Sub-micron spherical gold powder and method for preparing the same

Abstract

The application provides a sub-micron spherical gold powder and a preparation method thereof, and belongs to the field of noble metal powder. The application provides a preparation method of the sub-micron spherical gold powder, which comprises the following steps: adding a first alkylamine, a first reducing agent and a chloroauric acid solution into a first aqueous medium to obtain a gold crystal nucleus solution; adding a second alkylamine into the gold crystal nucleus solution, and then adding a second reducing agent and a chloroauric acid solution drop by drop to make gold grow on the surface of the gold crystal nucleus to obtain a precipitate; and performing post-treatment on the precipitate to obtain the sub-micron spherical gold powder; wherein the number of carbon atoms in the alkyl chain of the first alkylamine is 14-18, and the number of carbon atoms in the alkyl chain of the second alkylamine is 10-18. Through the cooperation of the first alkylamine and the second alkylamine, the particle size of the gold powder can be controlled in the range of 0.1 mu m-1.5 mu m, the dispersion is good, the morphology is regular, and it is beneficial to form a dense gold film during sintering.

Description

Technical Field

[0001] This invention relates to the field of precious metal powder technology, specifically to a submicron spherical gold powder and its preparation method. Background Technology

[0002] Electronic packaging, as a core component of microelectronics manufacturing, directly impacts chip reliability, signal transmission efficiency, and product lifespan. Currently, with the rapid development of technologies such as 5G communication, artificial intelligence, and the internet, electronic devices are evolving towards higher density, miniaturization, and flexibility, placing stringent demands on packaging materials: they must possess ultra-low resistivity, excellent resistance to electrochemical corrosion, high-temperature stability, and nanometer-level precision. Traditional silver and copper powders, due to their susceptibility to oxidation and insufficient conductivity, struggle to meet the demands of high-end packaging. Gold powder, with its chemical inertness, high conductivity, and malleability, has become a key material for overcoming these technological bottlenecks.

[0003] In existing preparation techniques, uneven concentrations of reducing agents or reactant mixing often exist within the reaction system, easily triggering bursts of nucleation in localized areas, generating a large number of gold atoms, while other areas suffer from a shortage of gold atoms. This uneven distribution leads to significant differences in the particle growth environment. Furthermore, due to a lack of effective control, the surface energies of different crystal faces of gold crystals differ, causing gold atoms to preferentially and rapidly deposit on crystal faces with higher surface energies. This results in preferential crystal growth along specific directions, ultimately forming plate-like or dendritic morphologies. In summary, traditional methods easily produce plate-like, dendritic, or irregular aggregates, affecting the performance of the gold powder.

[0004] In view of this, it is necessary to design a submicron spherical gold powder and its preparation method to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, the purpose of the present invention is to provide a submicron spherical gold powder and its preparation method. The preparation method adopts a chemical reduction method, and by using a first alkylamine and a second alkylamine in synergy, the particle size of the gold powder is controllable in the range of 0.1μm-1.5μm, with good dispersibility and regular morphology, which is conducive to the formation of a dense gold film during sintering.

[0006] To achieve the above objectives, this invention proposes a method for preparing submicron spherical gold powder, comprising:

[0007] In a first aqueous medium, a first alkylamine, a first reducing agent, and a chloroauric acid solution are added to obtain a gold crystal nucleus solution;

[0008] A second alkylamine is added to the gold crystal nucleus solution, followed by the addition of a second reducing agent and chloroauric acid solution, which causes gold to grow on the surface of the gold crystal nucleus, resulting in a precipitate.

[0009] The precipitate was post-processed to obtain submicron spherical gold powder; among which,

[0010] The first alkylamine has 14-18 carbon atoms in its alkyl chain, and the second alkylamine has 10-18 carbon atoms in its alkyl chain.

[0011] As a further improvement of the present invention, the first alkylamine includes at least one of tetradecylamine, hexadecylamine, and octadecylamine; and / or,

[0012] The second alkylamine includes at least one of decylamine, dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine.

[0013] In this embodiment, all three are straight-chain primary amines. The amino groups (-NH2) have a strong affinity for gold and can effectively adsorb to form a protective layer. The alkyl chains provide hydrophobic steric hindrance, preventing particle agglomeration. This is the basis for achieving high dispersibility of gold powder. Specifically, tetradecylamine (C14) has moderate steric hindrance, which is conducive to rapid nucleation and growth, and is suitable for high-efficiency preparation of larger-sized gold powder; hexadecylamine (C16) achieves the best balance between control and growth, and is the preferred reference reagent for obtaining highly regular spherical morphology and ensuring process stability; octadecylamine (C18) has the strongest steric hindrance, which can most effectively stabilize small gold nuclei, and is particularly suitable for preparing powders with smaller size and narrower distribution and high sphericity. In addition, they can be used in combination to effectively balance the growth rate of each crystal face through differentiated coating, thereby strongly suppressing anisotropic growth and ensuring that submicron spherical gold powder with regular morphology, good dispersibility and excellent sintering activity in the range of 0.1μm-1.5μm is finally obtained.

[0014] In this embodiment, decylamine (C10) has the shortest carbon chain and fast adsorption kinetics, enabling it to preferentially and rapidly coat the actively growing high-energy crystal faces, quickly bridging the growth rate differences between crystal faces. Dodecylamine (C12) strikes a balance between kinetic response and adsorption stability, forming an ideal chain length difference with the first alkylamine to construct a stable and finely tunable mixed adsorption layer, making it a choice to ensure high reproducibility of gold powder spherical morphology in the submicron range. Tetradecylamine (C14), hexadecylamine (C16), and octadecylamine (C18) can act as reinforcement and complement, providing stronger steric hindrance and denser surface coating, making them particularly suitable for suppressing the surface roughening or deformation tendency of larger particles in the later stages of growth.

[0015] In addition, they can be used in combination, providing more flexible dynamic control to adapt to different industrial production needs.

[0016] As a further improvement of the present invention, the concentration of the first alkylamine solution is 1 mg / mL-4 mg / mL; and / or,

[0017] The concentration of the second alkylamine solution is 0.1 mg / mL to 1 mg / mL.

[0018] In this embodiment, by setting the solution concentration of the first alkylamine in the range of 1 mg / mL to 4 mg / mL, it can be ensured that a sufficient number of molecules are provided during the gold nucleus formation stage to fully cover and stabilize the surface of all newly formed gold nuclei, forming an effective steric hindrance layer and preventing excessive aggregation of gold nuclei.

[0019] In this embodiment, by setting the solution concentration of the second alkylamine within the range of 0.1 mg / mL to 1 mg / mL, it can synergistically interact with the already adsorbed first alkylamine to selectively and dynamically adsorb onto the surface of the growing gold crystal. This allows the second alkylamine to respond more sensitively to the surface energy differences of different crystal faces, preferentially coating the active crystal faces with faster growth rates, thereby more precisely regulating the atomic deposition rate of each crystal face and effectively suppressing anisotropic growth.

[0020] As a further improvement of the present invention, the first reducing agent includes at least one of ascorbic acid, hydrazine hydrate, hydrazine carbonate, and sodium borohydride; and / or,

[0021] The second reducing agent includes at least one of ascorbic acid, hydrazine hydrate, hydrazine carbonate, and sodium borohydride.

