KR101442634B1 - Manufacturing method of aluminum titanate having high-temperature strength and manufacturing method of the same - Google Patents

Abstract

The invention, including SiO ₂ 8.0~12.0 mol%, ZrO ₂ 1.0~4.0 mol%, MgO 4.0~8.0 mol%, Al ₂ O ₃ and TiO ₂ 33.0~39.0 43.0~49.0% by mole% by mole in the chemical composition components To a process for producing aluminum titanate. The aluminum titanate of the present invention not only has a low coefficient of thermal expansion and high corrosion resistance, but also has high strength at high temperature and high decomposition stability.

Description

[0001] The present invention relates to a method for producing aluminum titanate having a high temperature strength,

The present invention relates to a method for producing aluminum titanate, and more particularly, to a method for producing aluminum titanate having a low thermal expansion coefficient and a high corrosion resistance property as well as an excellent high temperature strength and stability even in a high temperature environment.

Aluminum titanate (Al ₂ TiO ₅ ) is known as a heat-resistant material because of its low thermal expansion coefficient and high corrosion resistance.

Pure aluminum titanate has thermal instability that is decomposed into alumina (α-Al ₂ O ₃ ) and titanium oxide (TiO ₂ ) in the region of 750 to 1300 ° C. during cooling after sintering.

In addition, aluminum titanate has micro-cracks due to internal stress because it has different thermal expansion coefficients according to different crystal axes, and has low mechanical strength due to rapid particle growth at a high temperature of 1300 DEG C or more. Aluminum titanate has disadvantages such as interfacial displacement and microcracking caused by stress due to thermal expansion since the crystal grain of the sintered body is anisotropic.

For the above reasons, the conventional aluminum titanate has a limitation in exhibiting sufficient durability in a high temperature environment, and the low sinterability, the low mechanical strength and the thermal instability have many limitations in using aluminum titanate as a high-temperature structural material have.

A problem to be solved by the present invention is to provide a method for producing aluminum titanate having a low thermal expansion coefficient and a high corrosion resistance property as well as an excellent high temperature strength and stability even in a high temperature environment.

The invention, including SiO ₂ 8.0~12.0 mol%, ZrO ₂ 1.0~4.0 mol%, MgO 4.0~8.0 mol%, Al ₂ O ₃ and TiO ₂ 33.0~39.0 43.0~49.0% by mole% by mole in the chemical composition components Aluminum titanate.

The aluminum titanate may further contain 0.01 to 1.0 mol% of? -Fe ₂ O ₃ as a chemical composition component.

In addition, the present invention, SiO ₂ 8.0~12.0 mol%, from containing ZrO ₂ 1.0~4.0 mol%, MgO 4.0~8.0 mol%, Al ₂ O ₃ and TiO ₂ 33.0~39.0 43.0~49.0 mol% mol% A step of preparing a raw material, a step of adding and mixing an organic binder and a dispersant to the starting material, a step of molding the mixed product, and a step of sintering the molded product .

The starting material may further contain 0.01 to 1.0 mol% of? -Fe ₂ O ₃ .

The sintering may comprise maintaining at a first temperature of 400-800 C and holding at a second temperature of 1400-1650 C above the first temperature.

In order to improve the strength of aluminum titanate at a high temperature of 1300 ° C, Al ₂ O ₃ powder having an average particle size of 1 to 10 μm was used as a starting material, and ZrO ₂ powder having an average particle size of 1 to 50 μm It is preferable to use it as a raw material.

The aluminum titanate of the present invention not only has a low coefficient of thermal expansion and high corrosion resistance, but also has excellent high temperature strength and stability even in a high temperature environment.

The aluminum titanate produced by the present invention has a sufficient durability in a high temperature environment, an excellent mechanical strength, and a low thermal instability, and thus is highly likely to be industrially applicable as a high-temperature structural material.

The method of producing aluminum titanate according to the present invention is highly reproducible, simple in process, and can be stably applied to mass production.

