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:697149

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.

• Sponsoring Organization: USDOE
• OSTI ID: 697149
• Journal Information: American Mineralogist, Journal Name: American Mineralogist Journal Issue: 9 Vol. 84; ISSN AMMIAY; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
CRYSTAL STRUCTURE
FORMATION HEAT
LITHIUM OXIDES
ORDER-DISORDER TRANSFORMATIONS
QUARTZ
SILICON OXIDES
SOLUTION HEAT