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Charles A Geiger - One of the best experts on this subject based on the ideXlab platform.
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Almandine: Lattice and non-lattice heat capacity behavior and standard thermodynamic properties
American Mineralogist, 2012Co-Authors: Edgar Dachs, Charles A Geiger, Artur BenisekAbstract:The heat capacity of three synthetic polycrystalline Almandine garnets (ideal formula Fe3Al2Si3O12) and one natural Almandine-rich single crystal was measured. The samples were characterized by optical microscopy, electron microprobe analysis, X-ray powder diffraction, and Mossbauer spectroscopy. Measurements were performed in the temperature range 3 to 300 K using relaxation calorimetry and between 282 and 764 K using DSC methods. All garnets show a prominent λ-type heat-capacity anomaly at low temperatures resulting from a paramagnetic-antiferromagnetic phase transition. For two Fe3+-free or nearly Fe3+-free synthetic Almandines, the phase transition is sharp and occurs at 9.2 K. Almandine samples that have ~3% Fe3+ show a λ-type peak that is less sharp and that occurs at 8.0 ± 0.2 K. The low- T C P data were adjusted slightly using the DSC results to improve the experimental accuracy. Integration of the low- T C P data yields calorimetric standard entropy, S∘ , values between 336.7 ± 0.8 and 337.8 ± 0.8 J/(mol·K). The smaller value is recommended as the best S∘ for end-member stoichiometric Almandine, because it derives from the “best” Fe3+-free synthetic sample. The lattice (vibrational) heat capacity of Almandine was calculated using the single-parameter phonon dispersion model of Komada and Westrum (1997), which allows the non-lattice heat capacity ( C ex) behavior to be modeled. An analysis shows the presence of an electronic heat-capacity contribution ( C el, Schottky anomaly) superimposed on a larger magnetic heat-capacity effect ( C mag) around 17 K. The calculated lattice entropy at 298.15 K is S vib = 303.3 J/(mol·K) and it contributes about 90% to the total standard entropy at 298 K. The non-lattice entropy is S ex = 33.4 J/(mol·K) and consists of S mag = 32.1 J/(mol·K) and S el = 1.3 J/(mol·K) contributions. The C P behavior for Almandine above 298 K is given by the polynomial [in J/(mol·K)]: C P = 649.06 ( ± 4 ) - 3837.57 ( ± 122 ) · T - 0.5 - 1.44682 ( ± 0.06 ) · 10 7 · T - 2 + 1.94834 ( ± 0.09 ) · 10 9 · T - 3 which is calculated using the measured DSC data together with one published heat-content datum determined by transposed-drop calorimetry along with a new determination in this work that gives H 1181K − H 302K = 415.0 ± 3.2 kJ/mol. Using our S∘ value and the C P polynomial for Almandine, we derived the enthalpy of formation, Δ H °f, from an analysis of experimental phase equilibrium results on the reactions Almandine + 3rutile = 3ilmenite + sillimanite + 2quartz and 2ilmenite = 2Fe + 2rutile + O2. A Δ H °f = −5269.63 kJ/mol was obtained.
