JPH03213142A - Method for purifying particulate material - Google Patents

Abstract

PURPOSE:To obtain a ceramic sintered body having a uniform shape or dimension and high strength at high temp. by applying acid treatment to a ceramic particulate material subjected to classifying treatment, heat treatment and drying in succession and removing unnecessary inclusion to wash and dry the resulting particulate material. CONSTITUTION:A powdery or particulate material being a ceramic raw material is dispersed in a solvent to obtain a suspension which is, in turn, subjected to classifying treatment and applied to a screen having a predetermined mesh size to obtain a particulate material having a desired dimension or shape. Next, this particulate material is treated with an acid to volatilize and remove free carbon, carbon dioxide or carbon monoxide or to convert metal impurity to oxide. Next, the particulate is subjected to acid treatment (treatment with sulfuric acid, treatment with hydrochloric acid or treatment with a mixture of both acids), if necessary, to remove metal impurity or oxide previously formed by the treatment of metal impurity with the acid. Next, a washing process is performed two or more times, necessary, and the washed particulate material is dried to obtain a ceramic raw material as a purified one having a desired shape and/or dimension. By this method, unnecessary inclusion is removed to obtain a ceramic sintered body having a uniform shape and dimension and high strength at high temp.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for refining powder and granular materials, which includes: - removing unnecessary inclusions in the layer details, and producing inorganic, ceramic or non-containing materials with a uniform shape and size; The present invention relates to a method for refining powder and granules that can easily and reliably obtain powder and granules made of oxides.

“Prior Art” In general, raw materials for producing ceramics, for example, are
Obtained by crushing raw ore. At that time, it is necessary to adjust particle size, chemical components, etc. in order to achieve high purity and stabilize quality. For this purpose, the raw material in a pulverized state is subjected to a refining process and is commercially available as powder or granules that meet predetermined specifications.

However, when considering the intended use of commercially available powder or granules that have been purified as described above, they often still contain unnecessary contaminants or the particle size does not meet the desired requirements. . When attempting to obtain a ceramic or sintered body by using the powder or granular material as a base material or reinforcing material without meeting these requirements, the desired characteristics, such as high temperature It becomes difficult to obtain a ceramic sintered body with high strength.

[Problems to be Solved by the Invention] The present invention has been made in order to overcome the above-mentioned disadvantages, and in particular removes unnecessary contaminants from powder or powder raw materials for obtaining ceramics. In addition, the purpose of the present invention is to provide a method for refining powder and granules to obtain a ceramic sintered body that has a uniform shape or size and has high strength at high temperatures by using these powders and granules. .

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a first step of classifying ceramic powder as a raw material, and heating the classified powder. a second step of treating the heat-treated and dried granular material with an acid to remove unnecessary inclusions; and a third step of removing unnecessary inclusions from the powder after removing the unnecessary inclusions. The method is characterized by comprising: a fourth step of washing the granules with water; and a fifth step of drying the washed granules.

[Specific configuration of the invention 1 Powdered or granular materials (including shapes such as spheres, plates, and needles), which are raw materials for ceramics, are dispersed in a solvent to obtain a suspension, which is then classified. .

The raw material classified in this manner is passed through a sieve having a predetermined mesh to obtain a powder having a desired size or shape.

Next, the raw material with the correct shape or size is subjected to an acid treatment step. For example, it is used to volatilize and remove free carbon, carbon dioxide, or carbon monoxide, and it is also used to oxidize metal impurities to form oxides. Next, if necessary, the raw material powder is subjected to acid treatment. Depending on the possible impurities, for example, sulfuric acid treatment, hydrochloric acid treatment, or treatment with a mixed acid thereof is also possible. This removes metal impurities and oxides generated by acid treatment of metal impurities. For example, Al z O3
In order to remove this, sulfuric acid treatment is suitable, and hydrochloric acid treatment can also be used depending on the case. Furthermore, it is also possible to perform sulfuric acid treatment and hydrochloric acid treatment simultaneously or sequentially. This is because it is sufficient that the final product has a certain size and shape and that desired characteristics are obtained after firing.

Next, after repeating the water washing step several times as necessary, it is dried to obtain a ceramic raw material as a purified product having a desired shape and/or size.

[Example 1] The commercially available silicon carbide plate-shaped particles obtained from the boat contained unnecessary inclusions such as free carbon, silicon dioxide, and Al2O3;
It was also confirmed that the shapes and dimensions were irregular.

