US3758397A

US3758397A - Apparatus for oxygen determination

Info

Publication number: US3758397A
Application number: US00054986A
Authority: US
Inventors: R Rittiger; C Russell
Original assignee: Steel Corp
Current assignee: United States Steel Corp
Priority date: 1970-07-15
Filing date: 1970-07-15
Publication date: 1973-09-11
Anticipated expiration: 1990-09-11
Also published as: RO56715A; NO133048B; AT316902B; FI54744B; PL70884B1; BG20407A3; DE2133631A1; NL7109665A; JPS5548256B1; YU175771A; KR780000209B1; CA936916A; HU165461B; ZA714165B; SE379858B; DE2133631B2; ES392920A1; TR16961A; FI54744C; CS166775B2

Abstract

APPARATUS FOR MEASURING OXYGEN CONTENT OF FLUIDS AT ELEVATED TEMPERATURES BY MEANS OF A GALVANIC CELL WITH A SOLID OXIDE ELECTROLYTE AND A REFERENCE ELECTRODE OF A MIXTURE OF A METAL AND ITS OXIDE INCLUDES A SENSOR WHICH COMPRISES A REFRACTORY BODY MEMBER HAVING A FIRST LONGITUDINAL OPENINGS FOR RECEIVING A FUSED SILICA TUBE WHICH HAS THE SOLID ELECTROLYTE FUSED TO THE END THEREOF WHICH CONTACTS THE FLUID. A ROD OF MOLYBDENUM OR OTHER CONDUCTOR EXTENDS THROUGH THE TUBE WITH THE REFERENCE ELECTRODE BETWEEN THE END OF THE ROD AND THE SOLID ELECTROLYTE. A SECOND FUSED SILICA TUBE EXTENDS THROUGH A SECOND LONGITUDINAL OPENINGS ADJACENT THE FIRST OPENING AND CONTAINS A SECOND ROD OF THE SAME MATERIAL AS THE FIRST. THE SECOND ROD ALSO HAS ITS FIRST END EXTENDING INTO THE FLUID. A THERMOCOUPLE EXTENDS THROUGH THE BODY MEMBER WITH ITS FIRST END EXTENDING INTO THE FLUID AND ITS SECOND END CONNECTED TO A CONNECTOR. A STEEL LANCE HAS MEANS AT ONE END FOR RECEIVING THE CONNECTOR AND SECOND ENDS OF THE RODS, AND MEANS AT THE OTHER END FOR CONNECTING TO A VOLTAGE MEASURING MEANS. IN SOME INSTANCES THE THERMOCCOUPLE MAY BE OMITTED.

D R A W I N G

Description

Sept- 11, 1973 R. s. RITTIGER ETAL 3,758,397

APPARATUS FOR OXYGEN DETERMINATION Filed July l5, 1970 2 Sheets-Sheet l vF/at f Afro/'nay APPARATUS FOR OXYGEN DETERMINATION A/lorney United States Patent O APPARATUS FOR OXYGEN DETERMINATION Robert S. Rittiger, Allegheny Township, Westmoreland County, and Charles K. Russell, Franklin Township,

Westmoreland County, Pa., assignors to United States Steel Corporation Filed July 15, 1970, Ser. No. 54,986 Int. Cl. G01n 27/46 U.S. Cl. 204-195 S 4 Claims ABSTRACT OF THE DISCLOSURE Apparatus for measuring oxygen content of uids at elevated temperatures by means of a galvanic cell with a solid oxide electrolyte and a reference electrode of a mixture of a metal and its oxide includes a sensor which comprises a refractory body member having a rst longitudinal opening for receiving a fused silica tube which has the solid electrolyte fused to the end thereof which contacts the fluid. A rod of molybdenum or other conductor extends through the tube with the reference electrode between the end of the rod and the solid electrolyte. A second fused silica tube extends through a second longitudinal opening adjacent the first opening and contains a second rod of the same material as the tirst. The second rod also has its first end extending into the fluid. A thermocouple extends through the body member with its first end extending into the fluid and its second end connected to a connector. A steel lance has means at one end for receiving the connector and second ends of the rods and means at the other end for connecting to a voltage measuring means. In some instances the thermocouple maybe omitted.

