High-silica Porous Glass Research Articles

Kinetics of water vapor sorption on porous glass as a method of porometry

Equilibrium low temperature nitrogen adsorption and a new method based on the kinetics of water vapor sorption at room temperature are used for a comparative study of pore morphology of high-silica porous glass. The values of the total pore volume, the specific surfaces, the effective mesopore diameters, and the fraction of each mode in the total mesopore volume are established using both techniques. It is found that the rate of water vapor sorption at constant pressure grows in inverse ratio to the diameter of cylindrical menisci in pores. The time dependence of the volume of adsorbed water is linear, while the characteristic time of filling for each pore mode varies directly with the square of the effective pore mode diameter. The proposed new kinetic porometry technique based on analyzing water vapor adsorption kinetics at room temperature is quite simple as it requires no complicated vacuum equipment and allows the simultaneous examination of large numbers of porous material samples.

Structure and optical properties of photochromic quartz-like glass doped with silver halides

Photochromic quartz-like glasses (PCQGs) based on of high-silica porous glasses have been synthesized. The structure of PCQG plates have been investigated using the electron microscopy methods. Their optical properties (light transmission in the visible spectral range) before and after UV laser irradiation have also been investigated. It was demonstrated that a microcrystalline phase of silver halide had been formed in the bulk phase of the synthesized PCQG. Peaks of the plasmon resonance of quasi-metallic silver nanoparticles were founded on the spectral dependences of the optical density of PCQG subjected by UV laser irradiation.

Peculiarities of the formation of planar micro-optic elements on porous glass substrates under the effect of laser radiation followed by sintering

The theoretical and practical approaches to the formation of micro-optic elements (MOE) for the integrated optical communication on substrates made of different materials, including silicate glasses, have been reviewed. The applicability of high-silica porous glasses (PG) fabricated by a homogeneous acid leaching of two-phase alkali borosilicate glasses as basic matrices for laser formation of MOE of different types (microlenses and microchannels) has been discussed. It has been demonstrated that sintering laser-modified PGs at temperatures ensuring the collapse of the pore can be used to stabilize MOE optical properties. The results of choosing the time-temperature mode for sintering PG substrates with a planar MOE-strip waveguide (SW) providing the SW fixation on a completely sintered substrate were presented.

Adjusting valence state of europium in sintered porous glass by adding of aluminum and yttrium

We report on valence state adjusting of europium in porous glass by co-doping with aluminum or yttrium into porous glass. The influence of Al 3+ and Y 3+ on the emission intensity of Eu 3+ and Eu 2+ in sintered high-silica porous glass has been investigated. It is found that the emission intensity of Eu 3+ can be increased by adding of Y 3+ and Al 3+, and the emission intensity of Eu 2+ can be decreased by adding of Y 3+ and increased by Al 3+. At the same time, the emission peak position of Eu 2+ can also be changed by adding of Al 3+ or Y 3+. It is suggested that the adjusting of valence state and the peak position shift is relative to the optical basicity of glasses or crystal field strength around REs.

Influence of the composition and temperature of heat treatment of porous glasses on their structure and light transmission in the visible spectral range

The pore structure and light transmission of high-silica porous glasses in the visible spectral range have been investigated as a function of the heat treatment temperature and the composition of the initial two-phase alkali borosilicate glass. The character of light transmission in porous glasses has been analyzed in the framework of the concepts of structural features of their pore space and the processes occurring in the porous glass during heating. It has been demonstrated that an increase in the temperature of heat treatment of porous glasses with different compositions leads to an increase in the pore size and a decrease in their specific surface area (with a nearly constant total porosity), which is associated with the processes of overcondensation of pores due to the rearrangement and the change in the packing density of secondary silica particles. It has been revealed that the introduction of phosphate and fluoride ions into the initial sodium borosilicate glass results in an increase in the light extinction coefficient of porous glasses due to the increase in the sizes of phase-separated inhomogeneity regions in the initial two-phase glasses, the formation of larger pores, and the presence of nanosized microcrystalline phases in porous glasses.

