JPH02233568A - Hybrid inorganic fibrous form - Google Patents

Abstract

PURPOSE:To obtain the title form excellent in spalling resistance and creep resistance characteristics at elevated temperatures by making up the inner layer with a porous inorganic fibrous form and making up the surface layer with a dense sintered compact of this form, fine powder and coarse granules. CONSTITUTION:The surface of a porous inorganic fibrous form such as of alumina, mullite or zirconia is coated with a slurry containing (A) fine powder plus coarse granules such as of alumina, mullite or zirconia and (B) a binder (e.g. polyvinyl alcohol). The resulting product is baked to make the surface layer consisting of a dense sintered compact made up of the inorganic fibrous form, fine powder and coarse granules, thus obtaining the objective hybrid inorganic fibrous form, which can be suitably used as a lightweight setter for high-temperature baking, structural or functional lightweight ceramic, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inorganic fiber molded article having high heat resistance, spalling resistance, and creep resistance.

[Prior Art] Due to their low heat capacity and low thermal conductivity, the market for inorganic fiber molded bodies is rapidly growing as insulation materials for furnace materials and insulation boards.

In addition, lightweight setters made by adding binders and inorganic fillers to inorganic fibers, forming and firing them are beginning to be used.

This is an epoch-making setter that is lighter than conventional dense setters, saves energy, and has excellent spalling resistance. )
.

The present applicant has completed the invention of a hybrid inorganic fiber molded body in which the surface layer of the inorganic fiber molded body constitutes a dense inorganic sintered body containing the aforementioned fibers, and has previously filed a patent application. (Sho 62-298037).

[Problem to be solved by the invention] A setter made by adding an inorganic filler to inorganic fibers, molding and firing the setter (hereinafter referred to as a lightweight setter) has a bulk specific gravity of 1.
．． Although it is very light at 0g/1 and has advantages such as energy saving, it has significantly lower creep characteristics at high temperatures when compared to conventional dense setters. In this case, the decrease in creep properties specifically refers to the deflection of the setter itself during high temperature use.

This deflection at high temperatures becomes a fatal drawback when the setter is stacked in several stages in a furnace and used as a cutting board for firing ceramics.

In addition, this lightweight setter could be used as a structural material or a functional material for wear resistance by taking advantage of its excellent properties, but due to its structure, it still has insufficient strength and hardness to be used for these purposes. There are many points that need improvement.

The present invention improves the No. 1 hybrid inorganic fiber molded product previously proposed by the applicant to improve heat resistance, spalling resistance, and creep resistance for the various uses of inorganic fiber molded products as described above. This provides an even better molded product.

[Means for Solving the Problems] In view of the above-mentioned current situation, the present inventors conducted intensive research and found that the sintered layer of the surface layer of a hybrid inorganic fiber molded body is made of an inorganic fiber molded body, fine powder, and coarse particles. This structure maintains the excellent properties of an inorganic fiber molded body, such as light weight, spalling resistance, and heat insulation, while maintaining the excellent creep resistance, non-contamination, and high strength of a dense sintered body. The present invention was achieved by discovering that the material also has high hardness.

That is, the gist of the present invention is to provide a hybrid inorganic fiber molded article, wherein the inner layer is a porous inorganic fiber molded article, and the surface layer is a dense sintered body of the molded article, fine powder, and coarse particles. be.

The surface layer, which is a dense sintered body, is made by, for example, dipping the surface layer of the inorganic fiber molded body in a slurry containing coarse particles and fine powder as aggregate, and drying and firing the slurry. On this occasion,
The average particle diameter of coarse particles and the ratio of the total amount of coarse particles to fine powder are shown in Figure 1 at point A (200 m, 50%) and point B.
(200m, 30%), point C (1000m, 5%
) and point D (1000m, 30%). Here, fine powder means an average particle size of 10
One or less refers to powder with a diameter of about 11A1.

As a component of an inorganic fiber molded article, an S 1 0 component is often used as an inorganic binder for the purpose of suppressing shrinkage at high temperatures.

However, when an alumina substrate or the like is fired at a high temperature of 1800° C. or higher, this S t O 2 component causes contamination to the object to be fired.