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A powder infrared spectroscopic investigation of garnet binaries in the system Mg 3 Al 2 Si 3 O 12 - Fe 3 Al 2 Si 3 O 12 - Mn 3 Al 2 Si 3 O 12 - Ca 3 Al 2 Si 3 O 12
European Journal of Mineralogy, 1998Co-Authors: Charles A GeigerAbstract:The powder IR phonon spectra of synthetic garnets of the six binaries in the system Mg3Al2Si30i2 (Pyrope - Py) - Fe3Al2Si30i2 (Almandine - Al) - Mn3Al2Si3Oi2 (Spessartine - Sp) - Ca3AbSi30i2 (Grossular - Gr) have been recorded and analyzed. Between 14 and 17 Fiu-symmetry infrared active modes were observed for the different garnet end members and can, to a first approximation, be assigned to internal SiU4 vibrations and external lattice vibrations of the S1O4 tetrahedron and the Al3+ and X2+-site cations. This description is limited by mode mixing which is most pronounced for the lowest frequency modes. Two mode behavior is observed for X2+-cation translations for most of the binaries. The site-group and factor-group splittings have been calculated for all six binaries. For the Almandine/pyrope-grossular binaries, the factor-group splittings suggest that Si04 group vibrational interactions do not change linearly between the two end-members. No evidence in the IR spectra is found for long range X2+-cation order and all synthetic solid solutions are long-range disordered. The IR spectra provide information on the possible lattice heat capacities and entropies of mixing for the six solid solutions. The frequency changes of the lowest frequency external modes of pyrope-grossular and Almandine-grossular garnets are consistent with the proposal of excess lattice entropies of mixing at low temperatures. The Almandine-spessar tine binary should be thermodynamically ideal, while the almaridine-pyrope, spessartine-p yrope and spessartine- grossular binaries could show some excess lattice properties. The higher frequency modes above 400 cm"1 of the solid solution compositions can be estimated well from a linear interpolation between the two end-members. This is consistent with the proposal that no excess lattice entropies of mixing should be present in garnet solid solutions above 300 K.
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Raman spectra of silicate garnets
Physics and Chemistry of Minerals, 1998Co-Authors: B. A. Kolesov, Charles A GeigerAbstract:The single-crystal polarized Raman spectra of four natural silicate garnets with compositions close to end-members Almandine, grossular, andradite, and uvarovite, and two synthetic end-members spessartine and pyrope, were measured, along with the powder spectra of synthetic pyrope-grossular and Almandine-spessartine solid solutions. Mode assignments were made based on a comparison of the different end-member garnet spectra and, in the case of pyrope, based on measurements made on additional crystals synthesized with 26Mg. A general order of mode frequencies, i.e. R(SiO4)>T(metal cation)>T(SiO4), is observed, which should also hold for most orthosilicates. The main factors controlling the changes in mode frequencies as a function of composition are intracrystalline pressure (i.e. oxygen-oxygen repulsion) for the internal SiO4-vibrational modes and kinematic coupling of vibrations for the external modes. Low frequency vibrations of the X-site cations reflect their weak bonding and dynamic disorder in the large dodecahedral site, especially in the case of pyrope. Two mode behavior is observed for X-site cation vibrations along the pyrope-grossular binary, but not along the Almandine-spessartine join.
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Mn 3 Al 2 Si 3 O 12 spessartine and Ca 3 Al 2 Si 3 O 12 grossular garnet; structural dynamic and thermodynamic properties
American Mineralogist, 1997Co-Authors: Charles A Geiger, Thomas ArmbrusterAbstract:The structures of synthetic Mn 3 Al 2 Si 3 O 12 spessartine and Ca 3 Al 2 Si 3 O 12 grossular garnet have been refined using single-crystal X-ray diffraction methods at 100 K, 293 K, and 500-550 K. The divalent X-site cations, located in large dodecahedral sites, show measurable anisotropic dynamic disorder in contrast to the rigid vibrational behavior of the SiO 4 tetrahedra and AlO 6 octahedra. The amplitudes of vibration of Mn (super 2+) in spessartine are similar to those of Fe (super 2+) of Almandine, in the plane of the longer X-O(4) bonds, and both are about twice that of Ca (super 2+) in grossular, despite the lighter mass of the latter. Heat capacities measured between 300 and 1000 K on synthetic polycrystalline spessartine and two natural nearly end-member spessartine crystals are similar to those of Almandine. In addition, the IR active modes of spessartine at low frequencies are very similar to those of Almandine suggesting that their heat capacities are also similar at lower temperatures. The low-energy phonon spectra of pyrope and grossular are probably considerably distinct from the two transition metal-containing garnets as suggested by their different low frequency IR active modes, reflecting the different bonding properties for Mg and Ca in garnet. The large pressure-temperature stability field of spessartine, relative to the other aluminosilicate garnets, does not appear to be due to any sort of intrinsic entropy stabilization.
