JP5531341B2 - Method for producing metal oxide particles by hybrid heating method - Google Patents

Description

  The present invention relates to a method for producing metal oxide particles by a hybrid heating method 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.
JP-A-5-139704

  In the case of producing metal oxide fine particles, a method for efficiently producing metal oxide fine particles by application of the liquid phase method has been studied, and in the production process, after usually generating hydroxide and the like, a heat treatment furnace The oxide is obtained by thermally decomposing with the above, and in addition to the reaction step by the liquid phase method, a step of raising the temperature 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. In addition, 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 directly 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 the above-mentioned problems, the invention according to claim 1 is characterized in that a metal oxide precursor or a metal nitrate or a metal oxide oxide solution is adjusted as a metal oxide precursor, and the adjustment is performed in the adjustment process. An accommodation step of containing the solution in the reaction vessel; a placement step of placing the reaction vessel in a heating chamber provided with a microwave introduction port ; a heater disposed around the reaction vessel; and the microwave introduction port. A heating step of heating the solution with microwaves that are introduced into the heating chamber and indirectly incident on the solution through the reaction vessel into the reaction vessel, and heated in the heating step. A measuring step for measuring the temperature of the solution, and a control step for controlling the heating by the heater and the heating by the microwave based on the temperature measured in the measuring step. In the manufacturing method of the oxide particles, wherein at least part of the heating step, the composite heating method for heating by the heating and the microwave by the heater at the same time that is used to control the absorption form of heat by the solution, said solution The particle size control of the metal oxide particles is performed by adjusting the temperature rising rate .

  The invention according to claim 2 is the method for producing metal oxide particles according to claim 1, wherein the metal in the metal oxide is Li, Cu, Zn, Al, Mg, Co, Sr, Ba, Y, One metal selected from In, Ce, Si, Ti, Zr, Sn, Nb, Sb, Ta, Bi, Cr, W, Mn, Fe, Ni, Ru, U, Pu, Np, Am, and Cm. It is characterized by that.

  According to the method for producing metal oxide particles of the present invention, in the heating step, the heat absorption mode by the solution that is the metal oxide precursor is appropriately controlled by the combined heating method in which heating by the heater and heating by the microwave are performed simultaneously. Therefore, it is possible to control the reaction process for generating the metal oxide particles, and it is possible to control the average particle diameter of the generated metal oxide particles.

  In addition, according to the method for producing metal oxide particles of the present invention, it is possible to control the average particle diameter of the metal oxide particles to be produced, and further, the sintered body using the metal oxide particles as a raw material can be controlled. Since there is a possibility that the density can be controlled by changing the particle size of the sintered body, application to the raw material powder adjustment process in the sintered body manufacturing field is also possible.

It is a figure explaining the outline of the apparatus used for the manufacturing method of the metal oxide particle by the hybrid heating method which concerns on embodiment of this invention. It is a figure explaining the outline of the apparatus used for the manufacturing method of the metal oxide particle which concerns on a comparative example. It is a figure explaining the outline of the apparatus used for the manufacturing method of the metal oxide particle which concerns on a comparative example. It is a figure which shows the average particle diameter of the copper oxide produced | generated when the temperature increase rate was changed with each heating apparatus. It is a figure which shows the cumulative particle diameter distribution of the copper oxide produced | generated by each heating apparatus. It is a figure which shows the energy for obtaining a predetermined temperature increase rate in a heating apparatus. It is a SEM photograph of the copper oxide particle obtained by the microwave heating method. It is a SEM photograph of the copper oxide particle obtained by the heater heating system. It is a SEM photograph of the copper oxide particle obtained by the composite heating system (hybrid heating system) employ | adopted with the manufacturing method of the metal oxide particle concerning this invention. It is a figure which illustrates typically the relationship between the temperature distribution in a microwave heating apparatus, and the growth of a copper oxide particle. It is a figure which illustrates typically the relationship between the temperature distribution in a heater heating apparatus, and the growth of a copper oxide particle. It is a figure which illustrates typically the relationship between the temperature distribution in a composite wave heating apparatus, and the growth of a copper oxide particle.

