CN108439982B - Axial composite negative temperature coefficient thermal sensitive ceramic material and preparation method thereof - Google Patents

Axial composite negative temperature coefficient thermal sensitive ceramic material and preparation method thereof Download PDF

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CN108439982B
CN108439982B CN201810454224.8A CN201810454224A CN108439982B CN 108439982 B CN108439982 B CN 108439982B CN 201810454224 A CN201810454224 A CN 201810454224A CN 108439982 B CN108439982 B CN 108439982B
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关芳
黄世峰
林秀娟
戴晗
程新
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University of Jinan
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Abstract

The invention provides an axial composite negative temperature coefficient thermal sensitive ceramic material, which is compounded by two-phase materials, wherein one phase is a perovskite phase or doped perovskite phaseA perovskite phase, the other phase being a spinel phase or a doped spinel phase; the interface of the two phases is a transition interlayer for uniformly mixing the two-phase powder; the volume ratio of the spinel phase or doped spinel phase to the perovskite phase or doped perovskite phase is 1:9-9: 1. The spinel phase oxide has a molecular formula of AxB2‑xO4Wherein A is one or more of Al, Ni, Co and Fe, B is one or more of Mn, Mg and Ti, and x is more than or equal to 0.4 and less than or equal to 1.5; the perovskite phase oxide has a molecular formula of LaCr1‑yByO3Wherein B is one or more of Fe, Co and Mn, and y is more than or equal to 0 and less than or equal to 0.8. The axial composite negative temperature coefficient thermal sensitive ceramic material is formed by compounding two-phase materials, the resistance value change of the axial composite negative temperature coefficient thermal sensitive ceramic material accords with the change rule of a parallel resistor, and the measured resistance value is basically consistent with a theoretical calculated value; the material resistance can be effectively reduced, the change of the B value is small, and the material stability is high.

Description

Axial composite negative temperature coefficient thermal sensitive ceramic material and preparation method thereof
Technical Field
The invention relates to the technical field of negative temperature coefficient thermistors, in particular to an axial composite negative temperature coefficient thermistor ceramic material and a preparation method thereof.
Background
A Negative Temperature Coefficient (NTC) thermistor refers to a resistor whose resistance value decreases as the temperature increases. The NTC thermistor ceramic material is widely applied to the aspects of temperature measurement, temperature control, temperature compensation, surge current suppression and the like due to the advantages of high sensitivity, high temperature measurement precision, good interchangeability, low price and the like, and is an electronic component with great development potential. With the development of science and technology and requirements, the market demand of the NTC temperature sensor is increased greatly. The NTC thermal sensitive ceramic material comprises the following main parameters: (1) rho25℃Electrical resistivity at 25 ℃; (2) the material constant B is a parameter describing the physical characteristics of the thermistor, and the larger the value B is, the higher the sensitivity is. Different rho is required according to different application fields25℃And B value are combined. For example, NTC thermistors used for suppressing surge current are required to have a low resistivity and a high B value; thermistors used at high temperatures are required to have a high resistivity and a high B value. The traditional NTC material is generally composed of spinel type oxide composed of Mn, Ni, Co, Fe, Cu and other elements, such as Cu-Ni-Mn-OFe-Ni-Mn-O, Zn-Ni-Mn-O, etc. The relationship between the resistivity rho and the temperature T of the spinel-type NTC thermosensitive material conforms to an Arrehenius equation: ρ = ρ0exp (B/T), the B value of such materials generally increases with increasing resistivity, and vice versa. It is difficult to obtain NTC materials with low resistivity and high B-value. The previous researches mainly improve the composition of a material system, for example, Cu is doped into a spinel material, so that the resistivity can be greatly reduced, but the B value and the stability are reduced; if a high-conductivity phase is introduced into the spinel material for traditional two-phase compounding, namely, the powder is uniformly mixed and then molded and sintered, the resistivity of the spinel material can be greatly reduced, and meanwhile, the B value can be reduced. So far, no method for effectively reducing the resistance value and ensuring small change of the B value and good stability is reported. Therefore, the exploration of a new method for reducing the resistivity of the thermosensitive material and simultaneously keeping the B value unchanged is particularly important for preparing the NTC material with high B value, low resistivity and high stability.
Disclosure of Invention
Aiming at the problems of the lack of NTC materials with high B value, low resistivity and high stability and the preparation method, the invention provides the preparation method of the axial composite negative temperature coefficient thermal sensitive ceramic material, which can effectively reduce the resistance value of the material, and has small change of the B value and high stability of the material.
In order to achieve the purpose, the invention adopts the following technical scheme.
