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GB2324372A - Determining hydrogen content of liquid metal - Google Patents

Determining hydrogen content of liquid metal Download PDF

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Publication number
GB2324372A
GB2324372A GB9707626A GB9707626A GB2324372A GB 2324372 A GB2324372 A GB 2324372A GB 9707626 A GB9707626 A GB 9707626A GB 9707626 A GB9707626 A GB 9707626A GB 2324372 A GB2324372 A GB 2324372A
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United Kingdom
Prior art keywords
hydrogen
liquid metal
electrode
hydrogen content
electrodes
Prior art date
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Withdrawn
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GB9707626A
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GB9707626D0 (en
Inventor
David Spencer Harvey
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British Steel PLC
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British Steel PLC
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Publication date
Application filed by British Steel PLC filed Critical British Steel PLC
Priority to GB9707626A priority Critical patent/GB2324372A/en
Publication of GB9707626D0 publication Critical patent/GB9707626D0/en
Publication of GB2324372A publication Critical patent/GB2324372A/en
Withdrawn legal-status Critical Current

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403Cells and electrode assemblies
    • G01N27/406Cells and probes with solid electrolytes
    • G01N27/411Cells and probes with solid electrolytes for investigating or analysing of liquid metals
    • G01N27/4112Composition or fabrication of the solid electrolyte
    • G01N27/4114Composition or fabrication of the solid electrolyte for detection of gases other than oxygen
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/20Metals
    • G01N33/202Constituents thereof
    • G01N33/2022Non-metallic constituents
    • G01N33/2025Gaseous constituents

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  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Pathology (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Physics & Mathematics (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Engineering & Computer Science (AREA)
  • Food Science & Technology (AREA)
  • Medicinal Chemistry (AREA)
  • Investigating And Analyzing Materials By Characteristic Methods (AREA)

Abstract

The apparatus comprises an electro chemical cell for immersion in the liquid metal whose hydrogen content is to be measured. The cell includes a first electrode 5 which is permeable to hydrogen at the temperature at which the hydrogen content is to be measured and which is placed in communication with a material of known hydrogen activity, and a second electrode 2 which is permeable to hydrogen at the temperature at which the hydrogen content is to be measured and which comprises or, in use, is in contact with the liquid metal. An electrolyte 4 through which hydrogen ions can flow at the temperatures at which the hydrogen content is to be determined is positioned between the electrodes. Electrical current is passed to and through the electrodes of the cell and means are provided for detecting an electromotive force across the electrodes to provide a measure of the hydrogen content of the liquid metal.

