Preparation method of seed crystal-PVP (Polyvinyl Pyrrolidone) coordinated regulation high-tap-density spherical palladium powder

Abstract

The invention relates to the technical field of precious metal powder materials, in particular to a preparation method of seed crystal-PVP coordinated regulation high-tap-density spherical palladium powder, which comprises the following steps: by taking sponge palladium with the purity of more than or equal to 99.9% as a raw material, dissolving by aqua regia, driving nitrate by hydrochloric acid and complexing by ammonia water to obtain a tetraammonium chloride palladium solution; a part of the solution is acidified and dried to obtain a palladium diammonium chloride solid; carrying out reduction reaction on the residual solution to obtain a seed crystal suspension; and carrying out ball-milling mixing on the two materials and PVP according to a ratio, then carrying out segmented heating roasting, quenching in boiling water, washing and drying to obtain the spherical palladium powder with high purity and high tap density. The palladium powder prepared through the method is high in sphericity degree, the tap density is larger than 5 g / cm < 2 >, the purity is larger than 99.99%, the technology is environmentally friendly and free of waste water, the process is simple and convenient, repeatability is good, batch stability is high, and the palladium powder is suitable for industrial large-scale production and can be widely applied to the fields of 3D printing, high-end electronic components and the like.

Description

Technical Field

[0001] This invention relates to the field of precious metal powder materials technology, specifically to a method for preparing high tap density spherical palladium powder with seed-PVP synergistic regulation. Background Technology

[0002] High-taper density, high purity, and high sphericity—the "three highs"—exhibit optimal packing properties, flowability, and chemical purity, making them a key foundational material for high-end manufacturing fields such as 3D printing, advanced electronic components, and chemical gas sensors. While the production cost of this type of high-taper density palladium powder is relatively high, the actual benefits it brings in improving product performance and increasing production efficiency far outweigh its higher cost.

[0003] Currently, there are two main methods for preparing palladium powder both domestically and internationally, as detailed below: 1. Chemical liquid-phase reduction method This method prepares palladium powder by reducing palladium salt solutions with reducing agents such as formaldehyde, hydrazine hydrate, and sodium borohydride. Inevitably, it introduces the reducing agent and its decomposition products (such as Na₂O₃). + Impurities such as B and S require additional complex washing processes to remove them, which not only increases production difficulty and cost but also reduces palladium recovery rate. At the same time, palladium particles in the liquid phase system have high surface energy and are prone to agglomeration to form irregular dendritic or clump-like structures, making it difficult to control them to have high sphericity. In addition, a large amount of wastewater containing palladium and reducing agent residues will be generated, resulting in high treatment costs and environmental pollution.

[0004] 2. Dichlorodiamminepalladium calcination method This method, a mature process in palladium refining, is commonly used to prepare palladium powder with a purity of over 99.99%. However, in practical applications, those skilled in the art have found that during the calcination process, the decomposition of dichlorodiamminepalladium and the reduction of palladium are rapid reactions in a solid-state state. The palladium powder particles generated by calcination have high surface energy and strong interparticle attraction, making them prone to agglomeration, forming irregular aggregates and destroying their spherical morphology. For example, the patent document CN1037532C, "Method for Preparing Pure Palladium," describes a method of placing purified dichlorodiamminepalladium in a pit furnace, heating it to 650°C for decomposition, and then cooling it to room temperature by introducing nitrogen gas. This method yields palladium powder with a purity higher than 99.99%, but the prepared palladium powder is spongy, exhibits significant agglomeration, and has poor tap density, failing to meet the requirements of high-end manufacturing applications.

