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Manufacturing,
Engineering
and
Sales
Since
lg38
Phone: 017-527-4385
Fax:
6 I
7-9
64-3
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Ceramic Protection
Tubes-
Alumina, Mullite, ?hd
Zarconia
Alumina
Alumina
has a maximum service temperature
of
3450'F
(1900"C)
in
both oxidizing
and
reduc-
ing atmospheres. Alumina
is
considered
to
have
better
mechanical
strength (twice
the
tensile
strength
of
Mullite)
and chemical
resistance than
Mullite.
Alumina tubes also
have
excellent
abra-
sion resistance.
Secondary metal tubes
can
be
added
for
additional protection
from
mechanical
damage. Alumina tubes
are
considered
gas tight
so they make excellent primary
protection tubes.
All
tubes,
which are used
in
horizontal
installa-
tions
and
at
elevated temperatures,
should
be
supported.
Alumina
tubes can
be
used
for
pri-
mary and
secondary protection
tubes
on
noble
metal
(platinum based) thermocouples.
Since
they have
a very
low silica content, they
will
not
contaminate platinum elements
above
2200"F
(1200"C)
as a
mullite
protection
tube.
Composition -
99.87o
Aluminum
Oxide.
Mullite
Porcelain
Mullite has
a
maximum service
temperature
of
2900"F (1590"C).
lt
is
considered
to
be
better
than
Alumina
for
thermal
shock
resistance.
Mullite tubes should be used with care, since they
have
poor
mechanical
shock
resistance.
Secondary
metal
tubes can be added
for
protec-
tion from mechanical
damage.
Mullite
tubes
are
considered
gas tight
at
high temperatures.
All
tubes,
which
are used
in
horizontal
installations
and at elevated temperatures, should be support-
ed.
Mullite
tubes should not be
used
for
primary
protection
tubes on noble
metal (platinum based)
thermocouples
if
the
temperature
will
exceed
2200'F (1200"C).
Above
these
temperatures the
silica
in
the
Mullite
can contaminate the
platinum
element
if
there
is not enough air circulation
in
the
tube.
Composition
-
63.5%
Aluminum
Oxide,
Balance
Silicon
Dioxide.
Zitconia
Zirconia
has
a
maximum
service
temperature
of
4172'F (2300"C)
in
oxidizing, reducing,
and
vacuum
environments.
This
material
is
yttria
(10.5%)
stabilized.
Zirconia
in
chemically
inert
and
has excellent corrosion
resistance
.
Zirconia
tubes should
not
be used
in contact with Alumina
above
1112"F
(600"C).
Zuconia is gas tight,
but
above
1112"F (600"C) Oxygen
will
permeate
through its
structure.
To prevent thermal
shock
heat or cool
at
arate
less
than
302"F
(150'C) pei
hour.
Composition
-
89.5o/o
Zirconia,
10.5o/o
Yttria.
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Visit
our
Web
site
At www.AsRtcHARDs.coM
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