JPH0513101B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a composition capable of providing ceramics having a small coefficient of thermal expansion and excellent thermal shock resistance. BACKGROUND ART Conventional ceramic compositions with a small coefficient of thermal expansion and excellent thermal shock resistance include cordierite ceramics, lithium ceramics, aluminum titanate ceramics, and the like, which are most commonly used. Cordierite ceramics are ceramics composed of MgO-Al ₂ O ₃ -SiO ₂ system. Cordierite is _{a combination} of talc ( _Mg3 ( _Si4O10 )(OH) ₂ ) and kaolin ( _{Al2Si2O5 ).}
(OH) ₄ ) and alumina (Al ₂ O ₃ ) in any ratio, and are manufactured by mixing, dehydrating, molding, drying, and sintering. By the way, the sintering temperature is about 1400℃.
~5 days (Special Publication No. 54-1564, Special Publication No. 1564,
51-20358). In addition, aluminum titanate ceramics refers to titanium oxide (anatase type).
It is produced by firing an equimolar mixture at 1,600 to 1,700°C using α-Al ₂ O ₃ of high purity as raw materials (Ceramic Engineering Handbook P. 1274). Problems to be solved by the invention In such conventional thermal shock resistant ceramics,
High-temperature sintering is not an option, and it is difficult to obtain a dense sintered body from the synthesized ceramics, and the thermal shock resistance is poor due to grain boundary cracks caused by the large anisotropy of thermal expansion of the constituent crystals. He had sexual problems. The present invention has been made in view of this point, and an object of the present invention is to provide thermal shock resistant ceramics at a relatively low firing temperature of 1100 to 1300°C. Means for Solving the Problems In order to solve the above problems, the present invention provides a composition obtained by sintering a composition comprising at least three components of rehydratable alumina, an alkali titanate, and fused silica as at least essential components. It is made of ceramics. Function The present invention has the above configuration, and the rehydratable alumina which is an essential component in the present invention is transition alumina other than α-Al ₂ O ₃ obtained by thermally decomposing alumina hydrate, such as ρ-Al ₂ O ₃ and amorphous alumina, etc., and industrially, for example, alumina hydrate such as alumina hydrate obtained from the Bayer process is
By contacting hot gas at 1200°C for usually a fraction of a second to 10 seconds, or by exposing alumina hydrate to about 250°C under reduced pressure.
Examples include those having a loss on ignition of about 0.5 to 15% by weight, which can be obtained by heating and holding at ~900°C for usually 1 minute to 4 hours. Next, an alkali titanate salt has the general formula M′ ₂ O・
It is a substance represented by nTiO ₂ (wherein M' represents an alkali metal atom selected from lithium, sodium, potassium, rubidium, cesium, barium, strontium, and calcium, and n is an integer of 1 or more). Next, we will discuss fused silica, which is another essential component. The thermal expansion coefficient of fused silica
At 0.5×10 ^-6 /deg (room temperature to 1000°C), it is one of the smallest materials among substances, and is generally known as a material that reduces thermal expansion. However, fused silica is also a glass-forming oxide, in a mixture with other substances (e.g. alkaline components such as sodium, potassium, calcium and alumina, titania, etc.).
When heat treated at a temperature of 1000℃ or higher, crystals such as cristobalite or tridymanite are formed, and the coefficient of thermal expansion is 4 to 5 × 10 ^-6 /deg (from room temperature to
For this reason, it has not been used as a thermal shock-resistant refractory, but the composition consisting of the above three components is heated to 1100-1250°C.
By firing within this range, ceramics with excellent thermal shock resistance were obtained, although the reason is not clear. In addition to the above-mentioned rehydratable alumina, alkali titanate, and fused silica, forming aids (for example,
CMC, MC, etc.) and plasticizers (glycerin, petrolatum), etc. can be optionally added. Example 1 10% by weight of rehydratable alumina, 5% by weight of potassium titanate (K ₂ O.6TiO ₂ ), 85% by weight of fused silica,
Furthermore, a mixture of 4.0 parts by weight of methylcellulose as a molding aid, 2.0 parts by weight of chrycerin as a plasticizer, and 30 parts by weight of water was kneaded for 10 minutes using a screw kneader, and then fed to a screw type extrusion molding machine. 100〓, a honeycomb molded body consisting of square cells with a wall thickness of 0.3〓 and a side of 1.5〓 was formed. Next, this molded body was heated to 1200°C at a heating rate of 100°C/hour, and further baked at 1200°C for 1 hour. Table 1 shows the physical properties of the honeycomb structure thus obtained. For comparison, Comparative Example A uses α-Al ₂ O ₃ powder instead of rehydrating alumina, Comparative Example B uses titanium oxide (anatase type TiO ₂ ) instead of potassium titanate, and Comparative Example B uses fused silica. A honeycomb-shaped ceramic was produced in the same manner as in the above Example using Comparative Example C, in which cordierite powder was used in place of Cordierite powder. The physical properties at this time are also shown in Table 1.

