Alumina Composite Ceramic Composition and Method of Manufacturing the Same

Abstract

Provided is an alumina composite ceramic composition which has electrical insulation properties as well as better mechanical strength and thermal conductivity than a typical alumina-based material. Thus, the alumina composite ceramic composition is promising for a material of a substrate or an insulating package of an electronic device. The alumina composite ceramic composition of the present invention may include alumina (Al.sub.2O.sub.3), zirconia (ZrO.sub.2) or yttria-stabilized zirconia as a first additive, and graphene oxide and carbon nanotubes, as a second additive. In this case, in consideration of two aspects of sinterability and electrical resistivity characteristics of the alumina composite ceramic composition, the graphene oxide may be appropriately adjusted to be in the form of a graphene oxide phase and a reduced graphene phase which coexist in the alumina composite ceramic composition.

Claims

1. An alumina composite ceramic composition comprising: alumina (Al.sub.2O.sub.3); zirconia (ZrO.sub.2) or yttria-stabilized zirconia as a first additive; and graphene oxide and carbon nanotubes, as a second additive.

2. The alumina composite ceramic composition of claim 1, wherein an amount of the first additive is 30 wt % or less based on a weight of the alumina.

3. The alumina composite ceramic composition of claim 1, wherein an amount of the second additive is 2.0 wt % or less based on a total weight of the alumina and the first additive.

4. The alumina composite ceramic composition of claim 2, wherein the amount of the first additive is 10 wt % or more based on the weight of the alumina.

5. The alumina composite ceramic composition of claim 3, wherein the amount of the second additive is 0.5 wt % or more based on the total weight of the alumina and the first additive.

6. The alumina composite ceramic composition of claim 1, wherein the graphene oxide is in a form of a graphene oxide phase and a reduced graphene phase which coexist in the alumina composite ceramic composition.

7. The alumina composite ceramic composition of claim 1, wherein the yttria-stabilized zirconia has a composition including zirconia and 3 mol % of yttria.

8. A method of manufacturing an alumina composite ceramic composition, the method comprising: mixing alumina (Al.sub.2O.sub.3) and zirconia (ZrO.sub.2) or yttria-stabilized zirconia, as a first additive, to form a first mixture; adding graphene oxide and carbon nanotubes, as a second additive, to the first mixture and mixing to form a second mixture; and molding and sintering the second mixture.

9. The method of claim 8, wherein the sintering is performed at a temperature of 1,600 C. to 1,750 C.

10. The method of claim 9, wherein the sintering is performed for 4 hours or less.

11. The method of claim 9, wherein the sintering is performed in a nitrogen (N.sub.2) gas atmosphere or a mixed gas atmosphere of nitrogen (N.sub.2) and hydrogen (H.sub.2).

12. The method of claim 11, wherein an amount of the hydrogen in the mixed gas atmosphere of nitrogen (N.sub.2) and hydrogen (H.sub.2) is in a range of 0.5 wt % to 3.0 wt % based on a total weight of the mixed gas.

13. The method of claim 8, wherein the second mixture is heat-treated at a temperature of 350 C. to 400 C. before the molding and at least a portion of the graphene oxide is reduced.

14. The method of claim 13, wherein the heat treatment is performed in an air atmosphere or a N.sub.2 atmosphere.

15. The method of claim 13, wherein the heat treatment is performed for 1 hour or less.

16. The method of claim 11, wherein the atmosphere promotes reduction of the graphene oxide and adjusts a ratio of an amount of the graphene oxide reduced to an amount of the graphene oxide not reduced to obtain a predetermined range of resistivity of the alumina composite ceramic composition.

17. The method of claim 8, wherein the graphene oxide and the carbon nanotubes are respectively added to the first mixture in a form of an aqueous solution.

18. The method of claim 8, wherein the aqueous solutions are prepared by respectively dispersing 0.5 wt % to 1 wt % of the graphene oxide and 0.5 wt % to 1 wt % of the carbon nanotubes in water.

