Low-temperature Ti-containing 3:2 and 2:1 mullite nanocrystals from single-phase gels

• Published in: Journal of the European Ceramic Society 2007, Vol.27 (7), p.2655-2663
• Main Authors: Ruiz de Sola, Esther, Estevan, Francisco, Alarcón, Javier
• Format: Article
• Language: English
• Subjects: Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Microstructure-final; Mullite; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Physics; Solid solution; Sol–gel processes
• ISSN: 0955-2219; 1873-619X
• DOI: 10.1016/j.jeurceramsoc.2006.09.014

TiO 2-containig single-phase gels with (Al 2O 3 + TiO 2)/(SiO 2) molar ratios 3/2 and 2/1 were prepared by gelling mixtures of aluminium nitrate, tetraethylorthosilicate and titanium isopropoxide. Gels were fast heated at several temperatures up to 1100 °C. Dried and heated gels were characterized by differential thermal analysis (DTA), magic angle spinning nuclear magnetic resonance (MAS-NMR), X-ray powder diffraction (XRD), and scanning and transmission electron microscopies (SEM and TEM). Coupled DTA and XRD results of gels fast heated at 900 °C showed the crystallisation of two mullites as well as a small amount of alumina-silica spinel. 27Al NMR spectra showed the formation of pentacoordinated aluminium before mullite crystallization. The increase of lattice parameters of single-phase mullites heated at 1100 °C indicated that the amount of TiO 2 incorporated into the mullite structure increased on raising the amount of nominal TiO 2 in both series. SEM and TEM images of heated gels at 1100 °C displayed the formation of well-shaped parallelepiped of titanium-doped mullite nanocrystals with crystalline anisotropy.