A NTC thermistor material and preparation method thereof

Abstract

The present invention belongs to the field of thermistor materials, and specifically discloses an NTC thermistor material and a preparation method thereof. The NTC thermistor material of the present invention comprises components in the following mass percentages: aMn3O4 bCo3O4 cFe2O3 dNi2O3 eCuO, wherein 39% ≤ a ≤ 48%, 37% ≤ b ≤ 48%, 2% ≤ c ≤ 10%, 1% ≤ d ≤ 12%, 0.5% ≤ e ≤ 4%, and a + b + c + d + e = 100%. The NTC thermistor material of the present invention is a low-resistance NTC thermistor material, its phase structure is a spinel pure phase, the resistivity is 143 ± 5% to 234 ± 5% Ω·cm, the B value is 3370 ± 3% to 3573 ± 3% K, and the bending resistance, heat resistance and durability are all less than 3%R 25 .

Description

Technical Field

[0001] The invention belongs to the field of thermistor materials, and in particular relates to an NTC thermistor material and a preparation method thereof. Background Art

[0002] Ternary or more d-block transition metal oxides can form a continuous solid solution of spinel phase, which has a wide formation temperature range, close lattice parameters, high mutual solubility, and electrical parameters (such as resistivity ρ and material characteristic constant B value) with small changes in component content, easy production control, and conducive to the improvement of the accuracy, consistency and reliability of thermistor material products. However, it is difficult to control the resistance value of NTC thermistor materials in the low resistance range (100-300Ω·cm) and the B value in the range of 3300-3600K through the current thermistor material formula and process, and meet the requirements of bending resistance, temperature resistance and durability, so as to meet the product requirements of temperature control / compensation / inrush current suppression of high thermal stability NTC. In addition, the thermistor materials generally prepared are non-pure phases and belong to multi-phase ceramics. They need to rely on the mutual regulation between multi-phases, and their performance is relatively unstable.

[0003] Therefore, there is still a need to develop an adjustable NTC thermistor material with a resistance in the low resistance range (100-300Ω·cm), a B value of 3300-3600K, and meeting the requirements of bending resistance, temperature resistance and durability, so as to meet the product requirements of temperature control / compensation / inrush current suppression of high thermal stability NTC. Summary of the invention

[0004] In view of the problem in the prior art that it is difficult to adjust the resistance and B value of NTC thermistor materials within the low resistance and low B range, the present invention provides an NTC thermistor material and a preparation method thereof.

[0005] To achieve the above purpose, the following technical solutions are specifically included:

[0006] An NTC thermistor material comprising the following components in percentage by mass: aMn 3 O 4 bCo 3 O 4 cF 2 O 3 dNi 2 O 3 eCuO, wherein 39%≤a≤48%, 37%≤b≤48%, 2%≤c≤10%, 1%≤d≤12%, 0.5%≤e≤4%, and a+b+c+d+e=100%.

[0007] As a preferred embodiment of the present invention, the NTC thermistor material comprises the following components in mass percentage: aMn 3 O 4 bCo 3 O 4 cF 2 O 3 dNi 2 O 3 eCuO, 41%≤a≤46%, 39%≤b≤45%, 3%≤c≤8%, 2%≤d≤10%, 1.5%≤e≤3%.

[0008] According to the characteristics of transition metals Mn (VIIB), Co / Fe / Ni (VIII), Cu (IB) and their oxides belonging to three subgroups respectively, the present invention takes a pure phase formula and a pure phase polycrystalline structure as the target, regards non-spinel phase, glass phase (amorphous phase) and glass ceramic phase as impurity phases, and prepares a structurally stable continuous solid solution, i.e., a pure phase inverse or semi-inverse spinel polycrystalline (ceramic), by interactively regulating material formula and process parameters, eliminating all possible impurity phases, so as to improve the accuracy, consistency and reliability of NTC products, thereby obtaining an NTC thermistor with controllable physical and chemical properties.

