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CN116283244B - Method for preparing alumina ceramic flake by casting - Google Patents

Method for preparing alumina ceramic flake by casting Download PDF

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CN116283244B
CN116283244B CN202310553930.9A CN202310553930A CN116283244B CN 116283244 B CN116283244 B CN 116283244B CN 202310553930 A CN202310553930 A CN 202310553930A CN 116283244 B CN116283244 B CN 116283244B
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alumina
alumina ceramic
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CN116283244A (en
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杨斌
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Hunan Zhiyue Technology Co.,Ltd.
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Hunan University
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Abstract

The invention provides a preparation method of an alumina ceramic flake, which comprises the following steps: adding PEI and nano graphite powder into an organic solvent, then adding soluble salt of tin and hydrazine to reduce tin ions, coating the surface of the nano graphite powder, and then adding zirconia powder, alumina powder, an adhesive and a plasticizer to obtain casting slurry; and defoaming the casting slurry, casting, forming and discharging glue, and sintering to obtain the final product. The method provided by the invention can be used for preparing the alumina ceramic flake with high toughness and low thermal expansion coefficient.

Description

Method for preparing alumina ceramic flake by casting
Technical Field
The invention relates to a preparation method of an alumina ceramic flake, and belongs to the field of ceramic sensors.
Background
The pressure sensor is a device capable of converting perceived external signals into electric signals according to a certain rule, and is widely applied to various fields such as railway traffic, intelligent building, production automatic control, aerospace, automobiles, petrifaction, oil wells, electric power, ships, machine tools, pipelines and the like.
With the increasing demand for sensors in the fields of 3C electronics, new source automobiles, artificial intelligence, internet of things and the like, and the rapid development of downstream markets.
Pressure sensors are one of the main sensor types for automotive applications, and are used in a large number in critical systems such as air conditioning systems, engine systems, and brake systems.
The pressure sensors commonly used at home and abroad at present are distinguished from the sensing principle and mainly comprise the following main categories: silicon piezoresistive technology, glass micro-melting technology, and ceramic pressure sensing technology. Wherein the ceramic pressure sensing technology comprises ceramic resistance sensing technology and ceramic capacitance sensing technology. For a capacitive sensor, an elastic diaphragm is a key sensitive element, and when the diaphragm is subjected to small-deflection deformation under the action of force, the capacitance and the pressure are approximately in a linear function relation. Conventional 96 alumina ceramics have a large modulus of elasticity and a low toughness, which negatively affects the sensitivity and lifetime of the sensor. How to ensure the improvement of ceramic toughness at low thermal expansion coefficients is a problem to be solved.
Disclosure of Invention
The invention aims to provide a preparation method of an alumina ceramic flake with high toughness and low thermal expansion coefficient.
The invention is realized by the following technical scheme:
a preparation method of an alumina ceramic flake comprises the following steps:
adding PEI and nano graphite powder into an organic solvent, then adding soluble salt of tin and hydrazine to reduce tin ions, coating the surface of the nano graphite powder, and then adding zirconia powder, alumina powder, an adhesive and a plasticizer to obtain casting slurry;
and defoaming the casting slurry, casting, forming and discharging glue, and sintering to obtain the final product.
The purity of the alumina powder is greater than or equal to 96%;
the average particle diameter D50 of the alumina powder is 1-2 mu m;
the average particle diameter D50 of the zirconia powder is 0.1-0.2 mu m.
The addition amount of PEI is 0.3-0.6wt% of the graphite powder;
the adding amount of the hydrazine is 0.8-1.2wt% of the graphite powder;
the addition amount of the soluble salt of tin is 3-5wt% of the graphite powder.
The adding amount of the zirconia powder is 0.15-0.2wt% of the adding amount of the alumina powder.
The sintering temperature is 1450-1520 ℃;
the sintering heat preservation time is 30-60min.
The organic solvent is selected from one of ethanol, isopropanol, xylene and n-butanol;
the mass of the organic solvent is 60-70 wt% of the mass of the alumina.
