Whole-series lead-free barium titanate thermistor with Curie point of 60-125 DEG C and preparation method of whole-series lead-free barium titanate thermistor

Abstract

The invention relates to the technical field of preparation of electronic ceramic components, in particular to a whole-series lead-free barium titanate thermistor with the Curie point of 60-125 DEG C and a preparation method of the whole-series lead-free barium titanate thermistor. The whole-series lead-free barium titanate thermistor is prepared from the following raw materials in parts by mole: 0.99 part of a frit material, 0.01 part of sodium bismuth titanate and 0.001-0.008 part of lithium carbonate, the frit material is prepared from the following components in parts by mole: 0.669 to 0.868 part of barium carbonate, 0.10 to 0.181 part of calcium carbonate, 0.011 to 0.153 part of strontium carbonate, 0.0023 to 0.0032 part of yttrium oxide, 0.002 to 0.01 part of aluminum oxide, 0.0005 to 0.0012 part of manganous nitrate, 0.008 to 0.02 part of silicon dioxide and 0.992 to 1.3 part of titanium dioxide. According to the invention, BNT and strontium titanate are added at the A site at the same time, and lead titanate is replaced by BNT, so that the lead-free whole series of thermistors at the temperature of 60-125 DEG C is realized.

Description

Technical Field

[0001] This invention relates to the field of electronic ceramic component manufacturing technology, specifically to a full range of lead-free barium titanate thermistors with Curie points of 60℃-125℃ and their manufacturing methods. Background Technology

[0002] Traditional barium titanate ceramic thermistors have a Curie point of 60℃-125℃. To refine the grain size and thus improve the voltage withstand performance of PTC (positive temperature coefficient) ceramics, besides commonly using calcium doping at the A-site, strontium-lead co-addition at the A-site is also frequently used to further refine the grain size and improve the voltage withstand capability. Lead causes irreversible environmental pollution, and banning its use is a challenge that humanity must face. Correspondingly, how to further refine the PTC ceramic grain size and improve the voltage withstand capability of PTC thermistors without using lead is a problem that needs to be addressed.

[0003] This invention attempts to replace lead titanate with sodium bismuth titanate (BNT) and co-dope it with strontium titanate at the A-site to fabricate a full range of lead-free barium titanate thermistors with Curie points ranging from 60℃ to 125℃. The performance of the PTC thermistors fabricated by this invention fully meets or even exceeds that of the original strontium-lead co-doped PTC thermistors.

[0004] Currently, most high-voltage PTC thermistors with a Curie point of 60℃-125℃ in China are produced using strontium-lead co-addition technology. This invention replaces lead titanate with BNT and performs composite doping with strontium titanate at the A-site, creating a full range of lead-free barium titanate-based high-voltage thermistors with a Curie point of 60℃-125℃, filling a significant gap in the domestic production of lead-free thermistors. Summary of the Invention

[0005] This invention employs high calcium doping at the A-site to obtain a PTC thermistor ceramic material with low resistivity, fine grains, and high voltage withstand capability. Furthermore, this invention simultaneously adds sodium bismuth titanate (BNT) and strontium titanate at the A-site, further refining the grain size and improving voltage withstand capability through composite doping at the A-site. By replacing lead titanate with BNT, a full range of lead-free thermistors with operating temperatures from 60℃ to 125℃ is achieved.

[0006] To achieve the above objectives, the present invention employs the following technical solution: The Curie point range is 60℃-125℃. This series of lead-free barium titanate thermistors is mainly used in overheat protection circuits, overcurrent protection circuits, and air conditioner starter circuits. The raw materials for manufacturing the thermistors, by molar parts, are: 0.99 parts of frit, 0.01 parts of sodium bismuth titanate, and 0.001-0.008 parts of lithium carbonate. The ceramic material composition of the frit, by molar parts, is: barium carbonate: 0.669-0.868 parts, calcium carbonate: 0.10-0.181 parts, strontium carbonate: 0.011-0.153 parts, yttrium oxide: 0.0023-0.0032 parts, alumina: 0.002-0.01 parts, manganese nitrate: 0.0005-0.0012 parts, silicon dioxide: 0.008-0.02 parts, and titanium dioxide: 0.992-1.3 parts.

