JPH026325A - Hollow lightweight magnesia particle and production thereof - Google Patents

Abstract

PURPOSE:To obtain lightweight hollow magnesia particles having high strength by drying combustible pore-forming material particles having formed a MgO- forming component layer on the periphery and calcining. CONSTITUTION:Combustible pore-forming material particles (e.g., oil coke) having 0.05-9mm average particle diameter are blended with a MgO-forming component (e.g., natural magnesia powder) having a particle size distribution of <=5wt.% residue of 100 meshes sieve and <=5wt.% residue of 350 meshes sieve, granulated, a layer of MgO-forming component is made on the periphery of nuclei of the combustible pore-forming material particles to give particles having 0.1-10mm average particle diameter. Then the particles are dried, then calcined at 1,200-1,800 deg.C to give hollow lightweight magnesia particles having an average diameter r of a hollow part 1 of >=3/10 average diameter R of the particles, consist of the hollow part 1 and a wall part 2 of MgO formed on the periphery thereof and has 0.1-10mm average particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to light:j1 magnesia particles and a method for producing the same.

[Background of the Invention] Conventionally, in steelmaking technology, when transferring molten steel using a tundish, ladle, etc., a heat insulating material or a heat insulating material is suspended on the surface of the molten steel to reduce contact between the molten steel and the outside air. This is a known technology that prevents heat loss and also prevents reactions between molten steel and the outside air.

[It is known to use magnesia grains, which are made porous by forming pores throughout the grains, as the above-mentioned heat insulating material or heat retaining material. As such porous magnesia particles, there are, for example, heat-insulating refractory particles disclosed in JP-A-62252363. According to the description in the publication, the particles consist of natural magnesite lumps of 1000 to 145
It is manufactured by firing at a temperature range of 0°C and then crushing. It has a volumetric specific gravity of 0.2 to 1.5, and has excellent heat resistance and heat insulation properties. It is said to be effective in reducing heat loss from molten steel or reaction between molten steel and outside air in applications where contact with molten steel is reduced.

It is generally known that the higher the firing temperature of 7 gnesia, the harder the product will be obtained. In the above-mentioned manufacturing method, when firing is performed at a temperature close to the upper limit of the above-mentioned temperature range, magnesia particles which become porous but are considerably compacted and have a high specific gravity are obtained. When used as a heat insulator or heat insulating material, especially when floating on the surface of molten steel, it is common to deposit it to a considerable thickness, and it is common to use it for such purposes. When doing so, use large magnesia particles! Since it is used for t, it is desirable that its specific gravity be relatively small.

In order to obtain magnesia particles with low specific gravity using the above-mentioned manufacturing method, firing must be performed at a relatively low temperature within the above-mentioned temperature range. However, according to the inventor's study, magnesia particles fired at the above-mentioned low temperature result in insufficient sintering between magnesium oxide crystals.
It tends to be brittle. When such magnesia particles are used as a heat insulating material or a heat insulating material, there is a problem that when the particles are piled up and sold, many particles disintegrate, causing contamination of molten steel.

Therefore, it is desired to develop magnesia particles that are light f11 (low specific gravity) and have sufficient strength to be used as a heat insulator or heat insulator.

[Objective of the Invention] The object of the present invention is to create a lightweight material that is lightweight and has sufficient strength to be used as a heat insulating material or a heat insulating material. 11
An object of the present invention is to provide magnesia particles and a method for producing the same.

[Summary of the Invention] The present invention is characterized in that the average particle diameter of the hollow part and the wall part of magnesium oxide formed around the hollow part is 0.1 to 10 mm.
The present invention relates to hollow lightweight magnesia particles, characterized in that the average diameter of the hollow portion of the particles is 3/10 or more of the average diameter of the particles.

The above light magnesia particles have an average particle diameter of 0.05
A layer of a magnesium oxide forming component is formed around particles of a combustible pore-forming material having a diameter of ~9 mm as cores, and the particles are granulated so that the average particle diameter is in a range of 0.1 to 10 mm.
After drying the particles, further 1200 to 1800"
It can advantageously be produced by firing at a temperature in the range of C.

In producing the lightweight magnesia particles of the present invention, since the core is a combustible pore-forming material, hollow portions are formed even when fired at high temperatures, and the wall portions are further baked and compacted. Therefore, light 1i1 magnesia particles having a light weight of 4 and sufficient strength as a heat insulating material or heat insulating material can be obtained.

Preferred embodiments of the present invention are described below.

In the lightweight magnesia particles having a hollow portion according to the present invention, the wall portion marked with - contains magnesium oxide with 851n Fit.
% or more.

2) In the lightweight magnesia particles having hollow portions of the present invention, the average particle diameter thereof is in the range of 0.3 to 5 mm.

