JP2023057657A - Inorganic molding and manufacturing method thereof - Google Patents

Abstract

To provide an inorganic molding that is not easily defected even when fired in a strongly reducing atmosphere, and a method for manufacturing the same.SOLUTION: In one embodiment, the present invention is a method for manufacturing an inorganic molding that includes adding an aluminous fiber, an alumina particle and an inorganic binder into a liquid medium to obtain a slurry and removing the liquid medium from the slurry to form the inorganic molding. The present invention relates to a method for manufacturing an inorganic molding in which the inorganic binder contains silica includes firing the inorganic molding in a non-reducing atmosphere to mullite the inorganic binder, and the inorganic molding as obtained by the method.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to an inorganic molded article and a method for producing the same. In particular, the present invention relates to an inorganic molded article that is resistant to destruction even when used for a long period of time in a strongly reducing atmosphere, and a method for producing the same.

2. Description of the Related Art Conventionally, electronic components such as multilayer ceramic capacitors are subjected to firing treatment in industrial furnaces.

Thermal insulation materials provided inside industrial furnaces are required to have low heat capacity and thermal conductivity. Examples of such thermal insulation materials include alumina fibers, alumina particles and inorganic Inorganic moldings containing binders are known.

By using such a heat insulating material, the heat energy during heating is efficiently used, and the tact time is shortened to improve the production efficiency.

JP 2010-155733 A

Among laminated ceramic capacitors, low-temperature co-fired ceramics (LTCC) substrates and high-temperature co-fired ceramics (HTCC) substrates in particular are often fired in a reducing atmosphere in order to prevent oxidation of wiring. Reducing atmospheres include hydrogen, nitrogen and water vapor, although hydrogen is typically used at less than 4 vol % outside its flammable range for safety reasons.

As long as it is fired in a reducing atmosphere within such a range, there is no particular problem with the inorganic molded article of the prior art. It turns out that the body will be destroyed in a short period of time.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an inorganic molded article that is resistant to destruction even when fired in a strongly reducing atmosphere, and a method for producing the same.

The inventors have found that the above problems can be solved by the present invention having the following aspects.
<<Aspect 1>>
A method for producing an inorganic molded article, comprising: adding aluminous fibers, alumina particles and an inorganic binder to a liquid medium to obtain a slurry; and removing the liquid medium from the slurry and molding the article,
the inorganic binder comprises silica,
A method for producing an inorganic molded body, further comprising firing the inorganic molded body in a non-reducing atmosphere to convert the inorganic binder into mullite.
<<Aspect 2>>
The method for producing an inorganic molded body according to aspect 1, wherein the firing is performed at 1400°C or higher and 1600°C or lower.
<<Aspect 3>>
The method for producing an inorganic molded article according to aspect 1 or 2, wherein the non-reducing atmosphere is an air atmosphere.
<<Aspect 4>>
A method for producing an inorganic molded article, comprising: adding aluminous fibers, alumina particles and an inorganic binder to a liquid medium to obtain a slurry; and removing the liquid medium from the slurry and molding the article,
A method for producing an inorganic molded body, wherein the inorganic binder contains silica-containing fine particles and alumina-containing fine particles.
<<Aspect 5>>
The method for producing an inorganic compact according to aspect 4, wherein the silica-containing fine particles and the alumina-containing fine particles each contain a molar ratio of alumina to silica in the range of 1.0 to 2.5.
<<Aspect 6>>
A method for producing an inorganic molded article, comprising: adding aluminous fibers, alumina particles and an inorganic binder to a liquid medium to obtain a slurry; and removing the liquid medium from the slurry and molding the article,
A method for producing an inorganic molded body, wherein the inorganic binder contains alumina-containing fine particles, titania-containing fine particles, zirconia-containing fine particles, or a mixture of two or more of these.
<<Aspect 7>>
An inorganic molded article comprising alumina fibers and alumina particles bound together by at least an inorganic binder, wherein the inorganic binder contains mullite.
<<Aspect 8>>
1. An inorganic molded article comprising alumina fibers and alumina particles bound together by at least an inorganic binder, wherein the inorganic binder comprises alumina, titania, zirconia, or a mixture of two or more thereof.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an inorganic molded article that is resistant to destruction even when fired in a strongly reducing atmosphere, and a method for producing the same.

FIG. 1 shows an SEM photograph of an inorganic compact that has been repeatedly fired for a long period of time in a strongly reducing atmosphere and destroyed. FIG. 2 shows an SEM photograph of an inorganic compact that was repeatedly fired for a long period of time in a strongly reducing atmosphere but was not destroyed. FIG. 3 shows changes in flexural strength of inorganic compacts sintered at a temperature of 500° C. to 1700° C. for 24 hours in an air atmosphere. FIG. 4 shows changes in X-ray diffraction (XRD) data of an inorganic compact sintered at a temperature of 500° C. to 1700° C. for 24 hours in an air atmosphere.

