Re: shadow mask

[Brian Whatcott <betwys@DIRECTVINTERNET.COM>]

At 10:27 AM 11/21/02, you wrote:
> Bernard Cleyet is correct that Invar (an iron/nickel alloy) is
> used as a shadowmask because of its low thermal expansion.


> Michael D. Edmiston, Ph.D.


Michael's note led me to the Hitachi site which supplies
Invar and Superinvar. Hitachi mentioned an application which had
not come to mind - as one side of a bimetal actuator:
for some reason, I generally get a picture of two dissimilar metals;
but most any metal and Invar is a most  potent combination.

I have a pair of marble and granite floor tiles as a stable low-expansion
substrate, for some future application. While Invar handily beats
either of these for thermal expansion coefficient: 9E-7 /K vs. 9E-6/K
it is said to squirm while aging, so that it is often not preferred for
length standards; better a metal with very predictable thermal
expansion over time. Fused quartz does best at 4E-7/K.


Brian Whatcott
  Altus OK                      Eureka!

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.