Clean vacuum systems

The contaminants in commercial boron trichloride usually are HCI and COCI2, as well as oxychlorides which have some volatility. The oxyhalides are readily removed by one or two trap-to-trap distillations in a clean vacuum system. Most of the HCl can be removed by holding the BCI3 at — 78°C and pumping away the volatiles for a brief period (some BCI3 is sacrificed in the process). Phosgene, which may be detected by its gas-phase infrared absorption at 850 cm"1, is very difficult to remove. Liquid boron tribromide is generally supplied in sealed ampules. If it is straw colored, dibromine is a likely impurity, and this... 

The surface extended X-ray absorption fine structure (SEXAFS) method can use either an electron or an ion detection signal (Koningsberger and Prins, 1988). The classification of analytical techniques may be considered in terms of incident and emitted radiation, resolution, and sensitivity, according to Table 4.7, which lists eight of the many possible techniques (Briggs and Seah, 1990 Buckley, 1981 Watts, 1990). Many of the surface analysis techniques were introduced into many laboratories over the years of 1968 to 1970. This resulted from the maturing of clean vacuum systems which could achieve pressures, down to 10"8 Pa. At these low pressures, it is possible to obtain and maintain atomically clean surfaces. 

The cross section for the 3H(maximum value at only 107 KeV incident deuteron energy. When thick ( 1 mg cm-2 thick deposit of titanium) titanium-tritium targets are used, however, the neutron yield continues to increase even above 200 KV acceleration potential. This is due to increased penetration of the deuteron beam into the tritium enriched layer. Since the penetration of molecular deuterium ions is less than that for monatomic deuterium ions for the same acceleration potential, accelerators using Penning ion sources require extremely clean vacuum systems to minimize build-up of deuteron absorbing deposits on the surface of the target. 

Use HEP A vacuum system before wet cleaning. Vacuum system should be dedicated for operating area... 

It is believed that the rate and the point of cleavage in the above reactions are sensitive to the presence of trace amounts of catalysts, and that for consistent results the syntheses should be carried out in a clean vacuum system. The checkers found that hydrogen iodide cleaved ClC8H4SiH3 to give ClC H4SiH2l and hydrogen when the reaction was carried out in a vacuum line W hich previously had been used for handling cobalt carbonyl compounds. 

The bombarding particle beam is accelerated and transported in the high vacuum system of the accelerator. The X-ray detector unit is encapsulated in a separate clean vacuum system. The irradiation of the sample may be performed in vacuum or under atmospheric conditions, depending on the size, physical state, and other parameters of the sample. To define the physical conditions mentioned above, special PIXE chambers of internal beam and external beam configurations are used for in vacuo and atmospheric irradiations, respectively. 

Cleaning, handling, and storage of vacuum surfaces should be done with as much care as the preparation of substrate surfaces discussed in Ch. 13. When cleaning vacuum system surfaces, care should be taken to not increase the surface area any more than necessary. Often simple cleaning processes work better than more elaborate processes. 

A vacuum system can be constmcted that includes a solar panel, ie, a leak-tight, instmmented vessel having a hole through which a gas vacuum pump operates. An approximate steady-state base pressure is estabUshed without test parts. It is assumed that the vessel with the test parts can be pumped down to the base pressure. The chamber is said to have an altitude potential corresponding to the height from the surface of the earth where the gas concentration is estimated to have the same approximate value as the base pressure of the clean, dry, and empty vacuum vessel. 

The burner and associated equipment must be wrapped up or otherwise protected against dirt and soot. The front doors are opened and plastic sheeting is attached to minimize the spread of soot. The tubes are brushed, and the soot and dirt are vacuumed away while brushing takes place. Some contractors have truck-mounted vacuum systems to increase efficiency and minimize post-boiler cleaning work. 

When constructing high vacuum apparatus, waxed tools should only be used when the apparatus under construction can be thoroughly cleaned afterwards. Otherwise wax may be present in the vacuum system, and will be removed by pumping only with extreme slowness. 

Polymer films were produced by surface catalysis on clean Ni(100) and Ni(lll) single crystals in a standard UHV vacuum system H2.131. The surfaces were atomically clean as determined from low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). Monomer was adsorbed on the nickel surfaces circa 150 K and reaction was induced by raising the temperature. Surface species were characterized by temperature programmed reaction (TPR), reflection infrared spectroscopy, and AES. Molecular orientations were inferred from the surface dipole selection rule of reflection infrared spectroscopy. The selection rule indicates that only molecular vibrations with a dynamic dipole normal to the surface will be infrared active [14.], thus for aromatic molecules the absence of a C=C stretch or a ring vibration mode indicates the ring must be parallel the surface. 

A clean and dry vacuum system (qpy = 0) with V = 2000 I (as in example 1) is to be pumped down to a pressure of Pend - 10 tAbar. Since this pressure is smaller than the ultimate pressure of the rotary piston pump (Sg max ... 

Caution. Metal hexafluorides are volatile, toxic, corrosive, and highly hygroscopic materials. They must be handled in a very dry, clean, fluorine-preconditioned metal vacuum system. The vacuum system should be constructed from stainless steel or Monel materials (glass is not acceptable if pure products are desired). Hydrogen fluoride also is quite toxic and volatile. If only one metal... 

I. Sodium. Probably the best known active hydrogen remover is sodium. When used outside a vacuum system, for instance as sodium wire to dry solvents, the sodium is little more than a support for a skin of sodium hydroxide. Inside a vacuum system, however, one can prepare films of sodium metal and one can prepare really clean sodium which will give a colourless solution of sodium ethoxide (see Section 5.2.1.). The method of making sodium films for the removal of acidic compounds from liquid reagents will be described and also a very much less well-known method involving sodium vapour and colloidal sodium. 

Document that the reservoir conforms to purchase specification and invoice. Verify and document that the vessel meets or exceeds the pressure rating (vacuum) specified in the purchase specifications. Perform vacuum hold tests on the tank and document. Acceptance ID tests will vary with the size of the system. A positive pressure test is often done in order to find leaks. Perform and document cleaning procedures used prior to placing the vessel in service. This completes the normal testing done on the tank prior to joining it to the vacuum system. 

The cleaning of the various catalyst samples has to be scrutinized for each material studied. For iron for example, the major impurity is sulfur, and its removal must be carried out outside the vacuum system in a furnace in a constant hydrogen flow for a long period of time (days). Trace metallic impurities or nonmetallic impurities may be removed either by argon ion bombardment in the vacuum chamber or by chemical treatment using gas-surface interactions of different types. 

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