KR20090081047A - Ceramic material of garnet crystal structure with low thermal conductivity and manufacturing method of the same - Google Patents

Abstract

A ceramic material with a garnet crystal structure showing low thermal conductivity and a manufacturing method thereof are provided to show a high thermal expansion coefficient as much as that of a metal parent material while showing low thermal conductivities. A ceramic material showing low thermal conductivity has a garnet crystal structure of A3B5O12. In the garnet crystal structure, the A is one rare earth material selected from the group consisting of Er, Gd, Y and La; and the B is one material selected from the group consisting of Al and Ga. The A consists of Er and the B consists of Al and/or Ga. The ceramic material with a garnet crystal structure shows 2.5-3.6W/mk of thermal conductivity at the temperature of 1000°C.

Description

Ceramic material of garnet crystal structure with low thermal conductivity and manufacturing method of the same

The present invention relates to a ceramic material and a method for manufacturing the same, and more particularly, to a low thermal conductivity ceramic material having a garnet crystal structure that can be used as a heat shield coating material and a method for manufacturing the same.

The actual operating temperature of the gas turbine using heat shield coating is 1100 ℃ ~ 1200 ℃, when exposed to high temperature atmosphere, the surface of the metal material is easy to oxidize. Superalloys developed for use at high temperatures, such as gas turbines, also suffer from long-term endurance at temperatures above 1000 ° C. Therefore, in order to improve the life of the metal material exposed to high temperature, it is necessary to coat with a material having excellent heat shielding properties.

Ceramic materials used in these thermal barrier coatings have low sinterability to suppress the increase in thermal conductivity at high temperatures, phase stability at high temperatures, low thermal conductivity for thermal shielding, and high thermal expansion coefficients approaching the thermal expansion coefficient of the metal matrix. Conditions are required (R. Vassen, X. Cao, F. Tietz, D. Basu, and D. Stover, "Zirconates as New Materials for Thermal Barrier Coating", J. Am . Ceram . Soc. , 83, [8] 2023-2028 (2000)). However, very few ceramic materials satisfy the requirements, and only a few of the ceramic materials satisfy these requirements. Therefore, new materials need to be developed.

Currently, 7-8 wt% YSZ (Y ₂ O ₃ -stabilized zirconia) is widely used as a material for TBC (Thermal Barrier Coating). However, if the material is kept for a long time at a high temperature, the sintering proceeds to increase the density of the TBC, increase the thermal conductivity, and also cause a crack in the TBC layer during the cooling / heating cycle due to the volume change due to the phase transformation (RL). Jones, RF Reidy, and D. Mess, "Scandia, Yttria-Stabilized Zirconia for Thermal Barrier Coatings", Surf . Coat . Technol ., 82, 7076 (1996)) (RL Jones and D. Mess, "Improved Tetragonal Phase Stability at 1400 ° C. with Scandia, Yttria-Stabilized Zirconia ", Surf . Coat . Technol ., 867, 94101 (1996)). In addition, ZrO ₂ has excellent thermal stability, has low sintering property and thermal conductivity, but has a lower thermal expansion coefficient than YSZ (Y ₂ O ₃ -stabilized zirconia).

In order to overcome this problem, recently, materials based on CeO ₂ instead of YSZ (Y ₂ O ₃ -stabilized zirconia) have been studied. Thus, rare earths such as La ₂ O ₃ , Gd ₂ O ₃ , and Y ₂ O ₃ have been studied. Many studies have been conducted to reduce the thermal conductivity by adding elements. However, although the thermal conductivity of the compositions added La ₂ O ₃ to CeO ₂ was low, an abnormal phenomenon in which the coefficient of thermal expansion rapidly decreased was observed in the range of 200-400 ° C. of the coefficient of thermal expansion (W. Ma, S. Gong, H.). Xu, and X. Cao, "On Improving the Phase Stability and Thermal Expansion Coefficients of Lanthanum Cerium Oxide Solid Solutions", Scripta Materialia , 54, 15051508 (2006).

The technical problem to be achieved by the present invention is low sinterability to suppress the increase in thermal conductivity at high temperature, phase stability at high temperature, low thermal conductivity for heat shielding, and high value of the high thermal expansion coefficient approaching the thermal expansion coefficient of the metal matrix. To provide a low thermal conductivity ceramic material of garnet crystal structure that can be used as a heat shield coating material.

