Thermal decomposition of the magnesium sulphate hydrates under quasi-isothermal and quasi-isobaric conditions

Abstract

In the course of thermal decomposition of the magnesium sulphate hydrates MgSO4.nH20 (n = 7; 6; 5; 4; 3; 2; 5/4; 1) the intermediate steps MgSO4.3H20, MgSO4.2H20, MgSO4.H20 and fl -MgSO4 are observed under quasi-isothermal and quasi-isobaric conditions at p ~ 0.1 MPa dependent on the water contents. The structure of the obtained monohydrate phase is identical with that of kieserite. Thermal decomposition of the magnesium sulphate hydrates is essentially influenced by the water vapour partial pressure.The system MgSO4.H20 is characterized by the occurrence of a great number of hydrates; however, above 25 ~ only MgSO4.7H20 (epsomite), MgSO4.6H20 (hexahydrite) and MgSO4.H20 (kieserite) are contained in the form of stable solid phases in aqueous solution [

Experimental investigation of the mechanical properties of synthetic magnesium sulfate hydrates: Implications for the strength of hydrated deposits on Mars

“…As shown in Figure 1a, the X-ray powder diffraction patterns of the surface scraping contains numerous sharp Bragg reflections, which, in both position and intensity, agree with the expected diffraction pattern of sanderite (MgSO 4 · 2H 2 O) [Ma et al, 2009]. The remaining observed Bragg reflections match well with those reported from the poorly known MgSO 4 · 1.25H 2 O phase, which has been previously referred to as "synthetic kieserite" [Emons et al, 1990]. On the basis of these X-ray diffraction data, it appears that no (or very little) kieserite [Aleksovska et al, 1998] is present.…”

“…In particular, the single broad feature at ∼2θ = 32° in our X‐ray powder diffraction pattern cannot be explained by kieserite, but instead, this closely matches two close Bragg peaks in the 1.25 hydrate. Consequently, we checked the exact water content of the MS1 starting material as supplied by Sigma‐Aldrich using a thermogravimetric method, similar to that of Emons et al [1990]. We heated a small (∼5 g) sample of the supplied MS1 to 400°C for 24 hours and measured a mass reduction of 16.9%; the water contents of MgSO 4 · H 2 O, MgSO 4 · 1.25H 2 O, and MgSO 4 · 2H 2 O are 13.0%, 15.8%, and 23.0%, respectively.…”

Microstructure of minerals and yerba mate extract co-crystallized with sucrose

“…2a). Emons et al (1990) and Paulik et al (1981) studied the dehydration of magnesium sulphate heptahydrate by thermogravimetric and X-rays measurements. These authors determined that the decomposition of the trihydrate form of magnesium sulphate was at 115°C, however a previous overheating to 130°C was needed for nucleus formation.…”

Sulfate deposition in subsurface regolith in Gusev crater, Mars

“…Thus either some areas with high water concentrations occur that have not yet been found by the rover at the Gusev site (e.g., deeper than 10–11 cm or in some other locations within the GRS footprint), or the Mg‐sulfates in the near surface are in a higher hydration state than is stable at the surface under current Mars atmospheric conditions. Recent experimental studies [ Bish et al , 2003; Chipera et al , 2005; Chou and Seal , 2003, 2005; Emons et al , 1990; Vaniman et al , 2004] suggest that highly hydrated Mg‐sulfates could have formed and been retained at the moderate relative humidity and warmer temperatures expected for Mars during periods of high obliquity [ Richardson and Mischna , 2005]. Some of the Mg sulfate hydrates (e.g., starkeyite MgSO 4 · 4H 2 O) have stability fields that could be expanded by metastability to allow their persistence where lower hydrates might be anticipated [ Chipera et al , 2005; Wang et al , 2005a].…”