JPH0750062B2 - Sensor for measuring silicon concentration in molten metal − - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sensor for measuring silicon concentration, which can measure the silicon concentration in a molten metal quickly and accurately. In particular, the present invention relates to an improvement of the sensor for measuring silicon concentration in molten metal described in JP-A-61-260156.

[Conventional technology]

In the melting and smelting of metals, it is often necessary to rapidly measure the concentration of silicon in the molten metal. For example, in iron and steel smelting, it is often necessary to quickly measure the silicon concentration in molten pig iron (hereinafter referred to as molten pig iron). In recent years, so-called hot metal pretreatment for dephosphorization and desulfurization of hot metal has been actively performed in the converter pretreatment. However, in this hot metal pretreatment, the reaction efficiency greatly varies depending on the silicon concentration in the hot metal. It is necessary to change the amount of the agent input according to the silicon concentration in the hot metal, and it is essential to understand the silicon concentration in the hot metal before and / or during the treatment. Conventionally, the instrumental analysis method widely used in the industry for detecting the silicon concentration has a problem that it takes a long time from the collection of the hot metal sample to the acquisition of the analysis result, which causes a delay in the process time.

As a solution to this problem, Japanese Patent Laid-Open No. 61-260156 discloses a tube having a solid electrolyte capable of transmitting oxygen ions, one end of which is fixed by refractory cement and the other end of which is closed.
Melting in combination with a potentiometer with a sensor consisting of a reference electrode that gives a constant oxygen potential at the measured temperature filled in the tube, and a solid auxiliary electrode containing silica distributed and coated on the outer surface of the tube An apparatus and method for measuring silicon concentration in metal are disclosed.

[Problems to be solved by the invention]

According to the method and apparatus described in JP-A-61-260156, the silicon concentration in the target molten metal can be instantaneously measured. However, even in a short time, various disturbances are likely to occur in the measurement environment in which the sensor is immersed in high temperature molten metal to measure the potential difference, and therefore the true potential difference between the molten metal and the reference electrode is generated. There was an inconvenience that it was difficult to detect. For example, when measuring the silicon concentration in the hot metal, the obtained potential difference measurement values include the true potential difference between the hot metal and the reference electrode, and the gas evolution due to the reaction of the refractory cement fixing the sensor at high temperature. And / or there is a disadvantage that a hunting phenomenon occurs due to noise added by the influence of reaction heat. In addition, depending on the manner of distribution coating of the sub-electrode on the outer surface of the solid electrolyte tube, the quasi-chemical equilibrium zone where the SiO ₂ activity is constant, which is the original role of the sub-electrode, is not formed. As a result, there was a drawback that the measured potential difference value fluctuated away from the correspondence with the silicon concentration in the molten metal. The silicon concentration obtained from the potential difference measurement value obtained under such a condition has a large error from the true silicon concentration, and thus the required measurement accuracy is often not satisfied.

In addition, if the sub-electrode containing SiO ₂ is not composed of an appropriate material, it may peel off when immersed in hot metal.

The present invention is intended to solve such problems,
An object of the present invention is to provide a silicon concentration measuring sensor capable of measuring the silicon concentration in molten metal quickly and accurately.

[Means for solving problems]

In principle, the present invention can be applied to the measurement of the silicon concentration regardless of the metal phase of the molten metal. However, the need for rapid measurement of silicon in the hot metal in steel smelting is particularly high, and the present invention By applying it, a great effect is expected. Therefore, in the following description, the present invention will be described by taking the measurement of the silicon concentration in the hot metal as an example.

The inventors of the present invention have conducted many measurements of the silicon concentration in the hot metal using the silicon sensor of the type described in JP-A-61-260156, but the potential difference between the reference electrode and the hot metal described above has been measured. The cause of hunting occurs in the gas and reaction heat generated by the reaction of the refractory cement that fixes the sensor (the sensor is fixed by fixing one end of the solid electrolyte tube) in the hot metal. Was judged. Then, in order to avoid the hunting phenomenon of the undesired potential difference, it was found that it is important to fill the solid electrolyte tube with the reference electrode at a distance of 10 mm or more, preferably 15 mm or more from the fixed end made of refractory cement. It was If the distance between the fixed end of the refractory cement and the reference electrode is substantially shorter than 10 mm, the difference in the measured potential difference will be significant.

