the silver existed in the form of Ag+ ions in the glasses. For the composition Al/Ag = 0, the silver ions got released rapidly into the water, whereas, for the compositions Al/Ag > or = 1, they gradually got released into the water at a controlled rate. A composite of the obtained powders with Al/Ag atomic ratio of 1 with Bis-GMA/TEGDMA in 70:30 weight ratio showed excellent antibacterial property. The sol-gel derived silica glass powders containing silver with compositions Al/Ag > or = 1 are believed to be useful as an antibacterial material for medical applications such as filler of composite resin for dental restoration.

Sol—gel preparation and photoelectrochemical properties of TiO2 films containing Au and Ag metal particles

Abstract TiO 2 film electrodes with a TiO 2 overlayer containing dispersed Au or Ag metal particles were prepared by the sol-gel method, and the effect of the metal particles on the photoelectrochemical properties of the TiO 2 electrodes were investigated. An increase in the anodic photocurrent in the visible region was observed for both the Au and Ag particle dispersed electrodes, which was thought to result from the surface plasma resonance of the metal particles. The introduction of Au metal particles, however, reduced the anodic photocurrent in the ultraviolet region, resulting in a decrease of the anodic photocurrent under the illumination of xenon lamp light. On the other hand, for the Ag particle dispersed electrodes, the anodic photocurrent in the ultraviolet region increased and then decreased with an increasing amount of Ag particles. These effects of the dispersed metal particles on the photoelectrochemical properties of the TiO 2 electrodes were explained on the basis of the band models.

Effects of solvent on properties of sol—gel-derived TiO2 coating films

Abstract The effects of the kind of solvent on the properties of TiO2 coating films prepared by the sol—gel method using titanium isopropoxide (Ti(OC3H74)i) as the starting material have been investigated. Ethanol, ethanol mixed with isopropyl alcohol, and ethanol with 2-ethoxyethanol were used as the solvents. The kind of solvent was found to affect the crystallization behaviour, microstructure, and photoelectrochemical properties of the resultant TiO2 coating films.

Crack-Free, Thick Ceramic Coating Films via Non-Repetitive Dip-Coating Using Polyvinylpyrrolidone as Stress-Relaxing Agent

BaTiO3 and PZT films were prepared from alkoxide-acetate solutions containing polyvinylpyrrolidone (PVP) by non-repetitive dip-coating. It was demonstrated that PVP incorporated in gel films suppresses crack formation during heating and increases the critical thickness, the maximum thickness achievable without crack formation via single-step deposition. Using PVP crack-free BaTiO3 and PZT films 1.2 and 0.5 μm in thickness could be prepared, respectively, via single-step dip-coating. The films were fairly transparent and dense in microstructure. The tensile stress in heat-treated BaTiO3 films was also demonstrated to decrease significantly by incorporating PVP in gel films.

Sol-gel preparation of Ti1−xVxO2 solid solution film electrodes with conspicuous photoresponse in the visible region

Titanium–vanadium oxide films have been prepared by the sol-gel method using a starting solution containing titanium isopropoxide and vanadium(IV) oxyacetyl acetonate. Solid solubility of VO2 in TiO2 matrix and the effects of vanadium incorporation on the crystallization behavior of TiO2 were investigated by an X-ray diffraction analysis. It was found that the absorption edge of Ti1−xVxO2 films shifted to longer wavelengths when x increased. The sol-gel derived Ti0.95V0.05O2 film electrode was found to exhibit a conspicuous photoresponse in the visible region. Moreover, this film electrode was proved to be photoelectrochemically quite stable.

PVP-assisted sol-gel deposition of single layer ferroelectric thin films over submicron or micron in thickness

Abstract PZT, BaTiO3 and BaBi4Ti4O15 films were prepared on Pt/Ti/SiO2/Si substrates by spin-coating using alkoxide solutions containing polyvinylpyrrolidone (PVP). Deposition and firing of the gel films were performed just once, not repeated. Crack-free, single-phase PZT, BaTiO3 and BaBi4Ti4O15 films as thick as 2.2, 0.77 and 0.40 μm could be prepared, respectively, via non-repetitive spin-coating. The 2.2 μm thick PZT film exhibited P–E hysteresis with remanent polarization and coersive field of 21 μC cm−2 and 90 kV cm−1, respectively. The dielectric constant of the PZT, BaTiO3 and BaBi4Ti4O15 films were 370, 310 and 380, respectively, at 1 kHz.

