JPH0762663B2 - Sensor for measuring Cr concentration in molten metal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a Cr concentration measuring sensor capable of accurately measuring the Cr concentration in a molten metal in real time. Particularly, the present invention relates to an improvement of the chromium sensor in the apparatus for measuring the metal concentration in molten metal described in Japanese Patent Application Laid-Open No. 61-260155.

[Conventional technology]

In the melting and refining of metals, it is often necessary to quickly measure the Cr concentration in the molten metal. For example, in iron and steel smelting, Cr in molten steel must be strictly adjusted as one of the elements that affect the properties of steel, and its concentration must be adjusted strictly. Understanding the Cr concentration is essential. Conventionally, the instrumental analysis method widely used in the industry for detecting this Cr concentration is
It took a long time from collecting the molten steel sample to obtaining the analysis result, and there was a problem that the process time was delayed.

As a solution to this problem, Japanese Unexamined Patent Publication No. 61-260155 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, and a measurement temperature filled in the tube. Measurement of Cr concentration in molten metal by combining a sensor consisting of a reference electrode giving a constant oxygen potential and a solid sub-electrode made of Cr ₂ O ₃ distributed on the outer surface of the tube with a potentiometer An apparatus and a measuring method are disclosed.

[Problems to be solved by the invention]

According to the method and apparatus described in JP-A-61-260155, the Cr concentration in the target molten metal can be measured in principle. However, when the sub-electrode is composed of Cr ₂ O ₃ alone, it easily peels off when immersed in molten metal, and when peeled off, the Cr ₂ O ₃ activity, which is the role of the sub-electrode, is observed. The quasi-chemical equilibrium zone where the amount is constant is not formed, and as a result, the obtained potentiometric value is Cr in the molten metal.
There was a drawback that it fluctuated away from the correspondence with the concentration. The Cr concentration obtained from the potential difference measurement value obtained under such a condition has a large error from the true Cr concentration, and the required measurement accuracy is not satisfied.

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

[Means for solving problems]

The gist of the present invention to achieve the above object is a tube made of a solid electrolyte capable of transmitting oxygen ions, the tube having one end fixed by refractory cement and the other end closed: For measuring Cr concentration in molten metal, consisting of: a reference electrode filled in the tube, which gives a constant oxygen potential at a measurement temperature; and a solid sub-electrode containing Cr ₂ O ₃ provided on the outer surface of the tube. In the sensor, the auxiliary electrode is Cr ₂ O ₃ ; 5 to 50% by weight, Z
This is a sensor for measuring the Cr concentration in molten metal, characterized by comprising rSiO ₄ ; 5 to 85 wt%, Na ₂ O; 1 to 8 wt%, and the balance ZrO ₂ and inevitable impurities.

The sensor of the present invention can be applied to the measurement of Cr concentration in principle regardless of the metal phase of the molten metal, but there is a need for rapid measurement of Cr in molten steel (including hot metal) particularly in iron and steel smelting. It is high, and a great effect is expected by applying the present invention. Therefore, in the following description, the present invention will be described by taking the measurement of the Cr concentration in molten steel (including molten pig iron) as an example.

Wherein, in the mold of Cr sensor described in JP-A-61-260155, the sub electrode used is generally expressed as 2 C r + 3 O = Cr 2 O 3 on the periphery of this sub-electrode when immersed into the molten steel It is composed of a solid oxide of Cr (that is, Cr ₂ O ₃ ) that can establish a chemical equilibrium. The present inventors have carried out the measurement of the Cr concentration in molten steel using the Cr sensor of the type described in JP-A-61-260155, but
As described above, in the sub-electrode composed of Cr ₂ O ₃ alone, when immersed in molten steel, it immediately exfoliates and falls off, resulting in what is called the “quasi-chemical equilibrium zone” in the publication. We found that the molten steel zone where the activity of Cr ₂ O ₃ was constant was not formed near the surface of the Cr sensor, and the obtained potential difference value fluctuated away from the correspondence with the Cr concentration in the molten steel.

Therefore, this undesirable to avoid delamination of the sub-electrodes, as a result of the sub-electrode material of various studies, the material of the sub-electrode containing Cr ₂ O _3, the composition of Cr ₂ O _3; 5~50 wt %, Zr
It was found that SiO ₄ ; 5 to 85% by weight, Na ₂ O; 1 to 8% by weight, and the balance being ZrO ₂ and inevitable impurities are preferable. With this material, good adhesion to the solid electrolyte tube can be maintained even in molten steel at high temperature, peeling and falling can be prevented, and the obtained potentiometric value is the Cr content in molten steel.
It is possible to accurately correspond to the concentration.

