US20040221685A1 - Method for manufacturing nano-scaled copper powder by wet reduction process - Google Patents
Method for manufacturing nano-scaled copper powder by wet reduction process Download PDFInfo
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- US20040221685A1 US20040221685A1 US10/451,232 US45123203A US2004221685A1 US 20040221685 A1 US20040221685 A1 US 20040221685A1 US 45123203 A US45123203 A US 45123203A US 2004221685 A1 US2004221685 A1 US 2004221685A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
- B22F9/24—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from liquid metal compounds, e.g. solutions
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
Definitions
- the present invention relates to a method for manufacturing a nano-scaled copper powder by a wet reduction process, and more particularly to a method for manufacturing a nano-scaled copper powder by a wet reduction process, comprising adding appropriate amounts of hydrazine (N 2 H 4 ) and alkaline hydroxide to an aqueous copper salt(CuX, X ⁇ Cl 2 , Br 2 , SO 4 , (NO 3 ) 2 . . . ) solution to finally obtain copper powders having 100 nm ⁇ 1 ⁇ m graded particle size via chelate.
- Copper (Cu) powder is employed in an electrically conductive paste material for multilayer passive devices, for example, a multilayer ceramic chip capacitor (MLCC). Recently, in order to produce the conductive material for inner electrode, a copper powder with a submicron scaled particle size ranging from 0.8 ⁇ m ⁇ 1 ⁇ m has been used.
- MLCC multilayer ceramic chip capacitor
- nano-scaled copper powder with good dispersibility may be considered. It is anticipated that such nano-scaled copper powder be applied to any miniaturized passive devices for which development is in progress in the pertinent art.
- a metal conductive paste material is required to be sintered at a low temperature of 550° C.
- Various application industries also tend to lower the sintering temperature.
- a metal compound that has a weak binding force between metal and anion is thermally decomposed using a gas reducing agent and milled to obtain a metal powder.
- This method provides a fine metal powder.
- the metal powder may be burned during a heat treatment the burned powder is required to be milled and classified. Therefore, this method has a lower yield than a liquid phase reduction method when used in preparing a metal powder for forming a thick film conductive paste material.
- an evaporation material is evaporated by heating its source under an inert gas such as He and Ar or an active gas such as CH 4 and NH 4 , and the evaporated gas is reduced and condensed in the seducing gas such as H 2 obtain a fine metal powder.
- This method is advantageous in preparing a metal powder having its particle size of 5 nm ⁇ several ⁇ m.
- productivity is very low and thus the metal powder is very expensive.
- a liquid phase reduction method is an exemplary chemical method for manufacturing a metal powder. This method can more easily control the shape of the powder and can prepare an ultrafine powder having a particle size of a submicron unit, compared with the aforementioned methods. The complete procedure of preparing a metal powder by reducing an initial precipitate is carried out in a liquid phase.
- a metal powder can be prepared by a procedure comprising a initial intermediate forming, producing an intermediate product and adding a reducing agent.
- the reducing agent comprises formalin, hydrazine, an organic compound and the like.
- the liquid phase reduction method provides easy control of the powder shape, high sphericity, and narrow particle size distribution. Furthermore, it is possible to prepare an ultrafine powder having a submicron-scaled particle size that is excellent in the surface property of the powder. Therefore, a powder that is high in tap density, one of the most important characteristics for a conductive paste material can be prepared. Despite these advantages, optimization of concentration, temperature, pH, and reaction rate is a prerequisite to prepare a metal powder.
- a conventional wet method such as the liquid phase reduction method, for preparing a copper powder controls the particle size of the powder through a multi-step reaction, as shown in FIG. 1.
- CuO copper oxide
- NaOH sodium hydroxide
- CuSO 4 aqueous copper sulfate
- a stable Cu 2 O solution is obtained by reacting the obtained CuO with glucose (C 6 H 12 O 6 ), a representative aldohexose (a monosaccharide having 6 carbons and an aldehyde group).
- glycine NH 2 —CH 2 —COOH
- a kind of amino acid a kind of amino acid
- arabic gum are added to the Cu 2 O solution and uniformly dispersed.
- hydrazine N 2 H 4 as a reducing agent is added to the mixture to thereby reduce Cu 2 O, to obtain a copper powder as a precipitate.
- the glycine and arabic gum as the third additives are added to control the size and surface shape of the final copper powder.
- CuO copper oxide
- CuSO 4 aqueous copper sulfate
- the particle size of the copper powder is different depending on the addition condition of the additives and thus it is difficult to control the particle size.
- the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for manufacturing an ultrafine copper powder having particle size of 100 nm grade ⁇ 1 ⁇ m grade by a wet reduction process, comprising the steps of adding sodium hydroxide (NaOH) to an aqueous copper chloride (CuCl 2 ) solution with high anionic effect, and reducing the resulting copper oxide (Cu x O) by the addition of hydrazine (N 2 H 4 ).
- the method is a relatively simple process and also affords a high degree of reproducibility.
- copper powder having particle size of 100 nm grade ⁇ 1 ⁇ m grade can be prepared which has good surface quality, narrow particle size distribution, and good powder sphericity.
- a method for manufacturing a nano-scaled copper powder by a wet reduction process comprising the steps of adding sodium hydroxide (NaOH) to an aqueous copper chloride (CuCl 2 ) solution to give an aqueous solution containing copper oxide and copper hydroxide;
- the sodium hydroxide (NaOH) is added in an amount of 2 to 33 moles per mole of the copper chloride (CuCl 2 ) when the aqueous copper chloride (CuCl 2 ) solution is kept within a temperature of 30 to 80° C.
- the hydrazine (N 2 H 4 ) is added in an amount of 0.5 to 12 moles per mole of the copper chloride when the aqueous solution containing the copper oxide and the copper hydroxide is kept within a temperature of 40 to 80° C.
