JPS61191514A - Production of silicon dioxide - Google Patents

Abstract

PURPOSE:To produce high-quality SiO2 without by-producing hydrogen chloride by subjecting alkoxysilane to a vapor phase thermal decomposition in the pesence of ammonia. CONSTITUTION:A homogeneously mixed gas of alkoxysilane having the formula RnSi(OR')m, (wherein R and R' are a alkyl, aryl or phenyl radical; n is 0-3; m is 4-n), ammonia and inert gas or non-oxidative gas is introduced into an external heating-type reaction column and said mixed gas is subjected to the vapor phase thermal decomposition at >=800 deg.C, thereafter SiO2 obtained by collecting in a collector is heated at about 400 deg.C for about 3hr to remove its volatile components and then to obtain the globular SiO2 having <=0.1mu particle diameter. Consequently, the counterplan or corrosion of the apparatus and the use of high-class material are unnecessary because hydrogen chloride is not by-produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing silicon dioxide. More specifically, the invention relates to a method for producing silicon dioxide, which is characterized by subjecting alkoxysilane to gas phase thermal decomposition in the presence of ammonia.

[Industrial application field]

Silicon dioxide is widely used in industrial fields such as ceramics. In recent years, ultrafine particles of silicon dioxide with a particle size of several microns or less have attracted attention as a new material because they have a large specific surface area and high surface energy, so they have good properties such as sinterability. Silicon dioxide is also used as a raw material for producing silicon carbide and silicon nitride.

[Conventional technology]

Conventionally, the following methods are known as main methods for producing silicon dioxide.

(1) A method of thermally decomposing vapor of a silicon halide compound in oxygen and hydrogen, (2) A method of thermally decomposing an organic silicon compound, and the like are known.

[Problem that the invention seeks to solve]

However, each of these methods has the following problems that must be solved.

Regarding (2), the raw materials are expensive. Regarding (1), extremely fine and high-purity silica can be obtained, but metals are likely to be mixed in due to corrosion due to the hydrogen chloride gas generated at the same time, which requires some ingenuity in the equipment. There is a possibility of contamination.

The present inventors conducted intensive research on obtaining silicon dioxide that does not contain metals or chlorine without producing hydrogen chloride as a by-product in a method for producing silicon dioxide by gas phase reaction. The present invention was completed based on the discovery that silicon dioxide can be obtained by thermal decomposition in the presence of silicon dioxide.

[Means for solving problems]

The raw materials used in the method of the present invention are produced in large quantities and at low cost, and are also used in large quantities in the silicon industry and the like.

Furthermore, according to the present invention, since the raw materials used do not contain chlorine, unlike conventional gas phase reactions, hydrogen chloride is not produced as a by-product. Therefore, the method of the present invention has advantages such as preventing corrosion of the equipment and not requiring the use of high-grade materials.

Furthermore, since the raw materials can be easily purified by operations such as distillation or sublimation, the products obtained by the method of the present invention have extremely high purity.

In the method of the present invention, the general formula is RnSi as a raw material.
(OR') m (wherein R and Ro are alkyl groups,
It is an alkoxysilane represented by an allyl group or a phenyl group, n is an integer of 0 to 3, and m is an integer of 4 to n.

Examples of the compound represented by the above general formula include the following compounds.

(CH+0)4Si% (CJsO)asi, CH
35i (OCHz)+, (CH:+)zsi(OCRj
)z These raw materials are refined to extremely high purity by ordinary distillation, sublimation, etc. Furthermore, when supplying to a gas phase reaction, two or more of these raw materials may be mixed.

These raw materials are gasified in advance and introduced into the reactor, and at the same time ammonia is mixed with an inert or non-oxidizing gas such as hydrogen, argon, helium, etc. and supplied. Although the amount of ammonia varies depending on the raw materials used, it is usually appropriate to supply the amount of ammonia at least 10 times the amount of the alkoxysilane.

