Inorganic molded article and method for manufacturing the same

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]

[0001] 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 damage even when used for a long period of time in a strongly reducing atmosphere and a method for producing the same. [Background technology]

[0002] Traditionally, electronic components such as multilayer ceramic capacitors have been fired in industrial furnaces.

[0003] For insulation materials installed inside industrial furnaces, low heat capacity and thermal conductivity are required. As such insulation materials, inorganic molded articles containing alumina fibers, alumina particles, and an inorganic binder, as described in Patent Document 1, are known.

[0004] By using this type of insulating material, thermal energy during heating is utilized efficiently, and the cycle time is shortened, thereby improving production efficiency. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2010-155733 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In particular, the firing of low-temperature co-fired ceramic (LTCC) and high-temperature co-fired ceramic (HTCC) substrates in multilayer ceramic capacitors is sometimes carried out in a reducing atmosphere to prevent oxidation of the wiring. Reducing atmospheres include hydrogen, nitrogen, and water vapor, but hydrogen is usually used at less than 4 vol%, which is outside its flammability range, for safety reasons.

[0007] While conventional inorganic molded bodies pose no particular problems when fired in a reducing atmosphere within this range, it was found that conventional inorganic molded bodies break down in a short period of time when fired in a reducing atmosphere containing high concentrations of hydrogen.

[0008] Therefore, the present invention aims to provide an inorganic molded article that is less susceptible to destruction even when fired in a strongly reducing atmosphere, and a method for producing the same. [Means for solving the problem]

[0009] The inventors have found that the above problems can be solved by the present invention having the following aspects. 《Aspect 1》 A slurry is obtained by adding alumina fibers, alumina particles, and an inorganic binder to a liquid medium, and The liquid medium is removed from the slurry and then molded. A method for producing an inorganic molded article containing, The inorganic binder contains silica, A method for producing an inorganic molded article, further comprising firing the inorganic molded article in a non-reducing atmosphere to mulliteize the inorganic binder. 《Aspect 2》 A method for producing an inorganic molded article according to embodiment 1, wherein the firing is performed at a temperature of 1400°C or higher and 1600°C or lower. 《Aspect 3》 A method for producing an inorganic molded article according to embodiment 1 or 2, wherein the non-reducing atmosphere is an atmospheric atmosphere. Appearance 4 A slurry is obtained by adding alumina fibers, alumina particles, and an inorganic binder to a liquid medium, and The liquid medium is removed from the slurry and then molded. A method for producing an inorganic molded article containing, A method for producing an inorganic molded article, wherein the inorganic binder contains silica-containing fine particles and alumina-containing fine particles. Appearance 5 The method for producing an inorganic molded body according to aspect 4, wherein the molar ratio of alumina to silica contained in each of the silica-containing fine particles and the alumina-containing fine particles is in the range of 1.0 to 2.5. <<Aspect 6>> 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 and molding. A method for producing an inorganic molded body, comprising: The 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 body in which alumina fibers and alumina particles are at least bound by an inorganic binder, and the inorganic binder contains mullite. <<Aspect 8>> An inorganic molded body in which alumina fibers and alumina particles are at least bound by an inorganic binder, and the inorganic binder consists of alumina, titania, zirconia, or a mixture of two or more of these.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an inorganic molded body that is difficult to be destroyed even when fired in a strongly reducing atmosphere and a method for producing the same.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 shows a SEM photograph of an inorganic molded body that was destroyed after being repeatedly fired under a strongly reducing atmosphere for a long time. [Figure 2] FIG. 2 shows a SEM photograph of an inorganic molded body that was not destroyed after being repeatedly fired under a strongly reducing atmosphere for a long time. [Figure 3] FIG. 3 shows the change in the flexural strength of an inorganic molded body fired at a temperature of 500°C to 1700°C for 24 hours in an air atmosphere. [Figure 4] Figure 4 shows the changes in X-ray diffraction (XRD) data of inorganic molded bodies fired at temperatures of 500°C to 1700°C for 24 hours in an atmospheric environment. [Modes for carrying out the invention]

[0012] 《First Embodiment》 In the first embodiment, the method for manufacturing an inorganic molded article of the present invention is a method for manufacturing an inorganic molded article comprising 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 inorganic molded article, wherein the inorganic binder contains silica, and the inorganic molded article is fired in a non-reducing atmosphere to mulliteize the inorganic binder. Furthermore, the inorganic molded article of the present invention is obtained by such a manufacturing method and is an inorganic molded article comprising alumina fibers, alumina particles, and an inorganic binder, wherein the inorganic binder contains mullite.