Figure 1 is an Al ₂ O ₃ -TiO _{2 2-component} phase diagram.
2 is a field emission scanning electron microscope (FE-SEM) photograph of micro ZrO ₂ powder used as a starting material in Experimental Example 1. FIG.
3 is an FE-SEM photograph of nano-ZrO ₂ powder used as a starting material in Experimental Example 1. FIG.
4 is an FE-SEM photograph of aluminum titanate prepared according to Experimental Example 1 for Sample 1 and Sample 2.
5 is an X-ray diffraction (XRD) pattern of aluminum titanate prepared according to Experimental Example 1, for Sample 1 and Sample 2.
6 is a high temperature three point flexural strength graph of aluminum titanate prepared according to Experimental Example 1, for Sample 1 and Sample 2.
7 is an FE-SEM photograph of micro Al ₂ O ₃ powder used as a starting material in Experimental Example 1. FIG.
8 is an FE-SEM photograph of nano-Al ₂ O ₃ powder used as a starting material in Experimental Example 1. FIG.
9 is an FE-SEM photograph of the aluminum titanate prepared according to Experimental Example 1, for Sample 1 and Sample 3.
10 is an X-ray diffraction (XRD) pattern of aluminum titanate prepared according to Experimental Example 1 for Sample 1 and Sample 3.
11 is a high-temperature three-point curvature graph of aluminum titanate prepared according to Experimental Example 1, for Sample 1 and Sample 3.
12 is a graph showing room temperature and high-temperature bending strength according to sintering time of aluminum titanate sintered at 1500 ° C according to Experimental Example 2. FIG.
13 is a graph showing room temperature and high-temperature bending strength according to sintering time of aluminum titanate sintered at 1600 ° C according to Experimental Example 2. FIG.
FIG. 14 shows X-ray diffraction results according to sintering time of aluminum titanate sintered at 1500 ° C. according to Experimental Example 2. FIG.
Fig. 15 is a result of X-ray diffraction according to sintering time of aluminum titanate sintered at 1600 DEG C according to Experimental Example 2. Fig.
16 is a microstructure of sintered aluminum titanate sintered at 1500 DEG C according to Experimental Example 2. FIG.
17 is a microstructure according to sintering time of aluminum titanate sintered at 1600 DEG C according to Experimental Example 2. FIG.
FIG. 18 is a result of energy dispersive spectroscopy (EDS) showing the mole fraction (atomic%) of phases for a specimen sintered at 1600 ° C. for 16 hours according to Experimental Example 2.
19 is a graph showing the thermal expansion behavior of sintered aluminum titanate sintered at 1500 ° C according to Experimental Example 2, and is a hysteresis curve during heating and cooling processes.
20 is a graph showing the thermal expansion behavior of the aluminum titanate sintered at 1600 ° C according to sintering time according to Experimental Example 2. FIG.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, it should be understood that the following embodiments are provided so that those skilled in the art will be able to fully understand the present invention, and that various modifications may be made without departing from the scope of the present invention. It is not.

Hereinafter, the term " nano " refers to a size in nanometers (nm), which is 1 nm or more and less than 1 탆, and the term " micrometer " It is used to mean size.

The thermal expansion coefficient can be classified into a low thermal expansion, a heavy thermal expansion, and a high thermal expansion. In the case of low thermal expansion, the expansion coefficient is 2 × 10 ^-6 / ° C. or less, and in the case of high thermal expansion, the expansion coefficient is 8 × 10 ^-6 / ° C. Commonly known low thermal expansion ceramic materials include silicate-based, alumino-silicate materials and aluminum titanate.

Aluminum T taneyi (Al ₂ TiO ₅₎ represents the thermal shrinkage in the opposite direction according to the determined direction. For example, aluminum titanate has very large (+) thermal expansion coefficients of 11.8 × 10 ^-6 / ° C and 19.4 × 10 ^-6 / ° C for a and b axes, but -2.6 × 10 ^-6 / ° C, and thus the coefficient of expansion is (-) comprehensively.

1 is Al ₂ O ₃ -TiO _{2 2-component} represents the phase diagram. As can be seen from Fig. 1, aluminum titanate is a compound of two oxides, and its melting temperature is around 1860 ° C. However, since pure aluminum titanate tends to decompose between 750 and 1300 ° C, MgO, Fe ₂ O ₃ and TiO ₂ are added for thermal stability.

The development of low thermal expansion properties of aluminum titanate is reported to be due to microcracks, which is due to the anisotropy of thermal expansion as described above. Aluminum titanate is an unusual material that appears to be inflated along the crystal direction when the cracks generated during the heat treatment process are finely generated, and this microcrack absorbs and thus does not expand as a whole. Although aluminum titanate has such good high-temperature properties and thermal stability, it is known that it is difficult material to obtain dense body due to such fine structure. However, various additives can be introduced as an improvement to such a dense body.

Al ₂ TiO ₅ decomposes into starting materials α-Al ₂ O ₃ and TiO ₂ (rutile) in the temperature range of 750-1300 ℃, resulting in low mechanical strength and thermal properties. In order to suppress such decomposition, there is MgO as a thermodynamic stabilizer which distributes solid solution in the unit lattice to relax the c-axis shrinkage and alleviate the structural strain. At this time, Mg ^{2 +} is substituted with Al ^{3 +} to alleviate the structural deformation, thereby exhibiting a thermal stabilizing effect. In order to improve the low mechanical strength due to microcracks, Mullite (3Al ₂ O ₃ · 2SiO ₂ ) and ZrO ₂ can be used. By forming a secondary phase between the grain boundaries of Al ₂ TiO ₅ , the propagation of microcracks is prevented, and rapid grain growth at 1300 ° C. or higher can be suppressed.