<<1st Embodiment>>
In a first embodiment, the method for producing an inorganic molded article of the present invention includes adding alumina fibers, alumina particles and an inorganic binder to a liquid medium to obtain a slurry, and removing the liquid medium from the slurry to form the article. wherein the inorganic binder contains silica, and firing the inorganic molded body in a non-reducing atmosphere to convert the inorganic binder to mullite. Further, the inorganic molded article of the present invention is obtained by such a production method, and is an inorganic molded article containing alumina fibers, alumina particles and an inorganic binder, wherein the inorganic binder contains mullite. is the body.

The present inventors have discovered that the Si component is lost in inorganic compacts fired in a strongly reducing atmosphere. This is because amorphous silica mainly derived from the inorganic binder and crystalline silica (cristobalite) contained in alumina fibers react with hydrogen when the inorganic molded body is fired in a strongly reducing atmosphere. It is considered that it volatilized as silane or silanol.

Therefore, the reason why the inorganic molded body is likely to be destroyed by firing in a strongly reducing atmosphere is thought to be that the strength of the inorganic molded body decreases due to the loss of these amorphous silica and crystalline silica. .

On the other hand, the inventors of the present invention conducted extensive studies so that amorphous silica and crystalline silica would not be lost even in firing in a strongly reducing atmosphere, and found that pre-firing an inorganic molded body in a non-reducing atmosphere is possible. It was found that the loss of silica from the inorganic molded body can be reduced by This is because the alumina from the aluminous fibers and alumina particles and the silica from the inorganic binder and the like turn into mullite during the preliminary firing, so that even if the firing is performed in a strongly reducing atmosphere after that, the silica will not be lost. This is probably because it has become harder.

In addition, the inventors of the present invention analyzed a conventional inorganic molded body that was destroyed by firing in a strongly reducing atmosphere, and discovered that crystals contained in aluminous fibers and the like were undergoing grain growth. . Therefore, the reason why the inorganic molded body is likely to be destroyed by firing in a strong reducing atmosphere is that in the case of a strong reducing atmosphere, the grain growth of the crystals of the components contained in the alumina fiber etc. progresses more quickly. , it is also conceivable that the aluminous fibers became susceptible to embrittlement. On the other hand, it is thought that the grain growth of this crystal can be suppressed by pre-firing the inorganic compact in a non-reducing atmosphere.

The firing conditions in a non-reducing atmosphere are not particularly limited as long as the temperature and time are sufficient to mulliteize the silica derived from the inorganic binder while suppressing the grain growth of the crystals contained in the aluminous fibers. The firing temperature may be, for example, 1000°C or higher, 1200°C or higher, 1300°C or higher, 1350°C or higher, 1400°C or higher, or 1450°C or higher, and 1600°C or lower, 1550°C or lower, 1500°C or lower, and 1450°C. or less, or 1400° C. or less. For example, the firing temperature may be 1000° C. or higher and 1600° C. or lower, or 1400° C. or higher and 1550° C. or lower. The firing time may be 1 hour or more, 3 hours or more, 6 hours or more, 12 hours or more, or 24 hours or more, and may be 5 days or less, 3 days or less, 2 days or less, or 24 hours or less. good. For example, the firing time may be 1 hour or more and 5 days or less, or 12 hours or more and 3 days or less.

The non-reducing atmosphere may be somewhat reducing as long as it is an atmosphere in which silica is not substantially lost under the firing conditions described above. air atmosphere is preferred.

The inorganic binder used in the first embodiment is not particularly limited as long as it produces silica that is lost in firing in a strongly reducing atmosphere after manufacturing an inorganic molded body without firing. Examples of inorganic binders include dry silica such as fumed silica, wet silica such as silica sol, water glass, liquid silicon-containing compounds such as alkoxysilane, and clay silicon-containing compounds such as kaolin. Among these, silica sol can be used in particular.

<<Second embodiment>>
In a second embodiment, the method for producing an inorganic molded article of the present invention comprises adding alumina fibers, alumina particles and an inorganic binder to a liquid medium to obtain a slurry, and removing the liquid medium from the slurry to form the article. wherein the inorganic binder contains silica-containing fine particles and alumina-containing fine particles. Further, the inorganic molded article of the present invention is obtained by such a production method, and is an inorganic molded article containing alumina fibers, alumina particles and an inorganic binder, wherein the inorganic binder contains mullite. is the body.

The present inventors have found that the inorganic binder formed from silica-containing fine particles and alumina-containing fine particles has very small particle diameters of both the silica-containing fine particles and the alumina-containing fine particles, and the presence of these particles in close proximity , When an inorganic molded body is fired, mullite formation is likely to proceed, so that the inorganic binder is less likely to be lost even in a strongly reducing atmosphere, and as a result, the strength of the inorganic molded body is less likely to decrease. rice field. For example, since silica sol and alumina sol are calcined to mullite from around 1150° C., silica can be mullitized before silica is substantially lost in a strongly reducing atmosphere.

