JPS6027647A - Low expansion ceramics and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to low expansion ceramics and a method for producing the same.

[Prior art]

Cordierite sintered bodies are known as a typical low-expansion ceramic. The thermal expansion coefficient of cordierite sintered body is 1/1 of that of alumina ceramics.
It is extremely small at 0 to 1/20. Therefore, it exhibits excellent thermal shock resistance and does not break even when used in situations involving rapid temperature changes such as rapid heating and cooling.

Due to its excellent thermal shock resistance, cordierite sintered bodies are used in places where cooling and heating cycles are frequently repeated, such as catalyst carriers for exhaust gas purification and carriers for collecting diesel particulates. .

However, in industry, research is underway to further improve the thermal shock resistance of cordierite sintered bodies.

[Purpose of the invention]

A further object of the present invention is to provide a low-expansion ceramic having a small coefficient of thermal expansion and a method for manufacturing the same.

[Structure of the invention]

The present inventor discovered a phenomenon in which ceramics in which titania crystals are dispersed in cordierite crystals have a small coefficient of thermal expansion. The present invention is based on this knowledge.

The low expansion ceramic of the present invention is composed of cordierite crystals and titania crystals, has a mixed crystal structure in which the titania crystals are dispersed in the grain boundaries of the cordierite crystals, and has a thermal expansion range from room temperature to 1000°C. The coefficient is 1.7X1
It is characterized by being less than or equal to 0-"/"C.

Cordierite crystals refer to cordierite crystals and similar crystal structures. Cordierite crystal is a crystal of 2Mg0.2Al zo3.58102. Cordierite crystals as used in the present invention include pure cordierite crystals in which other metal oxides are solidly dissolved. The main components of this Coop Yerei crystal are alumina, magnesia, and silica, and generally contain 33 to 42% alumina and 11 to 16% magnesia by weight.
%, with a composition range of 46-53% silica. The low-expansion ceramic of the present invention has this cordierite crystal as its main component.

As the raw material powder, natural materials such as talc, kaolin, clay, magnesite, and chloride can be used, and as pure chemicals, alumina, magnesium hydroxide, silica, etc. can be used. Calcined material may be added to facilitate molding and firing, and feldspar, zirconia, alumina, etc. may be added to reduce water absorption.

Titania crystal is a crystal of titanium oxide (TiOx).

In the low expansion ceramic of the present invention, the titania crystals are dispersed in the grain boundaries of cordierite crystals. The amount of titania crystals is preferably in the range of 1 to 20 parts by weight when the total amount is 100 parts by weight. In addition, the remaining portion is 80-99
The parts by weight are cordierite crystals and impurities.

Note that it is desirable that the titania crystal be in a range of 3 to 6 parts by weight when the total amount is 100 parts by weight. This is because the coefficient of thermal expansion becomes small especially in that range.

The grain size of the titania crystals is desirably smaller than the grain size of the cordierite crystals. When the grain size of cordierite crystals is 1 to 10μ, the grain size of titania crystals is 0.
A range of 1 to 1 μm is preferable.

As described above, in the low expansion ceramic of the present invention, titania nodules are dispersed in the grain boundaries of cordierite crystals. That is, the titania crystals exist at the grain boundaries of the cordierite crystals without chemically reacting with the cordierite crystals.

The method for producing low expansion ceramics of the present invention involves molding and firing a mixed raw material powder consisting of 1 to 20 parts by weight of titanium oxide, the balance being cordierite-forming raw material powder and unavoidable impurities, to a total of 100 parts by weight. This is characterized by the formation of a mixed crystal structure in which titania crystals are dispersed at the grain boundaries of cordierite crystals. The raw material powder for producing cordierite crystals is Coop Yerai 1 from firing.
- Refers to raw material powder that produces quality crystals. Specifically, weight%
It refers to a powder having a composition range of 33 to 42% alumina, 11 to 16% magnesia, and 46 to 53% silica. As the raw material powder, natural materials such as talc, kaolin, clay, magnesite, and chloride can be used, and as pure chemicals, alumina, magnesium hydroxide, silica, etc. can be used. Calculated products, to facilitate shaping and firing.
Feldspar, zirconia, alumina, etc. may be added to reduce water absorption.

