Wear and Degradation Characteristics of Perfluoroalkylpolyethers (PFPEs) in High Vacuum©

Wear and degradation as exhibited by degassing of three commercially available perfluoroalkylpolyethers, A, straight chain with acetal linkage (OCF2CF2)p(OCF2)q;B, straight chain without acetal linkage (CF2CF2CF2O)n; C, branched chain (CFCF3CF2O)m, were evaluated at 0.025 mis under 1 to 300 N at 10−5 Pa in a four-ball configuration using 440C and Si3N4 balls, Φ:6.35 mm, as test specimens. A quadrupole mass spectrometer having a mass range of 1 to 200 amu was employed to analyze gaseous products released from the sliding surfaces. Disregarding the gas released, Oil C showed slightly better wear characteristics than B, but far better than A when tested with a 440C ball on 440C balls. Taking gas evolution into account, Oil B carried the highest load; the initial degassing was detected at the Hertzian pressure of 1 GPa for A, 2 GPa for B, and 1.75 GPa for C when using 440C balls, and at 1.5 GPa for A and 2.75 GPa for C when using Si3N4 balls. Oil B evaluated with Si3N4 balls did not evolve gases even at 2.75 GPa. The initial outgassing load of sliding pairs of a Si3N4 ball against 440C balls and vice versa was closer to that of a 440C ball on 440C balls than to a Si3N4 ball on Si3N4 balls. Mass spectra patterns obtained from experiments with a Si3N4 ball on Si3N4 balls were similar to those from experiments with a 440C ball on 440C balls. Oil A released more CFO+ (m/e = 47) and CF2O+ (m/e = 66) than Oil B or C, which could originate from the acetal linkage of its molecular structure as shown by Mori and Morales (1).