- silver nitrate (AgNO 3 ) is added to the aqueous copper chloride (CuCl 2 ) solution in an amount of 1/1,000 to 1/10,000 moles per mole of the copper chloride.
- a method for manufacturing a nano-scaled copper powder by a wet reduction process comprising the steps of adding hydrazine (N 2 H 4 ) to an aqueous copper chloride (CuCl 2 ) solution to give an aqueous solution containing a copper complex (Cu(N 2 H 4 ) m Cl n ); adding sodium hydroxide (NaOH) to the aqueous copper complex solution to obtain a nano-scaled copper powder; and filtering and drying the nano-scaled copper powder.
- the hydrazine (N 2 H 4 ) is added in an amount of 0.5 to 12 moles per mole of the copper chloride (CuCl 2 ) when the aqueous copper chloride (CuCl 2 ) solution is kept within a temperature of 20 to 70° C.
- the sodium hydroxide (NaOH) is added in an amount of 2 to 33 moles per mole of the copper chloride when the aqueous solution containing the copper complex is kept within a temperature of 40 to 80° C.
- FIG. 1 is a schematic flow diagram showing the conventional wet method for preparing a copper powder
- FIG. 2 is a schematic flow diagram showing the wet reduction method for preparing a nano-scaled copper powder according to the first embodiment of the present invention
- FIG. 3 is a schematic flow diagram showing the wet reduction method for preparing a nano-scaled copper powder according to the second embodiment of the present invention.
- FIG. 4 is a Scanning Electron Microscopy (SEM) photograph of the nano-scaled copper powder prepared according to the first embodiment of the present invention
- FIG. 5 is a SEM photograph of the nano-scaled copper powder prepared according to the second embodiment of the present invention.
- FIG. 6 is a SEM photograph of the nano-scaled copper powder prepared by adding a trace amount of silver nitrate for use with the first embodiment of the present invention.
- FIG. 7 is a SEM photograph of the nano-scaled copper powder prepared by adding a trace amount of silver nitrate for use with the second embodiment of the present invention.
- copper chloride (CuCl 2 ) is used as a copper salt for preparing a copper powder, instead of copper sulfate (CuSO 4 ) in a conventional wet method.
- Copper chloride (CuCl 2 ) has an anionic group that is higher in terms of electronegativity, relative to copper sulfate (CuSO 4 ), whereby the chlorine ion has a higher anionic effect than the sulfate ion in a solution. Therefore, agglomeration of the copper powder is more effectively prevented, thereby causing a much finer powder to be produced. Furthermore, copper chloride acts to effectively control the shape of the powder surface.
- a nano-scaled copper powder is prepared by adding sodium hydroxide (NaOH) to an aqueous copper chloride solution (CuCl 2 ) to give copper oxide (CuO) and copper hydroxide (Cu(OH) 2 ) as intermediate products, reducing the intermediate products using hydrazine (N 2 H 4 ), followed by filtered and dried.
- NaOH sodium hydroxide
- CuCl 2 aqueous copper chloride solution
- CuO copper oxide
- Cu(OH) 2 copper hydroxide
- Cu(OH) 2 copper hydroxide
- the temperature of the aqueous CuCl 2 solution it is preferable to limit the temperature of the aqueous CuCl 2 solution to a range of 30 to 80° C. upon the addition of NaOH. If the temperature of the aqueous CuCl 2 solution is less than 30° C., it is difficult to prepare the intermediate products. On the other hand, if the temperature of the aqueous CuCl 2 solution exceeds 80° C., the intermediate products are quickly prepared, thus causing severe agglomeration. At the same time, because the reduction reaction is carried out at too high a temperature, 100° C. or more, the thermal stability of the intermediate products is lowered.
- the amount of the added N 2 H 4 ranges from 0.5 to 12 moles per mole of CuCl 2 . If the amount of N 2 H 4 is less than 0.5 moles, the reduction reaction may be incomplete. On the other hand, if it exceeds 12 moles, although the reaction rate is increased, the product is severely agglomerated and the surface quality of the copper powder is lowered.
- hydrazine to an aqueous solution containing the copper oxide (CuO) and copper hydroxide (Cu(OH) 2 ) when the temperature of the aqueous solution is kept within a range of 40 to 80° C. If the temperature is less than 40° C., the reduction reaction is not easily carried out, resulting in an incomplete reduction reaction. On the other hand, if it exceeds 80° C., the reduction reaction is easily carried out but it is carried out at too high a temperature, thereby causing agglomeration of the product.
- CuO copper oxide
- Cu(OH) 2 copper hydroxide
- the precipitated copper powder is filtered to eliminate NaCl salt and then dried under a non-oxidizing atmosphere, to thereby finally produce a nano-scaled copper powder.
- silver nitrate (AgNO 3 ) may be added in a trace amount of 1/1,000 to 1/10,000 moles per mole of the copper chloride. Because silver is reduced faster than copper, the addition of silver nitrate enables an increase in the reduction rate of the copper.
- silver acts as a catalyst to promote the nucleation of copper, thereby increasing the reduction rate of copper. As a result, the total reduction rate of copper is increased.
- the obtained copper powder is filtered to eliminate NaCl salt and a nitrate ion (NO 3 ⁇ ) and then dried under a non-oxidizing atmosphere to thereby finally produce a nano-scaled copper powder.
- a nano-scaled copper powder can also be prepared, even though the addition sequence of NaOH and hydrazine (N 2 H 4 ) is changed.
- the amount of the added hydrazine (N 2 H 4 ) is less than 1 mole, the desired intermediate product is not obtained; while, if it exceeds 12 moles a large amount of ions are left in the aqueous copper chloride solution, thereby increasing impurities. Furthermore, a partial reduction reaction may occur.
- the obtained nano-scaled copper powder is filtered and dried, to thereby finally give an ultrafine copper powder having a particle size of 100 nm grade.
- the copper powder obtained is filtered and dried under a non-oxidizing atmosphere to thereby finally produce a nano-scaled copper powder.
