FR2596525A1 - OXYGEN PROBE FOR HIGH TEMPERATURES FOR GLASS FUSION FURNACES AND CERAMICS OR THE LIKE - Google Patents

Abstract

A) OXYGEN PROBE FOR HIGH TEMPERATURES FOR GLASS AND CERAMIC OR SIMILAR FUSION OVENS. B) PROBE CHARACTERIZED IN THAT IN A SOLID ELECTROLYSIS TUBE 1, AN AIR SUPPLY TUBE 2, POROUS, ALKALINORESIST, WITH A REFRACTORY METAL STRUCTURE 3, IS SLIDED AXIALLY, AND BETWEEN THIS TUBE AND THE INNER WALL OF THE TUBE A SOLID ELECTROLYTE, IN THE ELECTRODE AREA, GRAINS OF AN OXIDIZING MATERIAL, ELECTRONICALLY CONDUCTED OR MIXED CONDUCTION 7 WERE FREELY SPILLED, THE SOLIDIFIED CERAMIC MASS 4 LIMITING THIS SPILL AND IN THE REST A FREE SPILL OF ' AN INSULATING POWDER 5 AND AT THE OPEN ENDS OF THE SOLID ELECTROLYTE TUBE, AN INSULATING 6, 8 MASS, CLOSING THE INTERMEDIATE VOLUME IN THE CASE OF A SOLID ELECTROLYTE TUBE WITH OPEN END.

Description

"Oxygen probe for high temperatures - for ovens

  melting glass and ceramics or the like. "

  The invention relates to an oxygen sensor for high temperatures comprising a galvanic solid electrolyte cell housed in a protective casing and an air supply tube placed in a support tube, for continuously performing oxygen measurements. preferably at temperatures above 10000C in gaseous phases above glass melting furnaces, in ceramic furnaces

  of all types and in metallurgical installations.

  In order to measure oxygen at high temperatures, closed tubes at one end having a length of 40 to 60 cm and containing zirconium dioxide as the main component are generally used. In order to have stability against the high temperatures and parasitic components contained in the gaseous phases of the technical gas, large amounts of noble metals and protective tubes are used around the measuring cell. By way of example, the entire inner surface of the solid electrolyte tube is covered with platinum to form the air reference electrode and its electrical conductor; externally to form the measuring electrode, a thick layer of a noble metal is applied over a length of the order of 5 cm on the electrolyte; in this way, between 8 and 10 grams of platinum metal (excluding the thermocouple) is used per probe and without the sensor being able to recover simply. Despite the implementation of such important means, probes rarely resist more than three months under the strict conditions * existing in practice. When elements such as lead, arsenic or antimony exist as parasitic components in the gas analyzed, platinum electrodes exposed directly to this gas are very quickly destroyed especially under oxidizing conditions. The molten particles in the liquid state contained in the gas analyzed stick when these particles arrive on the pores of the electrode layers or on the protective ceramic material and render the sensor very rapidly inert and unusable. Finally, vapors passing through the test gas in the case of high temperatures, vapors which normally come from glasses and many ceramics, contain non-organic combinations and cause significant destruction. These vapors can be combined directly with solid body parts of the probe by exiting the gas phase and destroying combinations of solid bodies. The object of the present invention is to provide a means which minimizes the materials used and which enables oxygen to be accurately measured continuously over a long period of time even in the high temperature range, even under the conditions of component creation. existing parasites in the gaseous phase above the melting crucibles of

glass or ceramic material.

  It is therefore an object of the invention to modify the construction of solid electrolyte cell probes for measuring oxygen in gases in order to employ a minimum of solid electrolyte and noble metals while permitting non-potentiometric recording. long-term deterioration of the oxygen concentration of the gas stream containing low glass dust and high temperatures of liquefied particles and, depending on the temperature increase, the increasing amounts of

  more important non-organic matter.