[0005] Therefore, developing a preparation method that can simultaneously achieve high purity, high sphericity, and high tap density of palladium powder, and is environmentally friendly, efficient, and suitable for industrial production, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing high-tap-density spherical palladium powder through synergistic regulation of seed crystals and PVP. This method uses sponge palladium with a purity ≥99.9% as raw material, which is dissolved in aqua regia, denitrated with hydrochloric acid, and complexed with ammonia to obtain a dichlorotetraammonium palladium solution. A portion of the solution is acidified and dried to obtain dichlorodiammonium palladium solid. The remaining solution is used to prepare a seed crystal suspension through precise control of the reduction reaction. The two solutions are then ball-milled and mixed with PVP in a specific ratio, followed by staged heating and calcination, boiling water quenching, washing, and drying to obtain the target product. This invention effectively solves the problems of severe agglomeration, poor sphericity, and insufficient purity associated with traditional methods by using seed crystals to provide uniform nucleation sites, PVP to regulate particle morphology, and staged calcination and boiling water quenching to refine the grains. The prepared palladium powder has high sphericity, a tap density >5 g / cm³, and a purity >99.99%. The process is environmentally friendly with no wastewater, simple, and highly reproducible, making it suitable for large-scale industrial production and applicable to fields such as 3D printing and high-end electronic components.

[0007] The objective of this invention is achieved through the following method: a method for preparing high-tap-density spherical palladium powder with seed-PVP synergistic regulation, comprising the following steps: 1) Take sponge palladium with a purity ≥99.9%, dissolve it, remove the nitrate, cool it, and then add ammonia water to make the pH 8-9 to obtain a tetraammonium dichloropalladium solution; 2) Take a portion of the dichlorotetraammonium palladium solution obtained in step 1) and add concentrated hydrochloric acid until the pH becomes acidic. After filtration and washing, dichlorodiammonium palladium precipitate is obtained. Dry the precipitate to obtain dichlorodiammonium palladium solid. Heat the remaining dichlorotetraammonium palladium solution to 50-70°C and maintain the temperature. While stirring, slowly and uniformly add a reducing agent solution. When the solution color changes from light yellow to light gray, immediately stop stirring, heating, and adding the reducing agent solution to obtain a seed crystal suspension (this seed crystal suspension must be prepared and used immediately). 3) Add the diammonium chloride palladium solid and seed crystal suspension obtained in step 2) to the surfactant polyvinylpyrrolidone (PVP) and ball mill them together at a mass ratio of 10-15 diammonium chloride palladium solid: 2-4 seed crystal suspension: 0.3-0.5 polyvinylpyrrolidone to obtain a uniform palladium mixture. 4) The palladium mixture obtained in step 3) is calcined and quenched, then washed with deionized water until the pH of the washing solution is neutral, and then dried to obtain high tap density spherical palladium powder.

[0008] Preferably, in step 1), the sponge palladium is dissolved using aqua regia.

[0009] Preferably, in step 1), concentrated hydrochloric acid is added to perform denitrification treatment.

[0010] Preferably, in step 2), the washing method is: washing 2 to 3 times with dilute hydrochloric acid with a mass fraction of 5 to 10%.

[0011] Preferably, in step 2), the drying method is: drying under vacuum, drying temperature is 40-50°C, and drying time is 8-12 hours.

[0012] Preferably, in step 2), the remaining portion of the dichlorotetraammonium palladium solution is first diluted with water to adjust the concentration to 10-15 g / L, and then heated to 50-70°C and kept warm while adding the reducing agent solution dropwise.

[0013] Preferably, in step 2), the reducing agent solution includes a hydrazine hydrate solution with a mass fraction of 1-5%, an ascorbic acid solution with a mass fraction of 10-20%, and a formic acid solution with a mass fraction of 1-5%.

[0014] Preferably, in step 3), the ball milling time is 3 to 5 minutes.

[0015] Preferably, in step 4), the specific process of roasting is as follows: a segmented heating method is adopted, with the heating rate of each stage being 10±0.5℃ / min, and the following operations are performed in sequence: first, the temperature is kept at 100~150℃ for 0.5~1h, then the temperature is raised to 350~400℃ and kept for 1.5~2h, and then the temperature is raised to 700~800℃ and kept for 0.5~1h.

[0016] Preferably, in step 4), the quenching method is: quenching with boiled deionized water.

