Use of Beryllium in the Electron Microscope Laboratory
A brief overview of the risks associated with the use of beryllium metal products in the electron microscopy laboratory
Some research and technical organizations now prohibit the use of beryllium
in their institutions no matter what might be the intended use or the
quantities or physical form involved. The purpose of this over view is
neither to promote or disparage the use of beryllium, our intent only is to
bring some rationale to a subject that has of late been given to wild
misunderstandings. As one of the world's largest suppliers of
beryllium planchets
and
beryllium TEM grids,
we would like to set the record straight.
There is no question that beryllium has the potential for being a health
hazard. However, it is the oxide that is the hazard, not the metal,
per se.
For example, an SPI beryllium planchet is about as innocuous an item
imaginable. It has no vapor pressure, nothing is escaping, nothing is being
inhaled and nothing is being absorbed through the skin. Beryllium is a
refractory metal and we are unaware of anyone reporting a
"vaporizing" or some other volatilization of beryllium, in a commercial SEM
or microprobe, from a beryllium planchet.
The hazard is from beryllium oxide, BeO, which in fine particle form, when
inhaled can, in at least some of the population react with terrible
consequences, leading to the condition of berylliosis. The percent of the
population at large at this kind of risk is arguable among toxicologists
specializing in the area, but it seems to be 30%.
At least one scenario by which an inert and seemingly innocuous beryllium
planchet then can get into the atmosphere in the form of beryllium oxide
would be if a beryllium planchet was being "cleaned" for reuse with other
sample mounts, and in the process, was subjected to grinding on a grinding wheel,
or polishing on a wet polishing wheel. A dry grinding wheel obviously will
create fine particulates in the respirable range, that would be of the size
that would fairly quickly oxidize to the oxide. And this could create a
significant health hazard for anyone inhaling those grinding wheel generated
particulates.
Polishing on a wet polishing table would be less risky. If the waste water
stream from the polishing table is being dumped into a public sewer, one has
to be concerned about the release of BeO particles in the effluent stream.
But the greatest hazard of all could be the polishing table itself, that is,
if it dried out, and then the now dry cloth was disturbed, it could send up a
plume of BeO particles clearly in the respirable range.
So that is why we recommend strongly that some decision be made about just
how the Be mounts are going to be recycled (and we strongly believe that
they should be recycled because beryllium is clearly a non-renewable
resource). Therefore, some kind of identifier or coding should be applied
to the outside cylindrical surface. If it is a color coding, without much
relief, after a few cycles of carbon or gold coating, the color is covered
up and the beryllium planchet looks indistinguishable from a normal aluminum mount.
Therefore, we believe the best coding of all is something literally
scratched into the sides of the mount, as one would do using a
diamond scribe.
If the coding is just a series of "X's" or other shorthand scratchings, with
the passing of time, in the typical laboratory setting, the memory of the
interpretation can be lost. Therefore we believe that the words "beryllium"
or "Be" should be scratched in the side by the ultimate user and in the
local language, whatever that might be. This way the the planchets would
always be instantly recognizable as being Be and not Al or something else.
If these kinds of practices are not implemented in a laboratory using
beryllium planchets, it becomes too easy for a beryllium planchet to somehow
become comingled with aluminum mounts, with the resulting generation of
small particles of Be quickly converting to small particles of BeO.
There is a parallel set of considerations for the use of beryllium TEM grids.
However, in this discussion, we will be talking only about the SPI Supplies
brand of Be grids and this reason will explained in a few paragraphs later.
So far as a Be grid representing a hazard, it is, after all, just like the
case of a Be planchet, an innocuous refractory metal with no vapor pressure,
and therefore there is nothing evaporating and nothing contaminating the
environment. None of the usual methods of TEM sample preparation are known
to abrade the grid itself, hence we see no mechanism by which the picking up
of a Be grid, or its processing or handling, could create the oxide
particles that are the well-known health hazards that that are.
One might however question the possibility of a concentrated beam of a TEM
being focussed, at cross-over, to cause some evaporation of the Be metal.
However, Be is a refractory metal with an extremely high melting point. We
have never heard of even the slightest suggestion that this could be happening
and no one, to our knowledge, has ever reported such an experience. Hence,
we don't see how the origin of any kind of a hazard associated with the use
of a Be TEM grid in a TEM.
These above comments would not apply to beryllium coated TEM grids, that is,
where some other (and lower priced) grid is sputter coated with beryllium
metal. We have heard reports of the beryllium coating flaking off and
delaminating, and of course, that could pose an inhalation risk since the
small particles would be susceptible to oxidation to the oxide.
But the real risk here relative to the use of Be grids might be different
from what is more commonly accepted. From the institutional standpoint,
especially in the USA and a small but growing number of other countries, the
exposure is not the actual risk but the construed risk that could be
presented in a court room in the event an employee claims that a medical
condition was caused or aggravated by beryllium oxide exposure. Consequently, some number
of institutions, as part of their program of risk analysis and loss
prevention, have summarily banned the use of beryllium containing products
from their laboratories.
What are the alternatives?
Although we ourselves believe that the use of beryllium in the microscopy
laboratory does not pose a risk of greater magnitude than many of the other
chemicals and reagents regularly used in microscopy, we do want to make
clear that there are alternatives. Like with other aspects of life, there
are trade offs, but one's work should not necessarily be stopped because of
an inability to use beryllium.
Planchets:
We believe that for most users, the very best of the alternatives is the
SPI Diamond Planchets made from pure artificially grown diamond using CVD (chemical vapor deposition)
methods. The planchets come one side polished (so in smoothness it is similar to the pyrolitic carbon planchets)
and the other side is more rough, so it could serve almost like sandpaper for the removal of small amount of a
surface or surface deposit.
For those seeking the ultimate in smoothness, SPI Supplies offers a full range of qualities of
highly ordered pyrolytic graphite (HOPG), and for a less demanding application, one can use the
polished pyrolitic carbon planchets, or even our
regular SEM carbon specimen mounts.
We believe that diamond as an alternative to beryllium should be acceptable to just about anyone, since
the low Bremsstrahlung background radiation level is approximately the same as it is for beryllium. However those
selecting the pyrolytic carbon alternative, while cheaper, may find the
higher Bremsstrahlung background levels to be unacceptable.
However, for most users, the
SPI SuppliesŪ Brand Beryllium Planchets
are the best choice, both technically as well as economically.
Grids:
The two alternatives are the SPI Carbon
Composite Grids, and the SPI Diamond Grids.
The carbon composite grids will exhibit higher Bremsstrahlung background
radiation so for some, this higher background will be sufficiently
undesirable to render them unusable as a beryllium substitute. The diamond
grids have low background, and in most respects should be an acceptable if
not slightly more expensive substitute for beryllium. For the
environmentally conscious, we want to point out that the diamond is man-made
and not natural, and therefore would not be considered a non-renewable
resource as would be beryllium.
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Tuesday February 07, 2012
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