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GEOREF RECORD

Thermochemistry of stuffed quartz-derivative phases along the join LiAlSiO (sub 4) -SiO (sub 2)

Hongwu Xu, Peter J. Heaney, Alexandra Navrotsky, Letitia Topor and Jun Liu
Thermochemistry of stuffed quartz-derivative phases along the join LiAlSiO (sub 4) -SiO (sub 2)
American Mineralogist (September 1999) 84 (9): 1360-1369

Abstract

Enthalpies of drop-solution (Delta H (sub drop-soln) ) of a suite of stuffed quartz-derivative phases with the composition Li (sub 1-x) Al (sub 1-x) Si (sub 1+x) O (sub 4) (0< or =x< or =1) have been measured in molten 2PbO.B (sub 2) O (sub 3) at 974 K. Substitution of Si (super 4+) for Li (super +) +Al (super 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 congruent to 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+ or -2.6 kJ/mol. Standard molar enthalpies of formation of the stuffed quartz-derivative phases from constituent oxides (Delta H (super 0) (sub f,ox) ) and elements (Delta H (super 0) (sub f,el) ) at 298 K also are presented. Delta H (super 0) (sub f,ox) = -69.78+ or -1.38 kJ/mol and Delta H (super 0) (sub f,el) = -2117.84+ or -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.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 84
Serial Issue: 9
Title: Thermochemistry of stuffed quartz-derivative phases along the join LiAlSiO (sub 4) -SiO (sub 2)
Affiliation: University of California at Davis, Department of Chemical Engineering and Materials Science, Davis, CA, United States
Pages: 1360-1369
Published: 199909
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 53
Accession Number: 1999-066383
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 7 tables
Secondary Affiliation: Pennsylvania State University, USA, United StatesPrinceton University, USA, United StatesState University of New York at Stony Brook, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 199922
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