Description

APPARATUS FOR AND METHODS OF DETERMINING THE HYDROGEN CONTENT OF LIQUID METAL This invention relates to apparatus for and methods of determining the hydrogen content of liquid metal. More especially the invention relates to an electro chemical cell for determining the hydrogen content of a liquid metal such as a bath of liquid steel in which the cell is immersed.
A knowledge of the hydrogen content of liquid metal is frequently required as an aid to effective processing of the metal. Hitherto, it has not been possible accurately to measure the hydrogen content of liquid metal in situ, that is to say within a processing vessel. if measurements are to be made, samples are taken for subsequent analysis in a laboratory. The time taken to process and analyse such samples limits their value to providing a measure of the hydrogen content of the processed metal; such measurements cannot be used to provide a control over the final hydrogen content of the metal during processing. This is recognised as being unsatisfactory particularly because the introduction of hydrogen to a melt is difficult to control. Thus, the hydrogen content of, say, slag additions can vary in dependence upon the dryness or otherwise of the additions and the ambient humidity.
Apparatus or a method which enables in situ measurement of the hydrogen contents of liquid metals to be made would provide a clear improvement over existing measuring apparatus and methods. The present invention sets out to provide such apparatus and method. This apparatus essentially comprises an electrochemical cell and the method entails the use of such an electrochemical cell.
The development of electrochemical cells for determination of hydrogen has hitherto been dismissed on the grounds that no materials are available which are stable and can conduct hydrogen ions at steelmaking temperatures. Whilst it is correct that there are no such stable compounds, applicants have established that there are certain slag-type materials which are able to retain significant amounts of hydrogen in an ionic form at steelmaking temperatures. Applicants have also established that these can be used as an electrolyte in an electro chemical concentration cell.
Accordingly, the present invention provides in one aspect apparatus for determining the hydrogen content of a liquid metal, the apparatus comprising an electro chemical cell for immersion in the liquid metal whose hydrogen content is to be measured and comprising a first electrode which is permeable to hydrogen at the temperature at which the hydrogen content is to be measured and which is placed in communication with a material of known hydrogen activity, a second electrode which is permeable to hydrogen at the temperature at which the hydrogen content is to be measured and which comprises or, in use, is in contact with the liquid metal, an electrolyte positioned between the electrodes through which hydrogen ions can flow at the temperatures at which the hydrogen content is to be determined, means for passing an electrical current to and through the electrodes of the cell, and means for detecting an electromotive force across the electrodes to provide a measure of the hydrogen content of the liquid metal.
In another aspect there is provided apparatus for determining the hydrogen content of a liquid metal, which apparatus comprises an electro chemical cell capable of immersion in the liquid metal whose electrodes are permeable to hydrogen at the immersion temperature and are separated by an electrolyte through which hydrogen ions can flow at the immersion temperature, one electrode of the cell being a reference electrode in communication with a source of known hydrogen activity and the other electrode comprising or being exposed to the liquid metal whose hydrogen content is to be determined and which, in use, attains an equilibrium hydrogen activity which is representative of the hydrogen activity of the liquid metal, and means for passing an electric current to and through the electrodes and for measuring the resulting electromotive force across the electrodes.
In essence, therefore, the invention provides an electro chemical cell which is capable of functioning when immersed in liquid metal and which generates an electromotive force which is related to measured differences between the hydrogen activities of its two electrodes.
The electrolyte preferably comprises a stable ionic compound or mixture of such compounds. Examples of such compounds include silica, calcium oxide, alumina and magnesia. One preferred electrolyte comprises a homogenous mix of between 40 to 70% by weight silica, up to 40% by weight calcium oxide, up to 30% by weight alumina and up to 20% by weight magnesia. A small amount of water, typically up to 1% by weight, may be included.
In one arrangement, the electrode exposed to the liquid metal comprises a cermet sheath of, for example, 80% molybdenum and 20% alumina, in which is positioned the electrolyte and electrode which communicates with a source of known hydrogen activity. In an alternative arrangement, the first mentioned electrode comprises the liquid metal itself.