[0007] Furthermore, PTCs with corresponding Curie point temperatures are obtained by dynamically adjusting the strontium carbonate ratio, specifically including: The molar fraction of strontium carbonate in PTC at the Curie point of 60℃ is 0.143–0.153 parts. The molar fraction of strontium carbonate in PTC at the 70℃ Curie point is 0.115–0.131 parts. The molar fraction of strontium carbonate in PTC at the 80℃ Curie point is 0.093–0.112 parts. The molar fraction of strontium carbonate in PTC at the 90℃ Curie point is 0.078–0.088 parts. The molar fraction of strontium carbonate in PTC at the Curie point of 100℃ is 0.0583–0.0653 parts. The molar fraction of strontium carbonate in PTC at the Curie point of 110℃ is 0.035–0.047 parts. The molar fraction of strontium carbonate in PTC at the Curie point of 120℃ is 0.019–0.025 parts. The molar fraction of strontium carbonate in PTC at the Curie point of 125℃ is 0.011 to 0.016 parts.

[0008] The nominal resistance of the thermistor of this invention is 47 ohms, and the resistance-to-weight ratio is (1~3)*10. 6 It has a withstand voltage of 1000VDC.

[0009] The present invention discloses a method for manufacturing a full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃, comprising the following steps: 1) The raw materials barium carbonate, calcium carbonate, strontium carbonate, yttrium oxide, aluminum oxide, manganese nitrate, silicon dioxide, and titanium dioxide are mixed and pre-calcined to synthesize frit; 2) Mix the frit with sodium bismuth titanate and lithium carbonate to form grinding balls; 3) Add binder and release agent to the material obtained in step 2), then perform spray granulation, and press the granules into blank sheets; 4) The blank sheet is sintered at high temperature under air conditions to obtain PTC disc ceramic body, and the PTC disc ceramic body is made into resistor.

[0010] Furthermore, step 1) involves wet ball milling the mixture and then pre-sintering it. The ball milling particle size is 2.0μm to 2.5μm, the pre-sintering temperature is 1170℃±10℃, and the temperature is maintained for 2 to 3 hours.

[0011] Furthermore, the grinding ball particle size in step 2) is 1.8μm to 2.3μm.

[0012] Furthermore, the particle size of the granules in step 3) is 124μm to 250μm.

[0013] Furthermore, the high-temperature sintering process in step 4) is as follows: room temperature → 600℃, heating rate 250℃~300℃ / hour, holding at 600℃ for 30 minutes; 600℃ → 1350℃, heating rate 250℃~300℃ / hour, holding at 1350℃ for 1~2 hours; 1350℃ → 1200℃, cooling rate 300℃~350℃ / hour, holding at 1200℃ for 30~50 minutes; 1200℃ → 850℃, cooling rate 150℃~300℃ / hour, cooling down with the furnace below 850℃, then removing from the furnace to obtain PTC disc-shaped ceramic bodies.

[0014] Furthermore, the preparation method of the sodium bismuth titanate is as follows: 1) The composition of sodium bismuth titanate is in the following molar ratio: bismuth oxide: sodium carbonate: titanium dioxide = 1:1:4; 2) Prepare the ingredients according to the above proportions, add water, wet ball mill for 24±1 hours, discharge the material, and dry it in an oven at 120±1℃; 3) Solid-phase synthesis regime: The temperature is increased from 0℃ to 800℃~850℃ at a heating rate of 250℃ per hour, and held at the high temperature for 2~3 hours. Compared with existing technologies, the beneficial effects of this invention are: 1) This invention employs high calcium doping at the A-site to obtain a PTC thermistor ceramic material with low resistivity, fine grains (2-4 micrometers), and high voltage withstand capability. This invention also incorporates BNT and strontium titanate at the A-site, further refining the grain size and improving voltage withstand capability through composite doping at the A-site. By replacing lead titanate with BNT, a full range of lead-free thermistors with operating temperatures from 60℃ to 125℃ is achieved.

