JPS594660B2 - A measuring device that electrochemically detects the oxygen potential in the furnace atmosphere. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention consists of an oxygen ion-conducting solid electrolyte based on zirconium oxide, the outer electrode of which is capable of contacting the furnace atmosphere, and the inner electrode of which is capable of contacting air or oxygen-containing solid electrolytes. The present invention relates to a measuring device for electrochemically detecting the oxygen potential of a furnace atmosphere, which can be brought into contact with other reference gases, and in particular for indirectly detecting and controlling the carbon level of a carburizing atmosphere containing hydrocarbons. .

Such oximeters are known.

In these instruments, the solid electrolyte consists of a wall made of stabilized zirconium dioxide. On one side of this wall is a reference gas (usually air) with a known oxygen content.
and is in conductive connection with an electrode called the inner electrode. The other side of this wall is in contact with the furnace atmosphere and is electrically conductively connected to another electrode, referred to as the outer electrode. These electrodes are mostly made of platinum. As a measurement point,
A common point of contact between the electrode and the zirconium dioxide and the furnace atmosphere or reference gas is used. Such an oxygen meter is used to detect and control the atmosphere in a heat treatment furnace.

At the high temperatures present, the zirconium dioxide acts as a solid electrolyte that conducts oxygen ions when the inner and outer surfaces are exposed to an atmosphere of different oxygen partial pressures. The potential difference between the electrodes is expressed in voltage form in MV and can be used to characterize the furnace atmosphere. The evaluation of oxygen meter readings in relation to furnace operation is based on tables and curves that are found empirically or calculated and represent the relationship between solid electrolyte voltage, furnace temperature, and carbon level in the furnace atmosphere. It is carried out by. These curves apply to starting fuels of known composition. If processing time is included, the decarburization effect of the atmosphere can be determined from this, for example. The advantage of this oxygen meter is that it provides specific continuous readings very rapidly over a wide temperature range, which can be used in particular for automatic process control, and it can also be used for practically all available heat treatments. You can get the atmosphere. The disadvantage of using known oxygen meters is that undesirable local gas reactions occur at the outer electrode, which are initiated by the catalytic action of the outer electrode.

The platinum used there catalyzes the decomposition of CH4, resulting in a more pronounced combined oxygen reaction locally at the measuring point, which corresponds to the oxygen potential of the atmosphere in the furnace chamber. Furthermore, as in the case of steel workpieces, the ceramic material of the solid electrolyte cannot dissolve carbon. If the product remains in the furnace atmosphere with a high carbon level for a long time, soot will gradually precipitate at the measurement location. The deposited soot acts as a re-catalyst to precipitate further carbon from the furnace atmosphere. This process, which begins gradually at first and then rapidly accelerates due to autocatalytic action, reduces the measurement accuracy and therefore also the useful life of the oxygen meter.

The object of the present invention is to improve the initially opened type of measuring device while avoiding these drawbacks, in order to maintain the initial measurement accuracy over a long period of use and to avoid undesirable gas reactions on the outer electrode. The purpose is to prevent gas reactions.

In order to solve this problem, according to the present invention, the outer electrode is
A non-carburizing scavenging gas is applied intermittently and alternately with the furnace atmosphere to prevent local gas reactions and soot deposition at the outer electrode.

The scavenging gas, such as air, should have a decarburizing effect. The measurement accuracy and useful life of the oxygen measuring device according to the present invention are significantly improved, and the outer electrode of the measuring device is intermittently supplied with scavenging gas instead of the furnace atmosphere! By being pushed,
For example, it was found that the drawbacks of controlling the carburizing process did not occur.

In order to achieve a precise carburizing effect on the furnace atmosphere, it is important to monitor or correct the furnace atmosphere with precise control variables, and this is ensured by the invention. In the measuring device of the present invention, it is preferable to bring the scavenging gas supply conduit directly close to the measuring point of the outer electrode.

This can be carried out simply if at least the solid electrolyte is provided with a measuring space surrounding the outer lid electrode, which is connected to the scavenging gas supply line and connectable to the furnace chamber. The measuring space is formed by a solid electrolyte protective tube made of ceramic material, which protective tube is provided with at least one opening leading to the furnace chamber, through which the scavenging gas is alternately passed from the estimation space to the furnace chamber. Further, the furnace atmosphere can be made to flow from the furnace chamber to the measurement space.
The type of scavenging gas used can be adapted to the requirements for the quality of the workpieces being processed in the furnace. If nitrogen is selected as the non-carburizing scavenging gas, no effect will occur. If a scavenging gas containing oxygen is used when carburizing a workpiece made of ordinary carbon steel, quality deterioration due to so-called surface oxidation will not occur. It is particularly advantageous in this case to use air as scavenging gas. This is because in any case air is used as a reference gas to impinge on the inner electrode. A pumping device can be provided for rapid gas exchange in the measuring space.

However, the solid electrolyte consists of a capillary made of stabilized zirconium oxide with one side closed, an inner electrode is inserted into this capillary, and the capillary is surrounded at intervals by a ceramic protective tube, and the bottom of this protective tube has a plurality of A special embodiment of the invention is preferred in which an opening is provided and an outer electrode and a scavenging gas supply are provided in the space between the capillary tube and the protective tube. The supply of scavenging gas to the measurement location is facilitated by arranging the protective tube concentrically with respect to the zirconium dioxide capillary, forming an air gap. Furnace atmosphere or scavenging gas can flow freely around all contact points between the outer electrode and the solid electrolyte without any turbulent areas, so that the outer electrode and the solid electrolyte are connected in a circle at one or more points. It is proposed that the contact be made in the form of a shape or a point.

