JPS61133103A - Purification of fine ceramic powder - Google Patents

Abstract

PURPOSE:To remove impurities in the fine ceramic powder selectively and effectively by prepg. acidic slurry of the fine ceramic powder and filtering with a porous membrane having a specified mean pore size. CONSTITUTION:Fine ceramic powder of SiC, Si3N3, etc., contg. impurities such as iron, aluminum, etc. is dispersed in water, stirred after adding HCl and then allowed to stand. The acidic slurry is filtered through an acid-resistant porous membrane having 0.1-1mum mean pore size, and pure water is added to the slurry at the time when a fixed amt. of filtrate is withdrawn from the system. The concentration-water addition is repeatedly performed. The end point of the concentration-water addition procedure is confirmed by measuring the pH or electroconductivity.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for purifying ceramic fine powder.

[Conventional technology]

Ceramics, especially silicon carbide and silicon nitride, have superior heat resistance and high-temperature strength properties compared to metals, and can be used under harsh conditions, so they hold great promise as materials for various mechanical parts and structures. However, it contains impurities derived from the raw materials.

Since these impurities greatly affect the physical properties, it is desirable to remove them as much as possible.

Generally, silicon carbide and silicon nitride are produced by reducing silica sand or derivatives from silica sand such as silicon tetrachloride at high temperatures, but iron, aluminum, etc. contained in silica sand are present as impurities. ing.

Methods for removing these impurities include magnetic separation by adsorption to a magnetic material, dispersion of fine powder in water, addition of acid and decantation, and separation using a filter press, but these methods have the following problems: There is.

When using magnetic force, it is difficult to bring all the fine powder into contact with the magnetic material, so not only is the removal efficiency of iron extremely poor, but it is also impossible to remove iron from aluminum.

In addition, in the decantation method, in the case of acidic slurry, the solid content in the slurry settles relatively easily, so impurities can be removed as a supernatant liquid, but in order to reduce the impurities to a predetermined amount, pure water must be added to the supernatant liquid. The operation of removing the clear liquid must be repeated nine times, and as it approaches the neutral range, the dispersibility of the slurry improves and the solid content becomes difficult to settle, making it difficult to remove the supernatant liquid, making it difficult to remove impurities. There are limits to

The filter press method not only has problems with workability, such as difficult and labor-intensive continuous processing, but also has drawbacks such as clogging of the furnace material and slow filtration rate.

[Problem that the invention seeks to solve]

An object of the present invention is to efficiently remove impurities contained in fine ceramic powder and to produce fine ceramic powder of high purity.

[Means for solving problems]

The inventors of the present invention conducted intensive studies on a method for efficiently removing impurities contained in silicon carbide and silicon nitride fine powders, and found that these fine powders were dispersed in water at a concentration of 5 to 40%, and then the impurities were converted into salts. After adding enough acid to dissolve in water to form an acidic slurry, the average pore size is 0.1.
The inventors have discovered that impurities can be selectively removed without deteriorating the over-containing property by supplying it to a porous membrane of ~1 μm and repeating the concentration-hydration operation, leading to the present invention.

The average pore diameter of the porous membrane used in the present invention is 0.1 to
It is necessary that the amount of milk is 1 μm, preferably 0.3 to 0.5 μm. Porous membranes with an average pore size smaller than 0.1 μm can achieve the purpose of removing impurities, but when filtering with a slug IJ-4 that contains relatively many impurities, the membrane becomes clogged over time and the filtration rate decreases. Significantly decreased.

In addition, in porous membranes with an average pore size larger than 1 μm, it is thought that the dispersion state of slurry particles changes depending on the start of overfeeding, filtration pressure, and other operating conditions, and the amount of impurities. When a slurry is filtered, a portion of the solid content permeates through the filter, making it impossible to remove only impurities in a stable manner. Note that the average pore diameter shown in the present invention is determined by the rejection rate of standard latex spheres.

The acid used in the present invention may be any acid that can react with impurities to produce a water-soluble salt, and hydrochloric acid is usually used.

