TY - JOUR
T1 - 29Si and27AIMAS-NMR spectroscopy of β-eucryptite (LiAlSiO4)
T2 - The enthalpy of Si,Al ordering
AU - Phillips, Brian L.
AU - Hongwu, X. U.
AU - Heaney, Peter J.
AU - Navrotsky, Alexandra
PY - 2000
Y1 - 2000
N2 - 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).
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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U2 - 10.2138/am-2000-0117
DO - 10.2138/am-2000-0117
M3 - Article
AN - SCOPUS:0034067011
SN - 0003-004X
VL - 85
SP - 181
EP - 188
JO - American Mineralogist
JF - American Mineralogist
IS - 1
ER -