FIG. 1a shows an electron micrograph of the raw material before classification. In addition, in the figure, the photograph on the left is an enlarged photograph of the raw material where 1 cm is 100 μm, and the photograph on the right is an enlarged photograph of the raw material where 1 cm is 50 μm. Hereinafter, electron micrographs will be shown after classification, oxidation, sulfuric acid treatment, and hydrogen fluoride treatment, and the dimensions of the enlarged photographs are the same as above.

Therefore, as described above, the obtained silicon carbide plate-like particles were dispersed in ethyl alcohol as a solvent to obtain a suspension, and this suspension was classified by water strainer to a particle size of 30 μm. did. In fact, the settling time of a raw material with a particle size of 30 μm was obtained using Stokes' equation. The strained suspension was passed through a sieve with an opening of 15 μm, and the residue on the sieve was dried to obtain desired silicon carbide plate-like particles.

Table 1 shows the chemical analysis results before and after classification in weight percent.

For example, silicon was 62.12% by weight before classification, but increased to 66.32% by weight after classification. This is thought to be due to a relative increase in weight due to the removal of unnecessary inclusions. Furthermore, the aluminum content was 1.56% by weight before classification, but it has become 0.061% by weight. Similarly, for iron, the content was 0.17% by weight, but now it is 0.10% by weight. Furthermore, free silicon dioxide is 0
．． The free carbon is reduced from 87% to 0.49% by weight and from 3.19% to 1.12% by weight.

An electron micrograph after classification is shown in Figure 1.

When compared with the enlarged photograph of the composition of the raw material before classification shown in FIG.

The silicon carbide plate-like particles classified as described above were then subjected to an acid treatment step in order to remove unnecessary inclusions of free carbon and metal. This acid treatment step is achieved by essentially performing a heat treatment at 650° C. for 20 hours. In this case, the content of free carbon was 1.12% by weight after classification, but it was confirmed that the content was reduced to 0.42% by weight after acid treatment at 650° C. for 20 hours. Free carbon combined with oxygen and volatilized as CO2 or CO. In addition, silicon is combined with oxygen to form a 5in2
Furthermore, aluminum is combined with oxygen to form Al2
This is for O3. In fact, free silicon dioxide was contained in an amount of 0.49% by weight after classification, but this increased to 2.10% by weight after acid treatment at 650° C. for 20 hours. This is understood to be that free silicon combined with oxygen to produce silicon dioxide, and that the surface of the silicon carbide platelet particles was oxidized to produce silicon dioxide.

Furthermore, it was subjected to a sulfuric acid treatment step to remove AI and 03. That is, sulfuric acid is introduced into the powder or granules to remove Al2O3, and the sulfuric acid as a solvent is evaporated until it disappears, thereby drying the powder or granules.

In the evaporation to dryness treatment, Al2O3 was removed by heating with an alcohol lamp in a glass beaker.

In this case, there is a concern that sulfuric acid may remain, so
It was subjected to a water washing step until the pH reached 7.

Furthermore, in order to remove silicon dioxide, evaporation to dryness was performed in a platinum dish using hydrofluoric acid. by this,
Unwanted contaminants consisting of oxides such as silicon dioxide were removed. Silicon dioxide is 2.10 after acid treatment at 650℃ for 20 hours.
It was confirmed that the content was 1.76% by weight after treatment with sulfuric acid, and further reduced to 0.05% by weight after treatment with hydrofluoric acid.

After being treated with hydrofluoric acid in this manner, it was subjected to a water washing step. The water washing step may be carried out once over a long period of time, or may be carried out multiple times by repeating drying and washing.

Figure 1C shows an electron micrograph of silicon carbide granules after oxidation, Figure 1d shows an enlarged photograph of silicon carbide after sulfuric acid treatment, and Figure 1e shows hydrogen fluoride treatment. An enlarged electron microscope photograph after treatment is shown.

In addition, if it is confirmed in advance that the silicon carbide plate-shaped particles used as a raw material contain an extremely large amount of iron, a hydrochloric acid treatment step is added to the step after the sulfuric acid treatment.
It is also possible to remove this unwanted inclusion as iron oxide.

[Example 2] A ceramic sintered body was prepared by adding silicon carbide plate-like particles obtained by refining in Example 1 and unrefined silicon carbide plate-like particles to a silicon nitride base material as reinforcing materials, and then , four-point bending strength measurements were performed. Four-point bending strength is JIS R1601
Measured according to the ``Fine Ceramics Bending Strength Test Method''.

