A melt-spun Mg-1.5%wtCa-6wt%Zn alloy was analyzed by means of transmission electron microscopy, energy dispersive X-ray spectroscopy, and scanning transmission electron microscopy. The as-solidified alloy exhibited both spherical matrix precipitates and elongated precipitates at the grain boundaries (grain-boundary films). After heat treatment, the alloy showed faceted precipitates (cuboidal shape), mostly on dislocations. It was found that the observed precipitates are the same compound, Ca2Mg6Zn3. As there was no crystallographic data for this compound in the literature, its crystal structure was investigated by comparison of experimental and simulated selected-area electron-diffraction patterns and high-resolution electron microscopy images. This study indicated that Ca2Mg6Zn3 is a trigonal compound with space group P31c and lattice parameters a = 0.97 nm, c = 1.0 nm.

Every time we take a breath, we are inhaling the results of twentieth century combustion technology. Combustion processes generally produce a multitude of soot and other sub micron sized particulates. The human lungs, via the process of cilia movement expel most of these particles; others are broken down with the aid of macrophage agents. These macrophages absorb particles and incorporate the constitute elements into our bodies. These elements maybe expelled, or they may remain in the body and accumulate over time, as is the case with certain heavy metals. Limited prior research on ‘single-particle’ interaction with lung or bronchial tissue has been conducted. Related research has focused on the statistical significance of soot inhalation on the lung tissue of rodents and primates [1]. Using the methods of single particle examination, founded by previous research into single particle source allocation [2], the examination particles of from human lung and bronchial tissues was performed.

Research on the particle characterization shown here is based on the application of an innovative method developed at MIT, which utilized high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis (EDX).

It has long been known that carbons have order at the microcrystalline level. Soots have been characterized as having a turbostratic structure and chars have been described as crumpled sheets. The value of electron microscopy in studying the morphology of such materials has been well established although only a few attempts have been made toward quantification.

The Methodology is based upon High Resolution Transmission Electron Microscopy (HRTEM) and further image analysis. The HRTEM image of each sample is recorded, digitized and processed with an image analysis software. Computer generated diffractograms are produced through Fourier Transformation and subsequent reverse transformation yields two color ‘extracted structures’ (Figure 1). The extracted structure is then undergoes statistical analysis. The analysis is aimed at identifying quantifiable structural parameters. Currently the following parameters are studied: circularity (C), elongation (E), and length of fringes (La) orientation of the fringes (cti), the inter-layer spacing (d002), and the fractional coverage of the extracted pattern (F).

The atomic structure of [001] tilt grain boundaries of Σ25 (210), Σ5 (310), Σ213 (320) and Σ217 (410) in TiO2 (rutile) were studied using high resolution electron microscopy and computer simulation. Regularly separated small steps (1/2 [120] high) and big steps (3/2 [120] high) which contain secondary dislocations were found in the (210) boundary as a result of deviation from the exact Σ5 misorientation and (210) symmetric plane. Similar steps were also found in (310) and (320) boundaries. Flat segments between the steps were found to have very accurate misorientation of their, Σ's and a nearly symmetric boundary plane. Their rigid body translation, volume expansion and relaxed structures were determined by comparing HRTEM images with computer calculated structures and simulated images. An irregular core structure was found in the (410) boundary when its misorientation deviated 2° from the exact Σ17 misorientation.

Metallic alloy ribbons of Bi–Sr–Ca–Cu with nominal compositions of 2-2–1-2, 2-2–2-3, 2-2–2-4, and 2-2–3-4, with or without Pb, were made by vacuum induction melting followed by melt-spinning. Ag, at the level of 20–80 wt. %, was added to aid in the alloy melting and metallic ribbon formation processes. These ribbons were then subjected to a controlled atmosphere oxidation and annealing to produce superconducting oxide/silver microcomposites. Among the four alloy groups investigated in the present work, 2-2–3-4 alloys with 0.6Bi replaced by Pb possess the best superconducting properties after suitable treatment. These specimens exhibited zero resistance at T = 104–110 K and a critical current density of 600 A/cm2 at 77 K in zero field with excellent reproducibility. The annealing conditions, namely the annealing temperature, time, and atmosphere, are discussed in terms of the formation kinetics of the superconducting phases. While the 85 K Tc “2212” phase formed over a wide temperature range (740 to 845 °C) after an ∼2 h anneal, the 110 K high-Tc transition appeared only after an ∼10 h anneal at 810–840 °C, suggesting that the “2223” phase grew from the 2212 phase controlled by diffusion. The microstructures of these superconducting microcomposites were observed and analyzed by a combination of optical and scanning electron microscopy, x-ray powder diffraction, and electron probe microanalysis. The high Tc “2223” phase exhibited plate-like grains which were distributed randomly in orientation. The silver addition improved the mechanical properties of the metallic precursor ribbons and the superconducting microcomposites, promoted the formation of the 2223 phase, and influenced the oxidation and the annealing conditions.