[0022] In this embodiment, the choice of the first reducing agent affects the generation rate, size, and number density of gold nuclei. Strong reducing agents, such as sodium borohydride, can instantly generate a large number of gold atoms, promoting homogeneous nucleation and forming numerous small initial gold nuclei, laying the foundation for subsequent growth. Mild reducing agents, such as ascorbic acid, provide a controllable reduction environment, which is beneficial for obtaining gold nuclei of uniform size. By selecting specific reducing agents or combinations, the initial state of the gold nuclei can be precisely controlled.

[0023] In this embodiment, the choice of the second reducing agent determines the deposition of gold atoms on the surface of the gold nucleus. The same or different reducing agent as the first can be used, allowing for flexible control of the reduction potential and atomic supply rate during the growth stage, directly affecting the deposition process of gold atoms on the pre-formed gold nucleus surface.

[0024] As a further improvement of the present invention, the concentration of the first reducing agent solution is 0.01 mg / mL to 0.1 mg / mL; and / or,

[0025] The concentration of the second reducing agent solution is 0.1 g / mL to 0.5 g / mL.

[0026] In this embodiment, by setting the concentration of the first reducing agent solution within a low range of 0.01 mg / mL to 0.1 mg / mL, the gold atom supply rate during the nucleation stage can be precisely controlled. Too low a concentration may result in insufficient nuclei, affecting the final yield; too high a concentration may easily trigger instantaneous burst nucleation, leading to uneven gold nucleus size or even agglomeration. Within this concentration range, the reducing agent can provide a stable and adequate reducing environment, thereby generating uniformly sized and well-dispersed initial gold nuclei. This is beneficial for the subsequent formation of spherical gold powder.

[0027] In this embodiment, the concentration of the second reducing agent solution is set to 0.1 g / mL-0.5 g / mL. This concentration range ensures that a suitable supersaturation of gold atoms is formed in the reaction system, which can promote the uniform and stable growth of gold crystals along the preset crystal plane direction, and is conducive to finally obtaining spherical gold powder with regular morphology and uniform size.

[0028] As a further improvement of the present invention, the concentration of the chloroauric acid solution is 0.1 g / mL to 1 g / mL; and / or,

[0029] The mass ratio of the first alkylamine to gold in the chloroauric acid solution is (50-120):1; and / or,

[0030] The mass ratio of the first reducing agent to the gold in the chloroauric acid solution is (1-8):1; and / or,

[0031] The mass ratio of the second alkylamine to gold in the chloroauric acid solution is (0.001-0.1):1; and / or,

[0032] The mass ratio of the second reducing agent to the gold in the chloroauric acid solution is (1-5):1.

[0033] In this embodiment, by setting the concentration of chloroauric acid solution in the range of 0.1 g / mL to 1 g / mL, the reaction system can have a suitable initial concentration, which can stably and continuously release gold atoms, providing a material basis for the uniform growth of gold crystal nuclei.

[0034] In this embodiment, by setting the mass ratio of the first alkylamine to gold in the chloroauric acid solution within the range of (50-120):1, a sufficient amount of the first alkylamine is provided to fully coat the surface of the newly formed gold crystal nuclei. This ensures that each gold crystal nucleus is effectively isolated, which is beneficial for the subsequent uniform growth of spherical gold powder.

[0035] In this embodiment, by setting the mass ratio of the first reducing agent to gold in the chloroauric acid solution within the range of (1-8):1, it can be ensured that sufficient gold particles in chloroauric acid are reduced to gold atoms, promoting homogeneous nucleation, while avoiding nucleation bursts caused by excessively fast reduction rates.

[0036] In this embodiment, by setting the mass ratio of the second alkylamine to gold in the chloroauric acid solution within the range of (0.001-0.1):1, it can synergize with the already adsorbed first alkylamine and, with its shorter carbon chain and faster adsorption kinetics, preferentially occupy crystal faces with higher surface energy and faster growth. This selective weakening coating effectively balances the growth rates of different crystal faces and strongly suppresses anisotropic growth.

[0037] In this embodiment, the atomic deposition rate during the growth stage was controlled by setting the mass ratio of the second reducing agent to gold in the chloroauric acid solution within the range of (1-5):1. Compared to the nucleation stage, the growth stage requires a higher concentration of the second reducing agent to maintain a suitable gold atom supersaturation, thereby driving the continuous and uniform deposition of gold atoms on the surface of the gold crystal nucleus. This ratio range ensures a stable and sufficient supply of gold atoms at the growth interface, enabling the crystal to undergo epitaxial growth according to a preset isotropic mode under the control of the second alkylamine.

[0038] As a further improvement of the present invention, the first aqueous phase medium includes deionized water; and / or,

[0039] The dropping rate of the second reducing agent and chloroauric acid solution is 10 mL / min to 100 mL / min.

[0040] In this embodiment, by using deionized water as the first aqueous phase medium, impurity ions (such as Na+) can be eliminated. + Cl - Ca 2 + To prevent interference with the reaction by impurity ions and avoid the formation of complexes between impurity ions and the first alkylamine or gold ions, the first alkylamine is ensured to be specifically adsorbed on the surface of the gold crystal nucleus, maintaining the stability of the reduction efficiency of the reducing agent, providing a pure reaction environment for the uniform nucleation and growth of gold crystal nuclei, and helping to ensure the high purity and morphological consistency of gold powder.

[0041] In this embodiment, the dropping rate of the second reducing agent and chloroauric acid solution is set in the range of 10 mL / min to 100 mL / min, so that gold atoms can be deposited on the surface of the gold crystal nucleus at a stable flux, which promotes the uniform growth of the crystal along the isotropic direction.

[0042] As a further improvement of the present invention, the preparation of chloroauric acid solution includes:

[0043] The gold raw material is reacted with a mixed acid containing hydrochloric acid and nitric acid to dissolve it and obtain a precursor solution;

[0044] The precursor solution was purified to obtain a chloroauric acid solution.

[0045] In this embodiment, nitric acid, as a strong oxidizing agent, can oxidize gold atoms to Au. 3+Hydrochloric acid provides Cl. - , with Au 3+ A stable [AuCl4] is formed. - The complex ion significantly improves the dissolution efficiency of gold. After the reaction is complete, the precursor solution contains only the target product [AuCl4]. - In addition, it contains unreacted free acid, excess nitrate ions, and nitrogen oxides (such as NO and NO2) generated during the reaction. If these nitrogen oxides are not removed, they will exist as oxidizing impurities in subsequent reduction reactions, potentially reacting with the reducing agent, consuming the reducing agent, and interfering with the reduction process of gold ions, leading to abnormal gold crystal nucleus formation or irregular gold powder morphology. By removing impurities, nitrogen oxides in the solution can be effectively removed, ensuring the purity and stability of the subsequent reduction reaction system, and providing pure chloroauric acid raw material for the preparation of high-purity, regularly morphologically regular submicron spherical gold powder.

[0046] As a further improvement of the present invention, the precipitate is post-processed to obtain submicron spherical gold powder, which includes:

[0047] The precipitate is washed to remove soluble impurities and then dried to obtain submicron spherical gold powder; wherein the washing includes at least one water wash and at least one organic solvent wash.

