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Apiezon® Diffusion Pump Fluids The Apiezon diffusion pump fluid is known for its exceptional higher degree of oxidation resistance. Cryogenic Applications: We are very excited about the new Apiezon N grease specially formulated for cryogenic use. Indeed we know of no other vacuum grease that has been specifically formulated for use down to -269° C. This is of course nearly down to liquid helium temperatures. Laboratory glassware applications: We would recommend for stopcocks and ground glass joints, Apiezon AP 101. Applications on Electrical Contacts: We are also often times asked about the use of Apiezon greases for the protection of metal contacts. As a general statement, although all of the Apiezon greases are good insulators, in a metal to metal switch or contact, the grease film is so thin at the actual point of contact that it just is not enough to interfere with the passage of current for all but the smallest of voltages. For example, Apiezon L has an electrical strength of 720 volts per mil (0.001"/25 µm). In a metal-to-metal contact, the film of grease would be only on the order of 0.00001" (250 nm) or less, giving an electrical strength of only 7 volts. These comments were for operation at or in the vicinity of room temperature. For higher temperature operation, we would recommend the use of Apiezon T or possibly even Apiezon H. Such decisions should be made on the basis of the table of technical information for this unique family of greases. But make sure that if you have a critical application, you are not picking up some tube that is of unknown age or origin. These greases do not have an unlimited shelf life. Electronics industry applications: Virtually all of the Apiezon greases have applications in the electronics industry and we work hard to make sure that the greases offered by SPI Supplies are indeed described properly for this application. This has been especially true in terms of sodium content measurements on the Apiezon greases. Effects of Apiezon Greases on O Rings: All of the Apiezon greases are generally OK with most commonly used "O" ring materials such as silicone rubber, Viton® fluoroelastomer, Neoprene®, and polyurethane. While there could very well be others, we are aware of at least three polymers for which the Apiezon greases are absolutely not compatible. The first is PVC (polyvinyl chloride), but we are not aware that this polymer would ever be used as an "O" ring material of construction. However, the other polymers are ethylene propylene rubber (EPR) and EPDM, and under no circumstances should any of the Apiezon greases or oils be used in conjunction with these elastomers. Both EPR and EPDM elastomer are readily plasticized by petroleum hydrocarbons so any of the Apiezon greases or oils can have a softening and/or swelling effect on them. The magnitude of the effect depends on the particular polymer, and in some instances, one should also realize that a slight swelling of the "O" ring seal need not always be considered detrimental if it can enhance the efficiency of the seal. As in any materials selection process, be sure to do adequate testing to make sure that the particular grease/elastomer selected will indeed give the desired results. Which Apiezon grease is the best for "O" rings? This is one of the most often asked questions so we would like to answer it here. Actually any of the Apiezon greases would be just fine on "o" rings (see above discussion on compatibility issues). The main determining considerations for grease selection would be temperature range of operation and vapor pressure requirements. So if operation was going to be roughly around room temperature, our philosophy is to use the cheapest, which would be Apiezon M. Another candidate would be Apiezon 101, which is a PTFE filler, and which was originally formulated to be an "anti-seizing" grease, but it does have greater water repellency than the others. Of course, as already stated, none of the Apiezon greases should be used on EPR or EPDM elastomers. If one of these two polymers are present, we would suggest one of the Braycote® greases be considered. Corrosion inhibitors: We are often asked if Apiezon greases contain corrosion inhibitors and the answer is a simple "no". The reason why the question gets asked is that when certain corrosion inhibitors are added to a lubricant, they tend to reduce somewhat the vapor pressure characteristics of the final formulated lubricant. However, we are told that all of the Apiezon greases, unlike certain other vacuum greases, are considered compatible with aluminum. Remember, though, if you think you could have a corrosion problem, do the testing you feel necessary in order to be convinced that the grease is indeed suitable for your intended application. MSDS sheets and ancient greases: We would urge caution with the use of a modern day MSDS sheet to describe the potential hazards of a grease discovered in the laboratory of unknown age, storage conditions, and history. Although it is easy to download current MSDS information from the SPI website, remember that they were prepared to describe reasonably fresh material and not what might exist in a tube five or ten years old. Shelf life considerations: All Apiezon grease products are guaranteed for ten years from the date of manufacturer provided they are in their unopened tubes and have been stored at recommended temperatures. Since there is no reason why even at ten years, the grease should go into some kind of state of sudden deterioration, the actual lifetime could very well be longer. On the other hand, if the tube has been opened, and the contents exposed to the effects of oxidation, deterioration in properties might occur in less than a ten year period. If you have in your possession one of the Apiezon grease products and you wish to know the date of manufacturer, send SPI Supplies both the lot number on the maroon SPI Supplies label as well as the six figure lot number stamped right on the tube and by return e-mail, we will send you the date of manufacture. |
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