[0013] The inventors of the present invention have discovered that the Si component is lost in inorganic molded articles fired under a strongly reducing atmosphere. This is thought to be because, when inorganic molded articles are fired under a strongly reducing atmosphere, amorphous silica mainly derived from the inorganic binder and crystalline silica (cristobalite) contained in alumina fibers, etc., react with hydrogen to form silane or silanol, which then volatilize.

[0014] Therefore, the reason why inorganic molded bodies become more susceptible to fracture when fired in a strongly reducing atmosphere is likely due to the loss of amorphous and crystalline silica, which reduces the strength of the inorganic molded body.

[0015] In response to this, the inventors diligently investigated how to prevent the loss of amorphous and crystalline silica even during firing in a strongly reducing atmosphere. They discovered that pre-firing the inorganic molded body in a non-reducing atmosphere significantly reduces the loss of silica from the inorganic molded body. This is thought to be because the alumina from the alumina fibers and alumina particles, and the silica from the inorganic binder, etc., become mullite during the pre-firing process, making it less likely for silica to be lost even if the subsequent firing is performed in a strongly reducing atmosphere.

[0016] In addition, the inventors analyzed a conventional inorganic molded body that had been fired and fractured under a strongly reducing atmosphere and discovered that crystals contained in alumina fibers and the like were undergoing grain growth. Therefore, one possible reason why inorganic molded bodies become easily fractured when fired under a strongly reducing atmosphere is that, in a strongly reducing atmosphere, the crystal growth of components contained in alumina fibers and the like progresses more rapidly, making the alumina fibers more brittle. Conversely, it is thought that this crystal growth can be suppressed by pre-firing the inorganic molded body in a non-reducing atmosphere.

[0017] 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 crystals contained in the alumina 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, or 1600°C or lower, 1550°C or lower, 1500°C or lower, 1450°C or lower, or 1400°C or lower. 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, or 5 days or less, 3 days or less, 2 days or less, or 24 hours or less. 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.

[0018] As for non-reducing atmospheres, any atmosphere in which silica is not substantially lost under the calcination conditions described above may have some reducing properties. Examples include inert atmospheres such as nitrogen and argon, and air. Air is preferred.

[0019] The inorganic binder used in the first embodiment is not particularly limited as long as it generates silica that would otherwise be lost during firing in a strongly reducing atmosphere after the inorganic molded body has been manufactured without firing. For example, the inorganic binder can be dry silica such as fumed silica, wet silica such as silica sol, liquid silicon-containing compounds such as water glass and alkoxysilane, or clay-based silicon-containing compounds such as kaolin. Among these, silica sol can be used in particular.

[0020] 《Second Embodiment》 In a second embodiment, the method for producing an inorganic molded article of the present invention is a method for producing an inorganic molded article comprising 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 inorganic molded article, wherein the inorganic binder includes silica-containing fine particles and alumina-containing fine particles. Furthermore, the inorganic molded article of the present invention is obtained by such a production method and is an inorganic molded article comprising alumina fibers, alumina particles, and an inorganic binder, wherein the inorganic binder includes mullite.

[0021] The inventors have found that an inorganic binder formed from silica-containing fine particles and alumina-containing fine particles undergoes mullite formation more easily when the inorganic molded body is fired, because both the particle sizes of the silica-containing fine particles and the alumina-containing fine particles are very small and are located in close proximity to each other. As a result, the inorganic binder is less likely to be lost even under a strongly reducing atmosphere, and consequently, the strength of the inorganic molded body is less likely to decrease. For example, silica sol and alumina sol undergo mullite formation from around 1150°C when fired, so silica can be mulliteized before it is substantially lost under a strongly reducing atmosphere.

[0022] The inorganic binder preferably contains silica and alumina to approximate the mineral composition of mullite. The molar ratio of alumina to silica (moles of alumina / moles of silica) used when forming the inorganic binder may be 1.0 or more, 1.2 or more, or 1.4 or more, and may also be 2.5 or less, 2.2 or less, 2.0 or less, or 1.8 or less. For example, this molar ratio is in the range of 1.0 to 2.5 or 1.4 to 2.2.

