KR20220102821A - Colored Alumina Liquid Phase Sintered Body Contained Cobalt Oxide And Manufacturing Method Thereof - Google Patents

Abstract

The present invention relates to the optimal addition amount of cobalt oxide which functions as an impurity to change the mechanism of liquid phase sintering, similar to a sintering aid used mainly as a coloring agent but added for the liquid phase sintering; and optimizes a thermal treatment condition thereby. Accordingly, by using a manufacturing method of an alumina sintered body using a liquid phase sintering method of the present invention, there is an advantage of manufacturing a high quality alumina sintered body having improved density and hardness compared to a general alumina sintered body without cobalt oxide added, even though the cobalt oxide is added.

Description

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

The present invention relates to a colored alumina liquid sintered compact containing cobalt oxide and a method for manufacturing the same, and to a method for producing an alumina sintered compact having excellent quality by adding cobalt oxide as a colorant and improving density and hardness by a liquid phase sintering method.

Alumina is a representative 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 has the inherent brittleness of ceramics, so it is weaker to fracture than other metals or polymers.

In order to obtain an alumina sintered compact having excellent mechanical properties, it is basically necessary to prepare a sintered compact having a dense microstructure and high density. Fracture starts from defects such as pores, impurities, and coarse particles, and stress is concentrated in the defects to cause failure.

As a relatively simple and economical alumina sintering method, there is a method of controlling the particle shape of the alumina sintered body or enhancing densification by adding oxides such as SiO ₂ , MgO, CaO, and the like. 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 the sintering phenomenon accompanied by most of the shrinkage occurs in the rearrangement stage of the solid particles. This liquid phase sintering promotes material diffusion by the liquid phase and can accelerate the optimal filling of solid particles, so it is possible to manufacture an alumina sintered body having a high density and dense microstructure even at a relatively low temperature. In addition, since the sintering temperature is low, it has an economical advantage compared to other sintering methods.

The liquid phase generated during liquid phase sintering must have excellent wettability with the solid particles, and the solubility of the solid particles in the liquid phase must be high so that the liquid phase can be evenly distributed among the solid particles. In the case of commercial alumina, about 8% of liquid sintering aid is added to prepare 92% alumina, and various colorants are additionally added for color expression of alumina. Usually, color is expressed by mixing one or two or more colorants, and the oxides added to these colorants also play the role of anhydrous to create a liquid phase, which greatly affects the liquid phase sintering mechanism, which lowers 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 amount of oxide added additionally during the liquid phase sintering of alumina and the heat treatment conditions accordingly, it is expected that various kinds of alumina products that meet the preferences of consumers can be produced.

The patents and references mentioned in this specification are hereby incorporated by reference to the same extent as if each publication 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 an optimal amount of cobalt oxide used as a colorant and an optimal heat treatment condition therefor in a method for producing an alumina sintered body by a liquid phase sintering method, so that an alumina sintered body of excellent quality with high density and improved hardness is manufactured. The purpose is to provide a method.

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

The present invention relates to a method for producing an alumina sintered body using a liquid phase sintering method, to prepare an alumina mixture comprising 90 to 94 wt% of alumina (Al ₂ O ₃ ) fine powder and 6 to 10 wt% of a sintering aid, 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 mixed powder and wet mixing using an alumina ball, followed by drying; a third step of sieving the dried alumina mixed powder to 200 mesh and then uniaxially pressing to prepare an alumina mixed powder compact; and a fourth step of preparing an alumina sintered body by heat-treating the alumina mixed powder compact 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 of 40 to 42.5% from the alumina mixed powder compact, and a hardness of 12 to 13 GPa, and the alumina sintered body is aluminum oxide (Al ₂ O) as a crystalline phase. ₃ ), aluminum cobalt oxide (Al ₂ CoO ₄ ) and ileite (Anorthite).

The present invention is mainly used as a colorant, but acts as an impurity similar to the sintering aid added for liquid phase sintering to change the mechanism of liquid phase sintering and optimizes the optimum amount of cobalt oxide added and heat treatment conditions accordingly. Therefore, by using the method for manufacturing an alumina sintered body using the liquid phase sintering method of the present invention, it is possible to manufacture a high-quality alumina sintered body having improved density and hardness compared to a general alumina sintered body in which cobalt oxide is not added even though cobalt oxide is added. There is this.

