JPH01208330A - Method for producing ultrafine molybdenum trioxide and its production apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing ultrafine molybdenum trioxide and an apparatus for producing the same.

[Conventional technology]

Generally, molybdenum trioxide is produced by roasting molybdenum alone or a compound in an oxygen-containing atmosphere such as the air, or by oxidizing it with an oxidizing acid such as concentrated nitric acid.

Molybdenum trioxide is a white powder that is insoluble in water and has a smooth feel similar to talcum powder. When heated, it becomes pale yellow and melts at 795C to become a brown liquid. Further, since the temperature rise begins at a temperature near this melting point, molybdenum trioxide is purified to a high degree by utilizing this property.

Molybdenum trioxide is used in structural alloy steel, high-strength steel,
It is used as an additive for alloys such as stainless steel and tooling, pigments, reagents, catalysts, etc., and as an intermediate raw material for these. Furthermore, recently, utilizing its slipperiness, use as a lubricant in toner for dry copying machines has been considered, and for this purpose, ultrafine molybdenum trioxide is required.

However, ultrafine molybdenum trioxide suitable for the above requirements has not yet been provided. This is because ultrafine molybdenum trioxide cannot be obtained using conventional methods for producing molybdenum trioxide.

For example, when ammonium molybdate is decomposed with concentrated nitric acid, the free molybdate produced becomes glue-like.
It is difficult to crystallize it in the form of crystals, and even if molybdenum trioxide is produced by washing this glue-like molybdic acid with water and drying it by heating or vacuum drying, it will only become lumpy or powdery. Fine powder cannot be obtained.

Further, even if ammonium molybdate is exposed to the atmosphere, weathered, and then heated to obtain molybdenum trioxide, ultrafine molybdenum trioxide cannot be obtained.

Even if molybdenum trioxide is sublimated and agglomerated, it will precipitate in the form of crystals in a relatively low-temperature area above the melt, or even if it does not precipitate, particles will grow in the gas phase. Only molybdenum trioxide powder with a particle size of 1 to several tens of micrometers can be obtained.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method and apparatus for producing molybdenum trioxide powder having an average particle diameter of 0.05 μm or less, which is smaller than the conventional powder.

[Means to solve the problem]

Means for solving the problems according to the present invention are as follows: 1) Molybdenum trioxide vapor is heated to 10,000 t using a non-reducing gas.
A method for producing ultrafine molybdenum trioxide by cooling at a cooling rate of 1/sea or higher; 2) While supplying high-temperature air above the liquid level of molten molybdenum trioxide, the high-temperature air containing the molybdenum trioxide vapor is , the method for producing ultrafine molybdenum trioxide as described in the previous section 1), in which the liquid is suctioned and discharged from above the liquid level and mixed with a non-reducing gas for cooling; 3) a hole is provided in the upper side surface and suction is carried out at the closed upper end; a crucible having a mouth formed therein; and a heating furnace that surrounds the area above the hole provided in the crucible and has a gap between the crucible and the outer periphery of the crucible, and is formed so as to draw outside air into the outer periphery of the crucible; The ultrafine molybdenum trioxide powder is equipped with a suction tube whose one end has a smaller outer diameter than the suction port of the crucible and whose one end is arranged concentrically with the suction port so that it is flush with the top surface of the crucible suction port. Manufacturing equipment, located at.

In the method of the present invention, molybdenum trioxide vapor is produced by heating molybdenum trioxide to melt and sublimate, or by thermally decomposing ammonium molybdate trioxide to decompose it into molybdenum trioxide and alemonia. Obtain molybdenum trioxide vapor.

The cooling gas may be any gas that does not have reducing properties, and usually air may be used.

The lid of the crucible and crucible used in the present invention may be made of materials that do not react with molybdenum trioxide, and are preferably made of graphite, which is easy to process and does not introduce impurities into the product. Ruh, gate. Upper side, hole. It is sufficient to use a crucible with an internal volume of about 21 mm, and to provide four holes with a diameter of 4 mm at equal intervals around the periphery. In addition, the iron lead pipe should be made of corrosion-resistant stainless steel.

[Effect]

The reason why molybdenum trioxide vapor is cooled using a non-reducing gas in the present invention is to prevent a reaction such as reduction of molybdenum trioxide from occurring.

