KR102540727B1 - Colored Alumina Liquid Phase Sintered Body Contained Cobalt Oxide And Manufacturing Method Thereof - Google Patents

Abstract

The present invention is mainly used as a colorant, but similar to the sintering aid added for liquid phase sintering, it acts as an impurity to change the mechanism of liquid phase sintering. Therefore, by using the manufacturing method of an alumina sintered body using the liquid phase sintering method of the present invention, even though cobalt oxide is added, a high quality alumina sintered body having improved density and hardness can be manufactured compared to a general alumina sintered body in which cobalt oxide is not added. there is

Description

Colored Alumina Liquid Phase Sintered Body Contained Cobalt Oxide And Manufacturing Method Thereof

The present invention relates to a colored alumina liquid phase sintered body containing cobalt oxide and a method for producing the same, and to a method for producing an alumina sintered body having excellent quality due to the addition of cobalt oxide as a colorant and improved density and hardness by a liquid phase sintering method.

Alumina is a typical oxide-based ceramic and is used in various fields due to its excellent physical and chemical properties. Alumina has been widely used as a structural ceramic, but it is weak against fracture compared to other metals or polymers due to its inherent brittleness, and its mechanical properties vary greatly depending on microstructures such as pores, aggregates, and overgrown particles.

In order to obtain an alumina sintered body having excellent mechanical properties, it is basically necessary to prepare a sintered body having a dense microstructure and high density. Destruction starts from defects such as pores, impurities, and coarse particles, and since stress is concentrated on the defects and destruction occurs, it is necessary to remove these defects by adjusting the sintering process in order to obtain excellent mechanical properties.

As a relatively simple and economical alumina sintering method, there is a method of adjusting the particle shape of the alumina sintered body or enhancing densification by adding oxides such as SiO ₂ , MgO, and CaO. Among them, liquid phase sintering using the liquid phase generated by additives has a sintering mechanism established by WD Kingery. It goes through the sintering mechanism of the coalescence stage, and most of the sintering phenomenon accompanied by shrinkage occurs in the rearrangement stage of the solid particles. This liquid phase sintering is a method capable of producing an alumina sintered body having a high-density and dense microstructure even at a relatively low temperature because it can promote material diffusion and accelerate the optimal filling of solid particles by the liquid phase. In addition, since the sintering temperature is low, it has an economical advantage over other sintering methods.

The liquid phase generated during liquid phase sintering must have excellent wettability with the solid particles, and the liquid phase can be evenly distributed among the solid particles only when the solubility of the solid particles in the liquid phase is high. In the case of alumina for commercial use, 92% alumina is prepared and used by adding about 8% of a liquid sintering aid, and various colorants are additionally added to express the color of alumina. Usually, one or two or more colorants are mixed to express color. Since the oxides added to these colorants also play the role of an anhydride that creates a liquid phase, they have a great influence on the liquid phase sintering mechanism, which deteriorates the mechanical properties of the alumina sintered body. leads to

Therefore, if the mechanical properties of the alumina sintered body are improved through the optimization of the addition amount of the oxide additionally added during the liquid phase sintering of the alumina and the subsequent heat treatment conditions, it is expected that various types of alumina products that meet the consumer's taste can be produced.

The patents and references mentioned herein are incorporated herein by reference to the same extent as if each document were individually and expressly specified by reference.