Hereinafter, the method for producing metal oxide particles of the present invention will be described with reference to the drawings as appropriate. The metal in the metal oxide produced by the method for producing metal oxide particles of the present invention is Li, Cu, Zn, Al, Mg, Co, Sr, Ba, Y, In, Ce, Si, Ti, Zr, Sn. , Nb, Sb, Ta, Bi, Cr, W, Mn, Fe, Ni, Ru, U, Pu, Np, Am, Cm, which is one kind of metal, and is manufactured by the manufacturing method of the present invention. The purpose is to control the average particle size of these metal oxides. In the method for producing metal oxide particles of the present invention, first, a metal nitrate or metal oxide nitrate solution of these metals is prepared as a metal oxide precursor. Then, the prepared solution is heated to denitrate to obtain a metal oxide. In this heating step, at least part of the heating step, heating by a heater and heating by a microwave are performed. A composite heating method that performs the above simultaneously is used. In the heating process in the production method of the present invention, the heat absorption mode by the solution that is the metal oxide precursor is appropriately controlled by such a combined heating method in which heating by the heater and heating by the microwave are simultaneously performed. It is possible to control the reaction process for generating the product particles and to control the average particle size of the metal oxide particles to be generated.

In addition, according to the method for producing metal oxide particles of the present invention, it is possible to control the average particle diameter of the metal oxide particles to be produced, and further, the sintered body using the metal oxide particles as a raw material can be controlled. Since there is a possibility that the density can be controlled by changing the particle size of the sintered body, application to the raw material powder adjustment process in the sintered body manufacturing field is also possible.
(Example-combined heating method)
Next, the manufacturing method of the metal oxide particle of this invention is demonstrated in detail based on an Example. FIG. 1 is a diagram for explaining the outline of an apparatus used for producing metal oxide particles according to an embodiment of the present invention. In FIG. 1, 10 is a heating chamber, 11 is a control unit, 12 is a heater, 13 is a temperature detection unit, 14 is a heat insulating member, 15 is a reaction vessel, 20 is a magnetron, and 21 is a microwave inlet.

  In FIG. 1, in the heating process in the present embodiment, a composite heating method in which heating by a heater and heating by microwaves are performed simultaneously is adopted. For this reason, the heating apparatus 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, there is provided a heat insulating member 14 on which a reaction vessel 15 for storing a solution of a metal nitrate or a metal oxide nitrate serving as an adjusted precursor is placed.

  The heat insulating member 14 is provided with a heater 12 such as a ribbon heater for heating the precursor (metal nitrate or metal oxide nitrate solution) accommodated in the reaction vessel 15. In addition, the microwave generated by the magnetron 20 is guided from a waveguide (not shown) to the microwave introduction port 21 and is introduced into the heating chamber 10 from the microwave introduction port 21.

  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. This measured value is input to the control unit 11, and the control unit 11 can control the outputs of the heater 12 and 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, 100 ml / sec of compressed air is introduced by a compressed air supply system (not shown), and denitration reaction is performed from the Out side. The H ₂ O and N component gas generated in the above are discharged.
(Comparative Example 1-heater heating method)
Next, a comparative example of the method for producing metal oxide particles of the present invention will be described. FIG. 2 is a diagram for explaining the outline of an apparatus used in the method for producing metal oxide particles according to the comparative example. The apparatus of FIG. 2 employs a heating method in which heating is performed only by a heater in the heating process. Therefore, the configuration for microwave heating is omitted from the hybrid heating device shown in FIG. The same reference numerals are assigned to the same components, and the description thereof is omitted.
(Comparative Example 2-microwave heating method)
Next, a comparative example of the method for producing metal oxide particles of the present invention will be described. FIG. 3 is a diagram illustrating an outline of an apparatus used in the method for producing metal oxide particles according to the comparative example. The apparatus shown in FIG. 3 employs a heating method that performs only microwave heating in the heating process. Therefore, the configuration for heating the heater is omitted from the hybrid heating device shown in FIG. The same reference numerals are assigned to the same components, and the description thereof is omitted.

  Metal oxide particles were manufactured by three manufacturing methods including the method for manufacturing metal oxide particles according to the present embodiment as described above. More specifically, as a precursor, a solution obtained by dissolving 20 g of Cu nitrate hydrate in 20 ml of ion-exchanged water is contained in a reaction vessel 15, and the hybrid heating device of the present invention, the heater heating device of Comparative Example 1, And the heating process was implemented using the microwave heating apparatus of the comparative example 2.