A specific example in this case will be described.

First, the matrix and reinforcement were placed in a bot mill and mixed for 24 hours in water or ethyl alcohol to form a mixture. Next, the obtained mixture was dried at 120° C. for 24 hours and passed through a sieve with an opening of 149 μm to obtain a powder for molding.

Next, it was press-formed and fired at a pressure of 200 kg/cm.
I went there. In addition, when the sintering temperature becomes 1700℃ or higher,
Because the decomposition of silicon nitride becomes intense, the N2 pressure is 9.5 atm.
And so.

Table 2 shows the bending strength measurement results of the ceramic sintered bodies thus obtained.

In this table, Example Nos. 1 to 6 indicate ceramic sintered bodies using refined silicon carbide plate-like particles,
Moreover, Comparative Examples Nos. 097 to 12 show experimental results regarding ceramic sintered bodies using unrefined silicon carbide plate-like particles.

As is clear from Table 2, at the bending strengths of 1200°C and 1400°C, the ceramic sintered body using purified silicon carbide plate-like particles with high purity is the same as the ceramic sintered body using unrefined silicon carbide plate-like particles. The strength was higher than that of the ceramic sintered body. In particular, Y203, Y b 20s with high melting point grain boundary phase
The effect was greater in the system with the addition of , and a difference of 154 to 249 MPa in bending strength at 1400°C was observed. This revealed that impurities have an effect on high-temperature strength. That is, it was confirmed that it is effective to use highly purified silicon carbide plate-like particles from which impurities have been removed by purification in order to obtain a ceramic sintered body with high high-temperature strength.

[Effects of the Invention] As can be easily understood from Table 1, nearly half of the unnecessary inclusions such as fine free carbon, silicon dioxide, and Al2O3 were removed by the water droplets. In particular, the removal rate of Al2O3 was extremely remarkable, from 1.56% by weight to 0.061% by weight. Furthermore, acid treatment at 650° C. for 20 hours removed free carbon from 0.061% by weight to 0.048% by weight. On the other hand, in the sulfuric acid treatment step, A1.03 was 0.041% by weight, and it can be understood from Table 1 that the removal rate was extremely remarkable.

Furthermore, it has been found that hydrofluoric acid treatment has a remarkable effect on removing oxides such as silicon dioxide.

The content before classification was 0.87% by weight, but it decreased to 0.05% by weight, which is a significant decrease.

The purified silicon carbide plate-like particles obtained as described above have extremely low unnecessary inclusions, so they have high high-temperature strength and can be used as structural ceramics to further improve quality. I can expect it.

[Brief explanation of drawings]

Figure 1 shows silicon carbide plate-shaped particles before classification, after classification, and after oxidation.
These are enlarged electron micrographs after sulfuric acid treatment and hydrofluoric acid treatment. (Q) Line [ (b) Separate line ≦Mine CXlpm FIG, 1 141m De stone m Procedural amendment (method) % formula % Name of invention Method for refining powder and granular material 3゜Relationship with the case of the person making the amendment

Claims (6)

[Claims] (1) A first step of classifying ceramic powder as a raw material, a second step of heat-treating the classified powder, and the heat-treated and dried powder. a third step of removing unnecessary contaminants by acid treatment; a fourth step of performing a water washing treatment on the granular material after removing the unnecessary contaminants; A method for refining a powder or granule, comprising: a fifth step of drying the powder or granule. (2) The method according to claim 1, wherein the second step is carried out in the air or in an oxygen atmosphere. (3) In the method according to claim 1 or 2, the third step of performing acid treatment includes using an acid selected in accordance with the unnecessary contaminants contained in the powder or granular material in order to remove the unnecessary contaminants. A method for refining powder or granular material, which is a processing step. (4) In the method according to any one of claims 1 to 3, in order to remove silicon dioxide as an unnecessary contaminant contained in the powder or granular material, after the acid treatment step, evaporation to dryness with hydrofluoric acid is performed. A method for refining powder or granular material, characterized by performing the steps. (5) In the method according to any one of claims 1 to 4, the powder or granule containing a non-oxide as an unnecessary inclusion is subjected to an acid treatment after the second step. How to purify the body. (6) The method according to any one of claims 1 to 5, wherein the acid treatment is performed with sulfuric acid, hydrochloric acid, nitric acid, or a mixed acid of a plurality of these.