JP5861183B2 - Method for producing metal oxide particles - Google Patents

Description

  The present invention relates to a method for producing metal oxide particles used for various applications including ceramic raw materials.

  Conventionally, the production method of metal oxide fine particles used for ceramic raw materials, coloring raw materials, etc. is based on the gas phase method such as CVD or gas evaporation method, liquid phase method such as precipitation method or spraying method, mechanical pulverization depending on the starting phase. It is classified as a solid phase method. In addition, these are classified into a so-called breakdown method, which is obtained by refining a bulk material, represented by a mechanical grinding method, and a build-up method, which is obtained by growing from a molecular level. Since there is a limit to miniaturization by mechanical pulverization, and impurities are mixed from the pulverization equipment, the build-up method is mainly applied to the production of high-purity fine particles. Here, taking the liquid phase method as an example, a pH adjuster such as an alkali is added to an aqueous solution of a metal salt to precipitate a hydroxide and the like. Desired metal oxide fine particles can be obtained by raising the temperature to a certain extent and decomposing. As a specific example, in Patent Document 1, for example, an aqueous solution of a metal salt and an aqueous solution of a neutralizing agent are simultaneously added to an aqueous solution in which a carboxylic acid compound is dispersed to produce fine particles such as metal hydroxides. A method for producing a particulate metal oxide is disclosed in which the obtained fine particles are fired.

  However, in this liquid phase method, in the production process, after usually producing hydroxide and the like, the oxide is obtained by thermal decomposition in a heat treatment furnace or the like. In addition to the reaction step in the liquid phase method, The process of heating to a high temperature and processing is required. For example, in the manufacture of copper oxide, copper oxide is obtained by thermally decomposing copper hydroxide, copper nitrate, copper carbonate, etc. at about 700 ° C., and this high temperature treatment hinders the simplification of the manufacturing process.

  On the other hand, while heating a solution of a copper compound such as cupric chloride, a copper oxide such as copper oxide is produced by adding an alkaline solution, washed with water, dried, and then pulverized by a direct wet method or the like. Although it is possible to generate oxides, in such a method, the reaction process of copper oxide generation occurs rapidly, so it is difficult to control the particle size and it is difficult to obtain uniform fine particles was there.

  In order to solve these problems, the present inventors have studied a method for producing metal fine particles by using a metal nitrate solution as a metal and heating the metal nitrate solution, and the results are disclosed in Patent Documents 2 to 4. I am applying. FIG. 10 shows a production flowchart of a method for producing these metal fine particles. The process includes a step of producing a metal nitrate solution by mixing a metal, nitric acid and water (ion-exchanged water, etc.) to be finely divided. This is a method for producing metal fine particles that undergo a denitration step, a (coarse) pulverization step, a roasting step, a step of reducing with a reducing agent such as hydrogen, and further a pulverization step, followed by treatment according to the purpose of utilization of the fine particles. .

Patent Document 2 performs the heating / denitrification process by heating the metal nitrate solution with an external heater or the like, and the purpose is to control the heating temperature at that time and the rate of temperature rise to the heating temperature. This is a method for producing metal fine particles.
Patent Document 3 is a method for producing metal fine particles by irradiating a metal nitrate solution with microwaves in a heating / denitration process.

Patent Document 4 is a method for producing metal fine particles by performing a heating / denitration process in a metal nitrate solution using both microwaves and heating by an external heater or the like.
JP 05-139704 A JP 2010-195605 A JP 2011-088767 A JP 2011-088766 Gazette

In the method of manufacturing the metal fine particles using the metal nitrate solution heated by microwave irradiation, the external heater or the like, and the metal fine particles using them together, as shown in FIG. In addition, a reduction step using a reducing agent is necessary, and an increase in the number of processing steps, a reduction in processing efficiency, and an increase in the number of treatments of the residue due to the addition of a reducing agent and the like have occurred.
The present invention improves the processing speed and processing efficiency of the denitration process itself, and reduces the simplification of the reduction process, which is a subsequent process of the denitration process. An object is to improve the processing efficiency.

