U.S. patent number 3,773,641 [Application Number 05/138,985] was granted by the patent office on 1973-11-20 for means for determining the oxygen content of liquid metals.
Invention is credited to George R. Fitterer.
United States Patent |
3,773,641 |
Fitterer |
November 20, 1973 |
MEANS FOR DETERMINING THE OXYGEN CONTENT OF LIQUID METALS
Abstract
A probe capable of being plunged into a high temperature liquid
metal without destructive thermal shock for determining the
dissolved oxygen content of the liquid metal comprises an elongated
electrically insulating refractory envelope and a small mass of
refractory oxide-type oxygen-anion permeable solid electrolyte
material supported adjacent one end of the envelope. At least a
portion of at least one side of the mass is exposed through an
opening in the envelope for contact with the liquid metal, and the
aforementioned side portion is disposed adjacent the one envelope
end. Reference means are provided in the envelope for contacting an
apposed side of the mass with an oxygen reference material. The
probe is provided with circuit means extending into the envelope
for electrically contacting the apposed side of the mass, together
with additional circuit means disposed for electrically contacting
the liquid metal for measuring an emf developed across the mass in
proportion to the aforesaid dissolved oxygen content.
Inventors: |
Fitterer; George R. (Oakmont,
PA) |
Family
ID: |
26836751 |
Appl.
No.: |
05/138,985 |
Filed: |
April 30, 1971 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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786866 |
Dec 23, 1968 |
3619381 |
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570855 |
Aug 8, 1966 |
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Current U.S.
Class: |
204/423 |
Current CPC
Class: |
G01N
27/4118 (20130101) |
Current International
Class: |
G01n 027/46 () |
Field of
Search: |
;136/86F,153
;204/1T,195S |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Horsley "AERE Report R 3427," United Kingdom Atomic Energy
Authority, 1961, pp. 1-6 & FIG. 2. .
Turkdogen et al. "Rapid Oxygen Determination in Liquid Steel," 76th
General Meeting of AISI, May 23, 1968, pp. 1-23. .
Fitterer, "Reprint from Journal of Metals," Aug. 1966, pp.
1-6..
|
Primary Examiner: Tung; T.
Parent Case Text
This application is a continuation-in-part of my copending
application entitled DETERMINING OXYGEN CONTENT OF MATERIAL, Ser.
No. 786,866 filed Dec. 23, 1968, now U.S. Pat. No. 3,619,381, which
in turn is a continuation-in-part of my then copending application
Serial Number 570,855 filed Aug. 8, 1966, now abandoned.
Claims
I claim:
1. A probe for determining the dissolved oxygen content of a high
temperature liquid metal, said probe being capable of being plunged
directly into liquid steel without destructive thermal shock, said
probe comprising an elongated electrically insulating refractory
envelope, a small mass of oxygen-ion permeable solid electrolyte
material supported near one end of said envelope to seal said end
of said envelope, at least a portion of the outer side of said mass
being exposed through an opening in said envelope for contact with
said liquid metal, means to provide an oxygen reference material in
contact with the inner side of said mass, circuit means including a
conductor extending into said envelope, and a second conductor
disposed for contacting said liquid metal, said circuit means
cooperating with said second conductor to measure an emf developed
across said mass in proportion to the concentration of said
dissolved oxygen in said liquid metal.
2. The probe according to claim 1 further including a thermocouple
for measuring the temperature of said liquid metal and for
correlation with said probe emf, said thermocouple forming part of
said circuit means.
3. The probe according to claim 1 further including means for
measuring the temperature of said liquid metal.
4. The probe according to claim 1 wherein said envelope is
fabricated from alumina.
5. The probe according to claim 1 wherein said envelope is
fabricated from either fused silica or from fused quartz.
6. The probe according to claim 1 wherein said electrolyte material
is an unsaturated oxide-spinel type crystalline material selected
from a group conforming to the following general equations:
MO + N.sub.2 O.sub.3 = MN.sub. 2 O.sub.4
2MO + NO.sub.2 = NM.sub.2 O.sub.4
M.sub.2 O + NO.sub.3 = NM.sub.2 O.sub.4
where M is a metal of lower valence than metal N and is present in
less than the stoichiometric amount to form the saturated spinel
thereof.
7. The probe according to claim 1 wherein said electrolyte is
selected from a group consisting of stabilized zirconia and
stabilized thoria.
8. The probe according to claim 1 wherein said electrolyte material
is calcia-stabilized zirconia and said envelope is fabricated from
alumina.
9. The probe according to claim 1 wherein said electrolyte material
is calcia-stabilized zirconia and said envelope is fabricated from
fused quartz.
10. The probe according to claim 1 wherein said means to provide an
oxygen reference material includes means for circulating an oxygen
containing reference gas continuously through said probe.
11. The probe according to claim 1 wherein said envelope is mounted
on a support, and said second conductor is substantially
coterminous with said envelope to facilitate the determination of
said oxygen content at a given location within said liquid
metal.
12. The probe according to claim 1 wherein said second conductor
has a tubular shape, and said probe further includes means for
mounting said envelope generally within said tubular conductor.
13. The probe according to claim 1 further including an elongated
support and a plug member, said envelope being mounted on said plug
member which is detachably mounted on said elongated support.
14. The probe according to claim 13 wherein said plug member and
said elongated support include interfitting portions respectively,
and mating contact members disposed respectively on said
interfitting portions, said circuit means being connected to said
plug member contacts, and external measuring circuitry being
connected to said elongated support contacts.
15. The probe according to claim 14 wherein contacts on at least
one of said portions are commutative so that said plug member
contacts are electrically connected to said support member contacts
irrespective of the rotative position of said plug member on said
support.
16. The probe according to claim 13 further including a thermal
insulating member provided on said support adjacent said probe.
17. The probe according to claim 13 further including a thermal
insulating member comprising a refractory tube provided on said
elongated support.
18. The probe according to claim 1 wherein said envelope is mounted
on a support therefor, a cap member is mounted on said support,
said cap member being shaped to enclose the otherwise exposed end
of said envelope and said mass.
19. The probe according to claim 18 wherein said cap is fabricated
from a material which melts or dissolves in said liquid metal.
Description
The present invention relates to methods and means for the direct
determination of oxygen content of various materials, and more
particularly to means and methods for the substantially
instantaneous determination of oxygen in liquid metals and other
materials maintained at elevated temperatures, for example, molten
steel. Certain arrangements of the invention are adapted for use
with conductive and non-conductive materials, respectively,
particularly at elevated temperatures.
There are many applications throughout industry wherein it is
necessary to ascertain the oxygen content of various materials.
However, in order for such information to be useful in many
manufacturing processes, it is essential that the oxygen analyses
be timely made to permit corrective adjustment of manufacturing
processes. In the case of liquid steels and other high-temperature
liquid metals, various methods have long been used for the sampling
and analysis of their oxygen contents. In the manufacture of
rimming steel, certain high quality steels, and other metals which
are melted at high temperatures, it is essential that the quantity
of oxygen or other gas dissolved in the steel be closely
controlled. In various liquid metal processes, a technique for
continuously monitoring the dissolved oxygen content is sorely
needed, particularly for those high temperature liquid metals
maintained at 800.degree. C or 1,000.degree. C and higher. In all
of the analytical methods developed previously, however, it has
been necessary to extract a sample of the molten steel or other
liquid metal or alloy from the ladle or from the furnace as the
case may be. The sample then is carried elsewhere for analysis, for
example, by vacuum fusion procedures.
The analysis made in the foregoing manner is time-consuming, in
addition to involving considerable labor costs, and does not
provide an up-to-the-minute picture or analysis of gas content in
the molten material during the manufacturing process. Therefore,
corrective measures have to be delayed until the analysis becomes
available from the laboratory. In consequence, such corrective
measures usually are ineffective or at best serve merely to provide
background or post-mortem information relative to succeeding heats,
batches, or melts.
