A manufacturing method of a 135-degree lead-free barium titanate-based thermistor

Abstract

This invention relates to the field of functional ceramic materials technology, specifically to a method for manufacturing a 135°C lead-free barium titanate thermistor. This method addresses the problems of existing thermistor materials relying on lead compounds, exhibiting unstable Curie temperature, high room temperature resistivity, and low resistance-to-lift ratio. The method utilizes Bi... 0.5 Na 0.5 TiO3, as the primary Curie temperature shifter, replaces toxic lead-based compounds in traditional PTC materials, achieving lead-free production. Composite donor doping, through the synergistic effect of yttrium oxide, lanthanum oxide, and niobium pentoxide, achieves efficient and stable semiconductorization, optimizes carrier concentration, and obtains low room-temperature resistivity. Composite acceptor doping, through the synergistic effect of Mn and Co, significantly enhances the PTC effect; the introduction of Co effectively increases the grain boundary barrier height and improves the lift-to-resistivity ratio. Through Bi... 0.5 Na 0.5 TiO3 and Ca 2+ The combined peak-shifting effect can precisely stabilize the Curie temperature at 135℃.

Description

Technical Field

[0001] This invention relates to the field of functional ceramic materials technology, specifically to a method for manufacturing a 135°C lead-free barium titanate thermistor. Background Technology

[0002] A thermistor is a resistive element that can respond to changes in external temperature. It is widely used in temperature control, measurement and sensing. These elements need to have characteristics such as good high-temperature stability, fast response speed and high long-term reliability. Most traditional thermistor materials rely on lead compounds, such as lead lead oxide. This material has good thermal stability, but under the requirements of modern environmental regulations, lead compounds are gradually being phased out due to their potential harm to human health and the environment.

[0003] With increasing emphasis on environmental protection, there is an urgent need in the field of electronic ceramics to develop lead-free positive temperature coefficient resistive ceramic materials with high Curie temperature, low room temperature resistivity, and high resistance-to-weight ratio.

[0004] Therefore, this invention provides a method for manufacturing a 135°C lead-free barium titanate thermistor, which is of great significance for applications in environmentally friendly and efficient temperature control systems. Summary of the Invention

[0005] In order to overcome the above-mentioned technical problems, the present invention aims to provide a method for manufacturing a 135-degree lead-free barium titanate thermistor, which solves the problems of existing thermistor materials relying on lead compounds, having unstable Curie temperature, high room temperature resistivity, and low resistance-to-lift ratio.

[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, this application provides a method for manufacturing a 135°C lead-free barium titanate thermistor, comprising the following steps: Step a1: Bismuth oxide, sodium carbonate, and titanium dioxide are added to a planetary ball mill at a ball-to-material ratio of 2-3:1. Wet ball milling is performed at 300-400 r / min for 24 h. The mixture is then dried in a 120℃ forced-air drying oven for 8-12 h. After crushing, the mixture is sieved through an 80-mesh sieve and transferred to a muffle furnace for solid-state synthesis. The sintering process is as follows: heating from 25℃ to 800℃ at a rate of 250℃ / h, then heating to 850℃ at a rate of 100℃ / h, holding at that temperature for 2 h, and then naturally cooling to 25℃ to obtain Bi. 0.5 Na 0.5 TiO3; Step a2: Dry the primary material in an 80℃ oven for 2 hours, then add it to a planetary ball mill with a ball-to-material ratio of 5:1. Perform wet ball milling at a speed of 300-400 r / min for 20-24 hours. Then, dry it in a 120℃ forced-air drying oven for 8-12 hours. After crushing, sieve it through a 100-mesh screen and press it into blocks at 15-25 MPa. Transfer it to a muffle furnace for sintering. The sintering process is as follows: heat the material from 25℃ to 600℃ at a rate of 200℃ / h, continue heating at a rate of 180℃ / h to 1150-1200℃, hold for 2-3 hours, cool it to 25℃ in the furnace, crush and grind it, and sieve it through a 100-mesh screen to obtain the main crystalline phase. Step a3: Add the secondary material to a planetary ball mill at a ball-to-material ratio of 5:1 and wet ball mill at 300-400 r / min for 16-18 h to obtain a ball mill slurry. Add polyvinyl alcohol and deionized water to a beaker, heat to 90-95℃, stir at a constant temperature for 1-2 h, cool naturally to 60℃, add anhydrous ethanol, continue stirring for 30 min, and sieve through a 60-mesh sieve to obtain a binder. Let the ball mill slurry stand for 6-12 h, filter, mix the filter cake, binder, and release agent and stir for 2-3 h, and perform spray granulation: inlet temperature 180-200℃, outlet temperature 80-100℃. Sieve the granulated powder through a 60-120 mesh sieve, pour it into a mold, and press it under 4-6 MPa pressure for 1-5 min using a benchtop tablet press to obtain a green body. Step a4: Place the billet in a high-temperature sintering furnace for sintering. The sintering curve is as follows: heat up to 600℃ at a rate of 100-150℃ / h, hold for 1h, continue to heat up to 1350℃ at a rate of 200-250℃ / h, hold for 1-2h, cool down to 1200℃ at a rate of 200-250℃ / h, hold for 30-40min, cool down to 800℃ at a rate of 150-200℃ / h, and cool down to 25℃ with the furnace below 850℃ to obtain the precursor. Step a5: Immerse the precursor in a roughening agent for 5-8 minutes, remove the precursor, ultrasonically clean it for 5-10 minutes, then sensitize it in a stannous chloride solution for 3-5 minutes, and then activate it in a palladium chloride solution at 45-50℃ for 3-5 minutes. Use a chemical nickel plating process to plate nickel in a water bath at 80-90℃ for 8-10 minutes. After nickel plating, wash it 2-3 times with distilled water, then boil it in deionized water at 95-100℃ for 5-10 minutes. Then perform external cylindrical grinding to remove the nickel plating layer on the side surface, leaving the nickel plating layer on the top and bottom surfaces. Use a screen to print solderable silver paste on the surface of the nickel plating layer on the top and bottom surfaces, and then burn silver to form silver electrodes. Solder the tin-plated copper wire to the silver electrodes with tin solder, inject silicone resin, and cure to obtain a lead-free barium titanate thermistor.

