JP2000351667A - Oxide ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide ceramic which has a larger negative thermal expansion coefficient than those of conventional ceramics and especially shows an extremely large negative thermal expansion coefficient of -2 to -13×106/ deg.C which was impossible to realize by conventional techniques. SOLUTION: This oxide ceramic has a composition comprising 40<=SiO2<=50, 33<=Al2O3<=43, 0<=TiO2<=6.5, and 6<=Li2O<=16, and a thermal expansion coefficient of -2 to -13×106/ deg.C, and especially contains an eucryptite crystal as an essential component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxide ceramic, and more particularly, to a ceramic having a large negative coefficient of thermal expansion than ever before.

[0002]

2. Description of the Related Art As a ceramic having a low coefficient of thermal expansion, a polycrystalline body composed of β-spodumene, eucryptite, cordierite, etc. is known, and its coefficient of thermal expansion is 2 × 10 ⁻⁶ / cordierite. It is known that the temperature is about 1 × 10 ^-6 / ° C. for β-spodumene. On the other hand, eucryptite is known to exhibit a negative coefficient of thermal expansion, but its value is generally about 0 to −2 × 10 ⁻⁶ / ° C., and a larger negative value is used. Ceramics to have are not known.

[0003]

SUMMARY OF THE INVENTION The present invention has a smaller thermal expansion coefficient (large negative) than conventional ceramics.
An object of the present invention is to provide a ceramic having a very large negative coefficient of thermal expansion of -2 to -13 × 10 ^-6 / ° C., which was impossible in the prior art.

[0004]

The ceramic of the present invention has a composition of 40 ≦ SiO ₂ ≦ 50 33 ≦ Al ₂ O ₃ ≦ 430 ≦ TiO ₂ ≦ 6.56 6 ≦ Li ₂ O ≦ 16 by weight. A ceramic comprising an oxide ceramic having a thermal expansion coefficient from room temperature to 1000 ° C. of −2 to −13 × 10 −6 / ° C., and particularly containing eucryptite crystals as an essential component. .

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for quantitative limitation are described below. Basically, when the value is less than the above range or exceeds the upper limit, the predetermined thermal expansion coefficient cannot be obtained.
In particular, when SiO ₂ and Li ₂ O are less than the lower limit, Al ₂
If O ₃ exceeds the upper limit, the coefficient of thermal expansion tends to increase. Meanwhile, since SiO ₂ is less likely to densify exceeds the upper limit, and because the bubbles are easily generated in the sintered body in the Li ₂ O exceeds the upper limit, even less than Al ₂ O ₃ lower the thermal expansion coefficient Undesirably increases.

TiO2 is a nucleating agent, and when it exceeds the upper limit, there is no particular inconvenience, but when the amount is extremely large, T
It is not preferable because the coefficient of thermal expansion of iO2 is reflected and the coefficient of thermal expansion increases. On the other hand, although the lower limit of TiO2 varies depending on the production method, it is preferably about 2.5% or more in the case of once melting and recrystallization as described later, but may be 0% in the case of not melting.

The preferred range of the above composition is as follows. 43.5 ≦ SiO ₂ ≦ 47.5 36.5 ≦ Al ₂ O ₃ ≦ 40.50 ≦ TiO ₂ ≦ 5.59 ≦ Li ₂ O ≦ 13 Further, a more preferable range is 45 ≦ SiO ₂ ≦ 46. 38 ≦ Al ₂ O ₃ ≦ 390 0 TiO ₂ ≦ 5 11 ≦ Li ₂ O ≦ 12

The above ceramics contain eucryptite crystals as an essential component. Unless eucryptite is contained, a thermal expansion coefficient of −2 to −13 × 10 ⁻⁶ / ° C. cannot be obtained. In addition to eucryptite, various lithium aluminosilicates such as β-spodumene, petalite, and β-quartz solid solution may be contained. In addition, unavoidable impurity components may be contained in an amount of about several weight%.

The ceramic according to the present invention is obtained by molding a crystalline powder and / or an amorphous powder having the above-defined composition range into a desired shape, and then subjecting the compact to a predetermined heat treatment, or The above-mentioned crystalline powder and / or amorphous powder are melted, cast into a mold and molded, and then heat-treated at a high temperature, or the crystalline powder and / or amorphous powder are melted. Is dropped and quenched underwater,
It can be obtained by a method of obtaining an amorphous coarse glass, pulverizing and molding the same, and then performing a heat treatment at a high temperature.

