High-temperature negative temperature coefficient thermosensitive ceramic material and preparation method thereof

Abstract

The application relates to a high-temperature negative temperature coefficient thermosensitive ceramic material and a preparation method thereof. 1‑ x Nb x O3 is prepared by a solid phase reaction method. The following raw materials are weighed according to percentage by weight: lanthanum sesquioxide 73.315-76.112%, aluminum sesquioxide 20.701-23.888%, and niobium pentoxide 1.540-5.985%; the preparation method comprises the following steps: S1. weighing; S2. mixing; S3. grinding; S4. pre-sintering; S5. secondary grinding; S6. tabletting; S7. cold isostatic pressing; S8. sintering; S9. platinum slurry coating; and S10. annealing. The high-temperature negative temperature coefficient thermosensitive ceramic material has a wide temperature range (600-1400 DEG C) and excellent aging stability; after aging for 400-600 hours at a high temperature of 1000 DEG C, the resistance drift rate of the LaAl 1‑x Nb x O3 sample is 0.906-3.352%, and the service life is long; in addition, the powder particles prepared by the application have high dispersity and are not prone to agglomeration, and the material strength is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of heat-sensitive materials, and particularly relates to a high-temperature-zone negative-temperature-coefficient heat-sensitive ceramic material and a preparation method thereof. BACKGROUND

[0002] Semiconductor ceramics, referred to as semi-conductive ceramics, are materials with semiconductor properties prepared by using ceramic technology. The electrical conductivity of semiconductor materials is between that of metals and insulators, and is about 10 -10 -10 3 Ω -1 cm -1 , and the electrical conductivity can be significantly changed by external conditions such as temperature, light, atmosphere and humidity. Due to this characteristic of semiconductor materials, the change of external physical quantities can be converted into an electrical signal that is easy to process, thereby making various sensor devices. From the field of sensitive elements, semiconductor ceramics can be divided into heat-sensitive ceramics, pressure-sensitive ceramics, light-sensitive ceramics, gas-sensitive ceramics and humidity-sensitive ceramics.

[0003] Heat-sensitive ceramics refer to the change of the electrical resistance of semi-conductive ceramics in various ways when the external temperature changes. According to the relationship between resistivity and temperature, they can be divided into PTC (positive temperature coefficient thermistor), NTC (negative temperature coefficient thermistor) and CTR (critical temperature coefficient thermistor). Compared with PTC and CTR thermistors, NTC thermistors have a series of advantages such as small size, fast response, high measurement accuracy and low cost, and have very important application value in the fields of automobile exhaust temperature control systems, household appliances and aviation. At present, a large number of perovskite materials are mainly applied in temperature zones higher than 300 degrees Celsius due to their unique crystal structure and variable crystal adjustability, and have become a research hotspot in the NTC field in recent years. At the same time, since the valence state of niobium elements is variable, it can provide a structural basis for the optimization of electrical properties of materials. With the continuous development of technology, NTC heat-sensitive materials applied in high-temperature zones have certain limitations in aging stability, and the resistance drift rate is high after use in a high-temperature environment for a period of time. Therefore, in order to improve the service life of NTC thermoelectric elements and broaden the application field of NTC thermoelectric elements, it is very important to develop a high-temperature heat-sensitive material with excellent stability. SUMMARY

[0004] The application aims to provide a novel high-temperature-zone negative-temperature-coefficient heat-sensitive ceramic material and a preparation method thereof.

[0005] The application provides a high-temperature-zone negative-temperature-coefficient heat-sensitive ceramic material, and the chemical composition of the heat-sensitive ceramic material is LaAl 1-x Nb x O3, wherein x=0.025-0.10.

[0006] Preferably, the heat-sensitive ceramic material is made mainly from the following raw materials by weight percentage: lanthanum trioxide 73.315-76.112%, aluminum trioxide 20.701-23.888%, and niobium pentoxide 1.540-5.985%.

[0007] Preferably, the heat-sensitive ceramic material has a resistivity of 68971.9-151582.3 Ω·cm at a temperature of 1000℃, and a resistance drift rate ΔR / R0(%) of 0.906-3.352% after aging at a high temperature of 1000℃ for 400-600 hours.

[0008] The present application provides a method for preparing a high-temperature negative temperature coefficient heat-sensitive ceramic material, comprising the following steps:

[0009] a. respectively weigh the raw materials lanthanum trioxide, aluminum trioxide, and niobium pentoxide, mix them, grind the mixture, and obtain a powder;

[0010] b. calcine the powder obtained in step a, grind it again, and obtain a LaAl 1-x Nb x O3 powder, wherein x=0.025-0.10;

[0011] c. press and form the LaAl 1-x Nb x O3 powder material obtained in step b, cold isostatic press the formed block material, and then sinter to obtain a high-temperature heat-sensitive ceramic material;

[0012] d. coat electrodes on both sides of the high-temperature ceramic material sintered in step c, and then anneal to obtain a high-temperature negative temperature coefficient heat-sensitive ceramic material.

