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Easy-clean surfaces built to order
Plasma deposition creates a range of very hard hydrophobic coatings
Current technologies for producing self-cleaning or low adhesion coatings have limitations,- PTFE is relatively soft, and while CrN is on the other hand very hard, but not stable in the long term. Diamond-like carbon coatings (DLC) have the advantage that their very hard basic structure can be modified by including other elements to give low surface energy, increased hardness or other desired properties. Multi-layer coatings can combine the properties of different modifications, while structured coatings imitate lotus-leaf properties. Practical applications include the reduction of material adhesion on stamps used in tablet production as well as the reduction of fouling on heating elements. In the case of heat exchangers, fouling still occurs on the DLC coated surfaces, but the poor adhesion allows it to be stripped off by the water flow or by thermal stresses. 'Sicon' (a-C:H:Si:O) has a rather low surface energy and is considerably harder than PTFE. With hard coatings such asSicon (a-C:H:Si:O) or Sican (a-C:H:Si) mechanically and chemically stable coating materials with low surface energies are available. If the base material is soft and the abrasive particles are much larger than the thickness of the coating, the particles can penetrate the coating and destroy it. The ideal case would be to know the complete system hardness of the base material, particle size, the bonding links and the adhesion of the soiling. Modified DLC coatings are prepared by Plasma-Assisted Chemical Vapour Deposition (PACVD) processes. DLC coatings can be prepared as monolayers as well as multi-layers. Multi-layers can combine the properties of the individual layers and thus optimise the coating system. In order to investigate the fouling on surfaces, heat exchanger plates were covered with different types of DLC-based coatings.