WO2014035292A2

WO2014035292A2 - Process for producing nano dispersed metal oxides and apparatus for carrying out the same

Info

Publication number: WO2014035292A2
Application number: PCT/RU2013/000713
Authority: WO
Inventors: Artem Aleksandrovich SELYUTIN
Original assignee: Selyutin Artem Aleksandrovich
Priority date: 2012-08-30
Filing date: 2013-08-16
Publication date: 2014-03-06
Also published as: RU2538585C2; WO2014035292A3; RU2012138786A

Abstract

The invention relates to processes for producing metal oxides and, in particular, to processes for producing nano-dispersed powder-like metal oxides, in particular Group III, IV, V, VI, VII, and VIII metal oxides, such as 3d-metal (scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc) oxides, 4d-metal (yttrium, zirconium) oxides, and Group IIIA metal (aluminum, gallium, indium) oxides. A process for producing nano-dispersed metal dioxide powders has been developed, the process comprising continuous, in a flow-through mode, reaction of metal nitrates with carbamide, wherein the reaction medium is subjected to microwave radiation. An apparatus for carrying out the said process has been developed, the apparatus comprising containers for starting reagents, a mixer, a reactor, a condenser, and a product receptacle, wherein the reactor is a microwave oven having a cylinder inserted therein, with the end parts of the cylinder expanding outside the microwave oven. The reactor is provided with a gas outlet line for discharging gaseous products from the cylinder to the condenser having a condensate return line for reversing a condensate back into the container for starting reagents. The reactor cylinder is made of a material conductive of the microwave radiation and having low dielectric loss (for instance, fluoroplastic-4).

Description

PROCESS FOR PRODUCING NANO DISPERSED METAL OXIDES AND APPARATUS FOR CARRYING OUT THE SAME

The present invention relates to processes for producing metal oxides and, in particular, to processes for producing nano-dispersed powder-like metal oxides, in particular Group III, IV, V, VI, VII, and VIII metal oxides, such as 3d-metal (scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc) oxides, 4d- metal (yttrium, zirconium) oxides, and Group IIIA metal (aluminum, gallium, indium) oxides.

The main applications of such metal oxides include using them as starting materials for production of various ceramic materials, powder coatings, catalysts, catalyst carriers, additives to polymer materials, magnetic powders, and biomedical materials. For example, zirconia-based ceramics have long found orthopedic application in the production of implants and prosthetic devices.

The use of metal oxides in nano-dispersed state allows lowering a sintering temperature in the production of ceramic materials. Seeking for simple ways of synthesizing nano-dispersed metal oxide crystals is a topical problem in preparative chemistry.

A number of recent technologies for preparation of nano-dispersed ceramic materials are known:

- Milling of coarsely dispersed oxides in planetary-type or ball mills (mechanochemical technology);

- Plasma-chemical sputtering of a precursor metal or salts thereof [RU 2071678, IPC C01G25/02, 18.05.1994];

- Chemical co-precipitation from a solution [RU 2194028 C2, IPC C04B35/486,

26.02.2001]; and

- Hydrothermal synthesis [CN1636932, IPC C01G25/02, published 13.07.2005]. Disadvantages of the known methods include multistage processes; the necessity to use specialized equipment to maintain high pressure during the synthesis; and the use of further reagents, e.g. a precipitator added to form a favorable oxide structure.

Qi Pang et al. (A Novel Approach For Preparation of Y2o3:Eu3+ Nanoparticles By Microen ulsion-Microwave Heating. Qi Pang, Jianxin Shi, Yu Liu, Desong Xing, Menglian Gong, and Ningsheng Xu; State Key Laboratory of Optoelectronic Materials and Technologies, Materials Science And Engineering B103 (2003) 57_ 61 www.elsevier.com/locate/mseb) disclose the use of europium (Ill)-doped yttrium oxide (Y203:Eu3+) as a substitute of phosphorus in optical display devices and luminous screens. This material is synthesized in the reaction of aqueous yttrium nitride and europium nitride solutions with aqueous ammonia solution by the reverse microemulsion composed of Triton X-100, n-hexanol, cyclohexane, and water. Nanoparticles thus synthesized are processed in the microwave radiation to obtain a nanoscrystalhne oxide of Y₂0₃:Eu₃. EP 2377506 (IPC: A61C5/08; A61K6/02; published on 19.10.2011) discloses a process of producing a ceramic material, the process comprising:

(i) preparing an aqueous solution containing salts of zirconium, cerium, aluminum and at least one further metal;

(ii) adding a base to obtain a precipitate; and

(iii) drying and/or calcining the precipitate.