H. J. Lim, D. H. Cho, M. K. Kim, S. M. Han, M. Iwasa, “The Evaluation of Mechanical Properties for Alumina Ceramics”, J. Kor. Ceram. Soc. 33 (1996) 339. W. J. Clegg, “Controlling Cracks in Ceramics”, Am. Assoc. Adv. Sci. 286 (1999) 1097. C. K. Moon, B. A. Kim, “Cyclic Crack Healing Effect of Al2O3 Ceramics”, J. OceanEng. Technol.27(2)(2013)69. Y. I. Cho, S. G. Chung, S. Y. Cho, S. J. Kim, ”Effect of Starting for MgO on the Mechanical Properties of Alumina Ceramic”, J. Kor. Ceram. Soc. 39 (2002) 51. H. Y. Kim, J. A. Lee, J. J. Kim, “Effect of MgO Addition on Densification and Microstructural Development during Liquid-Phase Sintering of Alumina-Anorthite System”, J. Kor. Ceram. Soc. 36 (1999) 1243. I. G. Song, T. S. Kim, K. M. Kang, J. S. Kim, “Influence of MgO Additive and Sintering Temperature on Mechanical Strength for Alumina Ceramic Anchor”, J. Kor. Inst. Met. Mater. 52 (2013) 181. I. G. Song, J. S. Kang, “Enhancement of the mechanical Properties of Alumina Ceramic by a Granulation process and Y2O3additive”, J.Kor.Inst.Met.Mater.53(2014)262. W. D. Kingery, “Densification during Sintering in the Presence of a Liquid Phase. I. Theory”, J. Appl. Phys. 30(3) (1959) 301. H. Y. Kim, J. A. Lee, J. J. Kim, “Effect of particle size of Alumina on Densification Behaviors of Alumina-Talc System during Liquid-Phase Sintering”, J. Kor. Ceram. Soc., 35 (1998) 1308. W. Huang, M. Hillert, X. Wang, “Thermodynamic Assessment of the CaO-MgO-SiO System”, Metall. Mater. Trans. A, 26 (1995) 2293.

The present invention establishes the optimal addition amount of cobalt oxide used as a colorant and the optimum heat treatment conditions accordingly in the method of manufacturing an alumina sintered body by the liquid phase sintering method, thereby manufacturing an alumina sintered body of excellent quality with high density and improved hardness. Its purpose is to provide a method.

Other objects and technical features of the present invention are presented more specifically by the following detailed description, claims and drawings.

The present invention is a method for producing an alumina sintered body using a liquid phase sintering method, wherein an alumina mixture containing 90 to 94 wt% of alumina (Al ₂ O ₃ ) fine powder and 6 to 10 wt% of a sintering aid is prepared, and 100 parts by weight of the alumina mixture A first step of preparing an alumina mixed powder by adding 9 to 13 parts by weight of cobalt oxide (Co ₂ O ₃ ,); A second step of adding distilled water to the alumina mixture powder, wet-mixing it using an alumina ball, and drying it; A third step of sieving the dried alumina mixed powder to a 200 mesh and then uniaxially pressing to produce an alumina mixed powder molded body; and a fourth step of preparing an alumina sintered body by heat-treating the alumina mixed powder molded body at 1320 to 1390° C. for 30 minutes to 2 hours.

The alumina sintered body has a density of 3.6 to 3.9 g / cm ³ , a shrinkage rate from the alumina mixed powder molded body of 40 to 42.5%, and a hardness of 12 to 13 GPa, and the alumina sintered body is characterized by aluminum oxide (Al ₂ O as a crystal phase) ₃ ), aluminum cobalt oxide (Al ₂ CoO ₄ ), and anorthite.

The present invention is mainly used as a colorant, but similar to the sintering aid added for liquid phase sintering, it acts as an impurity to change the mechanism of liquid phase sintering. Therefore, by using the manufacturing method of an alumina sintered body using the liquid phase sintering method of the present invention, even though cobalt oxide is added, a high quality alumina sintered body having improved density and hardness can be manufactured compared to a general alumina sintered body in which cobalt oxide is not added. there is

1 shows the microstructure of the alumina (AES-11C) of the present invention.
2 shows the microstructure of the alumina sintered body according to the amount of cobalt oxide added according to the present invention.
Figure 3 shows the results of measuring the density (▲) and shrinkage (■) of the alumina sintered body of the present invention.
Figure 4 shows the change in the microstructure of the sintered body according to the sintering temperature of Example 4 of the present invention.
Figure 5 shows the results of measuring the density (▲) and shrinkage (■) of the alumina sintered bodies of Examples 7 to 12 of the present invention.
Figure 6 shows the measured hardness of the alumina sintered body according to the addition amount of cobalt oxide and the sintering temperature of the present invention. Panel (a) shows the measured hardness of alumina sintered bodies prepared by sintering the alumina mixtures of Examples 1 to 6 at 1400° C., and panel (b) shows the measured hardness of alumina sintered bodies of Examples 7 to 12.
7 shows the results of X-ray diffraction analysis on the alumina sintered bodies of Examples 1 and 4 of the present invention. The red line (a) shows the analysis result for the alumina sintered body of Example 1, and the black line (b) shows the analysis result for the alumina sintered body of Example 4.