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

The present invention relates to a method for producing an alumina sintered body using a liquid phase sintering method, to prepare an alumina mixture comprising 90 to 94 wt% of alumina (Al ₂ O ₃ ) fine powder and 6 to 10 wt% of a sintering aid, 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 mixed powder and wet mixing using an alumina ball, followed by drying; a third step of sieving the dried alumina mixed powder to 200 mesh and then uniaxially pressing to prepare an alumina mixed powder compact; and a fourth step of preparing an alumina sintered body by heat-treating the alumina mixed powder compact 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 a liquid phase does not exist at the sintering temperature. Accordingly, the liquid phase disappears and sintering is performed in a state where 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 may be used. Preferably, an alumina having an average particle size of 0.4 μm and an irregular particle shape is used. In particular, the irregularly shaped alumina particles form irregular agglomeration and irregular pores compared to granular alumina particles, which are difficult to change the shape of pores due to particle rearrangement due to local densification between solid particles at the temperature before liquid phase is formed. Therefore, there is an advantage that a more dense sintered body can be manufactured by smoothing the flow of the liquid phase during liquid phase sintering and facilitating the rearrangement of particles. Therefore, using the manufacturing method of the present invention, it is possible to manufacture high-quality commercial alumina with high density even including cobalt oxide.

The cobalt oxide serves as a pigment and an impurity determining the characteristics of liquid phase sintering together with the sintering aid. The amount of the cobalt oxide added is, according to a number of examples, when an alumina sintered body is obtained by heat-treating the alumina mixed powder at 1320 to 1390° C. for 30 minutes to 2 hours, 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 compact is 40 to 42.5% and the hardness is 12 to 13 GPa. Therefore, when the cobalt oxide is used in less than 9 parts by weight or in excess of 13 parts by weight, the characteristics of the alumina sintered body as described above may not be expressed.

The alumina mixed powder prepares 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 ,) with respect to 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 alumina (Al ₂ O ₃ ) An alumina mixture containing 92 wt% of fine powder and 8 wt% of a sintering aid is prepared and oxidized with respect to 100 parts by weight of the alumina mixture Cobalt (Co ₂ O ₃ ,) may 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 to 200 mesh to remove aggregates formed in the drying process, and then uniaxially pressed to prepare an alumina mixed powder compact. The alumina mixed powder compact may be manufactured by uniaxial pressure molding by maintaining the mold at a pressure of 5 to 15 MPa for 1 minute or more.

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

The manufacturing method of the 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). The alumina sintered body having a shrinkage ratio of 40 to 42.5% and a hardness of 12 to 13 GPa from the alumina mixed powder compact can be prepared.

The alumina sintered compact containing cobalt oxide of the present invention is subjected to liquid phase sintering under the same conditions, but the density (3.47 g/cm ³ ) and hardness (11.3 GPa) of the alumina sintered compact that does not contain cobalt oxide is improved compared to the density value and hardness There are features that show value. The reason is that the cobalt oxide-containing alumina sintered body of the present invention contains a specific aluminum cobalt oxide (Al ₂ CoO ₄ ) along with aluminum oxide (Al ₂ O ₃ ) and ilealite (Anorthite) as a crystalline phase. .

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 together with aluminum oxide (Al ₂ O ₃ ) and ileite (Anorthite) -Al spinel is identified as the crystalline phase. On the other hand, in the alumina sintered compact of the present invention, aluminum cobalt oxide (Al ₂ CoO ₄ ), not Mg-Al spinel, is confirmed as a crystalline phase, which is the same as that of a general commercial 92% alumina sintered compact containing cobalt oxide of the present invention. % composition and it is judged as one of the causes of having more improved density and hardness despite further containing cobalt oxide, which is an additional colorant.

Therefore, if the manufacturing method of the present invention is used, a high-quality aluminum liquid sintered body having improved density and hardness despite having a specific color including cobalt oxide as a colorant in manufacturing a commercial 92% aluminum sintered body can be manufactured. is judged

Hereinafter, the present invention will be described in detail by way of Examples.

Example

1. Experimental method

1) Preparation of alumina sintered body

The alumina used in the present invention was AES-11C manufactured by Sumitomo Chemical. The alumina has an average particle size of 0.4 μm and is characterized in that it has an irregular polygonal shape. 1 shows the microstructure of the alumina (AES-11C) fine powder 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 SiO ₂ :CaO:MgO=2:1:1 by weight ratio was prepared by mixing. The alumina fine powder and the sintering aid were mixed to be 92wt% and 8wt%, respectively, to prepare an alumina mixture.

