Tribological properties of PTFE-based fabric composites at cryogenic temperature

Fabric composites are widely employed in self-lubricating bearing liners as solid lubrication materials.Although the tribological behaviors of fabric composites have been extensively studied,the cryogenic tribological properties and mechanisms have been scarcely reported and are largely unclear to instruct material design for aerospace and other high-tech applications.Herein,the tribological properties of polytetrafluoroethylene(PTFE)-based hybrid-fabric composites were investigated at cryogenic and ambient temperatures in the form of pin-on-disk friction under heavy loads.The results suggest that the friction coefficients of the hybrid-fabric composites obviously increase with a decrease in wear when the temperature drops from 25 to−150°C.Moreover,thermoplastic polyetherimide(PEI),as an adhesive for fabric composites,has better cryogenic lubrication performance than thermosetting phenol formaldehyde(PF)resin,which can be attributed to the flexible chemical structure of PEI.The excellent lubrication performance of hybrid-fabric composites is attributed to the transfer film formed by PTFE fibers on the surface of fabrics.

Tribological behavior of shape memory cyanate ester materials and their tunable friction mechanism

High-performance polymer friction materials with tunable tribological behavior to fit varied work conditions remain a challenge of widespread interest for a variety of applications.Shape memory polymer exhibits morphing and modulus changing over temperature changing provides a promising material to adjust the friction process.Herein,we investigated the tribological properties of shape memory cyanate ester(SMCE)under different conditions.The SMCE exhibits the tribological behavior of good friction material with stable high coefficient of friction(COF)and a low wear rate.Besides,the COF increases and wear rate decreases with the temperature increasing show the tunable friction property of the SMCE.We propose a new model of wear-compensation through shape recovery to explain the adjustable friction behavior of thermal-responsive polymer from the aspect of shape recovery and energy conversion.This study provides a high-performance friction material and paves the route for the application of shape memory polymer(SMP)in tribology field with tunable property.

A WO3 nanorod-Cr2O3 nanoparticle composite for selective gas sensing of 2-butanone

The hexagonal （h）-WO3-Cr2o3 nanocomposites with different W/Cr molar ratio of 4：1,10：1 and 40：1 were prepared by a facile two-step hydrothermal method, and its gas sensing properties were investigated under optimum working temperature. X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, high resolution transmission electron microscopy （HRTEM） were used to characterize the morphology, microstructure and crystallinity of the as-synthesized samples. The hexagonal WO3 nanorods show a better crystallinity than Cr2O3 nanoparticles. When the molar ratio of W/Cr is 10：1, the hexagonal WO3-Cr2O3 nanocomposite shows obvious selectivity toward 2-butanone at 205℃ compared with other typical reducing gases, and the response value to 100 ppm 2- butanone can reach 5.6. However, there is no selectivity toward 2-butanone when the Cr/W molar ratio is 1：4 and 1：40. Furthermore, hexagonal WO3-Cr2O3 nanocomposites have a short response and recovery time to 5ppm 2-butanone, which is lOs and 80s, respectively. The measured results indicate that hexagonal WO3-Cr2O3 nanocomposite is a potential gas sensing material for monitoring volatile organic compounds （VOCs）.