[0048] In this embodiment, water washing removes residual water-soluble impurities from the reaction system, such as unreacted chloroauric acid, excess reducing agent, and inorganic ions generated during the reaction. If these impurities remain on the surface of the gold powder, they will affect the purity of the powder and its subsequent dispersion performance, and may even introduce defects during drying or sintering. Multiple water washes utilize the polarity of water to dissolve and carry away the water-soluble impurities, thus initially purifying the surface of the gold powder. Organic solvent washing effectively removes organic substances (i.e., the first and second alkylamines) adsorbed on the surface of the gold powder. Through synergistic action with water, residual organic substances can be gradually peeled off and dissolved, preventing organic impurities from forming hard agglomerates after drying or affecting the surface activity of the gold powder. Drying after washing removes water and organic solvents, maintaining good dispersion of the spherical gold powder particles and preventing particle adhesion or agglomeration caused by residual liquid.

[0049] To achieve the above objectives, the present invention also provides a submicron spherical gold powder, which is prepared by the preparation method of submicron spherical gold powder of any of the aforementioned technical solutions. The particle size of the spherical gold powder is 0.1μm-1.5μm, and it is used in the fields of electronic packaging, thick film circuits, LTCC, and 3D printing.

[0050] The beneficial effects of this invention are:

[0051] This invention provides a submicron spherical gold powder and its preparation method. The preparation method employs a chemical reduction approach, utilizing the synergistic action of a first alkylamine and a second alkylamine to achieve controllable gold powder particle size ranging from 0.1 μm to 1.5 μm, resulting in good dispersibility and regular morphology, which is beneficial for forming a dense gold film during sintering. By employing a synergistic regulatory mechanism between the first alkylamine (C14-C18) and the second alkylamine (C10-C18), during the gold nucleus formation stage, the long-chain first alkylamine acts as the main surface dispersant. Its amine groups are adsorbed onto the gold nucleus surface through electrostatic interaction, and the long alkyl chain forms a stable steric hindrance layer, effectively isolating and stabilizing the gold nucleus, laying the foundation for subsequent uniform growth. During the crystal growth stage, the addition of the second alkylamine (C10-C18), with a wider chain length range, synergizes with the first alkylamine on the gold crystal surface, forming a more flexible and adjustable composite coating environment. By selecting second alkylamines with different chain lengths, the coating strength and adsorption kinetics of different crystal planes of gold crystals can be more precisely controlled. When using second alkylamines with shorter chain lengths (such as C10-C12), their molecular mobility is stronger, enabling rapid adsorption and adjustment of surface energy. Synergistically with the first alkylamine, they effectively balance the growth rate of each crystal plane, strengthening the isotropic growth trend. When using second alkylamines with longer chain lengths (such as C16-C18), their structure is closer to that of the first alkylamine, forming a denser and thicker spatially stable layer, providing stronger stereoscopic shielding. This is particularly beneficial for suppressing abnormal grain aggregation or morphological deviation caused by localized overconcentration of reactants in the later stages of growth, maintaining the stability of the spherical morphology within a wider range of process parameters. This enhances the ability to control the microenvironment of crystal growth. By regulating the competitive adsorption and synergistic arrangement of two amines on the crystal surface, it can more effectively balance the surface energy differences of each crystal face and suppress the preferential deposition of gold atoms on specific high-energy crystal faces. This overcomes the tendency of plate-like or dendritic morphology caused by anisotropic growth in traditional methods, promotes continuous isotropic growth of crystals, and finally forms a regular spherical structure with good dispersion and uniform morphology.

[0052] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0053] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the present invention will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0054] Figure 1The image shows the scanning electron microscope (SEM) results of the spherical gold powder prepared in Example 1.

[0055] Figure 2 The image shows the scanning electron microscope (SEM) results of the spherical gold powder prepared in Example 2.

[0056] Figure 3 The image shows the scanning electron microscope (SEM) results of the spherical gold powder prepared in Example 3.

[0057] Figure 4 The image shows the scanning electron microscope (SEM) results of the spherical gold powder prepared in Example 4.

[0058] Figure 5 The image shows the scanning electron microscope (SEM) results of the spherical gold powder prepared in Example 5.

[0059] Figure 6 The image shows the scanning electron microscope (SEM) results of the spherical gold powder prepared in Comparative Example 1.

[0060] Figure 7 The image shows the scanning electron microscope (SEM) results of the spherical gold powder prepared in Comparative Example 2.

[0061] Figure 8 The image shows the scanning electron microscope (SEM) results of the spherical gold powder prepared in Comparative Example 3.

[0062] Figure 9 The image shows the scanning electron microscope (SEM) results of the spherical gold powder prepared in Comparative Example 4. Detailed Implementation

[0063] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0064] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0065] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0066] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0067] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0068] In the description of the embodiments of the present invention, the term "multiple" refers to two or more (including two), similarly, "multiple groups" refers to two or more (including two groups), and "multiple pieces" refers to two or more (including two pieces).

[0069] In the description of the embodiments of the present invention, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention.

[0070] In the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0071] Electronic packaging, as a core component of microelectronics manufacturing, directly impacts chip reliability, signal transmission efficiency, and product lifespan. Currently, with the rapid development of technologies such as 5G communication, artificial intelligence, and the internet, electronic devices are evolving towards higher density, miniaturization, and flexibility, placing stringent demands on packaging materials: they must possess ultra-low resistivity, excellent resistance to electrochemical corrosion, high-temperature stability, and nanometer-level precision. Traditional silver and copper powders, due to their susceptibility to oxidation and insufficient conductivity, struggle to meet the demands of high-end packaging. Gold powder, with its chemical inertness, high conductivity, and malleability, has become a key material for overcoming these technological bottlenecks.

[0072] In existing preparation techniques, uneven concentration of reducing agent or mixing of reactants often exists within the reaction system, easily triggering explosive nucleation in localized areas, generating a large number of gold atoms, while other areas suffer from a shortage of gold atoms. This uneven distribution leads to significant differences in the particle growth environment. Furthermore, due to the lack of effective control, the surface energies of different crystal faces of gold crystals differ, causing gold atoms to preferentially and rapidly deposit on crystal faces with higher surface energies. This results in preferential crystal growth along specific directions, ultimately forming plate-like or dendritic morphologies. In summary, traditional methods easily produce plate-like, dendritic, or irregular aggregates, affecting the performance of the gold powder.

[0073] In view of this, it is necessary to design a submicron spherical gold powder and its preparation method to solve the above problems.

[0074] This invention proposes a method for preparing submicron spherical gold powder, comprising:

[0075] In a first aqueous medium, a first alkylamine, a first reducing agent, and a chloroauric acid solution are added to obtain a gold crystal nucleus solution;

[0076] A second alkylamine is added to the gold crystal nucleus solution, followed by the addition of a second reducing agent and chloroauric acid solution, which causes gold to grow on the surface of the gold crystal nucleus, resulting in a precipitate.

