JP2699304B2 - Ultra fine powder production equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an apparatus for producing ultrafine powders of metals and ceramics utilizing a gas phase thermochemical reaction.

[Conventional technology]

Conventional ultrafine powder production technology by gas phase thermochemical reaction is the fifth
Figure (H. Lamprey and RLRipley; J. Electrochemical Soc
As shown in Society, 109,713 ('62) and Fig. 4 (JP-B-59-7775), a vaporized metal compound and a reactive gas (usually hydrogen)
Are reacted at normal pressure (atmospheric pressure) or higher.

In these reactors, the vapor of the vaporizable metal compound and the gas reacting with the vapor are mixed and then reacted in the gas phase (homogeneous phase) to form atoms of metals and ceramics,
It is considered that molecules are generated and nuclei are generated by their association (aggregation), and further, they grow into ultrafine particles by the association between nuclei and a precipitation reaction on the nuclei. (Yoshizawa, Otsuka; Journal of the Society of Powder Engineering, 21,759 ('84)) The particle size can be controlled by adjusting the concentration (partial pressure) of the easily vaporizable metal compound. Need to be diluted.

However, since these are all performed at normal pressure, the concentration of the reaction gas is large, nucleation and growth progress rapidly, and it is extremely difficult to obtain ultrafine particles of a certain size or less determined according to the reaction. there were.

For example, in the gas phase hydrogen reduction of cuprous chloride, under normal pressure, even if a large amount of argon gas is used for dilution, 0.06
This is the minimum average particle size at which about μm can be obtained.

0.02μm for iron ultra fine powder by hydrogen reduction of ferrous chloride,
For titanium dioxide obtained by oxidation of titanium tetrachloride, the thickness is about 0.04 μm. Using a large amount of dilution gas is economically
Not only is the price of the gas added to the cost, but the heating and cooling also have a factor that further increases the cost. There are also attempts to suppress the growth of particles by quenching to obtain a smaller particle size,
It is technically difficult to rapidly cool from a high-temperature reaction zone. For example, if a cooling plate is provided, there is a problem that powder adheres to the cooling plate, and heat loss is large.

[Problems to be solved by the invention]

In order to make nucleation relatively easy, suppress growth of nuclei, and obtain ultrafine particles having a small particle size, it is necessary to reduce the probability of nuclei coalescing. For this purpose, the reaction system has conventionally been diluted with an inert gas.

Heretofore, when a reaction is excited using plasma or laser, it has been necessary to reduce the pressure of the reaction system in order to control the plasma or laser.

However, in the case of a chemical reaction caused by thermal excitation, coating by reduced pressure CVD has been performed, but reduced pressure has not been performed when producing powder.

 It is for the following reasons.

B) It is not easy to recover ultrafine powder under reduced pressure.

B) There is a problem in the maintenance of the vacuum pump, and it is difficult to realize it. In other words, in order to generate ultrafine powder by thermochemical reaction under reduced pressure, a pump of some type is necessary, but technical problems such as clogging and abrasion due to mixing of powder into the pump and problems of corrosion by reaction gas are required. There is.

The present invention solves such a problem, and focuses on reducing the coalescence of nuclei and suppressing grain growth by reducing the pressure of the system and performing the reaction at a low pressure, and determining the pressure reduction conditions and equipment conditions. It is an object of the present invention to provide an apparatus for producing ultrafine powder.

[Means for solving the problem]

The present invention has been made in order to solve the above problems, and has a reactor for reacting a reaction gas with a vaporized metal compound, a heater for heating the reactor, and a final heater disposed downstream of the reactor. A multi-stage ultra-fine powder recovery device having a fine filter in a stage, and a liquid that is disposed downstream of the multi-stage ultra-fine powder recovery device and that is inert to or absorbs the reaction gas of the gas phase chemical reaction is used. And a liquid ring vacuum pump.

In this apparatus, the inside of the reactor is kept at 500 Torr to 50 Torr.
It is preferable to provide a device for maintaining the state of r, since an ultrafine powder can be efficiently produced under such reduced pressure.

[Action]

To solve the problem of the collection and blockage of the ultrafine powder, a multistage recovery device is used, and a filter with a fine opening is used in the final stage so as to complete the recovery of the ultrafine powder.

