JPH0790165B2 - Purification method of powder - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for purifying a granular material, and more particularly to removing unnecessary inclusions, and further, morphologically and dimensionally arranged inorganic substance, ceramic or non-oxidized substance. TECHNICAL FIELD The present invention relates to a method for purifying a powder or granular material, which can easily and reliably obtain a powder or granular material.

[Prior Art] Generally, for example, it is obtained by pulverizing a raw material for producing a ceramic, ore ore. At that time, it is necessary to adjust the particle size, chemical components, etc. in order to achieve high purity and stable quality. For this reason, the raw material in a pulverized state is subjected to a refining process and is commercially available as a powder or granular material conforming to a predetermined standard.

However, the powder or granular material as a commercially available product that has been purified as described above, when considered in view of its application, still contains undesired inclusions, or the particle size may not meet the desired requirements. Many. Then, when trying to obtain a ceramic sintered body by using the powder or granular material as a base material or a reinforcing material without conforming to this requirement, a desired characteristic, for example, high temperature and high temperature, may be obtained depending on the amount of impurities, uneven size, etc. It becomes difficult to obtain a ceramic sintered body having strength.

[Problems to be Solved by the Invention] The present invention has been made in order to overcome the above-mentioned inconveniences, and particularly removes unnecessary inclusions from a powder or granular material or a raw material of the granular material for obtaining a ceramic. In addition, it is an object of the present invention to provide a method for purifying a powder or granular material for obtaining a ceramic sintered body which has a uniform shape or size and therefore has high strength at high temperature by using these powder or granular materials. .

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides a first step of classifying a ceramic granular material as a raw material, and heating the classified granular material. A second step of treating, a third step of removing unnecessary inclusions by subjecting the heat-treated and dried powder and granules to an acid treatment, and a powder after removing the unnecessary inclusions It is characterized by comprising a fourth step of subjecting the granular material to a water washing treatment, and a fifth step of drying the water washed particulate material.

[Specific Structure of the Invention] A powder or granular material (including spherical, plate-shaped, needle-shaped, etc.), which is a raw material of ceramics, is dispersed in a solvent to obtain a suspension, which is subjected to a classification treatment. . The raw material thus classified is passed through a sieve having a predetermined mesh to obtain a powder or granule having a desired size or shape.

Next, the raw material having the adjusted shape or size is subjected to an acid treatment step. For example, it is for volatilizing and removing as free carbon, carbon dioxide or carbon monoxide, and for oxidizing metal impurities to form an oxide. Next, if necessary, the raw material powder is subjected to an acid treatment. Depending on the impurities recalled, for example, sulfuric acid treatment, hydrochloric acid treatment, or treatment with a mixed acid of these is also possible. As a result, the metal impurities and the oxide generated by the acid treatment of the metal impurities are removed. For example, a sulfuric acid treatment is suitable for removing Al ₂ O ₃ , and a hydrochloric acid treatment can be used in some cases. Further, it is possible to perform the sulfuric acid treatment and the hydrochloric acid treatment simultaneously or with time. This is because the final product should have a certain size and shape, and the desired properties can be obtained after firing.

Next, the water washing step is repeated a plurality of times as necessary, and then dried to obtain a ceramic raw material as a refined product having a desired form and / or size.

[Example 1] It was confirmed that the obtained commercially available silicon carbide plate-like particles generally contained unnecessary contaminants such as free carbon, silicon dioxide, and Al ₂ O ₃ and were irregular in shape and size. went.

Fig. 1a shows an electron micrograph of the raw material before classification. In the figure, the photograph on the left side is an enlarged photograph with 1 cm being 100 μm, and the photograph on the right side is an enlarged photograph of the raw material with 1 cm being 50 μm. Hereinafter, electron microscope photographs after classification, after oxidation, after treatment with sulfuric acid, and after treatment with hydrogen fluoride are shown. The dimensions of the enlarged photographs are the same as above.