[0010]

The embodiments will be described below. (Example 1) Using lithium carbonate (reagent first grade), silicic anhydride (same as above), titanium oxide (same as above), and alumina (Sumitomo Aluminum Refining A-HPS30), converted to oxides, Table 1
Was prepared and put into a platinum crucible and melted at 1600 ° C. for 100 minutes. Next, the melt was quenched in water, dried, and pulverized by a pot mill. To this powder was added 5% by weight of paraffin as a binder, and the mixture was placed in a mold and molded at 1 ton / cm ² . The obtained molded body was heated from room temperature to 750 ° C. at 12.5 ° C./min, kept for 2 hours, heated to 850 ° C. at 10 ° C./min and kept for 2 hours, and then cooled to room temperature and cooled in a furnace with a diameter of 50 mm.
A ceramic having a thickness of 4 mm was obtained. A sample of 3 × 4 × 15 mm was taken out of this ceramic,
The coefficient of thermal expansion was measured in the range of 00 ° C (Rigaku TAS)
100: differential thermal dilatometer). Quartz was used for all measurement jigs in terms of measurement accuracy. Table 1 also shows the test results. As is clear from the table, the ceramic of the present invention was an unprecedented low thermal expansion ceramic. In addition, the crystal phase thereof was mainly composed of eucryptite. (Example 2) After melting at 1600 ° C, the furnace was cooled as it was, and after the furnace cooling was completed, the same heat treatment as in Example 1 was applied, and then pulverization was performed. Other conditions are exactly the same as in the first embodiment. (Examples 3 to 5) Same as Example 1 except that the blending amounts were as shown in Table 1. (Example 6) The blending amounts were as shown in Table 1, and the temperature was raised to 1400 ° C at a rate of 10 ° C / min without melting, kept for 2 hours and cooled in a furnace. (Comparative Examples 1 to 5) The same test as in Example 1 was performed for the formulations shown in Table 1. All of these had a large coefficient of thermal expansion and were inferior in performance to those of the examples.

Table 1 Each blended amount (% by weight) and coefficient of thermal expansion of ceramics (× 10 ⁻⁶ / ° C.) Formulated amount SiO ₂ Al ₂ O ₃ TiO ₂ Li ₂ O Thermal expansion coefficient Example 1 45.45 38.64 4.55 11.36 − 10.5 Example 2 45.45 38.64 4.55 11.36 -12.5 Example 3 40.5 42.5 6.2 10.8 -2.3 Example 4 49.2 33.4 6.3 11.1 -9.4 Example 5 40.5 42.5 2.6 14.4 -5.8 Example 6 48.0 40.0 0 12.0 -2.5 Comparative example 1 38.0 44.0 4.55 13.45 −0.6 Comparative Example 2 51.4 32.0 11.2 5.4 −1.4 Comparative Example 3 55.0 28.1 0 16.9 −1.9

[0012]

The ceramics according to the present invention is a ceramic having a large negative coefficient of thermal expansion, whereas the conventional coefficient of thermal expansion was about ^{-2.times.10.sup.-6} / .degree.
It exhibits an excellent performance of up to ^-13 × 10 ^-6 / ° C.

Claims (3)

[Claims] An oxidation characterized by having a composition of 40 ≦ SiO ₂ ≦ 50 33 ≦ Al ₂ O ₃ ≦ 430 ≦ TiO ₂ ≦ 6.56 ≦ Li ₂ O ≦ 16 by weight%. Thing ceramics. 2. The composition has a composition of 40 ≦ SiO ₂ ≦ 50 33 ≦ Al ₂ O ₃ ≦ 43 2.5 ≦ TiO ₂ ≦ 6.5 6 ≦ Li ₂ O ≦ 16 in weight%, and has a composition at room temperature to 1000 ° C. An oxide ceramic having a coefficient of thermal expansion in the range of -2 to -13 x ^10-6 / C. 3. The oxide ceramic according to claim 1, comprising eucryptite crystals as an essential component.