JPH04132610A - Production of silicon dioxide powder - Google Patents

Abstract

PURPOSE:To produce SiO2 powder having a specific particle diameter and high purity with simple operation at a low cost by washing metallic Si powder with an aqueous solution of a mineral acid to remove U and Th, introducing the treated metallic Si powder into an O2-containing gas stream and burning the powder. CONSTITUTION:Metallic Si powder is washed with an aqueous solution of a mineral acid to decrease the content of U and Th to <=1ppb each. An aqueous solution of nitric acid of 0.1-5N or thereabout is preferably used as the mineral acid solution at >=50 deg.C or thereabout. The maximum particle diameter and the average particle diameter of the metallic Si powder are preferably about <=100mum and about 1-30mum, respectively. The purified Si powder is supplied from a hopper 4 through a powder-feeding apparatus 5 to a burner 2. The powder is burnt in an O2-containing gas stream in a reaction chamber 10 of a reaction vessel 1. The metallic Si powder is oxidized to SiO2 by this process and the existing impurities are evaporated. The high-purity SiO2 powder F produced by the above process and having an average particle diameter of 0.01-10mum and U and Th content of <=0.5ppb each is recovered with a collector 3 provided with a bag filter 31, a blower 32, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for producing high-purity silicon dioxide powder that can be suitably used as a filler in a encapsulating material for (7) VLSI such as 4M-DRAM. Regarding.

Epoxy compositions heavily loaded with silicon dioxide (silica) powder have been utilized.

However, some silica powders contain large amounts of radioactive elements such as uranium and 1-100% lium, and for this reason,
When a memory is sealed with an epoxy resin composition manufactured using this type of silica powder, there is a problem in that the memory malfunctions due to alpha rays. Therefore, many methods for producing silica powder that do not contain such radioactive elements have been proposed as described below.

For example, JP-A-60-81.011 discloses a method for producing high-purity fused silica using natural high-purity quartz as a raw material, and JP-A-61-190556 discloses a method for producing high-purity fused silica using a high-purity silicon compound as a raw material. A method for producing high-purity silica by sol-gel method or hydrolysis/thermal oxidation, JP-A No. 5
Publication No. 8-168267 describes a method for highly purifying natural high-purity silica by chemical treatment, and furthermore, Japanese Patent Application Laid-Open No. 60-422
Publication No. 1-7 discloses a method for producing high-purity silica by using water glass as a raw material, treating this raw material with an ion exchange resin, and then gelling and firing.

However, the following two types of manufacturing processes for high-purity silica are currently in practical use.

[Sol-gel method]

Alkoxysilane → reaction process → gelation → drying → calcination → pulverization [water glass method] Water glass → reaction process → purification → gelation → drying → calcination → pulverization Therefore, all methods for producing high-purity silica powder are It has the drawback that it requires a large number of man-hours because it goes through a very complicated process, and is cumbersome to operate.

Furthermore, in order to reduce the content of radioactive elements such as uranium in silica powder, the raw material itself must be purified, so conventionally commercially available high-purity silica powder is extremely expensive. There was also the problem of putting it away.

Therefore, it has been desired to develop an industrially advantageous manufacturing method for high-purity silica powder.

The present invention was made in view of the above circumstances, and aims to provide a method for producing silicon dioxide powder that can inexpensively and easily produce high-purity silica powder with a low content of radioactive elements. purpose.

Means and Action for Solving the Problems The present inventor has made extensive studies to achieve the above object, and as a result, has washed metal silicon powder with an aqueous mineral acid solution to reduce the content of uranium and thorium to 1 ppb or less, respectively. After that, by feeding this metal silicon powder into an oxygen-containing air stream and burning it, an average particle size of 0.01 to 0.01 is easily obtained by a one-step method from an inexpensive raw material of metal silicon powder washed with an aqueous mineral acid solution.
] It is possible to produce high-purity silicon dioxide powder with an O micron content of uranium and thorium of 0.5 PPb or less, and the silicon dioxide powder obtained by this method can be used as a filler. 4. Even if the memory is sealed with the epoxy resin composition synthesized using the epoxy resin composition, there is no problem of the memory malfunctioning due to alpha rays.
We have found that it is optimal as a filler for the sealing material of cutting-edge VLSIs such as M-DRAM, and is therefore extremely useful in the semiconductor industry, etc., and have arrived at the present invention.

Therefore, the present invention provides the steps of: washing metal silicon powder with an aqueous mineral acid solution to reduce the uranium and thorium contents to 1 pPb or less, and then supplying the metal silicon powder into an oxygen-containing air stream;
Provided is a method for producing silicon dioxide powder, characterized by producing high purity silicon dioxide powder having an average particle size of 0.01 to 10 microns and a uranium and thorium content of 0.5 ppb or less each by combustion. do.

