Contamination, protecting vacuum

Figure 4. Two techniques for protecting vacuum system from contamination...

Almost any spectrometer can be used in the vacuum ultraviolet (about 1100-2000 A) by properly designing the enclosure and utilizing a vacuum pumping system. Vacuum pumping systems usually include a mechanical pump with an oil diffusion pump. A cold trap provides protection of the grating and the internal optics from long-term oil contamination. A vacuum as low as 10 Torr frequently is used. 

Non-contamination/Decontamination Protect vacuum pumps against contamination by scrubbers or HEPA filters and vent them into the hood (49). Decontaminate vacuum pumps or other contaminated equipment, including glassware, in the hood before removing them from the controlled area (49, 50). Decontaminate the controlled area before normal work is resumed there (50). 

HEPA vacuum heavily contaminated protective work clothing while it is still being worn. At no time may lead be removed from protective clothing by any means whioh result in uncontrolled dispersal of lead into the air ... 

Each newly cleaved mica surface is very clean. Flowever, it is known that mica has a strong tendency to spontaneously adsorb particles [45] or organic contaminants [46], which may affect subsequent measurements. The mica sheets are cut into 10 nun x 10 nun sized samples using a hot platinum wire, then laid down onto a thick and clean 100 nun x 100 nun mica backing sheet for protection. On the backing sheet, the mica samples can be transferred into a vacuum chamber for themial evaporation of typically 50-55 mn thick silver mirrors. 

Since about 1965, efficient vacuum evaporators have been used in most plants. Second stage evaporators, where the ammonium nitrate is concentrated to more than 99%, are designed to retain only a small volume of melt, have short residence times, and are protected from overheating and contamination by sensitizers. Falling film units are especially suited for this appHcation. 

Pyridinecarboxaldehyde (nicotinaldehyde) was supplied by Aldrich-Europe, Beerse, Belgium. The checkers purified this reagent by fractional distillation, b.p. 95-97° (15 mm.). The submitters stress that 3-pyridinecarboxaldehyde should be completely free from contamination by the acid. They stirred 150 g. of the aldehyde with 100 g. of potassium carbonate and 300 ml. of ethanol for 12 hours, filtered the suspended solid, and fractionally distilled the filtrate through a 30-cm. Vigreux column using a water aspirator. However, the checkers found that the recovery of aldehyde from this procedure was very low, and recommend vacuum distillation instead. 3-Pyridinecarboxaldehyde is a powerful skin irritant and should be handled with protective gloves. 

The chemical Industry requires vacuum pumps which are highly reliable and which do not produce waste materials such as contaminated waste oil or waste water. If this can be done, the operating costs of such a vacuum pump are low in view of the measures otherwise required for protecting the environment (disposal of waste oil and water, for example). For operation of the simple and rugged ALL-ex pump from LEYBOLD there are no restrictions as to the vapor flow or the pressure range during continuous operation. The ALL-ex may be operated within the entire pressure range from 5 to 1000 mbar without restrictions. 

A vacuum pump should be scrupulously protected from corrosive vapors and materials which will be absorbed in the pump oil or condense in the pump. For most laboratory operations a low-temperature trap is employed for this purpose, and in the case of fluorine handling systems a soda-lime trap is used to neutralize the corrosive gases. Despite these precautions, the pump oil does eventually break down and become contaminated. Regular oil changes should be scheduled for a pump at about yearly intervals for a well-protected pump and more often for pumps which are not well protected. 

Wear breathing apparatus, eye protection, laboratory coat, and butyl rubber gloves. Cover spill with 1 1 1 mixture by weight of sodium carbonate or calcium carbonate, clay cat litter (bentonite), and sand.8 For each 1 mL of iron pentacarbonyl, place 45-50 mL of household bleach (about 5% sodium hypochlorite solution) in a plastic bucket equipped with a stirrer and located in a fume hood. Dilute the bleach with three times its volume of water and, to this solution, slowly add the contaminated spill mix while stirring. Continue the stirring for a period of 48 hours, and then filter the slurry using vacuum filtration. The... 

However, if a glove box is not available for the synthesis, the reaction can also be performed in a dry, inert solvent which covers the reaction mixture and protects it from hydrolysis. An advantage of this procedure is that the solvent, which is typically an alkane, can also react as a heat carrier in the exothermic reaction. After completion of the reaction the ionic liquid forms a second layer below the solvent. The solvent can be removed by simple distillation before use of the ionic liquid. However, the ionic liquid will be contaminated with the organic solvent, which has to be removed under vacuum. 

Ballasting decreases the potential vacuum a pump could normally produce (about one decade of performance capability ). However, it dramatically improves its performance over the long run in the presence of condensable vapors. Plus, it helps to protect pump oils from contamination, which decreases pump breakdown possibilities and increases the longevity of the pump oils. Incidentally, running a pump with a ballast causes the pump to run a bit hotter than it otherwise would, which decreases the potential gas-carrying ability of the oil. 

Balzers TPU 170 and the Welch 3134 are good-quality turbomolecular pumps. They have an ultimate vacuum limit of 10 Torr and pumping speeds of 300 L s from 10 to 10 Torr. Other pumps with speeds up to 10,000 L s are available, although these rates are reduced somewhat for light gases such as H2 and He, which have high molecular velocities. The turbomolecular pump is a very clean pump, requires no trap between itself and the system, and is not sensitive to contamination (although in some cases the forepump should be protected by a cold trap). It is not widely used in routine laboratory applications however, as it is quite expensive and demands careful maintenance. 

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