JPH11292618A - High temperature ceramic material of aluminum titanate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic material that has improved thermal properties, resistance to thermal shock and mechanical properties by specifying the contents of MgO, Al2 O3 , TiO2 and SiO2 in the ceramic composition. SOLUTION: This aluminum titanate ceramic comprises <=1% of MgO, 60-65% of Al2 O3 , 20-32% of TiO2 , and 5-15% of SiO2 . This ceramic has a thermal expansion coefficient of 0-2.0*10<-6> / deg.C in the temperature range of from 20-1,330 deg.C. This high strength, thermal expansion-resistant material is produced by mixing alumina, titania and magnesia as raw materials, crushing, granulating and sintering them, further admixing alumina and kaolin thereto to form a composite sintered product. In this formulation composition, ultra-fine powders of MgO and SiO2 with particle sizes about 100 Å are formulated to increase its stability and mechanical strength and retain its low thermal expansion.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structural material using an aluminum titanate-based ceramic having high heat resistance, excellent thermal shock resistance, and which does not decrease in strength at high temperatures.

[0003]

2. Description of the Related Art Along with the development of technology, unprecedentedly high requirements have been generated. In other words, ceramics with excellent touch resistance are required to have further heat resistance, thermal shock resistance and mechanical strength, but the thermal shock characteristics of ceramics depend on the properties of the material such as thermal expansion coefficient, Young's modulus, Poisson's ratio, and strength. It depends on the size and shape of the product, as well as the heating and cooling conditions. However, among these, the development of a low expansion material that has the highest correlation with the thermal expansion coefficient of the material and has high heat resistance is strongly desired. On the other hand, aluminum titanate ceramics have a remarkably low thermal expansion property, but it has already been revealed that this is an apparent property due to grain boundary cracks caused by the large thermal expansion anisotropy of aluminum titanate crystals. Due to the grain boundary cracks, the mechanical strength is low, and the crystal is unstable in a low temperature range of 1250 ° C. or less, and has a problem that it is decomposed when heated. However, since it has a melting point of 1800 ° C. or more, exhibits an apparently low expansive property, and is a ceramic which is difficult to obtain, it has been strongly desired to develop a material for the purpose of improving these properties.

[0004] In order to meet such demands, studies have been made on materials which increase the mechanical strength by adding various additives and exhibit low expansion properties. Also, without adding additives,
Samples with different mineral species and particle sizes of synthetic raw materials have been prepared, and the microstructure and mechanical and thermal properties of sintering properties have been studied. However, in any of these methods, a sintered body having sufficient mechanical strength was not obtained, and the difference in thermal expansion and contraction was large.

[0005]

SUMMARY OF THE INVENTION The present invention relates to TiO ₂ , A
Starting from l ₂ O ₃ and MgO, then Al ₂ O ₃
It is an object of the present invention to improve thermal properties, thermal shock resistance, and mechanical strength by mixing with SiO ₂ and to provide a high-temperature material.

[0006]

In order to obtain a high-strength heat-resistant expansion material having aluminum titanate as a constituent phase, alumina, titania and magnesia are used as starting materials.
After mixing, grinding, granulating and sintering, alumina and New Zealand kaolin were added and mixed to prepare a composite fired body.

The chemical composition is MgO 1% or less, Al
₂ O ₃ 60-65%, TiO ₂ 20-32%, SiO
_The essential configuration is to be 25 to 15%. In the above-mentioned composition, by adding ultrafine powder MgO and SiO ₂ of about 100 °, the thermal stability was increased, the mechanical strength was increased, and the low thermal expansion was maintained.

[0008]

Example 1 Table 1 shows the composition and characteristics of Example 1. In the table represents the aluminum titanate of the reference example, ~
Is a formulation example of the present invention, and the raw materials used are purified rutile, high-purity low soda alumina, high-purity fine powder magnesia 100 kg, and New Zealand kaolin. 3mm * 4mm * 40m for physical property and bending strength test
For m and TMA, test pieces having a size of φ4 * 15 l were prepared. High temperature creep resistance test is 10mm * 50mm * 1mm
^t was placed in an electric furnace, and one side was held for 60 hours.
The sample was heated at a predetermined temperature for minutes and evaluated. As is clear from the examples, the composition No. The superiority of both the strength and the thermal shock resistance exists within the range of ~. No. When TiO ₂ increases and SiO ₂ decreases, the strength decreases. If TiO ₂ decreases and SiO ₂ and Al ₂ O ₃ increase, the thermal expansion coefficient increases and the thermal shock characteristics decrease.

