Method for preparing superfine nickel powder by using glycine-methylhydrazine mixed fuel

Abstract

The application provides a method for preparing superfine nickel powder by using glycine-hexamethylene tetramine mixed fuel, which comprises the following steps: mixing a nickel nitrate solution with a mixed fuel to obtain a precursor solution; heating and stirring the precursor solution to evaporate water and form a gel; performing self-sustaining oxidation-reduction combustion on the gel in an oxygen-containing atmosphere; cooling the combustion product to room temperature to obtain superfine nickel powder with a primary average particle size of less than or equal to 150 nm; and the composition of the mixed fuel comprises glycine and hexamethylene tetramine. The application utilizes the functional complementation of the two types of fuel decomposition temperature windows and reducing species to construct a staged synergistic reduction mechanism, realizes the partial decoupling of combustion heating and reducing atmosphere, and can quickly prepare superfine nickel powder with a purity of greater than or equal to 99 wt%, a primary average particle size of less than or equal to 150 nm and a residual carbon content of less than or equal to 0.3 wt% in an air atmosphere, thereby solving the problem that high purity and fine particle size are difficult to achieve in a single fuel system.

Description

Technical Field

[0001] This invention belongs to the field of nickel powder preparation technology, and relates to a method for preparing ultrafine nickel powder, particularly a method for preparing ultrafine nickel powder from a glycine-hexamethylenetetramine mixed fuel. Background Technology

[0002] Solution Combustion Synthesis (SCS) technology uses metal nitrates as oxidants and organic fuels as reducing agents to rapidly prepare metal or metal oxide powders through a self-sustaining redox reaction. It boasts advantages such as simple process, rapid reaction, uniform products, and low energy consumption, making it a crucial technological direction in the preparation of ultrafine metal powders. In the SCS process, the organic fuel simultaneously serves the dual functions of providing combustion heat to sustain the reaction and thermally decomposing to release reducing species, thus achieving metal reduction. The thermal decomposition characteristics of the fuel directly determine the evolution of the combustion temperature field and reducing atmosphere, ultimately affecting the phase purity and grain size of the product.

[0003] Existing technologies for preparing nickel powder using SCS (sulfuric acid sulfide) generally employ a single organic fuel system, such as glycine, urea, or citric acid. However, the two main functions of heating and reduction are highly coupled and cannot be independently controlled. Increasing the fuel dosage can enhance the reduction capacity and improve the purity of the metallic phase, but it also increases the peak combustion temperature and exacerbates grain sintering and growth. Conversely, reducing the fuel dosage to control grain size leads to insufficient reducing atmosphere, resulting in a large amount of residual nickel oxide in the product. This contradiction makes it difficult for a single fuel system to simultaneously meet the requirements of high purity and ultrafine powder preparation. Furthermore, the decomposition temperature window of a single fuel is fixed, and the heat release curve and the reduction species release curve highly overlap in time. This prevents the achievement of sufficient heating to form a large number of nucleation sites first, followed by continuous hydrogen supply to ensure complete oxide conversion, thus limiting the optimization space for product performance.

[0004] Besides combustion synthesis, existing ultrafine nickel powder preparation methods include sol-gel combined high-temperature calcination and other processes. However, these processes rely on prolonged external heating, typically requiring the introduction of a protective or reducing atmosphere. They suffer from drawbacks such as long reaction cycles, high energy consumption, and demanding equipment requirements, making low-cost, large-scale preparation difficult. Therefore, developing novel fuel systems that overcome the technical bottleneck of the trade-off between purity and particle size in single-fuel SCS systems, while retaining the advantages of efficient and simple combustion synthesis processes, is a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing ultrafine nickel powder from glycine-hexamethylenetetramine mixed fuel. This method utilizes the complementary functions of the decomposition temperature windows and reducing species of the two types of fuels to construct a staged synergistic reduction mechanism, achieving partial decoupling between combustion heating and the reducing atmosphere. It can rapidly prepare ultrafine nickel powder with a purity ≥99wt%, a primary average particle size ≤150nm, and a residual carbon content ≤0.3wt% under an air atmosphere, solving the problem of achieving both high purity and fine particle size in a single fuel system.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a method for preparing ultrafine nickel powder from a glycine-hexamethylenetetramine mixed fuel, the method comprising:

