Original paper

Structure analyses of a partially dehydrated synthetic Ca-garronite single crystal under different T, PH2O conditions

Schröpfer, Lothar; Joswig, Werner

European Journal of Mineralogy Volume 9 Number 1 (1996), p. 53 - 66

21 references

published: Dec 30, 1997
manuscript accepted: Sep 16, 1996
manuscript received: Mar 28, 1996

DOI: 10.1127/ejm/9/1/0053

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Abstract

Abstract X-ray diffraction studies on a synthetic single crystal of type Ca-Pt3 zeolite, Ca2.83Al5.66Si10.34O32 · 13H2O, Ca-garronite, I4I/a, ao = 9.873(1), co = 10.288(1) Å, were carried out at different hydration conditions: 25°C and 20(3) mbar PH2O (partial pressure of aqueous vapour), 25°C and 27(3) mbar PH2O, and 145°C and 27(3) mbar PH2O. Utilizing reflections up to 29 = 60° (MoKα), the Rw values converged at 2.4, 3.4, and 2.1 %, respectively, the conventional R at 4.1, 4.7, 3.7 %. On heating, Ca-garronite underwent a structural transformation at 135°C induced by partial dehydration. The lattice constants decreased to ao = 9.790(2) Å and co = 9.097(1) Å, leading to a 13 % decrease of the unit cell volume. The space group transformed from I4I/a to P4I2I2. The framework was found to be remarkably distorted, although no bonds were broken. The distorted framework resembled dehydrated gismondine. In the partially dehydrated structure at 145°C, H2O occupied only one equipoint. At room temperature, the distribution of water molecules was disordered. A thermogravimetric curve up to 950°C showed three steps at 120°C, 300°C, and 790°C, corresponding to losses of 4.7, 5.2, and 2.5 H2O per unit cell, respectively. Using single crystals, the first dehydration reaction could be reversed upon cooling. Additional in situ heating experiments up to 320°C performed on single crystals showed a decrease of lattice constants with increasing temperature

Keywords

Ca-garronitesynthetic zeolitedehydrationstructure