It is also possible to use a liquid such as water that does not react with molybdenum trioxide instead of a gas, but in this case, the aggregated molybdenum trioxide may become coarse in the liquid or form secondary particles, resulting in ultrafine molybdenum trioxide powder. difficult to obtain. In order to prevent the coarsening of ultrafine molybdenum trioxide powder in a liquid and the formation of vertical particles, it is necessary to add a surface stabilizer to the liquid used, and in addition, it is necessary to separate water to make it into a product. This is not preferable because it requires post-processing. When gas is used as the coolant, it is sufficient to simply suck in the powdered molybdenum trioxide and collect it with a bag filter, electric precipitator, or the like.

In the present invention, molybdenum trioxide vapor is produced for 1000017 sec.
Cooling at the above cooling rate is as shown in Figure 1.
The cooling rate of molybdenum trioxide vapor is 10000'c/8
It has been found that by setting the particle diameter to 0c or more, it is possible to stably obtain ultrafine powder with an average particle diameter of 0.05 μm or less.

The cooling rate in Figure 1 is the average cooling rate up to 300 C, and the particle size was obtained by measuring molybdenum trioxide powder collected in a bag filter using a BET specific surface area meter manufactured by Digestion Ionics. Average particle size. 100 from Figure 1
In the cooling rate range of 0.00 to 9000 rjsec, the particle size varies significantly in the range of 0.05 to 1.2 μm due to slight fluctuations in the cooling rate, making it difficult to obtain a desired particle size. In order to reduce the particle size to 0.02 μm or less, the cooling rate must be set to 50,000 Vsec or more, and even if the cooling rate is higher than this, the particle size will hardly decrease, which is uneconomical.

In the present invention, high-temperature air is supplied to the molybdenum trioxide vapor by keeping the temperature above the molten molybdenum trioxide close to the melt temperature and lowering the vapor density to prevent the formation of crystal nuclei of molybdenum trioxide. This is to prevent the growth of

Furthermore, by supplying high-temperature air in this manner, the vapor density can be diluted, the evaporation rate can be increased, and productivity can also be improved. When using a crucible, high temperature air is preferably supplied near the suction port on the top of the crucible. This is because when the suction pipe is not directly and airtightly connected to the suction port, room temperature outside air can be prevented from entering through the suction port and lowering the temperature of the space above the crucible.

By forming a gap between the outer periphery of the crucible and the heating furnace so that outside air can be sucked into the gap, as the molybdenum trioxide-containing gas is exhausted from the suction port of the crucible, it will enter the heating furnace. Heated outside air is naturally drawn into the crucible through the hole provided on the upper side of the crucible, and an appropriate amount is naturally drawn into the crucible without the need for any particular air heating device or supply pipe for heated air into the crucible. The heated air can be easily supplied, and the temperature of the heated air can be made equal to the temperature inside the heating furnace without any particular temperature adjustment.

A suction port is provided at the upper end of the crucible, and one end of the suction tube, which has an outer diameter smaller than the suction port, is placed concentrically with the suction port so that it is flush with the top surface of the suction port, thereby reducing the high temperature inside the crucible. Very rapid cooling can be easily achieved by allowing a large amount of cooling gas to come into immediate contact with the molybdenum trioxide vapor.

[Example] The apparatus shown in FIG. 1 was used as a manufacturing apparatus. This device consists of a heating furnace 1 consisting of a bottomed cylindrical electric furnace with an open top.
A graphite crucible 2 with an open top and an internal volume of 2 mm was placed inside the furnace so that the top surface of the heating furnace 1 and the top surface were located on the same plane. A gap of five scratches is formed between the circumferential side of the crucible 2 and the inner surface of the heating furnace 1, and four holes 3 with a diameter of 4 a% are provided at equal intervals on the upper side of the crucible 2. A graphite lid 4 having a suction port 5 with a diameter of 4 mm in the center was simply placed on the crucible 2 with the suction port 5 positioned in the center of the opening on the top surface of the crucible 2, and the opening of the crucible 2 and the opening of the heating furnace 1 were closed. . A suction tube 6 made of stainless steel with an external size of 3 times and a wall thickness of 1 mm was arranged concentrically with one end on the same plane as the upper surface of the suction port 5, and the other end was connected to a vacuum pump through a bag filter.