An axial composite negative temperature coefficient thermal sensitive ceramic material is compounded by two phases of materials, wherein one phase is a perovskite phase or a doped perovskite phase, and the other phase is a spinel phase or a doped spinel phase; the interface of the two phases is a transition interlayer for uniformly mixing the two-phase powder; the volume ratio of the spinel phase or the doped spinel phase to the perovskite phase or the doped perovskite phase is 1:9-9: 1; preferably 1:9 to 1: 1.
Preferably, the spinel phase oxide has the formula AxB3-xO4Wherein A is one or more of Al, Ni, Co and Fe, B is one or more of Mn, Mg and Ti, and x is more than or equal to 0.4 and less than or equal to 1.5; the perovskite phase oxide has a molecular formula of LaCr1-yByO3Wherein B is one or more of Fe, Co and Mn, and y is more than or equal to 0 and less than or equal to 0.8.
Preferably, the axially compounded negative temperature coefficient thermal ceramic material is compounded from a spinel phase and a perovskite phase.
The axial composite negative temperature coefficient thermal sensitive ceramic materialρ 25℃Is 124-17149 omega cm +/-2 percent, B25/503365 and 3393K +/-1.5 percent; the resistance change rate after aging for 1000h at 125 ℃ is 0.41-0.52%.
The preparation method of the axial composite negative temperature coefficient thermal sensitive ceramic material comprises the following steps:
(1) according to spinel phase AxB3-xO4Or perovskite phase LaCr1-yByO3Weighing each oxide according to the mole ratio of the primary atoms, and wet-grinding to obtain two kinds of slurry;
(2) respectively drying the slurry obtained in the step (1), and then grinding to obtain two kinds of powder;
(3) respectively calcining the two kinds of powder in the step (2) to obtain a spinel phase AxB3-xO4And perovskite phase LaCr1- yByO3Powder; then granulating by using a binder to obtain a two-phase powder material with uniform granularity and good fluidity;
(4) putting the powder material in the step (3) into a mould according to a certain volume ratio, putting two-phase uniformly mixed powder at the interface of the two-phase powder as a transition layer, and pressing into a block material;
(5) and (4) heating the block material in the step (4) to 500 ℃, preserving heat, then heating to 1300-1450 ℃, then cooling to 1200-1300 ℃, preserving heat, and cooling along with the furnace to obtain the axial composite negative temperature coefficient thermal sensitive ceramic material.
The die is of a cylindrical structure, two ends of the die are opened, and a detachable movable partition valve is arranged in an inner cavity of the die; the movable isolating valve is formed by connecting two rectangular isolating pieces along a long-edge rotating shaft; the axis of the rotating shaft is positioned in the center of a cross section of the die; the long side of the spacer is as high as the height of the die, and the short side of the spacer is as large as the inner radius of the die. When the material pressing die is used, the two spacers of the movable partition valve rotate by taking the rotating shaft as a center, so that the inner cavity of the die is divided into two spaces with different volumes, two-phase materials and the transition layer are respectively filled in the two spaces, and then the movable partition valve is taken out to press the materials in the inner cavity.
In the step (1), agate balls are used as a ball milling medium in the wet milling, and absolute ethyl alcohol is used as a dispersion medium; the mass ratio of the raw materials to the absolute ethyl alcohol is 2.5:1: 1; preferably, the wet grinding is alternately carried out clockwise and anticlockwise, and the interval time between clockwise and anticlockwise is 30 min; the wet milling time is 10-24 h.
In the step (2), the drying temperature is 80-100 ℃; the grinding time is 1 h.
The calcination temperature in the step (3) is 900-; the calcination time is 1-3 h.
In the step (3), before granulation, the method also comprises the step of mixing AxB3-xO4And LaCr1-yByO3Grinding to obtain powder with uniform granularity. A is describedxB3-xO4D of (A)500.128-1.763 μm and LaCr1-yByO3D of (A)50Is 0.247-1.836 μm. Said D50Refers to the corresponding particle size when the cumulative volume distribution percentage of particle size reaches 50%.
In the step (3), the granulated binder is preferably PVA; the amount of PVA added is 1-3.5wt% of the powder.
In the step (4), the volume ratio of the perovskite phase or the doped perovskite phase to the spinel phase or the doped spinel phase in the two-phase uniformly mixed powder is 1: 1.
In the step (4), the preferable preparation method is to press the wafer with the diameter of 10mm under the pressure of 10MPa, the pressure maintaining time is 3min, and then the wafer is subjected to cold isostatic pressing for 4min under the pressure of 350MPa, thus obtaining the product.