19. The method of claim 8, wherein the second additive comprises a mixture of the graphene oxide and the carbon nanotubes.

20. The method of claim 11, wherein the atmosphere is adjusted so that the graphene oxide is in a form of a graphene oxide phase and a reduced graphene phase which coexist in the sintered alumina composite ceramic composition.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which:

[0027] FIG. 1 is a flowchart schematically illustrating a method of manufacturing an alumina composite ceramic composition in accordance with an exemplary embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

[0028] Hereinafter, specific embodiments will be described in detail with reference to the accompanying drawings.

[0029] The present invention provides an alumina composite ceramic composition having electrical insulation properties as well as more improved mechanical strength and thermal conductivity than a typical alumina-based material.

[0030] A method of manufacturing the composite ceramic composition in accordance with an exemplary embodiment of the present invention is schematically illustrated in FIG. 1.

[0031] First, in the present invention, mechanical strength is increased by adding zirconia (ZrO.sub.2) or yttria-stabilized zirconia to alumina (Al.sub.2O.sub.3) as a basic composition. In the present invention, conventional yttria-stabilized zirconia (3YSZ), in which 3 mol % of Y.sub.2O.sub.3 is added to zirconia, may be used as the yttria-stabilized zirconia, but the present invention is not limited thereto.

[0032] The zirconia (ZrO.sub.2) or the yttria-stabilized zirconia (3YSZ) is mixed in an amount of 30 wt % or less, preferably 10 wt % to 30 wt %, based on a weight of the alumina (Al.sub.2O.sub.3) to form an alumina+zirconia mixed matrix.

[0033] However, in this case, although the mechanical strength increases as intended, thermal conductivity of the zirconia added is low at about 4 W/mK. Thus, thermal conductivity of the manufactured composite ceramic composition will be significantly reduced.

[0034] In consideration of this, in the present invention, the reduction of the thermal conductivity of the composite ceramic composition may be buffered and the mechanical strength may be further improved by adding graphene oxide (GO) and carbon nanotubes (CNT) to the alumina+zirconia mixed matrix.

[0035] That is, according to the addition of the GO and CNT, the mechanical strength of the composite ceramic composition may be increased due to excellent mechanical strengths of graphene (G) and the oxide GO themselves, crack detour function of a GO nanosheet, and intergranular clutch function by a transgranular insertion structure as well as matrix intergranular bridging function of CNT.

[0036] The GO and CNT are in the form in which an amount ratio (wt %) of GO/CNT is in a range of 0 to 1, wherein the GO and CNT may be added to the alumina+zirconia mixed matrix in a maximum amount of 2.0 wt %, preferably in an amount of 0.5 wt % to 2.0 wt %, based on a weight of the mixed matrix, According to an exemplary embodiment, the GO and CNT may be respectively provided as solutions, in which 0.5 wt % to 1 wt % of the GO and 0.5 wt % to 1 wt % of the CNT are respectively dispersed in pure water (deionized (DI) water), and mixed, and a mixed solution may then be added to alumina powder and mixed.

[0037] Also, in the present invention, the composite composition thus prepared may be sintered at a temperature of 1,600 C. to 1,750 C. for 4 hours or less, and may be molded by a conventional molding process, such as pressing, before the sintering. According to an exemplary embodiment, the sintering may be performed in a nitrogen (N.sub.2) gas atmosphere or a mixed gas atmosphere of nitrogen (N.sub.2) and hydrogen (H.sub.2), and an amount of the hydrogen may be in a range of about 0.5 wt % to about 3.0 wt % based on a total weight of the mixed gas.

[0038] In the present invention, the composite composition may be heat-treated at a temperature of 350 C. to 400 C. for at least 1 hour in an air or a N.sub.2 atmosphere as a pretreatment before the sintering process. Since the GO mixed in the zirconia or yttria-stabilized zirconia/alumina composite matrix is partially reduced and the density of the composite ceramic is increased by the pretreatment, porosity may be particularly reduced. As a comparative example, in a case in which the GO is mixed in the composite matrix and then sintered without the above-described pretreatment, it is observed that a large amount of pores is generated to significantly reduce the densification. Here, the presence of the reduction of the Go may be confirmed by conventional Raman spectroscopy.

