Patent Application
20240157443
This application claims the benefit of Korean Patent Applications No. 10-2022-0153122, filed on Nov. 15, 2022 and No. 10-2023-0142320, filed on Oct. 23, 2023, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
The following description relates to a method for producing nickel-based metal powder, and more specifically, to a method for producing a spherical nickel-based metal powder using chemical vapor synthesis.
A multi-layer ceramic capacitor (MLCC) is a chip-shaped capacitor used in electronic circuits to temporarily store electrical charge and remove noise. The MLCC is a component that stores current and supplies electricity reliably only as needed to ensure the proper operation of electronic devices. In modern times, there is a high demand for the MLCCs, often referred to as the “rice” of the electronic industry. For example, around 1,000 are required for personal computers or smartphones, and about 2,000 are needed for televisions.
There is a need to reduce the size of these multilayer ceramic capacitors and increase the storage capacity. For this purpose, the MLCC is constructed with an alternating stack of approximately 500 ceramic layers and metal electrode layers. The manufacturing process of the MLCC involves forming a ceramic sheet on a release film, printing electrode patterns on the ceramic sheet, cutting the ceramic sheet, removing the release carrier film, and then laminating the ceramic sheet and a metal electrode layer. The metal electrode layer is typically formed through the application and drying of a conductive paste containing nickel powder, followed by sintering the nickel powder in a subsequent heat treatment process.
One of the crucial technologies in the aforementioned MLCC is the formation of the metal electrode layer as densely and uniformly as possible. To this end, nickel powder with a high packing density and excellent flowability is required. If the nickel powder has an angular, polyhedral shape, it may increase packing density but presents flowability issues. Therefore, it is desirable for the nickel powder used in the metal electrode layer to have a spherical shape.
Nickel powder used in MLCCs may be fabricated using a method called chemical vapor synthesis. Chemical vapor synthesis involves reacting precursor gases and a reducing gas in a sealed reactor under a vacuum environment to produce solid powder. For example, in the production of nickel powder, solid NiCl2 is vaporized to create nickel precursor gas, and a reducing gas such as hydrogen is used to chemically react within the reactor to produce nickel powder. In this case, the resulting nickel powder often takes on an angular shape such as a cube or an octahedron. This is due to a reaction that occurs during the initial formation of the nickel powder, where the nickel precursor gas selectively adsorbs on specific surfaces with a face-centered cubic (FCC) crystal structure and the surface is stabilized, which leads to the formation of an angular shape in the final nickel powder.
As described above, to apply nickel powder with a spherical shape to the metal electrode layer of the MLCC, it is important to prevent the common occurrence of angular shapes in nickel powder produced by the chemical vapor synthesis method.
One method to prevent this is to induce a rapid reaction during the chemical vapor synthesis, depleting the nickel precursor gas quickly to prevent adsorption on specific surfaces. However, this method suffers from the limitation of very low process flexibility, making it difficult to stably produce nickel powder.
Another method involves introducing hydrogen sulfide (H2S) gas into a reactor where the chemical vapor synthesis occurs, adding sulfur to the nickel powder to induce changes in surface energy of the nickel powder. However, H2S gas is a highly toxic and corrosive gas, which can raise environmental concerns. Additionally, it poses challenges for workers to handle safely and may require additional equipment or costs for safe use.
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The following description relates to a method for producing a spherical nickel-based metal powder that allows for the efficient and cost-effective production of spherical nickel-based metal powder with greater ease.
However, these tasks are illustrative, and the technical idea of the present invention is not limited thereto.
In one general aspect, there is provided a method for producing a spherical nickel-based metal powder using chemical vapor synthesis.
According to an embodiment of the present invention, the method for producing spherical nickel-based metal powder may include the steps of: providing a metal precursor, which includes nickel precursor, and a sulfur compound; introducing the metal precursor and the sulfur compound into a reactor, vaporizing the metal precursor and the sulfur compound within the reactor, and producing nickel-based metal powder containing sulfur through a reaction of the metal precursor and the sulfur compound with the reducing gas introduced into the reactor.
According to an embodiment of the present invention, in the providing step, the metal precursor and the sulfur compound may be provided in the form of a mixture of metal precursor powder and sulfur compound powder, and in the introducing step, the mixture may be introduced into the reactor.
According to an embodiment of the present invention, the mixture may be formed by mixing the metal precursor powder and the sulfur compound powder using a mechanical mixing method.
According to an embodiment of the present invention, the mixture may be in the form of mixed precursor granules produced using a spray-drying method, which involves using a precursor mixture solution prepared by dissolving the metal precursor powder and the sulfur compound powder in a solvent.
