Formation and processing of mesoporous barium titanate powders via the micelle template method
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Ren-Jay Lin and Syh-Yuh Cheng Materials Research Laboratories, Industrial Technology Research Institute, Chu-Tung, Hsinchu 300, Taiwan, Republic of China (Received 8 October 2005; accepted 5 January 2006)
Mesoporous barium titanate powders having a 100- to 300-nm size were prepared by hydration and condensation of titanium tetra-isopropoxide and barium precursors in the presence of an organic surfactant, tetradecylamine, which was used as a self-assembly micelle. The processing and sintering of these mesoporous barium titanate powders has been investigated. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to identify the structural characteristics and morphologies of the powders. Mesoporous wormhole-like powders with surface areas around 53 ∼ 108 m2/g could be obtained after removing the micelle organics by calcination at 400 °C for 3 h. Powders derived using barium hydroxide were found to form a larger pore size and a higher surface area. The addition of acetic acid was also effective in increasing the surface area. A formation mechanism for the mesoporous structure is depicted. Heat treatment caused the mesoporous spheres to shrink, and 155- ∼ 330-nm grain sizes were readily obtained after pressureless sintering at 900 ∼ 1000 °C for 1 h in air.
I. INTRODUCTION
There has been much interest in porous structures prepared by a templating method using surfactants.1–9 Surfactants above a critical micellar concentration in aqueous solution form a globular micelle, cylindrical micelle, and an ordered nanostructure of hexagonal and lamellar, depending on the concentration.5 One of the best known materials was mesoporous aluminosilicate (M41S), which was synthesized at Mobil in 1992.1–4 Using a selfassembly template and by manipulation of the solution conditions, metal oxide-based materials can be fabricated with uniform pore sizes in the 5 to 100 Å range. Mesoporous silica having an ordered nanostructure such as a hexagonal array of cylindrical micropores (MCM-41) and lamellar structure (MCM-50) are well known.5 Mesoporous titania was first synthesized using alkyl phosphate surfactants and titanium isopropoxide bisacetylacetonate in 1995.6–9 High surface areas were usually achieved upon the removal of the template. Metal oxide materials such as TiO2, ZrO2, WO3, CeO2, etc. with mesoand macro-size pores have been investigated intensively
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0131 J. Mater. Res., Vol. 21, No. 4, Apr 2006
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and applied in electromagnetics, photoelectronics, and high-surface-area catalysis.9–11 A method for the preparation of mesoporous titania powders was reported by Antonelli.12 The mesoporous structure was achieved by the hydrolysis and condensation of titanium tetraisopropoxide (TTIP) on surfactants such as dodecylamine, which was used as a template. Because of the order pore arrangement, a high surface area up to 700 ∼ 1000 m2/g was obtained.1
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