Fluids, Krytox

In addition to the fluoroplastics and fluororubbers already described other fluoropolymers have been marketed. Polymers of hexafluoropropylene oxide are marketed by Du Pont (Krytox). These materials have a low molecular weight (2000-7000) and are either oils or greases. The oils are uses as lubricants, heat transfer fluids and non-flammable oils for diffusion pumps. The greases are also used as lubricants. They have good heat and oil resistance but it is said that explosions may result from contact with the surfaces aluminium or magnesium cuttings. 

Perfluoropolyethers have found widespread use as high-performance lubricants and several companies manufacture a range of these materials (Krytox , Du Pont Fomblin , Montefluos Demnum , Daikin). The Fomblin fluids and Krytox require the use of fluorine in the finishing stages [81] whilst Demnum is synthesised by polymerisation of the fluorooxetane 16 followed by per-fluorination using fluorine (Fig. 27) [82]. 

Perfluoropolyether fluids (ex., Krytox ) are commonly used as lubricants, dielectric fluids or heat transfer fluids in a number of space and military products. These fluids and other perfluorolubricants are almost impossible to dissolve in solvents other than halocarbons. Additionally, other halogenated damping fluids have compatibility problems with some of the common solvents which can dissolve the fluid. Early experiments with supercritical carbon dioxide indicated that it would dissolve both halogenated damping fluids and perfluoropolyether lubricants and thus was a candidate as a replacement solvent cleaning process. 

After the SCF system was operational, it was necessary to determine process parameters for removal of the common contaminants. Temperature, pressure, flow rate and time were identified as critical parameters and a number of experiments were designed using Taguchi methods to minimize the number of experiments necessary to accurately determine the effects of these parameters on the cleaning effectiveness. Damping fluid, Krytox 143AZ lubricant, and hydrocarbon vacuum pump oil were selected as the contaminants for removal. 

The results of the these experiments showed that the damping fluid, Krytox , and hydrocarbon oils all could be successfully removed using supercritical carbon dioxide at pressures in the range of 1200-3000 psi and temperatures in the range of 90 to 185°F. The Krytox lubricant was easily removed at the lower extremes, while the hydrocarbon oil was the most difficult to remove. 

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