TWI747694B - Method for fabricating zirconia ceramics by aqueous gel-casting technology - Google Patents

Abstract

The present invention relates to a method for fabricating zirconia ceramics by aqueous gel-casting technology. The method includes: mixing yttria-stabilized zirconia with a dispersant to form a first mixture; mixing an organic monomer and a plasticizer with the first mixture to form a second mixture; mixing a polymerization initiator with the second mixture to form a third mixture; mixing a polymerization inhibitor with the third mixture to form a zirconia suspension; pouring the zirconia suspension into a mold and drying the zirconia suspension at temperature ranging from 45℃ to 60℃ for 11 to 13 hours to obtain a zirconia green body; sintering the zirconia green body at temperature ranging from 1250℃ to 1300℃ to form a zirconia ceramic. With the aqueous gel-casting technology, the dispersibility of zirconia suspension is improved so that the compactness of zirconia ceramics is improved.

Description

Method for producing zirconia ceramics by water-based rubber casting

The invention relates to a method for producing zirconia ceramics by water-based rubber casting, in particular to mixing yttrium stabilized zirconia with dispersant, organic monomer, plasticizer, polymerization initiator and polymerization inhibitor to form zirconia slurry And by controlling the drying temperature and time of the zirconia slurry in the mold to obtain the zirconia green body, and control the sintering temperature and time of the zirconia green body to obtain the invention of high-density zirconia ceramics.

Zirconia ceramics have the advantages of high melting point and high chemical stability, so zirconia ceramics are a ceramic material with great industrial application potential. In addition, zirconia ceramics are also widely used on ceramic substrates due to their excellent mechanical properties and wear resistance due to their high mechanical strength, high toughness, and high hardness (Mohs hardness 8.5, second only to diamond and corundum).

In addition to the above advantages, zirconia ceramics also have the characteristics of scratch resistance and wear resistance, no signal shielding, excellent heat dissipation performance, and good appearance. Therefore, it has become a new type of mobile phone body material after plastic, metal, and glass. At present, the application of zirconia ceramics is mainly in the backplane and fingerprint recognition cover of mobile phones. The advantages of zirconia ceramics as a mobile phone backplane are as follows:

(1) Mechanical strength: A small amount of yttrium oxide is added to the widely used yttrium stabilized zirconia (Y-TZP), which causes residual compressive internal stress in the ceramic material. When the ceramic body is impacted, the additional tensile stress will offset the residual compressive internal stress, so that the toughness of the zirconia ceramic is improved and it is not easy to break.

(2) Signal penetration: In the future, mobile phones will move towards the 5G generation. 5G communications will use a spectrum above 3Ghz, and the millimeter wave wavelength is very short, and interference from metals is very severe. The antenna layout of the existing mobile phone terminal is full. If you want to deploy the 5G antenna with strict requirements, you need to change the existing metal casing material. Zirconia ceramics have "innate advantages", which can allow signals to easily pass through the casing and directly reach the internal antenna. Makes the signal strength transmitted or received is stronger.

(3) Heat conduction: When the internal parts of the mobile phone produce heat, the traditional use of glass or plastic mobile phone casing will make the user feel hot and uncomfortable. When using the zirconia ceramic casing, because of the better heat conduction, a better heat dissipation effect can be obtained, and it is warmer to the touch and skin-friendly.

(4) Hardness: The hardness of zirconia ceramics is second only to diamonds and corundum, which also means its ability to resist scratches is extremely strong. When zirconia ceramics are used as mobile phone shells, it can greatly reduce the generation of scratches and keep the appearance of the phone intact .

Conventional zirconia ceramics are made by a wet molding method, as shown in the Republic of China Invention Patent Publication No. I576094 "Method of Coloring Zirconia Green Body". The case disclosed that the zirconia process steps include: wet mixing a mixture to prepare a mixed slurry, and the mixture contains zirconia powder, alumina powder, mica powder, ferric nitrate powder and adhesive; dry mixed slurry , In order to obtain agglomerates, and the agglomerates are composed of zirconia powder, alumina powder, ferric nitrate powder and mica powder bonded to each other through an adhesive; the agglomerates are ground through a sieve to form a powder ; Press molding powder to form a block; and at 800 to 1100 ℃, calcining the block to obtain a zirconia green body.