[0010]

Example 2 Using the composition shown in Table 1, pipe shapes (φ7
0 ~ φ50) * 130l and thin plate shape (100mm * 50
mm * 1 mm ^t ) was prepared and subjected to a heating / cooling cycle test using a high-temperature gas. In this experiment, a connection pipe with a fire-resistant and heat-insulating structure was used. A thermal spray burner using city gas was attached to the entrance of the connection pipe, and a test piece was fitted into the gas outlet on the opposite side. In the case of the pipe shape, only the increase or decrease of the city gas flow rate, and in the case of the thin plate, after stopping the combustion, the cooling air was blown, and rapid cooling and rapid heating were repeated. The temperature at which the pipe was taken out was 750 ° C. For pipe-shaped products, 10 cycles between 850 and 1400 ° C, temperature rise 1000
No abnormal appearance such as cracks at ° C / min. The temperature curve is shown in FIG. The temperature rise and fall during the cycle is 550 ° C / m
in, switching operation 1 min, high-temperature side gas amount 10.1 N
m ³ / hr, flow rate 1.4 m / sec, low-temperature side gas amount 9.
The flow rate was 5 Nm / hr and the flow rate was 1.3 m / sec. The maximum heating rate is 1176 ° C / min between 400 and 1100 ° C,
Gas flow rate 11.2 Nm ³ / hr, flow rate 1.6 m / sec
Met. Further, as a result of measuring the bending strength of a test piece cut out from the pipe after the test, no reduction in strength was found at 61 MPa. In the case of corrugated sheet-shaped products, the temperature is raised to 1000C / min up to 1400C, and 10
Endured cycles. The temperature curve is shown in FIG. The maximum heating rate is 1300 ° C / min, 765 ° C / min on average,
The switching operation was 1.7 min. At the time of combustion, the gas flow rate is 12.0 Nm ³ / hr and the flow rate is 0.9 m / sec. At the time of cooling, the gas flow rate is 16.8 Nm ³ / hr and the flow rate is 1.2 m / sec.
sec.

[0011]

Example 3 A switching valve shown in FIG. 3 was produced using the composition shown in Table 1. This switching valve switches the flow direction of the fluid by communicating one of the two flow paths and closing the other, and includes a cylindrical rotating body 1 connected to the two flow paths and And a housing 2 that accommodates the rotating body 1 and is connected to one system of flow passages. Then, the rotating body 1 is connected to a driving motor, and while the combustion gas is passed from one side of the housing 2, 90 times once every 30 seconds.
The degree was rotated forward and backward in one second. According to this example, the composition No.
The switching valve manufactured using the method described above normally operated with respect to the passage of the combustion gas at 1400 ° C., and the heat resistance, thermal shock resistance, and mechanical strength of the material were also confirmed. FIG. 4 shows the temperature curve and the combustion gas flow rate.

[0012]

As described in detail above, the aluminum titanate-based ceramic high-temperature material of the present invention is an excellent ceramic material having high thermal shock resistance and high mechanical strength, and will be widely used as a high-temperature member in the future. May be used.

[Brief description of the drawings]

FIG. 1 is a graph showing a temperature curve of a test using a pipe-shaped product.

FIG. 2 is a graph showing a temperature curve of a test using a thin plate-shaped product.

FIG. 3 shows the shape of a high-temperature combustion gas switching valve manufactured using the aluminum titanate-based ceramic material of the present invention.

FIG. 4 is a graph showing a temperature curve and a combustion gas flow rate of a test using a switching valve.

[Explanation of symbols]

 1 rotating body 2 housing

Claims (2)

[Claims] (1) a chemical composition of MgO 1% or less, Al ₂ O _{3
60~65%, TiO 2 20~32%,} SiO 2 5~
An aluminum titanate-based ceramic characterized by comprising 15%. 2. The thermal expansion coefficient between 20 ° C. and 1330 ° C.
2. The aluminum titanate-based ceramic according to claim 1, which has a temperature of 2.0 * 10 ^-6 / ° C. [0002]