Output Characteristics of a Gas-Polarographic Oxygen Sensor Using a Zirconia Electrolyte in the Knudsen Diffusion Region

Abstract

Output characteristics of a gas-polarographic oxygen sensor using a zirconia electrolyte have been investigated at 450°C and low pressures (∼1 mmHg) in O2-N2 gas mixtures with the aim of clarifying those in the Knudsen diffusion region. The limiting current obtained at 1 mmHg of the total pressure increased linearly with the oxygen concentration up to 100% in the ambient atmosphere as expected from the theoretical consideration on the output characteristics of the sensor in the Knudsen diffusion region.

Humidity‐Sensing Characteristics in Wet Air of a Gas Polarographic Oxygen Sensor Using a Zirconia Electrolyte

“…As n = 2 in the case of the electrochemical decomposition of water, the theoretical decomposition voltage of water vapor at 400~ is estimated as 1.1V from Eq. [3] and [4]. As can be seen from Fig.…”

“…[2] (11) H20(g) + Vo + 2e----, H2(g) + O~ [2] It is significantly important to estimate the theoretmal decomposition voltage, E~ of water vapor at a temperature of T, using the following relationship hG~ = nFE~ [3] where AG~ is the standard Gibbs free energy change at a temperature of T, n denotes the number of electrons concerning decomposition, and F is the Faraday constant. The standard free energy change for the decomposition of water vapor is given by the following relationship (15) AG~ = -247.657 + 0.05520T (kJ mo1-1) [4] where T is the absolute temperature in degrees Kelvin.…”

“…As can be seen from Eq. [5] and [6], the limiting current is virtually independent of the total pressure (3,4). Since Xoz = 0,21 in dry air in Eq.…”

“…Recently, gas polarographic oxygen sensors using an electrochemical oxygen pump with a zirconia electrolyte have been extensively investigated (1)(2)(3)(4)(5)(6)(7). This type of oxygen sensor shows the reproducible limiting current plateau (saturated current plateau against the applied voltage) due to the oxygen diffusion overpotential at the cathode with an artificial technique.…”

Limiting current oxygen sensors for the percentage to ppm range

“…Amperometric limiting-current oxygen sensors are of this type and were reported by Dietz, Jahnke et al [1][2][3], Usui et al [4][5][6] and Takeuchi et al [7], who all used cubic stabilized zirconia (CSZ), and more recently by Liaw and Weppner [8] who used tetragonal zirconia polycrystals (TZP) as solid electrolyte. The output signal is an electrical current limited by the diffusion of oxygen through a small hole, Ili m, which is directly proportional to Po2.…”