JPS62294416A - Collecting and recovering method for fine powder of submicron order - Google Patents

Abstract

PURPOSE:To collect and recover formed fine powder in the manufacture of fine powder efficiently by using a collecting and recovering device constituted with an agglomerated and piled layer of fine powder of submicron order. CONSTITUTION:Floating fine powder introduced and formed from a raw gas nozzle 7 of a reaction tube 1 is introduced into a fluidized bed 4 of a fluidized bed type collector 3 through a duct. The fluidized bed type collector 3 introduces nitrogen gas and the like from a fluidized gas introduction tube 6 and forms the fluidized bed 4 of agglomerated particles. Also, at a gas vent of the fluidized bed type collector 3, a spiral agglomerator type collector is installed to prevent fine powder from flying off all over. The device, therefore, is suitable for collecting and recovering non-crystalline fine powder of submicron order such as SiC, Si3N4, SiO2 or the like formed by CVD.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for collecting and recovering submicron fine powder,
More specifically, the present invention utilizes the characteristics of submicron fine powder to achieve simple and effective collection and collection in the gas phase.
Regarding the collection method, for example, it is a method for efficiently collecting and recovering fine powder produced in the production of fine powder by a vapor phase method such as a CVD method.

[Prior art and its problems]

Submicron fine powder has a particle size of approximately several μm to 0.1 μm.
It is a fine powder in the micrometer range, and its behavior is larger than several micrometers.
It is different from the second so-called general powder and also from ultrafine powder of 0.1 μm or less. For ultrafine powders of 0.1 μm or less, the surface energy of each particle such as volume effect and surface area effect cannot be ignored, resulting in changes in physical properties such as a drop in melting point, abnormal crystal structure, and significant increase in reactivity, and van der Waals forces. It acts strongly and particles stick together well, resulting in a powder that has a sticky feel as a whole. On the other hand, powders larger than several μm exhibit powder characteristics such as agglomeration behavior that vary depending on the substance, but the properties reflect the physical properties of the bulk.

Submicron fine powder, which has a primary particle diameter between several μm or less and about 0.1 μm, has a strong cohesive force and does not exist as a primary particle. Further, submicron fine powder has a property that it has a small bulk density, poor fluidity, and is susceptible to powder crosslinking.

One of the major problems in the industrial production of submicron fine powder with such characteristics is the collection and recovery of the secondary product fine powder.

Since it is almost impossible to extract submicron fine powder in its primary particle state, it must be collected and collected by agglomerating it to some extent. A back filter or a wet method in which the material is introduced into a liquid phase and collected is used.

By the way, for example, when submicron fine powder produced by the CVD method is collected and recovered using a fine filter, the differential pressure increases due to clogging, reducing the collection and recovery efficiency and making it impossible to operate for a long time. Not only that, but the loss due to scattering is also large. Further, it is necessary to separate the filter and the fine powder, and this separation work is also extremely troublesome.

In addition, the method using an electrostatic back filter is a method that applies an electric charge to the particles themselves, so there is no increase in differential pressure and the collection efficiency is relatively high, but it is necessary to apply a strong electric field to the transport path depending on the fine powder, making it difficult for industrial This is troublesome, expensive, and has safety issues.

Another method that can be considered is the so-called thermal deposition method, in which fine powder is moved as primary particles from a high-temperature region to a low-temperature region, and the fine powder is agglomerated and deposited.However, even in this case, loss due to scattering is inevitable, and there is a means to prevent loss due to scattering. is necessary. Although the wet collection method has a high recovery rate, a subsequent dry smoke process is required.

[Purpose of the invention]

An object of the present invention is to eliminate the disadvantages observed in the conventional method described in 1. and to efficiently collect and recover submicron fine powder.

[Structure of the invention]

Submicron fine powder aggregates and accumulates due to suspension, collision of fine particles with each other during convection or collision with the container wall surface, electrostatic action due to friction, or cooling from a high temperature area to a low temperature area.

The present invention is a method that utilizes such characteristics of submicron fine powder.

That is, the present invention relates to a method for collecting and collecting submicron fine powder using a collecting and collecting device consisting of an agglomerated and deposited layer of submicron fine powder.

Submicron fine powder has a small bulk density of around 0.2, so even if it is piled up, it will not be compressed and the differential pressure increase due to gas will be extremely small, and moderately agglomerated fine powder will act as a filter against fine powders of the same size. show.

