JPH075361B2 - Aluminum titanate-mullite ceramic body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention provides aluminum titanate and light, which have high heat resistance and good thermal shock resistance and thermal shock durability, as main crystal phases. The present invention relates to a ceramic body.

(Prior Art) In an industrial technology for solving a new social problem caused by the development of the technology, a material having a high performance as never before is required for a material used in the industrial technology.

Ceramics with excellent corrosion resistance are required to have even better heat resistance and thermal shock resistance. The thermal shock resistance of ceramics depends on the thermal expansion coefficient, thermal conductivity, strength, elastic modulus, Poisson's ratio, etc. of the material. In addition to being affected by the characteristics of, the size and shape of the product and the heating / cooling state, that is, the heat transfer rate are also affected. It is known that among these various properties that affect thermal shock resistance, the coefficient of thermal expansion has a particularly large contribution rate, and in particular, when the rate of heat transfer is high, it is greatly influenced only by the coefficient of thermal expansion. Therefore, it is strongly desired to develop a low thermal expansion coefficient material having excellent thermal shock resistance, and at the same time, a material having high heat resistance is desired.

On the other hand, aluminum titanate-based ceramics with a low coefficient of thermal expansion have a large difference in the coefficient of thermal expansion depending on the direction of the crystal axes of the crystals that make up the ceramics, and thermal stress is generated inside the ceramics, which is the strength of the constituent crystals and grain boundaries. If the value exceeds the limit, the strength will be weak because minute cracks will be generated in the grains and grain boundaries, and the products will easily crack or break.Therefore, it is strongly desired to develop a material with high strength and low expansion. It was rare.

In order to meet such a demand, a low expansion ceramics whose main component of a crystal phase is magnesium oxide-aluminum oxide-titanium oxide-iron oxide-silicon oxide has been developed [Japanese Patent Publication No. 59-19069].

Then, a material containing aluminum titanate and mullite as a main crystal phase, iron oxide and / or a rare earth metal oxide as a sintering aid, and added in an amount such that the low expansion of aluminum titanate is not lost was developed. JP 60-
No. 36364].

(Problems to be Solved by the Invention) The above materials have excellent fire resistance, high thermal shock resistance, and high mechanical strength, and are excellent ceramic bodies in consideration of the crystal stability of aluminum titanate under continuous high temperature. However, if a honeycomb type catalytic converter with many fine holes as shown in both publications is manufactured and used, the size gradually becomes larger than the original size due to the thermal cycle used. It will not return to its original size and will crack and eventually be destroyed. That is, there is a problem that the durability after the heat cycle is inferior.

However, the conventional improvement of aluminum titanate-mullite-based materials is focused on the crystal stability of aluminum titanate under continuous high temperature, and has fire resistance, heat resistance, thermal shock resistance, and high mechanical strength. Further, there is a problem that it is a very difficult technique to obtain a material that also has the thermal cycle durability.

An object of the present invention is to provide a ceramic body that solves this difficult problem, and particularly to focus on the mullite glass phase, and to minimize the glass phase of this mullite matrix. is there.

(Means for Solving the Problems) The aluminum titanate-mullite ceramic body of the present invention has a chemical composition of MgO: 0.8% or less, Al ₂ O ₃ : 53 to 74%, TiO 2.
_{2: 14~33%, Fe 2 O} 3: 1.2~5%, SiO 2: 6~20%, CaO + Na
₂ O + K ₂ O: 0.3% or less, and an essential constitution is that the amount of glass in the mullite matrix of the sintered body is 5% or less measured on the cross section of the sintered body.

And the average coefficient of thermal expansion between 40 ~ 800 ℃ -2.0 ~ 2.0 × 1
0 ^-6 / ℃, heating time from 40 ℃ to 1260 ℃ 6
Min, thermal cycle from 1260 ℃ to 40 ℃ for 5 minutes
The linear dimension increase after exposure 40 times is 1.0% or less,
40 to 1260 ℃ to 30 at a heating rate of 5 ℃ / min and a cooling rate of 5 ℃ / min
In the 0 ° C heat cycle, the maximum value of the difference between the thermal expansion curve value at the time of temperature rise and the thermal expansion curve value at the time of cooling at the same temperature is 0.18%.
The following is a preferable embodiment in which the ceramic body is a honeycomb structure.

