Note: Descriptions are shown in the official language in which they were submitted.
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HIGH SPEED OXYGE~ SENSOR FOR MOLTEN METALS
BACKGROUND OF THE INVENTION
This invention relates to devices for developlng
a voltage related to the level of dissolved oxygen in molten
metal~ and particularly to such devices which produce an
output voltage related to the dissolved oxygen content w,hen
the device is immersed in molten steel.
For some tlme galvanic cells have been used for
determining the concentration o~ oxygen in molten metal
wherein the cell includes a solid'electrolyte which is in
conkact with material to provide a re~erence ~alue of
oxygen. The voltage output of the cell is related to the
difference in partial pressure of oxygen applied to
opposite faces of the electrolyte.
For the measurement of oxygen in liquid steel, the
electrolyte is generally calcium stabili,zed zlrconium oxide
and ~he re~erence electrode may be metal in combination
with an oxide of the metal. U. S. Patent 3,723,279 teaches
that the oxygen re~erence is produced by a mixture o~ ¦
chromium and chromic oxide.
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In using such devices, the cell is generally
supported in one end'of a cardboard tube for immersion in
the liquid steel. It has been ~ound that with the devices
taught by the prior art that it is generally necessary to
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maintaln the cell tmmersed in the liquid steel for l0 seconds
or longer. In order to suppo~t the oxygen sensor in the
liquid steel for such a length o~ time, it has been necessary
to use cardboard tubes of significant thickness to prevent
the llquid steel ~rom burning through the cardboard tube and
destroying the electrical contact elements for the cell.
Furthermore, cells produced in accordance with the prior art
have produced output voltages that show signiPicant erratic
. variations which make it difficult to determine with any
degree of accuraey the dissolved oxygen in.the molten steel.
It is an.ob~ect of this invention to provide a
cell for immersion in molten metal that will have a much
faster speed of response and a more stable output voltage.
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BRIEF DESCRIPTION OF THE DRAWING . .
Fig. l is a side elevation partially in section
o~ a sensor manu~actured in accordance wlth this invention.
Referring to the Figure, there is shown an
, expendable..immersion sensing device l0 comprised of a
molded plastic body structure which may include a cup portion
ll and a tubular portion 13. The cup portion ll contains a -
quantlty of refractory cement.14 which supports in
protruding relation with the cup.ll a connector. electrode
15 which is connected at the end embedded in the refractory
cement l4 with an electrical.conductor 16 having an end
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portion i6a bent over through a notch 13a in the tubular
portion~ 13 in order to provide a plug-in contact ~or the I .
- connector electrode 15.
An electrolyte cell electrode structure 17 is
also supported by the re~ractory cement 14 in a manner to
extend.outwardly there~rom in substantially parallel
relation to the connector electrode 15. The cell structure
17 is comprised o~ a closed end tube 18 made o~ a material
suitable for use as a solid electrolyte which for oxygen
may be calcium stabllized z~rconium oxide. The tube 18
. contains a small mass 20 o~ a reference material in the .
~orm of a powder. When the element.to be measured is
oxygen, a re~erence partial pressure o~ oxygen may be
provided by a powdered metal and a stable oxide thereo~g
such as chromium.in powdered form mixed with chromic oxide
powder. In order to provide.for a high speed o~ response
~or the cell? it has been ~ound that the mass 20 o~
re~erence material should be kept small and should not
more than 1/8th o~ an.inch o~ the tube 18. ~.urther to
enhance the speed of response, and to provide the desired
stability, it has been ~ound that the ratio o~ chromium
powder to chromic oxide powder is ~uite critical and
should be substantially 75~ chromium and 25% chromic oxide.
The mixture of chromium-chromic oxide ~orming the
small mass 20 is preferably tamped in place in order to
effeot a good mecha~ical and electrical contact in the end
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of the tube 18. To insure that .the.'chr'omium-chr'om~c oxide
retains its contact with the end of the tube''18, a thin layer
of fibrous alumlnum oxide 21l is pressed firmly against the
exposed surface of the powder mass.20. To reduce the tlme
for the partial pressure of oxygen produced.by,the mass 20
of reference material to reach a stable equ~libr~um value
and thus to insure a high speed.o~ response from the cell, .
that portion of the tube 18 that is not ~illed w~th'the small
mass 20 and the layer 24 should contain a filler 21 to reduce
substantially to zero the air contained ln the tube 1.8.
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While any suitable dry filler material may be used, ,~
it has been found that a cell having a high speed of response
can be obtained.by introducing into the tube 18 above the ' ,:
layer 24 a.quantity of aluminum oxide which preferably is ,:
introduced into the,tube 18 in powdered form to provide
the filler 21. When the aluminum oxide powder is used,as
the ~iller 21 to eliminate air in the tube 18, the powder
should be quite :fine or at least contain a percentage of
, fine powder to eliminate interstlces that could form air ,
pockets within the filler 21. The elimination of air within
, the tube 18 may also be accomplished in other ways by
inserting other types of powder, or by inserting within
. ~ the tube 18 a solid materia]. such as quartz or ~ycor, or I.
.' utilizing a supercooled liquid to constitute the ~iller 21. '
Whatever substance is.used to fill the void within the tube
18 above the small mass 20 and layer 24, there must be
provided a passageway to permit a conductor 22 to pass
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through the lengkh of the tube 18 to make an electri.cal
connection to the inner sur~ace of the electrolyte tube 18.
This electrical connection may be completed ~rom the
. conductor 22 to the inner surrace o~ the tube 18 by way of
the small mass 20 o~ the reference material. The end of
the tube 18 with the conductor 22 in place is preferably
sealed by an epoxy or other suitable cement 19 which
serves to retain the aluminum oxide powder 21 and the mass
20 of the re~erence electrode in position. ¦
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The electrical connection to the inner sur~ace of
the electrolyte tube l8 is completed by way of the
conductor 22 and.a conductor 23 which.is connected to the
conductor 22 at a point submerged in the re~ractory cement
. 14. The conductor 23 extends upwardly into tubular
portion 13 and has a terminal end 23a bent in a conventional
manner through a slot or notch 13b to ~orm a plug-in contact
for the cell electrode structure 17. ~ metal cap, not
shownl serves to protect the electrode structures prior to
and during the time the device 10 is being immersed to a
sub-surface level in a bath Or molten steel.
While there has been described an lmmersion
device.comprising an oxygen determinlng.cell,.it is to be
understood.that in practice such a cel-l is generally used
in combination with other devices, such as, ~or example~
. ~amplers,temperature measuring devices, and thermal arrest
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analysis deviaes~ combined into a single unlk for .
simultaneous immersion into the molten metal.
. Cells constructed in accordance with the above
: teachings have responded rapidly upon.immersion in molten
steel achieving full output within ~our seconds. This
is a significant improvement over the response o~ the
devices o~ the prior art which have required ten seconds,
Because of the speed of response of the cell.of this
inventlon, it is possible to use a cardboard tube having
a thinner wall and thus provide a device that is easier
to handle and less expensive to manufacture without in
any way sacrificing the performance o~ the oxygen
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