Nano nickel powder slurry with high dispersion stability as well as preparation method and application of nano nickel powder slurry

Abstract

The invention relates to the technical field of ceramic surface metallization, and discloses nano nickel powder slurry with high dispersion stability and a preparation method and application thereof.According to the slurry, pure nickel powder is replaced with Ni-Sn alloy powder, tin reacts with sulfur preferentially to generate a SnS protection layer, a sulfur source is consumed to protect a nickel core, an organic tin compound is added into the slurry to serve as an in-situ repairing agent, and the surface of the nano nickel powder is repaired. Active Sn < 2 + > is decomposed and released in the rubber discharging stage and migrated to the surface defect position to be combined with sulfur, repairing of a protection layer is achieved, a weak coordination type dispersing agent is adopted, steric hindrance is provided through hydrogen bonds and Van der Waals force to maintain storage stability, meanwhile, interference of a strong anchoring group on tin migration is avoided, the adding time of organic tin is controlled through a step-by-step feeding process, and the stability of the organic tin is improved. And a compact SnS protection layer is formed in cooperation with slow heating, nickel cores are exposed after complete decomposition at high temperature, the long-term dispersion stability of the slurry in a sulfur-containing system is achieved, and the method is suitable for manufacturing of an MLCC inner electrode.

Description

Technical Field

[0001] This invention relates to the field of ceramic surface metallization technology, and in particular to a nano-nickel powder slurry with high dispersion stability, its preparation method and application. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are the most critical basic components in electronic devices. Due to their excellent conductivity and anti-electromigration properties, nano-nickel powder has become the mainstream material for the internal electrodes of MLCCs. In order to reduce the sintering temperature of MLCCs and improve their dielectric properties, researchers have begun to introduce sulfur-containing compounds, such as sulfides and sulfur-based glass phases, into the dielectric materials. These sulfur-containing dielectrics can promote grain growth and reduce dielectric loss during high-temperature co-firing, thereby meeting the process requirements of the next generation of ultra-thin dielectric layers.

[0003] To ensure the long-term stable dispersion of nano-nickel powder in an organic carrier, existing technologies typically employ surface passivation treatment. For example, Chinese Patent CN116386930B discloses a highly dispersed nickel slurry and its preparation method. By pre-oxidizing the nickel powder in a nitrogen-oxygen mixed atmosphere, a dense NiO passivation layer is formed on its surface. This not only inhibits further oxidation of the nickel powder in the air but also establishes a dual stabilization mechanism of electrostatics and steric hindrance in the slurry system through synergistic effects with organic dispersants. Furthermore, a removable azeotropic temporary diluent is introduced to further optimize the dispersion effect.

[0004] However, when the aforementioned nickel paste is applied to a sulfur-containing MLCC system, the sulfur-containing medium releases sulfide gases such as H2S and SO2 during co-firing, which react chemically with the NiO passivation layer on the surface of the nickel powder to generate low-conductivity sulfides such as NiS and Ni3S2. This causes the NiO passivation layer to be corroded and destroyed, and the dispersant that originally relied on NiO for anchoring falls off the surface due to the loss of binding sites, resulting in a decrease in colloidal stability. Secondly, the generated NiS and Ni3S2 themselves have high catalytic activity, which will accelerate the decomposition of the organic carrier during storage and further deteriorate the rheological properties of the paste. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to construct a surface interface structure that is compatible with the sulfur chemical environment, thermally stable, and removable during the sintering stage in a sulfur-containing MLCC media system, so as to maintain the long-term dispersion stability of the slurry system. To this end, we propose a nano-nickel powder slurry with high dispersion stability, its preparation method, and its application.

[0006] To achieve the above objectives, this application adopts the following technical solution: a nano-nickel powder slurry with high dispersion stability, comprising Ni-Sn alloy powder, an organic carrier, an organotin compound, and a dispersant. The tin content in the Ni-Sn alloy powder is 0.5-3.0 wt%, and the organotin compound can decompose and release active Sn during the debinding stage. 2+ The dispersant interacts with the nickel powder surface through reversible weak interactions via hydrogen bonds and van der Waals forces.

[0007] Preferably, the composition of the nano-nickel powder slurry includes, by weight, 65-75 parts Ni-Sn alloy powder, 20-30 parts organic carrier, 0.5-3.0 parts organotin compound, 1.0-3.0 parts dispersant, and 0-2 parts additives.

[0008] Preferably, the Ni-Sn alloy powder is a binary alloy of nickel and tin, wherein the tin content is 1.5 wt%.

[0009] Preferably, the Ni-Sn alloy powder has an average particle size D50 of 100-150 nm and a specific surface area of ​​6-10 m². 2 / g.

[0010] Preferably, the organic carrier is composed of terpineol and ethyl cellulose, with terpineol accounting for 70-80% of the total mass of the organic carrier and ethyl cellulose accounting for 20-30% of the total mass of the organic carrier.

[0011] Preferably, the dispersant is a polyester or polyether polymer with a number average molecular weight of 1000-5000 and an acid value of less than 5 mg KOH / g.

[0012] Preferably, the dispersant is selected from one of polycaprolactone triol, trihydroxypolyoxypropylene ether, and DISPERBYK-2155.