3) In the lightweight magnesia particles having a hollow portion of the present invention, the average diameter of the hollow portion of the particles is 3/1 of the average diameter of the particles.
Must be in the range of 0 to 9/10.

4) The lightweight magnesia particles having hollow parts of the present invention have a bulk density in the range of 0.2 to 15 g/cc.

5) In the production method of the present invention, the magnesium oxide-forming component is a powder having a particle size distribution of 5% or less with a 100 mesh sieve residue.

6) In the production method of the present invention, 5 to 60 parts of the combustible pore-forming material are used per 100 parts by weight of the magnesium oxide-forming component.

7) In the production method of the present invention, when forming the layer of the magnesium oxide forming component around the particles of the combustible pore-forming material as a core, the particles are sprayed with water.

8) In the production method of the present invention, when forming a layer of the magnesium oxide forming component around the particles of the fine powdered combustible pore-forming material as a core, performing this while spraying an aqueous magnesium salt solution onto the particles. .

9) In the production method of the present invention, the particles obtained by forming a layer of magnesium oxide forming component around particles of a combustible pore-forming material as cores are fired for a period of 0.5 to 8 hours. thing.

[Detailed Description of the Invention] The hollow lightweight magnesia particles of the present invention are hollow lightweight magnesia particles having an average particle diameter of 0.1 to 10 mm and consisting of a hollow portion and a magnesium oxide wall formed around the hollow portion. Therefore, the average diameter of the hollow portion is 3/3 of the average diameter of the particle.
It is characterized by being 1O or more.

The shape of the magnesia particles mentioned above may be any shape such as spherical, columnar, or pellet shape.

In addition, in the present invention, the average diameter of the hollow part and particles means the diameter assuming that each particle is spherical, and when the particle has an anisotropic shape such as a columnar shape or a pellet shape, It refers to the average value of the diameter in each direction. Furthermore, the lightweight magnesia of the present invention is an aggregate of a large number of particles, most of which have the particle diameter and hollow portion defined above.

]-The average particle diameter of the magnesia particles is 0.1 to 10 m.
m, preferably in the range of 0.3 to
5 mm, more preferably in the range of 0.5 to 3 mm. - If the Y average particle diameter exceeds 10 mm, for example, when floating on the surface of molten steel and using it as a heat insulating material, it is not preferable because gaps may be formed between the particles, making it difficult for the molten steel to come into contact with the outside air. Furthermore, if the average particle diameter is less than 0.1 mm, light Ill formation becomes insufficient and elution resistance becomes insufficient, which is not preferable.

1-The magnesia grains-r each have the following characteristics:
1. 3/lO of the average diameter of the mud hollow part or the average diameter of its particles
It is necessary that the ratio be less than or equal to 100%, and it is preferably in the range of 3/10 to 9/10. If the average diameter of the hollow portion is less than 3/10 of the average diameter of the particles, it is not suitable for providing light 1-it magnesia particles, which is the first aspect of the present invention.

+frr The magnesia particles have a bulk density of 0.2 to 1.5.
g/cc, more preferably in the range of 0.3 to 1.0 g/cc. When the bulk density is not within the range of
It may be disadvantageous as an insulating material. The above-mentioned bulk density is expressed as the quotient (W/V) of the weight jlW and the dimensional volume V of the magnesia particles when the magnesia particles are filled into a container with a constant volume by a natural deposition method.

Preferably, the wall portion of the surface magnesia particles contains 85% by weight or more of magnesium oxide, and 90% by weight.
It is even more preferable to include the following.

If the magnesium oxide content is less than the above range,
The melting point of the magnesia particles tends to decrease. That is, it is preferable that the wall portion of the magnesia particle is made only of magnesia, or if a material containing some impurities (silica, alumina, etc.) such as natural magnesia or seawater magnesia is used as the raw material for forming the wall portion. , sow impurities get mixed into the formed wall. There is usually no problem with the inclusion of impurities in the straw as long as it is within 15% by weight of the wall forming material.

The average diameter of the N-shaped hollow part and the average diameter of the particles are determined by measuring the particle diameter and wall thickness at several locations on a cross section of the L-rated magnesia particle cut in multiple directions (different directions). This is a numerical value calculated by The measuring method described in item 1- will be explained in detail with reference to the attached drawings. FIG. 1 is a schematic diagram showing the relationship between the diameter of the hollow lightweight magnesia particles of the present invention, the diameter of the hollow part, and the J-dimensionality of the wall part. l
2 indicates a hollow part and 2 indicates a wall part. First, several (usually one)
(0 or more) magnesia particles are each cut along planes in a plurality of directions, and the particle diameter R is measured at an arbitrary position on the cross section. The thickness d of the wall 2 is then measured at the corresponding position. At this time, the diameter of the corresponding hollow portion 1 is approximately determined by the following equation.

r=R-2d Furthermore, the above-mentioned measurement operation is repeated at several points on the cross section in different directions for each of the above-mentioned magnesium particles, the average of the obtained values of r and R is obtained, and the average of each hollow part is calculated. and the average diameter of the grains t.