  It is another object of the present invention to provide a method capable of adjusting the degree of reduction of completed metal particles by changing the processing conditions of the denitration process.

  It is another object of the present invention to provide a method capable of changing the processing conditions of the denitration step to obtain a desired particle size distribution of the completed metal fine particles.

The first invention of the present invention, as a metal oxide precursor, an adjustment step of adjusting a solution of metal nitrate or metal oxide nitrate added with a predetermined amount or more of carbon particles, a heating step of heating the solution, have a different method of manufacturing a reduction of the metal oxide particles for producing metal oxide particles, wherein in the heating step, the metal oxide particles, characterized by pulverizing and mixing the carbon particles in the solution This is a method for producing metal oxide particles, wherein the characteristics of the metal oxide particles are adjusted.

According to a second aspect of the present invention, there is provided a method for producing metal oxide particles, characterized in that at least a part of the heating step performs heating by microwaves.

A third invention of the present invention is a method for producing metal oxide particles, wherein the heating step is performed under an inert gas atmosphere.

According to a fourth aspect of the present invention, the metal in the metal oxide is Li, Cu, Zn, Al, Mg, Co, Sr, Ba, Y, In, Ce, Si, Ti, Zr, Sn, Nb, Sb, A method for producing metal oxide particles, which is one kind of metal selected from Ta, Bi, Cr, W, Mn, Fe, Ni, Ru, U, Pu, Np, Am, and Cm.

  According to the method for producing metal oxide particles of the present invention, by adding carbon particles to a metal nitrate solution, the added carbon absorbs microwaves and generates heat. Further, the generated oxide and carbon It is possible to perform denitration and reduction at the same time by the reduction reaction and accompanying heat generation.

In addition, the degree of reduction of the metal oxide particles produced by the amount of carbon particles added to the metal nitrate solution, for example, metal oxides with different degrees of reduction such as CuO, Cu ₂ O, Cu, etc. in a copper nitrate solution The production ratio of particles can be controlled, and as a result, the reduction process shown in the prior art can be simplified.

  As a result, the generated metal oxide particles are extremely porous, and metal oxide particles having a small particle size distribution width can be realized by pulverization.

  On the other hand, since denitration and reduction can be performed without using a reducing agent in the denitration step, there is no need for treatment of the residue resulting from the conventional reducing agent, and an environmentally friendly process can be realized. In particular, when the metal is a radioactive element such as uranium, plutonium, or a fission product, it is possible to eliminate adverse effects such as an increase in radioactive waste caused by the addition of a reducing agent.

It is a figure explaining the outline of the apparatus used for the manufacturing method of the metal oxide particle which concerns on embodiment of this invention. It is a figure which shows the temperature history by the heating of the copper nitrate solution which added the carbon particle of 1 g or less in Example 1 of this invention. It is a figure which shows the temperature history by the heating of the copper nitrate solution which added the carbon particle over 1g in Example 1 of this invention. It is the figure which showed the reaction process by the heating of the copper nitrate solution of this invention. It is a figure which shows the particle size distribution after performing ultrasonic irradiation to the copper oxide particle manufactured by Example 1 of this invention. It is a figure of the X-ray-diffraction pattern of the copper oxide particle manufactured by changing the carbon addition amount in Example 1 of this invention. It is the figure which showed the relationship between the amount of carbon addition in Example 1 of this invention, and the composition of the copper oxide particle computed from the peak area of the X-ray-diffraction pattern. It is a figure which shows the process sequence of the heating and denitrification in Example 2 of this invention. It is the figure which showed the relationship between the amount of carbon addition in Example 2 of this invention, and the composition of the copper oxide particle computed from the peak area of the X-ray-diffraction pattern. It is a figure which shows the manufacturing-process order of the metal oxide particle in a prior art.

