Vacuum working range

Fig. 2.25. Working range of vacuum pumps and multistage pumpsets.

There were no substantial differences between the magnitudes of the photovoltages on the different substrate electrodes despite the 1,4-V range in their vacuum work functions (Fig. 7). The slight decrease in Voc on Pt substrates was caused by the enhanced rate of recombination at this highly catalytic electrode... 

Vacuum pumps, either singly or, more usually, as part of a pumping system, create and maintain the conditions appropriate to a required process. Each of the types of vacuum pump available has a characteristic working range in which it is effective. Outside that range, shortcomings in performance become apparent. 

In the high-vacuum range, fractionating vapour jet pumps are employed as diffusion pumps after oil seal vacuum pumps. These vapour jet diffusion pumps are equipped with especially constmcted nozzles with a diffusion slot. The working range of this type only starts in medium high vacuum and leads to high vacuum or molecular distillation. 

Due to the principle of operation, the working range of LRVPs is hmited by the vapour pressure of the ring liquid. However, if a vacuum is necessary below the double vapour pressure of the operating liquid, then a further compressor must be connected upstream, with the aid of which one can realise lower intake pressures. 

Speciai working range of vacuum pumps I I Normal working range of vacuum pumps Figure 5.2 Common operating pressure ranges of mechanical vacuum pumps. 

The relationship between the BET monolayer capacity of physically adsorbed water and the hydroxyl content of the surface of silica has been examined by Naono and his co-workers in a systematic study, following the earlier work by Morimoto. Samples of the starting material—a silica gel—were heated for 4 hours in vacuum at a succession of temperatures ranging from 25 to 1000°C, and the surface concentration of hydroxyl groups of each sample was obtained from the further loss on ignition at 1100°C combined with the BET-nitrogen area. Two complete water isotherms were determined at 20°C on each sample, and to ensure complete... 

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