When cobalt oxide (Co ₂ O ₃ ), which is mainly used as a colorant, is added to alumina, there are many differences in the mechanism of effect on liquid phase sintering depending on the amount added. In the present invention, when cobalt oxide is added as a colorant together with liquid sintering aids SiO ₂ , CaO, and MgO, the liquid phase sintering mechanism according to the amount added is analyzed to provide a method for producing the most dense alumina sintered body.

The present invention is a method for producing an alumina sintered body using a liquid phase sintering method, wherein an alumina mixture containing 90 to 94 wt% of alumina (Al ₂ O ₃ ) fine powder and 6 to 10 wt% of a sintering aid is prepared, and 100 parts by weight of the alumina mixture A first step of preparing an alumina mixed powder by adding 9 to 13 parts by weight of cobalt oxide (Co ₂ O ₃ ,); A second step of adding distilled water to the alumina mixture powder, wet-mixing it using an alumina ball, and drying it; A third step of sieving the dried alumina mixed powder to a 200 mesh and then uniaxially pressing to produce an alumina mixed powder molded body; and a fourth step of preparing an alumina sintered body by heat-treating the alumina mixed powder molded body at 1320 to 1390° C. for 30 minutes to 2 hours.

The liquid-phase sintering involves a small amount of liquid phase during sintering, and is distinguished from solid-phase sintering in which the liquid phase does not exist at the sintering temperature. The liquid phase exists at the beginning of sintering, but as sintering progresses There is a characteristic that sintering is performed in a state in which the liquid phase disappears and only the solid phase exists.

The alumina of the present invention has a purity of 99% or more and an average particle size of 0.1 to 0.6 μm, preferably an average particle size of 0.4 μm and an irregular particle shape. In particular, the irregularly shaped alumina particles form irregular aggregation and irregular pores in preparation for granular alumina particles, in which it is difficult to change the shape of pores by particle rearrangement due to local densification between solid particles at a temperature before the liquid phase is formed. Therefore, there is an advantage in that a more dense sintered body can be manufactured by smoothing the flow of the liquid phase and facilitating particle rearrangement during liquid phase sintering. Therefore, by using the production method of the present invention, high-quality commercial alumina having high density can be produced even though it contains cobalt oxide.

The cobalt oxide is a pigment and at the same time acts as an impurity that determines the characteristics of liquid phase sintering together with the sintering aid. When the amount of cobalt oxide added is obtained by heat-treating the alumina mixed powder at 1320 to 1390 ° C. for 30 minutes to 2 hours through a number of examples to obtain an alumina sintered body, the density of the sintered body is 3.6 to 3.9 g / cm ³ and the alumina It is optimized so that the shrinkage rate from the mixed powder molding is 40 to 42.5% and the hardness is 12 to 13 GPa. Therefore, when the cobalt oxide is used in an amount of less than 9 parts by weight or more than 13 parts by weight, the characteristics of the alumina sintered body as described above may not be expressed.

The alumina mixture powder is prepared by preparing an alumina mixture containing 90 to 94 wt% of alumina (Al ₂ O ₃ ) fine powder and 6 to 10 wt% of a sintering aid, and cobalt oxide (Co ₂ O ₃ ,) based on 100 parts by weight of the alumina mixture. It is prepared by adding 9 to 13 parts by weight, but preferably, the alumina mixed powder is prepared by preparing an alumina mixture containing 92 wt% of alumina (Al ₂ O ₃ ) fine powder and 8 wt% of a sintering aid, and oxidizing 100 parts by weight of the alumina mixture. Cobalt (Co ₂ O ₃ ,) can be prepared by adding 11 parts by weight.

The prepared alumina mixed powder is wet-mixed by adding distilled water and then dried. The wet mixing may be performed for 12 hours using an alumina ball, and the wet-mixed alumina mixture may be completely dried at a temperature of 100° C. for 24 hours.

The dried alumina mixed powder is sieved with a 200 mesh to remove aggregates formed in the drying process, and then molded under uniaxial pressure to prepare an alumina mixed powder molded body. The alumina mixed powder molded body may be manufactured by uniaxial pressing in a mold by holding the pressure of 5 to 15 MPa for 1 minute or more.