According to an embodiment of the present invention, within the mixture, a molar ratio of the sulfur compound to the metal precursor may be in the range of 0.00001 to 0.1.
According to an embodiment of the present invention, in the introducing step, the metal precursor and the sulfur compound may be introduced separately into the reactor, without being mixed.
According to an embodiment of the present invention, the nickel precursor may include at least one of NiCl2, NiSO4, Ni(NO3)2, Ni(CO)4, or NiCO3.
According to an embodiment of the present invention, the sulfur compound may include metal sulfide or metal sulfur oxide, and a metal constituting the metal sulfide or metal sulfur oxide may include at least one of Li, Na, K, Rb, Cs, Be, and Mg., Ca, Sr, Ba, Y, V, Cr, Mn, Zn, Al, Dy, Co, Cu, W, Mo, Pt, Pd, Ni, Zr, Nb, Mo, Ru, or Sn.
According to an embodiment of the present invention, the metal precursor may further include an alloying element precursor.
According to an embodiment of the present invention, the alloying element precursor may include a metal compound, and the metal compound may include at least one of metal sulfate, metal chloride, metal carbonyl, metal nitrate, or metal carbonate.
According to an embodiment of the present invention, a metal constituting the metal compound may include at least one of Cu, Fe, Co, Pd, Ag, Pt, Au, Sn, W, or Mo.
According to an embodiment of the present invention, the alloying element precursor may include at least one of CuCl, CuCl2, or AgCl.
According to an embodiment of the present invention, the method may further include, after producing the nickel-based metal powder, forming a powder-coating layer composite by forming a coating layer surrounding the surface of the nickel-based metal powder, subjecting the powder-coating layer composite to desulfurization heat treatment to reduce the sulfur content within the nickel-based metal powder, and obtaining the nickel-based metal powder by selectively removing the coating layer.
According to an embodiment of the present invention, the desulfurization heat treatment may be conducted in a vacuum atmosphere, an oxidizing atmosphere, a reducing atmosphere, or an inert atmosphere within a temperature range of 200° C. to 900° C.
In another general aspect, a method for producing spherical nickel-based metal powder may include the steps of: providing a metal precursor including nickel precursor, a sulfur compound, and a metal compound for shell formation; introducing the metal precursor, the sulfur compound, and the metal compound for shell formation into a reactor, vaporizing the metal precursor, the sulfur compound, and the metal compound for shell formation; forming a powder-shell layer composite consisting of nickel-based metal powder containing sulfur and a shell layer surrounding the surface of the nickel-based metal powder through a reaction of the metal precursor, the sulfur compound, and the metal compound for shell formation with a reducing gas introduced into the reactor, subjecting the powder-shell layer composite to desulfurization heat treatment to reduce the sulfur content within the nickel-based metal powder, and obtaining the nickel-based metal powder by selectively removing the shell layer.
According to an embodiment of the present invention, the metal compound for shell formation may include at least one of metal acetate, metal bromide, metal carbonyl, metal carbonate, metal chloride, metal fluoride, metal hydroxide, metal iodide, metal nitrate, metal oxide, metal phosphate, metal silicate, metal sulfate, or metal sulfide.
According to an embodiment of the present invention, a metal constituting the metal compound for shell formation may include at least one of aluminum (Al), barium (Ba), calcium (Ca), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), lithium (Li), magnesium (Mg), manganese (Mn), mercury (Hg), nickel (Ni), potassium (K), rubidium (Rb), silver (Ag), sodium (Na), strontium (Sr), tin (Sn), lanthanum (La), silicon (Si), gallium (Ga), scandium (Sc), titanium (Ti), vanadium (V), zirconium (Zr), yttrium (Y), cadmium (Cd), actinium (Ac), cesium (Cs), hafnium (Hf), or zinc (Zn).
According to an embodiment of the present invention, the metal compound for shell formation may include at least one of LiCl, NaCl, KCl, MgCl2, CaCl2, ZnCl2, or BaCl2.
In still another general aspect, a method for producing spherical nickel-based metal powder may include the steps of: providing a metal precursor, which includes nickel precursor, and a sulfur compound; introducing the metal precursor and the sulfur compound into a reactor, vaporizing the metal precursor and the sulfur compound within the reactor, producing nickel-based metal powder containing sulfur through a reaction of the metal precursor and the sulfur compound with a reducing gas introduced into the reactor; preparing a slurry by dispersing the nickel-based metal powder in a solution containing a sintering inhibitor, followed by forming a powder-anti-sintering layer composite in which the sintering inhibitor surrounds the nickel-based metal powder through spray drying treatment using the slurry; subjecting the powder-anti-sintering layer composite to desulfurization heat treatment to reduce the sulfur content within the nickel-based metal powder; and obtaining the nickel-based metal powder by selectively removing the anti-sintering layer.
