What kind of magnetic particles are commonly used in MPT?

The correct choice highlights that iron-based particles are typically utilized in Magnetic Particle Testing (MPT) due to their superior magnetic properties. MPT is a non-destructive testing method that relies on the application of a magnetic field to ferromagnetic materials, such as iron and its alloys. The magnetic particles, when applied to the surface of the test material, are drawn into any surface or near-surface flaws creating an indication that can be observed under suitable lighting conditions.

Iron-based particles possess high magnetic permeability, which makes them particularly effective in adhering to the magnetic flux leakage fields produced by defects. This adherence enhances the visibility of the indications, allowing for accurate identification of flaws like cracks or inclusions in the tested material. Given their effectiveness and compatibility with the method, iron-based particles are the industry standard for MPT applications.

Other materials listed, such as plastic-based, aluminum, and copper oxide particles, lack the requisite magnetic properties to be effectively used in this testing technique. Plastic particles do not respond to magnetic fields, aluminum is not ferromagnetic, and copper oxide particles are not conducive to creating the magnetic indications necessary for detecting defects in ferromagnetic materials. Hence, their use is inappropriate within the context of MPT.