GRAIN-GRADE ZIRCONIA TOUGHENED ALUMINA CERAMIC SUBSTRATE AND METHOD FOR PREPARING THE SAME

Abstract

A grain-grade zirconia toughened alumina ceramic substrate and a method for preparing the same. The ceramic substrate is prepared from alumina power (main phase) and zirconia powder (secondary phase) in a binary azeotrope of anhydrous ethanol and butanone in the presence of magnesia-alumina spinel powder (as sintering aid), phosphate ester (as dispersant), polyvinyl butyral (as binder) and dibutyl phthalate (as plasticizer). In a mixture of the alumina power and the zirconia powder, a volume percentage of the alumina power is 82.44-96.7%, and a volume percentage of the zirconia powder is 3.30-17.56%. The magnesia-alumina spinel powder is 0.1-4.0% by weight of the mixture of the alumina power and the zirconia powder. A particle size ratio of the alumina powder to the zirconia powder is 2.415-4.444.

Claims

1. A grain-grade zirconia toughened alumina ceramic substrate, wherein the grain-grade zirconia toughened alumina ceramic substrate is prepared from a main phase material and a secondary phase material in a solvent in the presence of a sintering aid, a dispersant, a binder and a plasticizer; the main phase material is an alumina power; the secondary phase material is a zirconia powder; the sintering aid is a magnesia-alumina spinel powder; the solvent is a binary azeotrope of anhydrous ethanol and butanone; the dispersant is a phosphate ester; the binder is polyvinyl butyral; the plasticizer is dibutyl phthalate; the alumina power accounts for 82.44-96.7% of a total volume of the alumina power and the zirconia powder, and the zirconia powder accounts for 3.30-17.56% of the total volume of the alumina power and the zirconia powder; a weight of the magnesia-alumina spinel powder is 0.1-4.0% of a total weight of the alumina power and the zirconia powder; the alumina powder, the zirconia powder and the magnesia-aluminum spinel powder constitute an inorganic powder; the binary azeotrope of anhydrous ethanol and butanone is 20-35% by weight of the inorganic powder; the phosphate ester is 0.5-2.0% by weight of the inorganic powder; the polyvinyl butyral is 5-15% by weight of the inorganic powder; the dibutyl phthalate is 2-6% by weight of the inorganic powder; and in a microstructure of the grain-grade zirconia toughened alumina ceramic substrate, a grain size ratio of the alumina power to the zirconia powder is 2.415-4.444.

2. The grain-grade zirconia toughened alumina ceramic substrate of claim 1, wherein the zirconia powder accounts for 8.57% of the total volume of the alumina power and the zirconia powder; and the alumina powder accounts for 91.43% of the total volume of the alumina power and the zirconia powder.

3. The grain-grade zirconia toughened alumina ceramic substrate of claim 1, wherein the zirconia powder is a 3-mol %-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) powder; and the alumina powder is an α-alumina powder.

4. The grain-grade zirconia toughened alumina ceramic substrate of claim 1, wherein in the binary azeotrope of anhydrous ethanol and butanone, a weight ratio of the anhydrous ethanol to the butanone is 1:(1-1.2).

5. A method for preparing the grain-grade zirconia toughened alumina ceramic substrate of claim 1, comprising: (1) adding the alumina powder, the zirconia powder, the magnesia-aluminum spinel powder, the solvent and the dispersant into a ball mill followed by a primary ball milling for 24-48 h; and adding the binder and the plasticizer into the ball mill followed by a secondary ball milling for 48 h to obtain a mixture; and (2) subjecting the mixture to vacuum degassing to obtain a casting slurry with a viscosity of 20000-24000 mPa.Math.s; subjecting the casting slurry to tape casting on a casting machine to obtain a green sheet; cutting the green sheet by a punching die followed by pressureless sintering in a furnace at 1600-1630° C. for 3-6 h to obtain the grain-grade zirconia toughened alumina ceramic substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 partially depicts octahedral interstices in a cubic crystal structure of a zirconia toughened alumina (ZTA) ceramic according to an embodiment of the disclosure;

