The step by step thermal dehydration process of slightly hydrated boron leucite K16[B16Si32O96], was studied in situ by synchrotron radiation powder diffraction. A time-resolved experiment was performed using a translating imaging plate system. Rietveld refinements were carried out on 41 consecutive powder patterns in the 25°C to 940°C temperature range. Results show that temperature-induced transformations can be schematized into two main steps. In the 25-565°C temperature range, the symmetry remained cubic I-43d and the unit cell parameter increased with an increase in temperature. The migration of H2O molecules through the [111] channels during dehydration determined an opening of the six-member ring apertures which was as wide as possible and, at the same time, a narrowing in the eight-ring along [111]. This process was accomplished by a twisting in the tetragonal prism, constituting a leucite framework, which led to an opposed tilting in the tetrahedra connecting the prisms. Above 565°C, a continuous structural transformation led to a displacive polymorphic transition. Rietveld structure refinement of the unit cell parameters showed remarkable change, thus indicating an I-43d → Ia-3d change in symmetry. This was associated with a relaxation in the continuous structural distortions of the leucite framework and the T-O-T and O-T-O angles indicated the formation of more regular apertures
Dehydration process and transient channel deformations of slightly hydrated boron leucite: an “in situ” time-resolved synchrotron powder diffraction study
MARTUCCI, Annalisa;CRUCIANI, Giuseppe
2011
Abstract
The step by step thermal dehydration process of slightly hydrated boron leucite K16[B16Si32O96], was studied in situ by synchrotron radiation powder diffraction. A time-resolved experiment was performed using a translating imaging plate system. Rietveld refinements were carried out on 41 consecutive powder patterns in the 25°C to 940°C temperature range. Results show that temperature-induced transformations can be schematized into two main steps. In the 25-565°C temperature range, the symmetry remained cubic I-43d and the unit cell parameter increased with an increase in temperature. The migration of H2O molecules through the [111] channels during dehydration determined an opening of the six-member ring apertures which was as wide as possible and, at the same time, a narrowing in the eight-ring along [111]. This process was accomplished by a twisting in the tetragonal prism, constituting a leucite framework, which led to an opposed tilting in the tetrahedra connecting the prisms. Above 565°C, a continuous structural transformation led to a displacive polymorphic transition. Rietveld structure refinement of the unit cell parameters showed remarkable change, thus indicating an I-43d → Ia-3d change in symmetry. This was associated with a relaxation in the continuous structural distortions of the leucite framework and the T-O-T and O-T-O angles indicated the formation of more regular aperturesI documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