The material of the porous membrane is polyethylene, polypropylene, poly7
Any acid-resistant material such as vinylizo fluoride 7 can be selected, and is not particularly limited.

The method of the present invention uses a porous membrane with an average pore diameter of 0.1 to 1 μm, and repeats the concentration and water addition operations to convert acidic slurry into neutral slurry and remove impurities. The concentration of is an important factor that greatly influences the impurity removal efficiency. In general, the filtration rate in membrane separation is largely controlled by the preparation of the substance to be filtered, but this slurry 41
The filtration rate in the case of −F does not change much depending on the solid content concentration.

Therefore, in the present invention, it is more efficient to concentrate to a concentration of 45 to 50 in one go. The end point of the concentration-hydration operation is confirmed by measuring pH or conductivity.

〔Example〕

Example 1 40% silicon carbide fine powder containing 1.6% iron
Then, 1.4 Kp of 35% hydrochloric acid was added and left overnight with strong stirring. This thing has a temperature of 28
While controlling the temperature to ~30°C, the inlet pressure 1-aKf/aAG% outlet pressure o, sK is applied to the membrane shown below.
The filtrate was continuously supplied for 48 hours while being returned to its original state under the conditions of ty/cdG, and the -transmittance was measured and the turbidity of the F solution was observed.

■ Polyacrylonitrile hollow fiber ultrafiltration membrane with a nominal molecular weight cut off (hereinafter referred to as CMW) soooo (hollow fiber inner diameter 1.3 mm, φ membrane area 0.1 d) ■ Fluororesin hollow fiber with an average pore diameter of 20.1 μm Type porous membrane (hollow fiber inner diameter 1.1 tmφ, membrane area 0.1 mm)■
Fluororesin hollow fiber porous membrane with an average pore diameter of 0.3 μm (hollow fiber inner diameter 1.1 mφ, membrane area o, xi) ■ Average pore diameter 1
．． Fluorine-containing lipid-based hollow fiber porous membrane of 1 μm (hollow fiber inner diameter 1
．． 1! IJφ, membrane area 0. In? ) Table 1 shows the retention rate of filtration rate defined by the following formula and the presence or absence of turbidity of liquid F by visual observation.

Table 1 Example 2 Table 2 shows the results of carrying out the same operations as in Example 1 except that the iron content was 0.3%.

Table 2 Example 3 2 OL of 2 kg of silicon carbide fine powder s containing 1.2% iron
of water, then 35% hydrochloric acid to 560% of water. After adding and leaving overnight with strong stirring, the average pore size was 0.3 μm.
Fluororesin hollow fiber porous membrane (hollow fiber inner diameter 1.1wφ
, membrane area 0.1/) and inlet pressure 1.5 KqladG
, the temperature was set to 25 to 2 with outlet pressure of 0.5 Kf/dG.
It was supplied under control at 8°C. Slurry pH
was 1.2.

Next, when the furnace liquid t-101 was extracted from the system, the operation of adding pure water of 106 was repeated tl-20 times. During this time, the F solution was completely clear, and the filtration rate was 415 t before knitting.
/Hr -rd, 361 when concentrated to twice the concentration
! , /Hr-go, and no change was observed until the 20th test. In addition, the pH after completing 20 repetitions is 5.
-4, and a part of the slurry was sampled and analyzed for iron content after heating and drying, and the iron content was 510 ppm.

〔Effect of the invention〕

As described above, the method of the present invention can selectively and efficiently remove impurities in silicon carbide or silicon nitride fine powder, and can be removed by a simple operation, so it can be used as a means for purifying ceramic fine powder. It is valid as

Claims (1)

[Claims] (1) After dispersing ceramic fine powder in water in an acidic state to form an acidic slurry, the acidic slurry is mixed with an average pore size of 0.
A method for purifying fine ceramic powder, characterized by selectively removing impurities in a slurry by filtering through a porous membrane of 1 to 1 μm.