Abstract
A fluorocarbon fluid (“Fomblin”) has been investigated as a lubricant for a rotary mechanical pump. Although the backstreaming rate was only marginally (30 per cent) less than that of a mineral oil the emitted vapour and fragmented species (CF 2, CF 3, C 3F 3) were resistant ot the formation of carbonaceous and polymerized films (as occurs with hydrocarbons or silicone vapours) when exposed to electron bombardment. Resistance to polymerization and carbon deposition may arise from the low adsorption time and high bond strength of CF-radicals. The fluorocarbon fluid can also be evaporated by electron bombardment without leaving a decomposition residue. A rotary pump was operated at 110°C for 500 hr without signs of wear so that vapour with a saturated vp at this temperature may be pumped without gas-ballasting. The fluid shows marked resistance to reaction with exhausted gases (eg fluorinated species) and can afford corrosion protection to the pump. In conclusion experiments show that an all fluorocarbon system is possible with both diffusion and rotary pumps charged with the fluid, such an arrangement would be of value for electron beam systems if fluorocarbon radicals could be tolerated. However, the high cost of the fluid will currently restrict its use.
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