Liuding Wang

Co2+/Co3+ ratio dependence of electromagnetic wave absorption in hierarchical NiCo2O4–CoNiO2 hybrids

Amorphous hierarchical NiCo2O4–CoNiO2 hybrids have been successfully fabricated via a facile one-pot hydrothermal route, followed by morphological conversion into urchin-like structured NiCo2O4–CoNiO2 nanorods and irregular-shaped hierarchical NiCo2O4–CoNiO2 polyhedral nanocrystals through air-annealing treatment at 450 °C and 650 °C, respectively. The phase structure, morphology and chemical composition have been characterized in detail. Calcined hierarchical NiCo2O4–CoNiO2 hybrids show improved microwave absorption properties, which are ascribed to the synergistic effect of dielectric CoNiO2 and NiCo2O4 phases. In particular, the calcined hierarchical NiCo2O4–CoNiO2 hybrids at 450 °C exhibit significant enhancement in complex permittivity with respect to others due to their remarkable dipole polarization and interfacial polarization. The maximum reflection loss (RL) of the calcined hierarchical NiCo2O4–CoNiO2 hybrids at 450 °C reaches −42.13 dB at 11.84 GHz with a matching thickness of 1.55 mm, and a relatively broad absorption bandwidth (RL ≤ −10 dB) in the 13.12–17.04 GHz range. Very interestingly, the electromagnetic (EM) wave absorption performance of the hierarchical NiCo2O4–CoNiO2 hybrids shows dependence on the Co2+/Co3+ ratio. The calcined NiCo2O4–CoNiO2 hybrids at 450 °C of the most defect concentration possess the best EM wave absorption ability among all the samples. The results suggest that appropriate interactions between the building blocks in hybrids can guide us to design and fabricate highly efficient EM wave absorption materials.

Multishelled Metal Oxide Hollow Spheres: Easy Synthesis and Formation Mechanism

Uniform multishelled NiO, Co3 O4 , ZnO, and Au@NiO hollow spheres were synthesized (NiO and Co3 O4 hollow spheres for the first time) by a simple shell-by-shell self-assembly allowing for tuning of the the size, thickness and shell numbers by controlling the heat treatment, glucose/metal salt molar ratio, and hydrothermal reaction time. These findings further the development of synthetic methodologies for multishelled hollow structures and could open up new opportunities for deeper understanding of the mechanisms of shell-by-shell self-assembly. Moreover, the double-shelled NiO hollow sphere exhibits a higher photocatalytic activity for degradation of methyl orange than its morphological counterparts.

Enhanced Microwave Absorption Properties of α-Fe2O3-Filled Ordered Mesoporous Carbon Nanorods

A novel kind of α-Fe2O3-filled ordered mesoporous carbon nanorods has been synthesized by a facial hydrothermal method. Compared with dendritic α-Fe2O3 micropines, both a broader effective absorption range—from 10.5 GHz to 16.5 GHz with reflection loss (RL) less than −10 dB—and a thinner matching thickness of 2.0 mm have been achieved in the frequency range 2–18 GHz. The enhanced microwave absorption properties evaluated by the RL are attributed to the enhanced dielectric loss resulting from the intrinsic physical properties and special structures.

Vacuum hot roll bonding of titanium alloy and stainless steel using nickel interlayer

Abstract Vacuum hot roll bonding of titanium alloy and stainless steel using a nickel interlayer was investigated. No obvious reaction or diffusion layer occurs at the interface between stainless steel and nickel. The interface between titanium alloy and nickel consists of an occludent layer and diffusion layers, and there are the intermetallic compounds (TiNi3, TiNi, Ti2Ni and their mixtures) in the layers. The total thickness of intermetallic layers at the interface between titanium alloy and nickel increases with the bonding temperature, and the tensile strength of roll bonded joints decreases with the bonding temperature. The maximum tensile strength of 440·1 MPa was obtained at the bonding temperature of 760°C, the reduction of 20% and the rolling speed of 38 mm s–1.

Fast Synthesis of Pt Nanocrystals and Pt/Microporous La2O3 Materials Using Acoustic Levitation

Usually, we must use an appropriate support material to keep the metal species stable and finely dispersed as supported metal nanoparticles for industry application. Therefore, the choice of support material is a key factor in determining the dispersion and particle size of the noble metal species. Here, we report the synthesis of a single-atom Pt material in the solution and supported Pt nanoclusters on microporous La2O3 by a one-step acoustic levitation method without any pretreatment/modification of raw oxide. We have strongly contributed to the synthetic methodology of the surface/interfacial heterogeneous catalysts in this study, and this finding could open another door for synthesis of supported metal nanoparticles on porous materials for environmental catalysis.