- a sodium hydroxide (NaOH) with varying concentrations was added to 100 ml of an aqueous copper sulfate (CuSO 4 ) solution to produce an aqueous solution containing copper oxide (Cu x O) as a precipitate. Then, the copper oxide was filtered and recovered.
- NaOH sodium hydroxide
- CuSO 4 aqueous copper sulfate
- the average particle size of each copper powder (samples 11 to 13) prepared by the conventional wet method varied, depending on the amounts of added reaction agents and additives. Specifically, the particle size distribution ranged from about 0.4 to 1 ⁇ m.
- the particle size of the final product, copper powder depends on the concentration of the sodium hydroxide; the amount of the sodium hydroxide can be adjusted according to the desired particle size.
- the copper powder obtained according to the above procedure was washed with secondary distilled water and filtered.
- the filtered copper powder was dried at an appropriate temperature under a non-oxidizing atmosphere to thereby finally obtain a nano-scaled copper powder.
- the conventional wet method for preparing a copper powder comprises various processes such as filtering, recovering and addition of distilled water.
- the wet reduction method according to the present invention is carried out in one reaction vessel and the process for recovering a copper powder is carried out only once.
- the particle size distribution of the copper powder obtained according to the present invention is given in Table 2.
- TABLE 2 Particle size distribution of copper powder according to the concentration of NaOH Particle size distribution Av- Sam- erage ple D10 D50 D90 size Section No. CuCl 2 NaOH N 2 H 4 ( ⁇ m) ( ⁇ m) ( ⁇ m) ( ⁇ m) Com- 21 1 1 12 0.05 0.10 0.14 0.10 parative sample Inventive 22 1 2 12 0.05 0.10 0.16 0.10 samples 23 1 4 12 0.06 0.13 0.22 0.14 24 1 8 12 0.09 0.15 0.25 0.17 25 1 16 12 0.12 0.38 0.50 0.36 26 1 33 12 0.20 0.50 0.70 0.45 Com- 27 1 35 12 0.29 0.70 0.87 0.63 parative sample
- the sodium hydroxide (NaOH) was added with varying concentrations of 2 to 33 moles per mole of the copper chloride (CuCl 2 ).
- the copper powder obtained according to the above procedure was washed with secondary distilled water and filtered.
- the filtered copper powder was dried to obtain a nano-scaled copper powder.
- Table 4 shows the particle size distribution according to the amount of NaOH per mole of the copper chloride (CuCl 2 ). As shown in Table 4, as the amount of NaOH increased, the particle size of the obtained powder increased and a wide particle size distribution was obtained.
- Example 3 Although the intermediate product of the present example was different than that of Example 2, the final result was almost similar. It can be seen from the forgoing that the method of Example 3 is suitable for preparing a copper powder having a particle size of 100 nm grade, similar to Example 2.
- Example 4 a trace amount of silver nitrate (AgNO 3 ) is further added to the aqueous copper chloride solution in Examples 2 and 3. Because silver is reduced faster than copper, the addition of silver nitrate enables the promotion of a heterogeneous nucleation of copper, thereby increasing the reduction rate of copper.
- AgNO 3 silver nitrate
- Example 4 The copper powder according to Example 4 was compared with those according to Examples 2 and 3 in terms of the particle size distribution of a copper powder. The results are given in Table 5. TABLE 5 Particle size distribution of copper powder according to presence or absence of AgNO 3 Particle size distribution Sample D10 D50 D90 Average No CuCl 2 NaOH N 2 H 4 AgNO 3 ( ⁇ m) ( ⁇ m) ( ⁇ m) size ( ⁇ m) Remarks 22 1 2 12 X 0.05 0.10 0.16 0.10 NaOH N 2 H 4 31 1 2 12 X 0.06 0.10 0.20 0.10 N 2 H 4 NaOH 41 1 2 12 0.006 0.05 0.12 0.20 0.11 NaOH N 2 H 4 42 1 2 12 0.007 0.05 0.11 0.22 0.11 N 2 H 4 NaOH
- sample 41 NaOH and N 2 H 4 were in sequence added to an aqueous (CuCl 2 +AgNO 3 ) solution, and in sample 42, N 2 H 4 and NaOH were added in sequence to an aqueous (CuCl 2 +AgNO 3 ) solution, for the purpose of obtaining a copper powder.
- the copper powders prepared according to the conventional wet method had relatively coarse average particle size of 0.4 to 1 ⁇ m.
- the copper powders prepared according to the present invention had ultrafine average particle size of 100 nm grade ⁇ 1 ⁇ m grade.
- the present invention provides two mechanisms for preparing an ultrafine copper powder having a particle size of (100 nm grade ⁇ 1 ⁇ m grade).
- the two mechanisms are very suitable for preparing an ultrafine copper powder having a particle size of 100 nm grade.
- the nano-scaled copper powder prepared according to the present invention is excellent in particle size distribution and dispersibility.
- the particle size of the copper powder varies according to the amount of sodium hydroxide (NaOH), thereby making it possible to control the particle size and distribution thereof.
- NaOH sodium hydroxide
- AgNO 3 silver nitrate
- the method according to the present invention is a relatively simple process and also affords a high degree of reproducibility.
- copper powder having a particle size of 100 nm can be prepared which has a good surface quality, narrow particle size distribution, and good powder sphericity.
Abstract
The present invention relates to a method for manufacturing a nano-scaled copper powder by a wet reduction process, comprising adding appropriate amounts of sodium hydroxide (NaOH) and hydrazine (N2H4) to an aqueous copper chloride (CuCl2) solution to finally obtain a copper powder having a particle size of 100 nm (0.1 nm) grade via an intermediate product such as a copper complex.
