WO2001061333A1 - Sensors - Google Patents

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Publication number
WO2001061333A1
WO2001061333A1 PCT/GB2001/000630 GB0100630W WO0161333A1 WO 2001061333 A1 WO2001061333 A1 WO 2001061333A1 GB 0100630 W GB0100630 W GB 0100630W WO 0161333 A1 WO0161333 A1 WO 0161333A1
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WO
WIPO (PCT)
Prior art keywords
sensor
sensor according
metal
magnesium
lithium
Prior art date
Application number
PCT/GB2001/000630
Other languages
French (fr)
Inventor
Girish Kale
Original Assignee
University Of Leeds
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by University Of Leeds filed Critical University Of Leeds
Priority to AU2001235758A priority Critical patent/AU2001235758A1/en
Publication of WO2001061333A1 publication Critical patent/WO2001061333A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/406—Cells and probes with solid electrolytes
    • G01N27/411—Cells and probes with solid electrolytes for investigating or analysing of liquid metals
    • G01N27/4112—Composition or fabrication of the solid electrolyte

Definitions

  • This invention relates to a novel sensor and to a novel method of analysis.
  • Lithium is the lightest metal in the periodic table having a density of 0.53 g cm “3 , whereas magnesium has a density of 1.74 g cm “ . However, both lithium and magnesium are lighter than aluminium which has a density of 2.7 g cm “3 . Lithium and magnesium readily form alloys with aluminium when melted together and aluminium alloys containing varying proportions of lithium and magnesium are widely used in applications where high strength, light weight and corrosion resistance are important design parameters. For example, aluminium alloys are widely used in fabricating beverage cans, alloy wheels for automobiles, aircraft wings and body parts, automobile parts, window frames, flood-light support systems, automobile body panels and many more.
  • aluminium (£1,000 per ton), lithium (£55,000 per ton) and magnesium (£1,800 per ton) are expensive metals and consume a large amount of energy during their production.
  • the annual production of aluminium and its alloys in USA alone is in the range of 315,000 - 320,000 tons.
  • aluminium scrap produced today because of the excessive use of aluminium and its alloys.
  • the process of remelting, refining and casting ingot grade aluminium from scrap aluminium requires only 5% of the total energy required to produce primary aluminium from aluminium ore.
  • Kale for measuring lithium and magnesium dissolved in molten aluminium at elevated temperature has been successfully tested in the laboratory and does not suffer from any of the problems suffered by those investigated earlier [1-1 1].
  • Such solid state sensors are advantageous in that, inter alia, they have been shown to last several hours in, for example, molten aluminium.
  • lithium and magnesium sensors developed in our laboratory are in the area of measuring and monitoring lithium and magnesium dissolved in molten aluminium in particular either during the extraction of refining process.
  • these sensors can be used in measuring and monitoring lithium and magnesium in any of the non-ferrous metals including aluminium. It is very well known that on-line, in situ monitoring of metal extraction and refining process will soon replace the traditional analytical procedure of sampling and analysis of molten metal, which is not accurate enough, followed by most of the metallurgical industries world-wide because of financial gains.
  • a sensor for determining the amount of a selected element in a sample comprising of a reference electrode, a working electrode and a solid electrolyte characterised in that;
  • the reference electrode comprises an intimate mixture of a metal alloy oxide and, a group Via or group VIII metal oxide; wherein at least one of the elements in the metal alloy oxide is the same as the element to be determined;
  • the solid electrolyte comprises a metal alloy compound wherein at least one of the elements in the metal alloy compound is the same as the element to be determined.
  • the senor is designed to be an oxygen detector and therefore the element defined above is oxygen.
  • the element to be determined is a metal.
  • the metal in the metal alloy oxide of the reference electrode is the same as the metal to be determined and the metal in the metal alloy compound in the solid electrolyte is the same as the metal to be determined.
  • the working electrode preferentially comprises a material selected from graphite, Pt, Mo and Fe-Cr.