The adhesive is at least one of a polyvinyl butyral adhesive, a vinyl adhesive and an acrylic adhesive;
the addition amount of the adhesive is 5-10% of the mass of the alumina;
the plasticizer is at least one of dibutyl phthalate, dioctyl phthalate and polyethylene glycol;
the addition amount of the plasticizer is 3-6% of the total mass of the alumina.
The viscosity of the casting slurry is 10000-12000 cps.
The casting rate of the casting molding is 0.2-0.4 m/min.
The volume density of the alumina ceramic flake is more than or equal to 3.75g/cm 3 ；
The elastic modulus of the alumina ceramic flake is 330+/-15 GPa;
the flexural strength of the alumina ceramic flake is more than or equal to 380MPa;
the volume resistivity of the alumina ceramic flake is greater than or equal to 1.0X104 omega cm;
the thermal expansion coefficient of the alumina ceramic flake is 7-7.5X10-6/DEG C.
Compared with the prior art, the invention has the following beneficial effects:
the method provided by the invention is simple, and the porous tin oxide exists at the grain boundary of the prepared alumina ceramic, so that the alumina ceramic has low thermal expansion coefficient and high toughness.
Drawings
FIG. 1 shows SEM pictures of alumina ceramic flakes prepared in example 1;
fig. 2 shows an enlarged SEM photograph of the alumina ceramic platelet prepared in example 2 at the grain boundary.
Detailed Description
The invention provides a preparation method of an alumina ceramic flake, which comprises the following steps: first, branched PEI and nano graphite powder are added into an organic solvent. Because branched PEI is a quaternary ammonium base, the branched PEI can improve the surface potential of nano graphite powder, so that the nano graphite powder is uniformly dispersed. A soluble salt of tin is then added. Because of the existence of amino in the branched PEI, the branched PEI can form a coordination compound with tin ions, so that the tin ions are easy to adsorb on the surface of the nano graphite powder, and at the moment, hydrazine is added, and the tin ions are reduced by the hydrazine and then coated on the surface of the nano graphite powder by utilizing an alkaline environment formed by the branched PEI. After the hydrazine reaction is completed, adding zirconia powder and alumina powder, wherein the zirconia powder and the alumina powder can be uniformly dispersed due to the existence of branched PEI, and then adding an adhesive and a plasticizer to obtain the casting slurry. Finally, the casting slurry is defoamed, cast and molded, and sintered after the adhesive is discharged, so that the adhesive is obtained. The alumina ceramic flake prepared by the method has smaller crystal grains of alumina, higher toughness and smaller thermal expansion coefficient. This is because tin is converted into porous tin oxide and remains in the grain boundaries of aluminum oxide as the nano graphite powder is gasified and the tin is oxidized during sintering. The tin oxide remained in the grain boundary can prevent the growth of alumina crystals, thereby improving the toughness of the alumina ceramic flake. Since the porous tin oxide remains in the grain boundary, the porous tin oxide can be elastically deformed to a certain extent when the aluminum oxide ceramic sheet expands due to heating, so that the expansion of the aluminum oxide ceramic sheet is buffered, and the thermal expansion coefficient of the aluminum oxide ceramic sheet is further reduced.
Specifically, the purity of the alumina powder is greater than or equal to 96%; of course, the alumina powder may have a purity of 99% or more. Specifically, the average particle diameter D50 of the alumina is 1-2 mu m; the smaller average particle size can improve the sintering power of the alumina ceramic flake, reduce the sintering temperature, prevent the growth of crystal grains and further improve the toughness of the alumina ceramic flake.
Specifically, the average particle diameter D50 of the zirconia is 0.1-0.2 mu m. The addition of zirconia can also improve the toughness of the alumina, and the growth of alumina grains can be better controlled by selecting proper grain size.
The addition amount of PEI is 0.3-0.6wt% of the graphite powder. The proper adding amount can well disperse graphite powder, and can also more disperse alumina powder and zirconia powder which are needed to be added later. Meanwhile, the alkalinity of the system can be controlled, the reducibility of hydrazine is reduced, and the uneven tin coating on the surface of the graphite powder caused by the rapid reduction of tin ions is prevented. Preferably, the adding amount of the hydrazine is 0.8-1.2wt% of the graphite powder; too high an amount of hydrazine added results in rapid reduction of tin, which makes it difficult to uniformly coat the surface of the graphite powder with tin.
