JPH0690175B2 - Method for measuring phosphorus concentration in hot metal - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for rapidly measuring the phosphorus concentration in hot metal.

Prior Art Hot metal from blast furnaces usually contains 0.05 to 0.2 weight percent phosphorus. Prior to refining the above hot metal in a converter, it is usually subjected to a preliminary dephosphorization treatment. Although various fluxes are used for preliminary dephosphorization, the required amount of flux varies depending on the phosphorus concentration in the hot metal and the target final phosphorus concentration. Therefore, in order to properly determine the required amount of flux, it is necessary to know the phosphorus concentration in the hot metal before and during the dephosphorization treatment. Usually, hot metal is sampled and analyzed by a method such as cant back to determine the phosphorus concentration. However, in such a method, it takes 3 to 10 minutes until the analysis result is obtained.

On the other hand, about 10 tons per minute are fired from the blast furnace, and the dephosphorization treatment cannot be performed efficiently if the dephosphorization treatment is performed after waiting for the analysis result. Therefore, at present, preliminary phosphorus removal is performed by adding a flux for dephosphorization to the hot metal while the phosphorus concentration in the hot metal is unknown. In this way,
As a matter of course, the amount of flux used becomes excessive in some cases and in some cases less than necessary. Therefore, the phosphorus concentration in the hot metal after the dephosphorization treatment is not stable.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In view of such circumstances, the present inventors have aimed to develop a phosphorus sensor capable of quickly measuring the phosphorus concentration in hot metal, and have conducted repeated research and applied the principle of a concentration battery, We have found a method to quickly measure the phosphorus concentration in hot metal.

Means for Solving the Problems The gist of the present invention is as follows.

(1) Solid ZrO ₂ , solid CaO.4ZrO ₂ (Ca of cubic structure)
O-ZrO ₂ type solid solution), and solid 3CaO / P ₂ O ₅ coexistent, and an electrolyte in which the activity of P ₂ O ₅ is determined only by temperature is used. A substance with a known chemical potential of phosphorus or oxygen is used for the other electrode, and the other electrode forms a phosphorus concentration battery as hot metal with an unknown phosphorus concentration, and the phosphorus concentration in the hot metal is measured by measuring the potential difference between the electrodes. A method for measuring phosphorus concentration in hot metal, comprising:

₍₂₎ CaO · ZrO 2 solid, be one solid CaO · 4ZrO ₂ (cubic CaO-ZrO ₂ solid solution structure), and solid 3CaO · P ₂ O ₅ of coexisting, P ₂ O ₅ An electrolyte whose activity is determined only by the temperature is used, one electrode of this electrolyte is a substance with a known chemical potential of phosphorus or oxygen, and the other electrode is a phosphorus-concentrated battery as hot metal with an unknown phosphorus concentration. And measuring the potential difference between the electrodes to measure the phosphorus concentration in the hot metal, the method for measuring the phosphorus concentration in hot metal.

(3) CaO · ZrO ₂ solid, there is a solid 4CaO · P ₂ O _5, and solid 3CaO · P ₂ O ₅ of coexisting, as activity of P ₂ O ₅ is determined only by the temperature The electrolyte used is a material having a known chemical potential of phosphorus or oxygen for one electrode of this electrolyte, and the other electrode forms a phosphorus concentration cell as hot metal with an unknown phosphorus concentration, and the potential difference between the electrodes is A method for measuring phosphorus concentration in hot metal, which comprises measuring the phosphorus concentration in the hot metal by measuring.

(4) Solid ZrO ₂ , solid BaO · ZrO ₂ , and solid 3Ba
O.P ₂ O ₅ coexists, and an electrolyte in which the activity of P ₂ O ₅ is determined only by temperature is used.One electrode of this electrolyte has a known chemical potential of phosphorus or oxygen. Using a substance, the other electrode forms a phosphorus concentration cell as hot metal with an unknown phosphorus concentration, and the phosphorus concentration in the hot metal is measured by measuring the potential difference between the electrodes, measuring the phosphorus concentration in the hot metal. Method.

