Thermochemistry of stuffed quartz-derivative phases along the join LiAlSiO[sub 4]-SiO[sub 2]

Journal Article · Wed Sep 01 04:00:00 EDT 1999 · American Mineralogist

DOI:https://doi.org/10.2138/am-1999-0913· OSTI ID:6063909

Xu, H; Heaney, P J; Navrotsky, A; Topor, L ^[1]; Liu, J ^[2]

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1. Princeton Univ., NJ (United States)
2. State Univ. of New York, Stony Brook, NY (United States)

Enthalpies of drop-solution ([Delta]H[sub drop-soln]) of a suite of stuffed quartz-derivative phases with the composition Li[sub 1[minus]x]Al[sub 1[minus]x]Si[sub 1+x]O[sub 4] (0 [le] x [le] 1) have been measured in molten 2PbO[center dot]B[sub 2]O[sub 3] at 974 K. Substitution of Si[sup 4+] for Li[sup +] + Al[sup 3+] results in more exothermic enthalpies of drop-solution, which is consistent with behavior seen in other crystalline and glassy aluminosilicates. Al/Si ordering serves to stabilize these phases, and long-range ordering for compositions with x approximately <0.3 can be discerned in both calorimetric data and in structural data obtained by electron and synchrotron X-ray diffraction (XRD). In contrast, a structural but not an energetic discontinuity is apparent at x [approx equal] 0.65, which corresponds to a compositionally induced [alpha]-[beta] quartz transition with a small enthalpy of transformation. An enthalpy for the Al/Si order-disorder reaction in [beta]-eucryptite was measured as 25.9 [+-] 2.6 kJ/mol. Standard molar enthalpies of formation of the stuffed quartz-derivative phases from constituent oxides ([Delta]H[sub f.ox][sup 0]) and elements ([Delta]H[sub f.el][sup 0]) at 298 K also are presented. [Delta]H[sub f.ox][sup 0] = [minus]69.78 [+-] 1.38 kJ/mol and [Delta]H[sub f.el][sup 0] = [minus]2117.84 [+-] 2.50 kJ/mol for [beta]-eucryptite, which are in good agreement with results previously determined by HF solution calorimetry at 346.7 K (Barany and Adami 1966). The enthalpies of formation of other compositions are reported for the first time.

• OSTI ID: 6063909
• Journal Information: American Mineralogist, Journal Name: American Mineralogist Vol. 84:9; ISSN AMMIAY; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602 -- Other Materials-- Structure &amp; Phase Studies
360606* -- Other Materials-- Physical Properties-- (1992-)
ALKALI METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CRYSTAL STRUCTURE
ENTHALPY
FORMATION HEAT
LITHIUM COMPOUNDS
LITHIUM OXIDES
MINERALS
ORDER-DISORDER TRANSFORMATIONS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
QUARTZ
REACTION HEAT
SILICON COMPOUNDS
SILICON OXIDES
SOLUTION HEAT
THERMODYNAMIC PROPERTIES