4 examples of using sintering to make magnets

Manufacture of uniform flux sintered magnet

A rare earth sintered magnet with uniform magnetic flux can be made by applying a slurry containing a compound of the rare earth elements R2 on the sintered magnet followed by dried rotation and then heat treatment.

The magnet thus made has crystal grains of composition: (R1, R2)2T14B. The symbols here represent:

  • R1 represents a rare earth element except for Dysprosium (Dy) and Terbium (Tb).
  • R2 represents a rare earth element including Dysprosium (Dy) and Terbium (Tb).
  • T represents transition metal elements including Iron (Fe) and Cobalt (Co).
  • B is boron.

Ratio of R2 to a sum of R1 and R2 in the crystal grain boundaries is higher than the ratio of R2 to a sum of R1 and R2 in the crystal grains. Concentration of R2 increases from the central portion of the magnet body toward the surface.

The figure below shows the steps in complete manufacturing process:

Refer to this patent for more information.

Making a MnBi permanent magnet using sintering

The process of making a Mn-Bi (Manganese-Bismuth) alloy based magnet first involves mixing and crushing Mn, Bi and other alloying agents to form a powder. This powder is then compacted to form a magnet and sintered to obtain the final product.

The process of manufacturing includes:

  1. Sintering a Manganese and Bismuth powder compact at a temperature between 360 and 900° C for 40 to 80 minutes to generate a TP (temperature phase) transition driving force. This decreases the formation energy barrier for transition to MnBi LTP (low temperature phase).
  2. Sintering the compact between 260 to 450° C for 24 hours to form a magnet, such that an Mn-Bi LTP x-ray peak intensity is at least twice that of Bi.

Refer to this patent for more information.

Sintered magnets with improved residual magnetic flux density and coercivity

R-T-B based permanent magnets have high residual magnetic flux density, coercive force, and squareness ratio with improved sintering temperature range. Here,

  • R is a rare earth element (29.0% to 33.0%)
  • T is Fe or a combination of Fe and Co (0.85% to 1.05%)
  • B is boron.

The composition can also have carbon, oxygen (0.03% to 0.20%), and gallium (or Zirconium, 0.30% to 1.20%).

The R-T-B based permanent magnet satisfies 3.48m(B)−2.67 ≤ m(Zr) ≤ 3.48m(B)−1.87 in which m (B) (mass %) is B content and m (Zr) (mass %) is Zr content.

Refer to this patent for more information.

Recycling scrap magnets by sintering

Recycling scrap magnets can be done by grinding a recovered scrap magnet to obtain a raw material powder. Then, this powder is sintered to make magnets. Following steps are involved:

  1. Heating the sintered body in a processing chamber.
  2.  Thereafter, evaporation of Dysprosium and Terbium is conducted.
  3.  Finally, the adhered metal vapors are diffused into the sintered body’s grain boundary or phase.

Refer to this patent for more information.

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