[0008] A nickel nitrate solution is mixed with a mixed fuel to obtain a precursor solution; the precursor solution is heated and stirred to evaporate water and form a gel; the gel is subjected to self-sustaining redox combustion in an oxygen-containing atmosphere, and the combustion products are cooled to room temperature to obtain ultrafine nickel powder with a primary average particle size ≤150nm.

[0009] The blended fuel comprises glycine and hexamethylenetetramine.

[0010] This invention utilizes a mixed fuel system composed of glycine and hexamethylenetetramine, leveraging the differences in decomposition characteristics and reducing capabilities of the two fuels to achieve functional decoupling of combustion heating and reducing atmosphere. Glycine decomposes over a wide temperature range with gradual heat release, while hexamethylenetetramine decomposes with concentrated heat release. Their synergy effectively controls the peak shape of the combustion temperature curve, suppresses grain coarsening caused by localized overheating, and maintains the primary average particle size of the product stably below 150 nm. Simultaneously, the NH3 produced by glycine pyrolysis and the N2H4 and CH4 produced by hexamethylenetetramine pyrolysis form a composite reducing atmosphere, achieving phased synergy between initial and deep reduction during combustion. This ensures the full conversion of nickel oxides, yielding high-purity ultrafine nickel powder. This method can be implemented in an oxygen-containing atmosphere, is rapid, energy-efficient, requires no complex post-processing, uses readily available and inexpensive raw materials, and is simple and efficient, demonstrating excellent versatility and potential for large-scale application.

[0011] In some embodiments, the molar ratio of glycine to hexamethylenetetramine in the blended fuel is 1:3 to 3:1.

[0012] In some embodiments, the concentration of the nickel nitrate solution is 0.1 mol / L to 0.5 mol / L.

[0013] In some embodiments, the molar ratio of the mixed fuel to nickel nitrate in the nickel nitrate solution is 1.25:1 to 2.5:1.

[0014] In some embodiments, the heating and stirring temperature is 60°C to 80°C.

[0015] In some embodiments, the solid content of the gel is 60wt% to 70wt%.

[0016] In some embodiments, the temperature of the self-sustaining redox combustion is 350°C to 450°C.

[0017] In some embodiments, the self-sustaining redox combustion time is 2 min to 5 min.

[0018] In some embodiments, the method further includes: the ultrafine nickel powder having a purity ≥99wt%, a primary average particle size ≤150nm, and a residual carbon content ≤0.3wt%.

[0019] In some embodiments, the method includes the following steps:

[0020] S1. Mix a nickel nitrate solution with a concentration of 0.1 mol / L to 0.5 mol / L with a mixed fuel to obtain a precursor solution;

[0021] The mixed fuel comprises glycine and hexamethylenetetramine in a molar ratio of 1:3 to 3:1;

[0022] The molar ratio of the mixed fuel to nickel nitrate in the nickel nitrate solution is 1.25:1 to 2.5:1;

[0023] S2. The precursor solution is heated and stirred at a temperature of 60℃~80℃ to evaporate water and form a gel with a solid content of 60wt%~70wt%.

[0024] S3. In an oxygen-containing atmosphere, the gel is heated to 350℃~450℃ to initiate self-sustaining redox combustion for 2min~5min. The combustion product is cooled to room temperature to obtain ultrafine nickel powder with a purity ≥99wt%, a primary average particle size ≤150nm, and a residual carbon content ≤0.3wt%.

