Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For ion concentration
Patent
1997-06-16
1998-10-13
Bell, Bruce F.
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For ion concentration
2057805, 205781, 2057835, 205784, 205786, 2057795, 205782, 204425, 204426, 422 83, 422 88, 422 98, G01N 2726
Patent
active
058207457
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/EP95/04899 filed on Dec. 12, 1995.
BACKGROUND OF THE INVENTION
The invention relates to a procedure for measuring the concentration of at least one predetermined gas in a gas mixture by means of an electrolyte provided with a first and second surface-mounted electrode, which together with the electrode connected to a voltage source is exposed to the gas mixture, wherein the voltage source causes a flowing electrical current through electrodes and electrolyte which is dependent upon the ion concentration, and which is measured as an indicator of the gas concentration, as well an electrochemical sensor.
A procedure for determining fuels in a gas mixture with excess oxygen is known from U.S. Pat. No. 4,190,499, wherein the gas mixture is fed to the first and second electrodes on opposite sides of an oxygen ion-conducting solid state electrolyte, wherein the electrodes are provided with different materials having varying catalytic activity in relation to the gas mixture at a predetermined temperature. The difference which is generated in the oxygen potentials at the respective electrodes as a result of a varying catalytic activity forms an oxygen ion conductivity in the solid electrolyte cell which produces an electric signal in the strength which is characteristic for the combustion in the mixture at the moment, that is, for methane, oxygen, carbon and monoxide. The thermoelectric potential developed on the basis of the various electrode materials is evaluated either with regard to voltage or to current. In the event that no fuel or combustible material is present in the gas mixture, no potential difference is developed.
The procedure proves to be problematic on account of its comparatively expensive construction for generating the thermoelectric potential and, if need be, temperature regulation.
Furthermore, a polarographic measuring probe for determining the oxygen content in gases, especially in exhaust gases from internal combustion motors is known from EP-OS 0 019 731, which has an oxygen ion-conducting solid electrolyte element provided with an anode and a cathode on which a constant voltage is to be applied. The cathode is covered by a pore or channel-containing layer as a diffusion barrier and provided with catalytically active material with reference to the adjustment of the thermodynamic gas equilibrium, while the anode is made of a catalytically inactive material. Both electrodes are exposed to the gas to be measured in connection with the measuring probe operating according to the diffusion limiting current principle.
Here, limiting the current on the basis of the diffusion barrier and the thereby restricted measurement range proves to be especially problematic.
Furthermore, a process for determining the oxygen partial pressure and an oxygen partial pressure sensor is known from U.S. Pat. No. 5,344,549. A solid electrolyte with an alterable electron conductivity is provided with two electrodes, of which only one electrode, which is porously disconnected, is exposed to the gas to be measured, while the other electrode, as a so-called blocking electrode, is not exposed to the exhaust gas to be measured. A flow of oxygen within the solid electrolyte is not provided for.
A comparatively expensive construction of the sensor arises owing to the special sealing measures of the solid electrolyte.
A solid electrolyte exhaust gas sensor with two platinum electrodes is known from U.S. Pat. No. 4,199,425, which is provided for measuring oxygen and nitrogen oxides in exhaust gas. The outer platinum electrode is equipped with a rhodium-containing ceramic protective layer (aluminum oxide), whereby the addition of rhodium is supposed to make possible maintaining chemical equilibrium and nitrogen oxide measurement.
An electrochemical measuring probe for determining the oxygen content in gases, especially in exhaust gases of internal combustion engines, with a solid electrolyte and at least one electrode as a measuring probe is known from DE-OS 37 37 215, which is arranged on the
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W. A. Fischer, D. Janke, Mettallurgische Elecktrochemie, Verlag Stahleisen m.b.H. Dusseldorf, Chapter 3.3.3.1, pp. 40-42, 1975. No month Available.
Bell Bruce F.
Hergeus Electro-Nite International, N.V.
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