Method for preparing porous metal through direct reduction of metal oxide
A direct reduction method using metal oxides in an ammonia atmosphere simplifies the production of porous metals, addressing inefficiencies and high costs in existing methods, enabling efficient and cost-effective production with controllable pore structure and shape.
Patent Information
- Application Number
- CN202411403833.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-09
- Publication Date
- 2025-07-15
AI Technical Summary
The existing porous metal preparation methods are complicated and costly, involving the addition and removal of pore-forming agents or foaming agents, resulting in complex and high cost.
Using metal oxides as raw materials, reducing heat treatment is carried out under an ammonia atmosphere, pores are generated through nitriding and in-situ denitrition, and porous metals are directly prepared to avoid adding additional pore-forming agents or foaming agents, and simplifying the process flow.
It realizes simple, efficient and low-cost large-scale preparation of porous metals, with adjustable pore size and porosity, and the shape can be changed according to demand, expanding application scenarios.
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Figure CN120306641A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of preparation of porous metal materials, and specifically to a method for directly preparing porous metal by reducing metal oxides. Background Art
[0002] Porous metal, also known as metallic foam, has properties such as low specific gravity, large specific surface area, good permeability, high porosity, and stable shape. It has excellent properties such as filtration and separation, sound absorption, shock buffering, fluid distribution, electromagnetic shielding, electrical and thermal conductivity, and catalysis, and is widely used in automotive, aerospace, biomedical, catalyst carriers, electrochemistry, thermal energy storage, etc. [See the literature: Zheng Min, Yang Jin, Zhang Hua, Research Progress on the Preparation and Application of Porous Metal Materials, Materials Review, 2022, 36(18), 20110092; Cao Feng, Zhang Wenyan, Zhang Sisi, Yan Yangtian, Yang Ruifeng, Research Progress on Chemical Preparation Methods and Properties of Porous Metal Materials, Materials Review A: Review Articles, 2017, 31(11), 139 - 145.]. There are many methods for preparing porous metal. According to the physical state (solid, liquid, gas, or ionized state) of the metal when voids are generated during the processing of porous metal materials, various preparation processes are classified. The commonly used preparation methods for porous metal can be divided into three categories: one is the solid-phase method (mainly including powder sintering method, powder foaming method, and oxidation-reduction sintering method), the second is the liquid-phase method (mainly including infiltration casting method, melt foaming method, and solid-gas eutectic directional solidification method), and the third is the deposition method (mainly including electrolytic deposition method and vapor deposition method) [See the literature: Li Feifei, Zhang Fang, Preparation Methods and Applications of Porous Metal Materials, China Foundry Equipment & Technology, 2021, 56(1), 82 - 88.]. Although these existing methods have their own characteristics, they generally involve the addition and removal of pore-forming agents or foaming agents, resulting in a long process, complex operation, and high cost during the preparation process. Therefore, exploring new preparation methods with simple processes, high efficiency, and low cost has always been the research frontier in this field. Summary of the Invention
[0003] The purpose of the present invention is to provide a method for directly preparing porous metal by reducing metal oxides. Using metal oxides as the starting material, after pre-forming by die pressing, it is placed in a tubular furnace and directly prepared into the corresponding porous metal through reduction heat treatment in an ammonia atmosphere. It is a preparation method that is simple in process, high in efficiency, and free of impurity introduction, and can directly prepare porous metal on a large scale. Moreover, the shape of the porous metal maintains the shape of the pre-formed metal oxide pressing body and can be arbitrarily changed according to the requirements of the usage scenario.
[0004] The technical solution of the present invention is as follows:
[0005] A method for preparing porous metal by direct reduction of metal oxide uses metal oxide powder as the starting material. After being compacted and formed by a mold, it is placed in a tubular furnace and subjected to reduction heat treatment in an ammonia atmosphere to directly reduce the metal oxide into the corresponding porous metal. The metal oxide undergoes nitridation and in-situ denitrification to release nitrogen gas to generate pores. By controlling the reduction heat treatment temperature and time and the compaction tightness of the metal oxide, the pore size and porosity of the porous metal can be regulated.
