Preparation method of barium titanate coated nickel powder

Abstract

The invention belongs to the technical field of metal powder materials, and particularly relates to a preparation method of barium titanate coated nickel powder, which comprises the following steps: carrying out pre-oxidation treatment on nickel powder before use, mixing the nickel powder with a composition of barium titanate or titanium compound and barium compound powder, adding the mixture into a plasma arc, heating and evaporating the nickel powder to form nickel vapor, and carrying out vacuum drying on the nickel vapor to obtain the barium titanate coated nickel powder. Cooling and condensing to form a nickel powder inner core, and combining pre-existing oxygen and / or sulfur elements with the surface of the nickel powder to form an inner shell layer; and the composition of the barium titanate or the titanium compound and the barium compound is condensed on the surface of the nickel powder and is condensed to form a barium titanate coated shell. According to the nickel powder with the double-shell structure prepared by the technical scheme, the co-firing property of the nickel powder and a dielectric material is improved through the barium titanate shell of the outer shell, and the combination degree of nickel and the dielectric material can be improved through the nickel oxygen compound and / or the nickel sulfide of the inner shell; therefore, the yield of the nickel powder and the dielectric material in the process of preparing the electronic component is improved, and the electrical property of the electronic component is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal powder materials, and particularly relates to a method for preparing barium titanate-coated nickel powder. Background Art

[0002] As the degree of miniaturization of electronic products continues to increase, electronic components are gradually moving towards miniaturization. The advantages of chip components such as small size, light weight, easy assembly and high reliability have also greatly improved the performance of electronic products.

[0003] Multilayer ceramic capacitors (MLCCs) are one of the most important chip passive devices in the modern electronics industry. They are known as the rice of the electronics industry and are widely used in consumer electronics, industrial electronics and modern military electronics. Traditional MLCC internal electrodes use precious metals such as silver and palladium. In addition to being expensive, their high-temperature co-firing, high resistivity and high melting point physical and chemical properties also affect their application in industrial devices. After the 1990s, nickel, as a base metal with good physical and chemical properties, has been widely used in MLCC internal electrodes.

[0004] Nickel is a high melting point metal that is not easily oxidized. When co-fired with the dielectric barium titanate at high temperatures, it will not be seriously oxidized, volatilized, or lost. When co-fired with the dielectric, it will not diffuse into the dielectric to affect the electrical insulation of the dielectric material. It also has many characteristics such as easy size control and good dispersibility. However, when nickel powder is used alone in the MLCC production process, the following problems still exist: nickel electrodes are prone to oxidation and lose their good conductivity, and nickel paste shrinks during the firing process, causing MLCC warping and fracture.

[0005] Barium titanate (BaTiO3) is a lead-free piezoelectric ceramic material discovered in the early 20th century. It has excellent high dielectric, low loss characteristics, and excellent piezoelectric and ferroelectric properties. It is widely used in MLCC, PTC and other fields, becoming one of the raw materials for electronic ceramics and is known as the "pillar of the electronic ceramics industry." The earliest industrial coating method for BaTiO3 powder is the solid phase method, which uses BaCO3 and TiO2 as raw materials. After ball milling to fully mix the raw materials, they are calcined at a temperature above 1000°C to synthesize BaTiO3 powder. The chemical equation for this process is:

[0006] BaCO3+TiO2→BaTiO3+CO2↑.

[0007] BaTiO3 is a consistent melting compound with a melting point of 1618°C, and its crystal structure will also change with the change of temperature. In the temperature range from 1460°C to the melting point, its crystal structure is a hexagonal system, which is a stable phase, and crystal growth must be carried out below 1460°C. When the temperature is between 130 and 1460°C, the crystal structure is a cubic phase system, at which time the BaTiO3 crystal structure has the highest symmetry, so there is no ferroelectricity and piezoelectricity; in the temperature range of 0 to 130°C, BaTiO3 undergoes a paraelectric-ferroelectric phase transition, the crystal symmetry decreases, and it changes from a cubic system to a tetragonal system with ferroelectricity, at which time its ferroelectric and dielectric properties are the best; at -90 to 0°C, it changes to an orthorhombic system (monoclinic system), and the ferroelectricity does not disappear; when the temperature drops below -90°C, the BaTiO3 crystal structure changes to a trigonal system. Under normal circumstances, the room temperature dielectric constant of BaTiO3 ceramics is about 2400; when the temperature reaches the Curie point of BaTiO3, its dielectric constant will increase rapidly to about 10000. This characteristic of BaTiO3, coupled with its inherent high dielectric constant and low dielectric loss, makes it the preferred dielectric material in MLCC manufacturing.