  • the metal to be determined is selected from magnesium and lithium.
  • the metal to be detected is magnesium.
  • the metal to be detected is lithium.
  • a preferred embodiment of the invention provides a sensor wherein the sample to be analysed is a molten non-ferrous metal and especially an aluminium sample.
  • the sensor does not require the reference electrode to be sealed from the ambient atmosphere.
  • the probe has a unique design. It involves casting of the sensor elements into a non- wetting refractory castable cement in order to provide the sensor with a long lasting time in molten aluminium. Identical design is also adopted for a long life oxygen sensor for non-ferrous metals/ and/or metal salts.
  • an yttria stabilised zirconium electrode is preferred with an Ni/NiO reference electrode.
  • Cr metal may also be included as an internal oxygen retriever.
  • the electrical lead connecting molten metal is chemically inert to molten aluminium, magnesium and lithium.
  • the open circuit voltage, here after referred as emf, of the sensor is a measure of concentration of a metal, e.g. magnesium or lithium, in molten metal, e.g. aluminium with respect to the reference electrode potential.
  • the emf of the sensor is measured between the two electrically conducting wires, one of which contacting the working electrode i.e. molten aluminium and the other contacting the solid-state reference electrode packed inside the solid electrolyte tube.
  • the magnesium sensor of the invention may incorporate two different types of novel reference electrodes and two different types of novel solid electrolytes that have never been used to design a complete solid-state sensor for measuring magnesium in molten aluminium.
  • the two solid electrolytes conducting divalent magnesium cations used for designing the magnesium sensor are: MgAl 2 O and MgZr 4 (PO4) 6 .
  • the two reference electrodes used for designing the magnesium sensor are: MgFe 2 O 4 +Fe 2 O 3 and MgCr 2 O 4 +Cr 2 O 3 .
  • the group Via or group VIII metal used in the metal oxide of the reference electrode i ⁇ the same metal as that used in the metal alloy oxide.
  • the magnesium sensor electrode may be selected from the group:
  • the lithium sensor incorporates two different types of novel reference electrodes and two different types of novel solid electrolytes that have never been used to design a complete solid-state sensor for measuring lithium in molten aluminium.
  • the two solid electrolytes conducting divalent magnesium cations used for designing the magnesium sensor are: Li
  • the two reference electrodes used for designing the lithium sensor are: Li 2 Fe ⁇ oO ⁇ +Fe 2 O 3 and Li 2 Fe ⁇ 0 O ⁇ +Li 2 Fe 2 O .
  • the lithium sensor electrodes can be selected from the group:
  • the solid electrolyte used in the magnesium and lithium sensor is in the form of a high density one end closed round-end tube having length equal to 25 mm, internal diameter equal to 3 mm and a wall thickness of 1 .5 m n.
  • the magnesium and lithium sensors of the invention are highly selective to magnesium and lithium, respectively present in molten aluminium and can be easily used in any other molten metal depending on temperature of application.
  • Both the sensors are capable of measuring concentration of magnesium or lithium in molten aluminium and also the temperature of the molten metal bath at the same time.
  • a K-type thermocouple having an outer diameter of 2.5 mm is an integral part of the sensor and the tip of the thermocouple is protected from corrosive liquid metal, dross and slag by a high density one end closed round-end zirconia-8mol% yttria
  • figure 1 is a schematic representation of the sensor of the invention
  • figure 2 is a schematic representation of the experimental set up of the sensors of the invention
  • figure 3 shows the response of a pair of solid state magnesium sensors to change in concentration of magnesium in molten aluminium as a function of time at a fixed temperature of 963 K
  • figure 4 shows the response of a pair of solid state magnesium sensors to change in concentration of magnesium in molten aluminium as a function of time at a fixed temperature of 1003 K
  • figure 5 shows the response of a pair of solid state lithium sensors to change in concentration of lithium in molten aluminium as a function of time at a fixed temperature of 1003 K.
