135 DEG C lead-free barium titanate thermistor and preparation method thereof

Abstract

The invention relates to a 135 DEG C lead-free barium titanate thermistor and a preparation method thereof. The ceramic material for preparing the thermistor comprises the following components in parts by mole: 0.799 to 0.88 part of barium carbonate, 0.10 to 0.181 part of calcium 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 manganese nitrate, 0.008 to 0.02 part of silicon dioxide, 0.992 to 1 part of titanium dioxide, 0.02 part of sodium bismuth titanate, 0.001 to 0.008 part of lithium carbonate and 0.002 to 0.025 part of boron nitride. According to the PTC thermistor specially manufactured for the air conditioner starting circuit, the resistance value is 47 omega + / -20%, the chip size phi is (13.7-13.8) mm * 2.8 mm, the Curie point is 135 DEG C, the lift-to-drag ratio reaches 106 or above, the voltage resistance capacity is DC900V, and the impact resistance capacity is hundreds of thousands of times or above.

Description

Technical Field

[0001] This invention relates to the field of electronic ceramic component manufacturing technology, specifically to a 135℃ lead-free barium titanate thermistor and its manufacturing method, which is mainly used in overheat protection circuits, overcurrent protection circuits, and air conditioner starter circuits. Background Technology

[0002] Traditional barium titanate ceramic PTC materials have a Curie point of 120℃. Below 120℃, strontium titanate doping is typically used for peak shifting, while above 120℃, lead titanate doping is used. Lead pollution is an irreversible environmental problem that humanity must address; therefore, the lead-free development of high Curie point PTC materials is an urgent priority. Replacing lead titanate with BNT, BKT, or BLT doping for peak shifting represents a development direction for high Curie point lead-free barium titanate ceramic PTC materials.

[0003] The invention patent with application number 202310423375.8 developed a lead-free thermistor with a Curie point of 130℃. It mainly utilizes traditional barium titanate ceramic doped with BNT material to shift the Curie point. By adjusting the amount of donor Y2O3 and acceptor Mn(NO3)2, adding mineralizer CaCO3, and adding glass phase Al2O3, SiO2, TiO2, and Li2CO3, a PTC ceramic material with a Curie point of 130℃ is produced.

[0004] However, during the later stages of research and development, the inventors attempted to increase the Curie point of PTC ceramic materials by increasing the content of BNT materials. But after numerous experiments, the inventors were unable to achieve semiconductorization of PTC materials by increasing the amount of BNT by 0.01 moles.

[0005] Currently, due to the difficulty in semiconductorization, most domestic manufacturers and research institutions use reducing atmosphere furnaces for sintering lead-free PTC materials at 135℃ and above, followed by a re-oxidation process. This process is extremely difficult for large-scale production, hindering its smooth progress. Using conventional sintering methods under air conditions, high-content BNT materials can be sintered and semiconductorized to achieve a high resistance-to-weight ratio (10). 5 The production of lead-free barium titanate thermistors with a Curie point of 135℃ has not yet been publicly reported to be achieved. Summary of the Invention

[0006] To address the issue that the original ALST glass phase in 135℃ PTC materials cannot achieve semiconductivity during air sintering, this invention provides a 135℃ lead-free barium titanate thermistor that can be manufactured under conventional air sintering conditions. It utilizes traditional barium titanate ceramic doped with BNT material for peak shifting, adjusting the donor and acceptor components, adding calcium mineralizer, and changing the glass phase from the original ALST to an ABLST glass phase (with added boron nitride), resulting in a 135℃ Curie point PTC material with a main crystalline phase of 0.98BT-0.02BNT. This invention specifically manufactures a PTC thermistor for air conditioner starting circuits, with a resistance of 47Ω±20%, a chip size of Φ (13.7~13.8)mm*2.8mm, a Curie point of 135℃, and a rise-resistance ratio of 10. 6 The above specifications include a withstand voltage of DC 900V and an impact resistance of over 100,000 cycles.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A 135℃ lead-free barium titanate thermistor is prepared by means of the following raw materials in molar amounts: 0.98 parts of frit, 0.02 parts of sodium bismuth titanate, 0.001-0.008 parts of lithium carbonate, and 0.002-0.025 parts of boron nitride. The ceramic material composition of the frit in molar amounts is as follows: barium carbonate: 0.799-0.88 parts, calcium carbonate: 0.10-0.181 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 parts.

