A novel nonevaporable getter (NEG) coating was developed with an activation temperature as low as 133 °C, that is, a palladium/titanium coating with extremely low oxygen concentration (oxygen-free Pd/Ti coating). The substrate was coated with Ti and then overcoated with Pd using sublimation under ultrahigh vacuum conditions. The morphology and surface elemental composition of the Pd/Ti thin film were investigated with electron microscopes and x-ray photoelectron spectroscopy, respectively. The thicknesses of Ti and Pd films were approximately 1.3 μm and 50 nm, and the Ti film was completely overcoated by the Pd film. Ti and oxygen were found to be negligible on the oxygen-free Pd/Ti surface. The oxygen-free Pd/Ti coating was applied to the formed bellows. The bellows was successively baked at 133 °C for 12 h, 176 °C for 3.5 h, and 200 °C for 3.5 h. After sealing off a turbomolecular pump from the vacuum system containing the bellows, the pressure reached values of 4.6 × 10−6, 1.7 × 10−7, and 6.1 × 10−8 Pa, respectively. The pumping speeds of the bellows were estimated to be 0.028, 0.23, and 0.23 l s−1, respectively. These results demonstrate that oxygen-free Pd/Ti deposition can be used as a new NEG coating for vacuum systems with a baking temperature of 133 °C or higher.
We have developed a new non-evaporable getter (NEG) coating using titanium and palladium vacuum sublimation. The inner wall of the test chamber was coated with a 1-µm Ti thin film using the Ti sublimation pumps under a vacuum of 6.5×10-6 Pa (Ti-coated chamber). This chamber was then coated with a 10-nm Pd thin film using the Pd sublimation filament under a vacuum of 2.4×10-4 Pa (Pd/Ti-coated chamber). The uncoated, Ti-coated, and Pd/Ti-coated chambers were baked for 6 h at a maximum temperature of 185℃. Five hours after closing the valve, the pressures in the Pd/Ticoated chamber were about 1.4×10-6 Pa even after six heating-venting cycles. The relatively low activation temperature was attributed to the low concentration of oxygen in the Pd/Ti thin films. The Pd/Ti coating can be used for vacuum systems that are frequently vented.
We have developed a novel nonevaporable getter named oxygen-free Pd/Ti. After activation at 133℃, oxygen-free Pd/Ti evacuates H2 and CO. Its pumping speeds do not decrease even after repeated cycles of activation and exposure to the air. Surface analysis by synchrotron radiation X-ray photoelectron spectroscopy showed that the carbon contamination decreased to an extent on heating in UHV, but decreased considerably on heating under an O2 pressure. The partial pressures of H2, CO, H2O, and CH4 in an oxygen-free-Pd/Ti coated chamber reduced to some degree after baking in UHV, but reduced remarkably after baking under an O2 pressure (O2 baking). Catalytic chemical reactions which remove carbon and hydrogen adsorbed on Pd surfaces appear to be responsible for the reduction of the partial pressures of H2, CO, H2O, and CH4. The pumping speeds of the oxygen-free Pd/Ti coated chamber for H2 and CO improved remarkably after O2 baking.
The grain growth behavior and the geometrical aspects of grain boundaries in Fe±Al wire which was fabricated by the liquid metal spinning method (LMSM) were investigated with respect to grain size distributions and geometrical features of the grain boundaries. An improved method previously proposed by the present authors was applied to Scanning Electron Microscopy-Electron Channeling Pattern (SEM-ECP) in order to clarify the boundary characteristics. The present investigation showed that grains initially smaller in size than the diameter of the wire grew up during heat treatments, and subsequently transformed into the ªbamboo-likeº structure in which the grains were aligned one-dimensionally along the wire direction. General boundaries were much more frequently observed than special boundaries after the heat treatments. Most of the boundary planes which remained until the late stages of the heat treatments were asymmetric, i.e., they had two different sets of crystallographic indices which were individually attached with two grains adjacent to each other. In the characterization of the tilt±twist component of the grain boundaries, double peaks outstandingly appeared in the distribution curves. The mobility of the grain boundaries was not sensitive to the crystallographic symmetry of the boundaries.Das Wachstumsverhalten von Ko È rnern in Fe±Al-Dra È hten, die mit Hilfe der ¹Flu È ssigmetall-Spinning-Methodeª (LMSM) hergestellt wurden, ist hinsichtlich der Verteilung der Korngro È ûe sowie der geometrischen Eigenschaften untersucht worden. Ein verbessertes Rasterelektronenmikroskop mit ¹Elektronen-Channeling-Patternª (SEM-ECP), das von einem der Autoren bereits vorgeschlagen wurde, wurde verwendet, um die Grenzfla È cheneigenschaften aufzukla È ren. Die Untersuchung zeigte, daû die kleinen Ko È rner anfa È nglich eine Gro È ûe annehmen, deren Ausdehnung kleiner als der Drahtdurchmesser ist. Die Korngro È ûe nahm wa È hrend des Heizexperimentes zu und ging schlieûlich in eine ¹Bambus-a È hnlicheª Struktur u È ber, in welcher die Ko È rner eindimensional entlang der Drahtrichtung ausgerichtet sind. Korngrenzen, die einen Koinzidenzwinkel aufweisen, traten ha È ufiger auf als andere. Die Beweglichkeit der Korngrenzen wurde nicht durch die kristallographischen Symmetrieebenen der Korngrenzen beeinfluût.
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