  The present invention, as a metal oxide precursor, a solution generation step of generating a solution of metal nitrate or metal oxide nitrate added with carbon particles, a heating step of performing denitration by heating the generated solution, A method for producing metal oxide particles, wherein the degree of reduction of the metal oxide particles is controlled by the amount of the carbon particles added.

  The metal in the metal oxide is Li, Cu, Zn, Al, Mg, Co, Sr, Ba, Y, In, Ce, Si, Ti, Zr, Sn, Nb, Sb, Ta, Bi, Cr, W, Although it is one type of metal selected from Mn, Fe, Ni, Ru, U, Pu, Np, Am, and Cm, Cu will be described as an example in the present invention.

  The carbon particles to be added are not particularly specified, but in this embodiment, description will be made by taking amorphous carbon having a median diameter of 0.247 μm as an example.

  The metal nitrate or metal oxide nitrate solution is a solution in which any one of the metals in the metal oxide, an appropriate amount of nitric acid, water (ion-exchanged water, etc.), and an appropriate amount of carbon particles are added and mixed. is there.

In the heating step, at least heating by infrared heating, heating by an electric tubular furnace, heating by microwaves, or a combination thereof is performed.

  Furthermore, in the heating step, when a predetermined temperature is reached during the heating, the intermediate product in the solution generated by the heating so far is pulverized and mixed, and the particles are again made into fine particles to promote the denitration reaction. It can also be made.

  The configuration of the heating device in the heating process for performing denitration will be described.

  FIG. 1 is a diagram for explaining the outline of a heating apparatus 1 used for producing metal oxide particles according to the present invention, and illustrates heating by microwave irradiation as an example. Reference numeral 10 denotes a heating chamber, 11 denotes a control unit, 13 denotes a temperature detection unit, 15 denotes a reaction vessel, 20 denotes a magnetron, and 21 denotes a microwave inlet.

  In FIG. 1, a heating method using a microwave is employed in the heating step in the present embodiment. For this reason, the heating apparatus 1 in this embodiment is provided with a heating chamber 10 for the purpose of preventing microwaves from leaking to the surroundings. In the heating chamber 10, a reaction vessel 15 is placed that houses a metal nitrate or metal oxide nitrate solution 25 to which carbon particles as a precursor are added.

  Microwaves generated by the magnetron 20 are guided from a waveguide (not shown) to a microwave introduction port 21 and introduced from the microwave introduction port 21 into the heating chamber 10. Further, a temperature detection unit 13 such as a thermocouple is set in the solution in the reaction vessel 15 to measure the temperature of the metal nitrate or metal oxide nitrate solution 25 to which carbon particles are added. This measured value is input to the control unit 11, and the control unit 11 can control the output of the magnetron 20 in accordance with the temperature of the solution.

Both ends of the reaction vessel 15 are connected to In and Out gas pipes. From the In side, atmospheric gas such as air or nitrogen gas is introduced at a predetermined flow rate by an atmospheric gas supply system (not shown), and the Out side H ₂ O, CO ₂ and NO _x gas generated by the denitration reaction and reduction reaction are discharged.

  The oscillation frequency of the magnetron 20 used in the present invention is 2.45 GHz, and the output can be varied between 40 W and 770 W.

In the case of infrared heating or heating with an electric tubular furnace, although not shown, instead of the magnetron 20 and the microwave inlet 21, infrared heating, resistance heating, electric tubular furnace, etc. of the existing technology are provided around the reaction vessel 15. The metal nitrate or metal oxide nitrate solution 25 to which the carbon particles are added is heated.
Example 1
Next, an example of producing metal oxide particles using copper nitrate will be described as Example 1 of the present invention.

As the metal nitrate solution 25, 20.0 g of Cu (NO ₃ ) ₂ .3H ₂ O and 15.0 ml of ion exchange water were mixed to prepare the copper nitrate solution 25. Further, the median diameter was 0.247 μm. And amorphous carbon particles (a) 0.0 g, (b) 0.4 g, (c) 0.
6 g, (d) 0.8 g, (e) 1.0 g, (f) 1.2 g, (g) 1.4 g, (h) 1.6 g, (i) 1.8 g, (j) 2.0 g (K) 2.2 g, (l) 2.4 g, and (m) 2.6 g were added to prepare a copper nitrate solution 25 to which 14 types of carbon were added. The copper nitrate solution temperature at this time was 25 ° C.

