Introduce solid particles into the lubrication system. Machined metal surfaces are inherently rough. Since particles used are generally uniform in size, there's no way to produce uniformly smooth surfaces on varying metal surface roughness. Therefore, engineered tolerances may be affected. Treatment dosage does not take differing engine sizes and metal surface area into consideration.
Particles can bond with each other to form larger solids.
Solid particles may clog filters and block oil galleries. Solids may dam up around bearings. Heat must be quickly transferred away from metal surfaces. No industry standard for testing or how much is safe to use in automotive engines. Lubrication is a complex science.