In the step (5), the first heating rate is 1-5 ℃/min; the second heating rate is 5-10 ℃/min; the cooling time is 1-5 min; the first heat preservation time is 2-6h, and the second heat preservation time is 2-15 h.
The invention has the following advantages:
the axial composite negative temperature coefficient thermal sensitive ceramic material is compounded by two-phase materials, and the resistance value change of the axial composite negative temperature coefficient thermal sensitive ceramic material accords with the change rule of parallel resistance, namely 1/RAnd are=1/R1+1/R2The measured resistance value is substantially identical to the theoretical calculation value.
According to the ohm law and the principle that the resistance is reduced in parallel, a brand-new NTC material composite form-axial composite is designed, the resistance value can be effectively reduced, meanwhile, the B value is kept almost unchanged, and the method has practical guiding significance for preparing the NTC thermistor with low resistance and high B value: in the spinel region, the spinel phase is conductive, the perovskite phase is non-conductive, and the resistivity is determined by the spinel oxide; in the perovskite region, the perovskite phase is conductive and the resistivity is determined by the perovskite phase. Therefore, in the axial composite NTC thermistor, the resistors with two structures form a parallel circuit, and the resistance value of the material can be effectively reduced by adjusting the volume ratio of two-phase materials, so that the B value is almost unchanged.
In the invention, the spinel and the perovskite oxide have high electrical stability, and the two-phase interface has good phase stability and high thermal expansion matching property due to the existence of the transition layer, so the axial composite ceramic material has stable electrical property.
The density is high: in order to avoid the growth of crystal grains in the high-temperature sintering process and influence on the electrical property of the crystal grains, a two-step sintering method is adopted, namely the temperature is quickly reduced to a certain temperature after being increased to the highest sintering temperature, and the temperature is kept for a long time at the low temperature, so that the crystal grain boundary diffusion is kept in an active state while the crystal grain boundary migration is inhibited, and the purpose of sintering is achieved on the premise that the crystal grains do not grow; in addition, from the perspective of environmental protection, the sintering system can effectively save energy.
Drawings
FIG. 1 is a schematic view of a mold;
FIG. 2 is a schematic cross-sectional view of a mold;
FIG. 3 is a SEM photograph of a negative temperature coefficient thermal sensitive ceramic material of example 1;
wherein, 1 is a mould, 2 is a movable isolating valve, 3 is an isolating piece, and 4 is a rotating shaft.
Detailed Description
The present invention will be further described with reference to the following examples and drawings, but the present invention is not limited to the following examples.
Example 1
(1) First to analytically pure Ni2O3、MnO2、La2O3、Cr2O3、Fe2O3As raw material, according to spinel phase NiMn2O4And perovskite phase LaCr0.7Fe0.3O3And (2) respectively weighing each oxide according to the medium atomic molar ratio, placing the oxide into an agate ball milling tank, carrying out wet milling for 15 hours by taking agate balls as a ball milling medium and absolute ethyl alcohol as a dispersion medium, and controlling the mass ratio of each substance in the ball milling tank to be: agate balls are prepared from anhydrous ethanol =2.5:1:1, ball milling is carried out alternately in clockwise and anticlockwise directions, and the interval time between clockwise and anticlockwise directions is 30min, so that two kinds of slurry are obtained;
(2) respectively drying the slurry obtained in the step (1) at 80 ℃, and then grinding for 1h to obtain two kinds of powder;
(3) calcining the spinel component and the perovskite component in the step (2) at 900 ℃ and 1000 ℃ respectively to obtain spinel phase NiMn2O4And perovskite phase LaCr0.7Fe0.3O3Powder; grinding the mixture in an agate mortar for 4 hours respectively to obtain NiMn2O4And perovskite phase LaCr0.7Fe0.3O3Particle size of powder (D)50) Respectively 0.984 mu m and 1.124 mu m, and then granulating by taking PVA as a binder, wherein the addition amount of the PVA is 3wt% of the powder material, so as to obtain a two-phase powder material with uniform granularity, good fluidity and good formability;
(4) the die is arranged on a tabletting base, two spacers (3) of a movable partition valve (2) of the die (1) rotate by taking a rotating shaft (4) as a center, the inner cavity of the die is divided into two spaces with the volume ratio of 1:1, and the two spaces are divided into V (NiMn) according to the volume ratio2O4）：V(LaCr0.7Fe0.3O3) Filling the materials in the two phases in the step (3) respectively in a ratio of 1:1, and putting the two materials at the interface of the two-phase powderTaking the uniformly mixed powder (volume ratio 1: 1) as a transition layer, taking out the movable spacer, and pressing: pre-pressing the wafer into a wafer with the diameter of 10mm under the pressure of 10Mpa for 3min, and then carrying out cold isostatic pressing on the wafer for 4min under the pressure of 350Mpa to obtain a well-formed axial composite block material;
the mould is shown in figures 1 and 2: the mould (1) is of a cylindrical structure, two ends of the mould are opened, and a detachable movable isolating valve (2) is arranged in an inner cavity of the mould; the movable isolating valve (2) is formed by connecting two rectangular isolating pieces (3) along a long-edge rotating shaft (4); the axis of the rotating shaft (4) is positioned at the center of a circle of the cross section of the die; the long edge of the spacer is as high as the height of the die, and the short edge of the spacer is as same as the inner radius of the die;
(5) and (3) heating the block material obtained in the step (4) to 500 ℃ at the speed of 1 ℃/min, preserving heat for 5h, then heating to 1350 ℃ at the speed of 10 ℃/min, then rapidly cooling to 1200 ℃ within 4min, preserving heat for 10h, and furnace-cooling to obtain the axial composite negative temperature coefficient thermal sensitive ceramic material.