  • figure 6 shows the response of a pair of solid state lithium sensors to change in concentration of lithium in molten aluminium as a function of time at a fixed temperature of 1003 K.
  • figure 7 shows the variation of the emf of a pair of magnesium sensors as a function of logarithm of concentration of magnesium in molten aluminium; and
  • figure 8 shows the variation of the emf of a pair of lithium sensors as a function of logarithm of concentration of lithium in molten aluminium.
  • High density alumina tube High density alumina tube
  • the solid electrolyte tube has been attached to a long high density alumina tube by applying a refractory cement at the joint.
  • the molybdenum rod of 1.5 mm outer diameter has been sealed inside a high density alumina sleeve to prevent it from oxidation during the exposure to high temperature in ambient atmosphere.
  • Molten salt layer on top of molten aluminium containing either magnesium or lithium is to prevent the loss of either solvent or solute metal from any oxidation at elevated temperature during the testing of magnesium and lithium sensor.
  • Figure 3 shows the response of a pair of solid state magnesium sensor to change in concentration of magnesium in molten aluminium as a function of time at a fixed temperature of 963 K.
  • the solid electrolyte used in the pair of sensors is MgAl 2 O 4 .
  • the reference electrode used in the two sensors is a mixture containing MgFe 2 O 4 +Fe 2 O 3 (top) and MgCr 2 O 4 +Cr 2 O 3 (bottom).
  • Figure 4 shows the response of a pair of solid state magnesium sensor to change in concentration of magnesium in molten aluminium as a function of time at a fixed temperature of 1003 K.
  • the solid electrolyte used in the pair of sensors is MgZr 4 (PO ) 6 .
  • the reference electrode used in the two sensors is a mixture containing MgFe 2 O 4 +Fe 2 O 3 (top) and MgCr 2 O 4 +Cr 2 O 3 (bottom).
  • Figure 5 shows the response of a pair of solid state lithium sensor to change in concentration of lithium in molten aluminium as a function of time at a fixed temperature of 1003 K.
  • the solid electrolyte used in the pair of sensors is Li ⁇ . 3 Al 0 . Ti ⁇ . 7 P O ⁇ 2 .
  • the reference electrode used in the two sensors is a mixture containing Fe 2 O +LiFe 5 O 8 (top) and LiFeO 2 +LiFe 5 O 8 (bottom).
  • Figure 6 shows the response of a pair of solid state lithium sensor to change in concentration of lithium in molten aluminium as a function of time at a fixed temperature of 1003 K.
  • the solid electrolyte used in the pair of sensors is Li 2 BeGeO .
  • the reference electrode used in the two sensors is a mixture containing Fe 2 O 3 +LiFe 5 O 8 (top) and LiFeO 2 +LiFe 5 O 8 (bottom).
  • Figure 7 shows the variation of the emf of a pair of magnesium sensor as a function of logarithm of concentration of magnesium in molten aluminium.
  • Figure 8 shows the variation of the emf of a pair of lithium sensor as a function of logarithm of concentration of lithium in molten aluminium.
  • the emf of the sensor e.g. the magnesium, lithium or oxygen sensor is measured using a high impedance voltmeter having an internal impedance greater than 10 1 Ohms. This prevents any mass transport across the electrolyte from one electrode to another.

Abstract

There is described a sensor for determining the amount of a selected element in a sample comprising of a reference electrode, a working electrode and a solid electrolyte characterised in that; (i) the reference electrode comprises an intimate mixture of a metal alloy oxide and, a group VIa or group VIII metal oxide; wherein at least one of the elements in the metal alloy oxide is the same as the element to be determined; and (ii) the solid electrolyte comprises a metal alloy compound wherein at least one of the elements in the metal alloy compound is the same as the element to be determined. The working electrode may be selected from graphite Pt, Mo and Fe-Cr. There is also described a method of determining levels of impurities in molten metal.

Description

SENSORS
This invention relates to a novel sensor and to a novel method of analysis.
