Diffusion Pump Fluid.
Thermal stability; resists oxidation; chemically inert
Dow Corning 704 Diffusion Pump Fluid is a single-component fluid for high vacuums of 10-6 to 10-8 torr (untrapped)and 10-10 to 10-11 torr (trapped). It performs well in tough, rugged applications
and offers quick pumpdown, even after exposure to air at operating temperatures.