  To this end, the invention relates to an oxygen measurement probe for high temperatures comprising a solid electrolyte cell, galvanic with a protective envelope and an air supply tube in a support tube, a probe characterized in that a relatively short solid electrolyte tube with respect to the length of the probe, a porous, alkaline-resistant, porous air supply tube was slid axially with a noble and non-noble refractory metal structure applied at the region of the electrode and between this tube and the inner wall of the solid electrolyte tube, in the region of the electrode, grains of an oxidizing material, with electron conduction or with mixed conduction, are discharged freely, the solidified ceramic mass limiting the spill as well as in the rest a free spill of an insulating powder, fine ceramic and at the open ends of the solid electrolyte tube, an isolated mass a ceramic closing the intermediate volume in the case of an open-ended solid electrolyte tube, in that the solid electrolyte tube thus prepared and having a second refractory metal structure in the region of the electrode may be slid axially in a tubular casing of alkaline-resistant ceramic material having pores or openings for the passage of gas, and containing a free spill of a powder

  thin, ceramic, insulating, alkaline-resistant, this layer being limited by layers in an alkaline-resistant ceramic mass which solidifies, in that the tube-

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  thus filled casing is mounted on the gas-tight support tube and in the gap between the casing tube and the support tube on a ring made of a prefabricated ceramic mass, filled with free powder, fine ceramic, alkaline-resistant and around the tubelefoil is mounted a protective envelope attached to a support tube, which envelope is made of a prefabricated mass of alkaline-resistant porous ceramic and in the support tube, integrates the air supply tube freely fitted on the tube porous air supply with the electrical conductors of the sensor in a mass of free ceramic particles.

  According to another characteristic of the invention, the gap between the solid electrolyte tube and the jacket tube is provided at the measuring electrode with a free filling of grains of an oxidizing material, preferably a conductive material. electrons and which is enclosed in the interval by a porous layer prefabricated alkaline-resistant ceramic material.

  According to another feature, in the alkaline-resistant ceramic tubular casing, there are openings for the passage of gas and most of the gap between the solid electrolyte tube and the casing tube is filled with a powder fine ceramic, alkaline-resistant.

  To simplify the assembly according to another feature, the tubelefoil and the protective envelope form by their assembly a porous alkaline-resistant protective body attached to a support tube and most of the gap between the solid electrolyte tube. the protective body and the supporting tube are filled with a free spill, equal to a fine powder of insulating alkaline-resistant ceramic material.

  The short solid electrolyte tubes required for the described probes do not require any precise measurement and are therefore relatively easy to manufacture. In the probes, the elements are protected against mechanical, thermal and chemical incidents. On assembly, the electrodes are stabilized in the long term by oxidizing electron conductors, in that the resistance of the cell no longer increases as a result of the recrystallization and the evaporation of the platinum. When non-noble, refractory metal wires are used, there are probes that do not contain noble metals for temperatures up to about 12000C and which, unlike platinum-containing probes, can also be used in exhaust containing lead. In the case of probes made from platinum-rhodium alloys which may in other cases be used up to 15000C,

  the protected arrangement of noble metal wires has an advantageous effect on the reliability of such probes.

  Compared to existing commercially available probes, only about half of the noble metal elements are required, and the wires made of noble metals can recover to a very large extent.

  after the shutdown of the probe.

  In order to obtain alkaline resistance characteristics with negligible electrical conductivity, components such as Al 2 O 3, MgO, CaO and ZrSiO 4 are used for producing the probe. The aluminum silicate used for example in the usual filter tubes are to be avoided. Better than pure sintered corundum, we consider sintered spinel or spinel magnesite, the expansion coefficient of sintered spinel MgA1204 better corresponding to the solid electrolyte of zirconium dioxide. The permeability of the powder layers to the gases is regulated using a

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  coarser powder if you want a good permeability and a finer powder for sealing parts. Solidification of certain parts is accomplished by adding chemically prepared materials which are or are not weakly sintered to highly sintered ceramic powders. By using freely discharged powder of a highly sintered material as a sealing layer, the formation of gas-permeable cracks that could form during continuous use is avoided. The recessed position of the measuring electrode and the fact that on the back side of the casing there are free pores for the flow, protects the sensor against clogging resulting from glass droplets.

