Apiezon® oils consist of esters or specially selected hydrocarbon fractions. They have very low vapor pressures and are very stable.
They were developed for, and are ideally suited as, vapor-diffusion pump fluids. Apiezon oils have advantages over other types of vacuum pump oils in many high vacuum applications particularly with electrical and electronic equipment. The main thermal degradation product of Apiezon oils is carbon which forms conducting layers, as distinct from the insulating layers formed by silicones and their degradation products. This is of particular importance; for example, in vacuum operations with systems containing electrical relays where a minute trace of silicone can effectively open-circuit the relay. Similarly, in apparatus involving the movement of charged particles, as in electron microscopes, mass spectrographs, or pumped X-ray machines, minute traces of silicone or silicate deposits can seriously affect the operation of the equipment. Apiezon oils are extremely efficient pumping oils for this type of equipment and deposits of degradation products have little or no harmful effect.
Table 1 – Properties of Diffusion Pump Oils
| AP 201 | AP301 | Oil J | Oil K | |
| Ultimate Pressure obtainable, torr | 4×10-5 | 10-7 | ||
| Average boiling point, °C at 1 torr | 160 | 225 | ||
| Specific gravity at 20 °C Specific Gravity at 30 °C |
0.862 | 0.979 | 0.918 0.911 |
0.919 0.914 |
| Density g/mL at 10°C Density g/mL at 20°C Density g/mL at 30 °C Density g/mL at 40 °C |
0.923 0.918 0.909 0.903 |
0.921 0.916 0.912 0.904 |
||
| Flash Point, Pensky-Martins, oF closed (ASTM D93 and IP 36/63, open fire | 385
399 |
530
581 |
590 665 >700 |
645 660 >700 |
| Viscosity, dynamic at 40 °C | 3005 | 5160 | ||
| Pour Point, ASTM, oF (D97/66) | -22 | -40 | 30 | 30 |
| Coefficient of expansion per °C (a) | 0.00070 | 0.00070 | 0.00062 | |
| Coefficient of expansion per °C (b) | 0.00083 | 0.00070 | ||
| Average Molecular Weight | 310 | 470 | 1130 | 1355 |
| Refractive Index at 20 °C (c) | 1.4760 | 1.453 | ||
| Thermal Conductivity w/m/ °C | 0.167 | 0.169 | ||
| Specific heat at 25 °, cal/g | 0.46 | 0.48 | 0.46 |
(a) over 20 °C to 30 °C (ASTM D 1903/61T)
(b) over 10 °C to 40 °C
(c) ASTM D 1807-62T Sodium Line