[0035] FIG. 2 partially depicts tetrahedral interstices in the cubic crystal structure of the ZTA ceramic according to an embodiment of the disclosure;

[0036] FIG. 3 is a scanning electron microscope (SEM) backscattered-electron image of a surface of a ZTA ceramic substrate with 8% (v/v) of ZrO.sub.2;

[0037] FIG. 4 is a SEM backscattered-electron image of a surface of a ZTA ceramic substrate with 13% (v/v) of ZrO.sub.2;

[0038] FIG. 5 is a SEM backscattered-electron image of a casting green body of a ZTA ceramic with 8.57% (v/v) of ZrO.sub.2;

[0039] FIG. 6 is a SEM backscattered-electron image of a surface of a ZTA ceramic substrate with 8.57% (v/v) of ZrO.sub.2;

[0040] FIG. 7 shows power-on test results of a ZTA ceramic heating sheet in accordance with an embodiment of the present disclosure after working for 60 seconds;

[0041] FIG. 8 shows power-on test results of the ZTA ceramic heating sheet in accordance with an embodiment of the present disclosure after working for 60 seconds and being cooled; and

[0042] FIG. 9 depicts a change of a surface temperature of a ZTA ceramic heating sheet with 8.57% (v/v) of ZrO.sub.2 in accordance with an embodiment of the present disclosure over time.

DETAILED DESCRIPTION OF EMBODIMENTS

[0043] The present disclosure will be further described in detail below with reference to the embodiments, but these embodiments are not intended to limit the scope of this disclosure.

Example 1

[0044] A zirconia-doped alumina ceramic substrate was prepared herein, where an alumina powder was used as a main phase material; a zirconia powder was used as a secondary phase material; a magnesia-alumina spinel powder was used as a sintering aid; a binary azeotrope of anhydrous ethanol and butanone was used as a solvent; a phosphate ester was used as a dispersant; polyvinyl butyral was used as a binder; and dibutyl phthalate was used as a plasticizer.

[0045] Specifically, a 3-mol %-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) powder (particle size: 0.25 μm), an α-alumina powder (particle size: 0.7 μm) and the magnesia-alumina spinel powder together constituted an inorganic powder, where a volume ratio of the 3Y-TZP powder to the α-alumina powder was 3.30:96.7, and the magnesia-alumina spinel powder was 0.1% of a total weight of the 3Y-TZP powder and the α-alumina powder. The inorganic power, the binary azeotrope and the phosphate ester were added into a ball mill, and subjected to primary ball milling for 24 h, where the binary azeotrope was 20% by weight of the inorganic powder, and the phosphate ester was 0.5% by weight of the inorganic powder. Then the polyvinyl butyral and the dibutyl phthalate were added into the ball mill, and the mixture in the ball mill was subjected to secondary ball milling for 48 h, where the polyvinyl butyral was 5% by weight of the inorganic powder, and the dibutyl phthalate was 2% by weight of the inorganic powder. The mixture was discharged from the ball mill, and then subjected to vacuum degassing to obtain a casting slurry with a viscosity of 20,000 mPa.Math.s. The casting slurry was subjected to tape casting on a casting machine to obtain a casting green body, which was sintered at 1600° C. for 3 h to obtain the ceramic substrate with a size of 138×190×0.32 mm.

Example 2

[0046] A zirconia-doped alumina ceramic substrate was prepared herein, where an alumina powder was used as a main phase material; a zirconia powder was used as a secondary phase material; a magnesia-alumina spinel powder was used as a sintering aid; a binary azeotrope of anhydrous ethanol and butanone was used as a solvent; a phosphate ester was used as a dispersant; polyvinyl butyral was used as a binder; and dibutyl phthalate was used as a plasticizer.

