JPH04338178A - Porous magnesia sintered body and production thereof - Google Patents

Abstract

PURPOSE:To uniformize the size and distribution of closed pores and to enhance strength by heating and sintering a molded body of a mixture contg. prescribed amts. of fine powdery magnesium of a regulated particle diameter, org. beads of a regulated diameter and an org. binder under prescribed conditions. CONSTITUTION:Fine powdery magnesium of 1-20mum average particle diameter is mixed with 1-20vol.% org. beads of 3-50mum diameter such as styrene polymer beads and an org. binder such as PVA. A molded body of the resulting mixture is heated to 350 deg.C at <=50 deg.C/hr heating rate in the case of 1-10vol.% org. beads or at <=20 deg.C/hr heating rate in the case of 10-20vol.% org. beads. It is further heated to the sintering temp. at <=200 deg.C/hr heating rate and sintered at 1,550-1,700 deg.C to obtain a porous magnesia sintered body having closed pores of 1-50mum pore diameter.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a porous magnesia sintered body and a method for manufacturing the same, and more specifically, it is lightweight,
The present invention also relates to a porous magnesia sintered body having high strength, low heat capacity, and closed pores suitable for use as furnace material or pod material, and a method for manufacturing the same.

0002

[Prior Art] Sintered bodies are manufactured by molding and firing powder, but in order to obtain dense sintered bodies, particles are mixed according to the densest packing method. As described above, porous sintered bodies are manufactured by dividing crushed powder into various particle sizes, blending them with various particle sizes, mixing these with a binder, and then shaping and sintering.

This porous sintered body has open pores or continuous pores and closed pores or independent pores, but when used as a furnace material or setter material, sintered pores with closed pores are used for the purpose of preventing gas diffusion. The body is used. When manufacturing such a porous sintered body, the porosity of the sintered body has been controlled by mixing particles based on the particle size structure based on experience.

0004

[Problems to be Solved by the Invention] However, in the method of manufacturing a porous sintered body, particles are mixed by considering the particle size composition empirically, so it is difficult to determine the pore distribution of the obtained sintered body, that is, the shape of the pores. The average particle diameter of the pores was non-uniform, and the amount of pores, that is, the porosity could not be sufficiently controlled.

Furthermore, since the pores themselves are gaps between particles, their sizes are also irregular, making it impossible to create a material in which fine pores are uniformly dispersed. Therefore, in the conventional method for manufacturing a porous sintered body, the strength of the porous sintered body is low, making it difficult to manufacture high-quality furnace material products such as thin products.

Therefore, the present inventors conducted various studies on porous sintered bodies, particularly porous magnesia sintered bodies, which do not suffer from the above-mentioned problems of non-uniformity in pore size, pore distribution, etc., and found that the raw material magnesia It was discovered that the initial problem could be solved by mixing organic beads into the liquid, and the present invention was accomplished based on this knowledge. therefore,
The problem to be solved by the present invention is to obtain a porous magnesia sintered body and a method for manufacturing the same, which can yield high-grade furnace material products such as thin products with uniform pore size and distribution and excellent strength. .

[0007]

[Means for Solving the Problems] The means for solving the problems described above are based on the following matters (1) to (3). (1) A porous magnesia sintered body characterized in that the pore diameter of the magnesia sintered body is in the range of 1 μm to 50 μm and the pore form is independent pores.

(2) A molded body obtained by adding and mixing 1% to 20% by volume of organic beads with a particle size of 3 μm to 50 μm and an organic binder to fine powder magnesia with an average particle size of 1 μm to 20 μm, and then molding the mixture. Raise the temperature to 1550℃~1
A method for producing a porous magnesia sintered body, characterized by sintering in a temperature range of 700°C.

(3) In the temperature increase described in item 2 above, 3
Below 50℃, the amount of organic beads added is 1% by volume or more.
The heating rate is 50°C/hour or less within the range of 10% by volume, and the heating rate is 20°C/hour or less when the amount of organic beads added exceeds 10% by volume and reaches 20% by volume. , furthermore, the temperature increase rate from 350℃ to the sintering temperature is 200℃.
A method for producing a porous magnesia sintered body, characterized in that the temperature is below ℃/hour.

The present invention will be explained in more detail below. The porous magnesia sintered body having closed pores of the present invention is
Because the pore size and pore distribution are uniform, it has excellent strength.Also, since the molded mixture of fine magnesia and organic beads is sintered in the range of 1550°C to 1700°C, the pore size and pore distribution are uniform. etc. can be obtained.

Furthermore, since the rate of temperature rise up to the sintering temperature is limited, the pores can be formed into a uniform spherical shape, and the pore size and distribution can be made even more uniform. As the raw material magnesia used in the present invention, fused magnesia, magnesia clinker, etc. are used.

[0012] The raw material magnesia is pulverized to an average particle size of 1 μm.
Powder raw material with a diameter of m to 20 μm is used. More preferably 1 μm
~10 μm. If the average particle size is smaller than 1 μm, it is undesirable from the viewpoint of grinding cost and handling of the powder raw material, and if the average particle size exceeds 20 μm, large grain boundaries remain after forming and sintering, making it impossible to achieve high strength.