[0077] The precipitate was post-processed to obtain submicron spherical gold powder; among which,

[0078] The first alkylamine has 14-18 carbon atoms in its alkyl chain, and the second alkylamine has 10-18 carbon atoms in its alkyl chain.

[0079] This invention provides a submicron spherical gold powder and its preparation method. The preparation method employs a chemical reduction approach, utilizing the synergistic action of a first alkylamine and a second alkylamine to achieve controllable gold powder particle size ranging from 0.1 μm to 1.5 μm, resulting in good dispersibility and regular morphology, which is beneficial for forming a dense gold film during sintering. By employing a synergistic regulatory mechanism between the first alkylamine (C14-C18) and the second alkylamine (C10-C18), during the gold nucleus formation stage, the long-chain first alkylamine acts as the main surface dispersant. Its amine groups are adsorbed onto the gold nucleus surface through electrostatic interaction, and the long alkyl chain forms a stable steric hindrance layer, effectively isolating and stabilizing the gold nucleus, laying the foundation for subsequent uniform growth. During the crystal growth stage, the addition of the second alkylamine (C10-C18), with a wider chain length range, synergizes with the first alkylamine on the gold crystal surface, forming a more flexible and adjustable composite coating environment. By selecting second alkylamines with different chain lengths, the coating strength and adsorption kinetics of different crystal planes of gold crystals can be more precisely controlled. When using second alkylamines with shorter chain lengths (such as C10-C12), their molecular mobility is stronger, enabling rapid adsorption and adjustment of surface energy. Synergistically with the first alkylamine, they effectively balance the growth rate of each crystal plane, strengthening the isotropic growth trend. When using second alkylamines with longer chain lengths (such as C16-C18), their structure is closer to that of the first alkylamine, forming a denser and thicker spatially stable layer, providing stronger stereoscopic shielding. This is particularly beneficial for suppressing abnormal grain aggregation or morphological deviation caused by localized overconcentration of reactants in the later stages of growth, maintaining the stability of the spherical morphology within a wider range of process parameters. This enhances the ability to control the microenvironment of crystal growth. By regulating the competitive adsorption and synergistic arrangement of two amines on the crystal surface, it can more effectively balance the surface energy differences of each crystal face and suppress the preferential deposition of gold atoms on specific high-energy crystal faces. This overcomes the tendency of plate-like or dendritic morphology caused by anisotropic growth in traditional methods, promotes continuous isotropic growth of crystals, and finally forms a regular spherical structure with good dispersion and uniform morphology.

[0080] In summary, by using two alkylamines through synergistic adsorption and steric hindrance, the surface energy differences of the gold crystal facets were balanced, promoting uniform deposition of gold atoms on different crystal faces and suppressing preferential growth on specific crystal faces. This directional control enabled the crystal to grow isotropically, forming a regularly shaped spherical structure. Ultimately, spherical gold powder with a diameter of 0.1 μm to 1.5 μm can be prepared, exhibiting regular morphology, good dispersibility, and good sintering activity.

[0081] As a further improvement of the present invention, the first alkylamine includes at least one of tetradecylamine, hexadecylamine, and octadecylamine.

[0082] In this embodiment, all three are straight-chain primary amines. The amino groups (-NH2) have a strong affinity for gold and can effectively adsorb to form a protective layer. The alkyl chains provide hydrophobic steric hindrance, preventing particle agglomeration. This is the basis for achieving high dispersibility of gold powder. Specifically, tetradecylamine (C14) has moderate steric hindrance, which is conducive to rapid nucleation and growth, and is suitable for high-efficiency preparation of larger-sized gold powder; hexadecylamine (C16) achieves the best balance between control and growth, and is the preferred reference reagent for obtaining highly regular spherical morphology and ensuring process stability; octadecylamine (C18) has the strongest steric hindrance, which can most effectively stabilize small gold nuclei, and is particularly suitable for preparing powders with smaller size and narrower distribution and high sphericity. In addition, they can be used in combination to effectively balance the growth rate of each crystal face through differentiated coating, thereby strongly suppressing anisotropic growth and ensuring that submicron spherical gold powder with regular morphology, good dispersibility and excellent sintering activity in the range of 0.1μm-1.5μm is finally obtained.

[0083] As a further improvement of the present invention, the second alkylamine includes at least one of decylamine, dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine.

[0084] In this embodiment, decylamine (C10) has the shortest carbon chain and fast adsorption kinetics, enabling it to preferentially and rapidly coat the actively growing high-energy crystal faces, quickly bridging the growth rate differences between crystal faces. Dodecylamine (C12) strikes a balance between kinetic response and adsorption stability, forming an ideal chain length difference with the first alkylamine to construct a stable and finely tunable mixed adsorption layer, making it a choice to ensure high reproducibility of gold powder spherical morphology in the submicron range. Tetradecylamine (C14), hexadecylamine (C16), and octadecylamine (C18) can act as reinforcing and complementary agents, providing stronger steric hindrance and denser surface coating, particularly suitable for suppressing surface roughening or deformation tendencies of larger particles in the later stages of growth. Furthermore, they can be used in combination, providing more flexible dynamic control to adapt to different industrial production needs.

[0085] As a further improvement of the present invention, the concentration of the first alkylamine solution is 1 mg / mL to 4 mg / mL.

[0086] In this embodiment, by setting the solution concentration of the first alkylamine in the range of 1 mg / mL to 4 mg / mL, it can be ensured that a sufficient number of molecules are provided during the gold nucleus formation stage to fully cover and stabilize the surface of all newly formed gold nuclei, forming an effective steric hindrance layer and preventing excessive aggregation of gold nuclei.

[0087] For example, the concentration of the first alkylamine solution can be 1 mg / mL, 1.1 mg / mL, 1.3 mg / mL, 1.5 mg / mL, 1.9 mg / mL, 2.1 mg / mL, 2.2 mg / mL, 2.5 mg / mL, 2.7 mg / mL, 2.9 mg / mL, 3 mg / mL, 3.1 mg / mL, 3.5 mg / mL, 3.7 mg / mL, or 4 mg / mL.

[0088] As a further improvement of the present invention, the concentration of the second alkylamine solution is 0.1 mg / mL to 1 mg / mL.

[0089] In this embodiment, by setting the solution concentration of the second alkylamine within the range of 0.1 mg / mL to 1 mg / mL, it can synergistically interact with the already adsorbed first alkylamine to selectively and dynamically adsorb onto the surface of the growing gold crystal. This allows the second alkylamine to respond more sensitively to the surface energy differences of different crystal faces, preferentially coating the active crystal faces with faster growth rates, thereby more precisely regulating the atomic deposition rate of each crystal face and effectively suppressing anisotropic growth.

[0090] For example, the concentration of the second alkylamine solution can be 0.1 mg / mL, 0.2 mg / mL, 0.25 mg / mL, 0.29 mg / mL, 0.3 mg / mL, 0.31 mg / mL, 0.37 mg / mL, 0.44 mg / mL, 0.5 mg / mL, 0.6 mg / mL, 0.77 mg / mL, 0.84 mg / mL, 0.9 mg / mL, or 1 mg / mL.

[0091] As a further improvement of the present invention, the first reducing agent includes at least one of ascorbic acid, hydrazine hydrate, hydrazine carbonate and sodium borohydride.