[0039] However, in the present invention, since the G is electrically conductive whereas the GO is electrically insulating, it is desirable to maintain an appropriate ratio of these additives contained in the composite matrix in order to maintain predetermined insulating properties which are required depending on the use. Thus, it is desirable to control the atmosphere so that the GO is not completely reduced, but G and GO phases coexist by the pretreatment and the sintering to allow a sintered body to have an appropriate resistance value.

[0040] Hereinafter, exemplary embodiments of the present invention will be described in more detail. The following examples are merely provided to allow for a clearer understanding of the present invention, rather than to limit the scope thereof.

EXAMPLES

[0041] (A) Manufacture of Composite Composition Powder

[0042] First, as a matrix, alumina powder having a purity of 99% or more and an average particle diameter of 150 nm and 3 mol % yttria-doped zirconia powder (3YSZ) having an average particle diameter of 30 nm to 50 nm were mixed, wherein the 3YSZ powder was included in an maximum amount of 40 wt %, for example, 0 wt %, 10 wt %, 20 wt %, 30 wt %, and 40 wt %, based on a weight of the alumina powder.

[0043] As an additive for improving mechanical strength and thermal conductivity, graphene oxide (GO) and carbon nanotubes (CNT) were respectively added to the matrix in a maximum amount of 2.0 wt % based on a weight of the alumina+zirconia mixed matrix, Wherein the GO and the CNT were mixed in a weight ratio of 1:0, 1:3, 1:1, 3:1, and 0:1, among GO/CNT ratios of 0 to 1. In this case, the GO used in the present embodiment is flake-shaped nanopowder having a particle diameter of 0.5 m to 5 m, but the present invention is not limited thereto and bulk or acicular nanopowder may also be used. Also, the CNT used in the present embodiment has a diameter of 50 nm and a length of 20 m to 50 m, but the present invention is not limited to the above numerical range.

[0044] An amount of the alumia/zirconia was weighed at a predetermined ratio as described above, and the GO/CNT was also simultaneously added to a jar for ball milling. In this case, since the GO and the CNT are conventionally difficult to be handled in the form of powder, the GO and the CNT were respectively prepared as 0.5 wt % to 1 wt % aqueous solutions to be mixed with the alumia/zirconia, Wherein the viscosity of a slurry for bail milling was adjusted by separately adding ethanol. As ball milling conditions, zirconia balls having a diameter of 0.3 mm to 10 mm were used in a HDPE jar, a rotational speed of ball mill was 130 rpm, and the ball milling was performed for 6 hours. Thereafter, the slurry was put in a glass container and dried in an oven, and the dried slurry was then ground with a mortar.

[0045] (B) Pretreatment

[0046] The dried and ground powder was introduced into an alumina crucible and heat-treated at 400 C. for 1 hour in a N.sub.2 atmosphere to partially reduce the GO.

[0047] (C) Molding and Sintering

[0048] A 2 wt % PVA aqueous solution was sprayed and mixed with the pretreated alumina/zirconia (Al.sub.2O.sub.3/3YSZ)+carbon material (GO/CNT) mixed powder or the mixture was granulated and then molded at a pressure of 98 MPa. In this case, two types of molded samples were prepared in which the sample for measuring thermal conductivity was molded to have a diameter of 12.5 mm and a thickness of 1 mm to 2 mm, and the sample for measuring mechanical strength, i.e., 3-point flexural strength, was molded in the form of a bar with a size of 3440 mm.sup.3.

[0049] The molded samples were loaded on a zirconia setter in a furnace for adjustable atmospheres, first subjected to a binder removal process at 400 C. for 1 hour, heated to a sintering temperature of 1,600 C. to 1,750 C. at a heating rate of 5 C./minute and maintained for 4 hours, and cooled to room temperature at a cooling rate of 10 C./minute. In this case, a sintering atmosphere was a mixed gas of 2.85 wt % H.sub.2 and N.sub.2.