The obtained axial composite negative temperature coefficient thermal sensitive ceramic material is subjected to electrical property test, and the electrical parameter isρ 25℃=785Ω·cm±2%，B25/50=3373K ± 1.5%; the resistance change rate after aging for 1000h at 125 ℃ is 0.51 percent, and the material is suitable for inhibiting surge current; the SEM photograph is shown in figure 3, and the two-phase interface has no obvious defect and high density.
Example 2
(1) First to analytically pure Ni2O3、MnO2、La2O3、Cr2O3、Fe2O3As raw material, according to spinel phase NiMn2O4And perovskite phase LaCr0.7Fe0.3O3And (2) respectively weighing each oxide according to the molar ratio of the medium atoms, placing the oxide into an agate ball milling tank, carrying out wet milling for 24 hours by taking agate balls as a ball milling medium and absolute ethyl alcohol as a dispersion medium, and controlling the mass ratio of each substance in the ball milling tank to be: agate balls are prepared from absolute ethyl alcohol =2.5:1:1, ball milling is carried out alternately in clockwise and anticlockwise directions, and the interval time between clockwise and anticlockwise directions is 30min, so that two kinds of slurry are obtained;
(2) respectively drying the slurry obtained in the step (1) at 80 ℃, and then grinding for 1h to obtain two kinds of powder;
(3) calcining the spinel component and the perovskite component in the step (2) at 900 ℃ and 1000 ℃ respectively to obtain spinel phase NiMn2O4And perovskite phase LaCr0.7Fe0.3O3Powder; grinding the mixture in an agate mortar for 4 hours respectively to obtain NiMn2O4And perovskite phase LaCr0.7Fe0.3O3Particle size of powder (D)50) Respectively 0.128 μm and 0.274 μm, and then granulating by using PVA as a binder, wherein the addition amount of the PVA is 2.4wt% of the powder material, so as to obtain a two-phase powder material with uniform granularity, good fluidity and good formability;
(4) the die is arranged on a tabletting base, two spacers (3) of a movable partition valve (2) of the die (1) rotate by taking a rotating shaft (4) as a center, the inner cavity of the die is divided into two spaces with the volume ratio of 1:2, and the two spaces are divided into V (NiMn) according to the volume ratio2O4）：V(LaCr0.7Fe0.3O3) Filling the two-phase material in the step (3) in a ratio of 1:2, putting two-phase uniformly mixed powder (in a volume ratio of 1: 1) at an interface of the two-phase powder as a transition layer, taking out the movable spacer, and pressing: pre-pressing the wafer into a wafer with the diameter of 10mm under the pressure of 10Mpa for 3min, and then carrying out cold isostatic pressing on the wafer for 4min under the pressure of 350Mpa to obtain a well-formed axial composite block material; the mold structure was as in example 1;
(5) and (3) heating the block material obtained in the step (4) to 500 ℃ at the speed of 3 ℃/min, preserving heat for 4h, then heating to 1400 ℃ at the speed of 10 ℃/min, then rapidly cooling to 1250 ℃ within 5min, preserving heat for 12h, and furnace-cooling to obtain the axial composite negative temperature coefficient thermal sensitive ceramic material.
The obtained axial composite negative temperature coefficient thermal sensitive ceramic material is subjected to electrical property test, and the electrical parameter isρ 25℃=345Ω·cm±2%，B25/50=3365K ± 1.5%; the resistance change rate after aging for 1000h at 125 ℃ is 0.45 percent, and the material is suitable for inhibiting surge current.