These difficulties are overcome by my disclosed
direct-determination apparatus and methods which involve the
insertion of a probe into a high temperature material such as
molten steel or other liquid metal. In the case of liquid steels or
the like, means are afforded for penetrating any overlying slag
without affecting the reading. Upon contact with the liquid metal
or other material, the probe through suitable electric circuitry
yields an indication of the oxygen content substantially at the
instant of insertion. In one arrangement of my apparatus, liquid
metal or other high temperature material can be brought into
contact with a solid electrolytic cell of specialized construction,
when the probe is inserted therein. Such contact is established in
a manner so as to expose the electrolytic cell to the material
having an unknown oxygen content, without either oxidation or
deoxidation of the sample by contact with extraneous materials. The
resultant electromotive force generated by the cell when contacted
with the material is found to vary in direct proportion to the
dissolved or uncombined oxygen content of the molten metal. A
suitable calibration can be readily established to relate oxygen
content to the emf value, depending upon temperature and the
characteristic oxygen pressure developed by the reference material
inside the probe. The emf is a function of the ratio of the oxygen
pressure of the oxygen dissolved in the metal and the oxygen
pressure exhibited by the reference material at the termperature of
insertion.
In either case, the substantially instantaneous analysis of the
oxygen content in the molten metal or other material at elevated
temperatures is completed in a few seconds after the probe is
inserted. Thus, useful manufacturing information can be obtained
even where the oxygen level is changing rapidly. On the other hand,
with previous analytical techniques, the values of oxygen content,
even if accurate, would be useless insofar as that particular batch
or heat would be concerned.
Most importantly, my apparatus is capable of being plunged into
molten steel or other materials maintained at extremely high
temperatures without fracturing or otherwise suffering destructive
thermal shock. A measurement of the dissolved oxygen content is
obtained, owing to the novel construction of my apparatus, at a
predetermined point or location within the bath of molten steel or
the like. Previous apparatus for this purpose have been subject to
fracturing or other thermal shock when plunged into molten steel.
Prior oxygen measuring devices used closed-end elongated tubes
which were entirely composed of a stabilized, solid,
oxygen-ion-conducting electrolyte which in this form is not
resistant to thermal shock.
The structural and technical disadvantages of the prior art which
have been noted during the preceding discussion are illustrated by
the U. S. Pats. to Hickam No. 3,347,767; Alcock No. 3,297,551;
McPheeters et al No. 3,309,233; Kolodney et al No. 3,378,478; and
Fischer No. 3,359,188. Each of these patents contemplates the
provision of an elongated tube made from a solid electrolyte
material. This representative sampling of the prior art emphasizes
the inability of prior devices to measure the dissolved oxygen
content of liquid metals without exceptionally slow preheating.
That the relatively large electrolyte tube is subject to thermal
shock is abundantly illustrated by Kolodney et al who provided a
surrounding mesh basket for collecting pieces of the electrolyte
tube upon fragmentation. These references further represent the
difficulty of suitably insulating the walls of the electrolyte tube
from its holder to prevent shorts in the electric circuit.
My apparatus, on the other hand, employs a probe using a relatively
small mass of solid electrolyte, supported near the end of an
elongated, insulating tube. The assembly thus formed is highly
resistant to thermal shock, and only a very small area of the
electrolyte is exposed to the high temperature material being
measured. A further advantage arises from confining the measurement
to a very small, predetermined point or area within the heat or
melt.
A number of laboratory instruments for the direct measurement of
oxygen have also been proposed from time to time. These are
typified by Horsley, AERA Report R3427 pp. 1-6 and FIG. 2, 1961. An
electrolyte disc is sandwiched between two cermet electrodes for
the purpose of measuring the free energy in the cermets. The
sandwich is held together by a pair of tubes, an additional purpose
of each of which is to supply a controlled, inert atmosphere
respectively to the outward surfaces of the cermets. Further, the
cermet discs are separated from the supporting tubes by nickel
discs or foils. If the lower supporting tube of the Horsley device
were removed, the entire assembly would, of course, fall apart.
Obviously, there is no teaching of submerging the Horsley device in
a liquid material particularly in a high temperature liquid
material. Similarly, there is no teaching of securing a small mass
or pellet of solid electrolyte material near the end of a
supporting and insulating tube.
Similar apparatus for the direct measurement of oxygen is described
in the literature, representative references to which are tabulated
below:
1. K. Kiukkola and C. Wagner: J. Electrochemical Soc., 104, 397,
1957.
2. H. Schmalzried: z. f. Physicalische Chemie NF, 25, 178,
1960.
3. c. b. alcock and T. N. Belford, Trans. Faraday Soc. 60, 822,
1964.
4. W. Pluschkell and H. Engel: J. Metallkunde, 56, (7), 450,
1965.
5. W. A. Fisher and W. Ackermann: Arch. f.d. Eisenhuttenw 36, 643,
1965.
6. M. Kolodney, B. Minushkin, and H. Steimnetz: Electrochem. Tech,
3, (9-10), 244, 1965.
7. Y. Matsushita and Goto: Thermodynamics IAEA (Vienna) 1,
1966.
8. T. C. Wilder: Trans Met. Soc. AIME, 236, 1035, 1966.
9. r. baker and J. M. West: J. British Iron & Steel Inst., 204,
212, 1966.
10. E. T. Turkdogen and R. E. Fruehan: 76th General Meeting AISI,
May, 1968.
In certain forms of my novel direct measurement apparatus, the
probe structure can be enclosed with a self-contained oxygen-based
reference material therein. This avoids the necessity of conducting
air or other oxygen-containing material into the probe structure
from an external source during use of the probe.
I accomplish the desirable results described heretofore and
overcome the defects of the prior art by providing a probe capable
of being plunged into a high temperature liquid metal without
destructive thermal shock for the purpose of determining the
dissolved oxygen content of said liquid metal, said probe
comprising an elongated electrically insulating refractory
envelope, a small mass of a refractory oxide-type oxygen-anion
permeable solid electrolyte material supported adjacent one end of
said envelope, at least a portion of at least one side of said mass
being exposed through an opening in said envelope for contact with
said liquid metal, said one side portion being disposed adjacent
said one envelope end, reference means within said envelope for
contacting an apposed side of said mass with an oxygen-reference
material, and circuit means extending into said envelope for
electrically contacting said apposed mass together with additional
circuit means disposed for electrically contacting said liquid
metal for measuring an emf developed across said mass in proportion
to the concentration of said dissolved oxygen in said liquid
metal.
I also desirably provide a similar combination wherein said
envelope is fabricated from a material selected from the group
consisting from alumina, fused silica and fused quartz.
I also desirably provide a similar combination wherein said
electrolyte material is an unsaturated oxide spinel-type
crystalline material selected from the group consisting of
materials conforming to the following general equations:
MO + N.sub.2 O.sub.3 = MN.sub.2 O.sub.4
2MO + NO.sub.2 = NM.sub.2 O.sub.4
M.sub.2 O + NO.sub.3 = NM.sub.2 O.sub.4
MO.sub.2 = N.sub.2 O.sub.3 = MN.sub.2 O.sub.5
where M and N equal metals of dissimilar valances, and the oxide of
the lower valence metal is present in less than the stoichiometric
amount thereof.
I also desirably provide a similar combination wherein said
reference means include a metal member positioned substantially
against said apposed mass side, said member being fabricated from a
metal which is oxidizable at the temperature of said liquid metal
to an oxide capable of providing an appreciable equilibrium oxygen
reference pressure at said temperature.
I also desirably provide a similar combination wherein said metal
member includes a powdered mass of said metal.
I also desirably provide a similar combination wherein said metal
member is relatively thin foil of said metal.
I also desirably provide a similar combination wherein said metal
member includes an alloy of dissimilar metals capable of shifting
the calabration curve of said probe.
I also desirably provide a similar combination wherein temperature
sensing means are mounted within said envelope for measuring the
temperature of said apposed mass side.
I also desirably provide a similar combination wherein said
envelope is mounted on a support therefor, a cap member is
removably mounted on said support, said cap member being shaped to
enclose the otherwise exposed end of said envelope and said
mass.