[0092] In this embodiment, the choice of the first reducing agent affects the generation rate, size, and number density of gold nuclei. Strong reducing agents, such as sodium borohydride, can instantly generate a large number of gold atoms, promoting homogeneous nucleation and forming numerous small initial gold nuclei, laying the foundation for subsequent growth. Mild reducing agents, such as ascorbic acid, provide a controllable reduction environment, which is beneficial for obtaining gold nuclei of uniform size. By selecting specific reducing agents or combinations, the initial state of the gold nuclei can be precisely controlled.

[0093] The second reducing agent includes at least one of ascorbic acid, hydrazine hydrate, hydrazine carbonate, and sodium borohydride.

[0094] In this embodiment, the choice of the second reducing agent determines the deposition of gold atoms on the surface of the gold nucleus. The same or different reducing agent as the first can be used, allowing for flexible control of the reduction potential and atomic supply rate during the growth stage, directly affecting the deposition process of gold atoms on the pre-formed gold nucleus surface.

[0095] As a further improvement of the present invention, the concentration of the first reducing agent solution is 0.01 mg / mL to 0.1 mg / mL.

[0096] In this embodiment, by setting the concentration of the first reducing agent solution within the range of 0.01 mg / mL to 0.1 mg / mL, the gold atom supply rate during the nucleation stage can be precisely controlled. Too low a concentration may result in insufficient nuclei, affecting the final yield; too high a concentration may easily trigger instantaneous burst nucleation, leading to uneven gold nucleus size or even agglomeration. Within this concentration range, the reducing agent can provide a stable and adequate reducing environment, thereby generating uniformly sized and well-dispersed initial gold nuclei. This is beneficial for the subsequent formation of spherical gold powder.

[0097] For example, the concentration of the first reducing agent solution can be 0.01 mg / mL, 0.015 mg / mL, 0.02 mg / mL, 0.03 mg / mL, 0.042 mg / mL, 0.05 mg / mL, 0.069 mg / mL, 0.07 mg / mL, 0.08 mg / mL, 0.085 mg / mL, 0.09 mg / mL, or 0.1 mg / mL.

[0098] As a further improvement of the present invention, the concentration of the second reducing agent solution is 0.1 g / mL to 0.5 g / mL.

[0099] In this embodiment, the concentration of the second reducing agent solution is set to 0.1 g / mL-0.5 g / mL. This concentration range ensures that a suitable supersaturation of gold atoms is formed in the reaction system, which can promote the uniform and stable growth of gold crystals along the preset crystal plane direction, and is conducive to finally obtaining spherical gold powder with regular morphology and uniform size.

[0100] For example, the concentration of the second reducing agent solution is 0.1 g / mL, 0.11 g / mL, 0.15 g / mL, 0.17 g / mL, 0.19 g / mL, 0.23 g / mL, 0.25 g / mL, 0.29 g / mL, 0.3 g / mL, 0.34 g / mL, 0.37 g / mL, 0.45 g / mL, or 0.5 g / mL.

[0101] As a further improvement of the present invention, the concentration of chloroauric acid solution is 0.1 g / mL to 1 g / mL.

[0102] In this embodiment, by setting the concentration of chloroauric acid solution in the range of 0.1 g / mL to 1 g / mL, the reaction system can have a suitable initial concentration, which can stably and continuously release gold atoms, providing a material basis for the uniform growth of gold crystal nuclei.

[0103] For example, the concentration of the chloroauric acid solution can be 0.1 g / mL, 0.11 g / mL, 0.15 g / mL, 0.17 g / mL, 0.2 g / mL, 0.26 g / mL, 0.3 g / mL, 0.33 g / mL, 0.39 g / mL, 0.4 g / mL, 0.47 g / mL, 0.5 g / mL, 0.66 g / mL, 0.73 g / mL, 0.75 g / mL, 0.8 g / mL, 0.99 g / mL, or 1 g / mL.

[0104] As a further improvement of the present invention, the mass ratio of the first alkylamine to gold in the chloroauric acid solution is (50-120):1.

[0105] In this embodiment, by setting the mass ratio of the first alkylamine to gold in the chloroauric acid solution within the range of (50-120):1, a sufficient amount of the first alkylamine is provided to fully coat the surface of the newly formed gold crystal nuclei. This ensures that each gold crystal nucleus is effectively isolated, which is beneficial for the subsequent uniform growth of spherical gold powder.

[0106] For example, the mass ratio of the first alkylamine to gold in the chloroauric acid solution can be (50:1), (55:1), (59:1), (60:1), (65:1), (70:1), (77:1), (85:1), (90:1), (105:1), (115:1), or (120:1).

[0107] As a further improvement of the present invention, the mass ratio of the first reducing agent to the gold in the chloroauric acid solution is (1-8):1.

[0108] In this embodiment, by setting the mass ratio of the first reducing agent to gold in the chloroauric acid solution within the range of (1-8):1, it can be ensured that sufficient gold particles in chloroauric acid are reduced to gold atoms, promoting homogeneous nucleation, while avoiding nucleation bursts caused by excessively fast reduction rates.

[0109] For example, the mass ratio of the first reducing agent to gold in the chloroauric acid solution is (1∶1), (1.1∶1), (1.2∶1), (1.5∶1), (1.7∶1), (2∶1), (2.5∶1), (3∶1), (3.9∶1), (4.5∶1), (5∶1), (6∶1), (7∶1), (7.9∶1), or (8∶1).

[0110] As a further improvement of the present invention, the mass ratio of the second alkylamine to gold in the chloroauric acid solution is (0.001-0.1):1.

[0111] In this embodiment, by setting the mass ratio of the second alkylamine to gold in the chloroauric acid solution within the range of (0.001-0.1):1, it can synergize with the already adsorbed first alkylamine and, with its shorter carbon chain and faster adsorption kinetics, preferentially occupy crystal faces with higher surface energy and faster growth. This selective weakening coating effectively balances the growth rates of different crystal faces and strongly suppresses anisotropic growth.

[0112] For example, the mass ratio of the second alkylamine to gold in the chloroauric acid solution is (0.001∶1), (0.002∶1), (0.004∶1), (0.007∶1), (0.009∶1), (0.01∶1), (0.02∶1), (0.04∶1), (0.044∶1), (0.05∶1), (0.066∶1), (0.069∶1), (0.071∶1), (0.083∶1), (0.098∶1), or (0.1∶1).

[0113] As a further improvement of the present invention, the mass ratio of the second reducing agent to the gold in the chloroauric acid solution is (1-5):1.

[0114] In this embodiment, the atomic deposition rate during the growth stage was controlled by setting the mass ratio of the second reducing agent to gold in the chloroauric acid solution within the range of (1-5):1. Compared to the nucleation stage, the growth stage requires a higher concentration of the second reducing agent to maintain a suitable gold atom supersaturation, thereby driving the continuous and uniform deposition of gold atoms on the surface of the gold crystal nucleus. This ratio range ensures a stable and sufficient supply of gold atoms at the growth interface, enabling the crystal to undergo epitaxial growth according to a preset isotropic mode under the control of the second alkylamine.