[0007] In a preferred embodiment of the present invention, the ratio of bismuth oxide, sodium carbonate and titanium dioxide in step a1 is 0.5-1 mol: 0.5-1 mol: 2-4 mol.

[0008] In a preferred embodiment of the present invention, the primary material in step a2 is a mixture of base material, composite donor dopant, composite acceptor dopant, flux, and sintering aid in a mass ratio of 255-265g: 0.9-1.3g: 0.3-0.4g: 0.6-0.8g: 0.4-0.7g.

[0009] In a preferred embodiment of the present invention, the base material is composed of barium carbonate, calcium carbonate, and titanium dioxide in a molar ratio of 0.82-0.85 mol: 0.14-0.17 mol: 0.995-1.005 mol; the composite donor dopant is composed of yttrium oxide, lanthanum oxide, and niobium pentoxide in a molar ratio of 0.002-0.0025 mol: 0.0008-0.0012 mol: 0.0008-0.0012 mol; the composite acceptor dopant is composed of manganese nitrate and cobalt nitrate in a molar ratio of 0.0008-0.001 mol: 0.0004-0.0006 mol; the flux is silicon dioxide; and the sintering aid is aluminum oxide.

[0010] In a preferred embodiment of the present invention, the ratio of the secondary material, polyvinyl alcohol, deionized water, anhydrous ethanol and release agent in step a3 is 240-270g: 2-3g: 20-30mL: 5-10mL: 1-2g; the polyvinyl alcohol is PVA2399H; and the release agent is zinc stearate.

[0011] In a preferred embodiment of the present invention, the secondary material in step a3 consists of a main crystalline phase and Bi. 0.5 Na 0.5 TiO3 and sintering aids are mixed in a ratio of 235-265g:0.02mol:0.4-0.7g; the sintering aids are mixed from lithium carbonate and boron nitride in a molar ratio of 0.003-0.005mol:0.008-0.012mol.

[0012] In a preferred embodiment of the present invention, the solvent for wet ball milling in steps a1-a3 is deionized water, and the ratio of material to solvent is 1:5.

[0013] In a preferred embodiment of the present invention, the roughening agent in step a5 is a 5% hydrofluoric acid solution; the concentration of the stannous chloride solution is 10-20 g / L; and the concentration of the palladium chloride solution is 0.1-0.5 g / L.

[0014] The beneficial effects of this invention are: This invention discloses a method for manufacturing a 135°C lead-free barium titanate thermistor, using Bi... 0.5 Na 0.5 TiO3, as the primary Curie temperature shifting agent, replaces the toxic lead-based compounds widely used in traditional PTC materials, achieving lead-free production and eliminating the environmental and human health hazards of lead, thus laying the material foundation for the development of green electronic products. Employing multi-element synergistic doping, composite donor doping achieves more efficient and stable semiconductorization through the synergistic effect of yttrium oxide, lanthanum oxide, and niobium pentoxide. This A-site and B-site co-doping strategy optimizes carrier concentration, resulting in lower room temperature resistivity and good batch consistency. Composite acceptor doping significantly enhances the PTC effect through the synergistic effect of Mn and Co. The introduction of Co effectively increases the grain boundary barrier height, resulting in extremely high resistance-to-weight ratio above the Curie temperature and improved overcurrent protection sensitivity of the thermistors. Through Bi... 0.5 Na 0.5 TiO3 and Ca 2+ The composite peak shifting effect can precisely stabilize the Curie temperature at 135℃ to meet the needs of specific application scenarios. The "core-shell" structure formed by the multi-element doping system helps to broaden the phase transition range, making the resistance-temperature characteristic curve smoother and improving the working stability of the device. The Curie temperature is precisely controllable and the stability is improved. Detailed Implementation