One method for the synthesis of superconducting oxides is high temperature oxidation of a metallic alloy (a metallic precursor) that contains the metallic constituents of the oxide. In addition, a noble metal can be added to the precursor such that, after oxidation, a two phase, finely divided oxide/metal composite results. Superconducting oxides have been produced from Eu-Ba-Cu and Yb-Ba-Cu alloys by oxidizing the alloys at 300°C followed by an “oxygen anneal” at elevated temperatures. Similarly, a Eu1,Ba2Cu3O7−x /Au composite has been formed from a quaternary metallic precursor. each case an onset of superconductivity occurred at about 92K. This approach to producing superconducting oxides is felt to have a number of advantages associated with it, not the least of which is the improvement of the mechanical properties of the superconducting product.

The particulate produced by many of the methods of rapid solidification, such as atomized powder, is of order 50 microns in diameter and is thus much too small to form the 3mm diameter disc conventionally used for thin-foil microscopy. 50 microns is, however, much too thick for direct TEM study on a support film and grid. A technique is described in detail that produces a composite wafer where atomized metal powder is sandwiched between two layers of electroplated nickel. This wafer is about 25 mm in diameter and about 250 microns thick. 3mm diameter TEM discs can be punched from the wafer and thinned by combinations of grinding, dimpling, jet-polishing, and ion milling. Depending on the composition and structure of the powder under study, the composite nature of the wafer can sometimes promote undesirable galvanic effects during jet polishing and differential thinning rates during ionmilling. Typical results are presented and discussion of the benefits and shortcomings of this technique is made. The method should be applicable to a variety of materials and geometries.

Nucleation temperatures are calculated for the case of solidification in atomized metal droplets where spherical substrate particles act as nucleation catalysts. Following the method of Fletcher, the effect of substrate size on catalytic potency is illustrated, and the model is applied to the nucleation of bcc solid from pure, liquid iron containing oxide substrate particles as catalysts. Supercooling data from the literature are used to determine wetting angles for alumina, silica, and rare-earth oxide. Oxide particle-size distributions are then used to predict the supercooling behavior of atomized liquid droplets based on the probability that a given size of droplet will contain a particular size of substrate particle. A transition size regime is found separating droplet sizes undergoing very small and very large supercoolings, respectively. This is discussed in terms of the types and number densities of inclusions present during atomization of the melt.

This paper discusses the application of the scanning transmission electron microscope (STEM) to the detection of segregation at interfaces via the monitoring of X-rays generated when the incident electrons interact with the segregant. Issues of spatial resolution and minimum detectable concentration are discussed. Specific examples, emphasizing the importance of probe size, sample thickness, and sample orientation, are presented.

The techniques of scanning transmission electron microscopy and field iron microscopy/atom probe are briefly described. The advantages of these techniques for high spatial resolution compositional analysis are discussed and examples cited.

The microstructures and local composition variations in centrifugally atomized high-sulfur stainless steel powder are investigated. Both fcc and bcc are found to be primary solidification phases in the as-solidified powder of this nominally austenitic steel where the smaller powder particles (≲ 70 micron diameter) tend to be bcc.Cellular solidification structures, with sulfide precipitates (100 to 200 nm diameter in size) at the cell walls, are observed in both fcc and bcc particles. The bcc structure, however, has many small sulfide precipitates (10 to 20 nm diameter) in the cell interior with few larger sulfide precipitates at the cell walls. The small precipitates, observed only in the bcc structures, form on cooling from a supersaturated solid solution that results from reduced solute partitioning during solidification. Partitioning of chromium and nickel is minimal in these cellular structures. A non-cellular bcc structure is also observed with small sulfide precipitates throughoutthe entire structure. This non-cellular bcc structure results from smooth-front massive solidification. Analysis of the nucleation process for solidification indicates that a transition from fcc nucleation to bcc nucleation occurs with increasing wetting angle in heterogeneous nucleation. Thus bcc should nucleate in the smaller droplets of a liquid dispersion where catalytic surfaces of low potentcy (large wetting angle) tend to be the only heterogeneous nucleants available.