Small Particles – Big Problems

AFM_WearParticles

AFM_WearParticles

Tiny particles are all over around us and sometimes they may create problems. This is especially of concern with metal particles formed due to wear in man-made engineering devices. Particles formed in car disk brakes may harm lung cells, metal particulate limits the service life of artificial hip implants and other engineering machines. They even may lead to a catastrophic failure. Severity of the impact is often related to the size of these tiny particles, which in many cases is in the range of 1 hundred nanometer – approximately 1000 times smaller than the diameter of the human hair. The small size also brings the complexity in the analysis of these particles.

Our research group in University of Twente recently had studied the metal (steel and brass) particles formed in lubricated contact pairs. These particles, once formed, start to decrease the lubricating properties of the oil or grease and may significantly decrease the lifetime of the component. In a set of experiments, tiny wear particles were collected using specifically designed experimental procedure and analyzed to obtain the size as a function of the applied conditions. By using Dynamic Light Scattering technique and Atomic Force Microscopy, the size of the particles was assessed. It was found, that it was in the range of 200 nm and slightly varied with the applied load, but not temperature. The amount of particles formed was found to be terrific: the number of particles formed during 1 meter of sliding with 1 N load reached 2 million! How many of those are generated during a typical car break? No wonder the huge amount of these particles can create big problems.

With this measurement data in hand, it is possible to build and validate wear models to predict the size of the wear particles. This in turn can help researchers to create a better component design and control the negative effects coming from these tiny debris.

The details of the research can be found in the original article: Analysis of Wear Particles Formed in Boundary-Lubricated Sliding Contacts“, A. Akchurin, R. Bosman, P.M. Lugt.

Credit for image: Analysis of Wear Particles Formed in Boundary-Lubricated Sliding Contacts“, A. Akchurin, R. Bosman, P.M. Lugt.

Aydar Akchurin
About Aydar Akchurin 35 Articles
Editor-in-Chief, PhD (Tribology), Researcher at ASML, Eindhoven, the Netherlands. Expertise in modeling of lubrication, friction and wear.

6 Comments

  1. Thank you Aydar and University of Twente!

    Two things: 1. Yes, those “small” particles abound from any frictional contact; 2. Yes, they are normally mechanically destructive and potentially dangerous to human health.

    This is why previous (earlier) ex-situ ISN techniques represent health concerns. Those lab-created nanoparticles can absorb transdermally through the skin and (in some cases) through cell membranes. In lubrication, there is currently a push to use lots of externally added nanoparticles in oils and greases.

    This is another reason why ISS (in-situ synthesis) ISN is so important. The ISS-ISN nanoparticles don’t exist yet until they are made within the mechanical system as it operates! This makes them safer, as the mechanic/technician is not exposed to them initially and once formed, they adhere to the metal surfaces due to paramagnetism.

  2. Thank you! It would be great to apply the models, predicting the wear particle size, rather than the wear volume, to control the generation of these particles. Or maybe to help in establishing the ISN? Is there any critical size for the ISN to be established?

    • Nope . . . nature takes care of that for you.

      The particle diameters will be determined by the surface morphology and operating conditions. With ISS-ISN, you just sit back and let it happen by itself. The “harder” you drive the system, the faster the polishing effect occurs.

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