Sol-gel synthesis of a nanoparticulate aluminosilicate precursor for homogeneous mullite ceramics

Abstract

An amorphous nanoparticulate aluminosilicate 3/2-mullite precursor has been synthesized and carefully characterized. The sol contained 2-nm particles of Q3(3Al) silica species together with six-coordinated alumina, which suggested an allophane-like structure of the nanoparticles. The sol remained stable for years, and formed an easily redispersible physical gel upon solvent evaporation. The gel crystallized to mullite at temperatures below 1000 °C, without going through any intermediate spinel phase. Thus, the nanoparticulate precursor is regarded as a homogeneous high-purity mullite precursor with a high Si–O–Al bond density, which is useful in the preparation of various nanostructured Al-rich aluminosilicate materials. The sols and gels were characterized by small-angle x-ray scattering, dynamic light scattering, x-ray diffraction, 27Al and 29Si magic-angle spinning (MAS) nuclear magnetic resonance spectroscopy, and differential thermal analysis.

Evolution of aluminosilicate structure and mullite crystallization from homogeneous nanoparticulate sol–gel precursor with organic additives

“…Mismatches in hydrolysis kinetics or low sol stability may induce heterogeneous regions within the gel (then denoted Type III precursor), [7][8][9] leading to the formation of an intermediate spinel phase at ∼1000 • C. 16 We have recently described a fast and an easy method for preparation of a homogeneous aluminosilicate/mullite high-purity precursor (of Type I) in the form of nanoparticles in a water-based sol that can remain stable for years. 17 The sol consists of partially hydrolysed 2 nm hydroxy-alkoxoaluminosilicate nanoparticles, structurally closely resembling a proto-imogolite allophane phase (PI/A), which crystallizes into a nanocrystalline transitional mullite with no spinel phase formation. The gel can easily be re-dispersed if dried at room temperature, indicating that interparticulate condensation reactions are slow.…”

Sol–gel derived aluminosilicate coatings on alumina as substrate for osteoblasts

“…T/Rmac was a thermally sprayed amorphous aluminosilicate, and the diphasic D/Smes coating contained heterogeneous c-Al 2 O 3 and SiO 2 nanophases. For the aluminosilicate coatings, the alkoxide sol-gel precursor solution was prepared from Si(OC 2 H 5 ) 4 (TEOS; 99%; ABCR, Germany), Al(NO 3 ) 3 AE 9H 2 O (ANN; P98.0%; Sigma-Aldrich, USA), and Al(O i C 3 H 7 ) 3 (AIP; +98%; ABCR) according to Leivo et al [17]. Briefly, the components were dissolved in water with the final molar ratio of TEOS:0.75ANN:2.25AIP:95H 2 O, and the as-received alkoxide precursor solution was aged for 1 day at room temperature followed by aging for 4 days under reflux at 60°C.…”

“…On the basis of the XRD, DTA, and AEM results, solgel derived aluminosilicate materials were chemically homogeneous [14][15][16][17], and the presence of transitional 2/ 1-mullite crystals in M/S and M/R was therefore typical. However, we did not find that the transitional nanocrystalline phase would have possessed a higher amount of osteoblast functioning than the plain amorphous one: in fact, the trend was more the reverse.…”

“…In a similar manner, the nanosized transitional mullite phase should improve the osteoblast functions of mullite. The formation of the amorphous aluminosilicate phase with subsequent crystallization of transitional mullite occurs if homogeneous 3Al 2 O 3 -2SiO 2 sol-gel precursors are carefully heat-treated at around 1000°C [14][15][16][17] and, in contrast to the conventional 3/2-mullite, the high-purity sol-gel derived transitional mullite is usually nanosized, with a slightly Al-rich 2Al 2 O 3 AE SiO 2 (2/1) composition. In addition to chemical and mineralogical composition, both surface physico-chemical and topographical features are of great importance in biomaterials [18][19][20].…”

Evaluation of the Compatibility of Repair Materials for Concrete Structures

“…Both narrow and wide dormant cracks (in dormant cracks width does not change over time may be repaired by routing and sealing, which is the simplest and most common technique for crack repair. Narrow, dormant cracks may be effectively sealed by epoxy injection (Do and Kim 2012;Iowa Department of Transportation 2008;Rodler et al 1989;Leivo et al 2006). In some cases concrete structural elements can be bonded together with repair materials.…”