[0015] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Example 1: This embodiment describes a method for manufacturing a 135°C lead-free barium titanate thermistor, comprising the following steps: Step S1: 0.5 mol bismuth oxide, 0.5 mol sodium carbonate, and 2 mol titanium dioxide were added to a planetary ball mill at a ball-to-material ratio of 2:1. Wet ball milling was performed at 300 r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After milling for 24 h, the mixture was dried in a 120℃ forced-air drying oven for 8 h. The resulting material was crushed, sieved through an 80-mesh screen, and transferred to a muffle furnace for solid-state synthesis. The sintering process was as follows: the temperature was increased from 25℃ to 800℃ at a rate of 250℃ / h, then increased to 850℃ at a rate of 100℃ / h, held for 2 h, and naturally cooled to 25℃ to obtain Bi. 0.5 Na 0.5 TiO3; Step S2: Place 255g of the base material, 0.9g of the composite donor dopant, 0.3g of the composite acceptor dopant, 0.6g of silicon dioxide, and 0.4g of alumina into an 80℃ oven and dry for 2 hours. Then, add the mixture to a planetary ball mill with a ball-to-material ratio of 5:1. Perform wet ball milling at 300r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After ball milling for 20 hours, dry the mixture in a 120℃ forced-air drying oven for 8 hours. After crushing, sieve through a 100-mesh screen and press into blocks at 15MPa. Transfer the blocks to a muffle furnace for sintering. The sintering process is as follows: heat from 25℃ to 600℃ at a rate of 200℃ / h. The temperature was further increased to 1150℃ at a rate of 180℃ / h, held for 2 hours, and then cooled to 25℃ in the furnace. The mixture was then crushed, ground, and sieved through a 100-mesh sieve to obtain the main crystalline phase. The basic main material was composed of barium carbonate, calcium carbonate, and titanium dioxide in a molar ratio of 0.82mol:0.14mol:0.995mol. The composite donor dopant was composed of yttrium oxide, lanthanum oxide, and niobium pentoxide in a molar ratio of 0.002mol:0.0008mol:0.0008mol. The composite acceptor dopant was composed of manganese nitrate and cobalt nitrate in a molar ratio of 0.0008mol:0.0004mol. Step S3: Add 235g of the main crystalline phase and 0.02mol of Bi 0.5 Na 0.5TiO3 and 0.4g of sintering aid were added to a planetary ball mill at a ball-to-material ratio of 5:1. Wet ball milling was performed at 300 rpm using deionized water as the solvent at a material-to-solvent ratio of 1:5. The milling process lasted 16 hours to obtain a slurry. 2g of polyvinyl alcohol (PVA2399H) and 20mL of deionized water were added to a beaker, heated to 90℃, and stirred at this temperature for 1 hour. The mixture was then allowed to cool naturally to 60℃, and 5mL of anhydrous ethanol was added. Stirring continued for 30 minutes. The mixture was then further milled. The binder was obtained by sieving through a 0-mesh sieve. The ball-milled slurry was allowed to stand for 6 hours, filtered, and the filter cake, binder, and 1g of zinc stearate were mixed and stirred for 2 hours. Spray granulation was then carried out: the inlet temperature was 180℃ and the outlet temperature was 80℃. The granulated powder was sieved through a 60-mesh sieve, poured into a mold, and pressed under 4MPa pressure for 1 minute using a benchtop tablet press. The green body was then demolded. The sintering aid was composed of lithium carbonate and boron nitride mixed in a molar ratio of 0.003mol:0.008mol. Step S4: Place the billet in a high-temperature sintering furnace for sintering. The sintering curve is as follows: heat up to 600℃ at a rate of 100℃ / h, hold for 1h, continue to heat up to 1350℃ at a rate of 200℃ / h, hold for 1h, cool down to 1200℃ at a rate of 200℃ / h, hold for 30min, cool down to 800℃ at a rate of 150℃ / h, and cool down to 25℃ with the furnace below 850℃ to obtain the precursor. Step S5: Immerse the precursor in a 5% hydrofluoric acid solution for 5 minutes, remove the precursor, ultrasonically clean it for 5 minutes, then sensitize it in a 10 g / L stannous chloride solution for 3 minutes, and then activate it in a 0.1 g / L palladium chloride solution at 45°C for 3 minutes. Perform electroless nickel plating, plating in an 80°C water bath for 8 minutes. After nickel plating, wash twice with distilled water, then boil in deionized water at 95°C for 5 minutes. Then perform external cylindrical grinding to remove the nickel plating layer on the side surface, retaining the nickel plating layer on the top and bottom surfaces. Use screen printing to print solderable silver paste on the surface of the nickel plating layer on the top and bottom surfaces, and then heat the silver to form silver electrodes. Soldered tin-plated copper wire is soldered to the silver electrodes, silicone resin is injected, and cured to obtain a lead-free barium titanate thermistor.