Another technical problem to be solved by the present invention is low sinterability that suppresses the increase in thermal conductivity at high temperature, phase stability at high temperature, low thermal conductivity for thermal shielding, and high value of high thermal expansion coefficient approaching the thermal expansion coefficient of the metal matrix. The present invention provides a method for producing a low thermal conductivity ceramic material of garnet crystal structure that can be used as a heat shield coating material.

The present invention has a garnet crystal structure, wherein in the A ₃ B ₅ O ₁₂ composition of the garnet crystal system, the A site is composed of at least one rare earth element selected from Er, Gd, Y, and La, and the B site is selected from Al and Ga. A low thermal conductivity ceramic material having a garnet crystal structure composed of at least one selected element is provided.

The A site is composed of Er, and the B site may be composed of Al, Ga, or a combination of Al and Ga.

The A site is composed of Gd, the B site may be composed of Al, Ga or a combination of Al and Ga.

The A site may be composed of La, and the B site may be composed of Al.

The A site may be composed of Y, and the B site may be composed of Ga.

The low thermal conductivity ceramic material of the garnet crystal structure has a value in the range of 2.5 to 3.6 W / mk thermal conductivity at 1000 ° C.

In addition, the present invention, Er ₂ O ₃ , Gd ₂ O ₃ , La ₂ O ₃ as a source raw material of the element to be added to the A site to have a composition of A ₃ B ₅ O ₁₂ of the garnet crystal structure And at least one oxide powder selected from Y ₂ O ₃ and Ga ₂ O ₃ and Al ₂ O ₃ as source materials of the element to be added to the B site. Charging at least one oxide powder selected from among them into a ball mill, followed by wet mixing with a solvent, stirring and drying the slurry mixed by the ball mill to prevent precipitation, and pulverizing the powdered slurry It provides a method of producing a low-heat conductive ceramic material of the garnet crystal structure comprising the steps of, charging and shaping the pulverized powder into a mold, and sintering the molded specimen to form a ceramic material of garnet crystal structure.

The low thermal conductivity ceramic material of the garnet crystal structure of the present invention has excellent phase stability in a high temperature oxidizing atmosphere, has a high value of thermal expansion coefficient approaching the thermal expansion coefficient of a metal base material, and has a low thermal conductivity value. It is suitable as a composition.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments are provided to those skilled in the art to fully understand the present invention, and may be modified in various forms, and the scope of the present invention is limited to the embodiments described below. It doesn't happen.

Garnet crystal system (A ₃ B ₅ O ₁₂ ) is a new material emerging as a heat shielding material because of excellent thermal phase stability, low thermal diffusion coefficient, and excellent mechanical properties at high temperature. In addition, the Garnet crystal system A ₃ B ₅ O ₁₂ has a large cubic unit cell with a lattice constant of 1200 pm, and one cell has about 160 cells. It contains atoms of. Therefore, various materials can be doped, and the properties can be easily adjusted to the composition.

The present invention provides a ceramic material of garnet crystal structure that can be used as a heat shield coating material for improving the heat resistance and life of the base metal which is a metal used in a gas turbine. Low thermal conductivity ceramic material with heat shielding function to protect the base metal, which is a metal at high temperature, has a garnet structure, and Er, at the A site in the general composition of A ₃ B ₅ O ₁₂ of Garnet, A rare earth element of Gd, Y, or La, and a material composed of Al or Ga of the B site will be described.

The ceramic material of the garnet crystal structure according to the preferred embodiment of the present invention is a stable material having excellent high temperature characteristics and no phase deformation. In the ceramic material of the garnet crystal structure according to the preferred embodiment of the present invention, the thermal expansion coefficient at 1200 ° C. is 9.0 × 10 ⁻⁶ / K or more, and the thermal conductivity at 1000 ° C. is about 2.5 to 3.6 W / mK. The thermal conductivity of the garnet crystal system (Er ₃ (GaAl) ₅ O ₁₂ ) is as low as 2.5W / mK, the material of the present invention can be utilized as a material such as heat shield coating.

Hereinafter, a method of manufacturing a ceramic material of garnet crystal structure according to a preferred embodiment of the present invention.

