A method for preparing an alumina ceramic tube for a temperature sensor for shielding electromagnetic interference

Abstract

The present invention relates to a method for preparing an alumina ceramic tube for a shielding electromagnetic interference temperature sensor. The alumina ceramic tube prepared by the method through processes such as material composition selection, forming and sintering, and shielding coating has the advantages of high temperature resistance and insulation, and can effectively shield the alternating electromotive force generated by electromagnetic induction in a large furnace body. The sensor prepared by using the alumina ceramic tube described in the application has the advantages of high temperature measurement, high temperature measurement accuracy, and high stability.

Description

Technical Field

[0001] The invention relates to the field of ceramic materials for sensors, and in particular to a method for preparing an alumina ceramic tube for a temperature sensor for shielding electromagnetic interference. Background Art

[0002] In the field of temperature sensor temperature measurement, alumina ceramics have excellent thermal conductivity and thermal stability. They are widely used as high-temperature insulating carriers inside temperature sensors, playing the role of protecting the wire. The excellent performance of alumina ceramic tubes directly determines the service life of temperature sensors. At present, large furnaces commonly used have the characteristics of high-power induction heating, long constant temperature zone span, and high working temperature. Because the furnace heating coil is arranged in a ring, the heating coil uses AC power to generate an alternating magnetic field through the coil. The electromagnetic induction generated by the alternating magnetic field induces an alternating electromotive force in the temperature sensor measurement circuit, which generates serious electromagnetic interference signals for the measurement of the temperature sensor, causing the measured temperature to fluctuate greatly or produce errors, and over-temperature and under-temperature phenomena occur in the furnace, resulting in unstable temperature control and affecting the normal operation of the heating furnace.

[0003] Therefore, the development of alumina ceramic tubes that are both resistant to high temperature insulation and can shield electromagnetic interference is of great significance to the application of temperature sensors. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies in the prior art and to provide a method for preparing an alumina ceramic tube for a temperature sensor that shields electromagnetic interference. The alumina ceramic tube prepared by the method of the present invention has the advantages of high temperature resistance and insulation, and can effectively shield the alternating electromotive force generated by electromagnetic induction in a large furnace body. The sensor prepared by the alumina ceramic tube described in this application has the advantages of high temperature measurement, high temperature measurement accuracy, and high stability.

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

[0006] The preparation method of an alumina ceramic tube for a temperature sensor for shielding electromagnetic interference comprises the following steps:

[0007] 1) Uniform mixing:

[0008] Alumina powder, binder polyoxymethylene and deionized water are mixed to obtain an alumina block, wherein the mass ratio of the alumina powder, binder polyoxymethylene and deionized water is 6-7:2-3:1;

[0009] 2) Precision molding:

[0010] Alumina blocks are extruded into cylindrical blanks with double holes by using a hard alloy die, and then dried; the purpose of drying is to make the blanks have a certain strength.

[0011] 3) Gradient sintering:

[0012] Low temperature stage:

[0013] Pre-sinter the cylindrical billet at a heating rate of 5-7°C / min to 700-800°C and keep it for 2-3h;

[0014] High temperature stage:

[0015] The blank is placed in a vertical furnace for hanging firing at a heating rate of 5-7°C / min, heated to 1600-1700°C and kept for 18-24h, and cooled with the furnace to obtain a ceramic tube;

[0016] 4) Shielding layer preparation:

[0017] Platinum powder, glass powder and diethylene glycol butyl ether are taken, ground, atomized and sprayed on the surface of the sintered ceramic tube, dried in the shade, sintered, and cooled in the furnace to obtain an alumina ceramic tube.

[0018] The slurry is atomized and sprayed on the surface of the sintered ceramic tube with a spray gun in a stainless steel tank. The advantages of atomized spraying are uniform shielding layer, high working efficiency and material saving.