[0006] In the method for preparing porous metal by direct reduction of metal oxide described above, the starting material is metal oxide powders with various different particle sizes, and the particle size is below 100 μm.
[0007] In the method for preparing porous metal by direct reduction of metal oxide described above, the ammonia atmosphere is ammonia or a mixed gas containing ammonia.
[0008] In the method for preparing porous metal by direct reduction of metal oxide described above, the heat treatment temperature in the ammonia atmosphere is between 200 and 1200 °C, and the heat treatment time is 15 min to 60 h.
[0009] In the method for preparing porous metal by direct reduction of metal oxide described above, first, it is treated at a lower temperature of 200 to 600 °C for 10 min to 30 h to carry out the nitridation reaction to convert into metal nitride, and then it is continuously heated to a higher temperature of 400 to 1200 °C and treated for 5 min to 30 h to carry out denitrification to generate nitrogen gas to form porous metal.
[0010] In the method for preparing porous metal by direct reduction of metal oxide described above, the metal oxide is one or more of the corresponding higher-valent or lower-valent oxides of the metal.
[0011] In the method for preparing porous metal by direct reduction of metal oxide described above, the appearance shape of the porous metal depends on the shape after pre-compaction and forming of the metal oxide powder, and the shape remains basically unchanged during the heat treatment process.
[0012] In the method for preparing porous metal by direct reduction of metal oxide described above, the pore size distribution range of the porous metal is 20 nm to 100 μm, and the porosity is 10 to 85%.
[0013] The design concept of the present invention is as follows:
[0014] At present, the common preparation methods of porous metals all involve the addition and removal of pore-forming agents or foaming agents, or require relatively harsh preparation conditions such as high-pressure dissolution of pore-forming gases in a high-temperature molten state, resulting in a complex preparation process, a long preparation process flow, and a high cost. The present invention only uses a simple heat treatment method in an ammonia atmosphere under normal pressure. Directly using metal oxide raw materials, without introducing external impurities such as pore-forming agents or foaming agents, only through a simple strategy of nitriding at a relatively low temperature and subsequent heating to decompose and release nitrogen to form pores, directly through a simple one-step heat treatment, realizes the efficient preparation of porous metals by reducing and converting metal oxides, providing an opportunity for simple, efficient, and low-cost preparation of porous metals.
[0015] The present invention conducts reduction heat treatment on metal oxide (MO) in a flowing ammonia atmosphere. First, it is heat-treated at a relatively low temperature (200 - 600 °C) for a nitriding reaction to convert it into metal nitride (MN). Subsequently, it is continuously heat-treated at a temperature higher than the nitriding temperature (400 - 1200 °C) for in-situ denitrification to decompose and release nitrogen to generate pores, thereby directly converting the metal oxide into the corresponding porous metal (M). The schematic formula of the reaction process is as follows:
[0016] NH3 + MO → MN + H2O (1)
[0017] MN → M + N2 (2)
[0018] It should be particularly noted that in addition to the ammonia atmosphere, other reducing gases (such as hydrogen, etc.) can reduce oxides to metals, but pores cannot be generated to form porous metals without adding pore-forming agents and heating to the molten state at the same time, further illustrating the novelty and uniqueness of the method of the present invention.
