Study of the changes in the microstructures and properties of grease using ball milling to simulate a bearing shear zone on grease.

The effects of shear degradation on the microstructures and properties of grease were investigated using a planetary ball mill to simulate a bearing shear zone on grease. The microstructure, cone penetration, colloidal stability, rheological properties noise properties, water washout characteristics and low-temperature torque of lithium grease were characterized. The microstructure of the initial lithium grease is a three-dimensional network structure formed by the uniform fibers. The entanglement level is high. As the ball milling shear time increases, the network structure of lithium grease is destroyed and the fibers are sheared to become short. Eventually all of them become short fibers. The performance test of lithium grease reveal that the cone penetration increases, colloidal stability, structural strength, noise properties, water washout characteristics of lithium grease gradually decreased with the increase of ball milling shear time. Additionally, the low-temperature starting torque and running torque of the grease gradually decrease. This phenomenon occurs due to changes in the microstructure of lithium grease. The shear degradation of lithium grease was mainly divided into two stages: the rapid stage was the destruction of the thickener network structure and the fibers being shortened by shearing. The slow stage was the process in which short fibers were sheared into shorter fibers.

TOCN/copper calcium titanate composite aerogel films as high-performance triboelectric materials for energy harvesting.

The development of high-performance cellulose-based triboelectric nanogenerators (TENG) has been a subject widely concerned by researchers. Here, we prepared a composite aerogel film based on TEMPO-oxidized cellulose nanofiber (TOCN) and copper calcium titanate (CaCu3Ti4O12, CCTO) nanoparticles. Under their comprehensive effects of the enhanced dielectric performance, the TOCN/CCTO-20 composite film with 20 % CCTO content based TENG device showed the best output performance of an open circuit voltage of 152 V, a short circuit current of 33.8 µA and a power density of 483 mW/m2, which were 3.37, 4.07 and 3.71 times higher than that of the pure TOCN based TENG device, respectively. In addition, effects of external force conditions, aerogel film size parameters and the agglomeration state of high filler content on the output performance were also studied. These results indicated that the TOCN/CCTO composite aerogel films can be used as efficient and low-cost cellulose-based triboelectric positive materials for energy harvesting.

A phosphorus-containing imidazole derivative towards the liquid oxygen compatibility and toughness of epoxy resin.

In order to develop a liquid oxygen-compatible (LOX-compatible) matrix resins for polymer-based fiber-reinforced composites, a novel phosphorus-containing imidazole derivative called VAD containing multifunctional groups was synthesized and used as a co-curing agent for epoxy resin (EP) with simultaneous LOX-compatibility and mechanical improvement. A phosphorus group was introduced into the EP to capture the free radicals generated during the pyrolysis of the polymer to improve LOX compatibility, and the trimethylene group was introduced as a flexible spacer to enhance the toughness of the cured material. In comparison to pure EP, the modified EP with only 2.5 wt% VAD showed excellent mechanical properties with 23.0% and 75.6% increase in tensile and impact strength, respectively. Furthermore, as the content of VAD increased, a thermoset compatible with LOX (according to the liquid oxygen impact test) was obtained, and the flame retardancy was improved (according to the limiting oxygen index test). However, there was no significant sacrifice of transparency or thermal stability. In addition, the LOX compatibility mechanism was analyzed using X-ray photoelectron spectroscopy. As an efficient multi-functional modifier, VAD has a bright future in the modification realm of EP materials.

Self-Healing of SiC-Al2O3-B4C Ceramic Composites at Low Temperatures.

Self-healing ceramics have been researched at high temperatures, but few have been considered at lower temperatures. In this study, SiC-Al2O3-B4C ceramic composite was compacted by spark plasma sintering (SPS). A Vickers indentation was introduced, and the cracks were healed between 600 °C and 800 °C in air. Cracks could be healed completely in air above 700 °C. The ceramic composite had the best healing performance at 700 °C for 30 min, recovering flexural strength of up to 94.2% of the original. Good crack-healing ability would make this composite highly useful as it could heal defects and flaws autonomously in practical applications. The healing mechanism was also proposed to be the result of the oxidation of B4C.

Enhancement of the electrochemical performance of lithium-ion batteries by SiO2@poly(2-acrylamido-2-methylpropanesulfonic acid) nanosphere addition into a polypropylene membrane.