[0023] In this specification, fine particles may have an average particle size of 1 nm or more, 3 nm or more, 5 nm or more, 10 nm or more, 15 nm, or 20 nm or more, and may also be less than 1000 nm, 500 nm or less, 200 nm or less, 150 nm or less, 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 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 means the particle size at 50% of the cumulative value in the particle size distribution based on the number of particles, measured by measuring the long axis of 100 or more primary particles by randomly selecting a screen containing a large number of representative particles using a scanning electron microscope (SEM) or transmission electron microscope (TEM).

[0024] The silica-containing fine particles and alumina-containing fine particles of the inorganic binder used in the second embodiment are not particularly limited as long as they are calcined to produce mullite. For example, examples of silica-containing fine particles include dry silica fine particles such as fumed silica and wet silica fine particles such as silica sol. Examples of alumina-containing fine particles include dry alumina fine particles and wet alumina fine particles such as alumina sol. Among these, silica sol and alumina sol can be used in particular.

[0025] In this embodiment as well, firing in a non-reducing atmosphere as in the first embodiment may be performed. This will promote the mulliteization of the inorganic binder.

[0026] 《Third Embodiment》 In a third embodiment, the method for producing an inorganic molded article of the present invention is a method for producing an inorganic molded article comprising 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 inorganic molded article, wherein the inorganic binder comprises alumina-containing fine particles, titania-containing fine particles, zirconia-containing fine particles, or a mixture of two or more of these. Furthermore, the inorganic molded article of the present invention is obtained by such a production method and is an inorganic molded article comprising alumina fibers, alumina particles, and an inorganic binder, wherein the inorganic binder consists of alumina, titania, zirconia, or a mixture of two or more of these.

[0027] The inventors have found that inorganic binders formed from alumina-containing fine particles, titania-containing fine particles, zirconia-containing fine particles, or mixtures of two or more of these, are less likely to be lost even under a strongly reducing atmosphere, and consequently, the strength of the inorganic molded article is less likely to decrease.

[0028] The alumina-containing fine particles, titania-containing fine particles, and zirconia-containing fine particles used in the third embodiment of the inorganic binder are not particularly limited as long as they do not generate silica that would be lost during firing in a strongly reducing atmosphere after the inorganic molded body has been manufactured without firing. For example, examples of 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; and examples of zirconia-containing 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 in particular.

[0029] The following details the technical aspects common to the above embodiments.

[0030] Inorganic molded body The inorganic molded body contains alumina fibers, alumina particles, and an inorganic binder, and can be used as an insulating material. This inorganic molded body is advantageous because it is resistant to damage even when repeatedly fired over a long period of time in a strongly reducing atmosphere.

[0031] Here, a strongly reducing atmosphere refers to an atmosphere containing more than 4 volume percent of hydrogen. A strongly reducing atmosphere may contain hydrogen in amounts of 5 volume percent or more, 8 volume percent or more, 10 volume percent or more, 12 volume percent or more, or 15 volume percent or more, and may contain hydrogen in amounts of 20 volume percent or less, 15 volume percent or less, or 10 volume percent or less. For example, a strongly reducing atmosphere may contain hydrogen in amounts of 5 volume percent or more and 20 volume percent or less, or 10 volume percent or more and 15 volume percent or less.

[0032] To further enhance the reducing properties of a strongly reducing atmosphere, a reducing gas, such as water vapor, may be added. In addition to hydrogen and the reducing gas, other inert gases such as nitrogen or argon may be used.

[0033] The firing temperature in a strongly reducing atmosphere may be, for example, 1250°C or higher, 1300°C or higher, 1350°C or higher, or 1400°C or higher, or 1500°C or lower, 1450°C or lower, or 1400°C or lower. 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. If firing at such temperatures is repeated for a short period of time over several months to several years, conventional inorganic molded articles may break.

[0034] 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, but for example, 100 kg / m³ 3 More than 150kg / m 3 More than 200kg / m 3 More than 250kg / m 3 Above, or 300 kg / m 3 It may be greater than or equal to 1200 kg / m 3 Below 1000kg / m 3Hereinafter, 700 kg / m 3 Hereinafter, 500 kg / m 3 Hereinafter, 400 kg / m 3 Hereinafter, 300 kg / m 3 Hereinafter, or 250 kg / m 3 It may be the following. For example, the bulk density of the inorganic molded body is 100 kg / m 3 Hereinafter, 1200 kg / m 3 Hereinafter, 150 kg / m 3 Hereinafter, 500 kg / m 3 It may be the following.

