5. Examples of particle separation and identification obtained by non-analytical ferrography

Although non-magnetic particles are not sensitive to the magnetic field when passing through the ferrograph, they are deposited randomly. This results in a ferrogram with two types of particles:

• magnetic ones;

• non-magnetic.

These appear completely white and are indistinguishable under an optical microscope. A few drops of a 0.1 mol/L acidic or basic solution are then added and the ferrogram is heated to 90°C using a hot plate. Some particles become soluble and, as the temperature is increased, color changes can be observed depending on the type of metal. The different treatments and results are shown in the table 8 .