Thermistor composite material with room temperature ultra-high sensitivity response and anti-humid heat aging and preparation method thereof

Abstract

The application belongs to the technical field of thermistor materials and preparation, and particularly relates to a thermistor composite material with room-temperature super-high sensitivity response and anti-humid heat aging and a preparation method thereof. The composite material comprises a base material, a bulk dopant and a grain boundary modifier; the base material is a Mn-Ni-Co-Cu quaternary transition metal oxide, the bulk dopant is a W-Mo composite oxide, and the grain boundary modifier is a Y-Si-Zr-O composite oxide. In the preparation, the W-Mo composite oxide is mixed with the base material to obtain a bulk doping powder by pre-sintering, and then the Y-Si-Zr-O composite sol is added step by step, a part of which is used for spray granulation, and the remaining part is brushed on the surface layer of the primary sintered body, and after secondary sintering, the thermistor composite material is obtained. Through the synergistic effect of bulk doping and surface layer grain boundary modification, the material has high sensitivity and excellent anti-humid heat aging performance, and is suitable for temperature detection in the fields of automobile electronics, new energy battery management and the like.

Description

Technical Field

[0001] This invention belongs to the field of thermistor materials and preparation technology, specifically relating to a room temperature ultra-high sensitivity response and resistant to damp heat aging thermistor composite material and its preparation method. Background Technology

[0002] Negative temperature coefficient (NTC) thermistors, with their outstanding advantages such as high sensitivity, low thermal inertia, and low cost, have become one of the most widely used sensitive components in the field of temperature detection and control, playing an irreplaceable role in many applications such as automotive electronics, home appliances, new energy battery management, and industrial control systems. As electronic systems continue to evolve towards higher integration and higher power density, and as various end applications increasingly demand higher accuracy and real-time performance in temperature monitoring, the industry has set increasingly stringent standards for the overall performance of NTC thermistors. These standards not only require extremely high temperature detection sensitivity and rapid response speed at room temperature, but also demand that they withstand the corrosive effects of harsh environments such as humidity and heat during long-term service, maintaining stable and reliable electrical performance.

[0003] Numerous technological attempts have been made to improve the sensitivity and response speed of thermistors. For example, Chinese patent CN104167269B discloses a fast-response thermistor chip and its fabrication method. By printing and sintering surface electrodes on the surface of a ceramic substrate and sealing it with a thermistor material layer, the thermal time constant of the thermistor chip is significantly reduced, effectively meeting the high sensitivity requirements of temperature detection. However, this type of technology mainly focuses on optimizing the device structure, and its core sensitive material itself still uses the traditional oxide semiconductor ceramic system, without achieving a substantial breakthrough in the intrinsic sensitivity of the material. Chinese patent CN114388209A proposes a negative temperature coefficient thermistor suitable for harsh environments and its fabrication process. By setting an upper electrode and a second front electrode at the junction of the resistive layer and the electrode, corrosive gases and other contaminants cannot penetrate into the resistor, thereby improving the resistor's service life in harsh environments. However, this technology mainly relies on the protective design of the electrode structure to resist external corrosion, and the damp heat stability of its core sensitive material itself has not been fundamentally improved. Furthermore, the complex electrode structure design also brings certain process difficulties to large-scale production.

[0004] In fact, damp heat aging has always been one of the key bottlenecks restricting the long-term reliability of NTC thermistors. In high-temperature and high-humidity environments, the intrusion of moisture can trigger a series of failure problems, such as the electrochemical migration of silver ions inside the thermistor, solder joint corrosion, and electrode corrosion, leading to significant resistance drift or even complete failure. For chip-type NTC sensors, the accelerated hydrothermal degradation under humid conditions is particularly pronounced, potentially causing direct circuit failures or even short circuits. Currently, how to effectively improve the resistance to damp heat aging while maintaining the intrinsic high sensitivity of the material has become a pressing technical challenge in this field. Existing solutions often only address one aspect of performance, making it difficult to achieve effective synergistic optimization between ultra-high room temperature sensitivity response and resistance to damp heat aging.