  FIG. 4 is a diagram showing the average particle diameter of the copper oxide produced when the heating rate is changed by each heating device. The particle size of the resulting denitrated body (copper oxide) was measured by dispersing the sample in an aqueous solution of sodium hexametaphosphate and applying ultrasonic dispersion, and then measuring with a laser scattering particle size distribution analyzer (LA-920, manufactured by HORIBA). did. In addition, ultrasonic dispersion was set to 2 minutes and 30 minutes, and each was evaluated as secondary particles and primary particles. FIG. 4A shows the result of secondary particles, and FIG. 4B shows the result of primary particles.

  As can be seen from FIG. 4, the average particle size is smaller as the heating rate is faster, regardless of which heating method is used among the composite heating method (hybrid heating method), the heater heating method, and the microwave heating method. Tend to be. In addition, the copper oxide particles obtained by the microwave heating method have a smaller particle diameter than the copper oxide particles obtained by the heater heating method, but the copper oxide particles obtained by the composite heating method (hybrid heating method) The particle size is between the two heating methods. As described above, in the heating process in the method for producing metal oxide particles of the present invention, the heating process is controlled by simultaneously performing both the heater heating method and the microwave heating method. I have control. It is considered that the reaction process for generating metal oxide particles can be controlled by the difference in the heat absorption mode, and the average particle diameter of the generated metal oxide particles can be controlled.

  Moreover, FIG. 5 has shown the cumulative particle diameter distribution of the copper oxide produced | generated with each heating apparatus. FIG. 5A shows the cumulative particle size distribution of secondary particles, and FIG. 5B shows the cumulative particle size distribution of primary particles. In the graph of the cumulative particle size distribution shown in FIG. 5, the more upright the curve is, the narrower the particle size distribution and the more uniform the particle size of the particles. From FIG. 5, it can be seen that according to the composite heating method (hybrid heating method) employed in the method for producing metal oxide particles according to the present invention, copper oxide particles having a uniform particle diameter can be obtained.

  Moreover, FIG. 6 is a figure which shows the energy for obtaining a predetermined temperature increase rate in each heating apparatus. According to FIG. 6, when the combined heating method (hybrid heating method) and the microwave heating method are compared, the energy required to obtain the same rate of temperature increase, for example, 40 ° C./min, is almost halved. It can be said that the composite heating method (hybrid heating method) employed in the method for producing metal oxide particles is more energy efficient than the microwave heating method.

  Next, the particle shape of the copper oxide particles obtained by each heating method will be described. 7 is an SEM photograph of copper oxide particles obtained by the microwave heating method, FIG. 8 is an SEM photograph of copper oxide particles obtained by the heater heating method, and FIG. 9 is a metal oxide particle according to the present invention. It is a SEM photograph of the copper oxide particle obtained by the compound heating method (hybrid heating method) employ | adopted with the manufacturing method of this. In any of FIGS. 7 to 8, (A) shows a 2000 times SEM image, and (B) shows a 400 times SEM image.

  The copper oxide particles obtained by the microwave heating method shown in FIG. 7 have a very small particle diameter, and the surface has a large and uneven shape. In addition, although there are small variations in the size of the particles, there are large distorted particles that grow after aggregation.

  The copper oxide particles obtained by the heater heating method shown in FIG. 8 have a large particle diameter and a fibrous surface. The shape is often a sphere. There is also a variation in particle size. However, this is not an aggregate growth, but appears to have grown at different degrees of growth depending on the particles.

  The copper oxide particles obtained by the composite heating method (hybrid heating method) employed in the method for producing metal oxide particles according to the present invention shown in FIG. 9 have a smaller particle size and are slightly smaller than particles by the microwave heating method. It is a big degree. The surface is fibrous. Further, the variation in particle size is small, and the shape is often a sphere. There are not many large particles with strain such as those grown after aggregation.

  From the above, it can be seen that according to the method for producing metal oxide particles according to the present invention, the shape of the particles can be controlled.

  Next, the growth process prediction of the particles produced by each heating device will be described. FIG. 10 is a diagram schematically illustrating the relationship between the temperature distribution and the growth of copper oxide particles in the microwave heating apparatus, and FIG. 11 is a schematic diagram illustrating the relationship between the temperature distribution and the growth of copper oxide particles in the heater heating apparatus. FIG. 12 is a diagram schematically illustrating the relationship between the temperature distribution and the growth of copper oxide particles in the composite wave heating apparatus. In any of FIGS. 10 to 12, (A) shows a schematic diagram of the temperature distribution in the entire apparatus, and (B) shows a schematic diagram of the local temperature distribution.

