The zirconia oxygen analyzer is acceptable for measurements of ppm to % levels of oxygen in a gasoline or combination of gases. The zirconia cell is an electrochemical galvanic cell employing a significant temperature ceramic sensor containing stabilised zirconium oxide.













Inside of an instrument the zirconia mobile is mounted in a temperature controlled furnace with the important electronics to method the sign from the detection cell. Normally measurements are shown right via a electronic exhibit as oxygen focus more than the assortment .01ppm to a hundred%.













The idea behind Systech’s zirconia oxygen analyzer













The zirconia cell is a large temperature ceramic sensor. It is an electrochemical galvanic cell comprising of two electrically conducting, chemically inert, electrodes attached to both aspect of a strong electrolyte tube. This is proven schematically in Determine one beneath.













The tube is completely gas restricted and designed of a ceramic (stabilised zirconium oxide) which, at the temperature of procedure, conducts electricity by implies of oxygen ions. (Be aware: In sensors of this sort, the temperature has to be above 450°C just before they become active as an electrolyte conductor). The opportunity big difference throughout the mobile is presented by the Nernst equation.



























Where:













E is the prospective variation (volts)






R is the fuel consistent (8.314 J mol-one K-1)






T is the absolute temperature (K)






F is the Faraday regular (96484 coulomb mol-1)






P1 & P2 are the partial pressures of the oxygen on both facet of the zirconia tube













The Nernst equation can consequently be reduced to:



























So, if the oxygen partial tension at one particular of the electrodes is identified and the temperature of the sensor is controlled, then oxygen measurement of the potential distinction concerning the two electrodes permits the not known partial strain to be calculated.













Note













The partial tension of the gas is equivalent to the molar focus of the part in a gas combination times the overall force of the gasoline combination.













PO2 = CO2 P2













where:













PO2 = Oxygen partial pressure






CO2 = Molar concentration of oxygen






P2 = Full strain













Case in point













For atmospheric air:













CO2 = 20.9%






P2 = 1 atmosphere













PO2 = (.209/100) x 1













PO2 = .209 atmospheres













Theory of Procedure






The zirconia mobile applied by Systech Illinois is manufactured of zirconium oxide stabilised with yttrium oxide as the ceramic with porous platinum electrodes. This mobile is demonstrated in Determine one.



























Figure one: Enlarged cross sectional illustration of the zirconia substrate













Molecular oxygen is ionised at the porous platinum electrodes.













PtO → Pt + ½ O2






½ O2 + 2e- → O2–













The platinum electrodes on each individual facet of the mobile present a catalytic floor for the change in oxygen molecules, O2, to oxygen ions, and oxygen ions to oxygen molecules. Oxygen molecules on the large concentration reference fuel aspect of the mobile get electrons to become ions which enter the electrolyte. Simultaneously, at the other electrode, oxygen ions lose electrons and are launched from the area of the electrode as oxygen molecules.













The oxygen content material of these gases, and hence the oxygen partial pressures, is different. Consequently, the level at which oxygen ions are generated and enter the zirconium oxide electrolyte at every electrode differs. As the zirconium oxide permits mobility of oxygen ions, the variety of ions shifting in every single course throughout the electrolyte will rely on the rate at which oxygen is ionised and enters the electrolyte at each and every electrode. The mechanism of this ion transfer is advanced, but it is acknowledged to require vacancies in the zirconia oxide lattice by doping with yttrium oxide.













The outcome of migration of oxygen ions throughout the electrolyte is a net move of ions in 1 direction relying on the partial pressures of oxygen at the two electrodes. For instance in the Nernst equation:



























If P1>P2 ion move will be from P1 to P2 i. Oxygen Analyzers e. a constructive E.M.F.






If P1<P2 ion flow will be from P2 to P1 i.e. a negative E.M.F.






If P1=P2 there will be no net ion flow i.e. a zero E.M.F.













In the zirconia analyzer, the Nernst equation is written



























The zirconia analyzer uses air as a reference, a constant oxygen concentration of 20.9%, and the zirconia cell is mounted inside a furnace whose temperature is controlled to 650°C (923 K).













Thus, our Nernst equation further reduces to:



























The zirconia analyzer electronically calculates the oxygen partial pressure, and therefore oxygen concentration, of a sample gas with unknown oxygen concentration. This is accomplished by measuring the potential, E, produced across the zirconium cell electrodes, substituting for E in the Nernst equation and anti-logging to obtain PO2. The cell potential output is shown in Figure 2.



























Figure 2 Graph of cell potential vs. oxygen concentration of zirconia cell.













By anti-logging the equation, the output signal can be displayed directly on a digital readout meter as oxygen concentration in ppm or %.













Calibration






As the zirconia instrument uses an absolute measurement principle once built and factory calibrated, it does not require any further factory calibration.













Factory calibration consists of calibration of the electronics to accept the millivolt input signal from the detection cell and checking that the instrument then reads correctly on air, 20.9%. The instrument is then further checked for correct reading on ppm oxygen content in nitrogen.













Applications of zirconia oxygen analyzers













The zirconia analyzers may be used for measurement of oxygen at any level between 0-100% in gases or gas mixtures.













The only restriction on the instrument’s usage is that the gas to be measured must not contain combustible gases or any material that will poison the zirconium oxide detection cell.













Any combustible gas, e.g. CO, H2, hydrocarbons such as methane, in the sample gas entering the instrument will combine with any oxygen in the sample gas in the furnace due to the high temperature at which the furnace is kept. This will actually reduce the amount of oxygen in the sample gas and cause the instrument to give an incorrect low reading.













Materials that will poison the detection cell are:













Halogens e.g. Chlorine






Halogenated Hydrocarbons e.g. Methylchloride






Sulphur containing compounds e.g. Hydrogen Sulphide






Lead containing compounds e.g. Lead Sulphide






Gases or gas mixtures containing any of the above are not suitable for oxygen determination with a zirconia type oxygen analyzer.
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