ICMCTF2009 Session G3: Atmospheric Plasma, Hollow Cathode, and Hybrid Technologies

In industries like aeronautics, automotive and pneumatics there is a great need for tailoring and extending the performance and functionalities of rubber-like materials used in sliding and sealing systems. An important driving factor for new developments in the field of tribology are environmental considerations concerning the effects and consumption of greases and lubricants. Therefore there is a steady demand for materials and surface coatings with solid lubricant ability and dry friction capability.

To improve the tribological properties (friction coefficient, wear, noise, lubricant,…) of elastomer parts moving against a metal counter body, an atmospheric pressure plasma treatment of the surface could be an efficient process.

The PLASMASPOT^(r)is a DBD plasma torch system working at atmospheric pressure and developed at VITO. It can be used for chemical activation or surface modification of different kind of materials as well as for coating by adding a polymerizable precursor to the plasma afterglow.

We applied siloxane based coatings on soft elastomer substrates starting from hybrid organic-inorganic precursors. They were characterized with FTIR, XPS and SEM-EDX. Furthermore different tribological testing against metal counter bodies was performed to have an idea of the improvement of the frictional behaviour and the wear resistance of these coatings. Although soon after deposition cracks appear in the coating, a significant lowering of the initial friction coefficient can be maintained during a long sliding distance.

Electrical plasmas operating at atmospheric pressure are now in widespread use for materials processing and in related areas such as surface characterisation. Highly functional surfaces can be deposited on a variety of materials, including textiles, plastics, and polymers. Other processes include medical applications such as the sterilisation of surgical instruments and localised treatment of biological tissues. For surface analysis of a wide range of materials, plasma treatment at atmospheric pressure combined with mass analysis is increasingly used to supplement vacuum SIMS. In all these areas, a variety of plasma sources are in use, including RF 'needle' sources, corona discharges, glow discharge jets, and dielectric barrier discharges. Plasmas are also being incorporated in catalytic conversion systems to allow lower operating temperatures.

It is essential when improving any plasma processing system to have information available on the nature and energies of the active species produced in the discharge, ideally measured at the point where they impact on the target substrate, and of any interaction products. Such measurements can be made using either a quadrupole mass spectrometer to sample neutral species via a capillary inlet tube, or a molecular beam instrument, incorporating an electrostatic energy analyser, to examine positive and negative ions as well as neutral species. Typical data for a number of different plasma sources will be described and correlated with measured properties of surfaces exposed to the plasmas. Preliminary data for a micro-reactor combining catalysis with a surface barrier discharge will also be outlined.