JPS6135145B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing spherical ceramic particles having excellent sinterability, volume stability and filling properties. Traditionally, the raw materials used to manufacture refractories have been natural minerals or light baked products synthesized from hydroxides.
Hard-fired products and even electrically fused products are known. To manufacture refractories, these raw materials are crushed, adjusted to an appropriate particle size, and a binder is added.
After being molded by any molding method, it may be fired if necessary. The sinterability and volumetric stability of raw materials are important because they greatly affect the quality of refractories, but since sinterability and volumetric stability are contradictory properties, it is necessary to obtain refractories that simultaneously satisfy both properties. It was extremely difficult. In other words, if we take as an example a light fired product made by firing hydroxides such as alumina and magnesia at low temperatures below 1300°C, these are highly active and have excellent sinterability, but on the other hand, they undergo a large amount of heat during firing. causes contraction,
When refractories are manufactured using this raw material, cracking and deformation occur significantly. Therefore, from the standpoint of volumetric stability, the raw materials for producing refractories are mainly either lightly calcined alumina or magnesia hard-baked at high temperatures of 1800°C or higher to form clinker, or molten clinker. It is used. However, since raw materials sintered or melted at high temperatures are inert, ceramic bonds cannot be easily formed when producing refractories;
This method requires a higher firing temperature and has disadvantages in terms of manufacturing cost and time required. On the other hand, in order to satisfy both sinterability and volume stability, it is known to manufacture refractories by blending light-fired materials into fine particles and hard-fired materials into coarse particles; Microcracks occurred between the matrices due to the difference in shrinkage during firing, and sufficient strength could not be obtained. In addition, conventional raw materials have an angular shape because they are made into fine particles by pulverization, resulting in large frictional resistance between particles, which poses difficulties in fluidity during mixing and kneading and filling properties during molding. . The purpose of the present invention is to produce ceramic particles that can satisfy all of the properties of sinterability, volume stability, and filling properties in order to solve the above-mentioned drawbacks of conventional materials. This method of producing spherical ceramic particles is characterized by passing ceramic fine particles through a high-temperature flame with oxygen to make them molten or semi-molten, and then cooling them. The method of the present invention will be explained in further detail. First, we prepare a flame generator that uses combustible gases such as propane, butane, propylene, acetylene, and hydrogen as fuel.
Average diameter 30~100μ, maximum diameter 500μ during high temperature flame of °C
Supply a certain amount of ceramic particles of the following size,
When melted or semi-molten, it becomes spherical due to surface tension, and spherical ceramic particles are obtained by further cooling. Ceramic particles used in the present invention include silicon, titanium, aluminum, chromium,
Compounds such as hydroxides, chlorides, sulfates, nitrates, carbides, organic acid salts, nitrides, etc. of magnesium, calcium, zirconium, etc., or oxides obtained by lightly baking, hard baking, or melting the above compounds. Among these, active lightly calcined oxides are more effective for melting and spheroidizing. Regarding the supply of ceramic particles into the flame, the concentration in the flame [ceramic particle supply amount (Kg)/gas usage amount ( ^m3 )] depends on the chemical composition of the ceramic particles, particle size, and type of combustion gas. Therefore, it is slightly different, but it is operated with 6.0 or lower. When the concentration of ceramic particles exceeds 6.0, the temperature of the flame and the dispersibility of ceramic particles in the flame decrease, and as is clear from Figure 2, the sphericity rate rapidly deteriorates and becomes a true sphere or close to a true sphere. In addition to not being able to obtain spherical particles, a phenomenon of fusion between ceramic particles occurs, resulting in a decrease in product yield. The reason why the spherical alumina particles obtained by the method of the present invention are preferable as a refractory raw material is as follows. Once molten or semi-molten, it has a dense structure and therefore has excellent volume stability. 1 to 10 for cooling after melting or semi-melting
It becomes an active surface state formed by micro-sized crystals, and is highly sinterable between particles. Because it is a spherical particle, there is less frictional resistance between particles.
Therefore, the filling property during molding is good. Next, examples of the present invention and comparative examples thereof will be shown. FIG. 1 is a schematic diagram of the apparatus used in the embodiment of the present invention. 1 is a burner, to which a combustible gas supply pipe 3 such as propane, a ceramic powder supply pipe 4 and an oxygen supply pipe 5 are connected, and the flame Ceramic powder is now gushing out along with 2. Reference numeral 8 is a heat-insulating cover, and a hopper 6 for collecting spherical ceramic particles is provided in front of the cover. Among the spherical ceramic particles, ultrafine particles pass through a duct 7 and are collected by a dust collector. Example 1 Aluminum hydroxide (Al(OH) ₃ =99.78%) was kneaded, molded and dried, and fired at 1300° C. for 3 hours to obtain lightly calcined alumina. This is finely pulverized to a weight average diameter of 30 to 80μ, and the powder concentration is
In step 2.4, a fixed amount of the mixture was fed into a propane-oxygen flame at 2800°C and allowed to cool to produce spherical particles. These spherical particles were classified at 10, 50, and 100μ. In addition, as a comparative example, light calcined alumina (powder before thermal spraying), sintered alumina, and fused alumina were sieved into 10, 50, and 100 μm particles similar to the spherical particles obtained by thermal spraying. The above four types of alumina are 100~50μ40%, 10~50
Mix 30% μ and 30% below 10 μ, add 0.5% of gum arabic as an outer layer, add an appropriate amount of water, mix thoroughly, and form into a 40〓× ^40H cylinder shape under a pressure of 1000Kg/ ^cm2 . did. This is then dried in a high-temperature gas oven.
It was fired at 1650°C for 1 hour and used as a test sample. Table 1 shows the properties of the powder used and the properties of the molded articles.

