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Thoriated magnesium was even used in the Apollo program. The frames of the
computers (CM and LM) and some of the other electronics were made using it.
NASA did a study of the radiation from these components and determined that
given the duration of the lunar missions, it would not be a risk. The
radiation exposure from the Van Allen belts would be higher. NASA designed
the trajectories to minimize time passing through the belts and to pass
through (or near) the less energetic area of them. I was visiting the
Kansas Cosmosphere when they received a Titan I for their collection. It
was in segments. The body segments were all stamped with "Thoriated
magnesium" so the government determined at some point to warn people.

Beryllium is very interesting stuff. Again, the Apollo spacecraft used a
lot of it. Most of the structure of the optical assemblies (sextant and
telescope in the CM, alignment telescope in the LM) were made of beryllium
because of the light weight and high rigidity. The inertial measurement
unit had a beryllium stable member into which the gyros and accelerometers
were bolted. The mirrors in the sextant and LM telescope were also made of
beryllium. It was nickel plated, then aluminized for the reflective
surfaces. A company called Speedring made most of these parts - they had
the facility to machine beryllium without causing berylliosis among the
workers (or the people in neighboring areas!)

Beryllium is not toxic in the same way that say, arsenic is toxic. What it
does is to cause a severe allergic reaction in the lungs which leads to
severe chronic lung disease. If enough dust is breathed in, there is a form
of acute beryllium toxicity which produces a chemical pneumonia. If you get
a sliver of beryllium, you develop a localized allergic reaction to it. So
it is poisonous in the sense that it will kill you but not like cyanide or
other toxins that immediately affect your metabolism.

I don't know when they started making beryllium oxide parts pink, but the
manufacturers did. The early BeO parts were white and looked like aluminum
oxide. Dust from those would also be toxic. I once contacted a surplus
seller because they had insulators listed in their catalog. The photo
showed them to be pink and they were designed as heat conductor/insulators
for high-power transistors. I warned them that these were made of BeO and
at the least, they should warn purchasers about them. They pulled them from
the catalog. I also was in a scrap yard and they had these huge tubes -
maybe 12 feet long and 6 inches in diameter - that were all white ceramic.
They had a tag that said they were beryllium oxide. I've no idea what they
were for. I'd never seen any BeO parts that large. I warned the surplus
dealer about them - he didn't know. But he knew of someone who would buy
them as beryllium scrap so he did not do his usual thing with stuff he
could not identify and smash or cut it up.

I don't recall seeing any BeO insulators in Tek stuff. I think there were
some silicone ones or in early stuff, mica ones. I am pretty sure that the
500-series scopes with the ceramic terminal strips used aluminum oxide or
porcelain for them. Maybe someone in this group knows. I doubt they were
beryllium oxide.

As a radiologist, I've seen chest x-rays of people with berylliosis and
also asbestosis. The Philadelphia Navy Yard had a lot of people exposed to
asbestos and there were a couple of aerospace companies that used beryllium
parts, but I don't know that they machined the parts in-house. Both are
very nasty diseases.

Steve Horii





On Mon, Mar 8, 2021 at 7:45 PM Ed Breya via groups.io <edbreya=
[email protected]> wrote:

Steve, you may be thinking of beryllium alloyed with magnesium. Many
structural and precision mechanical parts were made with Be in the old
days, for light weight and strength. Be particles can be highly toxic if
inhaled. Same with things containing it, like the alloys and BeO ceramics.
It's still used today, but only where essential, like Be X-ray tube windows
(transparent), and BeO for very high thermal conductivity - although newer,
better, less toxic things have emerged, offering more choices in critical
thermal applications. If you have any microwave gear, you may find it
interesting that the tiny YIG spheres in YTOs and such, are typically
mounted on tiny BeO rods.

As far as I recall, the only things in electronics with thorium are
thoriated-tungsten in high power and other special tubes, and TIG welding
electrodes. The old lantern mantles with Th do indeed make handy sources,
but need proper safe handling.

I think the common indirectly heated tubes we normally see use a nickel
cathode sleeve with zirconia and maybe barium coating. The tungsten heater
wire inside is similarly coated for insulation, but also forms a rectifier
from it to the cathode, so the H-K bias voltage and leakage is a
consideration for operation.

Ed