CN1334461A - Process for preparing air/fuel ratio thick-film sensor with wide temp range and narrow resistance band - Google Patents

Abstract

The preparation method of thick film air/fuel ratio sensor with wide temperature and narrow resistance band, according to the increase of grain boundary barrier height of N-type transition metal oxide semiconductor in oxidizing atmosphere and the reduction of grain boundary barrier height in reducing atmosphere, adopts rutile type TiO ₂ structure N-type doping is carried out in the body, and P-type compound diffusion is carried out at the grain boundary. The conductance of the sample decreased sharply in the oxidizing atmosphere, and increased sharply in the reducing atmosphere. Thick film technology is used to make the sample in the range of 250 ℃ ~ 800 ℃, so that the lowest resistance value in the oxidation state at the high temperature end and the highest resistance value in the reduction state at the low temperature end have a difference of 1 to 3 orders of magnitude. The performance of the sensor is greatly improved by adopting the preparation method, and the cost is low.

Description

Preparation method of thick film air/fuel ratio sensor with wide temperature and narrow resistance band

1. Technical field

The invention relates to an air/fuel ratio control sensor, and further relates to a preparation method of the sensor for air/fuel ratio control of various engines, combustion equipment and appliances.

2. Background technology

Air-fuel ratio control sensors have appeared on the market with ZrO ₂ concentration battery type, TiO ₂ and other oxide single-phase mixed resistance type. The ZrO ₂ concentration battery type has the problems of lead poisoning, structural phase change and high price in the range of room temperature to 800 ℃, and has the disadvantages of early failure and high cost in use. For this reason, people have done a lot of research on TiO ₂ and other oxide single-phase mixed resistance sensors, because in the wide temperature range from room temperature to 800 ° C, there are: (1) wide resistance band, high resistance state in the reduced state ; (2) Short life; (3) Shortcomings such as complex signal circuit. So it has not been put into use in large quantities so far. The research of IBMD method has been carried out again recently, but due to problems such as high preparation cost, difficulty in guaranteeing performance, and high heating temperature, it has not been popularized. However, with the increase in the number of automobiles, urban air pollution mainly comes from the emission of automobile exhaust. When the air/fuel ratio of various combustion equipment, appliances and automobile engines is improper, on the one hand, a large amount of harmful gases will be emitted, polluting the environment; on the other hand The energy cannot be fully utilized, resulting in waste.

3. Contents of the invention

The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a long-life, low-price, high-performance preparation method of a thick-film air/fuel ratio sensor with wide temperature and narrow resistance band. The technical scheme adopted in the present invention is: according to the improvement of the grain boundary barrier height of the N-type transition metal oxide semiconductor in the oxidizing atmosphere, and the reduction of the grain boundary barrier height in the reducing atmosphere, the N-type N-type transition metal oxide semiconductor is carried out in the body by using the rutile _TiO2 structure. Doping, the grain boundary undergoes P-type recombination diffusion. The conductivity of the sample decreases sharply in an oxidizing atmosphere, and increases sharply in a reducing atmosphere. The thick film process is used to make the sample in the range of 250 ° C to 800 ° C, so that the lowest resistance value in the oxidation state at the high temperature end and the highest resistance value in the reduction state at the low temperature end have a difference of 1 to 3 orders of magnitude.

The preparation process of the present invention is:

1) Grinding the semiconductor ceramic powder reagent capable of synthesizing (TiSnNb) _O2- based rutile structure into a compact, and then firing at 1000°C to 1350°C for 30 minutes to 4 hours;

2) After pulverization, it is mixed with (0-20)%wt medium-temperature glass powder to make a sensitive powder paste for printing;

3) After screen-printing the interdigitated electrodes on the alumina substrate, place them at 800°C to 1000°C for 20 minutes to 1 hour;

4) After screen-printing the sensitive powder paste, place it at 1000°C-1350°C for 1-2 hours and control the cooling rate at 120°C-180°C per minute to cool the sample and make a sensitive element;

5) Then use platinum slurry to weld the platinum wire and the interdigitated electrode lead-out end of the sensitive element, place it at 800°C-1000°C for 10-20 minutes, and let the sample cool down naturally;

6) Screen-print the heater paste on the back of the sensitive element, and place it at 650°C-850°C for 10-45 minutes;

7) After impregnating or coating 10%-50% catalyst salt solution, place it at 700°C-1000°C and burn for 30 minutes-2 hours.