According to an embodiment of the present invention, the sintering inhibitor may include a metal compound, and the metal compound may include at least one of LiCl, NaCl, KCl, MgCl2, CaCl2), ZnCl2, or BaCl2.
Other features and aspects will be apparent from the following detailed description, the drawings, and the claims.
The above and other purposes, features and other advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The embodiments of the present invention are provided for more fully describing the present invention to those skilled in the art, and the embodiments below may be modified in various forms, and the scope of the present invention is not limited to the embodiments below. Rather, these embodiments are provided such that this disclosure will be thorough and complete and will fully convey the spirit of the present invention to those skilled in the art. Like numbers refer to like elements throughout. Furthermore, various elements and regions in the drawings are schematically shown. Thus, the technical idea of the present invention is not limited by a relative size or distance in the attached drawings.
In the following description, while explaining the use of the chemical vapor synthesis (CVS) method to produce metal powder, it is illustrative, and the technical concept of the present invention is not limited to this, but it also includes the use of physical vapor synthesis (PVS) methods such as DC plasma or RF plasma.
In this specification and claims, the term “nickel-based metal powder” is defined to encompass both nickel powder and nickel alloy powder with nickel as the main component. Therefore, “nickel-based metal powder” may refer to either nickel powder or nickel alloy powder.
When forming the aforementioned nickel-based metal powder, an alloying element precursor for alloying nickel powder may be added along with the nickel precursor. In this case, nickel precursor, alloying element precursor, and a sulfur compound may be separately introduced into a reactor, or added together as described below. By introducing the alloying element precursor along with the nickel precursor, nickel alloy powder may be produced as nickel-based metal powder. The method of fabricating spherical nickel alloy powder is essentially the same as the method of forming nickel-based metal powder, except for the further addition of alloying element precursor along with the nickel precursor.
Therefore, in this specification and claims, the term “solid metal precursor” is defined to necessarily include solid nickel precursor and optionally include solid alloying element precursor added for alloying nickel powder. Thus, “solid metal precursor” may refer to either solid nickel precursor or both solid nickel precursor and solid alloying element precursor.
Hereafter, an example of fabricating spherical nickel-based metal powder in accordance with the technical concept of the present invention using mixed precursor granules as a mixture will be provided. In describing an embodiment of the present invention, the method of fabricating spherical nickel powder will be described first, and, as a modified example thereof, a method for producing nickel alloy powder will be described. In the present invention, the fundamental technical concept in the production steps of nickel powder and nickel alloy powder is the same. However, compared to the method for producing nickel powder, there is a difference in that an alloying element precursor is added in addition to the nickel precursor to produce nickel alloy powder.
Referring to
Referring to
The method S100 for producing spherical nickel-based metal powder may further include the step (S150) of cleaning the nickel-based metal powder. The nickel-based metal powder formed within the reactor is discharged to the outside of the reactor, and any reaction by-products formed on the surface of the nickel-based metal powder may be removed through an additional cleaning process.
In the providing step S110, the metal precursor, which includes the nickel precursor, and the sulfur compound are prepared. The nickel precursor, the metal precursor, and the sulfur compound may be in a solid or liquid phase.
The nickel precursor may contain nickel compounds, for example, at least one of NiCl2, NiSO4, Ni(NO3)2, Ni(CO)4, or NiCO3.
The sulfur compound may be used as a source of sulfur for adding sulfur to the nickel-based metal powder when producing spherical nickel-based metal powder using chemical vapor synthesis. When the sulfur compound is in a solid phase, it may be in various forms, such as powder, pellets, or rods. The sulfur compound may be vaporized from a solid phase to a gas phase by heat in a heating area inside the reactor, or it may contain a substance in solid form, which, when introduced, reacts with other gases, such as hydrogen, within the reactor to produce sulfur-containing gas. Therefore, the solid sulfur compound, along with the solid nickel precursor, may be introduced into the reactor and vaporized together, reacting with the reducing gas introduced into the reactor or reacting in solid form with other gases, contributing to the production of spherical nickel powder containing sulfur.
The sulfur compound may include, for example, metal sulfide or metal sulfate. The metal constituting the metal sulfide or metal sulfate may include at least one of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Y, V, Cr, Mn, Zn, Al, Dy, Co, Cu, W, Mo, Pt, Pd, Ni, Zr, Nb, Mo, Ru, or Sn, for example.