[0008] The thermistor has a resistance of 47Ω ± 20%, a Curie point of 135℃, and a resistance-to-weight ratio of 10. 6 The above specifications indicate a withstand voltage of DC 900V. The chip dimensions are Φ13.7mm*2.8mm.

[0009] A method for manufacturing a 135℃ lead-free barium titanate thermistor includes the following steps: 1) Barium carbonate, calcium carbonate, yttrium oxide, aluminum oxide, manganese nitrate, silicon dioxide, and titanium dioxide are mixed and pre-calcined to synthesize a frit material; 2) Mix the frit with sodium bismuth titanate, lithium carbonate, and boron nitride to form grinding balls; 3) Add binder and release agent to the mixture 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] Step 1) involves wet ball milling of the mixture followed by pre-sintering. The ball milling particle size is no greater than 2.0 μm, and the pre-sintering temperature is 1170℃±10℃, with a holding time of 2-3 hours.

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

[0012] Furthermore, the particle size of the granules in step 3) is 124μm-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℃ → 1310℃, heating rate 250℃-300℃ / hour, holding at 1310℃ for 1-2 hours; 1310℃ → 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 the high temperature is maintained for 2~3 hours.

[0015] Compared with existing technologies, the beneficial effects of this invention are: 1) Regarding the problem that the original ALST glass phase combination in 135℃ PTC material cannot achieve semiconductivity when sintered in air, this invention also adds boron nitride (B) to the glass phase. AST is added during the first batching, and BN, Li2CO3, and BNT are added during the second batching. This effectively inhibits the decomposition of BNT and successfully promotes the semiconductivity of high-ratio raw material BNT under air conditions, making it possible to sinter lead-free PTC material at 135℃ in air.

[0016] 2) Based on the original Curie point of 130℃, this invention increases the proportion of BNT material and utilizes traditional barium titanate ceramic doping of BNT material for peak shifting, aiming to raise the Curie point of lead-free PTC material to 135℃. Under this condition, the raw material ratio is adjusted as follows: the molar ratio of barium carbonate, calcium carbonate, yttrium oxide, alumina, manganese nitrate, silicon dioxide, and titanium dioxide mixed frit is 0.98 parts, and lithium carbonate (L) is 0.001-0.008 parts. The addition of 0.02 parts of sodium bismuth titanate (BNT) and 0.002 to 0.025 parts of boron nitride in the secondary batching process, along with 0.02 parts of sodium bismuth titanate (BNT), lowered the sintering temperature of PTC ceramics under air conditions. This provided a strong condition for inhibiting the decomposition of sodium bismuth titanate (BNT) under air conditions, ultimately resulting in a 135℃ lead-free barium titanate thermistor.

[0017] 3) The exploration and determination of the donor, acceptor, and donor-acceptor ratios in this invention ensures a high α coefficient, high resistance-to-voltage ratio, and high withstand voltage for the lead-free PTC thermistor. The thermistor of this invention has a resistance of 47Ω ± 20%, a Curie point of 135℃, and a resistance-to-voltage ratio of 10. 6 The above specifications include a withstand voltage of DC 900V and an impact resistance of over 100,000 cycles. The chip size is Φ (13.7~13.8)mm*2.8mm.

[0018] 4) 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. 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 formula, this firing process ensures the acquisition of uniform fine-grained ceramics from the perspective of microstructure.

[0019] 5) This invention employs calcium doping at site A to obtain a PTC thermistor ceramic material with low resistivity, fine grains, and high voltage resistance. 6) This invention uses a scientific and reasonable combination of five glass phases from ABLST to control the production of the fine-grained ceramics we want, thereby improving the voltage resistance characteristics of lead-free PTC thermistor ceramic materials. It is also because of this careful formulation that the mass production of 135℃ PTC materials can proceed smoothly. 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 method for fabricating a 135℃ Curie point PTC thermistor according to the present invention is as follows: 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, 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 2.0 μm - 2.5 μm; the insulation resistance of the deionized water used for ball milling is greater than 10 MΩ.