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Molar volumes of mixing of Almandine-pyrope and Almandine-spessartine garnets and the crystal chemistry and thermodynamic-mixing properties of the aluminosilicate garnets
American Mineralogist, 1997Co-Authors: Charles A Geiger, Anne FeenstraAbstract:The aluminosilicate garnet binaries Almandine-pyrope and Almandine-spessartine were studied by powder X-ray and 57 Fe Mossbauer methods. Refinements of the unit-cell con- stants along the Almandine-pyrope join show that the volumes of mixing are ideal. Those of the Almandine-spessartine join show very small positive deviations from ideality, which can be fitted with a symmetric model having an interaction parameter ofW V 5 0.24 (60.05) cm 3 /mol. Mossbauer spectra recorded at 298 and 77 K show the presence of small amounts of (6) Fe 31 , which in the case of Almandine-pyrope garnets is also measurable from micro- probe analyses. The amount of Fe 31 is generally less than 3.5% of the total Fe for the Almandine-pyrope garnets and 1-2% for Almandine-spessartine garnets. The molar volumes of mixing of the aluminosilicate garnet binaries are interpreted using a crystal-chemical model involving rigid tetrahedral rotation. The degree of tetrahedral rotation is not linear with increasing size of the divalent X-site cation for the four common aluminosilicate garnet end-members or along the solid solution binary pyrope-grossular. The vibrational entropies of mixing should be positively correlated with the volumes of mixing in the case of garnet, but the masses of the X-site cations must also be considered. The phonon density of states at low energies should show the vibrations of the weakly bonded divalent cations and rigid-unit modes related to tetrahedral rotation. Positive excess vibrational entropies of mixing along a binary could result from increased amplitudes and lower frequencies of vibration of the smaller of the two X-site cations substituting within larger and more distorted dodecahedral sites, as compared to the X site in the smaller volume end-member.
Hui Zhong - One of the best experts on this subject based on the ideXlab platform.
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high adsorption capacity and super selectivity for pb ii by a novel adsorbent nano humboldtine Almandine composite prepared from natural Almandine
Chemosphere, 2020Co-Authors: Qiang Zeng, Yongji Huang, Leiming Huang, Wei Sun, Hui ZhongAbstract:This study firstly reported a novel nano humboldtine/Almandine composite (NHLA composite) prepared directly from Almandine through one-pot method based on the interaction of Almandine and oxalic acid. The formation of humboldtine/Almandine binary phase from natural Almandine was determined by X-ray diffraction. Analysis of scanning & transmission electron microscope showed that large amount of nano humboldtine with uniform size (average size of 15.59 nm) were loaded on the Almandine sheets. Compared with raw minerals, Pb(Ⅱ) removal capacity of synthesized composite was significantly increased, demonstrating that the main active ingredient for Pb(Ⅱ) removal was humboldtine phase rather than Almandine itself. Pb(Ⅱ) adsorption capacity was increased with the increasing of initial pH value or temperature. Langmuir isotherm and Pseudo-second order kinetic equation were well fitted with experimental results and the maximum Pb(Ⅱ) adsorption capacity from Langmuir isotherm was 574.71 mg/g at temperature of 25 °C. In addition, heavy metal removal experiments in coexisting systems of multiple heavy metal ions manifested that the composite had a high selectivity for Pb(Ⅱ) adsorption. Ion exchange, surface complexation and electrostatic interaction have involved in the Pb(Ⅱ) adsorption. The synthesized composite was considered as a low cost, high efficiency, super selectivity and easy to mass production material for Pb(Ⅱ) adsorption from solution.
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High adsorption capacity and super selectivity for Pb(II) by a novel adsorbent: Nano humboldtine/Almandine composite prepared from natural Almandine.
