Perfluoropolyether—a Vacuum Pump Fluid resistant to Electron Induced Polymerization

GROWTH of polymer films on the components of electron beam instruments is a problem experienced widely because of the extensive use of oil pumps on such apparatus. Recently, new thermally stable fluids have become available which are based on oxygen linkage of fluorocarbon groups; we have found that they can be used in vacuum pumps without the attendant polymerization problems. An earlier study1 has shown that a high molecular weight (∼6,500 a.m.u.) perfluoropolyether fluid has lubricating properties suitable for use in rotary pumps. The work indicated that a similar fluid of greater volatility (molecular weight ∼3,000 a.m.u.) should be suitable for use in vapour stream pumps and here we give conclusive evidence of its value for this purpose. The fluids, known as ‘Fomblin’, are prepared for us by Montecatini Edison S.p.A. (see ref. 2).