[0013] Preferably, the organotin compound is selected from dibutyltin dilaurate and stannous octoate.

[0014] A method for preparing a highly dispersed and stable nano-nickel powder slurry includes the following steps: S1: Mixing Ni-Sn alloy powder, dispersant, and the first part of organic carrier, stirring to form a paste, wherein the first part of organic carrier accounts for 66%-82% of the total organic carrier; S2: Grinding and dispersing the paste, adding an organotin compound to the slurry during the grinding and dispersion process, and continuing grinding until the fineness is less than 5μm; S3: Adding the remaining organic carrier to adjust the viscosity, and obtaining the nano-nickel powder slurry after degassing.

[0015] The application of a nano-nickel powder slurry in the preparation of sulfur-containing MLCC internal electrodes includes coating the nano-nickel powder slurry onto a sulfur-containing MLCC dielectric green blank and co-firing it under a protective atmosphere. The co-firing process includes slowly heating from 380-420℃ to a temperature range of 580-620℃ at a rate of 1-2℃ / min.

[0016] The technical effects and advantages of this invention are as follows:

[0017] In this invention, Ni-Sn alloy powder is used instead of pure nickel powder. Utilizing the strong affinity between tin and sulfur, tin preferentially reacts with H2S, SO2, etc., to form a SnS protective layer, consuming the sulfur source. An organotin compound is introduced into the slurry as an in-situ repair agent, which decomposes and releases active Sn during the debinding stage. 2+ The tin migrates to defects on the surface of nickel powder and combines with residual sulfur to fill weak parts of the protective layer. A weak coordination type dispersant is used instead of a conventional strong anchoring type dispersant. The steric hindrance provided by hydrogen bonds and van der Waals forces maintains storage stability. At the same time, it can be reversibly desorbed during the debinding stage, freeing up surface sites for tin migration and avoiding interference with the sacrificial protection mechanism. The timing of adding organotin is controlled by a step-by-step feeding process, and the SnS is ensured to form densely and decompose completely at high temperature by staged heating. This allows the slurry to remain stably dispersed for more than 30 days in a sulfur-containing environment. After sintering, the nickel core is not corroded, and the electrode layer is continuous and dense with a sheet resistance comparable to that of pure nickel powder. This breakthrough overcomes the technical problem that traditional pre-oxidized passivation layers are prone to failure in sulfur-containing systems. Attached Figure Description

[0018] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts:

[0019] Figure 1 This is a schematic diagram showing the changes in Zeta potential of various samples of the present invention after heat treatment at different temperatures.

[0020] Figure 2 This is a graph showing the sedimentation rate changes of each sample of the present invention over 30 days;

[0021] Figure 3 This is a scanning electron microscope image of the cross-section of the sintered film in Embodiment 1 of the present invention. Detailed Implementation

[0022] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0023] This invention provides a nano-nickel powder slurry with high dispersion stability, comprising the following components by weight: 65-75 parts Ni-Sn alloy powder, 20-30 parts organic carrier, 0.5-3.0 parts organotin compound, 1.0-3.0 parts dispersant and 0-2 parts additives. The components are described in detail below.

[0024] The Ni-Sn alloy powder is a binary alloy of nickel and tin, wherein the tin content is 0.5-3.0 wt%, preferably 1.5 wt%.

[0025] The average particle size D50 of the Ni-Sn alloy powder is 100-150 nm, and the specific surface area is 6-10 m². 2 / g, in spherical or near-spherical form, tin is uniformly dissolved in the nickel lattice in the alloy, without elemental tin or tin-rich phase segregation, to ensure that tin can uniformly migrate to the surface and react with sulfur during sintering.

[0026] The Ni-Sn alloy powder can be prepared by hydrogen reduction, including the following steps:

[0027] C1: Dissolve nickel salt and tin salt in deionized water at the target molar ratio to prepare a mixed salt solution;

[0028] C2: Add a precipitant to the mixed salt solution, and control the pH value by adjusting the dropping rate of the mixed salt solution and the precipitant solution, so that nickel ions and tin ions co-precipitate to form a Ni-Sn composite carbonate precursor;

[0029] C3: After washing and drying the precipitate, it is reduced under a hydrogen atmosphere to obtain Ni-Sn alloy powder.

[0030] The nickel salt is preferably nickel chloride hexahydrate (NiCl2·6H2O), and the tin salt is preferably tin chloride pentahydrate (SnCl4·5H2O). Taking Ni-Sn alloy powder with a tin content of 1.5wt% as an example:

[0031] C1: Weigh out nickel chloride hexahydrate and tin chloride pentahydrate according to the molar ratio of Ni to Sn 98.5:1.5, dissolve them in deionized water to prepare a mixed salt solution with a total metal ion concentration of 0.5 mol / L;

[0032] C2: Prepare a 1.0 mol / L Na2CO3 solution as a precipitant. Under constant temperature water bath conditions of 25℃, add the mixed salt solution and precipitant solution dropwise into the reaction vessel in a parallel flow manner, control the pH value at 8.5±0.2, stir at 300 r / min, continue stirring for 2 hours after the addition is complete, and let stand for 4 hours to obtain the precipitate.

