JPH0535708B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a refractory material used to place a raw material molded body in a firing furnace when firing highly reactive ceramics such as barium titanate. [Prior art] Generally, to fire ceramics in a kiln, a raw material molded body is placed on or placed in a refractory plate or container made of alumina, mullite, silicon carbide, or zirconia, and the raw material molded body is welded. It is fired in such a way that no dust or ash adheres to it. When firing highly reactive ceramics such as barium titanate, plates and containers made of sintered zirconia particles were used, as plates and containers made of materials other than zirconia would react with the firing raw materials. Such refractories are heavy, have a large heat capacity, take time to raise and lower the temperature of the furnace, are difficult to handle, and have low spalling resistance. In order to solve this problem, the surface of a sintered compact made of refractory fibers such as alumina, silica, alumina, and silica fibers and refractory powders such as silica and mullite was coated with zirconia and sintered. It is conceivable to use a lightweight refractory material with a thin film formed thereon. However, when this refractory was fired with barium titanate on it, some reaction remained and it was not possible to completely eliminate the reaction with barium titanate. Products such as barium titanate react during firing at the parts where they come into contact with the stand or container, and the contamination of impurities has a negative impact on quality and performance, and must be avoided as much as possible. [Problems to be Solved by the Invention] The present invention aims to provide a refractory material for firing ceramics that does not cause a reaction in the part that comes into contact with the object to be fired when firing ceramics having such reactivity. be. [Means for Solving the Problems] The means for solving the problems according to the present invention is to partially stabilize the surface of a sintered base consisting of alumina fibers, easily sinterable alumina fine powder, and silica fine powder. In refractory materials in which a thin layer of zirconia is integrally sintered, the external ratio is
0.3 to 1.5 parts by weight of MgO are mixed and sintered together, and the thickness of the thin layer of partially stabilized zirconia is more than 100 μm and less than 300 μm. In this invention, alumina fibers are used to reduce the weight of this refractory material, and can withstand temperatures of 1,400 to 1,600°C for firing objects to be fired. When molding this fiber using the papermaking method, this fiber alone does not have enough compressive strength to support the object to be fired, so easy-sintering fine alumina powder is added to increase the bulk density to 0.8~
The amount is approximately 1.2 g/cc, and the strength is sufficient to support the object to be fired. For this reason, when both are 100 parts by weight, it is preferable that the ratio is 25 to 85 parts by weight of easily sinterable alumina fine powder to 15 to 75 parts by weight of alumina fiber. The fine silica powder is used as a binder between the alumina fibers and the easily sinterable fine alumina powder, and silica sol, which is generally used as an inorganic binder, is used. The amount of this fine silica powder used is 100 in total, including the alumina fiber and easily sinterable fine alumina powder.
It is preferable to use 2 to 20 parts by weight. Alumina fiber itself does not have sinterability and is easy to sinter. Fine alumina powder has little sinterability because it has not been compression molded, so if it is less than 2 parts by weight, it will lack bonding properties even if the firing temperature is high. The strength is insufficient for use, and if it exceeds 20 parts by weight, it not only lowers the fire resistance temperature but also reacts with the alumina fibers to form mullite, which coarsens the crystals of the alumina fibers and causes them to become brittle during use. As MgO, it is preferable to use reagent-grade MgO that is easily available as a fine powder in order to improve dispersion in the solid content. Partially stabilized zirconia is Y ₂ O ₃ , CaO, MgO,
A commercially available product with a size of several to several tens of μm partially stabilized with a stabilizer such as CeO ₂ is used. Partially stabilized zirconia is superior to stabilized zirconia in terms of spalling resistance after firing. For molding, alumina fibers, easily sinterable alumina fine powder, silica sol, MgO fine powder, and a small amount of organic binder are mixed in water to a solids concentration of approximately 0.5% by weight, and then molded using a wet papermaking method. do. this