[0017] The beneficial effects of this invention are as follows: 1. This invention achieves the synergistic attainment of high tap density, high purity, and high sphericity in palladium powder through seed-PVP synergistic regulation and refined control throughout the entire process. First, the seed suspension in this invention provides uniformly dispersed nanoscale nucleation sites, guiding the directional decomposition and growth of diammonium dichloropalladium, avoiding the randomness of homogeneous nucleation. Second, this invention utilizes PVP adsorbed onto the surface of the crystal nucleus through steric hindrance, isolating reduced palladium atoms and small palladium clusters, effectively suppressing free collisions and agglomeration of palladium particles. Finally, the combination of segmented heating calcination (stepwise removal of moisture, PVP removal, and promotion of precursor decomposition and growth) and boiling water quenching (rapid cooling in a low-oxygen, impurity-free environment)... (It both refines the grain size and prevents oxidation), and then, in conjunction with the purification process of diammonium chloride palladium precipitate followed by washing with dilute hydrochloric acid (to remove ammonium salts and impurity ions) and vacuum drying (to thoroughly remove moisture and volatile impurities), the final palladium powder has high sphericity, smooth surface, tap density > 5 g / cm³ (optimally up to 5.7 g / cm³), and purity > 99.99%, fully meeting the stringent requirements for material packing performance, flowability, and chemical purity in high-end manufacturing fields such as 3D printing, high-end electronic components, and chemical gas sensors.

[0018] 2. The process described in this invention is environmentally friendly and cost-controllable. Compared with traditional preparation methods, this process combines environmental friendliness and economy. Compared with the chemical liquid-phase reduction method, it eliminates the need for easily residual reducing agents (such as sodium borohydride), avoids complex impurity removal and washing processes, and generates virtually no wastewater containing palladium and reducing agent residues. Waste gases (such as NH3 and HCl) are easily centrally treated. Compared with the traditional dichlorodiamminepalladium calcination method, the process solves the problems of particle agglomeration and irregular morphology during solid-phase thermal decomposition through seed crystal-PVP synergistic regulation. Simultaneously, the process eliminates multiple filtration and purification steps, shortening the production process while reducing palladium loss and significantly improving palladium recovery rate. The equipment investment and operating costs are low, requiring no complex high-end processing equipment, meeting the environmental and cost requirements of industrial production.

[0019] 3. The preparation process of this invention is stable and highly reproducible. By precisely controlling key process parameters (such as the concentration of tetraammonium dichloroammonium palladium solution at 10-15 g / L, the rate of addition of reducing agent, the staged calcination heating rate and holding time, etc.), combined with quality control of core components (preparing and using the seed suspension immediately to avoid seed aggregation and sedimentation leading to uneven nucleation; ball milling for 3-5 minutes to ensure uniform material dispersion), the consistency of the nucleation and growth process can be effectively guaranteed. This invention utilizes the synergistic effect of seed crystals and PVP to fundamentally solve the problems of uneven particle morphology and severe agglomeration in traditional processes. The performance difference between batches of products is minimal, enabling large-scale stable industrial production and meeting the batch stability requirements of high-end manufacturing.

[0020] 4. This invention is simple and easy to operate, with a wide range of applications: the entire process involves only conventional steps such as dissolution, complexation, ball milling, calcination, and quenching, relying on common equipment such as muffle furnaces and ball mill jars, requiring no special high-end equipment, thus having a low operating threshold and being easy to promote. The process has strong compatibility; by flexibly adjusting the raw material ratio (diammonium chloride palladium, seed suspension, PVP mass ratio 10-15:2-4:0.3-0.5) and process parameters (calcination holding time, reducing agent type and concentration, etc.), it can be adapted to the subtle requirements of different application scenarios for palladium powder tap density, particle size, and other properties. Its applicable fields cover multiple high-end manufacturing fields such as 3D printing, high-end electronic components, and chemical gas sensors, with broad application prospects. Attached Figure Description