[0047] Specifically, a 3-mol %-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) powder (particle size: 0.25 μm), an α-alumina powder (particle size: 0.7 μm) and the magnesia-alumina spinel powder together constituted an inorganic powder, where a volume ratio of the 3Y-TZP powder to the α-alumina powder was 8:92, and the magnesia-alumina spinel powder was 2% of a total weight of the 3Y-TZP powder and the α-alumina powder. The inorganic power, the binary azeotrope and the phosphate ester were added into a ball mill, and subjected to primary ball milling for 32 h, where the binary azeotrope was 25% by weight of the inorganic powder, and the phosphate ester was 1.0% by weight of the inorganic powder. Then the polyvinyl butyral and the dibutyl phthalate were added into the ball mill, and the mixture was subjected to secondary ball milling for 48 h, where the polyvinyl butyral was 8% by weight of the inorganic powder, and the dibutyl phthalate was 4% by weight of the inorganic powder. The mixture was discharged from the ball mill, and then subjected to vacuum degassing to obtain a casting slurry with a viscosity of 22,000 mPa.Math.s. The casting slurry was subjected to tape casting on a casting machine to obtain a casting green body, which was sintered at 1610° C. for 4 h to obtain the ceramic substrate with a size of 138×190×0.32 mm.

Example 3

[0048] A zirconia-doped alumina ceramic substrate was prepared herein, where an alumina powder was used as a main phase material; a zirconia powder was used as a secondary phase material; a magnesia-alumina spinel powder was used as a sintering aid; a binary azeotrope of anhydrous ethanol and butanone was used as a solvent; a phosphate ester was used as a dispersant; polyvinyl butyral was used as a binder; and dibutyl phthalate was used as a plasticizer.

[0049] Specifically, a 3-mol %-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) powder (particle size: 0.25 μm), an α-alumina powder (particle size: 0.7 μm) and the magnesia-alumina spinel powder together constituted an inorganic powder, where a volume ratio of the 3Y-TZP powder to the α-alumina powder was 13:87, and the magnesia-alumina spinel powder was 3% of a total weight of the 3Y-TZP powder and the α-alumina powder. The inorganic power, the binary azeotrope and the phosphate ester were added into a ball mill, and subjected to primary ball milling for 40 h, where the binary azeotrope was 30% by weight of the inorganic powder, and the phosphate ester was 1.5% by weight of the inorganic powder. Then the polyvinyl butyral and the dibutyl phthalate were added into the ball mill, and the mixture was subjected to secondary ball milling for 48 h, where the polyvinyl butyral was 12% by weight of the inorganic powder, and the dibutyl phthalate was 5% by weight of the inorganic powder. The mixture was discharged from the ball mill, and then subjected to vacuum degassing to obtain a casting slurry with a viscosity of 24,000 mPa.Math.s. The casting slurry was subjected to tape casting on a casting machine to obtain a casting green body, which was sintered at 1630° C. for 5 h to obtain the ceramic substrate with a size of 138×190×0.32 mm.

Example 4

[0050] A zirconia-doped alumina ceramic substrate was prepared herein, where an alumina powder was used as a main phase material; a zirconia powder was used as a secondary phase material; a magnesia-alumina spinel powder was used as a sintering aid; a binary azeotrope of anhydrous ethanol and butanone was used as a solvent; a phosphate ester was used as a dispersant; polyvinyl butyral was used as a binder; and dibutyl phthalate was used as a plasticizer.