An oxide powder containing an element to be added to the A site and an oxide powder containing an element to be added to the B site are respectively weighed so as to have an A ₃ B ₅ O ₁₂ composition of the garnet crystal structure. Elements to be added to the A site are Er (erbium; erbium), Gd (gadolinium; gadolinium), La (lanthanum; lanthanum) Or at least one rare earth element selected from y (yttrium), and an oxide which is a source material of these elements may include Er ₂ O ₃ , Gd ₂ O ₃ , La ₂ O ₃ , and Y ₂ O _3. Etc. can be used. Elements be added to the B site, Ga (gallium; gallium) is Ga ₂ with at least one may be a single element, the source material of oxide of these elements selected from, Al (aluminium;; aluminum), and Fe (ferrous iron) O ₃ , Al ₂ O ₃ , Fe ₂ O _3, etc. may be used.

Oxide powder, which is a source material containing an element to be added to the A site, and oxide powder, which is a source material containing an element to be added to the B site, are charged into a ball milling machine and wetted with a solvent. Mix. The ball mill is rotated at a constant speed to mechanically grind and uniformly mix the source raw materials.

The balls used for ball milling may use balls made of ceramics such as zirconia, and the balls may be all the same size or may be used with balls having two or more sizes. Grind to the size of the target particles by adjusting the size of the ball, milling time, rotation speed per minute of the ball mill. For example, in consideration of the particle size, the size of the ball can be set in the range of about 1 mm to 10 mm, and the rotational speed of the ball mill can be set in the range of about 50 to 500 rpm. Ball milling is performed for 1 to 100 hours in consideration of the target particle size and the like.

By ball milling, the source raw materials are ground to finely sized particles, have a uniform particle size distribution, and are mixed evenly.

A drying process is performed while stirring using a magnetic bar so that the mixed slurry is not precipitated. The drying process can be weight-dried for 24 hours in an oven at 80 ℃.

The dried slurry is pulverized to prepare a powder. The grinding can be carried out using alumina induction.

The pulverized powder is charged into a mold and molded. The molding may be carried out by charging into a mold having a diameter of 16 mm, first uniaxially molding for 1 minute at a pressure of 50 MPa, and then cold isostatic pressing (Cold Isostatic Pressing) for 1 minute at a pressure of 150 MPa.

The molded specimen is sintered to form a ceramic material of garnet crystal structure. It is preferable to perform the said sintering for about 1 hour-about 3 hours at the temperature of about 1300 degreeC-1600 degreeC. The sintering step can be carried out by heating up to a sintering temperature at a heating rate of 10 ° C./min, sintering for a predetermined time (for example, about 1 hour to 3 hours), and quenching to room temperature.

In the ceramic material of the garnet crystal structure according to the preferred embodiment of the present invention, the thermal expansion coefficient at 1200 ° C. is 9.0 × 10 ⁻⁶ / K or more, and the thermal conductivity at 1000 ° C. is about 2.5 to 3.6 W / mK. In the garnet crystal system (Er ₃ (GaAl) ₅ O ₁₂ ), the thermal conductivity is about 2.5 W / mK.

It is a ceramic material of garnet crystal structure to improve the heat resistance and lifespan of the base metal, which is a metal.Er ₂ O ₃ as a source raw material of element to enter the A site in the Garnet crystal system (A ₃ B ₅ O ₁₂ ) , Gd ₂ O ₃ , La ₂ O ₃ Alternatively, the thermal properties were analyzed by sintering at a constant temperature using (Fe · Al) ₂ O ₃ or (Ga · Al) ₂ O ₃ as a source raw material of elements to enter Y ₂ O ₃ and B sites. Hereinafter, the high temperature thermal characteristic analysis method of the ceramic material of the garnet crystal structure of this invention is demonstrated concretely.

<Examples 1-7>

Table 1 schematically shows the sinterability of Er ₃ (Ga · Al) ₅ O ₁₂ , Er ₃ (Fe · Al) ₅ O _{12 in} the garnet crystal system. In Table 1, 'O' indicates that the sintering was performed without melting at the corresponding temperature, and 'X' indicates that it was not sintered and melted at the corresponding temperature.

