Nickel-zinc ferrite (Ni
Zn
Fe
O
) powders were prepared by the conventional solid-state route and sintered at 1100 and 1300 °C for utilization as a tile electromagnetic wave absorber. Structural, ...magnetic, and microwave absorption properties were investigated by characterization techniques of X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, electron microscopy, vibrating sample magnetometry, and vector network analyzer. The samples sintered at 1300 °C showed high magnetic saturation of 87 emu/g and low coercivity of 4 Oe. Electromagnetic investigations exhibit high reflection losses up to - 48.1 dB at certain high and low gigahertz frequencies, as clearly depicted in the 3D contour plot. The optimized condition between reflection loss, thickness, and bandwidth revealed a reflection loss of about - 36.1 dB at the matching thickness of 3.7 mm for the X-band. Furthermore, the effective working bandwidth at - 10 dB was up to ~ 7.1 GHz for the minimum thickness of 4.3 mm, which thoroughly covered the C-band. The microwave absorption performance of the well-sintered Ni-Zn ferrite was attributed to the incorporation of dielectric and magnetic loss mechanisms in which the magnetic part prevails.
The LaSrCuO4 and LaSrCu0.9Pd0.1O4 catalysts were prepared by a novel solid state synthesis method at low temperature. LaSrCuO4 perovskite with tetragonal structure was successfully prepared at ...600 °C. All the samples were characterized by XRD, TEM, H2-TPR, O2-TPD, FESEM and BET analyses and the prepared samples were employed as catalyst for methane combustion and CO oxidation reactions. The results confirmed that the catalytic performance of the LaSrCuO4 can be considerably improved via 10% Cu substitution by palladium. This improvement was ascribed to enhancement in the mobility of lattice oxygen, which plays an important role in CO oxidation and methane combustion. The results showed that the increase in calcination temperature of the LaSrCu0.9Pd0.1O4 catalyst decreased the catalytic activity due to decrease in the surface area and the concentration of lattice oxygen. The H2-TPR results of the LaSrCu0.9Pd0.1O4 catalysts showed that the reduction peak of the copper oxide was moved to lower temperatures by increasing in calcination temperature.
In situ HfB2-SiC-MoSi2 composites were fabricated using HfB2, Si, Mo, and C powders as starting materials. Fully-dense composites achieved by Reaction Spark Plasma Sintering (RSPS) method at 1850 °C ...under 40 MPa for 5 min. Thermodynamic calculations and microstructural studies proved that SiC and MoSi2 second phases were formed and homogeneously distributed according to the following reactions: Si+CSiC and Mo+2SiMoSi2. In addition, the presence of in situ SiC and MoSi2 reinforcement phases have also confirmed by field emission scanning electron microscopy, X-ray diffraction pattern and considering thermodynamics calculations made by HSC software. Besides, the mechanical investigations revealed that in comparison with monolithic HfB2, the hardness and fracture toughness of these composites were increased dramatically, and reached up to 25.2 GPa and 5.1 MPa m−1/2, respectively.
•In situ HfB2-SiC-MoSi2 composites were produced by reactive spark plasma sintering at 1850 °C.•SiC and MoSi2 reinforcement phases completely formed during RSPS process.•Hardness and fracture toughness of composite were reached to 25.2 GPa and 5.1 MPa m1/2, respectively.
Hierarchical porous Ni0.5Zn0.5Fe2O4 ferrite powders were prepared by using metal nitrates as oxidants and glycine as fuel. The fuel contents were used for tuning the microstructure, magnetic, ...permittivity, and permeability properties to obtain a high microwave absorption performance. The pure NiZn ferrite powders were directly crystallized at lower fuel contents, while about 2 wt% intermetallic FeNi3 phase appeared at fuel to total metal nitrates molar ratio of 2. The combusted powders with high specific surface areas of 51 m2/g showed porous and foamy microstructure. The saturation magnetization of the combusted powders increased from 36.5 to 78.5 emu/g by the formation of FeNi3 phase at the higher fuel contents. With the increase of glycine fuel to total metal nitrates molar ratio from 1 to 2, the real and imaginary parts of permittivity increased from 4.5 to 6 and from 0.8 to 1.1, respectively, while the values of real and imaginary permeability slightly increased. The high microwave absorption performance, including reflection loss of −48 dB with effective bandwidth of 2.9 GHz in Ku band at the matching thickness of 4.5 mm, was obtained at the fuel to total metal nitrates ratio of 2.
•Porous Ni0.5Zn0.5Fe2O4 powders were prepared by a facial solution combustion route.•Increasing the glycine contents enhanced the Ms value from 36.5 to 78.5 emu/g.•The surface area was reduced while the crystallinity improved at higher fuel ratios.•Dual-region microwave absorption was observed with the lowest RL of −19 and −48 dB.•Attenuation ability was related to intrinsic and synergic losses of the porous NZF.
