The first step in making magnet powder looks almost like magic: alloy flakes go into a sealed vessel, hydrogen gas is pumped in, and the metal quietly cracks itself apart — no crusher, no hammers. Think of bread dough rising in a warm kitchen: the gas soaks in, the material swells, and it splits along its lines of least resistance.
How it works, in one sentence
Hydrogen soaks into the alloy and forms compounds that take up more space; the growing pressure splits the brittle metal apart, and what comes out is a fine powder.
Why it breaks along the grain boundaries
The alloy is made of tiny crystals — grains — held together by a thin neodymium-rich cement between them. The cement absorbs hydrogen first and swells the most, so the material cracks cleanly between the grains. The result is powder made of individual crystals, each still carrying a thin layer of that neodymium-rich phase on its surface — exactly what the next steps want.
Keeping the temperature in check
The reaction gives off heat, and the temperature must stay under control. Above about 600 °C the magnetic phase itself breaks down into other compounds, and the material is ruined. Stay cooler, and the crystal structure survives intact.
The step you cannot skip
Before the powder can be used, the absorbed hydrogen must be pumped back out under vacuum. Trapped hydrogen makes finished magnets brittle — a flaw that shows up as cracked magnets later.
The result is a coarse powder — roughly the size of sand grains — made of clean, single crystals. It is ready for the jet mill, which grinds it down to the micron scale the magnet actually needs.
Read on: jet milling → · how NdFeB is made →