This invention relates to apparatus for measuring the oxygen content and/or activity of fluids at elevated temperatures, and more particularly, to apparatus that rapidly determines the oxygen content of liquid steel in a furnace or container without removing a sample. Since our invention, at present, is most useful and most needed for this purpose, this use will be stressed hereinafter. However, our invention is also applicable for determining oxygen in other fluids at temperatures above approximately 700 C., such as liquid copper and hot furnace gases.

Apparatus suitable for this purpose is disclosed in the copending application of Fruehan and Turkdogan, Ser. No. 39,530, filed May 21, 1970. However, the apparatus disclosed therein is basically laboratory apparatus and is not suitable for use in large steelmaking furnaces and containers because of cost, fragility, reliability when used by relatively unskilled workmen, ease of use and other factors important in adapting the basic cell concept to industrial use.

It is therefore an object of our invention to provide apparatus for measuring oxygen content and temperature in substantially the same theoretical manner as that of the Fruehan et al. application, but which is cheaper to manufacture, more rugged and which overcomes the other disadvantages of the Fruehan et al. device.

This and other objects will be more apparent after referring to the following specification and attached drawings, in which:

FIG. 1 is a view, mostly in longitudinal section of one embodiment of our invention;

FIG. 2 is a sectional view, similar to FIG. l, showing a second embodiment of our invention, but with the upper part of the apparatus and the connections to the potentiometer omitted;

FIG. 3 is a view taken on line III- III of FIG. 2 with parts omitted;

FIG. 4 is a viewtaken on line IV-IV of FIG. 2; and

FIG. 5 is a sectional view of the lower part of a third sensor of our invention.

ICC

Referring more particularly to FIG. 1 of the drawings, reference numeral 2 indicates the sensor unit of our apparatus. This includes a body member 4 which is made of a heat and thermal-shock resistant refractory such as cast aluminum oxide. A iirst longitudinal opening 6 extends through the body member 4 and contains a first tube 8 whose first end extends into the molten steel or other lluicl L. The tube 8 is made of an electrical insulator such as fused silica. A solid electrolyte in the form of a disc 10 of ZrO2 containing 3 to 10% by weight of CaO is fused to the inside of tube 8, and a reference electnode 12 in the form of a mixture of powdered Cr and Cr203 is placed on top of the electrolyte 10 in contact with the first end of a rod 14 which extends through tube 8 beyond the second end of body member 4. The rod 14 is made of an electrical conductor, preferably molybdenum. A second longitudinal opening 16 extends through the body member 4 adjacent to and generally parallel to opening 6. A tube 18, similar to tube 8, extends through opening 16 and receives a rod 20 of the same material as rod 14. The periphery of disc 10 is covered with a refractory coating 22 and the periphery of the first end of rod 20 is covered with a similar coating 24 to prevent too rapid disintegration of the disc and rod. The ends of the disc 10 and rod 20 are free of the coating which is preferably of the same composition as body member 4.

A third longitudinal opening 26 is provided adjacent to and generally parallel to the

openings

6 and 16, but does not extend the full length of the body member 4. A closed end tube 28, made of insulating materials such as fused silica or quartz tits within the opening 26 and receives a 2-hole refractory protection tube 30 for the wires of a thermocouple 32 which is preferably a standard Pt, Pt+10% Rh thermocuple when used with molten steel. The exposed upper ends of the thermocouple wires are coated with an epoxy or other impervious electrically insulating cement and are crimped into suitable thermocouple terminals 34. The second or top ends of

rods

14 and 20 also act as

terminals

14T and 20T.