I also desirably provide a similar combination wherein said
reference means are retained against said apposed mass side, an
elongated electrically insulating tube is inserted through said
envelope to a position of engagement with said reference means to
retain said reference means against said mass, said tube forming
passage means for conducting excess or residual gas out of said
envelope.
These and other objects, features, and advantages of the invention,
together with structural details thereof, will be elaborated upon
as the following description of presently preferred embodiments and
presently preferred methods of practicing the same proceeds.
In the accompanying drawings, I have shown presently preferred
embodiments of the invention and have illustrated presently
preferred methods of practicing the same, wherein:
FIG. 1 is a longitudinally sectioned view of one form of probe
structure arranged in accordance with the invention;
FIG. 2 is a cross sectional view of the probe structure shown in
FIG. 1 and taken along reference line II--II thereof;
FIG. 3 is an enlarged elevational view, partially sectioned, of one
form of the insulating envelope and electrolyte pellet arrangement
which can be utilized in the probe structures of FIGS. 2 and 4;
FIG. 4 is a partial longitudinally sectioned view of another form
of probe structure arranged in accordance with the invention;
FIG. 5 is a partial longitudinally sectioned view of the probe
structure of FIG. 4 and showing the probe structure in its
extended, operative position with reference to the molten material
being analyzed;
FIG. 6 is a graphical representation of the calibrated electrical
output of my novel probe utilizing various types of
oxygen-reference materials;
FIG. 7 is a partial, longitudinally sectioned view of still another
form of my novel probe structure having self-contained
oxygen-reference means;
FIG. 8 is a similar view showing still another form of my novel
probe structure with self-contained oxygen-reference means in a
partially sealed probe structure;
FIG. 9 is a similar view of another form of my novel probe
structure having a combined electrode, electrode lead and
oxygen-reference material within the probe structure;
FIG. 10 is an isometric view of still another form of my direct
oxygen measurement apparatus;
FIG. 11 is a partial cross sectional view of still another form of
my direct oxygen measuring apparatus shown in a unique arrangement
with a continuous casting machine or the like;
FIG. 12 is a partial longitudinally sectioned view similar to FIG.
9 and showing a modified probe structure; and
FIG. 13 is a similar view of still another form of my probe
structure.
Referring now to FIGS. 1-2 of the drawings, the illustrative form
of the probe structure 44 shown therein includes an envelope 46
fabricated from fused silica, alumina, or fused quartz or the like
electrically insulating material which is sufficiently refractory
and chemically resistant to withstand molten metal or other high
temperature material for an interval at least sufficient to permit
a reading to be made. In the case of molten steel analyses, fused
silica or quartz is preferred. Fused silica has a melting point of
about 1,710.degree. C. and begins to soften at a temperature of
about 1,650.degree. C., which is higher than that of most liquid
steels during refining. In any event, slight softening of the
envelope 46 does not interfere with the reading, which is
substantially instantaneous. Moreover, a rapid heating of the
envelope to an elevated temperature, particularly one in the
vicinity of its softening temperature, prevents cracking of the
envelope by the mass 52 (described below), which may have a
considerably higher coefficient of expansion. The relatively small
sizes of the envelope 46 and mass 52 also mitigate the effects of
their differing rates of thermal expansion. Proper selection of
refractory materials is important since the probe may be used in
lqiuid metals at elevated temperatures above 1,000.degree. C. to
include the complete range of melting temperatures of the wide
variety of liquid steels, and other high temperature liquid metals,
such as molten copper. More critically, in the case of certain
electrolyte materials useful herein, a significant oxygen-ion
conductance does not occur until a temperature of about 800.degree.
C. is attained.
This envelope 46 in this example is retained in a length of iron
tubing 48 or other suitable support, on the outer surface of which
is supported an electrode 50, which is fabricated from an
electrically conductive material capable of withstanding molten
metal at elevated temperatures. The electrode 50, if desired, can
be separated from the probe structure for independent insertion
into the liquid metal. Of course, the iron tubing 48 itself can
serve as the external electrode in place of the electrode 50. In
any event, the electrode 50 can be shaped for coinsertion with the
probe 44 to a predetermined depth in the liquid metal. Examples of
such coinsertion are evident from FIGS. 10, 12, and 13 described
below.
At the outward end of the envelope 46, a mass 52 of solid
electrolyte material, such as one of the solid electrolytes
described below, is retained as by melting or heat-forming the
walls of the envelope 46 about the mass 52 or by sintering the mass
52 (in either pellet or pulverulent form) to the adjacent internal
wall surfaces of the envelope 46 without appreciable forming of the
envelope, as noted below. For maximum thermal resistance the mass
52, in any case, is of small size and compact of configuration, as
evident from the drawings, particularly FIG. 3 (enlarged as
aforesaid). A desirable configuration for the mass 52, as evident
from FIGS. 1 and 3 and from FIGS. 7-9, 12 and 13, is
right-cylindrical wherein the diameter and height of the cylinder
are about equal. For operation of the probe, it is necessary only
that the mass 52 be sealed to the envelope 46, to an extent to
prevent leakage of liquid metal into or gas out of the probe.
In this example, a very reliable seal is produced as by
heat-forming the envelope material about the mass 52. Heat-forming
of the envelope can be accomplished by spinning or rotating the
envelope about its longitudinal axis while heating at least that
portion thereof adjacent the mass 52 to the softening point of the
envelope material.
The seal results from a sintering action which inherently occurs
when solid electrolyte and envelope materials of comparable
sintering and softening temperature ranges are employed. For
example, a zirconia-calcia mass 52 (or an electrolyte of similar
melting point such as yttria-stabilized thoria) has a sintering
temperature range of about 2,000.degree. F. to about 3,000.degree.
F. and is inherently sintered to a fused silica envelope having a
softening point of about 3,000.degree.-3,100.degree. F. Sintering
occurs between the electrolyte mass 52 and the adjacent surface of
the silica envelope to form an excellent ceramic-to-ceramic seal.
In addition, individual particles of the mass 52 are sintered or
resintered, as the case may be, to one another for increased
strength and reduced porosity of the electrolyte mass 52. The probe
44 is highly resistant to thermal shock.
In one arrangement, the mass 52 can be provided in the form of a
discrete pellet or disc to which the walls of the envelope 46 can
be shaped thereabout, as shown in FIG. 1; or alternatively the
pellet can be inserted into a length of tubing 46' (FIG. 3) made of
the aforementioned insulating materials and having about the same
inner diameter as the outer diameter of the mass 52'. In the latter
case, the adjacent wall positions of the envelope 46' can be
heat-formed and spun upon the outer cylindrical periphery of the
pellet 52' to form a seal therewith, as noted above.
In another arrangement the mass 52 can be inserted as a small bit
of paste of a pulverulent solid electrolyte material in a suitable
binder or agglutinant material such as a relatively small amount of
colloidion.
In forming a powdered zirconia-containing electrolyte into a
special shape, such as the mass or disc 52 in the end of the
envelope 48, or other structure, such as the electrolyte insert of
FIG. 12, I convert the powder into a paste or plastic mass by
mixing it with the aforesaid agglutinants. Certain polymers, such
as polyvinyl alcohol, carboxy methylcellulose and/or gum gatti in
an aqueous solution, can also be used for this purpose. The
agglutinant or binder aids in compacting the mass against the
surface of the envelope, and thus improves the bond between the
envelope and the electrolyte mass.
Zirconium citrate or other organic compound of zirconium also can
be used. Upon heating the mass, in situ, in an oxidizing
atmosphere, the zirconium compound binder is decomposed and
ZrO.sub.2 is formed thus bonding the particles together. The mass
then retains its shape when heated to high temperatures, such as in
baking or sintering, or in subsequent use, and is rendered more
impervious by this treatment.
The preparation of an oxygen sensor or probe which has a
combination of chemical and physical properties for resisting
destruction and malfunction when plunged into a high temperature
liquid metal such as steel has been accomplished by at least two
features of the invention which constitute essential bases for this
invention.
