Hollow micro-/nanostructures are of great interest in many current and emerging areas of technology. Perhaps the best-known example of the former is the use of fly-ash hollow particles generated from coal power plants as partial replacement for Portland cement, to produce concrete with enhanced strength and durability. This review is devoted to the progress made in the last decade in synthesis and applications of hollow micro-/nanostructures. We present a comprehensive overview of synthetic strategies for hollow structures. These strategies are broadly categorized into four themes, which include well-established approaches, such as conventional hard-templating and soft-templating methods, as well as newly emerging methods based on sacrificial templating and template-free synthesis. Success in each has inspired multiple variations that continue to drive the rapid evolution of the field. The Review therefore focuses on the fundamentals of each process, pointing out advantages and disadvantages where appropriate. Strategies for generating more complex hollow structures, such as rattle-type and nonspherical hollow structures, are also discussed. Applications of hollow structures in lithium batteries, catalysis and sensing, and biomedical applications are reviewed.

Hollow Micro-/Nanostructures: Synthesis and Applications**

Electroactive phases of poly(vinylidene fluoride) : determination, processing and applications

The synthesis of CoNi@SiO2 @TiO2 core-shell and CoNi@Air@TiO2 yolk-shell microspheres is reported for the first time. Owing to the magnetic-dielectric synergistic effect, the obtained CoNi@SiO2 @TiO2 microspheres exhibit outstanding microwave absorption performance with a maximum reflection loss of -58.2 dB and wide bandwidth of 8.1 GHz (8.0-16.1 GHz, < -10 dB).

CoNi@SiO2@TiO2 and CoNi@Air@TiO2 Microspheres with Strong Wideband Microwave Absorption

Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

In this Review, we aim to provide an updated summary of the research related to hollow micro- and nanostructures, covering both their synthesis and their applications. After a brief introduction to the definition and classification of the hollow micro-/nanostructures, we discuss various synthetic strategies that can be grouped into three major categories, including hard templating, soft templating, and self-templating synthesis. For both hard and soft templating strategies, we focus on how different types of templates are generated and then used for creating hollow structures. At the end of each section, the structural and morphological control over the product is discussed. For the self-templating strategy, we survey a number of unconventional synthetic methods, such as surface-protected etching, Ostwald ripening, the Kirkendall effect, and galvanic replacement. We then discuss the unique properties and niche applications of the hollow structures in diverse fields, including micro-/nanocontainers and rea...

Synthesis, Properties, and Applications of Hollow Micro-/Nanostructures

Flow behavior and microstructures of superalloy 718 were investigated by hot compression tests performed at temperatures ranging from 950 to 1100 °C with strain rates of 10−3 to 1 s−1. The dependence of the peak stress on deformation temperature and strain rate can be expressed by a hyperbolic-sine type equation. The activation energy for superalloy 718 is determined to be 443.2 kJ mol−1. A power exponent relationship between the peak strain and the Z parameter is obtained. Microstructure analysis shows that the dynamically recrystallized grain size is inversely proportional to the Z parameter. The nucleation mechanisms of DRX are closely related to the value of Z parameter. Under low Z conditions, DRX nucleation and development are mainly assisted by the formation of twins near the original grain boundaries.

Flow behavior and microstructures of superalloy 718 during high temperature deformation

Microstructure evolution during dynamic recrystallization (DRX) of superalloy 718 was studied by optical microscope and electron backscatter diffraction (EBSD) technique. Compression tests were performed at different strains at temperatures from 950 °C to 1120 °C with a strain rate of 10−1 s−1. Microstructure observations show that the recrystallized grain size as well as the fraction of new grains increases with the increasing temperature. A power exponent relationship is obtained between the dynamically recrystallized grain size and the peak stress. It is found that different nucleation mechanisms for DRX are operated in hot deformed superalloy 718, which is closely related to deformation temperatures. DRX nucleation and development are discussed in consideration of subgrain rotation or twinning taking place near the original grain boundaries. Particular attention is also paid to the role of continuous dynamic recrystallization (CDRX) at both higher and lower temperatures.

Microstructure evolution during dynamic recrystallization of hot deformed superalloy 718

The precipitation behavior and related hardening in AA 7055 aluminum alloy aged at 120 and 160 °C was investigated in detail. GPI zones were the dominant phase in the alloy upon ageing at 120 °C for 60 min. The metastable η′ phase begins to precipitate in the alloy after being aged at 120 °C for 60 min, and turns to be the main phase after ageing for 300 min. When the alloy was aged at 160 °C, the precipitation was significantly promoted. The results also revealed that the transformation of small GPI zone to η′ phase is the dominant mechanism for η′ formation. Formation and growth of GPI zones and η′ phases led to the increase of the yield strength, while formation and coarsening of η resulted in the decrease of the strength. η′ is responsible for the peak hardening of this alloy.

Investigation of precipitation behavior and related hardening in AA 7055 aluminum alloy

Deformation behavior and microstructure evolution of 7050 aluminum alloy were investigated by tensile tests conducted at different temperatures (340, 380, 420, and 460 ◦ C) with different strain rates of 10 × 10 −4 , 10 × 10 −3 , 10 × 10 −2 and 01 s −1  The results show that the stress level of the alloy can be presented by a Zener-Holloman parameter in a hyperbolic sine-type equation with the hot activation energy of 2566 kJ/mol Ductile transgranular fracture transforms progressively into ductile intergranular (or inter-subgranular) fracture with the decrease of Z value At the same time, the soften mechanism of the alloy during high temperature deformation transforms from dynamic recovery to continuous dynamic recrystallization with decreasing Z value The main deformation mechanism is usual slipping when the alloy was deformed at high Z value Grain boundaries sliding takes part in deformation with low Z value Grain boundaries migration plays the role with medium Z value © 2007 Elsevier BV All rights reserved

Deformation behavior and microstructure evolution of 7050 aluminum alloy during high temperature deformation

Nearly monodispersed FeNi3 submicrometre spheres with an average diameter of 220 nm were synthesized by a simple low temperature reduction method SiO2@FeNi3 core–shell structured submicrometre spheres with 25 nm thick SiO2 shell were then fabricated by a sol–gel process A significant enhancement of electromagnetic absorption (EMA) performance was achieved by the silica coating over the 2–18 GHz The reflection loss (RL) exceeding −20 dB of the composite was obtained over 67–151 GHz by choosing an appropriate sample thickness between 21 and 33 mm, and an optimal RL of −613 dB was obtained at 87 GHz with a thin absorber thickness of 29 mm The coating of the dielectric silica shell significantly enhanced the EMA performance due to the enhancement of interface polarization at the alloys and dielectric interfaces

https://iopscience.iop.org/article/10.1088/0022-3727/43/24/245003/pdf

Wen-Zhu Shao

Papers

Flow behavior and microstructures of superalloy 718 during high temperature deformation

Microstructure evolution during dynamic recrystallization of hot deformed superalloy 718

Investigation of precipitation behavior and related hardening in AA 7055 aluminum alloy

Deformation behavior and microstructure evolution of 7050 aluminum alloy during high temperature deformation

Microwave absorption properties of FeNi3 submicrometre spheres and SiO2@FeNi3 core–shell structures