  The present invention will be described in more detail with the aid of the accompanying drawings, in which =

  FIG. 1 shows a sensor in the form of a component comprising a solid electrolyte tube whose two ends are open.

  FIG. 2 shows the head of the probe comprising a porous shell tube and a hidden measuring electrode.

  - Figure 3 shows a probe head with a dense ceramic tubeenveloppe and an open measuring electrode.

  FIG. 4 shows a sensor in the form of a component comprising a solid electrolyte tube closed on one side.

  - Figure 5. shows a probe head with porous body-envelope.

  The sensor composed of a solid electrolyte tube 1 whose two ends are open is prefabricated as a component; for this, introduced a porous air supply tube 2, open at both ends and carrying a metal conductor 3 wound in the electrode area; then, a layer 4 is introduced which solidifies and is loaded on one side, the ceramic powder 5, thin, then covered by the layer 6 which solidifies; at the other end the grains 7 are dropped from an oxidizing electron conductor and covered with a mass of material 8 which solidifies. Outside in the region of the electrode, a winding 9 of a second conductor is put in place

  metallic and on top, the insulation elements 10 are placed.

  The sensor heads shown in FIGS. 2 and 3 comprise in the middle the component 11

shown in Figure 1.

  According to Figure 2, the component 11 is in a tubular envelope 12 in porous spinel MgA1204. On a spinel mortar layer 13 which solidifies, a thin, highly sintered spinel powder MgA1204 is applied on one side and covered with a layer 15 which solidifies; on the other side, the grains 16 of an oxidizing electron conductor are introduced and covered with a layer 17 of spinel mortar which hardens. There is thus obtained a component corresponding to the second step; this component is placed in a support tube 18 by first introducing a ring 19 of ceramic mortar which will harden, then over, we put a fine ceramic powder 20, free 25 which is filled by shaking. The end of the realization of the probe head is constituted by the coating with a highly refractory concrete which, inside a mold, in the lower part 21, is made relatively gas-tight by a fine powder of spinel very sintered and a larger fraction of a highly refractory cement not containing silicon, and which is finely ground; in the upper part 22, a coarse powder of highly sintered spinel and a smaller fraction

  relatively porous of a highly refractory cement, finely ground and not containing silicon.

  or-- __ According to Figure 3, the component 11 is placed in a tubaineveloppe 23 corundum sintered

  gastight and with gas passages 24.

  After having provisionally covered the outer surface of the openings 24 with a fine powder 14 of combustible material on the spinel mortar constituting the layer 13 which hardens, it is filled with highly sintered spinel MgAl 2 O 4.

  and covered with a layer 15 which hardens.

  A component corresponding to the second stage is thus obtained and which is mounted on the support tube 18 as already described with reference to FIG. 2 or as represented in FIG. 3. The wave assembly is completed by that on the end of the air supply tube 2 which protrudes from the solid electrolyte tube 1, a ceramic air supply tube 25 is freely engaged and the gap which remains between the tubes 18 and 25 are filled with corundum powder to drown the metallic lead wires. On the unrepresented side, that is the side which remains at room temperature, the probes are closed in a simple and functional manner and are connected in known manner by their electrical conductors to

  signal processing apparatus.

  V25 In different locations in the probes, a thermoelement can be mounted that withstands the operating temperatures; one of the conductive wires can be used as one of the branches of the thermocouple and be soldered to a second appropriate branch. As the electron conductor, oxidizer or mixed conductor constituting the grains 7 and 16, it is possible to use, for example, lanthanestrontium or a mixed oxide comprising cerium oxide, praseodynium oxide or - 35 lanthanum. Embodiments lacking noble metals are made of, for example, nickel, chromium-nickel alloys or iron-aluminum alloys. Figure 4 shows the mounting of a sensor with a solid electrolyte tube 27 closed on one side and constituting a component. The parts correspond to those already described in the case of the sensor of FIG. 1. However, FIG. 4 shows that the porous air supply tube 2 can also be terminated inside the tube. solid electrolyte. The component 28 shown in FIG. 4 can be mounted in place of the component 11 in the

  devices described in Figures 2 and 3.