[0033] C3: The obtained precipitate was filtered and washed with deionized water until the conductivity of the filtrate was <50μS / cm. It was then washed once with anhydrous ethanol to remove water. The filter cake was vacuum dried at 80℃ for 12 hours and then placed in a tube furnace. Under H2 atmosphere, the temperature was increased to 500℃ at 5℃ / min and held for 2 hours. After naturally cooling to room temperature, Ni-Sn alloy powder was obtained.

[0034] The organic carrier, which provides suitable rheological properties and printing performance for the slurry, is composed of a solvent and a film-forming agent.

[0035] The solvent is preferably terpineol, which accounts for 70-80% of the total mass of the organic carrier. Terpineol has a suitable evaporation rate and solubility, and can form a uniform wet film after printing.

[0036] The preferred film-forming agent is ethyl cellulose, which accounts for 20-30% of the total mass of the organic carrier. As a thickener and film-forming agent, ethyl cellulose can adjust the viscosity of the slurry and provide a certain wet film strength after printing to prevent the printed pattern from collapsing.

[0037] The organotin compound acts as an in-situ repair agent in the slurry, decomposing and releasing active Sn during the desizing stage. 2+ These Sn 2+ It has strong migration ability and can migrate to the defects on the surface of nickel powder through solid-phase diffusion or gas-phase mass transfer. It reacts with sulfide gases such as H2S and SO2 released by sulfur-containing media to generate SnS, thereby achieving dynamic repair of the surface protective layer.

[0038] The thermal decomposition temperature of the organotin compound must match the debinding temperature range of the organic carrier to ensure the release of Sn during the debinding stage. 2+ It should also have good compatibility with terpineol to avoid precipitation in the slurry.

[0039] In one embodiment of the present invention, the organotin compound is dibutyltin dilaurate (DBTDL), with the chemical structure shown in formula (Ⅰ), CAS number 77-58-7, purity ≥95%, decomposing at 150-200℃ and completely decomposing at 200-350℃, and matching well with the debinding window of the terpineol and ethyl cellulose system. Formula (Ⅰ);

[0040] In another embodiment of the present invention, the organotin compound is stannous octoate (C 16 H 30 O4Sn), with the chemical structure shown in formula (Ⅱ) below, CAS number 301-10-0, has a slightly higher thermal decomposition temperature and is suitable for sintering processes with a faster heating rate; Formula (II);

[0041] The dispersant is used to maintain the long-term dispersion stability of nickel powder in the organic carrier. Unlike conventional strong anchoring dispersants such as carboxylic acids and phosphonic acids, the present invention uses a weak coordination dispersant.

[0042] Strongly anchoring dispersants form stable coordination bonds with the nickel powder surface through carboxyl groups, phosphonic acid groups, etc., which can provide good dispersion effect. However, in the Ni-Sn alloy system of this invention, these strongly anchoring groups will occupy the active sites on the nickel powder surface, hindering the migration of tin and the formation of SnS during the debinding stage.

[0043] The dispersant molecules do not contain strong anchoring groups. They interact with the surface through reversible weak interactions via hydrogen bonds and van der Waals forces. The balance between adsorption and desorption is dynamically reversible. During the storage stage, it can provide steric hindrance to maintain dispersion stability. During the debinding stage, it gradually desorbs as the temperature rises, freeing up surface sites for tin migration.

[0044] The dispersant is preferably a polyester or polyether polymer with a branched structure, a number average molecular weight of 1000-5000, which can provide an effective steric hindrance effect, has good compatibility with the organic carrier, and an acid value of <5mgKOH / g to avoid interference of acidic groups on tin migration.

[0045] In one embodiment of the present invention, the dispersant is polycaprolactone triol, CAS number 37625-56-2, hydroxyl value 80-90 mgKOH / g, acid value <1 mgKOH / g, and the dispersant is commercially available;

[0046] In another embodiment of the present invention, the dispersant is trihydroxy polyoxypropylene ether, CAS number 25791-96-2, hydroxyl value 55-65 mgKOH / g;

[0047] In one embodiment of the present invention, the dispersant is DISPERBYK-2155 produced by BYK Chemical, with an amine value of 48 mg KOH / g and an acid value of <5 mg KOH / g.

[0048] As needed, at least one of leveling agent, defoamer or coupling agent may be added to the slurry of the present invention, with the total addition amount not exceeding 2% of the total mass of the slurry. The selection and dosage of these additives are well known to those skilled in the art and will not be described in detail here.

[0049] This invention also provides a method for preparing a nano-nickel powder slurry with high dispersion stability, comprising the following steps:

[0050] S1: Add Ni-Sn alloy powder, dispersant and the organic carrier from the first part into a mixing tank and stir to form a uniform paste without dry powder. The organic carrier from the first part accounts for 66%-82% of the total organic carrier.

[0051] S2: Add the paste obtained in S1 to a three-roll mill for grinding and dispersion. Perform the first grinding with a roller gap of 50μm, the second grinding with a roller gap of 30μm, the third grinding with a roller gap of 15μm, and the fourth grinding with a roller gap of 10μm in sequence. Collect the slurry after each grinding.