The prepared alumina mixed powder molded body is heat treated at 1320 to 1390 ° C. for 30 minutes to 2 hours to prepare an alumina sintered body. The heat treatment may be performed for 30 minutes to 2 hours after raising the temperature to 1320 to 1390 ° C at a heating rate of 3 ° C / min in an air atmosphere, and preferably to 1350 ° C at a heating rate of 3 ° C / min in an air atmosphere. After that, heat treatment for 1 hour. If the heat treatment conditions are out of the range, the density, shrinkage, and hardness of the alumina sintered body sintered through the heat treatment may deviate from the ranges suggested above.

The method for producing an alumina sintered body using the liquid phase sintering method of the present invention has a density of 3.6 to 3.9 g/cm ³ through liquid phase sintering of alumina having a purity of 92 to 99% while containing a certain amount of cobalt oxide as a colorant (pigment). It can be manufactured into an alumina sintered body having a shrinkage rate of 40 to 42.5% and a hardness of 12 to 13 GPa from the alumina mixed powder molded body.

The alumina sintered body containing cobalt oxide of the present invention is subjected to liquid phase sintering under the same conditions, but has improved density and hardness compared to the density (3.47g/cm ³ ) and hardness (11.3GPa) of an alumina sintered body not containing cobalt oxide. It has features that show value. It is believed that the reason is that the alumina sintered body containing cobalt oxide of the present invention contains specific aluminum cobalt oxide (Al ₂ CoO ₄ ) together with aluminum oxide (Al ₂ O ₃ ) and anorthite as crystal phases. .

According to an embodiment of the present invention, in the case of a general commercial alumina sintered body that does not contain cobalt oxide, the aluminum cobalt oxide (Al ₂ CoO ₄ ) does not exist, and Mg is combined with aluminum oxide (Al ₂ O ₃ ) and anorthite. -Al spinel is identified as a crystalline phase. On the other hand, in the alumina sintered body of the present invention, aluminum cobalt oxide (Al ₂ CoO ₄ ) is confirmed as a crystal phase, not Mg-Al spinel, which means that the alumina liquid-phase sintered body containing cobalt oxide of the present invention has the same aluminum 92% as the general commercial 92% alumina sintered body. It is determined as one of the causes of improved density and hardness despite the fact that it has a % composition and additionally contains cobalt oxide, which is a colorant.

Therefore, by using the manufacturing method of the present invention, in manufacturing a commercial 92% aluminum sintered body, it is possible to manufacture a high-quality aluminum liquid phase sintered body having improved density and hardness despite having a specific color including cobalt oxide as a colorant. judged

In the following, the present invention will be described in detail through examples.

Example

1. Experiment method

1) Manufacture of alumina sintered body

The alumina used in the present invention was Sumitomo Chemical's AES-11C. The alumina has an average particle size of 0.4 μm and is characterized by having an irregular polygonal shape. 1 shows the microstructure of the alumina (AES-11C) micropowder of the present invention. As a sintering aid for liquid phase sintering of alumina, silicon oxide (SiO ₂ , Daejung, 97%), calcium oxide (CaO, Junsei, 98%), and magnesium oxide (MgO, Junsei, 98%) are mixed with SiO ₂ :CaO:MgO=2:1:1 was prepared by mixing in a weight ratio. An alumina mixture was prepared by mixing the alumina fine powder and the sintering aid to be 92wt% and 8wt%, respectively.

An alumina mixture powder was prepared by further adding cobalt oxide as a coloring agent to the alumina mixture. The alumina mixed powder was prepared by adding 0 to 18 parts by weight of cobalt oxide (Co ₂ O ₃ , Umicore, 95%) based on 100 parts by weight of the prepared alumina mixture.

Table 1 below shows the composition of the alumina mixture powder containing alumina, a sintering aid, and cobalt oxide.

alumina sintering aid cobalt oxide note Example 1 92wt% 8wt% 0 parts by weight Cobalt oxide is added based on 100 parts by weight of the alumina-sintering aid mixture Example 2 82wt% 8wt% 3 parts by weight Example 3 92wt% 8wt% 7 parts by weight Example 4 92wt% 8wt% 11 parts by weight Example 5 92wt% 8wt% 15 parts by weight Example 6 92wt% 8wt% 18 parts by weight

An alumina mixture wet-mixed for 12 hours using distilled water as a solvent and an alumina ball having a diameter of 3 mm was completely dried in a dryer at a temperature of 100° C. for 24 hours. The dried alumina mixed powder was sieved through a 200 mesh.

