JPS5930668B2 - Manufacturing method for alumina-containing ceramic molded product - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing alumina-containing ceramic moldings from double oxides.

Conventional ceramic molded products of this type are widely used in electronic parts, filters, etc., and known methods for producing them include the dry press method, the doctor blade method, and the Tyco method.

However, the dry pressing method requires a pressurizing machine and has the disadvantage that it is difficult to mass produce.

On the other hand, although the doctor blade method is suitable for mass production, it has the disadvantage of being thin and difficult to obtain in micron thickness.

In addition, the Tyco method is a method in which a high-temperature melt of over 2,000°C is pulled through a slit into a plate shape, so it not only requires a large amount of heat, but also requires strict manufacturing conditions. Moreover, the manufacturing environment is poor and there are many drawbacks.

The present invention eliminates the drawbacks of these conventional methods and provides a method that does not require a large amount of heat and can produce an alumina-containing ceramic molded product extremely easily.

In the production of an alumina-containing ceramic molded product from a double oxide, the present invention involves hydrolyzing an aluminum alkoxide and then peptizing the resulting alumina monohydrate sol with a metal oxide sol of another ceramic raw material. Mix one or more of
The problem was solved by making a gel-like molded product from the obtained mixed sol and firing it.

The alcohol of the aluminum alkoxide used to produce the alumina sol in the present invention includes methyl alcohol,
Ethyl alcohol, flobyl alcohol, butyl alcohol (including iso- and tertiary alcohols), etc. are used.

Next, a method for producing pseudo-boehmite using aluminum isopropoxide will be described.

○Production of pseudo-boehmite 1) Hydrolysis method using aluminum isopropoxide powder.

pH per mole of aluminum isopropoxide powder
100 mol of prepared ion-exchanged water was added, and hydrolysis was carried out at room temperature with vigorous stirring using a magnetic stirrer.

The results are shown in Table 1 below.

As the above results show, at pH 2.0 to 3.0,
Hydrolysis for up to 6 hours produced only pseudoboehmite.

However, when the pH increases and the time for hydrolysis increases, alumina trihydrate is produced, resulting in a mixture of pseudoboehmite and trihydrate.

Although not shown in this table, when the pH is 1.0, the hydrolysis rate is slow and it takes 20 hours for complete hydrolysis, and the resulting hydrolyzate is obtained when the pH is 2.0 or higher. It is not a powdery substance, but contains a large amount of spherical particles with a diameter of about 1 mm.

When the hydrolysis time is 15 to 30 minutes, only broad diffraction lines of pseudo-boehmite can be seen, but beyond that time, sharp diffraction lines of bayerite and gibbsite can be seen in addition to the diffraction lines of pseudo-boehmite. .

Therefore, the hydrolysis time is preferably about 15 minutes to 30 minutes.

However, the hydrolysis time for obtaining pseudo-boehmite is also influenced by the amount of ion-exchanged water.

The results of using 80 moles of ion-exchanged water per mole of aluminum isopropoxide are shown in Table 2 below.

As is clear from a comparison of Tables 1 and 2, even if water of the same pH is used, the higher the concentration of aluminum isopropoxide, the more trihydrate is produced by hydrolysis in a shorter time.

2) A method of hydrolysis using an aluminum isopropoxide solution.

1 mol of aluminum isopropoxide to 5 oo of benzene
cc to form a homogeneous solution, and hydrolyzed in the same manner as when using the powder in 1).

The results were as shown in Table 3 below.

When used as a solution in this way, it is possible to slow down the formation of trihydrate even in neutral or alkaline solutions where trihydrate is more likely to be formed than when used as a powder.

Further, the short-time hydrolysis product is X-ray amorphous, and the particle size of the generated pseudoboehmite is extremely small.

Pseudo-boehmite is produced by the method described above.

When trihydrate is mixed, a uniform sol cannot be formed, becomes unstable, and cannot be peptized.

Production of O-pseudo-boehmite sol A sol is prepared by adding an acid to pseudo-boehmite and using a homogenizer, for example.

Although the acid used is not limited, the amount of acid used relative to the pseudo-boehmite affects the properties of the molded product obtained.

Using hydrochloric acid, to describe the addition molar ratio of hydrochloric acid, H
As a result of making a sol by changing the ratio of C4/pseudo-boehmite and using this to make a gel-like molded body, the ratio was o, i ~ 0.
．． At No. 5, a transparent molded body was obtained.

○Production of blue side sill, which is a ceramic raw material other than alumina 50 moles of methanol was added to 1 mole of metallic magnesium, and the mixture was reacted with heating at 40°C to synthesize magnesium methoxide.

To this, 400 moles of distilled water per mole of magnesium methoxide are gradually added at room temperature while stirring with a magnetic stirrer, and the mixture is stirred for 2 hours and then hydrolyzed to obtain blue side sill.

However, the sol is not limited to this method, and sol produced by other methods may be used.

However, those prepared from magnesium alkoxides according to the process described above are preferred.

Silica sol is obtained by adding 250 moles of distilled water to 1 mole of ethyl orthosilicate and heating and refluxing at 90°C for 24 hours for hydrolysis.

However, the method is not limited to this, and other methods may be used.

However, those made from the silicate alkoxides of the process described above are preferred.

The ceramic molded article of the present invention can be obtained by mixing the respective sols produced as described above in a desired composition ratio, making a gel-like molded article from this mixed sol, and firing this.