[0009] The NTC thermistor material prepared by the present invention is a low-resistance NTC thermistor material, the phase structure of which is a pure spinel phase, the resistivity is 143±5% to 234±5% Ω·cm, the B value is 3370±3% to 3573±3%K, and the bending resistance, temperature resistance and durability are all less than 3%R 25 It is an adjustable low-resistance Mn-Co-Fe-Ni-Cu quinary NTC thermistor.

[0010] A method for preparing an NTC thermistor material comprises the following steps:

[0011] (1) mixing manganese oxide, cobalt oxide, iron oxide, nickel oxide and copper oxide, adding water and ball milling to obtain a raw material slurry;

[0012] (2) drying and calcining the raw material slurry in sequence to obtain a mixed material;

[0013] (3) ball milling and sand milling the mixture in sequence to obtain prefabricated porcelain powder;

[0014] (4) mixing the prefabricated ceramic powder with a binder and an organic solvent to obtain ceramic powder slurry; and sequentially performing tape casting, cutting, lamination, isostatic pressing, cutting, debinding, and sintering on the ceramic powder slurry to obtain the NTC thermistor material.

[0015] As a preferred embodiment of the present invention, the manganese oxide in step (1) comprises MnO, Mn 2 O 3 、MnO 2 or at least one of other manganese oxides;

[0016] As a preferred embodiment of the present invention, the cobalt oxide in step (1) comprises CoO, Co 2 O 3 or at least one of other cobalt oxides;

[0017] As a preferred embodiment of the present invention, the iron oxide in step (1) includes FeO, Fe 3 O 4 or at least one of other iron oxides;

[0018] As a preferred embodiment of the present invention, the nickel oxide in step (1) comprises Ni 2 O 3 or at least one of other nickel oxides;

[0019] As a preferred embodiment of the present invention, the copper oxide in step (1) comprises Cu 2 O or at least one of other copper oxides.

[0020] As a preferred embodiment of the present invention, during the ball milling in step (1), the mass ratio of material to water (the material in the material to water refers to the total raw materials) is 1:(0.8-2).

[0021] As a further preferred embodiment of the present invention, during the ball milling in step (1), the mass ratio of material to water is 1:1.5.

[0022] As a preferred embodiment of the present invention, the rotation speed of the ball mill in step (1) is 10-200 rpm, and the ball milling time is 10-40 h.

[0023] As a further preferred embodiment of the present invention, the rotation speed of the ball mill in step (1) is 30 rpm, and the ball milling time is 30 h.

[0024] As a preferred embodiment of the present invention, the drying temperature in step (2) is 200-300° C., and the drying time is 20-30 h.

[0025] As a preferred embodiment of the present invention, the calcination temperature in step (2) is 600-1000° C., and the calcination time is 1-5 h.

[0026] As a further preferred embodiment of the present invention, the calcination temperature in step (2) is 870-890° C., and the calcination time is 2-3 h.

[0027] As a preferred embodiment of the present invention, the rotation speed of the sand milling in step (3) is 500-1000 rpm, and the sand milling time is 8-24 h.

[0028] As a further preferred embodiment of the present invention, the rotation speed of the sand milling in step (3) is 600 rpm, and the sand milling time is 12 h.

[0029] As a preferred embodiment of the present invention, the rotation speed of the ball mill in step (3) is 10-200 rpm, and the time of the ball mill is 1-10 h.

[0030] As a further preferred embodiment of the present invention, the rotation speed of the ball mill in step (3) is 30 rpm, and the ball milling time is 4 h.

[0031] As a preferred embodiment of the present invention, the sintering temperature in step (4) is 1100-1230° C., and the sintering time is 5-12 hours.

[0032] As a preferred embodiment of the present invention, the sintering temperature in step (4) is 1120-1200° C., and the sintering time is 8-10 h.

[0033] As a preferred embodiment of the present invention, the heating rate of the sintering in step (4) is 1-5°C / min, and the cooling rate of the sintering is 1-5°C / min.