[0017] Example 2: This embodiment describes a method for manufacturing a 135°C lead-free barium titanate thermistor, comprising the following steps: Step S1: 0.8 mol bismuth oxide, 0.8 mol sodium carbonate, and 3 mol titanium dioxide were added to a planetary ball mill at a ball-to-material ratio of 3:1. Wet ball milling was performed at 350 r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After milling for 24 h, the mixture was dried in a 120℃ forced-air drying oven for 10 h. The resulting material was crushed, sieved through an 80-mesh screen, and transferred to a muffle furnace for solid-state synthesis. The sintering process was as follows: the temperature was increased from 25℃ to 800℃ at a rate of 250℃ / h, then increased to 850℃ at a rate of 100℃ / h, held for 2 h, and naturally cooled to 25℃ to obtain Bi. 0.5 Na 0.5 TiO3; Step S2: 260g of the base material, 1.1g of the composite donor dopant, 0.35g of the composite acceptor dopant, 0.7g of silicon dioxide, and 0.55g of alumina were dried in an 80℃ oven for 2 hours. The dried material was then added to a planetary ball mill at a ball-to-material ratio of 5:1 and wet-milled at 350r / min using deionized water as the solvent at a material-to-solvent ratio of 1:5. After milling for 22 hours, the material was dried in a 120℃ forced-air drying oven for 10 hours. The resulting material was crushed, sieved through a 100-mesh screen, and pressed into blocks at 20MPa. These blocks were then transferred to a muffle furnace for sintering. The sintering process involved heating from 25℃ to 600℃ at a rate of 200℃ / h. The temperature was increased to 1175℃ at a rate of 180℃ / h, held for 2.5h, cooled to 25℃ in the furnace, crushed and ground, and sieved through a 100-mesh sieve to obtain the main crystalline phase. The basic main material was composed of barium carbonate, calcium carbonate, and titanium dioxide in a molar ratio of 0.835mol:0.155mol:1mol. The composite donor dopant was composed of yttrium oxide, lanthanum oxide, and niobium pentoxide in a molar ratio of 0.00225mol:0.001mol:0.001mol. The composite acceptor dopant was composed of manganese nitrate and cobalt nitrate in a molar ratio of 0.0009mol:0.0005mol. Step S3: Add 250g of the main crystalline phase and 0.02mol Bi 0.5 Na 0.5TiO3 and 0.55g of sintering aid were added to a planetary ball mill at a ball-to-material ratio of 5:1. Wet ball milling was performed at 350 rpm using deionized water as the solvent, with a material-to-solvent ratio of 1:5. The milling process lasted 17 hours to obtain a slurry. 2.5g of polyvinyl alcohol (PVA2399H) and 25mL of deionized water were added to a beaker, heated to 93℃, and stirred at this temperature for 1.5 hours. The mixture was then allowed to cool naturally to 60℃, and 8mL of anhydrous ethanol was added. Stirring continued for 30 minutes. The binder was obtained by sieving through a 60-mesh sieve. The ball-milled slurry was allowed to stand for 9 hours, filtered, and the filter cake, binder, and 1.5g of zinc stearate were mixed and stirred for 2.5 hours. Spray granulation was then carried out: the inlet temperature was 190℃ and the outlet temperature was 90℃. The granulated powder was sieved through a 90-mesh sieve, poured into a mold, and pressed under 5MPa pressure for 3 minutes using a benchtop tablet press. The green body was then demolded. The sintering aid was composed of lithium carbonate and boron nitride mixed in a molar ratio of 0.004mol:0.01mol. Step S4: Place the billet in a high-temperature sintering furnace for sintering. The sintering curve is as follows: heat up to 600℃ at a rate of 125℃ / h, hold for 1h, continue to heat up to 1350℃ at a rate of 225℃ / h, hold for 1.5h, cool down to 1200℃ at a rate of 225℃ / h, hold for 35min, cool down to 800℃ at a rate of 175℃ / h, and cool down to 25℃ with the furnace below 850℃ to obtain the precursor. Step S5: Immerse the precursor in a 5% hydrofluoric acid solution for 7 minutes, remove the precursor, ultrasonically clean it for 8 minutes, then sensitize it in a 15 g / L stannous chloride solution for 4 minutes, and then activate it in a 0.3 g / L palladium chloride solution at 48°C for 4 minutes. Perform electroless nickel plating, plating in an 85°C water bath for 9 minutes. After nickel plating, wash it three times with distilled water, then boil it in deionized water at 98°C for 8 minutes. Then perform external cylindrical grinding to remove the nickel plating layer on the side surface, retaining the nickel plating layer on the top and bottom surfaces. Use screen printing to print solderable silver paste on the surface of the nickel plating layer on the top and bottom surfaces, and then heat the silver to form silver electrodes. Soldered tin-plated copper wire is soldered to the silver electrodes, silicone resin is injected, and cured to obtain a lead-free barium titanate thermistor.

[0018] Example 3: This embodiment describes a method for manufacturing a 135°C lead-free barium titanate thermistor, comprising the following steps: Step S1: 1 mol of bismuth oxide, 1 mol of sodium carbonate, and 4 mol of titanium dioxide were added to a planetary ball mill with a ball-to-material ratio of 3:1. Wet ball milling was performed at 400 r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After milling for 24 h, the mixture was dried in a 120℃ forced-air drying oven for 12 h. The resulting material was crushed, sieved through an 80-mesh screen, and transferred to a muffle furnace for solid-state synthesis. The sintering process was as follows: the temperature was increased from 25℃ to 800℃ at a rate of 250℃ / h, then increased to 850℃ at a rate of 100℃ / h, held for 2 h, and naturally cooled to 25℃ to obtain Bi. 0.5 Na 0.5 TiO3; Step S2: Place 265g of the base material, 1.3g of the composite donor dopant, 0.4g of the composite acceptor dopant, 0.8g of silicon dioxide, and 0.7g of alumina into an 80℃ oven and dry for 2 hours. Then, add the mixture to a planetary ball mill with a ball-to-material ratio of 5:1 and perform wet ball milling at 400r / min. The solvent is deionized water, and the material-to-solvent ratio is 1:5. After ball milling for 24 hours, dry the mixture in a 120℃ forced-air drying oven for 12 hours. After crushing, sieve through a 100-mesh screen and press into blocks at 25MPa. Transfer the blocks to a muffle furnace for sintering. The sintering process is as follows: heat from 25℃ to 600℃ at a rate of 200℃ / h. The temperature was further increased to 1200℃ at a rate of 180℃ / h, held for 3 hours, cooled to 25℃ in the furnace, crushed and ground, and sieved through a 100-mesh sieve to obtain the main crystalline phase. The basic main material was composed of barium carbonate, calcium carbonate, and titanium dioxide in a molar ratio of 0.85mol:0.17mol:1.005mol. The composite donor dopant was composed of yttrium oxide, lanthanum oxide, and niobium pentoxide in a molar ratio of 0.0025mol:0.0012mol:0.0012mol. The composite acceptor dopant was composed of manganese nitrate and cobalt nitrate in a molar ratio of 0.001mol:0.0006mol. Step S3: Add 265g of the main crystalline phase and 0.02mol of Bi 0.5 Na 0.5TiO3 and 0.7g of sintering aid were added to a planetary ball mill at a ball-to-material ratio of 5:1. Wet ball milling was performed at 400 rpm using deionized water as the solvent at a material-to-solvent ratio of 1:5 for 18 hours to obtain a ball mill slurry. 3g of polyvinyl alcohol (PVA2399H) and 30mL of deionized water were added to a beaker, heated to 95℃, and stirred at a constant temperature for 2 hours. The mixture was then allowed to cool naturally to 60℃, and 10mL of anhydrous ethanol was added. Stirring continued for 30 minutes. The mixture was then further milled at 60℃. The binder was obtained by sieving through a 120-mesh sieve. The ball-milled slurry was allowed to stand for 12 hours, filtered, and the filter cake, binder, and 2g of zinc stearate were mixed and stirred for 3 hours. Spray granulation was then carried out: the inlet temperature was 200℃ and the outlet temperature was 100℃. The granulated powder was sieved through a 120-mesh sieve, poured into a mold, and pressed under 6MPa pressure for 5 minutes using a benchtop tablet press. The green body was then demolded. The sintering aid was composed of lithium carbonate and boron nitride mixed in a molar ratio of 0.005mol:0.012mol. Step S4: Place the billet in a high-temperature sintering furnace for sintering. The sintering curve is as follows: heat up to 600℃ at a rate of 150℃ / h, hold for 1h, continue to heat up to 1350℃ at a rate of 250℃ / h, hold for 2h, cool down to 1200℃ at a rate of 250℃ / h, hold for 40min, cool down to 800℃ at a rate of 200℃ / h, and cool down to 25℃ with the furnace below 850℃ to obtain the precursor. Step S5: Immerse the precursor in a 5% hydrofluoric acid solution for 8 minutes, remove the precursor, ultrasonically clean it for 10 minutes, then sensitize it in a 20 g / L stannous chloride solution for 5 minutes, and then activate it in a 0.5 g / L palladium chloride solution at 50°C for 5 minutes. Perform electroless nickel plating, plating in a 90°C water bath for 10 minutes. After nickel plating, wash it three times with distilled water, then boil it in deionized water at 100°C for 10 minutes. Then perform external cylindrical grinding to remove the nickel plating layer on the side surface, retaining the nickel plating layer on the top and bottom surfaces. Use screen printing to print solderable silver paste on the surface of the nickel plating layer on the top and bottom surfaces, and then heat the silver to form silver electrodes. Soldered tin-plated copper wire is soldered to the silver electrodes, silicone resin is injected, and cured to obtain a lead-free barium titanate thermistor.