[0015] 2) The addition of BNT addresses the issue of PTC materials with a Curie point of 60℃-125℃. Traditional PTC materials using the original AST glass phase combination cannot achieve semiconductivity when sintered in air. This invention creatively employs the ALST glass phase. In addition to the conventional alumina (A), silicon dioxide (S), and titanium dioxide (T), the addition of lithium carbonate (L) lowers the sintering temperature of PTC ceramics and effectively inhibits the decomposition of sodium bismuth titanate (BNT), making it possible to sinter PTC materials with a Curie point of 60℃-125℃ in air.

[0016] 3) This invention obtains fine-grained ceramics that meet design requirements through the scientific and reasonable combination of four glass phases of ALST, thereby improving the voltage resistance characteristics of lead-free PTC thermistor ceramic materials; and because of this careful formulation, the mass production of PTC materials with a Curie point of 60℃-125℃ can proceed smoothly.

[0017] 4) This invention adds the glass phase in the PTC ceramic formulation in two stages: AST is added during the first batching, and Li2CO3 is added during the second batching. BNT is also added during the second batching, ensuring smooth mass production. This method of adding the glass phase and the addition of BNT during the second batching are key features of this invention.

[0018] 5) The exploration and determination of the donor amount, acceptor amount and donor-acceptor ratio in this invention ensures that the lead-free PTC thermistor has a high α coefficient (above 32.8%, test points: 15℃ / 25℃), high resistance ratio and high withstand voltage.

[0019] 6) In the exploration and design of the sintering curve, this invention adopts a sintering process in which the temperature is rapidly increased to the maximum sintering temperature after 600℃, and then rapidly decreased to 1200℃ after holding for a period of time. This process avoids the growth of abnormal grains and is also conducive to the thickening of the barium vacancy diffusion layer. Based on the selection of raw material formulation, this firing process ensures the acquisition of uniform fine-grained ceramics from the perspective of microstructure. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to specific examples of the present invention. Obviously, the described embodiments are merely illustrative and are not intended to limit the present invention.

[0021] The present invention discloses a method for manufacturing a full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃, as detailed below: 1. BNT crafting: The composition of BNT is: analytical grade bismuth oxide, analytical grade sodium carbonate, and electronic grade titanium dioxide in a molar ratio of 1:1:4.

[0022] Prepare the ingredients according to the above proportions, add water, wet ball mill for 24 hours, discharge the material, and dry it in an oven at 120 degrees Celsius.

[0023] Solid-phase synthesis procedure: heating from 0°C to 800°C-850°C at a rate of 250°C per hour, and holding at the high temperature for 2-3 hours.

[0024] 2. Weigh the raw materials barium carbonate, calcium carbonate, strontium carbonate, yttrium oxide, aluminum oxide, manganese nitrate, silicon dioxide, and titanium dioxide and perform wet ball milling to make the materials uniformly mixed with a particle size of 2.0μm-2.5μm; the deionized water used for ball milling has an insulation resistance greater than 10MΩ.

[0025] Pre-calcination synthesis: Dry the ball-milled material, press it into blocks, and heat it at a rate of 150℃-180℃ per hour until it reaches 1170℃±10℃. Hold the temperature for 2-3 hours for pre-calcination synthesis.

[0026] 3. Wet ball mill 0.99 molar parts of frit, BNT and lithium carbonate in a ball mill to make the materials uniformly mixed with a particle size of 1.8μm-2.3μm; the insulation resistance of the deionized water used for ball milling is greater than 10MΩ.

[0027] 4. Add adhesive and release agent and stir: Place the material obtained in step 3 into a mixing tank, let it stand and settle, remove the settled water, and then add the adhesive and release agent according to the ratio of material: adhesive: release agent = 1: (0.12-0.14): (0.004-0.005). Stir to fully combine the adhesive and release agent with the material to obtain the slurry.

