Sensor for measuring density of oxygen in molten metal

Details Sensor for measuring density of oxygen in molten metal Sensor for measuring density of oxygen in molten metal

1982-03-29

1984-05-29

Kaplan, G. L.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204423, G01N 2758

Patent

active

044513500

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

This invention relates to an improvement of a sensor for measuring density of oxygen in molten metal such as steel, copper and others, in which an oxygen concentration cell is generated by means of solid electrolytic element having oxygen ion conductivity.


BACKGROUND ART

Since the density of oxygen in the molten metal effects the quality of product, oxygen is a very important control ingredient. As development of the solid electrolyte has been advanced, there has recently been practised such a manner which measures the density of oxygen by directly immersing a sensor composing an oxygen concentration cell as an element of the solid electrolyte into the molten metal.
The cell is, as shown in FIG. 1, composed of Mo pole 5--molten steel--solid electrolyte 1--standard pole 3--Mo pole 4, and this composition utilizes generation of electromotive force (emf) in proportion to difference in partial pressure of oxygen, between both Mo poles.
For the standard pole 3, such mixture is in general used as Ni+NiO, Mo+MoO.sub.2, Cr+Cr.sub.2 O.sub.3 and others. For the oxygen ion conductive solid electrolyte 1, a formation of a certain shape is used of metallic oxides as ZrO.sub.2 radical or TiO.sub.2 radical. Further the temperature of the molten metal can be concurrently measured with a thermocouple 6 incorporated in the sensor (with respect to others in FIG. 1, 7 is a ceramic housing, 8 is a connector, 9 is an iron-made cap, 10 is a ceramic fiber refractory sleeve and 11 is a paper sleeve). Herein, if an object to be measured is the molten steel, the content of of molten oxygen may be obtained in calculation with following expression by the Nernst's formula. ##EQU1## wherein; a.sub.0 : Density of molten oxygen (ppm)
There have been many proposals for shapes of the sensors. If measuring were carried out to determine the amount of oxygen in the molten steel by means of such a sensor where the standard pole substance 3 is, as shown in FIG. 1, filled in the solid electrolytic element 1 closing its one end (called as "element" hereafter), wave of electromotive force thereby would show an action which generates a large peak at standing due to thermal and electrical transient phenomenon as shown in FIG. 2, and changes into an equilibrium state. Herein, the ordinate in FIG. 2 designates passing time, one interval being 9 seconds, and the abscissa thereof shows the temperature of the steel bath and electromotive force. The value of "a.sub.0 " thereunder is obtained by substituting into the Nernst's formula the value in parentheses ( ) when the wave of electromotive force reaches up to the equilibrium state (the same in FIGS. 3 to 9).
This fact depends upon the cause that, just after immersion, large difference in temperature arises between the inner and outer surfaces of the element, whereby it takes long time for the partial pressure of dissociated oxygen of the standard pole having temprature reliance filled in the element to reach the equilibrium partial pressure.
Already known is such a sensor where the element has a coating agent 2 on its surface for providing satisfactory wettability with the molten steel in order that emf controls the peak at the low level when the wave stands to shorten the time until it reaches the equilibrium state. For the characteristics of the coating agent, the requirements are:
(1) not generating crackings or exfoliation if it were immersed into the molten steel from the room temperature, and
(2) not obstructing the oxygen ion conductivity of the element.
However, the conventional coating agent of combination of Al.sub.2 O.sub.3 powder and organic powder does not pay careful attention to the above (1) item. Just after immersion into the molten steel, cracking is created due to thermal shock, and the coating layer is exfoliated in a short period of time and the element is exposed so that the wettability with the molten steel is not fully kept, and its effect is poor. This is because the organic binder may secure combination among Al.sub.2 O.sub.3 powder and adhesion with the elem

REFERENCES:
patent: 3698955 (1972-10-01), Lilly et al.
patent: 3764269 (1973-10-01), Oldham et al.
patent: 3809639 (1974-05-01), Faurschou et al.
patent: 3837920 (1974-09-01), Liang et al.
patent: 4177112 (1979-12-01), Suzuki et al.
patent: 4216279 (1980-08-01), Mellors
Rapp et al., Techniques of Metals Research, vol. 4, Physicochemical Measurements in Metals Research, Part 2, 1970, pp. 132-135.

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