[0019] Comparative Example 1: This comparative example illustrates a method for manufacturing a lead-free barium titanate thermistor, comprising the following steps: Step S1: 0.8 mol bismuth oxide, 0.8 mol sodium carbonate, and 3 mol titanium dioxide were added to a planetary ball mill at a ball-to-material ratio of 3:1. Wet ball milling was performed at 350 r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After milling for 24 h, the mixture was dried in a 120℃ forced-air drying oven for 10 h. The resulting material was crushed, sieved through an 80-mesh screen, and transferred to a muffle furnace for solid-state synthesis. The sintering process was as follows: the temperature was increased from 25℃ to 800℃ at a rate of 250℃ / h, then increased to 850℃ at a rate of 100℃ / h, held for 2 h, and naturally cooled to 25℃ to obtain Bi. 0.5 Na 0.5 TiO3; Step S2: Place 260g of the base material, 0.7g of silica, and 0.55g of alumina in an 80℃ oven and dry for 2 hours. Then add them to a planetary ball mill with a ball-to-material ratio of 5:1. Perform wet ball milling at 350r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After milling for 22 hours, dry in a 120℃ forced-air drying oven for 10 hours. After crushing, sieve through a 100-mesh screen and pressurize under 20MPa. The material is formed into blocks and transferred to a muffle furnace for sintering. The sintering process is as follows: the temperature is increased from 25°C to 600°C at a rate of 200°C / h, and then further increased to 1175°C at a rate of 180°C / h. The temperature is held for 2.5 hours, and then cooled to 25°C in the furnace. The blocks are crushed, ground, and sieved through a 100-mesh sieve to obtain the main crystalline phase. The main raw material is composed of barium carbonate, calcium carbonate, and titanium dioxide mixed in a molar ratio of 0.835 mol: 0.155 mol: 1 mol. Step S3: Add 250g of the main crystalline phase and 0.02mol Bi 0.5 Na 0.5 TiO3 and 0.55g of sintering aid were added to a planetary ball mill at a ball-to-material ratio of 5:1. Wet ball milling was performed at 350 rpm using deionized water as the solvent, with a material-to-solvent ratio of 1:5. The milling process lasted 17 hours to obtain a slurry. 2.5g of polyvinyl alcohol (PVA2399H) and 25mL of deionized water were added to a beaker, heated to 93℃, and stirred at this temperature for 1.5 hours. The mixture was then allowed to cool naturally to 60℃, and 8mL of anhydrous ethanol was added. Stirring continued for 30 minutes. The binder was obtained by sieving through a 60-mesh sieve. The ball-milled slurry was allowed to stand for 9 hours, filtered, and the filter cake, binder, and 1.5g of zinc stearate were mixed and stirred for 2.5 hours. Spray granulation was then carried out: the inlet temperature was 190℃ and the outlet temperature was 90℃. The granulated powder was sieved through a 90-mesh sieve, poured into a mold, and pressed under 5MPa pressure for 3 minutes using a benchtop tablet press. The green body was then demolded. The sintering aid was composed of lithium carbonate and boron nitride mixed in a molar ratio of 0.004mol:0.01mol. Step S4: Place the billet in a high-temperature sintering furnace for sintering. The sintering curve is as follows: heat up to 600℃ at a rate of 125℃ / h, hold for 1h, continue to heat up to 1350℃ at a rate of 225℃ / h, hold for 1.5h, cool down to 1200℃ at a rate of 225℃ / h, hold for 35min, cool down to 800℃ at a rate of 175℃ / h, and cool down to 25℃ with the furnace below 850℃ to obtain the precursor. Step S5: Immerse the precursor in a 5% hydrofluoric acid solution for 7 minutes, remove the precursor, ultrasonically clean it for 8 minutes, then sensitize it in a 15 g / L stannous chloride solution for 4 minutes, and then activate it in a 0.3 g / L palladium chloride solution at 48°C for 4 minutes. Perform electroless nickel plating, plating in an 85°C water bath for 9 minutes. After nickel plating, wash it three times with distilled water, then boil it in deionized water at 98°C for 8 minutes. Then perform external cylindrical grinding to remove the nickel plating layer on the side surface, retaining the nickel plating layer on the top and bottom surfaces. Use screen printing to print solderable silver paste on the surface of the nickel plating layer on the top and bottom surfaces, and then heat the silver to form silver electrodes. Soldered tin-plated copper wire is soldered to the silver electrodes, silicone resin is injected, and cured to obtain a lead-free barium titanate thermistor.

