In the field of modern magnet manufacturing, the efficiency and performance of NdFeB (neodymium iron boron) magnets are self-evident. The reason for the strong magnetic field of neodymium magnets is not only its raw materials, but also the manufacturing process. The powder making process is very important. Traditional powder metallurgy methods have certain limitations in terms of efficiency, material properties and environmental issues.
Hydrogen explosion is a technology that uses hydrogen to decompose rare earth metal alloys as a means to enhance refining and final products in magnet manufacturing. Hydrogen explosion does not affect the quality of raw materials and can improve the particle size of magnetic powders. Today, I will take you to take a look at the principle of hydrogen explosion and its advantages over traditional powder metallurgy.
Hydrogen Decrepitation During Neodymium Magnet Production
Hydrogen Decrepitation (HD) plays an important role in the production of NdFeB magnets, especially in the production of high-performance magnets for electric motors, wind turbines and various electronic applications. This step involves the introduction of hydrogen into the rare earth alloy (neodymium-rich phase and Nd2Fe14B grain matrix) to produce a series of physical changes. By producing the fine powder necessary for subsequent magnet manufacturing steps, the material and production methods are simplified.
The process begins by subjecting the solid NdFeB alloy to a hydrogen-rich environment at temperatures between 25-400 °C. As hydrogen diffuses into the metal lattice, when the volume change (ΔV) at the grain boundaries is 3 times the grain change, the lattice strain causes the magnet to burst and form microcracks. These cracks reduce the structural integrity of the alloy, making it brittle and easily broken into fine powders (particle sizes can reach the 6-600 μm range after hydrogenation). The generation of these fine powders is critical to the subsequent jet milling and jet milling processes that are essential to refine the material to the particle size required for efficient magnet production.
In addition, performing the Hydrogen Decrepitation process on NdFeB alloy does not simply decompose the material into fine powder. The brittleness of the material after hydrogenation helps improve the efficiency of the subsequent pressing process. Because by promoting hydrogen decomposition, the energy required for subsequent mechanical processes can be effectively reduced, thereby improving the overall sustainability and cost-effectiveness of NdFeB magnet manufacturing. Compared with traditional powder metallurgy, this process greatly reduces material waste and can reduce production costs by 25% (Cited from ACS). Also, from an environmental perspective: Hydrogen Decrepitation is a more environmentally friendly alternative, as traditional methods often involve high energy consumption and produce large amounts of waste.
Hydrogen Decrepitation vs Traditional Powder Metallurgy
HD (Hydrogen Decrepitation) and PM (Powder Metallurgy) are also techniques with different methodologies and material applications used in metal powder manufacturing. Whereas hydrogen decrepitation employs hydrogen absorption to generate fractured metal powders, powder metallurgy (PM) generally harnesses methods such as grinding and crushing to produce powders. Thus, a fundamental difference between these processes lies in the mechanism by which the powder used to create the final magnets is produced.
Traditional Powder Metallurgy (PM):
A conventional method for magnet manufacturing uses Powder Metallurgy (PM) which encompasses grinding and crushing techniques. One such method is to crush solid metals into powdery substances, which perform a pivotal role in the process of high-performance magnetic materials. Despite the frequent mention of atomization in PM, it is not typically applied to magnetic powders. Process techniques are primarily chosen for the production of magnets, as these techniques lead to materials with a defined particle size and homogeneity suitable for the magnet production process. As far as we know, PM can cover a wide variety of materials, even ferrous alloys, which are critical to the construction of permanent magnets. This adaptability allows PM to be well optimized for large-scale magnet manufacturing, particularly for growing sectors, such as automotive, electronics and renewable energy.
While both Hydrogen Decrepitation and Powder Metallurgy can be used for the same goal of producing permanent magnetic powders, there are clear differences in results and applications as well as material suitability.
Process Differences
Hydrogen Decrepitation (HD) makes metals such as iron or steel brittle at high temperatures with hydrogen gas, causing them to break into fine pieces. This process generates powders with a controlled particle size distribution that may be necessary to obtain magnets with specific magnetic properties. It focuses on hydrogen absorption causing fragmentation of the metal which can then be collected and purified. This approach is useful to achieve controlled and fine grains, especially for applications in magnet production.