[0050] (D) Physical Property Measurement

[0051] Diameter, thickness, density, and specific heat of the composite ceramic composition samples after completion of the sintering were first measured in order to measure thermal conductivity. The corresponding samples were coated with carbon, thermal diffusivity was measured by a conventional laser flash method (equipment used: Netzsch LEA 447), and the thermal conductivity was obtained according to a calculation formula of thermal diffusivitydensityspecific heat [W/m.Math.K]. Also, mechanical strengths of the composite ceramic composition samples were measured by using a conventional 3-point flexural strength measurement method (equipment used: universal testing machine (UTM)).

[0052] Hereinafter, various properties of the composite ceramic compositions of the present invention thus obtained will be examined as follows:

[0053] First, the following Table 1 lists physical properties of alumina/3YSZ composite: ceramic compositions which were prepared on a trial basis before the manufacture of the compositions of the present invention. These test composition samples were manufactured by the above-described method, but were sintered at a sintering temperature of 1,600 C.,

TABLE-US-00001 TABLE 1 Physical Properties of alumina/3YSZ Composite Ceramic Compositions Composite Physical properties compositions (1,600 C.) (wt %) 3-point Secondary Sintered flexural Thermal Test Matrix phase density strength conductivity compositions Al.sub.2O.sub.3 3YSZ (g/cc) (MPa) (W/mK) 1 100 0 3.91 283 38.71 2 90 10 4.11 360 30.92 3 80 20 4.33 352 24.56 4 70 30 4.50 382 22.39 5 60 40 4.70 368 17.61

[0054] Referring to Table 1, when the amount of the 3 YSZ in the alumina/3YSZ composite compositions was in a range of 20 wt % to 30 wt %, density close to 4.54 g/cc, a theoretical density (% TD) of a typical zirconia-containing alumina composite, was obtained. In contrast, when the amount of the zirconia was greater than 30 wt %, it may be understood that the thermal conductivity of the composite was significantly reduced.

[0055] Accordingly, in the present invention which is intended to improve the sintered density, flexural strength, and thermal conductivity, it may be considered that an appropriate amount of the zirconia (i.e., herein, 3YSZ) was in a range of 10 wt % to 30 wt %.

[0056] The following Table 2 lists sintered densities according to each composition ratio of the [alumina/3YSZ]+[GO/CNT] composite ceramic composition samples according to the present invention, i.e., sintered density characteristics according to an amount of the GO/CNT mixture added to the alumina/3YSZ and a mixing ratio of the GO/CNT. These samples were also manufactured by the above-described method, and an amount ratio (wt %) of 3YSZ/alumina was 20/80.

TABLE-US-00002 TABLE 2 Sintered Density of [alumina/3YSZ] + [GO/CNT] Composite Ceramic Composition Composite compositions (wt %) Mixing ratio of Sintered density Composition Matrix Additive GO/CNT 1,650 C. 1,700 C. 1,750 C. samples 20YSZ/80Al.sub.2O.sub.3 GO/CNT (weight ratio) g/cc g/cc g/cc Comparative Example 100 0 4.40 Example 1 99.5 0.5 1:0 4.46 Example 2 3:1 4.41 Example 3 1:1 4.38 Example 4 1:3 4.39 Example 5 0:1 4.38 Example 6 99 1.0 1:0 4.36 4.32 4.38 Example 7 3:1 4.39 4.35 4.39 Example 8 1:1 4.37 4.35 4.40 Example 9 1:3 4.43 4.34 4.46 Example 10 0:1 4.34 4.27 4.38 Example 11 98 2.0 1:0 4.24 Example 12 3:1 4.35 Example 13 1:1 4.39 Example 14 1:3 4.36 Example 15 0:1 4.41

[0057] Referring to Table 2, sintered densities of 4.24 g/cc to 4.46 g/cc were obtained at almost all of the composition ratios of the compositions of the present invention when sintered in a temperature range of 1,650 C. to 1,750 C., and these corresponded to densities of 93.4% to 98.2% relative to the theoretical density. Thus, it may be understood that the compositions of the present invention have excellent sinterability.

