JPH02221168A - fibrous molded body - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a fibrous molded body suitable as a jig used in a firing process in producing ceramics.

[Conventional technology]

In the production of ceramics, heavy refractories such as magnesia or zirconia, which have been used from early on as jigs to support the fired object during the firing process, have problems with spalling resistance and have a large heat capacity. This has disadvantages in that the firing cycle becomes long, resulting in poor firing efficiency and high thermal energy consumption.Furthermore, it is heavy and difficult to handle. Therefore, in order to reduce the thermal energy consumed by the firing jig itself and shorten the time required for heating and cooling during the firing process, we aim to reduce energy costs and improve productivity, making it lighter and more heat-insulating. As a result, lightweight refractories manufactured by molding a mixture of refractory powder and heat-resistant inorganic fibers using an inorganic binder (JP-A-63-206367, JP-A-59) -88378, etc.) was proposed as a firing jig.

However, in addition to the above-mentioned requirements, the ceramic firing jig is also required to not react with the ceramic to be fired. In other words, if the jig and the object to be fired react at the contact area, it will not only lead to deterioration of product performance due to fusion and changes in composition, but also shorten the life of the equipment.
It is desirable that no reaction occurs between the jig and the object to be fired. Whether or not this requirement can be met depends on the chemical composition of the material to be fired. Therefore, the above-mentioned fibrous lightweight refractories have many uses! For example, lead zirconate titanate (PZT) shows excellent performance.
When manufacturing a piezoelectric element made of barium titanate (BT), etc., it was difficult to use because of significant fusion and denaturation due to reaction.

[Problem to be solved by the invention]

An object of the present invention is to provide a lightweight fibrous molded body that has low reactivity and is therefore durable when used as a jig for firing ceramics. It is an object of the present invention to provide a fibrous molded body that can be sufficiently used as a lightweight jig for producing ceramics.

[Means to solve the problem]

The fibrous molded article provided by the present invention is a porous alumina fibrous molded article in which the surface of the alumina fibers is coated with a metal oxide selected from the group consisting of magnesia, spinel, cordierite, and zirconia. This is a characteristic feature.

Among these fibrous molded products, one with particularly excellent properties is the molded product of the invention of Japanese Patent Application No. 62-307453 by the present inventors, that is, high alumina short fibers with a length of 2000 μm or less, or the short fibers and alumina The base material is a porous molded body in which the mixture with the refractory powder is bonded with an alumina binder and does not contain free silica, and the above-mentioned metal oxide is applied to the fiber surface to the extent that the porosity is not impaired. It is coated.

In order to manufacture the refractory of the present invention, first, a lightweight alumina fiber molded body to be used as a base material is manufactured by any method.

Typically, alumina fibers are well mixed with an appropriate amount of refractory powder (e.g. alumina, alumina silica, zirconia, makushia, titania, etc.) and an inorganic binder (e.g. Nriyoku sol, alumina sol), and finally bulked. Density 0.5
It was molded under conditions that yielded a molded product of ~2.0.
Bake at 0-1500°C.

When the above-mentioned molded body made of high alumina short fibers having a length of 2000 μm or less is used as a base material, it is manufactured by the following manufacturing method. Polycrystalline alumina short fibers of 2000 μm or less, which are the main raw material, are prepared by cutting polycrystalline alumina fibers using a suitable wet or dry grinder. Note that if the fiber length is too small, it will be difficult to obtain a product with low specific gravity and excellent strength and durability, so it is desirable to set the lower limit to about 20 μm. A particularly preferred fiber length is about 50 to 500 μm, with an average of about 200 Fi1. The thickness of the fibers is not particularly limited, but is preferably in the range of about 1 to 5 μm. If necessary, high-purity alumina powder such as calcined alumina powder, fused alumina powder, or aluminum hydroxide is added to this. Alumina long fibers with a length of 1 to 40 mm
A small amount of the cut material may be added.