Referring to the attached drawings, FIG. 1 is a vertical cross-sectional view showing a main body of a sensor and its surroundings, reference numeral 1 is a sub-electrode, 2 is a tube made of solid electrolyte, 3 is a reference electrode, 4 is a sealing member for sealing the reference electrode filled in the solid electrolyte tube, 5 is an electrode (molybdenum) on the molten metal side, and 6 is a thermocouple. The potential difference for knowing the Cr concentration in the molten metal is measured by setting a potentiometer between the lead wire 7 from the reference electrode and the lead wire 8 from the electrode on the molten metal side. 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.

Taking the case where the molten steel metal is molten steel as an example, the sub-electrode 1 is a member for forming a local quasi-chemical equilibrium zone in which the activity of Cr ₂ O ₃ is constant in the molten steel. , C
It consists of a solid oxide containing r ₂ O ₃ . The solid in the present invention means a solid at the measurement temperature.
A preferable auxiliary electrode material is a fired material composed of Cr ₂ O ₃ ; 5 to 50% by weight, ZrSiO ₄ ; 5 to 85% by weight, Na ₂ O; 1 to 8% by weight, and the balance 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. The preferred solid electrolyte material is at least partially stabilized zirconium dioxide. MgO and CaO are known as stabilizers. The most preferred solid electrolyte is zirconium dioxide partially stabilized with about 7-9 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.
The filling range of the reference electrode in the solid electrolyte tube is as follows.
As shown in Fig. 2, the distance between the fixed end of the solid electrolyte tube made of refractory cement (the lowest end of the refractory cement) and the filling area of the reference electrode in the fixed electrolyte tube (the highest end of the filled reference electrode). (Dmm) is preferably 10 mm or more.

FIG. 3 shows an example in which the sub-electrode 1 is distributed and coated on the outer surface of the solid electrolyte tube 2 in spots. As long as the quasi-chemical equilibrium zone formed around the sub-electrode 1 can exist on the outer surface of the solid electrolyte tube 2, the coating form of the sub-electrode 1 is not limited to spots, but horizontal stripes, vertical stripes, grids or It can be in other forms. The sub-electrode 1 is preferably distributed and coated on the outer surface of the solid electrolyte tube 2 up to the end corresponding to the highest end of the reference electrode 3 filled in the solid electrolyte tube 2. The form of the distributed coating of the sub-electrode is the total of the perimeter of the sub-electrode (mm) and the effective external surface area of the solid electrolyte (m
m ² ) ratio (this is called the circumference ratio, the unit is mm ^-1 )
Is preferably 1.0 mm ^-1 or more.

The Cr concentration measuring sensor of the present invention described above has good adhesion between the sub-electrode and the solid electrolyte tube, and the obtained potential difference measurement value can accurately correspond to the Cr concentration in the molten steel.

[Example 1] Outer diameter 4.5 mm, inner diameter 3.0 mm, and length of a solid electrolyte composed of partially stabilized zirconium dioxide containing 9 mol% of MgO
On the outer surface of a 30 mm closed-ended tube, the auxiliary electrodes of each composition shown in Table 1 were spotted (diameter about 1 mm, circumference ratio 1.
1 mm ^-1 ), dried at 100 ℃ and baked at a temperature of 1400 ℃ for about 10 hours. Next, inside the solid electrolyte tube, Mo powder and M mixed in a weight ratio of 4: 1 were used as a reference electrode.
The 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 molten steel side composed of Mo in the state shown in Fig. 1, and was further protected by a fireproof cylinder.

The assembly prepared in this way was immersed in molten steel at 1650 ° C with a C concentration of 0.05% by weight for about 20 seconds to measure the potential difference, and a sample of the molten steel was taken to analyze the Cr concentration in the molten steel by instrumental analysis. analyzed. When the sensor consisting of each sub-electrode material was immersed in molten steel, some of the spots on the sub-electrode were peeled off and those that were not peeled off at all were examined.
The results are also shown in Table 1. Further, FIG. 4 shows the relationship between the potential difference obtained by each sensor and the Cr concentration.