When the silicon sensor of the type described in JP-A-61-260156 is dipped in hot metal containing silicon, Si + O is contained in the hot metal in the immediate vicinity of the sub-electrode as described in the publication.
₂ = chemical equilibrium generally represented by SiO ₂ is formed, since the band that chemical equilibrium is achieved formation is in contact with the secondary electrode of the solid containing SiO _2, activity of the SiO ₂ in the same band It is constant. Such a hot metal zone in which the activity of SiO ₂ is constant is called a quasi-chemical equilibrium zone in JP-A-61-260156. In order for the measured value of the potential difference between the hot metal and the reference electrode in contact with the hot metal via the solid electrolyte to correspond well to the silicon concentration in the hot metal, the above-mentioned quasi-chemical equilibrium at which the SiO ₂ activity is constant is established. The band must be formed stably. According to the present inventors, it has been found effective to increase the total perimeter of the auxiliary electrode for this purpose. Specifically, if the ratio of the total peripheral length of the sub-electrode to the effective outer surface area of the solid electrolyte is 1.0 or more, the potential difference reaches the equilibrium value in a short time, and the obtained measurement value is It was found that it corresponds to the silicon concentration with high accuracy.

Thus, the sensor for measuring silicon concentration in molten metal according to the present invention comprises a tube made of solid electrolyte capable of transmitting oxygen ions, one end of which is fixed by refractory cement and the other end of which is closed, and a measurement temperature filled in the tube. In a sensor for measuring silicon concentration in molten metal, which comprises a reference electrode which gives a constant oxygen potential in the tube, and a solid auxiliary electrode containing silica distributed and coated on the outer surface of the tube, It is characterized in that the tube is filled in the closed end side of the tube at a distance of 10 mm or more from the fixed end, and the ratio of the total peripheral length of the auxiliary electrode to the effective outer surface area of the solid electrolyte is 1.0 or more.

Here, as the material of the sub-electrode containing SiO ₂ , its composition is
ZrSiO ₄ : 10 to 90% by weight, Na ₂ O: 1 to 8% by weight, balance ZrO ₂
And unavoidable impurities are preferred. According to this material, the adhesiveness to the outer tube is kept good even in hot metal at high temperature, peeling and dropping can be prevented, and the obtained potential difference measurement value can correspond to the silicon concentration in hot metal with high accuracy.

Hereinafter, the silicon concentration measuring sensor according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a vertical cross-sectional view showing the main body of the sensor and its surrounding main attachments. Reference numeral 1 is a sub-electrode, 2 is a tube made of solid electrolyte, 3 is a reference electrode, and 4 is a solid electrolyte tube. Sealing member for sealing the filled reference electrode, 5
Is an electrode (made of molybdenum metal) on the molten metal side, and 6 is a thermocouple. For the potential difference for knowing the silicon concentration in the molten metal, set a potentiometer between the lead wire 7 from the reference electrode and the lead wire 8 from the electrode on the molten metal side.
measure. The sensor, thermocouple, and electrodes on the molten metal side are fixed by refractory cement 9, and the surroundings are further fixed and protected by a housing 10 and a fireproof cylinder 11.

Hereinafter, the case where the molten metal is hot metal will be described as an example.
The sub-electrode 1 is a member for forming a local quasi-chemical equilibrium zone in which the activity of SiO ₂ is constant in the hot metal, and is made of SiO ₂ or a solid oxide containing this. The term "solid" as used in this specification means that it is a solid at the measurement temperature. A preferred auxiliary electrode material is a two-phase mixture of ZrSiO ₄ and SiO ₂ obtained by mixing ZrSiO ₄ powder and SiO ₂ powder and firing. A more preferable auxiliary electrode material is ZrSi
O _4: 10 to 90 wt%, Na ₂ O: 1 to 8 wt%, a sintered material balance being ZrO ₂ and inevitable impurities.