In order to be able to effectively avoid the initially mentioned undesired catalytic effect of the outer electrode, an advantageous further development of the invention provides that the outer electrode is blocked, at least at the point of contact with the solid electrolyte. It is proposed that the d-level of the electron shell is completely occupied by 10 electrons and consists of an electrically conductive material containing at least 80 fl of an element that does not catalyze the decomposition of methane.

The outer electrode preferably consists of gold at the measuring point. Further details, features and advantages of the measuring device according to the invention will become apparent from the following description of the accompanying drawings, which schematically show two embodiments of the invention.

The measuring device of FIG. 1 consists of a capillary tube 1 made of stabilized zirconium dioxide, closed at one end, on the inside of which an inner electrode 2 is attached, and on the outside an outer electrode 3.

Both electrodes 2, 3 are made of gold in the area of the measuring point formed by the common contact point of these electrodes with the solid electrolyte zirconium dioxide. The points of contact between the outer electrode 3 and the zirconium dioxide capillary 1 are formed point-like to ensure free flow around the electrode without turbulent areas. A conduit 4 for supplying scavenging air to the outer electrode 3 is located close to the area of the measurement location.

A pump P is provided for supply. The measuring device of FIG. 1 is inserted into the wall of the heat treatment furnace so that the area of the measuring point extends into the furnace chamber. This makes it possible to alternately apply scavenging gas to the outer electrode 3 and apply the furnace atmosphere to this electrode 3. FIG. 2 shows another configuration of the measuring device in an installed state. The difference between this measuring device and the previously described measuring device is that the solid electrolyte 1 is surrounded by a protective tube 6 made of ceramic material, leaving a gap 5. That's true.

The closed end of the protective tube 6 entering the furnace chamber 8 has a plurality of openings 7.
These openings alternately allow the scavenging gas to flow from the measuring space 9 in the tip region of the measuring device into the furnace chamber 8 and the furnace atmosphere from the furnace chamber 8 to the measuring space 9. can. The supply of scavenging gas to the measuring space 9 takes place via a conduit 4, which is connected to a pump P, which is schematically shown in the drawing. In order to bring the outer electrode 3 into contact with the furnace atmosphere again as quickly as possible after the scavenging process, the pump P can be used to suck out the furnace atmosphere.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a simple measuring device supplied with scavenging gas.
FIG. 2 is a cross-sectional view of a scavenging air measuring device of a different construction inserted into the furnace wall. DESCRIPTION OF SYMBOLS 1...Solid electrolyte thin tube, 2...Inner electrode, 3...Outer electrode, 4...Scavenging gas supply conduit, 8...・Furnace room, P...Pump.

Claims (1)

[Claims] 1. Consists of an oxygen ion-conducting solid electrolyte based on zirconium oxide, the outer electrode of which is capable of contacting the furnace atmosphere, and the inner electrode of which is made of air or other material with a known oxygen content. In the measuring instrument which is in contact with the reference gas, the outer electrode 3 is intermittently applied alternately with the furnace atmosphere with a non-carburizing scavenging gas which prevents local gas reactions and soot deposition at this outer electrode. A measuring device that electrochemically detects the oxygen potential of the furnace atmosphere. 2. The measuring instrument according to claim 1, wherein the outer electrode 3 is scavenged with a scavenging gas that decarburizes the outer electrode 3. 3. The measuring instrument according to claim 2, characterized in that the outer electrode 3 is scavenged with air. 4 Conduit 4 for supplying scavenging gas directly to the measurement location of the outer electrode 3
A measuring instrument according to any one of claims 1 to 3, characterized in that the two are brought close to each other. 5. At least the solid electrolyte 1 is provided with a measuring space 9 surrounding the outer electrode 3, which is connected to the scavenging gas supply conduit 4 and connectable to the furnace chamber 8. Measuring device according to item 1. 6 Solid electrolyte 1 whose measurement space 9 is made of ceramic material
is formed by a protective tube 6 which is provided with at least one opening 7 leading into the furnace chamber 8, through which scavenging air alternately passes from the measuring space 9 into the furnace chamber 8 and the furnace atmosphere flows into the furnace chamber. 8. Measuring device according to claim 5, characterized in that the flow flows from 8 to the measuring space 9. 7. The measuring instrument according to claim 5 or 6, characterized in that a pump device is provided for gas exchange in the measurement space 9. 8 The solid electrolyte 1 consists of a capillary made of stabilized zirconium oxide with one side closed, the inner electrode 2 is inserted into this capillary, the capillary 1 is surrounded at intervals by a ceramic protective tube 6, and this protective tube Multiple openings 7 at the bottom of the
A measuring instrument according to claim 1, characterized in that an outer electrode 3 and a scavenging gas supply section are provided in a space 5 between the capillary tube 1 and the protective tube 6. 9. The measuring instrument according to claim 1, wherein the outer electrode 3 and the solid electrolyte 1 are in contact with each other in a circular or dotted manner at one or more locations. 10 The outer electrode 3 is made of a conductive material, at least at the point of contact with the solid electrolyte 1, in which the d-level of the occupied electron shell is occupied by 10 electrons and which comprises at least 80% of an element that does not catalyze the decomposition of methane. A measuring instrument according to claim 1, characterized in that: 11. Measuring device according to claim 10, characterized in that the outer electrode 3 consists of gold at the measuring point.