There are many types of applications where a lubricant can be exposed to radiation, such as medical appliances, nuclear power generation plants, x-ray imaging equipment, a sterilisation process and even aerospace related applications. The grease/lubricant can be exposed to different forms of radiation including alpha, beta, gamma, x-ray and neutron radiation.
Lubricant Degradation. All organic matter will be subject to radiolysis (molecular scission induced by ionising radiation) but lubricants made from molecules containing aromatic ring structures exhibit greater stability against radiation induced decomposition when compared with lubricants with straight chain hydrocarbon structures. When a lubricant is exposed to a radiation level that it cannot cope with, this results in the thickening and polymerisation of the base oil, a darkening in colour, oxidation and degradation of the thickening system and/or additives. If you are confused by the terminology use here, such as ‘base oil’ and ‘thickener’ then consider our article/video (opens in new tab) What Is Grease?
Radiation Resistant Lubricant Product Options. We offer a radiation resistant line of base oils containing aromatic ring structures such as Polyphenylether (PPE) and Alkylated Naphthalenes (AN) as well as product line up of non-hydrogenous Perfluoropolyether (PFPE) grease and oil; the fluorine-carbon bond is one of the strongest bonds known in organic molecules and therefore resistant to radiation degradation.
Radiation Resistance Data And Our Typical Customer. Why don’t we have stacks of radiation resistance data on our products? The answer to this is due to our typical customer so, before reading about the individual radiation resistant lubricants we offer it is relevant to have an insight into our typical customer, which is often beyond the needs of a maintenance repair operation (MRO) engineer. The Synrad 1252 is the nearest product we have to an general maintenance/MRO grease; most of our customers use our grease to lubricate component parts inside their own finished product/device, that could be a spring in a medical appliance, an actuator inside some lifting equipment, a collimator inside scanner/x-ray equipment etc. Typically a device manufacturer will need a specialist lubricant for their device and will have their own unique performance and functional life expectations; the device manufacturer may well ask for our advice on the most appropriate grease given the application criteria and will then purchase a small volume of the chosen lubricant from our range for extensive evaluation/testing; our lubricants are intended to be ‘lube for life’ and are at the premium end of the market, in terms of performance and price. The point here is that our customer owns the intellectual property (IP) for the device specific test data that is generated, so we are unable to publish the data on our website. We can offer samples for evaluation but a good level of engagement is required by the customer for this sample to be supplied free of charge; we would want information about the application, the commercial potential and would want performance feedback and/or test data insight.
Radiation resistance testing is complicated and is cost prohibitive. Even if we had extensive radiation resistance data, our typical customer would still have to conduct their own testing with the relevant lubricant as their own testing would be specific to their own device/application….e.g. radiation type and amount of exposure, speed, force, wear, functional life etc. So at best, any radiation resistance data we could use for marketing purposes would only help a device manufacturer determine whether it is worth short listing our grease/lubricant for evaluation.
Base Oil Selection Is The Key For A Radiation Resistant Grease. Whilst short on hard data, the radiation resistance levels of our products is not just theoretical, it is also based on real world customer feedback; from our experience is it possible to give crude radiation resistance ranking of our most popular radiation resistant grease products based on the type of base oil used in the grease. Below we have an insight into the base oils used in radiation resistant grease formulation, we also sell these type of oils separately. If the reader is just focused on product selection rather than background theory, you may want to skip over to the article overview of the radiation resistant grease range now or straight after reading the below. If the reader is a little confused by the terminology of ‘base oil’ and ‘thickener’ then it could be good idea to watch a short video to under stand What Is Grease? (opens in new tab)
The following base oils are listed in order by ranking, the most radiation resistant base being listed first:
1. Polyphenylether (PPE)
The structural formulation of a PPE lends itself to radiation resistance, the phenolic rings will spin when hit by radiation and re-attach. This makes PPE oil and any grease that is PPE based as the best option for device manufacturers that need to lubricate component parts that are exposed to radiation. A good example is that we offer a PPE based grease that has a superb pedigree as a collimator lubricant for a large medical scanning device manufacturer. It should be noted that PPEs are very costly but as quite often there is no other option that to pay the premium for the level radiation resistance offered by a PPE based oil or grease. We also have a PPE oil that is used often used for sintered bearings that are operating in devices with a high level of radiation exposure.
A PPE oil contains hydrogen, if hydrogen content is an issue then the reader should consider a PFPE (read further/below). PPE oils don’t have a wide temperature range and are not suitable for sub-zero applications, which is not normally a problem especially in a typical hospital/medical environment. Find out more about PPE oil (opens in new tab).
2. Perfluoropolyether (PFPE)
It is the fluorine-carbon bonds of the oil that give PFPEs the strength to resist radiation, so it resists radiation in a different way to a PPE oil. If a customer has concerns about the presence of hydrogen then a PFPE should be considered as it should have no hydrogen in the finished lubricant as hydrogen is replaced by fluorine; in reality there may be some small traces of hydrogen present, but this would be parts per million.
PFPE based lubricant are at the premium end of the product portfolio, in due to their inherently low vapour pressure characteristics, resistance to hazardous chemicals/gases and their ability to cope with extreme temperature, which could be a factor if the reader has a particular application in mind; the temperature capabilities of some PFPE lubricants is as low as -90°C and as high as 250°C. Find out more about PFPE oil (opens in new tab).
Alkylated Naphthalene (AN)
Considered to have a good level of radiation resistance, you’ll see from the molecular structure on the graphic below that this base oil benefits from aromatic ring structures which help to resist radiation. If the reader is interested in an MRO type application then then an AN based grease is the closest we have to something that could be considered a good mechanical lubricating grease for use in areas that are exposed to radiation. We do know that our AN based grease has performed very well in an environment where expected radiation resistance is 3 x 10 9 Rads but we are unable to disclose further information. Find out more about AN oil (opens in new tab).
We can assist with radiation resistance grease for both mechanical and electrical applications. From mechanical instruments requiring minimal viscosity change over wide temperature to slow and high speed gears and bearings, we are confident that we can meet your lubrication expectations, so now please take a look at our overview of the radiation resistant grease range article.