[0052] S3: Transfer the ground slurry to a mixing tank, add the remaining organic carrier, stir at 500 r / min for 30 minutes, adjust the slurry viscosity to 13-24 Pa·s, add the additives and continue stirring for 10 minutes, then place it in a vacuum degassing machine and degas for 30 minutes under a vacuum of -0.08 MPa, breaking the air 2-3 times intermittently during the process. After degassing, obtain nickel slurry, seal and store for later use.

[0053] It should be noted that in S2, before the third grinding begins, the organotin compound is added to the slurry and stirred evenly before the third grinding is carried out. This is to prevent the organotin compound from undergoing prolonged high-shear grinding too early, thus preventing its premature decomposition during the slurry preparation stage.

[0054] The present invention also provides an application of a highly dispersed and stable nano-nickel powder slurry in the preparation of sulfur-containing MLCC internal electrodes. Specifically, the nickel slurry prepared above is coated onto a sulfur-containing dielectric green blank by screen printing, casting, or other methods known in the art to form an electrode pattern, and then co-fired.

[0055] The co-firing process is carried out under a protective atmosphere, and the specific process is as follows:

[0056] The sulfur-containing MLCC green blank coated with the nickel paste of the present invention is placed in a tube furnace, and N2 is introduced as a protective atmosphere at a gas flow rate of 100 mL / min to ensure that the oxygen content in the furnace is <10 ppm. During the debinding stage at 200-400℃, the N2 flow rate can be increased to 200 mL / min to facilitate the rapid discharge of organic decomposition products.

[0057] The heating process is carried out in stages. The first stage heats the temperature from room temperature to 380-420℃ at a rate of 4-6℃ / min. The second stage heats the temperature from 380-420℃ to 580-620℃ at a rate of 1-2℃ / min. The third stage heats the temperature from 580-620℃ to 880-920℃ at a rate of 8-10℃ / min. The fourth stage involves holding the temperature at 880-920℃ for 15 minutes and then allowing it to cool naturally to room temperature.

[0058] The second stage described above uses a slow heating process. The sulfide gases such as H2S and SO2 released by the sulfur-containing medium during the debinding stage react with the tin in the Ni-Sn alloy powder to form SnS, which is the dominant reaction in this temperature range.

[0059] Slow heating allows sufficient time for the reaction between tin and sulfur, enabling the SnS protective layer to form densely and continuously, thereby consuming the sulfur source and protecting the nickel core. If the heating rate is too fast at this stage, the reaction between tin and sulfur may be incomplete, causing some sulfur to penetrate the protective layer and react with nickel, resulting in deterioration of electrode performance.

[0060] After sintering, the SnS protective layer formed on the nickel powder surface decomposes at high temperature, releasing tin and re-exposing the clean nickel core, thus ensuring good conductivity of the electrode layer. Simultaneously, the organotin compounds added to the slurry decompose and release Sn during the binder removal stage. 2+ It can migrate to surface defects and combine with sulfur, thus achieving in-situ repair of the protective layer.

[0061] The technical solution of the present invention will be further illustrated below through specific embodiments and comparative examples. The described embodiments are only for illustrating the present invention and do not constitute a limitation on the scope of protection of the present invention. If those skilled in the art make non-substantial modifications or adjustments to the technical solution of the present invention after reading the content of the present invention, they shall still fall within the scope of protection of the present invention.

[0062] Unless otherwise specified, all raw materials used in the embodiments and comparative examples are commercially available products, and their specifications and sources are described above.

[0063] Example 1: This example provides a nano-nickel powder slurry with high dispersion stability, which, by weight, includes 70 parts Ni-Sn alloy powder, 26.5 parts organic carrier, 1.0 part dibutyltin dilaurate, and 2.0 parts polycaprolactone triol.

[0064] The Ni-Sn alloy powder has a tin content of 1.5 wt% and an average particle size D50 of 128 nm.

[0065] The organic carrier was prepared with a mass ratio of terpineol to ethyl cellulose of 75:25.

[0066] This embodiment also provides a method for preparing a nano-nickel powder slurry with high dispersion stability, including the following steps:

[0067] S1: Weigh out the required amount of Ni-Sn alloy powder, polycaprolactone triol and 70% of the total organic carrier, add them to a mixing tank, stir for 10-15 minutes to form a uniform paste without dry powder.

[0068] S2: Add the paste to the three-roll mill. For the first grinding, set the initial roller gap to 50μm, grind and collect the slurry, adjust the roller gap to 30μm, and perform the second grinding. Collect the slurry and adjust the roller gap to 15μm.

[0069] S3: Before the third grinding begins, add dibutyltin dilaurate to the slurry, stir evenly, and then perform the third grinding. After the third grinding, adjust the roller gap to 10μm and perform the fourth grinding until the fineness is ≤5μm.

[0070] S4: Transfer the ground slurry to a mixing tank, add the remaining organic carrier, and stir with a mechanical stirrer at 500 r / min for 30 minutes to make the slurry uniformly mixed. The slurry viscosity is controlled at 18 Pa·s. Place the diluted slurry in a vacuum degassing machine and degas for 30 minutes under a vacuum of -0.08 MPa, breaking the air 3 times intermittently during the process to promote the escape of air bubbles. After degassing, the final nickel slurry is obtained and sealed for storage.

