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Glass formation and characterization in the 3Al2O3·2SiO2-LaPO4 system

Guo Malloy, S; McMillan, PF; Petuskey, WT; (2016) Glass formation and characterization in the 3Al2O3·2SiO2-LaPO4 system. Journal of Non-Crystalline Solids , 451 pp. 77-83. 10.1016/j.jnoncrysol.2016.03.017. Green open access

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Abstract

Rare earth oxide–aluminate–phosphate–silicate (REAPS) glasses are useful precursors for ceramic-matrix-composites (CMCs) with important thermal and mechanical properties. It is important to determine the glass structure, relaxation and crystallization properties for designing and controlling CMC formation. Transparent 3Al2O3·2SiO2-LaPO4 glasses containing 25–80 mol% mullite (3Al2O3·2SiO2) component were prepared by quenching from high temperature melts using a containerless technique. Glass transformation and crystallization behavior were examined by differential scanning calorimetry and X-ray diffraction. The glass transition onset increased from 845 to 906 °C with mullite content. The temperature interval between Tg and crystallization was maximized at 200 °C for 50 mol% mullite glass. Below 40 mol% mullite, successive appearance of LaPO4 (monazite) and mullite gave rise to two crystallization peaks, while at higher mullite content, only one combined exotherm was observed. A glass structure model constructed from 27Al, 31P and 29Si magic angle spinning (MAS) NMR and Raman spectroscopy results indicated that Si4 + and P5 + remained tetrahedrally bonded while Al3 + ions were predominantly in four-fold coordination with some five-coordinated sites. The presence of La2O3 component resulted in an increased proportion of AlO4 tetrahedra. The PO4 polymerization state varied from Q3 to Q2 with increasing LaPO4 content. The SiO4, AlO4, and PO4 units form a continuous network with PO4 tetrahedra attached to aluminosilicate framework through two or three P–O–Al linkages. SiO4 tetrahedra crosslink with AlO4 tetrahedra to form Q4(4Al) and Q4(3Al) units. The glass structure model helps explain the crystallization sequence as a function of mullite content and the formation of different CMC textures.

Type: Article
Title: Glass formation and characterization in the 3Al2O3·2SiO2-LaPO4 system
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.jnoncrysol.2016.03.017
Publisher version: http://dx.doi.org/10.1016/j.jnoncrysol.2016.03.017
Language: English
Additional information: Copyright © 2016 Published by Elsevier B.V. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/.
Keywords: Ceramic-matrix-composites; Glass-ceramics; Mullite; Monazite; Al2O3–SiO2–LaPO4 glasses
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/1498976
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