[0028] Adhesive preparation: Deionized water with an insulation resistance greater than 10MΩ: Polyvinyl alcohol 23-99: Alcohol = 100: (7-9): (18-22), stir and heat, boil for 60 minutes, cool and sieve before use.

[0029] 5. Spray granulation: The slurry obtained in step 4 is spray-granulated, the granules are cooled, de-ironized, and sieved to obtain granules with a particle size of 124μm-250μm.

[0030] 6. Compression molding: The granules obtained in step 5 are pressed into granules using a 20-station rotary vane press. The blank is a round sheet measuring 3.38 mm x 1.5 mm, with a density controlled at 3.2 g / cm³. 3 .

[0031] 7. Sintering: The circular blanks obtained in step 6 are sintered in a high-temperature kiln using the following sintering curve: Room temperature → 600℃, heating rate 250℃~300℃ / hour, hold at 600℃ for 30 minutes; 600℃ → 1350℃, heating rate 250℃~300℃ / hour, hold at 1350℃ for 1~2 hours; 1350℃ → 1200℃, cooling rate 300℃~350℃ / hour, hold at 1200℃ for 30~50 minutes; 1200℃ → 850℃, cooling rate 150℃~300℃ / hour, cool down with the furnace below 850℃, remove from the furnace, and obtain PTC disc-shaped ceramic body.

[0032] 8. Top nickel electrode: The PTC ceramic sheet obtained in step 7 is chemically nickel plated; then the PTC ceramic sheet is externally ground to remove the nickel plating layer on the side of the ceramic sheet, while retaining the nickel plating layer on the upper and lower end faces of the ceramic sheet.

[0033] 9. Silver electrode: Solderable silver paste is screen-printed onto the nickel-plated surface of the upper and lower ends of the disc-shaped PTC ceramic body, and then silver is fired to form silver electrodes.

[0034] 10. Welding, encapsulation, and curing: Wires are welded to the upper and lower ends of the disc-shaped PTC ceramic body obtained in step 9. The disc-shaped PTC ceramic body is then encapsulated with silicone resin material, and the silicone resin material is cured to obtain the product.

[0035] The ceramic material composition of the embodiments of the present invention is shown in Tables 1-1 and 1-2; the preparation process of sodium bismuth titanate (BNT) of the embodiments of the present invention is shown in Table 2; the parameters of the two ball milling processes of the embodiments of the present invention are shown in Table 3; the temperature parameters of the ceramic material manufacturing process of the embodiments of the present invention are shown in Table 4; and the product performance parameters of the embodiments of the present invention are shown in Table 5.

[0036] In the examples, the ratio (by weight) of adhesive and release agent is material: adhesive: release agent = 1:0.12:0.004; the adhesive is prepared by mixing and stirring deionized water with an insulation resistance greater than 10MΩ, polyvinyl alcohol 23-99: alcohol = 100:9:22 (by weight), heating, boiling for 60 minutes, cooling and sieving before use.

[0037] Table 1-1 Ceramic material composition (mol parts) of the frit material in the examples: Table 1-2 Raw material composition of thermistors (mol parts): Table 2. Preparation process of sodium bismuth titanate (BNT) in the examples: Table 3. Ball milling parameters for two examples: Table 4 Temperature parameters for high-temperature furnace sintering process of ceramic materials in the examples: Table 5. Product performance parameters for the examples: The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃, characterized in that... The raw materials for preparing the thermistor, by molar parts, are: 0.99 parts of frit, 0.01 parts of sodium bismuth titanate, and 0.001 to 0.008 parts of lithium carbonate. The ceramic material composition of the frit, by molar parts, is: barium carbonate: 0.669 to 0.868 parts, calcium carbonate: 0.10 to 0.181 parts, strontium carbonate: 0.011 to 0.153 parts, yttrium oxide: 0.0023 to 0.0032 parts, alumina: 0.002 to 0.01 parts, manganese nitrate: 0.0005 to 0.0012 parts, silicon dioxide: 0.008 to 0.02 parts, and titanium dioxide: 0.992 to 1.3 parts.