Action The present invention will be described in detail below.

First, the principle of the phosphorus sensor for hot metal of the present invention will be described.

For example, in the case of an oxygen concentration battery used for measuring the oxygen concentration in molten steel, the electrolyte zirconia is an oxygen ion conductor. Therefore, if there is an electrolyte that becomes a phosphorus ion conductor, it can be used to make a phosphorus sensor,
There is no suitable conductor for phosphorus ions. Therefore, the present inventors invented a method of measuring the phosphorus concentration in the hot metal by converting the activity of phosphorus in the hot metal into oxygen potential and measuring it.

That is, when a substance having a known chemical potential of phosphorus is brought into contact with the hot metal to be measured through the electrolyte, a potential difference corresponding to the chemical potential difference of phosphorus occurs. If the activity of P ₂ O ₅ in the electrolyte is determined only by the temperature (hereinafter, such an electrolyte is referred to as the electrolyte or a three-phase coexisting electrolyte), this potential difference The phosphorus concentration in the hot metal can be known by measuring the temperature.

That is, at the interface between the electrolyte and the hot metal (interface I),
At the interface (interface II) of the substance where the reaction of formula (1) reaches equilibrium and the chemical potentials of the electrolyte and phosphorus are known, (2)
When the reaction of the equation reaches the equilibrium, 2P (interface I) + (5/2) O ₂ (interface I) = P ₂ O ₅ (interface I) (1) 2P (interface II) + ( 5/2) O ₂ (interface II) = P ₂ O ₅ (interface II) (2) The activity of P ₂ O _{5 in} the electrolyte shows a constant value at a constant temperature. Takes the value shown in equation (3).

E: Potential difference between both electrodes R: Gas constant T: Temperature F: Faraday constant Po ₂ : Oxygen partial pressure, (I) and (II) correspond to interface I and interface II, respectively.

Here, the chemical equilibrium constant K of the equations (1) and (2) is represented by the equations (4) and (5), respectively.

ap205: P ₂ O ₅ activity ap: Phosphorus activity Since K in the equations (4) and (5) is the same, And the P ₂ O ₅ activity is constant in the electrolyte, ap205 (I) = ap205 (II), so equation (6) becomes (7)
It becomes like a formula.

From equations (3) and (7) In the equation (8), since ap (II) is known, ap (I) can be obtained by measuring the potential difference E and the temperature T between both electrodes. ap
Since (I) directly corresponds to the phosphorus concentration in the hot metal, the phosphorus concentration in the hot metal can be obtained from this.

On the other hand, when the activity of P ₂ O ₅ does not show a constant value at a constant temperature, an unspecified diffusion potential occurs due to the chemical potential difference between P ₂ O ₅ at interface I and interface II. The phosphorus concentration in the hot metal cannot be determined even by measuring.

I searched for a substance that guarantees a constant P ₂ O ₅ activity, but I could not find it easily. Therefore, the present inventors have found a way to solve this difficult problem by utilizing the phase rule shown in the expression (9).

f = C + 1−φ (9) f: degree of freedom C: number of components φ: number of phases (excluding gas phase) For example, in the case of a two-component equilibrium state, C = 2, so the degree of freedom f In order to set = 1, φ = 2, that is, a two-phase coexistence state is set. Similarly, in the case of a three-component system, the degree of freedom f
In order to set = 1, φ = 3, that is, a three-phase coexistence state is set. Similarly, in the case of a four-component system, the degree of freedom f =
To obtain 1, φ = 4, that is, a four-phase coexistence state is set.

Since the purpose is to measure the phosphorus concentration in the hot metal, it suffices to find a substance that can stably maintain the state of freedom f = 1 at the hot metal temperature (1200 ° C to 1600 ° C). The present inventors have conducted experiments and studies on various substances,
We have found a method of obtaining the target electrolyte by coexisting three kinds of solid phases.

That is, it was found that, when the following four pairs were selected as the solid phase, these systems had a degree of freedom f = 1 in the coexistence of three components and three phases, and the activity of P ₂ O ₅ was determined only by the temperature.