By adopting the preparation method of the invention, the performance of the air/fuel ratio sensor is improved, the manufacturing cost is reduced, and the control effect of the air-fuel ratio sensor is further improved.

4. Specific implementation

Example 1: After finely grinding the porcelain powder sample reagent whose composition is 0.63TiO ₂ +0.2SnO ₂ +0.05Nb ₂ O ₅ +0.12Bi2O ₃ , it was fired at 1000°C for 30 minutes to make a sensitive powder for printing Slurry; After screen-printing interdigitated electrodes on alumina substrates, place them at 800°C for 20 minutes; then use screen-printed sensitive powder paste, place them at 1000°C for 1 hour, and control the cooling rate Cool the sample at 120°C per minute to make a sensitive element; then use platinum slurry to weld the platinum wire and the interdigital electrode lead-out end of the sensitive element, and burn at 800°C for 10 minutes to cool the sample naturally; The heater paste is screen-printed on the back of the element, and fired at 650°C for half an hour; after being immersed in a 10% catalyst PdCl ₂ solution, fired at 700°C for 30 minutes.

The prepared sample is in an oxidizing atmosphere: within 250°C-800°C, the resistance value is 50kΩ-1000kΩ.

Under reducing atmosphere: within 250℃～800℃, the resistance value is 95Ω～50Ω.

Example 2: After grinding the ceramic powder sample reagent with the composition of 0.63TiO ₂ +0.2SnO ₂ +0.05Nb ₂ O ₅ +0.12Bi ₂ O ₃ into a compact, it was fired at 1350°C for 4 hours, and after fine powdering Mix with 20%wt medium-temperature glass powder to make a sensitive powder paste for printing; screen-print the interdigitated electrode on the alumina substrate, and then burn it at 1000°C for 1 hour; then use the screen-printed sensitive powder paste Finally, place it at 1350°C for 2 hours and control the cooling rate at 180°C per minute to cool the sample to make a sensitive element; then use platinum slurry to weld the platinum wire and the interdigitated electrode of the sensitive element. Burn at 1000°C for 20 minutes, let the sample cool naturally; screen print the heater paste on the back of the sensitive element, and place it at 850°C for 10 minutes; apply 30% catalyst H ₄ PtCl ₂ solution, place Burn at 1000°C for 2 hours.

The prepared sample is in an oxidizing atmosphere: within 250°C-800°C, the resistance value is 50kΩ-1000kΩ.

Under reducing atmosphere: within 250℃～800℃, the resistance value is 95Ω～250Ω.

Example 3: After the porcelain powder sample reagent with the composition of 0.63TiO ₂ +0.2SnO ₂ +0.05 Nb ₂ O ₅ +0.12Bi ₂ O ₃ was ground and crushed, it was fired at 1150°C for 2 hours, and the fine powder After melting, mix it with 10%wt medium-temperature glass powder to make a sensitive powder paste for printing; screen-print the interdigitated electrode on the alumina substrate, and then burn it at 900°C for 40 minutes; then use the screen-printed sensitive powder After making the slurry, place it at 1150°C for 1.5 hours and control the cooling rate at 150°C per minute to cool the sample to make a sensitive element; then use platinum slurry to weld the platinum wire and the interdigitated electrode lead-out end of the sensitive element , burn at 900°C for 15 minutes, and cool the sample naturally; screen-print the heater paste on the back of the sensitive element, and burn at 700°C for 45 minutes; after coating 50% catalyst salt PdCl2 solution, place Burn at 900°C for 1 hour.

The prepared sample is in an oxidizing atmosphere: within 250°C-800°C, the resistance value is 50kΩ-1000kΩ.

