[time-nuts] Re: ammonia, cesium, masers, etc.

[Bob kb8tq]

Hi

Heading off into the absorption A/C and remigration world …. They use various
salts to make the “magic happen”. The issue is with those salts. The EU is moving
towards banning manufacture of this gear fairly soon now ( 2026 ). This has the folks
that use these devices a bit concerned.

I think it’s safe to say that the interaction between the ammonia and whatever the 
structure is made of will be exciting on a number of levels. Corrosion is only the first
item on a very long list ….

Bob

> On Sep 20, 2021, at 8:14 PM, Dana Whitlow <k8yumdoober at gmail.com> wrote:
> 
> My dad worked in the absorption air conditioning field using ammonia and
> water,
> and he once told me that ammonia-water was hell on aluminum copper points,
> or
> even aluminum tubing that had impurities in the form of tiny copper flakes
> in it.
> 
> As to dry ammonia, intuition suggests to me that things would not be so bad,
> but if I were building one of these clocks I think I'd try to avoid
> aluminum-copper
> joints on general principles.
> 
> Once in a while Dad would take me with him when he went to work in the lab
> on a Saturday morning.  The ammonia odor was mighty potent, but he didn't
> seem bothered by it at all.  And despite his exposure to this supposedly
> toxic
> substance (by current thinking, anyway), he lived to be 94 years old.  I
> guess
> it can't be all bad.
> 
> Dana
> 
> 
> On Mon, Sep 20, 2021 at 5:34 PM ed breya <eb at telight.com> wrote:
> 
>> That's a fascinating article.
>> 
>> Regarding ammonia
>> 
>> Anhydrous liquid ammonia is a common commodity material, but probably
>> comes in many grades, depending on use. I'd break it into three basic
>> ranges. For something like this, you would want to look at reagent/lab
>> grade, to get it as clean and dry as possible to start with, with
>> minimal grief. Refrigeration grade may be good enough too, if you put
>> impurity traps and dryers in your system. The crappiest versions are
>> probably agricultural - as crude and cheap as possible. Don't forget,
>> you'd also need a bought or leased tank, and proper manifold/regulator
>> set to actually use it.
>> 
>> I don't recall how compatible ammonia is with copper or aluminum, but I
>> know it's good with steel, and most likely all stainless steels. Keeping
>> it absolutely dry would help to avoid any materials grief, but even so,
>> it's a good idea to check out the chemistry before committing to a design.
>> 
>> Regarding microwave gear
>> 
>> Like Jim mentioned, the 22-24 GHz microwave stuff is in the right
>> ballpark. I scrounged up some 1980s 22 and 38 GHz point to point
>> transceiver head-ends over the years, and saved the goodies for possible
>> re-use. In front of me right now are a couple of 22 GHz plumbing
>> sections. At first glance, it appears they use Gunn oscillator modules
>> as LOs, although they could be DROs, or a combination - hard to tell
>> from outside. Then there's a bunch of waveguide BPF sections, with lots
>> of tuning screws, and some directional couplers, altogether doing
>> filtering and diplexing. I think these sorts of parts from this era
>> would be great for this application. With all the fancy filters, it
>> could be that besides TX/RX separation, the LOs may operate at lower
>> frequencies, and the filters just let the right harmonics through. Can't
>> tell yet, without more investigation.
>> 
>> I have some newer - probably 1990s - pieces in 22 and 38 GHz, where the
>> guts are much more highly integrated into big modules that do
>> everything, and just have the waveguide directional couplers sticking
>> out, to connect an external diplexer. I've looked inside some of these
>> over the years, and recall that none use a fundamental LO - they were
>> all synthesized LOs in the maybe 6-8 GHz range, then amplified and
>> multiplied up.
>> 
>> Regarding waveguide
>> 
>> It seems that they had the right kind of waveguide stock in the 1950s,
>> so why not now? I know you can get flexible guide section, which is
>> corrugated, but I don't know if there's such a thing as a smooth,
>> semi-rigid form that can be bent or rolled up - kind of equivalent to
>> semi-rigid coax. Maybe there is, or maybe not. Another option, for
>> anyone with NC machines, could be to machine the internal structure into
>> a block, say in a spiral or serpentine form, then cap it off from the
>> side. It would have to be sealed though, somehow, to be good RF-wise and
>> ammonia-wise.
>> 
>> Ed
>> 
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