[0035] 〈Alumina fiber〉 Alumina fiber is a metal oxide fiber containing alumina as a main component. Alumina fiber means a fiber having alumina as a main component, and may contain one or more components selected from the group consisting of silica, zirconia, calcia, iron oxide, soda, and magnesia in addition to alumina.

[0036] The alumina content in the alumina fiber may be, 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 or more, and may be 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 alumina fiber 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.

[0037] The remainder of the alumina fiber other than alumina may be silica. The silica content in the alumina fiber 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, or 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 alumina fiber 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. The silica in the alumina fiber may exist in an amorphous state, or in a crystalline state, for example, as cristobalite, mullite, etc.

[0038] Furthermore, it was found that when only alumina fibers were calcined under a strongly reducing atmosphere, the silica contained in the alumina fibers was not substantially lost. Although alumina fibers also contain amorphous silica, the alumina fibers have crystalline alumina such as γ-alumina and α-alumina, silica, and mullite (alumina crystals) on their surface, while amorphous silica is mainly present in the core of the fibers. Therefore, it is thought that the silica was not substantially lost.

[0039] The average fiber length of the alumina 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 also be 100 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, 20 mm or less, or 15 mm or less. The average fiber length of the alumina fibers may be 0.1 mm or more and 100 mm or less, or 5 mm or more and 30 mm or less.

[0040] The average fiber diameter of the alumina fibers may be, for example, 1 μm or more, 2 μm or more, 3 μm or more, or 5 μm or more, and may also be 20 μm or less, 10 μm or less, 8 μm or less, or 5 μm or less. The average fiber diameter of the alumina fibers may be 1 μm or more and 20 μm or less, or 3 μm or more and 10 μm or less.

[0041] The ratio of the average fiber length to the average fiber diameter of alumina 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 may also be 10000 or less, 5000 or less, 3000 or less, 1000 or less, or 500 or less. This ratio may be 25 or more and 10000 or less, or 100 or more and 5000 or less.

[0042] <Alumina particles> Alumina particles are preferably those that have a high degree of crystallinity, similar to alumina fibers, and are particularly preferably alumina particles that contain or consist of α-alumina.

[0043] The average particle size of 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, and may also be 100 μm or less, 80 μm or less, 50 μm or less, 30 μm or less, 20 μm or less, or 10 μm or less. For example, the average particle size of 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 size refers to the median diameter measured by a laser diffraction particle size distribution analyzer. If the average particle size of alumina particles is within this range, it is possible to achieve both mechanical strength and chemical durability of the inorganic molded body.

[0044] In an inorganic molded article, the alumina fibers may be contained in amounts of 20 to 80 parts by mass, 30 to 70 parts by mass, or 40 to 60 parts by mass, per 100 parts by mass of the total of alumina fibers and alumina particles, and the alumina particles may also be contained in amounts of 20 to 80 parts by mass, 30 to 70 parts by mass, or 40 to 60 parts by mass.

[0045] <Inorganic Binder> The inorganic molded article comprises alumina fibers, alumina particles, and an inorganic binder for binding them together. In this specification, unless otherwise specified, the inorganic binder refers not only to the substance used during manufacturing (e.g., colloidal silica) but also to the alumina particles and the substance binding the alumina particles together after manufacturing (e.g., silica).

[0046] The inorganic binder is not particularly limited unless otherwise specified herein, as long as it does not impair the effects of the present invention, but for example, it may be one or more selected from the group consisting of colloidal silica (e.g., one or more selected from the group consisting of anionic colloidal silica and cationic colloidal silica), fumed silica, zirconia sol, titania sol, alumina sol, and bentonite.

[0047] 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. For example, it may be 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 30 parts by mass or less, 20 parts by mass or less, 15 parts by mass or less, or 10 parts by mass or less, per 100 parts by mass of the total of alumina fibers and alumina particles. 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, per 100 parts by mass of the total of alumina fibers and alumina particles.

[0048] <Inorganic fixing agent> The inorganic molded body may further contain an inorganic fixing agent for purposes such as uniformly adhering the inorganic binder to the surface of the alumina fibers. The inorganic fixing agent may be one or more selected from the group consisting of aluminum sulfate, alumina sol, and aqueous ammonia, with aluminum sulfate being preferred.