[0071] Example 2: This example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the tin content of the Ni-Sn alloy powder is adjusted. The Ni-Sn alloy powder is prepared according to the Ni to Sn molar ratio of 99.48:0.52, and the tin content is 0.52wt%.

[0072] Example 3: This example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the tin content of the Ni-Sn alloy powder is adjusted. The Ni-Sn alloy powder is prepared according to the molar ratio of Ni to Sn of 98.02:1.98, and the tin content is 1.98wt%.

[0073] Example 4: This example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the tin content of the Ni-Sn alloy powder is adjusted. The Ni-Sn alloy powder is prepared according to the Ni to Sn molar ratio of 97.05:2.95, and the tin content is 2.95wt%.

[0074] Example 5: This example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the organotin compound is replaced with stannous octoate, and the amount added is still 1.0 part.

[0075] Example 6: This example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the dispersant is replaced with polypropylene glycol triol, and the amount added is still 2.0 parts.

[0076] Example 7: This example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the dispersant is replaced with DISPERBYK-2155, and the amount added is still 2.0 parts.

[0077] Example 8: This example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the amount of each component added in the slurry formula is adjusted, including 65 parts Ni-Sn alloy powder, 30 parts organic carrier, 2.0 parts dibutyltin dilaurate, and 3.0 parts polycaprolactone triol.

[0078] Example 9: This example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the amount of each component added in the slurry formula is adjusted, including 75 parts Ni-Sn alloy powder, 20 parts organic carrier, 0.5 parts dibutyltin dilaurate, and 1.0 part polycaprolactone triol.

[0079] Comparative Example 1: This comparative example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the Ni-Sn alloy powder is replaced with an equal amount of pure nickel powder, and the average particle size of the pure nickel powder is the same as that of Example 1.

[0080] Comparative Example 2: This comparative example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the Ni-Sn alloy powder is replaced with pre-oxidized nickel powder, which is obtained by heat-treating the pure nickel powder of Comparative Example 1 in an air atmosphere at 300°C for 2 hours.

[0081] Comparative Example 3: This comparative example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that no organotin compound is added, that is, 1.0 part of dibutyltin dilaurate is replaced with an equal amount of organic carrier.

[0082] Comparative Example 4: This comparative example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that a strong anchoring dispersant is used to replace the dispersant, specifically, polycaprolactone triol is replaced with an equal amount of oleic acid.

[0083] Comparative Example 5: This comparative example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the tin content of the Ni-Sn alloy powder is adjusted. The Ni-Sn alloy powder is prepared according to the molar ratio of Ni to Sn of 99.8:0.2, and the tin content is 0.2wt%.

[0084] Comparative Example 6: This comparative example provides a nano-nickel powder slurry with high dispersion stability and its preparation method. The difference from Example 1 is that the tin content of the Ni-Sn alloy powder is adjusted. The Ni-Sn alloy powder is prepared according to the Ni to Sn molar ratio of 96.0:4.0, and the tin content is 4.0 wt%.

[0085] To verify the technical effect of the present invention, performance tests were conducted on the slurries and sintered films prepared in some embodiments and comparative examples. The test scheme is as follows.

[0086] Experimental Example 1: This experimental example aims to test the surface charge state of nickel powder particles in the slurry, and combined with the change in Zeta potential before and after heat treatment, to reflect the change in surface chemical properties caused by the migration of tin to the surface during heat treatment.

[0087] Ten samples were selected for testing: Examples 1, 3, 5, 6, Comparative Examples 1, 2, 3, 4, 5, and 6, and were denoted as A1, A3, A5, A6, D1, D2, D3, D4, D5, and D6, respectively. The changes in Zeta potential of each sample after heat treatment at different temperatures were measured.

[0088] Take 2g of freshly prepared slurry from each example and comparative example, dilute it 100 times with terpineol, and ultrasonically disperse it for 5 minutes at a constant temperature of 25℃. Inject the diluted suspension into the Zeta potential analysis cell, ensuring that there are no air bubbles. Set the Zeta potential analyzer to test at 25℃ and the equilibration time to 120 seconds. Test each sample 3 times consecutively, and take the arithmetic mean as the Zeta potential value of the sample in its fresh state, denoted as ζ0.

[0089] Test results are available Figure 1 As shown.

[0090] Take 5g of freshly prepared slurry from each of the embodiments and comparative examples, and coat it evenly on a ceramic substrate with a thickness of about 100μm. Place the coated substrate in a tube furnace and heat treat it at 200℃, 300℃, 400℃ and 500℃ respectively under N2 atmosphere protection. The heating rate is 5℃ / min. After reaching the target temperature, hold it at that temperature for 30 minutes and then let it cool naturally to room temperature.

[0091] A suitable amount of slurry was scraped from the heat-treated sample and subjected to Zeta potential testing using the same method as for fresh slurry. The test was performed three times at each temperature point, and the average value was recorded as ζ. T .