The hollow light i+t magnesia particles of the present invention can be advantageously produced by the method described below.

First, combustible pore-forming material particles having an average particle diameter in the range of 0.05 to 9 mm are prepared.

Examples of the above-mentioned combustible pore-forming material include oil coke, wood flour, cellulose powder, rice bran, and coal powder, but oil coke is particularly preferred. The above-mentioned combustible pore-forming material is crushed or granulated, and if necessary, classified to have a desired average particle diameter.

The above-mentioned crushing can be performed using, for example, a ball mill. Furthermore, L granulation can be carried out using a III type granulator or the like. The average particle size of the combustible pore-forming material (1) above must be in the range of 0.05 to 9 mm, preferably 02 to 4.0 mm. If the average particle size is less than the above range, the resulting magnesium particles may have insufficient heat insulation properties, and if it exceeds the above range, the strength of the magnesium particles may be insufficient. , Izuwa is also not desirable.

Next, a layer of a magnesium oxide forming component is formed around the particles of the above-mentioned combustible pore-forming material as a nucleus, and the particles are granulated so that the average particle diameter is in the range of 0.1 to 10 mm.

The above-mentioned magnesium oxide forming component is preferably a powder having a particle size distribution in which the residue on a 100 mesh sieve is 5% by weight or less, and the residue on a 350 mesh sieve is 5% by weight or less. As such magnesium oxide-forming components, magnesium carbonate, magnesium hydroxide, natural magnesia powder, seawater magnesia powder, activated magnesia powder, powders containing these components, etc. can be used by pulverizing them with a ball mill etc., if necessary. . In the method of the invention, in particular, magnesium oxide-forming components such as natural magnesia powder, seawater magnesia powder, and dust containing active magnesia taken from a rotary kiln during the production of magnesia granules F, comprising: - a particle size distribution as described above; Those that can be used can be suitably used.

By mixing active magnesia with magnesia powder as the above-mentioned magnesium oxide forming component, it is advantageous because the hardening of magnesia particles produced in the firing step described later is accelerated and the yield of the product is also improved. The amount of activated magnesia to be used is not particularly limited, and can be arbitrarily set in consideration of the curability and magnesium oxide content of the magnesia particles to be produced.

To form a layer of the magnesium oxide forming component around the combustible pore-forming material particles, first charge the combustible pore-forming material particles using a suitable granulation device such as a dish-type granulation device, and then -1 It is preferable to carry out this by adding powder of the above-mentioned magnesium oxide forming component. The amount of the combustible pore-forming material is preferably in the range of 5 to 60 parts by weight per 100 parts by weight of the magnesium oxide-forming component. iiJ If the amount of combustible pore-forming material used is less than 5 parts by weight, it may not be possible to obtain a hollow part of sufficient size.
, ffl lit portion, the strength of the formed wall portion is likely to be insufficient.

The above-mentioned layer formation of the magnesium oxide forming component may be carried out by spraying water or an aqueous magnesium salt solution by an appropriate method. By supplying moisture to the particle surfaces of the combustible pore-forming material, the magnesium oxide-forming component easily adheres to the particles, and layer formation can be advantageously carried out. The moisture supply meter may be any amount that produces a viscosity that makes it easy for the magnesium oxide-forming component to adhere to the particle surface of the combustible pore-forming material; ~301″
A clear range of 1-1 parts is sufficient. In the case of spraying an aqueous magnesium salt solution, it is convenient because the magnesium salt serves to help bond the particles of the magnesium oxide-forming component to each other in the firing step to be described later. The amount of the magnesium salt used is 20 parts by weight or less per 100 parts by weight of the magnesium oxide forming component in terms of anhydride. Examples of the magnesium salt include water-soluble magnesium salts such as magnesium chloride and magnesium sulfate.

The particles granulated by the method described above have a two-layer structure in which a layer of magnesium oxide-forming component is formed around the combustible pore-forming material particle as a core, and a layer of the magnesium oxide-forming component is formed all over the periphery of the core. The particles need to have an average particle diameter in the range of 0.1 to 10 mm, preferably 0.3 to 5 mm.
, more preferably in the range of 0.5 to 3 mm. When the average particle size is not within the above range, it is difficult to obtain hollow lightweight magnesia particles having the above-mentioned average particle size, which is not preferable. Further, the ratio of the particle size of the core to the particle size of the particles having the two-layer structure is preferably in the range of approximately 3/10 to 9/10.

Next, after drying the particles having the two-layer structure granulated as described above, they are further fired at a temperature in the range of 1200 to 1800°C to produce hollow lightweight magnesia f.

” The drying of the two layers may be carried out by heating the particles at 100 to 140°C using an air bath, fluidized bed dryer, etc.
This may be done by natural drying.