Therefore, as described above, the obtained silicon carbide plate-like particles are
The suspension was dispersed in ethyl alcohol as a solvent to obtain a suspension, and the suspension was classified by a water filter with a particle size of 30 μm. In fact, the time for the raw material having a particle size of 30 μm to settle was obtained by the Stokes equation. The hydrated suspension was passed through a sieve with an opening of 15 μm, and the residue on the sieve was dried to give desired silicon carbide plate-like particles.

Table 1 shows the results of chemical analysis before and after classification by weight%.
For example, with respect to silicon, 62.12% by weight before classification increased to 66.32% by weight after classification. It is considered that this is because the unnecessary inclusions were removed and the weight increased relatively. Furthermore, for aluminum, the content before classification was 1.56% by weight, but now it is 0.061% by weight. Similarly, for iron, 0.17 wt% was changed to 0.10 wt%. Furthermore, free silicon dioxide is 0.87% to 0.49% by weight
Also, the free carbon is reduced from 3.19% to 1.12% by weight.

An electron micrograph after classification is shown in FIG. 1b. It can be easily understood that the morphology is extremely uniform and the size, that is, the particle size is uniform, as compared with the composition enlarged photograph of the raw material before classification in FIG. 1a.

The silicon carbide plate-like particles after being 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 performing heat treatment at 650 ° C. for 20 hours. In this case, free carbon contained 1.12% by weight after classification, but when subjected to acid treatment at 650 ° C. for 20 hours, 0.4
It was confirmed that the amount was reduced to 2% by weight. Free carbon was combined with oxygen to volatilize as CO ₂ or CO. Also,
Silicon is combined with oxygen to form SiO _2, and aluminum is combined with oxygen to form Al ₂ O ₃ .
In fact, the content of free silicon dioxide was 0.49% by weight after classification, but it increased to 2.10% by weight after acid treatment at 650 ° C. for 20 hours. It is understood that this is because free silicon was combined with oxygen to produce silicon dioxide, and that the surface of the silicon carbide plate-like particles was oxidized to produce silicon dioxide.

Further, it was subjected to a sulfuric acid treatment step in order to remove Al ₂ O ₃ . That is, sulfuric acid is caused to flow into the powder or granules to remove the Al ₂ O _3, and the sulfuric acid as the solvent is evaporated to the end to dry the powder or granules. The evaporation to dryness treatment was performed by heating with an alcohol lamp in a glass beaker to remove Al ₂ O ₃ . In this case, it was feared that the sulfuric acid remained, so the washing step was performed until the pH reached 7.

Further, in order to remove silicon dioxide, a dry evaporation process was performed in a platinum dish using hydrofluoric acid. by this,
Unwanted inclusions made of oxides such as silicon dioxide were removed. It was confirmed that the content of silicon dioxide was 2.10% by weight after the acid treatment at 650 ° C. for 20 hours, but was reduced to 1.76% by the sulfuric acid treatment and to 0.05% by the hydrofluoric acid treatment.

After the hydrofluoric acid treatment was performed in this manner, a water washing process was performed. The water washing step may be continued once for a long time, or may be repeated several times by repeating drying and water washing.

FIG. 1c shows an electron micrograph of the silicon carbide particles after oxidation, FIG. 1d shows an enlarged photo of the silicon carbide after sulfuric acid treatment, and FIG. 1e shows the result of hydrogen fluoride. The electron microscope enlarged photograph after a process is shown.

Incidentally, in the case of silicon carbide plate-shaped particles as a raw material, when it was previously confirmed that an iron content was extremely large, a hydrochloric acid treatment step was added to the step after the sulfuric acid treatment,
It is also possible to remove this unwanted inclusion as iron oxide.

[Example 2] Silicon carbide plate-like particles obtained by purification in Example 1 and unpurified silicon carbide plate-like particles were added to a silicon nitride base material as a reinforcing material to produce a ceramic sintered body, and then, The four-point bending strength was measured. The four-point bending strength was measured according to JIS R1601 "Fine Ceramics Bending Strength Test Method".

A specific example in this case will be described.

