Sensors for measuring oxygen
Semiconductor Equipment
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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!
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