Oxygen activity measurement
The oxygen activity measurement is used in the metal extraction to estimate the currently available oxygen concentration in molten metals. Different concentrations of oxygen are required in the various processes during steel production or metallurgical treatment. During refining , the oxygen concentration is actively increased, among other things to reduce the carbon content in the melt. This unkilled steel cannot be used for every type of steel: The residual oxygen remaining in the melt would lead to significant errors when solidifying.
commitment
These processes are regulated with the oxygen activity measurement. The required amount of material is determined by determining the oxygen oxidation before the deoxidation . The success of the deoxidation is then confirmed with an oxygen activity measurement. The deoxidizing agent is often only tolerated in the melt in low concentrations.
functionality
The oxygen concentration is determined using a galvanic cell . The steel bath is a half-cell with the unknown oxygen concentration. A solid electrolyte is used to delimit a second half-cell, in which a metal / metal oxide mixture with a known oxygen concentration is present. The oxygen concentration is determined via the voltage that develops using the Nernst equation .
construction
The measurement is made with an oxygen probe which is intended for single use. The sensor consists of the EMF measuring cell and a thermocouple (type K or S). The electrical signals are brought out via an immersion lance . The sensor is attached to a cardboard tube to provide thermal protection for the immersion lance.
In order to protect the sensor head when it passes through the slag zone, it is provided with a thin steel cap, which quickly melts when it is immersed in the steel bath.
restrictions
The voltage that develops in the galvanic element also depends heavily on the other alloy elements in the steel melt. Corresponding coefficients are used for the conversion for the intended fields of application. In addition, the alloying elements can be taken into account in a further step with correction factors.
The oxygen activity resulting from this method correlates with the oxygen concentration in the melt. However, there is no exact determination of the oxygen concentration. The measurement results in different EMF values for different alloys with the same oxygen activity.
Web links
- Doctoral thesis on the development of the sensor
- Supplier Minkon
- Supplier Electro-Nite
- Supplier Sidermes
Individual evidence
- ↑ Michael Eike Vogel: Measurement and modeling of the oxygen activity in melts made from high-alloy cast steel . 2003.