2. The lead-free barium titanate thermistor with a Curie point of 60℃-125℃ according to claim 1, characterized in that, The PTC with the corresponding Curie point temperature is obtained by dynamically adjusting the ratio of strontium carbonate, specifically including: The molar fraction of strontium carbonate in PTC at the Curie point of 60℃ is 0.143–0.153 parts. The molar fraction of strontium carbonate in PTC at the 70℃ Curie point is 0.115–0.131 parts. The molar fraction of strontium carbonate in PTC at the 80℃ Curie point is 0.093–0.112 parts. The molar fraction of strontium carbonate in PTC at the 90℃ Curie point is 0.078–0.088 parts. The molar fraction of strontium carbonate in PTC at the Curie point of 100℃ is 0.0583–0.0653 parts. The molar fraction of strontium carbonate in PTC at the Curie point of 110℃ is 0.035–0.047 parts. The molar fraction of strontium carbonate in PTC at the Curie point of 120℃ is 0.019–0.025 parts. The molar fraction of strontium carbonate in PTC at the Curie point of 125℃ is 0.011 to 0.016 parts.

3. The full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃ as described in claim 1 or 2, characterized in that, The nominal resistance of the thermistor is 47 ohms, and the resistance-to-weight ratio is (1~3)*10. 6 It has a withstand voltage of 1000VDC.

4. A method for manufacturing a full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃ as described in any one of claims 1-3, characterized in that, Includes the following steps: 1) The raw materials barium carbonate, calcium carbonate, strontium carbonate, yttrium oxide, aluminum oxide, manganese nitrate, silicon dioxide, and titanium dioxide are mixed and pre-calcined to synthesize frit; 2) Mix the frit with sodium bismuth titanate and lithium carbonate to form grinding balls; 3) Add binder and release agent to the material obtained in step 2), then perform spray granulation, and press the granules into blank sheets; 4) The blank sheet is sintered at high temperature under air conditions to obtain PTC disc ceramic body, and the PTC disc ceramic body is made into resistor.

5. The method for manufacturing a full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃ according to claim 4, characterized in that, Step 1) involves wet ball milling of the mixture followed by pre-sintering. The ball milling particle size is 2.0 μm to 2.5 μm, the pre-sintering temperature is 1170℃ ± 10℃, and the temperature is maintained for 2 to 3 hours.

6. The method for manufacturing a full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃ according to claim 4, characterized in that, The grinding ball particle size in step 2) is 1.8μm to 2.3μm.

7. The method for manufacturing a full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃ according to claim 4, characterized in that, The particle size of the granules in step 3) is 124μm to 250μm.

8. The method for manufacturing a full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃ according to claim 4, characterized in that, The high-temperature sintering process in step 4) is as follows: room temperature → 600℃, heating rate 250℃~300℃ / hour, holding at 600℃ for 30 minutes; 600℃ → 1350℃, heating rate 250℃~300℃ / hour, holding at 1350℃ for 1~2 hours; 1350℃ → 1200℃, cooling rate 300℃~350℃ / hour, holding at 1200℃ for 30~50 minutes; 1200℃ → 850℃, cooling rate 150℃~300℃ / hour, cooling down with the furnace below 850℃, then removing from the furnace to obtain PTC disc-shaped ceramic bodies.

9. The method for manufacturing a full range of lead-free barium titanate thermistors with a Curie point of 60℃-125℃ according to claim 4, characterized in that, The preparation method of the sodium bismuth titanate is as follows: 1) The composition of sodium bismuth titanate is in the following molar ratio: bismuth oxide: sodium carbonate: titanium dioxide = 1:1:4; 2) Prepare the ingredients according to the above proportions, add water, wet ball mill for 24±1 hours, discharge the material, and dry it in an oven at 120±1℃; 3) Solid-phase synthesis regime: The temperature is increased from 0℃ to 800℃~850℃ at a heating rate of 250℃ per hour, and the high temperature is maintained for 2~3 hours.

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