The disclosed materials when combined not only jointly withstand
extreme thermal shock without shattering but also do not decompose
or melt. In addition, the combination resists erosion and
destructive chemical reaction or other contamination by the liquid
metal or its dissolved oxide during such immersion. Failure of the
probe to comply with any of these stipulations will result in
either malfunction or an erroneous indication of the oxygen content
of the material.
Thus, a primary feature of the invention is a proper selection of
the materials for the envelope and the electrolyte. For example,
fused silica when selected from one of the envelope materials and
calcia-stabilized zirconia when selected from one of the
electrolytes exhibit these properties either individually or
collectively in the proposed structure. A second primary feature
involves a special sintering method for installing or inserting a
mass of solid electrolyte into a fixed position at or near the end
of a tubular envelope.
In this procedure, after certain preliminary steps depending upon
whether a pellet or a powdered mass of electrolyte is being
installed, the tip of the probe containing the electrolyte is
heated to a temperature in the range of 2,000.degree. F and
preferably approaching 3,000.degree. F.
The selected materials are sufficiently compatible so that they
interact to form a secure bond. In the case of the combination of
calcia-stabilized zirconia and a silica tube, the CaO of the
electrolyte reacts with the SiO.sub.2 of the tube to form a film of
calcium silicate at the interface, thus securely bonding the two
materials. In the case of a probe structured with the
calcia-stabilized zirconia in an alumina tube, for example,
sintering results in a reaction between the CaO of the electrolyte
and the Al.sub.2 O.sub.3 of the tube to form an interfacial
compound of a spinel configuration (CaAl.sub.2 O.sub.4).
Rapid cooling from the sintering temperature tends to stabilize the
high temperature configuration so that the thermal shock is greatly
reduced when the probe is plunged into high temperature liquid
metal.
Desirably, but not necessarily, the envelope material has a
softening temperature range within the sintering range of the
electrolyte material to facilitate sintering and sealing thereof to
the envelope, as noted previously.
The envelope 46, together with the mass 52 is releasably held in
the probe structure 44 so that this portion of the assembly can be
discarded after one or more measurements. When using the probe 44,
the forward surface of the mass 52 is exposed to the molten
material through the otherwise open end of the envelope 46.
Desirably, the forward surface of the mass 52 is adjacent the
associated end of the envelope as shown. In certain applications,
however, the mass can project through the envelope opening. In most
applications, on the other hand, the envelope opening, and in this
case the I.D. of the tubular envelope, are kept small, so as to
reduce that surface of the mass 52 which must be exposed to the
liquid metal.
As is well-known, the coefficients of thermal expansion of many of
the electrolyte materials disclosed herein are larger than those of
the noted envelope materials. In those applications wherein the
electrolyte coefficient is substantially larger, the effects of
differential thermal expansion can be mitigated, when necessary, by
heating the envelope, during use of the probe, at a very rapid rate
from its initial temperature to the elevated temperature of the
liquid metal and preferably by selecting an envelope material which
begins to soften at the elevated temperature. The envelope, then,
becomes slightly plastic before sufficient heat penetrates the
walls thereof to the electrolyte to cause appreciable thermal
expansion of the latter.
Oxygen reference means can be placed in the envelope 46 or 46' and
desirably against the apposed surface of the mass 52 or 52'. The
reference means can take the form of a metal foil or coating 54 or
other metal member as described below. A cermet member, or an alloy
can also be used. Oxygen from suitable oxygen-reference means such
as those described below, diffuses readily through the coating. In
the case of pure iron, for example, reference oxygen quickly
saturates the iron foil before an oxidation commences. In other
arrangements of my invention, the coating is provided as a piece of
foil or other discrete member pressed or held against the mass 52
for contact purposes. Reference oxygen can then pass around as well
as through the contact member.
Although the coating 54 facilitates intimate contact between the
mass 52 and an electrical connection such as thermocouple 56, the
coating is not essential as pointed out below. The electrode
coating can be replaced by a discrete electrically conductive
member or mass held against the electrolyte member 52, for example,
by the elongated member 60 mentioned below. The electrode coating
or member 54 can be combined with or serve additionally as a solid
oxygen reference means, as also noted below. The thermocouple 56,
in this example, also provides an electrical connection to the
opposite or other apposed surface of the mass 52 through one of its
leads, for example, the lead 58. The other electrical connection
can be provided by lead 51 and electrode 50, since the envelope 46
is of insulating material.
The thermocouple leads 58 and 59 are insulated and conducted
through the envelope 56 to the thermocouple 56 by suitable means
such as an apertured and elongated insulating member 60, fabricated
like the envelope 46 from fused silica, alumina, quartz or the
like. The insulating member 60 desirably is spacedly fitted within
the envelope 56, and is provided with a pair of longitudinally
extending, laterally spaced apertures 62 through which the
thermocouple leads 58, 59 are loosely extended. The passages 62
therefore can provide access for external air or other
oxygen-containing gas to the thermocouple side of the electrolyte
disc 52. Desirably, the member 60 presses the thermocouple 56 into
good electrical and thermal contact with the mass 52, and with a
discrete electrode and/or oxygen reference member when used. In
this relation, the member 60 can be affixed after the teaching of
FIG. 9, for example.
Other oxygen containing materials such as CO.sub.2 or various
cermets, (and many other oxygen-bearing compounds some of which are
noted hereinafter) can be used as oxygen-reference means. These
materials dissociate at the elevated temperatures to which the
probe usually is subjected as follows:
CO.sub.2 = CO + 1/2 O.sub.2
Cr.sub.2 O.sub.3 = 2 Cr + 3/2 O.sub.2
NiO = Ni + 1/2 O.sub.2
As such compounds have differing dissociation energies, the probe
usually requires calibration for each such source of oxygen.
The aforementioned reference gas can be circulated inwardly through
the rod apertures 62 to the inner surface of the pellet 52 and then
outwardly through clearances 63 between the rod 60 and the envelope
46 as denoted by flow arrows 65. On the other hand, the rod 60 can
be closely fitted within the envelope 46 and a central
longitudinally extending baffle (not shown) can be utilized to
circulate a reference gas forwardly through one of the passages 62
and in the return direction through the other passage 62.
It has been found that ready access of the inner surface of the
solid electrolyte disc 52 to a standard oxygen-reference source is
necessary in order to obtain a prompt reading of stabilized emf
output from the probe, when the molten material contacts both the
mass 52 and the electrode 50. In one arrangement of my
oxygen-reference means, a steady but not necessarily strong flow of
reference gas is thus maintained. In fact, still air has been used
as a reference material. It is contemplated that the quantity or
concentration of oxygen available from the oxygen-reference means
can be varied as noted below or by adding a quantity of nitrogen or
other relatively inert gas, so as to shift the calibration curve of
the electrolyte cell to another, more easily measured potential
range (FIG. 6).
It will be understood, of course, that the use of the thermocouple
56, and one of its leads, such as the lead 59, are not essential to
the operation of the probe structure 44 and can be omitted,
particularly if other temperature measuring means are available.
Upon omission, the lead 58 will be connected directly to the inner
coating or the like of electrode member 54 of the electrolyte mass
52 in order to ensure the necessary electrical contact therewith.
The aforementioned electrically conductive coating or member 54 is
not essential, but is useful in facilitating electrical contact
with the lead or leads 58, 59 by pressure contact for example.
Also, one of the gas and conductor passages 62 can likewise be
omitted and the aforementioned circulation of oxygen-bearing gas
can be returned through the clearances 63. The leads can be of very
small diameter, so as not to obstruct the flow of an
oxygen-reference gas, when used.
The mass 52 is sufficiently small, in this example, that any
differential expansion between the solid electrolyte material
comprising the mass 52 and the material of the envelope 46 will not
cause the latter to fracture. In fact, the small size of the probe
structure does not interfere with the electro-chemical aspects of
its operation, and the probe can be "miniaturized", if desired, to
an extent consistent with manufacturing techniques.