[0025] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention utilizes a mixed fuel system composed of glycine and hexamethylenetetramine, leveraging the differences in decomposition characteristics and reducing capabilities of the two fuels to achieve functional decoupling of combustion heating and reducing atmosphere. Glycine decomposes over a wide temperature range with gradual heat release, while hexamethylenetetramine decomposes with concentrated heat release. Their synergy effectively controls the peak shape of the combustion temperature curve, suppresses grain coarsening caused by localized overheating, and maintains the primary average particle size of the product stably below 150 nm. Simultaneously, the NH3 produced by glycine pyrolysis and the N2H4 and CH4 produced by hexamethylenetetramine pyrolysis form a composite reducing atmosphere, achieving phased synergy between initial and deep reduction during combustion. This ensures the full conversion of nickel oxides, yielding high-purity ultrafine nickel powder. This method can be implemented in an oxygen-containing atmosphere, is rapid, energy-efficient, requires no complex post-processing, uses readily available and inexpensive raw materials, and is simple and efficient, demonstrating excellent versatility and potential for large-scale application. Detailed Implementation

[0028] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0029] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0030] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0031] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0032] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation 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 mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0033] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0034] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0035] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0036] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0037] This invention provides a method for preparing ultrafine nickel powder from a glycine-hexamethylenetetramine mixed fuel, the method comprising:

[0038] A nickel nitrate solution is mixed with a mixed fuel to obtain a precursor solution; the precursor solution is heated and stirred to evaporate water and form a gel; the gel is subjected to self-sustaining redox combustion in an oxygen-containing atmosphere, and the combustion products are cooled to room temperature to obtain ultrafine nickel powder with a primary average particle size ≤150nm.

[0039] The blended fuel comprises glycine and hexamethylenetetramine.

[0040] This invention utilizes a mixed fuel system composed of glycine and hexamethylenetetramine, leveraging the differences in decomposition characteristics and reducing capabilities of the two fuels to achieve functional decoupling of combustion heating and reducing atmosphere. Glycine decomposes over a wide temperature range with gradual heat release, while hexamethylenetetramine decomposes with concentrated heat release. Their synergy effectively controls the peak shape of the combustion temperature curve, suppresses grain coarsening caused by localized overheating, and maintains the primary average particle size of the product stably below 150 nm. Simultaneously, the NH3 produced by glycine pyrolysis and the N2H4 and CH4 produced by hexamethylenetetramine pyrolysis form a composite reducing atmosphere, achieving phased synergy between initial and deep reduction during combustion. This ensures the full conversion of nickel oxides, yielding high-purity ultrafine nickel powder. This method can be implemented in an oxygen-containing atmosphere, is rapid, energy-efficient, requires no complex post-processing, uses readily available and inexpensive raw materials, and is simple and efficient, demonstrating excellent versatility and potential for large-scale application.

[0041] In some embodiments, the molar ratio of glycine to hexamethylenetetramine in the blended fuel is 1:3 to 3:1, for example, it can be 1:3, 2:3, 3:3, 3:2 or 3:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] In some embodiments, the concentration of the nickel nitrate solution is 0.1 mol / L to 0.5 mol / L, for example, it can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L or 0.5 mol / L, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] In some embodiments, the molar ratio of the mixed fuel to nickel nitrate in the nickel nitrate solution is 1.25:1 to 2.5:1, for example, it can be 1.25:1, 1.5:1, 1.8:1, 2:1, 2.1:1, 2.4:1 or 2.5:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] In some embodiments, the heating and stirring temperature is 60°C to 80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] In some embodiments, the solid content of the gel is 60wt% to 70wt%, for example, it can be 60wt%, 62wt%, 64wt%, 65wt%, 66wt%, 68wt% or 70wt%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] In some embodiments, the temperature of the self-sustaining redox combustion is 350°C to 450°C, for example, it can be 350°C, 360°C, 380°C, 400°C, 420°C, 440°C or 450°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] In some embodiments, the self-sustaining redox combustion time is 2 min to 5 min, for example, it can be 2 min, 3 min, 4 min or 5 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] In some embodiments, the method further includes: the ultrafine nickel powder having a purity ≥99wt%, a primary average particle size ≤150nm, and a residual carbon content ≤0.3wt%.