[0013] Preferably, in step a, the raw materials lanthanum trioxide, aluminum trioxide, and niobium pentoxide are respectively weighed at 73.315-76.112%, 20.701-23.888%, and 1.540-5.985% by weight percentage, and the mixture is ground in a mortar for 6-10 hours.

[0014] Preferably, in step b, the calcination temperature is 1205-1350℃, the calcination time is 8-12 hours, and the grinding time is 6-8 hours.

[0015] Preferably, in step c, the pressure for pressing and forming is 10-20 Kg / cm 2 , the time is 1-2 min, the formed block material is cold isostatic pressed at a pressure of 250-350 MPa for 3-5 min, the sintering temperature is 1500-1550℃, and the sintering time is 15-25 hours.

[0016] Preferably, in step d, the high-temperature ceramic material is coated with platinum paste electrodes on both sides; the annealing temperature is 900-950℃, and the annealing time is 30-45min.

[0017] Compared with the prior art, the present application has the following advantages:

[0018] The high-temperature thermosensitive ceramic material of the present application uses lanthanum trioxide, aluminum trioxide and niobium pentoxide as raw materials, and is obtained by mixing, grinding, calcining, cold isostatic pressing, high-temperature sintering and electrode coating. The high-temperature thermosensitive ceramic material has a resistivity of 68971.9-151582.3Ω·cm at a material temperature of 1000℃, and a resistivity drift rate ΔR / R0(%) of 0.906-3.352% after aging for 400-600 hours at a high temperature of 1000℃. The resistive material has stable performance and good consistency, has obvious negative temperature coefficient characteristics in the temperature range of 600℃-1400℃, and is suitable for manufacturing high-temperature thermistor elements. In addition, the powder particles obtained by the present application have high dispersity and are not prone to agglomeration, and the material has high strength. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 XRD patterns of examples 1-5 of the present application;

[0020] Figure 2 Aging relationship diagram of the niobium-doped sample LaAl 1-x Nb x O3 obtained in examples 1-5 of the present application. DETAILED DESCRIPTION

[0021] The technical solutions of the present application will be described in detail below in combination with the drawings and examples.

[0022] Example 1

[0023] The present application provides a preparation method of a high-temperature negative temperature coefficient thermosensitive ceramic material, comprising the following steps:

[0024] a. According to the stoichiometric ratio of LaAl 1-x Nb x O3(x=0.025), lanthanum trioxide 75.4%, aluminum trioxide 23.06% and niobium pentoxide 1.54% are weighed according to the weight percentage and ground for 8 hours to obtain a powder;

[0025] b. The ground powder in step a is calcined at a temperature of 1300℃ for 10 hours, and then ground for 6 hours to obtain LaAl 1- x Nb x O3(x=0.025) powder;

[0026] c. The powder material obtained in step b is formed into briquettes at a pressure of 15 Kg / cm 2 for 1.5 min, and the formed briquette material is cold isostatic pressed at a pressure of 300 MPa for 3 min, and then sintered at a temperature of 1525°C for 20 hours to obtain a high-temperature thermosensitive ceramic material;

[0027] d. The sintered ceramic material of step c is coated with platinum paste electrodes on both sides, and then annealed at a temperature of 900°C for 30 min to obtain a high-temperature negative temperature coefficient thermosensitive ceramic material having a negative temperature coefficient characteristic in the temperature range of 600°C-1400°C, a resistivity of 151582.3 Ω-cm at a material temperature of 1000°C, and a resistance drift rate ΔR / R0 (%) of 1.967% after aging at a high temperature of 1000°C for 500 hours.

[0028] Example 2

[0029] a. A stoichiometric ratio of LaAl 1-x Nb x O3(x=0.05) is weighed in percentage by weight as follows: 74.69% of lanthanum trioxide, 22.26% of aluminum trioxide, and 3.05% of niobium pentoxide, and the mixture is ground in an agate mortar for 7 hours to obtain a powder;

[0030] b. The ground powder of step a is calcined at a temperature of 1330°C for 9 hours, and then ground for 7 hours to obtain a LaAl 1- x Nb x O3(x=0.05) powder;

[0031] c. The powder material obtained in step b is formed into briquettes at a pressure of 18 Kg / cm 2 for 1.5 min, and the formed briquette material is cold isostatic pressed at a pressure of 300 MPa for 3.5 min, and then sintered at a temperature of 1525°C for 20 hours to obtain a high-temperature thermosensitive ceramic material;

[0032] d. The sintered ceramic material of step c is coated with platinum paste electrodes on both sides, and then annealed at a temperature of 920°C for 35 min to obtain a high-temperature negative temperature coefficient thermosensitive ceramic material having a negative temperature coefficient characteristic in the temperature range of 600°C-1400°C, a resistivity of 84998.9 Ω-cm at a material temperature of 1000°C, and a resistance drift rate ΔR / R0 (%) of 3.352% after aging at a high temperature of 1000°C for 550 hours.