As the material forming the solid electrolyte 2 capable of transmitting oxygen ions and the material forming the reference electrode 3 that gives a constant oxygen potential at the measurement temperature, the materials used in the conventional oxygen sensor can be used. A preferred solid electrolyte material is at least partially stabilized zirconium dioxide. NgO and CaO are known as stabilizers. The most preferred solid electrolyte material is about 7-9
Zirconium dioxide partially stabilized with mol% MgO. Suitable reference electrode materials include a mixture of Mo powder and MoO ₂ powder and a mixture of Cr powder and Cr ₂ O ₃ powder.

In the quasi-chemical equilibrium band, the hot metal electrode 5 and the reference electrode 3
The potential difference caused by the difference in oxygen potential between
Since it corresponds to the silicon concentration in the hot metal, accurate detection of this potential difference leads to accurate measurement of the silicon concentration. The present inventors have shown in FIG. 2 that the fixed end of the solid electrolyte tube made of refractory cement (minimum level of refractory cement) and the filling area of the reference electrode in the solid electrolyte tube (highest level of filled reference electrode). We made a number of prototypes of sensors with different distances (Dmm) between and, and used them for potentiometric measurements. Results are shown in FIG. As can be seen from the comparative example in the figure, when the distance D between the filling area of the reference electrode in the solid electrolyte tube and the fixed end of the solid electrolyte tube made of refractory cement is substantially smaller than 10 mm, the hunting phenomenon appears prominently. ， It becomes difficult to measure the potential difference accurately. On the other hand, as can be seen from the example of the present invention in FIG. 3, as the distance D of the reference pole from the fixed end is increased, the hunting phenomenon is significantly reduced and D ≧ 10 mm.
Then, hunting was hardly recognized. Regarding the measurement accuracy of the silicon concentration in the hot metal, a satisfactory level of accuracy was obtained at D = 10 mm, but if D ≧ 15 mm, the measurement accuracy can be further improved.

Sub-electrode 1 covering the outer surface of the solid electrolyte tube 2 with a distribution ratio
This will be described with reference to FIGS. 4 and 5. 4 and 5 show an example in which the sub-electrode 1 is distributed and coated on the outer surface of the solid electrolyte tube 2 in spots. The coating form of the sub-electrode 1 is not limited to spots, but horizontal stripes as long as the outer surface of the solid electrolyte tube 2 can be advantageously present in the quasi-chemical equilibrium zone formed around the sub-electrode 1.
It can be vertical stripes, grids or other forms. The sub-electrode 1 is usually distributedly coated on the outer surface of the solid electrolyte tube 2 to a level corresponding to the maximum level of the reference electrode 3 filled in the solid electrolyte tube 2.

A parameter, which is the circumference ratio, is introduced as an index showing the mode of distributed coating of the sub-electrode. The circumference ratio is the ratio (mm ^-1 ) of the total perimeter (mm) of the sub-electrode to the effective external surface area (mm ₂ ) of the solid electrolyte. The effective external surface area of the solid electrolyte is It is the outer surface area (excluding the area occupied by the sub-electrode) of the solid electrolyte tube below the coated level, that is, in the area filled with the reference electrode. This circumference ratio is
As shown in the figure, the sensor in which the outer surface of the solid electrolyte is covered with a large number of small-sized sub-electrodes is large, and as shown in Fig. 5, the sensor in which the outer surface of the solid electrolyte is covered with a small number of large-sized sub-electrodes. Then it's small. FIG. 6 shows the stability of the potential difference waveform and a typical potential difference waveform by the sensor in which only the circumference ratio is variously changed. According to the figure, when the circumference ratio is set to 1.0 (mm ⁻¹ ) or more according to the present invention, the potential difference waveform reaches the equilibrium value in a short time and is very stable thereafter. On the other hand, in the comparative example in which the circumference ratio is less than 1.0, the potential difference hardly reaches the equilibrium value, and it can be seen that the detected value lacks accuracy even after long-time measurement.