Under reducing atmosphere: within 250℃～800℃, the resistance value is 95Ω～250Ω.

Example 4: After finely grinding the ceramic powder sample reagent of the component 0.64TiO ₂ +0.3SnO ₂ +0.06Nb ₂ O ₅ into a compact, it was fired at 1000°C for 30 minutes to make a sensitive powder paste for printing; After screen-printing interdigitated electrodes on the aluminum substrate, place them at 800°C for 20 minutes; then use screen printing for sensitive powder paste, place them at 1000°C for 1 hour, and control the cooling rate at 120°C per minute , to cool the sample to make a sensitive element; then use platinum paste to melt the platinum wire and the interdigitated electrode lead-out end of the sensitive element, and place it at 800°C for 10 minutes to cool the sample naturally; screen printing on the back of the sensitive element Heat the slurry and place it at 650°C for 10 minutes; after soaking in a 10% catalyst H ₄ PtCl ₂ solution, burn it at 700°C for 30 minutes.

The prepared sample is in an oxidizing atmosphere: within 250°C-800°C, the resistance value is 50kΩ-1000kΩ.

The prepared sample is under reducing atmosphere: within 250°C-800°C, the resistance value is 85Ω-150Ω.

Example 5: after finely grinding the porcelain powder sample reagent of the component 0.64TiO ₂ +0.3SnO ₂ +0.06Nb ₂ O ₅ to make a billet, place it at 1200°C for 2 hours, and after fine powdering, mix with 8%wt medium temperature glass powder mixed to make a sensitive powder paste for printing; after screen-printing interdigitated electrodes on an alumina substrate, burn at 900°C for 40 minutes; Burn for 1.5 hours, control the cooling rate at 150°C per minute, cool the sample, and make a sensitive element; then use platinum slurry to weld the platinum wire and the interdigitated electrode lead of the sensitive element, and place it at 900°C for 16 Minutes, let the sample cool down naturally; screen-print the heater paste on the back of the sensitive element, and place it at 700°C for 25 minutes; soak it in a 25% catalyst PdCl ₂ solution, and burn it at 900°C for 1 hour.

The prepared sample is in an oxidizing atmosphere: within 250°C-800°C, the resistance value is 50kΩ-1000kΩ.

The prepared sample is under reducing atmosphere: within 250°C-800°C, the resistance value is 85Ω-150Ω.

Example 6: after finely grinding the ceramic powder sample reagent of the component 0.64TiO ₂ +0.3SnO ₂ +0.06Nb ₂ O ₅ into a billet, place it at 1350°C for 4 hours, and after fine powdering, mix with 20%wt medium temperature glass powder mixed to make a sensitive powder paste for printing; after screen-printing interdigitated electrodes on an alumina substrate, place it at 1000°C for 1 hour; Burn for 2 hours, control the cooling rate at 180°C per minute, cool the sample to make a sensitive element; then use platinum slurry to weld the platinum wire and the interdigitated electrode lead-out end of the sensitive element, and place it at 1000°C for 20 minutes, let the sample cool naturally; screen-print the heater paste on the back of the sensitive element, and place it at 850°C for 45 minutes; after coating 50% catalyst H ₄ PtCl ₂ solution, burn it at 1000°C for 2 hours.

The prepared sample is in an oxidizing atmosphere: within 250°C-800°C, the resistance value is 50kΩ-1000kΩ.

The prepared sample is under reducing atmosphere: within 250°C-800°C, the resistance value is 85Ω-150Ω.

Example 7: after finely grinding the ceramic powder sample reagent of the component 0.63TiO ₂ +0.30SnO ₂ +0.07Nb ₂ O ₅ to make a billet, place it at 1000°C for 4 hours, and after fine powdering, mix with 20%wt medium temperature glass powder mixed to make a sensitive powder paste for printing; after screen-printing interdigitated electrodes on an alumina substrate, burn at 800°C for 1 hour; Burn for 2 hours, control the cooling rate at 120°C per minute, cool the sample to make a sensitive element; then use platinum slurry to melt the platinum wire and the interdigitated electrode lead-out end of the sensitive element, and place it at 1000°C for 10 minutes. , let the sample cool naturally; screen-print the heater paste on the back of the sensitive element, and place it at 850°C for 10 minutes; after coating 50% catalyst PdCl ₂ solution, burn it at 700°C for 2 hours.

