29Si and27AIMAS-NMR spectroscopy of β-eucryptite (LiAlSiO4): The enthalpy of Si,Al ordering

Brian L. Phillips, X. U. Hongwu, Peter J. Heaney, Alexandra Navrotsky

Research output: Contribution to journalArticle

24 Citations (Scopus)

Abstract

By combining data from oxide melt solution calorimetry and 29Si MAS-NMR spectroscopy, the enthalpy for short-range Si.Al ordering in β-eucryptite (LiAlSiQ4) was determined for a series of samples prepared by glass annealing. Si.Al ordered β-eucryptite gives a single 29Si NMR peak for two unresolved crystallographic sites, but two distinct 27A1 resonances that differ in both chemical shift and quadrupolar coupling. Samples of β-eucryptite crystallized from glass contain additional 29Si NMR peaks, indicating significant levels of short-range Si, Al disorder. This disorder decreases exponentially with annealing time at 1173 K, from 0.55(±0.04) Al-O-Al linkages per formula unit after one hour to 0.05(±0.01) after 70.5 hours. The decrease in the concentration of A1-O-A1 linkages with annealing time correlates linearly with enthalpies of drop-solution in molten lead borate, giving an enthalpy of ΔHord = -26 ± 3 kJ/mol for the reaction: Al-O-Al + Si-O-Si → 2(Si-O-Al). Additional NMR results are presented for samples synthesized along the SiO2-Li AlSiO4 join (quartz to β-eucryptite). Solid solution samples with compositions 20 and 69 mol% quartz appear to have very few Al-O-Al linkages (<0.04 per formula unit).

Original languageEnglish (US)
Pages (from-to)181-188
Number of pages8
JournalAmerican Mineralogist
Volume85
Issue number1
DOIs
StatePublished - Jan 1 2000

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enthalpy
Nuclear magnetic resonance spectroscopy
nuclear magnetic resonance
Enthalpy
Quartz
annealing
spectroscopy
Nuclear magnetic resonance
linkages
Annealing
Glass
Borates
quartz
glass
Chemical shift
disorders
Calorimetry
Oxides
MAS
borate

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

Phillips, Brian L. ; Hongwu, X. U. ; Heaney, Peter J. ; Navrotsky, Alexandra. / 29Si and27AIMAS-NMR spectroscopy of β-eucryptite (LiAlSiO4) : The enthalpy of Si,Al ordering. In: American Mineralogist. 2000 ; Vol. 85, No. 1. pp. 181-188.
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29Si and27AIMAS-NMR spectroscopy of β-eucryptite (LiAlSiO4) : The enthalpy of Si,Al ordering. / Phillips, Brian L.; Hongwu, X. U.; Heaney, Peter J.; Navrotsky, Alexandra.

In: American Mineralogist, Vol. 85, No. 1, 01.01.2000, p. 181-188.

Research output: Contribution to journalArticle

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AB - By combining data from oxide melt solution calorimetry and 29Si MAS-NMR spectroscopy, the enthalpy for short-range Si.Al ordering in β-eucryptite (LiAlSiQ4) was determined for a series of samples prepared by glass annealing. Si.Al ordered β-eucryptite gives a single 29Si NMR peak for two unresolved crystallographic sites, but two distinct 27A1 resonances that differ in both chemical shift and quadrupolar coupling. Samples of β-eucryptite crystallized from glass contain additional 29Si NMR peaks, indicating significant levels of short-range Si, Al disorder. This disorder decreases exponentially with annealing time at 1173 K, from 0.55(±0.04) Al-O-Al linkages per formula unit after one hour to 0.05(±0.01) after 70.5 hours. The decrease in the concentration of A1-O-A1 linkages with annealing time correlates linearly with enthalpies of drop-solution in molten lead borate, giving an enthalpy of ΔHord = -26 ± 3 kJ/mol for the reaction: Al-O-Al + Si-O-Si → 2(Si-O-Al). Additional NMR results are presented for samples synthesized along the SiO2-Li AlSiO4 join (quartz to β-eucryptite). Solid solution samples with compositions 20 and 69 mol% quartz appear to have very few Al-O-Al linkages (<0.04 per formula unit).

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