[0115] For example, the mass ratio of the second reducing agent to gold in the chloroauric acid solution is (1∶1), (1.1∶1), (1.3∶1), (1.5∶1), (1.7∶1), (1.9∶1), (2.2∶1), (2.8∶1), (3.3∶1), (3.7∶1), (4.6∶1 or (5∶1).

[0116] Understandably, the role of the first aqueous medium is to provide a clean reaction environment, avoid interference from impurity ions on the formation of gold crystal nuclei and subsequent crystal growth, and at the same time improve the controllability and repeatability of the reaction, and reduce deviations in the morphology, size and dispersion of gold powder caused by fluctuations in water quality.

[0117] As a further improvement of the present invention, the first aqueous phase medium includes deionized water.

[0118] In this embodiment, by using deionized water as the first aqueous phase medium, impurity ions (such as Na+) can be eliminated. + Cl -Ca 2 + To prevent interference with the reaction by impurity ions and avoid the formation of complexes between impurity ions and the first alkylamine or gold ions, the first alkylamine is ensured to be specifically adsorbed on the surface of the gold crystal nucleus, maintaining the stability of the reduction efficiency of the reducing agent, providing a pure reaction environment for the uniform nucleation and growth of gold crystal nuclei, and helping to ensure the high purity and morphological consistency of gold powder.

[0119] As a further improvement of the present invention, the dropping rate of the second reducing agent and the chloroauric acid solution is 10 mL / min to 100 mL / min.

[0120] In this embodiment, the dropping rate of the second reducing agent and chloroauric acid solution is set in the range of 10 mL / min to 100 mL / min, so that gold atoms can be deposited on the surface of the gold crystal nucleus at a stable flux, which promotes the uniform growth of the crystal along the isotropic direction.

[0121] For example, the dropping rates of the second reducing agent and the chloroauric acid solution are 10 mL / min, 15 mL / min, 19 mL / min, 23 mL / min, 26 mL / min, 30 mL / min, 44 mL / min, 55 mL / min, 64 mL / min, 68 mL / min, 71 mL / min, 75 mL / min, 80 mL / min, 81 mL / min, 99 mL / min, or 100 mL / min.

[0122] It is understandable that chloroauric acid solution can be prepared in various ways. For example, it can be prepared by electrochemical dissolution: using a high-purity gold plate as the anode, a constant current is applied in an electrolytic cell containing hydrochloric acid electrolyte to dissolve the gold, and Au is generated at the anode. 3+ It combines with chloride ions to form chloroauric acid; by monitoring the concentration of gold ions and pH value in the solution in real time, and adjusting the current density and electrolyte flow rate, a chloroauric acid solution of the target concentration can be obtained efficiently and controllably.

[0123] As a further improvement of the present invention, the preparation of chloroauric acid solution includes:

[0124] The gold raw material is reacted with a mixed acid containing hydrochloric acid and nitric acid to dissolve it and obtain a precursor solution;

[0125] The precursor solution was purified to obtain a chloroauric acid solution.

[0126] In this embodiment, nitric acid, as a strong oxidizing agent, can oxidize gold atoms to Au. 3+ Hydrochloric acid provides Cl. - , with Au 3+ A stable [AuCl4] is formed. -The complex ion significantly improves the dissolution efficiency of gold. After the reaction is complete, the precursor solution contains only the target product [AuCl4]. - In addition, it contains unreacted free acid, excess nitrate ions, and nitrogen oxides (such as NO and NO2) generated during the reaction. If these nitrogen oxides are not removed, they will exist as oxidizing impurities in subsequent reduction reactions, potentially reacting with the reducing agent, consuming the reducing agent, and interfering with the reduction process of gold ions, leading to abnormal gold nucleus formation or irregular gold powder morphology. Through impurity removal treatment, nitrogen oxides in the solution can be effectively removed, ensuring the purity and stability of the subsequent reduction reaction system, providing pure chloroauric acid raw material for preparing high-purity, regularly morphologically regular submicron spherical gold powder. Furthermore, it is worth mentioning that this invention can also improve the dissolution rate through heating. Compared to electrochemical dissolution methods, this method does not require complex electrochemical equipment, has a simpler operation process, and can quickly dissolve gold raw materials through a mixed acid system. Combined with targeted impurity removal treatment, it can efficiently obtain a high-purity chloroauric acid solution, suitable for large-scale production needs.

[0127] Specifically, in some embodiments of the present invention, the mixed acid is aqua regia, with a volume ratio of nitric acid to hydrochloric acid of approximately 1:3. This ratio of aqua regia has extremely strong dissolving power and can react rapidly with gold raw materials at room temperature, significantly shortening the dissolution time.

[0128] Specifically, in some embodiments of the present invention, the purity of the gold raw material is greater than or equal to 99.9%. This setting can minimize the introduction of impurity elements (such as silver, copper, iron, etc.) and reduce the interference of impurities on the formation of gold crystal nuclei and subsequent crystal growth from the source.

[0129] Understandably, some NO and NO2 from nitrogen oxides will leak out, but due to the complex chemical equilibrium and limitations of solution physics, they are difficult to completely remove from high-concentration aqua regia solutions, thus requiring impurity removal treatment. Nitrogen oxide removal can be achieved through various methods, such as heating removal, chemical reduction, or vacuum degassing. Furthermore, depending on actual production needs, these methods can be combined. For example, heating removal can be used to remove most of the nitrogen oxides, followed by short-time vacuum degassing for further purification; or a trace amount of reducing agent can be added for preliminary chemical treatment, followed by bubbling purging. Combined treatments can balance impurity removal efficiency and cost control, adapting to scenarios with different purity requirements. Excess nitrate ions and free acids can be removed through various methods, including selective precipitation or ion exchange.

[0130] Specifically, in some embodiments of the present invention, a chloroauric acid solution is obtained by dropwise addition of concentrated hydrochloric acid to a precursor solution, followed by concentration. This setup allows for the addition of concentrated hydrochloric acid (concentration can be 36%-38%), which then ionizes to release a large amount of Cl... - It will react with H in the solution ＋ Combined, forming a high concentration of Cl - The environment, and the addition of concentrated hydrochloric acid, will increase the acidity of the solution. During the concentration process, as water evaporates, the concentration of nitrate ions in the solution relatively increases, but at high concentrations of Cl... - Under strong acidic conditions, the oxidizing power of nitrate ions is somewhat suppressed, and they react more readily with H+. ＋ Nitric acid molecules are formed. Since nitric acid is highly volatile, under concentrated heating conditions, nitric acid molecules evaporate along with water vapor, further reducing the nitrate ion content in the solution. After dilution with deionized water, a chloroauric acid solution with higher purity is obtained. This method is simple to operate, utilizes the volatility of nitric acid, and effectively reduces the adverse effects of nitrate ions on subsequent reduction reactions, ensuring that the chloroauric acid solution is mainly composed of [AuCl4]. - The presence of complex ions ensures the subsequent preparation of submicron spherical gold powder. Furthermore, it is worth mentioning that the concentration of the concentrated chloroauric acid solution can be adjusted by adding deionized water to meet different application requirements.