The chemical composition% is expressed in% by weight.

Here, the amount of glass in the mullite matrix of the sintered body being 5% or less measured in the cross section of the sintered body means that the polished cross section of the sintered body has pores on a scanning electron microscope (SEM) photograph. The area of the mullite-based matrix and the area of the glass phase excluding the area of and the area of aluminum titanate were measured with a planimeter, and the amount of glass (area%) = glass phase area / mullite-based matrix area x 100 .

In an example of a conventional material, there is a polygonal part surrounded by mullite crystals in a mullite matrix, and when the chemical composition of this part is analyzed, there is a partial variation, but a typical value is SiO ₂ : 68 %, Al ₂ O ₃ : 24%, TiO ₂ : 4.4
%, CaO: 1.0%, KNaO: 2.0%. This composition corresponds to a composition forming a glass phase, and in the present invention, this portion is referred to as a glass phase in the mullite matrix.

(Examples) Examples are as shown in Tables 1 and 2.

In the table, AT indicates aluminum titanate raw material, and MU indicates mullite raw material.

The heat curve of the heat cycle test in which the test piece is exposed 40 times to the heat cycle from 40 ℃ to 1260 ℃ for 6 minutes and cooling time from 1260 ℃ to 40 ℃ for 5 minutes is as shown in Fig. 1. Is. The size of the test piece used for this is 1.27 cm square, and the size before and after the test is precisely measured using a super micrometer.

Thermal expansion hysteresis is known to indicate the presence of microcracks in the sintered body, but aluminum titanate ceramic also exhibits large thermal expansion hysteresis due to microcracks in the sintered body. There is a close relationship between the thermal expansion hysteresis, which indicates the state of microcracks, and the increase in dimension after exposure to thermal cycling. If the thermal expansion coefficient difference at the same temperature in the thermal expansion curve during heating and cooling exceeds 0.18%, thermal cycling It has been experimentally confirmed that there is a correlation that the dimensional increase due to the test exceeds 40% in the 40-cycle test.

The appearance of the glass phase in the mullite matrix is shown in FIGS.

FIG. 2 is a SEM photograph of a conventional material as-fired at 1300 times, showing the glass phase (1), mullite crystals (2), aluminum titanate (3), and pores (4). Fig. 3 shows this conventional material at 1260 ℃ -40
It is a 1300 times photograph by SEM after 250 thermal cycles between ° C. No glass phase is observed in mullite matrix. FIG. 4 is a SEM photograph of the as-fired material of Example 3 of the present invention at 1300 times, in which no glass phase is found in the mullite matrix. Fifth
The figure shows the material of Example 3 of the present invention which will be described later at 1260 ° C.
It is a 1300 times photograph by SEM after 250 thermal cycles between 40 ° C. Even after the thermal cycle, the aluminum titanate crystals and the mullite matrix show the same change as the conventional one. Absent.

For measuring the coefficient of thermal expansion,
A honeycomb structure having 80 pores and having the maximum partition wall thickness of 150 μm was extruded, and a test piece having a length of 50 mm, which was sampled in the direction of the pores, was used.

The raw materials blended with the aluminum titanate raw materials used in Examples and Reference Examples are purified rutile, low soda alumina,
Normal soda alumina, iron oxide, high-purity magnesia,
The pure raw material mixed with the mullite raw material is high-purity kaolin,
They are low soda alumina, high-purity silica, and high-purity alumina.

The honeycomb structure was also used for the other property evaluations of the examples and reference examples.