The material contains at least one further metal. The suitable counterions comprise chlorides, oxychlorides, nitrides, oxalates, hydroxides, and carbonates, wherein chlorides are preferred. Examples of suitable salts comprise ZrCl₄, CeCl₃, A1C1₃, ZnCl₂, MgCl₂, LaCl₃, and ZrOCl₂. For precipitation purpose, it is preferable to use a nitrogen-containing base, for instance, aqueous ammonia at a concentration of 20 - 35 weight %. The base is added dropwise to the aqueous salt solution under stirring until a pH of 7.5 to 10 has been reached, in order to effect precipitation of hydroxides. The precipitated hydroxides are then dried at a temperature of 100 to 120 °C during 12 - 48 hrs, milled and calcined at 500 - 900°C for 1 to 3 hrs. The above process provides a multi-coprecipitation technology allowing for parallel coprecipitation of at least two different crystal phases, namely, at least a Ce0₂-stabilized zirconia phase and an aluminate phase, such as a ZnAl₂0₄ phase, in a single processing step.

Aluminate is selected from the group consisting of ZnAl₂0₄, MgAl₂0₄, LaA10₃, and LaMgAl_nO,9. This technique, however, is too complicated.

Also Patent RU 2,058,939 (IPC⁶: C01G25/02; published on 27.04.1996 - the prior art) discloses a process of manufacturing zirconia powder for ceramic preparation. The zirconia powder is produced from zirconium oxynitrate and ammonia solutions which are poured simultaneously into a buffer solution. In the buffer, a pH of 7 - 8.5 is constantly maintained. The process is carried out under stirring and ultrasound processing at frequency of 22 - 44 kHz, using a UZDN-2T disperser.

In another embodiment, a solution of zirconium and yttrium nitrates is used. Yttrium-stabilized zirconium hydroxide is precipitated in a continuous mode (through series of reactors) under ultrasound processing within a range of 15 - 70 kHz without heating at the pH of 7.5. Then the product is dried, calcined and milled, with the milling time of 1.0 hr. The ultrasound field parameter is preferably selected within the range of 20 - 50 kHz.

Thus, the above technology involves dehydration and calcining along with ultrasound processing during precipitation of a hydroxide. The precipitation is carried out at a sound vibration frequency of 20 to 50 kHz for at least 5 min, which is followed by milling the dried mass for 0.5 - 1.0 hr. Following this technology process, a uniform powder having the particle size substantially of 0.1 - 4.0 microns is produced.

The ultrasound field combined with the hydroxide precipitation process contributes into coarsening the oxide powder grain. Structural homogeneity of hydroxide powder can be achieved through milling, so the technologies for manufacturing ceramic materials generally involve a milling step.

A common disadvantage of the described methods consists in a multiple-step production process required and the necessity of time- and energy-consuming step for milling the resulted product.

As follows from Patent RU 2,058,939 (IPC⁶: C01G25/02; published on 27.04.1996), a technology line utilized for carrying out the prior art process comprises feeding simultaneously the solutions of zirconium oxynitrate and of ammonium into a buffer solution. The reaction is carried out in a continuous mode using a series of reactors under ultrasound processing within the range of 15 - 70 kHz without heating, at the pH of 7.5. Then drying, calcining and milling of the dried product are carried out. The design of the apparatus is rather bulky as it has to incorporate the series of reactors and devices for calcining and milling the resulted product.

Therefore, the first object of the invention is to develop a simple and practically feasible process for producing nano-dispersed powdered metal oxides, in particular Group III, IV, V, VI, VII, and VIII metal oxides, in particular, 3d metal (scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc) oxides, 4d-metal (yttrium, zirconium) oxides, and Group IIIA metal (aluminum, gallium, indium) oxides, having grain size no more than 30 nanometers.