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

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

alumina sintering aid cobalt oxide note Example 1 92 wt% 8wt% 0 parts by weight Cobalt oxide is added based on 100 parts by weight of the alumina-sintering aid mixture Example 2 82 wt% 8wt% 3 parts by weight Example 3 92 wt% 8wt% 7 parts by weight Example 4 92 wt% 8wt% 11 parts by weight Example 5 92 wt% 8wt% 15 parts by weight Example 6 92 wt% 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 at a temperature of 100° C. in a dryer for 24 hours. The dried alumina mixed powder was sieved through 200 mesh.

The dried alumina mixed powder was uniaxially press-molded while maintaining a pressure of 10 MPa for 1 minute using a round mold with a diameter of 24 mm for molding. The alumina mixed powder compact was heat-treated in an air atmosphere, at a temperature range of 1200°C to 1450°C, at a temperature increase rate of 3°C/min.

2) Characterization of alumina sintered compact

The surface and fracture surface microstructure changes according to the amount of cobalt oxide added 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).

The shrinkage rate and density of the alumina sintered body were measured and then calculated by dimensional measurement.

The hardness of the alumina sintered compact is surface polished using #160~#2000 SiC sandpaper, and then, using a micro Vickers hardness machine (ZHμ-A, INDENTEC, U.K), the indentation load is 1kgf and different parts of the test piece are measured 5 times. and expressed as an average.

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

2. Experimental results and discussion

1) Changes in microstructure 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. A little lower than the sintering temperature of a general commercial 92% alumina sintered compact (alumina sintered compact prepared using alumina mixed powder (Example 1) without cobalt oxide), expecting an increase in the amount of liquid phase produced by the addition of cobalt oxide 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. In the alumina sintered body prepared using an alumina mixture (Example 4) to which 11 parts by weight of cobalt oxide was added, a densified microstructure having relatively fewer pores. was observed. In the present invention, densification between particles was induced through liquid phase sintering to reduce pores in the alumina sintered body, but commercial round granular alumina powder, which is advantageous for the homogeneous density of the compact, was not used during molding. Irregular pores exist, and it is believed that this may have had some influence on the rearrangement between particles, which accompanies the largest shrinkage among the liquid phase sintering mechanisms. In addition, this result is related to the previous study by H. Y. Kim et al. that it was difficult to change the shape of pores due to particle rearrangement due to local densification between solid particles at the temperature before liquid phase was formed during liquid phase sintering of fine particles. there seems to be

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

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

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 was 3.48 g/cm ³ , the lowest value in the alumina sintered body prepared using the alumina mixed powder (Example 1) without cobalt oxide, and the alumina mixed powder with 11 parts by weight of cobalt oxide was added (Example 1). 4) showed the highest density of the alumina sintered body prepared by using 3.68 g/cm ³ . 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 amount of cobalt oxide added was increased to more than 11 parts by weight, the shrinkage rate was also rapidly decreased along with the decrease in density, 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 the alumina particles by capillary force is not sufficiently expressed by the excessive addition of cobalt oxide reacts with CaO-MgO-SiO ₂ to lower the liquid phase formation temperature to lower the liquid phase viscosity. For this reason, the alumina sintered body prepared using the alumina mixed powder (Example 5) to which 15 parts by weight of cobalt oxide of FIG. 3 was added and the alumina mixed powder (Example 6) prepared by adding 18 parts by weight of cobalt oxide It may have been the cause of the occurrence of numerous pores with irregular shapes seen in the microstructure of one alumina sintered compact, and when the amount of cobalt oxide added is less than 11 parts by weight, the sintering shrinkage rate exhibited in commercial 92% alumina is similar to or slightly increased. It is thought that the increase of the liquid phase influenced the rearrangement effect of the particles to some extent. In FIG. 2 , the particle sizes of the alumina sintered body were observed to be similar, and it is determined that the grain growth phenomenon due to dissolution re-precipitation or coalescence after particle rearrangement was similarly expressed.

3) Change in density and shrinkage of alumina sintered compact according to sintering temperature

In order to examine the effect of the sintering temperature on the rearrangement of solid particles during liquid phase sintering and the effect on the microstructure of the sintered body, 11 parts by weight of cobalt oxide, which showed the best densification at 1400° C. and sintered in the range of 1200 to 1450 °C. 4 shows the microstructure change 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 mixed powder.