Unlike The Traditional Powder Metallurgy (PM) method for magnet production, which involves grinding or crushing metals into powders. These methods are excellent for producing magnetic powders, considering both specific particle size distribution and specific composition of magnetic materials, and they can be optimized to produce powders that meet the demanding requirements associated with magnet production. PM process is flexible enough to make magnets with the different necessary properties.
Material Suitability
Hydrogen Decrepitation is mainly suitable for metals which are absorptive to hydrogen without losing crystalline structure i.e. for ferrous alloys and hard metals like tungsten. The use of HD in manufacturing magnets is restricted by this tailored material requirement, as not all metals can be processed through HD.
On the other hand, Traditional Powder Metallurgy can be applied to a wide range of materials, including both ferrous and non-ferrous metals and specialized alloys. PM being more versatile and widely used in magnet manufacturing techniques enables manufacturers to select materials according to specific magnetic requirement.
Powder Characteristics
Thanks to its highly effective methods, HD is ideally suited to the production of very fine powders. It has a narrow particle size distribution, making it suitable for high-precision applications such as cutting tools or high-performance alloys. In this case, the homogeneity of the powder produced by HD is better than that of normal powder, a characteristic that is important because sintering is involved. Actually, compared to magnets prepared from common-milled powder (average particle size of about 40μm), the magnets constructed from hydrogen decrepitated powder (average particle size of around 100μm) showed changed demagnetization loops, enhanced intrinsic coercivities and elevated temperature stability.
In contrast, conventional PM may result in powder with a larger span of particle sizes, which can be advantageous in some instances. Nevertheless, powders made with conventional PM typically show a lower level of uniformity than those treated by HD.
Advantages of Hydrogen Decrepitation
- Fine Powder with High Uniformity: The hydrogen decrepitation method is especially beneficial when the particle size distribution is narrow and uniform. In the case of producing magnets, uniformity of powdered material is very important given that during the process of replacing the material, sintering improves the magnetic property owing to enhanced domain alignment.
- Enhanced Magnetic Performance: Because HD is available as a fine, homogenous powder, it enables a better control of the magnetic properties of the magnet. This increases the energy density and efficiency in high-drain applications like motors, renewable energy systems, and electronics.
- Material Efficiency: The HD process uses less material in production. Thanks to the material loss is lower than with conventional methods due to the controlled fracturing of the metal and an efficient powder collection.
- Environmental Benefits: Hydrogen decrepitation is considered more environmentally friendly than traditional powder metallurgy, as it can reduce emissions and energy consumption during the production process.
Advantages of Powder Metallurgy
- Versatility: PM is far more versatile and can be used on a greater variety of metals, including both ferrous and non-ferrous. This versatility makes it perfect for part production across numerous industries.
- Cost-Effectiveness: With well-established processes such as atomization and mechanical grinding, PM is usually more cost-effective and scalable for high-volume production.
- Lower Energy Costs: Certain PM processes, such as gas atomization, are less energy demanding than HD and cheaper in some instances.
Hydrogen Decrepitation and Traditional Powder Metallurgy advantages/pros and cons of process selection vary on material selection as well as product requirement. HD is well suited for fine, homogeneous powders to meet the demands of Advanced applications in select alloys. On the other side, Traditional PM is widely accepted among different fields as it covers a more diverse aspect of material and applications having the largest range of flexibility. It solves the expensive problem of having a larger range of particle sizes for select use as they are necessary in certain applications, thus making it a good fit for the industry, where such flexibility is essential.