The essence of the invention is in that a process for producing nano-dispersed metal dioxide powders has been developed, the process comprising continuous, in a flow- through mode, reaction of metal nitrates with carbamide, wherein the reaction medium is subjected to microwave radiation. The claimed process provides a substantial increase in the rate of nano-dispersed powder production process and, consequently, reduces processing time. In particular, the process according to the present invention allows producing nano-dispersed metal oxide powders within 20 - 30 min, which is at least 4 to 6 times faster as compared to the known processes. Furthermore, the claimed process is more cost-efficient as compared to the prior art processes due to lower power inputs required for the claimed process.

The process according to the present invention is intended for producing Groups III, IV, V, VI, VII and VIII metal oxides. In one of the specific embodiments, the claimed process is directed to producing 3d metal (scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc) oxides, and/or -/(/-metals (yttrium, zirconium), and/or Group IIIA metal (aluminum, gallium, indium) oxides, by the reaction of a corresponding metal nitrates solution with carbamide.

In one of the specific embodiments, the particle size of the resulted metal oxide powder ranges from 4 to 100 nm. In another specific embodiment, the particle size of metal oxide powder is no more than 30 nm. According to yet another preferable embodiment, the particle size of the metal oxide powder is 10 nm.

In more detail, the reaction can be described by the following equation:

ZrO(N0₃)₂ + NH₂CONH₂→ Zr0₂ + 2N₂0 + C0₂ + 2H₂0

Using the equation, the required amounts of reactants are calculated:

- Zirconyl nitrate dihydrate ZrO(N0₃)₂ ·2Η₂0;

- carbamide CO(NH₂) ₂.

Carbamide is added in an appropriate concentration to a starting aqueous solution of metal nitrates. According to one of the embodiments, the carbamide concentration ranges up to 150-200 g/1. According to a preferable embodiment, the carbamide concentration is up to 70-100 g/1. In yet another preferable embodiment, carbamide is introduced at a molar ratio of one mole of carbamide to two moles of the nitrate groups of metal salt. The second object of the claimed invention is to develop an apparatus for carrying out the disclosed process.

The essence of the claimed apparatus is in that it comprises containers for starting reactants, a mixer, a reactor, a condenser, and a product receptacle. The reactor comprises a microwave oven with a cylinder inserted therein. In one of the embodiments, the end parts of the cylinder extend outside the microwave oven to provide removal of the produced gases out of the oven.

Figure 1 displays a schematic representation of the claimed inventions.

Figures 2 and 3 display the scanning electron microscopy data for zirconium oxide

(Fig. 2) and magnesium oxide (Fig. 3) powders.

Figure 1 features:

1, 2 - containers for starting reagents (1 - for a solution of metal nitrates; 2 - for carbamide solution);

3 - dosing units;

4 -mixer;

5 -reagent feed line;

6 -reactor;

7 -microwave oven;

8 -cylinder;

9 -gas outlet line;

10 -condenser;

11 -product outlet line;

12 -product receptacle; and

13 -temperature sensor.

Thus, the claimed process is carried out as follows.

Solutions of metal nitrates from the starting reagent container 1 and carbamide from the container 2 are continuously fed through the dosing units 3 at a specified ratio to the mixer 4, wherein mixing of the solutions takes place. The resulted mixture is fed via the reagent feed line to the reactor 6 that comprises the microwave oven 7 with the cylinder 8 inserted therein, with the end parts of the cylinder extending outside the microwave oven 7. In the cylinder 8, the reagents interact under microwave radiation in the microwave oven, made to move either under the inlet pressure of reagents or by force of a screw (not shown).

While the starting reagents pass through the cylinder 8 of the reactor 6 under microwave radiation of the microwave oven 7, the nano-dispersed metal oxides are formed. Vapors resulted from the reaction are removed through the gas outlet line 9 into the condenser 10; and water condensed may optionally be used for recycling. The resulted products are led out via the product outlet line 1 1 to the receptacle 12.

Process parameters are monitored using the temperature sensor 13.

The claimed apparatus allows carrying out the process for producing nano- dispersed metal oxides continuously in a flow-through mode, and obtaining a powder product having a desirable particle size.

As a result, nano-dispersed powders having an average grain size of 10 nm have been produced according to the invention.

All the produced products were subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The X-ray diffraction analysis demonstrates that a single-phase preparation has been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials.

The scanning electron microscopy data (see Fig. 2 and Fig. 3) have demonstrated that the resulted powders are predominantly composed of flat crystals having particle size of not more than 30 nm.