[0033] Example 3

[0034] a. A stoichiometric ratio of LaAl 1-x Nb xThe stoichiometric ratio of O3(x=0.075) is weighed by percentage of lanthanum trioxide 73.995%, aluminum trioxide 21.475%, and niobium pentoxide 4.53% respectively, and the mixture is ground in an agate mortar for 9 hours to obtain a powder;

[0035] b. The ground powder in step a is calcined at a temperature of 1350℃ for 10 hours, and then ground for 8 hours to obtain LaAl 1- x Nb x O3(x=0.075) powder;

[0036] c. The powder material obtained in step b is briquetted at a pressure of 20 Kg / cm 2 for 2 minutes, and the briquetted material is cold isostatic pressed at a pressure of 320 MPa for 3 minutes, and then sintered at a temperature of 1530℃ for 25 hours to obtain a high-temperature thermosensitive ceramic material;

[0037] d. The ceramic material sintered in step c is coated with platinum paste electrodes on both sides, and then annealed at a temperature of 920℃ for 40 minutes to obtain a high-temperature negative temperature coefficient thermosensitive ceramic material having a negative temperature coefficient characteristic in a temperature range of 600℃-1400℃, a resistivity of 118363.4 Ω·cm at a material temperature of 1000℃, and a resistivity drift rate ΔR / R0(%) of 1.531% after aging at a high temperature of 1000℃ for 500 hours.

[0038] Example 4

[0039] a. The stoichiometric ratio of LaAl 1-x Nb x O3(x=0.1) is weighed by percentage of lanthanum trioxide 73.315%, aluminum trioxide 20.7%, and niobium pentoxide 5.985% respectively, and the mixture is ground in an agate mortar for 10 hours to obtain a powder;

[0040] b. The ground powder in step a is calcined at a temperature of 1320℃ for 10 hours, and then ground for 7.5 hours to obtain LaAl 1-x Nb x O3(x=0.1) powder;

[0041] c. The powder material obtained in step b is briquetted at a pressure of 10 Kg / cm 2 for 1 minute, and the briquetted material is cold isostatic pressed at a pressure of 350 MPa for 5 minutes, and then sintered at a temperature of 1525℃ for 20 hours to obtain a high-temperature thermosensitive ceramic material;

[0042] d, coating the sintered ceramic material of step c with platinum paste electrodes on both sides, then annealing at a temperature of 900 DEG C for 30 minutes, to obtain a high-temperature negative temperature coefficient thermosensitive ceramic material having a negative temperature coefficient characteristic in a temperature range of 600 DEG C-1400 DEG C, a resistivity of 145626.2 ohm-cm at a material temperature of 1000 DEG C, and a resistance drift rate AR / RO (%) of 0.906% after aging at a high temperature of 1000 DEG C for 600 hours.

[0043] Comparative Example 5

[0044] a, according to the stoichiometric ratio of LaAlO3, 15.222 parts of lanthanum trioxide and 4.778 parts of aluminum trioxide were weighed and mixed, and the mixed raw materials were ground in an agate mortar for 8 hours to obtain a powder;

[0045] b, the ground powder in step a was calcined at a temperature of 1300 DEG C for 10 hours, and after grinding for 6 hours, LaAlO3 powder was obtained;

[0046] c, the powder material obtained in step b was formed into a block with a pressure of 15 Kg / cm 2 for 2 min, and the formed block material was cold isostatic pressed at a pressure of 300 MPa for 4 min, and then sintered at a temperature of 1600 DEG C for 20 hours to obtain a high-temperature thermosensitive ceramic material;

[0047] d, coating the sintered thermosensitive ceramic material of step c with platinum paste electrodes on both sides, then annealing at a temperature of 900 DEG C for 30 minutes, to obtain a perovskite high-temperature thermosensitive ceramic resistor material having a negative temperature coefficient characteristic in a temperature range of 600 DEG C-1400 DEG C, a resistivity of 68971.9 ohm-cm at a material temperature of 1000 DEG C, and a resistance drift rate AR / RO (%) of 1.294% after aging at a high temperature of 1000 DEG C for 500 hours.

[0048] The experimental results are as follows:

[0049] Comparing any one of the new high-temperature negative temperature coefficient thermosensitive ceramic materials obtained in Examples 1-4 with the comparative example, see Figure 1 , the results show that as the content of niobium pentoxide increases, the diffraction peaks of all samples can well match the perovskite structure of LaAlO3, and no second phase is generated, indicating that the niobium element is successfully doped into the LaAlO3 phase.

[0050] Figure 2 The aging relationship diagram of the obtained sample LaAl 1-x Nb x O3 by niobium doping shows that after sintering, LaAl 1-x Nb xThe relationship between the aging resistance drift rate (AR / R0) of the O3 ceramic and the aging time t can be seen from the figure, and when the doping amount of niobium is between 0.025-0.075, the aging resistance drift rate (AR / R0) of the LaAl 1-x Nb x The aging resistance drift rate (AR / R0) of the O3 material is between 1.531-3.352% after aging for 400-600 hours at 1000 degrees Celsius, the aging resistance drift rate (AR / R0) of the undoped LaAlO3 material is 1.976% after aging for 500 hours at 1000 degrees Celsius, and when the doping amount of niobium is 0.1, the aging resistance drift rate (AR / R0) of the LaAl 1-x Nb x The aging resistance drift rate (AR / R0) of the O3 material is as low as 0.906% after aging for 500 hours at 1000 degrees Celsius, effectively improving the aging stability of the LaAlO3 material in the high temperature region, effectively prolonging the service life of the LaAlO3 material in the high temperature environment, and making the LaAl 1-x Nb x The O3 material becomes a new type of negative temperature coefficient thermosensitive ceramic material that can be applied to temperature measurement in the high temperature region, and is expected to be applied to temperature measurement in some special high temperature environments such as aviation and deep sea.

[0051] The new high-temperature negative temperature coefficient thermosensitive ceramic material LaAl 1-x Nb x O3 is prepared by a solid phase reaction method. The raw materials are weighed according to the following mass percentage: lanthanum trioxide 73.315-76.112%, aluminum trioxide 20.701-23.888%, and niobium pentoxide 1.540-5.985%; the preparation method comprises the following steps: S1. weighing; S2. mixing; S3. grinding; S4. pre-sintering; S5. secondary grinding; S6. tabletting; S7. isostatic pressing; S8. sintering; S9. platinum slurry coating; S10. annealing; and S11. welding a lead wire. The NTC thermistor has a wide temperature range (600-1400 degrees Celsius) and excellent aging stability, and the aging resistance drift rate (AR / R0) of the LaAl 1-x Nb x The resistance drift rate of the O3 sample is 0.906-3.352%, and the material has the advantages of long service life and the like; in addition, the powder particles prepared by the method have high dispersity and are not prone to agglomeration, and the material has high strength.

[0052] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the examples, those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present application do not deviate from the spirit and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for preparing a high-temperature negative temperature coefficient thermosensitive ceramic material, characterized in that: The chemical composition of the heat sensitive ceramic material is LaAl 1-x Nb x O3, wherein x = 0.10; The heat-sensitive ceramic material is mainly made of raw materials in percentage by weight: lanthanum trioxide 73.315%, aluminum trioxide 20.701%, and niobium pentoxide 5.985%; The heat-sensitive ceramic material has a resistivity of 145626.2 Ω·cm at a temperature of 1000 ℃, and a resistance drift rate ΔR / R0 of 0.906% after aging for 600 hours at a high temperature of 1000 ℃; The preparation method comprises the following steps: a. respectively weighing raw materials of lanthanum trioxide, aluminum trioxide and niobium pentoxide, mixing, and grinding the mixture to obtain a powder; b. calcining the powder obtained in step a, and grinding to obtain LaAl 1-x Nb x O3 powder; c. compressing the LaAl 1-x Nb x O3 powder material to form a block, cold isostatic pressing the block, and then sintering to obtain a high-temperature thermosensitive ceramic material. d. coating electrodes on both sides of the high-temperature ceramic material sintered in step c, and then annealing to obtain a high-temperature negative temperature coefficient heat-sensitive ceramic material.

2. The method for preparing high-temperature NTC thermistor ceramic material according to claim 1, characterized in that: In step a, the mixture is ground in a mortar for 6-10 hours.

3. The method for preparing high-temperature NTC thermistor ceramic material according to claim 1, characterized in that: In step b, the calcination temperature is 1205-1350 ℃, the calcination time is 8-12 hours, and the grinding time is 6-8 hours.

4. The method for preparing the high-temperature region negative temperature coefficient thermistor ceramic material according to claim 1, characterized in that: The pressure for briquetting in step c is 10-20 Kg / cm 2 The briquetted material is cold isostatic pressed at a pressure of 250-350 MPa for 3-5 min, and sintered at a temperature of 1500-1550℃ for 15-25 hours.

5. The method for preparing the high-temperature region negative temperature coefficient thermistor ceramic material according to claim 1, characterized in that: In step d, platinum paste electrodes are coated on both sides of the high-temperature ceramic material; the annealing temperature is 900-950 ℃, and the annealing time is 30-45 min.

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