The dried alumina mixture powder was uniaxially pressed while maintaining a pressure of 10 MPa for 1 minute using a circular mold having a diameter of 24 mm for molding. The alumina mixed powder molded body was heat-treated at a heating rate of 3°C/min in an air atmosphere in the temperature range of 1200°C to 1450°C, maintained at a high temperature for 1 hour, and then cooled in a furnace to prepare an alumina sintered body.

2) Characteristic analysis of alumina sintered body

The surface and fracture surface microstructure changes according to the addition amount of cobalt oxide and the sintering temperature of the liquid-phase sintered alumina sintered body were confirmed using a field emission scanning electron microscope (FE-SEM, JSM-7100F, JEOL, Japan).

Shrinkage and density of the alumina sintered body were measured and calculated by a dimension measurement method.

The hardness of the alumina sintered body was polished using SiC sandpaper of #160 to #2000, and then measured 5 times in different parts of the test piece using a micro Vickers hardness tester (ZHμ-A, INDENTEC, UK) with an indentation load of 1kgf. and expressed as an average.

The crystal phase change behavior of the alumina sintered body according to the addition of cobalt oxide was analyzed using an X-ray diffractometer (XRD, SmartLab, Rigaku, Japan) at a scan speed of 4 °/min using the Cu-Kα characteristic wavelength.

2. Experiment results and discussion

1) Microstructure change of alumina sintered body according to the amount of cobalt oxide added

2 shows the microstructure of the alumina sintered body according to the amount of cobalt oxide added according to the present invention. It is expected that the amount of liquid phase produced will increase by the addition of cobalt oxide, which is slightly lower than the sintering temperature of a general commercial 92% alumina sintered body (alumina sintered body prepared using alumina mixed powder without cobalt oxide (Example 1)). Sintered at 1400 °C for 1 hour.

As a result of the experiment, pores of various sizes were observed on the fracture surface of the alumina sintered body. The alumina sintered body prepared using the alumina mixture (Example 4) to which 11 parts by weight of cobalt oxide was added had a densified microstructure with relatively few pores. has been observed In the present invention, densification between particles was induced through liquid phase sintering to reduce pores in the alumina sintered body, but commercial circular granular alumina powder, which is advantageous for homogeneous density of the molded body during molding, was not used. Irregular pores exist, and it is judged that this has had some effect on the rearrangement between particles, which is accompanied by the highest shrinkage rate among the liquid phase sintering mechanisms. In addition, these results are related to previous studies by H. Y. Kim et al., which reported that it is difficult to change the shape of pores by rearrangement of particles due to local densification between solid particles at the temperature before the liquid phase is formed during liquid phase sintering of fine particles. It seems there is

The reason for the increase in pores again in the alumina sintered body prepared using the alumina mixed powder to which 15 parts by weight or more of cobalt oxide was added (Examples 5 and 6) is that the excessive liquid phase caused by the addition of cobalt oxide rather promotes the rearrangement process of the particles. It is judged as a result of not being able to smoothly.

2) Changes in density and shrinkage of alumina sintered body according to the amount of cobalt oxide added

Figure 3 shows the results of measuring the density (▲) and shrinkage (■) of the alumina sintered body of the present invention. The density of the sintered body showed the lowest value of 3.48 g / cm ³ in the alumina sintered body prepared using the alumina mixed powder (Example 1) without adding cobalt oxide, and the alumina mixed powder added with 11 parts by weight of cobalt oxide (Example 1). 4) showed the highest density of 3.68 g/cm ³ of the alumina sintered body. In the case of the alumina sintered body prepared using the alumina mixed powder (Example 5) to which 15 parts by weight of cobalt oxide was added, the sintered density was rather decreased. These results are judged to be consistent with the microstructure analysis results of the alumina sintered body of FIG. 2 to some extent. When the addition amount of cobalt oxide was increased to more than 11 parts by weight, the density decreased and the shrinkage rate also rapidly decreased, which means that the rearrangement of the particles did not occur smoothly during liquid phase sintering. That is, it is judged that the rearrangement process of alumina particles by capillary force is not sufficiently expressed because the addition of excessive cobalt oxide reacts with CaO-MgO-SiO ₂ to lower the liquid phase formation temperature and lower the viscosity of the liquid phase. This is because of the alumina sintered body prepared using the alumina mixed powder (Example 5) to which 15 parts by weight of cobalt oxide in FIG. 3 was added and the alumina mixed powder to which 18 parts by weight of cobalt oxide was added (Example 6). It may have been the cause of the occurrence of numerous pores with irregular shapes seen in the microstructure of an alumina sintered body, and when the amount of cobalt oxide added is less than 11 parts by weight, the sintering shrinkage expressed in commercial 92% alumina is similar or slightly increased. It is thought that the effect of the rearrangement of the particles according to the increase in the liquid phase was affected to some extent. In FIG. 2, the particle sizes of the alumina sintered bodies were all observed to be similar, so it was judged that all grain growth phenomena due to dissolution re-precipitation or coalescence after particle rearrangement were similarly expressed.