The inorganic binder preferably contains silica and alumina to approximate the mineral composition of mullite, and the molar ratio of alumina to silica used in forming the inorganic binder (moles of alumina/moles of silica ) may be 1.0 or more, 1.2 or more, or 1.4 or more, and may be 2.5 or less, 2.2 or less, 2.0 or less, or 1.8 or less. For example, this molar ratio ranges from 1.0 to 2.5, or from 1.4 to 2.2.

In this specification, fine particles may have an average particle diameter of 1 nm or more, 3 nm or more, 5 nm or more, 10 nm or more, 15 nm, or 20 nm or more, It may be 100 nm or less, 50 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less. For example, the average particle size of the fine particles may be 1 nm or more and 1000 μm or less, 3 nm or more and 200 nm or less, or 5 nm or more and 50 nm or less. Here, the average particle size is defined by randomly selecting a screen containing a large number of representative particles using a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and selecting 100 or more particles. It means the particle size at 50% of the integrated value in the number-based particle size distribution obtained by measuring the major axis of the primary particles.

The silica-containing microparticles and alumina-containing microparticles of the inorganic binder used in the second embodiment are not particularly limited as long as they form mullite when fired. Examples of silica-containing fine particles include dry silica fine particles such as fumed silica and wet silica fine particles such as silica sol. Further, examples of alumina-containing fine particles include dry alumina fine particles and wet alumina fine particles such as alumina sol. Among these, in particular, silica sol and alumina sol can be used.

Also in this embodiment, firing in a non-reducing atmosphere as in the first embodiment may be performed. Thereby, mullite-izing of an inorganic binder can be advanced.

<<Third Embodiment>>
In a third embodiment, the method for producing an inorganic molded article of the present invention comprises adding alumina fibers, alumina particles and an inorganic binder to a liquid medium to obtain a slurry, and removing the liquid medium from the slurry to form the article. wherein the inorganic binder contains alumina-containing fine particles, titania-containing fine particles, zirconia-containing fine particles, or a mixture of two or more thereof. Further, the inorganic molded article of the present invention is obtained by such a production method, and is an inorganic molded article containing alumina fibers, alumina particles and an inorganic binder, wherein the inorganic binder comprises alumina, titania, zirconia, Alternatively, it is an inorganic molded body consisting of a mixture of two or more of these.

The present inventors have found that an inorganic binder formed from alumina-containing fine particles, titania-containing fine particles, zirconia-containing fine particles, or a mixture of two or more of these particles is less likely to lose the inorganic binder even in a strongly reducing atmosphere. It was also found that the decrease in strength of the inorganic molded body is less likely to occur.

As the alumina-containing fine particles, titania-containing fine particles, and zirconia-containing fine particles of the inorganic binder used in the third embodiment, silica that is lost in firing in a strongly reducing atmosphere after manufacturing an inorganic molded body without firing is not particularly limited as long as it does not generate For example, alumina-containing fine particles include dry alumina fine particles and wet alumina fine particles such as alumina sol. Examples of titania-containing fine particles include dry titania fine particles and wet titania fine particles such as titania sol. Examples of the contained fine particles include dry zirconia fine particles and wet zirconia fine particles such as zirconia sol. Among these, alumina sol, titania sol, and zirconia sol can be used.

Hereinafter, technical matters common to the above embodiments will be described in detail.

<<Inorganic molding>>
The inorganic molded body contains alumina fibers, alumina particles and an inorganic binder, and can be used as a heat insulating material. This inorganic molded body is advantageous because it is less likely to be destroyed even if it is repeatedly fired for a long period of time in a strongly reducing atmosphere.

Here, the strongly reducing atmosphere refers to an atmosphere containing more than 4% by volume of hydrogen. The strongly reducing atmosphere may contain hydrogen at 5 vol% or more, 8 vol% or more, 10 vol% or more, 12 vol% or more, or 15 vol% or more, and 20 vol% or less, 15 vol% or less, Alternatively, it may contain hydrogen at 10% by volume or less. For example, the strongly reducing atmosphere may contain 5% by volume or more and 20% by volume or less of hydrogen, or 10% by volume or more and 15% by volume or less of hydrogen.

The strongly reducing atmosphere may contain a reducing gas, such as water vapor, in order to further enhance the reducing properties, or may be an inert gas, such as nitrogen, argon, etc., other than hydrogen and the reducing gas. .