[0049] The amount of inorganic fixing agent in the inorganic molded article is not particularly limited as long as it does not impair the effects of the present invention. For example, it may be 0.1 parts by mass or more, 0.3 parts by mass or more, 0.5 parts by mass or more, 1.0 part 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 part by mass or less, per 100 parts by mass of the total of alumina fibers and alumina particles. For example, the amount of inorganic fixing agent may be 0.1 parts by mass or more and 3.0 parts by mass or more, or 0.3 parts by mass or more and 2.0 parts by mass or less, per 100 parts by mass of the total of alumina fibers and alumina particles.

[0050] <Organic Binder> The inorganic molded article may 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 it is preferably one or more selected from the group consisting of polymer flocculants and starch. If the inorganic molded article contains a polymer flocculant, it may further contain starch, or it may not contain starch.

[0051] The polymer flocculant used as an organic binder is not particularly limited as long as it does not impair the effects of the present invention, but it is preferably one or more selected from the group consisting of polyacrylamide polymers, amide polymers, polyacrylic ester polymers, and polyacrylic ether polymers, and is particularly preferably a polyacrylamide polymer.

[0052] The starch used as an organic binder is not particularly limited as long as it does not impair the effects of the present invention. For example, it may be one or more selected from the group consisting of raw material starch (e.g., starch derived from natural raw materials (e.g., one or more selected from the group consisting of potato starch, tapioca starch, corn starch and their hydrolysates)), cationic starch, anionic starch, and amphoteric starch.

[0053] The inorganic molded body may further contain, as necessary, pulp, a suitable emulsion, or the like as an organic binder. In the production of the inorganic molded body, the type and amount of organic binder added to the liquid medium to form flocs of the desired size are optimized according to the charge amount and properties of the inorganic binder, the size of the alumina particles used, and so on.

[0054] When an inorganic molded article contains an organic binder, the total content of the organic binder is not particularly limited as long as it does not impair the effects of the present invention. 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, per 100 parts by mass of the total of alumina fibers and alumina particles, or it may be 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 an inorganic molded article may be 0.1 parts by mass or more and 15 parts by mass or 3.0 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of the total of alumina fibers and alumina particles.

[0055] Furthermore, when manufacturing inorganic molded articles, it is preferable to include an organic binder at least at the stage when obtaining the wet molded article. On the other hand, with respect to manufacturing methods other than the first embodiment, a firing treatment may be performed after molding, before shipment, or before use to remove the organic binder. In inorganic molded articles obtained by the first embodiment, it is preferable to use an organic binder during manufacturing, but since the organic binder is removed by a firing treatment at 700°C or lower, the organic binder is substantially absent after manufacturing.

[0056] Method for manufacturing inorganic molded products For each component of the method for manufacturing the inorganic molded article of the present invention, refer to the components described in relation to the inorganic molded article of the present invention. In particular, the content of the inorganic molded article can be referred to as the amount used during manufacturing in the method for manufacturing the inorganic molded article.

[0057] A method for producing an inorganic molded article includes adding alumina fibers, alumina particles, an inorganic binder, an optional inorganic fixative, and an optional organic binder to a liquid medium to obtain a slurry, optionally mixing and stirring the slurry, and removing the liquid medium from the slurry to form the article. Removal of the liquid medium from the slurry and forming the article may include deliquidation molding or papermaking to obtain a wet molded article, and drying the wet molded article. As the liquid medium, water, aqueous solvents, polar organic solvents, etc., can be used.

[0058] The wet volume of the slurry is not particularly limited as long as it does not impair the effects of the present invention, but may be, for example, 50 mL / 20 g or more, 100 mL / 20 g or more, 200 mL / 20 g or more, or 300 mL / 20 g or more, or 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 50 mL / 20 g or more and 1000 mL / 20 g or less, or 200 mL / 20 g or more and 800 mL / 20 g or less.

[0059] To obtain a wet molded article from a slurry, for example, the slurry can be dehydrated and molded or paper-formed by a well-known method. Here, if necessary (for example, when producing an inorganic molded article with a relatively high bulk density), the wet molded article may be pressed.

[0060] Subsequently, an inorganic molded body can be obtained by drying the wet molded body. The shape of the inorganic molded body is not particularly limited, but it is preferably in the form of a board, sheet, or block. Furthermore, the shape of the inorganic molded body can also be made into other shapes such as cylindrical or conical by selecting a suction mold according to the desired shape.

