A method of purifying a target powder having an oxygen content, the method comprising: flowing hydrogen gas through a microwave production chamber; applying microwaves to the hydrogen gas as the hydrogen gas flows through the microwave production chamber, thereby forming hydrogen radicals from the hydrogen gas; flowing the hydrogen radicals out of the microwave production chamber to the target powder disposed outside of the microwave production chamber; and applying the hydrogen radicals to the target powder, thereby removing a portion of the oxygen content from the powder. Preferably, the target powder is agitated as the hydrogen radicals are being applied.