The firing temperature in the strongly reducing atmosphere may be, for example, 1250° C. or higher, 1300° C. or higher, 1350° C. or higher, or 1400° C. or higher, and may be 1500° C. or lower, 1450° C. or lower, or 1400° C. or lower. good. For example, the firing temperature may be 1250° C. or higher and 1500° C. or lower, or 1300° C. or higher and 1400° C. or lower. When sintering at such temperatures is repeated for a short period of time, from several months to several years, the inorganic compacts of the prior art may be destroyed.

^The bulk density of the inorganic molded body is not particularly limited as long as it does ^not impair the effects of ^the present invention ^. or 300 kg/m ³ or more, 1200 kg/m ³ or less, 1000 kg/m ³ or less, 700 kg/m ³ or less, 500 kg/m ³ or less, 400 kg/m ³ or less, 300 kg/m ³ or less, or It may be 250 kg/m ³ or less. For example, the inorganic molded body may have a bulk density of 100 kg/m ³ or more and 1200 kg/m ³ or less, or 150 kg/m ³ or more and 500 kg/m ³ or less.

<Aluminous fiber>
Aluminous fibers are metal oxide fibers containing alumina as a main component. Aluminous fiber means a fiber containing alumina as a main component, and may contain one or more components selected from the group consisting of silica, zirconia, calcia, iron oxide, sodia, and magnesia in addition to alumina.

The alumina content in the aluminous fibers is, for example, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, 95% by mass or more, 97% by mass or more, or 99% by mass. 100% by mass or less, 99% by mass or less, 97% by mass or less, 95% by mass or less, or 90% by mass or less. The alumina content in the aluminous fibers may be, for example, 70% by mass or more and 100% by mass or less, or 75% by mass or more and 97% by mass or less.

The balance other than alumina in the aluminous fibers may be silica. The silica content in the aluminous fibers may be, for example, 1% by mass or more, 3% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, or 25% by mass or more. It may be 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, 10% by mass or less, or 5% by mass or less. The alumina content in the aluminous fibers may be, for example, 1% by mass or more and 30% by mass or less, or 3% by mass or more and 25% by mass or less. Silica in the aluminous fibers may exist in an amorphous state or in a crystalline state, such as cristobalite, mullite, and the like.

In addition, it was found that silica contained in the aluminous fibers is not substantially lost when only the aluminous fibers are sintered in a strong reducing atmosphere. Aluminous fibers also contain amorphous silica, but crystalline alumina such as γ-alumina and α-alumina, and mullite, which is a crystal of silica and alumina, are present on the surface of aluminous fibers, and are amorphous. It is considered that silica was not substantially lost because silica was abundantly present in the core portion of the fiber.

The average fiber length of the aluminous fibers may be 0.1 mm or more, 1 mm or more, 5 mm or more, 10 mm or more, 15 mm or more, or 20 mm or more, and may be 100 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, 20 mm or less, Alternatively, it may be 15 mm or less. The average fiber length of the aluminous fibers may be 0.1 mm or more and 100 mm or less, or 5 mm or more and 30 mm or less.

The average fiber diameter of the aluminous fibers may be, for example, 1 μm or more, 2 μm or more, 3 μm or more, or 5 μm or more, and may be 20 μm or less, 10 μm or less, 8 μm or less, or 5 μm or less. The average fiber diameter of the aluminous fibers may be 1 μm or more and 20 μm or less, or 3 μm or more and 10 μm or less.

The ratio of the average fiber length to the average fiber diameter of the aluminous fibers (average fiber length/average fiber diameter) may be 25 or more, 50 or more, 100 or more, 300 or more, or 500 or more, and 10000 or less and 5000 or less. , 3000 or less, 1000 or less, or 500 or less. This ratio may be from 25 to 10,000 or from 100 to 5,000.

<Alumina particles>
The alumina particles preferably have a high degree of crystallinity like the aluminous fibers, and are particularly preferably alumina particles containing or consisting of α-alumina.

The average particle size of the alumina particles may be 1 μm or more, 3 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, or 50 μm or more, 100 μm or less, 80 μm or less, 50 μm or less, 30 μm or less, 20 μm or less, Alternatively, it may be 10 μm or less. For example, the average particle size of the alumina particles may be 1 μm or more and 300 μm or less, or 3 μm or more and 20 μm or less. The average particle diameter means the median diameter measured with a laser diffraction particle size distribution analyzer. If the average particle size of the alumina particles is within such a range, both the mechanical strength and chemical durability of the inorganic compact can be achieved.

In the inorganic molded body, the amount of the alumina fibers is 20 parts by mass or more and 80 parts by mass or less, 30 parts by mass or more and 70 parts by mass or less, or 40 parts by mass or more and 60 parts by mass with respect to a total of 100 parts by mass of the alumina fibers and the alumina particles. 20 to 80 parts by mass, 30 to 70 parts by mass, or 40 to 60 parts by mass of alumina particles.

