Method for regulating the flow conductance of the gas inlet of a NOx sensor ceramic chip

Abstract

The application discloses a kind of NOx sensor ceramic chip air inlet flow conductance regulation and control method, belong to gas sensor manufacturing technical field.The method includes the following steps: (1) in the test atmosphere of specific NOx concentration, test the E2-IP2 curve of NOx sensor ceramic chip, obtain the limit current platform value IP 2T Of the chip;(2) according to the difference between the limit current platform value IP 2T Tested and target limit current platform value IP 2g , calculate the required porous diffusion barrier material thickness;(3) by screen printing process in the air inlet of sensor ceramic chip printing diffusion barrier material to the required thickness;(4) by high-temperature heat treatment solidifies diffusion barrier material.The method of the application can realize the regulation and control of the air inlet flow conductance of NOx sensor ceramic chip, make the limit current platform value of chip adjust to the required target range, with the characteristics of simple operation, regulation and control effect is good.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of gas sensor manufacturing, and particularly discloses a method for regulating and controlling the flow conductance of a NOx sensor ceramic chip air inlet. BACKGROUND

[0002] A NOx sensor is a key sensor device for detecting the content of NOx (nitrogen oxide, including NO, N02, etc.) in a gas, and is widely used in the fields of exhaust gas detection of fuel vehicles and industrial gas detection. A NOx sensor based on zirconia material and platinum electrode material prepared by using an HTCC (high-temperature co-fired ceramic) process utilizes the corresponding relationship between the limiting current platform value IP 2T of the NOx sensor and the NOx concentration to realize the test of the NOx concentration in a gas. However, due to the consistency problems of material performance and preparation process, the performance dispersion of the NOx sensor prepared in actual production is usually large, and the IP 2T signal values of different sensor samples under the same NOx concentration are usually distributed between 10 and 300 mu A, and the maximum difference can be more than ten times. Therefore, in the production process of the NOx sensor, the program of the electric control board card of the sensor usually needs to be regulated according to the actually measured IP 2T value of each sample. This results in a tedious calibration program of the sensor and seriously affects the production efficiency.

[0003] The IP 2T value of the NOx sensor is related to not only the material and internal structure of the sensor itself, but also the gas flow rate of the tested gas through the air inlet of the NOx sensor ceramic chip. Therefore, in principle, the regulation and control of the IP 2T value can also be realized by changing the flow conductance of the air inlet of the NOx sensor ceramic chip.

[0004] The application discloses a method for regulating and controlling the flow conductance of a NOx sensor ceramic chip air inlet, which can realize the accurate regulation of the limiting current platform value IP 2T of the NOx sensor, thereby meeting the performance consistency design requirements of the NOx sensor. SUMMARY

[0005] The application aims to provide a method for regulating and controlling the flow conductance of a NOx sensor ceramic chip air inlet, which can effectively regulate the gas flow rate of the tested gas through the air inlet of the NOx sensor ceramic chip, thereby regulating and controlling the limiting current platform value IP 2T of the NOx sensor to a specific target value, and effectively realizing the performance consistency design requirements of the NOx sensor in actual production.

[0006] To achieve the above object, the application adopts the following technical scheme:

[0007] A method for regulating the inlet flow conductance of a NOx sensor ceramic chip, the method comprising the steps of:

[0008] (1) testing the E2-IP2 curve of the NOx sensor ceramic chip under a test atmosphere with a specific NOx concentration, and obtaining the limiting current plateau value IP 2T of the chip;

[0009] (2) calculating the required thickness of the porous diffusion barrier material according to the difference between the tested limiting current plateau value IP 2T and the target limiting current plateau value IP 2c ;

[0010] (3) printing the diffusion barrier material to the required thickness on the inlet of the sensor ceramic chip by a screen printing process;

[0011] (4) curing the diffusion barrier material by high-temperature heat treatment.

[0012] In step (1), the specific NOx concentration can be any value in the range of 10-2000 ppm.

[0013] In step (2), the target limiting current plateau value IP 2G may be any value less than the tested limiting current plateau value IP 2T , and is usually between 10-30 μA.

[0014] In step (2), the thickness of the porous diffusion barrier material is calculated by formula (1):

[0015] D = (IP 2T - IP 2G ) / k (1)

[0016] In formula (1), D is the thickness of the diffusion barrier material, in units of μm;

[0017] IP 2T is the tested limiting current plateau value of the sensor before regulation, in units of μA;

[0018] IP 2G is the target limiting current plateau value of the sensor after regulation, in units of μA;

[0019] k is the characteristic regulation coefficient of the porous diffusion barrier material, in units of μA / μm.

[0020] In the screen printing process of the diffusion barrier material in step (3), the required printing thickness can be achieved by adjusting the screen mesh count and printing passes.

