KR100486121B1 - A Method for Producing Aluminum titanate- Zirconium titanate Ceramics with Low Thermal Expansion Behavior - Google Patents

Abstract

The present invention relates to the production of aluminum titanate-zirconium titanate (Al ₂ TiO ₅ -ZrTiO ₄ ) ceramics with low thermal expansion.

Ceramic manufacturing method of the present invention is mol%, 40 to 60% Al ₂ O ₃ and 60 to 40% of TiO ₂ by adding 3-7% MgO mixed and pulverized, then molded and sintered aluminum titanate After the powder was obtained, 40 to 60% of ZrO ₂ and 60 to 40% of TiO ₂ were mixed and pulverized, and then molded and sintered to obtain a zirconium titanate powder. Then, the aluminum titanate and zirconium titanate powder were mixed with each other. The technical gist of the aluminum titanate-zirconium titanate ceramic is produced by mixing, sintering and sintering.

Description

A method for producing aluminum titanate- zirconium titanate ceramics with low thermal expansion behavior}

The present invention relates to a portliner, a catalyst carrier, a caloric honeycomb for heat capacitor, a molten metal filter, a catalyst carrier for cooking or a nonferrous metal melt factory and a glass melt refractory plant. Manufacture of aluminum titanate-zirconium titanate (Al ₂ TiO ₅ -ZrTiO ₄ ) ceramics used as high-quality refractory materials or various high-temperature structural materials. More specifically, due to low thermal expansion coefficient, excellent thermal shock resistance, corrosion resistance and thermal insulation It relates to a method for producing an aluminum titanate-zirconium titanate ceramic.

Generally, pure aluminum titanate used as a high-temperature structural material has thermal instability that decomposes into starting materials alumina (α-Al ₂ O ₃ ) and titania (TiO ₂ -rutile) in the region of 800-1300 ℃ during cooling after sintering. Have In addition, since they have different coefficients of thermal expansion according to different crystal axes, microcracks occur due to internal stress, and at high temperatures of 1300 ° C. or higher, they have low mechanical strength due to rapid growth of aluminum titanate grains. In particular, when the starting material alumina and titania react to synthesize β-type aluminum titanate (β-Al ₂ TiO ₅ ), the theoretical density of low aluminum titanate (Al ₂ TiO ₅ ) (corundum: 3.99 g / cm 3, rutile: 4.25 g / cm 3 and tielite: 3.702 g / cm 3) resulting in 10-15% volume expansion. Such low sintering properties and the low mechanical strength and thermal instability thus limit many industrial applications of aluminum titanate as a high temperature structural material.

Therefore, the successful industrial application of aluminum titanate ceramics depends on how the microstructural phenomena of the above materials can be controlled. One such control method is to understand the properties of pure aluminum titanate decomposing into alumina and titania and to thermally and mechanically stabilize it.

The method of stabilizing the thermal instability of the aluminum titanate at 1300 ° C. or less can be largely classified into thermodynamic stabilization and kinetic stabilization. In the thermodynamic stabilization method, MgO, Fe ₂ O ₃ , TiO ₂ , Cr ₂ O ₃ , GaO ₂ and the like to form a solid solution with Al ₂ TiO ₅ , Mg ₂ similar to Fe ₂ TiO ₅ (pseudobrookite) structure TiO ₅ (karroite), Ti ₂ TiO ₅ (anosovite), FeTi ₂ O ₅ (ferropseudobrookite) or (Al, Cr) ₂ TiO ₅ to form a stabilization at a decomposition temperature of 1300 ℃ or less. On the other hand, the kinematic stabilization method, aluminum titanate particles by adding a material such as SiO ₂ , ZrO ₂ , α-Al ₂ O ₃ , mullite, ZrTiO ₄ , which does not form a solid solution with aluminum titanate It is a method of restraining and stabilizing aluminum titanate grain growth as a 2nd phase between them.

However, the methods for producing stabilized aluminum titanate by adding the conventional additives, the mechanical properties are lowered by the rapid growth of aluminum titanate particles at a high temperature of 1300 ℃, aluminum titanate is decomposed as a starting material. The stabilized aluminum titanate thus exhibits high thermal expansion and at the same time low thermal shock resistance.