<Inorganic binder>
The inorganic molded body contains alumina fibers, alumina particles, and an inorganic binder for binding them. In this specification, unless otherwise specified, the inorganic binder means not only a substance used during production (e.g., colloidal silica), but also a substance that binds alumina particles and alumina particles after production (e.g., silica ) means both.

The inorganic binder is not particularly limited as long as it does not impair the effects of the present invention, unless otherwise specified in this specification. one or more selected from the group consisting of), one or more selected from the group consisting of fumed silica, zirconia sol, titania sol, alumina sol, and bentonite.

The solid content of the inorganic binder in the inorganic molded article is not particularly limited as long as it does not impair the effects of the present invention. It may be at least 3 parts by mass, at least 3 parts by mass, at least 5 parts by mass, or at least 10 parts by mass, and may be at most 30 parts by mass, at most 20 parts by mass, at most 15 parts by mass, or at most 10 parts by mass. For example, the inorganic binder may be 1 part by mass or more and 30 parts by mass or less, or 3 parts by mass or more and 20 parts by mass or less with respect to a total of 100 parts by mass of the alumina fiber and the alumina particles.

<Inorganic fixing material>
The inorganic molded body may further contain an inorganic fixing material for the purpose of, for example, uniformly attaching the inorganic binder to the surfaces of the alumina fibers. The inorganic fixing material may be, for example, one or more selected from the group consisting of aluminum sulfate, alumina sol and aqueous ammonia, preferably aluminum sulfate.

The content of the inorganic fixing material in the inorganic molding is not particularly limited as long as it does not impair the effects of the present invention. Parts by mass or more, 0.3 parts by mass or more, 0.5 parts by mass or more, may be 1.0 parts by mass or more, 3.0 parts by mass or less, 2.0 parts by mass or less, 1.5 parts by mass or less , or 1.0 parts by mass or less. For example, the inorganic fixing material is 0.1 parts by mass or more and 3.0 parts by mass or less, or 0.3 parts by mass or more and 2.0 parts by mass or less with respect to a total of 100 parts by mass of the alumina fiber and the alumina particles. may

<Organic binder>
The inorganic molded body can contain an organic binder. The organic binder is not particularly limited as long as it does not impair the effects of the present invention, but is preferably one or more selected from the group consisting of polymer flocculants and starch, for example. When the inorganic molding contains a polymer flocculant, it may or may not contain starch.

The polymer flocculant as an organic binder is not particularly limited as long as it does not impair the effects of the present invention. It is preferably one or more selected from the group consisting of ether-based polymers, and particularly preferably polyacrylamide-based polymers.

The starch used as the organic binder is not particularly limited as long as it does not impair the effects of the present invention. one or more selected from the group consisting of)), one or more selected from the group consisting of cationic starch, anionic starch, and amphoteric starch.

The inorganic molded body may further contain pulp, a suitable emulsion, or the like as an organic binder, if necessary. In the production of the inorganic molded article, the type and amount of the organic binder added to the liquid medium to form flocs of a desired size depends on the charge amount of the inorganic binder, the nature of the charge, the size of the alumina particles used, etc. Optimized for

When the inorganic molded body contains an organic binder, the content of all organic binders is not particularly limited as long as it does not impair the effects of the present invention, but the total content of the alumina fibers and alumina particles is 100 parts by mass. On the other hand, for example, it may be 0.1 parts by mass or more, 0.5 parts by mass or more, 1.0 parts by mass or more, 3.0 parts by mass or more, or 5.0 parts by mass or more, and 15 parts by mass or less , 10 parts by mass or less, 8.0 parts by mass or less, or 5.0 parts by mass or less. For example, the content of the organic binder in the inorganic molded body is 0.1 parts by mass or more and 15 parts by mass or less, or 3.0 parts by mass or more and 10 parts by mass with respect to a total of 100 parts by mass of the alumina fiber and the alumina particles. It may be below.

In addition, when producing the inorganic molded article, it is preferable to include an organic binder at least at the time of obtaining the wet molded article. On the other hand, for manufacturing methods other than those of the first embodiment, after molding, before shipping or before use, a baking treatment may be performed to eliminate the organic binder. Although it is preferable to use an organic binder in the production of the inorganic molded body obtained by the first embodiment, the organic binder disappears by firing treatment at 700° C. or less, so the organic binder is substantially present after production. not.

<<Manufacturing method of inorganic molding>>
For each configuration of the method for producing the inorganic molded article of the present invention, each configuration described with respect to the inorganic molded article of the present invention can be referred to. In particular, the description of the content of the inorganic molded article can be referred to as the amount used during production in the method for producing the inorganic molded article.