[0021] Figure 1 This is a flowchart of the preparation method of high tap density spherical palladium powder by seed-PVP synergistic regulation in this invention; Figure 2 Microscopic morphology of the high tap density spherical palladium powder prepared in Example 1 of the present invention (magnified 5000 times). Figure 3 The image shows the microstructure of palladium powder prepared in Comparative Example 1 of this invention without the addition of seed crystal suspension (magnified 5000 times). Figure 4 The image shows the microstructure of palladium powder prepared without PVP in Comparative Example 2 of this invention (magnified 5000 times). Detailed Implementation

[0022] like Figure 1 As shown, a method for preparing high-tap-density spherical palladium powder with seed-PVP synergistic regulation includes the following steps: 1) Dissolve sponge palladium (purity ≥99.9%) slowly at low temperature using aqua regia. After the sponge palladium is completely dissolved, add concentrated hydrochloric acid to remove nitrates. During this process, keep the solution at a gentle boil to effectively remove nitrate impurities. After cooling to room temperature, slowly add ammonia water while stirring until the pH of the solution is adjusted to 8-9, so that palladium ions are fully complexed to obtain a uniform and stable tetraammonium dichloropalladium solution.

[0023] 2) Take a portion of the dichlorotetraammonium palladium solution obtained in step 1) and add concentrated hydrochloric acid dropwise while stirring until the pH of the solution becomes acidic. After filtration, wash 2-3 times with dilute hydrochloric acid with a mass fraction of 5-10% to obtain dichlorodiammonium palladium precipitate.

[0024] Washing with 5-10% dilute hydrochloric acid 2-3 times can effectively remove residual ammonium salts and impurity ions from the diammonium chloride palladium precipitate, avoiding interference from impurities during subsequent roasting and thus improving the purity of the final palladium powder.

[0025] Then, the dichlorotetraammonium palladium precipitate was dried in a vacuum environment at 40-50°C for 8-12 hours to completely remove moisture and residual volatile impurities, thus obtaining high-purity dichlorodiammonium palladium precipitate solid.

[0026] 3) Take the remaining portion of the dichlorotetraammonium palladium solution obtained in step 1), first dilute it with water to a concentration of 10-15 g / L, then heat the diluted dichlorotetraammonium palladium solution in a water bath to 50-70°C and keep it at that temperature. Under mechanical stirring, slowly and uniformly add the reducing agent solution (any one of the following can be used: 1-5% hydrazine hydrate, 10-20% ascorbic acid, or 1-5% formic acid). The reaction endpoint is judged in real time by the color change of the solution. When the solution color gradually changes from light yellow to light gray, immediately stop stirring, heating and adding the reducing agent to obtain a seed crystal suspension.

[0027] The essence of this seed suspension is that solid seed particles are uniformly dispersed in a liquid medium. After being uniformly mixed with diammonium chloride palladium, it can provide a large number of uniformly dispersed nanoscale nucleation sites, which significantly accelerates the calcination nucleation rate of diammonium chloride palladium and improves the sphericity of palladium powder. Moreover, the seed suspension should be prepared and used immediately to avoid the seed particles from agglomerating and settling, losing their uniform dispersion state, which would lead to uneven nucleation sites and affect the morphology and tap density of palladium powder.

[0028] 4) The dichlorotetraammonium palladium solid obtained in step 2), the seed crystal suspension obtained in step 3), and the surfactant PVP are mixed in a mass ratio of 10-15:2-4:0.3-0.5 and placed into a ball mill jar. The mixture is ball milled for 3-5 minutes until it is homogeneous to obtain a palladium mixture.

[0029] This invention employs wet ball milling, which ensures uniform mixing of materials and guarantees consistency in the subsequent palladium nucleation process. PVP, as a surfactant, can temporarily isolate the precursor, regulate reaction kinetics, and immediately adsorb onto the surface of the crystal nucleus, forming steric hindrance protection to prevent particles from approaching each other and agglomerating, thereby precisely controlling the final morphology of the palladium powder.