[0058] Also, it was observed that there was no big difference in the sintered densities according to each sintering temperature in a temperature range of 1,650 C. to 1,750 C. Accordingly, in Tables 3 to 5 as well as Table 2, characteristics data at two sintering temperatures of 1,700 C. and 1,750 C. were provided only for the compositions having a mixing ratio of [alumina/3YSZ]:[GO/CNT] of 99:1 and, with respect to the other compositions, data only at a sintering temperature of 1,650 C. were provided.

[0059] The following Table 3 lists 3-point flexural strength characteristics according to each composition ratio of the [alumina/3YSZ]+[GO/CNT] composite ceramic composition samples according to the present invention. These samples were the same as the samples of Table 2.

TABLE-US-00003 TABLE 3 3-point Flexural Strength of [alumina/3YSZ] + [GO/CNT] Composite Ceramic Composition Composite compositions (wt %) Mixing ratio of 3-point flexural strength (MPa) Composition Matrix Additive GO/CNT Sintering temperature samples 20YSZ/80Al.sub.2O.sub.3 GO/CNT (weight ratio) 1,650 C. 1,700 C. 1,750 C. Comparative Example 100 0 308 Example 1 99.5 0.5 1:0 593 Example 2 3:1 722 Example 3 1:1 679 Example 4 1:3 629 Example 5 0:1 556 Example 6 99 1.0 1:0 286 533 531 Example 7 3:1 491 589 546 Example 8 1:1 561 604 584 Example 9 1:3 532 587 563 Example 10 0:1 649 668 622 Example 11 98 2.0 1:0 307 Example 12 3:1 344 Example 13 1:1 624 Example 14 1:3 581 Example 15 0:1 520

[0060] Referring to Table 3, it may be understood that 3-point flexural strengths of the compositions of the present examples were significantly increased according to the addition of the GO/CNT. That is, the composition of the comparative example, in which the GO/CNT was not added, had a 3-point flexural strength of 308 MPa, but the 3-point flexural strengths of the compositions of the present examples were increased to 722 MPa according to the addition of the GO/CNT and thus, an improvement of about 234% was obtained. A mechanism of improving the mechanical strength according to the addition of the GO/CNT was previously described.

[0061] The following Table 4 lists thermal conductivity characteristics according to each composition ratio of the [alumina/3YSZ]+[GO/CNT] composite ceramic composition samples according to the present invention. These samples were the same as the samples of Table 2.

TABLE-US-00004 TABLE 4 Thermal Conductivity of [alumina/3YSZ] + [GO/CNT] Composite Ceramic Composition Composite compositions Thermal conductivity (wt %) Mixing ratio of (W/m .Math. K) Composition Matrix Additive GO/CNT Sintering temperature samples 20YSZ/80Al.sub.2O.sub.3 GO/CNT (weight ratio) 1,650 C. 1,700 C. 1,750 C. Comparative Example 100 0 18.41 18.32 18.24 Example 1 99.5 0.5 1:0 19.39 Example 2 3:1 20.60 Example 3 1:1 20.83 Example 4 1:3 21.29 Example 5 0:1 19.61 Example 6 99 1.0 1:0 19.51 16.80 18.43 Example 7 3:1 21.67 18.87 18.97 Example 8 1:1 21.54 18.61 19.99 Example 9 1:3 23.10 18.87 21.15 Example 10 0:1 22.04 17.94 20.60 Example 11 98 2.0 1:0 20.19 Example 12 3:1 20.90 Example 13 1:1 20.23 Example 14 1:3 22.81 Example 15 0:1 20.54

[0062] Referring to Table 4, thermal conductivities of the present examples, in which the GO/CNT was added, were increased in comparison to the composition of the comparative example in which the GO/CNT was not added, and the thermal conductivities were in a range of about 19 W/m.Math.K to about 23 W/m.Math.K. It was considered that the thermal conductivities were due to the coexistence of the G and GO phases in partially oxidized graphene and the contributions from high thermal conductivity of the G phase among the materials and thermal conductivity of the CNT material. When the sintering temperature was excessively increased, the thermal conductivity was somewhat decreased.