An object of the present invention is to suppress the rapid grain growth of the conventional aluminum titanate to the zirconium titanate phase to achieve thermal stabilization, so that the thermal expansion coefficient of aluminum titanate-zirconium titanate (Al ₂ TiO) is very low ₅ -ZrTiO ₄ ) ceramics.

Aluminum titanate-zirconium titanate ceramic manufacturing method according to the present invention for achieving the above object, in mol%, 40 to 60% Al ₂ O ₃ and 60 to 40% of TiO ₂ 3-7% MgO Adding, mixing, and pulverizing, followed by molding and sintering to obtain aluminum titanate powder;

40 to 60% of ZrO ₂ and 60 to 40% of TiO ₂ are mixed and ground, followed by molding and sintering to obtain zirconium titanate powder, and

The aluminum titanate and zirconium titanate powder are mixed with each other, followed by molding and sintering to obtain an aluminum titanate-zirconium titanate ceramic.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the aluminum titanate-zirconium titanate ceramic manufacturing method according to the present invention, aluminum titanate powder is prepared, zirconium titanate powder is prepared, and the two powders are sintered to prepare aluminum titanate-zirconium titanate powder. According to the present invention, the zirconium titanate as the second phase inhibits grain growth of aluminum titanate, thereby thermally stabilizing to produce an aluminum titanate-zirconium titanate ceramic excellent in thermal durability and thermal shock resistance.

First, the aluminum titanate powder may be prepared by adding iron oxide to alumina and titania powder and sintering it. At this time, the mixture of alumina and titania is made into alumina 40-40 mol% (hereinafter only referred to as%) of titania 60-40%, and magnesium oxide (MgO) is added to it in the range of 3-7% here, respectively. To pulverize them. If the mixing ratio of the alumina is less than 40%, unreacted titania is present, and if it exceeds 60%, the grain growth of the synthesized aluminum titanate can be suppressed, but it is not preferable because of the high coefficient of thermal expansion. The pulverized mixture is molded and sintered to prepare aluminum titanate powder. The sintering temperature is in the range of 1350 ~ 1600 ℃.

Next, zirconium titanate powder is prepared by mixing 40 to 60% of zirconia and 40 to 60% of titania, followed by molding and sintering the ground mixture.

The zirconium titanate added to the present invention has a low thermal expansion coefficient as a microcracked structure, such as HfTiO ₄ , and is structurally similar to the structure of α-PbO ₂ . Zirconium titanate is generally used as a dielectric material, pigments, etc. among electronic materials, and has been rarely applied as a high temperature structural material.

In the case of the present invention, if the mixing ratio of zirconia is less than 40%, unreacted titania is present, and if it exceeds 60%, the microstructure is dense, which is not preferable as a material having a low coefficient of thermal expansion.

Finally, the two powders prepared as above are appropriately mixed, molded and sintered. Aluminum titanate and zirconium titanate powder particles do not synthesize into solid solutions that form new compounds of each other, but exhibit physically uniformly mixed microstructures. The zirconium titanate added to the present invention inhibits grain growth of aluminum titanate and has a dense structure. As the zirconium titanate phase increases, the particles of aluminum titanate become smaller. Therefore, in this invention, it is necessary to control the mixing ratio of the said zirconium titanate powder to an appropriate range. Preferably, the aluminum titanate powder and the zirconium titanate powder are mixed at a ratio of 40: 60 to 90: 10%. The powder of zirconium titanate is undesirable due to the thermally unstable aluminum titanate when mixed to less than 10% and relatively high thermal expandability above 60%. More preferably, the aluminum titanate powder and zirconium titanate powder are mixed at a ratio of 40: 60 to 70: 30.

In the present invention, the two phases of aluminum titanate and zirconium titanate have a definite boundary, and the microcracks formed along the particle surface are filled with the zirconium titanate and exhibit low coefficient of thermal expansion even at a relatively high temperature of about 1350 ° C. In addition, in the case of the present invention, rapid grain growth of aluminum titanate occurring at about 1300 ° C. is suppressed onto the zirconium titanate phase and thermally stabilized.