[0019] The advantages and beneficial effects of the present invention are:
[0020] 1. In the traditional redox preparation method reported in the literature, which uses metal oxides as raw materials, it is necessary to add a foaming agent (such as CaCO3, etc.) and a reducing agent (such as C or hydrogen, etc.) simultaneously and under high-temperature molten state to generate pores and reduce oxides to prepare porous metals [see the literature: Taichi Murakami, Kensuke Ohara, Takayuki Narushima and Chiaki Ouchi, Development of a new method for manufacturing iron foam using gases generated by reduction of iron oxide, Materials Transactions, 2007.48(11), 2937 - 2944; Taichi Murakami, Takuma Akagi, Eiki Kasai, Development of porous iron based material by slag foaming and its reduction, Procedia Materials Science, 2014, 4, 27 - 32.]. Different from this, the present invention only uses metal oxides as raw materials, does not add any additional pore-forming agents or foaming agents, does not introduce other additional impurities, and prepares porous metals through a one-step reduction heat treatment in an ammonia atmosphere. The preparation process is very simple and efficient, with low cost and easy large-scale production.
[0021] 2. The present invention directly uses metal oxide powders as raw materials, which are easy to obtain and inexpensive.
[0022] 3. The preparation method of the present invention has strong universality and is generally applicable to metal oxides that can undergo nitridation reactions to turn into metal nitrides under heat treatment in an ammonia atmosphere and then generate voids by heating and releasing nitrogen.
[0023] 4. The preparation method of the present invention only undergoes nitridation and in-situ denitrification to generate nitrogen through simple heat treatment, and then forms voids, which belongs to a solid-phase reaction process. Therefore, the pore size of the prepared porous metal can be changed by adjusting the heat treatment temperature and time as well as the pressing preforming tightness, and the parameter adjustment is simple and easy to operate.
[0024] 5. The shape of the porous metal prepared by the present invention depends on the shape of the metal oxide pressing preform and can be arbitrarily changed by changing the pressing mold, expanding the application scenarios of the porous metal.
[0025] In summary, the method provided by the present invention prepares porous metal by directly reducing and heat-treating metal oxides in an ammonia atmosphere in one step. It has the remarkable advantages of simple process steps, easy availability of raw materials, low cost, no pollution, and adjustable appearance shape. It can greatly simplify the preparation process of porous metal, improve efficiency, reduce the preparation cost, and promote the value of the preparation and application fields of porous metal. Description of the Drawings
[0026] Figure 1 . Optical photograph after pressing and forming with copper oxide powder as the raw material.
[0027] Figure 2 . XRD pattern of the porous copper prepared by pressing and forming with copper oxide as the raw material and then reducing and heat-treating in an ammonia atmosphere at 600 °C for 3 hours; wherein, the abscissa is the diffraction angle 2θ, with the unit of degree; the ordinate is the diffraction peak intensity, in arbitrary unit.
[0028] Figure 3 . Optical photograph of the porous copper prepared by pressing and forming with copper oxide as the raw material and then reducing and heat-treating in an ammonia atmosphere at 600 °C for 3 hours.
[0029] Figure 4 . SEM photograph of the porous copper prepared by pressing and forming with copper oxide as the raw material and then reducing and heat-treating in an ammonia atmosphere at 600 °C for 3 hours.
[0030] Figure 5 . SEM photograph of the porous copper prepared by pressing and forming with copper oxide as the raw material and then reducing and heat-treating in a hydrogen atmosphere at 600 °C for 3 hours.
[0031] Figure 6 . SEM photograph of the porous copper prepared by pressing and forming with copper oxide as the raw material and then reducing and heat-treating in an ammonia atmosphere at 400 °C for 1 hour.
[0032] Figure 7 . SEM photograph of the porous iron-based material prepared by pressing and forming with iron oxide as the raw material and then reducing and heat-treating in an ammonia atmosphere at 800 °C for 4 hours. Detailed Embodiments
[0033] In the specific implementation process, the present invention provides a method for preparing porous metal. Starting from metal oxide powder, after pre-forming by die pressing (pressure above 1 MPa), it is placed in a tubular furnace for reduction heat treatment in a flowing ammonia atmosphere. The metal oxide undergoes nitridation and in-situ denitrification to release nitrogen gas to generate pores, and the metal oxide is directly converted into the corresponding porous metal. By changing the reduction heat treatment temperature and time and the compaction tightness, the pore size and porosity can be regulated. Specifically, it is characterized in that:
[0034] 1. The starting material is metal oxide powders with various particle sizes below 100 μm.