[0063] The following Table 5 lists resistivity characteristics according to each composition ratio of the [alumina/3YSZ]+[GO/CNT] composite ceramic composition samples according to the present invention. These samples were the same as the samples of Table 2.

TABLE-US-00005 TABLE 5 Resistivity value of [alumina/3YSZ] + [GO/CNT] Composite Ceramic Composition Composite compositions (wt %) Mixing ratio of Resistivity ( .Math. cm) Composition Matrix Additive GO/CNT Sintering temperature samples 20YSZ/80Al.sub.2O.sub.3 GO/CNT (weight ratio) 1,650 C. 1,700 C. 1,750 C. Comparative Example 100 0 3.4E11 Example 1 99.5 0.5 1:0 2.8E11 Example 2 3:1 3.8E11 Example 3 1:1 4.2E11 Example 4 1:3 4.2E11 Example 5 0:1 1.6E11 Example 6 99 1.0 1:0 1.0E11 3.1E11 5.4E9 Example 7 3:1 9.2E10 2.2E11 9.4E8 Example 8 1:1 4.7E10 1.7E11 3.9E8 Example 9 1:3 2.2E10 2.3E11 3.5E8 Example 10 0:1 1.6E10 6.1E11 2.7E8 Example 11 98 2.0 1:0 8.1E10 Example 12 3:1 5.7E10 Example 13 1:1 3.5E10 Example 14 1:3 1.7E10 Example 15 0:1 1.4E10

[0064] Referring to Table 5, resistivity values of the present examples, in which the GO/CNT was added, were slightly decreased in comparison to the composition of the comparative example in which the GO/CNT was not added, and, since the reduction of the insulating GO was promoted by the effect of a reducing atmosphere as the sintering temperature increased, the resistivity values were reduced.

[0065] As described above, since the G is electrically conductive but the GO is electrically insulating, it is desirable to maintain appropriate ratios of these additives contained in the composite matrix in order to maintain predetermined insulating properties which are required depending on the use. Thus, according to the present invention, it is desirable to control the atmosphere so that the GO is not completely reduced, but the G and GO phases coexist by the pretreatment and the sintering to allow the sintered body to have an appropriate resistance value.

[0066] Referring to FIG. 5, since a resistivity of at least 10.sup.10 .Math.cm or more was obtained when the sintering temperature was in a range of 1,650 C. to 1,700 C., the [alumina/3YSZ]+[GO/CNT] composite ceramic compositions may be promisingly applicable for a material of a substrate or an insulating package of an electronic device.

[0067] As described above, the [alumina/3YSZ]+[GO/CNT] composite ceramic compositions according to the present invention had excellent mechanical strengths, good thermal conductivities, and electrical insulating properties.

[0068] An alumina composite ceramic composition according to the present invention has electrical insulation properties as well as better mechanical strength and thermal conductivity than a typical alumina-based material. The alumina composite ceramic composition may be promisingly applicable for a material of a substrate or an insulating package of an electronic device.

[0069] It is obvious to those skilled in the art that there may be some variations in various characteristics of the above-described exemplary embodiments of the present invention within a typical margin of error, according to powder characteristics, such as average particle diameter, distribution, and specific surface area of the composition powder, purity of raw materials, amount of impurity added, and sintering conditions.

[0070] Although the alumina composite ceramic composition and the method of manufacturing the same have been described with reference to the specific embodiments, they are not limited thereto. Therefore, it will be readily understood by those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the present invention defined by the appended claims.