Testing for a passive surface is usually accomplished by looking for traces of free iron on the metal surface.
钝化表面的检测通常是通过查看金属表面的游离铁的踪迹来完成的。
2
The presence of exogenous surface contamination, including dirt, grease, free iron from contact with steel tooling, and so forth, may interfere with the formation of the passive film.
外生的表面污染，包括：尘土、油脂、来自钢铁加工的游离铁等等，可以影响到钝化膜的生成。
3
Two passive magnetic bearings were devised to resist the attractive force between the motor coil iron core and rotor driven magnets.