Crystallization of Barium Osumilite Glass

Abstract

The crystallization of stoichiometric barium osumilite (BaMg 2 Al 6 Si 9 O 30 ) glass manufactured by melting or by sol-gel processing using an all-alkoxide route (AAR) or a partial-alkoxide route (PAR) using mixed alkoxides and salts has been characterized by thermal methods, phase analysis, and microstructural analysis. In all glasses, crystallization with heat treatment at a finite heating rate (1 or 10 K/min) occurs via an initial phase separation, leading to regions devoid of and enriched in BaO. In PAR gel glass and melt glass, the BaO-deficient regions crystallize as µ-cordierite, but they appear to remain amorphous in AAR gel glass, in which hexacelsian is the first phase, to crystallize at the interface between the phase-separated regions. With further heat treatment, barium osumilite becomes the dominant phase. Crystallization with isothermal heat treatment at 1250°C leads to direct crystallization of barium osumilite in bulk and powder samples of melt glass, but not in bulk and powder samples of sol-gel glass, which again form precursor phases, such as µ-cordierite, ␣-cordierite, hexacelsian, and mullite. The crystallization mechanisms and morphologies are discussed here.

Study of the devitrification behaviour of a barium magnesium aluminosilicate glass-ceramic

“…4b), which has been previously reported during the devitrification of BaO-containing M 2 A 2 S 11 glasses 4 and BMAS glasses. 2 These previous studies suggested that the (0 0 1) and (4 2 0) planes of cordierite were parallel to the respective planes of osumilite, and that the epitaxial nucleation of cordierite on osumilite was caused by their similar lattice parameters: a is 9.770Å in ␣-cordierite and 10.160Å in Baosumilite.…”

“…M 2 A 2 S 7 crystal → M 2 A 2 S 5 crystal + 2 mol of vitreous SiO 2 (2) As mentioned in the beginning of Section 3, the BMAS glass devitrification behaviour is determined by the local glass composition. Therefore, when the glass was locally enriched in Mg, primary Mg-rich phases formed instead of the usual Ba- Fig.…”

“…This is attributed to the low thermal expansion coefficient (α = 2.8 × 10 −6 • C −1 in the 20-500 • C range) and good high-temperature resistance of Ba-osumilite (the osumilite melting point is T f ≈ 1370 • C). 1,2 For example, Ba-osumilite glass-ceramics have often been reinforced with continuous Nicalon ® SiC fibres due to the small thermal expansion coefficient mismatch between the fibres (α = 3.1 × 10 −6 • C −1 at 25 • C) and the osumilite-based matrix; the resulting SiC/BMAS composites combine a flexural strength of 400-700 MPa with a fracture toughness of 3-4 MPa m 1/2 , depending on the matrix microstructure and the fibre content. 1 The manufacturing of both strong and tough composites relies greatly on the understanding of the matrix crystallisation behaviour, which was limited and fragmented for the BMAS glass-ceramic.…”

“…1 The manufacturing of both strong and tough composites relies greatly on the understanding of the matrix crystallisation behaviour, which was limited and fragmented for the BMAS glass-ceramic. [1][2][3] This work tried to establish a good understanding of the BMAS glass devitrification.…”

Kinetics of Se75S25−xCdx glassy system using differential scanning calorimeter

“…Metallic glasses do not retain their atomic structure obtained on production and the rate of change is dependent on the conditions under which a sample is stored [2]. It has also been reported that the method of preparation of a silicate glass, by sol-gel or by conventional melting, affects its structure and therefore its crystallization behavior [3]. Moreover, it is suggested in many studies that the stability of metallic glasses is influenced by the production process and the composition, which lead to different initial structure and energy states [4].…”