EXAMPLES

Example 1

The process is carried out in an apparatus according to the schematic diagram as described above.

The starting aqueous solutions of manganese nitrate and carbamide are used at a molar ratio of two moles of the nitrate groups to 1 mole of carbamide. The reagents are fed into the mixer 4, wherein mixing takes place. The reagents are then subjected to microwave processing in the reactor for 15 min at a microwave radiation power of 700 W.

While passing through the reactor, the reagents are subjected to microwave radiation, which results in the formation of nano-dispersed magnesium oxide. The resulted powder was subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The analysis demonstrated that a single-phase preparation had been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials.

The scanning electron microscopy data demonstrated that the resulted magnesium oxide powder had particle size no more than 10 nm.

Example 2

Zinc oxide was synthesized from starting aqueous solutions of zinc nitride at a ratio of nitrate groups to carbamide as 2:1, with the zinc nitrate being fed from the container 1, and the aqueous carbamide solution (in the proportion of 0.01 mole of carbamide in 200 ml of distilled water) from the container 2. The reagents are subjected to microwave processing in the reactor for 20 min at a microwave radiation power of 700 W.

The resulted powder was subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The analysis demonstrated that a single-phase preparation of zinc oxide had been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials. The scanning electron microscopy data demonstrated that the resulted zinc oxide powder had particle size no more than 10 nm.

Example 3

Zinc oxide was synthesized from a solution of zinc nitrate at a ratio of 0.2 mol of the nitrate groups to 0.1 mol of carbamide dissolved in 400 ml of distilled water.

The process is run in an apparatus in the conditions as described above, only the microwave processing was carried out for 15 minutes at a microwave radiation power of 800 W.

The resulted powder was subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The analysis demonstrated that a single-phase preparation had been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials. The scanning electron microscopy data demonstrated that the resulted powder had particle size no more than 20 nm. Example 4

Zirconium oxide was synthesized from starting aqueous solutions of zirconium nitrate at a ratio of 0.02 mol of the nitrate groups to 0.01 mol of carbamide dissolved in 200 ml of distilled water. The process was run in an apparatus as described above.

The reagents were subjected to microwave processing in the reactor for 20 min at a microwave radiation power of 800 W. The resulted powder was subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The analysis demonstrated that a single-phase preparation had been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials. The scanning electron microscopy data demonstrated that the resulted powder had particle size no more than 10 nm.

Zirconium dioxide is obtained in the nano dispersed state owing to the complete solubility of the starting compounds and a high rate of the process.

It has been found that the microwave processing of the zirconyl nitrate solution, which also contains carbamide as a reducing agent for the nitrate medium, enables obtaining the dry powder of zirconium oxide, upon evaporation of all the water. According to the X-ray phase analysis data, the resulted powder is obtained as grains having the cubic form attributed to zirconium oxide.

The scanning electron microscopy confirms the small size of the grains. The powder of zirconium oxide is substantially in the form of flat grains of the thickness significantly no more than the grain length and width, with the grain thickness no more than 10 nm; i.e., the grains are nanosized.

Example 5

Copper oxide was synthesized from the starting aqueous solutions of copper nitrate at a ratio of 0.02 mol of the nitrate groups to 0.01 mol of carbamide dissolved in 200 ml of distilled water. The process was run as described above, using an apparatus illustrated in Fig. 1. The microwave processing was carried out for 20 minutes at a microwave radiation power of 700 W.

The resulted powder was subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The analysis demonstrated that a single-phase preparation had been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials. The scanning electron microscopy data demonstrated that the resulted powder had particle size no more than 5 nra.

Example 6

Nickel oxide was synthesized from the starting aqueous solutions of nickel nitrate at a ratio of 0.02 mol of the nitrate groups to 0.01 mol [of carbamide] dissolved in distilled water, using an apparatus illustrated above. The reagents were subjected to microwave processing for 10 minutes in the reactor at a microwave radiation power of 1,200 W.

The resulted powder was subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The analysis demonstrated that a single-phase preparation had been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials. The scanning electron microscopy data demonstrated that the resulted powder had particle size no more than 10 nm.