Due to the formulation problem of the above-mentioned wet molding method, the viscosity of the slurry is high and it is difficult to disperse, resulting in the solid content of the slurry cannot be too high. In addition, most of the solvents used in the wet molding method are organic solvents with higher costs.

In view of this, the present invention proposes a method for producing zirconia ceramics by water-based gel casting, which includes: stirring and mixing an yttrium stabilized zirconia and a dispersant to form a first mixture. Combine one organic monomer and one The plasticizer is added to the first mixture and mixed to form a second mixture. A polymerization initiator is added to the second mixture and mixed to form a third mixture. A polymerization inhibitor is added to the third mixture and mixed to form a zirconia slurry. The zirconia slurry is poured into a mold and dried at a temperature between 45 degrees Celsius and 60 degrees Celsius, and the drying time is between 11 hours and 13 hours to obtain a green zirconia. Take out the zirconia green body from the mold, place the zirconia green body in a cold equalizing pressure forming machine, perform cold equalizing pressure forming on the zirconia green body, and heat the zirconia green body at 1250°C to 1250°C Sintering is performed at a temperature of between 1300 degrees, and the zirconia green body is formed into zirconia ceramics.

Further, the solid content of the yttrium stabilized zirconia of the zirconia slurry is between 35% and 45% by volume.

Furthermore, the particle size of the yttrium stabilized zirconia is between 80 and 100 nanometers.

Furthermore, the weight of the yttrium stabilized zirconia is between 150 and 200, and the weight of the dispersant is between 0.5 and 1. Preferably, the weight ratio of the yttrium stabilized zirconia to the dispersant is 1000:4.

Further, the weight of the organic monomer is between 10 and 15, the weight of the plasticizer is between 8 and 10, the weight of the polymerization initiator is between 5 and 8, and the weight of the polymerization inhibitor is between 5 and 8. The weight part of the agent is between 0.05 and 0.1.

Furthermore, the zirconia green body is sintered in two stages. The sintering temperature in the first stage is between 1250°C and 1300°C, and the holding time is between 1 minute and 30 minutes. The sintering temperature in the second stage is between 1 minute and 30 minutes. Between 1200 degrees Celsius and 1240 degrees Celsius, the temperature holding time is between 20 hours and 30 hours.

Further, the dispersant is polyammonium methacrylate (Dolapix CE64), the organic monomer is ethylene glycol diglycidyl ether (EGDGE), the plasticizer is glycerin (GLY), and the polymerization initiator is imine Dipropylamine (DPTA), the polymerization inhibitor is hydroquinone (HQ).

Furthermore, the relative density of the zirconia ceramic is between 99.0 and 99.5%

The above technical features have the following advantages:

1. The present invention lowers the viscosity of the zirconia slurry through water-based rubber casting and improves the dispersibility of yttrium-stabilized zirconia in the zirconia slurry. Therefore, the solid content of the zirconia slurry is high, which can be improved when the zirconia slurry is sintered The compactness of zirconia ceramics, and the cost of water-based chemicals is lower than that of organic solvents, which reduces the production cost.

2. The present invention further improves the compactness of the zirconia ceramics after sintering through the two-stage sintering of the zirconia green embryos, and the relative density of the zirconia ceramics can be increased to about 99.0% to 99.5% after testing.

3. By controlling the drying temperature and time of the zirconia slurry in the mold, the present invention can increase the strength of the zirconia green body and reduce the defects generated during drying when the zirconia slurry is solidified to generate a zirconia green body.

[The first figure] is a flow chart of the method of producing zirconia ceramics by water-based gel casting according to the present invention.

[Second Figure A] is the SEM image of the yttrium stabilized zirconia raw powder of the present invention.

[Second Figure B] is a graph showing the relationship between the grain size and the distribution rate of the yttrium stabilized zirconia raw powder of the present invention.