Example 3
(1) First to analytically pure Ni2O3、MnO2、La2O3、Cr2O3、Fe2O3As raw material, according to spinel phase NiMn2O4And perovskite phase LaCr0.7Fe0.3O3And (2) respectively weighing each oxide according to the medium atomic molar ratio, placing the oxide into an agate ball milling tank, carrying out wet milling for 18h by taking agate balls as a ball milling medium and absolute ethyl alcohol as a dispersion medium, and controlling the mass ratio of each substance in the ball milling tank to be: agate balls are prepared from absolute ethyl alcohol =2.5:1:1, ball milling is carried out alternately in clockwise and anticlockwise directions, and the interval time between clockwise and anticlockwise directions is 30min, so that two kinds of slurry are obtained;
(2) respectively drying the slurry obtained in the step (1) at 80 ℃, and then grinding for 1h to obtain two kinds of powder;
(3) calcining the spinel component and the perovskite component in the step (2) at 900 ℃ and 1000 ℃ respectively to obtain spinel phase NiMn2O4And perovskite phase LaCr0.7Fe0.3O3Powder; grinding the mixture in an agate mortar for 4 hours respectively to obtain NiMn2O4And perovskite phase LaCr0.7Fe0.3O3Particle size of powder (D)50) Respectively 0.341 μm and 0.457 μm, and then granulating by using PVA as a binder, wherein the addition amount of the PVA is 3wt% of the powder material, so as to obtain a two-phase powder material with uniform granularity, good fluidity and good formability;
(4) the die is arranged on a tabletting base, two spacers (3) of a movable partition valve (2) of the die (1) rotate by taking a rotating shaft (4) as a center, the inner cavity of the die is divided into two spaces with the volume ratio of 1:3, and the two spaces are divided into V (NiMn) according to the volume ratio2O4）：V(LaCr0.7Fe0.3O3) Filling the two-phase material in the step (3) in a ratio of 1:3, putting two-phase uniformly mixed powder (in a volume ratio of 1: 1) at an interface of the two-phase powder as a transition layer, taking out the movable spacer, and pressing: pre-pressing under 10Mpa to obtain wafer of phi 10mm, holding pressure for 3min, cold isostatic pressing under 350Mpa for 4min to obtain well-formed axialA composite block material; the mold structure was as in example 1;
(5) and (4) heating the block material obtained in the step (4) to 500 ℃ at the speed of 5 ℃/min, preserving heat for 5h, then heating to 1450 ℃ at the speed of 10 ℃/min, then rapidly cooling to 1300 ℃ within 5min, preserving heat for 12h, and furnace-cooling to obtain the axial composite negative temperature coefficient thermal sensitive ceramic material.
The obtained axial composite negative temperature coefficient thermal sensitive ceramic material is subjected to electrical property test, and the electrical parameter isρ 25℃=128Ω·cm±2%，B25/50=3370K ± 1.5%; the resistance change rate after aging for 1000h at 125 ℃ is 0.50 percent, and the material is suitable for inhibiting surge current.
Example 4
(1) First to analytically pure Ni2O3、MnO2、La2O3、Cr2O3As raw material, according to spinel phase NiMn2O4And perovskite phase LaCr0.7Mn0.3O3And (2) respectively weighing each oxide according to the molar ratio of the medium atoms, placing the oxide into an agate ball milling tank, carrying out wet milling for 24 hours by taking agate balls as a ball milling medium and absolute ethyl alcohol as a dispersion medium, and controlling the mass ratio of each substance in the ball milling tank to be: agate balls are prepared from absolute ethyl alcohol =2.5:1:1, ball milling is carried out alternately in clockwise and anticlockwise directions, and the interval time between clockwise and anticlockwise directions is 30min, so that two kinds of slurry are obtained;
(2) respectively drying the slurry obtained in the step (1) at 80 ℃, and then grinding for 1h to obtain two kinds of powder;
(3) calcining the spinel component and the perovskite component in the step (2) at 900 ℃ and 950 ℃ respectively to obtain spinel phase NiMn2O4And perovskite phase LaCr0.7Mn0.3O3Powder; grinding the mixture in an agate mortar for 4 hours respectively to obtain NiMn2O4And perovskite phase LaCr0.7Mn0.3O3Particle size of powder (D)50) Respectively 0.223 mu m and 0.316 mu m, and then granulating by taking PVA as a binder, wherein the addition amount of the PVA is 3wt% of the powder material, so as to obtain a two-phase powder material with uniform granularity, good fluidity and good formability;
(4) the die is arranged on a tabletting base, two spacers (3) of a movable partition valve (2) of the die (1) rotate by taking a rotating shaft (4) as a center, the inner cavity of the die is divided into two spaces with the volume ratio of 1:3, and the two spaces are divided into V (NiMn) according to the volume ratio2O4）：V(LaCr0.7Fe0.3O3) Filling the two-phase material in the step (3) in a ratio of 1:4, putting two-phase uniformly mixed powder (in a volume ratio of 1: 1) at an interface of the two-phase powder as a transition layer, taking out the movable spacer, and pressing: pre-pressing the wafer into a wafer with the diameter of 10mm under the pressure of 10Mpa for 3min, and then carrying out cold isostatic pressing on the wafer for 4min under the pressure of 350Mpa to obtain a well-formed axial composite block material; the mold structure was as in example 1;
(5) and (4) heating the block material obtained in the step (4) to 500 ℃ at the speed of 5 ℃/min, preserving heat for 5h, then heating to 1450 ℃ at the speed of 10 ℃/min, then rapidly cooling to 1300 ℃ within 5min, preserving heat for 12h, and furnace-cooling to obtain the axial composite negative temperature coefficient thermal sensitive ceramic material.