[0013] The present invention uses organic beads to form spherical, uniform closed pores in a porous sintered body, and the organic beads are spherical in shape and have a particle size of 3 μm to 50 μm.
It has various particle sizes of m, and can be selected depending on the purpose. Various materials can be used for the organic beads, but materials that decompose and volatilize at relatively low temperatures are preferred, and for example, methacrylic acid polymers, styrene polymers, etc. are well used.

In the present invention, the amount of organic beads added to the raw material magnesia is 1% to 20% by volume, and the organic beads are mixed by a conventional method. When the amount of organic beads added is less than 1% by volume, uniform pores cannot be formed, and
If the amount exceeds % by volume, it becomes difficult to form closed pores. In the present invention, organic beads are added to magnesia as a raw material, and an organic binder is usually added in an amount of 1% to 1% by weight to enable molding or handling of molded products.
Add 5% by weight.

[0015] As the organic binder, commercially available organic binders such as polyvinyl alcohol and polyethylene glycol (PEG) are used. The size of the pores in the porous sintered body is preferably in the range of 1 μm to 50 μm, and if it exceeds 50 μm, the strength will decrease in the case of a thin product, which is not preferable. In the case of a magnesia sintered body, the volume shrinkage rate is about 20%, so the pores are slightly smaller than the size of the organic beads.

[0016] Furthermore, it is important to uniformly distribute the fine pores in the sintered body, and for this purpose it is necessary to sufficiently mix the raw material magnesia and organic beads. For mixing, a mixer commonly used in this technical field is used, and for molding, common molding means such as press or extrusion are similarly used. Furthermore, an electric furnace or the like is usually used for firing.

[0017] In the method for producing a porous magnesia sintered body of the present invention, when the temperature is below 350°C, the rate of temperature increase is 50°C while the amount of organic beads added is within the range of 1% by volume to 10% by volume.
/ hour or less, and the amount of organic beads added is 10% by volume.
If the temperature exceeds 20% by volume, the temperature increase rate will be 20°C.
The temperature increase rate is less than 200°C/hour from 350°C to the sintering temperature because the mixed organic beads decompose and volatilize at 200°C to 300°C. This is because it is necessary to slowly raise the temperature to around 350°C for degreasing.

Therefore, if the temperature increase rate is too high, the organic beads will decompose too rapidly, causing problems such as cracking and swelling of the molded product, which is not preferable. The molded body is sintered at a temperature of 1550°C to 1700°C. The porous magnesia sintered body with closed pores obtained by the production method of the present invention is useful for high-grade furnace materials, setters, sheath materials, etc., and can be applied to various materials from thin to thick materials. It is something.

[0019]

EXAMPLES The present invention will be explained in more detail with reference to examples below, but the present invention is not limited to these examples. Electrofused magnesia, which was a raw material for the example, was finely pulverized and classified to obtain particles having an average particle size of 5 μm.

To 100 g of this 5 μm electrofused magnesia, 15% by volume of methacrylic acid polymer beads were added, and further, 3% by weight of polyvinyl alcohol as an organic binder was added and thoroughly mixed.

[0021] The kneaded material thus obtained was heated to 200K.
After press-forming under pressure at
The temperature was raised to 00°C at a rate of 150°C/hr. Further 1600℃
It was heated for 1 hour. The results obtained are shown in Table 1.

[0022]

[Table 1]

As is clear from Table 1, the shape of the pores is as follows:
A sintered body was obtained which was spherical and had pores evenly distributed. It can also be seen that the bending strength is significantly superior to that of conventional products.

[0024]

[Effects of the Invention] Since the present invention has independent pores, it can be used for applications such as furnace materials, setter materials, and pod materials. In addition, since the material magnesia containing organic beads is fired, it is possible to obtain products with uniform pore size and pore distribution, which makes it possible to manufacture lightweight and thin products with excellent strength, as well as thermal shock resistance. You can get something strong.

Furthermore, since the rate of temperature increase up to the sintering temperature is limited, the pores can be formed into a uniform spherical shape, and the pore size and distribution can be made even more uniform.

Claims (3)

[Claims] [Claim 1] The pore diameter of the magnesia sintered body is 1 μm or more.
A porous magnesia sintered body characterized in that the pores are independent pores in the range of 50 μm. 2. Add and mix 1% to 20% by volume of organic beads with a particle size of 3 μm to 50 μm and an organic binder to fine powder magnesia with an average particle size of 1 μm to 20 μm, and then mold the resulting molded product. Raise the temperature to 1550℃~17
A method for producing a porous magnesia sintered body, characterized by sintering at a temperature in the range of 00°C. 3. In the temperature increase according to claim 2, 350
Below ℃, the amount of organic beads added is 1% to 10% by volume.
The temperature increase rate is 50°C/hour or less within the range of volume %,
The amount of organic beads added exceeds 10% by volume and is 20% by volume.
Within the range up to, the heating rate is 20°C/hour or less,
Furthermore, the temperature increase rate from 350℃ to the sintering temperature is 200℃/
A method for manufacturing a porous magnesia sintered body, characterized in that the manufacturing time is less than 1 hour.