[0005] Therefore, there is an urgent need for a thermistor composite material and its preparation method that combines ultra-high sensitivity response characteristics at room temperature with excellent resistance to damp heat aging, in order to meet the urgent requirements of high-reliability application scenarios for the comprehensive performance of thermistors. Summary of the Invention

[0006] The purpose of this invention is to provide a room-temperature ultra-high sensitivity response and resistant to damp heat aging thermistor composite material and its preparation method, aiming to overcome the technical defects of existing NTC thermistor materials that are difficult to balance high sensitivity and resistance to damp heat aging, so as to meet the urgent needs of high-performance thermistors in fields such as automotive electronics, new energy battery management and high-reliability industrial control.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] The first aspect of this invention provides a thermistor composite material with ultra-high sensitivity response at room temperature and resistance to damp heat aging, the composite material comprising a matrix material, a bulk dopant, and a grain boundary modifier;

[0009] The matrix material is a Mn-Ni-Co-Cu quaternary transition metal oxide, composed of Mn3O4, Ni2O3, Co3O4 and CuO, wherein the molar ratio of Mn, Ni, Co and Cu is 1:(0.2~0.4):(0.15~0.3):(0.1~0.2);

[0010] The bulk dopant is a W-Mo composite oxide, wherein the molar ratio of W to Mo is (3-5):1;

[0011] The grain boundary modifier is a Y-Si-Zr-O composite oxide, wherein the molar ratio of Y, Si and Zr is 1:(2-5):(1-3).

[0012] Furthermore, the amount of the bulk dopant added is 2 to 5% of the total mass of the matrix material.

[0013] Furthermore, the bulk dopant is prepared by the following method:

[0014] (a) Dissolve ammonium tungstate and ammonium molybdate in deionized water at a W to Mo molar ratio of (3 to 5):1 to prepare a mixed solution with a total metal ion concentration of 0.1 to 0.5 mol / L;

[0015] (b) Add citric acid and ethylenediaminetetraacetic acid as complexing agents to the mixed solution, adjust the pH to 6-8 with ammonia, stir the reaction to form a sol;

[0016] (c) Dry the sol to obtain a dry gel; pre-calcine and calcine the dry gel to obtain W-Mo composite oxide, i.e., bulk dopant.

[0017] Further, in step (b), the total molar ratio of citric acid to metal ions is (1-3):1, and the total molar ratio of ethylenediaminetetraacetic acid to metal ions is (0.5-1.5):1; in step (c), the pre-calcination temperature is 400-600℃, the pre-calcination time is 2-4 hours, and the calcination temperature is 700-850℃, the calcination time is 2-5 hours.

[0018] The conductivity process of an NTC thermistor depends on electrons in Mn 3+ / Mn 4+ Co 2+ / Co 3+ Ni and Cu play a supporting role in the jumping and migration between variable-valence ions. At room temperature, these electron jumps are smooth, and the material exhibits a normal resistance value. Under high temperature and humidity, water vapor penetrates into the material along the loose grain boundaries, causing the dissolution and migration of transition metal ions at the grain boundaries. The high temperature exacerbates this process, leading to an irreversible change in the grain boundary conductivity barrier, resulting in a shift in the resistance value. This is the main mechanism by which thermistors fail in humid environments. After W and Mo enter the crystal lattice, their high-valence states form strong bonds with surrounding oxygen ions, making the crystal framework more stable and inhibiting the migration of cations within the lattice. Simultaneously, the ion sizes of W and Mo differ from those of the matrix cations, and their entry creates local compression and distortion within the lattice. These distorted regions physically hinder ion migration. When W and Mo are present simultaneously, the distorted regions created by the two different ion sizes intertwine, and the ions constantly encounter various obstacles as they move within the lattice, effectively blocking their migration paths. Therefore, even under high temperature and humidity conditions, large-scale rearrangement of metal ions in the lattice is difficult, thus ensuring the stability of the resistance value.

[0019] Furthermore, the amount of the grain boundary modifier added is 4 to 10% of the total mass of the matrix material.

[0020] The second aspect of this invention provides a method for preparing the above-mentioned room-temperature ultra-high sensitivity response and resistant to damp heat aging thermistor composite material, comprising the following steps:

[0021] (1) Weigh Mn3O4, Ni2O3, Co3O4 and CuO raw materials according to the molar ratio of Mn, Ni, Co and Cu as 1:(0.2~0.4):(0.15~0.3):(0.1~0.2), mix them with bulk dopant W-Mo composite oxide, add deionized water and dispersant and ball mill to obtain a mixed slurry; dry and pre-calcine the mixed slurry, cool it and ball mill and dry it again to obtain bulk doped powder;

