[ARC5] WHINK and crystals.

[Dennis Monticelli]

Ken,

The etch rate is faster at first and then reduces.  Crystals of pre-1944
and partially of 1944 manufacture were simply washed after lapping.   This
left many loose particles still weakly attached to the surface as well as a
rough crystal surface in which the crystal bonds were partially broken.
 The HF attacks this mass of quartz first and after it has been removed
must then etch away at a more resistant well-ordered crystal surface.
 These WW2 crystals drifted upward soon after being placed in service (the
mass of loose particles redistributed) and that was a problem.  Bliley then
developed the HF dip process whereupon a crystal was ground to slightly
below its target freq and then given a short dip in HF to bring it the
final distance.  In the meantime the HF did a great job of "cleaning" the
blank.  Drift problem solved.  The government forced Bliley to disclose
their technique to all other US crystal makers.

Dennis AE6C


On Wed, Jun 26, 2013 at 10:27 PM, Kenneth G. Gordon <
kgordon2006 at frontier.com> wrote:

> So far, activity with this crystal has remained high despite the etching.
>
> I might add that although this particular crystal was a commercial job,
> made during WWII,
> dated 1944 on the case, and made by Standard Piezo, the crystal blank is
> NOT perfectly
> square! Not by a long shot! At least two sides have a pronounced curve to
> them, and it is
> very obvious that all edges have been hand-ground to a bevel.
>
> These are some of the reasons I chose that particular crystal to etch. I
> figured I couldn't hurt
> it.
>
> Yet when I first tested it, it had plenty of activity, and that has not
> yet fallen off.
>
> I am quite surprised, but pleased.
>
> More tomorrow.
>
> Ken W7EKB
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