Employing electrostatic self-assembly and free radical polymerization, the surface of SiO2 nanospheres was coated with poly(2-acrylamido-2-methylpropanesulfonic acid) (SiO2@PAMPS) bearing strong electron withdrawing sulfonic and amide groups, enhancing the dissociation ability of the lithium salt of the liquid electrolyte and absorbing anions via hydrogen bonds. After SiO2@PAMPS nanospheres were introduced into the polypropylene (PP) membrane (SiO2@PAMPS/PP), the electrolyte affinity and electrolyte uptake of the composite separators were significantly improved. The ionic conductivity of SiO2@PAMPS/PP-18% (where 18% represents the concentration of the solution used for coating) soaked in liquid electrolyte was even 0.728 mS cm-1 at 30 °C, much higher than that of the pristine PP membrane. The LiFePO4/Li half-cell with SiO2@PAMPS/PP-18% had a discharge capacity of 148.10 mA h g-1 and retained 98.67% of the original capacity even after 120 cycles at 0.5C. Even at a rate of 1.0C, the cell capacity could be maintained above 120 mA h g-1. Therefore, a coating formula was developed that could considerably improve the cycling ability and high rate charge-discharge performance of lithium ion batteries.

Water-Dispersed Poly(p-Phenylene Terephthamide) Boosting Nano-Al2O3-Coated Polyethylene Separator with Enhanced Thermal Stability and Ion Diffusion for Lithium-Ion Batteries.

Polyethylene (PE) membranes coated with nano-Al2O3 have been improved with water-dispersed poly(p-phenylene terephthamide) (PPTA). From the scanning electron microscope (SEM) images, it can be seen that a layer with a honeycombed porous structure is formed on the membrane. The thus-formed composite separator imbibed with the electrolyte solution has an ionic conductivity of 0.474 mS/cm with an electrolyte uptake of 335%. At 175 °C, the assembled battery from the synthesized composite separator explodes at 3200 s, which is five times longer than the battery assembled from an Al2O3-coated polyethylene (PE) membrane. The open circuit voltage of the assembled battery using a composite separator drops to zero at 600 s at an operating temperature of 185 °C, while the explosion of the battery with Al2O3-coated PE occurs at 250 s. More importantly, the interface resistance of the cell assembled from the composite separator decreases to 65 Ω. Hence, as the discharge rate increases from 0.2 to 1.0 C, the discharge capacity of the battery using composite separator retains 93.5%. Under 0.5 C, the discharge capacity retention remains 99.4% of its initial discharge capacity after 50 charge-discharge cycles. The results described here demonstrate that Al2O3/PPTA-coated polyethylene membranes have superior thermal stability and ion diffusion.

Electrospun Polyethylene Terephthalate Nonwoven Reinforced Polypropylene Separator: Scalable Synthesis and Its Lithium Ion Battery Performance.

A novel polyethylene terephthalate nonwoven reinforced polypropylene composite separator (PET/PP) with high thermal stability and low thermal shrinkage characteristic is developed through a scalable production process. In the composite separator, the electronspun polyethylene terephthalate nonwoven layer improves the electrolyte affinity and can sustain as the barrier layer after the shutdown of the polypropylene layer. Due to its high ionic conductivity, the PET/PP separator shows an excellent discharge capacity. In addition, the superior thermal stability of the separator significantly enhances the safety performance of the separator. Considering the feasibility of the large-scale production of the PET/PP separator and its superior battery performance, we expect that the novel separator could be a promising alternative to the existing commercial separators.

Facile Synthesis of Fe3 C@Graphene Hybrid Nanorods as an Efficient and Robust Catalyst for Oxygen Reduction Reaction.

Robust and efficient catalysts for the oxygen reduction reaction (ORR) are required for the development of various energy storage and conversion devices. In this study, a durable and high-performance Fe3 C@graphene ORR catalyst has been developed by the carbonization of urea- and agar-modified Fe2 O3 nanorods. The influence of the carbonization temperature and annealing time on the activity and stability of the resulting Fe/C catalyst was studied in detail. The Fe/C catalyst synthesized at a temperature of 700 °C (holding time: 60 min) showed better ORR activity and improved stability compared to a commercial Pt/C catalyst. The improved ORR catalytic activity of the catalyst is due to its high Fe3 C content and its good durability results from the unique microstructure of the Fe3 C@graphene hybrid.