ZrO ₂ , CaO ・ 4ZrO ₂ (cubic structure CaO-ZrO ₂ system solid solution), 3CaO ・ P ₂ O ₅ CaO ・ ZrO ₂ , CaO ・ 4ZrO ₂ (cubic structure CaO-ZrO ₂ system solid solution), 3CaO ・a substance _{P 2 O 5 CaO · ZrO 2} , 4CaO · P 2 O 5, 3CaO · P 2 O 5 ZrO 2, BaO · ZrO 2, 3BaO · P 2 O 5 3 kinds of solid phase coexist in a uniformly dispersed state In order to obtain the above, the reagents may be prepared in advance so as to have the compositions shown in FIG. 1 for the systems (1) and (2) in the systems (2).

For example, in the case of the above system, solid powder of zirconium oxide, calcium carbonate and phosphate is used. Here, the phosphoric acid salt is preferably a secondary ammonium salt of phosphoric acid (NH ₄ ) ₂ HPO ₄ . The mixing ratio is CO ₂ in calcium carbonate, and H ₂ O in phosphoric acid secondary ammonium salt (HN ₄ ) ₂ HPO ₄ is gasified during firing. Therefore, the ratio of ZrO ₂ : CaO: P ₂ O _{5 is} the highest. You can choose the one that falls within the shaded area in Figure 1.

If these solid powders are mixed, pressure molded and fired,
Target ZrO ₂ , CaO ・ 4ZrO ₂ (CaO-ZrO _{2 with} cubic structure)
An electrolyte in which the three phases (solid solution) and 3CaO · P ₂ O ₅ coexist as solids is obtained.

For the systems (1) to (3), a three-phase coexisting type solid electrolyte can be obtained in the same manner.

Next, a phosphorus sensor used for carrying out the method of the present invention and a galvanic cell which is a main part of the phosphorus sensor will be described.

3A and 3B show an example of the structure of the galvanic battery 8. In the case of (a), 1 is a three-phase coexisting type solid electrolyte formed at the tip of the holding tube 2 having an open tip (the side in contact with the hot metal when measuring the phosphorus concentration in the hot metal). The material of the holding tube 2 may be any material as long as it is a refractory pure material. As examples, alumina, magnesia, silica,
Examples include zirconia. Further, in FIG. 3A, the shape of the holding tube 2 may be any shape as long as it can hold the solid electrolyte. Reference numeral 3 denotes a substance (regardless of gas, liquid or solid) of which the chemical potential of phosphorus filled on the solid electrolyte 1 of the holding tube 2 is known. Hereinafter, this filling material is referred to as a reference electrode. Here, examples of the substance having a known chemical potential of phosphorus include a solid or liquid metal or alloy containing phosphorus. The phosphorus concentration in this metal or alloy is determined in advance by analysis. It is known that if the concentration of phosphorus in the molten metal or alloy is known, the chemical potential of phosphorus can be determined based on this.

Instead of a substance with a known chemical potential of phosphorus, a substance with a known chemical potential of oxygen can be used. For example, air can be used. When air is used, the reaction of equation (10) reaches equilibrium between the reference electrode and the three-phase coexisting electrolyte.

2P + (5/2) O ₂ (air) = P ₂ O ₅ (the electrolyte) ・ ・ ・ (1
0) Since the P ₂ O ₅ activity of the electrolyte is kept constant as described above, if the chemical potential of oxygen is known,
As a result, the chemical potential of phosphorus is the same as known. Therefore, a mixture of metallic chromium and chromium oxide, a mixture of metallic molybdenum and molybdenum oxide, or the like, which is known as a substance having a known chemical potential of oxygen, can be used. Reference numeral 4 is a lead wire that is inserted into the reference electrode 3 and fixed with refractory cement 5.