[Third Figure A] is the XRD pattern of the yttrium stabilized zirconia raw powder of the present invention.

[Third Figure B] is the XRD pattern of the zirconia ceramic of the present invention.

[Fourth graph] is a graph showing the relationship between the shear rate and viscosity of the zirconia slurry of the present invention with different contents of dispersant.

[Figure Fifth A] is the analysis diagram of the laser particle size of the zirconia slurry of the present invention with 0.2wt% dispersant added.

[Fifth Diagram B] is a diagram showing the particle size distribution of yttrium-stabilized zirconia in the zirconia slurry of the present invention.

[Figure 6] It is a spectrum of the influence of the polymerization inhibitor added to the zirconia slurry of the present invention on the polymerization reaction.

[The seventh graph] is a graph showing the viscosity curve of the zirconia slurry at different drying temperatures versus the gel time of the present invention.

[The eighth figure] is a graph showing the relationship between the pore size and the pore area of the zirconia green embryo of the present invention with and without cold equalization.

[Figure 9] is a thermal analysis curve of thermal expansion during the process of sintering zirconia green embryos into zirconia ceramics of the present invention.

[Figure 10A] is an SEM image of the fractured surface of the zirconia ceramic of the present invention.

[Figure 10B] is a graph showing the relationship between the crystal grain size and the distribution rate of the zirconia ceramic of the present invention.

[Figure 11A] is a graph showing the bending strength of the zirconia ceramic of the present invention.

[Figure 11B] is a graph of Vickers hardness data of the zirconia ceramics of the present invention.

[Figure 11C] is a graph of fracture toughness data of the zirconia ceramics of the present invention.

Based on the above technical features, the main effects of the method for producing zirconia ceramics by water-based gel casting of the present invention will be clearly presented in the following embodiments.

Please refer to the first figure. The present invention proposes a method for producing zirconia ceramics by water-based gel casting. The steps include: mixing an yttrium stabilized zirconia with a weight between 150 g and 200 g and a weight between 150 g and 200 g. A dispersant between 0.15 g and 0.5 g is stirred and mixed to form a first mixture. The shear rate of the stirring and mixing is 0.1 Hz. The viscosity of the first mixture is between 0.24 poise and 10 poise. The yttrium stabilized zirconia is mixed with The weight ratio of the dispersant is 1000:4.

The yttrium-stabilized zirconia of the present invention is a commercial yttrium-stabilized zirconia powder (3YTZ) prepared by a hydrothermal method, and the yttrium-stabilized zirconia powder contains 3 mol% yttrium oxide, and the particle size of the yttrium-stabilized zirconia ranges from 80 to 100 Among nanometers, although yttrium-stabilized zirconia powder is easier to make into nano- to sub-micron polycrystalline ceramics, due to the small particle size of the powder, the attractive force of Van der Waals is greater, which makes the yttrium-stabilized zirconia powder dispersed and The molding process is more difficult. It should be noted that because the van der Waals force between the particle diameters of yttrium-stabilized zirconia powder is relatively large, it is necessary to pay attention to each step of the production of zirconia slurry to successfully produce high density, less aggregates, and small pores. Zirconia slurry. In this embodiment, the dispersant is polyammonium methacrylate (Dolapix CE64), and through this dispersant, the Van der Waals force between the particle sizes of the yttrium stabilized zirconia powder can be reduced to achieve uniform dispersion without agglomeration.

Then, an organic monomer with a weight between 10 grams and 15 grams and a plasticizer with a weight between 8 grams and 10 grams are added to the first mixture and mixed to form a second mixture. In this embodiment, the organic monomer is ethylene glycol diglycidyl ether (EGDGE), and the plasticizer is glycerin (GLY). Among them, the organic monomer helps the subsequently formed zirconia green body to have a certain strength to facilitate subsequent mechanical processing, and the plasticizer helps to reduce the glass transition temperature of the polymer in the subsequently formed zirconia green body. Benefit from cold equalization to further increase the density of zirconia green body.