[0049] As a preferred embodiment of the method provided by the present invention, the method includes the following steps:

[0050] S1. Mix a nickel nitrate solution with a concentration of 0.1 mol / L to 0.5 mol / L with a mixed fuel to obtain a precursor solution;

[0051] The mixed fuel comprises glycine and hexamethylenetetramine in a molar ratio of 1:3 to 3:1;

[0052] The molar ratio of the mixed fuel to nickel nitrate in the nickel nitrate solution is 1.25:1 to 2.5:1;

[0053] S2. The precursor solution is heated and stirred at a temperature of 60℃~80℃ to evaporate water and form a gel with a solid content of 60wt%~70wt%.

[0054] S3. In an oxygen-containing atmosphere, the gel is heated to 350℃~450℃ to initiate self-sustaining redox combustion for 2min~5min. The combustion product is cooled to room temperature to obtain ultrafine nickel powder with a purity ≥99wt%, a primary average particle size ≤150nm, and a residual carbon content ≤0.3wt%.

[0055] Example 1

[0056] This embodiment provides a method for preparing ultrafine nickel powder from a glycine-hexamethylenetetramine mixed fuel, including:

[0057] S1. A nickel nitrate solution with a concentration of 0.3 mol / L is mixed with a mixed fuel to obtain a precursor solution;

[0058] The blended fuel comprises glycine and hexamethylenetetramine in a molar ratio of 1:1;

[0059] The molar ratio of the mixed fuel to the nickel nitrate in the nickel nitrate solution is 2:1;

[0060] S2. The precursor solution is heated and stirred at a temperature of 70°C to evaporate water and form a gel with a solid content of 65wt%.

[0061] S3. In an air atmosphere, the gel is heated to 400°C to initiate self-sustaining redox combustion for 4 minutes. The combustion product is then cooled to room temperature to obtain ultrafine nickel powder.

[0062] Example 2

[0063] This embodiment provides a method for preparing ultrafine nickel powder from a glycine-hexamethylenetetramine mixed fuel, including:

[0064] S1. A nickel nitrate solution with a concentration of 0.1 mol / L is mixed with a mixed fuel to obtain a precursor solution;

[0065] The blended fuel comprises glycine and hexamethylenetetramine in a molar ratio of 1:3;

[0066] The molar ratio of the mixed fuel to the nickel nitrate in the nickel nitrate solution is 1.25:1;

[0067] S2. The precursor solution is heated and stirred at a temperature of 60°C to evaporate water and form a gel with a solid content of 60wt%.

[0068] S3. In an air atmosphere, the gel is heated to 350°C to initiate self-sustaining redox combustion for 5 minutes. The combustion product is then cooled to room temperature to obtain ultrafine nickel powder.

[0069] Example 3

[0070] This embodiment provides a method for preparing ultrafine nickel powder from a glycine-hexamethylenetetramine mixed fuel, including:

[0071] S1. A nickel nitrate solution with a concentration of 0.5 mol / L is mixed with a mixed fuel to obtain a precursor solution;

[0072] The blended fuel comprises glycine and hexamethylenetetramine in a molar ratio of 3:1;

[0073] The molar ratio of the mixed fuel to the nickel nitrate in the nickel nitrate solution is 2.5:1;

[0074] S2. The precursor solution is heated and stirred at a temperature of 60°C to evaporate water and form a gel with a solid content of 70wt%.

[0075] S3. In an air atmosphere, the gel is heated to 450°C to initiate self-sustaining redox combustion for 2 minutes. The combustion product is then cooled to room temperature to obtain ultrafine nickel powder.

