JP2583796B2 - Fibrous ceramics - Google Patents

Description

The present invention relates to a structural material used in a high-temperature atmosphere, a jig for firing a ceramic product, or a fiber suitable for use in contact with a molten metal. Related to porous ceramics.

[Conventional technology]

Fibrous ceramics consist of a fiber portion and a matrix that binds the fibers.
Japanese Patent Publication No. -17147 is known from Japanese Patent Publication No. 63-27308.

The former fibrous ceramics are obtained by firing a molded article composed of 30 to 80% by weight of aluminosilicate fiber and 20 to 70% by weight of kaolin clay, and replacing kaolin clay with a metakaolin phase. The fibrous ceramics are composed of mineral fibers and sintered apatite selected from hydroxyapatite or the like which is fired at a low temperature in close contact with the fibers.

[Problems to be solved by the invention]

Thus, the above fibrous ceramics have been used in such a manner that they are rapidly heated at a high temperature or conversely cooled down to a low temperature. When used in this way,
The article undergoes very rapid expansion or contraction. If the expansion and contraction occur unevenly in each part of the article, the article will spall and break due to the generated strain energy.

Generally, it is well known that the spalling resistance of a refractory is inversely proportional to the coefficient of thermal expansion and proportional to the strength. Therefore, in order to increase the spalling resistance, it is necessary to reduce the coefficient of thermal expansion and increase the strength.

However, conventional fibrous ceramics are superior in spalling resistance to other general ceramic products because they are fibrous, but they are still insufficient.

Therefore, an object of the present invention is to provide a fibrous ceramic that can further increase spalling resistance.

[Means for solving the problem]

In order to solve the above-mentioned problems, the present invention provides a fibrous ceramic comprising a fiber portion occupying the most part, and a matrix consisting of a portion connecting the fibers and a small amount of deposits attached around the fibers. Alumina and silica both have a composition of 30 to 57% by weight, magnesia has a composition of 5 to 25% by weight, and the fiber portion is mainly composed of a cordierite phase and a mullite phase, while the matrix is mainly composed of a cordierite phase and a mullite phase. It consists of a forsterite phase.

[Action]

In the above means, the average linear thermal expansion coefficient is 0.8 to 4.5 ×
It has a fiber appearance with an apparent porosity of 27 to 39% while having a bending strength of 10 ^-6 / ° C and a bending strength of 100 to 230 kg / cm ² .

Ceramic fibers are generally made by a method called melt quenching, which is amorphous and has an average diameter of 3 μm and a length of 50 mm.
It is a collection of relatively short fibers before and after, and is called a bulk fiber. Bulk fibers accompany minute spherical particles that are not fibrillated other than fibers.

In the present invention, the ceramic fiber refers to a state in which both fibers and spherical particles are contained, a state in which only fibers are selected, or a state in which fibers are cut to about 5 μm.

The sum of alumina and silica forming the ceramic fiber is
If it is less than 75% by weight, the relative magnesia (MgO) is 2
If it exceeds 5% by weight, it will be deformed by melting during firing, and its bending strength will decrease.
Magnesia is relatively less than 5% by weight, the linear thermal expansion coefficient increases, and the flexural strength decreases.

Ceramic fibers include alumina (Al ₂ O ₃ ) and silica (S
In addition to iO ₂ ), those containing a small amount of chromia (Cr ₂ O ₃ ) or zirconia (ZrO ₂ ) are also included.

Magnesia raw materials include magnesium chloride (MgC
l _2), magnesium hydroxide (Mg (OH) _2), others will magnesia by heating such as magnesium carbonate (MgCO _3), magnesia itself is used.

In the production of fibrous ceramic products, in order to uniformly disperse and mold the ceramic fiber and magnesia raw material, those in which the magnesia raw material is soluble in water or organic solvents, such as magnesium chloride, should be converted into a high-concentration solution to form ceramic fibers. Although it is possible to attach it to the surface, it is better that the material that does not dissolve in the solvent is as fine as possible.

Also, bulk ceramic fibers are easily entangled by the fibers in a dry state and are difficult to disperse. Therefore,
In the case of mixing with the magnesia raw material in a dry state, it is cut into short pieces of about 5 μm using a pulverizer such as a ball mill to facilitate mixing with the magnesia raw material. Ceramic fibers that have been processed in this way can be mixed and molded by the usual method of handling ceramic raw materials, but if necessary, a small amount of water or a liquid organic binder may be used in combination to improve moldability. Done. If necessary, a suitable mineralizer is added at the same time.

On the other hand, in contrast to the method of mixing and molding the magnesia raw materials in a dry state, vacuum molding in which a ceramic fiber is dispersed in a liquid by using the characteristic that it is a short fiber to make a paper can also be used.

In the vacuum forming method, for example, the ceramyl fiber and the magnesia raw material are charged into a dispersion medium such as water, and the mixture is thoroughly stirred and uniformly dispersed. Thereafter, a coagulant such as aluminum sulfate (Al ₂ (SO ₄ ) ₃ ) or a polymer coagulant is added to fix the magnesia raw material on the surface of the ceramic fiber to form a raw material slurry.

Next, a mold made of a material having good filterability such as a wire net is immersed in the raw material slurry, and a layer made of a mixture of ceramic fibers and magnesia raw material is laminated on the surface of the mold while breathing inside. The molded article thus obtained is dried and provided for firing. Before drying, if necessary, light pressing is performed to adjust the shape accuracy.

