Tetsuo Yazawa

Precipitation of colloidal silica and pore size distribution in high silica porous glass

Abstract Porous glass was prepared by acid leaching of a phase separated soda borosilicate glass. Fine pores with radius smaller than 15 A and coarse pores with radius larger than 50 A were observed in the glass by nitrogen adsorption and mercury penetration methods, respectively. Effects of the time of heat treatment and the acid/glass ratio, that is, the ratio of volume of leaching acid to the weight of phase separated glass on the characteristics of fine and coarse pores were studied. The size of coarse pores which were ascribed to the phase separated structure was proportional to the cube root of the time of heat treatment. The extraction of silica from specimens by acid solution during leaching increased with increasing acid/glass ratio. The volume of coarse pores was proportional to the amount of extracted silica. These facts are discussed on the basis of the formation of colloidal silica particles from the soluble borate phase during leaching.

Preparation and optical property of monolithic silica gel uniformaly dispersed with gold colloid from aqueous solution

Abstract Gold colloids were prepared from aqueous HAuCl4 solutions ranging in concentration from 0.01 to 0.05 wt% by reducing with sodium citrate and dispersed in a monolithic disk, with 35 mm diameter and 1 mm thickness, by the sol-gel method. Tetramethoxysilane is the only useful reagent as Si source. The particle size of dispersed gold colloids was about 50 nm. This silica gel had a third-order optical non-linearity and its susceptibility, χ(3), was about 7×10−12 esu.

Preparation of water and alkali durable porous glass membrane coated on porous alumina tubing by sol-gel method

Abstract Composite porous glass membranes were prepared by the sol-gel method. A thin porous glass layer, about 2 μm thick, was coated on the surface of the porous ceramic tubing (Al 2 O 3 :99.9 wt.%, pore diameter: 200 nm). The composition of the porous glass layer of the composite membrane was SiO 2 -ZrO 2 . Considering from the fact that the desalination ratio of the feed aqueous NaCl solution (NaCl 0.5 wt.%) was about 90% by use of these membranes, they were defect-free. The best composition of the porous glass layer was 70 SiO 2 -30 ZrO 2 from the standpoint of preparing membranes. These membranes had a large water and alkali durability. These membranes can be expected to apply to recovering dyes and paints from organic solvents and to be used as a gas separation membrane.

Time-resolved luminescence studies of a ruthenium(II) complex on porous glass. Pore size dependence of photoinduced electron transfer

Abstract Photoinduced electron transfer occurs from Ru(bpy) 3 2+ (bpy, bipyridine) adsorbed on porous glass to aqueous titanium species in the pore. The lifetime of excited Ru(bpy) 3 2+ decreases with an increase in the pore size, indicating that the lifetime reflects the mobility of the molecules in the pore.

Rate equation analyses and energy transfer of Er3+-doped sulfide glasses

Decay curves of 1.5 micrometers (4I13/2) and 980 nm (4I11/2) emissions from Er3+ ions in Ga2S3-GeS2-La2S3 glasses were measured by the excitation of 1.5 micrometers laser diode pump. The decay curves were simulated using rate equations for a model consisting of four levels (4I15/2, 4I13/2, 4I11/2, and 4I9/2) of Er3+. A pair of unknown parameters, i.e., an excited state absorption coefficients for 4I13/2 yields 4I9/2, (sigma) esa, and a cooperative upconversion coefficient for (4I13/2, 4I13/2) yields (4I9/2, 4I15/2), C, were included in the rate equations. They were estimated by fitting the simulated curves to the measured ones. The obtained values were 3 X 10-21 cm2 and 1 or 3 X 10-21 cm3/s for the (sigma) esa and C, respectively.