JPS62216974A - Porous refractories - 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] [Field of Industrial Application] The present invention can be used as a furnace lining, a shelf board, a sagger, a tray, etc. in the firing of ceramics, glass, various metal oxides, etc. The invention relates to a lightweight and heat-resistant porous refractory.

[Conventional technology]

In recent information, in the electronics industry, functional parts such as sensors, capacitors, and IC boards are transitioning to ceramics. Among these, fine ceramics such as alumina and silicon nitride, dielectric elements such as barium titanate, and magnetic materials made of composite oxides such as iron, barium, or strontium are considered promising. These ceramics and metal oxides have excellent properties such as electrical insulation, semiconductivity, heat resistance, wear resistance, high strength, and high magnetic force, and their uses will continue to expand in the future. These functional parts are raw material 4
After mixing, it is formed into various shapes by extrusion molding, injection molding, cast molding, press molding, etc., and then placed on shelves, saggers, and baking trays in a furnace made of insulating bricks. Commercialized. The lining, shelf boards, saggers, firing trays, etc. of these furnaces are uneven (gold, alumina, zirconia, etc.).
Cordierite, silicon carbide, and silica refractories are used.

[Problem that the invention seeks to solve]

Conventionally, all of the trays for firing functional parts such as ceramics are formed by a method such as pressing and fired at a roughly high temperature. The decline in unit prices of these ceramics and other machine parts has made it urgent to reduce production costs. However, each member used in a conventional firing furnace has a high bulk density, and therefore requires a large amount of energy to heat itself. Furthermore, since saggers and trays are heavy, there is a limit to how much they can be stacked when firing in multiple tiers. Furthermore, it was difficult to make the temperature distribution uniform between the upper and lower stages in the furnace. Furthermore, if the firing speed was increased or the cooling/heating cycle was accelerated, the firing tray would crack, resulting in poor productivity. Furthermore, even if attempts were made to reduce the volume occupied by the baking tray in order to increase thermal efficiency by making the baking zone smaller, conventional baking trays could not be manufactured with a thickness below a certain level due to problems such as warping. On the other hand, lightweight molded products are known in which heat-resistant inorganic fibers such as ceramic fibers and inorganic binders (for example, silica sol, clay, Seviolite, etc.) are made into a slurry with a large amount of water and molded by a wet papermaking method. However, this molded product not only does not have a smooth surface, but because the inorganic binder is simply filled between the interstitial spaces of the heat-resistant inorganic TA fibers, the fibers themselves soften or shrink during heating, causing warpage and strength. It was not suitable for use inside the firing furnace of highly precise ceramics because the ram itself was weak and the ram itself fell off and turned into powder. Products that are highly reactive with metal oxides such as alumina, silica, or titania at high temperatures are fired by placing zirconia powder on a shelf, sagger, or tray L, or placing a zirconia plate on top. Furthermore, refractory trays coated with zirconia are being considered in order to reduce the complexity of work required to replace bedding and bedding, and to reduce costs. However, conventional zirconia coatings have an extremely dense structure, and the difference in thermal expansion coefficient between the coating film and the base material of the tray can cause cracks or peeling of the film, causing the object to be fired to stick to the tray. There were problems such as adhesion and formation of pinholes in the object to be fired.

As mentioned above, conventional fire-resistant insulating bricks, shelf board saggers, and heat-resistant trays account for a large amount of energy costs and consumables costs, and molded products made of fire-resistant inorganic fibers lack strength and are powdery. The zirconia coating deteriorated the working environment, making it unsuitable for firing precision, high-purity ceramics, and the zirconia coating was also prone to cracking and did not prevent reactions with the fired object.

In order to solve these problems, the present invention is an energy-saving, lightweight and strong ceramic firing method that is highly resistant to thermal changes, prevents reactions with objects to be fired, and improves the working environment. The purpose of the present invention is to provide a porous refractory for use.

[Means for solving problems]

That is, in the present invention, on the surface of a molded article made of heat-resistant inorganic fibers, fire-resistant powder, and an inorganic binder and having many voids,
40-60% by weight of zirconia powder with a particle size of 10-45 μm and a particle size of 0.5-5. u, m zirconia powder 40~
It is a porous refractory coated with zirconia with a thickness of 50 to 500 μm and a total amount of 100% by weight.

(Function) Therefore, in the present invention, since the one-porous refractory has the heat-resistant inorganic fiber as a main component, a large number of voids exist in the molded product, and the weight of the molded product can be reduced. In addition, porous refractories can be made into stronger structures by filling refractory powder and/or inorganic binder between the fibers of heat-resistant inorganic fibers and sintering these refractory powders and/or inorganic binder. A barrel molded product can be obtained, and the problems of conventional fire-resistant bricks, shelves, saggers, trays, etc. as described above can be solved.