[0022] (2) Weigh Y(NO3)3·6H2O, Si(OC2H5)4 and ZrOCl2·8H2O according to the molar ratio of Y, Si and Zr as 1:(2~5):(1~3), dissolve them in an ethanol-water mixed solvent, add acetylacetone as a chelating agent, adjust the pH to 2~4 with nitric acid, stir to hydrolyze, and age to obtain Y-Si-Zr-O composite sol;

[0023] (3) Mix 60-80% of the bulk doped powder obtained in step (1) with the total amount of Y-Si-Zr-O composite sol obtained in step (2), add a binder and spray granulate to obtain granulated powder; press the granulated powder into shape to obtain green body; sinter the green body and cool it to room temperature to obtain primary sintered body;

[0024] (4) The remaining 20-40% of the Y-Si-Zr-O composite sol obtained in step (2) is brushed onto the surface of the primary sintered body obtained in step (3). After brushing, the sol is dried, sintered again, and cooled to obtain the thermistor composite material.

[0025] Further, the ball milling time in step (1) is 6 to 15 hours; the pre-firing temperature is 800 to 1000°C and the time is 3 to 8 hours.

[0026] Further, the temperature of the stirring hydrolysis in step (2) is 40-70°C and the time is 3-6 hours; the temperature of the aging is 80-100°C and the time is 12-24 hours.

[0027] Further, the binder in step (3) is polyvinyl alcohol, and its addition amount is 1 to 5% of the mass of the bulk doped powder; the sintering temperature is 1150 to 1280°C, and the time is 2 to 6 hours.

[0028] Furthermore, the temperature of the secondary sintering in step (4) is 1120-1220℃, and the time is 1-4 hours.

[0029] NTC thermistors are polycrystalline ceramic materials with a loose grain boundary structure, which is the main channel for water vapor to penetrate into the material. Water molecules penetrating along the grain boundaries trigger the dissolution and migration of metal ions at the grain boundaries, permanently altering the grain boundary conductivity barrier and causing irreversible resistance drift. This invention introduces a Y-Si-Zr-O composite oxide at the surface grain boundaries. Y ions fill grain boundary vacancies, making the grain boundaries more compact; Si exists as a silicon-oxygen network, and its hydrophobic properties make it difficult for water molecules to wet and penetrate the grain boundaries; Zr further fills residual micropores. These three elements work synergistically to form a dense hydrophobic barrier at the surface grain boundaries, preventing water vapor from penetrating inwards along the grain boundaries. However, adding large amounts of Y, Si, and Zr throughout the material would dilute the spinel conductive network and reduce room temperature sensitivity. This invention addresses this contradiction using a step-by-step process: W-Mo is dissolved into the matrix lattice during the pre-sintering stage, uniformly distributed throughout the bulk phase to stabilize the lattice; the Y-Si-Zr-O composite sol is added in two parts. In step (3), 60-80% of the total solid content is added first during spray granulation, distributed in the bulk phase and internal grain boundaries. In step (4), the remaining 20-40% is brushed onto the surface layer, and after secondary sintering, the surface grain boundary modification is strengthened. This step-by-step design ensures a complete conductive network inside to guarantee sensitivity, while the surface layer receives moisture and heat protection. During service, water vapor first encounters the surface hydrophobic barrier, and after penetration is blocked, the internal bulk phase is protected, achieving synergistic optimization of sensitivity and anti-aging performance.

[0030] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0031] This invention employs W-Mo dual-element bulk co-doping. The inclusion of W and Mo in the crystal lattice strengthens the framework, preventing cations from shifting. Simultaneously, the interleaved distortion regions created by their insertion physically hinder cation migration, effectively blocking migration paths. Under high temperature and humidity conditions, large-scale cation rearrangement is difficult, thus ensuring the stability of the resistivity. Furthermore, this invention uses Y-Si-Zr-O composite oxide as a grain boundary modifier. Y, Si, and Zr synergistically form a dense hydrophobic modification layer at the surface grain boundaries, effectively preventing moisture penetration along the grain boundaries into the material interior, reducing the corrosive effect of moisture on the grain boundaries in humid and hot environments from the source. This invention achieves functional partitioning of the bulk and surface layers through a stepwise gradient modification process. W-Mo dissolves into the entire bulk phase during the pre-sintering stage, while Y-Si-Zr-O only forms a modification layer at the surface grain boundaries. The internal spinel conductive network is not diluted by inactive components, thus achieving excellent resistance to humid and hot aging while ensuring high sensitivity of the material at room temperature. Furthermore, this invention employs a sol-gel method to prepare W-Mo composite oxides, achieving atomic-level uniform mixing of W and Mo in the liquid phase and ensuring consistent bulk doping. A brush coating method is used to introduce grain boundary modifiers, simplifying the operation and avoiding material waste and uncontrollable dosage issues associated with traditional impregnation methods. The preparation process of this invention is highly compatible with existing industrial production processes for NTC thermistors, requiring no special equipment and facilitating mass production. Detailed Implementation

[0032] 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. Unless otherwise specified, the raw materials used in the embodiments are all commercially available products.