[0092] Calculate the rate of change of Zeta potential for each sample after heat treatment at different temperatures using the following formula: ;

[0093] The test results are shown in Table 1: ;

[0094] Depend on Figure 1 As can be seen, the absolute value of the Zeta potential of the fresh slurry in Examples 1-6 is between 17-19 mV, which is lower than that of conventional slurry systems stabilized by electrostatic repulsion mechanisms. Weak coordination dispersants such as polycaprolactone triol and trihydroxy polyoxypropylene ether mainly form reversible weak interactions such as hydrogen bonds and van der Waals forces with the nickel powder surface through hydroxyl and ester groups in the molecular chain, rather than through strong electrostatic adsorption or chemical bonding through carboxylic acid groups, phosphonic acid groups, etc. Therefore, the net charge density on the particle surface is low, and the absolute value of the Zeta potential is correspondingly small.

[0095] The absolute value of the Zeta potential in Comparative Example 3 is higher than that in the Example. This may be because the lack of organotin compounds changes the interaction mode between the dispersant and the nickel powder surface, resulting in different surface charge states. The Zeta potential of Comparative Example 6 is comparable to that of Comparative Example 3, indicating that high Sn content may affect the surface charge state.

[0096] As shown in Table 1, with the increase of heat treatment temperature, the absolute value of the Zeta potential of the samples in each embodiment continued to increase. Below 200℃, tin did not undergo significant migration, and the surface chemical state remained basically in its initial state, so the Zeta potential changed little. When the temperature rose to 300℃, the diffusion activation energy threshold of tin was reached, and tin began to migrate from the inside of the particles to the surface, changing the surface chemical state and causing the Zeta potential to rise. In the 400-500℃ range, tin migration intensified, and it reacted with sulfur in a sulfur-containing atmosphere to generate SnS. SnS, as a semiconductor material, has different surface charge characteristics than metallic nickel, which changed the Zeta potential.

[0097] Comparative Example 1 showed a zeta potential change rate of less than 8% throughout the entire heat treatment process. This is because pure nickel powder does not contain tin, and the surface chemical state remains essentially unchanged during heat treatment. Comparative Example 2 showed a slightly higher change rate than Comparative Example 1, but still lower than the Example. This is because although the pre-oxidized NiO layer may undergo structural changes during heat treatment, its chemical composition remains unchanged. Comparative Example 3 showed a slightly higher change rate than Comparative Example 2, but still much lower than the Example. This indicates that although tin in the Ni-Sn alloy powder migrates to some extent, the total amount of migration is limited due to the lack of supplementary repair by organotin. Comparative Example 4 showed a change rate of only 4.9%. This is because the strong anchoring dispersant forms a firm adsorption layer on the nickel powder surface, hindering the migration of tin to the surface. Comparative Example 5 showed a higher change rate than Comparative Examples 1-4, but still lower than the Example. This indicates that when the Sn content is too low, there is insufficient tin available for migration. Comparative Example 6 showed a change rate of only 8.1%. This may be because excess Sn exists as a segregated phase in the alloy and fails to effectively dissolve in the Ni lattice, thus limiting the amount of active tin that can migrate.

[0098] Experiment Example 2: This experiment aims to record the settling behavior of slurry under long-term static conditions and test the storage stability of slurry.

[0099] Eleven samples were selected for testing: Examples 1, 3, 5, 6, 8, Comparative Examples 1, 2, 3, 4, 5, and 6, and were denoted as A1, A3, A5, A6, A8, D1, D2, D3, D4, D5, and D6, respectively.

[0100] Referring to the relevant section on sedimentation testing in GB / T 6753.3-1986 "Test Method for Storage Stability of Coatings", the test cycle and observation time points were adjusted in combination with the characteristics of the slurry of this invention. Freshly prepared slurries from each embodiment and comparative example were taken, stirred evenly, and poured into 10mL graduated and stoppered glass test tubes. The sample height of each tube was about 8cm, and the initial total height of the slurry H0 was recorded. The test tubes were placed vertically in a constant temperature environment of 25℃, avoiding vibration and light exposure.

[0101] From the start of the settling period, observe and record the height of the supernatant or sediment interface in each test tube on days 1, 3, 5, 7, 10, 15, 20, 25, and 30. Keep the test tube vertical during observation, and record the interface height H at the lowest point of the interface. t .

[0102] Calculate the settlement rate at each time point using the following formula: ;

[0103] Each sample was tested in triplicate, and the arithmetic mean was taken as the sedimentation rate at that time point. The results are shown in the figure. Figure 2 As shown.

[0104] Depend on Figure 2 As can be seen, no clear liquid layer was observed in Example 1 for the first 5 days, a small amount of clear liquid appeared on the 7th day, and the sedimentation rate was only 2.1% by the 30th day. Example 3 performed the best, with a sedimentation rate of 2.0% on the 30th day. The sedimentation rates of Examples 5, 6 and 8 after 30 days were 2.4%, 2.8% and 3.1% respectively, all below 5%.

[0105] The sedimentation rates of Examples 1 and 3 were slightly lower than those of Examples 5 and 6, which may be related to the type of dispersant and the Sn content. Both Examples 1 and 3 used polycaprolactone triol as a dispersant, which had a slightly better affinity for the nickel powder surface and steric hindrance effect than stannous octoate replacing polypropylene glycol triol. The sedimentation rate of Example 8 was slightly higher than that of the other examples, which may be related to its lower solid content.

