The influence of surface contaminations on the ignition and maintenance of vacuum discharges is discussed qualitatively. Surface analysis of the electrodes and gas analysis during the discharges demonstrate that fresh electrodes contain always impurities within the upper surface layers, which affect the behaviour of vacuum arcs and vacuum breakdowns. The most effective way for cleaning the surfaces are the dischnrges themselves, if they burn in UHV. During that cleaning the following variations have been found: Arc cnthodes spots change from rapid moving ones with small erosion (type 1) to slow ones with strong erosion (type 2). The ignition of nanosecond discharges needs higher field strength and field emission current density. Polishing effects by short discharges (< 5 n s ) become more pronounced. Erosion craters in nanosecond discharges increase.
The synthesis of zeolite beta has been studied using the following templating agents : (i) tetraethylammonium hydroxide (TEA;) (ii) tetraethylammonium bromide-diethanolamine; and (iii) tetraethylammonium hydroxide-tetraethylammonium bromidetriethanolamine. TEA+ ions and TEAOH molecules only have a structure-directing effect. The ratio (Si + Al)/TEA+ in the gel was varied from 2 to 10, the Si/Al ratio from 12 to 10oO. The temperature of crystallization was chosen in the range 368-443 K. The samples were characterized using X-ray diffraction, micrographs, chemical analysis, thermal analysis, IR spectroscopy and nitrogen adsorption. Zeolite beta of good crystallinity (micropore volume = 0.28 cm3 g-') was obtained with Si/Al ratios from 14 to 72. The acid strength and number of acid sites were determined from the calorimetrically measured heat of NH, sorption and from the TPD of NH,. The initial acid strengths of zeolite beta (up to 185 kJ mol-') are higher than those of other high-silica zeolites.Polycrystalline agglomerates are formed instead of small single crystals on the addition of diethanolamine to the synthesis gel. The agglomerates are characterized by a high intercrystalline volume (>0.47 cm3 g-I), which can be influenced in a definite manner by variation of the TEABr/diethanolamine ratio. The presence of triethanolamine initiates the transformation of zeolite beta into a Si02 layer structure at 368 K.
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