[0033] Example 1

[0034] This embodiment provides a thermistor composite material with ultra-high sensitivity response at room temperature and resistance to damp heat aging. The preparation method includes the following steps:

[0035] (1) Using four oxide raw materials, Mn3O4, Ni2O3, Co3O4 and CuO, as matrix materials, each raw material was weighed according to the molar ratio of Mn, Ni, Co and Cu of 1:0.30:0.22:0.15. The raw materials were mixed with W-Mo composite oxide, which accounted for 3.5% of the total mass of the matrix materials. Deionized water and dispersant ammonium polyacrylate were added and ball milled. The mass ratio of raw materials, deionized water and dispersant was 1:1.8:0.03. The ball milling time was 10 hours and the ball milling speed was 450 rpm to obtain a mixed slurry. The mixed slurry was dried at 110℃ for 18 hours, pre-calcined at 900℃ for 5 hours, and then naturally cooled and ball milled and dried again to obtain bulk doped powder.

[0036] (2) Weigh Y(NO3)3·6H2O, Si(OC2H5)4 and ZrOCl2·8H2O according to the molar ratio of Y, Si and Zr of 1:3.5:2, dissolve them in an ethanol-water mixed solvent with a volume ratio of ethanol to water of 2:1, add acetylacetone as a chelating agent, adjust the pH to 3 with nitric acid, stir and hydrolyze at 55°C for 4.5 hours, and then age at 90°C for 18 hours to obtain Y-Si-Zr-O composite sol; In this embodiment, the solid content of the composite sol is 18%, and the mass of the solid phase component in the Y-Si-Zr-O composite sol is 7% of the total mass of the matrix material.

[0037] (3) Mix 70% of the total amount of the bulk doped powder obtained in step (1) with the Y-Si-Zr-O composite sol obtained in step (2), add 3% of polyvinyl alcohol as a binder, and perform spray granulation to obtain granulated powder; press the granulated powder under a pressure of 80 MPa to obtain a green body; debind the green body at 520℃ for 3.5 hours, and then sinter at 1200℃ for 4 hours at a heating rate of 4℃ / min, and naturally cool to room temperature to obtain a primary sintered body;

[0038] (4) The remaining 30% of the Y-Si-Zr-O composite sol obtained in step (2) is uniformly brushed onto the surface of the primary sintered body obtained in step (3). After brushing, it is dried at 100°C for 6 hours, and then sintered again at 1180°C for 2.5 hours with a heating rate of 3°C / min. After natural cooling, the thermistor composite material is obtained.

[0039] The bulk dopant is prepared by the following method:

[0040] (a) Ammonium paratungstate ((NH4) 10 H2(W2O7)6) and ammonium heptamolybdate ((NH4)6Mo7O) 24·4H2O) was dissolved in deionized water at a molar ratio of W to Mo of 4:1 to prepare a mixed solution with a total metal ion concentration of 0.3 mol / L;

[0041] (b) Citric acid and ethylenediaminetetraacetic acid were added to the mixed solution as a composite complexing agent. The total molar ratio of citric acid to metal ions was 2:1, and the total molar ratio of ethylenediaminetetraacetic acid to metal ions was 1:1. The pH was adjusted to 7 with ammonia water, and the mixture was stirred at 75°C for 3 hours to form a sol.

[0042] (c) The sol is dried at 120°C for 16 hours to obtain a dry gel; the dry gel is pre-calcined at 500°C for 3 hours and then calcined at 780°C for 3.5 hours, with a heating rate of 3°C / min, to obtain W-Mo composite oxide, i.e. bulk dopant.