[0034] As a further preferred embodiment of the present invention, the heating rate of the sintering in step (4) is 2°C / min, and the cooling rate of the sintering is 2°C / min.

[0035] As a preferred embodiment of the present invention, the adhesive is a conventional resin in the electronic ceramics industry, and the organic solvent includes an alcohol solvent.

[0036] As a preferred embodiment of the present invention, the mass ratio of the prefabricated ceramic powder, the adhesive and the organic solvent is prefabricated ceramic powder: adhesive: organic solvent = (400-600): (70-80): (300-400).

[0037] As a preferred embodiment of the present invention, the viscosity of the slurry for tape casting is 10-60 Pa·s, and the thickness is 20-60 μm; the number of the stacked layers is 20-40; and the isostatic pressure is 40-80 MPa.

[0038] As a further preferred embodiment of the present invention, the viscosity of the slurry for tape casting is 42 Pa·s, and the thickness is 40 μm; the number of the stacked layers is 27; and the isostatic pressure is 60 MPa.

[0039] Compared with the prior art, the present invention has the following beneficial effects: the NTC thermistor material prepared by the present invention is a low-resistance NTC thermistor material, the phase structure of which is a pure spinel phase, the resistivity is 143±5% to 234±5% Ω·cm, the B value is 3370±3% to 3573±3%K, and the bending resistance, temperature resistance and durability are all less than 3%R 25 It is an adjustable low resistance and low B value Mn-Co-Fe-Ni-Cu five-element NTC thermistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 1 is the XRD spectra of the NTC thermistor materials of Examples 1, 3-4, 6-7 and 11.

[0041] Figure 2 Graph showing the B value and resistivity results of the NTC thermistor materials of Examples 1-11.

[0042] Figure 3 The graph shows the bending resistance, temperature resistance and durability results of Examples 1-11. DETAILED DESCRIPTION

[0043] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below through specific comparative examples and embodiments.

[0044] The adhesive and organic solvent used in the following examples and comparative examples are all the same adhesive and organic solvent.

[0045] Examples 1-13 and Comparative Examples 1-2

[0046] An NTC thermistor material of Examples 1-13 and Comparative Examples 1-2, and a method for preparing the NTC thermistor material, comprising the following steps:

[0047] (1) Take manganese raw material Mn according to the ratio in Table 1 3 O 4 、Cobalt raw materials Co 3 O 4 、Iron raw materials Fe 2 O 3 , nickel raw materials NiO and / or Ni 2 O 3 , copper raw material CuO (if it is comparative example 1-2, refer to Table 1 to replace with other raw materials), add water at a mass ratio of 1:1.5 between the feed liquid and the ball mill at a ball mill speed of 30 rpm for 30 hours to obtain a raw material slurry, and obtain a raw material slurry;

[0048] (2) drying the ball-milled raw material slurry at 250° C. for 24 hours, and then calcining to obtain a calcined mixture;

[0049] (3) ball milling the calcined mixture at a ball mill speed of 30 rpm for 4 h, and then sand milling at a sand mill speed of 600 rpm for 12 h to obtain a prefabricated porcelain powder;

[0050] (4) Prefabricated porcelain powder, adhesive and organic solvent are mixed in a mass ratio of 500:75:350 to prepare porcelain powder slurry, and NTC thermistor material is obtained by tape casting, cutting, laminating, isostatic pressing, cutting, debinding and sintering;

[0051] The specific calcination and sintering temperatures and times are shown in Table 1. The binder is a conventional resin in the electronic ceramic industry, the organic solvent is an alcohol solvent, the viscosity of the slurry for tape casting is 42 Pa·s, the thickness is 40 μm, the number of layers is 27, and the isostatic pressing pressure is about 60 MPa. The sintering is carried out in a resistance furnace with a heating rate of 2°C / min and a cooling rate of 2°C / min.

[0052] Table 1

[0053]

[0054] The “(×)” represents that the value is out of the scope of the present invention or the corresponding performance does not meet the requirements, and the “(√)” represents that the value is within the scope of the present invention or the corresponding performance meets the requirements.