A prototype of a complete solid state sensor for measuring and monitoring in situ dissolved lithium and magnesium in molten aluminium, in other non-ferrous metals and/or molten salts has been successfully developed and tested in the laboratory.
Lithium is the lightest metal in the periodic table having a density of 0.53 g cm"3, whereas magnesium has a density of 1.74 g cm" . However, both lithium and magnesium are lighter than aluminium which has a density of 2.7 g cm"3. Lithium and magnesium readily form alloys with aluminium when melted together and aluminium alloys containing varying proportions of lithium and magnesium are widely used in applications where high strength, light weight and corrosion resistance are important design parameters. For example, aluminium alloys are widely used in fabricating beverage cans, alloy wheels for automobiles, aircraft wings and body parts, automobile parts, window frames, flood-light support systems, automobile body panels and many more. However, aluminium (£1,000 per ton), lithium (£55,000 per ton) and magnesium (£1,800 per ton) are expensive metals and consume a large amount of energy during their production. Furthermore, the annual production of aluminium and its alloys in USA alone is in the range of 315,000 - 320,000 tons. In addition, there is a large quantity of aluminium scrap produced today because of the excessive use of aluminium and its alloys. However, the process of remelting, refining and casting ingot grade aluminium from scrap aluminium requires only 5% of the total energy required to produce primary aluminium from aluminium ore.
In order to minimise the quantity of dross produced during aluminium refining and aluminium alloy making and to minimise the cost of safe disposal of the dross, there has been a need to continuously monitor at elevated temperatures the process of aluminium alloy making and scrap aluminium refinhg. This could be achieved by employing on-line in situ analysis and feed-back system incorporating solid state sensors. However, a few attempts have been recently made to develop such sensors for monitoring lithium and magnesium. The sensors developed so far suffer from some serious problems such as chemical and mechanical instability, short life span, slow response, interference from other dissolved metallic species in molten metal etc. The solid state sensor developed by Dr. Kale for measuring lithium and magnesium dissolved in molten aluminium at elevated temperature has been successfully tested in the laboratory and does not suffer from any of the problems suffered by those investigated earlier [1-1 1]. Such solid state sensors are advantageous in that, inter alia, they have been shown to last several hours in, for example, molten aluminium.
The potential applications of lithium and magnesium sensors developed in our laboratory are in the area of measuring and monitoring lithium and magnesium dissolved in molten aluminium in particular either during the extraction of refining process. However, these sensors can be used in measuring and monitoring lithium and magnesium in any of the non-ferrous metals including aluminium. It is very well known that on-line, in situ monitoring of metal extraction and refining process will soon replace the traditional analytical procedure of sampling and analysis of molten metal, which is not accurate enough, followed by most of the metallurgical industries world-wide because of financial gains.
We have now surprisingly found that a complete solid-state sensor can be developed for on-line continuous measurement of metallic impurities such as, magnesium and lithium, and their concentration in molten aluminium can be determined even at elevated temperatures, e.g. at 1003 K.
Thus, according to the invention we provide a sensor for determining the amount of a selected element in a sample comprising of a reference electrode, a working electrode and a solid electrolyte characterised in that;
(i) the reference electrode comprises an intimate mixture of a metal alloy oxide and, a group Via or group VIII metal oxide; wherein at least one of the elements in the metal alloy oxide is the same as the element to be determined; and
(ii) the solid electrolyte comprises a metal alloy compound wherein at least one of the elements in the metal alloy compound is the same as the element to be determined.
In one embodiment of the invention the sensor is designed to be an oxygen detector and therefore the element defined above is oxygen.
In a further embodiment of the invention the element to be determined is a metal. In such a case the metal in the metal alloy oxide of the reference electrode is the same as the metal to be determined and the metal in the metal alloy compound in the solid electrolyte is the same as the metal to be determined.
In a further embodiment the working electrode preferentially comprises a material selected from graphite, Pt, Mo and Fe-Cr.
