CN116283244B - A method for preparing alumina ceramic sheets by tape casting - Google Patents

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

A method for preparing alumina ceramic sheets by tape casting

technical field

The invention relates to a method for preparing an alumina ceramic sheet, belonging to the field of ceramic sensors.

Background technique

Pressure sensors are devices that can convert perceived external signals into electrical signals according to certain rules. Pressure sensors are widely used in many fields such as railway transportation, intelligent buildings, production automation, aerospace, automobiles, petrochemicals, oil wells, electric power, ships, machine tools, and pipelines.

With the increasing demand for sensors in 3C electronics, Xinyuan automobile, artificial intelligence, Internet of Things and other fields and the rapid development of the downstream market.

The pressure sensor is one of the main sensor types in automotive applications, and is widely used in key systems such as air conditioning systems, engine systems, and braking systems.

At present, the pressure sensors commonly used at home and abroad are distinguished from the sensing principle, mainly including the following categories: silicon piezoresistive technology, glass micro-fusion technology and ceramic pressure sensing technology. The ceramic pressure sensing technology includes ceramic resistance sensing technology and ceramic capacitance sensing technology. For capacitive sensors, the elastic diaphragm is the key sensitive element. When the diaphragm undergoes small deflection deformation under force, the capacitance and pressure are approximately linear functions. Conventional 96 alumina ceramics have a large elastic modulus and low toughness, which have a negative impact on the sensitivity and life of the sensor. How to improve the toughness of ceramics with low thermal expansion coefficient is an urgent problem to be solved.

Contents of the invention

The purpose of the present invention is to provide a method for preparing alumina ceramic flakes with high toughness and low coefficient of thermal expansion.

The present invention realizes through following technical scheme:

A preparation method of alumina ceramic flakes, comprising the steps of:

Add PEI and nano-graphite powder to the organic solvent, then add tin soluble salt and hydrazine to reduce tin ions and coat the surface of nano-graphite powder, then add zirconia powder, alumina powder, adhesive and plasticizer to obtain casting slurry;

The cast slurry is degassed, tape cast and degummed, and then sintered to obtain the 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 μm;

The average particle diameter D50 of the zirconia powder is 0.1-0.2 μm.

The addition of the PEI is 0.3-0.6wt% of the graphite powder;

The addition of the hydrazine is 0.8-1.2wt% of the graphite powder;

The added amount of the soluble tin salt is 3-5wt% of the graphite powder.

The added amount of the zirconia powder is 0.15-0.2wt% of the added amount of the alumina powder.

The sintering temperature is 1450-1520°C;

The holding time of the sintering is 30-60min.

Described organic solvent is selected from one in ethanol, isopropanol, xylene, n-butanol;

The mass of the organic solvent is 60-70 wt% of the alumina mass.

The adhesive is at least one of polyvinyl butyral adhesives, vinyl adhesives, and acrylic adhesives;

The amount of the adhesive added is 5-10% of the mass of alumina;

The plasticizer is at least one of dibutyl phthalate, dioctyl phthalate, polyethylene glycol;

The added amount of the plasticizer is 3-6% of the total mass of alumina.

The viscosity of the casting slurry is 10000-12000 cps.

The casting speed of the tape casting is 0.2-0.4 m/min.

The bulk density of the alumina ceramic flakes is greater than or equal to 3.75 g/cm ³ ;

The modulus of elasticity of the alumina ceramic sheet is 330 ± 15 GPa;

The flexural strength of the alumina ceramic sheet is greater than or equal to 380 MPa;

The volume resistivity of the alumina ceramic sheet is greater than or equal to 1.0×1014Ω.cm;

The coefficient of thermal expansion of the alumina ceramic sheet is 7-7.5×10-6/°C.

Compared with the prior art, the beneficial effects of the present invention are as follows:

The method provided by the invention adopts a simple method, and porous tin oxide exists at the grain boundary of the prepared alumina ceramic, so the coefficient of thermal expansion is low and the toughness is high.