[0051] Specifically, a 3-mol %-yttria-stabilized tetragonal zirconia polycrystalline (3Y-TZP) powder (particle size: 0.25 μm), an α-alumina powder (particle size: 2.0 μm) and the magnesia-alumina spinel powder together constituted an inorganic powder, where a volume ratio of the 3Y-TZP powder to the α-alumina powder was 17.56:82.44, and the magnesia-alumina spinel powder was 4% of a total weight of the 3Y-TZP powder and the α-alumina powder. The inorganic power, the binary azeotrope and the phosphate ester were added into a ball mill, and subjected to primary ball milling for 48 h, where the binary azeotrope was 35% by weight of the inorganic powder, and the phosphate ester was 2.0% by weight of the inorganic powder. Then the polyvinyl butyral and the dibutyl phthalate were added into the ball mill, and the mixture was subjected to secondary ball milling for 48 h, where the polyvinyl butyral was 15% by weight of the inorganic powder, and the dibutyl phthalate was 6% by weight of the inorganic powder. The mixture was discharged from the ball mill, and then subjected to vacuum degassing to obtain a casting slurry with a viscosity of 24,000 mPa.Math.s. The casting slurry was subjected to tape casting on a casting machine to obtain a casting green body, which was sintered at 16130° C. for 6 h to obtain the ceramic substrate with a size of 138×190×0.32 mm.

[0052] Mechanical and electrical properties of the ZTA ceramic substrates with a thickness of 0.32 mm prepared in Examples 1-4 were measured, and the results were shown in Table 1.

[0053] Table 1 Properties of zirconia-doped alumina ceramic substrates

TABLE-US-00001 Relative Bending 25° C. Volume V.sub.z/ % density/ % strength/MPa resistivity/(Ω .Math. cm) 3.3 99.32 545 3.7 × 10.sup.15 8 99.56 754 2.3 × 10.sup.15 13 99.39 802 1.2 × 10.sup.15 17.56 99.68 852 4.2 × 10.sup.14

[0054] Table 1 shows that when the volume percentage of ZrO.sub.2 is between 3.3-17.56%, the room-temperature volume resistivities of the ZTA ceramics are all greater than 10.sup.14 Ω.Math.cm, which meets the requirements of thick-film integrated circuit ceramic substrates for the room-temperature volume resistivity. As the volume percentage of ZrO.sub.2 increases, the bending strength of the ZTA ceramic gradually increases from 545 MPa to 852 MPa, which meets the requirements of ZTA ceramic substrates for mechanical strength.

[0055] In the ZTA ceramic provided herein, the volume percentage of zirconia is 3.30-17.56%; the volume percentage of alumina is 82.44-96.7%; and a g particle size ratio of alumina grain to zirconia grain is 2.415-4.444. The above-mentioned volume ratios are selected according to FIGS. 1-2, where FIG. 1 partially depicts octahedral interstices in a cubic crystal structure, and FIG. 2 partially depicts tetrahedral interstices in a cubic crystal structure.

[0056] As shown in FIGS. 1-2, the stable ion arrangement corresponds to a state of the crystal structure with the lowest energy. Cubic close packing leads to a stable structure with the largest packing density, reaching 74 vol %. Each layer of balls is in cubic form, and the upper layer is placed in the gap of the lower layer to form a close-packed structure. Each ball has twelve closest balls. If each ball grows at a constant speed and fills the gap, each ball will grow into a dodecahedron. According to the face-centered cubic stacking diagram, there are four atoms, four octahedral interstices and eight tetrahedral interstices in each unit cell.

[0057] According to Pauling's first rule, the number of anions around the cation in the crystal structure is determined by the diameter ratio of the two types of ions. In the ZTA ceramic green body, it is assumed that both alumina particles and zirconia particles are spherical and arranged in cubic close packing. In a basic unit, there are four alumina particles with a diameter of D.sub.a; four zirconia particles are filled into the octahedral interstices with a diameter of D.sub.20, and another eight zirconia particles are filled into the tetrahedral interstices with a diameter of D.sub.zt.

[0058] According to the Pythagorean theorem, it is calculated that D.sub.zo/D.sub.a=0.414. In the same way, in the tetrahedral interstice surrounded by 4 spheres, the D.sub.zt/D.sub.a is calculated to be 0.225.