  The reason why the copper oxide particles obtained by the microwave heating method have a smaller particle diameter than the copper oxide particles obtained by the heater heating method is considered as follows. When the precursor (metal nitrate or metal oxide nitrate solution) accommodated in the reaction vessel 15 is heated by microwaves, heat spots (local high-temperature fields) are locally distributed in the solution. In such a heat spot, the denitration reaction proceeds at a stretch, and copper oxide particles are formed. And since the copper oxide particle produced | generated by the heat spot has high microwave absorptivity, since it becomes very high temperature, it is thought that particle diameter cannot be grown but particle diameter becomes small. That is, in the case of microwave heating, a local high temperature field around the heat spot and the copper oxide particles is formed, so that the particle diameter is reduced.

  Further, in the case of microwave heating, when the entire solution in the reaction vessel 15 is viewed, the central portion is hot and the outer peripheral portion is cold. For this reason, it can be said that in the microwave heating, a local high temperature field, a steep temperature gradient, and a temperature distribution of the bulk scale in the apparatus are formed, so that the particle size distribution of the generated copper oxide particles becomes broad.

  On the other hand, in the case of heater heating, heat spots do not occur and heat is not generated by locally generated copper oxide particles, so the bulk temperature (overall temperature) and the temperature of the field where the particles are generated are equal, It is assumed that the denitration rate is slower than in the case of microwave heating, particle growth is possible, and the particle size is increased. In addition, since the microscopic temperature gradient and the bulk temperature distribution are small, the particle size distribution is sharp.

  In the hybrid heating method (composite heating method) employed in the method for producing metal oxide particles according to the embodiment of the present invention, the microwave output is reduced compared to the heating method using only microwaves. The number and temperature of heat spots generated by wave heating and the calorific value of the copper oxide particles will decrease. For this reason, in the hybrid heating method, the particles can grow to some extent, and the particle diameter is considered to be between the microwave heating method and the heater heating method. Moreover, since the outer peripheral part is thermally insulated by the heat insulation member 14, and the temperature distribution of the bulk scale is also uniform, it is considered that the particle size distribution is uniform.

  As described above, according to the method for producing metal oxide particles of the present invention, in the heating step, the heat absorption mode by the solution that is the metal oxide precursor is obtained by the combined heating method in which heating by the heater and heating by the microwave are performed simultaneously. Since it controls suitably, the reaction process of the production | generation of a metal oxide particle can be controlled, and it becomes possible to control the average particle diameter of the metal oxide particle produced | generated.

  In addition, according to the method for producing metal oxide particles of the present invention, it is possible to control the average particle diameter of the metal oxide particles to be produced, and further, the sintered body using the metal oxide particles as a raw material can be controlled. Since there is a possibility that the density can be controlled by changing the particle size of the sintered body, application to the raw material powder adjustment process in the sintered body manufacturing field is also possible.

DESCRIPTION OF SYMBOLS 10 ... Heating chamber 11 ... Control part 12 ... Heater 13 ... Temperature detection part 14 ... Heat insulation member 15 ... Reaction container 20 ... Magnetron 21 ... Microwave inlet

Claims (2)

As a metal oxide precursor, an adjustment step of adjusting a solution of metal nitrate or metal oxide nitrate,
An accommodating step of accommodating the solution adjusted in the adjusting step in a reaction vessel;
A placing step of placing the reaction vessel in a heating chamber provided with a microwave inlet;
A heater disposed around the reaction vessel, and a microwave that is introduced into the heating chamber from the microwave introduction port and indirectly incident on the solution through the reaction vessel into the reaction vessel; And a heating step of heating the solution;
A measuring step of measuring the temperature of the solution heated in the heating step;
Based on the temperature measured in the measurement step, a control step for controlling heating by the heater and heating by the microwave,
In the method for producing metal oxide particles having
In at least a part of the heating step, a combined heating method in which heating by a heater and heating by a microwave are simultaneously used is used to control the heat absorption mode by the solution and adjust the temperature rising rate of the solution. A method for producing metal oxide particles, comprising controlling the particle size of the metal oxide particles. 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 2. The method for producing metal oxide particles according to claim 1, wherein the metal oxide particles are one kind of metal selected from Fe, Ni, Ru, U, Pu, Np, Am, and Cm.