Check the Working Temperature
When selecting a grease, the working temperature is extremely important because the vapour pressure of materials is highly dependent on temperature. E.g., if the grease vapour pressure is higher than the vacuum level then the grease will evaporate, causing contamination and leaks. However, there are further temperature considerations unrelated to vacuum such as:
Too Hot (melting or thermal degradation)
If grease is used above its recommended operating temperature it can melt or, in some cases, thermally degrade. Melting is usually reversible but can cause leaks or contamination as the grease moves away from the site of application. Thermal degradation can lead to contamination as the grease breaks down into smaller molecules which can be deposited in the vacuum system, as well as leaks if it degrades and can no longer form a seal. Apiezon offer products rated for use up to 250°C (Apiezon PFPE 501) and 240°C (Apiezon H grease).
Too Cold (cracking or crazing)
If being used as a lubricant, as the grease hardens during cooling there will be a point which it can no longer provide adequate lubrication. Always check the product datasheet for recommendations of the lowest temperature for lubrication.
Even if the grease is being used as a sealant or sample mount it is still important to consider the lowest temperature. If taken below the recommended operating temperature then microcracks can form in the grease, known as crazing. These cracks can lead to leaks in the vacuum or a reduction in thermal conductivity as a sample mount.
Apiezon N Grease
Apiezon N grease is world renowned for its low temperature craze-free properties and can be used even at cryogenic temperatures as a sealant or sample mount.
The next issue to consider when selecting the right grease is Compatibility of Materials. Click Compatibility of Materials to find out more.
To find out more about the Apiezon family of silicone-free high vacuum greases manufactured by M&I Materials Ltd, contact our team of experts available via our helpline: Apiezon Technical Helpline +44 (0)161 864 5409. Alternatively, please Contact Us and will be in touch shortly.