FIG. 7 shows the potential difference (EMF) and the silicon concentration in the hot metal detected by the sensors of the invention examples No. 1 to 3 of FIG. 6 and the sensors of the comparative examples No. 4 to 7 of FIG. Show correlation. According to the figure, in the sensor of the comparative example whose circumference ratio is less than 1.0, the correlation between the potential difference and the circumference ratio concentration is weak, but in the sensor of the example of the present invention in which the circumference ratio is 1.0 or more, the measured potential difference is It can be seen that it accurately corresponds to the silicon concentration of the hot metal.

〔Example〕

Example 1 A solid electrolyte consisting of partially stabilized zirconium dioxide containing 9 mol% of MgO was used as a sub-electrode on the outer surface of a closed tube with an outer diameter of 4.5 mm, an inner diameter of 3.0 mm and a length of 30 mm.
A mixture of ZrSiO ₄ powder and ZrO ₂ powder mixed in a weight ratio of 3: 2, well kneaded with water, and spotted (diameter about 1 mm, circumference ratio 1.1 mm ^-1 ).
The composition was applied to a substrate, dried at 100 ° C, and baked at a temperature of 1400 ° C for about 10 hours. Then, inside the solid electrolyte tube, Mo powder and MoO mixed at a weight ratio of 4: 1 were used as reference electrodes.
The mixture with the _two powders was filled at a distance of 15 mm from the fixed end of the tube, 0.8 mm Mo wire was inserted as a lead wire, and sealed and fixed with Al ₂ O ₃ cement. The sensor thus prepared was fixed with refractory cement together with the thermocouple and the electrode on the hot metal side made of Mo, and was further protected by a refractory tube.

The assembly thus created is immersed in hot metal at 1380 ° C with a C concentration of 4.3% by weight for about 40 seconds, the potential difference is measured, and a sample of the hot metal is taken to determine the silicon concentration in the hot metal by instrumental analysis. analyzed.

The relationship between the obtained potential difference and the silicon concentration is shown in FIG. This figure shows that when the sensor of this example is used, the potential difference sensitively corresponds to the change in the silicon concentration, and the correlation between the silicon concentration in the hot metal and the potential difference is very strong. The measurement error of the silicon concentration remains within 0.02%, and this level sufficiently satisfies the measurement accuracy required for the rapid measurement of the silicon concentration at the steelmaking site.

Example 2 Example 1 was repeated except that each of the compositions shown in Table 1 was used as the auxiliary electrode material. When a sensor made of each sub-electrode material was immersed in hot metal, some spots of the sub-electrode were peeled off and those were not peeled off at all, and the results are also shown in Table 1. Also, FIG. 9 shows the relationship between the potential difference obtained by each sensor and the silicon concentration.

From the results shown in Table 1, when a ZrSiO ₄ composition of 10 to 90% by weight and Na ₂ O composition of 1 to 8% by weight was used as the auxiliary electrode material, peeling of the auxiliary electrode did not occur at all. I understand.
On the other hand, ZrSiO ₄ in the auxiliary electrode is less than 10% by weight or 90% by weight.
If it exceeds 1% by weight, or Na ₂ O in the auxiliary electrode is 1% by weight
If the amount is less than 8% or more than 8% by weight, peeling occurs.

Further, from FIG. 9, the correlation between the potential difference and the silicon concentration in the hot metal is weak in the sensor of the comparative example in which peeling of the sub-electrode occurred, but in the sensor in which peeling did not occur at all, the measured potential difference was the silicon concentration in the hot metal. It can be seen that it corresponds to.

Example 3 Solid electrolyte tube made of partially stabilized ZrO ₂ containing 9 mol% MgO (outer diameter 4.5 mm, inner diameter 3.0 mm, length 30 mm)
On the outer surface of ZrSiO ₄ : 50 wt%, Na ₂ O: 5 wt%, ZrO ₂ : 45
After mixing the mixed powder consisting of wt% well with water, apply it in spots (diameter about 1mm, circumference ratio 1.0mm ^-1 ), dry at 100 ℃, and at temperature of 1400 ℃ for about 10 hours. It was fired to form a sub electrode. . Then, inside the solid electrolyte tube, Mo powder and M mixed in a weight ratio of 4: 1 were used as a reference electrode.
A mixture with oO ₂ powder was filled at a distance of 15 mm from the fixed end of the tube, a 0.8 mm Mo wire was inserted as a lead wire, and sealed and fixed with Al ₂ O ₃ cement. The sensor thus prepared was fixed with refractory cement together with the thermocouple and the electrode on the hot metal side made of Mo, and was further protected by a refractory tube.