From the results shown in Table 1, when the auxiliary electrode material having a composition of 5 to 50% by weight of Cr ₂ O ₃ , 5 to 85% by weight of ZrSiO _{4 and} 1 to 8% by weight of Na ₂ O is used, It can be seen that peeling of the sub-electrode did not occur at all. On the other hand, when Cr ₂ O ₃ in the auxiliary electrode is less than 5% by weight or more than 50% by weight, or ZrSiO ₄ in the auxiliary electrode is less than 5% by weight or more than 85% by weight, and further in the auxiliary electrode. When the Na ₂ O content is less than 1% by weight or exceeds 8% by weight, peeling occurs in all cases.

In addition, from Fig. 4, the correlation between the potential difference and the Cr concentration in the molten steel is weak in the sensor of the comparative example in which peeling of the auxiliary electrode occurred, but in the sensor in which peeling did not occur at all, the measured potential difference was the Cr concentration in the molten steel. It can be seen that they correspond accurately.

Example 2 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 the, mixed powder of Cr ₂ O ₃ ; 20 wt%, ZrSiO ₄ ; 30 wt%, Na ₂ O; 6 wt%, ZrO ₂ ; 44 wt% was well kneaded with water and spotted. (Diameter about 1 mm, circumference ratio 1.0 mm ^-1 ) was applied, dried at 100 ° C, and baked at a temperature of 1400 ° C for about 10 hours to form a sub-electrode. Next, inside the solid electrolyte tube, Mo mixed at a weight ratio of 4: 1 was used as a reference electrode.
A mixture of powder and MoO 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 with Al ₂ O ₃ cement. As shown in Fig. 1, the sensor thus prepared was fixed with refractory cement together with a thermocouple and an electrode on the molten steel side made of Mo, and was further protected by a fireproof cylinder.

The assembly thus created is immersed in molten steel at 1650 ° C for 20 seconds with a C concentration of 0.05% by weight, the potential difference is measured, and a sample of molten steel is sampled and analyzed by instrumentation to determine the Cr concentration in the molten steel. Was analyzed.

The relationship between the obtained potential difference and the Cr concentration is shown in FIG. From the results of FIG. 5, when the sensor of this example is used, the potential difference is
It is sensitive to changes in the Cr concentration, and the correlation between the Cr concentration in molten steel and the potential difference appears very strongly, indicating that the measurement error of the Cr concentration is extremely small.

[Example 3] The same sensor as in Example 2 was prepared except that the outer surface of the solid electrolyte tube was entirely covered with the sub-electrode, and the same measurement was performed using the same assembly as in Example 2.
No peeling of the auxiliary electrode was observed, and stable measurement was possible. Further, the obtained potential difference sensitively corresponds to the change of the Cr concentration similarly to the result of FIG. 5 of Example 2, and the highly accurate measurement was possible.

〔The invention's effect〕

When the Cr concentration in the molten metal is measured using the Cr concentration measuring sensor according to the present invention, the sub-electrode does not peel off from the solid electrolyte surface even when immersed in high temperature molten steel, and stable measurement can be performed. As a result, the Cr concentration in the derived molten metal is extremely reliable and fully satisfies the measurement accuracy required at the smelting site.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a sensor according to the present invention and a main accessory member around the sensor, FIG. 2 is a vertical cross-sectional view of the sensor according to the present invention, and FIG. 3 is an example of a coating form of a sub-electrode in the sensor of the present invention. FIG. 4 is a graph showing the correlation between the potential difference measured by the sensor of the present invention and the comparative example and the Cr concentration, and FIG. 5 is the potential difference measured by the sensor of the other example of the present invention and the Cr concentration. It is a graph which shows correlation. 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 (1)

[Claims] 1. A tube made of a solid electrolyte capable of transmitting oxygen ions, the tube having one end fixed by refractory cement and the other end closed: a constant oxygen at the measured temperature filled in the tube. Reference electrode that gives potential: Cr provided on the outer surface of the tube
_{In the} sensor for measuring the Cr concentration in the molten metal, which comprises a solid sub-electrode containing ₂ O ₃ , the sub-electrode is Cr ₂ O ₃ ;
% By weight, ZrSiO ₄ ; 5 to 85% by weight, Na ₂ O; 1 to 8% by weight, the balance
A sensor for measuring the Cr concentration in molten metal, characterized by comprising ZrO ₂ and inevitable impurities.