In the case of FIG. 3 (B), 1 is a molded three-phase coexisting solid electrolyte. If the composition is such that the three-phase coexisting solid electrolyte can be easily molded, the inside of the molded three-phase coexisting solid electrolyte 1 is used as a reference without using the holding tube 2 used in (a). A galvanic cell can be produced by encapsulating the electrode 3 and the lead wire 4 and fixing them with refractory cement 5.

FIG. 4 shows a structural example of the hot metal phosphorus sensor 9 using the galvanic cell 8 shown in FIG. 1, in which the rear end of the galvanic cell 8 is embedded in the refractory holder 6 using refractory cement and the tip is Is made to protrude from the tip surface of the holder 6, and the tip of the lead wire 7 on the hot metal side is made to protrude from the tip surface of the refractory holder 6 and embedded in the refractory holder 6 using refractory cement.

The lead wires 4 and 7 may be made of molybdenum, platinum, or any other metal known to be used as a lead wire for oxygen sensors for molten steel.

The method of the present invention is carried out by immersing the phosphorus sensor 9 configured as described above in hot metal and measuring the potential difference between the lead wires 4 and 7.

In addition, it is necessary to know the temperature of the hot metal to be measured at the same time, but a sensor for this temperature measurement can be built in the above phosphorus sensor, and the temperature can be measured simultaneously by other means. If so, the temperature sensor may not be built in the phosphorus sensor. Further, when the hot metal temperature is known and is extremely stable, the temperature sensor may not be built in the phosphorus sensor.

Example 1 A commercially available zirconium oxide powder, a calcium carbonate powder and a diammonium phosphate salt powder were used in a weight ratio of 73.6: 15.9: 10.5.
To mix. This formulation is shown in Fig. 1 (molar ratio display).
Corresponds to ZrO ₂ 75%, CaO 20%, and P ₂ O ₅ 5%. This mixture of reagent powders was pressure-filled inside an alumina holding tube 2 and baked at 1400 ° C. for 48 hours. When the baked product was analyzed by X-ray diffraction, ZrO ₂ , CaO.4ZrO ₂ (cubic structure CaO
-ZrO ₂ type solid solution) and 3CaO · P ₂ O ₅ were confirmed, and other crystals did not exist. In this way, a three-phase coexisting solid electrolyte was obtained.

After cooling to room temperature, the inside of the holding tube 2 is filled with copper powder 3 containing 1 weight percent of phosphorus. A molybdenum wire 4 is inserted into the copper powder 3 and the end of the holding tube is fixed with refractory cement 5. This completes the assembly of the galvanic battery 8.

The galvanic cell 8 is embedded in the refractory holder 6 using refractory cement. On the other hand, as a lead wire on the hot metal side, a molybdenum wire 7 is embedded in the refractory holder 6 like the galvanic battery 8. This completes the assembly of the phosphorus sensor.

About 5 kg of hot metal is dissolved in an alumina crucible, and the phosphorus sensor 9 is immersed in hot metal at 1500 ° C. to measure the electromotive force between the molybdenum wire 4 which is the lead wire of the galvanic battery 8 and the molybdenum wire 7 which is the lead wire on the hot metal side. did. 5 to 10 after sensor immersion
A stable electromotive force was obtained in seconds. The relationship between the measured voltage and the phosphorus concentration in the hot metal is shown in FIG. The phosphorus concentration in the hot metal is measured by the conventional Cantobac method. From this, it is understood that the phosphorus concentration in the hot metal can be rapidly measured by the present invention.

Example 2 Commercially available zirconium oxide powder, barium carbonate powder and diammonium phosphate salt are mixed in a weight ratio of 28.3: 56.6: 15.1. This composition is Zr in Fig. 2 (molar ratio display).
O ₂ 40%, BaO50%, corresponding to a point P ₂ O ₅ 10%. This mixture of reagent powders was pressure-filled inside the alumina holding tube 2.
After firing at 1400 ° C for 48 hours, the fired product was analyzed by X-ray diffraction, and it was confirmed that ZrO ₂ , BaO / ZrO ₂ and 3BaO / P ₂ O ₅ were formed, and other crystals did not exist. It was In this way, a three-phase coexisting solid electrolyte of the system was obtained.

