JPH02286B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high-purity silica beads using high-purity ultrafine particulate silica as a raw material. High-purity silica beads are used in various applications requiring particularly high purity, such as high-concentration fillers for plastics and raw materials for quartz glass products, and the establishment of inexpensive manufacturing methods is attracting attention. Traditionally, silica beads made from natural quartz or silica have been used for most of these applications, but these are particularly unsuitable for applications requiring high purity. Furthermore, although synthetic quartz produced by known techniques such as a plasma method is used for some purposes, it has not been widely used because it is expensive. Based on these backgrounds, the present inventors conducted development to establish an inexpensive manufacturing method for high-purity silica beads, and as a result, they discovered that they are products of hydrolysis reaction in a flame using a halogenated silicon compound as a raw material. It has been found that it is advantageous to melt commonly used high-purity ultrafine particulate silica at a high temperature immediately after production to obtain desired silica beads. An example of a similar method carried out on a laboratory scale is described in a paper (Bull.Chem.Soc.Jpn., 53, 26-29 (1980)), but this method uses ultrafine silica as a raw material This method is fundamentally different from the method of the present invention in that it is pre-calcined at 1200°C for 3 hours and the particle size is further adjusted. In the method of the present invention, high-purity ultrafine particulate silica produced by hydrolyzing silicon halide in a flame is processed into gas or liquid fuel, combustion-supporting gas such as oxygen or air, or inert gas without pretreatment such as firing. Highly purified silica beads with a particle size of 0 to 250 μm are manufactured by dispersing it in a gas and supplying it to a burner, melting it in a flame, and rapidly cooling it in an air stream. As the raw material, high-purity ultra-fine particulate silica, is required to have agglomerated particle size and dispersibility suitable for the present invention, so high-purity ultra-fine particulate silica is used immediately after production by flame hydrolysis of a silicon halide compound. It is something to do. There are two methods for dispersing high-purity ultrafine particulate silica in a fluid, such as using a screw feeder and using an ejector.
Furthermore, the structures of the burner, combustion furnace (chamber), silica bead collection device, etc. used in the method of the present invention are also common, and are not limited to the method described in this specification. The feature of the method of the present invention is that the particle size distribution and powder characteristics of the silica beads produced by this method can be adjusted to a particle size of 0 to 250 μm by adjusting the powder concentration of high-purity ultrafine particulate silica as a raw material in a flame. This can be adjusted within the following range. As the powder concentration of the raw material high-purity ultrafine silica particles in the flame increases,
The silica beads that are generated become larger in particle size. In addition, if the high-purity silica ultrafine particles used as raw materials are well dispersed and completely melted in a high-temperature flame, the silica beads produced will be spherical; if the melting is incomplete, the silica beads will have an irregular shape. becomes fused particles. In order to take advantage of the characteristics of this method and prepare silica beads with the desired particle size distribution and powder properties, it is necessary to use high-purity ultrafine particles of the raw material that can be easily dispersed in a flame and become molten particles of an appropriate size. Silica is required. If the raw material contains aggregates caused by compaction or moisture absorption, these aggregates may be dispersed or
It passes through the flame without melting and mixes into the product silica beads as coarse aggregated particles, while the raw material ultrafine particles that adhere to the aggregates and pass through the flame become dispersed in the cyclone and cannot be collected. This results in significant raw material loss (decreased product yield). In addition, the particle size distribution and powder properties of the product silica beads are expanded in the direction where the particle size becomes larger than the desired particle size due to the localization of the raw material powder concentration due to these aggregates, and it is not possible to adjust the particle size distribution by changing the raw material powder concentration. It disappears. High-purity ultrafine particulate silica produced by flame hydrolysis is 5 to 10 mm thick after being left to absorb moisture or packaged and sold to the public.
In order to produce silica beads by the method of the present invention, it is necessary to adjust the particles to an appropriate size by some pretreatment as described in the literature cited above. be. However, by directly connecting the silica bead manufacturing equipment according to the method of the present invention to the production equipment for this high-purity ultrafine particulate silica, the particle size distribution can be improved by using the ultrafine particulate silica, which has good dispersibility before moisture absorption and compaction, as a raw material. and silica beads with controlled powder properties can be produced in high yield. This also reduces the cost of packaging and transporting the raw material, high-purity ultrafine particulate silica. Example An experiment was conducted to produce high-purity silica beads using an apparatus as shown in FIG. In this device, fresh high-purity ultrafine particle silica obtained by flame hydrolysis is supplied to a hopper 1. From this hopper 1, high-purity ultrafine particulate silica (0.01 μm) is fed at a constant flow rate into the oxygen airflow supplied from the conduit 10 using a screw feeder. This high purity ultra-fine particulate silica is dispersed in a stream of oxygen within the burner tube. The burner is of a triple tube type, and hydrogen gas is used as fuel in this embodiment. Hydrogen is supplied through a conduit 11 and sent to the combustion section through a central tube 13 and an outer circumferential tube 14. Oxygen in which ultrafine silica particles are dispersed is ejected from the inner tube 15. These gases are burned in a combustion chamber and their oxyhydrogen flame (temperature
At 3500℃), fine particulate silica is melted and silica beads are produced. This high-temperature combustion gas is cooled by secondary air blown from the inlet 16 at the exit of the combustion chamber. Silica beads are Cyclone 5,
Collected by back filter 6, receivers 8, 9
Accumulate in The separated air and water vapor are discharged into the atmosphere by a blower 7. The implementation conditions of each example are listed in Table 1. Also,
100mesh silica beads obtained by cyclone
(147μm), 200mesh (74μm), 325mesh (44μm)
The results obtained are listed in Table 2.