Green and red high-silica luminous glass suitable for near- ultraviolet excitation

We report on the preparation of transparent and colorless green-and red-emitting luminous glasses by sintering high-silica porous glass impregnated with rare-earth ions. These kinds of glasses can be efficiently excited by near-UV sources. The fluorescence of the glasses under near-UV excitation is dependent on energy transfer processes. In order to obtain strong visible emission, it is necessary to co-dope some optically inert rare-earth ions into the glasses. The roles of the optically inert rare-earth ions are discussed.

Study of Self-Diffusion Process of Water Molecules in Porous Glass by Stimulated Spin Echo Method with Pulsed Field Gradients

The self-diffusion process of water molecules through high-silica porous glass has been studied for three samples with different pore diameters using a stimulated echo method with pulsed field gradients. It was found that the diffusion process over a large distance can be described as a Gaussian diffusion process and that the effective diffusion constant is proportional to the porosity of the high-silica glass sample.

Thermal and chemical properties of TiO2-SiO2 porous glass-ceramics

The thermal and chemical stability of porous glass-ceramics of the TiO2-SiO2 system have been investigated. Porous glass-ceramics containing both anatase and rutile had thermal expansion coefficients of 40 to 55 x 10−7 K−1 in the range 0 to 700° C. They remained porous up to 1000° C, while the pores of high-silica porous glass of Vycor type collapsed completely at that temperature. The high thermal stability of the porous glass-ceramics may be attributed to a high viscosity due to dispersed crystallites of anatase and rutile in the skeleton. Most of the anatase in the skeleton was transformed to rutile by heat treatment at 900° C, but some of it remained untransformed even after 6 h. Surface -OH groups identified by IR spectroscopy were removed by dehydration polycondensation with heating up to 900° C. The porous glass-ceramics were quite durable to alkali solution compared with high-silica porous glass. The excellent durability of these porous glass-ceramics was attributed to the large amount of TiO2 contained in the skeletal structure.

Sintering Temperature of Porous Glass and Transition Temperature of High Silica Glass

High silica porous glasses were prepared by varying acid treatment of phase-separated soda borosilicate glass and one of them was impregnated by sodium nitrate solutions. The porous glasses were heat treated to form nonporous glasses and the end point of their thermal shrinkage (sintering temperature) was determined. The glass transition temperature was determined for NaNO3-impregnated and sintered glasses. The glass transition temperature was linearly related to the sintering temperature and decreased linearly with increasing logarithm of sodium oxide content. ΔTg/ΔlogC, where Tg is the glass transition temperature and C is the content of water (-0.1wt%) or sodium oxide (0.1-3wt%) of nonporous glasses, was determined. Sodium oxide lowered the glass transition temperature more strongly than water. ΔTg/ΔlogC was calculated for pure silica glass and some silicate glasses from the data available in the literatures and compared with the results of the present work. ΔTg/ΔlogC for water decreased and that for sodium oxide increased with decreasing glass transition temperature.

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.

ポーラスガラスの利用

ポーラスガラスの利用

Nonuniform deposition of silica gel in high silica porous glass.

Du verre microporeux prepare par lixiviation acide de verre de borosilicate de sodium a phases separees presente des heterogeneites au centre. L'origine de ces heterogeneites a ete etudiee par observations au microscope electronique a balayage et par spectrometrie IR. Au cours de la lixiviation acide de la phase borate du verre, la silice presente dans la phase precipite partiellement sous forme de gel. Une partie de la silice dissoute, qui provient de la phase borate est transportee par l'ecoulement de l'acide et se concentre sur les pores formes dans l'etape finale de la lixiviation

Metastable liquid immiscibility and Vycor-type glass in phosphate-silicate systems

Substitution of Li+, Mg2+, Sr2+, Ba2+ and Zn2+ for 50 or 100% of Na+ in glass with composition 3Na2O·7P2O5·10SiO2 resulted in liquid immiscibility in some of the new glasses. Glasses containing SrO and BaO were studied more thoroughly, and a high-silica porous glass was obtained from 3SrO·7P2O5·10SiO2 glass by heat treatment at 500 to 700° C and subsequent leaching with 3N HCl. However, this porous glass proved incapable of sintering into a bulk glassy body, because of its high rate of cystallization.