Hydration of Strontium Chloride and Rare-Earth Element Oxychlorides

Abstract

Hydration and dehydration (on calcination) of SrCl 2 , YOCl, and HoOCl powders were studied.Single-crystal chloride materials are of interest for photonics owing to their transparence in the IR range and a [soft] photon spectrum. The main problem in both growing the crystals and working with them is their hydration. In particular, chlorides of rare-earth elements are very hygroscopic; hydrated rare-earth chlorides are readily hydrolyzed on heating [13 6]. This substantially complicates the use of such materials, though the spectroscopic characteristics, e.g., of LaCl 3 : R 3+ single crystals are highly promising [7]. Among matrices resistant to moisture are PbCl 2 and KPb 2 Cl 5 [8310].In this study we examined the hydration of SrCl 2 powders and also of oxychlorides of rare-earth elements. Strontium chloride crystallizing in a cubic lattice of the fluorite type has a high isomorphous capacity with respect to chlorides of rare-earth elements [11]. Properties of SrCl 2 single crystals and of Sr 1 !x R x Cl 2 + x solid solutions have been studied repeatedly [12314]. Oxychlorides of rare-earth elements are more resistant to moisture than the chlorides [15]. Therefore they could be a convenient form for introducing dopants.We used ultrapure 73 4 grade SrCO 3 , chemically pure grade ammonium chloride NH 4 Cl, and chemically pure grade hydrates of rare-earth elements RCl 3 . 6H 2 O as starting substances. The initial chemicals were characterized by X-ray diffraction. The X-ray phase analysis was carried out on a DRON-2 diffractometer (CuK = radiation, focusing monochromator from pyrolytic graphite). We recorded variations in sample weights on an Acculab V-200 electron balance. The humidity was measured with a psychrometer. The hydration was carried out at 19 + 2oC and the relative humidity of 38 + 5%.We prepared strontium chloride by the reaction SrCO 3 + 2NH 4 Cl = SrCl 2 + H 2 O8 + CO 2 8 + 2NH 3 8. (1) We used a fourfold excess of NH 4 Cl. The reaction was carried out in an alundum crucible at 150 3350oC for 6 h. The yield of SrCl 2 was 99%. The resulting SrCl 2 had a cubic fluorite-type lattice with a = 6.977 A, which agrees with the published data (PDF card no. 38-0496). On exposure to air, the sample weight continuously increased; the process gradually decelerated with time (Fig. 1). The increase in the substance weight in the first hour was 7%. The increase in the sample weight was accompanied by changes in its X-ray pattern. Along with the SrCl 2 lines, an additional set of reflections appeared, and their intensities rapidly increased, whereas the lines of SrCl 2 weakened (Fig. 2). Analysis of the pattern using the PDF database revealed mixture of mono-, di-, and hexahydrates of SrCl 2 . The final hydration product was SrCl 2 . 6H 2 O. On calcination of strontium chloride hexahydrate at 350oC for 2 h, the weight loss corresponded to complete dehydration. The subsequent Dm, g t, h Fig. 1. Kinetics of SrCl 2 hydration. (,m) Change in the weight of the sample and (t) time.

Alkaline Earth Chloride Hydrates: Chlorine Quadrupolar and Chemical Shift Tensors by Solid‐State NMR Spectroscopy and Plane Wave Pseudopotential Calculations

“…Powder X-ray diffraction confirmed the identity of the sample as being the dihydrate (see Figure 2), with the structure reported by Mçller and Lutz. [72] Anhydrous SrCl 2 is known to form some SrCl 2 ·2 H 2 O as it hydrates in air to finally form the hexahydrate; however, this is not a viable method for obtaining pure hydrates, since the monohydrate is also produced, as discussed by Basiev et al [54] SrCl 2 ·6 H 2 O was obtained from Aldrich Chemical Company. Initial powder X-ray diffraction experiments revealed this sample to be a mixture of the dihydrate and the hexahydrate.…”

Hydration–dehydration interactions between glycine and anhydrous salts: Implications for a chemical evolution of life

“…Thus, in order to simplify the experimental conditions, we chose the above mentioned four simple anhydrous salts; MgSO 4, SrCl 2 , BaCl 2 and Li 2 SO 4 . Their hydration and dehydration processes can be clearly characterized by techniques such as XRD and TG-DSC (Okhotnikov et al, 1983;Lumpkin and Perlmutter, 1995;Valdivieso et al, 1997;Basiev et al, 2005;Tanner, 2005;Chipera and Vaniman, 2007;van Essen et al, 2009). Moreover, these salts have several advantages for this study: (1) reliable thermodynamic parameters were reported previously (Table 1), (2) high purity reagents are easily available, (3) hydration rates at ambient temperature are slow enough to be treated experimentally without significant hydration by water vapor in air (see Section 2), and (4) their hydration D r G 0 have large variation ranging from À6.7 kJ/mol for Li 2 SO 4 to À30.2 kJ/mol for MgSO 4 (at 25°C and 1 bar).…”

Identification of high-dielectric constant compounds from statistical design

“…Among all the newly discovered dielectrics with large ϵ values, tetragonal HoClO and monoclinic Eu 5 SiCl 6 O 4 stand out because of their very large DFT-calculated band gap energies (5.2 eV and 5.5 eV respectively). These two rare earth oxychlorides are reported to have been experimentally synthesized [41][42][43][44] but their dielectric properties remained unstudied to the extent of our knowledge. Both of these compounds are mixed-anionic inorganic compounds-a class of emerging functional materials 45 .…”