The Vacuum Stability and Outgassing test is also known as ASTM E-595. This test is performed using a high vacuum test rig. The ASTM E-595 test method has become an industry standard in the high vacuum world. The purpose of the test is to determine the amount of volatile content in a material when exposed to heat and vacuum in a closed system. The two parameters that are measured are total mass loss (TML) and collected volatile condensable materials (CVCM).
In the E-595 test, a sample is first exposed to 23°C and 50% relative humidity for 24 hours to condition all of the samples in the same manner. After this conditioning, the samples are re-weighed and put into one of the testing cells. The typical test can run up to two different materials at a time. After all the samples are weighed and loaded into the chamber, it is then evacuated to a vacuum level of at least 7 x 10-3 Pascals or 5 x 10-5 torr.
Once the vacuum level has been reached, the samples are heated to a temperature of 125°C and the 24 hour test period begins. A portion of the sample leaves as outgassing vapor which passes into a collector chamber where some of it condenses on a chromium-plated collector plate that is maintained at 25°C. Each sample compartment has a corresponding collector chamber that is isolated from the others to prevent cross contamination.
After 24 hours, the test apparatus is cooled and the vacuum chamber is re-pressurized with a dry, inert gas. The samples and the collector plates are then weighed. From these results and the sample mass determined prior to the vacuum exposure, the percentage TML and percentage CVCM are obtained. Normally, the reported values are an average of the percentages obtained from three samples of the same material.
Outgassing is an absolutely critical design parameter in the Vacuum, Aerospace, and Semiconductor markets. Condensable material from the outgassing onto nearby surfaces can become very problematic if they obscure optical instruments, cause a reaction, or contaminate materials in the system. Historically, the acceptable limits determined by NASA and adopted by other industries are 1.00% or less for TML and 0.10% or less for CVCM.
Take a look at our article about linear guide component lubrication in a cleanroom environment for practical relevance of vacuum data.