[0059] Ceramic powder has high surface free energy. Under the action of high temperature, the excess surface energy of the powder becomes the driving force for sintering, such that the powder is prone to grow into a polyhedral-crystal combination with the smallest surface energy. According to the principle of minimizing surface energy, in an ideal state, the microstructure of the ZTA ceramic after sintering should be similar to the Weaire-Phelan structure. According to the Weaire-Phelan structure, in a basic unit, there are two alumina grains and six zirconia grains. Assuming that the volume fraction of zirconia particles is V.sub.z, the volume fraction of zirconia grains in the ZTA ceramic is calculated according to formula (1):

[00001]$\begin{array}{cc}{V}_z=\frac{6\times \frac{\pi }{6}{D}_z^3}{6\times \frac{\pi }{6}{D}_z^3+2\times \frac{\pi }{6}{D}_a^3}.& \left(1\right)\end{array}$

[0060] Further, the formula (1) is simplified into formula (2):

[00002]$\begin{array}{cc}{V}_z=\frac{1}{1+\frac{1}{3}{\left(\frac{D_a}{D_z}\right)}^3}.& \left(2\right)\end{array}$

[0061] D.sub.zt/D.sub.a=0.225 (that is, D.sub.a/D.sub.zt=4.444) is substituted into the formula (2) to obtain V.sub.z=3.30%.

[0062] D.sub.zo/D.sub.n=a0.414 (that is, D.sub.a/D.sub.zo=2.415) is substituted into the formula (2) to obtain V.sub.z=17.56%.

[0063] In the ZTA ceramic, an optimal volume percentage of zirconia is 8.57%, and accordingly, the volume percentage of alumina is 91.43%; and a particle size ratio of the alumina grain to the zirconia grain is 2.415-4.444. In this case, the zirconia exhibits sufficient toughening effect on the alumina, such that ZTA has good mechanical performance; meanwhile, the zirconia grains are fully isolated by alumina grains, and thus the ZTA has good electrical insulation properties, especially at high temperature.

[0064] This phenomenon is explained as follows.

[0065] According to the cubic close packing, in a basic unit of the ZTA ceramic, there are four alumina particles with a diameter of D.sub.a; four zirconia particles are filled into the octahedral interstices with a diameter of D.sub.zo, and another eight zirconia particles are filled into the tetrahedral interstices with a diameter of D.sub.zt. In view of this, the volume fraction of the zirconia grains is calculated according to formula (3):

[00003]$\begin{array}{cc}{V}_z=\frac{4\times \frac{\pi }{6}{D}_{zo}^3+8\times \frac{\pi }{6}{D}_{zt}^3}{4\times \frac{\pi }{6}{D}_{zo}^3+8\times \frac{\pi }{6}{D}_{zt}^3+4\times \frac{\pi }{6}{D}_a^3}.& \left(3\right)\end{array}$

[0066] Further, the formula (3) is simplified into formula (4):

[00004]$\begin{array}{cc}{V}_z=\frac{1}{1+\frac{1}{{\left(\frac{D_{zo}}{D_a}\right)}^3+2\times {\left(\frac{D_{\mathrm{zt}}}{D_a}\right)}^3}}.& \left(4\right)\end{array}$

[0067] D.sub.zt/D.sub.a=0.225 and D.sub.zo/D.sub.a=0.414 are substituted into the formula (4) to obtain V.sub.z=8.57%.

[0068] In the microstructure of the ZTA ceramic substrate, the particle size ratio of alumina grain to zirconia grain is 2.415-4.444, where a particle size of the alumina grain is 1.5-2.8 and a particle size of the zirconia grain is 0.6-0.65 FIGS. 3-4 respectively show the scanning electron microscope (SEM) backscattered-electron images of surfaces of ZTA ceramic substrates with different contents of ZrO.sub.2, where FIG. 3 is a SEM backscattered-electron image of a surface of a ZTA ceramic substrate with 8% (v/v) of ZrO.sub.2, and FIG. 4 is a SEM backscattered-electron image of a surface of a ZTA ceramic substrate with 13% (v/v) ZrO.sub.2.