A polymerization initiator with a weight between 5 g and 8 g is added to the second mixture and mixed to form a third mixture. In this embodiment, the polymerization initiator is imine dipropylamine (DPTA). Wherein, the polymerization initiator can induce the epoxy group of the organic monomer to break and polymerize with the short chain of the organic monomer to form a network polymer to increase the strength.

A polymerization inhibitor with a weight between 50 mg and 100 mg is added to the third mixture and mixed to form a zirconia slurry, and the solid content of the zirconia slurry can reach between 35% and 45%. In this embodiment, the polymerization inhibitor is hydroquinone (HQ). Through the polymerization inhibitor, the polymerization reaction of the zirconia slurry is slowed down to facilitate subsequent shaping of the zirconia slurry.

The zirconia slurry is poured into a mold. The mold can be made according to the required shape and size. The mold with the zirconia slurry is placed in a drying space for drying, the drying temperature is between 45 degrees Celsius to 60 degrees Celsius, and the drying time is between 11 and 13 hours, so that the zirconia in the mold The slurry undergoes a solidification reaction to form a zirconia green body. After taking out the zirconia green body from the mold, the zirconia green body is placed in a cold equalizing pressure forming machine (CIP), and the zirconia green body is cold-equalized and pressed to make the zirconia green body compressed more densely , Reduce porosity and increase density.

The zirconia green body is subjected to two-stage sintering at high temperature. The sintering temperature of the first stage is between 1250°C and 1300°C, and the temperature holding time is between 1 minute and 30 minutes; the second stage sintering The junction temperature is between 1200 degrees Celsius and 1240 degrees Celsius, and the temperature holding time is between 20 hours and 30 hours, so that the zirconia green body is formed into zirconia ceramics. Among them, the heating curve of the first stage of sintering is at a heating rate of 1 degree Celsius per minute to 500 degrees Celsius and holding the temperature for two hours for degreasing, and then at a heating rate of 5 degrees Celsius per minute to 1300 degrees Celsius and then holding the temperature for 30 minutes Inside; the heating curve of the second stage sintering is at a heating rate of 5 degrees Celsius to 1240 degrees Celsius per minute for 24 hours. As a result, the relative density of the sintered zirconia ceramic can reach between 99.0 and 99.5%.

The material analysis of the yttrium-stabilized zirconia and the zirconia ceramics in the embodiment of the present invention: please refer to the second A and second B diagrams, the yttrium-stabilized zirconia is placed in a scanning electron microscope (SEM), the yttrium The image of stabilized zirconia is shown in the second picture A; as shown in the second picture B, the powder particle size cumulative distribution diagram is calculated and calculated through the second picture A. The average particle size (d50) of the zirconia slurry is about 94 Nano.

Please refer to Figure 3A which shows the yttrium-stabilized zirconia map of the yttrium-stabilized zirconia by placing the yttrium-stabilized zirconia in an X-ray diffraction (XRD). More monoclinic phase. By heating the yttrium-stabilized zirconia to a temperature higher than the phase transition temperature and cooling to room temperature, the monoclinic phase of the yttrium-stabilized zirconia is converted into a tetragonal phase and remains. The two-stage heated zirconia ceramics are placed in X-ray diffraction (XRD). It can be seen that after the two-stage high-temperature sintering and cooled to room temperature, the zirconia ceramics have a large amount of metastable tetragonal phases remaining, especially not all of them Do they all exist as tetragonal crystal phases or some monoclinic crystal phases, and these few monoclinic crystal phases indicate that their relative tetragonal crystal phases are relatively unstable and tend to transform into monoclinic crystal phases at any time. When subjected to crack tensile stress, The tetragonal crystal phase will expand in volume due to the transformation of the stress-induced phase into the monoclinic crystal phase and produce a compressive stress that cancels out the tensile stress of the crack, thereby preventing the extension of the crack and increasing the anti-drop ability of the ceramic body.