Commercially available molybdenum trioxide powder 1.1'C9 having a particle size of 5 to 10 μm was placed in the crucible 2 and heated and melted at 1000C.

On the other hand, the air in the suction pipe 6 is sucked by the vacuum pump, and the molybdenum trioxide vapor generated in the upper space of the crucible 2, the heated air in the crucible 2, and a large amount of outside air sucked from around the suction port 3. Mixed, cooled and pumped off. According to this discharge, outside air was sucked into the heating furnace 1 through the gap between the lid 4 and the upper end of the heating furnace 1, and the air heated within the heating furnace 1 was taken into the interior of the heating furnace 2 through the hole 3. The ultrafine powder of molybdenum trioxide produced by continuing heating and suction for 1.5 hours was collected using a bag filter.

The flow rate of the gas in the suction pipe 6 was measured by attaching an integrated flow meter to the exhaust side of the vacuum pump, and a thermometer was attached to the suction pipe 6 to measure the gas temperature in the suction pipe 6 to determine the cooling rate. .

As a result, the suction amount of the vacuum pump was 500 Nl/min.
The cooling rate was 17,000 tl/sea.

The amount of molybdenum trioxide obtained was 650 g.

As a result of measurement using a BIT specific surface area meter manufactured by Yuon Ionics, the specific surface area was 52 m/gs, and the average particle size was 0.0.
It was 2 μm. Figure 5 shows 10% of this molybdenum trioxide.
A 10,000x transmission electron micrograph is shown.

As shown in FIG. 3, if the top surface of crucible 2 is lower than the top surface of heating furnace 1, as shown in FIG. 4, even if the top surface of crucible 2 is higher than the top surface of heating furnace 1, When conditions were set to be similar to those of the apparatus, results similar to those shown in FIG. 2 were obtained.

Further, when the same procedure was carried out with the hole 3 of the crucible 2 in FIG. 2 closed, the amount of molybdenum trioxide obtained was 80 g and the cooling rate was 20,000 t78 eC.

Comparative Example In the apparatus shown in FIG.
The same procedure as in FIG. 1 above was carried out except that the molybdenum trioxide obtained was 65 g, and the average particle size was 4.5 μm. Also, when I calculated the cooling rate at this time, it was 8500
At Vsea, a large amount of molybdenum trioxide was crystallized above the inner surface of crucible 2.

〔Effect of the invention〕

According to the method of the present invention, ultrafine powder of molybdenum trioxide can be stably obtained by setting the cooling rate of molybdenum trioxide vapor to 10,000 C'sea or more. Good productivity can be obtained by supplying heated air.

Further, according to the apparatus of the present invention, ultrafine molybdenum trioxide powder can be obtained easily and efficiently.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the cooling rate of molybdenum trioxide vapor and the average particle size of the molybdenum trioxide powder obtained.
The figure is a sectional view of one embodiment of the device of the present invention, FIG. 3 is an explanatory diagram of the second embodiment of the device of the present invention, FIG. 4 is an explanatory diagram of the third embodiment of the device of the present invention, and FIG. FIG. 2 is a transmission electron micrograph showing the particle structure of ultrafine molybdenum trioxide obtained in Examples. 1. Heating furnace 2. Crucible 3. Hole 4. Lid 5.
・Suction port 6... Suction tube Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 0:01) Jm

Claims (3)

[Claims] (1) Using molybdenum trioxide vapor with non-reducing gas,
A method for producing ultrafine molybdenum trioxide by cooling at a cooling rate of 0,000°C/sec or more. (2) While supplying high-temperature air above the liquid surface of the molten molybdenum trioxide, the high-temperature air containing the molybdenum trioxide vapor is sucked and discharged from above the liquid surface to convert it into a non-reducing gas for cooling. The method for producing ultrafine molybdenum trioxide according to claim (1), wherein the ultrafine molybdenum trioxide is mixed. (3) a crucible with a hole provided in the upper side surface and a suction port formed in the closed upper end and a gap between the outer periphery of the crucible and surrounding the area above the hole provided in the crucible; A heating furnace formed so that outside air can be sucked into the outer periphery of the crucible, and one end having an outer diameter smaller than the suction port of the crucible and concentric with the suction port so as to be flush with the top surface of the suction port of the crucible. A device for producing ultrafine molybdenum trioxide, which is equipped with a suction tube in which