[0020] Comparative Example 2: This comparative example illustrates a method for manufacturing a lead-free barium titanate thermistor, comprising the following steps: Step S1: 0.8 mol bismuth oxide, 0.8 mol sodium carbonate, and 3 mol titanium dioxide were added to a planetary ball mill at a ball-to-material ratio of 3:1. Wet ball milling was performed at 350 r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After milling for 24 h, the mixture was dried in a 120℃ forced-air drying oven for 10 h. The resulting material was crushed, sieved through an 80-mesh screen, and transferred to a muffle furnace for solid-state synthesis. The sintering process was as follows: the temperature was increased from 25℃ to 800℃ at a rate of 250℃ / h, then increased to 850℃ at a rate of 100℃ / h, held for 2 h, and naturally cooled to 25℃ to obtain Bi. 0.5 Na 0.5 TiO3; Step S2: 260g of the base material, 1.1g of the composite donor dopant, 0.7g of silicon dioxide, and 0.55g of alumina were dried in an 80℃ oven for 2 hours. The dried material was then added to a planetary ball mill at a ball-to-material ratio of 5:1. Wet ball milling was performed at 350r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After milling for 22 hours, the material was dried in a 120℃ forced-air drying oven for 10 hours. The resulting material was crushed and sieved through a 100-mesh screen. It was then pressed into blocks at 20MPa and transferred to a muffle furnace for sintering. The sintering process was as follows: from 25℃... The temperature was increased to 600℃ at a rate of 200℃ / h, and then further increased to 1175℃ at a rate of 180℃ / h. The temperature was held for 2.5h, then cooled to 25℃ in the furnace. The mixture was crushed, ground, and sieved through a 100-mesh sieve to obtain the main crystalline phase. The basic raw material was a mixture of barium carbonate, calcium carbonate, and titanium dioxide in a molar ratio of 0.835mol:0.155mol:1mol. The composite donor dopant was a mixture of yttrium oxide, lanthanum oxide, and niobium pentoxide in a molar ratio of 0.00225mol:0.001mol:0.001mol. Step S3: Add 250g of the main crystalline phase and 0.02mol Bi 0.5 Na 0.5 TiO3 and 0.55g of sintering aid were added to a planetary ball mill at a ball-to-material ratio of 5:1. Wet ball milling was performed at 350 rpm using deionized water as the solvent, with a material-to-solvent ratio of 1:5. The milling process lasted 17 hours to obtain a slurry. 2.5g of polyvinyl alcohol (PVA2399H) and 25mL of deionized water were added to a beaker, heated to 93℃, and stirred at this temperature for 1.5 hours. The mixture was then allowed to cool naturally to 60℃, and 8mL of anhydrous ethanol was added. Stirring continued for 30 minutes. The binder was obtained by sieving through a 60-mesh sieve. The ball-milled slurry was allowed to stand for 9 hours, filtered, and the filter cake, binder, and 1.5g of zinc stearate were mixed and stirred for 2.5 hours. Spray granulation was then carried out: the inlet temperature was 190℃ and the outlet temperature was 90℃. The granulated powder was sieved through a 90-mesh sieve, poured into a mold, and pressed under 5MPa pressure for 3 minutes using a benchtop tablet press. The green body was then demolded. The sintering aid was composed of lithium carbonate and boron nitride mixed in a molar ratio of 0.004mol:0.01mol. Step S4: Place the billet in a high-temperature sintering furnace for sintering. The sintering curve is as follows: heat up to 600℃ at a rate of 125℃ / h, hold for 1h, continue to heat up to 1350℃ at a rate of 225℃ / h, hold for 1.5h, cool down to 1200℃ at a rate of 225℃ / h, hold for 35min, cool down to 800℃ at a rate of 175℃ / h, and cool down to 25℃ with the furnace below 850℃ to obtain the precursor. Step S5: Immerse the precursor in a 5% hydrofluoric acid solution for 7 minutes, remove the precursor, ultrasonically clean it for 8 minutes, then sensitize it in a 15 g / L stannous chloride solution for 4 minutes, and then activate it in a 0.3 g / L palladium chloride solution at 48°C for 4 minutes. Perform electroless nickel plating, plating in an 85°C water bath for 9 minutes. After nickel plating, wash it three times with distilled water, then boil it in deionized water at 98°C for 8 minutes. Then perform external cylindrical grinding to remove the nickel plating layer on the side surface, retaining the nickel plating layer on the top and bottom surfaces. Use screen printing to print solderable silver paste on the surface of the nickel plating layer on the top and bottom surfaces, and then heat the silver to form silver electrodes. Soldered tin-plated copper wire is soldered to the silver electrodes, silicone resin is injected, and cured to obtain a lead-free barium titanate thermistor.

