JPS6036320A - Preparation of fine powder of silicic acid - Google Patents

Abstract

PURPOSE:To prepare spherical fine powder of silicic acid having minute particle diameters, by feeding a silicon-containing substance to plasma flame, reducing viscosity of formed silicic acid to provide it with fluidity, releasing it to atmospheric pressure. CONSTITUTION:The torch 1 to generate plasma is provided with the non-conductive tubular gas passage ring 2 passing only high frequency, an auxiliary gas such as air, oxygen, nitrogen, argon, etc. is jetted from the feed opening 3 to the interior of the passage ring 2, and simultaneously a raw material for silicic acid is from the inlet 4 for raw material to it. While high frequency is applied to the high-frequency coils 5, 5', and 5'' set at the outside of the passage ring 2, magnetic field is generated in the torch 1, and the discharge plasma flames 6, 6', and 6'' are produced. Formed silicic acid is heated by the plasma flames 6, 6', and 6'', the viscosity is reduced gradually, it is provided with fluidity, released from one end of the passage ring 2 to atmosphere, quenched, atomized, and pulverized silicic acid is collected in the gathering container 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing finely powdered silicic acid using a plasma flame.

Conventionally, fine powdered silicic acid is called white carbon, and is produced by a wet method by hydrolyzing water glass, washing, dehydrating, drying, and pulverizing it, or by heating anhydrous silicic acid with coke in an electric furnace to produce metal. It is produced by a dry method in which silicon or ferrosilicon is obtained, chlorinated to produce silicon tetrachloride, heated and vaporized, hydrogen is added, and air is mixed and burned.

However, all of these finely powdered silicic acids are manufactured from silica as a starting material through complicated processes, and have the disadvantage of consuming a large amount of energy.

'On the other hand, although a method for obtaining fine metal powder or metal oxide using plasma flame, which has recently been put into practical use industrially, has been known, production of fine powder silicic acid by this method has not been carried out.

It is possible to heat silicic acid raw materials at 10,000 to 20,000°
Even if silicic acid is fed into a high-temperature plasma flame, heated and melted, and released into the atmosphere by a plasma jet and atomized, the residence time of the molten silicic acid in the plasma flame is extremely short, and the molten silicic acid does not melt. is the melting point of silicic acid]? 00-2
Since it is released from the plasma flame in a semi-molten state at about .000℃, the shape is not spherical when released, but is irregular, such as a dogleg shape, and the particle size is 30.
It is considered that it is not possible to obtain particles of 10 μm or less, which are the same as the conventional dry method or wet method.

As a result of research based on the above-mentioned knowledge, the present inventors have found that, by configuring the structure as claimed in the claims, it is possible to obtain fine powder silicic acid having a spherical shape and a fine particle size by heating and melting with a plasma flame. was completed.

The present invention will be explained in detail below.

The silicon-containing substance used in the present invention is silica.

Metallic silicon, ferrosilicon dust, organosilicon compounds, silicon alkoxide compounds, etc. can be used, and these silicon-containing substances are heated and melted in a plasma flame. Here, it is most important that the silicic acid produced by the decomposition or oxidation of these silicon-containing substances is allowed to remain in the plasma flame at a temperature that lowers its viscosity and becomes fluid.

When silicic acid is heated, it begins to melt at about 1700°C, but since it is highly viscous at this temperature, if it is released from a plasma flame in this state, it will become spherical in shape, and the viscosity of silicic acid will decrease, making it less fluid. temperature, specifically 2,1
Fine spherical silicic acid can be obtained by heating it to 00°C or higher and then releasing it from a plasma flame.

Further, the higher the heating temperature is than 2,100°C, the more spherical and fine silicic acid can be obtained.

Now, as specific means for retaining silicic acid in the plasma flame to a temperature at which the viscosity of the silicic acid decreases and becomes fluid, various devices shown in the drawings can be considered, for example.