[0106] Comparative Example 1 showed clear liquid on day 1, and the sedimentation rate continued to accelerate, reaching 18.5% by day 30. Comparative Example 2 was slightly better than Comparative Example 1, but the sedimentation rate on day 30 was still as high as 12.6%, indicating that traditional nickel powder is difficult to maintain long-term storage stability in sulfur-containing MLCC applications. The sedimentation rate of Comparative Example 3 on day 30 was 6.1%, which was better than Comparative Examples 1 and 2, but still significantly higher than the example, indicating that the presence of organotin compounds not only acts as an in-situ repair agent, but may also have a positive impact on the dispersion stability of the slurry.

[0107] The 30-day settling rate of Comparative Example 4 was 10.5%, which was higher than that of the Example. Oleic acid, as a strong anchoring dispersant, forms chemical adsorption with the surface of nickel powder through carboxyl groups. The adsorption is strong but irreversible. Although this strong adsorption has a good initial dispersion effect, it may cause problems in long-term storage. First, the adsorption layer lacks dynamic reversibility and cannot adapt to small changes on the particle surface. Second, excessive oleic acid may form multilayer adsorption or micelles, which may induce bridging flocculation between particles.

[0108] Experimental Example 3: This example aims to analyze the changes in the surface chemical state of the slurry from Example 1 before and after heat treatment in a sulfur-containing atmosphere using X-ray photoelectron spectroscopy, and to verify the protective mechanism of tin preferentially migrating to the surface and reacting with sulfur to form SnS.

[0109] The freshly prepared slurry from Example 1 was screen-printed onto a 10mm × 10mm alumina substrate, with a wet film thickness of approximately 20μm. After drying at 80℃ for 30 minutes to remove the solvent, the test piece was obtained. The dried test pieces were divided into two groups: the first group was the untreated group, which was directly subjected to XPS testing; the second group was the sulfur-containing atmosphere treated group, which was placed in a tube furnace and heated to 500℃ at 5℃ / min in a N2 mixed gas containing 500ppmH2S. After holding at this temperature for 1 hour, it was naturally cooled to room temperature and then removed for XPS testing.

[0110] XPS testing employed monochromatic Al Kα rays, with charge correction performed using contaminated carbon C1s. Full-spectrum scans of the sample surface and high-resolution narrow spectra of Ni2p, Sn3d, and S2p were acquired. Three different positions were measured for each sample. The chemical states of the elements were assigned based on standard binding energy data. The results are shown in Table 2. ;

[0111] As shown in Table 2, the main elements detected on the surface of the untreated sample are Ni, Sn, C, and O, with Ni in its metallic state. 0 Predominantly composed of a small amount of NiO, which is the natural oxide layer on the surface of nickel powder, with Sn in metallic state. 0 The main component is SnO, with a small amount of SnO. The total atomic concentration is about 1.1%, which is consistent with the Sn content in the alloy. No sulfur was detected.

[0112] After treatment in a sulfur-containing atmosphere at 500℃, Ni exists only in the metallic state, the NiO peak completely disappears, and no NiS characteristic peak appears, indicating that the nickel core has not been corroded. The Sn atom concentration increases to 4.7%, and the main peak shifts to 485.8 eV, belonging to SnS. A large amount of S element is detected, with an S2p3 / 2 binding energy of 161.6 eV, which matches the SnS characteristic peak. The C and O concentrations decrease, indicating that the organic components have decomposed and volatilized. This suggests that during the heat treatment process, tin dissolved in the Ni lattice migrates and enriches on the surface, preferentially reacting with H2S in the atmosphere to generate SnS, consuming the sulfur source, thereby protecting the nickel core from corrosion.

[0113] Experimental Example 4: This experimental example aims to test the conductivity of the electrode film after sintering and evaluate whether the slurry of the present invention can maintain conductivity after sintering in a sulfur-containing atmosphere.

[0114] Thirteen samples were selected for testing: Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 8, Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6.

[0115] Freshly prepared pastes from each embodiment and comparative example were screen-printed onto an alumina substrate to form 10mm × 10mm electrode patterns, with the wet film thickness controlled at 20 ± 2 μm. Five parallel samples were printed for each paste, and the solvent was removed by drying at 80°C for 30 minutes.

[0116] The dried sample was placed in a tube furnace and N2 was introduced as a protective atmosphere at a flow rate of 100 mL / min. In the first stage, the temperature was increased from room temperature to 400℃ at a rate of 5℃ / min; in the second stage, the temperature was increased to 580℃ at a rate of 1℃ / min; in the third stage, the temperature was increased to 900℃ at a rate of 10℃ / min; and in the fourth stage, the temperature was held at 900℃ for 15 min and then allowed to cool naturally to room temperature.

[0117] After sintering, the sheet resistance of the electrode film was tested using a four-probe sheet resistance meter. Five different locations were tested for each electrode sheet, and the average value was taken. The average value of the five parallel samples was taken as the average sheet resistance of the sample, and the standard deviation was calculated. The test results are shown in Table 3. ;

[0118] As can be seen from the data in Table 3, the sheet resistance values ​​of Examples 1, 3, 4, 5, and 6 are less than 0.55 Ω / sq, indicating that the slurry of the present invention can still maintain conductivity comparable to that of pure nickel powder after sintering in a sulfur-containing atmosphere. This proves that after the SnS protective layer is formed and plays a protective role at low temperature, it can be completely decomposed at high temperature, re-exposing the clean nickel core without any residual impurities that affect conductivity.