Sinterability Results 1300 ℃ 1400 ℃ 1500 ℃ 1600 ℃ Example 1 Er ₃ Ga ₅ O ₁₂ O O O O Example 2 _{Er 3 Ga 4 .3 Al 0 .7} O 12 O O O O Example 3 _{Er 3 Ga 3 .6 Al 1 .4} O 12 O O O O Example 4 _{Er 3 Ga 2 .5 Al 2 .5} O 12 O O O O Example 5 _{Er 3 Ga 1 .4 Al 3 .6} O 12 O O O O Example 6 _{Er 3 Ga 0 .7 Al 4 .3} O 12 O O O O Example 7 Er ₃ Al ₅ O ₁₂ O O O O Comparative Example 1 _{Er 3 Fe 4 .3 Al 0 .7} O 12 O O O X Comparative Example 2 Er ₃ Fe ₅ O ₁₂ O O X X

Examples 1 to 7 are Er ₂ O ₃ as a source raw material of an element that will enter the A site of the garnet crystal system (A ₃ B ₅ O ₁₂ ), and as a source raw material of an element that will enter the B site (Ga ₂ O ₃ ㆍ Al ₂ O ₃ ) is used.

The source raw materials are weighed to have the composition of Table 1. It is weighed to have the composition shown in Table 1 based on the molecular weight, molar ratio, and content ratio of the source raw material. For example, Example 1 is weighed to have 11.01 g of Er ₂ O ₃ powder and 9.99 g of Ga ₂ O ₃ powder to have the composition of Table 1, and Example 2 is 11.33 g of Er ₂ O ₃ powder, Al to have the composition of Table 1 ₂ O ₃ powder, 0.71g, Ga ₂ O ₃ powder 7.96g one would have to be weighed, the third embodiment is to have the composition of Table 1 Er ₂ O ₃ powder 11.68g, Al ₂ O ₃ powder, 1.45g, Ga ₂ O ₃ powder Example 6 weighed to 6.87g, Example 4 weighed to 12.27g Er ₂ O ₃ powder, 2.73g Al ₂ O ₃ powder, 5.01g Ga ₂ O ₃ powder to have the composition of Table 1, Example 5 12.92 g of Er ₂ O ₃ powder, 4.13 g of Al ₂ O ₃ powder, and 2.95 g of Ga ₂ O ₃ powder were weighed to have the composition of Table 1. Example 6 13.36 g of Er ₂ O ₃ powder to have the composition of Table 1. , 5.11 g of Al ₂ O ₃ powder, 1.53 g of Ga ₂ O ₃ powder, and Example 7 was weighed to 13.85 g of Er ₂ O ₃ powder and 6.15 g of Al ₂ O ₃ powder to have the composition of Table 1. will be.

Source raw materials weighed to have the composition of Table 1 were loaded into a ball mill and ethanol was wet mixed for 4 hours in a planetary mill using 3 mm zirconia balls as solvent.

The mixture was stirred and dried using a magnetic bar to prevent precipitation of the mixed slurry, followed by constant drying in an oven at 80 ° C. for 24 hours, and then pulverized using alumina induction to prepare a powder.

The mixed powder was charged into a mold having a diameter of 16 mm, first uniaxially formed at a pressure of 50 MPa for 1 minute, and further subjected to isostatic pressing (Cold Isostatic Pressing) at 150 MPa for 1 minute.

The molded specimens were heated to 1300 ° C, 1400 ° C, 1500 ° C, and 1600 ° C at a heating rate of 10 ° C / min, and then sintered for 2 hours, respectively, and cooled to room temperature.

As shown in Table 1, the Er ₃ (Ga · Al) ₅ O ₁₂ composition was sintered at all temperatures from 1300 ° C to 1600 ° C, indicating that the phase was stable.

1 is a high power X-ray diffractometer (D / max-2500 / PC, Rigaku Co., Japan) of a specimen sintered at 1600 ° C. for 2 hours to analyze the crystal structure of the sintered specimen. The diffraction pattern was observed up to 20 ° to 70 ° at a scan rate of 4 ° C./min using 40 kV and 200 Hz.

As shown in FIG. 1, observations showed that the compositions up to Examples 1-6 were YAG (yttrium aluminum garent) phases and the phase stability was excellent at 1600 ° C.

Table 2 schematically shows the density and specific heat values of Er ₃ (GaAl) ₅ O _{12 in} the garnet crystal system.

Density (g / cm 3) Theoretical density (g / cm3) Relative Density (%) Specific Heat (J / gK) Er ₃ Ga ₅ O ₁₂ 6.95 7.21 96.4 0.57 _{Er 3 Ga 4 .3 Al 0 .7} O 12 7.18 7.11 101.0 0.59 _{Er 3 Ga 3 .6 Al 1 .4} O 12 7.14 6.99 100.7 0.61 _{Er 3 Ga 2 .5 Al 2 .5} O 12 6.47 6.81 95.0 0.63 _{Er 3 Ga 1 .4 Al 3 .6} O 12 4.95 6.62 74.7 0.66 _{Er 3 Ga 0 .7 Al 4 .3} O 12 4.89 6.50 75.3 0.68 Er ₃ Al ₅ O ₁₂ 5.36 6.37 84.1 0.70

The sintered specimens shown in Table 2 were evaluated for thermal properties at high temperatures through experiments such as density measurement, XRD phase analysis, thermal expansion coefficient measurement, specific heat measurement, thermal diffusivity measurement, and thermal conductivity calculation.