[0030] 5) Place the palladium mixture obtained in step 4) in a muffle furnace and perform high-temperature calcination using a segmented heating program: first, hold at 100–150℃ for 0.5–1 h to remove the dispersion medium and residual moisture in the palladium mixture; then, heat to 350–400℃ at a heating rate of 10 ± 0.5℃ / min and hold for 1.5–2 h to promote the gradual decomposition of diammonium chloride palladium to form palladium black; then, heat to 700–800℃ at a heating rate of 10 ± 0.5℃ / min and hold for 0.5–1 h to ensure complete thermal decomposition of diammonium chloride palladium into elemental palladium, while simultaneously removing PVP at high temperature to further improve the purity of the palladium powder and obtain primary palladium powder.

[0031] After roasting, the primary palladium powder is quickly removed and poured into boiling deionized water for quenching. Since the boiling deionized water has a very low oxygen content, it can effectively prevent the palladium powder from oxidizing during the cooling process. In addition, the pure water does not contain other impurities, which can avoid the formation of impurities. The quenching process can ensure that palladium exists in its elemental form and refine the grains to obtain a fine and uniform microstructure. Then, it is repeatedly washed with deionized water and the supernatant is discarded until the pH of the washing liquid is neutral. After vacuum drying, high tap density spherical palladium powder is obtained.

[0032] In summary, this invention achieves this by uniformly mixing dichlorodiamminepalladium with a seed suspension and PVP. Under high temperature, the seed suspension provides directional nucleation centers for the thermal decomposition process, while PVP adsorbs onto the particle surface, regulating palladium nucleus growth and inhibiting agglomeration. This is combined with stepwise decomposition and purification through segmented calcination and grain refinement and oxidation prevention through boiling water quenching. Furthermore, the boiling water quenching rapidly cools the high-temperature palladium powder, refining the grains and resulting in a uniform structure. Ultimately, this yields a product with high sphericity and a tap density >5 g / cm³. 3 Palladium powder with a purity greater than 99.99%.

[0033] The following is an example of using the above method: Example 1

[0034] A method for preparing high-tap-density, high-purity spherical palladium powder with seed-PVP synergistic regulation, the specific steps of which are as follows: 1) Take 20g of sponge palladium with a purity of 99.9%, dissolve it in aqua regia, remove the nitrate, and complex it with ammonia water to obtain a tetraammonium dichloropalladium solution; 2) Take a portion of the dichlorotetraammonium palladium solution obtained in step 1), add concentrated hydrochloric acid dropwise while stirring to adjust the pH of the solution to acidic, and obtain a yellow precipitate of dichlorodiammonium palladium. Filter and wash 2-3 times with 5% dilute hydrochloric acid, and dry under vacuum at 50°C for 12 hours to obtain solid dichlorodiammonium palladium. 3) Take the remaining dichlorotetraammonium palladium solution obtained in step 1) and concentrate it to a concentration of 10 g / L. Heat it to 70°C and keep it at that temperature. Slowly and uniformly add 3% hydrazine hydrate solution under mechanical stirring. Stop adding the reducing agent and stop heating as soon as the solution changes from light yellow to light gray to obtain a seed crystal suspension. 4) The diammonium dichloride palladium solid obtained in step 2), the seed crystal suspension obtained in step 3), and the surfactant PVP are mixed in a mass ratio of 10:2:0.3 and placed into a ball mill jar. The mixture is ball milled for 5 minutes to obtain a palladium mixture. 5) Place the palladium mixture in a muffle furnace and hold it at 100℃ for 30 min. Then, raise the temperature to 350℃ at 10℃ / min and hold it for 1.5 h. Then, raise the temperature to 700℃ at 10℃ / min and hold it for 1 h. After calcination, quickly remove the primary palladium powder and quench it in boiling deionized water. Then wash it with deionized water until the pH is neutral. After drying, high-purity spherical palladium powder with high tap density is obtained.

