JPS59223217A - Manufacture of fine-grained silicon dioxide - Google Patents

Abstract

PURPOSE:To manufacture fine-grained SiO2 having a sharp particle size distribution by feeding gases each having a specified composition to a concentric double- tubed burner when a volatile Si compound is decomposed in a flame at a temp. above m.p. of SiO2. CONSTITUTION:A volatile Si compound, an inflammable gas and a gas contg. oxygen are fed to the central tube of a concentric double-tubed burner, and the inflammable gas is fed to the jacket tube. The gases are spouted from the burner to form a stable and short flame, and the volatile Si compound is decomposed in the flame at a temp. above the m.p. of SiO2. By this method, fine- grained SiO2 having a sharp particle size distribution can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing fine particulate silicon dioxide by subjecting a volatile silicon compound to a decomposition reaction in a flame. The present invention relates to a method for producing silicon dioxide.

Various methods have been proposed for producing fine particulate silicon dioxide by a so-called dry method in which a volatile silicon compound such as a silicon halide is subjected to a decomposition reaction in a flame. For example, Japanese Patent Publication No. 47-46274 discloses that silicon halide is subdivided into combustible, in particular hydrogen-containing or hydrogen-forming gases and oxygen-containing gases within the range of 700 to 1400°C. A method for producing finely divided silicon dioxide is disclosed by continuously feeding a flame at a temperature below the melting point of the finely divided silicon dioxide.

The present inventors have also conducted intensive research on the production of fine particulate silicon dioxide by decomposing and reacting silicon halides in flames. As a result, they discovered that by subjecting silicon halide to a decomposition reaction at a temperature higher than the melting point of silicon dioxide, fine particulate silicon dioxide with particularly excellent dispersibility and transparency can be easily obtained with a desired specific surface area. However, when silicon halide is decomposed in a flame at such a high reaction temperature, the flame from the burner is generally unstable and long, so the silicon dioxide produced suffers from uneven retention (thermal history). The result is that the particle size distribution of the resulting fine particulate dioxide is not maintained within a narrow range.

Therefore, the main object of the present invention is to decompose silicon halides in a flame at high reaction temperatures to produce finely divided silicon dioxide having a particularly sharp (narrow) particle size distribution.

The inventors of the present invention have carried out intensive development to achieve this objective, and have found that by using concentric double-tube burners and supplying and ejecting gases with specific compositions, a short flame with a more stable and high temperature can be produced. The present invention was completed based on the discovery that That is, in the present invention, when decomposing a volatile silicon compound in a flame at a temperature higher than the melting point of silicon dioxide, the silicon compound, a flammable gas, and an oxygen-containing gas are provided to the center tube of a concentric double tube burner,
The method for producing fine particulate silicon dioxide is characterized in that a combustible gas is supplied to the outer tube.

In the present invention, in order to arbitrarily adjust the specific surface area in the range of 50 to 500 m''7 g and obtain fine particulate silicon dioxide with particularly good dispersibility and transparency, a volatile silicon compound is heated in a flame. It is necessary to decompose the volatile silicon compound at a temperature higher than the melting point of silicon dioxide.Incidentally, when a volatile silicon compound is decomposed at a flame temperature lower than the melting point of silicon dioxide, fine particles having the same specific surface area as above are generated. However, the dispersibility and transparency of the silicon dioxide are extremely poor.

In the present invention, the method for making the decomposition temperature of a volatile silicon compound higher than the melting point of silicon dioxide is generally determined by the gas composition that forms a flame together with the silicon compound and the gas supply temperature. That is, a volatile silicon compound, so that a combustion flame having a predetermined reaction temperature is formed.
A method is adopted in which the raw material gas composition of flammable gas, oxygen-containing gas, and non-flammable gas (if necessary) is determined in advance, and the mixed gas is combusted in a reaction chamber via a burner.

As the volatile silicon compound used in the present invention, silicon halides such as silicon tetrachloride trichlorosilane and dichlorosilane are preferred, and organic halogenated silicon compounds such as trimethylchlorosilane can also be used.

The combustible gas is particularly preferably hydrogen gas that produces water by combustion, or a hydrogen-containing gas, such as methane, propane gas, coal gas, etc. Natural gas and refined petroleum gas are also used. The oxygen-containing gas includes oxygen, air, and the like. As the nonflammable gas, for example, nitrogen gas, carbon dioxide gas, argon gas, etc. are generally used.

Conventionally, silicon dioxide in the form of fine particles has generally been obtained by vaporizing silicon tetrachloride and burning it together with hydrogen gas and air in a flame.

Also in the present invention, in order to form a predetermined high flame temperature using such silicon tetrachloride, hydrogen gas, and air,
Furthermore, it is also recommended to use oxygen gas in combination, or to use silicon tetrachloride with a composition gas such as hydrogen gas-oxygen gas, hydrogen gas-oxygen gas-argon gas, or hydrogen gas-propane gas-air-oxygen gas. A predetermined high reaction temperature can also be achieved by preheating the above-mentioned raw material gas to a temperature of generally ~300°C.