Chemosphere, 2020Co-Authors: Qiang Zeng, Yongji Huang, Leiming Huang, Wei Sun, Hui ZhongAbstract:This study firstly reported a novel nano humboldtine/Almandine composite (NHLA composite) prepared directly from Almandine through one-pot method based on the interaction of Almandine and oxalic acid. The formation of humboldtine/Almandine binary phase from natural Almandine was determined by X-ray diffraction. Analysis of scanning & transmission electron microscope showed that large amount of nano humboldtine with uniform size (average size of 15.59 nm) were loaded on the Almandine sheets. Compared with raw minerals, Pb(Ⅱ) removal capacity of synthesized composite was significantly increased, demonstrating that the main active ingredient for Pb(Ⅱ) removal was humboldtine phase rather than Almandine itself. Pb(Ⅱ) adsorption capacity was increased with the increasing of initial pH value or temperature. Langmuir isotherm and Pseudo-second order kinetic equation were well fitted with experimental results and the maximum Pb(Ⅱ) adsorption capacity from Langmuir isotherm was 574.71 mg/g at temperature of 25 °C. In addition, heavy metal removal experiments in coexisting systems of multiple heavy metal ions manifested that the composite had a high selectivity for Pb(Ⅱ) adsorption. Ion exchange, surface complexation and electrostatic interaction have involved in the Pb(Ⅱ) adsorption. The synthesized composite was considered as a low cost, high efficiency, super selectivity and easy to mass production material for Pb(Ⅱ) adsorption from solution.
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A novel composite of Almandine supported humboldtine nanospheres, in situ synthesized from natural Almandine, possesses high removal efficiency of Cr(VI) over a wide pH range
Journal of hazardous materials, 2019Co-Authors: Qiang Zeng, Yongji Huang, Leiming Huang, Haibei Wang, Hui ZhongAbstract:Preparing a cost-effective material which can been applied in a wide pH range is very crucial for the remediation of Cr(Ⅵ) polluted water. In this study, a novel material, Almandine/humboldtine nanospheres (AHN) composites, was synthesized directly from Almandine by one-pot method. Characterizations of XRD and SEM/TEM showed that the structure changes of Almandine to nano-humboldtine leaded to significant increase of Cr(Ⅵ) removal capacities. And 96.45% of Cr(Ⅵ) was removed by AHN-24 composite at pH value of 3, initial Cr(Ⅵ) concentration of 20 mg/L, temperature of 298.15 K and dosage of 0.6 g/L. Furthermore, Cr(Ⅵ) removal capacity was only decreased from 48.23 mg/g to 34.33 mg/g when the initial pH value increased from 3 to 11, which demonstrated that the synthesized composite had a wide pH application range in Cr(Ⅵ) removal. The thermodynamic parameters (ΔG0 0 and ΔS0 > 0) illustrated that Cr(VI) removal process was spontaneous and endothermic. FTIR and XPS revealed that the Cr(Ⅵ) removal mechanisms included reduction-precipitation and reduction-complexation. Combined with cost analysis, all of results implied that the synthesized composites were a high efficient and low cost material for Cr(Ⅵ) pollution remediation in a wide pH range.
Artur Benisek - One of the best experts on this subject based on the ideXlab platform.