[0069] FIG. 5 is a SEM backscattered-electron image of a casting green body of a ZTA ceramic with 8.57% (v/v) of ZrO.sub.2. FIG. 6 is a SEM backscattered-electron image of a surface of a ZTA ceramic substrate with 8.57% (v/v) of ZrO.sub.2. It can be seen from FIG. 5 that an average particle size of the ZrO.sub.2 powder is 0.25 μm; and two types of Al.sub.2O.sub.3 powders are added, one with an average particle size of 0.7 μm and the other with an average particle size of 2.0 μm. FIG. 6 is the backscattered image of the ZTA ceramic substrate in which the ceramic powder in the green body is grown into crystals by sintering. The particle size of ZrO.sub.2 grain is 0.65 μm. There are also two sizes of Al.sub.2O.sub.3 grains, one with an average particle size of 1.55 μm, and the other with an average particle size of 2.85 μm. A diameter ratio of the ZrO.sub.2 grain to the Al.sub.2O.sub.3 grain is basically in line with a diameter ratio of the cubic-packed sphere to the tetrahedral interstice and the octahedral interstice.

Application Example

[0070] FIGS. 7-8 showed the power-on test results of the ZTA ceramic heating sheet. A platinum resistance paste was screen printed on the ZTA casting green body with 8.57% (v/v) of ZrO.sub.2, and then covered with a green body of the same size for laminating. The laminated product was subjected to warm isostatic press at 95° C., and then was sintered at 1600° C. to obtain a high-temperature co-fired ceramic heating element with a size of 19×4.7×0.38 mm; a heating section length of 10.5 mm; and an average resistance of 1.25Ω. When a 8V voltage was applied to the heating element, the power-on starting power was 51.2 W, which indicated that the specific volume power that the ZTA ceramic heating sheet can withstand during cold start was 1508 W/cm.sup.3, while the specific volume power that the ordinary alumina ceramic heating sheet can withstand during cold start was generally not more than 500 W/cm.sup.3. A bending strength of a ZTA ceramic heating sheet 2 was twice that of an ordinary alumina ceramic heating sheet, and during cold start, the specific volume power the ZTA ceramic heating sheet can withstand was three times the specific volume power that the ordinary alumina ceramic heating sheet can withstand. The ZTA heating test sheet was energized for 60 seconds, and the test results were shown in FIGS. 7-8. FIG. 7 illustrated power-on test results of a ZTA ceramic heating sheet 2 with 8.57% (v/v) of ZrO.sub.2 after heated for 60 seconds, where an area in a dashed box in FIG. 7 was red. FIG. 8 illustrated power-on test results of the ZTA ceramic heating sheet 2 with 8.57% (v/v) of ZrO.sub.2 after being heated for 60 seconds and cooled, where an area outside a heating wire 1 in FIG. 8 was yellow. FIG. 9 depicted a change of a surface temperature of a ZTA ceramic heating sheet with 8.57% (v/v) of ZrO.sub.2 over time.

[0071] After energized for 3 seconds, the temperature of the ZTA ceramic heating sheet 2 with 8.57% (v/v) of ZrO.sub.2 rose to 536° C., indicating that the ZTA ceramic heating sheet 2 had high power and fast heating speed. The temperature change curve with time was shown in FIG. 9. After being energized for 15 seconds, the ZTA ceramic heating sheet kept the surface temperature at about 792° C., and gaps between the heating wires 1 can be clearly observed (as shown in FIG. 7). As shown in FIG. 8, after being cooled, the ZTA ceramic heating sheet had no black spots appearing between the heating wires 1, indicating that the high-temperature volume resistivity of the ZTA ceramic heating sheet 2 with 8.57% (v/v) of ZrO.sub.2 met the requirements of ceramic substrates for insulation performance.