In order to eliminate this drawback, if the inorganic fiber molded body and the sintered body constituting the surface layer are made of alumina, mullite, or zirconia, it is possible to use it at high temperatures of IB00°C or higher. It becomes a durable molded body.

Hereinafter, the molded product of the present invention will be described in detail, taking as an example a molded product that can be used at high temperatures of 1600° C. or higher, and showing a method for producing the molded product.

First, regarding the fiber molded body that is the base material, in order to increase the heat resistance of the molded body to be obtained, especially the creep resistance at IB00℃, it is necessary to The temperature must also be 1600℃ or higher.

Therefore, the fibers that are the raw material for the fiber molded product must be substantially alumina fibers, mullite fibers, or zirconia fibers. Further, the sintered body of the surface layer also needs to be substantially alumina, mullite, or zirconia. Examples of alumina molded bodies will be described below. An alumina fiber molded article is obtained by adding an inorganic binder such as colloidal silica and an organic binder to the fibers, defibrating the fibers to form a slurry, and then shaping and drying the fibers using an absorption-dissipation method, a dehydration press method, or the like. Furthermore, these molded bodies are already known as heat insulating boards and can be easily made by hand. However, most commercially available heat insulating boards have already been heat-treated at a temperature of 100° C. or higher after molding. On the other hand, it is preferable that the fiber molded article used in the present invention is not subjected to heat treatment after molding.

Next, a process of forming a layer of a dense sintered body on the surface of this fiber molded body will be described.

First, regarding the composition of the surface layer, in order to improve the heat resistance of the molded body that is the final product to be obtained, especially the creep resistance at high temperatures such as 1600°C, it is necessary to Like the composition of bricks, coarse particles must be included as aggregate in fine α-alumina particles.

Although the detailed reason why the addition of coarse particles improves the creep resistance at high temperatures is unknown, it is thought to be as follows.

When a fine-grained sintered body of α-alumina is heated to a high temperature such as 1800° C., movement of particles occurs at the sintered surfaces of the particles, that is, at the grain boundaries. In particular, when this sintered body is plate-shaped like a setter, the sintered body itself becomes weighted, and particles move at the grain boundaries due to gravity, resulting in plastic deformation in the sintered body. occurs. However, this fine particle α-
When coarse particles such as fused alumina or fused mullite are added to an alumina sintered body as aggregate, the voids in the sintered body formed by the addition of coarse particles at high temperatures cause thermal stress during heating. In order to alleviate this, plastic deformation of the sintered body at high temperatures is suppressed.

The coarse particles added to prevent plastic deformation at high temperatures, that is, deflection, have an average particle diameter and a proportion of the total amount of fine powder at points A and B in Figure 1.
It is desirable that it be within the range surrounded by C and D.

In general, the larger the particles, the worse the sintering properties.
If it is 1 or more, sintering will not be promoted and coarse particles will peel off, resulting in a decrease in the strength of the molded product.

Furthermore, the surface of the molded body after firing is naturally very rough, and when used as a setter, it will have an adverse effect on the object to be fired. If the particle size is less than 200 mm, the effect of alleviating thermal stress due to the voids formed by the addition of coarse particles as described above is weakened, and sagging cannot be prevented.

The preferred proportion of coarse particles varies depending on the particle size,
For example, when coarse particles of 200 μs are used, the amount is 30 to 50% by weight. Below 30% by weight,
The effect of preventing deflection at high temperatures is weak, and
If it exceeds % by weight, the amount added is too large as described above, and sintering is not promoted and coarse particles peel off. 100
For the same reason, when using 0 m, 5 to 30% by weight is suitable.

As mentioned above, in order to prevent the molded body from sagging at high temperatures, coarse particles are used at point A (20
0m, 50%), point B (200m. 30%), point C
(1000m, 5%), point D (1000m. 80
%) is preferable.

These compositions are coated on the surface of a fiber molded body and fired, but during firing, the fiber molded body itself, which is the base material, hardly shrinks.

On the other hand, if the coating composition is fine particles α
- If only alumina is used, it will shrink by more than ten percent during phosphorization, and if this is coated on the surface of a fiber molded body and fired, the difference in shrinkage rate will cause cracks on the surface.