[Table] As is clear from Table 1, the compositions of Comparative Example A, Comparative Example B, and Comparative Example C other than the compositions consisting of rehydratable alumina, alkali titanate, and fused silica, which are essential components, are the above-mentioned compositions. Compared to the composition, the compressive strength was lower, the coefficient of thermal expansion was higher, and the thermal shock resistance was poor. Example 2 The ratios of rehydratable alumina, potassium titanate, and fused silica were varied, and a forming aid, plasticizer, and water were added in the same manner as in Example 1, and a honeycomb structure was created in the same manner as in Example 1. We conducted an evaluation. As a result, the composition range with excellent compressive strength and thermal shock resistance was the shaded area in FIG. The coefficient of thermal expansion and contraction at temperatures outside this range was as shown in Figure 2a. Moreover, in the ceramics of the present invention, it was as shown in b. From curve a, it is easy to believe that some of the fused silica was crystallized and substances such as cristobalite and tridymanite were produced, which increases the coefficient of thermal expansion and lowers the thermal shock resistance. Incidentally, the coefficient of thermal expansion (from room temperature to 1000° C.) of the ceramics of this example was all 1.3×10 ⁻⁶ /deg or more. Example 3 10% by weight of rehydratable alumina, 5% by weight of alkali titanate (titanium consisting of alkali metal atoms selected from lithium, sodium, potassium, rubidium, cesium, barium, strontium, and calcium as the alkali component) Honeycomb-shaped ceramics were prepared in the same manner as in Example 1 using a mixture containing 85% by weight of fused silica, 4.0 parts by weight of methylcellulose as a forming aid, 2.0 parts by weight of glycerin as a plasticizer, and 32 parts by weight of water. . The physical properties of this product are shown in Table 2.

【table】

[Table] As is clear from Table 2, the ceramics of the present invention comprising rehydratable alumina, each alkali titanate salt, and fused silica were excellent in both compressive strength and thermal shock resistance. Among them, those using potassium titanate had particularly excellent thermal shock resistance. Example 4 Table 3 shows the physical properties when each alkali titanate salt in Example 3 is a whisker. Note that the honeycomb-shaped ceramics for testing were prepared in the same manner as in Example 1.

[Table] From Table 3, the more whisker-like the alkali titanate salt is, the smaller the coefficient of thermal expansion tends to be, and the thermal shock resistance is also improved. Example 5 The physical properties of the No. 3 honeycomb formed body of Example 4 at a firing temperature in the range of 1000 to 1400°C are shown in FIG. As is clear from Fig. 2, the compressive strength sharply decreased at a firing temperature of 1100°C or lower, and the thermal shock resistance rapidly decreased at a firing temperature of 1300°C or higher. In this way, the thermal shock resistant ceramics of the present invention have a firing temperature of 1100~
The one produced at 1300°C had better retention. In addition, the scanning electron micrographs of the cross sections of the honeycomb-shaped ceramics obtained by firing at 1000℃ and the honeycomb-shaped ceramics obtained by firing at 1200℃ are shown in Section 4.
Shown in the figure. Figure 4A is a 10,000x enlarged photograph of a cross section of honeycomb-shaped ceramics fired at 1,000°C.
Figure 4B is a 10,000x enlarged photograph of a cross section of honeycomb-shaped ceramics fired at 1,200°C. From the above two scanning electron micrographs, it can be easily inferred that the physical properties of the ceramics obtained differ greatly depending on the firing temperature. From the photograph shown in Figure 4A, potassium titanate (K ₂ O.6TiO ₂ ) whiskers were recognized, but in Figure 4B, which is an example of the present invention, the whiskers were completely melted and integrated. ,
No fibers such as whiskers were observed. Effects of the Invention As described above, according to the present invention, it is possible to obtain practical ceramics at low cost that can be fired at a relatively low temperature, are dense, and have excellent thermal shock resistance and compressive strength. It is extremely useful.

[Brief explanation of the drawing]

FIG. 1 is a phase diagram showing the composition range of a thermal shock resistant ceramic according to an embodiment of the present invention. FIGS. Figures 4A and 4B are scanning electron micrographs showing whether the fiber state is maintained in an example and a comparative example of the same ceramics. A... Rehydratable alumina, B... Alkali titanate, C... Fused silica.

Claims (1)

[Scope of Claims] 1. A thermal shock-resistant ceramic obtained by sintering a composition consisting of fused silica and at least rehydrated alumina and an alkali titanate. 2 5-20% by weight of rehydratable alumina, 1-10% by weight of alkali titanate, 70-94% of fused silica
% by weight of the thermal shock resistant ceramic according to claim 1. 3. The thermal shock-resistant ceramic according to claim 1 or 2, wherein the alkali titanate salt is potassium titanate. 4. The thermal shock resistant ceramic according to claim 1, 2 or 3, wherein the alkali titanate salt is a whisker. 5. The thermal shock resistant ceramic according to any one of claims 1 to 4, characterized in that the firing temperature is 1100 to 1300°C. 6. The thermal shock-resistant ceramic according to any one of claims 1 to 5, which has a thermal expansion coefficient of 1.3×10 ^-6 /deg or less.