According to a preferred feature of the invention we provide a sensor wherein the metal to be determined is selected from magnesium and lithium. Alternatively, we provide a sensor wherein the metal to be detected is magnesium. In a yet further alternative, we provide a sensor wherein the metal to be detected is lithium.
Although the sensor of the invention may be used in conjunction with any molten metal, a preferred embodiment of the invention provides a sensor wherein the sample to be analysed is a molten non-ferrous metal and especially an aluminium sample.
The sensor does not require the reference electrode to be sealed from the ambient atmosphere. The probe has a unique design. It involves casting of the sensor elements into a non- wetting refractory castable cement in order to provide the sensor with a long lasting time in molten aluminium. Identical design is also adopted for a long life oxygen sensor for non-ferrous metals/ and/or metal salts. For use as an oxygen detector an yttria stabilised zirconium electrode is preferred with an Ni/NiO reference electrode. In an oxygen sensor of the invention Cr metal may also be included as an internal oxygen retriever.
The electrical lead connecting molten metal is chemically inert to molten aluminium, magnesium and lithium.
The open circuit voltage, here after referred as emf, of the sensor is a measure of concentration of a metal, e.g. magnesium or lithium, in molten metal, e.g. aluminium with respect to the reference electrode potential. The emf of the sensor is measured between the two electrically conducting wires, one of which contacting the working electrode i.e. molten aluminium and the other contacting the solid-state reference electrode packed inside the solid electrolyte tube.
We particularly prefer a sensor which incorporates two different types of reference electrodes and two different types of electrolytes.
The magnesium sensor of the invention may incorporate two different types of novel reference electrodes and two different types of novel solid electrolytes that have never been used to design a complete solid-state sensor for measuring magnesium in molten aluminium.
The two solid electrolytes conducting divalent magnesium cations used for designing the magnesium sensor are: MgAl2O and MgZr4(PO4)6.
The two reference electrodes used for designing the magnesium sensor are: MgFe2O4+Fe2O3 and MgCr2O4+Cr2O3. In a preferred embodiment the group Via or group VIII metal used in the metal oxide of the reference electrode i< the same metal as that used in the metal alloy oxide. Thus the magnesium sensor electrode may be selected from the group:
Pt or Fe-Cr, MgFe2O4+Fe2O3//MgAl2O4//Al(Mg), Mo Pt or Fe-Cr, MgCr2O4+Cr2O3//MgAl2O4//Al(Mg), Mo Pt or Fe-Cr, MgFe2O4+Fe2O3//MgZr4(PO4)6//Al(Mg), Mo Pt or Fe-Cr, MgCr2O +Cr2O3//MgZr4(PO4)6 //Al(Mg), Mo
The lithium sensor incorporates two different types of novel reference electrodes and two different types of novel solid electrolytes that have never been used to design a complete solid-state sensor for measuring lithium in molten aluminium.
The two solid electrolytes conducting divalent magnesium cations used for designing the magnesium sensor are: Li|.3Al0.3Tiι.7P3Oι and Li BeGeO4.
The two reference electrodes used for designing the lithium sensor are: Li2FeιoOι +Fe2O3 and Li2Feι0Oι +Li2Fe2O .
The lithium sensor electrodes can be selected from the group:
Pt or Fe-Cr, Li2Fe,0O,6+Fe2O3//Li1.3Alo.3Ti,.7P3Oι2//Al(Li), Mo Pt or Fe-Cr, Li2Fei0Oi6+Li2Fe2O4//Lii.3Al0.3Tii.7P3Oi2//Al(Li), Mo Pt or Fe-Cr, Li2FeιoOι6+Fe2o3//Li2BeGeO4//Al(Li), Mo
Pt or Fe-Cr, Li2Feι0Oι6+Li2Fe2O4/ Li2BeGeO4//Al(Li), Mo
The solid electrolyte used in the magnesium and lithium sensor is in the form of a high density one end closed round-end tube having length equal to 25 mm, internal diameter equal to 3 mm and a wall thickness of 1 .5 m n. The magnesium and lithium sensors of the invention are highly selective to magnesium and lithium, respectively present in molten aluminium and can be easily used in any other molten metal depending on temperature of application.