[0008] Coating a BaTiO3 ceramic layer on the surface of Ni powder can effectively improve its sintering performance and antioxidant properties. First, the introduction of pure BaTiO3 ceramic coating material can avoid the incorporation of other substances besides the core material components of MLCC, and will not have an adverse effect on the internal electrode slurry and the performance of MLCC products; secondly, the BaTiO3 ceramic coating layer can improve the compatibility of the Ni electrode with the BaTiO3 ceramic dielectric layer during the sintering process, and improve the reliability of MLCC. The current coating method of BaTiO3 coated Ni powder focuses on the liquid phase method, and the BaTiO3 coating layer is prepared by chemical reaction. Patent CN101774028A relates to BaTiO3 coated Ni powder and its coating method. This invention uses ultrasonic spray thermal decomposition to prepare composite powder. This method belongs to the chemical method. The addition of more chemical substances during the preparation process may have a negative impact on the subsequent slurry preparation. In addition, this method also has problems such as poor sphericity of the composite powder.

[0009] Patent CN103508736A relates to BaTiO3 coated Ni powder and its coating method. This invention adopts chemical hydrothermal crystallization method to prepare composite powder, and the sintering performance and antioxidant performance of powder product are improved to a certain extent. In the process of preparing single oxide (Cr2O3, or TiO2, or ZrO2) coated Ni powder by physical vapor phase method, the raw material is single, the process is simple and easy to control, and only the composition ratio between single oxide and Ni raw material is involved. However, in the coating process of multi-oxide system, there are melting, decomposition, evaporation of multiple oxide raw materials, and co-evaporation of Ni metal raw materials. The difference in evaporation rate of different raw materials makes it difficult to control the composition of powder product, and the composition, crystal structure and thickness of coating layer are difficult to control. These problems are solved in the present invention.

[0010] The DC arc plasma method is a physical vapor phase method for preparing core-shell type micro-nano composite powder materials. Its advantages are that it uses bulk raw materials, can be prepared on a large scale, has no chemical pollution, and is easy to control power and preparation atmosphere. Patent CN118847991 uses the DC arc plasma co-evaporation method to prepare core-shell BaTiO3 coated Ni powder materials in situ. On the basis of single oxide coated metal micro-nano powders, it further develops the preparation technology of multi-oxide ceramic material coated metal particles, realizes the preparation of complex oxide coated metal particles and their structural control. Compared with the conventional chemical solution method, it has the advantages of in-situ coating, rich raw material sources, high sphericity of powder products, no by-products, no chemical pollution, and easy scale-up.

[0011] However, in actual applications, it was found that whether the composite powder prepared by the hydrothermal crystallization method or the in-situ coated powder prepared by the DC plasma method, problems such as easy peeling of the coating shell, uneven coating, and loose bonding between the coating layer and nickel would occur. During the use of the slurry, there are still problems such as poor co-firing and warping. Summary of the invention

[0012] The object of the present invention is to provide a method for preparing barium titanate-coated nickel powder. The prepared barium titanate-coated nickel powder is a double-shell structure powder, which is used to solve the problem of inner electrode nickel powder shrinkage and ceramic dielectric mismatch during the co-sintering process of MLCC metal inner electrode and ceramic dielectric layer. A layer of nickel oxide and / or sulfide inner shell is arranged on the surface of the nickel powder, and a layer of barium titanate outer shell is arranged on the outer layer of the inner shell. The transition of the inner shell is used to enhance the bonding force between the inner core and the outer shell, and improve the stability of nickel in the inner electrode slurry during the firing process.