It is preferable to perform the said sintering in the range of 1350-1600 degreeC. If sintering is performed at less than 1350 ° C., the relative density is low, and if sintering is more than 1600 ° C., it is not preferable due to grain growth of aluminum titanate.

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

EXAMPLE

5 mol% of Mg0 was added to 50 mol% Al ₂ O ₃ and 50 mol% TiO ₂ , mixed in a ball mill for 10 hours, and then molded to about 150 MPa, and the molded body was calcined to obtain aluminum titanate powder. At this time, baking was performed by heating up to 500 degreeC at 100 degreeC / h, hold | maintaining for 2 hours, holding at 1600 degreeC for 4 hours, and performing on the conditions to cool to 600 degreeC / h to normal temperature.

Then, 50 mol% ZrO ₂ and 50 mol% TiO ₂ were mixed in a ball mill for 10 hours, and then sintered at 1600 ° C. for 4 hours to obtain a zirconium titanate powder.

The properties of each of the sintered powders thus synthesized are shown in Table 1.

material Prize Sintered Density (g / cm3) Theoretical density (g / cm3) Relative Density (%) Particle size Coefficient of thermal expansion at 25 ~ 1350 ℃ (x10 ^-6 / K) Al ₂ TiO ₅ β-Al ₂ TiO ₅ 3.68 3.70 93.2 50% <2.5mm 0.68 ZrTiO ₄ high-ZrTiO ₄ 4.85 5.06 95.0 100% <4.0mm 8.29

Thereafter, the synthesized sintered materials were dry pulverized, and then the pulverized powder was sieved by a sieve to prepare a powder having passed through 150 to 200mesh. Each of these powders were mixed in the molar ratio as shown in Table 2, and 3% Zusoplast 126/3, 3% Optapix PAF 35 and 5% water were mixed with a binder to uniaxially press-form at 100 to 200 N / mm2. It was. The molded compacts were sintered at 1500 DEG C and 1600 DEG C for 2 hours, respectively, to prepare a final aluminum titanate-zirconium titanate ceramic.

Specimens were taken from the aluminum titanate-zirconium titanate ceramics thus prepared, and the coefficient of thermal expansion was measured. The results are shown in Table 2. The coefficient of thermal expansion for the aluminum titanate ceramics with mullite is also shown for comparison.

The thermal expansion coefficient was measured from room temperature to 1350 ° C. at a temperature rising and cooling rate of 10 ° C./min with a load of 5 g applied to the specimen to reduce errors using a dilatometer.

division Chemical composition (mol%) Coefficient of Thermal Expansion (10 ^-6 K ^-1 ) Al ₂ TiO ₅ ZrTiO ₄ Mullite Conventional Materials 1 50 0 50 4.1 Conventional material 2 30 0 70 4.7 Invention 1 50 50 0 1.3 Invention 2 70 30 0 1.2 Invention 3 80 20 0 0.9 Invention 4 90 10 0 0.3

As shown in Table 2, when looking at the thermal expansion, the invention materials showed 0.3 ~ 1.3 × 10 ^-6 6K ^-1 , respectively, a much lower coefficient of thermal expansion than conventional aluminum titanate ceramics.

As described above, according to the present invention, aluminum titanate-zirconium titanate ceramics having a low coefficient of thermal expansion and stabilized at a high melting point (1830 ° C.), in particular, can be obtained, which are used in the automotive industry, nonmetal melt factory and glass. There is an expected effect that can be utilized as a heat insulating material and a refractory having high quality thermal durability in factories and the like.

Claims (3)

mol%, 40 to 60% of Al ₂ O ₃ and 60 to 40% of TiO ₂ by mixing 3-7% MgO, followed by grinding, shaping and sintering to obtain aluminum titanate powder; 40 to 60% of ZrO ₂ and 60 to 40% of TiO ₂ are mixed and ground, followed by molding and sintering to obtain zirconium titanate powder, and Mixing the aluminum titanate and the zirconium titanate powder in a ratio of 40% to 60 mol% to 90 mol% and then molding and sintering at 1350 to 1600 ° C. to obtain aluminum titanate-zirconium titanate ceramic. A low thermal expansion aluminum titanate-zirconium titanate ceramic manufacturing method comprising a. delete delete