Stress and cracks in gel-derived ceramic coatings and thick film formation

Residual stress was evaluated by measuring the substrate curvature for alkoxide-derived silica and titania films deposited on silica glass substrates. The residual stress was tensile, increasing with increasing heat-treatment temperature. The stress in fired films was affected greatly by water/alkoxide ratio and chelating agents in starting solutions. Secondly, in situ observation was made on cracking of gel films subjected to heat-treatment. Silica and titania gel films deposited on silicon wafers were cracked in the heating-up stage at temperatures of 100°–400°C, depending on the film thickness and heating rate. Larger thickness and lower heating rates were found to lower the cracking onset temperature. Finally, organic polymers with amide groups were demonstrated to increase the uncracking critical thickness. The polymers include polyvinylpyrrolidone and polyvinylacetamide, allowing single layer ceramic coating films over 1 μm in thickness to be formed without cracking.

Rheology of sols and fiber drawing

Abstract The investigations on the viscosity of the metal alkoxide solutions in the course of hydrolysis and condensation reactions leading to the gelation of sols have been reviewed. All the solutions which gel finally show a continuous increase in viscosity with time until they gel at a certain viscosity higher than about 100 P which is dependent on the composition of the starting solution. When a metal alkoxide solution is catalyzed with an acid and its water content is small at less than 4 or 5 in the water to alkoxide mol ratio, the solution exhibits spinnability at viscosities above about 10 P and becomes drawable into gel fibers, whereas no spinnability appears when a solution contains a large amount of water or is catalyzed with an alkali like ammonia. The investigations on the relation between the reduced viscosity and the concentration or the relation between the intrinsic viscosity and the number-averaged molecular weight have made it clear that the spinnable silicon alkoxide solutions have long-shaped siloxane particles and non-spinnable solutions have round particles. It has been established that spinnable solutions exhibit Newtonian flow behavior up to high viscosities, where fibers can be drawn, while non-spinnable solutions exhibit marked structural viscosity and, sometimes, thixotropy. Similar behavior is confirmed in the alumina solutions prepared from inorganic salts. It has been reported that the viscosity measurements provide information on the rate of the reaction leading to gelation. It is also known that the viscosity of the alkoxide solution controls the thickness of the thin coating film made by the dip-coating technique using an alkoxide solution.

Sol–gel preparation of single-layer, 0.75 μm thick lead zirconate titanate films from lead nitrate-titanium and zirconium alkoxide solutions containing polyvinylpyrrolidone

Lead zirconate titanate (PZT) films were deposited on nesa silica glass substrates by spin coating using a Pb(NO3)2–Zr(OC3H7n)4–Ti(OC3H7i)4 solution containing polyvinylpyrrolidone and acetylacetone. The coating solution had stable viscosity for over 1300 h at room temperature. Single-layer PZT films as thick as 0.75 μm could be obtained via single-step spin coating with successive gel film heat treatments at 80, 300, and 700 °C. The fired films were optically transparent and crack free, exhibiting P–E hysteresis loops with remanent polarization of 24.6±1.6 μC cm−2 and coercive field of 95.6±9.8 kV cm−1.

Effects of the incorporation of silver and gold nanoparticles on the photoanodic properties of rose bengal sensitized TiO2 film electrodes prepared by sol-gel method

Abstract Rose bengal-deposited TiO 2 film electrodes bearing dispersed Ag or Au nanoparticles were prepared by the sol-gel method. The dye-induced visible region photoresponse of the electrodes decreased with increasing Ag content up to a mole ratio of Ag/TiO 2 = 0.0207, while the UV photoresponse increased. On the other hand, the dye-induced visible region photoresponse decreased to a less extent by incorporation of a larger amount of Au particles of Au/TiO 2 = 0.06, along with decreased UV photoresponse. The effects of the metal particles on the dye sensitization of the electrodes were discussed in terms of band edge fluctuation induced by the surface metal particles, Schottky barriers at TiO 2 /metal interfaces, and surface plasma resonance.