[0013] To achieve the above objectives, this application is implemented through the following technical solutions:

[0014] A method for preparing barium titanate-coated nickel powder, wherein the barium titanate-coated nickel powder has a nickel powder core with a specific surface area equivalent particle size d of 30 to 600 nm, and a double-shell structure on the surface, wherein the inner shell layer is nickel oxide and / or sulfide, and the outer shell is barium titanate. The preparation method is as follows:

[0015] S1. Prepare nickel powder with a specific surface area equivalent particle size D of 200 to 2000, wherein the nickel powder is pre-oxidized before use so that the surface of the nickel powder contains oxygen and / or sulfur elements not exceeding 5% of the total mass of the powder;

[0016] S2, pre-dispersing and mixing the nickel powder pre-oxidized in step S1 with barium titanate, or a combination of titanium compound and barium compound powder, to obtain a mixture;

[0017] S3, adding the mixture into the plasma arc through a powder feeder, so that the nickel powder is heated and evaporated, accompanied by the formation or melting of barium titanate;

[0018] S4, the nickel powder is heated and evaporated to form nickel vapor, and then cooled and condensed into a nickel powder core with a specific surface area equivalent particle size of 30 to 600 nm, and the pre-existing oxygen and / or sulfur elements are combined with the surface of the nickel powder to form an inner shell layer;

[0019] S5. The barium titanate or the combination of titanium compound and barium compound is atomized or reacted in the plasma arc to generate tiny particles with a particle size of less than 50 nm, which are condensed on the surface of the nickel powder and solidified to form a barium titanate coating shell.

[0020] Furthermore, in step S1, the oxygen element and / or sulfur element present on the surface of the nickel powder is in the form of at least one of nickel oxide and nickel sulfide.

[0021] Furthermore, in step S3, the plasma flame used is a plasma arc sprayed by a non-transferred arc torch group or a rotating plasma arc torch.

[0022] Furthermore, the average inner shell thickness of the prepared barium titanate-coated nickel powder is 1-25 nm, and the average outer shell thickness is 0.5-12.5 nm; the outer shell layer is one of the discontinuously distributed porous, dot-shaped, and island-shaped barium titanate coatings.

[0023] Furthermore, the proportion of the barium titanate in the outer shell layer coating the inner shell layer surface is greater than 50%.

[0024] Furthermore, in the inner shell layer of the prepared barium barate-coated nickel powder, the oxide and / or sulfide is at least one of nickel oxide, nickel sulfide, nickel hydroxide and nickel carbonate.

[0025] Furthermore, the prepared barium barate-coated nickel powder has a discrete distribution, and according to the discreteness meter R=Dmax-Dmin>d, wherein Dmax is the particle size of the largest particle among 10,000 particles continuously counted in any SEM photo, and Dmin is the particle size of the smallest particle among 10,000 particles continuously counted in any SEM photo.

[0026] The beneficial effects of the present invention are:

[0027] The nickel powder with a double-shell structure prepared by the present technical solution, in addition to the advantage of improving the co-firing property of nickel powder and dielectric materials through the barium titanate shell of the outer shell, can also better improve the bonding degree between nickel and dielectric materials through the nickel oxide compound and / or nickel sulfide of the inner shell, so as to improve the yield rate of such nickel powder and dielectric materials in the process of preparing electronic components and improve the electrical properties of electronic components. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a SEM photograph of the nickel powder having nickel oxide on the surface of the present invention.

[0029] Figure 2 This is a SEM photograph of the barium titanate-coated nickel powder of the present invention.

[0030] Figure 3 TEM image of barium titanate-coated nickel powder with discrete distribution. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is described in detail below through examples. The following examples are merely exemplary and can only be used to explain and illustrate the technical solution of the present invention, and cannot be interpreted as limiting the technical solution of the present invention.

[0032] The present application provides a method for preparing barium titanate-coated nickel powder, wherein the barium titanate-coated nickel powder has a nickel powder core with a specific surface area equivalent particle size d of 30 to 600 nm, and a double-shell structure on its surface, wherein the inner shell layer is nickel oxide and / or sulfide, and the outer shell is barium titanate, and the preparation method thereof is as follows:

[0033] S1. Prepare nickel powder with a specific surface area equivalent particle size D of 200 to 2000, and pre-oxidize the nickel powder before use so that the surface of the nickel powder contains oxygen and / or sulfur elements not exceeding 5% of the total mass of the powder;

[0034] S2, pre-dispersing and mixing the nickel powder pre-oxidized in step S1 with barium titanate, or a combination of titanium compound and barium compound powder, to obtain a mixture;

[0035] S3, adding the mixture into the plasma arc through a powder feeder, so that the nickel powder is heated and evaporated, accompanied by the formation or melting of barium titanate;

[0036] S4, the nickel powder is heated and evaporated to form nickel vapor, which is then cooled and condensed into a nickel powder core with a specific surface area equivalent to a particle size of 30-600 nm, and the pre-existing oxygen and / or sulfur elements are combined with the surface of the nickel powder to form an inner shell layer;

[0037] S5. Barium titanate or a combination of titanium compounds and barium compounds is atomized or reacted in a plasma arc to generate tiny particles with a particle size of less than 50 nm, which are condensed on the surface of nickel powder and solidified to form a barium titanate coating shell.