Furthermore, the porous refractory has a particle size of 10 to
45I1. The film is composed of 40 to 60% by weight of zirconia powder having a particle size of 0.5 to 5 gm, and 40 to 60% by weight of zirconia powder having a particle size of 0.5 to 5 gm, and the film thickness is 50 to 60% so that the total amount is 100% by weight.
By applying a zirconia coating of 500 JLm, reaction with the object to be fired can be completely prevented.

In other words, in porous refractories, continuous voids are formed by mixing coarse zirconia powder and fine zirconia powder, and these voids alleviate thermal stress that occurs during heating and cooling, preventing peeling of the coating layer and cracking. It is possible to prevent the occurrence of , and as a result, to prevent reaction with the object to be fired. Furthermore, since the film can be made thicker, durability can be dramatically improved.

The coarser particles of the zirconia powder are preferably 10 to 45 μm, and the optimal particle size is 20 to 40 μm.
If it is less than 0 m, continuous voids cannot be formed, and 45 J
If Lm is exceeded, the bond between the particles becomes insufficient, which is undesirable.Furthermore, the blending amount is preferably 40 to 60% by weight, and optimally 45 to 55% by weight. If it is less than 40% by weight, cracks cannot be prevented due to fewer voids, and if it exceeds 60% by weight, bonding between particles becomes insufficient and a coating layer cannot be formed.

In addition, the finer zirconia powder has a particle size of 0.5 to 5μ.
m is suitable, 1 to 3 pm is optimal, particle size is 0
．． If it is less than 51 Lm, the sinterability will improve and the effect of filling voids will become stronger, making it easier to generate cracks, and if it exceeds 5 Lm, the bonding force between particles will be insufficient, which is undesirable. 40-60% heavy elevation is suitable and 45-55%
% by weight is optimal.

If it is less than 40% by weight, the bonding force between the particles becomes weak and a coating layer cannot be formed, and if it exceeds 60% by weight, the sinterability will improve and cracks will easily form, which is undesirable. Powders include various powders such as partially stabilized zirconia, stabilized zirconia, and unstabilized zirconia, which are widely used, and aqueous solutions such as basic zirconium chloride, basic zirconium acetate, and basic zirconium formate. Alternatively, it is also possible to use those that are used in the form of an aqueous sol or various alcoholates and that convert into zirconia particles after heating.

Moreover, the thickness of the zirconia coating layer is 50 to 5
001 Lm is suitable and 100-300 pm is optimal. If the film thickness is less than 50 gm, reaction with the object to be fired cannot be sufficiently prevented, and if it exceeds 500 gm, it becomes uneconomical and undesirable.

As the heat-resistant inorganic Wffl fiber in the present invention, at least one of amorphous silica-alumina fiber and alumina crystalline fiber is effective. The silica/alumina fibers are usually A,
0. is 4θ~60%It%, Sin is 40~BOwt
%, mullite crystals precipitate at around 300°C, and cristobalite crystals precipitate at around 120°C, causing grain growth and promoting sintering with the refractory powder and/or inorganic binder. Therefore, it is particularly preferable in the present invention.Furthermore, the alumina crystalline m fibers are A
ll, J is 70-99wt%, 5i02 is 1-30wt
%, and is composed of η-9γ-1δ-2θ-form transitional alumina, α-form stable alumina, or mullite. The transitional alumina is 14
When fired at around 00°C, it transforms into α-form and causes grain growth, and α-type alumina and mullite also cause grain growth, so they act as a sintering accelerator in the same way as the silica/alumina fibers mentioned above. This is promising and desirable. However, the non-fibrous substances in these heat-resistant inorganic fibers not only eliminate the smoothness of the surface of the molded product but also increase its weight.
Must be less than % by weight.

As the refractory powder, one or more selected from alumina, alumina/silica, zirconia, magnesia, and titania have a high refractory temperature and are suitable. Specifically, alumina, mullite, kaolinite, kibushi viscous, frog's eye viscosity, sillimanite, steatite,
Forsterite, zirconia, magnesia, spinel, titania, etc. are preferred.

Furthermore, the above-mentioned inorganic binder is preferably one or more selected from silica-soda-based calcium borate-based and silica-based frits. For example, feldspar, mica powder, boric acid, limestone, betalite, glass powder, crushed stone, etc. are preferred.

These refractory powders and inorganic binders are mixed in advance into a composition for sintering at a predetermined temperature, and then ground to approximately 50 pm or less using a grinder such as a ball mill before use. In particular, it is preferable that the inorganic binder be made into fine powder, and the optimum amount is one turn or less.

Alternatively, after blending a predetermined amount of the heat-resistant inorganic fiber, the fire-resistant powder, and/or the inorganic binder, the mixture is kneaded or dispersed in water, then molded, and then fired, or coated and then fired. The porous refractory of the present invention can be formed by this method.

