Geology topics

Bruce S. Hemingway

Publications and source records attributed to Bruce S. Hemingway.

8 recordsLinked to original sources

USGS1989

Heat capacities and entropies from 8 to 1000 K of langbeinite (K 2 Mg 2 (SO 4 ) 3 ), anhydrite (CaSO 4 ) and of gypsum (CaSO 4 ·2H 2 O)

Heat capacities of K 2 Mg 2 (SO 4 ) 3 (langbeinite) and CaSO 4 (anhydrite) were measured from approximately 8 to 1000 K by combined adiabatic shield calorimetry (8-365 K) and differential scanning calorimetry (350-1000 K). Heat capacities were also measured on natural crystals of gypsum (CaSO 4 · 2H 2 O) between 8.1 and 323.5 K. The molar entropies at 298.15 K, S m o (298.15 K), are 378.8 ± 0.6, 107.4 ± 0.2 and 193.8 ± 0.3 J K −1 mol −1 for langbeinite, anhydrite and gypsum, respectively. The heat capacity in J K −1 mol −1 of langbeinite can be represented by the equation C p,m o (K 2 Mg 2 (SO 4 ) 3 T ) = 535.9 + 0.11011 T -1.0200 × 10 6 / T 2 -4.909 × 10 −5 T 2 -4040.2/ T 0.5 between 300 and 1000 K with an average deviation of ± 0.4%. For anhydrite the heat capacity between 300 and 1000 K is given by C p,m o (CaSO 4 , T ) = 372.8 - 0.1574 T +1.695 × 10 6 / T 2 + 7.993 × 10 −5 T 2 - 4330.8/ T 0.5 with an average deviation of ±0.4%. Combining our heat-capacity and entropy data with the solution calorimetric results of Kelley et al. (U.S. Bur. Mines Tech. Paper, 625, 1941) yields an equilibrium temperature for the reaction gypsum → anhydrite + 2 water of 314.7 K (41.5 ° C). Our observations are in agreement with the conclusions of Speer and Salje (Phys. Chem. Miner., 13 (1986) 17); we see no evidence in our heat capacity measurements for the transformation of cubic langbeinite (P2 1 3) to a low temperature orthorhombic (P2 1 2 1 2 1 ) form as is seen in the isostructural Co, Zn, Ca, Mn and Cd langbeinites. Although Bond (Bell Sys. Tech. J., 22 (1943) 145) reported that langbeinite was piezoelectric at room temperature, we found no evidence in our C p o measurements for a Curie temperature above which langbeinite would no longer be piezoelectric.

Thermochimica Acta↗

USGS1987

Heat capacity and thermodynamic properties of andradite garnet, Ca 3 Fe 2 Si 3 O 12 , between 10 and 1000 K and revised values for ΔfGom (298.15 K) of hedenbergite and wollastonite

The heat capacity of synthetic andradite garnet (Ca 3 Fe 2 Si 3 O 12 ) was measured between 9.6 and 365.5 K by cryogenic adiabatic calorimetry and from 340 to 990 K by differential scanning calorimetry. At 298.15 K C o p , m and S o m are 351.9 ± 0.7 and 316.4 ± 2.0 J/(mol·K), respectively. Andradite has a λ-peak in C o p , m with a maximum at 11.7 ± 0.2 K which is presumably associated with the antiferromagnetic ordering of the magnetic moments of the Fe 3+ ions. The Gibbs free energy of formation, Δ f G o m (298.15 K) of andradite is −5414.8 ± 5.5 kJ/mol and was obtained by combining our entropy and heat capacity data with the known breakdown of andradite to pseudowollastonite and hematite at ≈ 1410 to 1438 K. From a reexamination of the calcite + quartz = wollastonite equilibrium data we obtained Δ f H o m (298.15 K) = − 1634.5 ± 1.8 kJ/mol for wollastonite. Between 300 and 1000 K the molar heat capacity of andradite can be represented by the equation C o p , m = 809.24 - 7.025 × 10−2 T − 7.403 × 10 3 T −0.5 − 6.789 × 10 5 T −2. We have also used our thermochemical data for andradite to estimate the Gibbs free energy of formation of hedenbergite (CaFeSi 2 O 6 ) for which we obtained Δ f G o m (298.15 K ) = −2674.3 ± 5.8 kJ/mol.

Geochimica et Cosmochimica Acta↗

USGS1977

Enthalpies of formation of low albite (NaAlSi 3 O 8 ), gibbsite (Al(OH) 3 ), and NaAlO 2 ; revised values for Δ H ° f,298 and Δ G ° f,298 of some aluminosilicate minerals

The enthalpies of formation from the elements Δ H ° t , of low albite, analbite, NaAlSi 3 O 8 glass, gibbsite (Al(OH) 3 ), and NaAlO 2 , have been determined by hydrofluoric acid solution calorimetry from measurements of the heats of solution, Δ H ° soln , of low albite, NaAlO 2 , SiO 2 , Al(OH) 3 , Al, H 2 O, NaCl, and HC1-12.731H 2 O in 20.1 weight percent HF(aq) at temperatures between 303.15 and 348.15 K. At 298.15 K the enthalpies of formation, Δ H ° f,298 , for low albite, analbite, NaAlSi 3 O 8 glass, gibbsite ( Al(OH) 3 ), and NaAlO 2 are -3 935 115±3415, -3 924 235±3640, -3 875 455±3700, ±1293130±1190, and 1135 990±1255 J mol -1 , respectively. Our values for the enthalpies of formation of low albite, analbite, and for NaAlSi 3 O 8 glass are approximately 13 810 J mol -1 more negative than the values calculated by D. R. Waldbaum in 1968. Our value for the enthalpy of formation of gibbsite at 298.15 K is 11234 J more negative than the value of R. Barany and K. K. Kelley obtained in 1961. The standard Gibbs free energies of formation, Δ G ° f,298 for low albite, analbite, and gibbsite calculated from the above enthalpies and the appropriate entropy data are -3 711 715±3435, -3 706 500±3660, and -1154 890±1200 J mol -1 , respectively. The enthalpy of solution of Standard Reference Material 1654, α-quartz (37 to 74 μm), in 20.1 wt percent HF(aq) is -137 737±209 J mol -1 at 333.15 K. This value is approximately 1255 J less negative than the value obtained by King in 1951 and 1952 for material that has a mean particle diameter of less than 5 μm and that has been used by the U.S. Bureau of Mines in their determinations of the enthalpies of formation of many silicates. Revised values of the enthalpies and Gibbs free energies of formation are presented for some aluminosilicate minerals, based upon this new data for Δ H ° f,298 of gibbsite and the heat of solution of α-quartz.