3) Density and shrinkage rate change of alumina sintered body according to sintering temperature

In order to examine the effect of sintering temperature on the rearrangement of solid particles during liquid phase sintering and the effect on the microstructure of the sintered body, an alumina mixed powder (Example 4) to which 11 parts by weight of cobalt oxide was added, which showed the best densification at 1400 ° C, was selected. and sintered in the range of 1200 to 1450 ° C. Figure 4 shows the change in the microstructure of the sintered body according to the sintering temperature of Example 4 of the present invention, and Table 2 shows the composition and sintering temperature of the alumina mixture powder.

alumina sintering aid cobalt oxide sintering temperature note Example 7 92wt% 8wt% 11 parts by weight 1200℃ Cobalt oxide is added based on 100 parts by weight of the alumina-sintering aid mixture Example 8 92wt% 8wt% 11 parts by weight 1250℃ Example 9 92wt% 8wt% 11 parts by weight 1300℃ Example 10 92wt% 8wt% 11 parts by weight 1350℃ Example 11 92wt% 8wt% 11 parts by weight 1400℃ Example 12 92wt% 8wt% 11 parts by weight 1450℃

In the case of Example 7 sintered at 1200 ° C., grain growth hardly occurred, and clear grain growth was observed from 1300 ° C., and densification was also increased at the same time. According to previous research results by W. Huang et al., the temperature at which the liquid phase is generated in the CaO-MgO-SiO ₂ three-component system is reported to be around 1330 °C, and when sintering alumina with cobalt oxide added, Al ₂ O ₃ and Co ₂ O It is judged that the liquid phase formation temperature will be lower than this due to the influence of ₃ , and considering this, at 1300 ℃, the rearrangement of solid particles due to the liquid phase formation occurs to some extent, and at the same time, the dissolution re-precipitation phenomenon is also accompanied, resulting in grain growth and It is judged that densification was expressed simultaneously. At the subsequent temperature, it can be seen that rearrangement of particles almost stops and coalescence of solid particles proceeds, resulting in continuous grain growth.

Figure 5 shows the results of measuring the density (▲) and shrinkage (■) of the alumina sintered bodies of Examples 7 to 12 of the present invention. In the case of the alumina sintered body of Example 7 sintered at 1200 ° C, it showed a shrinkage of 18.34% and a density of 2.78 g / cm ³ , which is formed at a lower temperature than commercial 92% alumina by the addition of cobalt oxide means The density continuously increased as the temperature increased. In the case of the alumina sintered body of Example 9 sintered at 1300 ° C, the sintered density of alumina increased with a shrinkage of 38.59%, and in the case of the alumina sintered body of Example 10 sintered at 1350 ° C, the density was the highest with 3.86 g / cm ³ showed numbers. In the case of sintering at a temperature of 1400℃ or higher, it can be seen that the density and shrinkage rate decrease slowly at the same time. On the other hand, it can be seen as a phenomenon caused by coalescence of pores. In particular, at 1450 ° C., the viscosity of the liquid phase is reduced by high-temperature heat treatment, and the presence of the liquid phase is clearly observed on the surface of the sintered body.

4) Hardness change of alumina sintered body according to sintering temperature and cobalt oxide content

Figure 6 shows the measured hardness of the alumina sintered body according to the addition amount of cobalt oxide and the sintering temperature of the present invention. Panel (a) shows the measured hardness of alumina sintered bodies prepared by sintering the alumina mixtures of Examples 1 to 6 at 1400° C., and panel (b) shows the measured hardness of alumina sintered bodies of Examples 7 to 12.