Description
- The present invention relates to a method for manufacturing a nano-scaled copper powder by a wet reduction process, and more particularly to a method for manufacturing a nano-scaled copper powder by a wet reduction process, comprising adding appropriate amounts of hydrazine (N2H4) and alkaline hydroxide to an aqueous copper salt(CuX, X═Cl2, Br2, SO4, (NO3)2 . . . ) solution to finally obtain copper powders having 100 nm˜1 μm graded particle size via chelate.
- Copper (Cu) powder is employed in an electrically conductive paste material for multilayer passive devices, for example, a multilayer ceramic chip capacitor (MLCC). Recently, in order to produce the conductive material for inner electrode, a copper powder with a submicron scaled particle size ranging from 0.8 μm˜1 μm has been used.
- In this regard, development of a nano-scaled copper powder with good dispersibility may be considered. It is anticipated that such nano-scaled copper powder be applied to any miniaturized passive devices for which development is in progress in the pertinent art.
- Meanwhile, in the fields of PDPs (Plasma Display Panels), FEDs (Field Emission Displays), automobile back light and the like using glass as a substrate, a metal conductive paste material is required to be sintered at a low temperature of 550° C. Various application industries also tend to lower the sintering temperature.
- The use of a nano-scaled (100 nm) metal powder can keep pace with the trend of lowering the sintering temperature of a metal conductive paste material. Therefore, it is anticipated that the conductive paste material can be used for forming electrodes that have up till now been exclusively carried out by a plating method, due to a higher sintering temperature.
- Many different methods have been involved in the synthesis of a copper powder used in the conductive paste as described above, such as a gas phase method and a liquid phase method.
- Conventional methods for manufacturing metal powders have various problems such as a low yield due to wide particle size distribution, large particle size, low sphericity, and difficulty in controlling a degree of oxidation. In order to overcome these problems, a wet method such as a liquid phase reduction method and a thermal decomposition method, as well as a gas phase method such as gas evaporation method and the like, have been developed.
- Methods generally used for manufacturing metal powders are summarized, as follows.
- With respect to a gas atomization method, a high-pressure inert gas is atomized to a molten metal flowing through a nozzle to obtain a metal powder. Although this method is suitable for mass production, it is difficult to prepare a nano-scaled powder, thereby powder yield being considerably lowered. Therefore, the gas atomization method is restrictively used.
- With respect to a thermal decomposition method, a metal compound that has a weak binding force between metal and anion is thermally decomposed using a gas reducing agent and milled to obtain a metal powder. This method provides a fine metal powder. However, because the metal powder may be burned during a heat treatment the burned powder is required to be milled and classified. Therefore, this method has a lower yield than a liquid phase reduction method when used in preparing a metal powder for forming a thick film conductive paste material.
- In a gas evaporation method, an evaporation material is evaporated by heating its source under an inert gas such as He and Ar or an active gas such as CH4 and NH4, and the evaporated gas is reduced and condensed in the seducing gas such as H2 obtain a fine metal powder. This method is advantageous in preparing a metal powder having its particle size of 5 nm˜several μm. However, productivity is very low and thus the metal powder is very expensive.
- A liquid phase reduction method is an exemplary chemical method for manufacturing a metal powder. This method can more easily control the shape of the powder and can prepare an ultrafine powder having a particle size of a submicron unit, compared with the aforementioned methods. The complete procedure of preparing a metal powder by reducing an initial precipitate is carried out in a liquid phase.
- In detail, a metal powder can be prepared by a procedure comprising a initial intermediate forming, producing an intermediate product and adding a reducing agent. The reducing agent comprises formalin, hydrazine, an organic compound and the like.
- Advantageously, the liquid phase reduction method provides easy control of the powder shape, high sphericity, and narrow particle size distribution. Furthermore, it is possible to prepare an ultrafine powder having a submicron-scaled particle size that is excellent in the surface property of the powder. Therefore, a powder that is high in tap density, one of the most important characteristics for a conductive paste material can be prepared. Despite these advantages, optimization of concentration, temperature, pH, and reaction rate is a prerequisite to prepare a metal powder.
- A conventional wet method, such as the liquid phase reduction method, for preparing a copper powder controls the particle size of the powder through a multi-step reaction, as shown in FIG. 1.
- In detail, in a first step, copper oxide (CuO) is precipitated by adding sodium hydroxide (NaOH) to an aqueous copper sulfate (CuSO4) solution, and then filtered.
- In a second step, a stable Cu2O solution is obtained by reacting the obtained CuO with glucose (C6H12O6), a representative aldohexose (a monosaccharide having 6 carbons and an aldehyde group).
- In a third step, when the color of the resulting solution changed into a dark red due to the production of Cu2O, glycine (NH2—CH2—COOH), a kind of amino acid, and arabic gum are added to the Cu2O solution and uniformly dispersed. Then, hydrazine (N2H4) as a reducing agent is added to the mixture to thereby reduce Cu2O, to obtain a copper powder as a precipitate.
- The glycine and arabic gum as the third additives are added to control the size and surface shape of the final copper powder.
- By obtaining the copper oxide (CuO) as a precipitate, by adding sodium hydroxide (NaOH) to an aqueous copper sulfate (CuSO4) solution, the effect of impurities that are left in the solution on the product can be minimized.
- As described above, in the conventional wet method for preparing a copper powder, copper sulfate (CuSO4) is used as a copper source. As a result, an anionic effect is reduced, whereby the particles of the copper powder become agglomerated.
- It is difficult adjust the input condition by addition of the glycine and Arabic gum as an organic additive to control the size and surface shape of the copper powder, whereby a high degree of reproducibility cannot be afforded.
- The particle size of the copper powder is different depending on the addition condition of the additives and thus it is difficult to control the particle size.
- The process is complicated due to many variables such as additives, reaction agents (NaOH, N2H4), together with its quantity and method of addition and a solution temperature and requires a longer preparation time.
- Relatively coarse copper powder, having a particle size of 0.5 to 4 μm grade, is obtained and the particle size distribution of the powder is not uniform.
