This is recommended as the standard diffusion pump oil in many Japanese electron microscopes. It is a naphthalene-based synthetic material and should not be mixed with other types of diffusion pump fluids.
Recommended for TEMs and SEMs, this is the original LION S diffusion pump oil, manufactured by the Lion Corporation, Japan. It has been and is still used in diffusion pumps used in instruments manufactured in Japan. Lion S diffusion oil has a high resistance against oxidation and works well with small and medium size diffusion pumps.
Download the MSD sheet here