PubMed · 5250346
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R Dufour. 1968. [Temporary ligatures].. https://pubmed.ncbi.nlm.nih.gov/5250346/
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The methodology and one of the first attempts to produce transmission electron microscopic (TEM) specimens of nanocrystalline metals, alloys and ceramics by ultramicrotomy are presented. Samples of the pure elements Co, Pd; alloys of Y-12 at. % Fe, Al-7 at. % Ag and W-30 at. % Ga; and ZnO ceramic, were found to section successfully to varying degrees. Advantages of sections prepared through ultramicrotomy over ion beam methods include extensive electron-transparent regions of uniform thickness and absence of ion beam damage. Typical artefacts were observed (knife marks, tearing, pull-out, shear lamellae, section curling, and anodic dissolution) but did not impede TEM analysis significantly. A potentially important effect observed was that of a texture development upon sectioning of the Co and Pd samples. It is thought that this unusual phenomenon results from the extremely fine scale of the microstructure and the purity of the Co and Pd samples, and may be enhanced by frictional heating effects and the state of the knife edge.
A recent advance in metallurgical technology has been the application of rapid solidification techniques to Al alloy production. FVS0812 is the designation given to a microcrystalline Al-based alloy consisting of 8 wt% Fe, 1 wt% V and 2 wt% Si. It is a two-phase alloy, consisting of ca. 27 vol percent of approximately spherical Fe-V-Si-rich dispersoids in an essentially pure Al matrix. The high strength, low density properties of this advanced material, and other related alloys, have not yet been realized, however, due, in part, to the inability of the alloy to form a thick, adherent, abrasion-resistant outer surface oxide film, a feature readily achieved at conventional Al alloys by normal anodizing methods. The present research has involved an electro-chemical study of oxide film growth at the 812 alloy, with the specific goals being to seek an understanding of the origin of the oxide film growth problem and ultimately to propose alternative approaches to the formation of a thick, stable oxide film at this material. The techniques used in this research have included electrochemical methodologies such as cyclic voltammetry and electrochemical impedance spectroscopy. Crucial information has been obtained through transmission electron microscopy (TEM) of ultramicrotomed specimens. Experiments were carried out initially in neutral borate solutions to characterize the compact barrier oxide film formed in this environment and expected to be present beneath the porous oxide film formed in the normal sulfuric acid anodizing medium.(ABSTRACT TRUNCATED AT 250 WORDS)
PURPOSE: To compare the misalignment error due to the fabrication of custom lead alloy blocks with the displacement error introduced by the finite resolution of a multileaf collimator relative to the prescribed smooth apertures. METHODS AND MATERIALS: Treatment field apertures for randomly selected patients for four clinical sites were obtained at various stages of the block fabrication process. These apertures and the corresponding multileaf collimator (MLC) apertures for each field were superimposed with the smooth apertures prescribed by physicians. The deviations from the prescribed apertures were measured at 10 degrees intervals. Comparisons of the magnitude and frequency of errors from block fabrication with those from the geometric displacements introduced by the finite leaf width of the multileaf collimator were made. RESULTS: The degree of conformity of the multileaf collimator is treatment-site dependent as, in general, are the shapes of fields. For three of the four sites examined, the multileaf collimator apertures track the prescribed apertures at least as accurately as custom blocking when the block design, construction, mounting, and alignment on the treatment machine are considered. CONCLUSIONS: The geometric conformality of multileaf collimation is comparable to, and in some cases superior to, that of custom blocks.