[0055] Performance tests of embodiments and comparative examples:

[0056] The phase composition was tested by X-ray diffractometer (XRD);

[0057] The specific surface area of ​​the powder was tested by BET analyzer;

[0058] The NTC thermistor was tested by a temperature controlled oil tank resistance meter. 1 ℃ and T 2 Resistance value (R 1 and R 2 , Ω), according to the formula ρ = RS / L and B = T 1 T 2 / (T 2 -T 1 )ln(R 1 / R 2 ) Calculate the resistivity ρ (Ω·cm) and material characteristic constant B value (K) of the sample, where S is the cross-sectional area of ​​the NTC thermistor (cm 2 ), L is the length of the NTC thermistor (cm), where T 1 =25℃, T 2 =50℃, B=B 25 / 50 =8873.9lg(R 25 / R 50 );

[0059] Bending resistance (%R 25 ): Take 10 groups of NTC thermistor samples, weld them on the test substrate, apply force at a speed of 0.5mm / s, and keep it for 30 seconds when the bending reaches 2.0mm. Test the average resistance change rate before and after the pressure is applied.

[0060] Temperature resistance (%R 25 ): Take 10 groups of NTC thermistor samples, put them into a 150±2℃ constant temperature box for thermal assessment, and test their average resistance change rate before and after 1000h.

[0061] Durability (%R 25 ): Take 10 groups of NTC thermistor samples, put them into a 125±2℃ constant temperature box for working test, pass 0.1mA DC current continuously, and test their average resistance change rate before and after 1000h.

[0062] From Examples 1-13, it can be seen that the calcination and sintering temperatures have a certain influence on the B value, resistance, bending resistance, temperature resistance and durability of the NTC thermistor material. The calcination temperature of Examples 12 and 13 is 920°C. Although the resistance and B value are within the range of the present invention, the BET of the material is 5.878m 2 / g, which means that the ceramic powder particle size is too large, which has an adverse effect on the uniformity of the chemical composition, crystal phase composition, grain size and electrical properties in the later stage. Considering the consistency and reliability during mass production, the preferred calcining temperature is 870-890°C, and the preferred sintering temperature is 1120-1200°C, corresponding to Examples 1-11.

[0063] From the perspective of manganese-cobalt ratio, the manganese-cobalt ratio of Example 1-3 (Formula A) is the lowest and less than 1 (=0.92); the manganese-cobalt ratios of Examples 4-6 (Formula B), 7-8 (Formula C) and 9-11 (Formula D) are all greater than 1 and slightly increase (1.00, 1.15, and 1.15, respectively); the manganese-cobalt ratio (Mn 3 O 4 / Co 3 O 4 ) increases, the tetragonal CoMn 2 O 4 As the ratio of positive spinel (insulator) increases, the resistivity tends to increase and the B value tends to decrease; on the contrary, cubic MnCo 2 O 4 As the ratio of semi-inverted spinel (p-type semiconductor) increases, the resistivity tends to decrease and the B value tends to increase.

[0064] From the perspective of the iron-nickel ratio, the iron-nickel ratio of Example 1-3 (Formula A) is the highest and greater than 3 (=3.67); the iron-nickel ratios of the remaining examples are all less than 1 and have the same value (=0.42); the iron-nickel ratio (Fe 2 O 3 / Ni 2 O 3 (NiO)) increases, forming cubic NiFe 2 O 4 As the ratio of inversion spinel (p-type semiconductor) increases, the resistivity tends to decrease and the B value tends to increase; conversely, the resistivity tends to increase and the B value tends to decrease.

[0065] From the perspective of copper content, if the copper content (CuO) increases, cubic Cu (Mn, Co, Fe, Ni) is formed. 2 O 4 As the ratio of semi-inverted spinel (p-type semiconductor) increases, the resistivity tends to decrease and the B value tends to increase; conversely, the resistivity tends to increase and the B value tends to decrease.

