Preparation method of NTC (Negative Temperature Coefficient) thermistor material with superfine particle size

Abstract

The invention relates to a preparation method of a superfine-particle-size NTC thermistor material, the material is a Ni-Cr-Fe-Mn-Co-O five-element system, NiO, Cr2O3, Fe2O3, MnO2 and CoO are selected as oxide raw materials, preliminary mixing and grinding treatment are performed, then drying and presintering are performed, secondary ball milling is performed to further refine powder particles, and the superfine-particle-size NTC thermistor material is obtained. The obtained thermistor powder has an ultrafine particle size (D50 is less than or equal to 1 [mu] m) and a high particle size distribution concentration ratio (D90-D10 is less than or equal to 2.04 [mu] m). The method provided by the invention has the characteristics of simple process, short preparation period, small material loss, wide raw material source, low cost and the like, and is easy to realize large-scale production. The NTC thermistor product prepared from the material prepared by the method disclosed by the invention has the advantages of high sensitivity, obvious negative temperature coefficient (B value is up to 4000 or above), and good thermal stability and consistency.

Description

Technical Field

[0001] The invention relates to the technical field of thermistor material preparation, and in particular to a method for preparing an ultra-fine particle size NTC thermistor material. Background Art

[0002] NTC thermistor refers to a semiconductor material whose resistance value changes with temperature. It is one of the most sensitive temperature sensors currently. It has the advantages of low cost, small size, fast response, etc. It can quickly respond to temperature changes and has broad application prospects in the fields of temperature measurement, temperature control, temperature compensation, etc. With the innovation of my country's industrial technology and the large demand for NTC thermistors in the aerospace, medical, vehicle, electrical and other industries, the research and development of NTC thermistors in my country is also developing rapidly. In order to meet the needs of the industry, NTC thermistor temperature sensors will develop towards miniaturization, high precision, fast response, high stability and other trends.

[0003] The preparation of NTC thermistor precursor powder is a key step in the preparation of NTC thermistors. The relevant parameters of the powder directly affect the final ceramic material phase composition, structure and electrical performance parameters of the thermistor. There are many methods for preparing thermistor powder, including solid phase method, coprecipitation method, sol-gel method, etc. These methods all require small powder particle size, uniform composition, good dispersibility, high purity, good sintering activity, etc., that is, the performance requirements for the powder are consistent. However, the preparation process of the coprecipitation method or sol-gel method is complex, not suitable for mass production, easy to introduce impurities, large loss and other defects. The solid phase method has become one of the important methods for preparing NTC thermistor powder due to its simple process, low cost, high output, ability to accurately control the chemical composition of the material, and mass production. The average particle size of thermistor powder prepared by the solid phase method in the past is generally 2μm, and the ball milling time is generally more than 12h. However, this method still has problems such as large powder particle size and wide distribution. The larger the particle size of the powder, the lower the sintering activity, which has a significant impact on the resistance value and B value of the thermistor, limiting its application effect. Therefore, it is necessary to further improve the preparation process to obtain NTC thermistor powder with finer particle size and higher distribution concentration. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing an ultra-fine particle size NTC thermistor material. The thermistor material prepared by the method has a finer particle size and a higher distribution range concentration.

[0005] The technical solution of the present invention is:

[0006] The method for preparing an ultra-fine particle size NTC thermistor material, wherein the NTC thermistor material is a Ni-Cr-Fe-Mn-Co-O quinary system, comprises the following steps:

[0007] 1) Weigh agate beads of different sizes according to the ratio and place them in a ball mill, then add 5-8 parts by weight of NiO, 1-3 parts by weight of Cr 2 O 3 , 2-4 parts by weight of Fe 2 O 3 , 4-10 parts by weight of MnO 2 , 3-5 parts by weight of CoO, then add the medium solution and perform ball milling once;

[0008] 2) Separate the ball material and the powder material, dry the powder material at 90°C for 12 hours, and grind it manually for 10 to 30 minutes to obtain a primary ball mill powder;

[0009] 3) The primary ball-milled powder is pre-sintered in a high-temperature furnace to obtain a pre-sintered powder;

[0010] 4) Add the medium solution to the pre-sintered powder and perform ball milling for the second time; separate the ball material and the powder material, dry the powder material at 90°C for 12 hours, and grind it manually for 10 to 30 minutes to obtain the NTC thermistor powder;

[0011] 5) The particle size distribution of the NTC thermistor powder was tested. The ultrafine particle size of the thermistor powder obtained was D50≤1μm, and the high particle size distribution concentration was D90-D10≤2.04μm.

[0012] Step 1) The diameters of the agate beads are 15 mm, 10 mm, and 5 mm, respectively, and the mass ratio of the three is 1:1:1.

[0013] Step 1) The mass ratio of the agate beads to the raw materials is 3 / 1 to 5 / 1.