[0021] Comparative Example 3: This comparative example illustrates a method for manufacturing a lead-free barium titanate thermistor, comprising the following steps: Step S1: 0.8 mol bismuth oxide, 0.8 mol sodium carbonate, and 3 mol titanium dioxide were added to a planetary ball mill at a ball-to-material ratio of 3:1. Wet ball milling was performed at 350 r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After milling for 24 h, the mixture was dried in a 120℃ forced-air drying oven for 10 h. The resulting material was crushed, sieved through an 80-mesh screen, and transferred to a muffle furnace for solid-state synthesis. The sintering process was as follows: the temperature was increased from 25℃ to 800℃ at a rate of 250℃ / h, then increased to 850℃ at a rate of 100℃ / h, held for 2 h, and naturally cooled to 25℃ to obtain Bi. 0.5 Na 0.5 TiO3; Step S2: 260g of the base material, 0.35g of the composite acceptor dopant, 0.7g of silicon dioxide, and 0.55g of alumina were dried in an 80℃ oven for 2 hours. The dried material was then added to a planetary ball mill at a ball-to-material ratio of 5:1. Wet ball milling was performed at 350r / min using deionized water as the solvent, with a material-to-solvent ratio of 1:5. After milling for 22 hours, the material was dried in a 120℃ forced-air drying oven for 10 hours. The resulting material was crushed, sieved through a 100-mesh screen, pressed into blocks at 20MPa, and then transferred to a muffle furnace for sintering. The formation process is as follows: the temperature is increased from 25℃ to 600℃ at a rate of 200℃ / h, and then further increased to 1175℃ at a rate of 180℃ / h, held at that temperature for 2.5h, cooled to 25℃ in the furnace, crushed and ground, and sieved through a 100-mesh sieve to obtain the main crystalline phase; the basic main material is composed of barium carbonate, calcium carbonate and titanium dioxide mixed in a molar ratio of 0.835mol:0.155mol:1mol; the composite acceptor dopant is composed of manganese nitrate and cobalt nitrate mixed in a molar ratio of 0.0009mol:0.0005mol. Step S3: Add 250g of the main crystalline phase and 0.02mol Bi 0.5 Na 0.5 TiO3 and 0.55g of sintering aid were added to a planetary ball mill at a ball-to-material ratio of 5:1. Wet ball milling was performed at 350 rpm using deionized water as the solvent, with a material-to-solvent ratio of 1:5. The milling process lasted 17 hours to obtain a slurry. 2.5g of polyvinyl alcohol (PVA2399H) and 25mL of deionized water were added to a beaker, heated to 93℃, and stirred at this temperature for 1.5 hours. The mixture was then allowed to cool naturally to 60℃, and 8mL of anhydrous ethanol was added. Stirring continued for 30 minutes. The binder was obtained by sieving through a 60-mesh sieve. The ball-milled slurry was allowed to stand for 9 hours, filtered, and the filter cake, binder, and 1.5g of zinc stearate were mixed and stirred for 2.5 hours. Spray granulation was then carried out: the inlet temperature was 190℃ and the outlet temperature was 90℃. The granulated powder was sieved through a 90-mesh sieve, poured into a mold, and pressed under 5MPa pressure for 3 minutes using a benchtop tablet press. The green body was then demolded. The sintering aid was composed of lithium carbonate and boron nitride mixed in a molar ratio of 0.004mol:0.01mol. Step S4: Place the billet in a high-temperature sintering furnace for sintering. The sintering curve is as follows: heat up to 600℃ at a rate of 125℃ / h, hold for 1h, continue to heat up to 1350℃ at a rate of 225℃ / h, hold for 1.5h, cool down to 1200℃ at a rate of 225℃ / h, hold for 35min, cool down to 800℃ at a rate of 175℃ / h, and cool down to 25℃ with the furnace below 850℃ to obtain the precursor. Step S5: Immerse the precursor in a 5% hydrofluoric acid solution for 7 minutes, remove the precursor, ultrasonically clean it for 8 minutes, then sensitize it in a 15 g / L stannous chloride solution for 4 minutes, and then activate it in a 0.3 g / L palladium chloride solution at 48°C for 4 minutes. Perform electroless nickel plating, plating in an 85°C water bath for 9 minutes. After nickel plating, wash it three times with distilled water, then boil it in deionized water at 98°C for 8 minutes. Then perform external cylindrical grinding to remove the nickel plating layer on the side surface, retaining the nickel plating layer on the top and bottom surfaces. Use screen printing to print solderable silver paste on the surface of the nickel plating layer on the top and bottom surfaces, and then heat the silver to form silver electrodes. Soldered tin-plated copper wire is soldered to the silver electrodes, silicone resin is injected, and cured to obtain a lead-free barium titanate thermistor.