Specifically, the addition amount of the soluble salt of tin is 3-5wt% of the graphite powder. Too high an addition amount will result in too much coating of tin and eventually a decrease in the properties of the alumina ceramic flakes produced. While too small an amount is more difficult to reduce the thermal expansion coefficient of the alumina ceramic flake.
Specifically, the adding amount of the zirconia powder is 0.15-0.2wt% of the adding amount of the alumina powder.
Specifically, the sintering temperature is 1450-1520 ℃; too high a sintering temperature can result in alumina grain growth. The sintering heat preservation time is 30-60min.
Specifically, the organic solvent is selected from one of ethanol, isopropanol, xylene and n-butanol; the mass of the organic solvent is 60-70 wt% of the mass of the alumina.
Specifically, the adhesive is at least one of a polyvinyl butyral adhesive, a vinyl adhesive and an acrylic adhesive; the addition amount of the adhesive is 5-10% of the mass of the alumina.
Specifically, the plasticizer is at least one of dibutyl phthalate, dioctyl phthalate and polyethylene glycol; the addition amount of the plasticizer is 3-6% of the total mass of the alumina.
Specifically, the viscosity of the casting slurry is 1000-3000 cps. The casting rate of the casting molding is 0.2-0.4 m/min.
The volume density of the alumina ceramic flake prepared by the method is more than or equal to 3.75g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The elastic modulus of the alumina ceramic flake is 330+/-15 GPa; the flexural strength of the alumina ceramic flake is more than or equal to 380MPa; the volume resistivity of the alumina ceramic flake is greater than or equal to 1.0X104 omega cm; thermal expansion of the alumina ceramic flakesThe coefficient is 7 to 7.5X10 -6 /℃。
The invention is further illustrated below with reference to specific examples.
Branched polyethylenimine (PEI, CAS. NO 9002-98-6) used in the present invention was purchased from sigma-aldrich. The structural formula is as follows:
although quaternary ammonium is not represented in its structural formula, it is inevitably present due to its preparation method.
Example 1
After adding 0.15g branched PEI to 300g ethanol, 50g graphite powder (d50=0.1 micron) was added, followed by ball milling for 30min (ball to charge ratio 5:1). Then, after adding 1.5g of tin chloride and 0.4g of hydrazine and reacting for 1 hour under stirring, 1000g of alumina (D50: 1 μm) and 1.5g of zirconia powder (d50=0.1 μm) were added, followed by ball milling again for 30 minutes (ball-to-charge ratio 5:1). Then 300g of ethanol, 50g of PVB76 and 30 g of DBP are added for full swelling and dissolution until the peptized solution is clear and transparent, and the solution is left for 6 hours and ball milling is carried out again for 30 minutes (ball material ratio is 5:1) to obtain the casting slurry. The casting slurry is conveyed into a defoaming tank in a pressing way, bubbles are removed by utilizing a vacuum stirring principle, partial solvent is removed, after defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000 cps. And (3) conveying the defoamed slurry into a trough of a casting machine, setting a reasonable casting drying curve, and obtaining a casting green belt with the thickness of 0.45mm, wherein the casting speed is 0.4m/min. And cutting the casting green belt according to the required size of the product to obtain a casting green body. And (3) discharging the adhesive from the tape-cast green body in an adhesive discharging furnace, and reasonably making an adhesive discharging curve (slowly discharging the adhesive at the temperature of 200-450 ℃) according to the thermal weight curve of the green body to obtain an adhesive discharging sheet. Sintering the sheet at 1500 deg.C for 60min.