The sensor is preferably made as follows: The disc 10 is placed inside of tube 8 which is heated to a temperature at which it softens and flows around the disc 10. Upon cooling, the fused silica of tube 8 forms a tight seal around the disc 10 so as to prevent leakage of steel during immersion. If desired, a small diameter tube with a closed end made of the electrolyte material may be substituted for the tube 8 and disc 10. The mixture 12 is then tamped into the tube 8 and the rod 14 inserted into the tube in contact with the mixture 12. 'Ihe rod 20 is placed in tube 16 and the parts 28 to 34 assembled into one unit. All three tube assemblies are then placed in a mold cavity and held in essentially parallel relationship with each other and the axis of the mold cavity by means of a suitable fixture. A slurry of refractory particles and bonding agents mixed with Water is then poured into the cavity and around the stated components until the mold cavity is filled. Each of the component ends that must contact the molten steel project approximately 3A inch beyond one end of the mold and are not covered by the slurry. Also, the other end of the components project beyond the opposite end of the mold and are not covered by the slurry. A small quantity of this slurry is painted onto the sides of the electrolyte disc 10 and the end of tube 8. However, the end surface of the electrolyte disc is not covered with slurry. Also, the exposed length of rod 20 that contacts molten steel is covered with refractory slurry except for its end.

After the bonding agents in the slurry form a hard compact mass with the refractory grains, the oxygen sensor unit is removed from the mold cavity and is subjected to a series of drying steps that will render the refractory body even stronger and free of moisture. lt is preferred to use a commercial refractory castable, such as Castola'st G, manufactured by the Harbison-Wa'lker Refractory Company, for this purpose and to follow their recommended for-ming and drying procedures.

It is preferred to cover the ends of the components of the sensor 2 extending below the body member 4 with steel caps 40 and 42 with cap 42 extending around cap 40 and around the end of body member 4. This protects the electrolyte from slag contamination during immersion and the entire sensor from physical damage during handling. Steel is preferred to Ibras's or aluminum since it gives better physical protection prior to use, and because of its higher melting point, permits a desirable delay in melting time during immersion.

A steel lance 44 has a receptacle 46 at its lower end for receiving

terminals

14T, 20T and 34, which are conneoted to a millivolt recorder 48, preferably a two-pen potentiometric Type-82 by means of a suitable twoconductor compensating lead wire 50 for the ther-mocouple and a two-conductor lead wire 52 for the oxygen cell. The length of lance 44 may be varied as desired and could also be omitted. Cardboard or

ceramic sleeves

54 and 56 are preferably provided to protect the parts from overheating during immersion.

In operation, the assembly is plunged into the melt to a suitable depth. The

sleeves

54 and 56, which extend above the top of the melt, protect the Wires and upper elements of the sensor from damage by the metal. Caps 40 and 42 protect the sensor from chemical attack by the slag as it is lowered through the slag into the molten metal. When the stabilized zirconium oxide electrolyte contacts the electrode of liquid steel, a galvanic cell results which may be represented as follows:

CaO are in solid form and Fe-O is liquid).

The voltage across the electrolyte is given by the free energy equation as follows:

[percent O] log Kpozl/Z E=aso3 (1) where The temperature dependence of the equilibrium iconstant K and p= for Cr-Cr203 equilibrium from known thermodynamic data is plunging the sensor into the melt fand provides continuous oxygen content readings up to 40 minutes.

By combining these equations and substituting values of the constants, the following equation is obtained for weight percent oxygen in liquid steel in terms of ELMF (E) in rnillivolts and T in degrees Kelvin for the Cr-CR2O3 reference electrode and receives a rod 72 of While the specific components set forth above are preferred since -they have proven very sucessful in use in determining the oxygen content of liquid steel, they may be varied ,as long as they meet the following requirements. The electrolyte 10 must be a solid oxide and an oxygen ion conductor with insignificant electronic conductivity under the conditions of its use, particularly at the temperature and oxygen partial pressure to which it is subjected. It must not react with the materials it contacts. ZrOlg with 3 to 10% by weight of OaOf or MgO; ThO2 with 3 to 20% by weight of YgO, A1203 or MgO are examples of materials which are suitable under vlarying conditions, but all electrolytes are not all suitable for use with all types of fluids.

