RSC Advances / Thermodynamics of the double sulfates Na2M2+(SO4)2·nH2O (M = Mg, Mn, Co, Ni, Cu, Zn,n= 2 or 4) of the blödite-kröhnkite family
| Autor: | Majzlan, Juraj, Marinova, Delyana, Dachs, Edgar |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2020 |
| Předmět: |
Nickel sulfates
Cobalt alloys Manganese alloys Sodium alloys Engineering main heading Binary alloys Engineering uncontrolled terms Engineering controlled terms Stability margins Calorimetric methods Copper alloys Sodium sulfate Liquid water Enthalpies of formation Gibbs free energy Chemical stability Double sulfates Sulfur compounds General formulas |
| DOI: | 10.1039/d0ra09501j |
| Popis: | The double sulfates with the general formula Na2M2+(SO4)2·nH2O (M = Mg, Mn, Co, Ni, Cu, Zn,n= 2 or 4) are being considered as materials for electrodes in sodium-based batteries or as precursors for such materials. These sulfates belong structurally to the blödite (n= 4) and kröhnkite (n= 2) family and the M cations considered in this work were Mg, Mn, Co, Ni, Cu, Zn. Using a combination of calorimetric methods, we have measured enthalpies of formation and entropies of these phases, calculated their Gibbs free energies (ΔfG°) of formation and evaluated their stability with respect to Na2SO4, simple sulfates MSO4·xH2O, and liquid water, if appropriate. The ΔfG° values (all data in kJ mol−1) are: Na2Ni(SO4)2·4H2O: −3032.4 ± 1.9, Na2Mg(SO4)2·4H2O: −3432.3 ± 1.7, Na2Co(SO4)2·4H2O: −3034.4 ± 1.9, Na2Zn(SO4)2·4H2O: −3132.6 ± 1.9, Na2Mn(SO4)2·2H2O: −2727.3 ± 1.8. The data allow the stability of these phases to be assessed with respect to Na2SO4, MSO4·mH2O and H2O(l). Na2Ni(SO4)2·4H2O is stable with respect to Na2SO4, NiSO4and H2O(l) by a significant amount of ≈50 kJ mol−1whereas Na2Mn(SO4)2·2H2O is stable with respect to Na2SO4, MnSO4and H2O(l) only by ≈25 kJ mol−1. The values for the other blödite-kröhnkite phases lie in between. When considering the stability with respect to higher hydrates, the stability margin decreases; for example, Na2Ni(SO4)2·4H2O is still stable with respect to Na2SO4, NiSO4·4H2O and H2O(l), but only by ≈20 kJ mol−1. Among the phases studied and chemical reactions considered, the Na-Ni phase is the most stable one, and the Na-Mn, Na-Co, and Na-Cu phases show lower stability. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|