5 Both the sensors are capable of measuring concentration of magnesium or lithium in molten aluminium and also the temperature of the molten metal bath at the same time. A K-type thermocouple having an outer diameter of 2.5 mm is an integral part of the sensor and the tip of the thermocouple is protected from corrosive liquid metal, dross and slag by a high density one end closed round-end zirconia-8mol% yttria
) tube, 25 mm long, 3 mm inner diameter and 1.5 mm wall thickness
According to a yet further feature of the invention we provide a method of determining the level of a metal impurity in a molten metal which comprises the use of a sensor as hereinbefore described.
Thus, we especially provide a method of determining amounts of magnesium and/or lithium in non-ferrous metals, e.g. aluminium.
The invention will now be described by way of example only and with reference to the accompanying drawings, in which;
figure 1 is a schematic representation of the sensor of the invention; figure 2 is a schematic representation of the experimental set up of the sensors of the invention; figure 3 shows the response of a pair of solid state magnesium sensors to change in concentration of magnesium in molten aluminium as a function of time at a fixed temperature of 963 K. figure 4 shows the response of a pair of solid state magnesium sensors to change in concentration of magnesium in molten aluminium as a function of time at a fixed temperature of 1003 K. figure 5 shows the response of a pair of solid state lithium sensors to change in concentration of lithium in molten aluminium as a function of time at a fixed temperature of 1003 K. figure 6 shows the response of a pair of solid state lithium sensors to change in concentration of lithium in molten aluminium as a function of time at a fixed temperature of 1003 K. figure 7 shows the variation of the emf of a pair of magnesium sensors as a function of logarithm of concentration of magnesium in molten aluminium; and figure 8 shows the variation of the emf of a pair of lithium sensors as a function of logarithm of concentration of lithium in molten aluminium.
Figure Legends
Referring to figures 1 and 2, there is schematically represented the following apparatus;
1. Molybdenum rod
2. Thermocouple leads
3. Pt or Fe-Cr alloy wire 4. Probe cast in non- wetting castable refractory cement
5. Molten aluminium containing magnesium or lithium
6. High density ZrO2(8mol%Y2O3) tube protecting thermocouple tip
7. High density solid electrolyte tube used in magnesium and lithium sensor
8. High impedance multi-channel digital electrometer 9. Data acquisition and analysis unit
10. On-line data display unit
11. Molybdenum rod
12. Pt or Fe-Cr alloy wire
13. High density alumina tube 14. High density alumina tube
15. Molten salt covering the aluminium alloy 16. High density alumina crucible holding the molten aluminium alloy
17. Molten aluminium alloy containing magnesium or lithium
18. K-type thermocouple
19. High density solid electrolyte tube cemented to the alumina tube 20. Reference electrode mixture for magnesium and lithium sensor
21. Long life magnesium and lithium sensor cast in non- wetting refractory castable cement
22. Molten salt protecting molten aluminium alloy from oxidation.
The solid electrolyte tube has been attached to a long high density alumina tube by applying a refractory cement at the joint.
The molybdenum rod of 1.5 mm outer diameter has been sealed inside a high density alumina sleeve to prevent it from oxidation during the exposure to high temperature in ambient atmosphere.
Molten salt layer on top of molten aluminium containing either magnesium or lithium is to prevent the loss of either solvent or solute metal from any oxidation at elevated temperature during the testing of magnesium and lithium sensor.
All the materials such as Mo, Zrθ2-8mol%Y2O3, MgAl2O4, MgZr4(PO4)6, Lil .3Al0.3Ti1.7P3O12 and Li2BeGeO4 have been found to be chemically and mechanically stable while in direct contact with molten aluminium containing magnesium and lithium for a prolonged periods in excess of 2 hours.