The prepared sample is in an oxidizing atmosphere: within 250°C to 800°C, the resistance value is 200kΩ to 5×10 ⁶ Ω.

The prepared sample is under reducing atmosphere: within 250°C-8000°C, the resistance value is 150Ω-220Ω.

Example 8: After finely grinding the ceramic powder sample reagent of the component 0.63TiO ₂ +0.30SnO ₂ +0.07Nb ₂ O ₅ to make a billet, place it at 1350°C for 30 minutes and make a sensitive powder paste for printing; After screen-printing the interdigitated electrodes on the alumina substrate, burn them at 1000°C for 20 minutes; then print the sensitive powder paste on the screen, burn them at 1350°C for 1 hour, and control the cooling rate at 180°C per minute , to cool the sample to make a sensitive element; then use platinum paste to melt the platinum wire and the interdigital electrode lead-out end of the sensitive element, and place it at 800 ° C for 20 minutes to cool the sample naturally; screen printing on the back of the sensitive element Heater the slurry and place it at 650°C for 45 minutes; soak it in a 10% catalyst H ₄ PtCl ₂ solution and burn it at 1000°C for 30 minutes.

The prepared sample is in an oxidizing atmosphere: within 250°C to 800°C, the resistance value is 200kΩ to 5×10 ⁶ Ω.

The prepared sample is under reducing atmosphere: within 250°C-800°C, the resistance value is 150Ω-220Ω.

Example 9: after finely grinding the ceramic powder sample reagent of the component 0.63TiO ₂ +0.30SnO ₂ +0.07Nb ₂ O ₅ to make a billet, place it at 1200°C for 3 hours, and after fine powdering, mix with 15%wt medium temperature glass powder mixed to make a sensitive powder paste for printing; after screen-printing interdigitated electrodes on an alumina substrate, burn them at 920°C for 45 minutes; Burn for 1.5 hours, control the cooling rate at 140°C per minute, cool the sample to make a sensitive element; then use platinum slurry to melt the platinum wire and the interdigitated electrode lead of the sensitive element, and place it at 900°C for 18 minutes. , Allow the sample to cool naturally; screen-print the heater paste on the back of the sensitive element, and place it at 750°C for half an hour, and then soak it in a 28% catalyst PdCl ₂ solution, and then burn it at 950°C for 1 hour.

The prepared sample is in an oxidizing atmosphere: within 250°C to 800°C, the resistance value is 200kΩ to 5×10 ⁶ Ω.

The prepared sample is under reducing atmosphere: within 250°C-800°C, the resistance value is 150Ω-220Ω.

Claims (8)

