Friday, August 08, 2008
Accelerated Aging - Getting Bad Data Even Faster - 2nd in a Series
A very common mistake in accelerated aging is to assume that "more is better", the the "more" applying to the stressing variable such as the lamp intensity. Such approaches can have numerous pitfalls. Accelerated UV aging already has advantages over natural aging since the lamp can be run 24/7 while old Sol runs (for most latitudes) at most about 16 hours, with most of this being at less than maximum intensity. But just like the endless pursuit of faster CPU speed (so that people can make stupid mistakes even faster than ever before!), the need for speed is also relentless in accelerated aging. Lamp intensity can be increased ever further (normal maximum intensity for Miami is 0.34 W/m2 and this is commonly increased to 0.55 W/m2 - all these measurements are most commonly done at 340 nm) but excessive increases lead to other problems. Increased lamp output increases the sample temperature which can lead to increases of reactions that are not of interest.