A method for producing an inorganic molded body includes adding alumina fibers, alumina particles, an inorganic binder, an optional inorganic fixing material, and optionally an organic binder to a liquid medium to obtain a slurry, and optionally mixing and stirring the slurry. , including removing the liquid medium from the slurry and shaping it. Removing the liquid medium from the slurry and shaping can include de-molding or sheeting to obtain a wet compact and drying the wet compact. Water, aqueous solvents, polar organic solvents, and the like can be used as the liquid medium.

The wet volume of the slurry is not particularly limited as long as it does not impair the effects of the present invention. Well, it may be 1000 mL/20 g or less, 8000 mL/20 g or less, or 600 mL/20 g or less. The wet volume of the slurry may be from 50 mL/20 g to 1000 mL/20 g, or from 200 mL/20 g to 800 mL/20 g.

In order to obtain a wet compact from the slurry, for example, the slurry can be deliquid molded or made into paper by a well-known method. Here, if necessary (for example, when producing an inorganic molded article having a relatively high bulk density), the wet molded article may be pressed.

Thereafter, by drying the wet molded article, an inorganic molded article can be obtained. Although the shape of the inorganic molded body is not particularly limited, it is preferably board-shaped, sheet-shaped, or block-shaped, for example. Also, the shape of the inorganic molded body can be made into other shapes such as a cylindrical shape or a conical shape by selecting a suction mold according to the desired shape.

Moreover, when the inorganic molded body is not subjected to the firing treatment as in the first embodiment, it may be subjected to further firing treatment to eliminate the organic binder. The method of the firing treatment is not particularly limited, and for example, it is performed using a known heating furnace. The firing temperature is not particularly limited as long as it does not impair the effects of the present invention, but is preferably 600° C. or higher and 1000° C. or lower, for example. The firing time is not particularly limited as long as it does not impair the effects of the present invention, but it is preferably 30 minutes or more and 60 minutes or less, for example.

The method for producing an inorganic molded article may further include a curing treatment. The curing treatment is, for example, impregnating an inorganic molding with a curing treatment liquid containing an inorganic binder (for example, one or more selected from the group consisting of colloidal silica and alumina sol), followed by drying. The curing treatment can effectively improve the hardness of the dried inorganic molded article.

The curing treatment liquid includes, for example, an inorganic binder, an organic thickener for controlling viscosity, and an inorganic powder (e.g., one or more selected from the group consisting of glass powder, alumina powder, and wollastonite powder). One or more selected from the group consisting of may also be included. The method for impregnating the inorganic molding with the curing treatment liquid is not particularly limited, but one or more selected from the group consisting of brush coating, spray coating, and immersion is preferably used, for example.

The method for producing the inorganic molded article may include surface coating treatment. That is, for example, by coating the surface of an inorganic molded article with a coating agent containing zirconia, silica and silicon carbide or a coating agent containing alumina and silica, the surface properties of the inorganic molded article can be effectively improved. can. Specifically, for example, when the inorganic molded body is placed in a furnace and used, the inorganic molded body is subjected to a surface coating treatment to improve corrosion resistance to scale (e.g., iron oxide) in the furnace and / or can effectively improve wind speed resistance against hot air.

The method for manufacturing the inorganic molded body may include an adhesion treatment. That is, for example, when bonding a plurality of inorganic molded bodies to each other or when bonding an inorganic molded body to another molded body, an adhesive containing alumina and silica or an adhesive containing iron and silica is applied to the inorganic molded body. By applying to the adhesive surface of , the adhesive strength can be effectively improved.

The present invention will be described in more detail with the following examples, but the invention is not limited thereto.

《Manufacturing example》
As the alumina fibers, alumina fibers (“B80” manufactured by Denka Co., Ltd., alumina content: 80% by mass, silica content: 20% by mass, average fiber diameter: 3 μm to 5 μm) were used.

As the alumina particles, alumina particles ("SA31" manufactured by Nippon Light Metal Co., Ltd., average particle size 5 μm, alumina content: about 99.6% by mass) were used.

As an inorganic binder, colloidal silica (manufactured by Nippon Kagaku Kogyo Co., Ltd., “Silicadol 30”, suspension with a solid content of 30% by mass, average particle size of the solid content of 15 nm, pH 10.0) was used.

As the organic binder, polyacrylamide (manufactured by Arakawa Chemical Industries, Ltd., "Polystrone 705", cationic, non-volatile content 10%, pH 2.5 to 3.5, viscosity 300 to 1000 mPa s), which is a polymer flocculant. was used.

40 parts by mass of aluminous fibers, 60 parts by mass of alumina particles, 10 parts by mass of solid content of an inorganic binder, and 3.4 parts by mass of an organic binder are added to water, and the slurry concentration is 2% by mass. Water was added to and stirred to prepare a slurry.