[0038] In the present application, in step S1, the oxygen element and / or sulfur element present on the surface of the nickel powder is in the form of at least one of nickel oxide and nickel sulfide.

[0039] In the present application, in step S3, the plasma flame used is a plasma arc sprayed by a non-transferred arc torch group or a rotating plasma arc torch.

[0040] In the present application, the average inner shell thickness of the prepared barium titanate-coated nickel powder is 1-25 nm, and the average outer shell thickness is 0.5-12.5 nm; the outer shell layer is one of the discontinuously distributed porous, dot-shaped, and island-shaped barium titanate coatings.

[0041] In the present application, the proportion of the barium titanate of the outer shell layer covering the surface of the inner shell layer is greater than 50%.

[0042] In the present application, in the inner shell layer of the prepared barium barate-coated nickel powder, the oxide and / or sulfide is at least one of nickel oxide, nickel sulfide, nickel hydroxide, and nickel carbonate.

[0043] In the present application, the prepared barium barate-coated nickel powder has a discrete distribution, and according to the discreteness meter R=D(max)-D(min)>d, D(max) is the particle size of the largest particle among 10,000 particles counted continuously in any SEM photo, and D(min) is the particle size of the smallest particle among 10,000 particles counted continuously in any SEM photo.

[0044] Example 1

[0045] The nickel powder with the equivalent particle size of 850nm in specific surface area was placed in a tube furnace, the heating temperature was controlled to be 285 degrees Celsius, a nitrogen mixed gas with an oxygen content of 5% was introduced, the heating was continued for 30 minutes, and then slowly cooled to room temperature for 100 minutes, and the nickel powder with nickel oxide on the surface was taken out ( Figure 1 SEM shown).

[0046] The barium titanate powder and the obtained nickel powder containing nickel oxide are then mixed uniformly by a ball mill.

[0047] The mixed barium titanate and nickel powder mixture was fed into a torch group consisting of three non-transferred arc plasma guns using a powder feeder at a rate of 6 kg per hour.

[0048] After the nickel powder and the oxide on its surface are heated and evaporated in the plasma arc, cooling gas is sprayed under the plasma arc, and the nickel vapor is re-condensed and focused to form nickel powder with a particle size of 265nm. In addition, the oxide forms an inner shell layer on the surface of the nickel powder during the process of particle formation and solidification.

[0049] After being heated by the plasma arc, the barium titanate powder melts and atomizes into fine molten droplets that adhere to the surface of the nickel powder. After the nickel oxide forming process, the barium titanate solidifies on the surface of the nickel powder with an inner shell layer to form an outer barium titanate shell layer.

[0050] Its surface has a double shell structure, the inner shell is oxide, XPS test shows that the oxide includes NiO and NI-CO, and the outer shell is barium titanate; the average thickness of the inner shell is 14nm, and the average thickness of the outer shell is 2.5nm. According to the discreteness meter R=Dmax-Dmin, wherein Dmax is the largest particle in the same field of view with a count of no less than 10,000 particles in its SEM photo, and its particle size is 1105nm, and Dmin is the smallest particle in the same field of view, and its particle size is 42nm, ( Figure 2 SEM shown).

[0051] Example 2

[0052] Nickel powder with a specific surface area equivalent particle size of 850nm and sulfur powder with a weight ratio of 0.1% were placed in a tube furnace, the heating temperature was controlled to 205 degrees Celsius, and a nitrogen mixed gas with an oxygen content of 5% was introduced. The heating was continued for 30 minutes, and then slowly cooled to room temperature for 100 minutes. The nickel powder with nickel oxide and nickel sulfide on the surface was taken out ( Figure 1 SEM shown).

[0053] The mixed powder of barium hydroxide and titanium dioxide and the obtained nickel powder containing nickel oxide and nickel sulfide are then mixed uniformly by a ball mill.

[0054] The mixed powder was fed into the rotating plasma arc at a rate of 1.2 kg per hour using a powder feeder.

