Existence Of Core-shell Structure Research Articles

Novel additive of PTFE@SiO2 core-shell nanoparticles with superior water lubricating properties

In order to solve the problems of poor dispersibility and wettability, as well as unsatisfactory wear resistance and load capacity of polytetrafluoroethylene (PTFE) as water lubricating additive, a new type of PTFE@silica (PTFE@SiO2) core-shell nanoparticles was prepared by encapsulating SiO2 layer on the surface of PTFE via chemical bonding. Electron microscope analysis showed that the synthesized particles had well-defined core-shell morphology. Special double/multi-core structure and a reduced thickness of the intermediate shell were found, and the formation mechanisms were also explored in detail. The water contact angle measurement proved that the wettability of PTFE could be greatly enhanced by coating SiO2 layer. The friction tests were performed to investigate the water lubrication properties of PTFE@SiO2 additive, the results indicated that the core-shell PTFE@SiO2 nanoparticles possessed the superior tribological properties, and the maximum friction coefficient and wear volume were respectively decreased by 75% and 99% when compared with pure water and water with PTFE/SiO2. Based on the analysis of worn surface, it was believed that the existence of core-shell structure and the formation of robust transfer film were the key to its excellent performance, and a possible lubrication mechanism was also proposed.

Microstructures and Highly Accelerated Lifetime Test of X5R Type BaTiO<sub>3</sub>-Based Ni-MLCC with Ultra-Thin Active Layers

Microstructure control in thin-layer multilayer ceramic capacitors (MLCCs) is one of the challenges for increasing capacitive volumetric efficiency and high voltage dielectric properties. In this paper, the X5R-MLCCs with ultra-thin dielectric layers (~1.2 μm) owning uniform grain size distribution were prepared by wet casting process. The microstructures and dielectric properties of the MLCCs were investigated. The existence of core-shell structure was proved by transmission electron microscopy observation and energy dispersive spectroscopy analysis. The existence of core-shell structure makes the temperature coefficient of capacitance (TCC) performance meet X5R standard. Moreover, a highly accelerated lifetime test (HALT) result shows that MLCCs with ultra-thin layers under high electric field are more easily to fail with increasing test temperatures. And the results reveal that the activation energy is similar to the value reported for mid-dielectric constant dielectrics.