Description of drawings

Fig. 1 shows the SEM photo of the aluminum oxide ceramic flakes that embodiment 1 prepares;

FIG. 2 shows an enlarged SEM photo of the grain boundaries of the alumina ceramic flakes prepared in Example 2.

Detailed ways

The invention provides a preparation method of alumina ceramic flakes, which specifically comprises the following steps: firstly, branched PEI and nano-graphite powder are added to an organic solvent. Since the branched PEI is a quaternary ammonium base, it can increase the surface potential of the nano-graphite powder, thereby making it uniformly dispersed. A soluble salt of tin is then added. Because of the presence of amino groups in branched PEI, it can form a coordination compound with tin ions, so that tin ions are easily adsorbed on the surface of nano-graphite powder. At this time, hydrazine is added to make use of the alkaline environment formed by branched PEI, so that tin ions are reduced by hydrazine and coated on the surface of nano-graphite powder. After the hydrazine reaction is complete, add zirconia powder and alumina powder. At this time, due to the presence of branched PEI, the zirconia powder and alumina powder can also be uniformly dispersed, and then add adhesive and plasticizer to obtain casting slurry. Finally, the casting slurry is degassed, tape-casted and degummed, and then sintered to obtain the final product. The aluminum oxide ceramic flakes prepared by the method have smaller crystal grains, higher toughness, and smaller coefficient of thermal expansion. This is because when tin is sintered, with the gasification of nano-graphite powder and the oxidation of tin, tin will be converted into porous tin oxide and remain in the grain boundaries of alumina. The residual tin oxide in the grain boundary will prevent the growth of alumina crystals, thereby improving the toughness of alumina ceramic flakes. Since the porous tin oxide remains in the grain boundary, when the alumina ceramic sheet is heated and expanded, the porous tin oxide can undergo a certain elastic deformation, thereby buffering the expansion of the alumina ceramic sheet and reducing its thermal expansion coefficient.

Specifically, the purity of the alumina powder is greater than or equal to 96%; of course, the purity of the alumina powder may also be greater than or equal to 99%. Specifically, the average particle size D50 of the alumina is 1-2 μm; a smaller average particle size can increase the sintering power of the alumina ceramic sheet, reduce the sintering temperature, prevent grain growth, and improve its toughness.

Specifically, the average particle diameter D50 of the zirconia is 0.1-0.2 μm. The addition of zirconia can also improve the toughness of alumina, and choosing a suitable particle size can also better control the growth of alumina grains.

Specifically, the added amount of PEI is 0.3-0.6wt% of the graphite powder. Appropriate addition amount can disperse graphite powder well, and at the same time, it can also disperse alumina powder and zirconia powder to be added later. At the same time, it can also control the alkalinity of the system, reduce the reducibility of hydrazine, and prevent the rapid reduction of tin ions to cause uneven tin coating on the surface of graphite powder. Preferably, the added amount of hydrazine is 0.8-1.2wt% of the graphite powder; if the added amount of hydrazine is too high, it will lead to rapid reduction of tin, which makes it difficult to uniformly coat tin on the surface of graphite powder.

Specifically, the added amount of the soluble tin salt is 3-5wt% of the graphite powder. If the added amount is too high, the coating of tin will be too large, and finally the performance of the prepared alumina ceramic flakes will be reduced. If the amount added is too small, it will be difficult to reduce the thermal expansion coefficient of the alumina ceramic flakes.

Specifically, the added amount of the zirconia powder is 0.15-0.2 wt% of the added amount of the alumina powder.

Specifically, the sintering temperature is 1450-1520° C.; if the sintering temperature is too high, the alumina grains will grow. The holding time of the sintering 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 alumina mass.

Specifically, the adhesive is at least one of polyvinyl butyral adhesives, vinyl adhesives, and acrylic adhesives; the amount of the adhesive added is 5-10% of the mass of alumina.