The obtained axial composite negative temperature coefficient thermal sensitive ceramic material is subjected to electrical property test, and the electrical parameter isρ 25℃=3401Ω·cm±2%，B25/50=3387K ± 1.5%; the resistance change rate after aging for 1000h at 125 ℃ is 0.51 percent, and the material is suitable for inhibiting surge current.
Comparative example 1
(1) First to analytically pure Ni2O3、MnO2As raw material, according to spinel phase NiMn2O4Weighing each oxide according to the molar ratio of the primary atoms, placing the oxide into an agate ball milling tank, carrying out wet milling for 12 hours by taking agate balls as a ball milling medium and absolute ethyl alcohol as a dispersion medium, and controlling the mass ratio of each substance in the ball milling tank to be: agate balls are prepared from absolute ethyl alcohol =2.5:1:1, ball milling is carried out alternately in clockwise and anticlockwise directions, and the interval time between clockwise and anticlockwise directions is 30min, so that slurry is obtained;
(2) respectively drying the slurry obtained in the step (1) at 80 ℃, and then grinding for 1h to obtain powder;
(3) calcining the powder in the step (2) at 900 ℃ to obtain spinel phase NiMn2O4Powder body(ii) a Grinding in an agate mortar for 4 hours to obtain NiMn2O4Particle size of powder (D)50) Is 0.211 mu m, then the granulation is carried out by taking PVA as a binder, the addition amount of the PVA is 3wt% of the powder material, and the spinel phase powder material with uniform granularity, good fluidity and good formability is obtained;
(4) pressing the powder obtained in the step (3) under the pressure of 10Mpa into a wafer with the diameter of 10mm, keeping the pressure for 3min, and then carrying out cold isostatic pressing on the wafer under the pressure of 350Mpa for 4min to obtain the spinel phase NiMn with good forming2O4A bulk material;
(5) and (4) heating the block material obtained in the step (4) to 500 ℃ at the speed of 5 ℃/min, preserving heat for 5h, then heating to 1250 ℃ at the speed of 10 ℃/min, then rapidly cooling to 1100 ℃ within 5min, preserving heat for 10h, and cooling along with the furnace to obtain the spinel phase negative temperature coefficient thermal sensitive ceramic material.
The obtained spinel phase negative temperature coefficient thermal sensitive ceramic material is subjected to electrical property test, and the electrical parameter isρ 25℃=106958Ω·cm±2%，B25/50=4477K ± 1.5%; the resistance change rate after aging for 1000 hours at 125 ℃ is 0.48 percent.
