Synthesis of nanocrystalline low temperature silica polymorphs

Colloidal silica (Dupont, Ludox 40) has been hydrothermally treated at temperatures between 125 and 220 °C at 100 MPa water pressure for 5 to 90 days. Final synthesis product was low quartz ( α-quartz) in all cases, which was obtained directly after five days at the highest experimental temperatures...

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Bibliographic Details
Published in:Solid state sciences 2006-06, Vol.8 (6), p.625-633
Main Authors: Schäf, O., Ghobarkar, H., Garnier, A., Vagner, C., Lindner, J.K.N., Hanss, J., Reller, A.
Format: Article
Language:English
Subjects:
Condensed matter: structure, mechanical and thermal properties
Cross-disciplinary physics: materials science
rheology
Crystalline state (including molecular motions in solids)
Crystallographic aspects of phase transformations
pressure effects
Exact sciences and technology
Hydrothermal synthesis
Lower low quartz
Materials science
Moganite
Nanocrystalline materials
Nanocrystalline silica
Nanoscale materials and structures: fabrication and characterization
Physics
Quartz
Structure of solids and liquids
crystallography
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Summary:Colloidal silica (Dupont, Ludox 40) has been hydrothermally treated at temperatures between 125 and 220 °C at 100 MPa water pressure for 5 to 90 days. Final synthesis product was low quartz ( α-quartz) in all cases, which was obtained directly after five days at the highest experimental temperatures. Silica phases obtained at 145 °C and below were all of nanocrystalline size. At 145 °C and below, the hydrothermal high pressure conversion of colloidal silica takes place in time dependent different steps, starting from a precipitated mixture of an amorphous phase and “phase X2” found after 5 days of synthesis at 145 °C, while at longer synthesis times (21 and 42 days respectively) moganite-low quartz mixtures are found. After 90 days of synthesis phase low quartz is established. At 125 °C the occurrence of these phases is moved to longer synthesis times, however moganite-low quartz mixtures are still present after 90 days. The experiments established that “phase X2” and moganite are low temperature polymorphs of low-quartz stable for kinetic rather than for thermodynamic reasons. Therefore, “phase X2” shall be renamed to “lower low quartz”.
ISSN:1293-2558
1873-3085
DOI:10.1016/j.solidstatesciences.2006.02.037