First, the base material and reinforcement were placed in a pot mill and mixed in water or ethyl alcohol for 24 hours to form a mixture.
Next, the obtained mixture was dried at 120 ° C. for 24 hours and passed through a sieve having an opening of 149 μm to obtain a molding powder.
Then, it was press-molded at a pressure of 200 kg / cm ² and fired. In this case, pressure sintering was applied, but hot pressing was 1a.
The test was performed in a tm N ₂ atmosphere at a pressure of 300 kg / cm ² . When the sintering temperature is 1700 ° C. or higher, the decomposition of silicon nitride becomes severe, so the N ₂ pressure was set to 9.5 atm.

Table 2 shows the bending strength measurement results of the ceramic sintered body thus obtained. In this table,
Examples No. 1 to 6 show ceramic sintered bodies using the silicon carbide plate-like particles obtained by purification, and Comparative Examples No. 7 to 12
Shows experimental results regarding a ceramic sintered body using unpurified silicon carbide plate-like particles. As is clear from Table 2, 12
At bending strengths of 00 ° C and 1400 ° C, the ceramic sintered body that uses refined silicon carbide plate-like particles is higher than the ceramic sintered body that uses unpurified silicon carbide plate-like particles. It was strong. In particular, Y ₂ O ₃ and Yb ₂ O having a high melting point grain boundary phase
_In the system with ₃ added, the effect was large and a difference of 154-249 MPa was observed in the bending strength at 1400 ℃. From this, it was found that impurities influence the high temperature strength.
That is, it was confirmed that the use of high-purity silicon carbide plate-shaped particles from which impurities have been removed by purification is effective for obtaining a ceramic sintered body having high high-temperature strength.

[Effects of the Invention] As is easily understood from Table 1, nearly half of unnecessary free carbon, silicon dioxide, Al ₂ O _{3 and} other unwanted inclusions were removed by hydration. In particular, Al ₂ O ₃ is from 1.56 wt% to 0.061
The removal rate to the weight% was extremely remarkable. Furthermore, the free carbon is 0.0 in the acid treatment at 650 ° C for 20 hours.
It was removed from 61% to 0.048% by weight. On the other hand, it is clear from Table 1 that Al ₂ O ₃ is 0.041% by weight in the sulfuric acid treatment step, and the removal rate thereof is extremely remarkable.

Further, it has been found that the hydrofluoric acid treatment has a remarkable effect on the removal of oxides such as silicon dioxide. What was 0.87% by weight before classification was 0.05% by weight, which is a significant decrease.

The purified silicon carbide plate-like particles obtained as described above have a large amount of unnecessary inclusions, and thus have high strength at high temperature, and further improved quality when used as a structural ceramic. Can be expected.

[Brief description of drawings]

FIG. 1 shows silicon carbide plate-like particles before classification, after classification, after oxidation,
It is a particle structure photograph enlarged with an electron microscope after a sulfuric acid treatment and a hydrofluoric acid treatment.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C04B 35/626

Claims (6)

[Claims] 1. A first step of classifying a ceramic powder or granule as a raw material, a second step of heat-treating the classified powder or granule, and the heat-treated and dried powder. A third step of removing unnecessary inclusions by subjecting the granular material to an acid treatment, a fourth step of performing a water washing treatment on the powdery particles after removing the unnecessary inclusions, and the water washing treatment A fifth step for drying the powder and granules thus obtained, and a method for purifying the powder and granules, comprising: 2. The method for purifying a powder or granular material according to claim 1, wherein the second step is performed in the air or an oxygen atmosphere. 3. The method according to claim 1 or 2, wherein the third step of carrying out the acid treatment is selected corresponding to the unnecessary inclusions in order to remove the unnecessary inclusions contained in the granular material. A method for purifying a powder or granular material, which is a step of acid treatment. 4. The method according to any one of claims 1 to 3, wherein in order to remove silicon dioxide as an unnecessary contaminant contained in the granular material, evaporation with hydrofluoric acid is carried out after the acid treatment step. A method for purifying a powder or granular material, which comprises performing a dry solidification step. 5. The method according to claim 1, wherein the granular material containing non-oxide as an unnecessary inclusion is subjected to an acid treatment after the second step. Purification method of powder and granules. 6. The method for purifying a powder or granular material 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 acids.