JPH0648257B2 - Sensor for measuring silicon concentration in molten metal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention provides a method for quickly and accurately measuring the silicon concentration in silicon in molten metal, particularly in molten pig iron (hereinafter referred to as molten pig iron) in the steel industry. It relates to a sensor for use.

(Problems to be Solved by the Invention) It is required that the concentration of silicon in molten metal, particularly in the iron and steel industry before being sent from a blast furnace and before being subjected to steelmaking treatment, be promptly and accurately measured. This is because it is necessary to reduce impurities such as silicon, manganese, phosphorus, and sulfur as the demand for steel becomes higher, and in particular, the measurement of silicon is important. That is,
Silicon removal (desiliconization) is performed by oxidizing metallic silicon in the hot metal in the form of silicon oxide (silica) or its composite oxide, and the amount of the silicon removal agent such as an oxidizing agent added at that time is adjusted to the silicon concentration. This is because it must be changed in an appropriate amount according to.

As a method for measuring silicon, at present, a part of molten steel is sampled for chemical analysis or instrumental analysis, but it takes 5 to 10 minutes for cant bag or the like. On the other hand, the desiliconization process was conventionally performed in a converter, but in recent years, in order to save energy and reduce costs, pretreatment has been carried out with a cast floor or a pot coming out of the blast furnace. However, there is a more rapid change in the concentration of silicon in the iron wash than during converter processing.
An accurate analysis method is required.

Therefore, recently, development of a sensor type silicon analysis method has been attempted, and a galvanic cell type sensor has been proposed.

One of them is a silicate slag containing silicon oxide as an electrolyte and metallic silicon as a reference electrode. However, since the silicate slag is a liquid at the hot metal temperature, there is a drawback that the sensor molding configuration is difficult.

In addition, there is another type called a sub-electrode type, in which a sub-electrode is attached to the surface of a zirconia solid electrolyte of an ordinary oxygen sensor, and these are added at the S-phase at the three-phase interface with the hot metal.
i + O ₂ = SiO ₂ , K = a sio ₂ / a si × Po ₂ is used to convert as i to Po ₂ , and the oxygen amount is measured with this oxygen sensor to indirectly obtain silicon. To do. In addition, a sio ₂ is each activity of SiO ₂ , asi is each activity of Si, Po ₂ is oxygen partial pressure, K is an equilibrium constant of this reaction.
At this time, the sub-electrode is used to keep a sio ₂ constant (Zro ₂ + ZrSiO ₄ ) and the like is being developed. However, it is difficult to fix and mold the zirconia solid electrolyte without changing the performance of the sub-electrode and the electrolyte, and even if it is possible, reheating high temperature adhesion causes a problem in the codeability of the sub-electrode and the electrolyte, resulting in high cost. There is a drawback that

Further, both of these galvanic battery type sensors have the problems that the measurement accuracy is slightly worse than that of the device analysis and that the response time is close to 1 minute, requiring further improvement. If the response time becomes long, the holder for holding the sensor needs to have a high degree of fire resistance, resulting in a significant increase in cost of the product. In addition, measurement by a thermoelectromotive force type sensor has been attempted, but there are many unsolved problems in practical use.

Therefore, the present invention can measure the silicon concentration in the molten metal, especially in the hot metal very quickly and accurately, and can speed up the determination of the amount of the silicon removal agent and the rapid response to changes in the silicon concentration. It is an object of the present invention to provide an inexpensive sensor by improving the efficiency and desiliconization rate and simplifying the configuration of the sensor and the holder.

(Means for Solving the Problems) Therefore, the present invention is an oxygen concentration battery type sensor for measuring silicon concentration, in which stabilized or partially stabilized zirconia is used as a matrix, and a silicate compound is used as a second phase. The main point of the constitution is to use a solid electrolyte of a sintered body that is contained.

(B) Here, there are calcia, magnesia, and the like as stabilizers for the stabilized or partially stabilized zirconia (hereinafter referred to as zirconia, etc.) that constitutes the matrix of the sintered body that becomes the solid electrolyte. Can be used. Of course, it does not prevent the use of other stabilizers of zirconia, such as yttria and ceria, in combination with calcia and magnesia as long as the effects of the present invention are not impaired.
The same applies to small amounts of sintering aids and impurities that are usually contained.

Silicate compound refers to a silicate and stabilizer such as zirconia, that is, when calcia Dicalcium silicate (2CaO · _SiO 2), in the case of magnesia refers to forsterite (2MgO · SiO ₂₎ or the like.

(B) The solid electrolyte of the sintered body containing these zirconia and the like as a matrix and the silicate compound as the second phase is
It can be produced by mixing each material of zirconia, a stabilizer, silicon oxide, or a material for forming these oxides by firing, molding the material into an appropriate shape and firing.

At this time, the stabilizer is used in the total amount necessary for forming the silicate compound and stabilizing or partially stabilizing the zirconia.

It is also possible to use a part or a part or a combination of all of these raw materials by pre-reacting them. For example, each of the partially stabilized zirconia and the silicate compound may be reacted in advance and used.

(C) According to the experiment, the mixing ratio of the zirconia or the like of the matrix and the silicate compound in the solid electrolyte is good when the content of the silicate compound in the sintered body is 1.5 to 25% by weight, and 5 to 20% by weight is the best. Met.