In the providing step S110, the metal precursor and the sulfur compound may be provided in the form of a mixture of metal precursor powder and sulfur compound powder. Consequently, in the introducing step S120, this mixture may be introduced into the reactor as the metal precursor and the sulfur compound. For example, after forming a mixture by mixing the solid nickel precursor and the solid sulfur compound, this mixture may be introduced into the reactor.
The mixture may be formed by mixing the metal precursor powder and the sulfur compound powder using a mechanical mixing method. The mechanical mixing method may be performed using a ball mill or a mixer. For example, the metal precursor powder and the sulfur compound powder may be introduced into a ball-milling device and mixed by ball milling. Alternatively, the metal precursor powder and the sulfur compound powder may be placed in a mixing container and mechanically mixed using ultrasonics or mechanical vibration to form a mixture. Through the mechanical mixing method such as ball-milling, a uniform mixture of the metal precursor powder and the sulfur compound powder may be obtained.
In addition, the mixture may be formed by spray-drying. For example, the mixture may be in the form of mixed precursor granules produced using the spray-drying method, which involves using a precursor mixture solution prepared by dissolving the metal precursor powder and the sulfur compound powder in a solvent. The spray-drying method may be used to produce mixed precursor granules in a powdered form in which solid nickel precursor and solid sulfur compound are mixed to create the mixture.
The spray-drying method may be performed as follows. A precursor mixture solution is prepared by dissolving the metal precursor powder and the sulfur compound powder in a solvent. Subsequently, the precursor mixture solution is sprayed and atomized and then the solvent is instantly evaporated with hot air, resulting in the formation of the mixed precursor granules. The solvent used to prepare the precursor mixture solution may be water or an organic solvent. The precursor mixture solution may be prepared by dissolving both the metal precursor powder and the sulfur compound powder in the same solvent. Alternatively, the precursor mixture solution may be prepared by dissolving the metal precursor powder and the sulfur compound powder in different solvents and then mixing the solvents.
In the case of mixed precursor granules produced using the spray-drying method, both the metal precursor and the sulfur compound dissolve and precipitate together, forming mixed granules where these substances are evenly mixed. Thus, this allows for more uniform control of the sulfur content added to the entire powder when producing metal powder. For example, when producing nickel powder, the sulfur content added to the nickel powder may be more uniformly controlled across the entire powder.
In this case, to adjust the sulfur content contained in the nickel-based metal powder, the quantitative ratio of the metal precursor and the sulfur compound within the mixture, such as the molar ratio, may be controlled. For example, within the mixture, the molar ratio of the sulfur compound to the metal precursor, where the molar amount of the sulfur compound is divided by the molar amount of the metal precursor, may be in the range of, for example, 0.00001 to 1, or it may be in the range of, for example, 0.00001 to 0.1, or it may be in the range of, for example, 0.0001 to 1.0.
For example, when the metal precursor includes only the nickel precursor, the molar ratio of the sulfur compound to the nickel precursor may be in the range of, for example, 0.00001 to 1, or it may be in the range of, for example, 0.00001 to 0.1, or it may be in the range of, for example, 0.0001 to 1.0.
For example, when the metal precursor includes both the nickel precursor and an alloying element precursor, the molar ratio of the sulfur compound to the sum of the nickel precursor and the alloying element precursor may be in the range of, for example, 0.00001 to 1, or it may be in the range of, for example, 0.00001 to 0.1, or it may be in the range of, for example, 0.0001 to 1.0.
For example, nickel-based metal powder produced according to an embodiment of the present invention may have a sulfur component content of 0.6% by weight (6000 ppm) or less.
In the introducing step S120, the mixture produced by the above-described method is introduced into the reactor. The mixed precursor granules introduced into the reactor contain both the metal precursor and the sulfur compound. Consequently, within the reactor, both the metal precursor and the sulfur compound vaporize, and as a result, the sulfur component is added to the nickel-based metal powder during the production stage. The sulfur component, in the early stages of metal powder formation, contributes to the metal powder having a spherical shape through surface energy modification.
Furthermore, in the introducing step S120, the metal precursor and the sulfur compound may be introduced separately into the reactor, without being mixed. In other words, the solid nickel precursor and the solid sulfur compound may be introduced into the reactor individually without being mixed. For example, they may be introduced independently into the reactor through separate inlets.
Using the solid sulfur compound in this way offers the advantage of being much safer and easier to handle compared to hydrogen sulfide (H2S), which is a toxic corrosive gas. Additionally, when introduced in the form of a mixture, it allows for easier control of the sulfur content in the nickel powder through content adjustment.
In the vaporizing step S130, the metal precursor and the sulfur compound within the reactor may be heated to vaporize them.
In the producing step S140, the nickel-based metal powder containing sulfur may be produced by a reaction of the metal precursor and the sulfur compound with the reducing gas introduced into the reactor.