As the titanium oxide, Ti0z and Ti01Ti203, which becomes TiO2 when oxidized in an oxidizing atmosphere, can be used.

In addition, T in an oxidizing atmosphere with a metal salt containing titanium ions
i0z T'1 (NOa>4, Ti (SO4)
2, TiCl4tt and $MtR can be obtained.

When mixing the titanium oxide and the cordierite forming raw material powder, either dry mixing or wet mixing may be used. In the case of dry mixing, titanium oxide powder is added to the raw material powder for cordierite production and uniformly dispersed using a ball mill or the like.

After mixing the titanium oxide and cordierite raw material powder, it may be molded in the same manner as in the conventional method, and the molded product may be fired. For molding, for example, after dry mixing the cordierite-generating raw material powder and titanium oxide, this powder may be filled into a mold and compressed by pressing with the mold. or,
Cordierite forming raw material powder and titanium oxide are wet mixed to form a slurry, and an organic structure such as a three-dimensional rope structure made of polyurethane foam is immersed in the slurry to form the structure. It may also be impregnated into the pores of the body and thereby shaped.

Firing is performed in a heating furnace. The atmosphere is popular but good.

It is important to control the firing temperature during firing. This is because, in general, if the amount of titanium oxide added is the same, the higher the firing temperature, the smaller the coefficient of thermal expansion of the resulting ceramic. Therefore, the firing temperature is preferably in the range of 1350 to 1430°C. Furthermore, a range of 1380 to 1430°C is desirable. Note that if the firing temperature is too high, the cordierite crystals will melt, making it difficult to obtain ceramics with a low coefficient of thermal expansion.

〔Effect of the invention〕

The low expansion ceramic of the present invention has a coefficient of thermal expansion from room temperature to 1000℃ of 1.7X10-6 and 1.581.
On the other hand, the coefficient of thermal expansion of conventional ceramics made only of cordierite crystals without titania crystals is 1.8 to 2.0XIO.
-6/'C. The thermal expansion coefficient of the low-expansion ceramic of the present invention is smaller than that of the cordierite crystal alone and the titania crystal alone.

Furthermore, the low expansion ceramic of the present invention has strength comparable to that of conventional cordierite ceramics. Therefore, the low expansion ceramic of the present invention has excellent thermal shock resistance.

〔Test results〕

First, raw material powders of kaolin, talc, aluminum hydroxide, and alumina were prepared and mixed to form a cordierite crystal composition. This cordierite forming raw material powder and 1 to 20 parts by weight of Chikunya were made to make a total of 100 parts by weight, and dry mixing and stirring were performed. The titania used had a particle size of 0.26 μm and a purity of 99.8%. Next, a binder is added to this mixed powder, followed by granulation and classification. As a binder, a carbon tetrachloride solution in which 4 to 6 parts by weight of paraffin was dissolved was used. Granulation classification was performed using a standard sieve. Next, the granulated and classified powder with a particle size of 350 μm was pressed in a mold to perform compression molding, and fired at the temperature of the inoculation to form a rod-shaped ceramic. 11 methods of rod-shaped Hiramix, size 5x5x50 (m3
).

The ceramics thus obtained were used as rod-shaped specimens, and their thermal expansion coefficients were measured.

The measurement results are shown in Figures 1 and 2. FIG. 2 is an enlarged view of the main part of FIG. 1. Here the firing temperature is 1350
℃, the coefficient of thermal expansion was 3.2×10 −6 /′C when titania crystals were not included. On the other hand, as the composition ratio of titania crystal increases, the coefficient of thermal expansion gradually decreases. In other words, the titania crystal is approximately 1
(The thermal expansion coefficient shows a minimum value when lff is 1 part, and thereafter increases as the amount of titania crystal added increases.

When the composition ratio of titania crystals is 20 parts by weight, the coefficient of thermal expansion is about 2.5×10 −6° C., but even this ceramic has a considerably smaller coefficient of thermal expansion than a ceramic that does not contain titania crystals.