Figure 3 shows the response of a pair of solid state magnesium sensor to change in concentration of magnesium in molten aluminium as a function of time at a fixed temperature of 963 K. The solid electrolyte used in the pair of sensors is MgAl2O4. The reference electrode used in the two sensors is a mixture containing MgFe2O4+Fe2O3 (top) and MgCr2O4+Cr2O3 (bottom). Figure 4 shows the response of a pair of solid state magnesium sensor to change in concentration of magnesium in molten aluminium as a function of time at a fixed temperature of 1003 K. The solid electrolyte used in the pair of sensors is MgZr4(PO )6. The reference electrode used in the two sensors is a mixture containing MgFe2O4+Fe2O3 (top) and MgCr2O4+Cr2O3 (bottom).
Figure 5 shows the response of a pair of solid state lithium sensor to change in concentration of lithium in molten aluminium as a function of time at a fixed temperature of 1003 K. The solid electrolyte used in the pair of sensors is Liι.3Al0. Tiι.7P Oι2. The reference electrode used in the two sensors is a mixture containing Fe2O +LiFe5O8 (top) and LiFeO2+LiFe5O8 (bottom).
Figure 6 shows the response of a pair of solid state lithium sensor to change in concentration of lithium in molten aluminium as a function of time at a fixed temperature of 1003 K. The solid electrolyte used in the pair of sensors is Li2BeGeO . The reference electrode used in the two sensors is a mixture containing Fe2O3+LiFe5O8 (top) and LiFeO2+LiFe5O8 (bottom).
Figure 7 shows the variation of the emf of a pair of magnesium sensor as a function of logarithm of concentration of magnesium in molten aluminium.
Figure 8 shows the variation of the emf of a pair of lithium sensor as a function of logarithm of concentration of lithium in molten aluminium.
The emf of the sensor, e.g. the magnesium, lithium or oxygen sensor is measured using a high impedance voltmeter having an internal impedance greater than 101 Ohms. This prevents any mass transport across the electrolyte from one electrode to another.
P36293WO. i

Claims

Claims
1. A sensor for determining the amount of a selected element in a sample comprising of a reference electrode, a working electrode and a solid electrolyte characterised in that;
(i) the reference electrode comprises an intimate mixture of a metal alloy oxide and, a group Via or group VIII metal oxide; wherein at least one of the elements in the metal alloy oxide is the same as the element to be determined; and
(ii) the solid electrolyte comprises a metal alloy compound wherein at least one of the elements in the metal alloy compound is the same as the element to be determined.
2. A sensor according to claim 1 characterised in that the element is oxygen.
3. A sensor according to claim 1 characterised in that the element is metal.
4. A sensor according to claim 1 characterised in that the working electrode comprises a material selected from graphite, Pt, Mo and Fe-Cr.
5. A sensor according to claim 3 characterised in that the metal to be determined is magnesium.
6. A sensor according to claim 3 characterised in that the metal to be determined is lithium.
7. A sensor according to claim 1 characterised in that the sample is a non- ferrous metal.
8. A sensor according to claim 7 characterised in that the sample is an aluminium sample.
9. A sensor according to claim 1 characterised in that the sensor incorporates two different types of reference electrodes and two different types of electrolytes.
10. A sensor according to claims 3 or 9 characterised in that the sensor is designed to measure magnesium in molten aluminium.
1 1. A sensor according to claim 10 characterised in that the two solid electrolytes are: MgAl2O4 and MgZr4(PO4)6.
12. A sensor according to claim 10 characterised in that the two reference electrodes are: MgFe2O4+Fe2O3 and MgCr2O4+Cr2O3.