Alternatively, it may comprise a stable refractory material of low electrical conductivity (e.g. an oxide, sulphide or halide), a basic oxide plus silica and sodium oxide, platinum or a solid or viscous liquid which adheres to the surface of a refractory electrode.
The electrode in communication with a source of known hydrogen activity may comprise a molybdenum tube flushed with a mixture of argon and hydrogen. The hydrogen content of this flushing gas is preferably of the order of 10%. Alternatively, this electrode may comprise a concentration created in-situ by thermal decomposition of a hydrogen-containing compound which decomposes at the operating temperature of the cell.
Alternatively, this electrode may comprise a solid or liquid material having a known hydrogen activity.
In a still further aspect, the invention provides a method for determining the hydrogen content of a liquid metal, the method comprising the steps of immersing in a bath of the liquid metal an electrochemical cell whose electrodes are permeable to hydrogen at the immersion temperature and are separated by an electrolyte through which hydrogen ions can flow, placing one electrode in communication with a source of known hydrogen activity and exposing the other electrode to the liquid metal, passing an electric current to and through the electrodes, and measuring the electromotive force produced across the electrodes to provide a measure of the hydrogen content of the liquid metal.
The invention will now be described by way of example only with reference to the accompanying diagrammatic drawings in which: Figures 1 to 3 are sections through three alternative electro chemical cells in accordance with the invention.
In each Figure, the same reference numerals have been used to denote the same integers.
In Figure 1, an electrochemical cell is shown partially immersed in a bath of liquid steel 1. The cell comprises a first electrode 2 having an outer sheath 3 of a cermet material (typically 80% by weight molybdenum and 20% by weight alumina) in direct contact with the liquid steel 1. Within the sheath 1 is an electrolyte 4 which comprises an intimate and homogenous mixture of silica (40-70% by weight), calcium oxide (up to 40%by weight), alumina (up to 30% by weight) and magnesia (up to 20% by weight). The electrolyte also contains a small amount of water. Typically the water content is less than 1% by weight. The tip of a second reference electrode 5 is positioned within the electrolyte 4 and comprises a molybdenum tube 6 which is flushed with a gas mixture of argon and hydrogen, the hydrogen content being typically 10%. The gas mixture is supplied by a tube 7 which extends into and through the molybdenum tube 6. Electrical connections 8 are made to the two electrodes 2,5 and the electromotive force between the electrodes is measured by any known method. The electromotive force is used in the Nernst equation to calculate the activity of hydrogen in the steel, thus: EMF= -RT in dH reference F dH metal where R is the gas constant, T is the temperature, F is Faradays constant, aH reference is the hydrogen activity at electrode 5 and "H metal is the hydrogen activity in the liquid steel.
In the embodiment illustrated in Figure 2, the molten steel 1 defines one electrode of the cell, connections between the steel and the electrical circuit being made by a conductor 9. In this embodiment the electrolyte 4 is confined by a body of a stable refractory material 10 which is of low electrical conductivity and is inert to chemical reaction, this material including compounds of, for example, oxides, sulphides and/or halides which are stable at the liquid steel temperature and which can retain hydrogen ions at typical operating pressures of up to 4 atmospheres.
Cells in accordance with the invention may also be employed to measure the hydrogen content of liquid metals other than steel e.g. liquid aluminium by use of an electrolyte which allows conduction of hydrogen ions at the liquid temperature of aluminium. Such an electrolyte may, for example, comprise up to 70% by weight boric oxide, 10-30% by weight silica, and up to 10% sodium oxide.
Thus the cell may be adapted for use with other molten metals by appropriate selection of electrodes which are compatible with the metal and are permeable to hydrogen at the required temperature, and an electrolyte which is stable and retains hydrogen ions at the required operating temperatures and pressures.
The reference electrode may contain a solid or liquid material which has a known hydrogen activity and which is stable at the operating temperature of the cell.
In the embodiment illustrated in Figure 3 the liquid steel 1 is in direct contact with the electrolyte 4. In this embodiment the electrolyte 4 is a solid, or a viscous liquid, and adheres to the reference electrode 5. As previously described, electrical contacts are made between the reference electrode 5 and the steel 1 and the electromotive force of the cell is measured through connections 8 to give a measure of the hydrogen content of the steel.
It will be appreciated that the foregoing is merely exemplary of apparatus in accordance with the invention and that modification can readily be made thereto without departing from the true scope of the invention.