Quick Comparison Table of Differences Between Hydrogen Decrepitation vs. Traditional Powder Metallurgy
| Aspect | Hydrogen Decrepitation (HD) | Traditional Powder Metallurgy (PM) |
|---|---|---|
| Process | Involves hydrogen absorption at elevated temperatures, making the metal brittle, which causes it to fracture into fine powder. | Includes methods like atomization, mechanical grinding, and chemical reduction to create metal powders. |
| Material Suitability | Limited to metals and alloys that can absorb hydrogen, such as certain ferrous alloys and hard metals (e.g., tungsten). | Works with a broad range of metals, including ferrous, non-ferrous, and specialized alloys. |
| Powder Characteristics | Produces fine powders with a narrow particle size distribution, ideal for precision applications. | Can produce powders with a wider range of particle sizes and shapes, depending on the method used. |
| Flexibility | More specialized and limited to specific alloys. | Highly versatile, can be applied to a wide variety of materials and industries. |
| Applications | Primarily used for high-performance materials like cutting tools, wear-resistant components, and magnetic materials. | Used across various industries including automotive, aerospace, and electronics for producing parts like gears, bearings, and structural components. |
| Energy Requirements | Generally more energy-intensive due to the hydrogen absorption process. | Energy requirements vary, but atomization methods are typically less energy-intensive than HD. |
| Cost | More complex and can be costlier due to hydrogen removal and specialized requirements. | Generally more cost-effective, especially for large-scale production, due to well-established methods. |
| Powder Uniformity | Produces highly uniform and fine powders. | Powders can have a broader size distribution, with more variation in particle shapes and sizes. |
Hydrogen Decrepitation is an innovative technology for manufacturing high-performance NdFeB magnets. This method can achieve optimal material utilization, fine and uniform powder production and excellent magnetic properties. Oscenmag specializes in customizing strong magnetic neodymium magnets to meet the unique high performance and stable magnetic needs of customers in industries such as motors, automobiles, aerospace and renewable energy. We highly value the trust of our customers and use advanced technologies such as Hydrogen Decrepitation to ensure magnet performance and help customers reduce costs. Contact us now to get a quote.
Implementing Hydrogen Decrepitation in NdFeB Magnet Production.
Hydrogen Decomposition (HD) is a crucial process to improve the properties of materials which occurs as one of the key steps in the production of permanent magnet alloy magnets. The efficient use and implementation of this technology leads us to the production of fine powder material for the manufacture of high performance permanent magnets. Well, as a practitioner, I will help you understand in this exposition how this hydrogen explosion is being put to practice in the manufacture of NdFeB magnets in our production hall.
- Raw material preparation
It is important to prepare raw materials before the hydrogen Decrepitation. For NdFeB magnets, solid neodymium (Nd), iron (Fe), and boron (B) ingots, or powders, are used as raw materials. We can call this procedure the preparation process where we make sure that the NdFeB crude material melted in the earlier stage was clear of the contaminants. This will ensure a clean, hydrogen absorbing, bursting process. When narrowing down SmCo5 magnets, because its magnets are quasi mono-phasic, the pressure allows the hydrogen reaction very different with NdFeB. The nature of the raw material dictates the needs of the subsequent process.
- Hydrogenation
The actual Hydrogen Decrepitation follows. Now, the rare earth magnet is exposed to a pure hydrogen reaction chamber, or (as will be described) to a mixture of hydrogen plus one or more inert gases (e.g., nitrogen or argon). The hydrogen content (or hydrogen gas mixture) is generally between 0.5% and 10% and should be adjusted according to the actual situation.
A non-explosive gas mixture allows simpler equipment and makes gas handling safer. If a selected magnet is designed to be positioned within an apparatus that is still part of a larger assembly, then the use of potentially explosive mixtures can be a hazardous activity.
- Control of hydrogen flow and temperature
Hydrogen is introduced into the reaction chamber at a controlled temperature, usually between 25°C and 400°C, and some special cases are slowly heated from -30°C to 600°C. The hydrogen flow and temperature must be carefully controlled throughout the process. If the temperature is too high, it may cause excessive decomposition. The temperature is too low and the hydrogen explosion reaction will be too slow.
If not enough hydrogen flows, the magnet structure may not be completely destroyed. As per our previous calculation of the previous data for the production of magnets, we have five most common and implementable hydrogen pressure data sets: 0.01 mbar-100 bar, 0.1 bar- 70 bar, 0.1 bar-50 bar, 0.5 bar-20 bar or 1 bar-10 bar. The gas pressure can strengthen whether the gas is moving and how the surface of the magnet is coated.