[0131] As a further improvement of the present invention, the precipitate is post-processed to obtain submicron spherical gold powder, which includes:

[0132] The precipitate is washed to remove soluble impurities and then dried to obtain submicron spherical gold powder; wherein the washing includes at least one water wash and at least one organic solvent wash.

[0133] In this embodiment, water washing removes residual water-soluble impurities from the reaction system, such as unreacted chloroauric acid, excess reducing agent, and inorganic ions generated during the reaction. If these impurities remain on the surface of the gold powder, they will affect the purity of the powder and its subsequent dispersion performance, and may even introduce defects during drying or sintering. Multiple water washes utilize the polarity of water to dissolve and carry away the water-soluble impurities, thus initially purifying the surface of the gold powder. Organic solvent washing effectively removes organic substances (i.e., the first and second alkylamines) adsorbed on the surface of the gold powder. Through synergistic action with water, residual organic substances can be gradually peeled off and dissolved, preventing organic impurities from forming hard agglomerates after drying or affecting the surface activity of the gold powder. Drying after washing removes water and organic solvents, maintaining good dispersion of the spherical gold powder particles and preventing particle adhesion or agglomeration caused by residual liquid.

[0134] Specifically, in some embodiments of the present invention, the washing process includes four water washes followed by four organic solvent washes. This arrangement allows the four water washes to fully dissolve and remove water-soluble impurities from the system. During each water wash, stirring and centrifugation ensure sufficient contact between water and gold powder particles, transferring free chloride ions, unreacted small-molecule reducing agents, and other water-soluble substances to the aqueous phase for removal. The four organic solvent washes target residual organic substances such as first and second alkylamines. The organic solvent forms a well-miscible system with the alkylamines, gradually displacing the organic substances adsorbed on the surface of the gold powder through penetration and dissolution. After centrifugation, the content of organic impurities is significantly reduced. Furthermore, deionized water is used for the water washes, and isopropanol is used as the organic solvent. This minimizes the interference of dissolved mineral ions in the water on the purity of the gold powder, avoiding the introduction of new impurities. Isopropanol, as an organic solvent, not only has good volatility, facilitating subsequent drying, but is also miscible with water. During the two washes, it gradually reduces the surface tension of the water film on the gold powder surface, more thoroughly removing residual organic substances.

[0135] This invention also provides a submicron spherical gold powder, which is prepared by any of the aforementioned methods for preparing submicron spherical gold powder. The particle size of the spherical gold powder is 0.1 μm-1.5 μm, and it is used in electronic packaging, thick-film circuits, LTCC, and 3D printing. This submicron spherical gold powder has all the beneficial effects of the aforementioned methods for preparing submicron spherical gold powder, which will not be elaborated further here.

[0136] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0137] I. Preparation Method

[0138] Example 1

[0139] Place 5g of gold raw material and 5mL of deionized water into a beaker. Heat the mixture in the beaker using a constant temperature heating plate. Add 10mL of prepared aqua regia to the beaker in batches. After the gold raw material is completely dissolved, add concentrated hydrochloric acid dropwise to the beaker to remove nitric acid. Continue until no yellow fumes are emitted. Heat and concentrate to a volume of 10mL. Repeat this process three times to obtain a concentrated solution. Add deionized water to the concentrated solution and heat to remove the hydrochloric acid. Repeat this process three times and concentrate to 20mL to obtain a chloroauric acid solution (concentration of 250mg / mL).

[0140] Take 40 mL of deionized water, add 72 mg of a first alkylamine (octadecylamine) and 3.5 mg of ascorbic acid to it. After dissolution, gradually add 3 μL of chloroauric acid solution (the content of gold raw material is 0.75 mg). After reacting for 1 h, the gold crystal nucleus solution is obtained.

[0141] Dissolve 46 mg of a second alkylamine (using dodecylamine) in 50 mL of deionized water to obtain a dodecylamine solution, and add it to the above gold nucleus solution. Dissolve 9.1 g of ascorbic acid in 45 mL of deionized water to obtain an ascorbic acid solution. Use the remaining chloroauric acid solution as the gold source, and add the chloroauric acid solution and ascorbic acid solution dropwise to the gold nucleus solution at a rate of 25 mL / min, stirring the reaction to obtain a precipitate.

[0142] The precipitate was washed four times with deionized water, then washed four times with isopropanol, and dried to obtain the submicron spherical gold powder of Example 1.

[0143] Example 2

[0144] The mass of the second alkylamine in Example 1 was replaced from 46 mg to 35 mg, and the remaining steps were roughly the same as in Example 1, which will not be repeated here. This yielded the submicron spherical gold powder of Example 2.

[0145] Example 3

[0146] In Example 1, the second alkylamine was replaced with 39 mg of decylamine instead of 46 mg of dodecylamine. The remaining steps were largely the same as in Example 1 and will not be repeated here. This yielded the submicron spherical gold powder of Example 3.

[0147] Example 4

[0148] In Example 1, the second alkylamine was replaced with 67 mg of octadecylamine instead of 46 mg of dodecylamine. The remaining steps were largely the same as in Example 1 and will not be repeated here. This yielded the submicron spherical gold powder of Example 4.

[0149] Example 5

[0150] In Example 1, the first alkylamine was replaced with 57 mg of tetradecylamine instead of 72 mg of octadecylamine. The remaining steps were largely the same as in Example 1 and will not be repeated here. This yielded the submicron spherical gold powder of Example 5.

[0151] Comparative Example 1

[0152] In Example 1, the first alkylamine was replaced with 50 mg of dodecylamine instead of 72 mg of octadecylamine. The remaining steps were roughly the same as in Example 1 and will not be repeated here. This yielded the gold powder of Comparative Example 1.

[0153] Comparative Example 2

[0154] In Example 1, the first alkylamine was replaced with 79 mg of eicosamine instead of 72 mg of octadecylamine. The remaining steps were roughly the same as in Example 1 and will not be repeated here. This yielded the gold powder of Comparative Example 2.

[0155] Comparative Example 3

[0156] In Example 1, the second alkylamine was replaced with 35 mg of nonylamine instead of 46 mg of dodecylamine. The remaining steps were roughly the same as in Example 1 and will not be repeated here. This yielded the gold powder of Comparative Example 3.

[0157] Comparative Example 4

[0158] In Example 1, the second alkylamine was replaced with 74 mg of eicosamine instead of 46 mg of dodecylamine. The remaining steps were largely the same as in Example 1 and will not be repeated here. This yielded the gold powder of Comparative Example 4.

[0159] II. Testing Methods

[0160] The scanning electron microscope used was a JEM JSM-6390A from Nippon Electron, and the tests were conducted at room temperature.

[0161] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0162] Please see Figure 1 As shown, the submicron spherical gold powder prepared in Example 1 has a size of about 0.3 μm, a regular morphology, and a smooth surface.

[0163] Please see Figure 2 As shown, the submicron spherical gold powder prepared in Example 2 has a size of about 0.5 μm, a regular morphology, and a smooth surface.

[0164] Please see Figure 3 As shown, the submicron spherical gold powder prepared in Example 3 has a size of about 1.2 μm, a regular morphology, and a smooth surface.

[0165] Please see Figure 4 As shown, the submicron spherical gold powder prepared in Example 4 has a size of about 0.1-0.2 μm, a regular morphology, and a smooth surface.

