Heat capacity and phase equilibria of almandine, Fe[sub 3]Al[sub 2]Si[sub 3]O[sub 12]

Journal Article · Wed Sep 01 00:00:00 EDT 1993 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(93)90315-N· OSTI ID:5121807

Anovitz, L M ^[1]; Essene, E J; Metz, G W; Westrum, Jr, E F ^[2]; Bohlen, S R ^[3]; Hemingway, B S ^[4]

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1. Univ. of Arizona, Tucson, AZ (United States)
2. Univ. of Michigan, Ann Arbor, MI (United States)
3. Geological Survey, Menlo Park, CA (United States)
4. Geological Survey, Reston, VA (United States)

The heat capacity of a synthetic almandine, Fe[sub 3]Al[sub 2]Si[sub 3]O[sub 12], was measured from 6 to 350 K using equilibrium, intermittent-heating quasi-adiabatic calorimetry and from 420 to 1000 K using differential scanning calorimetry. These measurements yield Cp[sub 298] = 342.80 [+-] 1.4 J/mol[center dot]K and S[degrees][sub 298] = 342.60 J/mol[center dot]K. Moessbauer characterizations show the almandine to contain less than 2 [+-] 1% of the total iron as Fe[sup 3+]. X-ray diffraction studies of this synthetic almandine yield a = 11.521 [+-] 0.001 [angstrom] and V[degrees][sub 298] = 115.11 [+-] 0.01 cm[sup 3]/mol, somewhat smaller than previously reported. The low-temperature Cp data indicate a lambda transition at 8.7 K related to an antiferromagnetic-paramagnetic transition with T[sub N] = 7.5 K. Modeling of the lattice contribution to the total entropy suggests the presence of entropy in excess of that attributable to the effects of lattice vibrations and the magnetic transition. This probably arises from a low-temperature electronic transition (Schottky contribution).

• DOE Contract Number: FG02-90ER14115
• OSTI ID: 5121807
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 57:17; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALUMINIUM SILICATES
PHASE STUDIES
SPECIFIC HEAT
IRON SILICATES
CHEMICAL REACTIONS
FREE ENTHALPY
ALUMINIUM COMPOUNDS
ENERGY
IRON COMPOUNDS
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SILICATES
SILICON COMPOUNDS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
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