【table】

[Table] Figure 2 shows the relationship between particle size and cumulative weight fraction based on the particle size distribution of each example shown in Table 2. From the above examples and FIG. 2, it can be seen that there is a strong correlation between the powder concentration of ultrafine particulate silica in oxygen gas and the particle size distribution of silica beads. A micrograph of the silica beads obtained in Example 3 is shown in FIG. Experiments were conducted in which the powder concentration of the raw material high-purity ultrafine particulate silica in the flame was adjusted by mixing air into oxygen gas, and the conditions and results are shown in Table 3 as Examples 7, 8, and 9. 4 and 4th
As shown in the figure.

【table】

[Table] Experimental results using liquid fuel are shown as Examples 10 and 11. Kerosene was used as the liquid fuel, and raw material high-purity ultrafine particulate silica was dispersed in a mixed gas of oxygen and air and then supplied into the flame.

【table】

[Table] Tables 5 and 6 and FIG. 5 show the experimental results. Comparative Example For comparison, an experiment was conducted using ultrafine particulate silica as a raw material, which had been manufactured, compressed and packaged, and had absorbed about 2% moisture by being left for one day. The experimental conditions are shown in Table 7, and the obtained experimental results are shown in Table 8. In addition, the values of Examples 3 and 4, which were conducted under the same conditions according to the method of the present invention, are also listed in the table.

【table】

[Table] In the case of Comparative Examples 1 and 2, the collection rate of silica beads by the cyclone was approximately 70% (based on raw material SiO ₂ )
In contrast to the collection rate of about 95% in Examples 3 and 4, a significant loss was observed. In addition, among the collected silica beads with a medium particle size of 147 [μm] or more, no silica beads generated by the intended melting and fusion were found, and almost all of the silica beads were coarse aggregates or sintered particles of the raw ultrafine silica particles. They were fragile particles of matter. These brittle agglomerated particles were also observed in all particle size distribution ranges and caused non-uniform dispersion during filling into plastics and the like. In addition, there was a general tendency for the particle size distribution to expand in the direction of larger particle sizes than in cases conducted under the same conditions (Examples 3 and 4) using raw materials with good dispersibility that had not been consolidated or moisture-absorbed immediately after production. It was done.

[Brief explanation of drawings]

FIG. 1 shows an outline of the manufacturing process of the method of the present invention. 1... Raw material hopper, 2... Screw feeder, 3... Burner, 4... Combustion chamber, 5... Cyclone, 6... Bag filter, 7... Blower, 8... Product bunker, 9... Recovered Raw Material Bunker FIG. 2 shows the particle size distribution of the silica beads of Examples 1 to 6 as a relationship between particle size and cumulative weight fraction based on the data in Table 2. FIG. 3 is a micrograph showing the structure of the silica beads obtained in Example 3. FIG. 4 shows the particle size distribution of the silica beads of Examples 7 to 9, and FIG. 5 shows the particle size distribution of the silica beads of Examples 9 and 10.

Claims (1)

[Claims] 1. High-purity ultra-fine particulate silica produced by flame-gas phase hydrolysis of silicon halide in a method for producing high-purity silica beads by melting high-purity ultra-fine particulate silica at high temperature. Immediately after production, high-purity silica with a particle size of 250 μm or less is produced by dispersing it in a gas or liquid fuel or combustion-supporting gas such as oxygen or air, introducing it into a burner, melting it in a flame, and then rapidly cooling it in an air stream. How to make beads. 2. The method according to claim 1, wherein the particle size distribution is adjusted by adjusting the raw material powder concentration in the flame with air or an inert gas such as nitrogen.