Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For oxygen or oxygen containing compound
Reexamination Certificate
1999-07-06
2001-11-06
Warden, Jill (Department: 1744)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For oxygen or oxygen containing compound
C205S780500, C205S781000, C205S786500, C205S787000, C204S425000
Reexamination Certificate
active
06312585
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of determining oxidizable constituents in a gas mixture.
BACKGROUND INFORMATION
Methods of determining oxidizable constituents in gas mixtures are known. The conventional method is to measure a voltage between a working electrode and a reference electrode, which then permits an inference regarding the concentration of the gas constituent to be determined. Moreover, in the field of oxygen sensors for example, also known as lambda probes, it is known that the limit current induced between a reference electrode and a working electrode by transporting oxygen anions through a solid electrolyte body can be measured, permitting a determination of the equilibrium partial pressure concentration of oxygen according to the Nernst equation. The gases (O
2
, NO) to be measured pass through a diffusion barrier and are pumped out by electrochemical forces at the working electrode. However, there is not yet any satisfactory method of determining individual combustible gas constituents in gas mixtures with sufficient accuracy. In the case of ammonia in particular, there are no reliable systems at the present. Cross sensitivity to various gas constituents also has not been minimized satisfactorily. Another problem so far has been the temperature control of such sensors, which has previously required various complicated measurement arrangements.
SUMMARY OF THE INVENTION
In comparison with the known related art, the method according to the present invention for determining oxidizable constituents in a gas mixture by using a solid electrolyte cell having at least one reference electrode and at least one working electrode which is sensitive to the oxidizable constituents has the advantage that it measures directly the current induced by electrochemical oxidation of a gas constituent to be determined. Since each gas constituent has a different electrochemical potential, a different current is also measured, the current depending on the concentration, so that each oxidizable gas constituent can be identified without any doubt and the concentration can be measured.
In a preferred embodiment, the working electrode is made of mixed metal oxides, which are electrically conducting and are selected from the group of spinels, pseudobrookites, eschynites and fergusonites. These classes of compounds permit a sufficient variation with regard to the sensitivity of the respective compound for specific gas constituents, such as NO, NH
3
, unsaturated hydrocarbons or sulfur compounds. Satisfactory variation and sensitivity of the compounds for specific substances are guaranteed by this wide variety of compounds.
In another preferred embodiment, the temperature-dependent electrical conductivity of the solid electrolyte body is used for temperature control using the solid electrolyte cell. It is known that yttrium stabilized zirconium dioxide is electrically conductive in its cubic modification, with the conductivity being dependent on temperature. Due to this simple measurement of the electrical conductivity of the solid electrolyte body, the entire solid electrolyte cell can be used for temperature control of the combustion process without requiring complicated and expensive equipment.
In an advantageous manner, an a.c. voltage is applied to the reference electrode via the solid electrolyte body; the voltage is especially advantageously in the range of 0.1 to 10
6
Hz, in particular in the range of 1 kHz to 200 kHz.
In a preferred embodiment, the voltage drop of the solid electrolyte cell is measured on a measuring shunt, and the resistance of the solid electrolyte body as a function of temperature is determined from the voltage drop, so that temperature control of the solid electrolyte cell is provided at all times due to the measurement of the voltage drop in the simplest possible manner.
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Demitras et al., Inorganic Chemistry, ISBN:0134663594, pp. 208-210, 1972 Month unknown.*
Logothetis et al “High Temperature Oxygen Sensors Based on Electrochemical Oxygen Pumping”, ACS Symposium Series 309, pp. 136-154, 1986.
Brinz Thomas
Schumann Bernd
Wahl Thomas
Kenyon & Kenyon
Olsen Kaj K.
Robert & Bosch GmbH
Warden Jill
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