[0076] Example 4

[0077] This embodiment provides a method for preparing ultrafine nickel powder from glycine-hexamethylenetetramine mixed fuel. Except for the molar ratio of glycine to hexamethylenetetramine being 0.5:3, all other aspects are the same as in Example 1.

[0078] Example 5

[0079] This embodiment provides a method for preparing ultrafine nickel powder from glycine-hexamethylenetetramine mixed fuel. Except for the molar ratio of glycine to hexamethylenetetramine being 4:1, the rest is the same as in Example 1.

[0080] Example 6

[0081] This embodiment provides a method for preparing ultrafine nickel powder from glycine-hexamethylenetetramine mixed fuel. Except that the molar ratio of the mixed fuel to nickel nitrate in the nickel nitrate solution is 1:1, everything else is the same as in Example 1.

[0082] Example 7

[0083] This embodiment provides a method for preparing ultrafine nickel powder from glycine-hexamethylenetetramine mixed fuel. Except for the molar ratio of the mixed fuel to nickel nitrate in the nickel nitrate solution being 3:1, all other aspects are the same as in Example 1.

[0084] Comparative Example 1

[0085] This comparative example provides a method for producing ultrafine nickel powder, which is the same as in Example 1 except that glycine is replaced with hexamethylenetetramine in equal molar amounts.

[0086] Comparative Example 2

[0087] This comparative example provides a method for producing ultrafine nickel powder, which is the same as in Example 1 except that hexamethylenetetramine is replaced with glycine in equal molar amounts.

[0088] Performance Characterization

[0089] The primary average particle size, purity, and residual carbon content of the ultrafine nickel powder obtained in the above examples and comparative examples were measured, and the results are shown in Table 1.

[0090] The phase composition was analyzed by X-ray diffraction (XRD) to calculate the content (purity) of the nickel phase; the morphology of the product was observed by scanning electron microscopy (SEM), and the size of 300 particles was counted and the average value was taken as the primary average particle size; the residual carbon content of the product was determined by carbon-sulfur analyzer.

[0091] Table 1

[0092]

[0093] As can be seen from Examples 1 to 3 in Table 1, the glycine-hexamethylenetetramine mixed fuel preparation method provided by the present invention can obtain ultrafine nickel powder with a purity ≥99wt%, a primary average particle size ≤150nm, and a residual carbon content ≤0.3wt%.

[0094] A comparison of Examples 4 and 5 with Example 1 shows that when the molar ratio of glycine to hexamethylenetetramine deviates from the preferred range of 1:3 to 3:1, the purity of the product decreases significantly or the particle size increases. This is because when the proportion of glycine is too low, the NH3 produced by its pyrolysis is insufficient, the initial reducing ability is weakened, and some NiO does not convert to metallic nickel in time before sintering, resulting in a decrease in purity. At the same time, the relative proportion of hexamethylenetetramine increases, and its characteristics of concentrated decomposition and intense heat release cause the peak combustion temperature to rise, resulting in the sintering and growth of grains in the high-temperature zone and an increase in the primary average particle size. When the proportion of glycine is too high, the high-temperature enhanced reducing effect of hexamethylenetetramine is weakened, and the combustion temperature curve tends to be flat and uniform, the heat release characteristics degenerate to a single fuel system, and the effect of controlling grain growth is weakened.

[0095] A comparison of Examples 6 and 7 with Example 1 shows that the molar ratio of the mixed fuel to nickel nitrate needs to be controlled within an appropriate range to balance product purity and particle size control. When the molar ratio is too low, the total amount of fuel is insufficient to provide a sufficient reducing atmosphere, resulting in incomplete NiO conversion and a significant decrease in purity. When the molar ratio is too high, excessive fuel causes excessively high combustion temperature and excessive heat release, which exacerbates grain coarsening and leads to an excessively high primary average particle size.