- In particular, because Cu2O is a chemically stable intermediate product, the growth rate of the copper powder is slow. Therefore, it is difficult to maintain the sphericity of the powder surface.
- For the forgoing reasons, it is difficult to prepare an ultrafine copper powder having a particle size of 0.1 μm (100 nm) grade using the conventional wet method.
- Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method for manufacturing an ultrafine copper powder having particle size of 100 nm grade˜1 μm grade by a wet reduction process, comprising the steps of adding sodium hydroxide (NaOH) to an aqueous copper chloride (CuCl2) solution with high anionic effect, and reducing the resulting copper oxide (CuxO) by the addition of hydrazine (N2H4). The method is a relatively simple process and also affords a high degree of reproducibility. Furthermore, copper powder having particle size of 100 nm grade˜1 μm grade can be prepared which has good surface quality, narrow particle size distribution, and good powder sphericity.
- In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a method for manufacturing a nano-scaled copper powder by a wet reduction process, comprising the steps of adding sodium hydroxide (NaOH) to an aqueous copper chloride (CuCl2) solution to give an aqueous solution containing copper oxide and copper hydroxide;
- reducing the copper oxide and the copper hydroxide to obtain a nano-scaled copper powder as a precipitate by adding hydrazine (N2H4) to the aqueous solution; and filtering and drying the precipitated nano-scaled copper powder.
- Preferably, the sodium hydroxide (NaOH) is added in an amount of 2 to 33 moles per mole of the copper chloride (CuCl2) when the aqueous copper chloride (CuCl2) solution is kept within a temperature of 30 to 80° C., and the hydrazine (N2H4) is added in an amount of 0.5 to 12 moles per mole of the copper chloride when the aqueous solution containing the copper oxide and the copper hydroxide is kept within a temperature of 40 to 80° C.
- Preferably, in the step of producing the copper oxide and the copper hydroxide, before the addition of NaOH, silver nitrate (AgNO3) is added to the aqueous copper chloride (CuCl2) solution in an amount of 1/1,000 to 1/10,000 moles per mole of the copper chloride.
- In accordance with another aspect of the present invention, there is provided a method for manufacturing a nano-scaled copper powder by a wet reduction process, comprising the steps of adding hydrazine (N2H4) to an aqueous copper chloride (CuCl2) solution to give an aqueous solution containing a copper complex (Cu(N2H4)mCln); adding sodium hydroxide (NaOH) to the aqueous copper complex solution to obtain a nano-scaled copper powder; and filtering and drying the nano-scaled copper powder.
- Preferably, the hydrazine (N2H4) is added in an amount of 0.5 to 12 moles per mole of the copper chloride (CuCl2) when the aqueous copper chloride (CuCl2) solution is kept within a temperature of 20 to 70° C., and the sodium hydroxide (NaOH) is added in an amount of 2 to 33 moles per mole of the copper chloride when the aqueous solution containing the copper complex is kept within a temperature of 40 to 80° C.
- Preferably, in the step of producing the copper complex (Cu(N2H4)mCln), before the addition of hydrazine, silver nitrate (AgNO3) is added to the aqueous copper chloride (CuCl2) solution in an amount of 1/1,000 to 1/10,000 moles per mole of the copper chloride.
- The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
- FIG. 1 is a schematic flow diagram showing the conventional wet method for preparing a copper powder;
- FIG. 2 is a schematic flow diagram showing the wet reduction method for preparing a nano-scaled copper powder according to the first embodiment of the present invention;
- FIG. 3 is a schematic flow diagram showing the wet reduction method for preparing a nano-scaled copper powder according to the second embodiment of the present invention;
- FIG. 4 is a Scanning Electron Microscopy (SEM) photograph of the nano-scaled copper powder prepared according to the first embodiment of the present invention;
- FIG. 5 is a SEM photograph of the nano-scaled copper powder prepared according to the second embodiment of the present invention;
- FIG. 6 is a SEM photograph of the nano-scaled copper powder prepared by adding a trace amount of silver nitrate for use with the first embodiment of the present invention; and
- FIG. 7 is a SEM photograph of the nano-scaled copper powder prepared by adding a trace amount of silver nitrate for use with the second embodiment of the present invention.
- Hereinafter, the present invention will be described in more detail.
- According to the present invention, copper chloride (CuCl2) is used as a copper salt for preparing a copper powder, instead of copper sulfate (CuSO4) in a conventional wet method.
- Copper chloride (CuCl2) has an anionic group that is higher in terms of electronegativity, relative to copper sulfate (CuSO4), whereby the chlorine ion has a higher anionic effect than the sulfate ion in a solution. Therefore, agglomeration of the copper powder is more effectively prevented, thereby causing a much finer powder to be produced. Furthermore, copper chloride acts to effectively control the shape of the powder surface.
- For the forgoing reasons, according to the present invention, a nano-scaled copper powder is prepared by adding sodium hydroxide (NaOH) to an aqueous copper chloride solution (CuCl2) to give copper oxide (CuO) and copper hydroxide (Cu(OH)2) as intermediate products, reducing the intermediate products using hydrazine (N2H4), followed by filtered and dried.
-
- In the above reaction, NaOH is added to produce copper oxide and copper hydroxide. The amount of the added NaOH ranges from 2 to 33 moles per mole of CuCl2. If the amount of NaOH exceeds 33 moles, the obtained aqueous solution is changed into a strong basic solution. Therefore, a reduction reaction does not completely occur in the subsequent step of adding N2H4. Furthermore, such addition is uneconomical and a large amount of ions are left in the aqueous solution, resulting in an increase of impurities.
- On the other hand, if the amount of NaOH is less than 2 moles, the desired intermediate product, copper oxide (CuxO) is not obtained. As a result, subsequent reaction cannot be accomplished.
