[rescue] Old Monitors

Ron Wickersham rjw at alembic.com
Wed Feb 14 21:49:19 CST 2018

On Wed, 14 Feb 2018, Patrick Giagnocavo wrote:

> Yes, the interior of the CRT is coated with lead oxide. Breaking a
> tube will release this.

not in any CRT manufacturing process I'm aware of.   the coating both
on the inside and the outside of the conical glass portion of the 
envelope is Aquadag, a water-based graphite coating.   the two coatings
form a capacitor, with glass as the dielectric as in the Leyden jar which
used metal foil conductors rather than the conductive graphite Aquadag
coating.   the Aquadag coating on the inside of the CRT is required to
form the uniform accelerating electrostatic field for the electron beam
to strike the phosphor coating on the inside of the face of the tube.
the Aquadag coating on the outside makes the second plate of an inexpensive
high-voltage capacitor for the high voltage supply.

as the accelerated beam strikes the face of the tube with high velocity,
X-rays are produced.   

the lead content of the CRT is primarily in the face-plate glass of the
tube to shield the user from these X-rays.   the lead is bound in the
glass, like in lead "crystal" glass vases, pitchers, and goblets.  the
lead content in lead "crystal" is 35-40 percent PbO, lead oxide, by
weight, and in CRT the lead content is slightly higher at 50-55 percent.


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