Sensors for measuring oxygen
Zirconium oxide is the most common component of the element Zirconium. ZrO2 is an oxide ceramic or refractory, which crystallizes in 3 lattice structurs. By doping the zirconium dioxide with Yttria, defects or voids are introduced in the crystal lattice. In the solid zirconia, some Zr4+ ions are replaced by Y3+ ions so that oxygen vacancies are created which allow oxide anions O2-, especially at high tempertures over 650°C to diffuse fast in the solid crystal lattice. Yttrrium doped Zirconia is a solid electrolyte. This conductivity for oxygen anions is used for measuring oxygen by Zirconium oxide (ZrO2) high temperature electrochemical sensors, known also as hot probes.
The oxygen measurement cell
In the measurement unit, a zirconium oxide membrane separates a reference gas (e.g. air) from the sample gas. Both sides of the membrane are coated with thin palladium films, which serve as electrodes so that a solid, electrochemical cell is formed. As long as the oxygen partial pressure is equal on both sides, the movement of oxygen ions within the membrane is random. When the oxygen concentration on both sides of the membran becomes different, then oxygen ions start migrating within the crystal lattice from the side of higher O2 partial pressure to the lower pressure side. A concentration gradient of oxygen ions is established in the ZrO2 lattice, which produces a voltage potential between the two platinum electrodes according to the Nernst Equation. The relationship between the voltage and the O2 partial pressure change in the gas sample is logarithmic. This methode can be used for measuring oxygen concentration in the percent-range as well as for oxygen trace measurements (ppm). Zirconium oxide oxygen analyzers have fast speed of response. It needs to be considered that already the presence of small amounts of reducing gases will disturb the trace measurement.
Due to the high operating temperature, zirconium oxide sensors can be used for measuring oxygen O2 in a furnace / in furnaces like vertical furnaces, horizontal furnace, conveyer furnaces, box ovens and industrial furnaces.
Stange O2-Sensor for the
determination of the leakage rate and process control
During many processes like vacuum processes, polyimide cure, debindering or ceramics it is important to know whether residual oxygen is still present in the furnace. With the oxygen sensor evidence can be provided that the process can run off safely. The signal of the oxygen sensor offers the possibility to set process specific limits, with which actions can be initiated, e.g. the termination of heating procedure or the discharging of emergency purging.
As an analysis tool a Stange controller can be used or also any other suitable display. The batch comparison function of the Stange software ECS-2000 ensures a simple checking of the continuity of the sensor signal of an unmodified processes. The signal of the oxygen sensor is pressure independent!