In the embodiment of the present invention, the viscosity and dispersibility analysis of adding different contents of dispersant to the zirconia slurry with the same solid content: Please refer to the fourth figure, when the solid content of the zirconia slurry is 45vol% and the dispersant added is 0.15wt%, the viscosity exceeds 10 poise (Pa.s) at a shear rate of 0.1 Hz (1/s) ), the measured viscosity is too high, which means that the dispersant is insufficiently added. When the added amount of the dispersant is increased to 0.2 to 0.3 wt%, the viscosity decreases significantly. However, when the added amount of the dispersant is increased to 0.5wt%, too much dispersant will increase the viscosity. Therefore, the optimal addition amount of the dispersant to the zirconia slurry is about 0.2 wt%, and its viscosity is 0.24 poise (Pa.s) when the shear rate is 0.1 Hz (1/s).

Please refer to Figure 5A and Figure 5B, the solid content of the zirconia slurry is 45vol1%, 0.2wt% of the dispersant is added to the laser particle size analysis, and the zirconia is measured through the laser particle size analysis results The particle size of the slurry is about 165 nanometers, which is not much different from the size of the original powder, and there is no agglomeration. It can be seen that the yttrium-stabilized zirconia of the zirconia slurry can be uniformly dispersed through the dispersant without obvious powder agglomeration.

Please refer to the sixth figure. When the polymerization inhibitor is mixed with the organic monomer of the zirconia slurry, even if the dispersant is contained in the zirconia slurry, no significant polymerization reaction will occur. The polymerizer can indeed prevent the dispersant from accelerating the polymerization of the organic monomer. However, by prolonging the monitoring mixing time and continuously observing the polymerization inhibition effect of the polymerization inhibitor, the hydroxyl peak produced by the polymerization reaction of the organic monomer and the polymerization initiator was not found. From this, it is known that adding the polymerization inhibitor to the zirconia slurry can indeed increase the residence time of the polymerization reaction, thereby increasing the stability of the zirconia slurry and the working time of the injection molding.

In the embodiment of the present invention, the drying temperature is controlled to observe the curing reaction of the zirconia slurry and the density analysis of the zirconia green body with or without cold equalization forming: please refer to the seventh figure, if the zirconia slurry is placed at room temperature If the viscosity of the zirconia slurry does not increase significantly after long-term measurement, it means that the molecular weight of the organic monomer of the zirconia slurry has not increased, and the polymerization reaction has hardly occurred, which is not suitable for practical applications because the zirconia slurry The curing reaction time of the slurry at room temperature is too long. Therefore, in order to improve the curing reaction of the present invention, the zirconia slurry is heated to 45 degrees Celsius to 60 degrees Celsius to clearly find that the viscosity of the zirconia slurry has increased significantly, indicating that the oxidation The zirconium slurry is undergoing a curing reaction. The curing reaction of the zirconia slurry at 60 degrees Celsius is more severe than that at 45 degrees Celsius, and the curing reaction time of the zirconia slurry is shortened to form the zirconia green body.

Please refer to the eighth figure. The zirconia green body is directly heated and then compressed by a cold equalizing press (CIP). It can be found that the zirconia green body after cold equalization is more dense , Make the pores smaller and increase the density, which is conducive to subsequent heating to make the zirconia ceramic more dense.

The microstructure and relative density analysis of the zirconia green body sintered into the zirconia ceramics in the embodiment of the present invention: please refer to the figure ninth, the thermal dilatometer is performed during the sintering of the zirconia green body into the zirconia ceramics Analysis (DIL) to obtain the relative density of the zirconia green body at different temperatures. The zirconia green body is sintered in two stages. The sintering temperature in the first stage is between 1250°C and 1300°C, and the temperature holding time is between 1 minute and 30 minutes; the first stage sintering can make the zirconia The densification of the green body can reach a relative density of 90%; the second stage of sintering temperature is between 1200°C and 1240°C, and the holding time is between 20 hours and 30 hours to suppress grain growth and continue Densification is performed to make the formed zirconia ceramic densify to a relative density of 99.5%.

Please refer to Figure 10A. The fractured section image of the zirconia ceramics taken with a scanning electron microscope (SEM) shows that the relative density of the zirconia ceramics reaches 99%. It can also be seen from the figure that the zirconia ceramics have a relative density of 99%. The ceramic has been almost completely densified, and the holes have been eliminated. Please refer to Figure 10B. It can be seen that the crystal grains of the zirconia ceramic are about 195 nm, and it can be seen that the zirconia ceramic is densified to a relative density of more than 99.5%.

