NTC ceramic material for preparing dynamic surface thermocouple and preparation method thereof

Abstract

The present invention relates to an NTC ceramic material for preparing a dynamic surface thermocouple and a preparation method thereof. The weight parts of the components of the ceramic material are: 74-88 parts of iron oxide, 9-20 parts of aluminum oxide, 0-1 part of nickel oxide, and 2-6 parts of manganese salt, wherein the manganese salt is one of manganese carbonate or manganese acetate. The NTC ceramic material B (25 / 200°C) of the present invention is ≈3000K, so that the dynamic surface thermocouple made of the NTC ceramic material can work at room temperature and can continue to work in a wider temperature range, and the working temperature range can reach 0°C to 850°C; the material crystal phase transformation is more sufficient, the powder is more uniform, and the working stability of the prepared dynamic surface thermocouple is better.

Description

Technical Field

[0001] The invention relates to a ceramic material, in particular to an NTC ceramic material for preparing a dynamic surface thermocouple and a preparation method thereof. Background Art

[0002] Dynamic surface thermocouples have the advantages of sensing temperature at any point of the cable and detecting the highest temperature along the line. They are particularly suitable for large areas, large spaces, and long-distance test sites where local hot spots may appear randomly at any time. If they are laid reasonably in the area, any hot spots in the area can be detected in real time. They have become the first choice for surface temperature detection of large high-temperature pressure vessels and pipelines such as chemical gasifiers and converters. The working temperature is usually between 0℃ and 250℃, and the maximum temperature can reach above 500℃. It uses armoring technology to combine metal tubes, core wires and NTC ceramic materials together, and uses the NTC characteristics of ceramic materials to form a "temporary measurement end" at the highest temperature point. The "temporary measurement end" is automatically formed at the hottest point along the line and is dynamic, that is, the dynamic surface thermocouple automatically tracks the "hot spot".

[0003] The core of the dynamic surface thermocouple is NTC ceramic material, which is composed of one or more transition metal oxides such as iron, manganese, nickel, cobalt, copper, and aluminum. For example, single manganese oxide is used abroad, while manganese-based oxide is used in China. However, single manganese oxide requires special equipment and atmosphere to accurately control the manganese-oxygen ratio of the material, which is difficult to achieve in China; manganese-based oxide has a material constant that is too large (B 室温 / 200℃>6000K) problem. In order to adapt to high temperature work, the room temperature resistance needs to be increased to MΩ or above, which makes it impossible to form a "temporary measurement end" at lower temperatures, and even does not conduct below 155℃, making it difficult for dynamic surface thermocouples to work at lower temperatures. Summary of the invention

[0004] The purpose of the present invention is to provide an NTC ceramic material for preparing a dynamic surface thermocouple and a preparation method thereof, wherein B (25 / 200°C) ≈ 3000K, the room temperature insulation resistance of the dynamic surface thermocouple is reduced to the KΩ level, and the working temperature can be as low as room temperature. The NTC ceramic material prepared by the present invention has uniform resistance components, excellent B value performance within the application range, and good thermal stability.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] An NTC ceramic material for preparing a dynamic surface thermocouple, wherein the weight parts of the components of the ceramic material are: 74-88 parts of iron oxide, 9-20 parts of aluminum oxide, 0-1 part of nickel oxide, and 2-6 parts of manganese salt, wherein the manganese salt is one of manganese carbonate or manganese acetate;

[0007] A better technical solution is that the weight proportions of the components of the ceramic material are: 76-85 parts of iron oxide, 15-19 parts of aluminum oxide, 0.5-1 parts of nickel oxide, and 2-4 parts of manganese salt;

[0008] A better technical solution is that the weight proportions of the components of the ceramic material are: 80 parts of iron oxide, 18 parts of aluminum oxide, 0.5 parts of nickel oxide, and 2.5 to 4 parts of manganese salt;