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Almandine: Lattice and non-lattice heat capacity behavior and standard thermodynamic properties
American Mineralogist, 2012Co-Authors: Edgar Dachs, Charles A Geiger, Artur BenisekAbstract:The heat capacity of three synthetic polycrystalline Almandine garnets (ideal formula Fe3Al2Si3O12) and one natural Almandine-rich single crystal was measured. The samples were characterized by optical microscopy, electron microprobe analysis, X-ray powder diffraction, and Mossbauer spectroscopy. Measurements were performed in the temperature range 3 to 300 K using relaxation calorimetry and between 282 and 764 K using DSC methods. All garnets show a prominent λ-type heat-capacity anomaly at low temperatures resulting from a paramagnetic-antiferromagnetic phase transition. For two Fe3+-free or nearly Fe3+-free synthetic Almandines, the phase transition is sharp and occurs at 9.2 K. Almandine samples that have ~3% Fe3+ show a λ-type peak that is less sharp and that occurs at 8.0 ± 0.2 K. The low- T C P data were adjusted slightly using the DSC results to improve the experimental accuracy. Integration of the low- T C P data yields calorimetric standard entropy, S∘ , values between 336.7 ± 0.8 and 337.8 ± 0.8 J/(mol·K). The smaller value is recommended as the best S∘ for end-member stoichiometric Almandine, because it derives from the “best” Fe3+-free synthetic sample. The lattice (vibrational) heat capacity of Almandine was calculated using the single-parameter phonon dispersion model of Komada and Westrum (1997), which allows the non-lattice heat capacity ( C ex) behavior to be modeled. An analysis shows the presence of an electronic heat-capacity contribution ( C el, Schottky anomaly) superimposed on a larger magnetic heat-capacity effect ( C mag) around 17 K. The calculated lattice entropy at 298.15 K is S vib = 303.3 J/(mol·K) and it contributes about 90% to the total standard entropy at 298 K. The non-lattice entropy is S ex = 33.4 J/(mol·K) and consists of S mag = 32.1 J/(mol·K) and S el = 1.3 J/(mol·K) contributions. The C P behavior for Almandine above 298 K is given by the polynomial [in J/(mol·K)]: C P = 649.06 ( ± 4 ) - 3837.57 ( ± 122 ) · T - 0.5 - 1.44682 ( ± 0.06 ) · 10 7 · T - 2 + 1.94834 ( ± 0.09 ) · 10 9 · T - 3 which is calculated using the measured DSC data together with one published heat-content datum determined by transposed-drop calorimetry along with a new determination in this work that gives H 1181K − H 302K = 415.0 ± 3.2 kJ/mol. Using our S∘ value and the C P polynomial for Almandine, we derived the enthalpy of formation, Δ H °f, from an analysis of experimental phase equilibrium results on the reactions Almandine + 3rutile = 3ilmenite + sillimanite + 2quartz and 2ilmenite = 2Fe + 2rutile + O2. A Δ H °f = −5269.63 kJ/mol was obtained.
Thomas Armbruster - One of the best experts on this subject based on the ideXlab platform.
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Mn 3 Al 2 Si 3 O 12 spessartine and Ca 3 Al 2 Si 3 O 12 grossular garnet; structural dynamic and thermodynamic properties
American Mineralogist, 1997Co-Authors: Charles A Geiger, Thomas ArmbrusterAbstract:The structures of synthetic Mn 3 Al 2 Si 3 O 12 spessartine and Ca 3 Al 2 Si 3 O 12 grossular garnet have been refined using single-crystal X-ray diffraction methods at 100 K, 293 K, and 500-550 K. The divalent X-site cations, located in large dodecahedral sites, show measurable anisotropic dynamic disorder in contrast to the rigid vibrational behavior of the SiO 4 tetrahedra and AlO 6 octahedra. The amplitudes of vibration of Mn (super 2+) in spessartine are similar to those of Fe (super 2+) of Almandine, in the plane of the longer X-O(4) bonds, and both are about twice that of Ca (super 2+) in grossular, despite the lighter mass of the latter. Heat capacities measured between 300 and 1000 K on synthetic polycrystalline spessartine and two natural nearly end-member spessartine crystals are similar to those of Almandine. In addition, the IR active modes of spessartine at low frequencies are very similar to those of Almandine suggesting that their heat capacities are also similar at lower temperatures. The low-energy phonon spectra of pyrope and grossular are probably considerably distinct from the two transition metal-containing garnets as suggested by their different low frequency IR active modes, reflecting the different bonding properties for Mg and Ca in garnet. The large pressure-temperature stability field of spessartine, relative to the other aluminosilicate garnets, does not appear to be due to any sort of intrinsic entropy stabilization.