[0035] The high-tap-density, high-purity spherical palladium powder obtained by the preparation method described in Example 1 has the following performance characteristics: high sphericity, smooth surface, and no obvious particle agglomeration (e.g., Figure 2 As shown), the tap density is 5.3 g / cm³. 3 The purity is greater than 99.99%. Example 2

[0036] A method for preparing high-tap-density, high-purity spherical palladium powder with seed-PVP synergistic regulation, the specific steps of which are as follows: 1) Take 20g of sponge palladium with a purity of 99.9%, dissolve it in aqua regia, remove the nitrate, and complex it with ammonia water to obtain a tetraammonium dichloropalladium solution; 2) Take a portion of the dichlorotetraammonium palladium solution obtained in step 1), add concentrated hydrochloric acid dropwise while stirring to adjust the pH of the solution to acidic, and obtain a yellow precipitate of dichlorodiammonium palladium. Filter and wash the precipitate 2-3 times with 5% dilute hydrochloric acid, and dry it under vacuum at 50°C for 12 hours to obtain solid dichlorodiammonium palladium. 3) Take the remaining dichlorotetraammonium palladium solution obtained in step 1) and concentrate it to a concentration of 15 g / L. Heat it to 70℃ and keep it at that temperature. Slowly and uniformly add 10% ascorbic acid solution under mechanical stirring. Stop adding the reducing agent and stop heating as soon as the solution changes from light yellow to light gray to obtain a seed crystal suspension. 4) The diammonium dichloride palladium solid obtained in step 2), the seed crystal suspension obtained in step 3), and the surfactant PVP are mixed in a mass ratio of 15:4:0.5 and placed into a ball mill jar. The mixture is ball milled for 5 minutes to obtain a palladium mixture. 5) Place the palladium mixture in a muffle furnace and hold it at 100℃ for 30 min. Then, raise the temperature to 350℃ at 10℃ / min and hold it for 1.5 h. Then, raise the temperature to 700℃ at 10℃ / min and hold it for 1 h. After calcination, quickly remove the primary palladium powder and quench it in boiling deionized water. Then wash it with deionized water until the pH is neutral. After drying, high-purity spherical palladium powder with high tap density is obtained.

[0037] The high-purity spherical palladium powder with high tap density obtained by the preparation method described in Example 2 has the following performance characteristics: high sphericity, smooth surface, no obvious particle agglomeration, and a tap density of 5.7 g / cm³. 3The purity is greater than 99.99%.

[0038] Comparative Example 1 A method for preparing palladium powder, the specific steps of which are as follows: 1) Take 20g of sponge palladium with a purity of 99.9%, dissolve it in aqua regia, remove the nitrate, and complex it with ammonia water to obtain a tetraammonium dichloropalladium solution; 2) Take a portion of the dichlorotetraammonium palladium solution obtained in step 1), add concentrated hydrochloric acid dropwise while stirring to adjust the pH of the solution to acidic, and obtain a yellow precipitate of dichlorodiammonium palladium. Filter and wash 2-3 times with 5% dilute hydrochloric acid, and dry under vacuum at 50°C for 12 hours to obtain solid dichlorodiammonium palladium. 3) The diammonium dichloride palladium solid obtained in step 2) is mixed with surfactant PVP at a mass ratio of 10:0.3 and placed into a ball mill jar. The mixture is then ball-milled for 5 minutes to obtain a palladium mixture. 4) Place the palladium mixture in a muffle furnace and hold at 100℃ for 30 min. Then, increase the temperature to 350℃ at 10℃ / min and hold for 1.5 h. Then, increase the temperature to 700℃ at 10℃ / min and hold for 1 h. After calcination, quickly remove the primary palladium powder and quench it in boiling deionized water. Then wash it with deionized water until the pH is neutral and dry it to obtain palladium powder.

[0039] The palladium powder obtained by the preparation method described in Comparative Example 1 has the following performance characteristics: poor sphericity (e.g., Figure 3 As shown in the figure, the tap density is approximately 3.5 g / cm³, and the purity is greater than 99.99%.

