Shape-controlled Synthesis of Porous SnO_2 Nanostructures via Morphologically Conserved Transformation from SnC_2O_4 Precursor Approach

Porous SnO_2 nanostructures with controlled shapes were synthesized by a facile morphologically conserved transformation from Sn C_2O_4 precursor approach. Well-defined Sn C_2O_4 nanostructures can be obtained through a solution-based precipitation process at ambient conditions without any surfactant. The formation mechanism of such microstructures was tentatively proposed on the basis of intrinsic crystal structure and the reaction conditions. We found that the morphologies of precursor were well maintained while numerous pores were formed during the annealing process. The combined techniques of X-ray diffraction, nitrogen absorption–desorption, field emission scanning electron microscopy, and(high-resolution) transmission electron microscopy were used to characterize the as-prepared SnO_2 products. Moreover, cyclic voltammetry(CV) study shows that the shape of CV presents a current response like roughly rectangular mirror images with respect to the zero-current line without obvious redox peaks, which indicating an ideal capacitive behavior of the SnO_2 electrodes. The photoluminescence(PL) spectrum study suggests that the as-obtained porous SnO_2 nanostructures might have a large number of defects, vacancies of oxygen, and local lattice disorder at the interface, interior and exterior surfaces.

Molecular design of recyclable thermosetting polyimide and its composite with excellent mechanical and tribological properties

Recyclability of thermosetting polymers and their composites is a challenge for alleviating environmental pollution and resource waste.In this study,solvent-recyclable thermosetting polyimide(PI)and its composite were successfully synthesized.The tensile strength,elongation at break,and Young’s modulus of PI are 108.70±7.29 MPa,19.35%±3.89%,and 2336.42±128.00 MPa,respectively.The addition of reduced graphene oxide(RGO)not only enhances the mechanical properties of PI but also endows it with excellent tribological properties.The PI illustrates a high recycling efficiency of 94.15%,but the recycled composite exhibits inferior mechanical properties.The recycling and utilization of PI and its composite are realized through imine bonds(-C=N),which provides new guidance for solving the problem of environmental pollution and resource waste and is potential application in the field of sustainable tribology.

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.

Efficacy of hierarchical pore structure in enhancing the tribological and recyclable smart lubrication performance of porous polyimide

Herein,a porous oil-containing material with hierarchical pore structure was successfully prepared through microtexturing large pores on the surface of porous polyimide(PPI)with single-level small pores.Compared to the conventional oil-containing material,the hierarchically porous oil-containing material exhibited high oil-content,and retained excellent mechanical properties and high oil-retention because of the synergistic effects of large pores and small pores.Furthermore,the lubricant stored in the hierarchically porous polyimide could release to the interface under thermal-and-mechano-stimuli,and the released lubricant could be reabsorbed into the hierarchically porous polyimide via the capillary-force offered by the porous channel.Based on the high oil-content and recyclable oil release/reabsorption,the hierarchically porous oil-containing polyimide exhibited excellent lubrication performance(coefficient of friction was 0.057).Furthermore,the composite could perform 1,069 cycles of smart lubrication(1 h per cycle),which significantly extended the service life of the hierarchically porous oil-containing smart lubrication material.

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.

The effect of different layered materials on the tribological properties of PTFE composites

Two-dimensional(2D)lamellar materials have unique molecular structures and mechanical properties,among which molybdenum disulfide(MoS2)and graphitic carbon nitride(g-C3N4)with different interaction forces served as reinforcing phase for polytetrafluoroethylene(PTFE)composites in the present study.Thermal stability,tribological and thermomechanical properties of composites were comprehensively investigated.It was demonstrated that g-C3N4 improved elastic deformation resistance and thermal degradation characteristics.The addition of g-C3N4 significantly enhanced anti-wear performance under different loads and speeds.The results indicated that PTFE composites reinforced by g-C3N4 were provided with better properties because the bonding strength of g-C3N4 derived from hydrogen bonds(H-bonds)was stronger than that of MoS2 with van der Waals force.Consequently,g-C3N4 exhibited better thermomechanical and tribological properties.The result of this work is expected to provide a new kind of functional filler for enhancing the tribological properties of polymer composites.

Exploring the friction and wear behaviors of Ag–Mo hybrid modified thermosetting polyimide composites at high tem-perature

Polyimide composites have been extensively used as motion components under extreme conditions for their thermal stability and special self-lubricating performance. In the present study, Ag–Mo hybrids as lubricant fillers were incorporated into thermosetting polyimide to prepare a new type of tribo-materials (TPI-1) at high temperature. Comprehensive investigations at different temperatures reveal that the newly developed TPI-1 exhibits a better reduction in friction and wear rate below 100 ℃, but all of them increase significantly when the bulk temperature exceeds 250℃. The wear mechanisms demonstrated that sandwich-like tribofilms with different layers were established at different temperatures, which was further verified by characterization of scanning electron microscope (SEM), Raman spectroscopy, and transmission electron microscope (TEM). Considering the high-performance TPI coupled with Ag–Mo hybrids, we anticipate that further exploration would provide guidance for designing TPI tribo-materials that would be used at high temperatures.

Self-lubrication of tribologically-induced oxidation during dry reciprocating sliding of aged Ti–Ni51.5 at% alloy

The tribological behaviors of Ti–Ni51.5 at%alloy strengthened by finely dispersed Ni_(4)Ti_(3) particles in reciprocating sliding against GCr15,Al_(2)O_(3),and ZrO_(2) at room temperature were studied.Interestingly,the coefficient of friction(COF)suffered a sheer drop(from 0.9 to 0.2)when the aged alloy slid against GCr15 at a frequency of 20 Hz under a 20 N load without lubrication.However,severe‐mild wear transition disappeared when a solutionized alloy was used.Moreover,the COF stabilized at a relatively high level when Al_(2)O_(3) and ZrO_(2) were used as counterparts,although their wear mechanisms showed signs of oxidation.Scanning electron microscopy(SEM)and X‐ray element mappings of the wear scars of the counterparts clearly indicate that the formation of well‐distributed tribo‐layer and material transfer between the ball and disk are pivotal to the severe‐to‐mild wear transition in the aged Ti–Ni51.5 at%alloy/GCr15 friction pair.The higher microhardness and superelasticity of the aged alloy significantly accelerate the material transfer from GCr15 to the disk,forming a glazed protective tribo‐layer containing Fe‐rich oxides.