[0061] Furthermore, if the inorganic molded body is not subjected to the firing treatment as in the first embodiment, it may be subjected to a firing treatment to remove the organic binder. The method of firing is not particularly limited, and can be carried out using, for example, 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, for example, 600°C to 1000°C. The firing time is not particularly limited as long as it does not impair the effects of the present invention, but is preferably, for example, 30 minutes to 60 minutes.

[0062] The method for manufacturing an inorganic molded article may further include a hardening treatment. The hardening treatment is, for example, a process in which an inorganic molded article is impregnated with a hardening treatment solution containing an inorganic binder as described above (for example, one or more selected from the group consisting of colloidal silica and alumina sol), and dried. The hardening treatment can effectively improve the hardness of the inorganic molded article after drying.

[0063] The curing solution may, for example, include an inorganic binder, an organic thickener for controlling viscosity, and one or more inorganic powders selected from the group consisting of, for example, glass powder, alumina powder, and wollastonite powder. The method for impregnating the inorganic molded body with the curing solution is not particularly limited, but one or more selected from the group consisting of, for example, brush application, spray application, and immersion is preferably used.

[0064] A method for manufacturing an inorganic molded body may include a surface coating treatment. That is, for example, by coating the surface of the inorganic molded body 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 body can be effectively improved. Specifically, for example, when an inorganic molded body is used by being placed in a furnace, by applying a surface coating treatment to the inorganic molded body, the corrosion resistance to scale (e.g., iron oxide) in the furnace and / or the wind speed resistance to hot air in the furnace can be effectively improved.

[0065] A method for manufacturing an inorganic molded body may include an adhesive treatment. That is, for example, when bonding multiple inorganic molded bodies to each other, or when bonding an inorganic molded body to another molded body, the adhesive strength can be effectively improved by applying an adhesive containing alumina and silica, or an adhesive containing iron and silica, to the bonding surface of the inorganic molded bodies.

[0066] The present invention will be described in more detail by the following examples, but the present invention is not limited thereto. [Examples]

[0067] Manufacturing example As the alumina fiber, we used alumina fiber (manufactured by Denka Co., Ltd., "B80", with an alumina content of 80% by mass, a silica content of 20% by mass, and an average fiber diameter of 3 μm to 5 μm).

[0068] As alumina particles, we used alumina particles (manufactured by Nippon Light Metal Co., Ltd., "SA31", average particle size 5 μm, alumina content: approximately 99.6% by mass).

[0069] Colloidal silica (manufactured by Nippon Chemical Industrial Co., Ltd., "Silica Doll 30", a suspension with 30% solid content by mass, average particle size of solids 15 nm, pH 10.0) was used as the inorganic binder.

[0070] As an organic binder, polyacrylamide (Polistron 705, manufactured by Arakawa Chemical Industries, Ltd., cationic, 10% non-volatile content, pH 2.5-3.5, viscosity 300-1000 mPa·s), a polymeric flocculant, was used.

[0071] 40 parts by mass of alumina fibers, 60 parts by mass of alumina particles, 10 parts by mass of an inorganic binder (solid content), and 3.4 parts by mass of an organic binder were added to water. Further water was added and the mixture was stirred to achieve a slurry concentration of 2% by mass to prepare a slurry.

[0072] The slurry obtained as described above was poured into a mold with a mesh at the bottom, and dewatered by a suction dewatering molding method to obtain a wet molded body having a flat plate shape. Furthermore, the bulk density of the final inorganic molded body was 300 kg / m³. 3 The wet molded body obtained as described above was pressed to achieve the desired consistency. Subsequently, the wet molded body was dried in a dryer at 110°C for 36 hours to obtain an inorganic molded body in the shape of a flat plate with a thickness of 25 mm, as shown in Reference Example 1.

[0073] Analysis of destroyed inorganic molded bodies The inorganic molded body from Reference Example 1 was installed as insulation material in an industrial furnace. In a strongly reducing atmosphere of 13 volume% hydrogen and the remainder nitrogen, with water vapor at a dew point of 20°C introduced, the maximum heating temperature was set to 1360°C, and firing treatment was carried out repeatedly for about six months with relatively rapid temperature increases and decreases. As a result, cracks appeared in some parts of the insulation material.

[0074] The inorganic molded body near the fractured area and the inorganic molded body in the unfractured area were compared using bending strength tests. Similarly, changes in the chemical composition of alumina and silica were investigated by X-ray fluorescence analysis (XRF) of these materials. Furthermore, these were observed using SEM images.