Abstract
HfB
2
, Si, and activated carbon powders were selected to fabricate 0–30 vol% SiC reinforced HfB
2
-based composite. Pressureless sintering process was performed at 2050 °C for 4 h under a ...vacuum atmosphere. Microstructural studies revealed that in situ SiC reinforcement was formed and distributed in the composite according to the following reaction: Si + C = SiC. A maximum relative density of 98% was measured for the 20 vol% SiC containing HfB
2
composite. Mechanical investigations showed that the hardness and the fracture toughness of these composites were increased and reached up to 21.2 GPa for HfB
2
-30 vol% SiC and 4.9 MPa.m
1/2
for HfB
2
-20 vol% SiC, respectively. Results showed that alpha-SiC reinforcements were created jagged, irregular, and elongated in shape which were in situ formed between HfB
2
grains and filled the porosities. Formation of alpha-SiC contributed to improving the relative density and mechanical properties of the composite samples. By increasing SiC content, an enhanced trend of thermal conductivity was observed as well as a reduced trend for electrical conductivity.
•Fabrication of Co3O4-graphene nano-composites for supercapacitor, is proposed.•A co-deposition of Co3O4-graphene via elctrophoretic deposition method is proposed.•The co-deposition with different ...morphology and size in EPD process is considered.
In this work, we used the electrophoretic deposition (EPD) technique for the fabrication of Co3O4-Graphene nano-composite as the binder-free electrode for electrochemical supercapacitors. Cobalt nitrate salt was used as the charging agent for EPD of graphene, Co3O4, and their co-deposition. Characterization of the obtained layer by optical microscopy and scanning electron microscopy (SEM) revealed that there was no deposition in the suspension without additive such as nitrate cobalt salt, whereas a uniform layer was formed in the presence of nitrate cobalt salt. Energy dispersive spectroscopy (EDS) analysis of the graphene coating deposited via EPD approved the successful electrodeposition of Co nano-petals between graphene nano-plates. Cyclic voltammetry (CV) was done for measuring the capacitance of the deposited layer in the range of 10–100 mVs−1. The Co3O4 and Co3O4-Graphene nano-composite revealed 236.5 and 319.6 F g−1 at 10 mVs−1 scan rate, respectively. Enhancement in the specific capacitance of the composite was attributed to association graphene in the microstructure.
Microwave dielectric ceramics with the composition of Li2ZnTi3O8 – 4 wt% TiO2 were synthesized by the conventional solid‐state reaction. 4 wt% TiO2 powders with different particles size were added to ...the Li2ZnTi3O8 ceramic. Then the ceramic samples were sintered at temperatures 1075°C, 1050°C, 1000°C, and 950°C for 4 h. The effect of the particles size of TiO2 additive on the microwave dielectric properties of the ceramics has been investigated. In the study two categories of particles size of TiO2 additive have been used; (i) Nanoparticle (50 nm), (ii) Micron sized (40, 5, 1 μm) powder. X‐ray showed that the TiO2 additive has not solved in the LZT structure and has not almost undergone chemical reaction with the LZT ceramic. The results showed that the addition of TiO2 nanoparticles to the LZT ceramics significantly improved the density and a dense and uniform microstructure and also abnormal grain growth were observed by SEM. The use of TiO2 nanoparticle reduces porosity and leads to an increase in green density. The maximum density was found to be 98.5% of the theoretical density and the best relative permittivity of 28, quality factor of 68000 GHz and τf value of −2 ppm/°C were obtained for the samples added with 4 wt% of the TiO2 nanoparticles, sintered at 1050°C for 4 h.
Wear properties of a nanostructured matrix of Al prepared via mechanical milling and hot extrusion were investigated before and after incorporation of B
4
C nanoparticles. The sample powders were ...milled for a period of 20 h to produce nanopowders. Mechanical milling was used to prepare nanocomposite samples by addition of 2 and 4 wt% of B
4
C nanoparticles into the Al matrix. A pin-on-disk setup was used to evaluate the wear properties of the hot extruded samples under dry condition. The results revealed a lower friction coefficient and a lower wear rate for the nanostructured matrix of Al in contrast to a commercial coarse grained Al matrix. The same pattern was also observed in the nanocomposite samples with respect to the base matrix. Hardness values were used to discuss the observed results. Scanning electron microscopy (SEM) was used to analyze the worn surface and wear debris.
Nano alumina powder can be widely used in the fields of electronics, catalyst supports and high temperature applications. In the present article, a nano Al
2O
3 powder was synthesized by a simple ...aqueous sol–gel method using inexpensive AlCl
3·6H
2O and Al powder as raw materials. It was shown that the gel calcined at 1100 °C resulted in the formation of a crystalline α-Al
2O
3 nano powder. It had a particle size distribution ranging from 32 to 100 nm after heat treatment at 1200 °C.
Boron carbide nanoparticles were produced using commercially available boron carbide powder (0·8
μ
m). Mechanical milling was used to synthesize Al nanostructured powder in a planetary ball-mill ...under argon atmosphere up to 20 h. The same process was applied for Al–4 wt % B
4
C nanocomposite powders to explore the role of nanosize reinforcements on mechanical milling stages. Scanning electron microscopy (SEM) analysis as well as apparent density measurements were used to optimize the milling time needed for completion of the mechanical milling process. The results show that the addition of boron carbide particles accelerate the milling process, leading to a faster work hardening rate and fracture of aluminum matrix. FE-SEM images show that distribution of boron carbide particles in aluminum matrix reaches a full homogeneity when steady state takes place. The better distribution of reinforcement throughout the matrix would increase hardness of the powder. To study the compressibility of milled powder, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B
4
C particles. For better distribution of reinforcement throughout the matrix,
r
, modified heckel equation was used to consider the pressure effect on yield strength as well as reinforcing role of B
4
C particles.
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