This process is not a simple blowing and heating, and the operator needs to maintain a balanced flow of hydrogen. The goal here is to introduce hydrogen into the material’s crystal structure, breaking brittle metallic bonds and thereby producing smaller, more uniform particles. Our construction personnel will need to continuously supply hydrogen and perform precise control to ensure that the required reaction occurs within the specified time.
- Explosion reaction
At this point, hydrogen penetrates the material, causing the particles to burst open because of the pressure created internally from hydrogen; true explosion reaction. The bits get smaller and flakier. It can take from several hours to several days, depending on the material properties and the specific alloy, for this reaction to take place. This is also why the temperature and airflow data above is grouped: this process is slow.
Not only does this reduce the material’s handling properties, it also assists with attaining a more homogenous microstructure. Failure to detonate hydrogen leaves you with a coarse, unsatisfactory powder that does not meet the ultra-high standards of permanent magnets. Properly done decrepitation leads to the magnetic powder being fine, uniform, and with compactability.
- Cooling and Post-Decrepitation Processing
Once the hydrogen decrepitation is done, our staff carefully retrieves the powder and lets it cool down. Make sure the hydrogen gets vented safely during this cooling process. The cooling needs to be controlled (i.e. gradual) to prevent any sudden drop in temperature which can result in cracks/fractures that will be detrimental to the hydrogen decrepitation process.
- Compact and Shape Magnets
Once the hydrogen decrepitation process has been completed, the next step is to compact the now fine and uniform NdFeB powder. This is usually done by molding or isostatic pressing, where the powder is pressed under intense high pressures into the desired shape for the magnet and sintered.
Hydrogen decrepitation makes the powder easier to handle and shape. The small particle size achieved by decrepitation helps achieve a higher green body density, resulting in a stronger, denser magnet after sintering.
In my opinion, there are two aspects of hydrogen decrepitation that are most easily overlooked in the effective implementation of permanent magnet production: feedstock composition and hydrogen release. It begins with suitable materials selection and alloy design, since not all permanent magnet alloys can be hydrogen decrepitated successfully. The alloy needs to be carefully designed as well so that absorbing hydrogen will not make the material too brittle. So the hydrogen imprisioned during hydrogen decrepitation has to be fully eliminated. Contamination by residual hydrogen can be detrimental to the properties of the powder.
Hydrogen decrepitation is such a powerful technique for treating NdFeB magnets, and every step is of great importance. During the hydrogen decrepitation process, our production lines meticulously regulate air pressure, temperature, time and post-processing steps at each stage, significantly reducing waste material, increasing the effective use of material and lowering production costs. Train fine, uniform, well-pressed and excellent performance magnest powder. We are welcome to contact us at any time, if there is a customization need for permanent magnets. We will leverage as much as we can and try our best to supply you with high-performance magnets.
FAQs
What is hydrogen decrepitation of magnets?
Magnet Hydrogen Demolition is a process step used in the production of Neodymium magnets to create extremely small grains in the material. Using this method, extremely small grains with a particle size of less than or equal to 5 microns can be produced, ensuring stable magnetic properties.
What is the hydrogen processing of magnetic scrap?
The HPMS (Hydrogen Processing of Magnetic Scrap) process is a very efficient recycling process in which sintered Nd-Fe-B magnets disintegrate into a loose, demagnetized, hydrogenated powder when exposed to hydrogen.
What is the temperature of hydrogen annealing?
The trapped hydrogen atoms are extracted from the container via effusion leading to hydrogen embrittlement and the material is placed in a Closed Container for 3-4 hours at 200 to 300 °C in a hydrogen annealing oven. This process is performed primarily immediately following the welding, coating or galvanising of the components.
What is the temperature coefficient of NdFeB?
The reversible temperature coefficient of coercivity for NdFeB ranges from -0.45 to -0.65 depending on grade. To perform satisfactorily at elevated temperatures, room temperature Hci must be high.
Does magnet attract hydrogen?
For the H₂ molecules, this means that two electrons in a orbital has a paired opposite spins and singularly occupied with respect to the bonding orbital. That is why H₂ is extremely weakly magnetic.