Analysis of the mechanical properties of the zirconia ceramic in the embodiment of the present invention: please refer to Figure 11A, the zirconia ceramic is calculated with three-point bending strength to calculate the bending strength, and then the average value is obtained through statistical analysis of multiple sets of data It is 770.9MPa and the standard deviation is 209.65.

Please refer to Figure 11B to calculate the Vickers hardness of this zirconia ceramic by Vickers indentation. After statistical analysis of multiple sets of data, the average value is 15.2 GPa and the standard deviation is 0.29.

Please refer to Figure 11C, use the indentation method to calculate the KIC value of fracture toughness of the zirconia ceramic. Calculate the indentation shape and crack length obtained by the Vickers hardness machine and statistically analyze multiple sets of data to get an average value of 7.8MPa*m ^1/2 and a standard deviation of 1.63.

Based on the description of the above-mentioned embodiments, when one can fully understand the operation and use of the present invention and the effects of the present invention, the above-mentioned embodiments are only the preferred embodiments of the present invention, and the implementation of the present invention cannot be limited by this. The scope, that is, simple equivalent changes and modifications made according to the scope of the patent application of the present invention and the content of the description of the invention, are all within the scope of the present invention.

Claims (7)

A method for producing zirconia ceramics by water-based gel casting, comprising: stirring and mixing an yttrium stabilized zirconia and a dispersant to form a first mixture; adding an organic monomer and a plasticizer to the first mixture and mixing to form a first mixture Two mixtures; adding a polymerization initiator to the second mixture and mixing into a third mixture; adding a polymerization inhibitor to the third mixture and mixing into a zirconia slurry; pour the zirconia slurry into a mold , And dry at a temperature between 45 degrees Celsius and 60 degrees Celsius, and the drying time is between 11 hours and 13 hours to obtain a zirconia green body; take out the zirconia green body from the mold, The zirconia green body is placed in a cold equalizing pressure forming machine, the zirconia green body is cold-equalized and pressed, and the zirconia green body is sintered at a temperature between 1250 degrees Celsius and 1300 degrees Celsius to make the zirconia green body The zirconia green body forms zirconia ceramics; wherein the yttrium stabilized zirconia solid content of the zirconia slurry is between 35% and 45% by volume, and the weight of the organic monomer is between 10 and 15 The weight part of the plasticizer is between 8 and 10, the weight part of the polymerization initiator is between 5 and 8, and the weight part of the polymerization inhibitor is between 0.05 and 0.1. The method for producing zirconia ceramics by water-based gel casting as described in claim 1, wherein the particle size of the yttrium-stabilized zirconia is between 80 and 100 nanometers. The method for producing zirconia ceramics by water-based gel casting as described in claim 1, wherein the weight of the yttrium stabilized zirconia is between 150 and 200, and the weight of the dispersant is between 0.5 and 1. . The method for producing zirconia ceramics by water-based gel casting as described in claim 3, wherein the weight ratio of the yttrium stabilized zirconia to the dispersant is 1000:4. The method for producing zirconia ceramics by water-based rubber casting as described in claim 1, further, the zirconia green body is sintered in two stages, and the sintering temperature in the first stage is between 1250°C and 1300°C, The holding time is between 1 minute and 30 minutes; the second stage sintering temperature is between 1200°C and 1240°C, and the holding time is between 20 hours and 30 hours. The method for producing zirconia ceramics by water-based gel casting as described in claim 1, wherein the dispersant is polyammonium methacrylate (Dolapix CE64), and the organic monomer is ethylene glycol diglycidyl ether (EGDGE) , The plasticizer is glycerin (GLY), the polymerization initiator is imine dipropylamine (DPTA), and the polymerization inhibitor is hydroquinone (HQ). The method for producing zirconia ceramics by water-based gel casting as described in claim 1, wherein the relative density of the zirconia ceramics is between 99.0 and 99.5%.

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