- It is preferable to limit the temperature of the aqueous CuCl2 solution to a range of 30 to 80° C. upon the addition of NaOH. If the temperature of the aqueous CuCl2 solution is less than 30° C., it is difficult to prepare the intermediate products. On the other hand, if the temperature of the aqueous CuCl2 solution exceeds 80° C., the intermediate products are quickly prepared, thus causing severe agglomeration. At the same time, because the reduction reaction is carried out at too high a temperature, 100° C. or more, the thermal stability of the intermediate products is lowered.
-
- In the above reaction, the amount of the added N2H4 ranges from 0.5 to 12 moles per mole of CuCl2. If the amount of N2H4 is less than 0.5 moles, the reduction reaction may be incomplete. On the other hand, if it exceeds 12 moles, although the reaction rate is increased, the product is severely agglomerated and the surface quality of the copper powder is lowered.
- It is preferable to add hydrazine to an aqueous solution containing the copper oxide (CuO) and copper hydroxide (Cu(OH)2) when the temperature of the aqueous solution is kept within a range of 40 to 80° C. If the temperature is less than 40° C., the reduction reaction is not easily carried out, resulting in an incomplete reduction reaction. On the other hand, if it exceeds 80° C., the reduction reaction is easily carried out but it is carried out at too high a temperature, thereby causing agglomeration of the product.
- The precipitated copper powder is filtered to eliminate NaCl salt and then dried under a non-oxidizing atmosphere, to thereby finally produce a nano-scaled copper powder.
- Meanwhile, before the addition of sodium hydroxide (NaOH) to the aqueous copper chloride (CuCl2) solution, silver nitrate (AgNO3) may be added in a trace amount of 1/1,000 to 1/10,000 moles per mole of the copper chloride. Because silver is reduced faster than copper, the addition of silver nitrate enables an increase in the reduction rate of the copper.
- That is, silver acts as a catalyst to promote the nucleation of copper, thereby increasing the reduction rate of copper. As a result, the total reduction rate of copper is increased.
-
-
- In the above reaction, the obtained copper powder is filtered to eliminate NaCl salt and a nitrate ion (NO3 −) and then dried under a non-oxidizing atmosphere to thereby finally produce a nano-scaled copper powder.
- Meanwhile according to the present invention, a nano-scaled copper powder can also be prepared, even though the addition sequence of NaOH and hydrazine (N2H4) is changed.
- This is feasible because CuCl2 reacts with hydrazine (N2H4) to form a copper complex (Cu(N2H4)mCln).
-
- In the above reaction, if the temperature of the aqueous copper chloride solution is less than 20° C., the desired intermediate product is not obtained. Rather, an undesirable intermediate product may be obtained or such an undesirable reaction may occur. On the other hand, if it exceeds 70° C., the desired intermediate product is obtained and at the same time, a partial reduction reaction thereof may occur.
- If the amount of the added hydrazine (N2H4) is less than 1 mole, the desired intermediate product is not obtained; while, if it exceeds 12 moles a large amount of ions are left in the aqueous copper chloride solution, thereby increasing impurities. Furthermore, a partial reduction reaction may occur.
-
- In the above reaction, if the temperature of the aqueous solution containing the copper complex is less than 40° C., a reduction reaction is not easily carried out and even then has a slow reaction rate. On the other hand, if the temperature exceeds 80° C., the reduction reaction is increased but the copper powder is easily agglomerated due to a too high temperature.
- If the amount of the added sodium hydroxide NaOH) is less than 2 moles, the reduction reaction is not easily carried out. On the other hand, if it exceeds 33 moles, the reduction reaction is increased but a large amount of ions are left in the aqueous solution, thereby increasing impurities. Furthermore, excess NaOH is wasteful from an economical point of view.
- Then, the obtained nano-scaled copper powder is filtered and dried, to thereby finally give an ultrafine copper powder having a particle size of 100 nm grade.
-
-
- The copper powder obtained is filtered and dried under a non-oxidizing atmosphere to thereby finally produce a nano-scaled copper powder.
- The present invention will hereinafter be described more specifically by non-limiting preferred examples.
- According to a conventional wet method, first, a sodium hydroxide (NaOH) with varying concentrations was added to 100 ml of an aqueous copper sulfate (CuSO4) solution to produce an aqueous solution containing copper oxide (CuxO) as a precipitate. Then, the copper oxide was filtered and recovered.
- Distilled water and glucose (C6H12O6) were added to the obtained copper oxide and agitated until the color of the solution changed into dark red. As a result, an aqueous solution containing a stable Cu2O was obtained.
- Then, glycine (NH2—CH2—COOH) and arabic gum were added to the aqueous solution containing Cu2O and then dispersed uniformly.
- Then, Cu2O was reduced to a copper powder as a precipitate by mixing hydrazine (N2H4), as a reducing agent, into the dispersion and then dried.
- The result of the conventional wet method is given in Table 1.
TABLE 1 Sample No. CuSO4:NaOH:N2H4:Glycine Average particle size (μm) 11 1:3:3:0.1 0.4 12 1:3:4:0.25 0.5 13 1:2:7:0.30 1 - As shown in Table 1, the average particle size of each copper powder (samples 11 to 13) prepared by the conventional wet method varied, depending on the amounts of added reaction agents and additives. Specifically, the particle size distribution ranged from about 0.4 to 1 μm.
- According to the present invention, first, 1 00 ml of 2M aqueous CuCl2 solution was heated to a temperature of 30 to 80° C. and vigorously agitated at that temperature.
- Sodium hydroxide (NaOH) was at a time added to the aqueous copper chloride solution at the above temperature.
- Because the particle size of the final product, copper powder, depends on the concentration of the sodium hydroxide; the amount of the sodium hydroxide can be adjusted according to the desired particle size.
- After the addition of sodium hydroxide (NaOH), hydrazine (N2H4) was added to the resulting aqueous solution at a temperature of 40 to 80° C., to obtain a copper powder. In this case, hydrazine (N2H4) was added at a time.
