Silicone Oil for Freeze Dryers: Types and Common Viscosity Specifications
I. Types of silicone oil for freeze dryers
The primary silicone oil used in freeze dryers is dimethyl silicone oil (Polydimethylsiloxane, PDMS). Methylphenyl silicone oil may be adopted in a small number of high-end applications, yet dimethyl silicone oil remains the mainstream option for the following merits:
- Extremely low freezing point (models with low viscosity can reach -80°C), maintaining fluidity under low-temperature working conditions of freeze dryers
- Low viscosity-temperature coefficient, with slight viscosity variation against temperature fluctuation to guarantee stable heat transfer
- Chemical inertness and excellent compatibility with metals, rubber, plastics and other materials
- Outstanding thermal stability, applicable within a wide temperature range of -80°C to 220°C
- High temperature control accuracy, achieving shelf temperature deviation within ±1°C when served as circulating medium
II. Common viscosity specifications (measured at 40°C or 25°C)
| Viscosity Grade | Typical Properties | Applicable Scenarios |
|---|---|---|
| 2cSt (e.g., Shin-Etsu) | Freezing point of -80°C, optimum fluidity and highest heat conduction efficiency | Ultra-low-temperature freeze-drying processes requiring rapid cooling |
| 5cSt (e.g., QL CHEMICAL) | Balanced fluidity and stability, the most widely used grade | General-purpose freeze dryers for laboratory and pilot-scale equipment |
| 10–20cSt | Higher flash point (approx. 246°C for 20cSt) and superior thermal stability | Production-scale equipment for complex processes requiring both heating and cooling |
| 50cSt and above | High viscosity, reduced fluidity and poorer heat conduction efficiency | Special high-temperature freeze-drying processes, not recommended for conventional use |
III. Selection Recommendations
- Prioritize low-viscosity silicone oil (2cSt, 5cSt) for superior low-temperature fluidity and heat transfer efficiency, ensuring uniform shelf temperature.
- Pharmaceutical or medical-grade freeze dryers shall adopt high-purity, low-volatility dedicated silicone oil to prevent sample contamination.
- Distinguish heat/circulation silicone oil for freeze dryers from vacuum pump silicone oil; the two are for separate purposes and cannot be mixed.
Summary
Dimethyl silicone oil is the standard choice for freeze dryers. Among all grades, 5cSt delivers the best overall performance for general use. 2cSt fits ultra-low-temperature applications, while 10–20cSt suits production equipment with high thermal stability requirements.
Links