[0009] The preparation method of the above ceramic material is as follows: prepare metal oxide powder material according to weight parts; add anhydrous ethanol, stir and mix at high speed, dry and place in a muffle furnace for pre-sintering according to a preset sintering curve to obtain pre-sintered powder with reaction activity; ball mill the pre-sintered powder and sinter and ball mill again; after molding and sintering, obtain NTC ceramic material for subsequent preparation of dynamic surface thermocouple. The specific steps are as follows:

[0010] 1) Weigh the powders of each component according to the above ratio, add 35-40 parts of anhydrous ethanol, stir and mix at high speed, and dry to obtain a mixed powder;

[0011] 2) Step 1) The mixed powder is pre-calcined at 600° C. to 1050° C. for 1 h to 3 h, cooled in the furnace, and ball-milled to obtain a pre-calcined powder;

[0012] 3) Step 2) the pre-sintered powder is sintered at 1000° C. to 1300° C. for 2 h to 4 h, cooled in the furnace, ball-milled, and sieved to obtain a sintered powder;

[0013] 4) Step 3) Add 2 parts by weight of methyl cellulose and pure water to the sintered powder, extrude it into a double-hole ceramic column, heat it at 800° C. to 1200° C. for 0.5 h to 2 h, and cool it in the furnace to obtain an NTC ceramic material;

[0014] Preferably, the speed of the high-speed stirring in step 1) is 180 rpm and the time is 1 hour;

[0015] Preferably, the drying temperature in step 1) is 80-90° C. and the drying time is more than 15 hours, until the anhydrous ethanol is dried;

[0016] Preferably, the ball milling speed in steps 2) and 3) is 200 rpm and the time is 2 h;

[0017] Preferably, in step 3), the mesh size of the sintered powder is within 200 meshes;

[0018] Preferably, the heating rate of the pre-sintering, sintering and heating in steps 2) to 4) is 300° C. / h.

[0019] The present invention has the following advantages over the prior art:

[0020] At present, the quaternary Mn-Ni-Cu-Fe system has a lower B value, and its resistance has the ability to change continuously with temperature. However, since the system contains Cu elements, it can only be used at lower temperatures (such as within 300-400°C), which cannot meet the use requirements of dynamic surface thermocouples with a wide temperature range. The present invention replaces the Cu element with Al elements, and the applicable temperature range can be up to 850°C, solving the problem that the quaternary thermistor cannot be used in dynamic surface thermocouples with a wide temperature range (such as more than 400°C);

[0021] The current NTC ceramic material is manganese-based oxide powder, but due to the large B value (B 室温 / 200℃>6000K), in order to ensure that its resistance can continuously change with temperature, the room temperature resistance of the dynamic surface thermocouple made by it reaches more than megohms, which cannot meet the use requirements of the dynamic surface thermocouple in a wide temperature range as low as 0℃. The present invention adopts Fe-Mn-Al-Ni series oxide powder, and its B 室温 / 200℃ down to about 3000K, so as to ensure that the room temperature resistance of the dynamic surface thermocouple made of it can still ensure that its resistance can continue to change with temperature when it is at the kilo-ohm level, so that the working temperature range of the dynamic surface thermocouple is widened to 0℃~850℃, solving the problem that the existing technology cannot work at low temperatures;

[0022] The B value of the NTC ceramic material of the dynamic surface thermocouple made by the present invention is about half of that of the existing material, so that the room temperature insulation resistance of the dynamic surface thermocouple is greatly reduced, the working temperature range is as low as room temperature, and it has a stable and relatively consistent thermoelectric potential at room temperature, and can work at room temperature;

[0023] Usually during sintering, the powder will undergo chemical reactions such as crystal phase transformation, water drainage shrinkage, manganese salt decomposition, and iron oxide oxygen loss. Sintering is generally carried out in cans, and there will be differences in temperature inside and outside. The temperature and action time determine the sintering effect. For a single sintering, the temperature of the powder in the can is not uniform enough, and the crystal phase transformation, water drainage shrinkage, manganese salt decomposition, and iron oxide oxygen loss are not uniform enough. Even if the time is extended, it is difficult to guarantee the effect. High temperature and long-term heating will cause the powder to shrink in volume, and the volume shrinkage will have a negative impact on the sintering effect.