Specifically, the plasticizer is at least one of dibutyl phthalate, dioctyl phthalate, and polyethylene glycol; the added amount of the plasticizer is 3-6% of the total mass of alumina.

Specifically, the viscosity of the casting slurry is 1000-3000 cps. The casting speed of the tape casting is 0.2-0.4 m/min.

The bulk density of the alumina ceramic flakes prepared by the method provided by the present invention is greater than or equal to 3.75 g/cm ³ ; the elastic modulus of the alumina ceramic flakes is 330±15 GPa; the flexural strength of the alumina ceramic flakes is greater than or equal to 380 MPa; the volume resistivity of the alumina ceramic flakes is greater than or equal to 1.0× ^1014Ω.cm ;

The present invention will be further described below in conjunction with specific examples.

The branched polyethyleneimine (PEI, CAS.NO 9002-98-6) used in the present invention was purchased from sigma-aldrich company. Its structural formula is as follows:

Although quaternary ammonium is not reflected in its structural formula, due to its preparation method, quaternary ammonium inevitably exists.

Example 1

Add 0.15g branched PEI to 300g ethanol, then add 50g graphite powder (D50=0.1 micron), then ball mill for 30min (ball-to-material ratio 5:1). Then add 1.5g of tin chloride and 0.4g of hydrazine to react for 1 hour under stirring, then add 1000g of alumina (D50 is 1 micron) and 1.5g of zirconia powder (D50=0.1 micron) and then ball mill for 30min again (ball-to-material ratio 5:1). Then add 300g of ethanol, 50g of PVB76 and 30g of DBP to fully swell and dissolve until the glue solution is clear and transparent, and let it stand for 6h, then ball mill for 30min again (ball-to-material ratio 5:1) to obtain casting slurry. The casting slurry is pressure-fed into the defoaming tank, and vacuum stirring is used to remove air bubbles and part of the solvent. After defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000cps. The defoamed slurry was pressure-fed to the trough of the casting machine, a reasonable casting drying curve was set, the casting speed was 0.4m/min, and a casting green tape with a thickness of 0.45mm was obtained. Cut the cast green belt according to the required size of the product to obtain the cast green body. The tape-cast green body is debinding in the debinding furnace, and the debinding curve is reasonably formulated according to the thermogravimetric curve of the green body (slowly debinding in the range of 200-450 ° C), and the debinding sheet is obtained. Sinter the adhesive sheet at a high temperature of 1500°C for a holding time of 60 minutes to obtain it.

Example 2

Add 0.15g branched PEI to 350g ethanol, then add 100g graphite powder (D50=0.2 microns), and then ball mill for 30min (ball-to-material ratio 5:1). Then add 5g of tin chloride and 1.2g of hydrazine to react for 1h under stirring conditions, add 1000g of alumina (D50 is 2 micron) and 2g of zirconia powder (D50=0.2 micron) and then ball mill for 30min again (ball-to-material ratio 5:1). Then add 350g of ethanol, 100g of PVB76 and 60g of DBP to fully swell and dissolve until the glue solution is clear and transparent, and let it stand for 6h, then ball mill for 30min again (ball-to-material ratio 5:1) to obtain casting slurry. The casting slurry is pressure-fed into the defoaming tank, and vacuum stirring is used to remove air bubbles and part of the solvent. After defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000cps. The defoamed slurry was pressure-fed to the trough of the casting machine, a reasonable casting drying curve was set, the casting speed was 0.2m/min, and a casting green tape with a thickness of 0.45mm was obtained. Cut the cast green belt according to the required size of the product to obtain the cast green body. The tape-cast green body is debinding in the debinding furnace, and the debinding curve is reasonably formulated according to the thermogravimetric curve of the green body (slowly debinding in the range of 200-450 ° C), and the debinding sheet is obtained. Sinter the adhesive sheet at a high temperature of 1500°C for a holding time of 60 minutes to obtain it.