Although research on suppression of high temperature phase decomposition or improvement of strength at room temperature for using Al ₂ TiO ₅ as a refractory has been widely discussed, there have been few studies on thermal and mechanical properties at high temperatures used as actual refractory materials. In order for Al ₂ TiO ₅ to be used as a high-temperature structural material, mechanical properties at high temperatures are important. Microcracks are a factor affecting high-temperature mechanical properties. The microcracks generated by the high crystallographic anisotropy are gradually closed by the thermal expansion of the crystal grains as the temperature rises. This is called micro-cracking healing, which improves the mechanical strength at higher temperatures than at room temperature. Also, due to the existence of microcracks, the thermal expansion coefficient is near to zero until a certain temperature range, and the thermal expansion coefficient is increased from the time when microcracks are almost closed.

Therefore, it is important to select the high temperature phase stabilizer for Al ₂ TiO _{5 and} to study the strength enhancing agent for improving the mechanical strength, so that it is important to develop the composition and to secure the sintering condition that exhibits the optimum physical properties.

Aluminum titanate, in accordance with a preferred embodiment of the present invention, SiO ₂ 8.0~12.0 mol%, ZrO ₂ 1.0~4.0 mol%, MgO 4.0~8.0 mol%, Al ₂ O ₃ 43.0~49.0 mol% and TiO ₂ 33.0~ 39.0 mol% as a chemical composition component.

The aluminum titanate may further contain 0.01 to 1.0 mol% of? -Fe ₂ O ₃ as a chemical composition component.

Method of producing an aluminum titanate according to a preferred embodiment of the present invention, SiO ₂ 8.0~12.0% mol, ZrO ₂ 1.0~4.0% by mole, MgO 4.0~8.0 mol%, Al ₂ O ₃ 43.0~49.0% by mole, and TiO _2, 33.0 to 39.0 mol%, adding an organic binder and a dispersant to the starting material and mixing them, molding the mixed product, and sintering the molded product do.

The starting material may further contain 0.01 to 1.0 mol% of? -Fe ₂ O ₃ .

The sintering may comprise maintaining at a first temperature of 400-800 C and holding at a second temperature of 1400-1650 C above the first temperature.

Hereinafter, a method for producing aluminum titanate according to a preferred embodiment of the present invention will be described in more detail.

From 8.0 to 12.0 mol% of SiO ₂ , from 1.0 to 4.0 mol% of ZrO _{2, from} 4.0 to 8.0 mol% of MgO, from 43.0 to 49.0 mol% of Al ₂ O ₃ and from 33.0 to 39.0 mol% of TiO ₂ as starting materials. The starting material may further contain 0.01 to 1.0 mol% of? -Fe ₂ O ₃ .

The starting material may be a raw material such as an oxide or an oxide powder, and the components of each raw material may be weighed so that the total composition of the starting material is 8.0 to 12.0 mol% of SiO ₂ , 1.0 to 4.0 mol% of ZrO ₂ , 8.0 mol%, Al ₂ O ₃ 43.0 to 49.0 mol%, and TiO ₂ 33.0 to 39.0 mol%, the starting material is not limited.

Together content of SiO ₂ is preferably about 8.0~12.0% by mole, if the content of SiO ₂ is too small, it is possible the mullite (mullite) the crystalline phase does not occur after sintering, the glass content of the SiO ₂ is too large after sintering And the high temperature strength may be lowered due to softening.

The content of ZrO ₂ is preferably about 1.0 to 4.0 mol%. If the content of ZrO ₂ is too small, the thermal expansion coefficient may become large after sintering. In order to improve the strength of aluminum titanate at a high temperature of 1300 캜, it is preferable to use micro ZrO ₂ powder having an average particle size of 1 to 50 탆 as a starting material. When the particle size of the ZrO ₂ powder is nano, the strength of the aluminum titanate at 1100 ° C is excellent, but the strength at 1300 ° C may be lower than that at 1100 ° C. Therefore, the strength of aluminum titanate is improved at a high temperature of 1300 ° C The micro ZrO ₂ powder is used.

The role of the MgO is suppressed to thermal instability which is decomposed in the area of 750~1300 ℃ of alumina (α-Al ₂ O ₃₎ and titanium oxide (TiO ₂₎ during cooling after the sintering, and the amount of the MgO is 4.0~ 8.0 mol%. If the content of MgO is too small, it may be decomposed at a high temperature of 750 to 1300 DEG C.

The Al ₂ O ₃ serves to improve the chemical durability and to form a mullite crystal phase after sintering. The mullite crystal phase inhibits grain growth of the aluminum titanate to enhance thermal stability, thermal durability and thermal shock resistance. If the content of Al ₂ O ₃ is too small, the effect of improvement in durability, thermal stability, and improvement in thermal shock resistance is weak. In order to improve the strength of the aluminum titanate at a high temperature of 1300 ° C, it is preferable to use micro Al ₂ O ₃ powder having an average particle size of 1 to 10 μm as a starting material. When the particle size of the Al ₂ O ₃ powder is nano, the strength of the aluminum titanate at 1100 ° C is excellent, but the strength at 1300 ° C may be lower than that at 1100 ° C. Therefore, the strength of the aluminum titanate at a high temperature of 1300 ° C The micro Al ₂ O ₃ powder is used.