- The copper powder obtained according to the above procedure was washed with secondary distilled water and filtered. The filtered copper powder was dried at an appropriate temperature under a non-oxidizing atmosphere to thereby finally obtain a nano-scaled copper powder.
- That is, the conventional wet method for preparing a copper powder comprises various processes such as filtering, recovering and addition of distilled water. However, the wet reduction method according to the present invention is carried out in one reaction vessel and the process for recovering a copper powder is carried out only once.
- The particle size distribution of the copper powder obtained according to the present invention is given in Table 2.
TABLE 2 Particle size distribution of copper powder according to the concentration of NaOH Particle size distribution Av- Sam- erage ple D10 D50 D90 size Section No. CuCl2 NaOH N2H4 (μm) (μm) (μm) (μm) Com- 21 1 1 12 0.05 0.10 0.14 0.10 parative sample Inventive 22 1 2 12 0.05 0.10 0.16 0.10 samples 23 1 4 12 0.06 0.13 0.22 0.14 24 1 8 12 0.09 0.15 0.25 0.17 25 1 16 12 0.12 0.38 0.50 0.36 26 1 33 12 0.20 0.50 0.70 0.45 Com- 27 1 35 12 0.29 0.70 0.87 0.63 parative sample - As shown in Table 2, in case of samples 22 to 26, NaOH was added with varying concentrations of 2 to 33 moles per mole of the copper chloride (CuCl2).
- It can be seen that when the concentration of hydrazine (N2H4) is constant, as the [NaOH]/[CuCl2] ratio increases, the particle size distribution of the copper powder increases.
- This is because the ratio of the obtained copper oxides, Cu2O and CuO, varies according to the concentration of sodium hydroxide (NaOH).
- As the amount of sodium hydroxide (NaOH) increases, a stable intermediate product, Cu2O, is produced in a large amount. As a result, a reduction reaction is not easily carried out.
- Due to differences in the degree of reduction, the particle size distribution of the obtained copper powder becomes less uniform as the concentration of NaOH increases.
- In case of sample 21, in spite of good characteristics of the copper powder, reaction rate was slow and thus productivity was lowered. Sample 27 had a fast reaction rate but the average particle size distribution of the copper powder exceeded 0.5 μm. Therefore, samples 21 and 27 are not preferable to prepare a nano-scaled copper powder.
- In particular, if the amount of added hydrazine (N2H4) exceeds 12 moles per mole of the copper chloride, a reaction rate is increased but the copper powder is easily agglomerated. As a result, the surface quality of the copper powder is lowered. Therefore, it is preferable to limit the amount of hydrazine to up to 12 moles.
- As shown in Table 3, copper powder having a particle size of 100 nm or less grade was easily obtained when the molar ratio between CuCl2 and NaOH was 1:2. In addition, the physical properties of the copper powder, such as particle size distribution and particle shape, were excellent.
- Table 3 shows chemical components of the copper powder obtained according to Example 2 under the condition of CuCl2:NaOH:N2H4=1:2:12.
TABLE 3 Chemical components Inspection Data (%) Method Na 0.0020 A.A.S. Ni No detection Pb 0.0040 Fe 0.0028 Mn No detection Mg 0.0009 C 0.140 KS D 1801-98 S 0.007 KS D 1673-97 K 0.004 (Korea Environment & Merchandise Testing Institute) Cl 0.0001 I.C. analysis (Korea Testing & Research Institute for the Chemical Industry) - First, 100 ml of 2M aqueous CuCl2 solution was heated to a temperature of 20 to 70° C. and vigorously agitated at that temperature.
- Hydrazine (N2H4) was mixed into the resulting aqueous copper chloride solution at the above temperature in an amount of 1 to 12 moles per mole of the copper chloride and vigorously agitated for about 5 minutes.
- Subsequently, when the aqueous solution containing hydrazine was kept at a temperature of 40 to 80° C., sodium hydroxide (NaOH) was added thereto.
- The sodium hydroxide (NaOH) was added with varying concentrations of 2 to 33 moles per mole of the copper chloride (CuCl2).
- Then, the copper powder obtained according to the above procedure was washed with secondary distilled water and filtered. The filtered copper powder was dried to obtain a nano-scaled copper powder.
- The particle size distribution of the finally obtained copper powder is given in Table 4.
TABLE 4 Particle size distribution of copper powder according to the concentration of NaOH Particle size distribution Av- Sam- erage ple D10 D50 D90 size Section No. CuCl2 N2H4 NaOH (μm) (μm) (μm) (μm) Inventive 31 1 12 2 0.06 0.10 0.20 0.10 samples 32 1 12 4 0.08 0.13 0.21 0.13 33 1 12 8 0.20 0.31 0.40 0.31 34 1 12 16 0.21 0.51 0.75 0.51 - Table 4 shows the particle size distribution according to the amount of NaOH per mole of the copper chloride (CuCl2). As shown in Table 4, as the amount of NaOH increased, the particle size of the obtained powder increased and a wide particle size distribution was obtained.
- As shown in Table 4, when the amount of added NaOH was 2 to 4 moles per mole of CuCl2, a copper powder having a particle size of 100 nm grade was obtained. Furthermore, dispersibility and shape of the powder surface were excellent.
- Although the intermediate product of the present example was different than that of Example 2, the final result was almost similar. It can be seen from the forgoing that the method of Example 3 is suitable for preparing a copper powder having a particle size of 100 nm grade, similar to Example 2.
- According to Example 4, a trace amount of silver nitrate (AgNO3) is further added to the aqueous copper chloride solution in Examples 2 and 3. Because silver is reduced faster than copper, the addition of silver nitrate enables the promotion of a heterogeneous nucleation of copper, thereby increasing the reduction rate of copper.
- That is, a trace amount of silver nitrate was added to the aqueous copper chloride solution in Example 2. Then, sodium hydroxide and hydrazine were added in sequence to obtain a copper powder.
- A trace amount of silver nitrate was added to the aqueous copper chloride solution in Example 3. Then, hydrazine and sodium hydroxide were added in sequence to obtain a copper powder.