As the heating apparatus 1, the heating apparatus 1 by microwave irradiation shown in FIG. 1 was used.
The magnetron 20 that irradiates the microwave can be variable between a transmission frequency of 2.45 GHz and an output of 40 W to 770 W.

  In this example, nitrogen gas was used as the atmospheric gas, and was introduced by the atmospheric gas supply system IN at a flow rate of 300 ml / min.

  The copper nitrate solution 25 of the above (a) to (m) was heated by the heating device 1 by microwave irradiation in FIG. 1 to perform denitration.

  FIG. 2 shows the relationship between the heating time and the heating temperature when the carbon addition amount is (a) 0.0 g to (e) 1.0 g, and the carbon addition amount is (f) 1.2 g to (m) 2. 6g is shown in FIG.

  Although the maximum temperature of heating in this example is set to 600 ° C., according to the study by the present inventors, in the case of microwave heating of the copper nitrate solution 25, the bias of the microwave output, and further the copper nitrate solution In order to maintain the entire copper nitrate solution 25 at about 350 ° C. for efficient denitration, the maximum temperature reached 600 ° C. It is set based on the examination result that it is necessary to set to ° C.

The relationship between the temperature rise of heating and the denitration reaction is described with reference to FIG. 4 for the reaction process described in Patent Document 2, but will be described in comparison with FIG. Both FIG. 2 and FIG. 3 show a temperature increase of about 45 degrees when H ₂ O of the copper nitrate solution 25 is discharged by evaporation and boiling up to about 120 ° C., regardless of the amount of carbon added. Yes. Thereafter, from 160 ° C. to around 200 ° C., a gradual temperature rise is followed in the dehydration stage of hydrated water.

Thereafter, C by denitration reaction to intermediate Cu ₂ (NO ₃ ) (OH) ₃ and denitration reaction of intermediate
uO is generated and reaches 600 ° C. with a rapid temperature rise.

In the case of heating by normal microwave irradiation, the denitration reaction is caused by a gentle temperature increase, but by adding the carbon of the present invention, the NO _x component generated by the decomposition of the nitric acid component of the copper nitrate solution 25 is reduced. It combines with the added carbon to become CO ₂ , and exhibits a rapid temperature rise from around 200 ° C. due to the heat of oxidation during this oxidation.

  It can be seen that the denitration reaction is carried out by the above heating temperature.

  Next, since the copper oxide particles produced by heating and denitration in this example are porous and in a fragile form, they are agglomerated but were subjected to a refinement treatment by ultrasonic irradiation. The particle size distribution of the copper oxide particles is shown in FIG.

  FIG. 5 (a) shows a state in which the produced copper oxide particles are in a porous and aggregated state, but the particle size distribution is obtained by reducing the particles by irradiating with ultrasonic waves for 2 minutes, and the amount of added carbon is increased. It can be seen that the median value of the particle diameter moves to the small diameter side although it is very small.

  Further, when the ultrasonic wave irradiation time is set to 30 minutes, as shown in FIG. 5B, the center value of the particle diameter further shifts to the small diameter side. Thereby, the particle size distribution of the copper oxide particles can be improved by the irradiation time of the ultrasonic waves.

  Furthermore, it should be noted here that the value of the minimum diameter on the small diameter side is not changed by ultrasonic irradiation, as can be seen in FIGS. 5 (a) and 5 (b). That is, reaggregation due to ultrasonic irradiation does not occur, and it can be said that the particle size distribution is extremely stable.

