JPH0324622B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an oxygen probe that measures the oxygen activity value in molten steel using a zirconia-based solid electrolyte, and which has improved responsiveness and stability by adjusting the thickness of the solid electrolyte. In recent years, demands regarding materials such as steel have increased, and as the ratio of continuous casting increases from the perspectives of energy saving, labor saving, and yield improvement, molten steel management in the steelmaking process is becoming more important than ever. I'm getting used to it. One of the most important guidelines for molten steel management is the oxygen activity value in molten steel and molten slag, and it is well known that the success or failure of this measurement generally affects the steelmaking process. For this reason, oxygen probes have been developed and commercially available that measure the oxygen activity value in solutions such as molten steel and molten slag using a zirconia-based solid electrolyte as an electrolyte and applying the principle of an oxygen concentration battery. The detection end of this oxygen probe is usually protected by a refractory, but because it is directly immersed in a high-temperature solution, there is a limit to the immersion time due to heat resistance. Therefore, in order to accurately measure the oxygen activity value using an oxygen probe, the electromotive force (hereinafter referred to as emf) generated by the oxygen probe must be stabilized within the allowable immersion time (te) and maintained in that stable state. It has to be something. However, with conventional oxygen probes, it takes a long time for the emf to stabilize after being immersed in the solution.
Alternatively, it was often observed that a predetermined stability range retention time could not be obtained, resulting in problems with response or stability. For example, when measuring with an oxygen probe with poor response, the emf curve does not reach the stable region as shown in Figure 1a, because it must be pulled out of the solution before the emf stabilizes due to the limit on the allowable immersion time te.
In addition, as shown in FIG. 1b, if the stability is poor, there may be repeated fluctuations or a clear equilibrium region may not be obtained, so there is no stable region, and accurate measurement cannot be performed. This lack of responsiveness and stability in conventional oxygen probes is particularly noticeable in solutions where low oxygen activity values must be measured, such as Al-killed molten steel, and stable measurements are impossible. Ta. Generally, the allowable immersion time te can be increased by reinforcing the oxygen probe's exterior or refractories, but adding reinforcement leads to an increase in price and is a disadvantage for oxygen probes, which are one-time consumables. will be at a significant disadvantage. Furthermore, increasing the allowable immersion time te also prolongs high-temperature work at steelmaking and refining sites, which is disadvantageous in terms of work. On the other hand, stability is a problem due to the nature of oxygen probes.
The solution requires the development of a new oxygen probe. Although conventional oxygen probes have various practical problems as described above, to the best of the present inventors' knowledge, there are no reports regarding these problems. Therefore, the present inventors focused on the solid electrolyte that has the most influence on the emf response and stability of the oxygen probe, and conducted various studies regarding its thickness. As a result, the inventors found that the thickness of the solid electrolyte should be set to 0.5 mm or more and less than 1.0 mm.
We found that the response time of the emf curve became shorter and the waveform became more stable. In other words, the present invention improves the thickness of the solid electrolyte in an oxygen probe using a zirconia solid electrolyte.
By setting the diameter to 0.5 mm or more and less than 1.0, the lack of responsiveness or stability of conventional oxygen probes has been overcome. A typical example of the zirconia solid electrolyte targeted in the present invention is ZrO ₂ −
MgO-based, ZrO ₂ -CaO-based, ZrO ₂ -Y ₂ O _3- based and their composite stabilized types (e.g. ZrO ₂ -MgO-
CaO type), etc. When measuring the oxygen activity value in a solution using these solid electrolytes as oxygen probes, the response and stability of the emf curve are significantly affected by its thickness, and when the thickness is 1.0 mm or more, Heat transfer is delayed, and it takes time for the interior of the reference electrode to reach a constant equilibrium oxygen partial pressure. As a result, the response time becomes longer and the permissible immersion time of the oxygen probe is exceeded. On the other hand, when the electrolyte thickness becomes thinner than 0.5 mm, the response time becomes shorter, but the amount of oxygen that directly passes through the electrolyte cannot be ignored, and as a result, the waveform of the emf curve becomes unstable, and the measured value itself has an error in oxygen transmission. It becomes an imaginary value containing . The present invention will be specifically explained below using Examples. Example 1 Figure 2 shows the cross section and bottom surface of the oxygen probe used to measure the oxygen activity value in molten steel in this example _.
8.1 mol% MgO tube 2 is a reference electrode material filled in this tube, which is filled with 0.1 to 0.3 g of Cr and Cr ₂ O ₃ sintered at a temperature of 1550° C. or higher and then ground. 3 is a Mo wire as a reference electrode wire, 4 is alumina powder, 5 is an iron ring that is an electrode on the molten steel side, 6 is a thermocouple for measuring the temperature of molten steel, 7 is an iron cap for preventing slag,
8 is a refractory body that supports these sensor parts, 9 is a refractory sleeve, and 10 is a paper sleeve. Table 1 shows this oxygen probe immersed in low carbon Al-killed molten steel (1600±10℃) in a 90t ladle.
The response time and waveform stability were determined from the emf curve, and these were summarized in relation to the thickness of the solid electrolyte. As shown in Figure 3, the response time is determined by measuring the time from the start of immersion of the oxygen probe into the molten steel until the waveform becomes stable. The measured values of 20 oxygen probes were averaged for each electrolyte size, judging by the presence or absence of time and its length.

