Funktionalisierte Graphene für tribologische Anwendungen

The main goal of this thesis was to identify the potential of functionalised graphene - thermally reduced graphite oxide (TRGO) - as tribological active filler respectively as solid lubricant. Therefor TRGO and other carbon based benchmark materials were used in different parts of a tribological system. Due to the versatile use of TRGO in lubricants, polymers and ceramics, as well as in coatings, better friction and wear properties were aspired. Stable dispersions of TRGO in lubricants like ester or mineral oil were obtained by high pressure homogenising. For the first time it could be shown in velocity dependant friction tests (Stribeck-curves), that low concentrated dispersions of TRGO lower friction in the boundary and mixed lubrication area, compared to other established fillers like graphite or carbon black. Responsible for this is on the one hand the plate like morphology of the filler, on the other hand the functional groups in the material, which positively influences the interaction with the lubricant matrix on the one side and the tribological stressed material on the other side. Also in less conventional lubricants like the Ionic Liquid 1-Hexyl-3-methylimidazoliumhexafluorophosphat [C6MIM][PF6] a decrease of friction coefficient in the mixed and boundary friction area of 40 % was realised. This can be attributed to the changed rheological properties. In further studies, which dealt with the modification of polyamide 12, it could be shown, that TRGO (5 wt.-%) led to improved wear behaviour (38 %) with unchanged friction coefficient. This is caused by the increased thermal stability and stiffness of the composite material in comparison to the unfilled reference system and by the formation of a TRGO rich protection layer, which minimizes the material removal due to continuous exposure. First test with aluminium oxide based ceramiccomposites (Al2O3) showed not yet improvement of the tribological properties. The filler particles acted as a sinter barrier, and disturbed the compacting process. For various application areas the usage requirements have degrade due to addition of carbon based fillers. Only the electrical conductivity could be improved by addition of 1 wt.-% TRGO in the same dimension compared to 5 wt.-% graphenenanoplatelets. Silicon carbide based ceramic composites (SiC) showed no change with 2 wt.-% TRGO. With more filler respectively same amount of carbon fibre (2 wt.-%) an increase of the friction coefficient with water lubrication in the mixed and boundary lubrication area could be detected. Since there are no more material properties data available, it is impossible to evaluate these results on the same way we did with the Al2O3 composites. It is not clear, if the same mechanisms are responsible for the worsening of the tribological properties. Several coating types with TRGO and carbon based benchmark materials with and without adhesion promoter or in shape of anti-friction coatings were successfully produced and showed improved frictional properties compared to the unmodified reference samples. Coatings without adhesion promoter are mostly instable against macroscopic mechanical or tribological stress, but can be used for nano- or micromechanical applications in extreme thin films. Especially the graphite - graphen and graphiteoxide - birnessite – coatings are of great interest. With addition of polydopamine as adhesive promoter, the application area can be expanded to higher frictional stress. After a short run-in period of high friction a decrease of friction (40 %) could be detected. The coating type with the highest potential was the anti-friction coatings containing TRGO as solid lubricant. With only 2 wt.-% TRGO a decrease of friction of about 25 % – 28 % could be achieved in epoxy resin and Ormocer®s