Conditions for atomic imaging of mullite

1989 ◽  
Vol 47 ◽  
pp. 418-419
Author(s):  
T. A. Epicier ◽  
G. Thomas
Keyword(s):  
Oxygen Vacancies ◽  
High Resolution Electron Microscopy ◽  
Ceramic Materials ◽  
Work Conditions ◽  
Real Space ◽  
Potential Candidate ◽  
Silicate Mineral ◽  
Resolution Electron ◽  
The Subject ◽  
Aluminium Silicate

Mullite is an aluminium-silicate mineral of current interest since it is a potential candidate for high temperature applications in the ceramic materials field.In the present work, conditions under which the structure of mullite can be optimally imaged by means of High Resolution Electron Microscopy (HREM) have been investigated. Special reference is made to the Atomic Resolution Microscope at Berkeley which allows real space information up to ≈ 0.17 nm to be directly transferred; numerous multislice calculations (conducted with the CEMPAS programs) as well as extensive experimental through-focus series taken from a commercial “3:2” mullite at 800 kV clearly show that a resolution of at least 0.19 nm is required if one wants to get a straightforward confirmation of atomic models of mullite, which is known to undergo non-stoichiometry associated with the presence of oxygen vacancies.Indeed the composition of mullite ranges from approximatively 3Al2O3-2SiO2 (referred here as 3:2-mullite) to 2Al2O3-1SiO2, and its structure is still the subject of refinements (see, for example, refs. 4, 5, 6).

Interface structures in polycrystalline ceramic materials

1986 ◽  
Vol 44 ◽  
pp. 468-471
Author(s):  
K. J. Morrissey
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Physical And Mechanical Properties ◽  
High Resolution Electron Microscopy ◽  
Ceramic Materials ◽  
Polycrystalline Materials ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Interface Structures

Grain boundaries and interfaces play an important role in determining both physical and mechanical properties of polycrystalline materials. To understand how the structure of interfaces can be controlled to optimize properties, it is necessary to understand and be able to predict their crystal chemistry. Transmission electron microscopy (TEM), analytical electron microscopy (AEM,), and high resolution electron microscopy (HREM) are essential tools for the characterization of the different types of interfaces which exist in ceramic systems. The purpose of this paper is to illustrate some specific areas in which understanding interface structure is important. Interfaces in sintered bodies, materials produced through phase transformation and electronic packaging are discussed.

scholarly journals Real-space Measurements of Bonding Charge Density in Aberration-corrected High Resolution Electron Microscopy

2009 ◽  
Vol 15 (S2) ◽  
pp. 1478-1479
Author(s):  
J Ciston ◽  
SJ Haigh ◽  
JS Kim ◽  
AI Kirkland ◽  
LD Marks
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Charge Density ◽  
High Resolution Electron Microscopy ◽  
Real Space ◽  
Resolution Electron ◽  
Aberration Corrected

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Microstructure and Lattice Defects in Polycrystalline Nuclear Ceramics

1968 ◽  
Vol 26 ◽  
pp. 270-271
Author(s):  
J. L. Daniel ◽  
S. J. Mayhan
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution Electron Microscopy ◽  
Ceramic Materials ◽  
Thin Sections ◽  
Small Areas ◽  
Physical Measurements ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Mechanical Thinning

Transmission electron microscopy of several nuclear ceramics has been extended to thin sections of as - fabricated poly-crystalline materials, by use of a thinning technique utilizing only common metallographic practices. The method is based on work by Doherty and Leombruno. However, while mechanical thinning (polishing) produces large, evenly thinned specimens, the surface of ceramic materials retains many shallow scratches and defects introduced by the polishing medium. On the other hand, the chemical thinning methods commonly applied produce only very small areas which are thin enough for examination by transmission electron microscopy, since preferential attack occurs on grain boundaries, inclusions, second phases, etc. By combining the chemical polish with the mechanical thinning procedures, large, relatively clean areas of ceramic materials can be produced. Another significant advantage is that in the course of thinning, the same specimens can be examined frequently and in detail by light microscopy, some physical measurements can be made along the way (e.g., microhardness, spectral transmission, autoradiography), and all observations can be closely correlated finally with the high resolution electron microscopy.

The internal structure of nephrite: experimental and computational evidence for the coexistence of multiple-chain silicates within an amphibole host

1980 ◽  
Vol 295 (1416) ◽  
pp. 537-552 ◽  
Keyword(s):  
High Resolution Electron Microscopy ◽  
Real Space ◽  
Chemical Compositions ◽  
Specimen Thickness ◽  
Structural Variations ◽  
Cell Content ◽  
X Ray ◽  
Structural Regularity ◽  
Resolution Electron ◽  
Computational Procedures

Ultra-structural variations in samples of nephrite jade have been elucidated by a combination of high resolution electron microscopy, which explores local structure in a direct, ‘real space’ manner, and computational procedures using the so-called ‘multislice’ approach which enables the image generated under a given set of electron-optical conditions to be calculated as a function both of unit cell content and of specimen thickness. Microanalyses by electron-stimulated X-ray emission and by optical diffractometry (of micrographs) were also used. Planar faults on (010) occur frequently in nephrite. These are of several distinct kinds, all of which have been characterized. The host amphibole, consisting of double chains of linked SiO 4 tetrahedra, is shown frequently to accommodate triplechain lamellae which are coherently attached to the double-chain matrix on (010) planes. These triple-chain faults may occur in isolated fashion, but sometimes are arranged recurrently, in a disordered manner, within the amphibole host. The nephrite may also accommodate extended regions of a new, triple-chain mineral structure, the maximum observed width of this coexistent phase being ca. 340 A. Other planar faults, composed of regions with chain widths ranging from one to six SiO 4 tetrahedra, have been detected and fully identified on the basis of the correspondence between theoretically calculated and observed images. Detailed structural drawings for the continuous planar faults, as well as others that are described, are given. It is shown that edge-sharing of tetrahedra probably occurs close to the termini of certain types of discontinuous fault and that, in other cases of defect termination, screw-type dislocations may be incorporated to preserve the strain-free, structural regularity of the host. It has not yet proved possible, with currently available in situ X-ray microanalytical techniques, to assign chemical compositions to the new structural types that have been brought to light by this study.

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