The coating on the porous refractory can be obtained according to various methods as follows. (1) Sufficiently disperse zirconia powder with a particle size of 10 to 45 lm and zirconia powder with a particle size of 0.5 to 5 lm in a predetermined ratio in an organic binder such as methylcellulose or vinyl acetate, and add the solution. It is obtained by adhering to the surface of the porous refractory material by coating, spraying, dipping, etc., drying, and then firing at 1200 to 1600°C. (2) So-called zirconia sol, Zr(OAc) and solution, Zr(OH)x (C1
) Disperse zirconia powder with a particle size of 10 to 45 JLm in a solution such as It is obtained by adhering it to the surface of a refractory material, drying it, and then firing it at 1200 to 1600°C. (3) A mixed solution of zirconia powder with a particle size of 10 to 45 gm and furkyl zirconate is applied to the surface of the porous refractory by spraying, dipping, etc. in an inert atmosphere, and then water vapor or mist is applied. It can be obtained by hydrolyzing alkyl zirconate using water and then calcination. In this case, it is also possible to omit the hydrolysis step and use a method based on thermal decomposition of the alkyl zirconate. Said (2)
In (3), the particle size can be adjusted by controlling the temperature and speed of hydrolysis and the speed of drying and calcination.

Examples of the present invention will be described below along with comparative examples.

〔Example〕

Amorphous silica/alumina flI as heat-resistant inorganic fiber
The present invention was applied to the surface of a flat molded body with a bulk density of 1.0 g/crn" obtained by compounding alumina and clay as a refractory powder and calcium borate as an inorganic binder and then sintering the male. Applying a zirconia coating and a zirconia coating not according to the present invention, respectively,
The coating layer was baked in air at 1400° C. for 24 hours and changes in the coating layer were observed. The observation results are shown in Table 1.

In Table 1, Comparative Examples 1 to 8 relate to zirconia coatings not according to the present invention, Comparative Examples 1 and 2 have an inappropriate amount of zirconia powder, and Comparative Example 3
In cases 4 and 4, the particle size of the finer zirconia powder was not suitable, and in Comparative Examples 5 and 6, the coarser particle size was inappropriate, and in comparative examples 7 and 8, the coating thickness was not suitable. .

Thus, from the results in Table 1, it can be seen that the zirconia coating of the present invention forms a very stable film.

Table 1 is shown below (margins below).Next, the reactivity with a ceramic part for use with a 7 ceramic component containing barium titanate as a main component was evaluated.

Mitate 1 40g of amorphous silica-alumina FIi fiber, 300g of calcined alumina fine powder, 240g of clay, 60g of calcium borate, and cationized starch (20% solution) 1
00+s sentence was added to 30 sentences of water and stirred. Subsequently, a polyacrylamide flocculant (0.5% solution) was added to form a slurry mixture, which was suction molded and then pressed to obtain a plate-shaped molded product with a bulk density of 1.0 g/am''.

Zirconia powder with an average particle size of 25 gm was added to this molded body.
5% by weight and average particle size 1. OJLm zirconia powder 4
Disperse 5% by weight in a 1% methylcellulose solution and apply.
Subsequently, it was fired at 1400° C. for 5 hours to obtain a lightweight heat-resistant tray having a zirconia coating layer with a thickness of 250 pm.

An electronic ceramic component made of barium titanate as a main component and a small amount of organic binder added to the surface of this lightweight heat-resistant tray was fired at a temperature of 1350° C. for 10 hours.

The results after firing were good, with no defects such as cracking or peeling of the coating layer, adhesion of barium titanate, or pinholes.

"Salt Comparison 1" A plate-shaped molded body with a bulk density of 1.0 g/cm'' was obtained in the same manner as in Example 11.This molded body was directly coated with barium titanate as the main component and some organic matter without being coated with zirconia. An electronic ceramic component formed by adding a binder was placed thereon and fired at a temperature of 1350° C. for 10 hours.

After firing, the barium titanate and the molded body were fused together, and the barium titanate molded body could not be recovered.

〔Effect of the invention〕

As described above, the zirconia coating of the present invention forms a strong and stable film, resulting in the following effects.

■ Work when firing ceramics can be simplified.

Firing costs can be reduced.

(Φ Reaction with the material to be fired is prevented and the product yield is improved.

■ Shelves - The lifespan of saggers, trays, etc. is extended, and consumables costs can be reduced.

■ Prevents pulverization of shelf boards, Φ sagger trays, etc., improves the working environment, and allows firing of high-purity, high-precision ceramics.

Claims (1)

[Claims] Consisting of heat-resistant inorganic fiber, fire-resistant powder, and inorganic binder,
Particles with a diameter of 10 to 45
μm zirconia powder 40-60% by weight and particle size 0.5
A film with a thickness of 50 to 50% consisting of 40 to 60% by weight of zirconia powder of ~5 μm and a total amount of 100% by weight.
Porous refractory with 0μm zirconia coating.