EFFECT OF CARBONIZATION TEMPERATURE ON DIELECTRIC AND MICROWAVE ABSORBING PROPERTIES OF COBALT DOPED MESOPOROUS CARBON COMPOSITES

Co doped mesoporous carbon composites (MC–Co) have been synthesized at different carbonization temperatures via evaporation-induced multicomponent co-assembly strategy. The nanostructures and chemical compositions of MC–Co composites were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM) and X-ray diffraction analysis (XRD), etc. Their electromagnetic and microwave absorption properties were investigated in the frequency ranging from 2 GHz to 18 GHz. By the measurement of electromagnetic parameters and theoretical simulation of reflection loss (RL), the results showed that the minimum RL value of the optimum composite MC–Co-800 reached up to -41.9 dB at 13.5 GHz with a thickness of only 1.80 mm, and the effective absorption bandwidth (< -10 dB) is 4.4 GHz (from 11.4 GHz to 15.8 GHz). This work demonstrated that the optimum carbonization temperature of the obtained composites is 800°C, which is critical to its electromagnetic properties. The excellent microwave absorption properties can be attributed to dielectric loss, Ohmic loss, and characteristic impedance matching. Therefore, the as-synthesized composites could be acted as a candidate of microwave absorber, especially for the light weight demand.

A Comparable Study on the Microwave Absorption Properties of Al/Fe/Co Doped OMC/Paraffin Wax Composites

Al/Fe/Co doped ordered mesoporous carbon (OMC) composites have been synthesized by a facile method, and the influence of dopant on the electromagnetic (EM) and microwave absorption properties was investigated in the frequency range of 2–18GHz. Compared with Fe/Co–OMC composites, the Al–OMC nanocomposite played a great role in adjusting values and frequency dependence of complex permittivity, which gives rise to significant improved microwave absorption and reduced thickness of the corresponding paraffin wax composites. Reflection loss (RL) values less than −5dB and −10dB were obtained in the frequency range of 9.2–18GHz and 10.7–14.7GHz with a single thickness of 2.00mm, respectively. Such enhanced EM wave absorption property of the Al–OMC/paraffin wax composite was ascribed to its superior impedance matching characteristic. Thin thickness, broadband absorption microwave absorbers with Al doped OMC nanocomposites were obtained.

Microwave Absorption Properties of Fe-Doped Ordered Mesoporous Carbon (CMK-3)/Silica Matrix Nanocomposites with Magnetic Multi-Resonance Mechanisms

Low-density Fe-doped ordered mesoporous carbon (CMK-3)-silica (SBA-15) nanocomposites with different Fe contents have been prepared by a catalytic carbonization procedure followed by high-temperature calcination in N2. From field emission-scanning electron microscope (FE-SEM) and high resolution-transmission electron microscope (HR-TEM) images, it can be concluded that CMK-3 particles are dispersed homogeneously into a silica matrix and form a novel, special and interesting composite nanostructure. The metal species (∼18nm) are dispersed on the surface of frameworks during the catalytic carbonization procedure and endow a magnetic property to the carbon–silica nanocomposites. The optimal reflection loss (RL) calculated from the measured permittivity and permeability is −19dB at 17.2GHz for an absorber thickness of 2.00mm. Moreover, the electromagnetic (EM) wave absorption less than −10dB is found to exceed 5.76GHz as the layer thickness is 2.37 mm. The permittivity dispersion behaviors have been explained based on the Cole–Cole model and the conductivity contribution model. A new simple empirical model was also supposed to find the fitted curves of the multi-resonance imaginary permeability spectra of the composites. The EM wave can hardly be reflected on the absorber surface because of a better match between dielectric loss and magnetic loss, which originates from the combination of dielectric carbon–silica and magnetic Fe species.

Dissolution of interdendritic σ phase in cast Ni–Fe–Cr alloy

Abstract Various sizes, fractions and morphologies of interdendritic σ phase in the as cast N08028 alloy due to different solidification conditions are characterised. Dissolution behaviours of the secondary phase in both the as cast and the forged alloys are investigated during heat treatment at 1100, 1150 and 1200°C. A recently developed analytical model, subjected to necessary modification, is applied to describe the dissolution process of σ phase in the alloys with and without prior hot deformation. A recipe derived from transformed fraction is applied to evaluate the effective activation energy for dissolution. It has been found that, the prior hot deformation accelerates the dissolution process, which can be attributed to the decreased particle size and the reduced effective activation energy.

MICROWAVE ABSORPTION BEHAVIOR OF MESOPOROUS TRANSITION METAL OXIDE TEMPLATED FROM SBA-15 AND KIT-6

In this paper, we have synthesized meso-oxides (i.e., Co3O4 and NiO) by using mesoporous silica as hard template. The microstructures and chemical compositions of the corresponding meso-oxides were characterized by the Transmission electron microscope-selected area electron diffusion (TEM-SAED), X-ray diffraction (XRD), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS), respectively. And, their electromagnetic and microwave absorption properties were investigated in the frequency range of 2–18 GHz. The results indicate that meso-oxide templated from KIT-6 (i.e., meso-K–Co/Ni) exhibit a dual absorption characteristic compared with those using SBA-15 as hard template. This phenomenon suggests that meso-oxides templated from SBA-15 and KIT-6 can exhibit different microwave absorption behaviors due to their respective microstructures.