[0019] The shielding layer slurry is composed of platinum powder, glass powder and diethylene glycol butyl ether. The advantage of platinum powder is that it has a high melting point and excellent conductivity, which can effectively conduct the alternating electromotive force generated by electromagnetic induction to avoid affecting the insulation of the inner hole of the ceramic tube; the glass powder plays the role of a bonding phase and can be bonded to the surface of the alumina ceramic tube; diethylene glycol butyl ether serves as a solvent for the slurry and plays a role in uniforming the slurry components.

[0020] Step 1) The alumina has a particle size of 15 to 35 μm and a purity of ≥ 99.9%.

[0021] Step 1) The mixed materials are mixed in a mixer, the mixing time is 60 to 90 minutes, and the rotation speed n is 30 to 60 r / min.

[0022] Step 2) The extrusion speed is 20-40 cm / min.

[0023] Step 2) The outer diameter of the cylindrical blank is φ3-3.5 mm, with a tolerance of ±0.01 mm; the length of the blank is 1.0-4.0 m, with a tolerance of ±1.0 mm; the diameter of the hole is φ0.8-1.2 mm, with a tolerance of ±0.01 mm.

[0024] Step 2) The drying is performed for 24 to 36 hours at a temperature of 50 to 75°C.

[0025] Step 4) The mass ratio of the platinum powder: glass powder: diethylene glycol butyl ether is 6-8:1-2:1-2.

[0026] Step 4) The drying time in the shade is 18 to 24 hours.

[0027] Step 4) The sintering temperature is increased at a rate of 5 to 7°C / min to 1000 to 1100°C and kept at this temperature for 3 to 5 hours.

[0028] The above-mentioned alumina ceramic tube is used in the preparation of temperature sensors that are resistant to high temperature insulation and shielding electromagnetic interference.

[0029] Beneficial Effects of the Invention

[0030] (1) The extrusion die of the present invention adopts a cemented carbide die, which has high hardness and good wear resistance, and the extruded cylindrical blank has high dimensional accuracy and surface quality.

[0031] (2) The present invention adopts a two-step gradient sintering method to remove volatiles, low melting point impurities and binders in the blank at the low temperature stage, thereby improving the purity of the alumina ceramic tube. In the high temperature stage, the blank sintering shrinks and further densifies, thereby improving the strength of the ceramic tube.

[0032] (3) The shielding layer slurry of the present invention uses platinum powder, glass powder, and diethylene glycol butyl ether. Platinum powder has a high melting point and excellent electrical conductivity, which can effectively guide the alternating electromotive force generated by electromagnetic induction and avoid affecting the insulation of the inner hole of the ceramic tube; glass powder plays the role of a bonding phase and can be firmly bonded to the surface of the alumina ceramic tube; diethylene glycol butyl ether serves as a solvent for the slurry and plays a role in uniformly dispersing the slurry components.

[0033] (4) The applicant's experiments verified that the surface of the alumina ceramic tube prepared by the method of the present invention is glossy and crack-free. The high-temperature insulation resistance of the alumina ceramic tube is tested in accordance with GB / T 10581-2006, and the high-temperature insulation resistance is ≥3MΩ at 800°C; the shielding effectiveness of the alumina ceramic tube is tested in accordance with GJB 6190-2008, and the shielding effectiveness is ≥30dB at 100MHz~2GHz, which can effectively shield the alternating electromotive force generated by electromagnetic induction in a large furnace. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of the present invention;

[0035] Figure 2 The invention prepares a shielding layer alumina ceramic tube. DETAILED DESCRIPTION

[0036] The reagents used in the method of the present invention are all commercial reagents. Example 1

[0037] See also Figure 1 and Figure 2 .