The TiO ₂ not only serves as a source for providing a Ti component and an oxygen component of aluminum titanate (Al ₂ TiO ₅ ), but also plays a role of suppressing thermal instability. The content of TiO ₂ is preferably about 33.0 to 39.0 mol%.

An organic binder and a dispersant are added to the starting material and mixed.

Examples of the organic binder include polyethylene glycol, ethyl cellulose, methyl cellulose, nitrocellulose, carboxycellulose, polyvinyl alcohol, acrylic acid ester, methacrylic acid ester, polyvinyl butyral, n-butyl acetate As the organic binder, generally known materials can be used.

As the substance generally known in the above dispersion system, those sold commercially can be used.

The mixing may be performed by dry mixing or wet mixing, and ball milling may be used for the dry mixing or wet mixing. Specifically, the starting material, the organic binder, and the dispersant are charged into a ball milling machine, and the mixture is mechanically pulverized by rotating at a constant speed using a ball milling machine and uniformly mixed. The ball used for ball milling may be a ball made of ceramics such as zirconia or alumina, and the balls may be all the same size or may be used together with balls having two or more sizes. The size of the ball, the milling time, and the rotation speed per minute of the ball miller. For example, the size of the balls may be set in the range of about 1 mm to 30 mm in consideration of the size of the particles, the rotational speed of the ball miller may be set in the range of about 50 to 500 rpm, . By ball milling, the starting material is pulverized into fine sized particles, having a uniform particle size distribution, and uniformly mixed.

The mixed result is molded. Various methods such as compression molding, extrusion molding and the like known in the art can be used for the above molding.

The molded product is sintered. The sintering may include maintaining at a first temperature of 400-800 C and holding at a second temperature of 1400-1650 C above the first temperature.

Hereinafter, the sintering process will be described in detail.

The molded product is charged into a furnace such as an electric furnace.

The temperature of the furnace is raised to a first temperature of 400 to 800 DEG C, and the organic binder is maintained at a first temperature of 400 to 800 DEG C for 2 to 12 hours to remove the organic binder, 2 < / RTI > temperature and held at a second temperature for 1 to 48 hours to effect sintering. It is desirable to keep the pressure inside the furnace constant during sintering.

The sintering is preferably performed at a second temperature in the range of 1400 to 1650 ° C. If the sintering temperature is lower than 1400 ° C, the thermal or mechanical properties of the aluminum titanate may be poor due to incomplete sintering. If the sintering temperature is higher than 1650 ° C, the energy consumption is high and the properties of the aluminum titanate are poor .

It is preferable to raise the temperature to the second temperature at a heating rate of 1 to 50 ° C / min. If the heating rate is too slow, it takes a long time to decrease the productivity. If the heating rate is too fast, It is preferable to raise the temperature at the temperature raising rate within the above range.

The sintering is preferably performed at a second temperature for 1 to 48 hours. If the sintering time is too long, it is not economical because the energy consumption is high, and further sintering effect is not expected. If the sintering time is short, the properties of aluminum titanate may not be good due to incomplete sintering.

The sintering is preferably performed in an oxidizing atmosphere (for example, oxygen (O ₂ ) or air atmosphere).

After the sintering process is performed, the furnace temperature is lowered to unload the aluminum titanate. The furnace cooling may be effected by shutting down the furnace power source to cool it in a natural state, or optionally by setting a temperature decreasing rate (for example, 10 DEG C / min). It is preferable to keep the pressure inside the furnace constant even while the furnace temperature is lowered.

Hereinafter, experimental examples according to the present invention will be specifically shown, and the present invention is not limited to the following experimental examples.

Physical properties were thermophysical properties, physical properties, mechanical properties, and chemical reaction characteristics. Thermal properties include thermal expansion coefficient, porosity and microstructure for physical properties, room temperature bending strength, high temperature bending strength and hardness for mechanical properties. The chemical reaction, on the other hand, selects the chemical reaction depth between the metal and the ceramic as an index.

The sintered density and the porosity were measured by Archimedes method after 5 hours of melting. The Archimedes method is described in detail in KSL 4008, "Determination of Absorption Rate, Volume Ratio, Apparent Specific Gravity and Porosity of Ceramics".

The equipment used for thermal expansion properties, which is thermal properties, is a dilatometer. The thermal expansion characteristics of the sintered body were measured using a dilatometer (DIL 402 PC, Netzsch, Germany) at a heating rate of 10 ° C / min up to 1300 ° C, and then cooled to a process of cooling. The result was shown by a hysteresis curve. At this time, the coefficient of thermal expansion is an expansion value during heating at a temperature of 50 ° C to 1000 ° C.

The evaluation of the physical properties of the sintered body was carried out by using an X-ray diffractometer (D / max 2500, Rigaku, Japan) at 40 kV and 100 mA at a scan rate of 5 ° / Were measured.

The microstructure was observed using a field emission scanning electron microscope (FE-SEM) (6701F, JEOL). The FE-SEM microstructure was observed after the sintered body was polished to a thickness of 1 μm or less using a diamond suspension and then thermally etched at a temperature of 100 ° C. lower than the sintering temperature for 30 minutes.

