What are the key characteristics of magnetic particles used in MPI?

The key characteristics of magnetic particles used in Magnetic Particle Inspection (MPI) center around their ability to effectively reveal surface and near-surface discontinuities in ferromagnetic materials. Ferromagnetic properties are essential because these particles need to respond to magnetic fields. When a magnetic field is applied to the test material, the particles will align along the lines of magnetic flux and accumulate at discontinuities, making them visible for inspection.

In addition to being ferromagnetic, the particles must be non-toxic to ensure safe handling during inspection, as MPI often involves human operators in close proximity to the materials. Furthermore, the size and shape of the particles are important for effective detection; they must be small enough to penetrate cracks and flaws but not so small that they become overly difficult to manage or visualize. An ideal particle will adhere to defects in a manner that allows for clear identification of potential issues, thus helping to ensure structural integrity.

Although some other characteristics like biodegradability or electrical conductivity may have relevance in other contexts, they are not fundamental to the effectiveness of magnetic particles in MPI. The emphasis on ferromagnetism, non-toxicity, and appropriate size and shape directly caters to the requirements of this specific non-destructive testing method.