In addition, to achieve various objectives such as increasing the oxidation resistance of the nickel-based metal powder or inhibiting sintering, a predetermined range of alloying elements may be added to the nickel-based metal powder. These alloying elements may include at least one of Cu, Fe, Co, Pd, Ag, Pt, Au, Sn, W, or Mo.
For this purpose, the solid metal precursor may include a solid alloying element precursor. The alloying element precursor may include a metal compound. The metal compound may include at least one of metal sulfate, metal chloride, metal carbonyl, metal nitrate, or metal carbonate, for example. The metal constituting the metal compound may include at least one of, for example, Cu, Fe, Co, Pd, Ag, Pt, Au, Sn, W, or Mo. The alloying element precursor may include at least one of, for example, CuCl, CuCl2, or AgCl. When the solid metal precursor further includes the alloying element precursor, the mixture may also include the alloying element precursor. For example, the solid metal precursor, the solid sulfur compound, and the solid alloying element precursor may be mixed together to form a mixture, which may then be introduced into the reactor. Alternatively, for example, metal precursor powder, sulfur compound powder, and alloying element precursor powder may be dissolved in a solvent to prepare a precursor mixture solution, which may be used to produce mixed precursor granules through the spray-drying method. The mixed precursor granules may include both the metal precursor and the sulfur compound, as well as the alloying element precursor.
Apart from the addition of the alloying element precursor, the process for producing nickel alloy powder containing sulfur through chemical vapor synthesis proceeds in a similar manner as in the above-described embodiment. When chemical vapor synthesis is performed using mixed precursor granules, both the nickel precursor and the alloying element precursor participate in the reaction, resulting in the production of nickel alloy powder with the alloying element added. At this time, spherical nickel alloy powder is produced by the sulfur compound included in the mixed precursor granules.
Alternatively, mixed precursor granules in which the solid metal precursor and the sulfur compound are mixed and the solid alloying element precursor may be separately introduced into the reactor. Alternatively, the solid metal precursor, the sulfur compound, and the alloying element precursor may be introduced separately into the reactor, without being mixed.
In the cleaning step S150, after the production is completed within the reactor, an additional cleaning process is performed on the nickel-based metal powder discharged from the reactor to remove reaction by-products formed on the surface of the nickel powder. If the sulfur content within the nickel-based metal powder exceeds a specific threshold, additional desulfurization heat treatment may be carried out. Subjecting the nickel-based metal powder to desulfurization heat treatment at high temperature without additional treatment may lead to agglomeration and sintering of the nickel powder due to diffusion between particles. To prevent this, a coating layer may be formed on the powder's surface, or anti-sintering agent may be used.
In the following description, an example in which desulfurization heat treatment is additionally performed to reduce the sulfur content of the nickel-based metal powder will be described in detail.
Referring to
In addition, the method S100a for producing spherical nickel-based metal powder may further include, after producing the nickel-based metal powder (S140), forming a powder-coating layer composite by forming a coating layer surrounding the surface of the nickel-based metal powder (S160); subjecting the powder-coating layer composite to desulfurization heat treatment to reduce the sulfur content within the nickel-based metal powder (S170); and obtaining the nickel-based metal powder by selectively removing the coating layer (S180).
The coating layer may be a shell layer or an anti-sintering layer, as described below. In addition, the powder-coating layer composite may be a powder-shell layer composite or a powder-anti-sintering layer composite, as described below.
The desulfurization heat treatment may be conducted in a vacuum atmosphere, an oxidizing atmosphere, a reducing atmosphere, or an inert atmosphere, for example, within a temperature range of 200° C. to 900° C.
Referring to
In the following description, descriptions of components that are substantially the same as those of the above-described embodiment will not be reiterated.
Compared to the method S100 of
In the providing step S210, the metal precursor, which includes the nickel precursor, the sulfur compound, and the metal compound for shell formation are prepared. The metal precursor, the sulfur compound, and the metal compound for shell formation may be provided separately or, as described above, may be prepared as a mixture using mechanical mixing or spray-drying. When the spray drying method is used, the precursor mixture solution and the mixed precursor granules may contain the metal precursor, the sulfur compound, and the metal compound for shell formation.
In the introducing step S220, the metal precursor, the sulfur compound, and the metal compound for shell formation may be introduced into the reactor as a mixture or separately, without being mixed together.
In the vaporizing step S230, the metal precursor, the sulfur compound, and the metal compound for shell formation within the reactor may be heated to vaporize them.