[0035] 2. The heat treatment atmosphere is an ammonia-containing atmosphere, which is ammonia or a mixed gas containing ammonia. The flow rate of the ammonia atmosphere is above 100 sccm. In the mixed gas containing ammonia, the ammonia content is 60 - 90 vol%, and the rest can be gases such as argon or nitrogen.
[0036] 3. The appearance shape of the porous metal depends on the shape of the pre-pressed metal oxide, such as sheets, blocks, and various other special-shaped forms. The forming die can be arbitrarily changed according to the actual usage scenario requirements.
[0037] 4. The heat treatment temperature is between 200 - 1200 °C, and the heat treatment time is 15 min - 60 h.
[0038] In the present invention, nitridation is first carried out at a lower temperature of 200 - 600 °C for 10 min - 30 h (preferably 1 h - 10 h), and then the temperature is continuously increased to a higher temperature of 400 - 1200 °C for 5 min - 30 h (preferably 1 h - 10 h) for denitrification to generate nitrogen to form porous metal.
[0039] 5. The metal oxide is one or more of the corresponding higher-valent or lower-valent oxides of the metal.
[0040] 6. The pore size distribution range of the porous metal is 20 nm - 100 μm, and the porosity is 10 - 85%.
[0041] Next, the present invention will be further described in detail with reference to the examples and the drawings.
[0042] Example 1
[0043] In this example, copper oxide powder is used as the raw material. The particle size of the copper oxide is about 1 μm. An appropriate amount of powder is weighed and pressed into a circular sheet (pressure: 2 MPa, time: 3 min) using a circular die. The size of the circular sheet is Φ10 mm. It is placed in a tube furnace and subjected to reduction heat treatment in a flowing ammonia atmosphere. The flow rate of ammonia is 300 sccm. Nitridation is first carried out at a lower temperature of 300 °C for 3 h, and then the temperature is continuously increased to 600 °C for 3 h for denitrification to generate nitrogen to form porous copper.
[0044] As Figure 1 shown, the optical photograph of the circular sheet after pressing the copper oxide powder, and the color is the dark gray of copper oxide; as Figure 2 shown, the XRD pattern of the porous copper formed after subjecting the pressed circular sheet to nitridation and denitrification reactions in an ammonia atmosphere in a tube furnace, and the results show that all the copper oxide is reduced and transformed into metallic copper; as Figure 3As shown, the optical photograph of the formed porous copper maintains the appearance shape and size of the compacted body, and its color changes from the dark gray of copper oxide to the red of metallic copper, which is consistent with Figure 2 the XRD results; as Figure 4 shown, the SEM photograph of the prepared porous metallic copper shows that the pore size is about 5 - 20 μm and the porosity is about 75%; as Figure 5 shown, the SEM photograph of the copper oxide compact disc after the same heat treatment in a reducing hydrogen atmosphere. Although the copper oxide is reduced to metallic copper, porous copper cannot be formed, which is also consistent with the literature reports that when using oxides as raw materials, a foaming agent and a reducing agent must be added simultaneously to prepare porous copper. This further clearly demonstrates the necessity and novelty of the preparation method of the present invention using an ammonia atmosphere for nitridation and nitrogen removal to form pores.
[0045] Example 2
[0046] In this example, copper oxide powder is used as the raw material. The particle size of the copper oxide is about 1 μm. An appropriate amount of powder is weighed and pressed (pressure: 5 MPa, time: 5 min) into a disc using a circular mold. The size of the disc is Φ10 mm. It is placed in a tubular furnace and subjected to reduction heat treatment in a flowing ammonia atmosphere. The flow rate of ammonia is 300 sccm. First, it is treated at a lower temperature of 300 °C for 2 h for nitridation, and then heated to 400 °C and treated for 1 h for nitrogen removal to generate nitrogen to form porous metallic copper. As Figure 6 shown, the SEM photograph of the prepared porous metallic copper shows that the pore size is about 5 - 10 μm and the porosity is about 23%, indicating that the pore size and porosity of the prepared porous copper can be regulated by changing the heat treatment temperature and time.