[0043] Example 2

[0044] This embodiment provides a thermistor composite material with ultra-high sensitivity response at room temperature and resistance to damp heat aging. The preparation method includes the following steps:

[0045] (1) Using four oxide raw materials, Mn3O4, Ni2O3, Co3O4 and CuO, as matrix materials, each raw material was weighed according to the molar ratio of Mn, Ni, Co and Cu of 1:0.25:0.28:0.12. The raw materials were mixed with W-Mo composite oxide, which accounted for 4.2% of the total mass of the matrix material. Deionized water and dispersant ammonium polyacrylate were added and ball milled. The mass ratio of raw materials, deionized water and dispersant was 1:2.0:0.04. The ball milling time was 12 hours and the ball milling speed was 500 rpm to obtain a mixed slurry. The mixed slurry was dried at 120℃ for 14 hours, pre-calcined at 850℃ for 6 hours, and then naturally cooled and ball milled and dried again to obtain bulk doped powder.

[0046] (2) Weigh Y(NO3)3·6H2O, Si(OC2H5)4 and ZrOCl2·8H2O according to the molar ratio of Y, Si and Zr of 1:4:1.5, dissolve them in an ethanol-water mixed solvent with a volume ratio of ethanol to water of 1.5:1, add acetylacetone as a chelating agent, adjust the pH to 2.5 with nitric acid, stir and hydrolyze at 65°C for 3.5 hours, and then age at 85°C for 22 hours to obtain Y-Si-Zr-O composite sol; In this embodiment, the solid content of the composite sol is 15%, and the total mass of the solid phase component in the prepared Y-Si-Zr-O composite sol is 5.5% of the total mass of the matrix material.

[0047] (3) Mix 65% of the total amount of the bulk doped powder obtained in step (1) with the Y-Si-Zr-O composite sol obtained in step (2), add 4% of polyvinyl alcohol as a binder, and perform spray granulation to obtain granulated powder; press the granulated powder under a pressure of 60 MPa to obtain a green body; debind the green body at 600℃ for 2.5 hours, and then sinter at 1230℃ for 3 hours with a heating rate of 5℃ / min, and naturally cool to room temperature to obtain a primary sintered body;

[0048] (4) The remaining 35% of the Y-Si-Zr-O composite sol obtained in step (2) is uniformly brushed onto the surface of the primary sintered body obtained in step (3). After brushing, it is dried at 90°C for 8 hours, and then sintered again at 1150°C for 3.5 hours with a heating rate of 4°C / min. After natural cooling, the thermistor composite material is obtained.

[0049] The preparation method of the bulk dopant is the same as that in Example 1.

[0050] Example 3

[0051] This embodiment provides a thermistor composite material with ultra-high sensitivity response at room temperature and resistance to damp heat aging. The preparation method includes the following steps:

[0052] (1) Using four oxide raw materials, Mn3O4, Ni2O3, Co3O4 and CuO, as matrix materials, each raw material was weighed according to the molar ratio of Mn, Ni, Co and Cu of 1:0.35:0.18:0.16. The raw materials were mixed with W-Mo composite oxide bulk dopant accounting for 2.8% of the total mass of the matrix material. Deionized water and dispersant ammonium polyacrylate were added and ball milled. The mass ratio of raw materials, deionized water and dispersant was 1:1.5:0.02. The ball milling time was 8 hours and the ball milling speed was 350 rpm to obtain a mixed slurry. The mixed slurry was dried at 115℃ for 20 hours, pre-calcined at 950℃ for 4 hours, and then naturally cooled and ball milled and dried again to obtain bulk doped powder.

[0053] (2) Weigh Y(NO3)3·6H2O, Si(OC2H5)4 and ZrOCl2·8H2O according to the molar ratio of Y, Si and Zr of 1:2.5:2.5, dissolve them in an ethanol-water mixed solvent with a volume ratio of ethanol to water of 2.5:1, add acetylacetone as a chelating agent, adjust the pH to 3.5 with nitric acid, stir and hydrolyze at 45°C for 5.5 hours, and then age at 95°C for 14 hours to obtain Y-Si-Zr-O composite sol; In this embodiment, the solid content of the composite sol is 22%, and the total mass of the solid phase component in the prepared Y-Si-Zr-O composite sol is 8.5% of the total mass of the matrix material.