A further advantage of the structure of FIGS. 1-3 lies in the fact
that the size and shape of mass 52 considerably reduces the cost of
manufacturing the probe structure 44, as compared to the case where
the entire envelope 46 or a substantial portion thereof is
fabricated from the solid electrolyte, which is a rather expensive
material. The latter advantage is an important consideration in
view of the fact that the electrolyte mass 52 and the envelope 46
in many applications must be replaced in the probe structure 44
after each reading particularly after insertion into high
temperature liquid metals, such as molten steel. The expendable
envelope 46 and mass 52 together represent a small fraction of the
cost of fabricating the entire envelope from an electrolyte
material. The latter envelope, even if it does not fracture from
thermal shock, must also be expended after each use, which renders
the cost thereof prohibitive for most applications.
Referring now to FIGS. 4 and 5 of the drawings, wherein similar
reference characters with primed accents denote similar components
of FIGS. 1 and 2, another probe structure 70, arranged in
accordance with the invention, is illustrated. The latter
arrangement is adapted particularly for determining oxygen content
of a liquid metal in most refining furnaces, such as the open
hearth, where it is necessary to protect the probe from contact
with an overlying layer of molten slag thereon as the probe is
immersed below the slag-metal interface. Thus, the probe structure
70 is provided with means for shielding the solid electrolyte from
contact with the overlying slag layer and for quickly inserting the
probe components into the molten bath in order to obtain a
stabilized reading.
In furtherance of these purposes, the supporting envelope 44'
together with the electrolyte mass 52' secured therewith are
mounted in a plug member 72, through which the envelope 44' is
extended centrally and longitudinally. The plug 72 is inserted into
a central and longitudinally extending channel 74 of a tubular
electrode 76 fabricated from a compatible material such as steel.
Electrical contact to the tubular electrode 76 and to the
electrolyte disc 52' is established by lead 51' and one of the
thermocouple leads 58' or 59' as described above in connection with
FIGS. 4 and 5. An oxygen reference gas, such as air or CO.sub.2,
can be circulated to the inner surface of the disc 52' and/or the
thermocouple 56' can be eliminated as described previously with
reference to FIGS. 4 and 5.
The tubular electrode 76 and the components of the probe structure
70 supported thereby, are slidably mounted within an outer
supporting tube 82, likewise fabricated from a compatible material
insofar as the material being tested is concerned. The tubular
electrode 76 is thus mounted for movement longitudinally of the
outer support tube 82, and in this example is secured to the
adjacent end of a compressed resilient member such as a coil spring
84. The spring 84 is maintained in its compressed condition in this
example by a pin 86 inserted through a suitable aperture in the
support tube 82 and movable laterally to restrain and to release
the compressed spring 84, as required. In the probe structure 70 as
shown in FIG. 4 4 the pin 86 engages the next to the last helix of
the coil spring 84 to maintain the major proportion of the spring
84 in its compressed condition and the tubular electrode 76 and
associated components in their inoperative position in the outer
support 82.
In this position, the insertable ends of the tubular electrode 76
and of the envelope 44' and disc 52' are covered by a removable cap
88, which can be frictionally or otherwise detachably secured to
the adjacent end of the outer support tube 82 by suitable quick
fastening means (not shown) secured to the outer flange 90 of the
cap and the adjacent end 92 of the support tube 82. The inward end
of tubular portion 94 of the cap 88 is of sufficient length to
engage the adjacent end of the tubular electrode 76 in this
position.
In the operation of the probe structure 70, the lower end of the
support tube 82, as viewed in the drawings, is inserted through any
overlying slag and well into the molten steel or other material to
be analyzed. The pin 86 is then withdrawn, for example by means of
its eye-hook 96, to release the ejection spring 84. The slidably
mounted tubular electrode 76 carrying with it the envelope 44' and
electrolyte disc 52' and the detachable cap 88, is then ejected
downwardly farther into the molten steel or other liquid metal,
where it comes to rest at the extended position of the ejection
spring 84 as shown in FIG. 5 of the drawings. The inserted movement
of the probe forces the protective metal cap 88 into the metal
where it dissolves or melts or falls away to allow normal use of
the probe. While in place, the cap 88 prevents contact of the
molten slag and concomitant erroneous readings caused by coating of
the slag on the ejected components of the probe structure 70. At
the fully extended position of the probe structure (FIG. 4), the
relatively small exterior surface of the solid electrolyte disc 52'
and the tubular electrode 76 thereto are exposed to the substance
being measured at a predetermined depth.
The electrolyte mass 52 or 52' desirably is fabricated from a
suitable solid material which resists melting at any anticipated
elevated temperature and exhibits solid electrolytic properties. In
those applications involving the testing of molten steel, where
high oxygen content with relatively low percentages of carbon,
silicon, and alloying constituents are anticipated, the electrolyte
mass can be made from zirconia stabilized with calcia, as noted
above. In applications involving other high-melting liquid metals,
stabilized zirconia or thoria, for example, can be used to
advantage.
In general, combinations of oxides can be utilized which exhibit
electrolytic properties by providing the necessary defects in the
crystalline lattice which allow the transport of oxygen ions.
Principal among these are partially saturated complex oxides, which
otherwise conform generally to the spinel-type crystalline
structure. Spinel type structures, for this purpose, are
approximated by the generalized formula (MN.sub.2 O.sub.4), which
results from at least three different combinations, as set forth
generally in the following Table I. The most common spinel involves
the combination of a monoxide with a sesquioxide, such as MgO plus
AL.sub.2 O.sub.3 yielding an unsaturated MgAl.sub.2 O.sub.4, when
combined in non-stoichiometric amounts as described below. Other
complexing procedures involve a dioxide and two molecules of
monoxide, such as 2CaO + ZrO.sub.2 = ZrCa.sub.2 O.sub.4 ; and a
trioxide with a suboxide for example Cu.sub.2 O + WO.sub.3 =
WCu.sub.2 O.sub.4. It will be seen that substantially the same
molecular structure results regardless of the particular forms of
oxide combinations involved. These spinel type compounds can
exhibit similarly unsaturated crystalline structures.
There are large numbers of other oxide complexes which fall into
one of the types of oxide complexes noted above and which form
spinel-type molecular structures. Some of these are noted in the
following table:
TABLE 1 TYPES OF SPINELS
TYPE I TYPE II TYPE III MO.N.sub.2 O.sub.3 or 2 MO.NO.sub.2 or
M.sub.2 O.NO.sub.3 or MN.sub.2 O.sub.4 NM.sub.2 O.sub.4 NM.sub.2
O.sub.4 MgAl.sub.2 O.sub.4 FeCr.sub.2 O.sub.4 TiMg.sub.2 O.sub.4
TaFe.sub.2 O.sub.4 MoCu.sub.2 O.sub.4 MgCr.sub.2 O.sub.4 NiCr.sub.2
O.sub.4 ZrMg.sub.2 O.sub.4 ZrNi.sub.2 O.sub.4 W Cu.sub.2 O.sub.4
MgFe.sub.2 O.sub.4 CuCr.sub.2 O.sub.4 CbMg.sub.2 O.sub.4 ZrNi.sub.2
O.sub.4 CaAl.sub.2 O.sub.4 ZnCr.sub.2 O.sub.4 TaMg.sub.2 O.sub.4
TaNi.sub.2 O.sub.4 MnAl.sub.2 O.sub.4 CbCr.sub.2 O.sub.4 TiCa.sub.2
O.sub.4 CbZn.sub.2 O.sub.4 MoAg.sub.2 O.sub.4 FeAl.sub.2 O.sub.4
CdCr.sub.2 O.sub.4 ZrCa.sub.2 O.sub.4 TaZn.sub.2 O.sub.4 WAg.sub.2
O.sub.4 CoAl.sub.2 O.sub.4 CoFe.sub.2 O.sub.4 CbCa.sub.2 O.sub.4
ZrCb.sub.2 O.sub.4 NiAl.sub.2 O.sub.4 MnFe.sub.2 O.sub.4 TaCa.sub.2
O.sub.4 ZnCd.sub.2 O.sub.4 ZnAl.sub.2 O.sub.4 FeFe.sub.2 O.sub.4
TiMn.sub.2 O.sub.4 TaCb.sub.2 O.sub.4 CbAl.sub.2 O.sub.4 NiFe.sub.2
O.sub.4 TiFe.sub.2 O.sub.4 TaCd.sub.2 O.sub.4 CdAl.sub.2 O.sub.4
ZnFe.sub.2 O.sub.4 TiNi.sub.2 O.sub.4 UMg.sub.2 O.sub.4 CaCr.sub.2
O.sub.4 MgV.sub.2 O.sub.4 TiCb.sub.2 O.sub.4 MCa.sub.2 O.sub.4
CaFe.sub.2 O.sub.4 FeV.sub.2 O.sub.4 TiCd.sub.2 O.sub.4 UMn.sub.2
O.sub.4 CoCr.sub.2 O.sub.4 ZnV.sub.2 O.sub.4 TiCo.sub.2 O.sub.4
UFe.sub.2 O.sub.4 MnCr.sub.2 O.sub.4 TiZn.sub.2 O.sub.4 UNi.sub.2
O.sub.4 ZrMn.sub.2 O.sub.4 UZn.sub.2 O.sub.4 CbMn.sub.2 O.sub.4
UCb.sub.2 O.sub.4 TaMn.sub.2 O.sub.4 UCd.sub.2 O.sub.4 ZrFe.sub.2
O.sub.4 VMg.sub.2 O.sub.4 CbFe.sub.2 O.sub.4 VZn.sub.2 O.sub.4
however, in order to be used for solid electrolytes one of the
constituent oxides must be present in less than the stoichiometric
amount to permit the formation of the ion transport defects in the
crystalline lattice. For example, in the monoxide-dioxide spinel
formation, such as ZrCa.sub.2 O.sub.4, 15 mol percent of calcium
oxide rather than the theoretical 66 percent is used, to produce an
unsaturated spinel lattice. The unsaturating percentage of the
stabilizing oxide will, of course, vary depending upon the
particular oxide complex which is used.
