What is the purpose of a wetting agent in a magnetic particle suspension?

The primary role of a wetting agent in a magnetic particle suspension is to reduce surface tension. By doing so, it allows the magnetic particles to spread more easily over the surface of the material being tested. This enhanced wetting capability ensures that the particles can penetrate into small cracks or defects that may be present on the surface. When the surface tension is lowered, the suspension can more effectively coat the areas that need to be inspected, leading to improved detection of faults. Therefore, the use of a wetting agent is crucial in ensuring the effectiveness and accuracy of the magnetic particle testing method, as it maximizes the ability to reveal surface and near-surface discontinuities.

The other options do not accurately represent the function of a wetting agent. For example, increasing the density of the particles or enhancing their magnetic properties are not direct roles of wetting agents. Similarly, while visibility of defects is important, enhancing visibility is more related to the contrast of the particles against the test medium or background rather than the role of a wetting agent itself.