1.1. Concentration type (Nernst type) zirconia oxygen sensor
The practical application of ZrO2 oxygen sensor has successfully realized the control of the air-fuel ratio of automobile engines. The central part is the Y2O3 stable ZrO2 (YSZ) solid electrolyte. Y3+ and Zr4+ are not equivalently replaced, and a large number of oxygen ion vacancies are generated in the formed cubic solid solution. The working principle is that the ZrO2-based ceramic material as a solid electrolyte has a high oxygen ion conductivity at a high temperature above 500°C. On both sides of the solid electrolyte are exhaust gas and air reference gas discharged from cars. The zirconia-based ceramics and the platinum electrodes coated on the surfaces of both sides together constitute an oxygen concentration difference battery, and the size of the oxygen concentration difference potential U reflects the change of the A/F value. However, for this type of oxygen sensor, it has higher sensitivity and accuracy only when the actual air-fuel ratio is close to the theoretical air-fuel ratio (14.7), and it is not sensitive enough in the entire rich combustion zone and lean combustion zone.
1.2 Chip zirconia limiting current oxygen sensor
The structure of the chip zirconia limiting current type oxygen sensor is similar to the oxygen concentration difference voltage type oxygen sensor, as shown in Figure 2. The main reason is that the working principle is different. The output of the flat-plate limiting current oxygen sensor is not the voltage value, but the current value. The specific working principle is that the oxygen in the car exhaust passes through the diffusion barrier to reach the inner electrode of the electrolyte (that is, the cathode). After being decomposed into oxygen atoms on the cathode, electrons are obtained to generate oxygen ions O2, and O2 is transported through the solid electrolyte to the outer electrode (that is, anode). Losing electrons on the anode generates O2 and is released. That is, under the action of an applied voltage (pump voltage), oxygen forms a current loop with the solid electrolyte through the process of obtaining electrons on the cathode and losing electrons on the anode.
1.3 Chip zirconia wide-area oxygen sensor
The sheet-type zirconia wide-area oxygen sensor is a combination of the oxygen concentration difference voltage type and the limiting current type oxygen sensor. It can be applied to the entire combustion range, including rich combustion, lean combustion and combustion near the theoretical air-fuel ratio. The schematic diagram of the component composition and structure of the chip wide-area oxygen sensor is shown in Figure 3. The chip wide-area oxygen sensor has two electrochemical cells, one is a limiting current pump oxygen battery, and the other is an oxygen concentration difference battery. The two cells are separated by a porous diffusion barrier. The exhaust gas enters the detection chamber through the diffusion barrier, and the sensor battery detects whether the ratio (λ) of the actual air-fuel ratio to the theoretical air-fuel ratio is greater than 1, less than 1, or equal to 1. When λ>1, it means lean combustion and the oxygen content in the exhaust gas is high, and the pump battery pumps oxygen out of the detection chamber; when λ<1, it means dense combustion, and the oxygen content in the exhaust gas is low, and the pump battery changes the direction of current flow. , The oxygen is pumped into the detection chamber; when λ=1, the theoretical air-fuel ratio is combusted, and there is no need to pump in and out of oxygen, and no current is generated.
The zirconia oxygen sensor is a transmitter that uses an oxygen concentration difference battery composed of zirconia solid electrolyte to measure oxygen. It only emerged in the 1960s. It belongs to an important application aspect in solid ionology. This type of oxygen sensor has been widely used in industrial furnaces to optimize combustion at home and abroad, and has produced significant energy-saving effects; widely used in automobile exhaust gas measurement, significantly improving urban environmental pollution; widely used in molten steel oxygen measurement, greatly improving The quality and output of high-quality steel; it is widely used for measuring oxygen in inert gas, and its sensitivity and measuring range are not comparable to other oxygen meters. This article expounds the above-mentioned problems from two aspects: theoretical analysis and practical application. The main applications of zirconia sensors can be summarized into the following five aspects:
1. Flue gas oxygen measurement: mainly used in power plants, oil refineries, steel plants, chemical plants, textile printing and dyeing plants, food processing plants, and other enterprises.
2. Automobile exhaust gas measurement: At present, it is mainly used for passenger cars and cars.
3. Oxygen measurement of molten steel: mainly used for smelting enterprises such as steel companies and copper smelters.
4. Inert gas oxygen measurement: mainly used in steel companies, air separation plants, fertilizer plants and electronics companies.
5. Physicochemical research: mainly used for the determination of thermodynamic and kinetic parameters in high-temperature oxidation-reduction reactions.
Since 1975, my country has also rapidly carried out research work in this application field. The Chinese Academy of Atomic Energy, Beijing Institute of Iron and Steel and the Institute of Marine Silicate, Chinese Academy of Sciences have all achieved important results in different applications. Among them, the China Institute of Atomic Energy has successfully developed a flue gas guillotine sensor and an inert wire gas guillotine sensor, and the Beijing Institute of Iron and Steel has successfully developed a liquid steel oxygen sensor that has reached or close to the foreign level, and has been promoted and applied in my country.
The voltage value at which a zirconia oxygen sensor
The voltage value at which a zirconia oxygen sensor switches from rich to lean
Bosch oxygen sensor
Broadband Lambda sensor