- The copper powder according to Example 4 was compared with those according to Examples 2 and 3 in terms of the particle size distribution of a copper powder. The results are given in Table 5.
TABLE 5 Particle size distribution of copper powder according to presence or absence of AgNO3 Particle size distribution Sample D10 D50 D90 Average No CuCl2 NaOH N2H4 AgNO3 (μm) (μm) (μm) size (μm) Remarks 22 1 2 12 X 0.05 0.10 0.16 0.10 NaOH N2H4 31 1 2 12 X 0.06 0.10 0.20 0.10 N2H4 NaOH 41 1 2 12 0.006 0.05 0.12 0.20 0.11 NaOH N2H4 42 1 2 12 0.007 0.05 0.11 0.22 0.11 N2H4 NaOH - Table 5 shows a particle size distribution according to the presence or absence of the optional additive, AgNO3 under the condition of CuCl2:NaOH:N2H4=1:2:12.
- In sample 41, NaOH and N2H4 were in sequence added to an aqueous (CuCl2+AgNO3) solution, and in sample 42, N2H4 and NaOH were added in sequence to an aqueous (CuCl2+AgNO3) solution, for the purpose of obtaining a copper powder.
- In the same conditions, the use of AgNO3 resulted in small average particle size and small particle size deviation. Furthermore, AgNO3 acted to increase the reaction rate. Samples 41 and 42 exhibited almost same characteristics of copper powders as corresponding sample 22 of Example 2 and sample 31 of Example 3.
- As shown in FIGS. 6 and 7, the copper powders prepared using AgNO3 exhibited smaller average particle size and smaller particle size deviation than those in corresponding Examples 2 and 3.
- The copper powders prepared according to the conventional wet method (samples 11 to 13) had relatively coarse average particle size of 0.4 to 1 μm. On the other hand, the copper powders prepared according to the present invention had ultrafine average particle size of 100 nm grade˜1 μm grade.
- Industrial Applicability
- As apparent from the above description, the present invention provides two mechanisms for preparing an ultrafine copper powder having a particle size of (100 nm grade˜1 μm grade). The two mechanisms are very suitable for preparing an ultrafine copper powder having a particle size of 100 nm grade.
- The nano-scaled copper powder prepared according to the present invention is excellent in particle size distribution and dispersibility. The particle size of the copper powder varies according to the amount of sodium hydroxide (NaOH), thereby making it possible to control the particle size and distribution thereof. At the same time, due to heterogeneous nucleation of copper by the addition of the optional additive, silver nitrate (AgNO3), the reduction reaction rate of copper increases and the particle size of the copper powder becomes finer.
- Accordingly, the method according to the present invention is a relatively simple process and also affords a high degree of reproducibility. In addition, copper powder having a particle size of 100 nm can be prepared which has a good surface quality, narrow particle size distribution, and good powder sphericity.
- Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
Claims (6)
1. A method for manufacturing a nano-scaled copper powder by a wet reduction process, comprising the steps of:
adding sodium hydroxide (NaOH) to an aqueous copper chloride (CuCl2) solution to give an aqueous solution containing copper oxide and copper hydroxide;
reducing the copper oxide and the copper hydroxide to obtain a nano-scaled copper powder as a precipitate by adding hydrazine (N2H4) to the aqueous solution; and
filtering and drying the precipitated nano-scaled copper powder.
2. The method as set forth in claim 1 , wherein the sodium hydroxide (NaOH) is added in an amount of 2 to 33 moles per mole of the copper chloride (CuCl2) when the aqueous copper chloride (CuCl2) solution is kept within a temperature of 30 to 80° C., and the hydrazine (N2H4) is added in an amount of 0.5 to 12 moles per mole of the copper chloride when the aqueous solution containing the copper oxide and the copper hydroxide is kept within a temperature of 40 to 80° C.
3. The method as set forth in claim 1 , wherein in the step of producing the copper oxide and the copper hydroxide, before the addition of NaOH, silver nitrate (AgNO3) is added to the aqueous copper chloride (CuCl2) solution in an amount of 1/1,000 to 1/10,000 moles per mole of the copper chloride.
4. A method for manufacturing a nano-scaled copper powder by a wet reduction process, comprising the steps of:
adding hydrazine (N2H4) to an aqueous copper chloride (CuCl2) solution to give an aqueous solution containing a copper complex (Cu(N2H4)mCln);
adding sodium hydroxide (NaOH) to the aqueous copper complex solution to obtain a nano-scaled copper powder; and
filtering and drying the nano-scaled copper powder.
5. The method as set forth in claim 4 , wherein the hydrazine (N2H4) is added in an amount of 0.5 to 12 moles per mole of the copper chloride (CuCl2) when the aqueous copper chloride (CuCl2) solution is kept within a temperature of 20 to 70° C., and the sodium hydroxide (NaOH) is added in an amount of 2 to 33 moles per mole of the copper chloride when the aqueous solution containing the copper complex is kept within a temperature of 40 to 80° C.
6. The method as set forth in claim 4 , wherein in the step of producing the copper complex (Cu(N2H4)mCln), before the addition of hydrazine, silver nitrate (AgNO3) is added to the aqueous copper chloride (CuCl2) solution in an amount of 1/1,000 to 1/10,000 moles per mole of the copper chloride.
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US11873566B2 (en) | 2019-02-28 | 2024-01-16 | Honda Motor Co., Ltd. | Cu/Cu2O interface nanostructures for electrochemical CO2 reduction |
CN111590088A (en) * | 2020-07-13 | 2020-08-28 | 江西省科学院应用物理研究所 | Preparation method of superfine nano copper powder |
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KR100486604B1 (en) | 2005-05-03 |
AU2003230317A1 (en) | 2004-05-25 |
WO2004039524A1 (en) | 2004-05-13 |
KR20040037824A (en) | 2004-05-07 |
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