The collection/recovery device in the present invention includes, for example, synthetic resin,
It has a structure in which a rubber tube is coiled around a tubular object, and atomized submicron fine powder is introduced into the tube, and due to the characteristics of the submicron fine powder, the fine powder agglomerates and forms a deposited layer inside the tube. A spiral agglomerator that forms a submicron powder, or a cylindrical tube in which suspended submicron fine powder is introduced, and the fine powder agglomerates and forms a deposited layer due to the characteristics of the submicron fine powder. It is. When agglomerating fine powder and forming a deposited layer on the above-mentioned cylindrical tube, for example, the tube is arranged horizontally so that the formation of the layer can be easily caused, and the floating submicron fine powder is It is preferable to introduce the liquid through an outlet having a diameter smaller than that of the tubular object.

If the diameter of the synthetic resin, rubber tube, or tubular material used for such collection, agglomeration in the collector, and formation of the deposited layer is too large, it is not suitable for forming the agglomerated layer, and the diameter is usually 10. ~50mm is used.

The agglomerated and deposited layer of fine powder thus formed has a small bulk density and forms appropriate pores, and acts as a filter suitable for collecting and recovering submicron fine powder.

In addition, when the agglomeration and accumulation layer of the collection/recovery device is used as a floating fluidized bed, it is usually vertically equipped with a fluidizing gas inlet, a submicron fine powder non-introducing port, a gas outlet, and a fluidizing gas dispersion plate. A predetermined amount of fine powder is put into a cylindrical container, and gas is introduced from the fluidizing gas inlet to cause it to float and fluidize. The suspended and fluidized fine powder exists as secondary agglomerated particles of about 10 to 100 μm. Examples of the fluidized gas distribution plate include those having a structure in which one or more sheets of carbon fiber or the like are arranged on a perforated plate, or those having a structure in which a perforated plate is further arranged on the sheet layer.

The introduction speed of the fluidizing gas introduced to maintain the agglomeration of fine powder and the deposited layer in a stable fluidized state varies depending on the type of fine powder to be suspended or to form a fluidized bed, but the superficial velocity is 3.0 to 10 cn+/sec. is appropriate. 3゜Ocm
If the flow rate is less than 10cm/sea, drifting tends to occur and a stable flow state cannot be obtained, and if it is more than 10cm/sea, the amount of scattering becomes large, which is not preferable. Although this linear velocity range is much higher than the terminal sedimentation velocity (0.icm/sea or less) of submicron-order particles, scattering is suppressed because they aggregate with each other to form secondary particles.

For example, as shown in Figure 2, a fluidized bed collector has a freeboard area (TI) of sufficient height above the fine powder fluidized bed (I) to stabilize the scattered fine powder. It is preferable to provide a part of the reflux section (1) with a diameter larger than the freeboard area to prevent loss of fine powder.

In the method of the present invention, the same layer as the submicron fine powder to be collected is used for the agglomeration and deposition layer as a collection/recovery device. As the fluidizing gas, an inert gas such as nitrogen, argon, helium, etc. is used.

When collecting and recovering fine powder by the method of the present invention, it is preferable from an industrial perspective to adopt a floating or fluidized bed type. Collection and recovery of fine powder by the method of the present invention can be carried out by, for example, CV
It is used by connecting to the fine powder outlet of an apparatus for producing submicron fine powder by method D. If desired, a large number of collectors may be arranged in series to prevent loss due to scattering and improve the recovery rate. Furthermore, by attaching the collector of the present invention to an off-gas purge line, it is possible to collect and recover fine powder that is scattered along with the purge gas. The spiral agglomerator type described above is suitable for this purpose.

A collector used in the method of the present invention will be explained with reference to the drawings.