Complex oxide combinations can be employed other than typically
spinel-type structures. For example, an oxide complex formed from a
dioxide and a sesquioxide, such as ThO.sub.2 + Y.sub.2 O.sub.3 =
ThY.sub.2 O.sub.5, exhibits electrolytic properties in the
non-stoichiometric condition. The essential requirement of the
electrolytic complex oxide combination is that one of the
complexing oxides be present in a non-stoichiometric amount to
provide the necessary crystalline lattice defects (oxygen
vacancies) and resulting oxygen ion transference. By this
mechanism, the unsaturated oxide complex from which the mass 52 or
52' is formed, develops an emf equivalent to the differential in
oxygen concentration at the apposed sides or surfaces thereof. A
suitable meter can be calibrated to read the emf output of the
probe in terms of oxygen concentrations in the material whose
oxygen content is unknown at one side of the mass. Such calibration
of course will be related to a given known oxygen concentration at
the other mass side.
FIG. 6 of the drawings is a logarithmic graph showing the variation
of probe emf in millivolts with concentration of dissolved oxygen
in parts per million. The illustrated curves for various types of
oxygen-reference materials were obtained in molten steel at
2,900.degree. F. The least desirable of these reference materials
is air, as denoted by curve 110, which exhibits relatively high
voltage requiring special instrumentation and in some cases causing
the electrolyte to break down. Curve 112, representing the use of
CO.sub.2 is of special interest, on the other hand, owing to its
substantially greater slope and lower voltage.
Except as provided by my invention, the use of CO.sub.2 or other
gaseous material as an oxygen reference entails the continuous
circulation of the gas through the probe structure. I avoid such
continuous circulation while preserving the advantage of a higher
.DELTA.emf/.DELTA.O characteristic from the use of a CO.sub.2
reference, with the self-contained feature of FIG. 8 or 9 described
below.
A number of cermet-like materials for example Ni-NiO, Fe-Fe.sub.x
O, Cr-Cr.sub.2 O.sub.3, W-WO.sub.2, Co-CoO, Cb-CbO.sub.2,
Mo-MoO.sub.2, and various other oxidizable metals and their oxides
have been proposed for use with known solid electrolyte structures.
These cermets, which desirably contain a preponderance of free
metal for the purposes of the present invention, are especially
advantageous when used in my novel probe structure, since their
electrical conductivities permit electrical contact with the mass
52 therethrough. To qualify for such usage, the cermet including
the free metal and its oxide must be sufficiently refractory at the
anticipated operating temperature range of the liquid metal or
other material to be measured. There must be no undue vaporization
of the oxide but there must be a discernible equilibrium
oxygen-pressure at the operating temperature range.
The emfs obtained with some of these materials are represented by
curves 114, 116 and 118. The Ni-NiO and Fe-Fe.sub.x O curves 114,
116 are satisfactory for certain applications. However, the
Cr-Cr.sub.2 O.sub.3 curve 118 crosses the zero emf line at point
120 with the result that concentrations of dissolved oxygen in the
range of 20-50 ppm are very difficult to measure. These and other
oxygen-reference materials can be utilized, including the disclosed
oxygen-reference means described below.
I have found that the addition of a dissimilar metal to the
aforementioned cermet-like materials displaces the emf curve, as
typified by curve 122 for the oxygen-reference material, NiCr -
Cr.sub.2 O.sub.3. This material which is a combination of nichrome
and chromium oxide displaces the undesirable curve 118 to the left
and away from the zero emf line 124. The curve 122 has the
additional advantage that the emf varies directly with dissolved
oxygen concentration. The calibrational curves of the other cermet
materials can be similarly displaced. It appears that a more nobel
metal shifts the emf curve as a function of the activity of the
diluent metal.
In FIG. 7 of the drawings, another arrangement 126 of my novel
direct measurement apparatus is shown. In this example oxygen
measuring probe 128 is inserted through a refractory holder 130.
The probe 128 and the block 130 are supported by a length of steel
or other metal tubing 132. A small mass of solid electrolyte 136 is
sealed into an insulating tube 128 of the probe structure 138 by
one of the methods described above.
A combined electrode and oxygen-reference member including in this
example of relatively pure foil 140 of an oxidizable metal is
supported against the inner surface 142 of the electrolyte 136. The
member 140 can be backed up by a metal foil or disc 144, or other
nobel metal. Electrical contact is made with a length of conductive
wire 146 which can be made of platinum. The wire 146 is supported
at the other end of the insulating tube 138 by means of refractory
cement 148. If desired, a suitable insulating tube, as in FIG. 8,
can be used to press the wire 146 against the member 144 if used
and the electrode oxygen reference member 140 or similar metallic
member and in turn against the adjacent surface 142 of the
electrolyte 146. I have found that such pressure is sufficient to
establish proper electrical contact between the lead 146 and the
solid electrolyte 136.
The small bit of foil or other member 140, which can be made from
an oxidizable metal such as iron, chromium, nickel, cobalt,
molybdenum, tungsten or columbium, provides the oxygen based
reference material for the proper operation of the electrolyte
cell. Thus, a small amount of air or other form of gaseous oxygen
contained within the interior 150 of the probe 128, is sufficient
to form a very thin layer of oxide on the member or foil 140. The
amount of the oxide layer is increased by the passage of oxygen
ions through the solid electrolyte 136 when the probe 126 is
immersed. I have found that the amount of oxide thus formed within
the envelope 128 is sufficient to attain an equilibrium and
reproducible emf reading. The addition of a more nobel but
oxidizable dissimilar metal to the reference foil or member 140
likewise shifts the calibrational emf curve as shown in FIG. 6. For
example, a disc 140 formed from nichrome shifts the calibration
curve to the left relative to the curve for a pure chromium disc
140, after the manner illustrated in FIG. 6.
A layer or tube of protective cardboard 142 or other refractory
material surrounds the outer surfaces of at least that part of the
supporting tube or holder 132 which may be immersed in the molten
metal bath or the like. The exposed surface 154 of the electrolyte
136 is protected during its passage through any slag or other
overlying layer on the bath or heat by means of a suitably shaped
cap 156, which can frictionally engage the adjacent end of the
cardboard layer 152. For use with molten steels the cap 156 can be
fabricated from a mild steel which is quickly melted to expose the
electrolyte surface 154 at some point or predetermined location
beneath the surface of the steel bath.
