Hi You do work pretty hard to turn the metal can into a getter. The other issue is that the adsorption and desorption rates are quite different. Once you get the “stuff” into a layer state, it takes a long time to get it back out. Much better to not have it there in the first place.
If the precision crystal is being used in a TCXO, water has the nasty tendency to freeze. When it does, you get a frequency bump. That’s a difficult thing to compensate for. Does it occur at < -65 (you hope) or at -45 (you hope not) ? The practical approach is to get rid of as much of it as you possibly can. Bob > On Jun 10, 2017, at 12:22 AM, Neville Michie <[email protected]> wrote: > > It is possible that the ageing of a crystal is associated with the > redistribution of the surface water > monolayer, under the influence of the minute temperature gradient of an > oscillating crystal. > Some energy is dissipated in the quartz, so some gradient may exist. > When a crystal is resting, the water may redistribute in the sealed package, > but when run again, the water > redistributes due to the temperature differences. > Adsorbed water is in equilibrium with its environment, and, given time, will > migrate along temperature gradients. > It could be just one more mechanism in frequency drift. > I would try using a reactive metal getter in the package to pick up any > mobile water molecules. > > cheers, > > Neville Michie > >> On 10 Jun 2017, at 9:52 AM, Bob kb8tq <[email protected]> wrote: >> >> Hi >> >> You can’t quite process a crystal at 300C, but you can get close. >> >> Bob >> >>> On Jun 9, 2017, at 7:38 PM, Neville Michie <[email protected]> wrote: >>> >>> My memory of high vacuum work is that you need to pump for 4 hours >>> at 300C to remove the water monolayer from glass. >>> On top of the that water monolayer is another water monolayer that comes >>> off more easily, >>> and on top of that another……….. >>> >>> cheers, >>> Neville Michie >>> >>> >>>> On 9 Jun 2017, at 10:57 AM, Richard (Rick) Karlquist >>>> <[email protected]> wrote: >>>> >>>> >>>> >>>> On 6/8/2017 5:08 PM, Bob kb8tq wrote: >>>>> Hi >>>>> In this case hydrogen + oxygen (like from oxidized metal) goes to H20. >>>>> You very much do >>>>> not want water running around inside your crystal holder… Helium is inert. >>>>> Bob >>>> >>>> Exactly right Bob. The 10811 guys used to go nuts >>>> about keeping water out of their vacuum system. >>>> There were certain temperatures known as "water >>>> points" at which some water was released. >>>> The retained water was in spite of the temperature >>>> already being above 100 degrees C (boiling). >>>> It has something to do with monolayers of >>>> water molecules not boiling away. >>>> >>>> Rick N6RK >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