In the step S240 of forming the powder-shell layer composite, by the reaction of the metal precursor, the sulfur compound, and the metal compound for shell formation with the reducing gas introduced into the reactor, a powder-shell composite consisting of nickel-based metal powder containing sulfur and a shell layer that surrounds the surface of the nickel-based metal powder, may be formed. For example, during the process where metal powder is formed by the reaction of the mixed precursor granules with the reducing gas, a reaction by-product in the form of a metal compound may encase the surface of the nickel powder and form a shell layer, creating a powder-shell layer composite. The shell layer may be formed as a reaction by-product during the chemical vapor reaction, and it may contain components supplied from the sulfur compound included in the mixed precursor granules.
The metal compound for shell formation may include at least one of LiCl, NaCl, KCl, MgCl2, CaCl2), ZnCl2, or BaCl2, for example.
The metal compound for shell formation may include at least one of, for example, metal acetate, metal bromide, metal carbonyl, metal carbonate, metal chloride, metal fluoride, metal hydroxide, metal iodide, metal nitrate, metal oxide, metal phosphate, metal silicate, metal sulfate, or metal sulfide.
The metal constituting the metal compound for shell formation may include at least one of, for example, aluminum (Al), barium (Ba), calcium (Ca), chromium (Cr), cobalt (Co), copper (Cu), iron (Fe), lead (Pb), lithium (Li), magnesium (Mg), manganese (Mn), mercury (Hg), nickel (Ni), potassium (K), rubidium (Rb), silver (Ag), sodium (Na), strontium (Sr), tin (Sn), lanthanum (La), silicon (Si), gallium (Ga), scandium (Sc), titanium (Ti), vanadium (V), zirconium (Zr), yttrium (Y), cadmium (Cd), actinium (Ac), cesium (Cs), hafnium (Hf), or zinc (Zn).
Similar to the nickel-based metal powder produced by the method S100 of
For example, when NiCl2 is used as the metal precursor and Na2SO4 is used as the sulfur compound in the mixed precursor granules, if the molar ratio of NiCl2 to Na2SO4 exceeds a predetermined value, for example, 0.001 or higher, NaCl may be generated as a reaction by-product during chemical vapor synthesis using the mixed precursor granules as a raw material. This may lead to the formation of a shell layer with a sufficient thickness on the surface of the nickel-based metal powder.
In the desulfurization heat treatment step S250, the powder-shell layer composite may undergo desulfurization heat treatment to reduce the sulfur content within the nickel-based metal powder. As the Na2SO4 content, serving as the source of sulfur within the mixed precursor granules, increases, an excess amount of sulfur may also be present within the nickel-based metal powder. When the sulfur content in the nickel-based metal powder exceeds a required level, problems may occur due to uneven sintering of the nickel powder during the formation of a metal electrode layer in a multilayer ceramic capacitor. Therefore, desulfurization heat treatment may be performed to remove and reduce the sulfur component within the nickel-based metal powder.
The desulfurization heat treatment may be performed in at least one of a vacuum atmosphere, an oxidizing atmosphere, a reducing atmosphere, or an inert atmosphere. The desulfurization heat treatment may be performed at temperatures in the range of, for example, 200° C. to 900° C. If the desulfurization heat treatment temperature is below 200° C., the desulfurization effect may be minimal. If the desulfurization heat treatment temperature exceeds 900° C., energy may be excessively used.
To perform the desulfurization heat treatment, it is necessary to maintain nickel powder containing an excess of sulfur in a high-temperature environment for a certain period. Typically, nickel powder particles exposed to such high temperatures may sinter and agglomerate.
However, the powder-shell layer composite surrounds the external surface of the nickel-based metal powder with a shell layer, preventing direct contact between the nickel-based metal powder particles. Therefore, when the desulfurization heat treatment is carried out using the powder-shell layer composite, the nickel-based metal powder particles do not come into direct contact, sinter, and agglomerate during the desulfurization heat treatment process. The shell layer serves to prevent sintering resulting from the contact and diffusion of the nickel-based metal powder particles during the desulfurization heat treatment.
In the case of the powder-shell layer composite, the interior of the shell layer may contain tiny space through which a gas can pass. Through the tiny space within the shell layer, the sulfur component contained in the nickel-based metal powder may pass through the shell layer in a gaseous state and be externally discharged. By reducing the sulfur content within the nickel-based metal powder through the desulfurization heat treatment, excess sulfur that is contained may be removed, bringing it to a level below a predetermined criterion.
In the step S260 of obtaining the nickel-based metal powder, after the desulfurization heat treatment is completed, a cleaning process may be performed in which the powder-shell layer composite is cleaned using a cleaning solution to selectively remove the shell layer. Accordingly, nickel-based metal powder with reduced sulfur content may be obtained. When the shell layer is NaCl, it is possible to produce spherical nickel powder with the desired sulfur content by dissolving and removing soluble NaCl using water as the cleaning solution.
