Über das Aluminiumsulfat und seine Hydrate. Zur Kenntnis der Doppelsulfate und ihrer Komponenten II

Krauß, F.; Fricke, A.

doi:10.1002/zaac.19271660114

Cited by 8 publications

(2 citation statements)

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“…The release of structural water has been reported to be connected with two (Bayliss 1964; Földvári 2011), four (Krauss and Fricke 1927; Náray-Szabó 1969; Bretsznajder and Rojkowski 1969; Chou and Soong 1984; Moselhy et al 1993; Çilgi and Cetişli 2009) or five (Barret and Thiard 1965a, b) step processes, respectively. Even for those publications claiming the same number of dehydration events, there are sometimes significant differences between the compositions of the proposed intermediate hydrates obtained from thermal decomposition.…”

Section: Introductionmentioning

confidence: 99%

“…In addition to uncertainties concerning the precise amount of water present in alunogen, especially when comparing starting materials from various sources and storage histories, there are also discrepancies related to the temperature stability between the results of thermoanalytical studies originating from different groups. The release of structural water has been reported to be connected with two (Bayliss 1964 ; Földvári 2011 ), four (Krauss and Fricke 1927 ; Náray-Szabó 1969 ; Bretsznajder and Rojkowski 1969 ; Chou and Soong 1984 ; Moselhy et al 1993 ; Çilgi and Cetişli 2009 ) or five (Barret and Thiard 1965a , b ) step processes, respectively. Even for those publications claiming the same number of dehydration events, there are sometimes significant differences between the compositions of the proposed intermediate hydrates obtained from thermal decomposition.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Temperature- and moisture-dependent studies on alunogen and the crystal structure of meta-alunogen determined from laboratory powder diffraction data

et al. 2016

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Starting from a synthetic sample with composition Al2(SO4)3·16.6H2O, the high-temperature- and moisture-dependent behavior of alunogen has been unraveled by TGA measurements, in situ powder X-ray diffraction as well as by gravimetric moisture sorption/desorption studies. Heating experiments using the different techniques show that alunogen undergoes a first dehydration process already starting at temperatures slightly above 40 °C. The crystalline product of the temperature-induced dehydration corresponds to the synthetic equivalent of meta-alunogen and has the following chemical composition: Al2(SO4)3·13.8H2O or Al2(SO4)3(H2O)12·1.8H2O. At 90 °C a further reaction can be monitored resulting in the formation of an X-ray amorphous material. The sequence of “amorphous humps” in the patterns persists up to 250 °C, where a re-crystallization process is indicated by a sudden appearance of a larger number of sharp Bragg peaks. Phase analysis confirmed this compound to be anhydrous Al2(SO4)3. Furthermore, meta-alunogen can be also obtained from alunogen at room temperature when stored at relative humidities (RH) lower than 20 %. The transformation is reversible, however, water sorption of meta-alunogen to alunogen and the corresponding desorption reaction show considerable hysteresis. For RH values above 80 %, deliquescence of the material was observed. Structural investigations on meta-alunogen were performed using a sample that has been stored at dry conditions (0 % RH) over phosphorus pentoxide. Powder diffraction data were acquired on an in-house high-resolution diffractometer in transmission mode using a sealed glass capillary as sample holder. Indexing resulted in a triclinic unit cell with the following lattice parameters: a = 14.353(6) Å, b = 12.490(6) Å, c = 6.092(3) Å, α = 92.656(1)°, β = 96.654(1)°, γ = 100.831(1)°, V = 1062.8(8) Å3 and Z = 2. These data correct earlier findings suggesting an orthorhombic cell. Ab-initio structure solution in space group P , using simulated annealing, provided a chemically meaningful structure model. The asymmetric unit of meta-alunogen contains three symmetry independent SO4-tetrahedra and two Al(H2O)6 octahedra. The polyhedra are isolated, however, linkage between them is provided by Coulomb interactions and hydrogen bonding. In addition to the water molecules which directly belong to the coordination environment of the aluminum cations there are two additional zeolitic water sites (Ow1 and Ow2). If both positions are fully occupied meta-alunogen corresponds to a 14-hydrate. Structural similarities and differences between the previously unknown structure of meta-alunogen and alunogen are discussed in detail. Since hydrous aluminum sulfates have been postulated to occur in Martian soils, our results may help identifying meta-alunogen by X-ray diffraction not only on the surface of the Earth but also using the Curiosity Rover’s ChemMin instrument.Electronic supplementary materialThe online version of this article (doi:10.1007/s00269-016-0840-7) contains supplementary material,...

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%