[0055] After the nickel powder and the nickel oxide and nickel sulfide on its surface are heated and evaporated in the plasma arc, a cooling chamber with a cooling jacket is set under the plasma arc, and the nickel vapor is re-condensed and focused to form nickel powder with a particle size of 53nm. In addition, the nickel oxide and nickel sulfide form an inner shell layer on the surface of the nickel powder during the process of particle formation and solidification.

[0056] After the titanium dioxide and barium hydroxide powders are heated by the plasma arc, they react with the high-temperature plasma arc to form fine molten droplets that adhere to the surface of the nickel powder. After the nickel oxide and nickel sulfide forming process, the barium titanate solidifies on the surface of the nickel powder with an inner shell layer to form an outer barium titanate shell layer. The outer shell layer is a discontinuously distributed island-shaped barium titanate coating, and the barium titanate coating of the outer shell layer accounts for 52% of the inner shell surface. From the structure, it can be seen that part of the inner shell is exposed.

[0057] The prepared barium titanate coated nickel powder has a discrete distribution, according to the discreteness meter R = Dmax-Dmin = 805-20 = 785nm> 57nm, wherein Dmax is the particle size of the largest particle among 10,000 particles counted continuously in any SEM photo, and Dmin is the particle size of the smallest particle among 10,000 particles counted continuously in any SEM photo. Figure 3 TEM shown.

[0058] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing barium titanate-coated nickel powder, characterized in that: Barium titanate coated nickel powder has a nickel powder core with a specific surface area equivalent particle size d of 30-600 nm, and a double shell structure on its surface, wherein the inner shell layer is nickel oxide and / or sulfide, and the outer shell is barium titanate, and the preparation method thereof is as follows: S1. Prepare nickel powder with a specific surface area equivalent particle size D of 200 to 2000, wherein the nickel powder is pre-oxidized before use so that the surface of the nickel powder contains oxygen and / or sulfur elements not exceeding 5% of the total mass of the powder; S2, pre-dispersing and mixing the nickel powder pre-oxidized in step S1 with barium titanate, or a combination of titanium compound and barium compound powder, to obtain a mixture; S3, adding the mixture into the plasma arc through a powder feeder, so that the nickel powder is heated and evaporated, accompanied by the formation or melting of barium titanate; S4, the nickel powder is heated and evaporated to form nickel vapor, and then cooled and condensed into a nickel powder core with a specific surface area equivalent particle size of 30 to 600 nm, and the pre-existing oxygen and / or sulfur elements are combined with the surface of the nickel powder to form an inner shell layer; S5. The barium titanate or the combination of titanium compound and barium compound is atomized or reacted in the plasma arc to generate tiny particles with a particle size of less than 50 nm, which are condensed on the surface of the nickel powder and solidified to form a barium titanate coating shell.

2. The method for preparing barium titanate-coated nickel powder according to claim 1, characterized in that: In step S1, the oxygen element and / or sulfur element present on the surface of the nickel powder is in the form of at least one of nickel oxide and nickel sulfide.

3. The method for preparing barium titanate-coated nickel powder according to claim 1, characterized in that: In step S3, the plasma flame used is a plasma arc sprayed by a non-transferred arc torch group or a rotating plasma arc torch.

4. The method for preparing barium titanate-coated nickel powder according to claim 1, characterized in that: The prepared barium titanate coated nickel powder has an inner shell thickness of 1-25 nm on average and an outer shell thickness of 0.5-12.5 nm on average; the outer shell layer is one of the discontinuously distributed porous, dot-shaped and island-shaped barium titanate coatings.

5. The method for preparing barium titanate-coated nickel powder according to claim 4, characterized in that: The proportion of the barium titanate coating the inner shell surface in the outer shell is greater than 50%.

6. The method for preparing barium titanate-coated nickel powder according to claim 1, characterized in that: In the inner shell layer of the prepared barium barate-coated nickel powder, the oxide and / or sulfide is at least one of nickel oxide, nickel sulfide, nickel hydroxide and nickel carbonate.

7. The method for preparing barium titanate-coated nickel powder according to claim 1, characterized in that: The prepared barium barate coated nickel powder has a discrete distribution, and according to the discreteness meter R=Dmax-Dmin>d, wherein Dmax is the particle size of the largest particle among 10,000 particles continuously counted in any SEM photo, and Dmin is the particle size of the smallest particle among 10,000 particles continuously counted in any SEM photo.

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