For pump corrosion, a liquid that does not interact with the reaction gas is used for the pump, or a liquid that absorbs the reaction gas is used. For example, in the case of a reaction that generates hydrochloric acid gas, a hydrochloric acid gas may be absorbed using a water ring pump, a part may be taken out while circulating the absorbing solution, and fresh water may be added.

When chloride is used as the easily vaporizable metal compound, a water ring pump is suitable for realizing the present invention,
There is not much problem even if there is some mixing of powder.

〔Example〕

FIG. 1 shows the configuration of an apparatus according to an embodiment of the present invention. Downstream of the reactor 8 for performing a gas phase chemical reaction, there are provided several stages of filters 11 such as a first stage dust collector, a second stage dust collector, a reaction product removing device, and a vacuum pump 12 is connected downstream thereof. I have. A pressure regulating valve for introducing a reaction gas 1 and a carrier gas 2 is provided upstream of the reactor. The reaction product removal device shown in FIG. 1 may not be necessary in some cases.

FIG. 2 shows a more specific example of FIG. A carrier gas 2 for transporting the vaporizable metal compound and a reaction gas 1 reacting with the vaporizable metal compound in the gas phase are introduced into the vaporization section inlet and the reactor 8 through the flow meter 3 and the pressure regulating valve 4 respectively. I do. In the reactor 8, an easily vaporizable metal compound is stored in the container 5. The electric furnaces 6 and 7 heat the reaction atmosphere. The ultrafine powder generated by the reaction is cooled by the water cooling unit 9 and collected by the filter 11.
Although FIG. 2 shows only one stage of the filter 11, the present invention has a multistage configuration. The remaining reaction gas, carrier gas, unreacted easily vaporizable metal compound, and product gas that have passed through the filter 11 are supplied to a vacuum pump 12 as shown in FIG. It is sucked by the provided aspirator 13.

The pressure of the reaction system is reduced by the action of the vacuum pump 12, but a part of the gas may be absorbed in the liquid by the liquid circulated by the pump 14.

The degree of pressure reduction is determined by the degree of opening of the pressure control valve 4, the size of the reactor 8, the capacity of the vacuum pump 12, and the like. In the case of a reaction that generates a condensable gas, a trap may be provided to remove the condensable gas, and then a vacuum pump may be used.

Further, the powder is preferably collected as it is in the liquid used for the vacuum pump.

Regarding the degree of pressure reduction, the effect of reducing the particle size of the generated ultrafine powder produced using the apparatus of the present invention is remarkable at 500 Torr or less, and the effect of reducing the particle size is reduced below 50 Torr, but the effect is substantially significant. It does not reach a certain ultrafine powder generation rate. Therefore, the specification of the decompression device attached to the reactor of the present invention was specified to be 500 to 50 Torr.

In addition, under reduced pressure, the flow in the reactor becomes uniform,
There is an advantage that the shape and particle size distribution of the particles are made uniform, and the amount of adhesion to the reactor is reduced.

Example 1 Copper ultrafine powder was experimentally produced using the apparatus shown in FIG. 1 using cuprous chloride as an easily vaporizable metal compound, hydrogen as a reactive gas, and Ar as a carrier gas. Hereinafter, the symbol N1 /
The minute indicates the gas flow rate per minute when converted to normal temperature and normal pressure.

Water was used for the circulating fluid of the aspirator. First, without reducing the pressure of the system, the temperature of the vaporization section: 900 ° C The temperature of the reaction section: 1000 ° C Argon gas flow rate: 4N1 / min Hydrogen flow rate: 2N1 / min The average particle size of the copper ultrafine powder obtained in a slightly pressurized state (about 0.01 atm) by the deposition of was 0.1 μm.

Next, an aspirator was connected, the amount of water circulated and the valve 4 were adjusted to adjust the pressure in the reaction tube to 500 Torr, and the other conditions were the same to produce ultrafine copper powder. The average particle size was 0.05 μm. When the pressure in the reaction tube was 600 Torr, the average particle size was 0.09 μm.

