Uniformly porous MgTi2O5 with narrow pore-size distribution: in situ processing, microstructure and thermal expansion behavior

Abstract

Porous ceramics based on refractory double oxides are promising for light-weight structural components and high-temperature filter materials. In this study, porous MgTi 2 O 5 ceramics with pseudobrookite-type structure have been prepared by in situ processing (viz. reactive sintering). High-temperature XRD revealed the in situ reaction behavior of the mixed powder, and indicated suitable sintering temperatures to obtain single phase MgTi 2 O 5 (²1000°C). Uniformly porous MgTi 2 O 5 ceramics with very narrow pore-size distribution at the diameter of ³1 µm were obtained by the pyrolytic reactive sintering at 10001200°C, where decomposed CO 2 gas from a carbonate source acted as an intrinsic pore forming agent. Thermal expansion behavior of bulk porous MgTi 2 O 5 (porosity: 42%) is also discussed.©2010 The Ceramic Society of Japan. All rights reserved.Key-words : MgTi 2 O 5 , Pseudobrookite, Karrooite, Pore-size distribution, In-situ process, High-temperature XRD, Thermal expansion [Received May 31, 2010; Accepted September 16, 2010] Multiple oxide ceramics with orthorhombic pseudobrookitetype structure (expressed as Me 3 O 5 ) generally have low average (bulk) thermal expansion coefficients among oxides. 1)3) In the pseudobrookite structure, one axis (a-axis in Cmcm notation, or c-axis in Bbmm) has negative or very-small thermal expansion. Such a strong expansion anisotropy induces the formation of microcracks, resulting in the low bulk thermal expansion. 1)Among pseudobrookite oxides, aluminum titanate (Al 2 TiO 5 , AT), has been most eagerly studied as a thermal-shock resistant material.1)11) However, undoped-Al 2 TiO 5 tends to decompose into Al 2 O 3 and TiO 2 at elevated temperatures; 12),13) due to the large distortion of MeO 6 -octahedra, Al 2 TiO 5 phase is metastable below 1200°C. Furthermore, microcracks induced by the strong thermal-expansion anisotropy gradually degrades mechanical properties.MgTi 2 O 5 (karrooite, MT 2 ) also has orthorhombic pseudobrookite-type crystal structure and shows relatively low thermal expansion ( Table 1 31) In this paper, high-temperature X-ray diffractometry for the in situ reaction, effect of sintering temperature on microstructure, and thermal expansion behavior of porous MgTi 2 O 5 are described.Similarly to previously reported UPC-3D (uniformly porous ceramic/composite with three dimension network structure), 33)37) carbonate is used as a starting material; decomposed CO 2 gas, emitted during the one-step pyrolytic reacting sintering, forms very uniform open porous structure. Commercially available MgCO 3 (basic) powder (approx. 3MgCO 3 Mg(OH) 2

Magnesium dititanate (MgTi2O5) with pseudobrookite structure: a review

“…This two-step reaction has been confirmed in our recent study using in situ high-temperature x-ray diffraction [23,24]. [70].…”

“…Since MgTi 2 O 5 has relativity high thermal stability among pseudobrookite-type phases, Al 2 TiO 5 -MgTi 2 O 5 solid solution has been investigated [17][18][19][20][21][22]. Moreover, our group has studied porous MgTi 2 O 5 as a third-generation diesel particulate filter material with well-balanced properties, such as low thermal expansion, low cost, high-temperature stability and potentially good mechanical properties [23][24][25][26]. Furthermore, MgTi 2 O 5 is a promising buffer layer between a Si substrate and Pt thin film [27] as well as a red-emitting phosphor (MgTi 2 O 5 : Eu) [28].…”

Morphology Control of Pseudobrookite-Type MgTi₂O₅ Powders by LiF Doping

“…Similarly to our previous work [6,7,9], commercially available MgCO 3 (basic) powder (99.9% purity, Kojundo Chemical Laboratory Co. Ltd., Saitama, Japan), TiO 2 anatase powder (99.9% purity, Kojundo Chemical Laboratory Co. Ltd.), and LiF powder (99.9%, Wako Pure Chemical Ind., Ltd, Osaka, Japan) were used as the starting materials. LiF acts as a mineralizer.…”

“…Magnesium dititanate (MgTi 2 O 5 ), with pseudobrookite-type structure, also has characteristic unidirectional low-thermal expansion, however, it is less crystallographically anisotropic and more thermally stable than Al 2 TiO 5 [1]. Suzuki et al have recently reported uniformly porous MgTi 2 O 5 ceramics with 3-D network structure [6][7][8][9]. By controlling the stoichiometry and the liquid phase content, idiomorphic MgTi 2 O 5 grains were formed [9].…”

Semiconductor MgTiO₃, MgTi₂O₅ and Mg₂TiO₄ Double-Oxide Electrodes for Dye-Sensitized Solar Cells

“…Similarly to our previous works [5][6][7][8] O molecules, quantitative analysis of the starting powder was performed by thermogravimetry and differential thermal analysis (TG-DTA). Based on the compositional calibration using TG-DTA data, MgCO 3 (basic) and TiO 2 powders (nominally, Mg:Ti = 1:1, 1:2 and 2:1 in mole fraction) were wet-ball milled in ethanol for 24h.…”