Examples 2 to 4 and Reference Example 1 and Reference Example 5 are
The aluminum titanate raw material was fired at 1600 ° C, and the mullite raw material was blended as a raw material, and the amount ratio was 35:65,
It was changed to 40: 60,50: 50,65: 35,70: 30. According to this, in Reference Example 1, the coefficient of thermal expansion becomes high, and in Reference Example 5, the glass phase in the mullite matrix increases and the dimensional change due to the heat cycle becomes large, which causes deterioration in performance. From the above, it can be seen that the quantitative relationship between aluminum titanate and mullite must be within the range of 40 to 65% for aluminum titanate raw material and 35 to 60% for mullite raw material.

Next, when Example 6 is compared with Reference Example 7 and Reference Example 8, especially when the alkali component in aluminum titanate increases, the glass phase in the mullite matrix increases, and the dimensional change due to the heat cycle becomes large. From the above, it is understood that Na ₂ O + K ₂ O in the aluminum titanate raw material needs to be 0.15% or less. The same applies to the comparison between Example 9 and Reference Examples 10 and 11.

Comparing Example 9 and Example 12 with Reference Example 13, Mg
When the amount of O exceeds 1.0%, the glass phase in the mullite matrix increases and the dimensional change due to thermal cycling becomes large, so it is understood that MgO must be 1% or less.

Comparing Example 15 and Example 16 with Reference Example 14 and Reference Example 17, it was found that Al ₂ O _{3 in} aluminum titanate was 45%.
When the TiO ₂ content exceeds 50%, the dimensional change due to thermal cycling becomes large, and the Al ₂ O ₃ content exceeds 62.0% and the TiO ₂ content exceeds 34%.
When it is less than%, the thermal expansion coefficient becomes high, and it is understood that the performance is deteriorated in all cases.

When Example 18 and Example 20 are compared with Reference Example 19 and Reference Example 21, when Fe ₂ O _{3 in} aluminum titanate exceeds 7.0% or when SiO ₂ exceeds 1%, it depends on the thermal cycle. It can be seen that the dimensional change becomes large and the performance deteriorates.

Next, Examples 24 and 25, Reference Example 23, and Reference Example 2
Comparing 6, Reference Example 27 and Reference Example 28, when Al ₂ O ₃ in the mullite raw material exceeds 82%, a large amount of corundum crystals are mixed in the mullite matrix, and the thermal expansion coefficient is high. However, it does not matter that the corundum crystal is present in a few percent to the extent that it does not affect the thermal expansion coefficient.

When Al ₂ O ₃ is less than 68%, the amount of glass phase in the mullite-based matrix increases, and the size increases due to thermal cycling. When SiO ₂ is less than 18%, the coefficient of thermal expansion becomes large, and when SiO ₂ exceeds 32%, the glass phase in the mullite matrix increases and the dimensional change due to thermal cycling becomes large. In addition, Fe ₂ O ₃ + TiO ₂ in the mullite raw material
+ CaO + MgO + Na ₂ O + K ₂ O exceeds 0.8%, especially
When the content of Na ₂ O + K ₂ O exceeds 0.25%, the glass phase in the mullite-based matrix increases and the dimensional change due to thermal cycling increases.

Next, as shown in Table 2, those having the same chemical composition as in Example 3 and different firing temperatures of the aluminum titanate raw material and the mullite raw material were used in Example 3 and Example 22 in Table 1.
Comparing Reference Example 35, Example 30, Example 31, Example 32, Reference Example 29, Reference Example 33, and Reference Example 34 in Table 2, the thermal expansion coefficient increases when the firing temperature is lower than 1550 ° C. If the temperature exceeds 1700 ° C, the firing deformation of the product will increase. When the firing temperature of the aluminum titanate raw material or the mullite raw material is higher than the firing temperature of the base material, the mass transfer between the aluminum titanate and the mullite is suppressed, and the purity of the mullite phase can be maintained. Therefore, the firing temperature of the raw material should be higher than the firing temperature of the green body. When neither aluminum titanate raw material nor mullite raw material is fired,
As seen in Reference Example 35, the amount of the glass phase in the mullite-based matrix increases and the dimensional change due to thermal cycling becomes large.