Example-2 Temperature of vaporization section: 900 ° C Temperature of reaction section: 1000 ° C Argon gas flow rate: 2N1 / min Hydrogen gas flow rate: 1N1 / min When the system was set to 50 Torr, hydrogen reduction of cuprous chloride The average particle size of the copper ultrafine powder was 0.03 μm. At this time, the ultrafine powder generation rate was 0.1 g / min, but the pressure was further increased by 30 Tor.
Assuming r, the production rate was reduced to 0.06 g / min.

Example 3 Using the same apparatus as in FIG. 1, tin tetrachloride was used as an easily vaporizable metal compound, and this was reacted with steam to produce ultrafine tin oxide particles.

Tin tetrachloride is liquid at room temperature and has a high vapor pressure, and a sufficient amount is vaporized at room temperature. Therefore, while vaporizing at room temperature, 4N1 /
Minutes of argon gas. On the other hand, water vapor as a reaction gas was generated at 0.2 N1 / min (0.15 g / min), transported with argon gas at 0.2 N1 / min, and led to a reaction section at 800 ° C.

When no decompression device was used, ultrafine tin oxide particles having an average particle size of 0.07 μm were obtained, but the average particle size became 0.02 μm by reducing the pressure to 280 Torr. In order to obtain an even smaller particle size under normal pressure conditions, the carrier gas Ar of tin tetrachloride was set to 10N1 / min, and the carrier gas of steam was changed to 0.8N1.
/ Min, but the average particle size of the obtained ultrafine powder is 0.04
Stopped at μm.

Example-4 Titanium dioxide was produced using the same device as in FIG.
Titanium tetrachloride is evaporated at room temperature, and argon gas flow rate 2N
It was transported to the reaction section together with 1 / min, while oxygen as a reaction gas was set at 1N1 / min.

At normal pressure at a reaction temperature of 1100 ° C, the average particle size is 0.15
However, when the pressure was reduced to 300 Torr, the size was reduced to 0.06 μm.

Example-5 To produce Fe-Co-based magnetic powder, ferrous chloride and cobalt chloride were evaporated in an Ar gas stream at a temperature of 1000 ° C. in a vaporizing section.
(Total of 4N1 / min of carrier gas) and 2N1 / min of hydrogen. At normal pressure, at an evaporation temperature of 1000 ° C and a reaction temperature of 1000 ° C, the resulting powder was 0.08 µm, and the Hc (coercive force) of these powders was only 540 Oersteds. Became 0.04 μm, and Hc rose to 1250 Oersted. This is suitable as a powder for a magnetic tape.

〔The invention's effect〕

According to the apparatus of the present invention, it is possible to easily obtain ultrafine metal and ceramic powder having a small particle diameter, which has been extremely difficult by the conventional gas phase thermochemical reaction method.

[Brief description of the drawings]

1 and 2 are explanatory views showing the configuration of an apparatus for producing ultrafine powder of the present invention, FIG. 3 is a cross-sectional view showing a structural example of a liquid ring pump,
FIG. 4 and FIG. 5 are explanatory views showing a conventional ultrafine powder production apparatus. DESCRIPTION OF SYMBOLS 1 ... Reaction gas 2 ... Carrier gas 3 ... Flow meter 4 ... Pressure control valve 5 ... (Evaporable metal compound) container 6 ... (Evaporation part heating) Electric furnace 7 ... (Reaction part heating) Electric furnace 8 ... Reactor 9 ... Water cooling unit 10 ... Stop valve 11 ... Filter 12 ... Vacuum pump 13 ... Aspirator 14 ... (Liquid circulation) pump 15 ... Evacuation after gas treatment 16 ... Pressure gauge

Claims (2)

(57) [Claims] 1. A reactor for reacting a reaction gas with a vaporized metal compound, a heater for heating the reactor, and a multistage ultrafine powder recovery device disposed downstream of the reactor and having a fine filter in a final stage. A liquid ring vacuum pump that is disposed downstream of the multi-stage ultrafine powder recovery device and that is inactive with respect to the reaction gas of the gas phase chemical reaction or that uses a liquid that absorbs the reaction gas. Characteristic ultra fine powder production equipment. 2. The apparatus for producing ultrafine powder according to claim 1, further comprising an apparatus for keeping the inside of the reactor at 500 Torr to 50 Torr.