The present invention will be explained in more detail below.

In the method for producing silicon dioxide powder (hereinafter referred to as silica powder) of the present invention, metallic silicon powder is used as a starting material, and this metallic silicon powder is washed with an aqueous mineral acid solution. In general, metal silicon powder contains impurities such as iron, calcium, aluminum, magnesium, etc., as well as radioactive elements such as uranium and 1-lium at about 5 to 15 ppb.
When silica powder is manufactured using such metal silicon powder as a raw material, uranium or thorium is contained in the silica powder from 2 to 10%.
However, in the present invention, the radioactive elements in the metal silicon powder are reduced to 1 by washing the metal silicon powder with an aqueous mineral acid solution in advance. - minutes, and the uranium and thorium contents can be reduced to 1 ppb or less.

Here, the metallic silicon powder used as a raw material is as follows:
Any material with a quality of 99.5% or higher may be used.

Furthermore, in order to improve the cleaning efficiency with mineral acid aqueous solution, the metal silicon powder is ground in advance using a ball mill, impact grinder, etc., so that the maximum particle size is 200 microns or less and the average particle size is 1 to 50 microns.
It is preferable to use micron powder, and in particular, in consideration of the next step, the combustion step, it is more preferable that the metal silicon powder has a maximum particle size of 100 microns or less and an average particle size of 1 to 30 microns.

Examples of mineral acid aqueous solutions include sulfuric acid and hydrochloric acid.

An aqueous solution of nitric acid or the like is preferably used, and a mixed aqueous solution of these mineral acids may also be used. Note that among these mineral acid aqueous solutions, nitric acid aqueous solution is preferable. This is because even if nitric acid remains in metal silicon, it will be oxidized and volatilized because it will be exposed to high temperatures in the next combustion process.

Furthermore, the acid concentration of the mineral acid aqueous solution is preferably 0.1N or more and 5N or less; if it is less than 0.1N, it may not be possible to remove radioactive elements such as uranium, and if it exceeds 5N, metal silicon and the acid may The yield of silica powder may decrease due to reaction.

In this case, cleaning the metal silicon powder with a mineral acid aqueous solution may be carried out by mixing the metal silicon powder and a mineral acid aqueous solution at room temperature and removing the radioactive elements efficiently, but it is not possible to efficiently remove radioactive elements with a low concentration mineral acid. It is better to react by mixing and stirring at 50°C or higher. Although the reaction time depends on the temperature and the concentration of the metal silicon powder, the radioactive elements in the metal silicon powder can be reduced to IPPb or less in 1 to 20 hours.

After the metal silicon powder is treated with a mineral acid aqueous solution, the mineral acid aqueous solution is removed by centrifugation or filtration, and then washed with ion-exchanged water or pure water. The content of uranium and thorium is reduced to 1 by drying with a dryer or other drying device.
High purity metal silicon powder with pPb or less can be obtained.

Next, in the present invention, the metallic silicon powder thus obtained is supplied into an air stream containing oxygen and combusted to directly produce silica powder.

Here, oxygen gas is normally used as the airflow containing oxygen, but air may also be used in some cases.

Further, the amount of high-purity metal silicon powder supplied into the oxygen-containing air stream is not particularly limited, but is substantially determined by the volume of the reaction chamber, and is usually 5-20 kg/hr.
, preferably 7-1.5 kg/hr.

In this case, combustion is initiated by supplying high-purity metallic silicon powder into an air stream containing oxygen and igniting it with an ignition source. When metallic silicon powder is supplied into an oxygen-containing air stream and combusted in this manner, the temperature of the reaction flame exceeds 2000°C. At such high temperatures, elements or compounds with lower boiling points volatilize preferentially. In other words, the small amounts of uranium and thorium compounds contained in highly purified metal silicon powder become gasified at high temperatures, and the silica powder formed when the metal silicon powder is oxidized cools and changes from a liquid to a solid. At this time, the above-mentioned volatilized radioactive element compounds such as uranium compounds do not enter the bulk of the silica particles and are discharged and separated along with the gas. It is possible to make changes.

In the present invention, in this combustion step, it is more desirable to increase the amount of gas in or after the reaction flame so that the volatilized radioactive element compound is discharged together with the residue. Thereby, the amount of radioactive elements adhering to the obtained silica powder can be further reduced.

According to the production method of the present invention, an inexpensive raw material of metal silicon powder washed with an aqueous mineral acid solution is used, and a pitching method of 0.01~
It is possible to arbitrarily produce spherical silica powder of 10 microns, and high-purity silica powder can be industrially advantageously produced at low cost with simple operations.

