Quantitative evaluation of polytetrafluoroethylene contamination on rock powder specimens during high-velocity rotary-shear experiments

Abstract

Because the frictional properties of fault gouge are important for understanding earthquake slip behavior, laboratory studies of high velocity rock friction have been conducted. A sleeve of polytetrafluoroethylene (PTFE) is used around the specimen to maintain pressure and prevent leaks during the experiment, and sometimes appeared to be worn and material from it was mixed into the specimen. However, the effect of PTFE contamination in the specimen is uncertain, although PTFE is known for its extremely low frictional coefficient. Here we reported new quantitative measurements of the amount of contamination by worn PTFE sleeve material in the specimen after experiments by a calorimetric technique using simultaneous thermogravimetry and differential scanning calorimetry. We also performed the friction experiments using mixtures of illite-rich shale and PTFE powder, and demonstrated that high PTFE contamination can affect the friction values of specimens.