Example 3

Add 0.15g branched PEI to 320g ethanol, then add 80g graphite powder (D50=0.1 micron), and then ball mill for 30min (ball-to-material ratio 5:1). Then add 3g of tin chloride and 0.8g of hydrazine to react for 1h under stirring conditions, add 1000g of alumina (D50 is 1 micron) and 1.5g of zirconia powder (D50=0.1 micron) and ball mill again for 30min (ball-to-material ratio 5:1). Then add 320g of ethanol, 70g of PVB76 and 40g of PEG to fully swell and dissolve until the glue solution is clear and transparent, and let it stand for 6h, then ball mill for 30min again (ball-to-material ratio 5:1) to obtain casting slurry. The casting slurry is pressure-fed into the defoaming tank, and vacuum stirring is used to remove air bubbles and part of the solvent. After defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000cps. The defoamed slurry was pressure-fed to the trough of the casting machine, a reasonable casting drying curve was set, the casting speed was 0.4m/min, and a casting green tape with a thickness of 0.45mm was obtained. Cut the cast green belt according to the required size of the product to obtain the cast green body. The tape-cast green body is debinding in the debinding furnace, and the debinding curve is reasonably formulated according to the thermogravimetric curve of the green body (slowly debinding in the range of 200-450 ° C), and the debinding sheet is obtained. Sinter the adhesive sheet at a high temperature of 1500°C for a holding time of 60 minutes to obtain it.

Example 4

Add 0.20g branched PEI to 300g ethanol, then add 50g graphite powder (D50=0.1 micron), and then ball mill for 30min (ball-to-material ratio 5:1). Then add 1.5g of tin chloride and 0.4g of hydrazine to react for 1 hour under stirring, then add 1000g of alumina (D50 is 1 micron) and 1.5g of zirconia powder (D50=0.1 micron) and then ball mill for 30min again (ball-to-material ratio 5:1). Then add 300g of ethanol, 50g of PVB76 and 40g of DOP to fully swell and dissolve until the glue solution is clear and transparent, and let it stand for 6h, then ball mill for 30min again (ball-to-material ratio 5:1) to obtain casting slurry. The casting slurry is pressure-fed into the defoaming tank, and vacuum stirring is used to remove air bubbles and part of the solvent. After defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000cps. The defoamed slurry was pressure-fed to the trough of the casting machine, a reasonable casting drying curve was set, the casting speed was 0.4m/min, and a casting green tape with a thickness of 0.45mm was obtained. Cut the cast green belt according to the required size of the product to obtain the cast green body. The tape-cast green body is debinding in the debinding furnace, and the debinding curve is reasonably formulated according to the thermogravimetric curve of the green body (slowly debinding in the range of 200-450°C), and the debinding sheet is obtained. Sinter the adhesive sheet at a high temperature of 1500°C for a holding time of 60 minutes to obtain it.

Example 5

Add 0.3g branched PEI to 300g ethanol, then add 50g graphite powder (D50=0.1 micron), then ball mill for 30min (ball-to-material ratio 5:1). Then add 1.5g of tin chloride and 0.4g of hydrazine to react for 1 hour under stirring, then add 1000g of alumina (D50 is 1 micron) and 1.5g of zirconia powder (D50=0.1 micron) and then ball mill for 30min again (ball-to-material ratio 5:1). Then add 300g of ethanol, 60g of polyacrylic acid and 30g of DBP to fully swell and dissolve until the glue solution is clear and transparent, and let it stand for 6h, then ball mill for 30min again (ball-to-material ratio 5:1) to obtain casting slurry. The casting slurry is pressure-fed into the defoaming tank, and vacuum stirring is used to remove air bubbles and part of the solvent. After defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000cps. The defoamed slurry was pressure-fed to the trough of the casting machine, a reasonable casting drying curve was set, the casting speed was 0.4m/min, and a casting green tape with a thickness of 0.45mm was obtained. Cut the cast green belt according to the required size of the product to obtain the cast green body. The tape-cast green body is debinding in the debinding furnace, and the debinding curve is reasonably formulated according to the thermogravimetric curve of the green body (slowly debinding in the range of 200-450°C), and the debinding sheet is obtained. Sinter the adhesive sheet at a high temperature of 1500°C for a holding time of 60 minutes to obtain it.