[0075] The bending strength of the inorganic molded material was measured as follows: A flat plate-shaped test specimen made of inorganic molded material, measuring 150 mm in length, 12.5 mm in width, and 5 mm in thickness, was subjected to a load applied at a head speed of 2 mm / min using a strength testing machine (Orientec Co., Ltd., "Tensilon Universal Testing Machine"), and the maximum load (breaking load) was measured. The bending strength of the inorganic molded material was then calculated using the following formula: Bending strength (MPa) = {3 × Maximum load (N) × Distance between lower supports (mm)} / {2 × Width of test specimen (mm) × Thickness of test specimen (mm)} 2}

[0076] The results of the bending strength test and compositional analysis by XRF are shown in Table 1 below. Figure 1 shows an SEM image of the fractured portion of the inorganic molded body, and Figure 2 shows an SEM image of the unfractured portion of the inorganic molded body.

[0077] [Table 1]

[0078] At the site of fracture, the bending strength is significantly reduced, and silica is lost. Comparing the 5000x magnification images in Figure 1 and Figure 2, the appearance of the alumina fibers is significantly different, indicating that crystal grain growth of the alumina fibers has occurred at the site of fracture.

[0079] Experiment 1: Changes in strength due to firing temperature in an atmospheric environment The inorganic molded body from Reference Example 1 was fired in an air atmosphere at a temperature of 500°C to 1700°C for 24 hours.

[0080] The change in bending strength is shown in Figure 3.

[0081] Referring to Figure 3, it can be seen that the inorganic molded body of Reference Example 1 immediately after manufacturing has a bending strength of about 1.3 MPa, but after firing at 500°C, the bending strength decreases to about 0.6 MPa. This is due to the disappearance of the organic binder. In contrast, firing at 800°C to 1100°C improves the bending strength, which is thought to be due to the alumina fibers becoming stronger through sintering. When firing at temperatures higher than that, the decrease in strength is slight up to about 1400°C, but above 1400°C the strength decreases significantly. This is thought to be due to the embrittlement of the alumina fibers.

[0082] Experiment 2: Changes in crystal state due to firing temperature in an air atmosphere. The inorganic molded body from Reference Example 1 was fired in an atmospheric environment at a temperature of 500°C to 1700°C for 24 hours. Next, the changes in the X-ray diffraction (XRD) data are shown in Figure 4. In Figure 4, "○" indicates the mullite peak, "△" indicates the cristobalite peak, and "□" indicates the corundum peak.

[0083] Referring to Figure 4, it can be seen that the mullite peak around 16.5° increases in size as the firing temperature increases. Also, while the corundum peak around 26° remains constant with each firing temperature, the mullite peak around 27° increases in size as the firing temperature increases. Therefore, the degree of mullite crystal growth can be understood by comparing these two peaks. The cristobalite peak around 22° began to appear around 1100°C but disappeared above 1500°C. This is thought to be because the cristobalite changed into mullite along with the surrounding alumina.

[0084] Experiment 3: Changes in chemical composition due to firing in an atmospheric and hydrogen atmosphere. The inorganic molded body of Reference Example 1 was heated at 1360°C in an air atmosphere and a hydrogen atmosphere for 72 hours. The hydrogen atmosphere contained 13 volume% hydrogen and 87 volume% nitrogen.

[0085] X-ray fluorescence analysis (XRF) was performed on these samples to investigate changes in the chemical composition of alumina and silica. The results are shown in Table 2 below.

[0086] [Table 2]

[0087] As is clear from these results, silica hardly decreased in an atmospheric environment, but decreased significantly in a hydrogen atmosphere.

[0088] Experiment 4: Changes in strength due to firing in an air atmosphere and a hydrogen atmosphere. The same firing process as in Experiment 3 was performed, and the change in bending strength was observed. In this experiment, firing at 1400°C was also performed in addition to the firing conditions used in Experiment 3. The results are shown in Table 3 below.

[0089] [Table 3]

[0090] In firing in an atmospheric environment, changing the temperature from 1360°C to 1400°C slightly improved the bending strength. This phenomenon is also observed in Figure 3, and it is thought that the bending strength of the inorganic molded body improved due to the sintering of the insulating material. On the other hand, in firing in a hydrogen atmosphere, changing the temperature from 1360°C to 1400°C resulted in a decrease in strength. This is thought to be due to the strong effect of silica loss during firing in a hydrogen atmosphere.