The reference electrode 12 must be a condensed phase mixture of la metal and its oxide which does not readily melt at the temperature to which it is subjected no1 react significantly with the materials itv contacts. Cr-Cr2O'3 is most suitable for use with steel. MolMoOg, Ta-TaO2, W-Wo2, Ni-NiO, Fe-FeO, and (Eo-C00, may also be used, but not all can be used with all types of iiuids. In place of Mo the

conductor rods

14 and 20 may be made of Pt, Rh, Pt and Rh, W, Ta, W and Re, Cr :and alloys thereof. Ni, Co, Fe, Cu, Al, Sn, Zn, Mg and their alloys may be used for testing most nonferrous metals including Al, Zn, Cu, Cr, Ni, Co and Sn and for testing most gases. However, it should be understood that it is the mechanical arrangement of the parts, nather than the specific materials used, that is the important feature of the invention.

FIGS. 2, 3 and 4 show the preferred embodiment of our invention. This includes a body member 58 preferably made of the same material as body member 4 of the first embodiment. A rst longitudinal opening 60 extends through the body member and contains a first tube 62 whose rst end extends into the molten steel or other fluid L. The tube 62 is made of an electrical insulator such as fused quartz. A solid electrolyte in the form of a disc 63 of ZrOlz containing 3 to 101% by weight of CaO is fused to the inside of tube 62, and a reference electrode 64 in the form of a mixture of powdered Cr and Cr2O3 is placed on top of the electrolyte 63 and held in position by a retainer washer 65 which may be a refractory. A rod 66 in tube 62 has its first end bent and its second end extending through the tube 62 lbeyond the second end of body member 58. The rod 66 is made of `an electrical conductor, preferably molybdenum. The washer 65 has an opening 68 therethrough for receiving the bent end of rod 66 which extends longitudinal opening 70 ber 58 adjacent to and into the electrode 64. A second extends through the body memgenerally parallel to opening 60 the same material as rod 66.

The exposed lower end of tube 62, the periphery of disc 68 and the exposed lower end of rod 72 may be covered with a refractory coating except for a short portion of the end of disc 63 and the end of rod 72.

Third and fourth

longitudinal openings

74 and 76 generally parallel to

openings

60 and 70 receive a U-tube 78 made of fused quartz or other insulating material.

Thermocouple wires

84 and 82 are received in the U-tube 78 and joined at the bend of the tube. This construction is essentially that shown in Mead Pat. No. 2,999,121. A body cap 84 of polyethylene or other electrically insulating material abuts the second end of body member 58 and also receives a polyethylene connector tube 86. Rod 66 passes through tube 86 with its top end bent around the bottom of a slot S8 in the tube 86 and back down the outside of the tube. Rod 72 likewise passes through tube 86 with its end bent around the free or top end of the tube. Thermocouple wire is connected to a conductor 90 which passes through tube 86 with its topend bent around the bottom of a slot 92 in the tube 86 to the outside of the tube. Thermocouple wire 82 is connected to a conductor 94 and passes through the tube 86 with its end bent around the bottom of a slot 96 in the tube 86 to the outside of the tube. The upper ends of

Wires

80 and 82 are coated with an epoxy as in the first embodiment. A receptable 9S of insulating material, such as rubber, having four spaced apart electrical contact rings 98a, 98b, 98e and 98d therein surrounds the tube 86 with the

rings

98a, 98b, 98C, and 98d in contact with

conductors

90, 94, 66 and 72, respectively. Four terminals 100:1, 100b, 100C and 100d secured in the end of receptacle 98 are electrically connected to

rings

98a, 98b, 98e` and 98d, respectively. A receptacle adapter 102 made of steel or black iron pipe surrounds receptacle 98 and is connected by means of threaded insert 104 to a lance 106 corresponding to lance 44 of the first embodiment. A cardboard sleeve 108 surrounds the body member 58, body cap 84 and

tubes

102 and 106. A steel protection cap 110 having a small hole 112 in the end thereof is secured to the sleeve 108. The connections of the terminals to the potentiometer may be as in the first embodiment and the operation is the same as that of the first embodiment. This embodiment is made in generally the same manner as the first embodiment.

