[Milsurplus] Crystal History Book and tips on etching

[Brooke Clarke]

Hi Dennis:

My reading of patent 2479286 is that after grinding, quartz crystals have micro cracks that propagate with aging and 
temperature cycling.  By using an HF etch the cracks are removed thus stabilizing the crystal for both aging and 
temperature (See Fig 6, 7 & 8 in patent).  The patent also includes a slide rule design (Fig 10) which, for a given 
frequency change and cut, tells you the etch time.
https://prc68.com/I/Xtal.shtml#Bliley

PS I worked in microwave semiconductors and they used HF.  Extremely dangerous stuff since it attacks humans in such a 
way that they are not aware of it.
https://en.wikipedia.org/wiki/Hydrofluoric_acid#Health_and_safety

-- 
Have Fun,

Brooke Clarke
https://www.PRC68.com
axioms:
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2. Everybody, with no exceptions, holds false beliefs.