Volume 4, Issue 10 (November 2007)
Mechanochemical Additive-Assisted Reconditioning Effects and Mechanism on Worn Ferrous Surfaces
An additive package of reconditioning functionality for worn ferrous surfaces has been designed in light of the mechanochemical reaction principle. The package is formulated from a fine-powdery multicomponent mixture of Serpentine minerals, surfactants, and catalysts. The main reconditioning component in the package is magnesium silicate hydroxide (Mg6(Si4O10)(OH)8), with the surfactants for dispersing the main component into bulk lubricant and the catalysts for facilitating interfacial mechanochemical reactions, particularly oil pyrolysis and carbonization. With commercial fully-formulated engine oils as benchmark, the reconditioning effects of the reconditioner package have been demonstrated in both laboratory tribotestings and in real-world heavy-duty (locomotive diesel engine) scenarios. Surface examination of sampled worn surfaces on both laboratory test specimens and cylinder bore of locomotive diesel engine has shown that a nano-crystalline layer has been generated which possesses nanometric roughness, higher surface hardness, and proper H/E ratio. Advanced analyses have indicated that the layer is composed of Fe3O4 and FeOOH nanoparticles which are dispersed on the Fe-C matrix. The smoother surface mitigates asperity interlocking which would otherwise induce high friction; the high surface hardness and appropriate H/E ratio result in less elastic deformation within nanocrystalline contact regions, which effectively lessens friction and wear arisen from plastic plowing and adhesion. Further characterization of sampled worn cylinder bore surface and analysis of used oils have suggested that generation of the nanocrystalline layer in presence of Mg6(Si4O10)(OH)8 involves three interwoven processes: oxidative mechanical polishing, lubricant carbonization and graphitization, and mechanical alloying.