When the firing temperature was 1380° C., the coefficient of thermal expansion of the ceramic not containing titania crystals was 1.8×10 −6 /′C. On the other hand, ceramics that contain titania crystals and have a higher composition ratio have a gradually smaller coefficient of thermal expansion, and the composition ratio of titania crystals is 3 to 6.
For ceramics by weight, their coefficient of thermal expansion is 1.
It became significantly smaller by 3 to 1°5x10-6/'C.

When the firing temperature is 1410℃, the coefficient of thermal expansion of ceramics that does not contain titania crystals is 1.75X10-6'/'C
Met. On the other hand, ceramics that contain titania crystals and have a higher proportion of titania crystals have a smaller coefficient of thermal expansion, and ceramics with a proportion of titania crystals of 3 to 6 parts by weight have a coefficient of thermal expansion of 1.2. ~1.4X1
It became extremely small at 0-6/''C.

The above measurement results show that the presence of titania crystals is effective in reducing the coefficient of thermal expansion in ceramics whose main component is cordierite crystals.

Furthermore, from FIG. 1 and FIG. 2, it can be seen that if the composition ratio of titania crystals is the same, a ceramic having a smaller coefficient of thermal expansion can be obtained at a higher firing temperature.

Next, FIG. 3 shows an X-time analysis diagram of the low expansion ceramic of the present invention containing 4 parts by weight of titania crystals.

This ceramic is made of cordierite-generating raw material powder 96
1410 parts by weight of mixed powder of 4 parts by weight of titanium oxide
It was fired at ℃. In FIG. 3, the peak indicated by symbol C is the peak of cordierite crystal, and the peak indicated by symbol T is the peak of titania crystal. As is clear from FIG. 3, in the low expansion ceramic of the present invention, the titania crystals do not react with the cordierite crystals and are dispersed at the grain boundaries of the cordierite crystals.

Next, the relationship between the grain size of titania crystals and the coefficient of thermal expansion was measured. In this case, the grain size of the titania crystal is 0.15μ,
It was changed to 0.35μ, 0.8μ, and 1μ. The composition ratio of titania crystals is 4 parts by weight when the total is 100 parts by weight. The firing temperature is 1410°C.

FIG. 4 does not show a relationship diagram between the grain size of titania crystals and the coefficient of thermal expansion of ceramics obtained from the above measurement results. As is clear from Figure 4, the grain size of the titania crystals is 0.15μ.
, 0.35μ, 0.8μ, and 1μ, the coefficient of thermal expansion shows a small value of approximately 1°3X10-6/'C, and the grain size of titania crystals has a large effect on the coefficient of thermal expansion of ceramics. You can see that it is not given.

Next, the relationship between the composition ratio of titania crystals and strength was measured. In this case, titania crystals with a grain size of 0.26μ are used,
Addition of titania crystals when the total is 100 parts by weight
was varied in the range of 0 to 10 parts by weight. Mixing time Q, 5hr
The firing temperatures were 1380°C and 1410°C.

FIG. 5 shows a relationship diagram between the composition ratio of titania crystals and the bending strength of ceramics obtained from the measurement results. As is clear from Fig. 5, even when the composition ratio of titania crystals increased, the bending strength showed slight variation, but it was 1.7 kg/mm2 to 2.3 kg/n++n.
It fell within the range of 2.

This measurement result shows that the strength of the low-expansion ceramic of the present invention does not decrease even if the composition ratio of titania crystals increases.

Next, the change in shrinkage rate when the amount of titania crystal added was increased was measured. In this case, titania crystals with a particle size of 0.26 μm were used, and when the total amount was 100 parts by weight, the amount of titania crystals added was varied within the range of 0 to 10 parts by weight. The firing temperatures were 1350'C, 11380C and 1410C.

