Pseudocubic Crystal Structure and Phase Transition in Doped Ye’elimite

Abstract

Sodalites are tridimensional alumino-silicate materials containing cages where loosely bonded anions are located. Ye'elimite, Ca 4 [Al 6 O 12 ]SO 4 , is outstanding as an aluminate sodalite with a flexible framework accepting several type of dopants with important structural consequences. Moreover, ye'elimite is also important from an applied perspective as it is the most relevant phase in calcium sulfoaluminate cements. The crystal structure of stoichiometric ye'elimite has recently been unraveled but the structure of dopant-containing ye'elimite, which is presents in cements, is not well studied. Here, we report the pseudo-cubic crystal structure of doped ye'elimite, Ca 3.8 Na 0.2 Al 5.6 Fe 0.2 Si 0.2 O 12 SO 4 , from high-resolution synchrotron powder diffraction data. The powder pattern is indexed with a cubic cell and a structural model is reported based on the I4 ̅ 3m space group. However, this compound displays diffraction peak narrowing on heating. Furthermore, some high-angle split peaks become single peak on heating and a phase transition is measured at 525ºC. Therefore, it is concluded that the crystal structure at room temperature has lower symmetry although it can be described as cubic. The structural study at 800ºC suggests a truly cubic structure and we speculate that this phase transition, on heating, is likely related with the dynamical disordering of the sulfate anions. Finally it is concluded that the high temperature cubic state was not quenchable to ambient, even when the tested chemical substituents are introduced into the structure.

Characterisation and hydration process of synthetic Sr-bearing ye'elimite

“…It can be also known that C 4 A 3 $ mainly yields AFm, but AFt can be also traced with relatively low intensity. The occurrence of AFt has been attributed to critically supersaturated domains and the fast nucleation rate of AFt (Damidot, 2007); similar results have also been reported by other researches (Berger et al, 2011;Cuesta et al, 2014aCuesta et al, , 2014b. Additionally, because the hydration product aluminium hydroxide (AH 3 ) is poorly crystalline or microcrystalline, the ranges between 17°and 22°( 2θ) of XRD patterns tend to have various peaks (Song et al, 2015).…”

“…With regard to the characterisation of C 4 A 3 $, the Rietveld method is well suited for investigating the crystal structural characteristics (Cuesta et al, 2013(Cuesta et al, , 2014a(Cuesta et al, , 2014bHargis et al, 2014;Kurokawa et al, 2014); moreover, Rietveld quantitative phases analysis (RQPA) can also be used to quantify the phases in cements containing ye'elimite (Li et al, 2014;Álvarez-Pinazo et al, 2012). In recent years, RQPA has also been expanded to hydrated systems to identify both the crystalline phases and total amorphous contents (Álvarez-Pinazo et al, 2014(Álvarez-Pinazo et al, , 2016Cuesta et al, 2014a).…”

“…As regards the C 3 ŠA 3 $_2C$H 2 pastes, residual C$H 2 cannot be traced after 24 h; with respect to hydration products, AFt can be clearly observed with high intensity; moreover, strontium sulfate can also be identified. Considering C$H 2 is completely consumed after 24 h in C 3 ŠA 3 $_2C$H 2 paste, it should be discussed as to whether AFm is present in the paste; however, a minor amount of AFm is difficult to identify clearly by XRD, because the main peak of AFm is likely to be overlapped by one peak of AFt (Cuesta et al, 2014a(Cuesta et al, , 2014b. Therefore, TG was conducted to further determine the phases of the hydration products.…”

X-ray diffraction, cements and environment, three worlds in one.

“…Moreover, the presence of foreign ions in the structure stabilizes a pseudo-cubic form [3]. Ye'elimite-containing cements can be gathered in three main groups [1]: i) Calcium Sulpho-Aluminate (CSA), ii) Belite Calcium Sulpho-Aluminate or sulphobelite (BYF, from Belite-Ye'elemite-Ferrite cements) and iii) Belite-Alite-Ye'elimite (BAY) cements.…”

Study on Sintering System of Calcium Barium Sulphoaluminate by XRD Quantitative Analysis

“…Hargis et al refined the three crystal systems separately by Rietveld refinement and showed that the fitting result of the orthorhombic is the best [11]. Cuesta et al indicated that CSA mineral could be orthorhombic and that orthorhombic crystal sometimes would transform into the cubic at around 470 °C [12,13]. Andac et al also showed that crystal system transition occurred at around 470 °C [14].…”