[0022] The lead-free barium titanate thermistors prepared in Examples 1-3 and Comparative Examples 1-3 were tested for Curie temperature and resistance ratio according to the temperature characteristic test method for step-type PTC thermistors in GB / T 6663.1-2007; the room temperature resistivity was tested according to GB / T41606-2022. The test results are shown in the table below. Comparing Examples 1-3 with Comparative Examples 1-3: Example 1 used a relatively mild process and a relatively small amount of raw materials, resulting in slightly lower performance than Examples 2-3. Example 2, through enhanced ball milling and appropriately increased sintering strength, achieved a balance between uniformity and grain boundary structure, thus improving performance. Example 3 had the best preparation process and a moderate amount of raw materials, achieving optimal doping uniformity, the densest ceramic body, and the most effective grain boundary acceptor segregation, thereby obtaining higher overall performance. Comparing Example 2 with Comparative Example 1, it can be seen that: Comparative Example 1 had no functional doping, and its matrix was a natural insulator with a large band gap. At room temperature, it had almost no free electrons, and without donor doping to provide electrons, the material could not conduct electricity, resulting in extremely high room temperature resistivity. Without acceptor doping forming a potential barrier at the grain boundaries, the resistance-temperature curve showed no abrupt changes. The resistance increase ratio is close to 1. Comparing Example 2 with Comparative Example 2, it can be seen that Comparative Example 2 lacks acceptor doping, while both examples successfully achieved semiconductorization through composite donor doping, resulting in a low room temperature resistivity. However, Comparative Example 2 lacks acceptor centers at the grain boundaries, making it impossible to form an effective barrier. Consequently, the grain boundary resistance is low, and even above the Curie temperature, the resistance only increases slightly, leading to an extremely low resistance increase ratio. Comparing Example 2 with Comparative Example 3, it can be seen that Comparative Example 3 lacks donor doping, and without donors to provide free electrons, the material maintains high resistance. In Example 2, donors provide sufficient electrons, successfully achieving semiconductorization. In Comparative Example 3, acceptors are present and form a barrier at the grain boundaries. However, due to the excessively high grain bulk resistance, the overall resistance of the device is dominated by the grain resistance. The change in the grain boundary barrier has a relatively small impact on the total resistance, thus exhibiting a limited resistance increase ratio.

[0023] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0024] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a 135°C lead-free barium titanate thermistor, characterized in that, Includes the following steps: Step a1: Bismuth oxide, sodium carbonate, and titanium dioxide are mixed, wet-milled, dried, crushed, sieved, sintered, and naturally cooled to obtain Bi. 0.5 Na 0.5 TiO3; Step a2: Dry the primary material, wet ball mill it, dry it again, crush it and sieve it, press it into blocks, transfer it to a muffle furnace for sintering, cool it in the furnace, crush and grind it, and sieve it to obtain the main crystalline phase; Step a3: Wet ball mill the secondary material to obtain ball mill slurry; add polyvinyl alcohol and deionized water to a beaker, heat and stir, cool naturally, add anhydrous ethanol, continue stirring, sieve to obtain binder; let the ball mill slurry stand, filter, mix the filter cake, binder and release agent, spray granulation, sieve the granulated powder, pour into a mold, press, demold to obtain green body; Step a4: Place the billet into a high-temperature sintering furnace for sintering, and cool it with the furnace to obtain the precursor; Step a5: Immerse the precursor in a roughening agent, ultrasonically clean it, then sensitize it in a stannous chloride solution, activate it in a palladium chloride solution, plate it with nickel using a chemical nickel plating process, wash it, then boil it in deionized water to remove the nickel plating layer on the side, print solderable silver paste on the nickel plating layer surface of the upper and lower end faces, burn silver to form silver electrodes; solder tin-plated copper wire to the silver electrodes with tin solder, inject silicone resin, and cure to obtain a lead-free barium titanate thermistor.

2. The method for manufacturing a 135°C lead-free barium titanate thermistor according to claim 1, characterized in that, The ratio of bismuth oxide, sodium carbonate, and titanium dioxide used in step a1 is 0.5-1 mol: 0.5-1 mol: 2-4 mol.

3. The method for manufacturing a 135°C lead-free barium titanate thermistor according to claim 1, characterized in that, The primary material in step a2 is composed of a base material, a composite donor dopant, a composite acceptor dopant, a fluxing agent, and a sintering aid mixed in a mass ratio of 255-265g: 0.9-1.3g: 0.3-0.4g: 0.6-0.8g: 0.4-0.7g; the base material is composed of barium carbonate, calcium carbonate, and titanium dioxide mixed in a molar ratio of 0.82-0.85mol: 0.14-0.17mol: 0.995-1.005mol.

4. The method for manufacturing a 135°C lead-free barium titanate thermistor according to claim 3, characterized in that, The composite donor dopant is composed of yttrium oxide, lanthanum oxide, and niobium pentoxide in a molar ratio of 0.002-0.0025 mol: 0.0008-0.0012 mol: 0.0008-0.0012 mol; the composite acceptor dopant is composed of manganese nitrate and cobalt nitrate in a molar ratio of 0.0008-0.001 mol: 0.0004-0.0006 mol.

5. The method for manufacturing a 135°C lead-free barium titanate thermistor according to claim 3, characterized in that, The flux is silicon dioxide; the sintering aid is aluminum oxide.

6. The method for manufacturing a 135°C lead-free barium titanate thermistor according to claim 1, characterized in that, The ratio of the secondary material, polyvinyl alcohol, deionized water, anhydrous ethanol and release agent in step a3 is 240-270g: 2-3g: 20-30mL: 5-10mL: 1-2g.

7. The method for manufacturing a 135°C lead-free barium titanate thermistor according to claim 6, characterized in that, The secondary material consists of the main crystalline phase and Bi. 0.5 Na 0.5 TiO3 and sintering aids are mixed in a ratio of 235-265g:0.02mol:0.4-0.7g; the polyvinyl alcohol is PVA2399H; and the release agent is zinc stearate.

8. The method for manufacturing a 135°C lead-free barium titanate thermistor according to claim 7, characterized in that, The sintering aid is composed of lithium carbonate and boron nitride mixed in a molar ratio of 0.003-0.005 mol: 0.008-0.012 mol.

9. The method for manufacturing a 135°C lead-free barium titanate thermistor according to claim 1, characterized in that, The solvent used in the wet ball milling process in steps a1-a3 is deionized water, and the ratio of material to solvent is 1:

5.

10. The method for manufacturing a 135°C lead-free barium titanate thermistor according to claim 1, characterized in that, The roughening agent in step a5 is a 5% hydrofluoric acid solution; the concentration of the stannous chloride solution is 10-20 g / L; and the concentration of the palladium chloride solution is 0.1-0.5 g / L.

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