Abstract

The heat capacities (CP0) of corundum, periclase, anorthite, CaAl2Si2O8 glass, muscovite, pyrophyllite, KAISi3Oe glass, grossular, and NaAlSi3Oe glass have been determined to an accuracy of ±1.0 percent by differential scanning calorimetry between 350 and 1000 K. Our results have been combined smoothly with existing low-temperature heat capacity and entropy data, and fitted by least squares to the following equations (T in Kelvin and CP0 in J/mol. K):

 
CP0(anorthite)=516.80.09249T1.408×106T24588T1/2+4.188×105T2 (2981800 K)
 
CP0(CaAl2Si2O8glass)=375.2+0.03197T2.815×106T22459T1/2 (2981500 K)
 
CP0(muscovite)=917.70.08111T+2.834×106T210348T1/2 (2981000 K)
 
CP0(pyrophyllite)=679.70.06412T6902T1/25.997×105T2 (298800 K)
 
CP0(KALSI3O8 glass)=629.50.1084T+2.496×106T27210T1/2+1.928×105T2 (2981300 K)
 
CP0(grossular)=1633.30.7599T+9.113×106T220783T1/2+2.669×104T2 (2981200 K)
 
CP0(NaAlSi3O8 glass)=934.40.3891T+5.594×106T211820T1/2+1.476×104T2 (2981200 K)

The accuracy of the differential scanning calorimeter was checked by measuring the heat capacities of corundum and periclase and comparing these results with those published by the U. S. National Bureau of Standards. We have combined our calorimetrie data for muscovite, pyrophyllite, and grossular with data from recent equilibrium studies to derive improved values for ΔHf,2980 and ΔGf,2980 for muscovite, pyrophyllite, and grossular. Our values for ΔHf,2980 and ΔGf,2980 are -5971600±5180 J/mol and -5595500±5190 J/mol respectively for disordered 2M, muscovite, -5639800±3950 J/mol and -5265900±3960 J/mol respectively for pyrophyllite, and -6657100±4720 J/mol and -6295300±4730 J/mol respectively for grossular.

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