Comparative example 2
(1) First, to analyze pure La2O3、Cr2O3、Fe2O3As raw material, according to perovskite phase LaCr0.7Fe0.3O3Weighing each oxide according to the molar ratio of the primary atoms, placing the oxide into an agate ball milling tank, carrying out wet milling for 12 hours by taking agate balls as a ball milling medium and absolute ethyl alcohol as a dispersion medium, and controlling the mass ratio of each substance in the ball milling tank to be: agate balls are prepared from absolute ethyl alcohol =2.5:1:1, ball milling is carried out alternately in clockwise and anticlockwise directions, and the interval time between clockwise and anticlockwise directions is 30min, so that slurry is obtained;
(2) respectively drying the slurry obtained in the step (1) at 80 ℃, and then grinding for 1h to obtain powder;
(3) calcining the powder in the step (2) at 1000 ℃ to obtain perovskite phase LaCr0.7Fe0.3O3Powder; grinding in an agate mortar for 4 hours to obtain the LaCr0.7Fe0.3O3The powder granularity (D50) is 0.342 mu m, then granulation is carried out by taking PVA as a binder, the addition amount of the PVA is 3wt% of the powder, and the perovskite phase powder material with uniform granularity, good fluidity and good formability is obtained;
(4) pressing the powder obtained in the step (3) under the pressure of 10Mpa into a wafer with the diameter of 10mm, keeping the pressure for 3min, and then carrying out cold isostatic pressing on the wafer under the pressure of 350Mpa for 4min to obtain the well-formed perovskite phase LaCr0.7Fe0.3O3A bulk material;
(5) and (4) heating the block material obtained in the step (4) to 500 ℃ at the speed of 5 ℃/min, preserving heat for 5h, then heating to 1350 ℃ at the speed of 10 ℃/min, then rapidly cooling to 1250 ℃ within 5min, preserving heat for 10h, and furnace-cooling to obtain the perovskite phase negative temperature coefficient thermal sensitive ceramic material.
The obtained perovskite phase negative temperature coefficient thermal sensitive ceramic material is subjected to electrical property test, and the electrical parameter isρ 25℃=871Ω·cm±2%，B25/50=3358K ± 1.5%; the resistance change rate after aging at 125 ℃ for 1000 hours is 0.49%.
Comparative example 3
(1) First, to analyze pure La2O3、Cr2O3、Mn2O3As raw material, according to perovskite phase LaCr0.7Mn0.3O3Weighing each oxide according to the molar ratio of the primary atoms, placing the oxide into an agate ball milling tank, carrying out wet milling for 12 hours by taking agate balls as a ball milling medium and absolute ethyl alcohol as a dispersion medium, and controlling the mass ratio of each substance in the ball milling tank to be: agate balls are prepared from absolute ethyl alcohol =2.5:1:1, ball milling is carried out alternately in clockwise and anticlockwise directions, and the interval time between clockwise and anticlockwise directions is 30min, so that slurry is obtained;
(2) respectively drying the slurry obtained in the step (1) at 80 ℃, and then grinding for 1h to obtain powder;
(3) calcining the powder in the step (2) at 1000 ℃ to obtain perovskite phase LaCr0.7Mn0.3O3Powder; grinding in an agate mortar for 4 hours to obtain the LaCr0.7Mn0.3O3The powder granularity (D50) is 0.379 mu m, and then PVA is used as a bonding agentGranulating, wherein the adding amount of PVA is 3wt% of the powder material, and the perovskite phase powder material with uniform granularity, good fluidity and good formability is obtained;
(4) pressing the powder obtained in the step (3) under the pressure of 10Mpa into a wafer with the diameter of 10mm, keeping the pressure for 3min, and then carrying out cold isostatic pressing on the wafer under the pressure of 350Mpa for 4min to obtain the well-formed perovskite phase LaCr0.7Mn0.3O3A bulk material;
(5) and (4) heating the block material obtained in the step (4) to 500 ℃ at the speed of 5 ℃/min, preserving heat for 5h, then heating to 1350 ℃ at the speed of 10 ℃/min, then rapidly cooling to 1250 ℃ within 5min, preserving heat for 10h, and furnace-cooling to obtain the perovskite phase negative temperature coefficient thermal sensitive ceramic material.
The obtained perovskite phase negative temperature coefficient thermal sensitive ceramic material is subjected to electrical property test, and the electrical parameter isρ 25℃=3683Ω·cm±2%，B25/50=3191K ± 1.5%; the resistance change rate after aging at 125 ℃ for 1000 hours was 0.52%.