【table】

[Table] When the solid electrolyte thickness is 0.5 mm or less, the response time becomes shorter, but the waveform stability deteriorates. Figure 4 shows emf curve waveforms inside and outside the present invention, (a)
is for No. 4, and (b) is for No. 6. On the other hand, when the solid electrolyte thickness is 1.0 mm or more, the waveform stability is good, but the response time is longer, at 9.1 seconds or more. In general, in the case of oxygen probes, the permissible immersion time te varies depending on the immersed molten steel temperature, but in the case of a normal oxygen probe without reinforcement, it is about 9 seconds at a molten steel temperature of 1600°C. Moreover, in order to confirm whether the emf curve has reached the stable range, the emf curve must be kept at almost the same potential for about 1.5 seconds, so the emf curve must reach the stable range within 7.5 seconds from the start of immersion. Must be. That is, the response time must be within 7.5 seconds, and the response time must be within 7.5 seconds.
If the electrolyte thickness is 1.0 mm or more and the time is 9.1 seconds or more, measurement becomes impossible. Example 2 An oxygen probe with the same structure as in Example 1 was created using a solid electrolyte with an inner diameter of 2 mm or 4 mm, with the thickness changed in the same manner as in Example 1, and it was immersed in molten steel under the same conditions as in Example 1. We investigated the response time and stability due to changes in solid electrolyte thickness. In addition, in the investigation, as in the case of Example 1, 20 oxygen probes were created for each solid electrolyte size, and the measured values were averaged for each size. Tables 2 and 3 show the results. The stability evaluation was the same as in Example 1.

【table】

【table】

[Table] As shown above, in the case of the present invention, the solid electrolyte thickness is
Responsiveness and stability can be improved by setting the diameter to 0.5 mm or more and less than 1.0 mm, so there is no need to reinforce the exterior or refractories, and the price is also low. In addition, the improved responsiveness shortens the working time, making the work easier.

[Brief explanation of the drawing]

Figure 1 shows emf curves that are often seen when measuring oxygen activity in molten steel with a conventional oxygen probe. (a) shows cases where response is poor, and (b) shows cases where stability is poor. It shows. FIG. 2 shows an oxygen probe used in an embodiment of the present invention, in which (a) is a sectional view and (b) is a bottom view of (a) with the bottom surface of the cap removed. FIG. 3 shows the relationship among the response time, stability range retention time, and allowable immersion time te in the emf curve of the oxygen probe. FIG. 4 shows emf curves inside and outside the present invention in Examples, where (a) shows the case of No. 4, and (b) shows the case of No. 6. 1... _ZrO2-8.1mol %MgO tube which is a solid electrolyte, 2...Reference electrode material (Cr/ _Cr2O3 mixed sintered powder), 3...Mo wire, ₄ ...Alumina powder, 5... Molten steel side electrode (iron) ring), 6...Thermocouple for measuring temperature of molten steel, 7...
Slag prevention iron cap, 8... refractory body,
9...Refractory sleeve, 10...Paper sleeve.

Claims (1)

[Claims] 1 In an oxygen probe that measures the oxygen activity value in molten steel using a zirconia solid electrolyte as the solid electrolyte, the solid electrolyte thickness is 0.5 mm or more and 1.0 mm.
An oxygen probe characterized in that: