High curie temperature low resistance lead-free thermosensitive ceramic and preparation method thereof

Abstract

The application provides high-curie-temperature low-resistance lead-free thermosensitive ceramic and a preparation method thereof, and belongs to the technical field of electronic ceramic elements. 1‑x‑y La x (Bi 0.5 Na 0.5 ) y )(Ti 0.9996 Mn 0.0004 )O3; wherein the value range of x is 0.001<=x<=0.004, and the value range of y is 0.001<=y<=0.0075. The preparation method comprises the following steps: mixing (Bi 0.5 Na 0.5 )TiO3 powder synthesized by two-stage heating hydrothermal method, (Ba 1‑x La x )TiO3 powder synthesized by solid-phase reaction method, Mn(NO3)2 aqueous solution and sintering auxiliary agent AST powder, then performing granulation, molding, glue removal and sintering. The barium titanate-based thermosensitive ceramic prepared by the method has extremely low room temperature resistivity and relatively high curie temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic ceramic elements, in particular to a high-curie-temperature low-resistance lead-free thermosensitive ceramic and a preparation method thereof. BACKGROUND

[0002] Barium titanate (BaTiO3) -based positive temperature coefficient resistance (PTCR) ceramic material, due to its unique resistance-temperature characteristics, can be used to manufacture various automatic constant temperature heating bodies, starting switch elements, overcurrent and overheat protection elements and side heat information sensing temperature sensors, etc., and is widely used in the fields of variable frequency controllers of household appliances, new energy automobile pre-charging and charging piles, various types of motors, etc. In recent years, the rapid development of new energy vehicles, power electronic systems, etc. requires thermistor elements to have higher use temperatures. For barium titanate-based PTCR ceramic materials, the temperature at which the resistance sharply rises is near the Curie temperature (Tc) T c ~120 °C), so increasing the Curie temperature is a prerequisite for expanding the use of barium titanate-based PTCR ceramic materials at relatively high temperatures. At present, for barium titanate-based PTCR ceramic materials with Tc T C >120 °C, lead oxide (PbO or Pb3O4) or lead titanate (PbTiO3, Pb2TiO4) is usually added to BaTiO3 to obtain a high Curie temperature. However, barium titanate-based PTCR ceramic materials containing Pb may cause environmental pollution during production and waste disposal, so the development of lead-free barium titanate-based PTCR thermosensitive ceramic materials with high Curie temperature has become a major development trend. T c =390 °C). However, barium titanate-based PTCR ceramic materials containing Pb may cause environmental pollution during production and waste disposal, so the development of lead-free barium titanate-based PTCR thermosensitive ceramic materials with high Curie temperature has become a major development trend.

[0003] (Bi 0.5 Na 0.5 )TiO3 (BNT) is a kind of material with relatively high Curie temperature (Tc T CLead-free ferroelectric materials with a perovskite structure (320 °C) can form a solid solution with BaTiO3 and increase its Curie temperature. In 2005, Takeda et al. discovered that doping with 5 mol% BNT could raise the Curie temperature of BaTiO3 to about 170 °C (Applied Physics Letters, 2005, 87(10): 102–104), sparking a surge in the research and development of lead-free barium titanate-based PTCR ceramics. Numerous studies have shown that doping BaTiO3 with BNT can increase the Curie temperature of BaTiO3-based PTCR ceramics, but the room temperature resistivity also increases significantly. When the BNT content exceeds 2 mol%, BaTiO3-based ceramics sintered in air cannot even be semiconductorized, making them difficult to apply in practice. Currently, lead-free PTCR ceramics with good overall performance require sintering in a reducing atmosphere followed by oxidation treatment. The preparation process is sensitive and not suitable for mass production of PTCR ceramics. Therefore, how to prepare BaTiO3-based lead-free PTCR ceramics with good overall performance by sintering in an air atmosphere remains an unsolved technical problem.

[0004] Currently, the preparation of BNT-doped BaTiO3-based lead-free PTCR ceramics mostly adopts the traditional solid-state reaction method to synthesize ceramic powder. Its advantages are mature technology, simple process and low cost. However, the ceramic powder synthesized by the solid-state reaction method is often not sufficiently dispersed and the chemical composition is not uniform enough, which affects the electrical properties of the PTCR ceramic after sintering.

[0005] By doping BaTiO3-based PTCR ceramics with trace amounts of BNT, and increasing the Curie temperature without significantly increasing the room temperature resistivity, good overall PTCR performance can be achieved. However, it is necessary to overcome the problem of uneven chemical composition in ceramic powders synthesized by solid-state reaction methods. Summary of the Invention

[0006] This invention proposes a high Curie temperature, low resistance lead-free thermistor ceramic and its preparation method, which solves the problem that in the preparation of BaTiO3-based lead-free PTCR ceramic materials, the ceramic powder synthesized by solid-state reaction method is not sufficiently dispersed and the chemical composition is not uniform enough, thus affecting the electrical properties of the PTCR ceramic after sintering.

[0007] The first aspect of this invention proposes a high Curie temperature, low resistance, lead-free thermistor ceramic, wherein the chemical formula of the thermistor ceramic is (Ba... 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004O3; where the range of x is 0.001 ≤ x ≤ 0.004, and the range of y is 0.001 ≤ y ≤ 0.0075.

[0008] A second aspect of this invention provides a method for preparing the above-mentioned high Curie temperature, low resistance, lead-free thermistor ceramic, comprising the following steps:

[0009] Step 1: Using BaCO3, TiO2, and La2O3 as raw materials, a solid-state reaction synthesis method is employed to prepare (BaCO3, TiO2, and La2O3). 1-x La x )TiO3 powder;

[0010] Step 2: Using Bi(NO3)3·5H2O, Ti(OC4H9)4, and NaOH as raw materials, a two-stage hydrothermal reaction method is employed to synthesize (Bi 0.5 Na 0.5 )TiO3 powder;

[0011] Step 3: According to (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 Weigh out the stoichiometric amount of O3 obtained in step one (Ba 1-x La x TiO3 powder, Bi obtained in step two 0.5 Na 0.5 TiO3 powder and Mn(NO3)2 were mixed with AST powder and ball-milled with anhydrous ethanol, then dried and ground.

[0012] Step 4: Add polyvinyl alcohol and liquid paraffin to the powder ground in Step 3 to granulate, and then put the granulated powder into a mold to press it into a green body;

[0013] Step 5: Place the green body obtained in Step 4 into a box furnace for debinding and sintering to obtain (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3 ceramic sheet.

[0014] Preferably, in step one, the preparation of (Ba) is carried out using a solid-state reaction synthesis method. 1-x La x The process of producing TiO3 powder is as follows: according to (Ba 1-x La xThe raw materials were weighed according to the stoichiometric ratio of TiO3, and ball-milled with anhydrous ethanol in a ball mill jar at a volume ratio of 1:1. After ball milling, the slurry was dried in an oven, ground, sieved, and calcined at 1200~1300℃ for 2 hours. Then, it was cooled to room temperature in the furnace to obtain (Ba 1-x La x )TiO3 powder.

[0015] Preferably, in step two, the synthesis of (Bi) is carried out using a two-stage heating hydrothermal reaction method. 0.5 Na 0.5 The process for producing TiO3 powder is as follows: Bi(NO3)3·5H2O and Ti(OC4H9)4 are weighed according to a Bi:Ti molar ratio of 1:2. Bi(NO3)3·5H2O is dissolved in dilute nitric acid solution to obtain solution a. Ti(OC4H9)4 is dissolved in anhydrous ethanol and added to solution a to obtain solution b. NaOH is dissolved in deionized water at a concentration of 6-14 mol / L to obtain a NaOH solution. Solution b is added to the NaOH solution to obtain a precursor solution. The precursor solution is placed in a stainless steel reactor with a polytetrafluoroethylene liner, and then the reactor is placed in a forced-air drying oven. The reactor is first heated to 170-200 °C and held for 0-60 minutes, then cooled to 160 °C and held for 5 hours. The reactor is then removed and allowed to cool naturally to room temperature. The product after the reaction is washed until neutral and placed in an 80 °C drying oven for 8 hours. The dried powder is then ground and sieved to obtain (Bi... 0.5 Na 0.5 )TiO3 powder.

[0016] Preferably, in step three, weigh (Bi) 0.5 Na 0.5 The molar percentage of TiO3 powder is 0.50 mol%, and the chemical composition of the AST powder is TiO2:Al2O3:SiO2 = 3:4:9 molar ratio. AST and (Ba 0.998 La 0.002 The proportion of TiO3 is 6% molar ratio.

[0017] Preferably, in step four, 6% polyvinyl alcohol and 2% liquid paraffin by mass are added to the ball-milled powder in step three for granulation. The granulated powder is then sieved and placed in a mold and pressed at 2.0 MPa to form a ceramic green body with a diameter of 12 mm and a thickness of 1.2 mm.

[0018] Preferably, in step five, the green body obtained in step four is placed in a box furnace for debinding, with a heating rate of 2°C / min, at 600°C. ○Hold at 4°C for 2 hours, then cool to room temperature in the furnace; place the debonded green body in a high-temperature box furnace and heat at 4°C. ○ The heating rate increased to 900 °C / min. ○ Keep warm at 5°C for 1 hour, then at 5°C for 1 hour. ○ Heating rate increased to sintering temperature of 1320~1350 °C / min ○ C, hold at this temperature for 15-120 minutes, then cool to room temperature in the furnace to obtain (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3 ceramic sheet.

[0019] Preferably, in step one, the calcination temperature is 1250°C. ○ C

[0020] Preferably, in step two, the NaOH solution concentration is 12 mol / L, the first stage heating temperature of the two-stage hydrothermal method is 180 ℃, and the holding time is 30 minutes.

[0021] Preferably, in step five, the degummed green body is placed in a high-temperature box furnace at 4... ○ The heating rate increased to 900 °C / min. ○ Keep warm at 5°C for 1 hour, then at 5°C for 1 hour. ○ Heating rate increased to sintering temperature of 1330 °C / min ○ C, keep warm for 30 minutes.

[0022] Beneficial effects:

[0023] Compared with the prior art, the present invention can achieve the following technical effects:

[0024] 1. The (Ba) obtained by this invention 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3 ceramic materials possess low room temperature resistivity and high Curie temperature, with room temperature resistivity, resistance ratio, and Curie temperature of 66.20 Ω∙cm, 2.57 × 10⁻⁶, and 2.57 × 10⁻⁶, respectively. 5 and 148 ○ C has good electrical properties.

[0025] 2. The preparation method of this invention involves synthesizing sodium bismuth titanate powder by a two-stage heating hydrothermal method and (Ba) sodium titanate powder by a solid-state reaction method. 1-x La xTiO3 powder, Mn(NO3)2 aqueous solution and sintering aid AST powder are mixed and then granulated, shaped, debinded and sintered. This avoids the problem of insufficient dispersion and insufficient chemical composition uniformity of ceramic powder synthesized by solid-state reaction method in ceramic material preparation.

[0026] 3. The method of the present invention has low temperature, low cost, environmental friendliness, and simple process, making it suitable for mass production. Attached Figure Description

[0027] Figure 1 The present invention uses a two-stage hydrothermal method to synthesize (Bi) 0.5 Na 0.5 SEM image of TiO3 powder.

[0028] Figure 2 The (Ba) obtained by this invention 0.998-y La 0.002 (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 XRD patterns of O3 ceramics. (y = 0.0000, 0.0025, 0.0050, 0.0075, 0.0100).

[0029] Figure 3 The (Ba) obtained by this invention 0.998-y La 0.002 (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 Dielectric constant-temperature curve of O3 ceramic.

[0030] Figure 4 The (Ba) obtained by this invention 0.998-y La 0.002 (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 Resistivity-temperature curves of O3 ceramics (y = 0.0000, 0.0025, 0.0050, 0.0075, 0.0100).

[0031] Figure 5 The (Ba) obtained by sintering under different sintering temperatures and holding times according to this invention 0.993 La 0.002 (Bi 0.5 Na 0.5 ) 0.005(Ti) 0.9996 Mn 0.0004 The room temperature resistivity of O3 ceramics.

[0032] Figure 6 For the present invention in 1330 ○ Ba was obtained by sintering at C for 0.5 hours. 1-x La x Electrical properties of TiO3 ceramics (x = 0.001, 0.002, 0.003, 0.004). Detailed Implementation

[0033] The invention will now be described in further detail with reference to the accompanying drawings.

[0034] This invention proposes a high Curie temperature, low resistance, lead-free thermistor ceramic, the chemical formula of which is (Ba... 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3; where the range of x is 0.001 ≤ x ≤ 0.004, and the range of y is 0.001 ≤ y ≤ 0.0075.

[0035] This invention also discloses a method for preparing the above-mentioned high Curie temperature, low resistance, lead-free thermistor ceramic, comprising the following steps:

[0036] Step 1: Using BaCO3, TiO2, and La2O3 as raw materials, a solid-state reaction synthesis method is employed to prepare (BaCO3, TiO2, and La2O3). 1-x La x )TiO3 powder;

[0037] Step 2: Using Bi(NO3)3·5H2O, Ti(OC4H9)4, and NaOH as raw materials, a two-stage hydrothermal reaction method is employed to synthesize (Bi 0.5 Na 0.5 )TiO3 powder;

[0038] Step 3: According to (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 Weigh out the stoichiometric amount of O3 obtained in step one (Ba 1-x La x TiO3 powder, Bi obtained in step two 0.5 Na 0.5TiO3 powder and Mn(NO3)2 were mixed with AST powder and ball-milled with anhydrous ethanol, then dried and ground.

[0039] Step 4: Add polyvinyl alcohol and liquid paraffin to the ball-milled powder from Step 3 to granulate it, and then put the granulated powder into a mold to press it into a green body.

[0040] Step 5: Place the green body obtained in Step 4 into a box furnace for debinding and sintering to obtain (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3 ceramic sheet

[0041] The specific implementation method is as follows:

[0042] Example 1:

[0043] Step 1: Using BaCO3, TiO2, and La2O3 as raw materials, synthesize (BaCO3) by solid-state reaction method. 0.998 La 0.002 TiO3 powder. According to (Ba 0.998 La 0.002 The above raw materials were weighed and placed in a ball mill jar according to the stoichiometric ratio of TiO3. Anhydrous ethanol was added at a volume ratio of raw materials to anhydrous ethanol of 1:1 for ball milling. The ball mill speed was 300 r / min, and the milling time was 6 hours. After ball milling, the slurry was dried in an 80 ℃ oven, then ground, sieved, and calcined. The calcination temperature was 1250 ℃, the holding time was 2 hours, and then the calcined material was cooled to room temperature in the furnace.

[0044] Step 2: Using bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), tetrabutyl titanate (Ti(OC4H9)4), and sodium hydroxide (NaOH) as raw materials, sodium bismuth titanate (Bi) is synthesized via a two-stage hydrothermal reaction method. 0.5 Na 0.5 TiO 3，Bismuth nitrate (BNT) powder was prepared by dissolving bismuth nitrate in dilute nitric acid solution (volume ratio of deionized water to nitric acid 1:1) at a Bi:Ti molar ratio of 1:2 and stirring for 10 minutes to obtain a clear and transparent solution a. Tetrabutyl titanate was then dissolved in anhydrous ethanol at a Bi:Ti molar ratio of 1:2 and stirred until clear and transparent before being added to solution a to obtain solution b. NaOH was dissolved in deionized water at a concentration of 12 mol / L and stirred for 40 minutes to obtain a clear and transparent aqueous solution, which was then added to solution b and stirred for another 30 minutes to obtain a pale yellow precursor solution. The precursor solution was placed in a stainless steel reactor with a polytetrafluoroethylene liner, and the reactor was then placed in a forced-air drying oven for the synthesis of (Bi) using a two-stage hydrothermal method. 0.5 Na 0.5 TiO3 powder. The reaction vessel was first heated to 180 °C and held for 30 minutes, then cooled to 160 °C and held for 5 hours. Afterwards, the reaction vessel was removed from the drying oven and allowed to cool naturally to room temperature. The product was washed until neutral and then placed in an 80 °C drying oven for 8 hours. The dried powder was ground and sieved to obtain a pale yellow (Bi) powder. 0.5 Na 0.5 )TiO3 powder.

[0045] Step 3: According to (Ba 0.998-y La 0.002 (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 Weigh out the stoichiometric ratio of O3 (Ba 0.998 La 0.002 TiO3, BNT powder (where y = 0.0025, 0.0050, 0.0075, 0.010) and Mn(NO3)2, then according to AST and (Ba 0.998 La 0.002 Pre-prepared AST powder (with a chemical composition of TiO2:Al2O3:SiO2 = 3:4:9 molar ratio) was weighed out at a TiO3 molar ratio of 6%, and placed into a ball mill jar. Anhydrous ethanol was added at a raw material:anhydrous ethanol volume ratio of 1:1 for ball milling. The ball mill speed was 300 r / min, and the milling time was 6 h. After ball milling, the slurry was dried in an 80 ℃ oven, and then ground in a mortar.

[0046] Step 4: Add 6% polyvinyl alcohol (PVA) and 2% liquid paraffin by mass to the ground powder for granulation, and then sieve. Place the granulated powder into a mold and press it at 2.0 MPa to form a ceramic green body with a diameter of 12 mm and a thickness of 1.2 mm.

[0047] Step 5: Place the green body in a box furnace to remove the glue, with a heating rate of 2 ℃ / min, at 600 ○ Hold at 4°C for 2 hours, then cool to room temperature in the furnace. Place the debonded green body into a high-temperature box furnace and heat at 4°C. ○ The heating rate increased to 900 °C / min. ○ Keep warm at 5°C for 1 hour, then at 5°C. ○ The rate increased to 1330 C / min. ○ The sample was sintered at a temperature of 30 minutes, and then cooled to room temperature in the furnace to obtain (Ba). 0.998-y La 0.002 (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3 ceramic sheet, where y = 0.0025, 0.0050, 0.0075, 0.010.

[0048] Bi synthesized using a two-stage hydrothermal method 0.5 Na 0.5 The crystal structure of TiO3 powder is a single rhombohedral phase (Bi). 0.5 Na 0.5 TiO3 particles are aggregates of approximately 50 nm cubes with an average size of 450 nm (see...). Figure 1 Doping (Bi) 0.5 Na 0.5 Four types of (Ba) powder were obtained from TiO3 powder. 0.998-y La 0.002 (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 The O3 ceramic sheets are all composed of a single tetragonal perovskite phase (see...). Figure 2 ). With (Bi 0.5 Na 0.5 As the molar ratio of TiO3 increases, the XRD diffraction peaks gradually shift to the right, indicating that (Bi...) 0.5 Na 0.5 TiO3 is dissolved into the BaTiO3 lattice. Additionally, with the addition of (Bi...) 0.5 Na 0.5As the molar ratio of TiO3 increases, the Curie temperature gradually rises (see...). Figure 3 ), and the room temperature resistivity also increases accordingly (see Figure 4 When y = 0.0025, the room temperature resistivity of the ceramic is 77.29 Ω∙cm, and the resistance-to-weight ratio is ( ). p max / min The value is 3.40 × 10 4 The Curie temperature is 140 ℃. When y = 0.005, the room temperature resistivity of the ceramic is 66.20 Ω∙cm, and the resistance-to-weight ratio is 2.57×10⁻⁶. 5 The Curie temperature is 148 ℃. When y = 0.0075, the room temperature resistivity of the ceramic is 18803.00 Ω∙cm, and the resistance-to-weight ratio is 1.50×10⁻⁶. 1 The Curie temperature is 150 ℃. When y = 0.010, the Curie temperature of the ceramic is 151 ℃, and its room temperature resistivity is 61644.1 Ω∙cm, with no PTCR effect (see...). Figure 4 Therefore, y is preferably 0.005.

[0049] Example 2:

[0050] Step 1: Using BaCO3, TiO2, and La2O3 as raw materials, synthesize (BaCO3) by solid-state reaction method. 0.998 La 0.002 TiO3 powder. According to (Ba 0.998 La 0.002 The above raw materials were weighed according to the stoichiometric ratio of TiO3 and placed in a ball mill jar for ball milling at a volume ratio of raw material to anhydrous ethanol of 1:1. The ball mill speed was 300 r / min, and the ball milling time was 6 hours. After ball milling, the slurry was placed in an 80 ℃ oven to dry, and then ground, sieved, and calcined. The calcination temperature was 1250 ℃, the holding time was 2 hours, and then the calcined material was cooled to room temperature in the furnace.

[0051] Step 2: Using bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), tetrabutyl titanate (Ti(OC4H9)4), and sodium hydroxide (NaOH) as raw materials, sodium bismuth titanate (Bi) is synthesized via a two-stage hydrothermal method. 0.5 Na 0.5 TiO 3，Bismuth nitrate (BNT) powder was prepared by dissolving bismuth nitrate in dilute nitric acid solution (volume ratio of deionized water to nitric acid 1:1) at a Bi:Ti molar ratio of 1:2 and stirring for 10 minutes to obtain a clear and transparent solution a. Tetrabutyl titanate was then dissolved in anhydrous ethanol at a Bi:Ti molar ratio of 1:2 and stirred until clear and transparent before being added to solution a to obtain solution b. NaOH was dissolved in deionized water at a concentration of 12 mol / L and stirred for 40 minutes to obtain a clear and transparent aqueous solution, which was then added to solution b. After stirring for another 30 minutes, a pale yellow precursor solution was obtained. The precursor solution was placed in a stainless steel reactor with a polytetrafluoroethylene liner, and the reactor was then placed in a forced-air drying oven for the synthesis of (Bi) using a two-stage hydrothermal method. 0.5 Na 0.5 TiO3 powder. The reaction vessel was first heated to 180 °C and held for 30 minutes, then cooled to 160 °C and held for 5 hours. Afterwards, the reaction vessel was removed from the drying oven and allowed to cool naturally to room temperature. The product was washed until neutral and then placed in an 80 °C drying oven for 8 hours. The dried powder was ground and sieved to obtain a pale yellow (Bi) powder. 0.5 Na 0.5 )TiO3 powder.

[0052] Step 3: According to (Ba 0.993 La 0.002 (Bi 0.5 Na 0.5 ) 0.005 (Ti) 0.9996 Mn 0.0004 Weigh out the stoichiometric ratio of O3 (Ba 0.998 La 0.002 TiO3, BNT powder and Mn(NO3)2, then according to AST and (Ba 0.998 La 0.002 The pre-prepared AST powder was weighed out at a TiO3 concentration of 6 moles and placed into a ball mill jar. Anhydrous ethanol was added at a volume ratio of 1:1 (raw material: anhydrous ethanol) for ball milling. The ball mill speed was 300 r / min, and the milling time was 6 h. After ball milling, the slurry was dried in an 80 ℃ oven and then ground in a mortar.

[0053] Step 4: Add 6% polyvinyl alcohol (PVA) and 2% liquid paraffin by mass to the ground powder for granulation, and then sieve. Place the granulated powder into a mold and press it at 2.0 MPa to form a ceramic green body with a diameter of 12 mm and a thickness of 1.2 mm.

[0054] Step 5: Place the green body in a box furnace to remove the glue, with a heating rate of 2 ℃ / min, at 600○ Hold at 4°C for 2 hours, then cool to room temperature in the furnace. Place the debonded green body into a high-temperature box furnace and heat at 4°C. ○ The heating rate increased to 900 °C / min. ○ Keep warm at 5°C for 1 hour, then at 5°C. ○ The rate of C / min increased to 1320~1350 ○ Sintering was carried out at a temperature of 30 minutes, followed by furnace cooling to obtain (Ba 0.993 La 0.002 (Bi 0.5 Na 0.5 ) 0.005 (Ti) 0.9996 Mn 0.0004 O3 ceramic sheet.

[0055] Between 1320 and 1350 ○ Ceramics sintered at C for 30 minutes generally have low room temperature resistivity (see...). Figure 5 This indicates that the sintering temperature window of this material system is relatively wide, ranging from 1320, 1330, 1340, and 1350. ○ The room temperature resistivity of ceramics prepared by holding at a temperature of 1330°C for 30 minutes were 77.0, 66.2, 78.3, and 87.5 Ω∙cm, respectively. Among them, the resistivity at 1330°C was... ○ C-sintered ceramics have the lowest room temperature resistivity, therefore the preferred sintering temperature is 1330°C. ○ C.

[0056] Example 3

[0057] Step 1: Using BaCO3, TiO2, and La2O3 as raw materials, synthesize (BaCO3) by solid-state reaction method. 0.998 La 0.002 TiO3 powder. According to (Ba 0.998 La 0.002 The above raw materials were weighed and placed in a ball mill jar according to the stoichiometric ratio of TiO3. Anhydrous ethanol was added at a volume ratio of raw materials to anhydrous ethanol of 1:1 for ball milling. The ball mill speed was 300 r / min, and the milling time was 6 hours. After ball milling, the slurry was dried in an 80 ℃ oven, then ground, sieved, and calcined. The calcination temperature was 1250 ℃, the holding time was 2 hours, and then the calcined material was cooled to room temperature in the furnace.

[0058] Step 2: Using bismuth nitrate pentahydrate (Bi(NO3)3·5H2O), tetrabutyl titanate (Ti(OC4H9)4), and sodium hydroxide (NaOH) as raw materials, sodium bismuth titanate (Bi) is synthesized via a two-stage hydrothermal reaction method. 0.5 Na 0.5 TiO 3，Bismuth nitrate (BNT) powder was prepared by dissolving bismuth nitrate in dilute nitric acid solution (volume ratio of deionized water to nitric acid 1:1) at a Bi:Ti molar ratio of 1:2 and stirring for 10 minutes to obtain a clear and transparent solution a. Tetrabutyl titanate was then dissolved in anhydrous ethanol at a Bi:Ti molar ratio of 1:2 and stirred until clear and transparent before being added to solution a to obtain solution b. NaOH was dissolved in deionized water at a concentration of 12 mol / L and stirred for 40 minutes to obtain a clear and transparent aqueous solution, which was then added to solution b and stirred for another 30 minutes to obtain a pale yellow precursor solution. The precursor solution was placed in a stainless steel reactor with a polytetrafluoroethylene liner, and the reactor was then placed in a forced-air drying oven for the synthesis of (Bi) using a two-stage hydrothermal method. 0.5 Na 0.5 TiO3 powder. The reaction vessel was first heated to 180 °C and held for 30 minutes, then cooled to 160 °C and held for 5 hours. Afterwards, the reaction vessel was removed from the drying oven and allowed to cool naturally to room temperature. The product was washed until neutral and then placed in an 80 °C drying oven for 8 hours. The dried powder was ground and sieved to obtain a pale yellow (Bi) powder. 0.5 Na 0.5 )TiO3 powder.

[0059] Step 3: According to (Ba 0.993 La 0.002 (Bi 0.5 Na 0.5 ) 0.005 (Ti) 0.9996 Mn 0.0004 Weigh out the stoichiometric ratio of O3 (Ba 0.998 La 0.002 TiO3, BNT powder and Mn(NO3)2, then according to AST and (Ba 0.998 La 0.002 The pre-prepared AST powder was weighed out at a TiO3 concentration of 6 moles and placed into a ball mill jar. Anhydrous ethanol was added at a volume ratio of 1:1 (raw material: anhydrous ethanol) for ball milling. The ball mill speed was 300 r / min, and the milling time was 6 h. After ball milling, the slurry was dried in an 80 ℃ oven and then ground in a mortar.

[0060] Step 4: Add 6% polyvinyl alcohol (PVA) and 2% liquid paraffin by mass to the ground powder for granulation, and then sieve. Place the granulated powder into a mold and press it at 2.0 MPa to form a ceramic green body with a diameter of 12 mm and a thickness of 1.2 mm.

[0061] Step 5: Place the green body in a box furnace to remove the glue, with a heating rate of 2 ℃ / min, at 600○ Hold at 4°C for 2 hours, then cool to room temperature in the furnace. Place the debonded green body into a high-temperature box furnace and heat at 4°C. ○ The heating rate increased to 900 °C / min. ○ Keep warm at 5°C for 1 hour, then at 5°C. ○ The rate of C / min increased to 1320~1350 ○ Sintering is carried out at a temperature of 15-120 minutes, followed by furnace cooling to obtain (Ba). 0.993 La 0.002 (Bi 0.5 Na 0.5 ) 0.005 (Ti) 0.9996 Mn 0.0004 O3 ceramic sheet.

[0062] 1320~1350 ○ The room temperature resistivity of ceramics sintered within the C range all increased with increasing holding time (see...). Figure 5 ). In 1330 ○ The room temperature resistivity of ceramics prepared by holding at temperature for 15, 30, 60, and 120 minutes were 97.9, 66.2, 396.8, and 2766.2 Ω∙cm, respectively. Among them, the ceramic prepared by holding at temperature for 30 minutes showed the lowest room temperature resistivity, therefore, a sintering holding time of 30 minutes is preferred.

[0063] Comparative Example 1:

[0064] Step 1: Prepare (Ba) using a solid-state reaction synthesis method. 0.998 La 0.002 TiO3 powder. According to (Ba 0.998 La 0.002 To prepare TiO3, BaCO3, TiO2, and La2O3 were weighed out as raw materials and placed sequentially into a ball mill jar. Anhydrous ethanol was added to the jar at a volume ratio of 1:1 (raw materials: anhydrous ethanol) for ball milling. The ball mill speed was 300 r / min, and the milling time was 6 hours. After milling, the slurry was dried in an 80 ℃ oven, then ground, sieved, and calcined. The calcination temperature was 1250 ℃, and the holding time was 2 hours, after which the calcined material was cooled to room temperature in the furnace.

[0065] Step Two: According to (Ba 0.998 La 0.002 (Ti) 0.9996 Mn 0.0004 Weigh out the stoichiometric ratio of O3 (Ba 0.998 La 0.002 TiO3 powder and Mn(NO3)2, then according to AST and (Ba 0.998 La 0.002The pre-prepared AST powder was weighed out at a TiO3 molar ratio of 6% and placed into a ball mill jar. Anhydrous ethanol was added at a volume ratio of 1:1 (raw material: anhydrous ethanol) for ball milling. The ball mill speed was 300 r / min, and the milling time was 6 hours. After ball milling, the slurry was dried in an 80 ℃ oven and then ground in a mortar.

[0066] Step 3: Add 6% polyvinyl alcohol (PVA) and 2% liquid paraffin by mass to the ground powder for granulation, and then sieve. Place the granulated powder into a mold and press it at 2.0 MPa to form a ceramic green body with a diameter of 12 mm and a thickness of 1.2 mm.

[0067] Step 4: Place the green body in a box furnace to remove the glue, with a heating rate of 2 ℃ / min, at 600 ○ Hold at 4°C for 2 hours, then cool to room temperature in the furnace. Place the debonded green body into a high-temperature box furnace and heat at 4°C. ○ The heating rate increased to 900 °C / min. ○ Incubate at 5°C for 1 hour, then incubate at 5°C for 1 hour. ○ Heating rate increased to 1330 °C / min ○ C, sinter at a temperature of 30 minutes, then cool to room temperature in the furnace to obtain (Ba 0.998 La 0.002 (Ti) 0.9996 Mn 0.0004 O3 ceramics.

[0068] The obtained (Ba 0.998 La 0.002 (Ti) 0.9996 Mn 0.0004 O3 ceramics consist of a single tetragonal perovskite phase (see...). Figure 2 (y = 0.0000), its Curie temperature is 128. ○ C (see) Figure 3 The room temperature resistivity is 24.19 Ω∙cm, and the step-up resistance ratio is 5.14×10⁻⁶. 3 (See Figure 4 ).

[0069] Compared with Comparative Example 1, although trace amounts of BNT (Ba 0.998-y La 0.002 (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 The room temperature resistivity of O3 ceramics increased, but the Curie temperature rose significantly, especially at 1330°C. ○ (Ba) was prepared by heat preservation for 30 minutes.0.993 La 0.002 (Bi 0.5 Na 0.5 ) 0.005 (Ti) 0.9996 Mn 0.0004 O3 ceramics have a Curie temperature as high as 148°C. ○ C (see) Figure 3 Its room temperature resistivity and resistance-to-stable-rise ratio are 66.20 Ω∙cm and 2.57 × 10⁻⁶, respectively. 5 (See Figure 6 The barium titanate-based lead-free thermistor ceramic prepared in this invention exhibits excellent overall PTCR performance, indicating that it has broad application prospects in devices such as starting and switching elements, overcurrent and overheat protection elements, and temperature sensors for sensing ambient heat.

[0070] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of the present invention is defined only by the appended claims.

Claims

1. A high Curie temperature, low resistance, lead-free thermistor ceramic, characterized in that: The chemical formula of the thermosensitive ceramic is (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3; where the range of x is 0.001 ≤ x ≤ 0.004, and the range of y is 0.0025 ≤ y ≤ 0.005; The thermosensitive ceramic is prepared by the following method: Step 1: Using BaCO3, TiO2, and La2O3 as raw materials, a solid-state reaction synthesis method is employed to prepare (BaCO3, TiO2, and La2O3). 1-x La x )TiO3 powder; Step 2: Using Bi(NO3)3·5H2O, Ti(OC4H9)4, and NaOH as raw materials, a two-stage hydrothermal reaction method is employed to synthesize (Bi 0.5 Na 0.5 )TiO3 powder; Step 3: According to (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 Weigh out the stoichiometric amount of O3 obtained in step one (Ba 1-x La x TiO3 powder, (Bi) obtained in step two 0.5 Na 0.5 TiO3 powder and Mn(NO3)2 were mixed with AST powder and ball-milled with anhydrous ethanol, then dried and ground. Step 4: Add polyvinyl alcohol and liquid paraffin to the ball-milled powder from Step 3 to granulate it, and then put the granulated powder into a mold to press it into a green body. Step 5: Place the green body obtained in Step 4 into a box furnace for debinding and sintering to obtain (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3 ceramic discs; The AST powder is a sintering aid with a chemical composition of TiO2: Al2O3: SiO2 = 3:4:9 molar ratio. The first stage of the two-stage heating hydrothermal reaction method is heated to 170-200℃ and held for 30-60 minutes, then cooled to 160℃ and held for 5 hours. In step five, the debonded green body is placed in a high-temperature box furnace and heated to 900°C at a rate of 4°C / min and held for 1 hour. Then, the temperature is increased to the sintering temperature of 1320~1350°C at a rate of 5°C / min and held for 15-60 minutes. After that, it is cooled to room temperature with the furnace.

2. A method for preparing a high Curie temperature, low resistance, lead-free thermistor ceramic as described in claim 1, characterized in that: Includes the following steps: Step 1: Using BaCO3, TiO2, and La2O3 as raw materials, a solid-state reaction synthesis method is employed to prepare (BaCO3, TiO2, and La2O3). 1-x La x )TiO3 powder; Step 2: Using Bi(NO3)3·5H2O, Ti(OC4H9)4, and NaOH as raw materials, a two-stage hydrothermal reaction method is employed to synthesize (Bi 0.5 Na 0.5 )TiO3 powder; Step 3: According to (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 Weigh out the stoichiometric amount of O3 obtained in step one (Ba 1-x La x TiO3 powder, (Bi) obtained in step two 0.5 Na 0.5 TiO3 powder and Mn(NO3)2 were mixed with AST powder and ball-milled with anhydrous ethanol, then dried and ground. Step 4: Add polyvinyl alcohol and liquid paraffin to the ball-milled powder from Step 3 to granulate it, and then put the granulated powder into a mold to press it into a green body. Step 5: Place the green body obtained in Step 4 into a box furnace for debinding and sintering to obtain (Ba 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3 ceramic sheet.

3. The method for preparing high Curie temperature, low resistance, lead-free thermistor ceramic according to claim 2, characterized in that, In step one, the solid-state reaction synthesis method is used to prepare (Ba 1-x La x The process of producing TiO3 powder is as follows: according to (Ba 1-x La x The raw materials were weighed according to the stoichiometric ratio of TiO3, and ball-milled with anhydrous ethanol in a ball mill jar at a volume ratio of 1:

1. After ball milling, the slurry was dried in an oven, ground, sieved, and calcined at 1200-1300℃ for 2 hours. Then, it was cooled to room temperature in the furnace to obtain (Ba 1-x La x )TiO3 powder.

4. The method for preparing high Curie temperature, low resistance, lead-free thermistor ceramic according to claim 2, characterized in that, In step two, the synthesis of (Bi) using a two-stage heating hydrothermal reaction method is described. 0.5 Na 0.5 The process of producing TiO3 powder is as follows: Bi(NO3)3·5H2O and Ti(OC4H9)4 are weighed according to the molar ratio of Bi:Ti = 1:

2. Bi(NO3)3·5H2O is dissolved in dilute nitric acid solution to obtain solution a; Ti(OC4H9)4 is dissolved in anhydrous ethanol and added to solution a to obtain solution b. NaOH solution is obtained by dissolving NaOH in deionized water at a concentration of 6-14 mol / L. Solution b was added to the NaOH solution to obtain the precursor solution; The precursor solution was placed in a stainless steel reactor lined with polytetrafluoroethylene (PTFE). The reactor was then placed in a forced-air drying oven. The reactor was first heated to 170-200℃ and held for 30-60 minutes, then cooled to 160℃ and held for 5 hours. The reactor was then removed and allowed to cool naturally to room temperature. The product was washed until neutral and then dried in an 80℃ drying oven for 8 hours. The dried powder was then ground and sieved to obtain (Bi). 0.5 Na 0.5 )TiO3 powder.

5. The method for preparing high Curie temperature, low resistance, lead-free thermistor ceramic according to claim 2, characterized in that, In step three, weigh (Bi) 0.5 Na 0.5 The molar percentage of TiO3 powder is 0.50 mol%, and the chemical composition of the AST powder is TiO2:Al2O3:SiO2 = 3:4:9 molar ratio. AST and (Ba 0.998 La 0.002 The proportion of TiO3 is 6% molar ratio.

6. The method for preparing high Curie temperature, low resistance, lead-free thermistor ceramic according to claim 2, characterized in that, In step four, 6% polyvinyl alcohol and 2% liquid paraffin by mass are added to the ball-milled powder in step three for granulation. The granulated powder is then sieved and placed in a mold and pressed at 2.0 MPa to form a ceramic green body with a diameter of 12 mm and a thickness of 1.2 mm.

7. The method for preparing high Curie temperature, low resistance, lead-free thermistor ceramic according to claim 2, characterized in that, In step five, the green body obtained in step four is placed in a box furnace for debinding, with a heating rate of 2 °C / min, held at 600 °C for 2 hours, and then cooled to room temperature with the furnace. The debinded green body is then placed in a high-temperature box furnace, heated to 900 °C at a rate of 4 °C / min, held for 1 hour, and then heated to a sintering temperature of 1320-1350 °C at a rate of 5 °C / min, held for 15-60 minutes, and then cooled to room temperature with the furnace to obtain (Ba). 1-x-y La x (Bi 0.5 Na 0.5 ) y (Ti) 0.9996 Mn 0.0004 O3 ceramic sheet.

8. The method for preparing high Curie temperature, low resistance, lead-free thermistor ceramic according to claim 3, characterized in that, In step one, the calcination temperature is 1250℃.

9. The method for preparing high Curie temperature, low resistance, lead-free thermistor ceramic according to claim 4, characterized in that, In step two, the NaOH solution concentration is 12 mol / L, and the first stage of the two-stage hydrothermal method is heated at 180℃ for 30 minutes.

10. The method for preparing high Curie temperature, low resistance, lead-free thermistor ceramic according to claim 7, characterized in that, In step five, the debonded green body is placed in a high-temperature box furnace and heated to 900°C at a rate of 4°C / min and held for 1 hour. Then, the temperature is increased to the sintering temperature of 1330°C at a rate of 5°C / min and held for 30 minutes.

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