[Table] As shown in Table 1, sintered and fused aluminas No. 3 and No. 4 have high porosity due to poor sintering activity, while light sintered alumina No. 2 has high porosity. Although the porosity decreased and the molded product became dense, microcracks were observed in the molded product with firing shrinkage of 10% or more, resulting in a decrease in strength. On the other hand, the spherical particles of the present invention are dense and have good filling properties, and furthermore, the surface of the particles is composed of fine fibrous δ-Al ₂ O ₃ and is highly active, resulting in stable volume. A molded product with excellent properties, density, and strength could be obtained. Example 2 Molten spinel (MgO = 28.0%, Al ₂ O ₃ = 71.10
%) to a weight-average diameter of 30 to 80μ and powder concentration.
In step 5.2, a fixed amount of the mixture was fed into an acetylene-oxygen flame at 3300°C and then cooled to obtain spinel spherical particles. These were sieved to 10, 50, and 100μ. A test sample was prepared in the same manner as in Example 1 and fired in a high-temperature gas furnace at 1650°C for 1 hour. Table 2 shows the properties of the powders used as well as the properties of the molded articles.

[Table] As shown in Table 2, similar results were obtained with spinel as with alumina. That is, the sintered and fused spinels of No. 3 and No. 4 have excellent volume stability, but are difficult to sinter and have high porosity. On the other hand, No. 2 lightly calcined spinel was very active and dense, but fine cracks were observed and the strength decreased. On the other hand, the spinel spherical particles of the present invention are dense and have good filling properties, and furthermore, the surface of the particles is composed of fern-shaped crystals of about several micrometers and is extremely active, so they have good volume stability and compactness. A molded product with excellent strength could be obtained.

[Brief explanation of the drawing]

FIG. 2 is a diagram showing the ratio of the amount of ceramic particles supplied (Kg)/the amount of gas used (m ² ) and the spheroidization rate. The spheroidization rate in FIG. 2 was measured by observing 500 to 700 particles with a scanning electron microscope and calculating the number ratio of spherical particles. Here, spherical means that the ratio of major axis/minor axis is 1.0 to 1.3. The conditions for spheroidization in FIG. 2 are as follows. (a) Combustion conditions Propane: 10m ³ /Hr Oxygen: 50m ³ /Hr (b) Particle size of ceramic particles Al ₂ O ₃ : Maximum diameter 210μm, average diameter 30-80μm SiO ₂ : Maximum diameter 210μm, average diameter 30 ~80μm Figure 1 is a schematic diagram of the flame generator used in the method of the present invention, and Figure 2 is the amount of ceramic particles supplied (Kg)/
FIG. 3 is a diagram showing the gas consumption (m ³ ) ratio and the spheroidization rate. 1: burner, 2: flame, 3: combustible gas supply pipe, 4: ceramic powder supply pipe, 5: oxygen supply pipe,
6: Hopper, 7: Duct, 8: Heat shield cover.

Claims (1)

[Claims] 1. The ceramic particles whose concentration (ceramic particle supply amount (Kg)/gas usage amount (m ³ )) has been adjusted to 6.0 or less are passed through a high-temperature flame of hydrocarbon or hydrogen and oxygen to melt or A method for producing spherical ceramic particles, which comprises bringing the spherical ceramic particles into a semi-molten state and then cooling the state.