The C concentration of the assembly thus created is 4.2
The sample was dipped in hot metal at 1400 ℃ for 30 seconds, and the potential difference was measured, and a sample of hot metal was sampled to analyze the silicon concentration in the hot metal by instrumental analysis.

The relationship between the obtained potential difference and the silicon concentration is shown in FIG. From the results of FIG. 10, when the sensor of this example is used,
The potential difference sensitively responds to changes in the silicon concentration, and the correlation between the silicon concentration in the hot metal and the potential difference appears very strongly, indicating that the measurement error of the silicon concentration is extremely small.

〔The invention's effect〕

When the silicon concentration in the molten metal is measured using the silicon concentration measuring sensor according to the present invention, a stable equilibrium value is obtained for the potential difference for deriving the silicon concentration in the molten metal in the short time, and the potential difference in the molten metal obtained from the measured potential difference is obtained. The silicon concentration is extremely accurate. In addition, if the composition of the sub-electrode is adjusted to an appropriate value, high-precision measurement is possible without the sub-electrode peeling off from the surface of the solid electrolyte even when immersed in high temperature hot metal. Thus, it is possible to prevent hunting phenomenon that may occur at the time of measuring the potential difference and the occurrence of defects such as an unstable waveform in which the equilibrium value cannot be obtained, and to perform stable measurement. ∙ Satisfy the measurement accuracy required at steelmaking sites.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a sensor according to the present invention and a main attachment member around the sensor, FIG. 2 is a longitudinal sectional view of a sensor according to the present invention, and FIG. 3 is a potential difference waveform diagram by the sensors of the present invention example and a comparative example. FIG. 4 is a perspective view showing an example of the covering form of the sub-electrode in the sensor of the present invention, and FIG. 5 is a perspective view showing an example of the covering form of the sub-electrode in the sensor of the comparative example.
FIG. 6 is a diagram showing the relationship between the circumferential length ratio and the potential difference waveform of the sensors of the present invention and comparative examples, and FIG. 7 shows the strength of the correlation between the measured potential difference and the silicon concentration by the sensors of the present invention and comparative examples. FIG. 8 is a graph showing the correlation between the potential difference measurement value by the sensor described in the embodiment of the present invention and the silicon concentration, and FIG. 9 is the potential difference measurement value by the sensor of another example of the present invention and the silicon concentration. FIG. 10 is a graph showing the strength of the correlation of the above, and FIG. 10 is a graph showing the correlation between the measured value of the potential difference by the sensors of other examples of the present invention and the comparative example and the silicon concentration. 1 ... Sub-electrode, 2 ... Solid electrolyte, 3 ... Reference electrode, 4 ... Seal member, 5 ... Molten metal side electrode, 6 ... Thermocouple, 7 ... Reference electrode lead wire, 8 ... … Leads of electrodes on the molten metal side, 9 ……
Refractory cement, 10 …… Housing, 11 …… Fireproof cylinder.

Claims (2)

[Claims] 1. A tube comprising a solid electrolyte capable of transmitting oxygen ions, one end of which is fixed by refractory cement and the other end of which is closed, and a reference which is filled in the tube and gives a constant oxygen potential at a measurement temperature. In a sensor for measuring silicon concentration in molten metal, comprising a pole and a solid sub-electrode containing silica, which is distributedly coated on the outer surface of the tube, the reference electrode is 10 mm from the fixed end of the tube. Filling the closed tube end side of the tube apart from each other, and the ratio of the total peripheral length of the auxiliary electrode to the effective outer surface area of the solid electrolyte is 1.
A sensor for measuring silicon concentration in a molten metal, which is set to 0 or more. 2. A sub-electrodes, ZrSiO _4: 10 to 90 wt%, Na ₂ O: 1
The sensor according to claim 1, wherein the sensor comprises ˜8% by weight, the balance being ZrO ₂ and inevitable impurities.