Electron microscopic study of the dehydration of diaspore
-
Lars Löffler
Abstract
The thermal transformation of natural, single-crystal diaspore (D) to corundum (C) and water has been analyzed in detail by means of transmission electron microscopy (TEM). Pieces of singlecrystal diaspore were partially dehydrated at temperatures ranging from 400 to 600 °C and were prepared in cross-section for TEM studies. The transformation of diaspore was studied at the faces (100)D, (010)D, and (001)D, with special attention to the microstructural details at the reaction interface.
Irrespective of the transformation direction, the dehydration product is highly porous. Nanometer- sized pores form two-dimensional arrays arranged parallel to the basal plane of corundum forming lamellae that are separated by thin regions of dense corundum. The periodicity of the lamellar structure is 3.7 nm, which causes distinct satellite reflections in diffraction patterns in the case of dehydration at moderate temperatures (<450 °C). At higher temperatures, the degree of regularity, as well as the satellite reflection intensities, decrease.
During transformation, the diaspore crystal cleaves parallel to (010)D, and micro-cracks are developed parallel to (100)D and to (001)D in the corundum due to the misfit of the lattices. The entire crack system as well as the lamellar pore system play an important role in the dehydration process because they serve as effective transport paths for the water vapor. The rapid dehydration at the (010)D faces is attributed to fast-propagating cracks along [010]D. The slow transformation processes along [100]D and [001]D are discussed in terms of difficulties in crack propagation and in generating suitable crack systems, respectively.
© 2015 by Walter de Gruyter Berlin/Boston
Artikel in diesem Heft
- Partitioning of Sr between coexisting minerals of the hollandite- and piemontite-groups in a quartz-rich schist from the Sanbagawa metamorphic belt, Japan
- Crystallization processes in migmatites
- Amblygonite-montebrasite solid solutions as monitors of fluorine in evolved granitic and pegmatitic melts
- Reduction of water loss from gold-palladium capsules during piston-cylinder experiments by use of pyrophyllite powder
- Trace-element partitioning between immiscible lunar melts: An example from naturally occurring lunar melt inclusions
- Assemblages with titanite (CaTiOSiO4), Ca-Mg-Fe olivine and pyroxenes, Fe-Mg-Ti oxides, and quartz: Part I. Theory
- Assemblages with titanite (CaTiOSiO4), Ca-Mg-Fe olivine and pyroxenes, Fe-Mg-Ti oxides, and quartz: Part II. Application
- The stability of clinopyroxene in the system CaO-MgO-SiO2-TiO2 (CMST)
- Ordering kinetics of Mg-Fe2+ exchange in a Wo43En46Fs11 augite
- Al,Si order in the crystal structure of α-eucryptite (LiAlSiO4)
- TEM-EDX study of weathered layers on the surface of volcanic glass, bytownite, and hypersthene in volcanic ash from Sakurajima volcano, Japan
- Electron microscopic study of the dehydration of diaspore
- Crystal properties and energetics of synthetic kaolinite
- Structures and energies of AlOOH and FeOOH polymorphs from plane wave pseudopotential calculations
- XPS measurement of fivefold and sixfold coordinated sulfur in pyrrhotites and evidence for millerite and pyrrhotite surface species
- Structure of synthetic 6-line ferrihydrite by electron nanodiffraction
- Atomic structures of planar defects in oxybiotite
- Potassium hydrogen disilicate: A possible model compound for 17O NMR spectra of hydrous silicate glasses
- Strain analysis of phase transitions in (Ca,Sr)TiO3 perovskites
- Triclinic liddicoatite and elbaite in growth sectors of tourmaline from Madagascar
- Letter. A simple inorganic process for formation of carbonates, magnetite, and sulfides in martian meteorite ALH84001
Artikel in diesem Heft
- Partitioning of Sr between coexisting minerals of the hollandite- and piemontite-groups in a quartz-rich schist from the Sanbagawa metamorphic belt, Japan
- Crystallization processes in migmatites
- Amblygonite-montebrasite solid solutions as monitors of fluorine in evolved granitic and pegmatitic melts
- Reduction of water loss from gold-palladium capsules during piston-cylinder experiments by use of pyrophyllite powder
- Trace-element partitioning between immiscible lunar melts: An example from naturally occurring lunar melt inclusions
- Assemblages with titanite (CaTiOSiO4), Ca-Mg-Fe olivine and pyroxenes, Fe-Mg-Ti oxides, and quartz: Part I. Theory
- Assemblages with titanite (CaTiOSiO4), Ca-Mg-Fe olivine and pyroxenes, Fe-Mg-Ti oxides, and quartz: Part II. Application
- The stability of clinopyroxene in the system CaO-MgO-SiO2-TiO2 (CMST)
- Ordering kinetics of Mg-Fe2+ exchange in a Wo43En46Fs11 augite
- Al,Si order in the crystal structure of α-eucryptite (LiAlSiO4)
- TEM-EDX study of weathered layers on the surface of volcanic glass, bytownite, and hypersthene in volcanic ash from Sakurajima volcano, Japan
- Electron microscopic study of the dehydration of diaspore
- Crystal properties and energetics of synthetic kaolinite
- Structures and energies of AlOOH and FeOOH polymorphs from plane wave pseudopotential calculations
- XPS measurement of fivefold and sixfold coordinated sulfur in pyrrhotites and evidence for millerite and pyrrhotite surface species
- Structure of synthetic 6-line ferrihydrite by electron nanodiffraction
- Atomic structures of planar defects in oxybiotite
- Potassium hydrogen disilicate: A possible model compound for 17O NMR spectra of hydrous silicate glasses
- Strain analysis of phase transitions in (Ca,Sr)TiO3 perovskites
- Triclinic liddicoatite and elbaite in growth sectors of tourmaline from Madagascar
- Letter. A simple inorganic process for formation of carbonates, magnetite, and sulfides in martian meteorite ALH84001