According to the method S200, in the step of producing the mixed precursor granules, a sufficient amount of sulfur compound, serving as the sulfur source, may be added to increase the sulfur content subsequently added to the nickel-based metal powder. This may ensure a reliable spherical formation of the nickel-based metal powder. Then, the excess sulfur added to the nickel-based metal powder, in a state where the shell layer is formed, with the shell layer already formed to prevent sintering and provide a gas passage, may be removed through the desulfurization heat treatment. This prevents excessive sulfur while avoiding agglomeration and sintering of the nickel-based metal powder.
In addition, the shell layer is composed of a metal compound that can be cleaned by water or an organic solvent. After the desulfurization heat treatment is completed, the powder-shell layer composite may be cleaned, selectively removing only the shell layer. This may allow the production of high-quality nickel-based metal powder with a spherical shape and sulfur content that meets the criterion.
Additionally, the method S200 may include further adding an alloying element precursor in addition to the metal precursor as described above. Description of this process has been provided above, and thus will not be reiterated.
Referring to
In the following description, descriptions of components that are substantially the same as those of the above-described embodiment will not be reiterated.
Compared to the method S100 of
Steps S310 to S340 are substantially the same as steps S110 to S140 described in the method S100 of
In the step S350 of forming the powder-anti-sintering layer composite, the nickel-based metal powder is dispersed in a solution containing a sintering inhibitor to prepare a slurry. Subsequently, the slurry may be used in spray-drying treatment to produce the powder-anti-sintering layer composite in which the sintering inhibitor surrounds the nickel-based metal powder.
The sintering inhibitor may include a metal compound. The metal compound constituting the sintering inhibitor may include at least one of LiCl, NaCl, KCl, MgCl2, CaCl2, ZnCl2, or BaCl2. The sintering inhibitor may be added to and dissolved in a solvent such as water or an organic solvent. After dissolving in the solvent, the sintering inhibitor may be re-precipitated during the subsequent spray-drying process.
By introducing the nickel-based metal powder into the solution in which the sintering inhibitor is dissolved and dispersing it within the solution, a slurry may be prepared. Subsequently, a granulation process using spray-drying treatment may be performed on the slurry to produce a powder-anti-sintering layer composite. During the spray-drying process, the sintering inhibitor, previously dissolved in the solvent, is re-precipitated to form an anti-sintering layer that surrounds the nickel-based metal powder.
In the desulfurization heat treatment step S360, the powder-anti-sintering layer composite is subjected to desulfurization heat treatment to reduce the sulfur content within the nickel-based metal powder. The desulfurization heat treatment may be performed in at least one of a vacuum atmosphere, an oxidizing atmosphere, a reducing atmosphere, or an inert atmosphere. The desulfurization heat treatment may be performed at temperatures in the range of, for example, 200° C. to 900° C.
The powder-anti-sintering layer composite encases the outer surface of the nickel-based metal powder with the anti-sintering layer, preventing direct contact between the nickel-based metal powder particles. Therefore, when the desulfurization heat treatment is carried out using the powder-anti-sintering layer composite, the nickel-based metal powder particles do not come into direct contact, sinter, and agglomerate during the desulfurization heat treatment process. The anti-sintering layer serves to prevent sintering resulting from contact and diffusion of nickel-based metal powder particles during desulfurization heat treatment.
In the case of the powder-anti-sintering layer composite, the interior of the anti-sintering layer may contain tiny space through which a gas can pass. Through the tiny space within the anti-sintering layer, the sulfur component contained in the nickel-based metal powder may pass through the anti-sintering layer in a gaseous state and be externally discharged. By reducing the sulfur content within the nickel-based metal powder through the desulfurization heat treatment, excess sulfur that is contained may be removed, bringing it to a level below a predetermined criterion.
In the step S370 of obtaining the nickel-based metal powder, a cleaning process may be performed by cleaning the powder-anti-sintering layer composite with a cleaning solution after the desulfurization heat treatment, selectively removing the anti-sintering layer. Consequently, high-quality nickel-based metal powder that is spherical and meets a specified sulfur content may be produced.
The anti-sintering layer may be removed by cleaning it with a cleaning solution that dissolves the sintering inhibitor. For instance, if the anti-sintering layer contains water-soluble metal chlorides, such as NiCl or BaCl2, they may be dissolved and removed by cleaning with water. Other cleaning solutions such as organic solvents or acid/alkali solutions may also be used.
Furthermore, the method S300 may include adding an alloying element precursor in addition to the metal precursor, as described above. Description of this process has been provided above, and thus will not be reiterated.
