Electron Microscopy of Sintered Beryllia

Porosity, etching characteristics, and general microstructural features of extruded and sintered beryllium oxide were studied by electron microscope observation of surface replicas. Both pore structures and etching characteristics were shown to be related to the hemimorphic hexagonal crystal structure of BeO. A form of twinning possible only in hemimorphic systems was also observed.     

Transmission Electron Microscopy of Glass-Ceramics

A new technique has been developed by which thin sections of glass-ceramics can be prepared for direct observation by transmission electron microscopy. Techniques for identifying crystalline phases are discussed, and the degree of crystallinity in several glass-ceramics is presented.     

Electron Microscopic Studies of Growth Structures in Hexagonal Ferrites

Electron microscopic studies of sintered hexagonal ferrites have revealed growth structures which indicate that crystal growth from a relatively highly saturated vapor phase occurs above certain temperatures during the sintering process. Illustrations of variations in the growth structures at various locations in the ferrite are given, and the probable importance of the vapor-phase growth mechanism in the over-all sintering process is discussed.     

Phase Separation in Borosilicate Glasses as Seen by Electron Microscopy and Scanning Electron Microscopy

Microstructures of two sodium borosilicate glasses were examined. Electron micrographs of replicas of water-etched fracture surfaces show that the microphases increase in size with the temperature and time of heat treatment. The relative amounts of soluble and insoluble microphases remain essentially unchanged. Scanning electron micrographs of completely leached glasses show that the insoluble phase is randomly interconnected. Scanning electron micrographs of colloidal deposits in the pores of the leached glass, which result from acid leaching of the heat-treated base glass, are shown. Electron micrographs showing re-solution of the phases are also included.     

Thin Films in Electron Microscopy

Thin films play an important role in electron microscopy as they can be used to improve the contrast and stability of specimens, as well as to make specimens electrically conductive. In order to avoid overlapping of specimen and coating structures, it is necessary to understand how thin films are formed in the various coating technologies and how to create them reproducibly as part of the different preparation techniques for electron microscopy. In contrast, electron microscopy can be applied to learn more about the structural details of thin films used, for instance, in the optical coating industry. Heat shock fracturing and Pt-C surface replication of the cross sections resulted in reliable transmission electron micrographs (TEM) of the coating microstructure. These studies demonstrate that, under optimal conditions, it is possible to find a correlation between the measured optical properties and the microstructure of the coatings. TEM replica investigations reveal single events, so they can be useful if discrepancies in the (statistical) physical data have to be investigated.     

Analytical Electron Microscopy of Heterogeneous Catalysts

Abstract

Conventional transmission electron microscopy (CTEM) is by now a quite well-established technique for the study of heterogeneous catalysts. It is commonly used for the determination of metallic particles shapes and size distribution on various types of carriers [1, 2]. In addition, dark field imaging and diffraction measurements (in selected area or microdiffraction mode) allows advantage to be taken of the diffraction of the electrons in order to identify the active phase on the basis of its crystal structure [3, 4].     

Analytical Electron Microscopy of Heterogeneous Catalysts

Conventional transmission electron microscopy (CTEM) is by now a quite well-established technique for the study of heterogeneous catalysts. It is commonly used for the determination of metallic particles shapes and size distribution on various types of carriers [1, 2]. In addition, dark field imaging and diffraction measurements (in selected area or microdiffraction mode) allows advantage to be taken of the diffraction of the electrons in order to identify the active phase on the basis of its crystal structure [3, 4].     

Scanning Electron Microscopy of Fracture Surfaces

Scanning electron microscopy has supplied information concerning the mechanism of failure of aluminium/epoxide joints: (1) evidence for a critical concentration of A-1100 silane that inhibits stress corrosion cracking; (2) evidence of plastic deformation at a crack tip; (3) observation of aluminum corrosion products.     

Electron Microscopy of Etched Plagiodase Feldspar

Single crystals of plagiodase feldspar were selectively etched by immersion in aqueous solutions of Na₂CO₃ and K₂CO₃ for 48 hr and in 48% HF for 1 to 3 sec. The etched surfaces are replicated using a two-stage Formvar-carbon replica shadowed with palladium. These replicas reveal that etching varies in different twin lamellas and that etch pits align along twin boundaries.     

