JPH0471464B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for measuring the activity of an impurity element in molten metal, particularly an impurity element that can be combined with oxygen, and a measuring probe used therefor. As the quality of steel properties has improved in recent years, the management of impurity elements has become a major issue.
Conventionally, no apparatus or method has been proposed that can accurately measure these impurity elements at the stage of molten metal. <Summary of the Invention> In view of this point, the present invention provides a method for measuring the activity α _M of an impurity element M that can be combined with oxidation in molten iron, and a probe thereof. In FIG. 1, 1 is a measuring electrode, 2 is a standard electrode, and 3 is a potentiometer. The standard electrode 2 is composed of a solid electrolyte 4, a reference substance 5, and an electrode 6, and has basically the same structure as a conventional oxygen sensor. The solid electrolyte 4 may be any material as long as it has oxygen ion conductivity at high temperatures and can be used in conventional oxygen sensors. Further, the reference substance 5 is used to define a reference oxygen partial pressure, and may be any substance that can be used in conventional oxygen sensors. In the illustrated example, the solid electrolyte 4 is formed into a cylindrical shape, into which the reference substance 5 is inserted and brought into contact. In the measurement method of the present invention, a coating 7 of a substance such that the activity α _MOx of the oxide MOx of the element M becomes a constant value is applied to the outside of the solid electrolyte 4, and then the measurement electrode 1 and the standard electrode 2 are coated. immersed in molten metal α. At the same time, the temperature of the molten metal α is measured using a thermocouple or the like. The electromotive force EMF appearing on the potentiometer 3 at this time is expressed by the formula. EMF=-1/4FRTlnP _O2 ()/P _O2 () ...... Where F: Faraday's constant, 23.05 (cal/mv/
mole) R: Gas constant, 1.99 (cal/deg/mole) T: Absolute temperature of molten metal (K) P _O2 (): Oxygen partial pressure at standard electrode (atm) P _O2 (): Oxygen content in molten metal Pressure (atm) When the impurity element M that can be combined with the oxygen to be measured in the molten metal is in an equilibrium state as shown in the equation, the equilibrium constant K _M is expressed by the equation. M + X / 2O ₂ ( ₎ = ^MOx ...... K _M = α _{MOx /} ^α _M ^・ _{P -MOx} = -RT lnK _M ...... However, x: Number of moles of oxygen atoms O required to generate 1 mole of oxide MOx If the above formula is substituted into the summary formula for P _O2 (), the following formula is obtained. . EMF=RT/4F{1nP _O2 () − (1nα ^2/x _MOx-1o −1nα ^2
/x _M -1nK ^2/x _M )}... Here, P _O2 ( ) is a known value determined by the reference substance N of the standard electrode 2 and its oxide NOy, and is expressed by the formula. Po ₂ () = exp (2/y・ΔG ^o / _NOy / RT) ...... However, ΔG ^o _N-NOy : Standard production freedom when element N in the reference material is oxidized to produce 1 mole of NOy Energy y: Number of moles of oxygen atoms O required to generate 1 mole of oxide NOy Substituting the formula into the formula, EMF = -1/4F (2/yΔG ^o _N-NOy -2RT/x1nα _M
Ox +2RT/x1nα _M -2/xΔG ^o _M-MOx ) ...... is obtained. To summarize this equation for α _M , α _M = exp (−2xF/RT・EMF+1/RTΔG ^o _M-MOx −x/y・1/RTΔG ^o _N-NOy +1nα _MOx ) ...... Here, the solid electrolyte 4 By applying the coating 7 to the surface, α _MOx can be kept at a constant value. If, for example, pure oxide MOx of the element to be measured is used as the material of the coating 7, 1nα _MOx =1. By applying coating 7 in this way, α _MOx can be kept at a constant value, so the above formula
By measuring the EMF, it becomes possible to determine the activity α _M of the impurity element M. In addition, as materials for the coating 7, materials considered to be suitable for each element to be measured are shown in Table 1 below.

