Fabrication and characterization of mesoporous borosilicate glasses with different boron contents
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an Liua) State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Shanghai, 200050 People’s Republic of China
Jiacheng Wang State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Shanghai, 200050 People’s Republic of China; and Graduate School of the Chinese Academy of Sciences, Beijing, 100039 People’s Republic of China (Received 30 September 2006; accepted 20 February 2007)
A series of wormhole-like mesoporous borosilicate glasses (MBSGs) with different compositions has been prepared by a combination of surfactant templating, sol-gel methods, and evaporation-induced self-assembly processes. Small-angle x-ray diffraction, high-resolution transmission electron microscopy, and N2 sorption isotherms analysis showed that all the MBSGs prepared possess the mesoporous structure. However, the stability of the mesoporous structure is strongly affected by the boron contents. When boron content was increased, boric acid was found in the final product, and the mesoporous structure was partially degraded. The formation and loss of boric acid through the whole process may account for the partial collapse of the mesostructure.
I. INTRODUCTION
An increasing number of studies in the fields of heterogeneous catalysis,1 solid phase biochemistry,2 confined matter,3 optical chemosensors,4 and membrane technology5,6 have evoked new interest in the science and industry of porous glasses in recent years. The porous glasses have some special properties that distinguish them from other porous silicates. The most significant feature is their very flexible geometric form, such as beads, rods, fibers, hollow fibers, ultrathin membranes etc. This allows them to have many applications. Borosilicate glasses are commercially important for their chemical, electrical, and optical properties. They have high chemical resistance and are nearly ideal for immobilizing highly radioactive nuclear waste.7 They are better insulators than silica for microelectronics because the addition of boron can raise the dielectric constant.8 Also, incorporation of boron oxide lowers refractive index of silica, and is therefore of interest for planar optical waveguides.9 Borosilicate glass coatings have also
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0251 1834 J. Mater. Res., Vol. 22, No. 7, Jul 2007 http://journals.cambridge.org Downloaded: 13 Jul 2014
been used as a doping source for making p-n junctions.10,11 Porous glasses consisting almost entirely of silica (96%) have been prepared by leaching products of phaseseparated melt-derived alkali borosilicate glasses and have been reviewed by Enke et al.12 Since the pioneering work of the Mobil scientists,13,14 great progress has been made in mesoporous materials. Recently, a kind of less ordered wormhole-like mesoporous materials has been developed.15–18 Although lacking regular long-range channel packing order, the wormhole-like mesopores exhibit
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