Gages, high vacuum

It is a high-vacuum gage made up of two cathodes and one anode placed in a magnetic field produced by a permanent magnet (see Fig. 1.33). Electrons due to natural radioactivity or to field emission start a discharge in the gas. The presence of the magnetic field produces paths about 100 times longer than the distance between the electrodes. Positive ions are collected by the cathodes. 

In the following procedures a standard glass vacuum line with high-vacuum stopcocks (lubricated with Kel-F-90 grease ) is used. Because of the reactivity of many of the compounds with mercury, it is convenient to use a null-point pressure device, such as a Booth-Cromer16 pressure gage or spiral gage. A mercury manometer covered with Kel-F-3 oil can be used. 

Apparatus and Materials. A standard Stock-type high vacuum line was used, except for experiments with S03 or CH3NF2. In these cases stopcocks lubricated witn Kel F-90 grease were used, and pressures were measured with a Bourdon gage. 

Careful application of some new experimental techniques promises advances in the elucidation of the relation between detailed surface structure and reactivity in the chemisorption of a gas on a metal. Among these experimental techniques are the field-emission microscope (1-3), the inverted ionization gage (4), and modern high-vacuum technology (5). The use of the field-emission microscope technique for the study of the adsorption of oxygen (6) on tungsten has yielded recently data on the surface mobility... 

Fig. 11.5. Diagram illustrating the components of an ESI source. A solution from a pump or the eluent from an HPLC is introduced through a narrow gage needle (approximately 150 pm i.d.). The voltage differential (4-5 kV) between the needle and the counter electrode causes the solution to form a fine spray of small charged droplets. At elevated flow rates (greater than a few pl/min up to 1 ml/min), the formation of droplets is assisted by a high velocity flow of N2 (pneumatically assisted ESI). Once formed, the droplets diminish in size due to evaporative processes and droplet fission resulting from coulombic repulsion (the so-called coulombic explosions ). The preformed ions in the droplets remain after complete evaporation of the solvent or are ejected from the droplet surface (ion evaporation) by the same forces of coulombic repulsion that cause droplet fission. The ions are transformed into the vacuum envelope of the instrument and to the mass analyzer(s) through the heated transfer tube, one or more skimmers and a series of lenses.

The pressure was measured using a borosilicate glass Bourdon gage which was sensitive to 0.1 mm. of mercury as a null instrument to a mercury manometer. The final pressure was measured after the reaction vessel had been heated above 200° C. for 8 hours or longer. The maximum dead space of 14 cc. was efficiently flushed with oxygen at the start of each experiment and was duly corrected for in the calculation (2) of the ozone concentrations. The hollow-bore vacuum stopcocks used in the system were lubricated with Halocarbon (high temperature grade) stopcock lubricant. The usual precautions were taken to minimize the amount of mercury vapor in the system. 

Figure 3.1. A schema of the apparatus for the kinetic investigation of the gas evoiution. 1, the reaction vessel 2, vacuum gage 3, gutters for sampling of the gaseous products 4, vacuum cocks 5, the heating furnace with rectangular profiles of temperatures, high-temperature thermocouple 7, thermoregulator 8, ampule with sample.

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