  FIG. 6 shows the results of analyzing the components of the copper oxide particles produced by changing the amount of carbon added and denitrating, using an X-ray diffraction pattern. As shown in FIG. 6, it can be seen that the composition of the product is changed by adding the carbon particles. Further, when no carbon particles are added, no hydroxide is generated. On the other hand, it is understood that the hydroxide remains when the added amount of the carbon particles is 0.2 g to 0.8 g.

  FIG. 7 is a diagram showing a difference in composition of manufactured metal particles due to a difference in the amount of carbon particles added to the solution. FIG. 7 shows the composition ratio of the product calculated from the peak area of the X-ray diffraction pattern.

The product is almost CuO only up to 0.4 g of carbon particles. However, the proportion of CuO decreases and the proportion of Cu ₂ O increases from an addition amount of 0.6 g or more. Addition amount 1
. If it is 0 g or more, it can be confirmed that the ratio of Cu starts to increase with the decrease of CuO. It can be seen that when the addition amount of carbon particles is further increased, Cu is further increased with a decrease in CuO and Cu ₂ O at an addition amount of 2.0 g or more. For example, when the carbon particle addition amount is 2.0 g, particles with a high degree of reduction are produced such that the ratio of CuO is 0.25, Cu ₂ O is 0.25, and Cu is 0.50. The ratio varies depending on the amount of carbon particles added. As described above, it was confirmed that by adding carbon particles, the oxygen ratio in the oxide, that is, the degree of reduction, can be controlled, and it is possible to simultaneously perform denitration and reduction reaction. (Example 2)
Next, as Example 2 of the present invention, another example of producing metal oxide particles using copper nitrate will be described.

FIG. 8 is a diagram for explaining the manufacturing process of the second embodiment. Although the basic configuration of the heating and denitration processes is not changed from that in Example 1, the stage prepared during heating and denitration, that is, the solution prepared by Cu (NO ₃ ) ₂ .3H ₂ O, ion-exchanged water and carbon particles is heated. In the process, heating is temporarily stopped at a temperature (160 ° C.) at which a hydroxide as an intermediate product is generated, the intermediate product is pulverized and mixed, and then heated to 600 ° C. again by microwave heating. A product is obtained.

As in Example 1, as the copper nitrate solution 25, 20.0 g of Cu (NO ₃ ) ₂ .3H ₂ O and 15.0 ml of ion-exchanged water were mixed to prepare the copper nitrate solution 25. Further, amorphous carbon particles having a median diameter of 0.247 μm are obtained as (a) 0.0 g, (b) 0.2 g.
(C) 0.4 g, (d) 0.6 g, (e) 0.8 g, (f) 1.0 g, (g) 1.2 g
(H) 1.4 g, (i) 1.6 g, (j) 1.8 g, and (k) 2.0 g were added to prepare a copper nitrate solution 25 to which 11 types of carbon were added. The copper nitrate solution temperature at this time was 25 ° C.

This copper (NO ₃ ) ₂ .3H ₂ O, ion-exchanged water, and the copper nitrate solution 25 prepared with carbon particles were converted into intermediate product hydroxide by the same microwave heating apparatus 1 as in Example 1. After heating to the temperature (160 degreeC) to produce | generate, and stopping once after that, an intermediate product was grind | pulverized and mixed, the copper oxide particle was manufactured by heating up to 600 degreeC by microwave heating again.

  Thus, in the middle of the heating step, the intermediate product is pulverized and mixed as described above, so that the carbon particles present in the intermediate product are uniformly dispersed, and further the reduction of the copper oxide particles. The reaction was accelerated.

As a result of finely pulverizing the copper oxide particles by ultrasonic waves of 2 min and 30 min as in Example 1, the produced copper oxide particles were not shown, but the particle size distribution of the copper oxide particles equivalent to that in Example 1 was obtained. I was able to get it.

Moreover, when the X-ray-diffraction pattern analysis of this copper oxide particle was performed and the composition ratio of the product calculated from the peak area was analyzed, the result shown in FIG. 9 was obtained.
When Example 1 and Example 2 are compared by the composition ratio of the product, for example, when the carbon particle addition amount is 2.0 g, CuO (Example 1) 0.25 → (Example 2) 0.04, Cu ₂ O 0.2
5 → 0.36 and Cu 0.50 → 0.60, it can be seen that the composition has shifted to a composition with a higher degree of reduction.

