Meaning
Electrolytic moisture measurement devices quantify trace water concentrations by converting absorbed moisture into hydrogen and oxygen gases. A phosphorus pentoxide sensor uses an anhydrous chemical coating across dual platinum electrodes to measure water content in gas streams or carrier gases from resin desorbers. Absorbed water reacts with phosphorus pentoxide to form phosphoric acid, which electrolyzes under an applied direct current voltage.
Measuring the resulting electrolysis current yields absolute moisture mass based directly on Faraday law of electrolysis. The active range spans parts-per-million levels, but exposure to high ambient humidity saturates the chemical layer and requires thermal regeneration.
Electrolytic Absorption
Direct current applied to the electrode winding drives continuous electrolysis of absorbed water molecules. Inside a phosphorus pentoxide sensor, current flow remains directly proportional to the rate of water absorption under constant carrier gas flow. Chemical reaction cycles regenerate anhydrous phosphorus pentoxide as water electrolyzes into hydrogen and oxygen off-gases.
Quantitative measurement depends on complete moisture absorption from the carrier gas passing through the sensor cell.
Cell Degradation
Volatile organic compounds and amine additives present in polymer off-gasses can react with the sensor coating. Contamination of a phosphorus pentoxide sensor reduces active surface area, leading to incomplete moisture absorption and falsely low concentration readings. Corrosive vapors degrade platinum electrode coils over extended operation.
Periodic recoating with fresh phosphoric acid solution restores measurement accuracy and baseline stability.
Current Yield
Electrical current measurements provide an absolute quantitative determination of water mass without requiring empirical calibration curves. Operating conditions require precise gas flow regulation, as signal output scales directly with sample volume delivered to the sensor cell. Saturated sensors display high background currents that require extended dry-down periods before reliable testing resumes.