【table】

[Table] Next, the specific configuration of the probe used in the above-mentioned measuring method of the present invention will be explained based on the embodiment shown in FIG. The measuring electrode 1 consists of a rod made of Mo, is mounted on a housing 10, and is connected to a potentiometer (not shown) via a connector 11.
The standard electrode 2 includes a bottomed cylindrical solid electrolyte 4, a reference substance 5 placed inside the solid electrolyte 4, a Mo wire electrode 6 whose tip is immersed in the reference substance 5, and is connected to a potentiometer via a connector 11. A coating 7 is formed on the surface of a solid electrolyte 4. In this example, ZrO _2.7 mol is used as the solid electrolyte 4.
MgO is used. In addition, reference material 5 is Cr and
A mixture of Cr ₂ O ₃ is used. Note that it goes without saying that the invention is not limited to these. In this example, the coating 7 is a pure oxide MOx of the same element as the impurity element to be measured, so that the above α _MOx = 1
(In other words, 1nα _MOx = 0). The appropriate coating thickness is 100 to 200 μm. A suitable binder or the like may be mixed into this oxide MOx and applied onto the solid electrolyte 4. Further, this coating 7 may be porous or dense. A thermocouple 8 is attached between the electrodes 1 and 2, so that temperatures can be measured at the same time. The lower part of the housing 10 is fitted into a protective tube 12, and the upper part is covered with a cap 13.
FIG. 3 shows another embodiment of the standard electrode 2. In this example, a quartz tube 14 is used, a reference substance 5 is placed in the tube, and a solid electrolyte 4 is inserted into the tip of the tube 14 to close the tube. A coating 7 is formed on the exposed portion of the solid electrolyte 4. <Example> Next, an example will be shown. Example 1 A probe with the structure shown in Fig. 2 was used to investigate molten iron.
The amount of SolAl was measured. A coating agent mainly composed of Al ₂ O ₃ is applied onto the solid electrolyte, and the thickness is
A coating of 100 μm was formed. Other conditions are as follows. Γ solid electrolyte: ZrO ₂ 7mol%MgO Γ reference material: mixture of Cr and Cr ₂ O ₃ Γ reference electrode: Mo wire 0.3mmφ Γ measurement electrode: Mo rod 3mmφ Γ thermocouple: Pt-Pt13%Rh or higher probe The molten iron was inserted into a ladle at 1600°C, and the EMF was measured using a potentiometer. Figure 4 shows the relationship between the amount of SolAl (equivalent to α _Al ) and EMF. As can be seen from this graph, the measurement method of the present invention provides extremely good linearity and enables highly accurate measurement. From this EMF,
The activity α _Al was determined based on the formula. α _Al = exP (−3F/RTEMF+1/RTΔG ^o _Al-AlO1.5 −1/RTΔG ^o _Cr-CrO1.5 ) ……… Here ΔG ^o _Al-AlO1.5 =−197575+49.99Tcal/mole ΔG ^o _{Cr -CrO1.5} = 1/2 (-257400 + 55.53T) cal/mole is calculated, and as shown in Figure 4, good correspondence with the measured value is observed. Example 2 Similarly, using a probe with the structure shown in Figure 2,
The amount of Si in molten iron at 1600℃ was measured. A coating agent containing SiO ₂ as a main component was applied to the solid electrolyte to form a coating with a thickness of 100 μm. Other conditions were the same as in Example 1. Insert such a probe into the ladle of molten iron,
I got an EMF. Figure 5 shows the relationship between EMF and the amount of Si (equivalent to the activity α _Si ). Good linearity is also obtained in this case. The activity α _Si was obtained from this EMF using the formula. α _Si = exp (-4F/RTEMF+1/RTΔG ^o _Si-SiO2 -1/3 1/RTΔG ^o _Cr-CrO15 ...... Here, ΔG ^o _Si-SiO2 = -206040+57.51T cal/mole ΔG ^o _{Cr-CrO1 .5} = 1/2 (-257400 + 55.53T) cal/mole is calculated, and as shown in Figure 5, good correspondence with the measured value is observed.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the method of the present invention, Fig. 2 is a front sectional view showing one embodiment of the probe, Fig. 3 is a front sectional view showing another embodiment of the standard electrode, and Fig. 4 is a diagram showing the amount of SolAl. The graph showing the relationship between the electromotive force and EMF, Figure 5, is
It is a graph showing the relationship between the amount of Si and the electromotive force EMF. 1... Measuring electrode, 2... Standard electrode, 3... Potentiometer,
4...Solid electrolyte, 5...Reference material, 6...Electrode, 7...
Covering.

Claims (1)

[Claims] 1. Measurement in molten metal on the surface of the solid electrolyte of a probe that has a solid electrolyte with oxygen ion conductivity, a standard electrode and a measuring electrode, and generates an electromotive force proportional to the oxygen partial pressure difference between the two electrodes. Coating with a substance that makes the oxide activity of the target impurity element a constant value,
Impurities in molten metal, characterized in that the probe is placed in molten metal to measure the electromotive force generated between the two electrodes, simultaneously measure the molten metal temperature, and measure the activity α _M of impurity element M. Method for measuring the activity of elements. 2. Impurities in molten iron, comprising a solid electrolyte having oxygen ion conductivity, a standard electrode, and a measuring electrode, the surface of the solid electrolyte being coated with an oxide of the same element as the impurity element to be measured in the molten iron. Elemental activity measurement probe.