The high-temperature bending machine is a device that can evaluate the bending strength by raising the temperature to 1500 ° C. The inside of the machine can be controlled not only by vacuum but also by atmosphere. It is designed to analyze six samples at the same time (R & R). The bending strength was measured by three point bending strength method with the specimen size of 3 × 4 × 40mm and polished with 2000 (Ewha diamond, CBN). The bending strength at high temperature was measured at 1100 ℃, 1200 ℃ and 1300 ℃.

<Experimental Example 1>

In order to improve the stability of the high-temperature phase of the aluminum titanate material and to optimize the microstructure of the aluminum titanate material, the composition as shown in Table 1 below was selected, and Al ₂ O ₃ , which is a raw material powder affecting the formation of the aluminum titanate phase, The effects of the size of ZrO ₂ , which is a mechanical strength enhancer, on the properties of aluminum titanate were tested with four compositions of 2 levels and 2 levels. Table 1 below is a composition table according to the starting materials of the compositions used in the experimental examples.

Starting material Company and Purity Average particle size
(탆) Sample 1
(mole%) Sample 2
(mole%) Sample 3
(mole%) Sample 4
(mole%) Al ₂ O ₃ SUMIMOTO (99.7%) 3.5 46 46 - - SUMIMOTO (99.99%) 0.5 - - 46 46 TiO ₂ COSMO CHEMICAL (98%) 0.4 35.8 35.8 35.8 35.8 SiO ₂ KOJUNDO (≥99.9)
Quartz 0.8 11.5 11.5 11.5 11.5 ZrO ₂ SINOCERA (> 99.9%) 0.07 2.1 - 2.1 - KOJUNDO (≥98%) One - 2.1 - 2.1 MgO KOJUNDO (≥99.9) One 4.5 4.5 4.5 4.5 Fe ₂ O ₃ KOJUNDO (≥99.9%)
α-Fe ₂ O ₃ One 0.1 0.1 0.1 0.1

For the synthesis of Al ₂ TiO ₅ , the starting materials were wet mixed. For wet mixing, ball milling was used. Miller was added to the solvent, ethanol, with metered starting materials, organic binder (PEG8000, 1 wt%) and dispersant (RE610 0.1 wt%). The ball used for ball milling was a ZrO ₂ ball (? 3).

The wet mixed resultant was kept at 80 DEG C for 24 hours for drying, and the obtained mixed powder was sieved to 200 mesh (75 mu m).

The resultant sieved product was subjected to primary molding at a pressure of 22 MPa for 30 seconds at a pressure of 22 MPa and subjected to cold isostatic pressing (CIP) at 200 MPa for 1 minute to prepare a disc-shaped specimen (Φ17) .

In order to remove the organic binder, the aluminum titanate was prepared by keeping at 600 ° C (temperature increase rate 5 ° C / min) for 1 hour and sintering at 1500 ° C (temperature increase rate 5 ° C / min) for 2 hours.

Table 2 shows the physical properties of the aluminum titanate sintered body according to the ZrO ₂ particle size.

Furtherance Sintered density (g / cm3) Porosity
(%) Room temperature bending strength (MPa) Coefficient of thermal expansion
(× 10 ^-6 / K)
(~ 1000 ° C) Crack onset (℃) High temperature strength (MPa) 1100 ℃ 1200 ℃ 1300 ℃ Sample 1 3.3 3.9 46.25 1.9 467.3 140.2 127.4 46.6 Sample 2 3.3 3.8 44.2 1.6 467.4 139.3 133.4 56.5

2 is an FE-SEM photograph of a micro-ZrO ₂ powder used as the starting material in Experiment 1, Figure 3 is an FE-SEM photograph of the nano-ZrO ₂ powder used as a starting material in the experimental example 1, the micro-ZrO ₂ powder Silver particles are weakly aggregated.

Fig. 4 is an FE-SEM photograph of aluminum titanate prepared according to Experimental Example 1, for Sample 1 and Sample 2. Fig. Sample 1 is a case of using a nano ZrO ₂ powder having an average particle diameter of 70 nm as a starting material and Sample 2 is a case of using micro ZrO ₂ powder having an average particle diameter of 1 탆 as a starting material.

5 is an X-ray diffraction (XRD) pattern of aluminum titanate prepared according to Experimental Example 1, for Sample 1 and Sample 2.

In FIG. 5, X-ray diffraction (XRD) results showing different main peaks in the direction of crystal growth of the aluminum titanate peak can be seen. It can be seen that there is a difference in the degree of formation of the aluminum titanate phase depending on the nano-ZrO ₂ powder and the micro ZrO ₂ powder. As a result, it can be expected that even the same mechanical stabilizer affects microcracks depending on the particle size, so that there will be a difference in thermal properties mainly.

6 is a high temperature three point flexural strength graph of aluminum titanate prepared according to Experimental Example 1, for Sample 1 and Sample 2.