[0091] Experiment 5: Changes in chemical composition and strength when fired in an air atmosphere and a hydrogen atmosphere after pre-firing. The inorganic molded body of Reference Example 1 was fired at 1500°C for 24 hours in an atmospheric environment to mulliteize the inorganic binder, thereby obtaining the inorganic molded body of Example 1.

[0092] Subsequently, the inorganic molded body of Example 1 was fired at 1360°C for 72 hours in both an air and hydrogen atmosphere, and the change in bending strength was observed. The results are shown in Table 4 below.

[0093] [Table 4]

[0094] In Experiment 3, when firing was performed in a hydrogen atmosphere without pre-firing, the silica content decreased significantly to 12.4 mass%, whereas in this experiment, when pre-firing was performed, the silica content was maintained at 15.0 mass% even after subsequent firing in a hydrogen atmosphere, indicating that silica loss was significantly reduced.

[0095] Furthermore, when pre-firing was performed, the bending strength did not change whether the subsequent firing was carried out in a hydrogen atmosphere or an air atmosphere. This is thought to be because the pre-firing caused the inorganic binder to mulliteize, resulting in no loss of silica and no deterioration of the binder's function.

[0096] Therefore, it was found that the inorganic molded body of Example 1, which underwent pre-sintering, was less susceptible to damage even when subsequently fired in a strongly reducing atmosphere.

[0097] Experiment 6: Effects of the present invention in other embodiments An inorganic molded article of Example 2 was obtained in the same manner as in Reference Example 1, except that the amount of colloidal silica in the inorganic binder was changed from 10 parts by mass to 4 parts by mass in terms of solid content, and 6 parts by mass of alumina sol (Nissan Chemical Industries, Ltd., "Alumina Sol 520", a suspension with 20% by mass of solid content, pH 4.0) was used in combination.

[0098] Furthermore, an inorganic molded article of Example 3 was obtained in the same manner as in Reference Example 1, except that the colloidal silica of the inorganic binder was changed to alumina sol (Nissan Chemical Industries, Ltd., "Alumina Sol 520", a suspension with a solid content of 20% by mass, pH 4.0).

[0099] In the inorganic molded body of Example 2, the inorganic binder mulliteizes at around 1150°C after firing. Therefore, the same results as the inorganic molded body of Example 1 can be obtained.

[0100] The inorganic molded body of Example 3 does not contain silica in the inorganic binder, and as a result, the same results as the inorganic molded body of Example 1 can be obtained.

Claims

1. A slurry is obtained by adding alumina fibers, alumina particles, and an inorganic binder to a liquid medium, and The liquid medium is removed from the slurry and then molded. A method for producing an inorganic molded article containing, The inorganic binder contains silica, The inorganic molded body is further fired at 1500°C or higher for 12 hours or more in a non-reducing atmosphere to mulliteize the inorganic binder and eliminate the cristobalite. The inorganic molded body is used in firing in a strongly reducing atmosphere containing more than 4 volume percent of hydrogen. A method for manufacturing inorganic molded articles.

2. The method for producing an inorganic molded article according to claim 1, wherein the firing is performed at a temperature of 1600°C or lower.

3. The method for producing an inorganic molded article according to claim 1 or 2, wherein the non-reducing atmosphere is an atmospheric atmosphere.

4. The method for producing an inorganic molded article according to Claim 1, wherein the strongly reducing atmosphere contains hydrogen in an amount of 5% by volume or more and 20% by volume or less.

5. A method for using an inorganic molded body in firing in a strongly reducing atmosphere containing more than 4 volume percent of hydrogen, The inorganic molded body is A slurry is obtained by adding alumina fibers, alumina particles, and an inorganic binder to a liquid medium, and The liquid medium is removed from the slurry and then molded. Manufactured using a manufacturing method that includes, The inorganic binder contains silica, The inorganic molded body is manufactured by a manufacturing method that further includes firing the inorganic binder at 1500°C or higher for 12 hours or more in a non-reducing atmosphere to mulliteize the inorganic binder and eliminate the cristobalite. Method of using inorganic molded products.

6. The method for using an inorganic molded article according to claim 5, wherein the strongly reducing atmosphere contains hydrogen in an amount of 5% by volume or more and 20% by volume or less.

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