1. A method for preparing a thick film air/fuel ratio sensor with wide temperature and narrow resistance band, characterized in that: 1) Grinding the semiconductor ceramic powder reagent capable of synthesizing (TiSnNb) _O2- based rutile structure into a compact, and then firing at 1000°C to 1350°C for 30 minutes to 4 hours; 2) After fine powdering, it is mixed with 0-20%wt medium-temperature glass powder to make a sensitive powder paste for printing; 3) After screen-printing interdigitated electrodes on an alumina substrate, burn them at 800°C to 1000°C for 20 minutes to 1 hour; 4) After printing the sensitive powder paste with screen printing, place it at 1000°C-1350°C for 1-2 hours and control the cooling rate at 120°C-180°C per minute to cool the sample and make a sensitive element; 5) Then use platinum slurry to weld the platinum wire and the interdigitated electrode lead-out end of the sensitive element, place it at 800°C-1000°C for 10-20 minutes, and let the sample cool down naturally; 6) Screen-print the heater paste on the back of the sensitive element, and place it at 650°C-850°C for 15-45 minutes; 7) Dip or apply 10% to 50% catalyst salt solution, and burn at 700°C to 1000°C for 30 minutes to 2 hours. 2. The preparation method of the wide temperature narrow resistance band thick film air/fuel ratio sensor according to claim 1, characterized in that: 1) Grinding the semiconductor ceramic powder reagent capable of synthesizing (TiSnNb) _O2- based rutile structure into a compact, and then firing at 1000°C for 30 minutes; 2) Make sensitive powder paste for printing after fine powdering; 3) After screen-printing interdigitated electrodes on an alumina substrate, burn them at 800°C for 20 minutes; 4) After screen-printing the sensitive powder paste, place it at 1000°C for 1 hour, and control the cooling rate of the sample at 120°C per minute to cool it down to make a sensitive element; 5) Then use platinum slurry to weld the platinum wire and the interdigitated electrode lead-out end of the sensitive element, place it at 800°C for 10 minutes, and let the sample cool down naturally; 6) Screen-print the heater paste on the back of the sensitive element, and burn it at 650°C for 10 minutes; 7) Soak in 10% catalyst salt solution and burn at 700°C for 30 minutes. 3. The preparation method of wide temperature narrow resistance band thick film air/fuel ratio sensor according to claim 1, characterized in that: 1) Grinding the semiconductor ceramic powder reagent capable of synthesizing (TiSnNb)O2 _- based rutile structure into a compact, and then firing at 1100°C for 2 hours; 2) After fine powdering, 10%wt medium-temperature glass powder is mixed to make a sensitive powder paste for printing; 3) After screen-printing interdigitated electrodes on an alumina substrate, burn them at 900°C for 40 minutes; 4) After screen-printing the sensitive powder paste, place it at 1100°C for 1.5 hours and control the cooling rate at 150°C per minute to cool the sample to make a sensitive element; 5) Then use platinum slurry to weld the platinum wire and the interdigitated electrode lead-out end of the sensitive element, place it at 900°C for 15 minutes, and let the sample cool down naturally; 6) Screen-print the heater paste on the back of the sensitive element, and burn it at 750°C for half an hour; 7) Apply 30% catalyst salt solution and burn at 850°C for 1 hour. 4. The preparation method of wide temperature narrow resistance band thick film air/fuel ratio sensor according to claim 1, characterized in that: 1) Grinding the semiconductor ceramic powder reagent capable of synthesizing (TiSnNb)O2 _- based rutile structure into a compact, and firing it at 1350°C for 4 hours; 2) After fine powdering, mix with 20%wt medium temperature glass powder to make sensitive powder paste for printing; 3) After screen-printing interdigitated electrodes on an alumina substrate, burn them at 1000°C for 1 hour; 4) After screen-printing the sensitive powder paste, place it at 1350°C for 2 hours and control the cooling rate at 180°C per minute to cool the sample to make a sensitive element; 5) Then use platinum slurry to melt the platinum wire and the interdigitated electrode lead-out end of the sensitive element, place it at 1000°C for 20 minutes, and let the sample cool down naturally; 6) Screen-print the heater paste on the back of the sensitive element, and burn it at 850°C for 45 minutes; 7) Soak in 50% catalyst salt solution, and burn at 1000°C for 2 hours. 5. The method for preparing a thick-film air/fuel ratio sensor with wide temperature and narrow resistance band base according to claim 1, characterized in that the content of TiO ₂ in the (TiSnNb)O ₂ base is 0.63mol-0.64mol. 6. The method for preparing a thick-film air/fuel ratio sensor with wide temperature and narrow resistance band according to claim 1, characterized in that the content of SnO ₂ in the (TiSnNb)O ₂ base is 0.2mol-0.3mol. 7. The preparation method of wide temperature and narrow resistance band thick film air/fuel ratio sensor according to claim 1, characterized in that: the content of Nb ₂ O ₅ in said (TiSnNb)O ₂ base is 0.05mol～0.07mol . 8. The preparation method of wide temperature and narrow resistance band thick film air/fuel ratio sensor according to claim 1, characterized in that: said salt solution is PdCl ₂ or H ₄ PtCl ₂ solution.