Therefore, the high purity silica powder obtained by the production method of the present invention is extremely useful for semiconductor industry and the like. For example, the obtained silica powders of various particle sizes can be combined and mixed to form a close-packed structure and used as a filler for epoxy resins, silicone resins, etc., and such compositions can be used for 4MDRAM etc. It is ideal as a sealing material for cutting-edge VLSIs, does not cause soft errors, and has low linear expansion. In addition, it can be used more widely by using it together with high-purity silica powder obtained by ordinary pulverization.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 4, Comparative Examples] After washing the metal silicon powder raw materials shown in Table 1 with an aqueous mineral acid solution under the conditions shown in Table 1, the metal silicon powders were introduced into the apparatus shown in the drawings to produce silica.

Here, this apparatus has a reaction chamber 1. A combustor 2 is provided on the two sides of the reaction vessel and communicates with a part of the reaction chamber 10J, and a combustor 2 is provided on the side of the reaction vessel 1 and communicates with the lower part of the reaction chamber 10. A collection device 3 and a hopper 4 into which the metal silicon powder washed with the mineral acid is charged.
and a powder supply device 5 that supplies the powder in the hopper 4 to the combustor 2.

As shown in an enlarged view in FIG. 2, the combustor 2 is provided in the center, and has a powder supply passage 20 opening to the reaction chamber]-〇, and a powder supply passage 20 provided coaxially with the powder supply passage 20, which is provided in the reaction chamber. ] A first oxygen supply path 21 opening in a ring shape to the reaction chamber 10, a first LPG supply path 22 provided coaxially outside the first oxygen supply path 21 and opening in a ring shape to the reaction chamber 10, 1. L
A cooling water passage 23 which is coaxially provided outside the PG supply passage 22 and through which cooling water (A) circulates, and a cooling water passage 23 which is coaxially provided outside the cooling water passage 23 and opens into the reaction chamber 10 in a ring shape. It is composed of a second LPG supply path 24 and a second oxygen supply path 25 that is coaxially provided outside the second LPG supply path 24 and opens into the reaction chamber 10 in a ring shape.

Here, from the powder supply path 20, the metal silicon powder (B) sent from the inside of the hopper 4 via the powder supply device 5 is supplied with air (
C). In this case, the amount of air supplied is 3 to 4 N m1/hr, and the amount of metal silicon powder supplied is 6 to 7 kg/hr. Furthermore, the first oxygen supply path 2
Oxygen gas (D) is supplied into the reaction chamber 10 from the first and second oxygen supply paths 25 at a rate of 17 Nrn'/hr and 10 Nrn'/hr, respectively.
It is supplied at a supply rate of rri'/hr. Also, the first
L from the LPG supply path 22 and the second LPG supply path 24
PG (E) respectively], 5Nm/hr and ]-,
It is supplied at a supply rate of ONm'/hr.

The collection device 3 includes an exhaust pipe 30 whose one end opens into the reaction chamber 10, a bag filter 31 provided at the other end of the exhaust pipe 30, and a blower 32. The exhaust gas in the chamber 10 is sucked and exhausted, and the generated silica powder (F) is collected. Note that due to the suction of the blower 32, the inside of the reaction chamber 10 is 5 to 1.0 +
+nn Aq Maintained at negative pressure.

Using the apparatus configured as above, oxygen scum and LPG
A predetermined amount of the powder was flowed into the reaction chamber to form an ignition flame, and then metal silicon powder was ejected from the powder supply path 20 into the flame to form a reaction flame.

As a result, the metallic silicon powder was oxidized to form silica powder. The silica powder collected in the bag filter 31 was sampled and its particle size and radioactive element content were measured. The measurement results are shown in Table 1.

Table 1 From the results in Table 1, according to the production method of the present invention (Examples 1 to 4), it was possible to obtain high purity silica powder containing 0.5 ppb or less of each of the radioactive elements uranium and 1 helium. It was confirmed that it can be done.

[Brief explanation of drawings]

FIG. 1 is a schematic structural explanatory diagram of a silica manufacturing apparatus used in a manufacturing method according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a main part of a combustor section thereof. ]・Reaction vessel 3...Collection device 5・Powder supply device 21.25・・Oxygen supply section 22.24・・LPG supply path 23・・Cooling water path 2・・Combustor 4・・Homper 20...Powder supply path

Claims (1)

[Claims] 1. After washing the metal silicon powder with an aqueous mineral acid solution to reduce the uranium and thorium contents to 1 ppb or less, the metal silicon powder is fed into an oxygen-containing air stream and burned to reduce the average particle size to 0. 1. A method for producing silicon dioxide powder, the method comprising producing highly pure silicon dioxide powder having a particle size of 0.01 to 10 microns and a uranium and thorium content of 0.5 ppb or less.