[0096] A comparison of Comparative Examples 1 and 2 with Example 1 shows that a single fuel system cannot simultaneously achieve high purity and fine particle size. When only hexamethylenetetramine is used, its decomposition temperature is concentrated and the heat release is intense. Although it can provide a strong reducing atmosphere, it leads to severe grain coarsening. When only glycine is used, its reducing ability is relatively weak, and the purity of the product does not meet the requirements.

[0097] In summary, this invention utilizes a mixed fuel system composed of glycine and hexamethylenetetramine, leveraging the differences in their decomposition characteristics and reducing capabilities to achieve functional decoupling between combustion heating and the reducing atmosphere. Glycine decomposes over a wide temperature range with gradual heat release, while hexamethylenetetramine decomposes with concentrated heat release. Their synergy effectively controls the peak shape of the combustion temperature curve, suppresses grain coarsening caused by localized overheating, and maintains the primary average particle size of the product stably below 150 nm. Simultaneously, the NH3 produced by glycine pyrolysis and the N2H4 and CH4 produced by hexamethylenetetramine pyrolysis form a composite reducing atmosphere, achieving phased synergy between initial and deep reduction during combustion. This ensures the full conversion of nickel oxides, yielding high-purity ultrafine nickel powder. This method can be implemented in an oxygen-containing atmosphere, is rapid, energy-efficient, requires no complex post-processing, uses readily available and inexpensive raw materials, and is simple and efficient, demonstrating excellent versatility and potential for large-scale application.

[0098] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing ultrafine nickel powder from a glycine-hexamethylenetetramine mixed fuel, characterized in that, The method includes: A nickel nitrate solution is mixed with a mixed fuel to obtain a precursor solution; the precursor solution is heated and stirred to evaporate water and form a gel; the gel is subjected to self-sustaining redox combustion in an oxygen-containing atmosphere, and the combustion products are cooled to room temperature to obtain ultrafine nickel powder with a primary average particle size ≤150nm. The blended fuel comprises glycine and hexamethylenetetramine.

2. The method according to claim 1, characterized in that, In the blended fuel, the molar ratio of glycine to hexamethylenetetramine is 1:3 to 3:

1.

3. The method according to claim 1, characterized in that, The concentration of nickel nitrate solution is 0.1 mol / L to 0.5 mol / L.

4. The method according to claim 2 or 3, characterized in that, The molar ratio of the mixed fuel to nickel nitrate in the nickel nitrate solution is 1.25:1 to 2.5:

1.

5. The method according to claim 1, characterized in that, The heating and stirring temperature is 60℃~80℃.

6. The method according to claim 5, characterized in that, The solid content of the gel is 60wt%~70wt%.

7. The method according to claim 1, characterized in that, The temperature of the self-sustaining redox combustion is 350℃~450℃.

8. The method according to claim 7, characterized in that, The self-sustaining redox combustion time is 2 min to 5 min.

9. The method according to claim 1, characterized in that, The method further includes: the ultrafine nickel powder has a purity of ≥99wt%, a primary average particle size of ≤150nm, and a residual carbon content of ≤0.3wt%.

10. The method according to claim 1, characterized in that, The method includes the following steps: S1. Mix a nickel nitrate solution with a concentration of 0.1 mol / L to 0.5 mol / L with a mixed fuel to obtain a precursor solution; The mixed fuel comprises glycine and hexamethylenetetramine in a molar ratio of 1:3 to 3:1; The molar ratio of the mixed fuel to nickel nitrate in the nickel nitrate solution is 1.25:1 to 2.5:1; S2. The precursor solution is heated and stirred at a temperature of 60℃~80℃ to evaporate water and form a gel with a solid content of 60wt%~70wt%. S3. In an oxygen-containing atmosphere, the gel is heated to 350℃~450℃ to initiate self-sustaining redox combustion for 2min~5min. The combustion product is cooled to room temperature to obtain ultrafine nickel powder with a purity ≥99wt%, a primary average particle size ≤150nm, and a residual carbon content ≤0.3wt%.

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