Chemical composition and Gibbs standard free energy of formation of Fe(II)-Fe(III) hydroxysulphate green rust and Fe(II) hydroxide

Clay Minerals ◽  
1999 ◽  
Vol 34 (3) ◽  
pp. 499-510 ◽  
Author(s):  
Ph. Refait ◽  
C. Bon ◽  
L. Simon ◽  
G. Bourrié ◽  
F. Trolard ◽  
...  
Keyword(s):  
Free Energy ◽  
Chemical Composition ◽  
Chemical Potential ◽  
Oxidation Process ◽  
Standard Free Energy ◽  
Free Energy Of Formation ◽  
Pure Phase ◽  
The One ◽  
Ph Metry ◽  
Energy Of Formation

AbstractThe redox potential and pH of aerated suspensions of iron(II) hydroxide in sulphate–containing aqueous solutions are measured during the oxidation process. Plateaux corresponding to the equilibrium conditions between Fe(OH)2(s) and Fe(II)-Fe(III) hydroxysulphate GR2(SO2-4)(s) on the one hand, and between GR2(SO2-4)(s) and FeOOH(s) on the other hand, are displayed. Potentiometry, voltammetry, pH-metry and Mössbauer spectroscopy are applied to follow all reactions. The thermodynamic meaning of the measured potential of the first plateau which corresponds to the GR2(SO2-4)(s)/Fe(OH)2(s) equilibrium is demonstrated. The chemical composition of GR2(SO2-4)(s) is found to be FeII4 FeIII2(OH)12SO4·nH2O all along the oxidation process, implying that this compound must be considered as a pure phase with a well-defined composition. The Gibbs standard free energy of formation or chemical potential μ°[GR2(SO2-4)(s)] in ‘anhydrous form’ (n = 0) is determined at −3790±10 kJ mol-1. A consistent value of μ°[Fe(OH)2(s)] at −490±1 kJ mol-1 is obtained.

Estimation of the Standard Free Energy of Formation of Bastnasite, REFCO3

2019 ◽  
Vol 36 (1) ◽  
pp. 227-233 ◽  
Author(s):  
Isehaq Al-Nafai ◽  
Hojong Kim ◽  
Kwadwo Osseo-Asare
Keyword(s):  
Free Energy ◽  
Standard Free Energy ◽  
Free Energy Of Formation ◽  
Energy Of Formation

High Temperature Electrochemical Determination of the Thermodynamic Stability of the Iron-Rich, Iron-Niobium Intermetallic Phase

1969 ◽  
Vol 24 (10) ◽  
pp. 1580-1585 ◽  
Author(s):  
Giovanni B. Barbi
Keyword(s):  
Free Energy ◽  
Intermetallic Phase ◽  
Standard Free Energy ◽  
Chemical Oxidation ◽  
Electrochemical Determination ◽  
Electrolytic Cell ◽  
Galvanic Cells ◽  
Free Energy Of Formation ◽  
Energy Of Formation

Abstract A non-stationary technique of e.m.f. measurements after polarization of solid galvanic cells, previously applied to the determination of the standard free energy of formation of metal oxides, has been extended to intermetallic phases. The chief condition of applicability of this technique to intermetallic compounds is that the rates of recombination of the cathodic reduction products to yield the stable intermetallic phase be high as compared with that of chemical oxidation at the interface with the solid intermediate electrolyte, due to oxygen impurities in the gas phase. In particular, the solid electrolytic cell:(y values expressing the ε-phase iron-rich boundary compositions according to different authors investigations) was examined.Values of the standard free energy of formation of Fe7-yNb2 from the elements, ranging between-3.77+0.72-10-3 T and -5.66+1.09 · 10-3 T kcal/atom were found.

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