[0024] The present invention adopts a method of pre-sintering and sintering with a secondary gradient temperature, so that the crystal phase transformation of the material is more complete, the powder is more uniform, and the working stability of the obtained dynamic surface thermocouple is better. Among them, the pre-sintering (first sintering) is carried out at a relatively low temperature. In this stage, the powder mainly undergoes chemical reactions such as drainage shrinkage, manganese salt decomposition, and iron oxide deoxygenation. At the same time, the temperature in this stage is relatively low, the time is relatively short, and the powder shrinks less, which has basically no effect on the sintering effect. Sintering (second sintering) is to re-crush and mix the powder after pre-sintering and then sinter at a higher temperature. In this stage, the iron oxide deoxygenation and crystal phase transformation are further completed. The higher temperature, re-combined and loose powder are more conducive to the crystal phase transformation, and the sintering effect also meets the requirements.

[0025] Applicant's experimental verification:

[0026] 1. The B value (25°C / 200°C) of the NTC ceramic material of the present invention is relatively uniform and small, so that the dynamic surface thermocouple made of it can work both at room temperature and continuously in a wider temperature range;

[0027] 2. The dynamic surface thermocouple made of NTC ceramic material of the present invention has a stable and consistent thermoelectromotive force at room temperature and can work at room temperature;

[0028] 3. The operating temperature range of the dynamic surface thermocouple made of NTC ceramic material of the present invention can reach 0°C to 850°C;

[0029] 4. The dynamic surface thermocouple made of the NTC ceramic material of the present invention has stable high temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the NTC ceramic material of the present invention. Specific embodiments

[0031] The present invention is further described below, but the present invention is not limited to the described embodiments.

[0032] Embodiment 1:

[0033] Weigh 80 parts of ferric oxide, 17.5 parts of aluminum oxide, 0.5 parts of nickel oxide, and 2.5 parts of manganese carbonate, add 40 parts of anhydrous ethanol, stir evenly at high speed, and then dry. Pre-sinter in a muffle furnace at 900℃ for 1.5 hours, cool with the furnace, and grind by ball mill; sinter in a muffle furnace at 1200℃ for 2 hours, cool with the furnace, and grind by ball mill; add 2 parts of methyl cellulose and pure water, extrude into a double-hole porcelain column, heat in a muffle furnace at 1030℃ for 1.5 hours, cool with the furnace, and set aside.

[0034] Embodiment 2:

[0035] Weigh 80 parts of ferric oxide, 17.5 parts of aluminum oxide, 0.5 parts of nickel oxide, and 4 parts of manganese acetate, add 40 parts of anhydrous ethanol, stir evenly at high speed, and then dry. Pre-sinter in a muffle furnace at 900℃ for 1.5 hours, cool with the furnace, and grind by ball mill; sinter in a muffle furnace at 1200℃ for 2 hours, cool with the furnace, and grind by ball mill; add 2 parts of methyl cellulose and pure water, extrude into a double-hole porcelain column, heat in a muffle furnace at 1030℃ for 1.5 hours, cool with the furnace, and set aside.

[0036] Table 1 B value of NTC ceramic thermocouple samples in the examples (25°C / 200°C)

[0037]

[0038] It can be seen from Table 1 that the B value (25°C / 200°C) of the NTC ceramic material of the present invention is relatively uniform and small, so that the dynamic surface thermocouple made of it can work both at room temperature and continuously in a wider temperature range.

[0039] According to GB / T36016-2018 test, in order to more accurately demonstrate the effect of the dynamic surface thermocouple made of the NTC ceramic material of the present invention, test temperature points are added to the dynamic surface thermocouple, and the results are shown in Table 2. The test results show that the thermoelectromotive force values ​​at each temperature point of the present invention meet the tolerance requirements in GB / T36016-2018.

[0040] Table 2 Thermoelectric potential of NTC ceramic thermocouple samples at room temperature 25℃~500℃ in the examples

[0041]

[0042] The dynamic surface thermocouple made of the NTC ceramic material of the present invention has a stable and relatively consistent thermoelectromotive force at room temperature and can work at room temperature.

