Thermal and chemical methods for producing zinc silicate (willemite): A review

Thermal and chemical methods for producing zinc silicate, Zn₂SiO₄ phosphor on industrial and laboratory scales are reviewed. Zinc silicate has a promising future in advanced materials as a highly versatile luminescent material due to the wide range of multi-colors that can be obtained from various guest ions. Candidates for future industrial methods of producing zinc silicate are critically reviewed from the point of view of phase formation and compared with the conventional solid-state reaction. Conventional methods require calcination at temperatures higher than 1000 °C and long reaction times to form Zn₂SiO₄ phase and these processes limit particle shape and size. Sol–gel methods are performed in a solvent at ambient pressure, while hydrothermal and solvothermal methods tend use high temperatures and high pressures, and especially supercritical water methods tend use conditions higher than 400 °C and 25 MPa. Hydrothermal and sol–gel literature shows that crystallization of Zn₂SiO₄ requires at least temperatures of around 100 °C. Of all the growth methods, supercritical water is able to bring about phase formation in the shortest reaction time. Vapor methods are performed with a gas phase as the reaction medium. Vapor and sol–gel methods require post-calcination for crystallization and have the advantage of providing characteristic particles such as uniform shapes, spherical particles, or nano-sized particles by varying the experimental conditions; they may be combined with the other crystallization routes in the future.     

Infrared spectroscopic study of thermal annealing effects of hydrocarbon species on a Si surface exposed to methane plasma

We have investigated the thermal annealing effects of hydrocarbon species on the methane-plasma exposed silicon surface, investigated by in situ infrared absorption spectroscopy (IRAS) in multiple internal reflection (MIR) geometry. The proportion of types of hydrocarbon species is not remarkably changed in the hydrocarbon network that consists of sp-, sp²- and sp³-CH_X species by annealing at moderate temperatures. On the other hands, the proportion is drastically changed in the network that is mainly composed of sp³-CH_X species by annealing at moderate temperatures. It suggests that excess CH₃ species in the film is not stable against thermal annealing and would be converted to sp³-CH_1-2 species by annealing at moderate temperatures. And the data also show that sp²-CH species is more stable against the thermal annealing than sp³-hydrocarbon species.     

Living cationic polymerization of an azide‐containing vinyl ether toward addressable functionalization of polymers

We first achieved the living cationic polymerization of azide‐containing monomer, 2‐azidoethyl vinyl ether (AzVE), with SnCl₄ as a catalyst (activator) in conjunction with the HCl adduct of a vinyl ether [H‐CH₂CH(OR)‐Cl; R ? CH₂CH₂Cl, CH₂CH(CH₃)₂]. Despite the potentially poisoning azide group, the produced polymers possessed controlled molecular weights and fairly narrow distributions (M_w/M_n ～ 1.2) and gave block polymers with 2‐chloroethyl vinyl ether. The pendent azide groups are easily converted into various functional groups via mild and selective reactions, such as the Staudinger reduction and copper‐catalyzed azide‐alkyne 1,3‐cycloaddition (CuAAC; a “click” reaction). These reactions led to quantitative pendent functionalization into primary amine (? NH₂), hydroxy (? OH), and carboxyl (? COOH) groups, at room temperature and without any acidic or basic treatment. Thus, poly(AzVE) is a versatile precursor for a wide variety of functional vinyl ether polymers with well‐defined structures and molecular weights. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1449–1455, 2010     

Hydrothermal synthesis of organic hybrid BaTiO3 nanoparticles using a supercritical continuous flow reaction system

Barium titanate (BaTiO₃: BT) nanoparticles were synthesized by the hydrothermal method in the presence of dispersants using a continuous supercritical flow reaction system. The reactants of TiO₂ sol/Ba(NO₃)₂ mixed solution and KOH solution were used as starting materials and that was heated quickly up to 400 °C under the pressure of 30 MPa for 8 ms as reaction time. The dispersant solution such as polyacrylic acid (PAA) and polyoxyethylene(20) sorbitan monooleate (Tween 80) was injected in the cooling process after the reaction. The crystal phase of the obtained particles was identified as perovskite cubic BaTiO₃ by X-ray diffractometry (XRD) and Raman spectroscopy. Raman spectra and thermogravimetric data revealed that PAA and Tween 80 fabricated hybrid BT nanoparicles. Primarily particle size of the BaTiO₃ nanoparticle was determined by means of BET surface area, as small as less than 10 nm irrespective of dispersants. In contrast, dispersed particle size in solution measured by dynamic light scattering (DLS) technique decreased from 282 nm to less than 100 nm depending on the dispersant. Aggregation of BaTiO₃ nanoparticles might be depressed in the presence of dispersants, especially PAA is the most effective among the dispersants examined.     

Lewis acid-promoted rearrangement of 2,3-epoxy alcohol derivatives: stereochemical control and selective formation of two types of chiral quaternary carbon centers from the single carbon skeleton

The Lewis acid-promoted rearrangement of 2,2,3,3-tetrasubstituted 2,3-epoxy alcohols with several kinds of protecting groups was investigated. When SnCl4 is used as a Lewis acid, the reaction proceeds in a regio- and stereo-controlled manner to afford two types of carbonyl compounds selectively from a single 2,3-epoxy alcohol only by changing the protecting group of the alcohol. The method was then applied to the formation of two types of acyclic and cyclic quaternary carbon centers from the single compound in optically active forms.     

Infrared diode laser spectroscopy of the deltanu=2 band of AlF

A vibrational-rotational spectrum of the deltanu=2 transitions of a high-temperature molecule AlF was observed between 1,490 and 1,586 cm(-1) with a diode laser spectrometer. Measurements were made on the nu=3-1, 4-2, 5-3 and 8-6 bands at a temperature of 900 degrees C. Measured spectral lines were fitted to effective band constants nu(0), B(nu) and D(nu) for each band. Present measurements were made with only one Pb-salt laser diode. Physical significance of the effective band constants is discussed.     

Infrared diode laser spectroscopy of the ν = 2 band of AlF

A vibrational–rotational spectrum of the ν = 2 transitions of a high-temperature molecule AlF was observed between 1490 and 1586 cm⁻¹ with a diode laser spectrometer. Measurements were made on the ν = 3–1, 4–2, 5–3 and 8–6 bands at a temperature of 900 °C. Measured spectral lines were fitted to effective band constants ν₀, B_ν and D_ν for each band. Present measurements were made with only one Pb-salt laser diode. Physical significance of the effective band constants is discussed.     

Epitaxial film growth and superconducting behavior of sodium-cobalt oxyhydrate, NaxCoO2.yH2O (x approximately 0.3, y approximately 1.3)

We have developed a unique multistep film growth technique, combining reactive solid-phase epitaxy (R-SPE) with an intercalation process, to fabricate epitaxial films of superconducting sodium-cobalt oxyhydrate, Na(0.3)CoO2.1.3H2O. An epitaxial film of Na(0.8)CoO2 grown on an alpha-Al2O3(0001) substrate by R-SPE was subjected to oxidation and hydration treatment, leading to the formation of a Na(0.3)CoO2.1.3H2O epitaxial film. The film exhibited metallic electrical resistivity with a superconducting transition at 4 K, similar to that of bulk single crystals. The present technique is suitable and probably the only method for the epitaxial growth of superconducting Na(0.3)CoO2.1.3H2O.