Silica Hollow Fiber Research Articles

Enhanced thermal performance of fibrous insulation containing nonhomogeneous fibers

This paper evaluates the applicability of nonhomogeneous fibers for improving the thermal insulation properties of fiber matrix composites. Hollow silica fibers and silica fibers coated with alumina and silicon are considered for enhancing the surface reflectance and thermal radiative resistance of fibrous composites in which fibers are oriented parallel to planar boundaries. Analytical models are developed to determine the influence of coating material and thickness on these radiative characteristics. Numerical results reveal that silicon-coated silica fibers are most effective in increasing the insulation capacity of a fiber matrix. The results also show that the radiative resistance can be tailored to exhibit the desired spectral variation by combining an appropriate proportion of coated fibers with different coating thicknesses. The present results establish the feasibility of utilizing silicon-coated silica fibers to substantially enhance the thermal insulation capacity of fibrous composites.

Adsorption, permeation, and diffusion of gases in microporous membranes. I. Adsorption of gases on microporous glass membranes

Adsorption of CO 2, H 2O, C 2H 4, CH 4, N 2, C 2H 5OH, and CH 2Cl 2 in microporous silica hollow fiber membranes was studied at temperatures of 30°C and 70°C and at pressures up to 1.3 MPa. The experimental date were fitted with Langmuir, Dubinin-Radushkevic, and Freundlich isotherms. The best fitting model was found to be the Dubinin-Radushkevich isotherm. Based on the fitting results the total under investigation. No capillary condensation of the water and ethanol vapors was observed in the microporous fibers. The limits for the pore diameter, d, of the membrane deduced from the study were 5 < d < 20 Å.

Hollow Fiber Inorganic Membranes for Gas Separations

Abstract Pure gas permeabilities of He, H2, CO2, N2, and CO were measured for microporous silica hollow fiber membranes as a function of temperature. The transport mechanism for gas permeation is clearly non-Knudsen since several heavier gases permeate faster than lighter gases. An excellent correlation is obtained between permeability and kinetic diameter of the penetrant. The proposed mass transfer mechanism is a combination of surface diffusion and molecular sieving. High ideal separation factors (permeability ratios) are observed at 343 K for H2/N2 and H2/CO of 163 and 62.4, respectively, which compare very favorably with polymeric and molecular sieve gas separation membranes.

Attenuation of incoherent infrared radiation in hollow sapphire and silica waveguides

The attenuation of incoherent infrared radiation for wavelengths from 6 to 20 microm was investigated for hollow sapphire and silica waveguides suitable for applications in spectroscopy and thermometry. A low-attenuation region was exhibited between 9.6 and 17.2 microm for hollow sapphire fibers and between 7.25 and 9.5 microm for hollow silica fibers as a result of the cladding index of refraction dipping below that of the air core (n approximately 1). Losses have been characterized as a function of fiber diameter, launch conditions, and waveguide bend radius for cladding regions of both n > 1 and n < 1. In addition, the remote infrared sensing capability of the hollow waveguides was demonstrated by the detection of CO(2) in N(2) by utilizing hollow sapphire fibers capped with ZnSe windows.

Broadband infrared generation in liquid-bromine-core optical fibers

A new Raman-gain medium suitable for use throughout the infrared spectral region is described. Hollow silica fibers with liquid-bromine cores are shown to have very large Raman-gain coefficients (gamma=1.7x10(-8)cm/W at 1.1 microm with a Raman shift of 312 cm(-1)). The liquid-bromine core, being a homonuclear diatomic material, has no first-order infrared absorption, and transparency between 1 and 16 microm has been verified. Broadband infrared radiationbetween 1.1 and 4 microm was generated by stimulated Raman scattering in bromine-core fibers pumped with 1.06- and 2.11-microm radiation.

Infrared generation by means of multiple-order stimulated Raman scattering in CCl_4-and CBrCl_3-filled hollow silica fibers

Near-infrared and midinfrared radiation has been generated by means of multiple-order stimulated Raman scattering in hollow-core silica fibers filled with CBrCl(3) and CCl(4) and pumped by Nd:YAG laser radiation. Radiation between 1.2 and 2.3 microm has been generated in 300-cm-long, 12-microm core-diameter liquid-filled fibers using peak powers of 11 kW. Single-mode liquid-core waveguides were constructed by using CCl(4)-CBrCl(3) mixtures of adjustable refractive index.