ASTM D2715 Test Method for Volatilization Rates of Lubricants in Vacuum
5. Apparatus
5.1 Recording Vacuum Microbalance, with capacity of 1 g or more, sensitivity of 0.01 mg or less, zero stability of 0.025 mg or less for 8 h with ranges of weight change of 10 mg or more, and 0.1 mg or less, capable of being pumped to 10(-5) Pa (10(-7) torr) or less.
5.1.1 When Procedure B for the more volatile samples is used, the vacuum requirement shall be 10(-2) Pa (10(-4) torr) or less.
5.2 Vacuum System - A pumping system capable of maintaining a starting pressure of 10(-6) to 10(-5) Pa (10(-8) to 10(-7) torr) (5.1.1). An optically dense baffle system should be used to ensure freedom from back-streaming. A conventional bell jar system with an oil diffusion pump, a mechanical back-up pump, and an optically dense, liquid, nitrogen-cooled baffle has been found satisfactory on the configuration as shown in Fig. 1.
5.3 Furnace, with thermocouple indicator, capable of maintaining a constant sample temperature +/-3°C. All parts of this furnace must be proved to be usable at the highest temperature and vacuum contemplated.
5.4 Recorder, capable of recording weight changes continuously with the balance used, to the performance specified in 5.1.
5.5 Specimen Container, made of 300 series stainless steel in the form of a straight cylinder with an aspect ratio of height to diameter of approximately 1:14. Where chemical reactions are experienced with the container, alternative materials may be used.
5.6 Contacting Thermocouple, touching solid or immersed in liquid specimens, with the leads brought out in such a way as not to influence balance indication.
5.7 Cold Plate - A condensing shield cooled with liquid nitrogen to immobilize molecules evaporated from the lubricant which subtends, at least, a 160° arc from the center of the sample.
5.8 Nude Ionization Gage, installed as described in ASTM Practice E 296 and calibrated as described in Method E 297.
5.9 Optional Supplemental Equipment:
5.9.1 Mass Spectrometer, to identify degassing products and evaporating species.
5.9.2 Infrared Optical Pyrometer System, for determining the specimen temperature. This must be calibrated against the thermocouple for each material used, due to emissivity effects.
5.9.3 Copper Tab, on a cold plate facing the specimen, for X-ray analysis of the condensate.
5.9.4 Noncontact Specimen Thermocouple, calibrated against 5.5.
5.9.5 Pressure Recording Pen, added to the recorder.
5.9.6 Time Derivative Computer, to report the rate directly.
6. Reagents and Materials
6.1 Antiwetting Agent - A low-surface tension material for coating the specimen container and the thermocouple. Its volatility must be low enough to contribute less than 5 % to the evaporation rate of any sample to be tested.
6.2 Calibration Material - Pure compound of suitable physical properties to simulate the lubricant under investigation. (N-heptadecane and bis m-(m-phenoxyphenoxy) phenyl ether have been found satisfactory. Tin provides a low evaporation rate material, the performance of which can be checked by the Langmuir equation.)
6.3 Liquid Nitrogen, commercial grade.
6.4 Helium, ACS purified grade.
