Sectioning spherical aluminum oxide particles for transmission electron microscopy

Abstract

A technique was developed to aid in the interpretation of nucleation and growth characteristics of otherwise electron-opaque A1203 particles. The technique involved embedding a dense collection of particles in a n Epon mixture and sectioning with a diamond knife on an ultramicrotome. Serial sections were utilized to obtain three-dimensional information. It was found that ultramicrotomy does not introduce artifacts in ceramics which would otherwise affect measurements of the crystallite size or phase fraction, nor does it affect the crystallographic data significantly.It was observed that a-Al203 nucleated at the surface of isolated particles and in the neck region of sintered particles. Other data, obtained from diffraction and in situ hot-stage studies, indicated that each polycrystalline y-A1203 particle transformed to a nearly single crystal of a-A1203, which extended into adjacent particles under favorable circumstances.

Mechanically Induced Phase Transformation of γ-Al2O3into α-Al2O3. Access to Structurally Disordered γ-Al2O3with a Controllable Amount of Pentacoordinated Al Sites

“…Quite recently, it has been proven by high-resolution 27 Al NMR that coordinatively unsaturated, i.e., 5-fold, coordinated Al 3+ centers on the γ-Al 2 O 3 surfaces act as binding sites for active catalyst phases such as widely used PtO being the precursor for metallic Pt . Interestingly, 5-fold Al ions , also show up during the thermally induced irreversible γ → α phase transformation which has been the topic of numerous studies. ,− It occurs according to the following transformation sequence involving the δ and θ phase of aluminum oxide γ -Al 2 O 3 → 1023 K δ -Al 2 O 3 δ -Al 2 O 3 → 1173 K θ -Al 2 O 3 → 1050 K see refs 12, 24 1373−1473 K α -Al 2 O 3 The thermally induced phase transformation is assumed to be a surface-controlled reaction: α-Al 2 O 3 is reported to grow from the γ-Al 2 O 3 surface toward the interior of the grain; unsaturated Al centers located on the surface are assumed to act as starting points. ,,,,− The formation and the role of 5-fold coordinated Al ions in the thermally induced transformation have been studied in detail by Kwak et al by 27 Al MAS NMR spectroscopy making use of the advantages of measurements carried out at ultrahigh magnetic fields. , In accordance ...…”

Micro‐/nanostructure evolution of C/SiFeO(N,C) polymer‐derived ceramic papers pyrolyzed in a reactive ammonia atmosphere

“…Cross-sections suitable for electron transmission (<70 nm) are determined by their interference color and transferred to a TEM sample holding grid series that can give access to three-dimensional structure information are notable advantages. 33,34 However, the mechanical stress applied through the diamond knife may affect the structure of the material, resulting in compressed, sheared, fractured, or textured cross-sections. 32 Nevertheless, due to the otherwise high sample quality as well as its time and cost efficiency, UM can be considered a genuine alternative to classical preparation methods for electron microscopic investigation of ceramics and other inorganic materials.…”

Ultra-Microtome for the Preparation of TEM Specimens from Battery Cathodes

“…1c), failing in thinning the NPs. This phenomenon is observed with multiple popular nanomaterials such as zeolite (Haswell et al, 2003), silicates (Messenger et al, 2003), and metal oxides (Tucker et al, 1985). In these materials, the internal chemical bonding within the NP is stronger than its connection with the epoxy matrix, so the interfacial connection preferably disassembles upon the microtome cutting.…”

“…A main challenge for ultra-microtomy is that the diamond knife sectioning may generate mechanical defects in the specimen such as cracking and porosity, as schematically shown in Figures 1a and 1b. Another challenge of the ultra-microtomy method resides in the cutting of robust inorganic nanoparticles (NP) such as silicates and metal oxides (Tucker et al, 1985;Mori et al, 1992;Hochella et al, 1999). The NPs are embedded within a matrix material (e.g., epoxy) and then sliced into thin films, as schematically shown in Figure 1c.…”