Figure 1 shows a collection/recovery device according to the present invention attached to an external heating furnace type pulverized powder production apparatus using the CVD method to collect and collect the generated pulverized powder in a fluidized bed, and to prevent scattering loss. An example of an embodiment in which a spiral agglomerator type collector is attached to the gas outlet is shown. FIG. 2 shows a spiral agglomerator type collector, and FIG. 3 shows an example of a fluidized bed type collector. In Fig. 1, 1 is a reaction tube, 2 is a heating furnace 3 is a fluidized bed type collector, 4 is a fluidized bed, 5 is a spiral agglomerator type collector, 6 is a fluidizing gas introduction pipe, and 7 is a raw material gas. Reference numeral 8 indicates an introduction nozzle, 8 indicates a by-product recovery section, 9 indicates a produced fine powder outlet, and 11.1213 indicates a conduit, respectively. In Fig. 2, 21 is a tube made of synthetic resin or rubber, and 22 is a tube made of synthetic resin or rubber.
23 is a gas and fine powder non-introduction port, and 24 is a gas outlet. In Fig. 3, ■ is a fine powder fluidized bed, ■ is a freeboard area, ■ is a coagulation reflux area, 31 is a fluidizing gas inlet, 32 is a port where suspended fine powder is not introduced, 33 is a fluidized gas distribution plate,
Reference numeral 34 indicates a gas discharge port.

According to the collection/recovery method of the present invention, the collection/recovery can be performed with a yield of 90% or more, and there is almost no scattering loss.

Next, an example in which the present invention is applied to an apparatus for producing fine powder using the CVD method will be shown.

EXAMPLE An externally heated reactor equipped with a fluidized bed collector as shown in FIG. 1 was used. Inner diameter 90mm, length 1200m
A vertical tubular reactor equipped with an alumina core tube of 105 m
Hexamethyldisilazane [5i (C113) 31 Nll 529
g/br was introduced into the reactor together with 672 L/hr of ammonia gas and 133 L/hr of nitrogen gas. The reaction proceeded immediately, and the resulting suspended fine powder was introduced into the fluidized bed of the collector through a conduit. The collector contains 1 as fluidizing gas.
000L/hr of nitrogen gas was introduced, and the diameter was 150mm.
A fluidized bed of secondary agglomerated silicon nitride particles with a height of about 250 mm was formed. In addition, a spiral agglomerator or collector is attached to the gas exhaust port of the gas collector to prevent scattering and loss of fine powder. After 10 hours of reaction, 82% of the total produced powder was collected in the fluidized bed and about 10% in the spiral agglomerator collector, respectively. Although film-like substances were observed to form in the temperature range of around 800° C. in the reactor, no contamination into the collector was observed.

〔Effect of the invention〕

The method of the present invention uses amorphous 5i produced by CVD method.
It is suitable for collecting and recovering submicron fine powders such as C1SI3N4 and SiO□, and the collection efficiency is quite high, and the collected and recovered fine powders do not require separation from the collector. This method is extremely advantageous as a method for collecting and recovering fine powder because it can be used as is in the next step of crystallization treatment.

[Brief explanation of the drawing]

Figure 1 shows a collection/recovery device according to the present invention attached to an external heating furnace type pulverized powder production apparatus using the CVD method to collect and collect the generated pulverized powder in a fluidized bed, and to prevent scattering loss. An example of an embodiment in which a spiral agglomerator type collector is attached to the gas outlet is shown. FIG. 2 shows a spiral agglomerator type collector, and FIG. 3 shows an example of a fluidized bed type collector. FIG. 2 shows an example of a spiral agglomerator type collector, and FIG. 3 shows an example of a fluidized bed type collector. ■ is a fine powder fluidized bed, ■ is a freeboard area, ■ is a coagulation reflux area, 1 is a reaction tube, 2 is a heating furnace, 3 is a fluidized bed type collector, 4 is a fluidized bed, 5 is a spiral agglomerator type A collector, 6 a fluidizing gas introduction pipe, 7 a raw material gas introduction nozzle, 8 a by-product recovery section, 9 a produced fine powder outlet, 11.
12 and 13 each indicate a conduit. 21 is a tubular member made of synthetic resin, rubber, or the like, 22 is a tube made of synthetic resin, rubber, etc., 23 is a fine powder non-introduction port, and 24 is a gas discharge port. 31 is a fluidizing gas inlet, 32 is a port where suspended fine powder is not introduced,
Reference numeral 33 indicates a fluidizing gas distribution plate, and 34 indicates a gas discharge port. Patent applicant Mitsubishi Gas Chemical Co., Ltd. Agent Patent attorney Sadafumi Kobori Figure 1

Claims (2)

[Claims] (1) A method for collection and collection of submicron fine powder, which is characterized by using a collection and collection device consisting of agglomeration and accumulation layer of submicron fine powder. (2) The collection/recovery method according to claim 1, wherein the agglomerated or deposited layer is a floating or fluidized layer.