[0014] Step 1) The order of adding the raw materials is: first add the raw material with the largest amount, then add the raw material with the smallest amount, and finally add the raw material with the largest amount.

[0015] The medium solution in step 1) is any one of anhydrous ethanol, deionized water, and anhydrous ethanol aqueous solution with a mass ratio of 1:1.

[0016] Step 1) The mass ratio of the medium solution to the raw material is 2:1.

[0017] Step 1) The ball milling speed is 200-400 rpm and the time is 4-8 hours.

[0018] The pre-sintering method described in step 2) is that the pre-sintering temperature is 900°C to 1000°C, the heating rate is 10°C / min, the insulation time is 1 to 3 hours, and the furnace is cooled to room temperature.

[0019] Compared with the prior art, the method of the present invention has the following beneficial effects: the process flow of the present invention is simple, the cost is low, the material loss is small, and it is suitable for large-scale production. The method can obtain NTC thermistor materials with ultra-fine particle size and high particle size distribution concentration by precisely controlling the ball milling process parameters without the need for sieving, and only 4 to 8 hours of ball milling is required. At the same time, the method does not introduce any other impurities such as dispersants, thereby ensuring the high purity of the material. The NTC thermistor products prepared by the materials prepared by the method described in the present invention have high sensitivity and high B value, as well as good thermal stability and consistency, which are crucial to improving the accuracy and stability of temperature measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a particle size distribution diagram of NTC thermistor material Example 1 obtained by the preparation method of the present invention.

[0021] Figure 2 1 is a particle size distribution diagram of NTC thermistor material Example 2 obtained by the preparation method of the present invention.

[0022] Figure 3 1 is a particle size distribution diagram of NTC thermistor material Example 3 obtained by the preparation method of the present invention. DETAILED DESCRIPTION

[0023] In order to better demonstrate the technical solutions, objectives and advantages of the present invention, the present invention will be described in more detail below in conjunction with specific embodiments, but the contents of the present invention are not limited thereby.

[0024] Example 1

[0025] 1. Weigh 7 parts of NiO and 3 parts of Cr by weight. 2 O 3 , 4 parts Fe 2 O 3 , 3 parts CoO, 5 parts Mn0 2 The oxide raw materials are 3 times the mass of the oxide raw materials, and agate ball milling beads are placed in an agate jar. The mass ratio of large, medium and small agate beads is 1:1:1. The weighed oxide raw materials are divided into the following order: NiO with the largest amount, Cr with the smallest amount, and NiO with the largest amount. 2 O 3 and CoO, followed by Fe 2 O 3 Finally, MnO 2 Add into the ball mill in the following order;

[0026] 2. Add anhydrous ethanol twice the mass of the oxide raw material to the ball milling jar in step 1 as the ball milling medium solution, place the agate jar in a planetary ball mill for ball milling, set the ball milling speed to 200 rpm, and the ball milling time to 8 hours. After the ball milling, separate the agate balls and the powder, dry them at 90°C for 12 hours, and grind them manually in a mortar for 15 minutes to obtain a primary ball milled powder;

[0027] 3. The ball-milled powder was placed in an alumina crucible and pre-sintered in a high-temperature furnace. The temperature of the high-temperature furnace was raised to 900°C at a heating rate of 10°C / min and kept at this temperature for 3 hours to obtain a pre-sintered powder.

[0028] 4. Take the pre-sintered powder obtained in step 3 and repeat step 2 to perform secondary ball milling on the pre-sintered powder to obtain NTC thermistor powder;

[0029] 5. The particle size distribution of the prepared NTC thermistor powder was tested according to the GB / T19077-2016 (laser diffraction method) test standard. The test results are shown in Table 1 and Figure 1 shown.

[0030] Table 1

[0031] <![CDATA[D 10 (μm)]]> <![CDATA[D 50 (μm)]]> <![CDATA[D 90 (μm)]]> <![CDATA[D 90 -D 10 (μm)]]> 0.41 1.00 2.36 1.95

[0032] Example 2

[0033] Weigh 7 parts of NiO and 1 part of Cr by weight 2 O 3 , 4 parts Fe 2 O 3 , 3 parts CoO, 8 parts Mn0 2 The oxide raw material is 3 times the mass of the oxide raw material, and agate ball milling beads are placed in an agate jar. The mass ratio of large, medium and small agate beads is 1:1:1. The weighed oxide raw materials are placed in order according to the largest portion of Mn0 2 , the minimum Cr 2 O 3 , followed by CoO and Fe 2 O 3 , and finally NiO was added to the ball mill;

[0034] In this embodiment, except that deionized water is used as the ball milling medium solution in the second step, the ball milling speed is set to 300 rpm, and the ball milling time is set to 6 hours, the remaining steps are the same as those in Example 1 to obtain NTC thermistor powder.