Example 2
After adding 0.15g of branched PEI to 350g of ethanol, 100g of graphite powder (d50=0.2 μm) was added, followed by ball milling for 30min (ball to charge ratio 5:1). Then, after adding 5g of tin chloride and 1.2g of hydrazine and reacting for 1 hour under stirring, 1000g of alumina (D50: 2 μm) and 2g of zirconia powder (d50=0.2 μm) were added, followed by ball milling again for 30 minutes (ball-to-charge ratio 5:1). Then 350g of ethanol, 100g of PVB76 and 60 g of DBP are added for full swelling and dissolution until the peptized solution is clear and transparent, and the solution is left for 6 hours and ball milling is carried out again for 30 minutes (ball material ratio is 5:1) to obtain the casting slurry. The casting slurry is conveyed into a defoaming tank in a pressing way, bubbles are removed by utilizing a vacuum stirring principle, partial solvent is removed, after defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000 cps. And (3) conveying the defoamed slurry into a trough of a casting machine, setting a reasonable casting drying curve, and obtaining a casting green belt with the thickness of 0.45mm, wherein the casting speed is 0.2 m/min. And cutting the casting green belt according to the required size of the product to obtain a casting green body. And (3) discharging the adhesive from the tape-cast green body in an adhesive discharging furnace, and reasonably making an adhesive discharging curve (slowly discharging the adhesive at the temperature of 200-450 ℃) according to the thermal weight curve of the green body to obtain an adhesive discharging sheet. Sintering the sheet at 1500 deg.C for 60min.
Example 3
After adding 0.15g of branched PEI to 320g of ethanol, 80g of graphite powder (d50=0.1 μm) was added, followed by ball milling for 30min (ball to charge ratio 5:1). Then, after 3g of tin chloride and 0.8g of hydrazine were added and reacted for 1 hour under stirring, 1000g of alumina (D50: 1 μm) and 1.5g of zirconia powder (d50=0.1 μm) were added and ball-milled again for 30 minutes (ball-to-charge ratio: 5:1). Then 320g of ethanol, 70 g of PVB76 and 40 g of PEG are added for full swelling and dissolution until the peptized solution is clear and transparent, and the solution is left for 6 hours and ball milling is carried out again for 30 minutes (ball material ratio is 5:1) to obtain the casting slurry. The casting slurry is conveyed into a defoaming tank in a pressing way, bubbles are removed by utilizing a vacuum stirring principle, partial solvent is removed, after defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000 cps. And (3) conveying the defoamed slurry into a trough of a casting machine, setting a reasonable casting drying curve, and obtaining a casting green belt with the thickness of 0.45mm, wherein the casting speed is 0.4m/min. And cutting the casting green belt according to the required size of the product to obtain a casting green body. And (3) discharging the adhesive from the tape-cast green body in an adhesive discharging furnace, and reasonably making an adhesive discharging curve (slowly discharging the adhesive at the temperature of 200-450 ℃) according to the thermal weight curve of the green body to obtain an adhesive discharging sheet. Sintering the sheet at 1500 deg.C for 60min.
Example 4
After adding 0.20g of branched PEI to 300g of ethanol, 50g of graphite powder (d50=0.1 μm) was added, followed by ball milling for 30min (ball to charge ratio 5:1). Then, after adding 1.5g of tin chloride and 0.4g of hydrazine and reacting for 1 hour under stirring, 1000g of alumina (D50: 1 μm) and 1.5g of zirconia powder (d50=0.1 μm) were added, followed by ball milling again for 30 minutes (ball-to-charge ratio 5:1). Then adding 300g of ethanol, 50g of PVB76 and 40 g of DOP, fully swelling and dissolving until the peptized solution is clear and transparent, standing for 6h, and ball milling for 30min again (ball-to-material ratio is 5:1) to obtain the casting slurry. The casting slurry is conveyed into a defoaming tank in a pressing way, bubbles are removed by utilizing a vacuum stirring principle, partial solvent is removed, after defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000 cps. And (3) conveying the defoamed slurry into a trough of a casting machine, setting a reasonable casting drying curve, and obtaining a casting green belt with the thickness of 0.45mm, wherein the casting speed is 0.4m/min. And cutting the casting green belt according to the required size of the product to obtain a casting green body. And (3) discharging the adhesive from the tape-cast green body in an adhesive discharging furnace, and reasonably making an adhesive discharging curve (slowly discharging the adhesive at the temperature of 200-450 ℃) according to the thermal weight curve of the green body to obtain an adhesive discharging sheet. Sintering the sheet at 1500 deg.C for 60min.
