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In vacuum coating and other high-vacuum processes, diffusion pump oil may sometimes be considered simply as:
“a silicone oil that can withstand high temperature.”
However, a diffusion pump fluid has a much more specific function.
Inside a diffusion pump, the working fluid is repeatedly heated, vaporized, directed as high-speed vapor jets, condensed and recirculated.
The real question is therefore not only:
“Can this silicone fluid withstand heat?”
It is:
“Can this fluid serve as the working medium of the diffusion pump and support the required vacuum environment?”
A diffusion pump uses vapor jets to transport gas molecules toward the backing-pump stage.
As the system reaches high vacuum, the behavior of the working fluid itself becomes increasingly important.
This is one reason diffusion pump fluids are designed with very low vapor pressure.
IOTA 704 is a silicone diffusion pump fluid designed for high-vacuum applications. Published IOTA specifications list an ultimate vacuum in the 10⁻⁷–10⁻⁸ torr range, viscosity of 38±3 cSt at 25°C, and a flash point of at least 210°C.
These specifications should be considered together rather than using one parameter alone as the selection criterion.
The working fluid experiences repeated heating and condensation during diffusion-pump operation.
Its stability under these operating conditions therefore matters for long-term vacuum performance and maintenance.
IOTA describes 704 as a thermally and chemically stable diffusion pump fluid intended for demanding high-vacuum operation.
Selection should therefore consider:
Target vacuum + pump model + operating temperature + operating cycle + process requirements
It should not be assumed that one silicone fluid can replace another simply because both are called “silicone oil.”
Conventional PDMS fluids, industrial lubricating silicone oils and diffusion pump fluids are designed for different functions.
For a 704-type replacement, first confirm:
Then evaluate the candidate fluid in the actual system.
Published IOTA application information includes:
For this reason, IOTA 704 is better described as a:
High Vacuum Silicone Diffusion Pump Oil
rather than simply a high-temperature silicone oil.
For an IOTA 704 evaluation, provide:
Current pump fluid + diffusion pump model + target vacuum + operating temperature + application + operating cycle
Replacement should be confirmed through equipment compatibility and actual operating tests before bulk use.
What is IOTA 704?
IOTA 704 is a silicone diffusion pump fluid developed for high-vacuum systems.
Can IOTA 704 be used for vacuum coating?
Yes. Vacuum and optical coating are among its published application areas.
Can conventional PDMS replace 704 diffusion pump fluid?
Direct replacement should not be assumed. Their intended functions are different.
What is the difference between IOTA 704 and IOTA 705?
They are positioned for different vacuum requirements, with 705 intended for more demanding ultra-high-vacuum applications.
What should be checked before replacing an existing 704 fluid?
Pump model, current fluid, target vacuum, operating conditions and process requirements should be reviewed.
Related Product:
IOTA 704 Silicone Diffusion Pump Oil