[0038] Weigh 1400g of alumina powder with a particle size of 15-35μm and a purity of ≥99.9% and add it to the mixer, then add 400g of polyoxymethylene and 200g of deionized water in turn. Mix for 90 minutes at a speed of 40r / min to prepare a uniform alumina block. Put the alumina block into the extruder silo, use a carbide die, the diameter of the hole is φ0.8±0.01mm, the outer diameter of the billet is φ3.5mm±0.01mm, the length is 4.0m±1.0mm, and the extrusion speed is 20cm / min. Then place it in an oven for drying for 36h at a drying temperature of 50℃. The dried cylindrical billet is placed in a box furnace for low-temperature pre-sintering at a heating rate of 5°C / min, and the temperature is raised to 800°C and kept for 3 hours to make the billet dense and have a certain strength; in the second high-temperature stage, the billet is placed in a vertical furnace for hanging firing at a heating rate of 5°C / min, and the temperature is raised to 1700°C and kept for 24 hours, and then cooled with the furnace.

[0039] Weigh 21g of platinum powder, 3g of glass powder, and 6g of diethylene glycol butyl ether into an agate ball mill and grind for 3 hours to mix evenly. Use a spray gun to spray the slurry on the surface of the sintered ceramic tube in a stainless steel tank. After the shielding layer is sprayed, dry it in the shade for 24 hours, then put it into a tube furnace for sintering the shielding layer. The heating rate is 5℃ / min, and the temperature is raised to 1100℃ for 5 hours, and then cooled with the furnace. The surface of the prepared alumina ceramic tube is glossy and crack-free. The high-temperature insulation resistance of the alumina ceramic tube is tested according to GB / T 10581-2006, and the high-temperature insulation resistance is 3.2MΩ at 800℃; the shielding effectiveness of the alumina ceramic tube is tested according to GJB 6190-2008. At 100MHz~2GHz, the shielding effectiveness can reach 35dB. Example 2

[0040] See also Figure 1 and Figure 2 .

[0041] Weigh 1200g of alumina powder with a particle size of 15-35μm and a purity of ≥99.9% and add it to the mixer, then add 600g of polyoxymethylene and 100g of deionized water in turn. Mix for 70 minutes at a speed of 50r / min to prepare a uniform alumina block. Put the alumina block into the extruder silo, use a carbide die, the diameter of the hole is φ1.0±0.01mm, the outer diameter of the billet is φ3.2mm±0.01mm, the length is 3.0m±1.0mm, and the extrusion speed is 25cm / min. Then place it in an oven for drying for 30h at a drying temperature of 60℃. The dried cylindrical billet is placed in a box furnace for low-temperature pre-sintering at a heating rate of 6°C / min, and the temperature is raised to 800°C and kept for 3 hours to make the billet dense and have a certain strength; in the second high-temperature stage, the billet is placed in a vertical furnace for hanging firing at a heating rate of 6°C / min, and the temperature is raised to 1700°C and kept for 24 hours, and then cooled with the furnace.

[0042] Weigh 16g of platinum powder, 2g of glass powder, and 4g of diethylene glycol butyl ether and put them into an agate ball mill for grinding for 2h and mix them evenly. Use a spray gun to spray the slurry on the surface of the sintered ceramic tube in a stainless steel tank. After the shielding layer is sprayed, dry it in the shade for 24h, then put it into a tube furnace for sintering the shielding layer. The heating rate is 6℃ / min, and the temperature is raised to 1100℃ for 4h, and then cooled with the furnace. The surface of the prepared alumina ceramic tube is glossy and crack-free. The high-temperature insulation resistance of the alumina ceramic tube is tested according to GB / T 10581-2006, and the high-temperature insulation resistance is 3.4MΩ at 800℃; the shielding effectiveness of the alumina ceramic tube is tested according to GJB 6190-2008. At 100MHz~2GHz, the shielding effectiveness can reach 42dB. Example 3

[0043] See also Figure 1 and Figure 2 .

[0044] Weigh 600g of alumina powder with a particle size of 15-35μm and a purity of ≥99.9% and add it to the mixer, then add 300g of polyoxymethylene and 100g of deionized water in turn. Mix for 60 minutes at a speed of 60r / min to prepare a uniform alumina block. Put the alumina block into the extruder silo, use a carbide die, the diameter of the hole is φ1.2±0.01mm, the outer diameter of the billet is φ3.5mm±0.01mm, the length is 1.0m±1.0mm, and the extrusion speed is 30cm / min. Then place it in an oven for drying for 24h at a drying temperature of 70℃. The dried cylindrical billet is placed in a box furnace for low-temperature pre-sintering at a heating rate of 7°C / min, and the temperature is raised to 700°C and kept for 3 hours to make the billet dense and have a certain strength; in the second high-temperature stage, the billet is placed in a vertical furnace for hanging firing at a heating rate of 7°C / min, and the temperature is raised to 1600°C and kept for 18 hours, and then cooled with the furnace.

