Vacuum, X rays

Barium improves the performance of lead ahoy grids of acid batteries (see Batteries) (34). In the form of thin films, barium has been found to be a good high temperature lubricant on the rotors of anodes operating at 3500 rpm ia vacuum x-ray tubes (35). 

Occasionally, especially in the developmental phase of catalyst research, it is necessary to determine the oxidation state, exact location, and dispersion of various elements in the catalyst. Eor these studies, either transmission electron microscopy (TEM) or scanning electron microscopy (SEM) combined with various high vacuum x-ray, electron, and ion spectroscopies are used routinely. 

Fig. 1-2. Schematic diagram of the Coolidge (high-vacuum) x-ray tube. Coolidge tubes are widely used because they are stable and long-lived and permit tube current and voltage to be controlled independently.

Direct kinetic measurements from the changes in diffracted beam intensities with time during heating of the reactant are illustrated in the work of Haber et al. [255]. Gam [126] has reviewed the apparatus used to obtain X-ray diffraction measurements in thermal analysis. Wiedemann [256] has designed equipment capable of giving simultaneous thermo-gravimetric and X-ray data under high vacuum. X-Ray diffraction studies enable the presence, or absence, of topotactic relationships between reactant and product to be detected [92,102,257—260], Results are sometimes considered with reference to the pseudomorphic shape of residual crystallites. 

Figure 10. Relationship between absorption intensities at 402 and 335 nm in UV absorption spectra after exposures. initial spectrum of 1 m thick unexposed SPP. Exposures O UV in air, UV in vacuum, A deep UV in air, A deep UV in vacuum, X-ray in air, X-ray in vacuum.

The most important use of barium is as a scavenger in electronic tubes. The metal, often in powder form or as an alloy with aluminum, is employed to remove the last traces of gases from vacuum and television picture tubes. Alloys of barium have numerous applications. It is incorporated to lead alloy grids of acid batteries for better performance and added to molten steel and metals in deoxidizing alloys to lower the oxygen content. Thin films of barium are used as lubricant suitable at high temperatures on the rotors of anodes in vacuum X-ray tubes and on alloys used for spark plugs. A few radioactive isotopes of this element find applications in nuclear reactions and spectrometry. 

The instrument used in this project was a Phillips manual vacuum x-ray fluorescence spectrometer. All analyses were made in the Analytical Chemistry Laboratories of the Illinois State Geological Survey. 

The X-ray images of extended lattice imperfections within the crystal arise fi om variations in beam intensity caused by local distortions of the lattice. Dislocation densities of up to 10 mm can be resolved in transmission studies or ten times this by the reflection technique. This resolution is lower than that obtainable by transmission electron microscopy, but the sample used may be thicker and does not have to be examined under high vacuum. X-ray beams also produce less radiation damage in the sample. When decomposition proceeds beyond a > 0.01, distortion of the lattice is such that the X-ray image loses resolution and the exposures required become even longer. Reflection data obtained at several different diffraction angles may be required to characterize the imperfections present. 

In the case of titanium, our aim was to determine the valence of some rare-earth titanates by the x-ray spectroscopic method. The secondary-reflection Koj j titanium lines were recorded photographically by means of a high-vacuum x-ray spectrograph with Johann focusing. 

Streitwieser noticed that the HOMOs of C Hg have the correct symmetry to interact with the 5/orbitals of an actinide (or 4/of a lanthanide). This led to the preparation of the sandwich complex bis(cyclooctatetraene)uranium (uran-ocene). Uranocene is pyrophoric in air, but it thermally very robust. It forms deep green crystals which can be sublimed under vacuum. X-ray diffraction shows that the rings are parallel and eclipsed (Dg ). 

Structural and physical properties of solid solutions Ce Sm B were studied by Aivazov et al. (1980) on a series of samples prepared by borothermal reduction of the mixed oxides at 1700°C in vacuum. X-ray and chemical analysis revealed a continuous solid solubility of SmBj, to CeB i, CaB -type, Pm3m (table 4). Magnetic susceptibilities (80-1000 K 3, 5, 10 kOe) revealed Sm-ions to be present in different valence states. Hall emf, electrical conductivity and thermo-emf were also measured on specimens obtained by hotpressing at 1900-2000°C, 500 kg/cm in vacuum. 

The nature of the exchange interaction in solid solutions La,Eu,, B6 was investigated by Mercurio et al. (1979). Samples were prepared by borothermal reduction of mixed oxides at 1550°C in high vacuum (X-ray and chemical analysis). No lattice parameter data were given. 

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