[0047] Example 3
[0048] In this example, iron oxide powder is used as the raw material. The particle size of the copper oxide is about 1 μm. An appropriate amount of powder is weighed and pressed (pressure: 5 MPa, time: 5 min) into a disc using a circular mold. The size of the disc is Φ10 mm. It is placed in a tubular furnace and subjected to reduction heat treatment in a flowing ammonia atmosphere. The flow rate of ammonia is 300 sccm. First, it is treated at a lower temperature of 300 °C for 4 h for nitridation, and then heated to 800 °C and treated for 4 h for nitrogen removal to generate nitrogen to form porous metallic iron. As Figure 7 shown, the SEM photograph of the prepared porous metallic iron shows that the pore size is about 2 - 10 μm and the porosity is about 67%, indicating that the method of the present invention can prepare different types of porous metals, demonstrating the universality of the method of the present invention.
[0049] In summary, the results of the above embodiments show that the present invention uses only metal oxides as raw materials to carry out the nitridation and denitridation processes through simple heat treatment in an ammonia atmosphere, directly reducing and converting the metal oxides into porous metal foams. Moreover, by controlling the heat treatment temperature, time, and the degree of compaction and molding, the pore size and porosity of the porous copper can be changed, effectively regulating the pore structure of the porous metal. The method of the present invention does not introduce additional impurities, has a simple process, and low cost, which will strongly promote the efficient, low-cost preparation and wide application of porous metals.
Claims
1. A method for preparing porous metal by direct reduction of metal oxide, characterized in that, Using metal oxide powder as the starting material, after being compacted and formed by a mold, it is placed in a tubular furnace and subjected to reduction heat treatment in an ammonia atmosphere to directly reduce the metal oxide into the corresponding porous metal. The metal oxide undergoes nitridation and in-situ denitrification to release nitrogen gas to generate pores. By controlling the reduction heat treatment temperature and time, as well as the compaction density of the metal oxide, the pore size and porosity of the porous metal are regulated.
2. The method for preparing porous metal by direct reduction of metal oxide according to claim 1, characterized in that, The starting material is metal oxide powders with various different particle sizes, and the particle size is below 100 μm.
3. The method for preparing porous metal by direct reduction of metal oxide according to claim 1, characterized in that, The ammonia atmosphere is ammonia or a mixed gas containing ammonia.
4. The method for preparing porous metal by direct reduction of metal oxide according to claim 1, characterized in that, The heat treatment temperature in the ammonia atmosphere is between 200 and 1200 °C, and the heat treatment time is 15 min to 60 h.
5. The method for preparing porous metal by direct reduction of metal oxide according to claim 4, characterized in that, First, it is treated at a lower temperature of 200 to 600 °C for 10 min to 30 h for the nitridation reaction to convert into metal nitride, and then it is continuously heated to a higher temperature of 400 to 1200 °C for 5 min to 30 h for denitrification to generate nitrogen gas to form porous metal.
6. The method for preparing porous metal by direct reduction of metal oxide according to claim 1, characterized in that, The metal oxide is one or more of the corresponding higher-valent or lower-valent oxides of the metal.
7. The method for preparing porous metal by direct reduction of metal oxide according to claim 1, characterized in that, The appearance shape of the porous metal depends on the shape after the pre-compaction and forming of the metal oxide powder, and the shape remains basically unchanged during the heat treatment process.
8. The method for preparing porous metal by direct reduction of metal oxide according to claim 1, characterized in that, The pore size distribution range of the porous metal is 20 nm to 100 μm, and the porosity is 10 to 85%.