[0054] (3) Mix 75% of the total amount of the bulk doped powder obtained in step (1) with the Y-Si-Zr-O composite sol obtained in step (2), add 2% polyvinyl alcohol as a binder, and perform spray granulation to obtain granulated powder; press the granulated powder into shape under a pressure of 100 MPa to obtain a green body; treat the green body at 480℃ for 4 hours to remove the binder, and then sinter at 1170℃ for 5 hours with a heating rate of 3℃ / min, and naturally cool to room temperature to obtain a primary sintered body;

[0055] (4) The remaining 25% of the Y-Si-Zr-O composite sol obtained in step (2) is uniformly brushed onto the surface of the primary sintered body obtained in step (3). After brushing, it is dried at 110°C for 5 hours, and then sintered again at 1200°C for 2 hours with a heating rate of 2°C / min. After natural cooling, the thermistor composite material is obtained.

[0056] The preparation method of the bulk dopant is the same as that in Example 1.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is that the bulk dopant W-Mo composite oxide is replaced with a single WO3, i.e., the Mo element is omitted, and the amount of W added is the same as the total molar amount of W and Mo in Example 1.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 1 is that the bulk dopant W-Mo composite oxide is replaced with a single MoO3, i.e., the W element is omitted, and the amount of Mo added is the same as the total molar amount of W and Mo in Example 1.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 1 is that the bulk dopant W-Mo composite oxide is replaced with W-Yb composite oxide, the molar ratio of W to Yb is 4:1, and the amount added is 3.5% of the total mass of the matrix material;

[0063] The W-Yb composite oxide was prepared by the following method:

[0064] (a) Ammonium paratungstate ((NH4) 10 H2(W2O7)6 and ytterbium nitrate (Yb(NO3)3·6H2O) were dissolved in deionized water at a molar ratio of W to Yb of 4:1 to prepare a mixed solution with a total metal ion concentration of 0.3 mol / L.

[0065] (b) Add citric acid as a complexing agent to the mixed solution, with a total molar ratio of citric acid to metal ions of 2:1, adjust the pH to 7 with ammonia, and stir the reaction at 75°C for 3 hours to form a sol.

[0066] (c) The sol is dried at 120°C for 16 hours to obtain a dry gel; the dry gel is pre-calcined at 500°C for 3 hours and then calcined at 780°C for 3.5 hours, with a heating rate of 3°C / min, to obtain W-Yb composite oxide.

[0067] Comparative Example 4

[0068] The difference between this comparative example and Example 1 is that the Y-Si-Zr-O composite sol is replaced with the La-Si-O composite sol.

[0069] Step (2) is as follows: Lanthanum nitrate (La(NO3)3·6H2O) and tetraethyl orthosilicate Si(OC2H5)4 are weighed according to the molar ratio of La to Si of 1:3.5. Lanthanum nitrate is dissolved in deionized water and tetraethyl orthosilicate is dissolved in anhydrous ethanol. The two solutions are mixed and deionized water is added. The pH is adjusted to 3 with nitric acid. The mixture is stirred and hydrolyzed at 55°C for 4.5 hours and then aged at 90°C for 18 hours to obtain La-Si-O composite sol. The solid content of the composite sol is 18%, and the total mass of the solid phase component in the prepared La-Si-O composite sol is 7% of the total mass of the matrix material.

[0070] The remaining steps are the same as in Example 1.

[0071] Comparative Example 5

[0072] This comparative example provides a thermistor composite material, the preparation method of which includes the following steps:

[0073] (1) Using four oxide raw materials, Mn3O4, Ni2O3, Co3O4 and CuO, as matrix materials, each raw material was weighed according to the molar ratio of Mn, Ni, Co and Cu of 1:0.30:0.22:0.15. The raw materials were mixed with W-Mo composite oxide, a bulk dopant accounting for 3.5% of the total mass of the matrix material, and Y-Si-Zr-O composite oxide powder, a grain boundary modifier accounting for 7% of the total mass of the matrix material. Deionized water and ammonium polyacrylate dispersant were added and ball milled. The mass ratio of raw materials, deionized water and dispersant was 1:1.8:0.03. The ball milling time was 10 hours and the ball milling speed was 450 rpm to obtain a mixed slurry. The mixed slurry was dried at 110℃ for 18 hours, pre-calcined at 900℃ for 5 hours, and then naturally cooled and ball milled and dried again to obtain doped powder.

[0074] (2) Add 3% polyvinyl alcohol by mass of the doped powder obtained in step (1) as a binder and spray granulate to obtain granulated powder; press the granulated powder under a pressure of 80 MPa to obtain a green body; debind the green body at 520°C for 3.5 hours, then sinter at 1200°C for 4 hours with a heating rate of 4°C / min, and naturally cool to room temperature to obtain the thermistor composite material.