Since this is used for the solid electrolyte by utilizing the oxygen ion conductivity of zirconia etc., the silicate compound that is not the oxygen ion conductor contained as the second phase impairs the oxygen ion conductivity of the sintered body used as the solid electrolyte for practical use. The content should be 25% by weight or less because it should not be lowered to the extent impossible. If the electron conductivity of the silicate compound is not sufficiently low with respect to the oxygen ion conductivity of zirconia or the like, the electromotive force of the oxygen concentration battery of the present invention will not be shown correctly, but there is no problem with these silicates.

Thus, it is preferable that the amount of these silicates in the matrix such as zirconia is as small as possible. However, if the amount is too small, the effect of the present invention of incorporating the silicate as the second phase is not recognized, so at least 1.5% by weight.
More is required.

(D) An oxygen concentration battery is constructed by using the thus obtained sintered body as a solid electrolyte.

The shape of the sintered body may be a shape used as a conventional solid electrolyte such as a rod shape, a disk shape, or a closed end tube.

A mixture of the solid electrolyte, a metal conventionally used in an oxygen sensor and an oxide of the metal, such as M
o + MoO ₂ , Cr + Cr ₂ O ₃ , Ni + NiO, Fe
The battery is constructed using a reference electrode such as + FeO.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

(Example-1) Magnesia powder and zirconia powder were added at 7 mol% and 93, respectively.
The mixture was mixed at a ratio of mol%, and this was heated at 1600 ° C. for 24 hours to obtain partially stabilized zirconia. This partially stabilized zirconia was crushed, and 10 wt% of separately synthesized forsterite powder was added and mixed. This mixed powder is compression molded into a rod shape and fired at 1750 ° C. to have a diameter of 6 mm and a length of 1
A 0 mm solid electrolyte was obtained. As shown in FIG. 1, this solid electrolyte 1 was replaced with an alumina tube 2 (inner diameter 7 mm, outer diameter 10 mm, length 60).
(0 mm) is fixed with refractory cement 3 and the inside of the alumina tube 2 is filled with a reference electrode 4 in which metallic molybdenum and molybdenum oxide are mixed, and then filled with refractory cement 5 and a lead wire 6 on the reference electrode side. The sensor of this example was constructed by using a molybdenum rod (diameter 3 mm) as the above.

In the experiment, the sensor of this example was immersed in hot metal containing 4.5% by weight of carbon. Iron was used for the lead wire on the hot metal side, and the electromotive force between this iron wire and the sensor-side molybdenum lead wire 6 was measured with a recorder. The measurement was carried out by changing the silicon concentration in the hot metal, and the measurement results showed a high correlation between the silicon concentration and the electromotive force as shown in FIG. 3, and the measurement accuracy was also very good. In addition, the response time varied somewhat, but was 10
The waveform was as good as 20 seconds, and the electromotive force also showed a stable waveform.

(Example-2) After mixing powders of calcium carbonate, zirconia and silica, the mixture was heated to 1550 ° C to obtain 6% by weight of stabilized zirconia.
A reaction product containing calcium silicate was obtained. The reaction product was crushed, molded into a tube with one end closed, and sintered at 1700 ° C. to obtain a sintered body having an inner diameter of 3.5 mm, an outer diameter of 5.5 mm and a length of 35 mm. The solid electrolyte 7 of this sintered body was filled with the reference electrode 8 having the configuration of Example 1, the lead wire 9 was projected, and the opening was sealed with the refractory cement 10 to form a sensor (second).
See figure). This was immersed in hot metal and the electromotive force was measured. The results are shown in FIG. According to this, as in Example-1, the correlation between the silicon concentration and the electromotive force was high, and the accuracy, response time, and electromotive force waveform were good.

(Other Examples) Experiments were conducted in the same manner as in Example 1 except that the amount of silicate was changed. The results are summarized in Table 1 below.

In addition, the reference electrode is changed to Mo-MoO ₂ and Cr-Cr ₂ O
_The experiment was conducted with No. ₃ , but the response time was slightly delayed, but a series of correlations were observed as in the above-mentioned Examples.

When the silicate amount was 1%, the waveform was good, but the correlation between the silicon concentration and the electromotive force was not obtained, and when the silicate amount was 40%, the electromotive force and response time were often unreadable due to poor waveform, and the reading was possible. Also in this case, no correlation was observed between the silicon concentration and the electromotive force.

(Effect of the invention) Therefore, according to the present invention, the effect of being able to measure the concentration of molten metal, particularly silicon in the hot metal, quickly and accurately is great, and it can be manufactured at low cost, and its industrial value is great. is there.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, FIG. 2 is a longitudinal sectional view of another example, and FIG. 3 is a correlation diagram of silicon concentration and electromotive force according to the embodiment. 1, 7: solid electrolyte, 4, 8: reference electrode, 6, 9: lead wire, 3, 5.10: refractory cement.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Yamada 1-10-1 Kikumoto-cho, Niihama-shi, Ehime Sumitomo Kagaku Kogyo Co., Ltd. Ehime Laboratory (72) Inventor, Kazumoto Tanaka 3 Kawabata-cho, Seto-shi, Aichi 30-chome Co., Ltd., Token Sangyo Co., Ltd. (56) References JP-A-62-102150 (JP, A)

Claims (2)

[Claims] 1. A sensor for measuring silicon concentration of an oxygen concentration battery type, comprising a solid electrolyte of a sintered body, comprising stabilized or partially stabilized zirconia as a matrix, and containing a silicate compound as a second phase. A sensor for measuring silicon concentration in molten metal, which is used. 2. The sensor according to claim 1, which is molded into a solid electrolyte in which the content of the silicate compound in the sintered body is 1.5 to 25% by weight.