[0035] The particle size distribution of the prepared NTC thermistor powder was tested according to the GB / T19077-2016 (laser diffraction method) test standard. The test results are shown in Table 2 and Figure 2 shown.

[0036] Table 2

[0037] <![CDATA[D 10 (μm)]]> <![CDATA[D 50 (μm)]]> <![CDATA[D 90 (μm)]]> <![CDATA[D 90 -D 10 (μm)]]> 0.24 0.58 2.27 2.03

[0038] Example 3

[0039] Weigh 7 parts of NiO and 1 part of Cr by weight 2 O 3 , 2 parts Fe 2 O 3 , 5 parts CoO, 8 parts Mn0 2 The oxide raw material is 3 times the mass of the oxide raw material, and agate ball milling beads are placed in an agate jar. The mass ratio of large, medium and small agate beads is 1:1:1. The weighed oxide raw materials are placed in order according to the largest portion of Mn0 2 , the minimum Cr 2 O 3 , followed by Fe 2 O 3 and Co O, and finally NiO were added into the ball mill in this order;

[0040] In this embodiment, except that in the second step, anhydrous ethanol aqueous solution with a mass ratio of 1:1 is used as the ball milling medium solution, the ball milling speed is set to 400 rpm, and the ball milling time is set to 4 hours, the remaining steps are the same as those in Example 1 to prepare NTC thermistor powder.

[0041] The particle size distribution of the prepared NTC thermistor powder was tested according to the GB / T19077-2016 (laser diffraction method) test standard. The test results are shown in Table 3 and Figure 3 shown.

[0042] Table 3

[0043] <![CDATA[D 10 (μm)]]> <![CDATA[D 50 (μm)]]> <![CDATA[D 90 (μm)]]> <![CDATA[D 90 -D 10 (μm)]]> 0.25 0.63 2.29 2.04

[0044] The ultra-fine particle size NTC thermistor material prepared by the method of the present invention has a particle size of submicron level (D50≤1μm) and shows a high particle size distribution concentration (D90-D10≤2.04μm). The effect of the method is very obvious. The material prepared by the method of the present invention has a high sensitivity and a significant negative temperature coefficient (B value is as high as 4000 or more), as well as good thermal stability and consistency.

[0045] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing an ultra-fine particle size NTC thermistor material, wherein the NTC thermistor material is a Ni-Cr-Fe-Mn-Co-O quinary system, characterized in that: The following steps are involved: 1) Weigh agate beads of different sizes according to the ratio and place them in a ball mill, add 5-8 parts by weight of NiO, 1-3 parts by weight of Cr2O3, 2-4 parts by weight of Fe2O3, 4-10 parts by weight of MnO2, 3-5 parts by weight of CoO as raw materials in sequence, then add the medium solution, and perform ball milling once; 2) Separate the ball material and the powder material, dry the powder material at 90°C for 12 hours, and grind it manually for 10 to 30 minutes to obtain a primary ball mill powder; 3) The primary ball-milled powder is pre-sintered in a high-temperature furnace to obtain a pre-sintered powder; 4) Add the medium solution to the pre-sintered powder and perform ball milling for the second time; separate the ball material and the powder material, dry the powder material at 90°C for 12 hours, and grind it manually for 10 to 30 minutes to obtain the NTC thermistor powder; 5) The particle size distribution of the NTC thermistor powder was tested. The ultrafine particle size of the thermistor powder obtained was D50≤1μm, and the high particle size distribution concentration was D90-D10≤2.04μm.

2. The preparation method according to claim 1, characterized in that: Step 1) The diameters of the agate beads are 15 mm, 10 mm, and 5 mm, respectively, and the mass ratio of the three is 1:1:

1.

3. The preparation method according to claim 1, characterized in that: Step 1) The mass ratio of the agate beads to the raw materials is 3 / 1 to 5 / 1.

4. The preparation method according to claim 1, characterized in that: Step 1) The order of adding the raw materials is: first add the raw material with the largest amount, then add the raw material with the smallest amount, and finally add the raw material with the largest amount.

5. The preparation method according to claim 1, characterized in that: The medium solution in step 1) is any one of anhydrous ethanol, deionized water, and anhydrous ethanol aqueous solution with a mass ratio of 1:

1.

6. The preparation method according to claim 1, characterized in that: Step 1) The mass ratio of the medium solution to the raw material is 2:

1.

7. The preparation method according to claim 1, characterized in that: Step 1) The ball milling speed is 200-400 rpm and the time is 4-8 hours.

8. The preparation method according to claim 1, characterized in that: The pre-sintering method described in step 2) is that the pre-sintering temperature is 900°C to 1000°C, the heating rate is 10°C / min, the insulation time is 1 to 3 hours, and the furnace is cooled to room temperature.

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