  FIG. 5 shows a probe head in which, in place of the tubelaband and a sheath, a porous shell body 29 has been used, in particular spinel or magnesium oxide. In this body-shell which has been cast with a mold using a mortar 20 in a slurry state or as a prefabricated part, the component 11 or 28 can be placed with a hidden or open measuring electrode. FIG. 5 represents the case in which the component 28 is housed in a long layer of a spinel powder 30, thin, free, intro25, by shaking inside a spinel body

29 porous, prefabricated.

  The body 29 is attached to the support tube 18 by means of a highly alkaline-resistant refractory mortar 31. The air supply tube 25 is engaged in the solid electrolyte tube 27 and contains the

  conductor 3 going to the inner electrode of the sensor.

  At the point of measurement where there is a permanent vacuum, in the case of sensors with an open solid electrolyte tube of both v * t '

  sides, the air reference electrode is supplied with fresh air by suction. On the other hand, in the case of pressure and for variable pressures, as well as in the case of solid electrolyte tube collectors with one end closed, there is a pump which supplies a continuous stream of air to the air supply tube.

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1.1

RE VE N DI C AT I 0 N S

  1) Oxygen measurement probe for high temperatures comprising a solid electrolyte cell, galvanic with a protective envelope 5 and an air supply tube in a support tube, characterized in that an electrolyte tube solid (1, 27) relatively short with respect to the length of the probe, a porous, alkaline-resistant air supply tube (2) was axially slid with a noble and non-noble refractory metal structure (3), applied to the level of the electrode area and between this tube and the inner wall of the solid electrolyte tube, in the region of the electrode, grains of an oxidizing material with electron conduction or mixed conduction 15 (7), the solidified ceramic mass (4) limiting the spill as well as in the rest a free spill of an insulating powder (5), fine ceramic and at the open ends of the solid electrolyte tube, a mass (6) , 8) insulating, ceramic closing the intermediate volume in the case of an open-ended solid electrolyte tube, in that the solid electrolyte tube thus prepared and the electrode area of which comprises a second metal structure (9), refractory may be axially slid into a tubular casing (12, 23) of alkaline-resistant ceramic material having pores or openings for the passage of gas, and containing a free spill of a fine, ceramic, insulating powder, alkaline-resistant, this layer being limited by layers of an alkaline-resistant ceramic mass (13, 15) which solidifies, in that the thus-filled casing tube is mounted on the gastight support tube (18) and in the the gap between the jacket tube and the support tube on a ring made of a prefabricated ceramic mass (19) is filled with free, fine (20) ceramic, alkaline-resistant powder and around the jacket tube

15 20 25 3O

  a protective casing fixed to a supporting tube, which is made of a prefabricated mass of porous alkaline-resistant ceramic (22), is mounted and in the support tube, the air supply tube (25) freely fitted on the porous air supply tube with the electrical conductors of the sensor in a mass of free ceramic particles (26).

  Probe according to Claim 1, characterized in that the gap between the solid electrolyte tube and the jacket tube is provided at the measuring electrode with a free filling of grains of an oxidising material (16). preferably electrically conductive and which is enclosed in the gap by a prefabricated porous layer of an alkaline ceramic material (17).

  ) Probe according to any one of claims 1 and 2, characterized in that in the tubular casing alkaline-resistant ceramic material

  (23) there are openings (24) for the passage of the gas and most of the gap between the solid electrolyte tube and the tubelefoil is filled with a fine, alkaline-resistant ceramic powder (14).

  A probe according to any one of claims 1 and 2, characterized in that the tubelefoil and the protective casing form by their union a porous alkaline-resistant protective body (29) attached to a support tube (18) and the greater part of the gap between the solid electrolyte tube (1, 27), the protective body and the support tube is filled by a free spill, equal to a fine powder (30) of alkaline-resistant insulating ceramic material .