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Fig.4 Demagnetization curve of isotropic MA fine powder (grade ISO 9-14) measured at 20°C
Fig.3 Particle size distribution of isotropic MA fine powder (grade ISO9-14)
Fig.2 SEM micrograph of isotropic MA fine powder (grade ISO 9-14)
1. Anisotropic HDDR Powder
The magnetic data measured by VSM were not corrected for demagnetizing fields
Table 1 Grades and properties of anisotropic HDDR powder
| Grade |
iHc(kOe) |
Br(kGs) |
(BH)max(MGOe) |
Remarks |
| ANISO 15-35 |
14-15 |
13.1-13.3 |
33-35 |
Co free, in stock |
| ANISO 13-40 |
12.5-13.5 |
13.9-14.2 |
37-39 |
Co free, in stock |
| ANISO 13-42 |
12.5-13.5 |
14.3-14.6 |
41-42 |
5% Co added,in stock |
Whether compression-molded or injection-molded, the HDDR powder can be used to produce anisotropic bonded magnets which are suitable for a wide variety of applications where higher performance than isotropic bonded magnets is required. The magnetic properties of the HDDR powder are somewhat affected by the particle size. In order to obtain the highest Br in the associated anisotropic bonded magnets, it is recommended that the particle sizes are widely distributed in a range from 50 to 150µm which are roughly the same as those of the original grains of 2:14:1 phase in the starting alloy ingots. Currently Magnapowders ships the products in the form of coarse lumps which will be pulverized on the consumer side.
The HDDR process is proven to be a simple and effective method for producing highly anisotropic and coercive NdFeB-based powder with energy densities around 40MGOe. For the last 10 years, the HDDR process has received various kinds of modifications made by a batch of institutes and companies, with the purpose of optimizing the magnetic properties of HDDR powder. Among them, Magnapowders has succeeded in developing its own unique HDDR processing and proprietary equipments. At present, Magnapowders is producing two standard grades of anisotropic HDDR powder, with another cobalt-containing grade as an option. The two standard grades have the same composition without Dy and Co additions, with one exhibiting higher coercivity for high-temperature applications and another exhibiting lower coercivity for a general purpose.The powder with Co added shows significant improvements in the squareness of demagnetization curves and possesses high over performance. Table 1 summarized the magnetic properties of the three grades of the HDDR powder.
Table 2 Grades and properties of isotropic MA fine powder
| Grade |
iHc(kOe) |
Br(kGs) |
(BH)max(MGOe) |
den.(g/cm3) |
gran.(Mesh) |
Remarks |
| ISO9-14 |
9-10 |
8.6-9.1 |
14-16 |
7.65 |
‹-160 |
in stock |
| ISO11-12 |
11-13 |
7.8-8.2 |
12-14 |
7.62 |
‹-160 |
in stock |
The magnetic data measured by VSM were not corrected for demagnetizing fields.
2. Isotropic MA Fine Powder (suspended)
The MA fine powder based on Nd-Fe-B compositions is mechanically alloyed from the pre-alloyed state in a high-energy ball mill. The unique MA process and subsequent annealing treatment result in a material which has an uniformly fine nano-scale microstructure of near single phase. Moreover, as can be seen in Figures 2-4, the MA fine powder has a near spherical morphology with the same superior magnetic properties as those of the mainstream melt spun flake-shaped powder with a near stoichiometric composition. These characteristics make MA fine powder ideally suited for the production of flexible rubber magnet, intricate small-sized injection molded magnet or sprayed film magnet.
Right now, there are two powder grades available for your choice. Grade ISO 9-14, with a little cobalt added, is designed specifically for applications that require the highest possible flux density and relatively strong resistance to demagnetizing field. Grade ISO 11-12, with no cobalt added, has a high intrinsic coercivity making it suitable for applications demanding a higher resistance to demagnetization. Table 2 summarized the magnetic and physical properties of the two grades of the MA fine powder.
The MA fine powder are so active, when coming into contact with air before being passivated, they will be rapidly oxidized to lose their magnetic characteristics. It has been shown that slow oxidation of the powder, by introducing repeatedly a very small amount of oxygen into the argon atmosphere of the powder container, is a effective way of passivating treatment. After the treatment, the MA fine powder can be handled safely in the air. For compounding at elevated temperatures, a protective coating given to the MA fine powder with a layer of epoxy resin will be necessary.
The near spherical morphology of the MA powder, together with the smaller particle size, offers benefits to the improvement of processibility during injection molding. By decreasing the apparent viscosity of the compound (mixture of polymer resin and magnetic powders), lower shear stresses can be applied and a higher volume fraction of magnetic powders can be utilized within the same injection molding capability, which results in a consequent augment in Br for the bonded magnet. Therefore, the MA fine powder with near spherical morphology are the most suitable for injection molding in terms of processibility. As for the rubber magnet sheet or strip, the MA fine powder will provide considerable improvements in mechanical flexibility and elasticity concurrently with good magnetic properties.
Fig.1 Hysteresis loops of the anisotropic HDDR powder which are typical for ANISO 15-35, ANISO 13-40 and ANISO13-42 respectively.
Company profile
Magnapowders company is the sole China supplier of anisotropic HDDR powder and isotropic MA fine powder based on Nd-Fe-B compositions. As a private and independent company, it began operations under the Magnapowders™ banner in 2003 to primarily commercialize the two new types of magnetic powder with high performance. Magnapowders is a high-tech company run by a group of young material scientists with an entrepreneurial spirit, engaging in the technology transfer from laboratory discovery to industry.
Magnapowders by far has the only facility in China capable of producing commercial quantities of anisotropic HDDR powder and isotropic MA fine powder based on Nd-Fe-B compositions. Currently, Magnapowders is building up a capacity leading to the economies of scale. The highly sophisticated production systems for both HDDR powder and MA fine powder were commissioned or home-made in order to meet the special requirements of the unique HDDR and MA processes we newly proposed. The systems incorporated state-of-the-art PLC design which is characterized by accurate control of process variables. By the way, the computer controlled systems insure much higher repeatability in terms of batch-to-batch powder performance.
In comparison with melt-spun Nd-Fe-B powder, anisotropic HDDR powder and isotropic MA fine powder have opportunities to serve different market segments and application requirements. Through product and process innovations, Magnapowders has been making contribution to the diversity of the rapidly growing bonded magnet market.
HDDR is an abbreviation of Hydrogenation-Disproportionation-Desorption-Recombination.
MA is an abbreviation of Mechanical Alloying/Milling.
Magnapowders offers responsive service to foster novel bonded magnet development and better serve our industrial customers. Magnapowders has expertise in all aspects of the manufacturing process that will be used to produce the novel bonded magnets. Whether you are from a global corporation or are just starting out, Magnapowders will be happy to provide technical assistance to advance the use of our newly developed magnetic powder and fit your needs.