Next, in the present invention, using a concentric double tube burner,
In particular, it is possible to form a flame by supplying a silicon compound, a flammable gas and an oxygen-containing gas to the center pipe of the double-tube burner, and supplying a flammable gas and, if necessary, an oxygen-containing gas to the outer mantle pipe. This is extremely important in order to obtain finely divided silicon dioxide with a uniform (sharp) particle size distribution. That is, in the double tube burner of the present invention, the raw material gas supplied to the center tube is slightly separated from the burner tip to form a stable short flame due to the effect of the flammable gas supplied to the outer tube. . Such a flame contributes to uniformizing the residence time in the high temperature region of silicon dioxide, which is generated by decomposing the raw material silicon compound at a high flame temperature, so that it is possible to obtain silicon dioxide in the form of fine particles with a uniform particle size distribution. It is assumed that

Conventionally, it has been known to use a double tube burner in producing fine particulate silicon dioxide from volatile silicon compounds, combustible gases, and oxygen-containing gases. For example, in Japanese Patent Publication No. 36-3359, for the purpose of preventing deposits of produced silicon dioxide (formation of so-called whiskers) on the burner,
It has been disclosed to allow a flushing gas, in particular air, to flow out of the jacket tube of a double tube burner. However, the conventional method for producing fine particulate silicon dioxide using a double-tube burner is aimed at preventing the formation of whiskers in the burner, as described above, and the present invention's method for producing fine particulate silicon dioxide with a uniform particle size distribution is In other words, by using the double-tube burner of the present invention and setting the flame temperature higher than the melting point of silicon dioxide, it is possible to produce fine particulate silicon dioxide with a uniform particle size distribution. This is a manufacturing method that is essentially different from conventional methods.

The concentric double tube burner in the present invention can be used without any particular restriction on conventionally known double tube burners, and can form a stable and short flame by supplying gases of a predetermined composition to the center tube and the outer tube, respectively. That's fine. In general, a concentric double tube in which an annular gap (slit) is formed at the edge of the burner of the central tube is preferably used. In the present invention, the length of the flame formed from the central tube of the burner by supplying a volatile silicon compound, flammable gas, and oxygen-containing gas is such that the length of the flame formed by supplying the volatile silicon compound, flammable gas, and oxygen-containing gas is controlled by the length of the flame formed from the central tube of the burner. By supplying
It is preferable to shorten it to 74 or less. For this purpose, the slit width of the outer tube in the concentric double tube burner of the present invention is generally designed to be in the range of /200 to 115 with respect to the diameter of the center tube, and the angle of the slit outlet of the outer tube is It is generally preferable to design the angle between 65 and 85 degrees with respect to the vertical direction.

Furthermore, in order to shorten the length of the flame as described above, the outflow velocity of the flammable gas and oxygen-containing gas supplied to the mantle tube at the burner outlet is generally set at 20 m/sac.
In other words, it is desirable to carry out the test at a rate of 30WL/BθC or more.

In this way, the fine particulate silicon dioxide obtained by the present invention has a uniform (sharp) particle size distribution, and as a result, the diameter of aggregated particles in the dispersion medium can be reduced and the particle size distribution of the aggregated particles can be made uniform.

Of course, the concentric double tube burner of the present invention also has the effect of preventing the formation of beards.

Example 1 25□0 single tube (primary burner) K1 exit angle is 70
Attach the outer tube (secondary burner) of °
-Used The slit width of the primary burner and secondary burner is 2.5 times. 8 i Q 14, Hz, O2 and inert gas were supplied at a flow rate of 30 ml sec, and P and air were mixed to the secondary burner at a flow rate of 3 Q ml.
sec to form a 1900°C flame. The supply amount of each of the above gases is 810 N45-9”/h
r-.

Hl 15.5 jL'/hr s, 02 9.
2 m”/hr, inert gas 22.6 tn”/b
It is r.

The generated silica (silicon dioxide) was collected and deoxidized by a known method, then dispersed in water, and the particle size distribution of the aggregate particle size was measured.

The results are shown as (1) in FIG.

In addition, the particle size distribution of the silica agglomerated particle size obtained as a result of carrying out the same procedure using only a single tube burner without using a secondary burner is shown as (2) in FIG.

[Brief explanation of drawings]

FIG. 1 shows the particle size distribution of silica obtained in Examples of the present invention. Patent applicant: Tokuyama Ittatsu Co., Ltd.

Claims (1)

[Claims] 1) When decomposing a volatile silicon compound in a flame at a flame temperature higher than the melting point of silicon dioxide, a concentric double tube burner is used, and silicon is added to the center tube of the double tube burner. A method for producing fine particulate silicon dioxide, comprising supplying a compound, a flammable gas, and an oxygen-containing gas, and supplying the combustible gas to a mantle. 2) Claim 1 in which the silicon compound is silicon tetrachloride
Manufacturing method described in section. 3) The manufacturing method according to claim 1, wherein the flammable gas is hydrogen gas. 4) The manufacturing method according to claim 1, wherein the outer tube has an outlet angle of 60 to 85 degrees with respect to the center tube outlet of the concentric double tube burner. 5) The manufacturing method according to claim 1, wherein the gas flow velocity at the outlet of the outer tube is equal to or higher than the gas flow at the outlet of the central tube.