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

[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 45-60 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 124um-250um.

[0030] 6. Compression molding: The granules obtained in step 5 were pressed into circular blanks with a diameter of Φ17.1 mm * 3.38 mm using a 20-station rotary vane press, 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: At room temperature to 600℃, the heating rate is 250℃-300℃ / hour, and the temperature is held at 600℃ for 30 minutes; at 600℃ to 1310℃, the heating rate is 250℃-300℃ / hour, and the temperature is held at 1310℃ for 1-2 hours; at 1310℃ to 1200℃, the cooling rate is 300℃-350℃ / hour, and the temperature is held at 1200℃ for 30-50 minutes; at 1200℃ to 850℃, the cooling rate is 150℃-300℃ / hour, and the temperature is lowered with the furnace below 850℃. After removing from the furnace, PTC disc-shaped ceramic bodies are obtained.

[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 technical performance of the lead-free PTC thermistor obtained by this invention is as follows: its resistance is 47Ω±20%, its Curie point is 135℃, its withstand voltage is DC900V, and its impact resistance is more than 100,000 cycles.

[0036] 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.

[0037] 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.

[0038] 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 the two examples. Table 4 Temperature parameters for high-temperature furnace sintering process of ceramic materials in the examples Example Temperature at first heating step (°C) Temperature rise rate (°C / hour) Incubation time (minutes) Secondary heating rate (°C / hour) Secondary heating temperature (°C) Insulation time (hours) Cooling rate per cycle (°C / hour) Temperature at which the temperature drops once (°C) Incubation time (minutes) Secondary cooling rate (°C / hour) Secondary cooling temperature (°C) 1 600 260 30 260 1310 2 350 1200 30 250 850 2 600 280 30 270 1310 2 330 1200 50 150 850 3 600 270 30 290 1310 1 340 1200 30 200 850 4 600 255 30 280 1310 2 320 1200 40 300 850 5 600 290 30 300 1310 2 350 1200 30 260 850 6 600 300 30 300 1310 1.8 330 1200 30 250 850 7 600 300 30 300 1310 2 340 1200 30 220 850 8 600 300 30 300 1310 1.7 310 1200 50 230 850 9 600 300 30 300 1310 1.8 350 1200 30 210 850 Table 5 Product Performance Parameters of 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 135℃ lead-free barium titanate thermistor, characterized in that, The raw materials for preparing the thermistor, by molar parts, are: 0.98 parts of frit, 0.02 parts of sodium bismuth titanate, 0.001-0.008 parts of lithium carbonate, and 0.002-0.025 parts of boron nitride. The ceramic material composition of the frit, by molar parts, is: barium carbonate: 0.799-0.88 parts, calcium carbonate: 0.10-0.181 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 part.

2. The 135℃ lead-free barium titanate thermistor according to claim 1, characterized in that, The thermistor has a resistance of 47Ω±20%, a Curie point of 135℃, and a withstand voltage of DC900V.

3. A 135℃ lead-free barium titanate thermistor according to claim 1 or 2, characterized in that, Its chip size is Φ (13.7~13.8)mm*2.8mm.

4. A method for manufacturing a 135℃ lead-free barium titanate thermistor as described in any one of claims 1-3, characterized in that, Includes the following steps: 1) Barium carbonate, calcium carbonate, yttrium oxide, aluminum oxide, manganese nitrate, silicon dioxide, and titanium dioxide are mixed and pre-calcined to synthesize a frit material; 2) Mix the frit with sodium bismuth titanate, lithium carbonate, and boron nitride to form grinding balls; 3) Add binder and release agent to the mixture 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 135℃ lead-free barium titanate thermistor 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 135℃ lead-free barium titanate thermistor 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 135℃ lead-free barium titanate thermistor 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 135℃ lead-free barium titanate thermistor 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℃ → 1310℃, heating rate 250℃~300℃ / hour, holding at 1310℃ for 1~2 hours; 1310℃ → 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 135℃ lead-free barium titanate thermistor according to claim 5, 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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