However, if the composition contains coarse particles among the fine α-alumina particles, the shrinkage during sintering is several percent or less.

When this composition is coated on the surface of a fiber molded body as a base material and fired, there is little difference in shrinkage rate between the two, and therefore the surface of the molded body after firing will not crack. Also from this point of view, it is useful to add coarse particles.

Further, in order to improve the sinterability of coarse particles, a flux component may be added. The flux component may include, for example, a silica component such as kaolinite, and the amount added is preferably IO parts or less in terms of silica per 100 parts by weight of the coating composition.

The reason why the silica component is set at 10 parts or less is that the silica component causes liquid phase sintering between alumina particles, but if there is too much sintered phase at the grain boundaries, it will promote slippage between particles at high temperatures. This is because it becomes

Another method for improving the sinterability of coarse particles is to add a small amount of alumina binder. The alumina-based binder is a binder that turns into alumina after firing, and may be aluminum oxychloride, alumina sol, or the like.

An organic binder is added as a binder when coating the surface of the fiber molded body, which is the base material, with this composition.

The organic binder may be a solution of polyvinyl alcohol, carboxymethyl cellulose, hydroxyethyl cellulose, or the like.

Next, the process of coating a fiber molded body with alumina particles will be described.

First, coating particles and an organic binder solution are mixed to form a slurry. The coating method may be spraying, brushing, roller coating, dipping, etc., but care must be taken to prevent coarse particles and fine α-alumina particles from separating in the slurry. It is also good to press the coated molded body before firing.

The purposes of pressing are: (1) to improve the adhesion between the coating particles and the base fiber molded body; and (2) to compress the fiber molded body to increase its density and strength.

Since the compact itself is compressed during pressing and the contact points between the fibers are shifted, it is not preferable to use a fiber compact that has been fired once, such as by sintering the contact points between the fibers. From this point of view, it is better to use a fiber molded body that is not heat-treated as a base material.

Phosphorescence consists of coated particles, particles and fiber molded bodies,
In order to sinter the fibers together, the sintering may be carried out at a temperature of 1600° C. or higher, which is the sintering temperature of alumina.

It is also a good idea to place a weight on it during firing.

The reason for this is that, as mentioned above, there is a slight difference in the shrinkage rate between the fiber molded body itself and the coating layer, so during firing, a (:I) weight is applied to the molded body to promote shrinkage in the thickness direction rather than in the surface direction. be.

The content of the present invention will be explained in more detail below with reference to Examples, but the present invention is not limited to these Examples.

〔Example〕

Table 1 shows the composition of the particles to be coated on the surface of the fiber molded body.
To 300 g of this powder, add 100 c of a 10% solution of polyvinyl alcohol (degree of polymerization 1500).
c was added to form a slurry.

The particles used were first fused alumina and fused mullite of various particle sizes as aggregates, and AL-1608G-4 (fried alumina with an average particle size of 0.B) as fine alumina (all from Showa). Manufactured by Electric Works.

The particle size of the coarse particles was adjusted as follows.

J of the 2Pli class closest to the average particle size to be obtained
Classify using an IS standard sieve. For example, when attempting to obtain coarse particles of 1000-1, the particles were classified using two JIS standard sieves with nominal sizes of 850- and 1180-, and the average particle size was set as too-.

As the fiber molded article, Super Fireboard SF-1700 manufactured by Taiyo Chemical ■ was used, and its surface was polished. Size is 150mm x 150mm x
It has 25 fins.

The surface of the Noko board was coated with the above mesylary by brushing, and after coating, it was pressed at a pressure of 40 kg/c-, and then it was baked at 1700°C for 2 hours while placing a weight of 20 g/cd, and it was heated to 150+nXl50+u.
A fiber molded body having a size of 6 mm was obtained. The surface of this compact was lapped with a diamond slurry.

As a weight at this time, a setter (T
PC-193C) were used in layers.

Table 2 shows the physical property values of the obtained molded product.

The room temperature strength of the obtained molded body is 50+uXl5+nX6m
This is the value obtained by cutting the sample into a size of m and performing a 3-point bending test using Suban 30W.