13. A sensor according to claim 7 characterised in that electrodes are selected from:
Pt or Fe-Cr, MgFe2O4+Fe2O3//MgAl2O4//Al(Mg), Mo; Pt or Fe-Cr, MgCr2O4+Cr2O3//MgAl2O4//Al(Mg), Mo; Pt or Fe-Cr, MgFe2O4+Fe2O3//MgZr4(PO4)6//Al(Mg), Mo; and Pt or Fe-Cr, MgCr2O4+Cr2O3//MgZr4(PO4)6 //Al(Mg), Mo.
14. A sensor according to claims 3 or 9 characterised in that the sensor is designed to measure lithium in molten aluminium.
15. A sensor according to claim 14 characterised in that the two solid electrolytes are: Liι.3Alo.3Tiι. P O)2 and Li2BeGeO4.
16. A sensor according to claim 14 characterised in that the two reference electrodes are: Li2Feι0Oi6+Fe2O3 and Li2FeιoO[6+Li2Fe O .
17. A sensor according to claim 14 characterised in that the electrodes are selected from
Pt or Fe-Cr, Li2Feι0Oι6+Fe2O3//Liι.3Al0.3Ti,.7P3Oι2//Al(Li), Mo; Pt or Fe-Cr, Li2Fe,oOι6+Li2Fe2θ4//Liι.3Alo.3Ti,.7P3Oi2//Al(Li), Mo; Pt or Fe-Cr, Li2Fe,0Oi6+Fe2O3//Li2BeGeO4//Al(Li), Mo; and Pt or Fe-Cr, Li2FeιoO,6+Li2Fe2θ4//Li2BeGeO4//Al(Li), Mo.
18. A sensor according to claim 1 characterised in that the sensor electrodes are cast into a non-wetting refractory castable cement.
19. A sensor according to claim 3 characterised in that the electrical leads are chemically inert to molten aluminium, magnesium and lithium.
20. A sensor according to claim 1 characterised in that the solid electrolyte used in the sensor is in the form of a high density tube having length equal to 25 mm, internal diameter equal to 3 mm and a wall thickness of 1.5 mm.
21. A sensor according to claims 5 or 6 characterised in that sensor is adapted for the determination of magnesium or lithium, in a molten metal other than aluminium.
22. A sensor according to claims 5 characterised in that sensor is capable of determining levels of magnesium or lithium and also the temperature of the molten metal bath at the same time.
23. A sensor according to claim 22 characterised in that the sensor is provided with a K-type thermocouple having an outer diameter of 2.5 mm is an integral part of the sensor and the tip of the thermocouple is protected from corrosive liquid metal, dross and slag by a high density one end closed round-end zirconia-8mol% yttria tube, 25 mm long, 3 mm inner diameter and 1.5 mm wall thickness
24. A sensor according Ό claim 1 characterised in that it is stable up to over 1003K.
25. A sensor according to claims 13 or 17 characterised in that the molybdenum rod is sealed inside a high density alumina tube by applying a refractory cement at the joint.
26. A method of determining the level of an element in a molten metal which comprises the use of a sensor according to claim 1.
27. A method according to claim 26 characterised in that the element is oxygen.
28. A method according to claim 26 characterised in that the element is a metal.
29. A method according to claim 28 characterised in that the metal is magnesium.
30. A method according to claim 28 characterised in that the metal is lithium.
31. A sensor or a method substantially as described with reference to the accompanying examples and drawings.
P36293WO
PCT/GB2001/000630 2000-02-16 2001-02-16 Sensors WO2001061333A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001235758A AU2001235758A1 (en) 2000-02-16 2001-02-18 Sensors

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0003469.4 2000-02-16
GB0003469A GB0003469D0 (en) 2000-02-16 2000-02-16 Sensors for measuring lithium and magnesium in molten, non-ferrous metals

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WO2001061333A1 true WO2001061333A1 (en) 2001-08-23

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DE10161494A1 (en) * 2001-12-14 2003-07-17 Andion Gmbh Sensor unit, measuring unit and method for their operation

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DE10161494A1 (en) * 2001-12-14 2003-07-17 Andion Gmbh Sensor unit, measuring unit and method for their operation

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