Adsorption Model
An empirical relationship describes how gas molecules distribute themselves across the surface of a non-uniform solid adsorbent. Engineers apply freundlich kinetics to characterize systems where the heat of adsorption decreases exponentially as the surface sites are filled. The model assumes a distribution of active sites with different affinities, which is common in polycrystalline metal oxide sensors.
Surface Heterogeneity
The mathematical form uses a power law equation to relate the quantity of gas adsorbed to the equilibrium pressure. This heterogeneity factor indicates the intensity of the adsorption process and the diversity of the energy levels available on the sensing film. Measurements are typically performed at constant temperature to isolate the pressure response from thermal effects.
Experimental Fit
Calibration involves plotting the logarithm of the sensor response against the logarithm of the analyte concentration to determine the slope. A straight line confirms the validity of the model for that specific gas and material pairing.
Measurement Accuracy
Deviations from the predicted curve often occur at very high concentrations where the surface reaches a saturation limit not accounted for by the power law. Reliable qualification of a sensor requires testing at the lower end of the detection range where the empirical constants remain stable. If the fit residuals exceed a five percent threshold, the instrument software must switch to a more complex model or adjust the temperature setpoint.