[0066] Based on the above effects, Example 1-3 (Formula A) is a high cobalt and low manganese, high iron and low nickel and high copper formula, and its B value is the highest, which is significantly greater than other examples (low cobalt and high manganese, low iron and high nickel and low copper formula); the B values ​​of the latter vary little. The resistivity of all examples varies little with the formula within the component control range of the present invention, and all are low resistance. These should be caused by interactions.

[0067] By interactively regulating the material formula and preparation process, the crystal structure and physical and chemical properties of low-resistance NTC thermistors can be regulated.

[0068] Combined with Table 1 and Appendix Figure 1-3 It can be seen that the NTC thermistor material prepared by the present invention is a low-resistance NTC thermistor material, whose phase structure is a pure spinel phase, the resistivity is 143±5% to 234±5% Ω·cm, the B value is 3370±3% to 3573±3%K, and the bending resistance, temperature resistance and durability are all less than 3%R 25 , is an adjustable low-resistance Mn-Co-Fe-Ni-Cu five-element NTC thermistor. The present invention obtains a spinel pure phase structure Mn-Co-Fe-Ni-Cu five-element NTC thermistor material by the above-mentioned interactive regulation of the material formula and the preparation process parameters, thereby regulating the physical and chemical properties of the NTC thermistor such as resistivity, B value, bending resistance, temperature resistance and durability.

[0069] It can be seen from Comparative Examples 1-2 that the Mn-Co-Fe-Ni-Cu quinary NTC that is not within the scope of the present invention cannot achieve the low resistance and low B value performance of the present invention. Therefore, the requirements of the formulation and process control technology are different. Randomly increasing elements or changing the content will lead to an increase in impurities, resulting in changes in resistance and B value.

[0070] The proportion of different elements in the lattice tetrahedron and octahedron, the gradation of ceramic grains, the purity / thickness of grain boundaries, the degree of suppression of impurity phase and glass phase, the control of firing density, etc. affect the excellent performance of the low-resistance NTC thermistor. The performance optimization of thermistors (ceramics) is more focused on element selection and ratio, dispersion and uniformity of powder raw materials, control of ceramic powder particles and their particle size distribution, control of green body molding process, control of ceramic firing process (temperature / heating rate), control of ceramic grains and their particle size distribution, etc.

[0071] The low-resistance Mn-Co-Fe-Ni-Cu quinary system NTC thermistor formula of the present invention is not a simple change of the components and (or) contents of the disclosed formula, nor a simple change of the preparation method. Instead, based on the characteristics of transition metals (Mn VIIB; Co / Fe / Ni VIII; Cu IB) and their oxides belonging to three subgroups, respectively, with a pure phase formula and a pure phase polycrystalline structure as the target, non-spinel phase, glass phase (amorphous phase) and glass ceramic phase are all regarded as impure phases, and a structurally stable continuous solid solution, i.e., a pure phase inverse or semi-inverse spinel polycrystal (ceramic) is prepared by interactively regulating material formula and process parameters. The pure phase is a uniform spinel pure phase without impure phases and high / low resistance partitions formed by the inverse phases, eliminating all possible impure phases, and not causing the problem of mismatch between the crystal structure / microstructure and the thermal expansion coefficient between the multiphases. The defects of potential gradient, electric field concentration, deformation or cracking in conventional technologies are overcome, and the accuracy, consistency and reliability of NTC products are improved, thereby obtaining an NTC thermistor with controllable physical and chemical properties.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. An NTC thermistor material, characterized in that: It includes the following components in percentage by mass: aMn3O4bCo3O4cFe2O3dNi2O3eCuO, wherein 39%≤a≤48%, 37%≤b≤48%, 2%≤c≤10%, 1%≤d≤12%, 0.5%≤e≤4%, and a+b+c+d+e=100% is satisfied; The NTC thermistor material is a pure spinel phase, the resistivity of the NTC thermistor material is 143±5% to 234±5% Ω·cm, the B value of the NTC thermistor material is 3370±3% to 3573±3%K, and the bending resistance, temperature resistance and durability of the NTC thermistor material are all less than 3%R 25 ; The test method for the resistivity and B value of the NTC thermistor material is: The resistance values ​​R1 and R2 of the NTC thermistor at T1℃ and T2℃ were tested by a temperature-controlled oil tank resistance meter. The resistivity ρ (Ω·cm) and the material characteristic constant B value (K) of the sample were calculated based on the formula ρ=RS / L and B=T1T2 / (T2-T1)ln(R1 / R2), where S is the cross-sectional area of ​​the NTC thermistor (cm 2 ), L is the length of the NTC thermistor (cm), where T1 = 25°C, T2 = 50°C, B = B 25 / 50 =8873.9lg(R 25 / R 50 ); The sintering temperature for preparing the NTC thermistor material is 1100-1230° C., and the sintering time is 5-12 hours.