FIG. 6 shows the measurement results. As is clear from FIG. 6, when the firing temperature was 1350° C., the shrinkage rate gradually decreased from 0.8% as the amount of titania crystal added increased. Further, when the firing temperature was 1380° C., the shrinkage rate decreased slightly up to 3 parts by weight of titania crystal, but increased thereafter. However, within this range, it has no or almost no effect on the strength of the low-expansion ceramic. Further, when the firing temperature was 1410° C., the shrinkage rate showed a minimum value when the titania addition m was 1 part by weight, and then increased. However, within this range, the strength of the low-expansion ceramics is hardly affected.

〔Example〕

4 parts by weight of titania crystals were added to 96 parts by weight of cordierite forming raw material powder prepared to have a composition of cordierite crystals, and the mixture was mixed and stirred in a dry manner. The titania crystal used had a purity of 99.8% and a particle size of 0.26 μm.

30 to 40 parts by weight of water was added to the above mixed powder and wet-kneaded, and further 120 to 150 parts by weight of water and 3 parts by weight of methyl cellulose were added and mixed and stirred to form a slurry.

Next, a three-dimensional network structure made of polyurethane foam was immersed in the slurry, and the slurry was adhered to the surface of the structure. After that, it was dried. By repeating the adhesion and drying of this slurry, a ceramic coating layer is formed on the surface of the three-dimensional network structure, and then heated to thermally decompose and disappear the three-dimensional network structure, forming a mold made of ceramic powder. I got the item. Then, the molded product was heated to 1410°C.
It was fired in

A specimen of an appropriate size was cut out from the three-dimensional mesh Hiramix thus formed, and the coefficient of thermal expansion of this specimen was measured. In this case, the coefficient of thermal expansion from room temperature to 1000°C was 1.3×10 −6 /°C. This three-dimensional mesh ceramic could be used as a carrier for collecting diesel particulates as a catalyst carrier for exhaust gas purification.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the content of titania crystals in a ceramic and the coefficient of thermal expansion of the ceramic. FIG. 2 is an enlarged diagram of the main part of FIG. 1. FIG. 3 is an X-ray diffraction diagram of ceramics containing titania crystals. FIG. 4 is a line diagram showing the relationship between the grain size of titania crystals in ceramics and the coefficient of thermal expansion of the ceramics. FIG. 5 is a diagram showing the relationship between the content of titania crystals in a ceramic and the bending strength of the ceramic. FIG. 6 is a diagram showing the relationship between the addition of titania crystals and the shrinkage rate. Patent Applicant Nippondenso Co., Ltd. Agent Patent Attorney Hirotoshi Okawa Patent Attorney Shudo Fujitani Patent Attorney Akio Maruyama 253- Figure 1 Ti0z Ill 7Jro 1 (wt°/,) times 柘廚@
7r) Figure 4 Addition amount (w t'10)

Claims (8)

[Claims] (1) It is composed of cordierite crystals and titania crystals, and has a mixed crystal structure in which the titania crystals are dispersed in the grain boundaries of the cordierite crystals, and has a thermal expansion coefficient of 1.7 from room temperature to 1000°C. A low-expansion ceramic characterized by a temperature of ×10-6/°C or less. (2) The low-expansion ceramic according to claim 1, wherein the proportion of titania crystals is 1 to 2 oxm parts when the total amount is 100 parts by weight. (3) The low-expansion ceramic according to claim 1, wherein the proportion of titania crystals is 3 to 6 parts by weight when the total amount is 100 parts by weight. (4) Thermal expansion coefficient from room temperature to 1000℃ is 1.5X
10-6/°C or less, the low-expansion Relamix according to claim 1. (5) The low expansion ceramic according to claim 1, wherein the grain size of the titania crystals is smaller than the grain size of the cordierite crystals. (6) The low expansion ceramic according to claim 1, wherein the titania crystal has a grain size of 0.1 to 1 μm. (7) By molding and firing a mixed raw material powder consisting of 1 to 20 parts by weight, the balance being cordierite-forming raw material powder and unavoidable impurities, and making a total of 100 parts by weight, the grain boundaries of cordierite crystals are formed. A method for manufacturing low-expansion ceramics with a mixed crystal structure in which titania crystals are dispersed. (8) The method for producing low-expansion ceramics according to claim 1, wherein the firing temperature is 1350 to 1430°C.