Surface Reaction
A kinetic mechanism describes the rate of a chemical reaction between two or more adsorbed molecules on a solid surface. In the context of gas sensors, the langmuir hinshelwood model predicts how the reaction rate depends on the fractional coverage of each species. It requires that all reactants are chemisorbed before they interact to form a product.
Adsorption Site
Competitive bonding occurs when different gas species vie for the same available locations on the metal oxide lattice. This competition can lead to inhibition effects where the presence of one gas reduces the sensor response to another.
Rate Law
The mathematical expression for the reaction velocity reaches a maximum at a specific ratio of partial pressures. Beyond this point, the surface becomes crowded with one reactant, preventing the other from finding a site.
Metrological Qualification
Accurate calibration of a sensor following this mechanism requires a multi gas test bench to determine the adsorption constants for every analyte. Environmental factors like humidity can interfere with the results by blocking active sites with water molecules. Laboratory technicians verify the model parameters by observing the steady state response at different temperatures and flow rates.
The drift in these parameters over time indicates the degradation of the catalytic surface.
