Thermochemistry of stuffed quartz-derivative phases along the join LiAlSiO{sub 4}-SiO{sub 2}
- Princeton Univ., NJ (United States)
- 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, Vol. 84, Issue 9; Other Information: PBD: Sep 1999
- Country of Publication:
- United States
- Language:
- English
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