2. The NTC thermistor material according to claim 1, characterized in that: 41%≤a≤46%, 39%≤b≤45%, 3%≤c≤8%, 2%≤d≤10%, 1.5%≤e≤3%.

3. The method for preparing the NTC thermistor material according to claim 1 or 2, characterized in that: The steps include: (1) mixing manganese oxide, cobalt oxide, iron oxide, nickel oxide and copper oxide, adding water and ball milling to obtain a raw material slurry; (2) drying and calcining the raw material slurry in sequence to obtain a mixed material; (3) ball milling and sand milling the mixture in sequence to obtain prefabricated porcelain powder; (4) mixing the prefabricated ceramic powder with a binder and an organic solvent to obtain ceramic powder slurry; and sequentially performing tape casting, cutting, lamination, isostatic pressing, cutting, debinding, and sintering on the ceramic powder slurry to obtain the NTC thermistor material.

4. The method for preparing the NTC thermistor material according to claim 3, characterized in that: The sintering temperature in step (4) is 1100-1230° C., and the sintering time is 5-12 hours.

5. The method for preparing the NTC thermistor material according to claim 4, characterized in that: The sintering temperature in step (4) is 1120-1200° C., and the sintering time is 8-10 hours.

6. The method for preparing the NTC thermistor material according to claim 3, characterized in that: The drying temperature in step (2) is 200-300° C., and the drying time is 20-30 hours.

7. The method for preparing the NTC thermistor material according to claim 3, characterized in that: The calcination temperature in step (2) is 600-1000° C. and the calcination time is 1-5 h.

8. The method for preparing the NTC thermistor material according to claim 7, characterized in that: The calcination temperature in step (2) is 870-890° C. and the calcination time is 2-3 hours.

9. The method for preparing the NTC thermistor material according to claim 3, characterized in that: Include at least one of the following: The speed of the sand milling in step (3) is 500-1000 rpm, and the sand milling time is 8-24 hours; The organic solvent is an alcohol solvent; The mass ratio of the prefabricated porcelain powder, the adhesive and the organic solvent is prefabricated porcelain powder: adhesive: organic solvent = (400-600): (70-80): (300-400); The slurry for tape casting has a viscosity of 10-60 Pa·s and a thickness of 20-60 μm; The number of laminated layers is 20-40; The isostatic pressure is 40-80 MPa.

10. The method for preparing the NTC thermistor material according to claim 3, characterized in that: Include at least one of the following: During the ball milling in step (1), the mass ratio of material to water is 1:(0.8-2); The ball milling speed in step (1) is 10-200 rpm, and the ball milling time is 10-40 h; The ball milling speed in step (3) is 10-200 rpm, and the ball milling time is 1-10 h; The manganese oxide in step (1) includes at least one of MnO, Mn2O3, MnO2 or other manganese oxides; The cobalt oxide in step (1) includes at least one of CoO, Co2O3 or other cobalt oxides; The iron oxide in step (1) includes at least one of FeO, Fe3O4 or other iron oxides; The nickel oxide in step (1) includes at least one of Ni2O3 or other nickel oxides; the copper oxide in step (1) includes at least one of Cu2O or other copper oxides.

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