When this type of solid electrolyte was used to measure the phosphorus concentration in the hot metal in the same manner as in Example 1, almost the same precision as the result of FIG. 5 was obtained. Similar results were obtained for the systems and and good results were obtained.

Effects of the Invention According to the present invention, the phosphorus concentration in hot metal can be measured quickly.

[Brief description of drawings]

FIG. 1 shows a substance that forms a three-phase coexisting solid electrolyte in which the activity of P ₂ O ₅ is determined only by the temperature by firing zirconium oxide powder, calcium carbonate powder and diammonium phosphate salt powder as starting materials. The composition of the above is shown, and the concentration is shown in mole percent. FIG. 2 shows that the activity of P ₂ O ₅ is determined only by the temperature by firing zirconium oxide powder, barium carbonate, and diammonium phosphate phosphate powder as starting materials.
The figure which shows the composition of the substance which forms a phase coexistence type solid electrolyte, and the density | concentration is displayed by the mol percentage. FIGS. 3A and 3B are cross-sectional views showing one form of a galvanic cell which is a main part of the phosphorus sensor. FIG. 4 is a sectional view showing an embodiment of the phosphorus sensor. FIG. 5 is a diagram showing the relationship between the phosphorus concentration in the pig iron at a temperature of 1500 ° C. and the electromotive force of the phosphorus sensor. 1 ... 3-phase coexisting solid electrolyte, 3 ... reference electrode, 4 ...
Reference electrode lead wire, 5 ... refractory cement, 6 ... refractory holder, 7 ... hot metal side lead wire, 8 ... galvanic battery, 9 ... hot metal phosphorus sensor.

Claims (4)

[Claims] 1. A solid ZrO ₂ , CaO.4ZrO ₂ solid (CaO-ZrO ₂ solid solution having a cubic structure), and solid 3CaO P ₂ O ₅ coexist, and P ₂ O ₅ An electrolyte whose activity is determined only by the temperature is used, one electrode of this electrolyte is a substance with a known chemical potential of phosphorus or oxygen, and the other electrode is a phosphorus-concentrated battery as hot metal with an unknown phosphorus concentration. And measuring the potential difference between the electrodes to measure the phosphorus concentration in the hot metal, the method for measuring the phosphorus concentration in hot metal. 2. A CaO · ZrO ₂ solid, solid CaO · 4ZrO ₂ (cubic CaO-ZrO ₂ solid solution structure), and solid 3CaO · P
₂ O ₅ coexists, an electrolyte whose P ₂ O ₅ activity is determined only by temperature is used, and one electrode of this electrolyte uses a substance with a known chemical potential of phosphorus or oxygen. Then, the other electrode forms a phosphorus concentration battery as hot metal having an unknown phosphorus concentration, and the phosphorus concentration in the hot metal is measured by measuring the potential difference between the electrodes, thereby measuring the phosphorus concentration in the hot metal. 3. A solid CaO · ZrO _2, be those solid 4CaO · P ₂ O _5, and solid 3CaO · P ₂ O ₅ of coexisting determined by activity of P ₂ O ₅ is a temperature only The electrolyte thus prepared is used, and one electrode of this electrolyte is made of a substance whose chemical potential of phosphorus or oxygen is known, and the other electrode is formed of a phosphorus concentration cell as molten pig iron having an unknown phosphorus concentration. A method for measuring the phosphorus concentration in hot metal, which comprises measuring the phosphorus concentration in the hot metal by measuring the potential difference. 4. A solid ZrO _2, be those BaO · ZrO ₂ solid, and the solid 3BaO · P ₂ O ₅ of coexist, electrolyte activity of P ₂ O ₅ is so determined by the temperature only A substance with a known chemical potential of phosphorus or oxygen is used for one electrode of this electrolyte, and the other electrode forms a phosphorus concentration battery as hot metal whose phosphorus concentration is unknown, and the potential difference between the electrodes is measured. A method for measuring phosphorus concentration in hot metal, which comprises measuring the phosphorus concentration in the hot metal.