[0075] The preparation method of the bulk dopant W-Mo composite oxide is the same as that in Example 1.

[0076] The grain boundary modifier Y-Si-Zr-O composite oxide was prepared by the following method:

[0077] (a) Weigh Y(NO3)3·6H2O, Si(OC2H5)4 and ZrOCl2·8H2O according to the molar ratio of Y, Si and Zr of 1:3.5:2, dissolve them in an ethanol-water mixed solvent with a volume ratio of ethanol to water of 2:1, add acetylacetone as a chelating agent, adjust the pH to 3 with nitric acid, stir and hydrolyze at 55°C for 4.5 hours, and then age at 90°C for 18 hours to obtain Y-Si-Zr-O composite sol;

[0078] (b) The composite sol was dried at 120°C for 16 hours to obtain a dry gel;

[0079] (c) The dry gel was pre-calcined at 500°C for 3 hours and then calcined at 780°C for 3.5 hours, with a heating rate of 3°C / min, to obtain Y-Si-Zr-O composite oxide powder, i.e. grain boundary modifier.

[0080] Performance testing

[0081] 1. Room temperature resistivity (ρ) 25 )

[0082] Referring to GB / T 6663.1-2007 "Directly Heated Negative Temperature Coefficient Thermistors - Part 1: General Specifications", the zero-power resistance of the thermistor composite material at 25℃±0.5℃ was measured using the four-probe method, and the room temperature resistivity was calculated based on the sample size. Five samples were tested for each example and comparative example, and the average value was taken.

[0083] 2. Material constant B value

[0084] Referring to GB / T 6663.1-2007, the zero-power resistance R of the thermistor composite material was measured at two temperature points: 25℃ and 85℃. 25 and R 85 Calculate B using the following formula 25 / 85 value:

[0085] B 25 / 85 = [ (T1×T2) / (T2-T1) ] × ln(R1 / R2)

[0086] Where T1 = 298.15K and T2 = 358.15K. Five samples were tested for each example and comparative example, and the average value was taken.

[0087] 3. Thermal time constant (τ)

[0088] Referring to GB / T 6663.1-2007, the thermal time constant of thermistor composite materials was measured using the self-heating and subsequent cooling method. The sample was placed in a constant temperature environment of 25℃, and heated until it reached the zero-power resistance value corresponding to 85℃. After power was cut off, the time required for the sample resistance value to decrease from the resistance value corresponding to 85℃ to 63.2% of the temperature difference (i.e., to decrease to the resistance value corresponding to approximately 47.1℃) was recorded. Five samples were tested for each example and comparative example, and the average value was taken.

[0089] 4. Resistivity drift after damp heat aging (ΔR / R0)

[0090] Referring to GB / T 2423.3 "Environmental Testing for Electrical and Electronic Products - Part 2: Test Methods - Test Cab: Constant Damp Heat Test", the thermistor composite material sample was placed in a constant temperature and humidity chamber and subjected to a 1000-hour steady-state damp heat aging test at a temperature of 85℃±2℃ and a relative humidity of 85%±3%. After the test, the sample was removed and allowed to recover at 25℃±2℃ for 24 hours. The zero-power resistance value R1 at room temperature after aging was measured, and the resistance drift rate was calculated using the following formula:

[0091] ΔR / R0 = (R1 - R0) / R0 × 100%

[0092] Where R0 is the initial room temperature zero-power resistance value before aging. Five samples were tested for each example and comparative example, and the average value was taken.

[0093] The test results are shown in Table 1.

[0094] Table 1 Performance Test Results

[0095]

[0096] The performance test results above show that the thermistor composite materials of Examples 1-3 all exhibit excellent comprehensive performance. The room temperature resistivity of the three examples is at a low level, the B value is above 4500K, and the thermal time constant is small, indicating that the material has the characteristics of high sensitivity and fast response; at the same time, the resistance drift rate after damp heat aging is controlled within 1%, indicating that the material has excellent long-term stability in high temperature and high humidity environments.

