A study of tribopolymerization under fretting conditions
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A study has been conducted to determine whether or not tribopolymerization can occur under conditions of fretting contact. Using a laboratory test consisting of oscillating hard steel balls loaded against flat steel or aluminum disks, effects of various monomers on friction, wear, and surface film fonnation were determined. Monomers, capable of polymerizing either by polycondensation or addition processes, were used at 1 % concentration in hexadecane. Under the conditions used (90N load, 65Hz frequency, 200Î¼m peak-to-peak amplitude, 1 hour), the monomers tested reduced friction or wear or both. Fourier Transfonn Infrared Microscopy (FTIRM) analysis of the test specimens shows that organic material is present in the wear scar regions and depends on the metal used, the monoester structure, location on the disk, and the method of cleaning the surface after a test. With aluminum-on-steet the addition of I % styrene to hexadecane reduced the wear volume of the disk by over 650/0; furthennore, positive evidence of polystyrene was found via FTIRM. These results support the hypothesis proposed by Kajdas that addition-type tribopolymerization can be initiated by exo-electron emission. Under these conditions of expected relatively low surface temperatures, tribopolymerization does not occur with polycondensation-type compounds such as the C36 dimer acid/ethylene glycol monoester. With this additive, known to be extremely effective in reducing wear at higher surface temperatures, effects on wear were small and no positive evidence of polymerization was found; however, metal soaps fonned under these conditions.
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