In the high bending strength curve of FIG. 6, the same value was obtained at 1100 ° C, but the tendency was shown to decrease as the temperature increased. In the case of using micro ZrO ₂ powder, the high temperature bending strength value was slightly increased. ZrO ₂ exists outside the grain boundaries as a secondary phase, and its strength is improved due to its high strength value and the effect of controlling the growth of aluminum titanate crystal grains. However, in the case of using micro ZrO ₂ powder rather than using nano ZrO ₂ powder ZrO ₂ Since the secondary phase size is large and the distribution is not wide, it is expected that there will be a difference in the microcracking behavior due to the temperature rise even though the microcracks are locally stable. Therefore, the area of the grain boundary is reduced due to the secondary phase size, which increases the interfacial energy and increases the resistance to thermal deformation energy. However, no large differences in crack onset temperatures were observed, suggesting that the density of microcracks is approximately the same. Experimental results show that the micro thermal expansion value and the improved high temperature bending strength can be obtained in the case of using the micro ZrO ₂ powder as compared with the case of using the nano ZrO ₂ powder.

Table 3 shows the physical properties of the aluminum titanate sintered body according to the particle size of Al ₂ O ₃ .

Furtherance Sintered density (g / cm3) Porosity
(%) Room temperature bending strength (MPa) Coefficient of thermal expansion
(× 10 ^-6 / K)
(~ 1000 ° C) Crack onset (℃) High temperature strength (MPa) 1100 ℃ 1200 ℃ 1300 ℃ Sample 1 3.3 3.9 46.25 1.9 467.3 140.2 127.4 46.6 Sample 3 3.3 3.8 50.5 1.8 458.9 200.4 152.8 44.9

Sample 3 using nano-Al ₂ O ₃ having an average particle size of 500 nm showed no difference in density and porosity from Sample 1 using micro Al ₂ O ₃ powder having an average particle size of 3.5 μm and showed no difference in mechanical properties at room temperature and high temperature The intensity value was increased.

7 is an FE-SEM photograph of micro Al ₂ O ₃ powder used as a starting material in Experimental Example 1, and FIG. 8 is an FE-SEM photograph of nano Al ₂ O ₃ powder used as a starting material in Experimental Example 1. FIG.

Referring to FIGS. 7 and 8, nano Al ₂ O ₃ has a size of about 200 nm, which is different from about 5.8 μm of micro Al ₂ O ₃ .

9 is an FE-SEM photograph of the aluminum titanate prepared according to Experimental Example 1, for Sample 1 and Sample 3. Sample 1 was a micro Al ₂ O ₃ powder having an average particle diameter of 3.5 μm as a starting material and Sample 3 was a nano Al ₂ O ₃ powder having an average particle diameter of 500 nm as a starting material.

9, the microstructure of Sample 1 using nano-Al ₂ O ₃ powder was observed to be smaller than that of Sample 1 using micro Al ₂ O ₃ powder. do. In addition, the distribution of mullite phase is more uniform than that of micro Al ₂ O ₃ powder.

10 is an X-ray diffraction (XRD) pattern of aluminum titanate prepared according to Experimental Example 1 for Sample 1 and Sample 3.

X-ray diffraction results in FIG. 10 show X-ray diffraction results showing different principal peaks in the crystal growth direction of aluminum titanate, respectively. According to nano Al ₂ O ₃ powder and micro Al ₂ O ₃ powder, aluminum titanate It can be seen that there is a difference in the degree of phase formation. In addition, it can be seen that the Al ₂ O ₃ peak is weakened when the nano Al ₂ O ₃ powder is used, and it is understood that the decomposition is less than that when the micro Al ₂ O ₃ powder is used. This can explain the strength improvement due to the stable aluminum titanate phase.

11 is a high-temperature three-point curvature graph of aluminum titanate prepared according to Experimental Example 1, for Sample 1 and Sample 3.

11 shows a high improvement value at high temperature bending strength. Especially, the strength of the specimens was increased from 1100 ℃ to 200MPa, and the strength of the specimens tended to decrease sharply with increasing temperature. It is expected that the size of the aluminum titanate grains synthesized with Al ₂ O ₃ of the same size as that of the nano-sized TiO ₂ is expected to be small. As a result, the grain size is smaller than that of the micro Al ₂ O ₃ powder and the density of the unstable aluminum titanate phases It is thought that it is not high. In addition, in the case of using the nano-Al ₂ O ₃ powder, not only the aluminum titanate but also the crystal grains of the mullite are widely distributed in a small size. However, in the case of Sample 3, the strength was remarkably lowered at 1300 ° C compared to Sample 1 at 1100 ° C. More research is needed later on.

<Experimental Example 2>

The composition of Sample 2 was selected in the composition shown in Table 2, and the process optimization was carried out by using sintering temperature and sintering time as parameters. In the case of the composition shown in Table 2, the specimen having a sintering temperature of 1500 ° C was higher than that of the specimen having a sintering temperature of 1600 ° C, and the coefficient of thermal expansion was also high. As the sintering time becomes longer, the amount of synthesis of aluminum titanate increases, resulting in an increase in crystallographic anisotropy and an increase in the amount of microcracks. Through the optimization of sintering temperature and sintering time conditions, we aim to establish process conditions with high thermal strength at 1300 ℃ with low thermal expansion coefficient. The sintering temperature was set to 1500 ℃ and 1600 ℃, and the sintering time was set to 2h, 4h, 8h and 16h. Aluminum titanate was synthesized under eight conditions and the thermal and mechanical properties were analyzed.