The slurry obtained as described above was poured into a mold provided with a net at the bottom, and was dehydrated and molded by a suction dehydration molding method in which a liquid medium was sucked to obtain a wet compact having a flat plate shape. Further, the wet molded body obtained as described above was pressed so that the finally obtained inorganic molded body had a bulk density of about 300 kg/m ³ . Thereafter, the wet molded body was dried at 110° C. for 36 hours in a dryer to obtain a flat inorganic molded body of Reference Example 1 having a thickness of 25 mm.

《Analysis of destroyed inorganic compacts》
The inorganic molded body of Reference Example 1 was installed as a heat insulating material in an industrial furnace. In a strongly reducing atmosphere of 13% by volume of hydrogen and the balance of nitrogen into which steam having a dew point of 20° C. was introduced, the maximum heating temperature was set to 1360° C., and the firing treatment was repeatedly performed for about half a year at a relatively rapid temperature rise and fall. As a result, a crack occurred in a part of the heat insulating material.

A bending strength test was performed to compare the inorganic molded body in the vicinity of the broken portion and the inorganic molded body in the unbroken portion. Similarly, X-ray fluorescence analysis (XRF) was performed on these samples to investigate changes in the chemical composition of alumina and silica. Furthermore, these were observed with SEM photographs.

The flexural strength of the inorganic molding was measured as follows. A flat plate-shaped test piece of 150 mm length, 12.5 mm width, and 5 mm thickness made of an inorganic molded body was measured using a strength tester ("Tensilon universal tester" by Orientec Co., Ltd.) at a head speed of 2 mm / min. A load was applied at a speed and the maximum load (breaking load) was measured. Then, the bending strength of the inorganic compact was calculated by the following formula:
Bending strength (MPa) = {3 × maximum load (N) × distance between lower fulcrums (mm)} / {2 × width of specimen (mm) × (thickness of specimen (mm)) ² }

The results of flexural strength testing and compositional analysis by XRF are shown in Table 1 below. FIG. 1 shows an SEM photograph of the broken portion of the inorganic molded article, and FIG. 2 shows an SEM photograph of the unbroken portion of the inorganic molded article.

It can be seen that at the location where the fracture occurred, the bending strength was greatly reduced and silica was lost. Comparing the photographs of FIG. 1 and FIG. 2, especially at 5000 times magnification, the appearance of the aluminous fibers is greatly different, and it can be seen that the crystal grains of the aluminous fibers have grown at the locations where the breakage occurred.

<<Experiment 1: Strength change due to firing temperature in air atmosphere>>
The inorganic molded body of Reference Example 1 was sintered at a temperature of 500° C. to 1700° C. for 24 hours in an air atmosphere.

FIG. 3 shows the change in bending strength.

Referring to FIG. 3, the inorganic compact of Reference Example 1 immediately after production has a bending strength of about 1.3 MPa, but it can be seen that the bending strength decreases to about 0.6 MPa by firing at 500 ° C. . This is due to the effect of disappearance of the organic binder. On the other hand, sintering at 800° C. to 1100° C. improved the bending strength. If the firing is performed at a temperature higher than that, the strength is slightly reduced up to about 1400°C, but the strength is greatly reduced above 1400°C. This is considered to be due to the progress of embrittlement of the aluminous fibers.

<<Experiment 2: Change in crystal state due to firing temperature in air atmosphere>>
The inorganic molded body of Reference Example 1 was sintered at a temperature of 500° C. to 1700° C. for 24 hours in an air atmosphere. Next, FIG. 4 shows changes in the X-ray diffraction (XRD) data. In FIG. 4, "○" indicates a peak of mullite, "Δ" indicates a peak of cristobalite, and "□" indicates a peak of corundum.

Referring to FIG. 4, it can be seen that the mullite peak near 16.5° increases as the firing temperature increases. Also, the corundum peak near 26° does not change with each firing temperature, while the mullite peak near 27° increases as the firing temperature increases. It is possible to understand the degree of crystal growth of The cristobalite peak around 22° began to appear around 1100°C, but disappeared when the temperature exceeded 1500°C. This is probably because cristobalite changed to mullite together with surrounding alumina.

<<Experiment 3: Change in chemical composition due to firing in air atmosphere and hydrogen atmosphere>>
The inorganic molded article of Reference Example 1 was heated at 1360° C. in an air atmosphere and a hydrogen atmosphere for 72 hours. Here, the hydrogen atmosphere contained 13% by volume hydrogen and 87% by volume nitrogen.

They were subjected to X-ray fluorescence analysis (XRF) to investigate changes in the chemical composition of alumina and silica. The results are shown in Table 2 below.

As is clear from this result, silica was hardly reduced in the air atmosphere, but was greatly reduced in the hydrogen atmosphere.

<<Experiment 4: Strength change due to firing in air atmosphere and hydrogen atmosphere>>
Firing was performed in the same manner as in Experiment 3, and changes in bending strength were observed. Here, in addition to the sintering conditions in Experiment 3, sintering at 1400° C. was also performed. The results are shown in Table 3 below.

