[time-nuts] Aging rate of crystals

[Neville Michie]

Apart from the humidity theory...
20 years ago I did a masters in material science. One of the major
sections of this field is the study of what was then composite materials
or now amorphous materials. These are defined as materials having an
observable glass transition temperature. The glass transition is a
secondary physical  transition and can be observed as a discontinuity
in the rate of change any one of a number of physical properties as
temperature is changed.
Primary transitions are phenomena like melting and crystalisation.
These materials are often described as visco-elastic,  when stretched
and released they partly recover and then slowly creep back to the
original state at a very slow rate.
Convolved with the visco-elasticity is a process
called physical ageing, where physical properties change with time.
The rate of ageing can be very sensitive to other parameters, moisture
absorbing polymers, like nylon and keratin, can change their rate of
physical ageing over 10 decades of time depending on their moisture
content.
Now crystaline materials, quartz, ceramics, most metals do not have
glass transition temperatures in our set of conditions. But most  
plastics,
  tin/lead alloys are amorphous materials and so would have properties
that would change on the timescale of oscillator drift when the
temperature is changed.
So may be that is where our oscillator drift comes from.
And it is possible that a zero moisture content might slow it down
considerably, that is shift the rate of physical ageing.
I was almost starting to forget all that stuff, I have had no  
application
for it for such a long time.
cheers, Neville Michie


On 18/02/2008, at 5:26 PM, Richard (Rick) Karlquist wrote:

> At the beginning of the E1938A project, I did a bunch of
> characterization of 10811 oscillators.  At the Santa Clara
> Division, we had first class environmental test chambers
> with heating, cooling, humidification, de-humidification,
> and nitrogen purge.  The nitrogen was also available for
> fast cooling.  The 10811 response to humidity was very rapid,
> like 10 or 15 minutes, almost as fast as the chamber
> itself could ramp.  This occurred whether going from
> dry to humid or the other way around.  I don't remember
> seeing any slow "tails" on the response.  The immediate
> humidity response was on the order of a month of aging,
> so any humidity related aging effects would be masked.
>
> Rick Karlquist N6RK
>
> Thomas A. Frank wrote:
>>> The best experiment I can think of to prove this is to run the
>>> oscillator in a paper bag until it is stable,
>>> then trickle a flow of dry nitrogen  into the bag for a day or two
>>> and watch for oscillator drift as the humidity
>>> in the oven drops to extremely low values.
>>> It is a pity that I do not have bottled gas on tap any more.
>>> cheers, Neville Michie
>>
>>
>> I like your theory, it has a marvelous macroscopic physical component
>> to it.
>>
>> A way to run that test without any bottled gas would be start during
>> a very humid spell (the stabilize things at a humid level; say 80%
>> RH), then to put the crystal assembly into a sealable plastic
>> container (Tupperware for US folks) with a bunch of silica gel or
>> other desiccant.
>>
>> The humidity in the container will drop to well below 20%, and stay
>> there until you open the container.  That's a pretty decent range to
>> work over.
>>
>> Tom Frank, KA2CDK
>>
>>
>>
>>
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