LU84328A1 - SOLID FORM OXYGEN DETECTOR - Google Patents

Description

The present invention relates to solid state electrochemical devices for measuring oxygen activity; these devices include an electrolyte which is a solid oxide and oxides as electrodes sensitive to oxygen.

Electrocellular cells are known in the art for measuring the partial pressure of oxygen; they consist of a solid electrolyte (oxide) having as electrodes stainless stainless conductors, for example in one of the noble metals, in particular platinum.

The solid electrolyte is a ceramic oxide or a glassy phase with pure ionic conduction, for example a solid solution of oxides having a deficit in oxygen ions.

'* Said cells, hereinafter called "oxygen detectors", have various defects mainly due to the metallic nature of the material constituting the electrode (Pt) which considerably limits their possibilities of use.

In fact, the measured partial pressures of oxygen are lower than the actual values when the gas mixtures to be analyzed contain traces of oxidizable substances, such as H 2, CO, SO 4 and hydrocarbons.

When measuring the activity of oxygen in CO / CO mixtures, good accuracy is observed in determining the proportion of the two gases, but the response times are very high for rapid variations in the composition of the gas mixture.

When the gases to be analyzed contain SO ^ (x = 2 or 3), the response times are very high.

Many metals can poison said material constituting the electrode (Pt) and the use of the oxygen detector, for monitoring the reducing atmosphere in metallurgical applications, is sometimes very critical or impossible.

The Pt electrode is in particular easily poisoned by lead; this is the reason why the use of such a device is excluded to control the exhaust gases of an engine supplied with gasoline containing organometallic compounds this feather.

2

To avoid said defects and to produce an electrochemical oxygen detector in solid form capable of being used in a wider range of applications, the applicant proposes, according to the invention, a new solid electrochemical device in which the constituent material the electrode (in general a stainless electronic conductor, such as a noble metal) consists of oxides having a mixed electrical conductivity (ionic and electronic).

Such materials are non-stoichiometric oxides (PrO. TbO or mixtures of said oxides, for example TbO + Ce0o; Pr0 „+ Ce0„) or mixed oxides (LaCrO.; La, Sr CrO; etc.).

2-x 2-x 3 1-x x 3

The appended drawing shows the design of the detector according to the invention (longitudinal section) and allows a better understanding of other characteristics and advantages of the invention,

The ceramic container 1 constitutes the solid electrolyte; Its internal wall 2 and / or its external wall 3 are in contact with an oxide (electrode sensitive to oxygen).

The internal reference compartment uses a chemical system made up of a gaseous mixture (for example pure oxygen, air, a gaseous mixture of oxygen, or mixtures CO / CO ^ or 20 i ^ / l ^ O) or a metal-oxide mixture, for example Ni, KiO, Fe-FeO, etc.

to set a known partial pressure of oxygen.

The internal reference compartment uses as the oxygen sensitive electrode either a noble metal or an oxide.

The external electrode is placed in the atmosphere of the gas to be analyzed and its oxygen-sensitive material is an oxide or a mixture of oxides.

- f. Under the operating conditions, an electromotive force (emf) is observed between said electrodes 2 and 3. It is the value of this electromotive force which gives the measurement of the activity of oxygen.

The device according to the invention can be used in the following fields: a) control of the atmosphere in the heat treatment of metals; 3 b) control of combustion in steam generators, ovens and boilers; c) control of exhaust gases from internal combustion engines; and I 5 d) to improve fuel economy and to fight pollution.

Of course, various modifications can be made by those skilled in the art to the devices or methods which have just been described only by way of nonlimiting examples without departing from the scope of the invention.

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Claims (19)

4 1. Oxygen detector in solid form for measuring the partial pressures of oxygen, characterized in that it is constituted by an electrolyte cell whose electrodes sensitive to oxygen 5 are non-stoichiometric oxides, the electrolyte consisting of ceramic in the solid state. 2. Oxygen detector in solid form according to claim 1, characterized in that the oxygen-sensitive electrodes are oxides having a mixed ionic and electronic conductivity. 10 3. Oxygen detector in solid form according to claim 1, characterized in that the oxygen-sensitive electrodes <· are oxides containing the possible metal poison present in the gaseous atmosphere to be analyzed. 4. Oxygen detector in solid form as claimed in claim 1, characterized in that the oxygen-sensitive electrodes are mixed oxides containing two or more cations. 5. Oxygen detector in solid form according to claim 1, characterized in that the oxygen-sensitive electrodes are mixtures of oxides. 20 6. Oxygen detector in solid form according to claim 1, characterized in that the cell consists of a ceramic container in solid form, one of the walls of which is in contact with the oxides which constitute the sensitive electrode. oxygen. 7. Oxygen detector in solid form according to claim 1, characterized in that the cell consists of a ceramic container in solid form, the two walls of which are in contact with the oxides constituting the sensitive electrodes oxygen. 8. Solid state oxygen detector according to any one of claims 145, characterized in that the cell has a wall in contact with the mixtures of oxides constituting the oxygen-sensitive electrode. 9. oxygen detector in solid form according to any one of claims 1 to 5. characterized in that the two cells of the cell are in contact with the mixtures of oxides. 5 * 10. Oxygen detector in solid form according to any one of claims 1 to 4, characterized in that the surface of the outer wall of the cell is coated with PrO. _. 11. Oxygen detector in solid form according to any one of claims 1 to 4, characterized in that the surface of the external wall of the cell is coated with TbO „2-x 12. Oxygen detector in solid form according to any one of claims 1, 2 or 6, characterized in that the external surface is coated with TbCL + and / or PrCL + CeO „2-x 2-x 2-x 10 13. Oxygen detector in solid form according to any one of claims 1, 2 or 4, characterized in that the outer surface is coated with lanthanide oxides. ; ,, 14. Oxygen detector in solid form according to any one of claims 1, 2 or 6, characterized in that the external surface is coated with mixed oxides of lanthanides and / or! transition metals. i 15. Oxygen detector in solid form according to any one of claims 1, 2 or 6, characterized in that the external surface of the solid electrolyte is coated with mixed oxides including at least one lanthanide oxide, transition metals and t \ alkali metals. 16. Solid state oxygen detector according to any one | of claims 1, 2 or 6, characterized in that the outer surface is coated with mixed oxides including at least one oxide of lanthanides, transition metals and alkaline earth metals. [17. Solid state oxygen detector according to any one b V! ^ of claims 1, 2 or 6, characterized in that the outer surface of the solid electrolyte is coated with mixed oxides i including at least one oxide of lanthanides, alkaline earth and transition metals. 18. oxygen detector in solid form according to any one of claims 1, 2 or 6, characterized in that the cell is} i formed of a solid ceramic container one of the walls of which is in contact with a noble metal and the other wall is in contact with the cables according to any one of the preceding claims. > 6 19. oxygen detector in solid form according to any one of claims 1 ^ 2 or 6, characterized in that one or both walls are in contact with simple or complex mixtures of a product according to one any of the preceding claims. * // £ [| if? | -ixextl.ourg, C £ Aug 19 '1; £ T ._____ n ^ βτ *! V juT it