Transmission Electron Microscopy of Thin Glass Samples

Mechanical thinning and fracturing techniques for preparing thin glass samples for direct-transmission electron microscopy are discussed. A modification of the Doherty and Leombruno procedure for mechanically thinning ceramic materials is described. These techniques make possible more reliable electron microscope studies of fine-scale submicrostructure in glass systems. Electron microscope observations on fused silica, an alkali borosilicate glass, and some binary silicate glasses are reported and discussed in terms of present understanding of glass structure.     

Modern Applications of Electron Microscopy to Catalysis

The active sites of ultra-dispersed Pt/-Al₂O₃ catalysts are studied using high-resolution electron microscopy, Z-contrast and dark field. In addition we have calculated using a method based in density functional theory the electrostatic potential and charge distribution of the active sites. It is conclude that the most likely Pt clusters that are formed correspond to Pt₁₃ and Pt with icosahedral and decahedral structure. It is shown that this is consistent with the electron microscopy data.     

Ultramicrotoming of Ceramic Powders for Electron Microscopy

Compacts of monosize TiO₂ particles and agglomerates of TiO₂ and γ-alumina were infiltrated with Spurr's epoxy resin, cured, and ultramicrotomed. Transmission electron microscopy of the thin sections revealed the packing of the TiO₂ spheres and the structure of the agglomerates.     

Scanning Electron Microscopy of Industrial Cement Clinkers

Scanning electron microscopy in combination with energy-dispersive X-ray analysis was used to study fracture surfaces of several industrial cement clinkers. This combination can be used successfully to locate some clinker components even when they are present in amounts smaller than the detection capabilities of methods such as X-ray diffraction and optical microscopy.     

High-Resolution Electron Microscopy and Convergent-Beam Electron Diffraction of Sintered Undoped Hydroxyapatite

Transmission electron microscopy (TEM) was used to characterize the microstructure of sintered undoped hydroxyapatite (OHAp). Conventional TEM observations were accom-panied by high-resolution electron microscopy (HREM) and convergent-beam electron diffraction (CBED) studies. CBED analysis enabled the determination of the space group of the OHAp, P6₃/m. Densification of the material was performed by pressureless sintering at 1250°C for 30 min. The undoped sample was comprised of apatite as the only crystalline phase, in addition to a small volume fraction (4%) of closed porosity. In general, the observed microstructure was homogeneous and consisted of equiaxed apatite grains with an average grain diameter of }1–2μm. No indication of a residual amorphous phase, which may have formed during sintering, was observed at multigrain junctions. HREM studies on grain boundaries also revealed that no intergranular glass film was present along two-grain junctions, indicating that densification proceeded without a liquid phase. A slightly disordered region at the interfaces was observed, suggesting an extended grain-boundary structure.     

An Introduction to Energy-Filtered Transmission Electron Microscopy

This article introduces the topic of energy-filtered transmission electron microscopy (EFTEM). It reviews the technique combining theory with a number of applications from materials science to highlight the progress made in the subject. Examples of EFTEM of catalysts are also reviewed with a discussion of how the technique could be used to study many more catalyst structures in the future.     

Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy Study of Nonstoichiometric Silicon-Carbon-Oxygen Glasses

Crystallization behavior of Si-C-O glasses in the temperature range of 1000°–1400°C was investigated using transmission electron microscopy (TEM) in conjunction with electron energy-loss spectroscopy (EELS). Si-C-O glasses were prepared by pyrolysis of polysiloxane networks obtained from homogeneous mixtures of triethoxysilane, T^H, and methyldiethoxysilane, D^H. Si-C-O glass composition depended on the molar ratio of the precursors utilized. At a ratio of T^H/D^H= 1, the formation of a carbon-rich glass was observed, whereas a ratio of T^H/D^H= 9 yielded a Si-C-O glass with excess free silicon. Both materials were amorphous at 1000°C, but showed a distinct difference in crystallization behavior on annealing at high temperature. Although T^H/D^H= 1 revealed a small volume fraction of SiC precipitates in addition to a very small amount of residual free carbon at 1400°C, T^H/D^H= 9 showed, in addition to SiC crystallites, numerous larger silicon precipitates (20–50 nm), even at 1200°C. Both materials underwent a phase separation process, SiC _x O_2(1-x)→ x SiC + (1 - x )SiO₂, when annealed at temperatures exceeding 1200°C.