As mentioned in certain of the preceding figures, it will be
understood, of course, that a second lead (not shown in FIG. 7) can
be introduced into the insulating tube or envelope 128 for the
purpose of making a thermocouple connection at the electrode member
140 or 144. It is also contemplated that the electrode and
reference member 140 can be replaced with a mixed metal or alloy
member such as a piece of nichrome. As set forth in FIG. 6, I have
found that the use of a nichrome foil displaces the emf calibration
curve to a more favorable position (curve 122) relative to that
obtained with chromium (curve 118). Similar alloys can be employed
to fabricate the member or foil 140 to displace the various
calibration curves more or less at will.
In construction of the probe 126 of FIG. 7 it is not necessary that
the member or foil 140 be sufficiently refractory to withstand
melting at the operating temperatures of the probe 126. For
example, I have obtained equally good results from the use of a
pure iron foil 140 or other metal which melts within the operating
temperature range of most liquid steels. For this reason, the foil
or other oxidizable metallic member 140 can be provided in the form
of particulate or pulverulent material.
Carbon or graphite can be substituted for the oxygen-reference
means 140 after the teaching of FIG. 7. It is also contemplated
that a suitable electrically conductive and self-contained oxygen
reference material such as cermet, can be substituted for the
member 140. The cermet, which can be selected from those materials
enumerated or characterized in connection with FIG. 6, is provided
as a suitable member or mass positioned against and hence in
electrical contact with the solid electrolyte mass 52. The cermet,
for this purpose, therefore can be provided in the form of a foil
or other discrete member, or as a pulverulent mass. Either form may
be pressed against the solid electrolyte 52 as by use of the
contact foil or disc 144 or similar contact, or, operating
conditions permitting, by gravity. Where the mass of reference
material 140 is a discrete member and is sufficiently refractory to
withstand melting at the anticipated operating temperatures, the
contact member 144 can be omitted and electrical contact made
directly to the reference member 140.
In FIGS. 8 and 9, I provide convenient means for generating carbon
dioxide (CO.sub.2) within the probe structure as an
oxygen-reference material. The desirability of using CO.sub.2 has
been established in connection with FIG. 6. As explained more fully
hereinafter, the probe structure 158 of FIG. 8 can be partially
closed, while the probe structure 160 of FIG. 9 is closed but not
sealed. The probe structures 158, 160, as is the case of the
structure 128 of FIG. 7, can be employed as part of the measuring
apparatus 126 or 126'(FIGS. 7 and 8). The probe support 126 may be
plunged manually into the molten steel bath or the like, with the
provision of a probe support 126 of suitable length, for example,
as used in connection with a conventional immersion thermocouple.
It is also contemplated that the emersion gun structure of FIGS. 4
and 5 can be used.
With more particular reference to FIG. 8, the solid electrolyte
136' is supported in insulating tube 138' in the manner described
previously. Electrical contact can be established with the inner
surface 142' of the electrolyte 136' by means of a conductive wire
lead 162 or the like. Electrical contact between the wire lead 162
and the electrolyte surface 142' can be established as shown in
FIG. 1. However, I have found, in most cases, that the platinum or
other metallic coating can be omitted from the surface 142', and
adequate electrical contact can be made between the electrical lead
and the electrolyte by merely pressing these components together.
In one arrangement, this is accomplished as shown in FIG. 9 by
forming an enlarged contact portion 164 adjacent the inner end of
the lead 162. An inner insulating tube 166 is then furnished for
the purpose of engaging and pressing the spiral 164 into firm
contact with the electrolyte surface 142'. Alternatively, the lead
is simply bent over the inward end of the inner tube 166. This
engagement is preserved by securing the adjacent surface of the
inner tube 166 to the other end of the probe tube 138' by means of
a refractory cement 168. Alternatively, the inner end of the lead
can be embedded in the electrolyte mass, particularly when the
latter is supplied as a bit of pulverulent material.
In further accordance with my disclosure of FIG. 8, I provide a
solid oxygen reference material 174 preferably within the space 172
between the inner or lead supporting tube 166 and the outer
electrolyte supporting tube 138'. The material 174 is conveniently
coated on the outer surfaces of the inner tube 166 and is capable
of releasing an oxygen reference gas at elevated temperatures for
the proper operation of the electrolyte cell 136'. As an example of
such material 174, I use magnesium carbonate (MgCO.sub.3) or
manganese carbonate MnCO.sub.3), or preferably calcium carbonate
(CaCO.sub.3), which decompose to release carbon dioxide (CO.sub.2)
at the respective operating temperatures of the probe 158. In this
arrangement, the outer end 170 of the inner tube 166 is left open.
As the material 174 decomposes, the liberated CO.sub.2 or other
oxygen reference gas travels toward the electrolyte 136' and comes
into intimate contact with the inner surface 142' thereof, owing to
the close proximity of the inner end 176 of the inner tube 166. For
use in measuring the dissolved oxygen content of liquid steels, the
inner insulating tube 166 desirably is fabricated from fused silica
or quartz or alumina as is the electrolyte supporting tube 138'.
The probe structure 158 is not sealed, and it possesses the
advantage of producing a very quick, equilibrium reading, owing to
the copious supply of CO.sub.2 from the decomposition of the rather
limited quantity of material 174. A more obvious advantage is, of
course, the elimination of an external source of CO.sub.2 and its
attendant conduit connections, metering valves, etc.
A similar measuring apparatus 126" is shown in FIG. 9. The probe
structure 160 used therein incorporates the advantageous use of CO
(in the presence of carbon) to provide an oxygen reference within
the probe. The inner surface 142' of the solid electrolyte is
contacted by combined electrode, electrode lead, and oxygen
reference member 178. In this example, the member 178 is a carbon
or graphite rod extending substantially through the insulating tube
138' and is pressed at its inner end 180 to contact with the inner
surface 142' of the electrolyte 136'. This relation, which produces
adequate electrical conductivity between the electrode 178 and the
electrolyte 136', is maintained by a rigid portion 182 of
refractory cement or the like, positioned between the outer end 184
of the electrolyte supporting tube 138' and the adjacent surface of
the electrode 178. The cement 182, however, can be porous or
otherwise provided with a passage for the escape of air or gas when
the probe 160 is heated.
When the other end, i.e., the electrolyte end of the insulating
tube 138' is plunged into a bath of molten metal, the adjacent end
180 of the electrode 178 naturally attains the highest temperature
along its length. At this time, the end portion 180 of the
electrode quickly combines with air or oxygen contained within the
insulating tube 138' to form carbon monoxide (CO) to yield a
standard oxygen reference base for the probe 160. Thus, different
forms of oxygen reference means are produced in accordance with the
following equilibrium reaction:
C + 1/2 O.sub.2 = CO
It is also contemplated that the rod can be made of other
conductive and oxidizable or partially oxidized materials, to
provide differing characteristics of the combined electrode, oxygen
reference means, and electrical lead or conductor. Thus, the rod
178 can be fabricated with any of the cermet materials enumerated
or characterized in connection with FIG. 6 or in connection with
the conductive, oxygen-reference mass or member 140 of FIG. 7.
Another novel arrangement of my direct oxygen measuring apparatus
184 is shown in FIG. 10. The apparatus includes a refractory mold
structure 186 through a wall section 188 of which are inserted an
oxygen probe 190 and electrode 192. The probe 190 can be
constructed in accordance with the insulating tube and electrolyte
assembly shown in any of the preceding figures. Desirably, the
probe 190 is one of the self-contained probe structures 128, 158,
or 160 of FIGS. 7-9 for ready portability of the measuring
apparatus 184. Suitable electric leads 194, 196 are connected to
the probe 190 and to the exterior electrode 196 and thence to
external emf measuring circuitry (not shown) of known construction.
Although the material of the mold 186 is of an insulating
character, it is not necessary, of course, to provide any
particular means of insulating the electrode 192 from the probe
structure 190, owing to the use of an insulating supporting tube
198.