Example 7

As described above, using an apparatus illustrated in Fig. 1, aluminum oxide was synthesized from the starting aqueous solutions of aluminum nitrate at a ratio of 0.02 mol of the nitrate groups to 0.01 mol of carbamide. The reagents were subjected to microwave processing for 10 minutes in the reactor at a microwave radiation power of 900 W.

The resulted powder was subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The analysis demonstrated that a single-phase preparation had been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials. The scanning electron microscopy data demonstrated that the resulted aluminum oxide powder had particle size no more than 10 nm.

Example 8

As described above, using an apparatus illustrated in Fig. 1, yttrium oxide was synthesized from the solutions containing yttrium nitrate and carbamide at a ratio of 0.02 mol of the nitrate groups to 0.01 mol of carbamide dissolved in 200 ml of distilled water. The reagents were subjected to microwave processing for 20 minutes in the reactor at a microwave radiation power of 800 W. The resulted powder was subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The analysis demonstrated that a single-phase preparation had been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials. The scanning electron microscopy data demonstrated that the resulted powder had particle size no more than 10 nm.

Example 9

As described above, using an apparatus illustrated in Fig. 1, gallium oxide was synthesized from the solutions containing gallium nitrate and carbamide at a ratio of 0.02 mol of the nitrate groups to 0.01 mol of carbamide. The reagents were subjected to microwave processing for 15 minutes in the reactor at a microwave radiation power of 800 W.

The resulted powder was subjected to X-ray phase analysis with a DRON-3 diffractometer using CuKa-radiation. The [X-ray diffraction] analysis demonstrated that a single-phase preparation had been obtained, with no reflections [on the X-ray diffraction patterns] attributable to the starting materials. The scanning electron microscopy data demonstrated that the resulted powder had particle size no more than 10 nm.

A substantial feature of the claimed invention is the novel method for obtaining nano- dispersed metal oxides, which comprises introducing carbamide into a metal nitrate solution at a specified ratio and heat-treating the starting nitrate solutions in a microwave oven. The ultra-dispersed material according to the claimed invention is obtained depending on the determining factors of carrying out the heat treatment in a single processing step, and using a specially designed apparatus, the reactor whereof is operative under the effect of microwave radiation and is designed for operation in a flow-through continuous mode.

In the present invention, the target purpose has therefore been achieved by the inventors: a simple and practically feasible process has been developed for preparing nano dispersed powdered Groups III, IV, V, VI, VII, and VIII metal oxides, in particular Group III, IV, V, VI, VII, and VIII metal oxides, such as 3d-metal (scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc) oxides, 4d-metal (yttrium, zirconium) oxides, and Group IIIA metal (aluminum, gallium, indium) oxides, having particle size no more than 10 nanometers.

Claims

We claim:

1. A process for producing nano-dispersed metal oxides from aqueous metal nitrate solutions, the process comprising carrying out a continuous reaction, in a flow- through mode, of metal nitrates with carbamide, wherein reaction medium is subjected to microwave radiation.

2. The process of claim 1, wherein the said metal oxides are oxides of metals of the Groups III, IV, V, VI, VII and VIII of the Periodic Table.

3. The process of claim 1, wherein the said metal oxides are 3d-metal oxides, such as scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc oxides.

4. The process of claim 1, wherein the said metal oxides are 4d-metal oxides, such as yttrium, zirconium.

5. The process of claim 1, wherein the said metal oxides are Group III A metal oxides, such as aluminum, gallium, indium oxides.

6. The process of claim 1, wherein the said metal oxides have particle size of about 4 to 100 nm.

7. The process of claim 6, wherein the said metal oxides have particle size no more than 30 nm, preferably no more than 10 nm.

8. The process of any one of claims 1 to 7, wherein the microwave radiation power is approximately 500 - 2,000 W.

9. The process of any one of claims 1 to 7, wherein the duration of the said subjection to microwave radiation is approximately 5 to 60 min.

10. An apparatus for carrying out the process for producing nano-dispersed metal oxides, the apparatus comprising containers for starting reagents, a mixer and a reactor, wherein the said reactor is a microwave reactor.

11. The apparatus of claim 10, wherein the apparatus further comprises a condenser and a product receptacle.

12. The apparatus of claim 10, wherein the microwave reactor is a microwave oven having a cylinder inserted therein with the end parts thereof extending outside the microwave oven.