2 is a graph showing a thermal expansion coefficient (TEC) according to the temperature of the ceramic material (Er ₃ (GaAl) ₅ O ₁₂ ) of the garnet crystal structure according to a preferred embodiment of the present invention.

2, in order to measure the coefficient of thermal expansion, a sintered compact specimen having a length of 20 mm and a diameter of 5 mm was used at a dilatometer (DIL 402C, Netzsch, Germany) at 10 ° C / 1200 ° C. It measured by heating up at the speed of min. As a result, zirconia added with 7-8 wt% Y ₂ O ₃ (YSZ, Y ₂ O ₃₎ , which is widely used as a conventional heat shielding material, has a value close to 10 × 10 ^-6 / K at 1200 ° C regardless of the composition. It was concluded that the thermal expansion coefficient of -stabilized zirconia was similar to that of 10.5 × 10 ^-6 / K.

Based on ASTM (American Society for Testing Materials) E1269, a sintered body of a circular disk having a diameter of 6 mm and a thickness of 0.6 to 0.7 mm was prepared, and a differential scanning calorimeter (DSC) (DSC) Specific heat was measured to 1200 degreeC using the temperature increase rate of 10 degree-C / min using 404C, Netzsch, Germany. As a result of specific heat measurement, it was obtained that it had a value of 0.57-0.70 J / gK at 1200 degreeC.

In order to measure the thermal diffusivity, a sintered compact of a circular disk having a diameter of 12.7 mm and a thickness of 2.0 mm was manufactured, and the upper and lower surfaces were polished using diamond having a diameter of 1 m. Graphite was coated on both sides in order to prevent the reflection of the laser from the specimen surface and to help the absorption into the test specimen, and thermal diffusivity was measured using a passion water meter (LFA427, Netzsch, Germany). As a result of thermal diffusivity measurement, it was concluded that it has a value of 0.6 ~ 0.7mm ² / s at 1000 ℃.

Thermal conductivity values were calculated by multiplying three values of specific heat, theoretical density, and thermal diffusivity measured by differential scanning calorimetry (DSC) according to American Society for Testing Materials (ASTM) E1461. However, this result does not take into account the density of the sintered compact, so that the thermal conductivity of the material according to the composition was recalculated using Equation 1 below.

In Equation 1, k _measured means measured thermal conductivity, Φ means porosity, k _true means thermal conductivity of the actual material.

3 is a graph illustrating thermal conductivity according to temperature of a ceramic material (Er ₃ (GaAl) ₅ O ₁₂ ) having a garnet crystal structure according to an exemplary embodiment of the present invention.

Referring to Figure 3, as a result of the thermal conductivity calculation, it had a value of 2.5 ~ 3.6W / mK at 1000 ℃. This is 7 ~ 8 wt% Y ₂ O ₃ addition zirconia (YSZ, Y ₂ O ₃ -stabilized zirconia) (Nitin, P. Padture, Klemens, G. Paul, J. Am ) with a thermal conductivity of 1.8 ~ 2.7W / mK. . Ceram. Soc. 80, it is a bit higher than the analogous (1997) 1018-1020).

<Comparative Examples 1 and 2>

Comparative Examples 1 and 2, as shown in Table 1, are the source raw materials of the elements to enter the B site of the garnet crystal system (A ₃ B ₅ O ₁₂ ) (Ga ₂ O ₃ ㆍ Al ₂ O of Examples 1 to 7). ₃ ) Specimens were prepared and sintered in the same manner as in Examples 1 to 7, except that (Fe ₂ O ₃ .Al ₂ O ₃ ) was used instead.

As a result of sintering at 1300 ° C. to 1600 ° C., the composition of Er ₃ (Fe · Al) ₅ O ₁₂ was observed to be melted from 1500 ° C. and found to be unsuitable for use as a heat shield coating composition.