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

In the case of Example 7 sintered at 1200°C, grain growth hardly occurred, and definite grain growth was observed from 1300°C, and at the same time, an increase in densification was also accompanied. According to the results of previous studies by W. Huang et al., the temperature at which the liquid phase is generated in the CaO-MgO-SiO ₂ three-component system is around 1330℃, and when sintering alumina with cobalt oxide, Al ₂ O ₃ and Co ₂ O ₃ , the liquid phase formation temperature is judged to be lower than this. Considering this, at 1300℃, the solid particles are rearranged due to sufficient liquid phase formation to some extent, and at the same time, the dissolution re-precipitation phenomenon is also accompanied by grain growth and It is considered that densification was simultaneously expressed. At a later temperature, it can be seen that the rearrangement of the particles is almost stopped and the solid particles are coalesced, and continuous grain growth is expressed.

5 shows the results of measuring the density (▲) and shrinkage (■) of the alumina sintered body 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 density of 2.78 g/cm ³ with a shrinkage of 18.34%, which was formed in a liquid phase at a lower temperature than that of commercial 92% alumina by the addition of cobalt oxide. means As the temperature increased, the density continued to increase. In the case of the alumina sintered body of Example 9 sintered at 1300° C., the sintered density of alumina increased with shrinkage of 38.59%, and in the case of the alumina sintered body of Example 10 sintered at 1350° C., the highest density was 3.86 g/cm ³ showed numbers. When sintering at a temperature of 1400 ° C or higher, it can be seen that the density and the shrinkage rate are simultaneously decreased gradually. On the other hand, it can be seen as a phenomenon that occurs due to the 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 on the surface of the sintered body is clearly observed.

4) Change in hardness of alumina sintered compact according to sintering temperature and content of cobalt oxide

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

According to the result of panel (a) of FIG. 6 , the alumina sintered compact 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 the lowest hardness value of pore coalescence. It is judged that it is the result of the presence of a glass phase due to the presence of a liquid phase and an excess of liquid phase. In the case of the alumina sintered compact prepared using the alumina mixed powder (Example 4) to which cobalt oxide was added in an amount of 11 parts by weight, the highest density was shown, and the hardness was also the highest of 12.32 GPa.

In the result 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 a result of insufficient bonding between particles due to coalescence between solid particles although shrinkage is achieved, and after Grain growth and densification increase with temperature increase, and hardness also increases accordingly, but also at high temperature, hardness decreases due to the influence of glass phase formation by low viscosity liquid phase.

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

7 shows the results of performing X-ray diffraction analysis on the alumina sintered body of Examples 1 and 4 of the present invention. The red line (a) shows the analysis result of the alumina sintered body of Example 1, and the black line (b) shows the analysis result of 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 the increase of the liquid phase by the addition of cobalt oxide.

3. Conclusion

The present invention is summarized as follows.

1. When sintering commercial 92% alumina, 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 the sintering temperature of 1400°C or higher lowered the viscosity of the liquid phase, a decrease in density and hardness was observed along with the formation of a glass phase.

3. In liquid phase sintering of 92% alumina, the rearrangement of the solid particles with the greatest shrinkage was 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 a later temperature.

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

The specific examples described herein 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 modifications and other uses of the present invention do not depart from the scope of the invention as set forth in the claims herein.

Claims (5)

In the manufacturing method of an alumina sintered body using the 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 aid was prepared, and cobalt oxide (Co ₂ O ₃ ,) was added to 9 to 13 parts by weight based on 100 parts by weight of the alumina mixture. A first step of preparing an alumina mixed powder by adding it in parts;
a second step of adding distilled water to the alumina mixed powder and wet mixing using an alumina ball, followed by drying;
a third step of sieving the dried alumina mixed powder to 200 mesh and then uniaxially pressing to prepare an alumina mixed powder compact; and
a fourth step of heat-treating the alumina mixed powder compact at 1320 to 1390° C. for 30 minutes to 2 hours to prepare an alumina sintered compact;
A method of manufacturing an alumina sintered body using a liquid phase sintering method comprising a.
The method of claim 1, wherein the alumina sintered body has a density of 3.6 to 3.9 g/cm ³ and a shrinkage rate from the alumina mixed powder compact is 40 to 42.5%.
The method of claim 1, wherein the alumina sintered body has a hardness of 12 to 13 GPa.
The alumina sintered body using a liquid phase sintering method according to claim 1, wherein the alumina sintered body comprises aluminum oxide (Al ₂ O ₃ ), aluminum cobalt oxide (Al ₂ CoO ₄ ), and ilealite (Anorthite) as crystalline phases. manufacturing method.
The method of claim 1, wherein the sintering aid comprises silicon oxide (SiO ₂ ), calcium oxide (CaO), and magnesium oxide (MgO).

Images