Synthesis of Al ₂ TiO ₅ proceeded in the same manner as in Experimental Example 1 except for sintering temperature and sintering time.

Table 4 below shows the physical properties according to the sintering time in the case of sintering at 1500 ° C. In Table 4, 1500_2h represents the case of sintering at 1500 ° C for 2 hours, 1500_4h represents the case of sintering at 1500 ° C for 4 hours, 1500_6h represents sintering at 1500 ° C for 6 hours, and 1500_16h at 1500 ° C Time is sintered.

Sintering temperature and sintering time Sintered density
(g / cm3) Porosity
(%) Coefficient of thermal expansion
(× 10 ^-6 / K)
(~ 1000 ° C) Room temperature bending strength
(MPa) High temperature bending strength (MPa) 1100 ℃ 1200 ℃ 1300 ℃ 1500_2h 3.29 3.83 1.0 34.1 106.3 105.2 55.4 1500_4h 3.25 5.56 0.9 30.7 113.3 112.3 65.5 1500_6h 3.23 6.08 0.5 28.3 112.7 105.4 72.9 1500_16h 3.21 5.28 -0.6 21.9 86.2 95.6 74.3

Table 5 below shows the physical properties according to sintering time when sintering at 1600 ° C. In Table 5 below, 1600_2h represents the case of sintering at 1600 ° C for 2 hours, 1600_4h represents the case of sintering at 1600 ° C for 4 hours, 1600_6h represents the case of sintering at 1600 ° C for 6 hours, and 1600_16h represents 16 Time is sintered.

Sintering temperature and sintering time Sintered density
(g / cm3) Porosity
(%) Coefficient of thermal expansion
(× 10 ^-6 / K)
(~ 1000 ° C) Room temperature bending strength
(MPa) High temperature bending strength (MPa) 1100 ℃ 1200 ℃ 1300 ℃ 1600_2h 3.14 7.10 -0.2 19.8 63.6 79.1 42.6 1600_4h 3.10 6.69 -0.5 15.8 58.2 71.6 30.8 1600_6h 3.09 5.84 -0.5 12.5 66.6 55.3 20.8 1600_16h 3.06 7.15 -1.1 11.0 53.0 56.9 18.1

12 is a graph showing room temperature and high-temperature bending strength according to sintering time of aluminum titanate sintered at 1500 ° C according to Experimental Example 2. FIG. In FIG. 12, 1500_2h represents the case of sintering at 1500 ° C for 2 hours, 1500_4h represents the case of sintering at 1500 ° C for 4 hours, 1500_6h represents sintering at 1500 ° C for 6 hours, and 1500_16h represents sintering at 1500 ° C for 16 hours. . In FIG. 12, 'RT' means room temperature.

12, the specimens sintered at room temperature for 2 hours showed the highest strength (34 MPa) and the specimens sintered at 1100 ° C and 1200 ° C for 4 hours showed the highest strength (113 MPa, 112 MPa). However, at 1300 ℃, the strength increased as the sintering time became longer, and the specimens sintered for 8 hours and 16 hours showed the highest strength (74 MPa).

13 is a graph showing room temperature and high-temperature bending strength according to sintering time of aluminum titanate sintered at 1600 ° C according to Experimental Example 2. FIG. In FIG. 13, 1600_2h indicates sintering at 1600 ° C for 2 hours, 1600_4h indicates sintering at 1600 ° C for 4 hours, 1600_6h indicates sintering at 1600 ° C for 6 hours, and 1600_16h indicates sintering at 1600 ° C for 16 hours. . In FIG. 13, 'RT' means room temperature.

13, the specimens sintered at room temperature for 2 hours showed the highest strength (19 MPa) and the strength decreased as the sintering time became longer. Unlike aluminum titanate sintered at 1500 ℃, it showed the highest strength at 1100 ℃ and the highest strength (79 MPa) at 1200 ℃. Also, the highest strength at 1300 ℃ was sintering (43 MPa) for 2 hours.

FIG. 14 shows X-ray diffraction results according to sintering time of aluminum titanate sintered at 1500 ° C. according to Experimental Example 2. FIG.

14, aluminum titanate, mullite _{(3Al 2 O 3 · 2SiO 2} ), ZrO 2 and Al ₂ O ₃ phase was detected in the specimen by the main peak of the sample sintered 2 sintered 4 hours or more major peaks with There was a difference. The main peak of aluminum titanate (PDF number 41-0258) is 26.5 degrees (2-theta). This is because the sintering time of aluminum titanate is insufficient. When the sintering time is sufficient, it is considered that the main peak of aluminum titanate sintered for 4 hours or more is constant, which means that sintering for 2 hours is insufficient for synthesis of aluminum titanate.