Claims (14)

1. Apparatus for determining the hydrogen content of a liquid metal, the apparatus comprising an electro chemical cell for immersion in the liquid metal whose hydrogen content is to be measured and comprising a first electrode which is permeable to hydrogen at the temperature at which the hydrogen content is to be measured and which is placed in communication with a material of known hydrogen activity, a second electrode which is permeable to hydrogen at the temperature at which the hydrogen content is to be measured and which comprises or, in use, is in contact with the liquid metal, an electrolyte positioned between the electrodes through which hydrogen ions can flow at the temperatures at which the hydrogen content is to be determined, means for passing an electrical current to and through the electrodes of the cell, and means for detecting an electromotive force across the electrodes to provide a measure of the hydrogen content of the liquid metal.
2. Apparatus for determining the hydrogen content of a liquid metal, which apparatus comprises an electro chemical cell capable of immersion in the liquid metal whose electrodes are permeable to hydrogen at the immersion temperature and are separated by an electrolyte through which hydrogen ions can flow at the immersion temperature, one electrode of the cell being a reference electrode in communication with a source of known hydrogen activity and the other electrode comprising or being exposed to the liquid metal whose hydrogen content is to be determined and which, in use, attains an equilibrium hydrogen activity which is representative of the hydrogen activity of the liquid metal, and means for passing an electric current to and through the electrodes and for measuring the resulting electromotive force across the electrodes.
3. Apparatus as claimed in Claim 1 or Claim 2 wherein the electrolyte comprises a stable ionic compound or mixture of such compounds.
4. Apparatus as claimed in Claim 3 wherein the ionic compound is selected from silica, calcium oxide, alumina and magnesia.
5. Apparatus as claimed in Claim 3 wherein the electrolyte comprises a homogenous mix of between 40 to 70% by weight silica, up to 40% by weight calcium oxide, up to 30% by weight alumina and up to 20% by weight magnesia.
6. Apparatus as claimed in Claim 5 wherein the electrolyte also includes water up to 1% by weight.
7. Apparatus as claimed in any one of the preceding Claims wherein the electrode exposed to the liquid metal comprises a cermet sheath.
8. Apparatus as claimed in Claim 7 wherein the cermet comprises 80% molybdenum and 20% alumina and wherein the electrolyte and electrode which communicate with a source of known hydrogen activity are positioned within the sheath.
9. Apparatus as claimed in any one of Claims 1 to 6 wherein the first mentioned electrode comprises the liquid metal itself.
10. Apparatus as claimed in any one of Claimsito 6-wherein the first mentioned electrode comprises a stable refractory material of low electrical conductivity, a basic oxide plus silica and sodium oxide, platinum or a solid or viscous liquid which adheres to the surface of a refractory electrode.
11. Apparatus as claimed in any one of Claims 1 to 10 wherein the electrode in communication with a source of known hydrogen activity comprises a molybdenum tube flushed with a mixture of argon and hydrogen.
1 2. Apparatus as claimed in Claim 11 wherein the hydrogen content of this flushing gas is of the order of 10%.
13. Apparatus as claimed in any one of the preceding Claims wherein the electrode in communication with a source of known hydrogen activity comprises a concentration created in-situ by thermal decomposition of a hydrogen-containing compound which decomposes at the operating temperature of the cell.
14. A method for determining the hydrogen content of a liquid metal, the method comprising the steps of immersing in a bath of the liquid metal an electrochemical cell whose electrodes are permeable to hydrogen at the immersion temperature and are separated by an electrolyte through which hydrogen ions can flow, placing one electrode in communication with a source of known hydrogen activity and exposing the other electrode to the liquid metal, passing an electric current to and through the electrodes, and measuring the electromotive force produced across the electrodes to provide a measure of the hydrogen content of the liquid metal.
1 5. Apparatus for determining the hydrogen content-of a liquid metal substantially as herein described and as described in Figure 1 or Figure 2 or Figure 3 of the accompanying diagrammatic drawings.
GB9707626A 1997-04-17 1997-04-17 Determining hydrogen content of liquid metal Withdrawn GB2324372A (en)

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GB9707626A GB2324372A (en) 1997-04-17 1997-04-17 Determining hydrogen content of liquid metal

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GB2324372A true GB2324372A (en) 1998-10-21

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1376117A4 (en) * 2001-04-03 2006-05-10 Tyk Corp Concentration cell type hydrogen sensor and method for preparing solid electrolyte capable of conducting proton

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1594223A (en) * 1977-01-21 1981-07-30 Nat Res Dev Determination of hydrogen
GB2109941A (en) * 1981-11-20 1983-06-08 Atomic Energy Authority Uk Hydrogen-exchanged beta- double-prime-alumina and measuring devices using this material

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1594223A (en) * 1977-01-21 1981-07-30 Nat Res Dev Determination of hydrogen
GB2109941A (en) * 1981-11-20 1983-06-08 Atomic Energy Authority Uk Hydrogen-exchanged beta- double-prime-alumina and measuring devices using this material

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1376117A4 (en) * 2001-04-03 2006-05-10 Tyk Corp Concentration cell type hydrogen sensor and method for preparing solid electrolyte capable of conducting proton

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Publication number Publication date
GB9707626D0 (en) 1997-06-04

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