The reaction between alkoxysilane and ammonia at high temperatures is not clear, but ammonia decomposes rapidly at temperatures above 1000°C, and hydrocarbons have been detected from off-gas analysis of the reaction. ) It is thought that active species such as N1 (2) attack carbon and a chain reaction progresses. On the other hand,
In a gas phase reaction involving only nitrogen or hydrogen, carbon is precipitated together with silicon dioxide. Therefore, if the amount of ammonia used is small, carbon will be mixed into the product, which is not preferable. Moreover, if the amount is too large, ammonia will be consumed unnecessarily, which is not economically desirable.

In addition, entraining hydrogen is effective in discharging the carbon components of alkoxysilanes out of the system as hydrocarbons such as methane and ethane through hydrolysis, and inert gases such as argon and helium are used as raw materials in the reaction. This is important for changing the partial pressure and controlling the reaction time.

In the method of the present invention, it is appropriate to select the reaction temperature at 800°C or higher; if it is lower than 800°C, the reaction progresses insufficiently, resulting in a small amount of product, which is not preferred.

The partial pressure of the raw material gas is preferably 0.01 to several atI11, and the reaction time is preferably 120 to 0.01 sec.

When the partial pressure of the raw material gas is greater than these values or when the reaction time is shorter than these values, the reaction may not substantially proceed or the amount of carbon may increase in the product, which is not preferable.

For example, when the raw material is a liquid, the specified ammonia and an inert gas or non-oxidizing gas are sufficiently and uniformly mixed and then introduced into an externally heated reaction tube. A flow-through type, such as an empty column or a packed column type, is used, but it is important to have a structure in which the gas flow is heated uniformly without pulsation or irregular pulses in order to obtain uniformity of the produced fine powder.

After cooling, the fine powder produced is guided to a collector. As the collector, a commonly used filtration type dust collector, electric dust collector, cyclone, etc. can be used as appropriate.

By further heating the resulting fine powder at 400'C for 13 hours, it is possible to remove volatile components. The obtained silicon dioxide was found to be spherical particles of 0.1 micron or less by scanning electron microscopy.

Further, no peak was observed in X-ray diffraction, indicating that the material was amorphous.

〔Example〕

Example 1゜The temperature of the electric furnace was maintained at 1200°C using a device consisting of a high-purity alumina reaction tube with an inner diameter of 25 mm and a length of 700 mm installed in an electric furnace and a collector attached to the outlet of the reaction tube. . Tetramethoxysilane gasified in advance in a preheater, NH3 and Ar (volume ratio 0.7:7:10)
) were mixed well, and then introduced into a reaction tube and reacted.

The resulting fine powder obtained in the collector was filled into an alumina tube and heat-treated in air at 400° C. for 3 hours.

This fine powder was identified as silicon dioxide based on the following facts.

Elemental analysis values were 0% carbon, 0.4x hydrogen, and 1.4x nitrogen, and strong absorption at 1060 cffi-' was observed in the infrared spectrum.

The obtained silicon dioxide was found to be amorphous by X&1 diffraction, and was spherical particles with a particle size of 0.1 micron or less.

Example 2 The procedure described in Example 1 was repeated, except that 0.61 i of tetraethoxysilane was used instead of 0.71 i of tetramethoxysilane, and 9β/hr was used instead of NH311/hr.

This fine powder was identified as silicon dioxide as follows.

The elemental analysis values are carbon 0%, hydrogen 0%, nitrogen 0.6χ, and the infrared spectrum is 800% due to 5i-0 vibration.
Broad absorption of ell- and strong absorption of 1060c and -' were observed.

The obtained silicon dioxide was found to be amorphous by X-ray diffraction, and was spherical particles with a particle size of 0.1 micron or less.

Claims (1)

[Claims] A method for producing silicon dioxide, characterized by vapor-phase thermal decomposition of alkoxysilane in the presence of ammonia.