Search

CeOHCO3 hierarchical structures with tunable size and defects were synthesized via a simple and rapid microwave-assisted hydrothermal approach for ultra-wide band microwave absorption for the first time.

To solve the severe electromagnetic (EM) radiation from the widespread application of electronic equipment, we developed a simple template-guided oxypolymerization strategy to synthesize polypyrrole (PPy) planar helixes as an efficient EM wave (EMW) absorber, and systematically investigated the morphology-dependent chirality, conductivity, and microwave absorption properties. As HCl concentration [HCl] varied from 0 to 2.0 M, the morphology evolved from planar helix to 3D cross-linking network structures, the conductivity increased from 0.0019 to 0.0302 S/cm, and the EM parameters peaked at [HCl]=0.5 M. Compared to other absorbers, the PPy planar helix formed at [HCl]=0 M possessed wider absorption band (5.84 GHz), smaller matching thickness (1.6 mm), lower loading (25 wt.%), and intenser absorption (−48.17 dB). The reason lies in the strong attenuation capability, multiple resonances, multiple scattering, and good impedance matching generated by chiral PPy planar helixes with a distinctive helical configuration, doped heteroatoms (O,S), and a local conductive network. Our results suggest that PPy planar helixes offer great promise for fields such as chiral sensors, electronics, optics, chiral catalysis, and EMW absorption and shielding due to their distinctive morphology, tunable conductivity, and outstanding EMW absorption properties (EMWAPs).

Electric rotary kiln is one of the key equipment in the chemical industry, which is mainly used for heating materials. In the current research, the heat calculation method of the electric rotary alumina kiln is constructed, and the heat transfer processes in the furnace, the furnace tube, and the furnace tube wall are systematically analyzed. The theoretical model of the electric rotary alumina kiln is established and solved by the fourth-order Runge–Kutta method, and the temperature rise curves in the kiln are obtained. The numerical simulation is carried out to investigate the temperature distribution of materials and gases in the furnace tube. It is revealed in the results that the temperature distribution of the electric rotary alumina kiln is more uniform than that of the internal rotary kiln, and the stable operation state can be reached in a very short time, which means that reduced furnace tube length and reduced production cost can be achieved under the same roasting requirements.

Lightweight, and broad and strong absorption are still a huge challenge for electromagnetic (EM) wave absorbers. Here, we propose a facile oxidative polymerization-carbonization strategy to synthesize O, S, N codoped carbon planar helixes for superior EM wave absorbers. The spiral cetyltrimethylammounium bromide crystallites act as a template for the in-situ oxidative polymerization of pyrroles into ordered PPy spiral nanowires. Sintering temperature (Ts) was used to adjust the defects, heteroatoms, graphitization degree, and properties of the carbonized products. With Ts varying from 400 °C to 800 °C, internal stress and heteroatom (N, O, S) content decreased, causing the decreased defect/dipole polarization and increased graphitization degree and conductivity loss. As a result, one broad high-frequency absorption band was exhibited by carbon planar helixes produced at 400 °C− 500 °C, two broad absorption bands were exhibited by those formed at 600 °C, and three absorption bands were exhibited by those formed at 700 °C − 800 °C. The carbon planar helix formed at 700 °C exhibited broader bandwidth (4.96 GHz), thinner sample thickness (1.4 mm), and stronger absorption (−35.44 dB) than those of other absorbers. The superior properties are attributed to a combination of dipole/defect polarization, interface polarization, conductivity loss, multiple scattering, and multiple LC-resonances generated from the unique planar helical structure, defects, heteroatoms, and local electric network.

A 3D thermal response model is developed to evaluate the thermal behavior of glass fiber/phenolic composite exposed to heat flux on one side. The model is built upon heat transfer and energy conservation equations in which the heat transfer is in the form of anisotropic heat conduction, absorption by matrix decomposition, and diffusion of gas. Arrhenius equation is used to characterize the pyrolysis reaction of the materials. The diffusion equation for the decomposition gas is included for mass conservation. The temperature, density, decomposition degree, and rate are extracted to analyze the process of material decomposition, which is implemented by using the UMATHT (User subroutine to define a material’s thermal behavior) and USDFLD (User subroutine to redefine field variables) subroutines via ABAQUS code. By comparing the analysis results with experimental data, it is found that the model is valid to simulate the evolution of a glass fiber/phenolic composite exposed to heat flux from one side. The comparison also shows that longer time is taken to complete the pyrolysis reaction with increasing depth for materials from the numerical simulation, and the char region and the pyrolysis reaction region enlarge further with increasing time. Furthermore, the decomposition degree and temperature are correlated with depths, as well as the peak value of decomposition rate and the time to reach the peak value.

The size and dispersity of magnetic metal absorbents need to be controlled for the inhibition of the eddy current and the enhancement of electromagnetic wave absorption performance (EMWAP). Herein, layered C/Ni nanoparticle (NP) composites were developed as an excellent electromagnetic wave absorbent via the size and dispersity control. The synthesis of layered C/Ni NP composites was achieved via a simple one-step calcination process. The amount of nickel acetate (n) and calcination temperature (Tc) were changed to not only control the diameter, content, and dispersity of Ni nanoparticles, but also adjust the electric/magnetic properties and EMWAP of layered C/Ni NP composites. The superior EMWAP was obtained at n = 3.99 mmol and Tc = 600 °C with high assimilation (−39.46 dB), thin thickness (2.3 mm), and broad bandwidth (9.68 GHz) in a low loading rate (25 wt%). Our results suggest that excellent EMWAPs relies on the cooperation of multiple polarization loss, multiple resonances, eddy current loss, electric/magnetic coupling, and good impedance matching. The synthetic method adopted in this work has advantages of simple operation, low cost, and high yield, which is recommended to other 2D materials.

High-performance absorbers are in urgent demand for dealing with the increasing electromagnetic wave (EMW) pollution caused by the rapid development of information technology. Herein, we developed a simple SDS/HCl-assisted oxidative polymerization method for the controllable synthesis of nanorod-coated PANI hierarchical microtubes as an efficient EMW absorber. The morphological evolution can be expediently achieved from hierarchical microtubes and solid nanofibers to nanorods by adjusting the HCl concentration. The formation of PANI hierarchical microtubes is caused by the cooperation of SDS and the minimum surface energy. What is more, morphology-dependent conductivity and EMW absorption properties were systematically investigated. Owing to the hierarchical 1D hollow structure and carrier concentration, the ultimate conductivity reached 0.08 S/cm at [HCl] = 7.5 mM. The corresponding HCl-doped PANI hierarchical microtubes exhibited superior EMW absorption properties (EMWAPs) with a large absorption of −43.6 dB and a wide absorption band of 5.84 GHz in relation to a 1.55 mm thick sample. The excellent EMWAPs are the consequence of the high conductivity and distinctive 1D, hierarchical, and hollow structure, which generate enhanced permittivity, multiple resonances, strong attenuation capability, multiple scattering, and EM radiation. Owing to their tunable morphology, tunable conductivity, and excellent EMWAPs, the PANI hierarchical microtubes offer great promise for fields such as sensors, electronics, optics, catalysis, energy storage, and EMW absorption and shielding.

Based on the force analysis of stand up lift, parametric modeling of the integral structure and interference analysis on the integral assembly model are conducted, and forces are analyzed on the key structure in accordance with the operating principles. The 3-D parametric model of stand up lift is imported directly into the finite element analytical module. Through static analysis and structure improvement on the basis of analysis results, the upgraded structure will be safer and more comfortable, and enable the stand up lift to be applied on more occasions, thus better supporting the engineering of products.