According to the results of panel (a) of FIG. 6, the alumina sintered body prepared using the alumina mixed powder (Example 6) to which 18 parts by weight of cobalt oxide was added showed the lowest hardness value of 11.23 GPa, which is a combination of pores. It is judged that this is the result of the existence of a glass phase due to an excessive amount of liquid. In the case of the alumina sintered body prepared using the alumina mixed powder (Example 4) to which 11 parts by weight of cobalt oxide was added, it showed the highest density and the highest hardness value of 12.32 GPa.

In the results of panel (b) of FIG. 6, the low hardness value of less than 10 GPa at a sintering temperature of 1250 ° C or lower is the result of insufficient inter-particle bonding due to coalescence of solid particles although shrinkage was achieved. Grain growth and densification increase with temperature rise, and the hardness also increases accordingly, but the hardness also decreases at high temperatures due to the formation of the glass phase by the low-viscosity liquid phase.

4) Analysis of the crystal phase of the alumina sintered body according to the sintering temperature and the content of cobalt oxide

7 shows the results of X-ray diffraction analysis on the alumina sintered bodies of Examples 1 and 4 of the present invention. The red line (a) shows the analysis result for the alumina sintered body of Example 1, and the black line (b) shows the analysis result for the alumina sintered body of Example 4. Crystal phases other than Al ₂ O ₃ having a corundum crystal phase are crystals generated during cooling after liquid phase sintering, and it can be seen that Al ₂ CoO ₄ was generated instead of Mg-Al spinel when 11 parts by weight of cobalt oxide was added. In addition, it was confirmed that an amorphous pattern was finely observed at a low angle when cobalt was added, and this is judged to be a result of an increase in the liquid phase by the addition of cobalt oxide.

3. Conclusion

The present invention is summarized as follows.

1. During commercial 92% alumina sintering, the liquid phase formation temperature was lowered due to the addition of cobalt oxide, and sintering was performed even at a ^relatively low sintering temperature of 1200 ° C. It was possible to manufacture a dense sintered body having a hardness of GPa.

2. When an excessive amount of cobalt oxide was added or at a sintering temperature of 1400 ° C or higher, the viscosity of the liquid phase was lowered, resulting in the formation of a glass phase and a decrease in density and hardness.

3. In liquid phase sintering of 92% alumina, the rearrangement of solid particles that is most accompanied by shrinkage is 11 parts by weight of cobalt oxide Upon addition, it was actively expressed between 1200 and 1300 ° C, and grain growth due to coalescence of solid particles was observed at the subsequent temperature.

4. The hardness value of the alumina sintered body to which cobalt oxide was added increased with the increase in grain growth and sintered density, and began to decrease from the time when the glass phase was observed in the microstructure.

Specific examples described in this specification are meant to represent preferred embodiments or examples of the present invention, and the scope of the present invention is not limited thereby. It will be apparent to those skilled in the art that variations and other uses of the present invention do not depart from the scope of the invention described in the claims.

Claims (5)

In the method for producing an alumina sintered body using a liquid phase sintering method,
An alumina mixture containing 90 to 94 wt% of alumina (Al ₂ O ₃ ) fine powder and 6 to 10 wt% of a sintering agent is prepared, and 9 to 13 wt% of cobalt oxide (Co ₂ O ₃ ) is added to 100 parts by weight of the alumina mixture. A first step of preparing an alumina mixture powder by adding it in parts;
A second step of adding distilled water to the alumina mixture powder, wet-mixing it using an alumina ball, and drying it;
A third step of sieving the dried alumina mixed powder to a 200 mesh and then uniaxially pressing to produce an alumina mixed powder molded body; and
A fourth step of preparing an alumina sintered body by heat-treating the alumina mixed powder molded body at 1320 to 1390 ° C. for 30 minutes to 2 hours;
The alumina sintered body has a density of 3.6 to 3.9g / cm ³ and a shrinkage rate from the alumina mixed powder molded body is 40 to 42.5%.
delete The method of claim 1, wherein the alumina sintered body has a hardness of 12 to 13 GPa.
The alumina sintered body according to claim 1, wherein the alumina sintered body includes aluminum oxide (Al ₂ O ₃ ), aluminum cobalt oxide (Al ₂ CoO ₄ ) and anorthite as crystal phases. Manufacturing method of.
The method of claim 1, wherein the sintering aid comprises silicon oxide (SiO ₂ ), calcium oxide (CaO), and magnesium oxide (MgO).

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