FIG. 5 shows a simplified and less expensive embodiment of our invention in which the thermocouple is omitted. Except for this omission the construction and materials are essentially the same as those of the other embodiments. This may be done because in many operations, particularly in steel making, other means are provided for continuously or intermittently measuring the temperature of the fluid and the temperature so obtained can be utilized in combination with the oxygen sensor to obtain an accurate oxygen reading. This embodiment includes a body member 114 made of the same material as body member 4. A first longitudinal opening 116 extends through the body member 114 and contains a silica tube 118 whose first end extends into the molten steel or other fiuid L. A solid electrolyte in the form of a disc 120 is fused to the inside of tube 118, and a reference electrode 122 in the form of a mixture of powdered Cr and Cr203 is placed on top of the electrolyte 120 in contact with the first end of a conductor rod 124 which extends through tube 118 beyond the second end of body member 114. A second longitudinal opening 126 extends through the body member 114 adjacent to and generally parallel to opening 116. A tube 128, similar to tube 118, may extend through opening 126 to receive a rod 130 of the same material as rod '124. If desired, the tube 118 may be omitted and the rod 130 received directly in opening 116. The remaining part of the sensor may be as shown in either of the other embodiments with the thermocouple connections omitted and hence are not shown or described here except to show a cardboard tube 132 and steel cap 134.

While several embodiments of our invention have been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

We claim:

1. In apparatus for determining the oxygen content of a liquid metal which comprises a galvanie cell including said liquid metal as an electrode, a solid oxide electrolyte and a reference electrode, said electrolyte being an oxygen ion conductor having insignificant electronic conductivity under conditions of use, said reference electrode being a powdery mixture of a metal and its oxide, and means for measuring the EMF of the cell when the electrolyte contacts the liquid metal, the improvement comprising a sensor; said sensor including said electrolyte and said reference electrode, an elongated heat and thermal shock resistant body member of cast alumina adapted to be partially inserted into said liquid metal and having a plurality of longitudinal openings therein, a first fused silica tube extending through the first of said openings beyond both ends of said body member, a disc of said electrolyte fused to the inside of one end of said first tube spaced away from said body member and adapted to contact said liquid metal, means for containing said powdery mixture of a metal and its oxide Within said tube and in contact with said electrolyte, a first conductor extending through the first tube thereby insulating said first conductor from said body member and having a first end contacting said powdery mixture of a metal and its oxide, a second conductor extending through the second of said openings beyond both ends of said body member with the first end of said second conductor adapted to contact said liquid metal near said electrolyte, said conductors being of the same material, terminal means connecting the second ends of said conductors to said voltage measuring means, a thermocouple comprising two dissimilar wires extending through said body member with the joined ends of said wires extending beyond the first end of said body member and the other ends connected to said terminal means said thermocouple adapted to contact said liquid metal near said electrolyte, and means for insulating said thermocouple Wires from one another, from said conductors and from said body members.

2. Apparatus according to claim 1 which includes a lance having means at one end for receiving said terminal means and means at its other end connected to said voltage measuring means, a cardboard sleeve surrounding at least a portion of said lance and said body member, and a steel cap surrounding the first end of said conductors and said thermocouple.

3. Apparatus according to claim 1 in which said conductors are molybdenum rods, said electrolyte is ZrOZ containing 3 to 10% by weight CaO and said reference electrode is a mixture of powdered Cr and Cr203.

4. Apparatus according to claim 2 in which said conductors are molybdenum rods, said electrolyte is ZrOZ containing 3 to 10% by Weight CaO and said reference electrode is a mixture of powdered Cr and Cr203.

References Cited UNITED STATES PATENTS 3,454,486 7/1969 Davies 204-195 3,464,008 8/1969 Meysson et al. 204-195 3,468,780 9/ 1969 Fischer 204-195 3,481,855 12/ 1969 -Kolodney et al 204-195 3,616,407 10/1971 lEngell et al. 204-195 S 3,619,381 11/1971 Fitterer 204-195 S FOREIGN PATENTS 1,191,222 5/ 1970 Great Britain 204-195 OTHER REFERENCES Wilder, Trans of the Metallurgical Soc. of AIME, v01. 236 July 1966, pp. 1035-1040.

Fitterer, Reprint from Journal of Metals, August 1966, pp. 1-6.

TA-HSUNG TUNG, Primary Examiner