Industries and combustion systems widely utilize zirconium dioxide (zirconia) oxygen sensors due to their precision and reliability. However, like most gas sensors, they can exhibit cross-sensitivity to certain gases and chemicals, which may affect both performance and sensor lifespan. Understanding which substances to avoid is crucial for engineers seeking to maintain accurate oxygen measurements and prolong sensor lifespan.
This article highlights the gases and chemicals that can negatively impact zirconium dioxide oxygen sensors, particularly those from SST Sensing.
Combustible Gases
Zirconia sensors rely on a hot platinum (Pt) electrode, which can catalyze the combustion of small amounts of combustible gases. This reaction consumes oxygen and can introduce measurement errors. While minor amounts may not immediately damage the sensor, we do not recommend using it in applications with significant concentrations of combustible gases if accurate oxygen readings are required.
SST has investigated the following gases:
- Hydrogen (H₂): up to 2%, stoichiometric combustion
- Carbon Monoxide (CO): up to 2%, stoichiometric combustion
- Methane (CH₄): up to 2.5%, stoichiometric combustion
- Ammonia (NH₃): up to 1500 ppm, stoichiometric combustion
Heavy Metal Vapours
Vapours from metals such as Zinc (Zn), Cadmium (Cd), Lead (Pb), and Bismuth (Bi) can degrade the catalytic properties of the sensor’s Pt-electrodes. Exposure to these metals must be strictly avoided to preserve sensor function.
Halogen and Sulfur Compounds
Zirconia oxygen sensors tolerate very low concentrations of halogen or sulfur compounds (<100 ppm) without performance issues. However, higher concentrations can eventually cause sensor readout problems or corrosion, especially in condensing environments. Key substances to avoid include:
- Halogens: F₂ (Fluorine), Cl₂ (Chlorine)
- Hydrogen halides: HCl (Hydrogen Chloride), HF (Hydrogen Fluoride)
- Sulfur compounds: SO₂ (Sulphur Dioxide), H₂S (Hydrogen Sulfide)
- Other chemicals: Freon gases, CS₂ (Carbon Disulfide)
Reducing Atmospheres
Long-term exposure to reducing atmospheres, which are low in free oxygen and rich in combustible gases, can impair the catalytic effect of Pt-electrodes. In these environments, oxygen is consumed during combustion reactions, affecting the sensor’s accuracy and lifespan.
In conclusion
Many people often confuse SST’s zirconia oxygen sensors with automotive Bosch Lambda sensors. Unlike Lambda sensors, SST optimizes its sensors for boiler combustion control applications and has subjected them to extensive life testing in:
- Laboratory atmospheres
- Exhaust gases from natural gas-fired boilers
- Exhaust gases from light oil combustion
These sensors exhibit cross-sensitivity in the presence of certain gases, metals, halogens, sulfur compounds, and reducing atmospheres. To ensure maximum sensor performance and longevity, avoid these substances wherever possible.
Important: This list includes substances that SST has tested. If your application contains gases or chemicals not listed above, we recommend conducting a test period to verify sensor performance under those conditions.