Dry at about 110℃, sinter at about 1500℃, cut the sintered body into the desired shape with a grindstone, apply paste-like ZrO ₂ fine powder several times, dry at about 110℃, then sinter at about 1400℃. The product is baked at ℃. [Function] In the present invention, by adding MgO to the sintered substrate, it is possible to eliminate the reaction between barium titanate and the thin zirconia layer on the surface. If the amount added is less than 0.3 parts by weight for a total of 100 parts by weight of alumina fiber, easily sinterable alumina fine powder, and silica fine powder, there will be a reaction with barium titanate, and if it exceeds 1.5 parts by weight, sintering will occur. Since the melting point of the substrate decreases, shrinkage increases, spalling resistance decreases, and the sintered substrate becomes undurable for use, the amount added is set in the range of 0.3 to 1.5 parts by weight. Although the exact reason for suppressing the reaction is unknown, the mechanism of reaction suppression is estimated as follows. In other words, it is well known that oxide evaporation occurs at high temperatures, and it is thought that at high temperatures, Al ₂ O ₃ and SiO ₂ partially evaporate from the base alumina-silica and react with barium titanate vapor. However, by adding MgO to the base
It is presumed that MgO traps the evaporation of Al ₂ O ₃ and partially forms spinel (MgO.Al ₂ O ₃ ), thereby suppressing the evaporation of Al ₂ O ₃ . In addition, it is assumed that the ZrO ₂ coating traps the evaporation of SiO ₂ and partially forms zircon (ZrO ₂ SiO ₂ ), but the reaction suppression mechanism has not been confirmed in either case, and this is just a possibility. It's only a guess. However, if the thickness of the zirconia thin layer is less than about 100 μm, some reaction will remain, and if the thickness is less than 150 μm,
When the thickness is about 300 μm, only the color that is presumed to be due to trace impurities occurs, and as the thickness increases, this color decreases, but when it becomes about 300 μm, the particle size of the zirconia powder is as fine as several to several tens of μm, so the zirconia Since cracks will occur in the thin layer, the thickness of the zirconia thin layer should not exceed 100μm and be 300μm.
It shall be less than m. When MgO was not added to the sintered substrate, the reaction occurred regardless of the thickness of the zirconia thin layer. [Example] Example 1 397g of alumina fiber and average particle size of 0.4μm
595 g of easily sinterable alumina fine powder, 8 g of silica sol as solid content, reagent grade MgO powder in the amount shown in Table 1, and 50 g of starch make the solid concentration in water 0.5% by weight. Mixed like this. This was wet molded on a screen, dried at 110°C for 30 hours, and then fired at 1500°C for 3 hours to sinter. This is shaped using a grindstone, and has a bulk specific gravity of 1.08g/cc.
A sintered substrate of 150 mm, width 100 mm, and thickness 5 mm was obtained. _{110 _}
The product was dried at ℃ for 4 hours and baked at 1400℃ for 1 hour. When this product was cut and the thickness of the thin layer of partially stabilized zirconia was examined under a microscope, the average thickness was 208 μm.
It was hot. This was placed in a furnace, barium titanate was placed on top of it, and fired at approximately 1,400 ℃ for 2 hours. The results are shown in Table 1. The formation of crystals was determined by X-ray diffraction analysis.

[Table] As shown in the above results, the amount of MgO added is 3 to 15 g.
This can prevent the reaction from occurring. Example 2 Products with different thicknesses of partially stabilized zirconia thin layers were produced in the same manner as in Example 1, except that the amount of MgO added was 5 g, and barium titanate was added in the same manner as in Example 1. The firing was carried out. The results are shown in Table 2.

〔Effect of the invention〕

According to the present invention, it is possible to provide a light, heat-efficient refractory material that does not react with ceramics and is used for firing highly reactive ceramics.

Claims (1)

[Claims] 1. On the surface of a sintered base consisting of alumina fibers, easily sinterable alumina fine powder, and silica fine powder,
In a refractory material in which a thin layer of partially stabilized zirconia is integrally sintered, 0.3 to 1.5 parts by weight of MgO is mixed and sintered to 100 parts by weight of the sintered base, resulting in partially stabilized zirconia. The thickness of the thin layer of oxidized zirconia is
A refractory material for firing ceramics with a diameter of more than 100μm and less than 300μm.