For example, a sol can be easily formed into a film by pouring it into a container made of fluororesin, which has good releasability.

In addition, various molded products can be formed by a molding method using a mixed sol instead of a melt in the conventional pulling method or by an extrusion method.

Example 1 Production of spinel thin film Blue side sill and pseudo-boehmite sol were mixed into a spinel composition to prepare a raw material sol.

Although it showed a temporary tendency to gel when mixed, it turned into a sol by vigorously stirring and did not gel again.

At this time, the state of each sol was slightly less transparent than when using a single sol, but it was very stable.

This mixed sol was poured into a fluororesin container and air-dried to obtain a gel thin film, which was then fired at 350°C or higher to obtain a spinel thin film.

MgO:Al2O3 molar ratio 53:47 50:50
The results of X-ray diffraction of the thin film obtained by changing the ratio to 40:6035:65 were as shown in FIG.

The thin film obtained by firing these at 1200℃ is Al2O3
Those containing 49.0 to 59.5 moles of was a thin film consisting of one spinel phase, and those with other compositions were thin films consisting of a mixture of magnesia and spinel or alumina and spinel.

In addition, 15 with a molar ratio of MgO:Al2O3 of 50:50
The results of measuring the transmittance in the ultraviolet to infrared region of a μ-thick gel thin film and that baked at 600°C are the second results.
It was as shown in the diagram.

In the figure, the dotted curve indicates the gel thin film, and the solid curve indicates the fired product.

When we conducted a similar experiment with this external molar ratio changed to 53:4740:60, we found that the change in composition did not have a major effect on the transmittance, but from the visible to the ultraviolet (800 mm to 200 mm) and infrared (2.5 to 25), it was found that spinel containing an excess of MgO exhibits a rather high transmittance.

Instead of thin films, spinel moldings of other shapes can also be produced by extrusion and pulling methods.

Example 2 Production of mullite thin film Silica sol and pseudo-boehmite sol were mixed with a mullite composition and stirred for 1 hour to form a uniform mixed sol.

This mixed sol was poured into a fluororesin container to form a sol thin film, which was naturally dried to form a gel thin film, which was then fired to obtain a mullite thin film.

Mullite thin films were made by changing the molar ratio of M2O3:SiO2, and the changes in the lattice constant were investigated by X-ray diffraction. The results are shown in Figure 3 (a).
,b.

C).

Based on the change in lattice constant in Figure 3, Al2O3/Si
130 with an O2 molar ratio in the range of 2/1 to 7/13
After firing at 0° C. for 1 hour, a thin film consisting of one phase of mullite was obtained.

Note that the relationship between firing temperature and time for obtaining a mullite phase thin film is difficult to specify, and mullite can be formed by firing for a long time even at low temperatures.

For example, when firing at 1200℃, Al-8
Although it is only the i-spinel, the X-ray peaks of Al-8i spinel and mullite are observed at 16 hours.

In the firing of the gel thin film, the peak of boehmite occurs at low temperatures, the peak of Al-8i spinel occurs at 500 to 1200°C, and the peak of Al-8i spinel becomes one phase at 1300°C or higher.

It is a transparent thin film up to a temperature of 1300℃, but at a temperature of 1500℃
It loses its transparency considerably at ℃.

Instead of forming a thin film, mullite molded products of other shapes can be produced using extrusion or pulling methods.

Example 3 Production of cordierite thin film Blue side sill, pseudoboehmite sol and silica sol are mixed with cordierite composition, stirred to make a uniform sol, poured this mixed sol into a fluororesin container,
A gel thin film was formed by air drying at room temperature, and this was fired to obtain a cordierite thin film.

The gel thin film was transparent and remained transparent even after baking at 1300°C.

During firing, it is stable as a gel and boehmite brucite up to 200℃, once it becomes an amorphous thin film at 400℃, it turns into spinel and α-crylodoparite at 600-1200℃, and above that it turns into cordierite. began to form, and at 1250°C it became a film consisting of three phases: cordierite, spinel, and α-cristobalite, and at 1300°C, a thin film with one phase of cordierite was obtained.

Instead of forming a thin film, molded articles of other shapes can also be produced using extrusion and pulling methods.

As described above, according to the method of the present invention, an alumina monohydrate sol obtained by hydrolyzing aluminum alkoxide and peptizing the alumina sol is used.
It is a pure and extremely stable sol, and even if other ceramic sol components are mixed with it, a stable and uniform sol can be obtained.

In addition, since this mixed sol can be molded at room temperature, it does not require heat unlike conventional melt molding, and can be manufactured with extremely simple equipment, and has the excellent effect of producing excellent ceramic molded products. has.

[Brief explanation of the drawing]

Figure 1 shows the change in the lattice constant of the spinel phase due to X-ray diffraction of the thin film. Figure 2 shows the light transmittance of the gel thin film and spinel thin film.
FIGS. 3, 4, and 5 show changes in the lattice constants (a, b, c) of the mullite phase by X-ray diffraction of the mullite thin film.

Claims (1)

[Claims] 1. When producing an alumina-containing ceramic molded product from a double oxide, aluminum alkoxide is hydrolyzed, this is peptized to form a sol of alumina monohydrate, and the sol is added with metal oxidation of other ceramic raw materials. Mix one or more types of substance sols, make a gel-like molded product from the obtained mixed sol,
A method for producing an alumina-containing ceramic molded article, which comprises firing the alumina-containing ceramic molded product.