Crystallization of Hydrosodalite Na<sub>6</sub>[AlSiO<sub>4</sub>]<sub>6</sub>(H<sub>2</sub>O)<sub>8</sub> and Tetrahydroborate Sodalite Na<sub>8</sub>[AlSiO<sub>4</sub>]<sub>6</sub>(BH<sub>4</sub>)<sub>2</sub> inside the Openings

Abstract

The zeolitic properties of hydrosodalite Na 6 [AlSiO 4 ] 6 (H 2 O) 8 and the reactivity and hydrogen content of tetrahydroborate sodalite Na 8 [AlSiO 4 ] 6 (BH 4 ) 2 favour both species for future industrial applications. A use in chemical process often efforts a sample preparation in form of membrane-like thin wafers. The present study presents experiments on hydrosodalite as well as BH 4 -sodalite formation as steel mesh supported thin wafers. Preparation of both sodalite wafers is performerd by the crossover synthesis (CS) from solution to melt flow, first described in [1] [2]. Whereas the space filling of the steel mesh with BH 4 -sodalite crystals was proved to be a complete close and stable package, hydrosodalite reached only a somewhat weaker quality. Beside the synthesis step, hydrosodalite formation requieres a treatment of the crystal filled mesh at 130˚C for 20 h in water to transform the as synthesized hydroxysodalite into hydrosodalite, as known from literature [3] [4] [5]. This leaching procedure was found to be responsible for the obtained loss of quality as demonstrated by a further experiment using a self supported hydrosodalite wafer. Further problems like evolution of pores as a result of the mechanically ripping out the steel inlay from the sample pellets after synthesis have to be solved in future. Nevertheless the results of the present paper are of significance for the development of steel mesh supported hydrosodalite and BH 4 -sodalite membranes.

A facile recrystallization strategy for fabrication of nanocrystalline microspheres of sulfatic sodalite with high thermal stability

“…1,7,8 In comparison, synthetic sodalite usually has variable amounts of water and hydroxyl in the formulas dependent on the conditions of hydrothermal synthesis or subsequent heat treatments at elevated temperatures: i.e., the basic sodalite (B-sodalite) series Na 8 [AlSiO 4 ] 6 (OH) 2 •nH 2 O (0 < n ≤ 4) and the hydrosodalite series Na 6 [AlSiO 4 ] 6 •nH 2 O (0 < n ≤ 8). 9 In order to obtain improved properties and applications, [9][10][11] the sodalite family has evolved into diverse chemical, topological, geometrical, and crystallographic variants with a general formula Na 6 [AlSiO 4 ] 6 (NaX)m•(H 2 O)n (where X = Cl, OH, SO 4 , CO 3 , …; m = 0-2; n = 0-8). [12][13][14] Applications of sodalite zeolites include optical materials, 15 hydrogen adsorption and storage, water sorption and separation, 16 ammonia adsorption, etc.…”

“…The primary, hydrothermally synthesized sodalite usually belongs to Na 8 [AlSiO 4 ] 6 (OH) 2 •nH 2 O (2 ≤ n ≤ 4) (B-sodalite), 21 not metastable Na 6 [AlSiO 4 ] 6 •8H 2 O (W-sodalite). 10,20 However, the thermal stability of B-sodalite is particularly low due to the presence of hydroxyl groups in the aluminosilicate framework. Therefore, direct synthesis of hydroxyl-free sodalite featuring improved thermal stability from common hydrothermal routes has not been possible so far, preventing potential applications of sodalite zeolites at elevated temperatures.…”