Claims (9)

1. An axial composite negative temperature coefficient thermal sensitive ceramic material is characterized in that the material is compounded by two phases, one phase is a perovskite phase or a doped perovskite phase, and the other phase is a spinel phase or a doped spinel phase; the interface of the two phases is a transition interlayer for uniformly mixing the two-phase powder; the volume ratio of the spinel phase or the doped spinel phase to the perovskite phase or the doped perovskite phase is 1:9-9: 1;
the spinel phase oxide has a molecular formula of AxB3-xO4Wherein A is one or more of Al, Ni, Co and Fe, B is one or more of Mn, Mg and Ti, and x is more than or equal to 0.4 and less than or equal to 1.5; the perovskite phase oxide has a molecular formula of LaCr1-yByO3Wherein B is one or more of Fe, Co and Mn, and y is more than or equal to 0 and less than or equal to 0.8;
the preparation method of the axial composite negative temperature coefficient thermal sensitive ceramic material comprises the following steps:
(1) according to spinel phase AxB3-xO4Or perovskite phase LaCr1-yByO3Weighing each oxide according to the mole ratio of the primary atoms, and wet-grinding to obtain two kinds of slurry;
(2) respectively drying the slurry obtained in the step (1), and then grinding to obtain two kinds of powder;
(3) respectively calcining the two kinds of powder in the step (2) to obtain a spinel phase AxB3-xO4And perovskite phase LaCr1-yByO3Powder; then granulating by using a binder to obtain a two-phase powder material with uniform granularity and good fluidity;
(4) putting the powder material in the step (3) into a mould according to a certain volume ratio, putting two-phase uniformly mixed powder at the interface of the two-phase powder as a transition layer, and pressing into a block material;
(5) heating the block material in the step (4) to 500 ℃, preserving heat, then heating to 1300-1450 ℃, then cooling to 1200-1300 ℃, preserving heat, and cooling along with the furnace to obtain the axial composite negative temperature coefficient thermal sensitive ceramic material;
in the step (3), before granulation, the method also comprises the step of mixing AxB3-xO4And LaCr1-yByO3Grinding to obtain powder with uniform particle size; a is describedxB3-xO4D of (A)500.128-1.763 μm; the LaCr1-yByO3D of (A)50Is 0.247-1.836 μm
The calcination temperature in the step (3) is 900-; the calcination time is 1-3h
In the step (5), the first heating rate is 1-5 ℃/min; the second heating rate is 5-10 ℃/min; the cooling time is 1-5 min; the first heat preservation time is 2-6h, and the second heat preservation time is 2-15 h.
2. The axial composite negative temperature coefficient thermal ceramic material of claim 1, wherein it isρ 25°CIs 124-17149 omega cm +/-2 percent, B25/503365 and 3393K +/-1.5 percent; aging at 125 deg.C for 1000 hr with resistance change rate of 0.41-0.52%。
3. A method for preparing an axial composite negative temperature coefficient thermal sensitive ceramic material as claimed in claim 1, comprising the steps of:
(1) according to spinel phase AxB3-xO4Or perovskite phase LaCr1-yByO3Weighing each oxide according to the mole ratio of the primary atoms, and wet-grinding to obtain two kinds of slurry;
(2) respectively drying the slurry obtained in the step (1), and then grinding to obtain two kinds of powder;
(3) respectively calcining the two kinds of powder in the step (2) to obtain a spinel phase AxB3-xO4And perovskite phase LaCr1-yByO3Powder; then granulating by using a binder to obtain a two-phase powder material with uniform granularity and good fluidity;
(4) putting the powder material in the step (3) into a mould according to a certain volume ratio, putting two-phase uniformly mixed powder at the interface of the two-phase powder as a transition layer, and pressing into a block material;
(5) and (4) heating the block material in the step (4) to 500 ℃, preserving heat, then heating to 1300-1450 ℃, then cooling to 1200-1300 ℃, preserving heat, and cooling along with the furnace to obtain the axial composite negative temperature coefficient thermal sensitive ceramic material.
4. The preparation method according to claim 3, wherein in the step (1), agate balls are used as a ball milling medium, and absolute ethyl alcohol is used as a dispersion medium in the wet milling; the mass ratio of the raw materials to the absolute ethyl alcohol is 2.5:1: 1; the wet milling time is 10-24 h.
5. The method according to claim 3, wherein step (3) further comprises granulating A before granulatingxB3-xO4And LaCr1-yByO3Grinding to obtain powder with uniform particle size; a is describedxB3-xO4D of (A)50Is 0.128-1.763Mu m; the LaCr1-yByO3D of (A)50Is 0.247-1.836 μm.
6. The method as claimed in claim 3, wherein the calcination temperature in step (3) is 1100 ℃ at 900-; the calcination time is 1-3 h.
7. The method according to claim 3, wherein in the step (3), the binder for granulation is PVA; the amount of PVA added is 1-3.5wt% of the powder.
8. The production method according to claim 3, wherein in the step (5), the first temperature increase rate is 1 to 5 ℃/min; the second heating rate is 5-10 ℃/min; the cooling time is 1-5 min; the first heat preservation time is 2-6h, and the second heat preservation time is 2-15 h.
9. The preparation method according to claim 3, wherein the mold is of a cylindrical structure, two ends of the mold are open, and a detachable movable partition valve is arranged in an inner cavity of the mold; the movable isolating valve is formed by connecting two rectangular isolating pieces along a long-edge rotating shaft; the axis of the rotating shaft is positioned in the center of a cross section of the die; the long side of the spacer is as high as the height of the die, and the short side of the spacer is as large as the inner radius of the die.
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