Comparative example 1

Add 50g of graphite powder (D50=0.1 micron) to 300g of ethanol, and then ball mill for 30min (ball-to-material ratio 5:1). Then add 1.5g of tin chloride and 0.4g of hydrazine to react for 1 hour under stirring, then add 1000g of alumina (D50 is 1 micron) and 1.5g of zirconia powder (D50=0.1 micron) and then ball mill for 30min again (ball-to-material ratio 5:1). Then add 300g of ethanol, 50g of PVB76 and 30g of DBP to fully swell and dissolve until the glue solution is clear and transparent, and let it stand for 6h, then ball mill for 30min again (ball-to-material ratio 5:1) to obtain casting slurry. The casting slurry is pressure-fed into the defoaming tank, and vacuum stirring is used to remove air bubbles and part of the solvent. After defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000cps. The defoamed slurry was pressure-fed to the trough of the casting machine, a reasonable casting drying curve was set, the casting speed was 0.4m/min, and a casting green tape with a thickness of 0.45mm was obtained. Cut the cast green belt according to the required size of the product to obtain the cast green body. The tape-cast green body is debinding in the debinding furnace, and the debinding curve is reasonably formulated according to the thermogravimetric curve of the green body (slowly debinding in the range of 200-450°C), and the debinding sheet is obtained. Sinter the adhesive sheet at a high temperature of 1500°C for a holding time of 60 minutes to obtain it.

Comparative example 2

Add 0.15g of tetramethylammonium hydroxide to 300g of ethanol, then add 50g of graphite powder (D50=0.1 micron), and then ball mill for 30min (ball-to-material ratio 5:1). Then add 1.5g of tin chloride and 0.4g of hydrazine to react for 1 hour under stirring, then add 1000g of alumina (D50 is 1 micron) and 1.5g of zirconia powder (D50=0.1 micron) and then ball mill for 30min again (ball-to-material ratio 5:1). Then add 300g of ethanol, 50g of PVB76 and 30g of DBP to fully swell and dissolve until the glue solution is clear and transparent, and let it stand for 6h, then ball mill for 30min again (ball-to-material ratio 5:1) to obtain casting slurry. The casting slurry is pressure-fed into the defoaming tank, and vacuum stirring is used to remove air bubbles and part of the solvent. After defoaming, the solid content of the slurry is 75-78%, and the viscosity of the slurry is 12000-15000cps. The defoamed slurry was pressure-fed to the trough of the casting machine, a reasonable casting drying curve was set, the casting speed was 0.4m/min, and a casting green tape with a thickness of 0.45mm was obtained. Cut the cast green belt according to the required size of the product to obtain the cast green body. The tape-cast green body is debinding in the debinding furnace, and the debinding curve is reasonably formulated according to the thermogravimetric curve of the green body (slowly debinding in the range of 200-450 ° C), and the debinding sheet is obtained. Sinter the adhesive sheet at a high temperature of 1500°C for a holding time of 60 minutes to obtain it.

It can be seen from Comparative Example 1 that when PEI is not added, the reducibility of hydrazine becomes worse, the coating of graphite powder by tin also becomes worse, and the performance of the prepared alumina ceramic flakes is not good.

It can be seen from Comparative Example 2 that when tetramethylammonium hydroxide is added, due to the poor coordination of tetramethylammonium hydroxide, the coating of tin on graphite powder is also poor, and the performance of the prepared alumina ceramic sheet is not good.

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 /℃。