[0045] Weigh 7g of platinum powder, 1g of glass powder, and 2g of diethylene glycol butyl ether and put them into an agate ball mill for grinding for 2h and mix them evenly. Use a spray gun to spray the slurry on the surface of the sintered ceramic tube in a stainless steel tank. After the shielding layer is sprayed, dry it in the shade for 18h, then put it into a tube furnace for sintering the shielding layer. The heating rate is 7℃ / min, and the temperature is raised to 1000℃ for 3h, and then cooled with the furnace. The surface of the prepared alumina ceramic tube is glossy and crack-free. The high-temperature insulation resistance of the alumina ceramic tube is tested according to GB / T 10581-2006, and the high-temperature insulation resistance is 3.0MΩ at 800℃; the shielding effectiveness of the alumina ceramic tube is tested according to GJB 6190-2008. At 100MHz~2GHz, the shielding effectiveness can reach 38dB.

Claims

1. A method for preparing an alumina ceramic tube for a temperature sensor for shielding electromagnetic interference, characterized in that: There are the following steps: 1) Uniform mixing: Alumina powder, binder polyoxymethylene and deionized water are mixed to obtain an alumina block, wherein the mass ratio of the alumina powder: binder polyoxymethylene: deionized water is 6-7:2-3:1; 2) Precision molding: Alumina blocks are extruded into cylindrical blanks with double holes using a hard alloy die, and then dried; 3) Gradient sintering: Low temperature stage: Pre-sinter the cylindrical billet at a heating rate of 5-7°C / min to 700-800°C and keep it for 2-3h; High temperature stage: The blank is placed in a vertical furnace for hanging firing at a heating rate of 5-7°C / min, heated to 1600-1700°C and kept for 18-24h, and cooled with the furnace to obtain a ceramic tube; 4) Shielding layer preparation: Platinum powder, glass powder and diethylene glycol butyl ether are taken, ground, sprayed on the surface of the sintered ceramic tube by atomization, dried in the shade, sintered, and cooled in the furnace to obtain an alumina ceramic tube; The mass ratio of the platinum powder: glass powder: diethylene glycol butyl ether is 6-8:1-2:1-2.

2. The method according to claim 1, characterized in that: Step 1) The alumina has a particle size of 15-35 μm and a purity of ≥99.9%.

3. The method according to claim 1, characterized in that: Step 1) The mixed materials are mixed in a mixer for 60 to 90 minutes at a speed of n=30 to 60 r / min.

4. The method according to claim 1, characterized in that: Step 2) The extrusion speed is 20-40 cm / min.

5. The method according to claim 1, characterized in that: Step 2) The outer diameter of the cylindrical blank is φ3-3.5 mm, with a tolerance of ±0.01 mm; the length of the blank is 1.0-4.0 m, with a tolerance of ±1.0 mm; the diameter of the hole is φ0.8-1.2 mm, with a tolerance of ±0.01 mm.

6. The method according to claim 1, characterized in that: Step 2) The drying is performed for 24 to 36 hours at a temperature of 50 to 75°C.

7. The method according to claim 1, characterized in that: Step 4) The drying time in the shade is 18 to 24 hours.

8. The method according to claim 1, characterized in that: Step 4) The sintering temperature is increased at a rate of 5 to 7°C / min to 1000 to 1100°C and kept at this temperature for 3 to 5 hours.

9. Use of the alumina ceramic tube prepared by the method according to any one of claims 1 to 8 in preparing a temperature sensor that is resistant to high temperature insulation and shields electromagnetic interference.

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