Example 5
After adding 0.3g of branched PEI to 300g of ethanol, 50g of graphite powder (d50=0.1 μm) was added, followed by ball milling for 30min (ball to charge ratio 5:1). Then, after adding 1.5g of tin chloride and 0.4g of hydrazine and reacting for 1 hour under stirring, 1000g of alumina (D50: 1 μm) and 1.5g of zirconia powder (d50=0.1 μm) were added, followed by ball milling again for 30 minutes (ball-to-charge ratio 5:1). Then 300g of ethanol, 60 g of polyacrylic acid and 30 g of DBP are added for full swelling and dissolution until the peptized solution is clear and transparent, and the solution is left for 6 hours and ball milling is carried out again for 30 minutes (ball material ratio is 5:1) to obtain the casting slurry. The casting slurry is conveyed into a defoaming tank in a pressing way, bubbles are removed by utilizing a vacuum stirring principle, partial solvent is removed, after defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000 cps. And (3) conveying the defoamed slurry into a trough of a casting machine, setting a reasonable casting drying curve, and obtaining a casting green belt with the thickness of 0.45mm, wherein the casting speed is 0.4m/min. And cutting the casting green belt according to the required size of the product to obtain a casting green body. And (3) discharging the adhesive from the tape-cast green body in an adhesive discharging furnace, and reasonably making an adhesive discharging curve (slowly discharging the adhesive at the temperature of 200-450 ℃) according to the thermal weight curve of the green body to obtain an adhesive discharging sheet. Sintering the sheet at 1500 deg.C for 60min.
Comparative example 1
To 300g of ethanol was added 50g of graphite powder (d50=0.1 μm), followed by ball milling for 30min (ball to charge ratio 5:1). Then, after adding 1.5g of tin chloride and 0.4g of hydrazine and reacting for 1 hour under stirring, 1000g of alumina (D50: 1 μm) and 1.5g of zirconia powder (d50=0.1 μm) were added, followed by ball milling again for 30 minutes (ball-to-charge ratio 5:1). Then 300g of ethanol, 50g of PVB76 and 30 g of DBP are added for full swelling and dissolution until the peptized solution is clear and transparent, and the solution is left for 6 hours and ball milling is carried out again for 30 minutes (ball material ratio is 5:1) to obtain the casting slurry. The casting slurry is conveyed into a defoaming tank in a pressing way, bubbles are removed by utilizing a vacuum stirring principle, partial solvent is removed, after defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000 cps. And (3) conveying the defoamed slurry into a trough of a casting machine, setting a reasonable casting drying curve, and obtaining a casting green belt with the thickness of 0.45mm, wherein the casting speed is 0.4m/min. And cutting the casting green belt according to the required size of the product to obtain a casting green body. And (3) discharging the adhesive from the tape-cast green body in an adhesive discharging furnace, and reasonably making an adhesive discharging curve (slowly discharging the adhesive at the temperature of 200-450 ℃) according to the thermal weight curve of the green body to obtain an adhesive discharging sheet. Sintering the sheet at 1500 deg.C for 60min.
Comparative example 2
After adding 0.15g of tetramethylammonium hydroxide to 300g of ethanol, 50g of graphite powder (d50=0.1 μm) was added, followed by ball milling for 30min (ball-to-charge ratio 5:1). Then, after adding 1.5g of tin chloride and 0.4g of hydrazine and reacting for 1 hour under stirring, 1000g of alumina (D50: 1 μm) and 1.5g of zirconia powder (d50=0.1 μm) were added, followed by ball milling again for 30 minutes (ball-to-charge ratio 5:1). Then 300g of ethanol, 50g of PVB76 and 30 g of DBP are added for full swelling and dissolution until the peptized solution is clear and transparent, and the solution is left for 6 hours and ball milling is carried out again for 30 minutes (ball material ratio is 5:1) to obtain the casting slurry. The casting slurry is conveyed into a defoaming tank in a pressing way, bubbles are removed by utilizing a vacuum stirring principle, partial solvent is removed, after defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000 cps. And (3) conveying the defoamed slurry into a trough of a casting machine, setting a reasonable casting drying curve, and obtaining a casting green belt with the thickness of 0.45mm, wherein the casting speed is 0.4m/min. And cutting the casting green belt according to the required size of the product to obtain a casting green body. And (3) discharging the adhesive from the tape-cast green body in an adhesive discharging furnace, and reasonably making an adhesive discharging curve (slowly discharging the adhesive at the temperature of 200-450 ℃) according to the thermal weight curve of the green body to obtain an adhesive discharging sheet. Sintering the sheet at 1500 deg.C for 60min.