[0040] Compared to Example 1, Comparative Example 1 lacked a seed suspension, resulting in a lack of a uniform nucleation template during calcination. The seed suspension could have provided uniformly dispersed nanoscale nucleation sites to guide the directional decomposition and growth of diammonium dichloropalladium, avoiding randomness in the nucleation process and ensuring orderly grain growth and uniform morphology. Without this guiding effect, the decomposition process of diammonium dichloropalladium decomposed into an energy-unstable and difficult-to-control "homogeneous nucleation," leading to random nucleation, abnormal grain growth, and disordered morphology and phase. The resulting palladium powder exhibited severe agglomeration and poor sphericity (e.g., ...). Figure 3 As shown in the figure, the tap density was only 3.5 g / cm³, significantly lower than the 5.3 g / cm³ of Example 1. This result demonstrates that the uniform nucleation sites provided by the seed suspension are a key factor in achieving high sphericity and high tap density of palladium powder.

[0041] Comparative Example 2 A method for preparing palladium powder, the specific steps of which are as follows: 1) Take 20g of sponge palladium with a purity of 99.9%, dissolve it in aqua regia, remove the nitrate, and complex it with ammonia water to obtain a tetraammonium dichloropalladium solution; 2) Take a portion of the dichlorotetraammonium palladium solution obtained in step 1), add concentrated hydrochloric acid dropwise while stirring to adjust the pH of the solution to acidic, and obtain a yellow precipitate of dichlorodiammonium palladium. Filter and wash 2-3 times with 5% dilute hydrochloric acid, and dry under vacuum at 50°C for 12 hours to obtain solid dichlorodiammonium palladium. 3) Take the remaining dichlorotetraammonium palladium solution obtained in step 1) and concentrate it to a concentration of 15 g / L. Heat it to 70℃ and keep it at that temperature. Slowly and uniformly add 10% ascorbic acid solution under mechanical stirring. Stop adding the reducing agent and stop heating as soon as the solution changes from light yellow to light gray to obtain a seed crystal suspension. 4) The diammonium dichloride palladium solid obtained in step 2) and the seed crystal suspension obtained in step 3) are mixed at a mass ratio of 10:2 and loaded into a ball mill jar. The mixture is ball milled for 5 minutes to obtain a palladium mixture. 5) Place the palladium mixture in a muffle furnace and hold at 100℃ for 30 min. Then, increase the temperature to 350℃ at 10℃ / min and hold for 1.5 h. Finally, increase the temperature to 700℃ at 10℃ / min and hold for 1 h. After calcination, quickly remove the primary palladium powder and quench it in boiling deionized water. Then, wash it with deionized water until the pH is neutral and dry it to obtain palladium powder.

[0042] The palladium powder obtained by the preparation method described in Comparative Example 2 has the following performance characteristics: extremely poor sphericity, tap density of 2.1 g / cm³, and purity greater than 99.99%.

[0043] Compared to Example 2, Comparative Example 2 did not include the surfactant PVP. Therefore, steric hindrance protection could not be formed on the surface of the crystal nuclei during calcination. PVP molecules could effectively slow down the growth rate after nucleation by temporarily "capturing" or "isolating" the reduced palladium atoms or small palladium clusters, limiting their free movement and collisions. Without this effect, the reduced palladium atoms and small palladium clusters easily move, diffuse, collide, and agglomerate, leading to disordered grain growth. The resulting palladium powder exhibited severe agglomeration and extremely poor sphericity (e.g., ...). Figure 4 As shown in the figure, the tap density was 2.1 g / cm³, which was only 36.8% of that of Example 2 (5.7 g / cm³). This result proves that the morphology regulation and dispersion effect of PVP is the core factor in inhibiting palladium powder agglomeration and optimizing sphericity.