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Single-crystal X-ray structure study of synthetic pyrope Almandine garnets at 100 and 293 K
American Mineralogist, 1992Co-Authors: Thomas Armbruster, Charles A Geiger, George A. LagerAbstract:The crystal structures of synthetic pyrope (Mg3AI2Si3012),Almandine (FeAI2Si3012), and the solid-solution garnet compositions PY8o-Alm2o, PY6o-Alm4o, and PY2o-Alm8o have been refined in space group Ia1d from high-precision X-ray diffraction data with sin 0/>..> 0.4 A-I measured at 100 and 293 K. There is no indication of lower symmetry for pyrope, Almandine, or solid-solution members. Experimentally determined atomic coordinates and displacement parameters for the solid-solution compositions are in good agreement with those linearly interpolated from the end-members. Thus there are no apparent structural features that could account for substantial nonideal enthalpies of mixing in the system pyrope-Almandine. The tetrahedral rotation angle is inversely correlated with the X-O distance. Fe2t substitution on the eight-coordinated X site of pyrope, or increasing temperature, decreases the rigid tetrahedral rotation in garnet. The large and anisotropic displacement parameters for the X-site cations in garnet are mainly a result of anisotropic thermal vibrations along the longer X-O bonds, which produce nonrigid polyhedral behavior for the dodecahedral site. The tetrahedra and octahedra behave as rigid bodies. These strong vibrations of the former give rise to the relatively large heat capacities and third-law entropies in garnet. Previous proposals concerning subsite dodecahedral ordering in pyrope must be revised.
Jiuhua Chen - One of the best experts on this subject based on the ideXlab platform.
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equation of state of pyrope Almandine solid solution measured using a diamond anvil cell and in situ synchrotron x ray diffraction
Physics of the Earth and Planetary Interiors, 2014Co-Authors: Shu Huang, Jiuhua ChenAbstract:Abstract The pressure–volume relations of three synthetic garnet samples along pyrope–Almandine (Py–Alm) join were measured at ambient temperature and high pressures up to 7, 21 and 19 GPa for Py83Alm17, Py54Alm46 and Py30Alm70, respectively. The obtained P–V data were fitted to the third order Birch–Murnaghan equation of state (EOS). The ambient cell volumes V0 of the three samples were measured to be 1511(1), 1515(2), and 1526(1) A3 respectively. With fixed pressure derivative of the isothermal bulk modulus K′ at 4.3, isothermal bulk moduli K0 of the three samples were determined to be 172(4), 174(2), and 183(2) GPa respectively. These results confirm that Almandine content (iron substitution) increase the bulk modulus of the garnet join following a nearly ideal mixing model. The relation between bulk modulus and Almandine mole fraction (n) in this garnet join is derived to be K0 = 170 + 15 n. These data can be used to contribute to construction of compositional model of earth mantle.
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Equation of state of pyrope–Almandine solid solution measured using a diamond anvil cell and in situ synchrotron X-ray diffraction
Physics of the Earth and Planetary Interiors, 2014Co-Authors: Shu Huang, Jiuhua ChenAbstract:Abstract The pressure–volume relations of three synthetic garnet samples along pyrope–Almandine (Py–Alm) join were measured at ambient temperature and high pressures up to 7, 21 and 19 GPa for Py83Alm17, Py54Alm46 and Py30Alm70, respectively. The obtained P–V data were fitted to the third order Birch–Murnaghan equation of state (EOS). The ambient cell volumes V0 of the three samples were measured to be 1511(1), 1515(2), and 1526(1) A3 respectively. With fixed pressure derivative of the isothermal bulk modulus K′ at 4.3, isothermal bulk moduli K0 of the three samples were determined to be 172(4), 174(2), and 183(2) GPa respectively. These results confirm that Almandine content (iron substitution) increase the bulk modulus of the garnet join following a nearly ideal mixing model. The relation between bulk modulus and Almandine mole fraction (n) in this garnet join is derived to be K0 = 170 + 15 n. These data can be used to contribute to construction of compositional model of earth mantle.