In the operation of the direct measuring apparatus 184, a quantity
of molten steel or other material having a temperature of at least
800.degree. C and desirably 1,000.degree. C or higher is poured
into the mold 186 from a suitable ladle or spoon 200. The mold 186
is filled until the surface 202 of the molten material covers the
probe 190 and the electrode 192. Electrical contact is established
with the outer surface 204 of the solid electrolyte mass 206
through the molten steel 202 or the like and the external electrode
192. On the other hand, the inner surface 208 of the electrolyte
mass 206 is contacted by means of the electrical lead 194. As noted
below respecting FIG. 11, a thermocouple can be associated with the
probe 190 in FIG. 10 for correlation with the emf reading of the
probe 190. Desirably, the probe emf is measured at the
solidification temperature of the liquid metal, as denoted by the
temperature thereof becoming essentially constant. In the case of
liquid steel, the melting temperature of specific alloys thereof
can be quickly determined along with percentages of certain
constituents such as carbon. The constant or freezing temperature
thus obtained can be correlated with the emf of the probe to
determine oxygen content.
In FIG. 11 another modification 210 of my novel direct measuring
apparatus for dissolved oxygen is disclosed. In this arrangement,
my apparatus is incorporated in a tundish 212 of a continuous
casting machine, or in other suitable container structure, and is
thereby enabled to perform a continuous monitoring of the oxygen
content in the liquid steel passing through the tundish.
Specifically I provide a stabilized zirconia (CaO .sup.. ZrO.sub.2)
insert 214 for one or more of the nozzle openings, such as the
opening 216 of the tundish 212. One of the other solid electrolyte
materials listed above can be substituted for the stabilized
zirconia, provided its melting or softening point is above the
anticipated temperature of the liquid steel.
The electrolyte insert 214 is contacted with an external measuring
circuit and with an oxygen reference material to complete the
electrolyte cell established by the insert 214. One arrangement for
establishing such contact includes the provision of an insulating
tube 218 extended through a conventional refractory wall structure
220 of the tundish 212. In this arrangement, a pair of electric
leads 222 are extended through the insulating tube 218 and
terminate in a thermocouple connection 224, which in turn is
closely fitted into an adjacent recess 226 of the electrolyte
insert 214 for electrical and thermal contact therewith.
Alternatively, the thermocouple can simply be pressed against the
bottom of the tube recess 227 in the insert 214.
Suitable oxygen reference material such as air or CO.sub.2 from a
suitable external source (not shown) can be conducted through the
insulating tube 218 as denoted by flow arrow 228 to the inner end
230 of the insulating tube 218 where the reference gas contacts the
adjacent surface of the electrolyte insert 214. The reference gas
can then be conducted out of the insulating tube 218 through an
inner tube 232 surrounding the leads 222. As noted below, other
oxygen reference means can be substituted.
Electrical contact with the inner surface or throat 234 of the
electrolyte insert 214 is established through the liquid steel in
the tundish 212 and through any metallic component of the
continuous casting machine which is in contact with the liquid
steel. To facilitate such contact, an external electrode 236 can be
sealed through the wall structure 220 of the tundish 212 or
inserted directly into the liquid metal through the open top of the
tundish.
With this arrangement, an oxygen reference material can be
continuously supplied to one side of the electrolyte insert 214 and
a material of unknown oxygen content to the other side. The emf
developed thereacross is continuously monitored by measuring the
potential developed across external electrode lead 238 and one of
the thermocouple leads 222. Owing to the rapid response of the
direct measuring apparatus 210, a continuous reading of the
dissolved oxygen content of the liquid metal passing through the
electrolyte insert 214 can be obtained. Such readings can be
calibrated against any changes of temperature, which are of course
continuously indicated by the thermocouple 224. It will be
appreciated that other suitable oxygen-reference means, such as one
of those described above, can be substituted depending upon the
specific application of the invention.
In FIG. 12 of the drawings, there is disclosed another form 240 of
my novel probe structure which can be immersed or submerged below
the surface of a liquid metal bath for simultaneously measuring the
temperature and the dissolved oxygen content of the metal bath. The
supporting tubing 242 as noted above in connection with FIG. 7 can
be of any desired length for insertion manually lance-wise or with
an ejection device into the metal bath. The tube 243 is protected
in this example by a thermally insulating jacket 152' to which is
fitted a protective cap 156'. Alternatively, the cap 156' can be
engaged with the plug 248 or other common support for the probe and
external electrode. A direct reading oxygen probe 244 and an
external electrode 246 such as a rod of steel or other compatible
conductive material are inserted through suitable openings therefor
in a refractory plug 248. In this example, the plug 248 can be
secured to the end of the supporting tube 242 after the manner of
FIG. 7.
A mass of electrolyte 250 is maintained within the exposed end of
the insulating envelope 244 as described previously. The probe
structure 244 can be fabricated as described in connection with any
of the preceding figures, and, in this example, is provided with a
thermocouple 252 positioned against an oxygen reference member 254
and the inside surface of the mass 250. Thermocouple and
electrolyte leads 256 are extended through the interior of the
envelope 244. As in other figures of the drawings, the refractory
cement at the end of the envelope 244 merely stabilizes the leads
256 but does not seal the envelope. A similar lead 258 is connected
to the external electrode 246, and all of the leads 256, 258 are
extended through the supporting tube 242 for connection to external
emf measuring circuitry (not shown). With the arrangement of FIG.
12 both the probe structure 244 and the external electrode 246 can
be immersed beneath the surface of a liquid metal bath to the same
predetermined depth, for measuring the dissolved oxygen content at
that location. Substantially at the same time, the temperature at
that location can be measured through the thermocouple 252.
A similar immersion and direct-reading probe 260 is shown in FIG.
13. In this arrangement the probe 244' and external electrode 246'
are supported by a refractory block or plug 262. At the forward end
of the plug 262, the protective cap 156' is engaged as in preceding
figures. As noted previously the cap 156 or 156' can be used to
prevent contact of the probe 244' with any overlying slag. By the
same token, the cap 156 or 156' can be employed to prevent contact
with the liquid metal until the forward ends of the probe and
electrode can be immersed to a predetermined depth below the
surface of the liquid metal.
In this example, the refractory block 262 is provided with a necked
down portion 266 covered with an insulating layer 267 to which is
secured an elongated supporting tube 268. Desirably, the supporting
tube 268 is fabricated from a suitable structural material and is
provided with longitudinally spaced commutator rings 269. The
external electrode 246 is connected through lead 270 to contact 272
extending through the insulating layer 267, which can be of
polyvinyl acetyl or the like for engagement with one of the
commutator rings 269.
A pair of additional leads 274 for the thermocouple 252' are
extended through the plug 262 to similar contacts 273 which are
longitudinally spaced along the plug neck 266 for respective
engagement with the remainder of the commutator rings 269.
The plug 262 together with the probe 244'and electrode 246', can be
snapped into the supporting tube 268 by groove and detent means
275, 276. When thus engaged, the contacts 272, 273 are respectively
engaged with the commutator rings 269, irrespective of the rotated
position of the plug relative to the supporting tube 268. The rings
269 are connected to suitable leas 278 extended through the
supporting tube 268. At least the forward end of the tube 268 is
afforded a protective layer 280 of cardboard or the like such as a
ceramic material. Desirably, the length of the insulation 280 is at
least equivalent to the thickness of an overlying slag layer (not
shown) on a melt of liquid metal. Preferably, however, the length
of insulation 280 exceeds such minimal length as the probe may be
inserted to more than a minimal depth below the slag layer.
A suitable vent 282 is provided to relieve internal pressures when
the probe 260 is heated.
From the foregoing, it will be apparent that novel and efficient
forms of methods and means for determining oxygen content of
materials have been described herein. While I have shown and
described certain presently preferred embodiments of the invention
and have illustrated presently preferred methods of practicing the
same, it is to be distinctly understood that the invention is not
limited thereto but may be otherwise variously embodied and
practiced with the spirit and scope of the invention.
* * * * *