<Examples 8-9>

Table 3 summarizes the sinterability of Gd ₃ (Ga · Al) ₅ O ₁₂ , Gd ₃ (Fe · Al) ₅ O _{12 in} the garnet crystal system. In Table 3, 'O' indicates that the sintering was performed without melting at the corresponding temperature, and 'X' indicates that it was not sintered and melted at the corresponding temperature.

Sinterability Results 1300 ℃ 1400 ℃ 1500 ℃ 1600 ℃ Example 8 Gd ₃ Ga ₅ O ₁₂ O O O O Example 9 Gd ₃ Ga _4.3 Al _0.7 O ₁₂ O O O O Comparative Example 3 _{Gd 3 Ga 3 .6 Al 1 .4} O 12 O O O X Comparative Example 4 Gd ₃ Al ₅ O ₁₂ O O O X Comparative Example 5 _{Gd 3 Fe 3 .6 Al 1 .4} O 12 O O O X Comparative Example 6 _{Gd 3 Fe 4 .3 Al 0 .7} O 12 O O O X Comparative Example 7 Gd ₃ Fe ₅ O ₁₂ O O X X

Specimens were prepared and sintered in the same manner as in Examples 1 to 7 except that Gd ₂ O ₃ was used as the source raw material of the element to enter the A site of the garnet crystal system (A ₃ B ₅ O ₁₂ ).

As a result of sintering, it was found that the compositions to which Gd ₂ O ₃ was added have a suitable phase stability for use as a heat shield coating material at all temperatures from 1300 ℃ to 1600 ℃.

<Comparative Examples 3 to 7>

In the same manner as in Examples 8 to 9, Gd ₂ O ₃ was used as the source raw material of the element to enter the A site, and (Ga ₂ O ₃ Al ₂ O was used as the source raw material of the element to enter the B site. ₃ ) or (Fe ₂ O ₃ ㆍ Al ₂ O ₃ ) to prepare a specimen and sintered.

As a result of the sintering, as the amount of Gd ₂ O ₃ was decreased and the amount of Fe ₂ O ₃ was increased, it was observed to melt from 1500 ° C. It was found that it was not suitable for use as a composition of the thermal barrier coating.

<Example 10>

Table 4 schematically shows the sinterability of La ₃ (Ga · Al) ₅ O ₁₂ , La ₃ (Fe · Al) ₅ O _{12 in} the garnet crystal system. In Table 4, 'O' indicates that sintering was performed without melting at the corresponding temperature, and 'X' indicates that the sintering was not sintered at the corresponding temperature.

Sinterability Results 1300 ℃ 1400 ℃ 1500 ℃ 1600 ℃ Example 10 La ₃ Al ₅ O ₁₂ O O O O Comparative Example 8 _{La 3 Fe 3 .6 Al 1 .4} O 12 O O X X Comparative Example 9 _{La 3 Fe 4 .3 Al 0 .7} O 12 O O X X Comparative Example 10 La ₃ Fe ₅ O ₁₂ O O X X Comparative Example 11 _{La 3 Ga 4 .3 Al 0 .7} O 12 O X X X Comparative Example 12 _{La 3 Ga 3 .6 Al 1 .4} O 12 O X X X Comparative Example 13 La ₃ Ga ₅ O ₁₂ O X X X

Specimens were prepared and sintered in the same manner as in Examples 1-7 except that La ₂ O ₃ was used as the source raw material of the element to enter the A site of the garnet crystal system (A ₃ B ₅ O ₁₂ ).

As a result of sintering, La ₃ Al ₅ O ₁₂ composition was found to have a suitable phase stability for use as a heat shield coating material at all temperatures from 1300 ℃ to 1600 ℃.

<Comparative Examples 8-13>

In the same manner as in Example 10, La ₂ O ₃ was used as the source raw material of the element to enter the A site of the garnet crystal system (A ₃ B ₅ O ₁₂ ), and as the source raw material of the element to enter the B site Specimens were prepared and sintered using (Ga ₂ O ₃ Al ₂ O ₃ ) or (Fe ₂ O ₃ Al ₂ O ₃ ).

As a result of sintering, as the amount of Fe ₂ O ₃ and Gd ₂ O ₃ increased, the melting proceeded from 1400 ° C., and it was found that it was not suitable to be used as a composition of the thermal barrier coating.

