| Theoretical Prediction of Gibbs Free Energies of Formation for Crystalline α-MOOH and α-M2O3 Based on a Linear Free-Energy Relationship |
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| 作者姓名： | SUN Xiaoming |
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| 作者单位： | 1 School of Marine Sciences, Sun Yat-Sen University, Guangzhou, Guangdong 510275, China； 2 Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510275, China； 3 Department of Earth Sciences, Sun Yat-Sen University, Guangzhou, Guangdong 510275, China |
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| 基金项目： | This work was jointly supported by the NSFC (no. 40473024 and 40343019), Project of the 11th and 10th Five-Year Research and Development of International Seabed (no. DYXM-115-02-1-11, PY105-01-04-13 and DY105-01-02-1), Project of Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry and South China Sea Institute of Oceanology, CAS (no. MSGL08-01, MSGLCAS03-4), Specialized Research Fund for the Doctoral Program of Higher Education (no. 20040558049), and the Fundamental Research Funds for the Central Universities. |
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| 摘 要： | In the present study, the modified Sverjensky–Molling equation, derived from a linear-free energy relationship, is used to predict the Gibbs free energies of formation of crystalline phases of α-MOOH (with a goethite structure) and α-M2O3 (with a hematite structure) from the known thermodynamic properties of the corresponding aqueous trivalent cations (M3+). The modified equation is expressed as ΔG0f,MVX=aMVXΔG0n,M3++bMVX+βMVXγM3+, where the coefficients aMVX, bMVX, and βMVX characterize a particular structural family of MvX (M is a trivalent cation M3+] and X represents the remainder of the composition of solid); γ3+ is the ionic radius of trivalent cations (M3+); ΔG0f,MVX is the standard Gibbs free energy of formation of MvX; and ΔG0n,M3+ is the non-solvation energy of trivalent cations (M3+). By fitting the equation to the known experimental thermodynamic data, the coefficients for the goethite family (α-MOOH) are aMVX=0.8838, bMVX=?424.4431 (kcal/mol), and βMVX=115 (kcal/mol.?), while the coefficients for the hematite family (α-M2O3) are aMVX=1.7468, bMVX=?814.9573 (kcal/mol), and βMVX=278 (kcal/mol.?). The constrained relationship can be used to predict the standard Gibbs free energies of formation of crystalline phases and fictive phases (i.e. phases that are thermodynamically unstable and do not occur at standard conditions) within the isostructural families of goethite (α-MOOH) and hematite (α-M2O3) if the standard Gibbs free energies of formation of the trivalent cations are known.
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| 关 键 词： | α-MOOH α-M2O3 Gibbs free energy theoretical prediction |
| 收稿时间： | 2010/12/1 0:00:00 |
Theoretical Prediction of Gibbs Free Energies of Formation for Crystalline α‐MOOH and α‐M2O3 Based on a Linear Free‐Energy Relationship |
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| Authors: | SUN Xiaoming |
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| Institution: | SUN Xiaoming~(1,2,3,) 1 School of Marine Sciences,Sun Yat-Sen University,Guangzhou,Guangdong 510275,China 2 Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering,Guangzhou 510275,China 3 Department of Earth Sciences,China |
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| Abstract: | In the present study, the modified Sverjensky–Molling equation, derived from a linear‐free energy relationship, is used to predict the Gibbs free energies of formation of crystalline phases of α‐MOOH (with a goethite structure) and α‐M2O3 (with a hematite structure) from the known thermodynamic properties of the corresponding aqueous trivalent cations (M3+). The modified equation is expressed as ΔG0f,MVX=aMVXΔG0n,M3++bMVX+βMVXγM3+, where the coefficients aMVX, bMVX, and βMVX characterize a particular structural family of MvX (M is a trivalent cation M3+] and X represents the remainder of the composition of solid); γ3+ is the ionic radius of trivalent cations (M3+); ΔG0f,MVX is the standard Gibbs free energy of formation of MvX; and ΔG0n,M3+ is the non‐solvation energy of trivalent cations (M3+). By fitting the equation to the known experimental thermodynamic data, the coefficients for the goethite family (α‐MOOH) are aMVX=0.8838, bMVX=–424.4431 (kcal/mol), and βMVX=115 (kcal/mol.Å), while the coefficients for the hematite family (α‐M2O3) are aMVX=1.7468, bMVX=–814.9573 (kcal/mol), and βMVX=278 (kcal/mol.Å). The constrained relationship can be used to predict the standard Gibbs free energies of formation of crystalline phases and Active phases (i.e. phases that are thermodynamically unstable and do not occur at standard conditions) within the isostructural families of goethite (α‐MOOH) and hematite (α‐M2O3) if the standard Gibbs free energies of formation of the trivalent cations are known. |
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| Keywords: | α‐MOOH α‐M2O3 Gibbs free energy theoretical prediction |
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