This vacuum forming method does not require cutting ceramic fibers, and is advantageous for forming a three-dimensionally complex shape having a constant thickness.

When the molded article thus obtained is fired at a temperature of 1300 to 1400 ° C., the magnesia raw material gradually diffuses from the surface of the ceramic fiber to the inside to cause a solid-phase reaction, and is a constituent component of the ceramic fiber. Reacts with alumina component and silica component, cordierite (2MgO.2Al ₂ O ₃ .5SiO ₂ )
Phase, spinel (MgO.Al ₂ O ₃ ) phase, forsterite (2M
gO ・ SiO ₂ ) phase, while mullite (3Al ₂ O ₃・ 2SiO ₂ )
Phase, cristobalite (SiO ₂ ) phase.

These reactions proceed while leaving the original shape of the ceramic fiber. At the same time as the conversion of the mineral phase proceeds, the bonding reaction at the contact point between the fibers progresses.

As a result of the reaction, the fiber portion, which occupies most of the reaction product, mainly produces a cordierite phase and a mullite phase, and is composed of a portion binding fibers and a small amount of deposits attached around the fibers. The matrix mainly produces a cordierite phase and a forsterite phase.

As the use of the fibrous ceramics as the reaction product, as a light, high strength, large spalling resistance, similar to general low expansion refractories, for example, structural materials and ceramic products used under high temperature atmosphere It is suitable for use in contact with a firing jig or molten metal. In addition, it can be used as a carrier for a catalyst or as a filter medium by utilizing the fact that it is fibrous and has many open pores and a large surface area.

〔Example〕

 Hereinafter, examples of the present invention will be described.

Example 1 Ceramic fibers (manufactured by Toshiba Monoflux Co., Ltd.) having a chemical analysis value of 48% by weight and 52% by weight of Al ₂ O ₃ and SiO ₂ were pulverized with a ball mill to obtain milled fibers having an average length of 5 to 15 μm. Obtained. After adding Mg (OH) ₂ reagent to the milled fiber at intervals of 1% by weight and mixing with a ball mill for 30 minutes,
Pressing was performed at a pressure of 100 kg / cm ^{2 to} form a 50 × 50 × 5 mm plate. Next, this molded body was fired at a temperature of 1300 ° C. and 1400 ° C. for 5 hours.

The relationship between the average thermal expansion coefficient of the obtained fibrous ceramic and the X-ray intensity of the produced cordierite is as shown in FIG.

Therefore, it can be seen that the higher the proportion of cordierite produced, the lower the average linear thermal expansion coefficient tends to be.

FIG. 2 shows the relationship between the average linear thermal expansion coefficient of the obtained fibrous ceramics and the amount of MgO added.

Therefore, it can be seen that the minimum value of the average linear thermal expansion coefficient exists at about 15% by weight of the added amount of MgO.

Furthermore, the bending strength and Mg of the obtained fibrous ceramics
The relationship with the amount of O added was as shown in FIG.

Therefore, it is understood that the maximum value of the bending strength exists at about 15% by weight of the added amount of MgO.

Furthermore, the apparent porosity of the obtained fibrous ceramics and
The relationship with the amount of MgO added was as shown in FIG.

Therefore, it can be seen that each of the fibrous ceramics has a considerably large porosity.

Example 2 A ceramic fiber having a chemical analysis value ratio of Al ₂ O ₃ and SiO ₂ of 40/60 and 56/44 was used in place of the ceramic fiber of Example 1 and subjected to the same process as in Example 1 to obtain a fibrous material. Ceramics were obtained.

As a result, those proportions of Al ₂ O ₃ analysis of the ceramic fibers is small, shows a slightly more trend the amount of cordierite is added the same amount of MgO as compared to Example 1, conversely Al ₂ O Those with a large ratio of the _three analytical values tended to have a slightly smaller amount of cordierite at the same MgO addition amount.

The bending strength was the same as that of Example 1.

〔The invention's effect〕

As described above, according to the present invention, the average linear thermal expansion coefficient is 1.
8 ~ 4.5 × 10 ^-6 / ℃, bending strength is 100 ~ 230kg / cm ² , while the apparent porosity is 27 ~ 39%, so it has a fibrous appearance. Can be further increased, and a fibrous ceramic which is lightweight, has high strength, and has small dimensional change upon firing can be obtained.

[Brief description of the drawings]

FIG. 1 shows the physical properties of the fibrous ceramics according to the present invention. FIG. 1 is an explanatory view showing the relationship between the average linear thermal expansion coefficient and the X-ray intensity of cordierite, and FIG. FIG. 3 is a diagram illustrating the relationship between the amount of MgO added and FIG. 3 is a diagram illustrating the relationship between the bending strength and the amount of MgO added, and FIG. 4 is a diagram illustrating the relationship between the apparent porosity and the amount of MgO added.

Claims (1)

(57) [Claims] 1. A fibrous ceramic comprising a fiber portion occupying a major part, a matrix consisting of a portion connecting the fibers and a small amount of deposits attached around the fibers, comprising alumina and silica. Has a composition of 30 to 57% by weight, magnesia has a composition of 5 to 25% by weight, and the fiber portion mainly comprises a cordierite phase and a mullite phase,
A fibrous ceramic characterized in that the matrix mainly comprises a cordierite phase and a forsterite phase.