[0043] Table 3 Thermoelectric potential of NTC ceramic thermocouple samples at 0℃~850℃ in the examples

[0044]

[0045] It can be seen from Table 3 that the operating temperature range of the dynamic surface thermocouple made of the NTC ceramic material of the present invention can reach 0°C to 850°C.

[0046] Since the main purpose of the dynamic surface thermocouple is to monitor the surface temperature of the pressure vessel, and the maximum design value of the surface temperature of the pressure vessel is 400°C, the high temperature performance stability of the dynamic surface thermocouple made of the material of the present invention is tested. Combined with its test method and conditions (the test requires a high temperature test chamber), the test temperature is set to 450°C (the high temperature of the pressure vessel surface), and the time refers to the armored cable test time of 250h. The results show that its maximum change is -5.0°C, which is much less than the Class I accuracy requirement in GB / T36016-2018. Therefore, the dynamic surface thermocouple made of the NTC ceramic material of the present invention has stable performance.

[0047] Table 4 Performance stability of NTC ceramic thermocouple samples at 450°C in the examples

[0048]

Claims

1. A dynamic surface thermocouple, characterized in that: The dynamic surface thermocouple is made of NTC ceramic material, and the weight proportions of the components of the NTC ceramic material are: 74-88 parts of iron oxide, 9-20 parts of aluminum oxide, 0.5-1 part of nickel oxide, and 2-6 parts of manganese salt, wherein the manganese salt is one of manganese carbonate or manganese acetate. The operating temperature range of the dynamic surface thermocouple is 0°C to 850°C.

2. The dynamic surface thermocouple according to claim 1, characterized in that: The weight proportions of the components of the NTC ceramic material are: 76-85 parts of iron oxide, 15-19 parts of aluminum oxide, 0.5-1 part of nickel oxide, and 2-4 parts of manganese salt.

3. The dynamic surface thermocouple according to claim 1 is characterized in that the weight proportions of the components of the NTC ceramic material are: 80 parts of iron oxide, 18 parts of aluminum oxide, 0.5 parts of nickel oxide, and 2.5 to 4 parts of manganese salt.

4. The method for preparing a dynamic surface thermocouple according to any one of claims 1 to 3, characterized in that: The dynamic surface thermocouple is made of NTC ceramic material, and the preparation method of the NTC ceramic material comprises the following steps: 1) Weigh the powders of each component according to any one of claims 1 to 3, add 35 to 40 parts by weight of anhydrous ethanol, stir and mix at high speed, and dry to obtain a mixed powder; The drying temperature is 80-90°C and the drying time is more than 15 hours, until the anhydrous ethanol is dried; 2) Step 1) The mixed powder is pre-calcined at 600° C. to 1050° C. for 1 h to 3 h, cooled in the furnace, and ball-milled to obtain a pre-calcined powder; 3) Step 2) the pre-sintered powder is sintered at 1000° C. to 1300° C. for 2 h to 4 h, cooled in the furnace, ball-milled, and sieved to obtain a sintered powder; 4) Step 3) Add 2 parts by weight of methyl cellulose and 18-20 parts by weight of pure water to the sintered powder, extrude it into a double-hole ceramic column, heat it at 800° C. to 1200° C. for 0.5 h to 2 h, and cool it with the furnace to obtain an NTC ceramic material.

5. The method for preparing the dynamic surface thermocouple according to claim 4, characterized in that: Step 1) The speed of the high-speed stirring is 180 rpm and the time is 1 hour.

6. The method for preparing the dynamic surface thermocouple according to claim 4, characterized in that: The ball milling speed in steps 2) and 3) is 200 rpm and the time is 2 h.

7. The method for preparing the dynamic surface thermocouple according to claim 4, characterized in that: Step 3) The mesh size of the sintered powder is within 200 meshes.

8. The method for preparing the dynamic surface thermocouple according to claim 4, characterized in that: The heating rate of the pre-sintering, sintering and heating in steps 2) to 4) is 300° C. / h.

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