[0119] Comparing the examples with different Sn contents, it can be seen that the sheet resistance of Example 2 is slightly higher than that of Example 1. This may be because the SnS protective layer formed when the Sn content is low is not dense enough, and trace amounts of sulfur penetrate, leading to local corrosion. The sheet resistance of Example 4 is slightly higher than that of Examples 1 and 3, indicating that although the protection is complete when the Sn content is too high, there may be trace amounts of tin remaining in the form of Sn or SnO2, which will have a scattering effect on electron transport.

[0120] Examples 5 and 6 are comparable to Example 1, indicating that different types of organotin and dispersants can meet the requirements of the present invention. The sheet resistance of Example 8 is slightly higher than that of Example 1, which may be related to the slightly thinner film layer after sintering, but it is still at an excellent level.

[0121] Experimental Example 5: This experimental example aims to observe the cross-sectional microstructure of the electrode film after sintering of the slurry using a scanning electron microscope, and to evaluate the compactness and sintering quality of the film.

[0122] Take the printed and sintered Example 1 from Experiment 4, scratch along the center of the sample with a diamond pen, and then break it by hand to obtain a fresh cross-section. Fix the sample with the cross-section facing upward on the sample stage, adjust the height of the cross-section to be flush with the surface of the sample stage, and perform gold sputtering treatment using an ion sputtering instrument with a sputtering current of 10mA and a time of 60 seconds to enhance the conductivity of the sample.

[0123] The cross-sectional morphology was observed using a scanning electron microscope. An accelerating voltage of 10 kV was used, and cross-sectional images were acquired at 2000x magnification. The results are as follows: Figure 3 As shown.

[0124] Depend on Figure 3 As can be seen, cross-sectional observation of the sintered film in Example 1 shows that the film layer is dense, with small and uniformly distributed pores, proving that the SnS protective layer has completely decomposed at high temperature, the nickel core surface has been restored to cleanliness, and good sintering activity has been maintained.

[0125] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A nano-nickel powder slurry with high dispersion stability, characterized in that, The product comprises Ni-Sn alloy powder, an organic carrier, an organotin compound, and a dispersant. The Ni-Sn alloy powder contains 0.5-3.0 wt% tin, and the organotin compound can decompose and release active Sn during the debinding stage. 2+ The dispersant interacts with the nickel powder surface reversibly through hydrogen bonds and van der Waals forces.

2. The nano-nickel powder slurry with high dispersion stability according to claim 1, characterized in that: The components of the nano-nickel powder slurry, by weight, include 65-75 parts Ni-Sn alloy powder, 20-30 parts organic carrier, 0.5-3.0 parts organotin compound, 1.0-3.0 parts dispersant, and 0-2 parts additives.

3. The nano-nickel powder slurry with high dispersion stability according to claim 1, characterized in that: The Ni-Sn alloy powder is a binary alloy of nickel and tin, wherein the tin content is 1.5 wt%.

4. A nano-nickel powder slurry with high dispersion stability according to claim 1, 2 or 3, characterized in that: The average particle size D50 of the Ni-Sn alloy powder is 100-150 nm, and the specific surface area is 6-10 m². 2 / g.

5. A nano-nickel powder slurry with high dispersion stability according to claim 1 or 2, characterized in that: The organic carrier is composed of terpineol and ethyl cellulose, wherein terpineol accounts for 70-80% of the total mass of the organic carrier and ethyl cellulose accounts for 20-30% of the total mass of the organic carrier.

6. A nano-nickel powder slurry with high dispersion stability according to claim 1 or 2, characterized in that: The dispersant is a polyester or polyether polymer with a number average molecular weight of 1000-5000 and an acid value of less than 5 mg KOH / g.

7. The nano-nickel powder slurry with high dispersion stability according to claim 6, characterized in that: The dispersant is selected from one of polycaprolactone triol, trihydroxypolyoxypropylene ether, and DISPERBYK-2155.

8. A nano-nickel powder slurry with high dispersion stability according to claim 1 or 2, characterized in that: The organotin compound is selected from dibutyltin dilaurate and stannous octoate.

9. A method for preparing a nano-nickel powder slurry with high dispersion stability as described in any one of claims 1-8, characterized in that, Includes the following steps: S1: Mix Ni-Sn alloy powder, dispersant and organic carrier from the first part, and stir to form a paste. The organic carrier from the first part accounts for 66%-82% of the total organic carrier. S2: Grind and disperse the paste, adding organotin compounds to the slurry during the grinding and dispersion process, and continue grinding until the fineness is less than 5μm; S3: Add the remaining organic carrier to adjust the viscosity, and after degassing, obtain nano-nickel powder slurry.

10. The application of a nano-nickel powder slurry obtained by the preparation method as described in claim 9 in the preparation of sulfur-containing MLCC internal electrodes, characterized in that, The process includes coating a nano-nickel powder slurry onto a sulfur-containing MLCC dielectric green body and co-firing it under a protective atmosphere. The co-firing process includes slowly heating from 380-420°C to a temperature range of 580-620°C at a rate of 1-2°C / min.

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