Use of excessive amounts will make the product dense and have poor insulation and durability. It is desirable to use an alumina binder as a binder for molding, and suitable examples include colloidal alumina, aluminum sludge (aluminum hydroxide gel produced during alumite treatment), and hydroxide obtained by reacting aluminum sulfate with alkali. Examples include aluminum gel. The amount of this binder used (A1.O, converted amount) is preferably 2 to 30% by weight based on the mixture of alumina fibers and refractory powder, and the use of an excessive amount may lead to excessive use of the refractory powder. There are similar disadvantages. Firing after molding is 140
0 to 180,000 until substantially no free silica is observed to cure the binder. In this process,
Alumina short fibers are contained in a small amount (usually 1 to 5% by weight).
Although the silica contained reacts with the surrounding alumina to form mullite, the remaining alumina portion is stabilized in a corundum state and remains in the product without any substantial change in fibrous morphology.

The obtained lightweight molded body is shaped by cutting, cutting, polishing, etc. as necessary, and is used as a base molded body.

After that, magnesium salt, magnesium alkoxide,
The base material molded body is immersed in a solution of a zirconium compound or a zirconium compound such as a zirconium salt or a zirconium alkoxide, pulled up, and after appropriately removing liquid, is dried and further fired at 800 to 1500°C. As a result, the magnesium compound and zirconium compound adhering to the fiber surface are converted into oxides, and a coating made of oxide is completed on the fiber surface. During this process, a part of the alumina fiber surface becomes spinel (M (A l 2
0*) or cordierite (2Mg0・2A1
20.・5SiOz) may occur, but this is not a problem.

[Action/Effect]

The lightweight molded article according to the present invention inherently exhibits a high degree of heat resistance because the base material is made of alumina fiber. Even when used as a jig for ceramics, particularly PZT-based materials, which easily react with alumina fibers, the magnesia-based or zirconia-based coating prevents the reaction with the fired materials. Therefore, the fired product is less likely to change in quality than conventional lightweight molded bodies of this type, and the molded body itself is also less likely to deteriorate.

Those whose base material is a molded body made of finely divided alumina fibers exhibit particularly excellent high-temperature durability.

〔Example〕

Polycrystalline alumina fiber (Al2O, 95%, 51025
A mixture of 60 parts by weight of alumina powder, 30 parts by weight of alumina powder, and 10 parts by weight of a siliceous binder was molded by a conventional method, and 1
Baked at 500°C for 4 hours, bulk density 0, 917cm
A base material molded body of No. 3 was manufactured. This substrate was immersed in a coating agent solution, then dehydrated, dried, and fired at 1200° C. to produce an oxide coating of about 10% based on the weight of the substrate.

The following characteristic tests were conducted on the obtained molded bodies and the base molded bodies not coated with oxide.

Bending strength: thickness 4 mm, radius 25 mm, length 120 mm
Measured on a test piece with a span of 10011111% and a load rate of 2 +u+/m.

Spalling Resistance: Heat to 2,600°C and then rapidly cool to room temperature. Repeat this until a crack appears,
Displays the limit heating/cooling times.

Creep resistance: A point load of 20g was applied to the center of a BOX 2Sx 4mm plate with a span of 100!111,
Hold at 00°C for 24 hours. Creep resistance is expressed by the amount of distortion of the plate after cooling.

Reactivity I: PZT green sheet (IOX lax l
a+m) on a test piece, put it in a heating furnace and heated it to 1200℃.
Heat for 1 hour. Thereafter, the test piece and PZT green sheet are removed from the furnace and checked for discoloration.

Reactivity II: A test similar to the test for reactivity I above is conducted using a BT green sheet instead of a PZT green sheet.

The results are shown in Table 1.

Claims (1)

[Claims] 1. A porous alumina fibrous molded product, wherein the surface of the alumina fibers is coated with a metal oxide selected from the group consisting of magnesia, spinel, cordierite, and zirconia.