The drawing shows a device for obtaining fine powder silicic acid using a plasma generation device called a tandem plasma, and a plasma generation torch 1 has a cylindrical gas passage ring 2 made of a poor conductor that allows only high-frequency waves to pass through. , Air enters the gas passage ring 2 through the gas inlet 3.

While injecting an auxiliary gas such as oxygen, nitrogen, or argon, a silicic acid raw material is simultaneously introduced from the raw material inlet 4 and transported to the other end of the gas passage ring 2 by the auxiliary gas flow.

Meanwhile, at the same time, high-frequency coils 5, 5', which are provided outside the gas passage ring 2 and are used to generate a plasma flame,
A high frequency voltage is applied from a power supply to 5" to generate a magnetic field in the plasma generation torch 1 and discharge it, thereby generating plasma flames 6, 6.
．． Generate 6.

Here, the silicic acid raw material carried by the auxiliary gas flow is first melted by the plasma flame generated by the first high-frequency coil 5.

Here, the diic acid is still in a semi-molten state and has high viscosity, so
Furthermore, the silicic acid is further heated by the plasma flame generated by the second high-frequency coil 5', and the viscosity of the silicic acid is reduced.
Furthermore, the viscosity of the silicic acid is completely reduced by heating it with a plasma flame generated by the third high-frequency coil 5'', and then the silicic acid is ejected from the other end of the gas passage ring 2 and released into the atmosphere to rapidly cool it. The finely divided silicic acid is recovered in the capture container 7.

Here, three high-frequency coils were installed as a means of reducing the viscosity of silicic acid and retaining it in the plasma flame until it reached a temperature at which it became fluid.
This is an example of a tandem plasma generator that is connected to each other.
When using a dandem type plasma generator, if two or more high-frequency coils are connected, the temperature of molten silicic acid can be increased to 2,100°.
C, and the shape of the atomized silicic acid released into the atmosphere is almost spherical, so it is sufficient to connect at least two high-frequency coils in these various devices, although it depends on the length of the plasma flame. Further, the particle size of the obtained silicic acid can be controlled by adjusting the number of connected high-frequency coils and the flow rate of arc gas. Moreover, it goes without saying that any other plasma generating apparatus may be used as long as it can extend the heating time.

The method of the present invention as described above is capable of obtaining spherical silicic acid with a fine particle size in a simple process, and is industrially useful.

Examples will be explained below.

EXAMPLE Using the apparatus shown in the drawings, 517 ml of air and white silica powder (-150 mesh) were supplied at a supply rate of 100 f/min, and after being melted by a plasma flame, they were captured in a capture container.

Table 1 shows the results.

Example 2 Under the same conditions as in Example 1, white silica powder was used as a raw material and was melted by plasma flame using a plasma generator in which two high-frequency coils were connected to obtain fine powder silicic acid.

The results are shown in Table 1.

Comparative Example Under the same conditions as in Example 1, white silica powder was used as a raw material and was melted by a plasma flame using a plasma generator having only one high-frequency coil to obtain finely powdered silicic acid.

The results are shown in Table 1.

Table 1 By using two or more coils, the particle size of the fine powder silicic acid can be reduced to 5μ or less, and the shape can be reduced to 90% or more.
It was also possible to make it spherical.

[Brief explanation of drawings]

The drawings are explanatory diagrams showing one embodiment of the present invention. 1... plasma generator, 2... gas passage ring,
3. Gas inlet, 4... Raw material inlet 15
15'15"... ・High frequency carp" 1 6 + 6
' + 6"""...Plasma flame, 7...
Capture container.

Claims (1)

[Claims] A method for obtaining finely powdered silicic acid by melting a silicon-containing substance using a plasma flame and releasing it into the atmosphere, comprising: feeding the silicon-containing substance into the plasma flame; The silicon-containing substance is retained in the plasma flame at a temperature at which the viscosity of the silicic acid produced by decomposition or oxidation of the plasma rapidly decreases and becomes fluid, and then released into the atmosphere. A method for producing finely powdered silicic acid.