[0097] Comparative Examples 1 and 2 used single WO3 and single MoO3 to replace W-Mo composite oxides, respectively. Due to the lack of the synergistic pinning effect of W and Mo, the single high-valence ion's ability to inhibit lattice cation migration was insufficient, and its resistance to damp heat aging was significantly worse than that of the examples. Simultaneously, the B value was also significantly reduced. Comparative Example 3 used W-Yb to replace W-Mo. Although Yb... 3+ It also has a certain effect on stabilizing the crystal lattice, but its valence compensation ability and ion size matching degree of the +3 valence state are not as good as those of Mo. 6+ Its contribution to the lattice distortion stress field is weaker, and its anti-aging effect is not as good as that of the examples. Comparative Example 4 uses La-Si-O instead of Y-Si-Zr-O, La 3+ The ionic radius is greater than that of Y. 3+ The matching degree of filling grain boundary vacancies is poor, and the lack of ZrO2 to fill micropores results in insufficient density and hydrophobicity of the grain boundary modification layer, failing to effectively suppress the penetration of water vapor along the grain boundaries. Comparative Example 5 uses a one-step mixing method to add all components at once, resulting in a large amount of Y-Si-Zr-O in the bulk phase. This not only dilutes the spinel conductive network but also forms a large amount of inactive second phase inside the bulk phase, which in turn becomes a defect source under humid and hot conditions, resulting in the worst overall performance.

[0098] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a thermistor composite material with ultra-high sensitivity response and resistance to damp heat aging at room temperature, characterized in that, Includes the following steps: (1) Weigh Mn3O4, Ni2O3, Co3O4 and CuO raw materials as matrix materials according to the molar ratio of Mn, Ni, Co and Cu of 1:(0.2~0.4):(0.15~0.3):(0.1~0.2), mix them with bulk dopant W-Mo composite oxide, add deionized water and dispersant and ball mill to obtain a mixed slurry; dry and pre-calcine the mixed slurry, cool it and ball mill and dry it again to obtain bulk doped powder; The amount of bulk dopant added is 2-5% of the total mass of the matrix material; the ball milling time is 6-15 hours; the pre-firing temperature is 800-1000℃ and the time is 3-8 hours; (2) Weigh Y(NO3)3·6H2O, Si(OC2H5)4 and ZrOCl2·8H2O according to the molar ratio of Y, Si and Zr as 1:(2~5):(1~3), dissolve them in an ethanol-water mixed solvent, add acetylacetone as a chelating agent, adjust the pH to 2~4 with nitric acid, stir to hydrolyze, and age to obtain Y-Si-Zr-O composite sol; (3) Mix 60-80% of the bulk doped powder with the total amount of Y-Si-Zr-O composite sol, add the binder polyvinyl alcohol and spray granulate to obtain granulated powder; press the granulated powder into shape to obtain green body; sinter the green body and cool it to room temperature to obtain primary sintered body; the sintering temperature is 1150-1280℃ and the time is 2-6 hours; (4) The remaining 20-40% of the Y-Si-Zr-O composite sol is brushed onto the surface of the primary sintered body. After brushing, it is dried, sintered a second time, cooled, and the thermistor composite material is obtained. The temperature of the second sintering is 1120-1220℃ and the time is 1-4 hours. The total addition amount of Y-Si-Zr-O composite sol is 4% to 10% of the total mass of the matrix material; Bulk dopants are prepared by the following method: (a) Dissolve ammonium tungstate and ammonium molybdate in deionized water at a W to Mo molar ratio of (3 to 5):1 to prepare a mixed solution with a total metal ion concentration of 0.1 to 0.5 mol / L; (b) Add citric acid and ethylenediaminetetraacetic acid as complexing agents to the mixed solution, adjust the pH to 6-8 with ammonia, stir the reaction to form a sol; (c) Dry the sol to obtain a dry gel; The dry gel was pre-calcined and then calcined to obtain W-Mo composite oxide, i.e., bulk dopant.

2. The preparation method according to claim 1, characterized in that, In step (b), the total molar ratio of citric acid to metal ions is (1-3):1, and the total molar ratio of ethylenediaminetetraacetic acid to metal ions is (0.5-1.5):1; in step (c), the pre-calcination temperature is 400-600℃, the pre-calcination time is 2-4 hours, and the calcination temperature is 700-850℃, the calcination time is 2-5 hours.

3. The preparation method according to claim 1, characterized in that, The temperature for stirring and hydrolysis in step (2) is 40-70℃ and the time is 3-6 hours; the temperature for aging is 80-100℃ and the time is 12-24 hours.

4. The preparation method according to claim 1, characterized in that, The amount of polyvinyl alcohol binder added in step (3) is 1 to 5% of the mass of the bulk doped powder.

5. A thermistor composite material with ultra-high sensitivity response at room temperature and resistance to damp heat aging, characterized in that, It is obtained by the preparation method according to any one of claims 1-4.

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