[0021] The porous diffusion barrier material is a zirconia-metal composite slurry, the main components of which are: zirconia powder, low-melting-point metal powder (for example, silver or copper, etc.) and an organic carrier, and the zirconia-metal composite porous material is formed after high-temperature curing.

[0022] The high-temperature heat treatment temperature in step (4) is 800-1200℃.

[0023] The present application has the advantages of:

[0024] The method of the present application can precisely adjust the flow conductance of the inlet of the NOx sensor ceramic chip, so that a NOx sensor ceramic chip with better E2-Ip2 curve consistency can be obtained, overcoming the large dispersion of E2-Ip2 curves of different samples in the current process, thereby avoiding the tedious process of adjusting the electronic control program for each sample during the joint debugging of the ceramic chip and the electronic control module, greatly improving the production efficiency and product consistency. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 E2-Ip2 curves of the first three samples of the NOx sensor ceramic chip before flow conductance regulation.

[0026] Figure 2 E2-Ip2 curves of the first three samples of the NOx sensor ceramic chip after flow conductance regulation using the method of the present application.

[0027] Figure 3 Surface morphology of the porous material after high-temperature heat treatment and curing. DETAILED DESCRIPTION

[0028] The present application will be further described in detail below in conjunction with the drawings and examples, but it is not meant to limit the scope of protection of the present application.

[0029] EXAMPLE

[0030] Three samples of the NOx sensor ceramic chip were selected, and the E2-Ip2 curves of the samples were tested in a N2 atmosphere containing 500ppm NO and 1000ppm O2, and the results are shown in Figure 1 The limit current plateau values Ip 2T of the three samples were obtained, as shown in Table 1. Zirconia-silver composite slurry with k = 10μA / μm was selected, and the required thickness was calculated according to the target Ip 2G value of 25μA, as shown in Table 1.

[0031] Different screen printing plates were used to print corresponding passes of zirconium oxide-silver paste on the sample's air inlet to obtain the desired material thickness. The sample was then heat-treated at 1200℃ for 40 minutes to fully cure the zirconium oxide-silver paste. The E2-Ip2 curves of the regulated sample were tested under an N2 atmosphere containing 500ppm NO and 1000ppm O2. The results are shown below. Figure 2 As shown. Ip was obtained after adjusting three samples. 2T The values ​​are shown in Table 1.

[0032] Table 1. Limiting current characteristic values ​​before and after sample conditioning

[0033] Sample 1# 2# 3# Ip 2T (μA) 248 182 134 IP 2T -IP 2G (μA) 223 157 109 D (pm) 22 16 11 Ip 2T (μA) 25 27 23

[0034] It can be seen that, after adjustment, the Ip of the three samples... 2T The value was 25±2 μA, showing a significant improvement in electrical performance dispersion compared to before regulation. The surface morphology of the cured zirconium oxide-silver composite porous material is as follows: Figure 3 As shown.

Claims

1. A method for regulating the inlet flow conductance of a NOx sensor ceramic chip, characterized in that, The method includes the following steps: (1) Under a test atmosphere with a specific NOx concentration, the E2-IP2 curve of the NOx sensor ceramic chip was measured, and the limiting current plateau value IP of the chip was obtained. 2T The NOx concentration is any value within the range of 10 to 2000 ppm; (2) Based on the measured limiting current plateau value IP 2T With the target limiting current plateau value IP 2G The difference between the two values ​​is used to calculate the required thickness of the porous diffusion barrier material. Target limiting current plateau value IP 2G Less than the measured limiting current plateau value IP 2T Target limiting current plateau value IP 2G The value range is 10~30μA; The porous diffusion barrier material is a zirconia-metal composite slurry. The main components of the slurry are zirconia powder, low-melting-point metal powder, and organic carrier. After high-temperature curing, it forms a zirconia-metal composite porous material. The thickness of the porous diffusion barrier material is calculated using equation (1): D=(IP 2T -IP 2G ) / k (1) In the formula: D is the thickness of the diffusion barrier material, in μm; IP 2T The measured value of the limiting current plateau of the sensor before adjustment, in μA; IP 2G The target value of the limiting current plateau value of the sensor after adjustment, in μA; k is the characteristic control coefficient of the porous diffusion barrier material, in μA / μm; (3) Print diffusion barrier material to the required thickness at the air inlet of the sensor ceramic chip using screen printing process; (4) The diffusion barrier material is cured by high-temperature heat treatment.

2. The method for regulating the inlet flow conductance of the NOx sensor ceramic chip according to claim 1, characterized in that, In the screen printing process described in step (3), the required printing thickness is achieved by adjusting the mesh count of the printing screen and the number of printing passes.

3. The method for regulating the inlet flow conductance of the NOx sensor ceramic chip according to claim 1, characterized in that, The low-melting-point metal is silver or copper.

4. The method for regulating the inlet flow conductance of the NOx sensor ceramic chip according to claim 1, characterized in that, The high-temperature heat treatment temperature mentioned in step (4) is 800~1200°C.

Images