SPI Supplies

Octoil®-S Diffusion Pump Fluid

Dioctyl sebacate



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Appearance: Liquid, light color
Odor: Mild
Boiling Point: 450-480 °C @ 4 min
Melting Point: -62deg;C (-80deg;F)
CAS #: 122-62-3
Vapor Pressure (mm Hg @ 21deg;C (70deg; F): 0.1 torr at 150 deg;C
Vapor Density (Air=1): 14.7
Specific Gravity (water=1): 0.912
Solubility In Water: 0.01 gm1L
Refractive Index @ 25deg; C: 1.483


This is the original fluid that was used in the diffusion pumps of electron microscopes starting in the mid-1960's. The good news was that it worked well, good vacuums could be attained, and perhaps even more importantly, it was low cost.

However, this fluid is very non-forgiving when exposed even to small amounts of oxygen when hot. One miscue or malfunction of the automatic valving systems and the oil would "crack", necessitating the dropping of the diffusion pump and immediate changing of the fluid.

This fluid is still used in many SEMs and TEMs around the world, however, if it can possibly be done, one should be using Santovac 5 instead. At any given time, their vacuum system will be cleaner and their results will show less contamination because after all, the Octoil-S eventually will have to be replaced, and its useful lifetime is a lot less than Santovac 5.

Other applications:
The refractive index is reported to be 1.483 at 25deg; C (77deg; F). Because of the extremely low vapor pressure at room temperature, Octoil-S is able to be used as a stable and reliable refractive index fluid.

RoHS Button MSDS 00031
Silicone Monomer

Octoil-S Diffusion pump fluid

SPI #EachIn Stock
100 ml 00031-MB $32.95 Add to cartYes
500 ml 00031-RA   145.10 Add to cartYes
1000 ml (1 liter)00031-XP 209.15 Add to cartNo
Gallon 00031-XK 809.18 Add to cartNo

Storage conditions: Room temperature
Non-hazardous from stand point of shipping


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Thursday April 24, 2014
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