Fig. 15 is a result of X-ray diffraction according to sintering time of aluminum titanate sintered at 1600 DEG C according to Experimental Example 2. Fig.

Referring to FIG. 15, it is considered that aluminum titanate synthesis was sufficiently performed when the main peak position was observed when sintered for 2 hours. As the sintering time became longer, it was observed that the mullite peak gradually decreased and the Al ₂ O ₃ peak increased. In the case of sintering for 16 hours, the main peak shifted 33 degrees and the mullite peak completely disappeared. As the sintering time becomes longer, the mullite phase is decomposed into Al ₂ O ₃ and SiO ₂ , and Al ₂ O ₃ forms a secondary phase. As a result, a peak is observed and SiO ₂ is solved in the solid solution of aluminum titanate to observe the peak It is judged that it can not be done. Therefore, if the sintering time is prolonged, it is expected that the strength improvement effect will be lessened by decomposing the mullite.

16 is a microstructure of sintered aluminum titanate sintered at 1500 DEG C according to Experimental Example 2. FIG. X-ray diffraction and EDS (energy dispersive spectroscopy) show that the light gray is aluminum titanate, the dark gray is the mullite phase and the white phase is the ZrO ₂ phase. At 2, 4, and 8 hours, no significant differences in microstructure were observed and crystal growth was observed at 16 hours.

17 is a microstructure according to sintering time of aluminum titanate sintered at 1600 DEG C according to Experimental Example 2. FIG.

Referring to FIG. 17, X-ray diffraction and EDS (energy dispersive spectroscopy) results show that the aluminum titanate sintered for two and four hours has a light gray aluminum titanate, a dark gray mullite phase and a white phase ZrO ₂ phase. As compared to a specimen sintered at 1500 ℃ shape ZrO ₂ on the second, the longer can be observed that the volume is also reduced. The grain size of specimen sintered at 1600 ℃ for 2 hours was similar to that of sintered specimen at 1500 ℃ for 16 hours. As a result, it was judged that the grain growth occurred at 2 hours at 1600 ℃. The morphology of the mullite secondary phase was similar to that of the mullite secondary phase at 1,500 ℃ for 2 hours and 4 hours. The specimen sintered for 8 hours and 16 hours had rough surface and blurred grain boundaries.

18 shows the results of EDS showing the molar fraction (atomic%) of phases for a specimen sintered at 1600 ° C for 16 hours according to Experimental Example 2. FIG.

Referring to FIG. 18, spectrum 1 was detected as aluminum titanate and spectrum 3 was detected as mullite, while in spectrum 2, the Si component was escaped and the Ti component was increased. As a result, it was observed that the mullite phase was decomposed.

19 is a graph showing the thermal expansion behavior of sintered aluminum titanate sintered at 1500 ° C according to Experimental Example 2, and is a hysteresis curve during heating and cooling processes.

Referring to FIG. 19, it can be seen that as the sintering time becomes longer, the thermal expansion is lowered, and the similar behavior is observed for 2, 4, and 8 hours. In the case of 16 hours, shrinkage is observed at about 1100 ° C . Also, except for 16 hours, all of them showed a positive expansion value. In the case of 16 hours, they showed a negative expansion value which shrinks in spite of being heated. After cooling, the volume returned to its original volume. In the case of 2, 4, and 8 hours, it increased by 0.5 to 1.5% than the original volume, but shrunk by 0.5% in the case of 16 hours.

20 is a graph showing the thermal expansion behavior of the aluminum titanate sintered at 1600 ° C according to sintering time according to Experimental Example 2. FIG.

20, negative expansion values were observed under all sintering time conditions, and specimens sintered for 2 hours were expanded at 1000 ° C, and the expansion start points were different from each other as the sintering time was longer. The specimen sintered for 16 hours began to expand at 1200 ℃. When cooling, it contracted by -0.4% under all sintering conditions and began to expand in the range of 600 to 700 ° C, returning to its original volume. Finally, the volume increased by 0.1-0.2%.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, This is possible.

Claims (6)

delete delete SiO ₂ 8.0~12.0 mol%, ZrO ₂ 1.0~4.0 mol%, MgO 4.0~8.0 _{mol%, α-Al 2 O 3} 43.0~49.0 _{mol%, α-Fe 2 O 3} 0.01~1.0% by mole, and TiO ₂ 33.0 To 39.0 mol% of a starting material;
Adding and mixing an organic binder and a dispersant to the starting material;
Molding the mixed result; And
And sintering the shaped product,
In order to improve the strength of aluminum titanate at a high temperature of 1300 ° C, α-Al ₂ O ₃ powder having an average particle size of 1 to 10 μm was used as a starting material, and ZrO ₂ powder having an average particle size of 1 to 50 μm As starting materials,
Wherein the sintering step comprises:
Maintaining at a first temperature of 400-800 [deg.] C; And
Lt; RTI ID = 0.0 &gt; 1600 C &lt; / RTI &gt; higher than the first temperature. delete delete delete

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