The above-mentioned calcination can be performed using an oxygen-propane furnace, an electric furnace, a rotary kiln, or the like. The firing temperature is preferably in the range of 1200 to 1800°C, more preferably in the range of 1400 to 1800°C. When the above firing temperature is less than 1200°C,
The magnesium oxide-forming components are not sufficiently sintered and the strength of the wall tends to be insufficient, and if the temperature exceeds 1800°C, the sintering of the magnesium oxide-forming components tends to proceed excessively, resulting in particles with a large specific gravity. Therefore, neither is preferable.

The firing time is generally in the range of 0.5 to 8 hours, more preferably in the range of 3 to 6 hours.

]-In the above-mentioned firing step, the combustible pore-forming material is usually burned and vaporized all at once, and is ejected out of the particles. At this time, small holes may be formed in the wall.

The light 1jl magnesia particles described in 1-1 may be particles having a large number of fine pores in their walls. In this case,
In addition to the hollow parts, a larger number of pores are formed, increasing the porosity of the entire particle and making it even lighter. In addition, the heat insulation or heat retention effect is improved, which is advantageous. The hollow light magnesia particles whose walls are porous are produced by forming a layer of magnesium oxide forming component around the core of the combustible pore-forming material in the manufacturing method described above. It can be manufactured by mixing a finely powdered combustible pore-forming material with a magnesium oxide-forming component.

[Effects of the Invention] Even though the hollow lightweight magnesia particles of the present invention are fired at high temperatures, a sufficiently large hollow portion is formed inside the particles, so that the ratio f of the particles as a whole is Furthermore, the wall formed around the mud hollow has sufficient strength as a heat insulator or heat insulator due to the magnesium oxide crystals being sintered at high temperatures.

Therefore, the lightweight magnesia particles of the present invention can be particularly advantageously used as a heat insulating material suspended on the surface of molten steel, and can also be used for other heat insulation or heat retention purposes such as various heat insulating materials and raw materials for refractories. It can also be suitably used.

Next, examples of the present invention will be shown.

[Example 1] Oil coke is crushed to have a particle size of 2.0 to 3.0 mm.
(lj average particle diameter 28 mm), and natural magnesia clinker (M
Particles tooog were prepared by pulverizing the particles (containing 90% g0) so that the amount passing through a JIS standard sieve of 44 μm (equivalent to 350 meshes) was 190 Blt, i1% or more.

The above-mentioned oil coke particles are put into a dish-type granulator, and then 250 g of a 10% by weight magnesium sulfate aqueous solution is sprayed into the rotating dish-type granulator, and the above-mentioned natural magnesia clinker powder is added in small portions, Particles with a two-layer structure were obtained in which natural magnesia clinker powder was attached to the entire surrounding surface of the oil coke particles to form a layer. The average particle diameter of the layer structure particles was 4 mm.

Next, the two-layer structure particles were dried in a dryer at 110°C for 24 hours, heated to 1450°C over 3 hours in an oxygen-propane furnace, and then fired by maintaining the temperature at 1450°C for 1 hour. Light and heavy magnesia particles were obtained. The average particle diameter of the particles was 4 mm, and the bulk density was 0.6 g/cc.

Arbitrarily take out 10 particles obtained in above, cut each particle on multiple planes, and measure the ・Y wall diameter of the particles and the ・Y wall diameter of the hollow part using a stereoscopic microscope (TS-3 manufactured by Senar ■). When measured using a stereoscopic microscope), the average diameter of the hollow portion was 3/4 of the average diameter of the particles. In addition, when observing the particle surface with a stereomicroscope, it was found that the surface of the particle was densely baked, and it was hardly destroyed by normal mechanical processing such as imaging, mixing, and flow, and had sufficient strength. It was confirmed that the

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the relationship among the diameter of the hollow light IU1 magnesia grains t of the present invention, the diameter of the hollow part, and the thickness of the wall part. 1: hollow part, 2: wall part, R: outer diameter of particle, r: diameter of hollow part, d: thickness of wall part

Claims (1)

[Scope of Claims] 1. Hollow lightweight magnesia particles having an average particle diameter of 0.1 to 10 mm, consisting of a hollow part and a wall part of magnesium oxide formed around the hollow part, wherein the average particle size of the hollow part of the particles is 0.1 to 10 mm. Hollow lightweight magnesia particles having a diameter of 3/10 or more of the average diameter of the particles. 2. A layer of magnesium oxide forming component is formed around particles of combustible pore-forming material having an average particle diameter of 0.05 to 9 mm as a core, so that the average particle diameter is in a range of 0.1 to 10 mm. A method for producing hollow lightweight magnesia particles, which comprises granulating the particles as described above, drying the particles, and then firing the particles at a temperature in the range of 1200 to 1800°C.