<Example 11>

Table 5 schematically shows the sinterability of Y ₃ (Ga · Al) ₅ O ₁₂ , Y ₃ (Fe · Al) ₅ O _{12 in} the garnet crystal system. In Table 5, 'O' indicates that the sintering was performed without melting at the corresponding temperature, and 'X' indicates that it was melted without sintering at the corresponding temperature.

Sinterability Results 1300 ℃ 1400 ℃ 1500 ℃ 1600 ℃ Example 11 Y ₃ Ga ₅ O ₁₂ O O O O Comparative Example 14 Y ₃ Ga _4.3 Al _0.7 O ₁₂ O O O X Comparative Example 15 _{Y 3 Ga 3 .6 Al 1 .4} O 12 O O O X Comparative Example 16 _{Y 3 Fe 3 .6 Al 1 .4} O 12 O O O X Comparative Example 17 _{Y 3 Fe 4 .3 Al 0 .7} O 12 O O O X Comparative Example 18 Y ₃ Fe ₅ O ₁₂ O O O X

Specimens were prepared and sintered in the same manner as in Examples 1 to 7 except that Y ₂ O ₃ was used as the source raw material of the element to enter the A site of the garnet crystal system (A ₃ B ₅ O ₁₂ ).

As a result of sintering, it was found that the Y ₃ Ga ₅ O ₁₂ composition has an appropriate phase stability for use as a heat shield coating material at all temperatures from 1300 ° C to 1600 ° C.

<Comparative Examples 14-18>

In the same manner as in Example 11, Y ₂ O ₃ was used as the source raw material of the element to enter the A site of the garnet crystal system (A ₃ B ₅ O ₁₂ ), and (Ga ₂ O _3. Specimens were prepared and sintered using Al ₂ O ₃ ) or (Fe ₂ O ₃ .Al ₂ O ₃ ).

As a result of sintering, the addition amount of Gd ₂ O ₃ decreases and the addition of Fe ₂ O ₃ increases the melting at 1600 ° C., and it is found that it is not suitable for use as a composition of the thermal barrier coating.

As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation by a person of ordinary skill in the art within the scope of the technical idea of this invention is carried out. This is possible.

1 is a graph showing the results of XRD image analysis of a ceramic material (Er ₃ (GaAl) ₅ O ₁₂ ) of the garnet crystal structure according to a preferred embodiment of the present invention.

2 is a graph showing a coefficient of thermal expansion according to the temperature of the ceramic material (Er ₃ (GaAl) ₅ O ₁₂ ) of the garnet crystal structure according to a preferred embodiment of the present invention.

3 is a graph showing thermal conductivity according to temperature of a ceramic material (Er ₃ (GaAl) ₅ O ₁₂ ) having a garnet crystal structure according to an exemplary embodiment of the present invention.

Claims (7)

Has a garnet crystal structure, and in the A ₃ B ₅ O ₁₂ composition of the garnet crystal system, the A site is composed of at least one rare earth element selected from Er, Gd, Y and La, and the B site is at least one selected from Al and Ga A low thermal conductivity ceramic material with a garnet crystal structure, which is composed of an element. The low thermal conductivity ceramic material of claim 1, wherein the A site is made of Er, and the B site is made of Al, Ga, or a combination of Al and Ga. The low thermal conductivity ceramic material of claim 1, wherein the A site is made of Gd, and the B site is made of Al, Ga, or a combination of Al and Ga. The low thermal conductivity ceramic material according to claim 1, wherein the A site is made of La, and the B site is made of Al. The low thermal conductivity ceramic material of claim 1, wherein the A site is made of Y, and the B site is made of Ga. The low thermal conductivity ceramic material according to claim 1, wherein the thermal conductivity at 1000 ° C. has a value in the range of 2.5 to 3.6 W / mk. Er ₂ O ₃ , Gd ₂ O ₃ , La ₂ O ₃ as a source raw material of the element to be added to the A site to have the A ₃ B ₅ O ₁₂ composition of the garnet crystal structure And at least one oxide powder selected from Y ₂ O ₃ and Ga ₂ O ₃ and Al ₂ O ₃ as source materials of the element to be added to the B site. Charging at least one oxide powder selected from among a ball mill and wet mixing with a solvent; Stirring and drying the slurry mixed by the ball mill to prevent precipitation; Pulverizing and drying the dried slurry; Charging the ground powder to a mold and molding; And A method of manufacturing a low thermal conductivity ceramic material having a garnet crystal structure, comprising sintering a molded specimen to form a ceramic material having a garnet crystal structure.

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