A thermodynamic prediction on the stability of the nukundamite + chalcopyrite and bornite + pyrite assemblages

1994 ◽  
Vol 58 (391) ◽  
pp. 235-245 ◽  
Author(s):  
Shoji Kojima ◽  
Teiichi Ueno
Keyword(s):  
Free Energy ◽  
Thermochemical Treatment ◽  
Experimental Result ◽  
Temperature Range ◽  
Thermodynamic Prediction ◽  
Free Energy Of Formation ◽  
Present Experimental Result ◽  
The Stability ◽  
Reported Data ◽  
Kuroko Deposits

AbstractA thermodynamic prediction of the Gibbs free energy of formation (ΔGfo) of nukundamite (empirical composition Cu5.5FeS6.5) was made in order to specify whether the nukundamite + chalcopyrite or the bornite + pyrite assemblage is stable in the Cu-Fe-S system. The results of calculations using previously reported data of ΔGfo values of some Cu-Fe-sulphide minerals in equilibrium with nukundamite indicate that the total free energy of the nukundamite + chalcopyrite assemblage is appreciably higher than that of the bornite + pyrite assemblage in the temperature range 250–400°C. This means that nukundamite + chalcopyrite is a metastable assemblage under common ore-forming conditions.The occurrence of nukundamite is not uncommon in the Fijian kuroko deposits in contrast to the Japanese kuroko deposits. A thermochemical treatment for this phenomenon leads to the interpretation that the black ore containing nukundamite in the Fijian deposit was formed under relatively highsulphidation and low-pH conditions. This suggestion is in good agreement with the present experimental result that the bornite + pyrite assemblage was produced in the temperature range 350–250°C by using near-neutral hydrothermal solutions.

The stability, free energy and heat of formation of imogolite

Clay Minerals ◽  
1979 ◽  
Vol 14 (2) ◽  
pp. 103-107 ◽  
Author(s):  
V. C. Farmer ◽  
B. F. L. Smith ◽  
J. M. Tait
Keyword(s):  
Free Energy ◽  
Heat Of Formation ◽  
Free Energy Of Formation ◽  
The Stability ◽  
Energy Of Formation

AbstractFrom equilibrium silica concentrations over imogolite and boehmite at 100–155°C, the heat and free energy of the reaction (HO)3Al2O3SiOH + H2O ⇌ 2AlOOH + Si(OH)4 have been obtained: ΔH°r (298·15 K)=38·6 ± 4·1, ΔG°r (298·15 K) = 26.8 ± 1·1 kJ mol−1, and hence the heat and free energy of formation of imogolite: ΔH°f (298·15 K) = −3189·6 ± 4·1, ΔG°f (298·15 K) = − 2926·7 ± 1·1 kJ mol−1 These results are consistent with observations indicating that imogolite, halloysite and gibbsite can co-exist in soils, but that imogolite is metastable relative to either halloysite or gibbsite in the long term. At temperatures above 25°C there is a widening range of silica concentrations in which imogolite is more stable than halloysite, although both are metastable relative to kaolinite.

Equilibrium in the formation of barium carbonate from barium sulphate

1976 ◽  
Vol 54 (24) ◽  
pp. 3872-3875
Author(s):  
Harry Horlings ◽  
Donald S. Scott ◽  
John R. Wynnyckyj
Keyword(s):  
Free Energy ◽  
Barium Carbonate ◽  
Equilibrium Constants ◽  
Barium Sulphate ◽  
Heat Of Reaction ◽  
Temperature Range ◽  
Free Energy Of Formation ◽  
Energy Of Formation

Heat of reaction and free energy of formation at 25 °C were determined from experimental equilibrium yields for the reaction[Formula: see text]in an aqueous solution.The values are 5045 and 1927 cal/mol respectively. Equilibrium constants for the reaction were determined over a temperature range from 20 to 193 °C.

Examining sharp restart in a Monte Carlo method for the linearized Poisson–Boltzmann equation

2020 ◽  
Vol 26 (3) ◽  
pp. 223-244
Author(s):  
W. John Thrasher ◽  
Michael Mascagni
Keyword(s):  
Monte Carlo ◽  
Free Energy ◽  
Monte Carlo Algorithm ◽  
Significant Bias ◽  
Poisson Boltzmann ◽  
Electrostatic Free Energy ◽  
Poisson Boltzmann Equation ◽  
The Stability ◽  
Potential Methods ◽  
The Individual

AbstractIt has been shown that when using a Monte Carlo algorithm to estimate the electrostatic free energy of a biomolecule in a solution, individual random walks can become entrapped in the geometry. We examine a proposed solution, using a sharp restart during the Walk-on-Subdomains step, in more detail. We show that the point at which this solution introduces significant bias is related to properties intrinsic to the molecule being examined. We also examine two potential methods of generating a sharp restart point and show that they both cause no significant bias in the examined molecules and increase the stability of the run times of the individual walks.

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