1.  The zirconia oxygen analyzer is appropriate for measurements of ppm to % amounts of oxygen in a gas or combination of gases. The zirconia mobile is an electrochemical galvanic mobile utilizing a higher temperature ceramic sensor made up of stabilised zirconium oxide.
2.  Within an instrument the zirconia mobile is mounted in a temperature controlled furnace with the necessary electronics to process the signal from the detection cell. Generally measurements are displayed directly through a digital display as oxygen concentration more than the range .01ppm to one hundred%.
3.  The concept guiding Systech’s zirconia oxygen analyzer
4.  The zirconia mobile is a substantial temperature ceramic sensor. It is an electrochemical galvanic mobile comprising of two electrically conducting, chemically inert, electrodes hooked up to both side of a sound electrolyte tube. This is demonstrated schematically in Determine 1 under.
5.  The tube is totally gas tight and created of a ceramic (stabilised zirconium oxide) which, at the temperature of operation, conducts electricity by means of oxygen ions. (Note: In sensors of this sort, the temperature has to be earlier mentioned 450°C ahead of they grow to be energetic as an electrolyte conductor). The potential variation across the mobile is provided by the Nernst equation.
6.  
7.  In which:
8.  E is the potential variation (volts)
9.  R is the gasoline continual (eight.314 J mol-1 K-1)
10.  T is the complete temperature (K)
11.  F is the Faraday constant (96484 coulomb mol-1)
12.  P1 & P2 are the partial pressures of the oxygen on possibly aspect of the zirconia tube
13.  The Nernst equation can consequently be decreased to:
14.  
15.  Therefore, if the oxygen partial strain at one of the electrodes is known and the temperature of the sensor is managed, then oxygen measurement of the prospective variation in between the two electrodes allows the unidentified partial force to be calculated.
16.  Notice
17.  The partial strain of the gasoline is equivalent to the molar focus of the component in a gasoline mixture moments the complete strain of the fuel combination.
18.  PO2 = CO2 P2
19.  in which:
20.  PO2 = Oxygen partial strain
21.  CO2 = Molar concentration of oxygen
22.  P2 = Whole strain
23.  Case in point
24.  For atmospheric air:
25.  CO2 = twenty.nine%
26.  P2 = one environment
27.  PO2 = (.209/100) x 1
28.  PO2 = .209 atmospheres
29.  Theory of Procedure
30.  The zirconia cell employed by Systech Illinois is produced of zirconium oxide stabilised with yttrium oxide as the ceramic with porous platinum electrodes. This cell is shown in Figure 1.
31.  
32.  Determine one: Enlarged cross sectional representation of the zirconia substrate
33.  Molecular oxygen is ionised at the porous platinum electrodes.
34.  PtO → Pt + ½ O2
35.  ½ O2 + 2e- → O2–
36.  The platinum electrodes on each and every facet of the mobile supply a catalytic surface for the change in oxygen molecules, O2, to oxygen ions, and oxygen ions to oxygen molecules. Oxygen molecules on the large focus reference gas side of the cell obtain electrons to become ions which enter the electrolyte. Concurrently, at the other electrode, oxygen ions drop electrons and are unveiled from the surface area of the electrode as oxygen molecules.
37.  The oxygen content material of these gases, and therefore the oxygen partial pressures, is diverse. As a result, the rate at which oxygen ions are created and enter the zirconium oxide electrolyte at each and every electrode differs. As the zirconium oxide permits mobility of oxygen ions, the variety of ions shifting in each and every direction throughout the electrolyte will rely on the fee at which oxygen is ionised and enters the electrolyte at each and every electrode. The mechanism of this ion transfer is complex, but it is acknowledged to require vacancies in the zirconia oxide lattice by doping with yttrium oxide.
38.  The result of migration of oxygen ions throughout the electrolyte is a web flow of ions in one particular route based upon the partial pressures of oxygen at the two electrodes. For instance in the Nernst equation:
39.  
40.  If P1>P2 ion movement will be from P1 to P2 i.e. a good E.M.F.
41.  If P1
42.  <p2 ion="" flow="" will="" be="" from="" p2="" to="" p1="" i.e.="" a="" negative="" e.m.f.<br="" />If P1=P2 there will be no net ion flow i.e. a zero E.M.F.
43.  In the zirconia analyzer, the Nernst equation is written
44.  
45.  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&deg;C (923 K).
46.  Thus, our Nernst equation further reduces to:
47.  
48.  
49.  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.
50.  
51.  Figure 2 Graph of cell potential vs. oxygen concentration of zirconia cell.
52.  By anti-logging the equation, the output signal can be displayed directly on a digital readout meter as oxygen concentration in ppm or %.
53.  Calibration
54.  As the zirconia instrument uses an absolute measurement principle once built and factory calibrated, it does not require any further factory calibration.
55.  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.
56.  Applications of zirconia oxygen analyzers
57.  The zirconia analyzers may be used for measurement of oxygen at any level between 0-100% in gases or gas mixtures.
58.  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.
59.  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.
60.  Materials that will poison the detection cell are:
61.  Halogens e.g. https://www.avcray.com/
62.  Halogenated Hydrocarbons e.g. Methylchloride
63.  Sulphur containing compounds e.g. Hydrogen Sulphide
64.  Lead containing compounds e.g. Lead Sulphide
65.  Gases or gas mixtures containing any of the above are not suitable for oxygen determination with a zirconia type oxygen analyzer.
66.