Comparing the method S200 of
Hereafter, detailed descriptions of the powder-shell layer composite and the powder-anti-sintering layer composite will be provided.
Referring to
Referring to
In the powder-shell layer composite 500 of
On the other hand, in the powder-anti-sintering layer composite 600 of
Hereinafter, experimental examples are provided to help understand the present invention. The following experimental examples are presented to aid in the understanding of the invention and should not be construed as limiting the scope of the invention.
A precursor mixture solution was prepared by dissolving metal precursor and a sulfur compound in water. Nickel precursor NiCl2 was used as the metal precursor, and NiSO4 and Na2SO4 were used as the sulfur compound.
Table 1 presents the molar ratios of the metal compound and the sulfur compound used in preparing the precursor mixture solution for Experimental Examples 1 to 5.
Experimental Example 1 used NiSO4 as the sulfur compound, with a molar ratio of MNiSO4/MNiCl2 equal to 0.002. Experimental Examples 2 to 5 used Na2SO4 as the sulfur compound, with a molar ratio of MNa2SO4/MNiCl2 varying from 0.001 to 1.0. Mixed precursor granules were produced by spray-drying with the produced precursor mixture solution at a temperature of 180° C.
Additionally, in Experimental Example 6, a precursor solution was prepared by dissolving NiCl2 in water without adding any sulfur compound, and NiCl2 granules were produced under the above-described conditions. This example, without the addition of a sulfur compound, serves as a comparative example.
Using the produced mixed precursor granules from Experimental Examples 1 to 5 and the NiCl2 granules from Experimental Example 6 as raw materials, nickel powder was synthesized using a chemical vapor synthesis method with hydrogen as a reducing gas.
Referring to
Conversely, when mixed precursor granules containing sulfur compounds, such as in Experimental Examples 1 to 5, were used, all of them exhibited a spherical shape.
Table 2 presents the morphology, particle size, and composition results of nickel powder for Experimental Examples 1 to 6. The composition results are obtained through X-ray fluorescence analysis (XRF).
Referring to Table 2, Experimental Examples 1 to 4 exhibited a smaller average particle size compared to Experimental Example 6. However, Experimental Example 5, which had a higher sulfur content, displayed spherical nickel powder but with a larger average particle size. Therefore, it is preferable to control the sulfur content to be below that of Experimental Example 5.
Table 3 presents the production conditions for Experimental Example 7. Experimental Example 7 is identical to Experimental Example 3, with the exception that CuCl powder was simultaneously introduced into the reactor as an alloying element precursor along with NiCl2 to produce nickel-copper alloy powder.
In Experimental Example 7, the molar ratio of CuCl to NiCl2 (MCuCl/MNiCl2) was 0.1. The molar ratio of Na2SO4 to the entire metal precursor (MNa2SO4/(MNiCl2+CuCl)) was 0.002. The composition analysis of the nickel-copper alloy powder in Experimental Example 7 showed that copper accounted for 10% by weight. Moreover, electron microscopy observations showed a spherical shape, similar to Experimental Example 3. Therefore, it was confirmed that even when including the alloying element precursor, such as CuCl, the desired spherical shape and the desired fine size of the metal powder could be achieved.
Experimental Example 8 was prepared by producing a powder-anti-sintering layer composite using nickel powder corresponds to Experimental Example 4 and BaCl2 as the sintering inhibitor, followed by a desulfurization heat treatment performed on the composite. Specifically, BaCl2 was dissolved in water, and the nickel powder corresponding to Experimental Example 4 was dispersed to create a nickel slurry, which was then subjected to spray-drying treatment to produce the powder-anti-sintering layer composite. The produced powder-anti-sintering layer composite was subjected to desulfurization heat treatment at 600° C. in a vacuum atmosphere for 5 minutes. After the desulfurization heat treatment was completed, the sintering inhibitor was removed by cleaning with water, resulting in spherical nickel powder. Therefore, it was confirmed that even when using a sintering inhibitor, such as BaCl2, the intended spherical shape and the desired fine size of the metal powder could be achieved.
Referring to
In accordance with the technical concept of the present invention, the method for producing spherical nickel-based metal powder is safer compared to using hydrogen sulfide, which is a highly corrosive gas, as a conventional sulfur source, and allows for the efficient production of spherical powder by easily adding sulfur to nickel powder or nickel alloy powder. In addition, by performing desulfurization heat treatment after forming a coating on the powder surface, the agglomeration and sintering of the powder particles can be prevented.
The above effects of the present invention have been described as examples, and the scope of the present invention is not limited by these effects.
While the present invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0153122 | Nov 2022 | KR | national |
| 10-2023-0142320 | Oct 2023 | KR | national |