[0166] Please see Figure 5 As shown, the submicron spherical gold powder prepared in Example 5 has a size of about 0.8 μm, a regular morphology, and a smooth surface.

[0167] Please see Figure 6 As shown, the gold powder prepared in Comparative Example 1 exhibits distinct anisotropic morphologies of flakes and rods. This is because the chain length of dodecylamine is relatively short, making it difficult to effectively coat the surface of the gold powder. This results in the formation of anisotropic morphologies during the preparation of the gold crystal nuclei, and the size of these anisotropic morphologies becomes more pronounced during subsequent growth.

[0168] Please see Figure 7 As shown, the gold powder prepared in Comparative Example 2 has a very small particle size and is agglomerated. This is because the eicosamine chain is relatively long, which tightly encapsulates the seed crystal, making it difficult for the seed crystal to grow. In subsequent growth, it can only grow along one side of the seed crystal, resulting in continuous agglomeration of the gold powder and a small particle size.

[0169] Please see Figure 8 As shown, the gold powder prepared in Comparative Example 3 has a wider particle size distribution. This is because the chain length of nonylamine is relatively short during the subsequent growth process, making it difficult to control the uniform growth of the gold powder, resulting in uneven particle size.

[0170] Please see Figure 9 As shown, the gold powder prepared in Comparative Example 4 had excessively small particle size, resulting in a flower-like shape. This is because eicosamine was used as a dispersant during the growth process, and its excessively long chain length made it difficult for the gold powder to grow. Furthermore, the smaller gold particles were difficult to exist independently and stably, ultimately forming a flower-like shape.

[0171] In Examples 1-2, as the amount of the second alkylamine (dodecylamine) decreased from 46 mg to 35 mg, the particle size of the prepared gold powder increased from about 0.3 μm to about 0.5 μm, while maintaining good sphericity and surface smoothness, demonstrating the controllability of the method for the particle size and morphology of gold powder.

[0172] In Examples 3-4, replacing 46 mg of dodecylamine with 39 mg of decylamine and 67 mg of octadecylamine resulted in gold powder particles with particle sizes increasing from 0.3 μm to 1.2 μm and decreasing to 0.1-0.2 μm, while maintaining a regular spherical morphology. This demonstrates that the particle size of the gold powder can be controlled by adjusting the chain length of the dispersant during the subsequent growth process.

[0173] In Example 5, replacing 72 mg of octadecylamine with 57 mg of tetradecylamine increased the particle size of the prepared gold powder from 0.3 μm to 0.8 μm while maintaining good sphericity, indicating that the particle size of gold powder can also be increased by increasing the size of the seed crystals in the early stage.

[0174] Comparative Example 1 used only dodecylamine as a gold nucleus dispersant, which resulted in anisotropic morphology at the gold nucleus stage, and this defect was further amplified in subsequent growth.

[0175] Comparative Example 2 used only eicosamine as a dispersant for gold crystal nuclei, which made it difficult for the gold crystal nuclei to grow and caused them to agglomerate into small-diameter strings.

[0176] Comparative Example 3 used nonylamine as a dispersant in the gold growth process. Due to the short chain, it was difficult to control the growth of gold powder into a uniform spherical morphology, resulting in the formation of spherical gold powder of uneven size.

[0177] Comparative Example 4 uses eicosamine as a dispersant in the gold growth process. Due to the excessively long chain length, the gold powder particles are small, forming flower-shaped clusters of gold powder.

[0178] Therefore, the submicron spherical gold powder preparation method of the present invention, by precisely controlling the type and dosage ratio of the first alkylamine and the second alkylamine and combining it with the precise control of the reducing agent drop acceleration rate, promotes the crystal growth along the isotropic direction, and finally forms a spherical structure with regular morphology, good dispersibility and excellent sintering activity, and successfully achieves the controllable preparation of submicron spherical gold powder with a particle size in the range of 0.1μm-1.5μm.

[0179] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for preparing submicron spherical gold powder, characterized by, The preparation method comprises the following steps: adding a first alkylamine, a first reducing agent and a chloroauric acid solution in a first aqueous medium to obtain a gold crystal nucleus solution; adding a second alkylamine in the gold crystal nucleus solution, and dropping a second reducing agent and the chloroauric acid solution to grow gold on the surface of the gold crystal nucleus to obtain a precipitate; carrying out post-treatment on the precipitate to obtain sub-micron spherical gold powder; wherein the number of carbon atoms in the alkyl chain of the first alkylamine is 14-18, and the number of carbon atoms in the alkyl chain of the second alkylamine is 10-18; the concentration of the first alkylamine solution is 1 mg / mL-4 mg / mL; the concentration of the second alkylamine solution is 0.1 mg / mL-1 mg / mL; the concentration of the chloroauric acid solution is 0.1 g / mL-1 g / mL; the mass ratio of the first alkylamine to gold in the chloroauric acid solution is (50-120):1; the mass ratio of the first reducing agent to gold in the chloroauric acid solution is (1-8):1; the mass ratio of the second alkylamine to gold in the chloroauric acid solution is (0.001-0.1):1; the mass ratio of the second reducing agent to gold in the chloroauric acid solution is (1-5):1; the first aqueous medium comprises deionized water; the dropping speed of the second reducing agent and the chloroauric acid solution is 10 mL / min-100 mL / min.

2. The method of claim 1, wherein the submicron spherical gold powder is prepared by the steps of: the first alkylamine comprises at least one of tetradecylamine, hexadecylamine and octadecylamine; and / or the second alkylamine comprises at least one of decylamine, dodecylamine, tetradecylamine, hexadecylamine and octadecylamine.

3. The method for preparing submicron spherical gold powder according to claim 1, characterized in that, the first reducing agent comprises at least one of ascorbic acid, hydrazine hydrate, hydrazine carbonate and sodium borohydride; and / or the second reducing agent comprises at least one of ascorbic acid, hydrazine hydrate, hydrazine carbonate and sodium borohydride.

4. The method for preparing submicron spherical gold powder according to claim 1, characterized in that, the concentration of the first reducing agent solution is 0.01 mg / mL-0.1 mg / mL; and / or the concentration of the second reducing agent solution is 0.1 g / mL-0.5 g / mL.

5. The method for preparing submicron spherical gold powder according to claim 1, characterized in that, The preparation of the chloroauric acid solution comprises: reacting a gold raw material with a mixed acid containing hydrochloric acid and nitric acid to dissolve to obtain a precursor solution; carrying out impurity removal treatment on the precursor solution to obtain the chloroauric acid solution.

6. The method for preparing submicron spherical gold powder according to claim 1, characterized in that, The post-treatment of the precipitate to obtain sub-micron spherical gold powder comprises: washing the precipitate to remove soluble impurities, and then drying to obtain the sub-micron spherical gold powder; wherein the washing comprises at least one water washing and at least one organic solvent washing.

7. A submicron spherical gold powder, characterized by, The sub-micron spherical gold powder prepared by the preparation method of any one of claims 1-6 has a particle size of 0.1 μm-1.5 μm, and is used in the fields of electronic packaging, thick film circuit, LTCC and 3D printing.

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