(Effects of the Invention) As described in detail above, the aluminum titanate-mullite ceramic body of the present invention is similar to conventional materials.
It is an excellent ceramic body with a high melting point of 1700 ° C or higher, high fire resistance, high thermal shock resistance, and high mechanical strength equal to or higher than that of conventional materials. Even if an open honeycomb type catalytic converter is manufactured and used, the size does not become larger than the original size due to many heat cycles, and the expansion of microcracks is suppressed. ,
Even in the case of isothermal aging in which aluminum titanate is most easily thermally decomposed for a long period of time at 1100 to 1200 ° C, which is not easily destroyed by a thermal cycle, even when it is added with an additive element such as a rare earth element, titanic acid is used. The crystal phase is more stable than the conventional material for the thermal stability of aluminum, and it has excellent thermal shock durability, and it has fire resistance, heat resistance, thermal shock resistance, and high mechanical strength. It is a product that overcomes the extremely difficult technique of obtaining a material that also has the thermal shock resistance while also having the above. Further, its application is also a ceramic member for automobiles that is required to have high thermal shock resistance and thermal shock durability at high temperatures, such as a honeycomb catalyst carrier for mounting a manifold, a port liner, a heat exchanger, a kiln fanature and other heat resistant materials, It can be widely applied as a heat shock resistant ceramic member, such as gas turbine parts, heat resistant ceramic materials for solar energy receivers, refractories, ceramics for the chemical industry, heat resistance, heat shock resistance, heat shock durability, wear resistance, Combined with the fact that it can be widely used as a ceramic material that is required to have anticorrosion properties, the present invention contributes to the development of industry and is extremely important.

[Brief description of drawings]

Fig. 1 is a graph showing the heat curve of the heat cycle test, Fig. 2 is a SEM 1300 times photograph showing the structure of the crystal of the conventional material as-fired, and Fig. 3 is the conventional material at 1260 ℃. Thermal cycle between ~ 40 ℃
1300 times photograph by SEM showing a crystal structure after 250 times, FIG. 4 is a 1300 times photograph by SEM showing a crystal structure of the as-fired material of Example 3 of the present invention, and FIG. The material of Example 3 of the present invention is 1260 ° C to 40 ° C.
SEM showing the crystal structure after 250 thermal cycles
It is a 1300 times photograph by.

Claims (5)

[Claims] 1. A chemical composition of MgO: 0.8% or less, Al ₂ O ₃ : 53-74.
%, TiO ₂ : 14 to 33%, Fe ₂ O ₃ : 1.2 to 5%, SiO ₂ : 6 to 20%,
CaO + Na ₂ O + K ₂ O: 0.3% or less, and the amount of glass in the mullite matrix of the sintered body is 5% when measured on the cross section of the sintered body.
An aluminum titanate-mullite ceramic body characterized by the following: 2. The average coefficient of thermal expansion between 40 and 800 ° C. is -2.0 to 2.
The aluminum titanate-mullite ceramic body according to claim 1, which has a temperature of 0 × 10 ^-6 / ° C. 3. A temperature rising time from 40 ° C. to 1260 ° C. for 6 minutes, 1260
The aluminum titanate-mullite ceramic body according to claim 1, which has a linear dimension increase of 1.0% or less after being exposed to a thermal cycle of 50 ° C. to 40 ° C. for a cooling time of 5 minutes for 40 times. 4. A heating rate of 5 ° C./min and a cooling rate of 5 ° C./min 40
Claim 1 wherein the maximum value of the difference between the thermal expansion curve value at the time of temperature rise and the thermal expansion curve value at the time of cooling at the same temperature is 0.18% or less in a heat cycle of ℃ ~ 1260 ℃ ~ 300 ℃. The aluminum titanate-mullite ceramic body according to the item. 5. The aluminum titanate-mullite ceramic body according to claim 1, wherein the ceramic body is a honeycomb structure.