The creep resistance test was conducted under the following conditions.

First, four legs are made of alumina sintered beads with a cross-sectional area of 1 cd, and the obtained size 15Q+nx150m is placed on top of the four legs.
Set the mX6 dragon molded body.

An alumina green sheet having a total weight of 20 i is placed on top of the molded body. In this state, a sintering test was conducted at 1800° C. for 2 hours, and the amount of deflection of the molded product at that time was measured using a dial gauge.

The values in Table 2 are the amounts of deflection after repeating the above sintering test 10 times. In addition, the reaction between the alumina substrate and the compact, which were fired at the same time, was visually confirmed.

Regarding the spalling resistance test, a test was conducted in which the molded body heated to 10°C was placed in water.

Table 2 shows the number of times the above test was repeated and cracks etc. occurred in the molded product. Regarding the molded body obtained by adding aggregate with an average particle size of 1000a as coarse particles and coating it,
If the proportion is 30% by weight or more, sintering properties are poor and aggregate flaking occurs.

The same applies to 500urn and 200-, and if 40.50% by weight or more is added to each, the aggregate will peel off.

Formulation Nl9.10 was coated with a composition in which kaolinite was added as a flux component.

This kaolinite contains 45% silica component.

ffill is obtained by changing the largest particle aggregate to fused mullite.

lkl2 has a surface coating layer formed only of fine alumina without containing coarse particles.

However, for this composition, the fiber molded body was immersed in a slurry of fine alumina particles and coated in consideration of the difference in shrinkage rate between the fiber molded body and the fine alumina particles.

In either case, the shape of the obtained molded product was good.

Table 2 is a list of physical properties of molded bodies obtained by coating and firing the compositions shown in Table 1.

Blend No. 2 has a small proportion of coarse particles, and sagging cannot be prevented.

Oni 6 also causes deflection for the same reason, but the amount of aggregate added to prevent this deflection is 5% by weight or more when coarse particles of 1000 m are used, and 20% by weight or more.
In the case of 0-, 30% by weight is required.

Considering the shape and creep resistance properties of the molded product obtained above, the average particle diameter and amount of coarse particles to be added are determined as follows:
The range surrounded by points A, B, C, and D in the figure is preferred.

As with Oni 10, if too much kaolinite is added, deflection will occur.

In addition, i0 reacted with the silica component in this kaolinite and the alumina substrate that was the object to be fired, and the fired substrate adhered to the setter.

Also&. Regarding 12, since the coating layer does not contain coarse particles in its composition, the surface smoothness is good, but sag occurs.

Spalling resistance tests were conducted only on those that did not exhibit deflection, but all showed better performance than precise setters.

Incidentally, electron micrographs of the molded body obtained by coating and firing the magnetic composition of 4 are shown in FIGS. 2 and 3.

Formation of a coating layer with a thickness of about lookum was confirmed on the surface.

(Space below) Figure 1 [Effects] This hybrid inorganic fiber molded product has excellent spalling resistance similar to conventional lightweight setters, and also has excellent creep resistance at high temperatures. It is used as a setter for government purposes.

It is also useful as a structural or functional lightweight ceramic.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the range of suitable combinations of the average particle diameter of coarse particles forming the surface layer of the hybrid inorganic fiber molded article of the present invention and the total ratio of fine powder, and FIG. FIG. 3 is a representative of the particle structure showing the particle structure in cross section and plane of the hybrid inorganic fiber molded product of Compound 4, which is an embodiment of the present invention.

Claims (3)

[Claims] 1. 1. A hybrid inorganic fiber molded body, wherein the inner layer is a porous inorganic fiber molded body, and the surface layer is a dense sintered body of the molded body, fine powder, and coarse particles. 2. The hybrid inorganic material according to claim 1, wherein the inorganic fiber molded body is an alumina, mullite, or zirconia fiber molded body, and the fine powder and coarse particles are alumina, mullite, or zirconia. Fiber molded body. 3. The average particle diameter of coarse particles and the ratio of coarse particles to the total amount of fine powder are at point A (200 μm, 50%
), point B (200 μm, 30%), point C (1000 μm
, 5%) and point D (1000 μm, 30%).