As is clear from comparative example 1, when PEI is not added, the reducibility of hydrazine is poor, the coating of graphite powder with tin is also poor, and the properties of the alumina ceramic flake obtained are poor.
As is clear from comparative example 2, when tetramethylammonium hydroxide was added, the coating of graphite powder with tin was also deteriorated due to poor complexation of tetramethylammonium hydroxide, and the properties of the alumina ceramic flake obtained were poor.

Claims (9)

1. A method for preparing an alumina ceramic flake by casting, which is characterized by comprising the following steps:
adding branched PEI and nano graphite powder into an organic solvent, then adding soluble salt of tin and hydrazine to reduce tin ions, coating the tin ions on the surface of the nano graphite powder, and then adding zirconia powder, alumina powder, an adhesive and a plasticizer to obtain casting slurry;
defoaming the casting slurry, casting, forming and sintering after discharging glue to obtain the adhesive;
the addition amount of PEI is 0.3-0.6wt% of the graphite powder;
the adding amount of the hydrazine is 0.8-1.2wt% of the graphite powder;
the addition amount of the soluble salt of tin is 3-5wt% of the graphite powder;
the addition amount of the nano graphite powder is 5-10wt% of the alumina powder.
2. The method for producing an alumina ceramic flake by casting according to claim 1, wherein:
the purity of the alumina powder is greater than or equal to 96%;
the average particle diameter D50 of the alumina powder is 1-2 mu m;
the average particle diameter D50 of the zirconia powder is 0.1-0.2 mu m.
3. The method for producing an alumina ceramic flake by casting according to claim 1, wherein:
the adding amount of the zirconia powder is 0.15-0.2wt% of the adding amount of the alumina powder.
4. The method for producing an alumina ceramic flake by casting according to claim 1, wherein:
the sintering temperature is 1450-1520 ℃;
the sintering heat preservation time is 30-60min.
5. The method for producing an alumina ceramic flake by casting according to claim 1, wherein:
the organic solvent is selected from one of ethanol, isopropanol, xylene and n-butanol;
the mass of the organic solvent is 60-70 wt% of the mass of the alumina.
6. The method for producing an alumina ceramic flake by casting according to claim 1, wherein:
the adhesive is at least one of a polyvinyl butyral adhesive, a vinyl adhesive and an acrylic adhesive;
the addition amount of the adhesive is 5-10% of the mass of the alumina;
the plasticizer is at least one of dibutyl phthalate, dioctyl phthalate and polyethylene glycol;
the addition amount of the plasticizer is 3-6% of the total mass of the alumina.
7. The method for producing an alumina ceramic flake by casting according to claim 1, wherein:
the viscosity of the casting slurry is 10000-12000 cps.
8. The method for producing an alumina ceramic flake by casting according to claim 1, wherein:
the casting rate of the casting molding is 0.2-0.4 m/min.
9. The method for producing an alumina ceramic flake by casting according to claim 1, wherein:
the volume density of the alumina ceramic flake is more than or equal to 3.75g/cm 3 ；
The elastic modulus of the alumina ceramic flake is more than or equal to 320GPa;
the flexural strength of the alumina ceramic flake is more than or equal to 380MPa;
the volume resistivity of the alumina ceramic flake is greater than or equal to 1.0X10 14 Ω.cm；
The thermal expansion coefficient of the alumina ceramic flake is less than or equal to 7.5X10 -6 /℃。
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