  By pulverizing and mixing the intermediate product in the intermediate stage (160 ° C.) of the heating process, it is possible to further control the oxygen ratio in the oxide, that is, the degree of reduction, and simultaneously perform denitration and reduction reaction. It became possible.

  As mentioned above, although the metal fine particle manufacturing method by carbon particle addition which made copper nitrate the example in Example 1 and Example 2 was described, it shows collectively in Table 1 as a specific application example.

本実施例の本実施例のＣｕ(ＮＯ₃)₂・３Ｈ₂Ｏ、さらには、Ｎｉ(ＮＯ₃)₂・６Ｈ₂Ｏ、Ｆｅ(ＮＯ₃)₃・９Ｈ₂Ｏ、ＵＯ₂(ＮＯ₃)₂・６Ｈ₂Ｏ等が好適である。

In this example, Cu (NO ₃ ) ₂ .3H ₂ O, Ni (NO ₃ ) ₂ .6H ₂ O, Fe (NO ₃ ) ₃ · 9H ₂ O, UO ₂ (NO ₃ ) ₂ · 6H ₂ O or the like is preferable.

  Any metal or metal oxide that has solubility, is soluble in water or ethanol, and has similar thermal characteristics such as melting point and boiling point can be used.

  As described above, according to the method for producing metal oxide particles of the present invention, when carbon particles are added to a metal nitrate solution, the added carbon absorbs microwaves and heat is generated. It is possible to perform denitration and reduction at the same time by the reduction reaction and the exothermicity associated therewith.

In addition, the degree of reduction of the metal oxide particles produced by the amount of carbon particles added to the metal nitrate solution, for example, metal oxides with different degrees of reduction such as CuO, Cu ₂ O, Cu, etc. in a copper nitrate solution The particle production ratio can be controlled, and as a result, the reduction process shown in the prior art can be eliminated or simplified.

  Moreover, the metal oxide particle produced | generated by the manufacturing method of the metal oxide particle of this invention is very porous, A metal oxide particle with a small particle size distribution width | variety is realizable by grind | pulverizing.

On the other hand, since denitration and reduction can be performed without using a reducing agent in the denitration step, there is no need for treatment of the residue resulting from the conventional reducing agent, and an environmentally friendly process can be realized. In particular, when the metal is a radioactive element such as uranium, plutonium, or a fission product, it is possible to eliminate adverse effects such as an increase in radioactive waste caused by the addition of a reducing agent.

DESCRIPTION OF SYMBOLS 10 ... Heating chamber 11 ... Control part 13 ... Temperature detection part 15 ... Reaction container 20 ... Magnetron 21 ... Microwave inlet 25 ... Metal nitrate solution, Copper nitrate solution

Claims (4)

As a metal oxide precursor, an adjustment step of adjusting a solution of metal nitrate or metal oxide nitrate added with a predetermined amount or more of carbon particles,
Have a, a heating process of heating the solution,
In the method for producing metal oxide particles for producing metal oxide particles having different degrees of reduction ,
In the heating step, the characteristics of the metal oxide particles are adjusted by pulverizing and mixing the carbon particles in the solution . The method for producing metal oxide particles according to claim 1 , wherein at least a part of the heating step is performed by microwave heating. The method for producing metal oxide particles according to claim 1 , wherein the heating step is performed under an inert gas atmosphere. The metal in the metal oxide is Li, Cu, Zn, Al, Mg, Co, Sr, Ba, Y, In, Ce, Si, Ti, Zr, Sn, Nb, Sb, Ta, Bi, Cr, W, Mn The metal oxide particles according to any one of claims 1 to 3 , wherein the metal oxide particles are one kind of metal selected from Fe, Ni, Ru, U, Pu, Np, Am, and Cm. Production method.

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