[0044] In summary, the comparison between Examples 1 and 2 and Comparative Examples 1 and 2 demonstrates that the "seed-PVP synergistic regulation" mechanism of this invention is key to achieving the synergistic attainment of "high sphericity, high tap density, and high purity" in palladium powder. In other words, in this invention, the seed crystal provides uniform nucleation sites, avoiding the disorder of homogeneous nucleation; the PVP provides steric hindrance, inhibiting particle agglomeration, and thermally decomposes at temperatures exceeding 400°C during calcination, thus not affecting the purity of the palladium powder; simultaneously, combined with segmented heating calcination and boiling water quenching (refining grains and preventing oxidation), the palladium powder ultimately achieves a tap density exceeding 5.5 g / cm³, purity ≥99.99%, and sphericity ≥90%, significantly superior to comparative products without seed crystals or PVP, fully meeting the application requirements of high-end manufacturing.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing high-tap-density spherical palladium powder with seed-PVP synergistic regulation, characterized in that, Includes the following steps: 1) Take sponge palladium with a purity ≥99.9%, dissolve it, remove the nitrate, cool it, and then add ammonia water to make the pH 8-9 to obtain a tetraammonium dichloropalladium solution; 2) Take a portion of the dichlorotetraammonium palladium solution obtained in step 1) and add concentrated hydrochloric acid until the pH is acidic. After filtration and washing, dichlorodiammonium palladium precipitate is obtained. Drying yields diammonium dichloride palladium alloy solid; the remaining diammonium tetraammonium dichloride palladium alloy solution is heated to 50-70℃ and kept at that temperature, while adding a reducing agent solution dropwise and stirring, until the solution color changes from light yellow to light gray, at which point stirring, heating, and the addition of the reducing agent are immediately stopped to obtain a seed crystal suspension; 3) Add the diammonium chloride palladium solid and seed crystal suspension obtained in step 2) to polyvinylpyrrolidone and ball mill them together at a mass ratio of 10-15 diammonium chloride palladium solid: 2-4 seed crystal suspension: 0.3-0.5 polyvinylpyrrolidone to obtain palladium mixture; 4) The palladium mixture obtained in step 3) is calcined and quenched, then washed with deionized water until the pH of the washing solution is neutral, and then dried to obtain high tap density spherical palladium powder.

2. The preparation method according to claim 1, characterized in that, In step 1), the sponge palladium is dissolved using aqua regia.

3. The preparation method according to claim 1, characterized in that, In step 1), concentrated hydrochloric acid is added to remove nitrates.

4. The preparation method according to claim 1, characterized in that, In step 2), the washing method is as follows: wash 2 to 3 times with dilute hydrochloric acid with a mass fraction of 5 to 10%.

5. The preparation method according to claim 1, characterized in that, In step 2), the drying method is as follows: under vacuum, the drying temperature is 40-50℃, and the drying time is 8-12 hours.

6. The preparation method according to claim 1, characterized in that, The remaining portion of the dichlorotetraammonium palladium solution in step 2) is first diluted with water to adjust the concentration to 10-15 g / L, and then heated to 50-70℃ and kept at that temperature, and the reducing agent solution is added dropwise.

7. The preparation method according to claim 1, characterized in that, In step 2), the reducing agent includes a hydrazine hydrate solution with a mass fraction of 1-5%, an ascorbic acid solution with a mass fraction of 10-20%, and a formic acid solution with a mass fraction of 1-5%.

8. The preparation method according to claim 1, characterized in that, In step 3), the ball milling time is 3 to 5 minutes.

9. The preparation method according to claim 1, characterized in that, In step 4), the specific roasting process is as follows: a segmented heating method is adopted, with a heating rate of 10±0.5℃ / min at each stage, and the following operations are performed in sequence: first, the temperature is held at 100~150℃ for 0.5~1h, then the temperature is raised to 350~400℃ and held for 1.5~2h, and finally the temperature is raised to 700~800℃ and held for 0.5~1h.

10. The preparation method according to claim 1, characterized in that, In step 4), the quenching method is: quenching with boiled deionized water.

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