As for firing in the air atmosphere, bending strength is slightly improved by changing the temperature from 1360°C to 1400°C. This phenomenon is also observed in FIG. 3, and it is believed that the sintering of the heat insulating material improved the bending strength of the inorganic compact. On the other hand, in sintering in a hydrogen atmosphere, the strength is lowered by changing from 1360°C to 1400°C. It is considered that this is because the loss of silica caused by firing in a hydrogen atmosphere has a strong effect.

<<Experiment 5: Change in chemical composition and change in strength when calcined in air atmosphere and hydrogen atmosphere after pre-calcination>>
The inorganic molded article of Reference Example 1 was fired at 1500° C. for 24 hours in an air atmosphere to convert the inorganic binder to mullite, thereby obtaining the inorganic molded article of Example 1.

Thereafter, the inorganic compact of Example 1 was fired at 1360° C. for 72 hours in an air atmosphere and a hydrogen atmosphere, and changes in bending strength were observed. The results are shown in Table 4 below.

In experiment 3, when sintering in a hydrogen atmosphere without pre-sintering, silica was significantly reduced to 12.4% by mass, whereas in this experiment, when pre-sintering was performed, hydrogen Silica was maintained up to 15.0% by weight even with atmospheric calcination, and loss of silica was very low.

In addition, when pre-firing was performed, the bending strength did not change even after firing in a hydrogen atmosphere or in an air atmosphere. This is presumably because the inorganic binder was converted to mullite by pre-firing, so that silica was not lost and the function of the binder was not lowered.

Therefore, it was found that the pre-fired inorganic molded body of Example 1 was less likely to be destroyed even if it was subsequently fired in a strongly reducing atmosphere.

<<Experiment 6: Effect of the present invention by another embodiment>>
The colloidal silica of the inorganic binder was changed from 10 parts by mass to 4 parts by mass in solid content, and 6 parts by mass in solid content Aluminasol (manufactured by Nissan Chemical Industries, Ltd., "Aluminasol 520", suspension of solid content 20% by mass An inorganic molded article of Example 2 was obtained in the same manner as in Reference Example 1, except that a liquid (pH 4.0) was also used.

In addition, the same procedure as in Reference Example 1 was performed except that the colloidal silica of the inorganic binder was changed to alumina sol (manufactured by Nissan Chemical Industries, Ltd., "Aluminasol 520", suspension with a solid content of 20% by mass, pH 4.0). Thus, an inorganic molded article of Example 3 was obtained.

In the inorganic molded body of Example 2, when fired, the inorganic binder turns into mullite from around 1150°C. Therefore, the same results as those of the inorganic molded article of Example 1 can be obtained.

The inorganic molded body of Example 3 does not contain silica in the inorganic binder, and as a result, the same results as those of the inorganic molded body of Example 1 can be obtained.

Claims (8)

A method for producing an inorganic molded article, comprising: adding aluminous fibers, alumina particles and an inorganic binder to a liquid medium to obtain a slurry; and removing the liquid medium from the slurry and molding the article,
the inorganic binder comprises silica,
A method for producing an inorganic molded body, further comprising firing the inorganic molded body in a non-reducing atmosphere to convert the inorganic binder into mullite. 2. The method for producing an inorganic molded article according to claim 1, wherein the firing is performed at 1400[deg.] C. or higher and 1600[deg.] C. or lower. 3. The method for producing an inorganic molded article according to claim 1, wherein said non-reducing atmosphere is an air atmosphere. A method for producing an inorganic molded article, comprising: adding aluminous fibers, alumina particles and an inorganic binder to a liquid medium to obtain a slurry; and removing the liquid medium from the slurry and molding the article,
A method for producing an inorganic molded body, wherein the inorganic binder contains silica-containing fine particles and alumina-containing fine particles. 5. The method for producing an inorganic molded article according to claim 4, wherein the molar ratio of alumina to silica contained in said silica-containing fine particles and alumina-containing fine particles is in the range of 1.0 to 2.5. A method for producing an inorganic molded article, comprising: adding aluminous fibers, alumina particles and an inorganic binder to a liquid medium to obtain a slurry; and removing the liquid medium from the slurry and molding the article,
A method for producing an inorganic molded body, wherein the inorganic binder contains alumina-containing fine particles, titania-containing fine particles, zirconia-containing fine particles, or a mixture of two or more of these. An inorganic molded article comprising alumina fibers and alumina particles bound together by at least an inorganic binder, wherein the inorganic binder contains mullite. 1. An inorganic molded article comprising alumina fibers and alumina particles bound together by at least an inorganic binder, wherein the inorganic binder comprises alumina, titania, zirconia, or a mixture of two or more thereof.

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