Bischofit
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Autoren: Hans-Jürgen Schwarz
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| Bischofit[1][2][3] | |
| Mineralogische Salzbezeichnung | Bischofit |
| Chemische Bezeichnung | Magnesiumchlorid Hexahydrat |
| Trivialname | |
| Chemische Formel | MgCl2•6H2O |
| Hydratformen | |
| Kristallsystem | monoklin |
| Deliqueszenzfeuchte 20°C | 33,1% |
| Löslichkeit(g/l) bei 20°C | 5,75 mol/kg |
| Dichte (g/cm³) | 1,57 g/cm3 |
| Molares Volumen | 129,6 cm3/mol |
| Molare Masse | 203,30 g/mol |
| Transparenz | |
| Spaltbarkeit | keine |
| Kristallhabitus | |
| Zwillingsbildung | |
| Phasenübergang | |
| Chemisches Verhalten | |
| Bemerkungen | zersetzt sich bei 116-118°C hygroskopisch bis zerfließend |
| Kristalloptik | |
| Brechungsindices | nx =1,495 ny = 1,509 nz = 1,528 |
| Doppelbrechung | Δ = 0,003 |
| Optische Orientierung | positiv |
| Pleochroismus | |
| Dispersion | 79° |
| Verwendete Literatur | |
| [Steiger.etal:2014]Autor / Verfasser: Steiger, Michael; Charola A. Elena; Sterflinger, Katja Buchtitel: Stone in Architecture Kapitel: 4 Herausgeber: Siegesmund S. and Snethlage R. Seiten: 223-316 Verlag: Springer Verlag Berlin Heidelberg Titel: Weathering and Deterioration Webadresse: https://link.springer.com/chapter/10.1007/978-3-642-45155-3_4 Jahr: 2014  [Broul.etal:1981]Autor / Verfasser: Broul M., Nyvlt J.; Soehnel O.Herausgeber: Elsevier Verlag: Elsevier Titel: Solubility in organic two component systems Jahr: 1981 [Dana:1951]Autor / Verfasser: Dana J.D.Edition: 7 Herausgeber: Dana E.S. Verlag: Wiley & Sons Titel: Dana's System of Mineralogy Band: 2 Jahr: 1951 [Steiger.etal:2011a]Autor / Verfasser: Steiger, M.; Linnow, K.; Ehrhardt, D.; Rohde, M. Journal / Magazin: Geochimica et Cosmochimica Act Notiz: We report new measurements of equilibrium relative humidities for stable and metastable hydration–dehydration equilibria involving several magnesium sulfates in the MgSO4·nH2O series. We also report a comprehensive thermodynamic treatment of the system including solution properties and experimental data from the published literature, i.e. solubilities, heat capacities and additional decomposition humidities. While for some magnesium sulfate hydrates solubility data in the binary system MgSO4–H2O are sparse, there is a reasonable database of solubility measurements of these hydrates in the ternary MgCl2–MgSO4–H2O and the quaternary reciprocal Na+–Mg2+–Cl−–SO42−–H2O systems. To make these data suitable for the determination of solubility products, we parameterized a Pitzer ion interaction model for the calculation of activity coefficients and water activities in mixed solutions of these systems and report the ion interaction parameters for the Na+–Mg2+–Cl−–SO42−–H2O system. The model predicted solubilities in the reciprocal system are in very good agreement with experimental data. Using all available experimental data and the solution model an updated phase diagram of the MgSO4–H2O system covering the whole temperature range from about 170 to 473 K is established. This treatment includes MgSO4·H2O (kieserite), MgSO4·4H2O (starkeyite), MgSO4·5H2O (pentahydrite), MgSO4·6H2O (hexahydrite), MgSO4·7H2O (epsomite) and MgSO4·11H2O (meridianiite). It is shown that only kieserite, hexahydrite, epsomite and meridianiite show fields of stable existence while starkeyite and pentahydrite are always metastable. Due to sluggish kinetics of kieserite formation, however, there is a rather extended field of metastable existence of starkeyite which makes this solid a major product in dehydration reactions. The model predicted behavior of the magnesium sulfates is in excellent agreement with observations reported in the literature under terrestrial temperature and relative humidity conditions. We also discuss the implications of the new phase diagram for sulfates on Mars. Nummer: 12 Seiten: 3600-3626 Titel: Decomposition reactions of magnesium sulfate hydrates and phase equilibria in the MgSO4-H2O and Na+-Mg2+-Cl--SO42--H2O systems with implications for Mars Band: 75 Jahr: 2011
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Lösungsverhalten[Bearbeiten]
Die Löslichkeit von Magnesiumchlorid in Wasser im Temperaturbereich von -40 bis 80 °C ist in Abbildung 1 gezeigt. Die Löslichkeit von Bischofit bei 20 °C beträgt 5,75 mol/kg.
Hygroskopizität[Bearbeiten]
Das Phasendiagramm des Systems MgCl2-H2O ist in Abbildung 2 gezeigt. Neben Bischofit gibt es in dem betrachteten Temperaturbereich von -40 bis 80 °C noch zwei weitere stabile Hydratstufen. Das Octa- und das Dodecahydrat sind bei niedrigen Temperaturen relevant.
| 0°C | 10°C | 20°C | 30°C | 40°C | 50°C |
| 34,1%r.F. | 33,7%r.F. | 33,1%r.F. | 32,4%r.F. | 31,5%r.F. | 30,5%r.F. |
Weblinks[Bearbeiten]
- ↑ http://webmineral.com/data/Bischofite.shtml gesehen 29.07.2010
- ↑ http://www.mindat.org/min-681.html gesehen 29.07.2010
- ↑ http://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Bischofit gesehen 29.07.2010
Literatur[Bearbeiten]
| [Broul.etal:1981] | Elsevier (Hrsg.) Broul M., Nyvlt J.; Soehnel O. (1981): Solubility in organic two component systems, %edition%, Elsevier, %address%, %pages%, %url%, %doi% | |
| [Dana:1951] | Dana E.S. (Hrsg.) Dana J.D. (1951): Dana's System of Mineralogy, 7, Wiley & Sons, %address%, %pages%, %url%, %doi% | |
| [Steiger.etal:2011a] | Steiger, M.; Linnow, K.; Ehrhardt, D.; Rohde, M. (2011): Decomposition reactions of magnesium sulfate hydrates and phase equilibria in the MgSO4-H2O and Na+-Mg2+-Cl--SO42--H2O systems with implications for Mars. Geochimica et Cosmochimica Act, 75 (12), 3600-3626, %url%, https://doi.org/10.1016/j.gca.2011.03.038 | |
| [Steiger.etal:2014] | Steiger, Michael; Charola A. Elena; Sterflinger, Katja (2014): Weathering and Deterioration. In: Siegesmund S.; Snethlage R. (Hrsg.): Stone in Architecture, Springer Verlag Berlin Heidelberg, 223-316, Webadresse, https://doi.org/10.1007/978-3-642-45155-3_4 | |